From: Subject: Record of Decision Date: Wed, 24 Feb 2010 15:11:45 -0700 MIME-Version: 1.0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Content-Location: http://silvercreekpc.accountsupport.com/ROD62805.htm X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Record of = Decision

DECISION SUMMARY

 

SECTION 1

 

SITE NAME, LOCATION AND=20 DESCRIPTION

 

 

The Richardson Flat Tailings (RFT) site (Site) is = located 1.5=20 miles northeast of Park=20 City, Utah, = and is part=20 of a 650 acre property owned by United Park City Mines (UPCM) Company = (Figure=20 1).  The Site is a = tailings=20 impoundment that covers 160 acres in the northwest corner of the UPCM = property,=20 a small portion of the much larger Upper Silver Creek Watershed (Figure = 2).  Silver Creek is the primary = surface=20 water source found in the area and is comprised of runoff from three = significant=20 drainages in the watershed, including Ontario Canyon, Empire Canyon=20 and Deer=20 Valley (Figure = 3).  Silver Creek is currently = listed on=20 Utah=92s 303(d)=20 list for zinc and cadmium and is targeted for total maximum daily load = (TMDL)=20 development.  Historic = mining=20 activities in the canyons left behind six active Comprehensive = Environmental=20 Response, Compensation and Liability = Information=20 System (CERCLIS) sites, including Empire Canyon,=20 Silver Creek Tailings, and Silver Maple Claims, each one impacting = Silver Creek=20 in some way.  While zinc = and cadmium=20 are the primary heavy metals found in Silver Creek, lead and arsenic are = the=20 main contaminants in the sediments and soils of the watershed.  Because of the volume of = mining activity=20 throughout the district and the dynamics of the watershed hydrogeology, = it is=20 difficult to target any one site as the main source of contamination = affecting=20 Silver Creek and the environmental media within the watershed.  The overall remedial goal for = the=20 watershed is to clean up the surrounding sites, including the Site, = thereby=20 eliminating current and future hazards to human health and welfare and = the=20 surrounding environment.

 

The RFT site is a geometrically closed basin, bound = by=20 highway 248 to the north, a main embankment to the west, and diversion = ditches=20 to the south and the northeast (Figure 4). =20 Silver Creek can be found on the northwest border of the Site, = separated=20 from the Site by a small stretch of wetlands and riparian = vegetation.  The impoundment was used as a = mine=20 tailings reservoir prior to 1950. =20 The Site now houses approximately seven million tons of = sand-sized=20 carbonaceous particles and minerals containing zinc, silver, lead, and = other=20 metals.  Use of the Site = by UPCM=20 ended in 1982.  To date, = the Site is=20 not listed on the National Priorities List (NPL).  The Site was considered for = listing in=20 both 1988 and 1992.  UPCM, = the=20 primary potentially responsible party (PRP), has taken responsibility = for=20 funding the majority of the remedial action at the Site. 

 

 

 

 

 

 

 

 

 

SECTION 2

 

SITE HISTORY AND ENFORCEMENT=20 ACTIVITIES

 

2.1 HISTORICAL = LAND=20 USE

 

In 1953, UPCM was formed through the consolidation = of Silver=20 King Coalition Mines Company and Park Utah Consolidated Mines = Company.  At that time, the Site was = already being=20 used as an impoundment for mine tailings consisting primarily of = sand-sized=20 carbonaceous particles and minerals containing lead, zinc, silver and = other=20 metals.  Additionally, = tailings were=20 transported to and placed in several distinct low elevation areas in the = southeast portion of the Site just outside of the main impoundment.  

 

In 1970, with renewed mining activity in the area, = Park City=20 Ventures (PCV), a joint venture partnership between Anaconda Copper = Company and=20 American Smelting Company (ASARCO), entered into a lease agreement with=20 UPCM.  This agreement = allowed PCV to=20 deposit additional mine tailings at the Site; however, the Site had to = be=20 partially reconstructed.  = Dames and=20 Moore provided PCV with design, construction and operation = specifications which=20 were approved by the State of Utah. =20 These specifications included installation of a large embankment = along=20 the western edge of the impoundment, and construction of containment = dike=20 structures along the southern and eastern boarders of the Site for = additional=20 tailings storage.  PCV = also created=20 a diversion ditch system along the higher slopes north of the = impoundment and=20 outside of the containment dikes along the east and south perimeters of = the=20 impoundment to collect surface run off. =20 As part of the approval process for the renewed use of the Site, = the=20 State of Utah=20 required installation of groundwater monitoring wells near the base of = the main=20 embankment.  =20

 

Over the course of PVC=92s use of the Site, about = 450,000 tons=20 of tailings were deposited at the Site through a slurry pipeline that = originated=20 at their mill facility.  = Dames and=20 Moore had recommended that the tailings be deposited around the = perimeter of the=20 Site, moving towards the center of the Site over time.  However, PVC chose to deposit = the=20 tailings from the slurry pipeline in one constant area in the center of = the=20 impoundment, creating a steep, cone-like structure in the middle of the=20 impoundment.  After PVC = discontinued=20 their use of the Site in 1982, high winds caused tailings from the = cone-shaped=20 feature to become airborne, creating a potentially significant exposure=20 pathway.  These operations = shaped=20 the topography of the impoundment which still exists today.

 

From 1980 to 1982, Noranda Mining, Inc. leased the = mining and=20 milling operations and placed an additional 70,000 tons of tailings at = the=20 Site.  Since then no = further use of=20 the Site has occurred, but UPCM began taking actions aimed at improving=20 environmental conditions of the Site almost immediately after operations = stopped.  This work = continued=20 intermittently through the mid-1990s. These actions are described in the = Site=20 Characteristics Section of this Record of Decision (ROD).

 

 

 

2.2 INVESTIGATION HISTORY

 

EPA became aware of the Site in the mid-1980s.  After initial site assessment = work, EPA=20 proposed the Site for listing on the NPL in 1988.  After considering public = comment, EPA=20 did not pursue the Site for listing on the NPL.  By 1992, the Hazard Ranking = System (HRS)=20 had been revised and EPA again proposed the Site for listing on the = NPL.  Ultimately, EPA decided not to = pursue=20 final listing on the NPL, and the Site remains proposed for the NPL at = this=20 time.

 

Subsequent to the second NPL proposal, the EPA = Region 8=20 Superfund Emergency Response Branch conducted an investigation under the = =93Make=20 Sites Safe=94 Initiative in 1993. =20 This investigation concluded that conditions of the Site did not = warrant=20 emergency removal actions, but may present unacceptable risks to human = health=20 and the environment and should be addressed through long-term remedial=20 action. 

 

Throughout the 1990s, EPA and the Utah Department = of=20 Environmental Quality (UDEQ) were hoping UPCM would address the Site = through the=20 Utah Voluntary Cleanup Program. =20 UPCM decided against this, but at the same time continued to = voluntarily=20 take steps to improve environmental conditions at the Site.  Additionally, UPCM began = collecting=20 hydrogeologic data, which was used to better understand the groundwater = flow and=20 depth of tailings at the Site.

 

In 1999, EPA, UDEQ, UPCM, Park City Municipal = Corporation,=20 and other stakeholders formed the Upper Silver Creek Watershed = Stakeholder=92s=20 Group (USCWSG).  This=20 community-based organization was formed to help EPA address = Superfund-related=20 environmental issues in the Park City area in a cooperative = fashion,=20 including issues related to the Site. =20 The USCWSG has been very successful and several investigations = and=20 cleanups have occurred in Park City as a result.  Early in USCWSG=92s history, = UPCM and EPA=20 agreed to address the Site as an =93NPL equivalent=94 site, using the = same process=20 for investigation and cleanup that is required for a NPL Site.

 

2.2 ENFORCEMENT HISTORY

 

EPA and UPCM signed an Administrative Order on = Consent (AOC)=20 on September 28, 2000 which called for UPCM to conduct a Remedial = Investigation/=20 Focused Feasibility Study (RI/FFS) for the Site.  EPA and UPCM have continuously = worked=20 well together since the inception of the USCWSG, and because of this, = EPA was=20 able to employ increasingly reduced oversight for the RI/FFS as it=20 progressed.  The RI/FFS = conducted by=20 UPCM provided the data and information used in this ROD. 

 

EPA conducted two Potentially Responsible Party = (PRP)=20 Searches for the Site that identified several parties that may have some = liability for cleanup of the Site. =20 The Site owner, UPCM, has conducted the RI/FFS pursuant to an=20 Administrative Order on Consent (AOC). =20 EPA has been facilitating the allocation of costs of = investigation and=20 cleanup between the PRP=92s and UPCM has indicated its willingness to = enter into a=20 Consent Decree (CD) with EPA for conduct of remedial design and remedial = action.=20

 
SECTION 3

 

COMMUNITY = PARTICIPATION

 

EPA recently published a Proposed Plan describing = the=20 preferred remedy at the Site.  = The=20 Proposed Plan, released for public comment on September 4, 2004, was = followed by=20 a public meeting held on September 28, 2004.   The public comment = period on the=20 proposed plan ran from September 5, 2004 to October 4, 2004.  All comments received during = this period=20 are addressed in the Responsiveness Summary of this ROD

 

Throughout the 1980's and early 1990s, there was = significant=20 opposition to cleanup of the Site under CERCLA authority. Public = participation=20 consisted primarily of comments on the proposed listings and letters to = EPA=20 urging that neither site be listed on the NPL. 

 

Since the formation of the USCWSG in 1999, = community=20 participation in Park City has increased and = improved.  The USCWSG meets regularly, in = well-advertised open meetings.  =20 The participants receive updates on individual sites in the = watershed and=20 discuss issues in a cooperative format. =20 The USCWSG has developed a web-site, funded by UPCM, which = details=20 actions related to the environmental investigations and cleanup.  The EPA project manager = discusses the=20 Site periodically with the local radio talk show and the local newspaper = reporter.  An information=20 repository, which includes the Administrative Record (AR) for the Site, = was=20 established at the Park City Library and Education Center.  Numerous public meetings have = occurred=20 on both general issues and to fulfill requirements for particular sites = in the=20 watershed.  Fact Sheets = are produced=20 annually with updates on progress. =20 Throughout conduct of the RI/FFS at the Site, UPCM and EPA have = provided=20 information to the public through all of these routes. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 
 
 
 
SECTION 4

 

SCOPE AND ROLE OF RESPONSE=20 ACTION

 

The Site is = one of=20 several historic mining sites in the Upper Silver Creek Watershed.   At present, six of these = sites are=20 listed in the CERCLIS database, and several more are being considered = for future=20 Superfund action.  The = past and=20 present impacts to surface water and sediment in Silver Creek result = from the=20 cumulative contributions of these sites over decades.  Because of the high density of = sites in=20 a relatively small area, as well as the long history involved, it is = often=20 difficult to apportion specific problems to a particular site or time=20 period.   For = example, sites=20 upstream of Richardson Flat, such as Empire Canyon or Prospector=20 Square, have impacted surface water and sediment conditions = at and=20 below Richardson Flat.  =20 However, it is difficult to determine exactly what contribution = each=20 made.   For this = reason, EPA=20 has sought to investigate and remediate the Upper Silver Creek Watershed = as a=20 whole, rather than trying to investigate each site seperately.  This ensures that remedies = selected for=20 the individual sites are complementary to each other and work toward the = goal of=20 cleaning up the entire watershed.    This ROD addresses = only the=20 actions necessary to address actual and potential impacts specific to = the Site,=20 but it is part of a broader strategy to clean up the entire Silver Creek = Watershed in a consistent, efficient manner.  

 

The remedy = selected by=20 EPA and documented in this ROD includes remedial actions necessary to = protect=20 human health or welfare or the environment.  The ROD is based primarily = upon=20 information set forth in the RI/FFS recently conducted by UPCM. An = important=20 purpose of the RI/FFS and associated risk assessment was to evaluate the = efficacy of these voluntary actions and the risks posed by the Site in = its=20 current condition.   = For=20 instance, there is a soil cover across the tailings impoundment that was = put in=20 place by UPCM in the 1990s.  = The=20 RI/FFS evaluated the soil cover and showed it protects groundwater and = other=20 media at the site from becoming heavily contaminated. The risk = assessment=20 determined that under the current conditions, threats to human health = are=20 low.   However, it is = clear=20 that in the absence of this soil cover, both human and ecological = receptors=20 would be exposed to high concentrations of heavy metals and contaminants = would=20 be free to migrate from the Site, thereby increasing the risk to human = health=20 and the environment.  = Thus,=20 decisions on remedial actions must consider not only the risks posed by = current=20 conditions, but also the risks posed if current conditions changed.  The selected remedy will = enhance and=20 ensure the integrity of the soil cover, reinforce the tailings = embankment, and=20 protect surface and ground waters from additional metals loading by = containing=20 the low level threat waste, thereby mitigating and abating the actual = and=20 potential risks to human health or welfare or the environment at the = Site.  Further, institutional = controls will=20 minimize potential, future, uncontrolled, human contact with = contamination in=20 any of the Site media.

 

 
 
 
 
 
SECTION 5

 

SUMMARY OF SITE=20 CHARACTERISTICS

 

 

This section summarizes the information = obtained=20 through the investigations and feasibility studies.  It includes a description of = the Site=20 conceptual model on which the investigations, risk assessments and = response=20 actions are based.  The = major=20 characteristics of the Site and the nature and extent of contamination = are=20 summarized below.  More = detailed=20 information is available in the Administrative Record for the=20 Site.

 

5.1 SITE CONCEPTUAL MODEL

 

The illustrated site conceptual model depicted in = Figure 5 is=20 a representation of the location, and movement of contamination at the = Site and=20 any potential impacts that may occur to human health, the environment, = or=20 beneficial uses of resources.  = Presently, the tailings in the main impoundment (Area A) and = the=20 tailings south of the diversion ditch (Area B) are considered the = primary waste=20 sources.  Impacted media = at the Site=20 include sediments in the south diversion ditch and the wetland area, and = the=20 surface waters.  Surface = water=20 sources include the wetlands area, Silver Creek, the site pond, and = intermittent=20 flow in the diversion ditches and unnamed drainages. Seasonally, = accumulated=20 precipitation and snow melt can be found on the surface of the main=20 impoundment.  There is a = clay layer=20 underlying the tailings in Area A and Area B, so infiltration of = groundwater=20 into the underlying aquifer is limited. =20 Additionally, heavy metal releases from the tailings are = currently=20 contained to a certain degree by a low permeability soil cap that was = placed=20 there by UPCM in the 1990's. Therefore, potential exposure to future = Site users=20 including high and low-intensity recreational visitors is limited.  However, these possible = exposure=20 pathways include ingestion of soils/tailings and sediment, dermal = exposure to=20 surface water, and inhalation of particulates in air.  The ecological exposure = pathways and=20 receptors are described in detail in Section 7.2, Ecological Risk.=20

 

5.2 OVERVIEW OF THE RICHARDSON FLAT TAILINGS=20 SITE

 

The Site is located in a broad valley with = undeveloped=20 rangeland.  The Site is = about 6,570=20 feet above mean sea level and is characterized by a cool, dry, semi-arid = climate=20 (RMC, 2003).  = Meteorological=20 stations located in Park City, Utah and Kamas, Utah estimate an annual=20 precipitation of about 20 inches of water, an average low temperature of = about=20 30=B0F,=20 and an average high temperature of about 57=B0F=20 (RMC, 2003).

 

5.2.1 Site Features=20

 

As described in the Site History, mine tailings = have been=20 deposited at the Site since 1950. =20 For two decades, tailings were systematically deposited in the=20 impoundment via a slurry line and eventually filled in all low lying = areas (Area=20 A).  In 1970, PCV took = over the use=20 of the impoundment, which required several structural changes and = improvements,=20 including enlargement of the main embankment in the northwestern corner = of the=20 Site, construction of containment dikes along the southern and eastern = borders=20 of the impoundment, and construction of a diversion ditch system outside = the=20 impoundment along the east and south perimeters.   On the south end of the=20 impoundment, the diversion ditch was cut through an area of existing = tailings,=20 resulting in some tailings being located outside (south of) the present = day=20 boundaries of the impoundment (Area B). =20 These additions, as well as the tailings south of the diversion = ditch,=20 make up the main surface features of the Site.  The Study Area Boundary = includes the=20 tailings south of the diversion ditch and the main impoundment.  The Site characteristics can = be found in=20 Figure 4.

 

Impoundment and=20 Containment Dikes

 

The majority of the tailings at the Site are = contained in the=20 impoundment basin, with a large earth embankment in place along the = western edge=20 of the Site (Area A).  The = "main=20 embankment" is vegetated and is approximately 40 feet wide at the top, = 800 feet=20 long, and has a maximum height of 25 feet. =20 A series of man‑made dikes contain the tailings along the = southern and=20 eastern perimeter of the impoundment. =20 The northern edge of the impoundment is naturally higher than the = perimeter dikes.

 

Off‑Impoundment=20 Tailings

 

Additional tailings materials are present outside = and to the=20 south of the current impoundment area (Area B).  During historic operations of = the=20 tailings pond, tailings accumulated in three naturally low-lying areas = adjacent=20 to the impoundment.  = Starting in=20 1983, UPCM covered these off-impoundment tailings with a = low-permeability,=20 vegetated soil cover.  = However,=20 recent surveys of off‑impoundment cover soils indicate that, at = some locations,=20 soil cover is thin or absent, leaving exposed surface tailings (RMC,=20 2001a).  In addition to = these=20 off-impoundment tailings deposits, prevailing winds from the southeast = carried=20 tailings from the main impoundment and deposited them in the surrounding = areas. 

 

Diversion Ditches=20 and Drainages

 

A diversion ditch system borders the north, south, = and east=20 sides of the impoundment to prevent surface water runoff from the = surrounding=20 land from entering the impoundment. =20 Precipitation falling on the impoundment area creates a limited = volume of=20 seasonal surface water.  = The north=20 diversion ditch collects snowmelt and storm water runoff from upslope,=20 undisturbed areas north of the impoundment and carries it in an easterly = direction towards the origin of the south diversion ditch.  An unnamed ephemeral drainage = to the=20 southeast of the impoundment also enters the south diversion ditch at = this=20 point.  Additional water = from spring=20 snowmelt and storm water runoff enters the south diversion ditch from = other=20 areas lying south of the impoundment at a point near the southeast = corner of the=20 diversion ditch structure.

 

 

Site = Wetlands and=20 Pond

 

Water in the south diversion ditch flows from east = to west=20 and ultimately empties into Silver Creek near the north border of the = Site.  Before its confluence with = Silver Creek,=20 water from the south diversion ditch enters a small one acre pond (RMC,=20 2003).  Water exiting the = pond flows=20 in a discrete channel where it mixes with flow from Silver Creek in a = wetlands=20 area below the main embankment (RMC, 2003).  Near the northwestern corner = of the=20 wetlands area, Silver Creek flows into the wetland beneath the rail = trail=20 bridge.  Water flow exits = the=20 wetlands area back into Silver Creek via a concrete box culvert under = State=20 Highway 248 (RMC, 2003).

 

Silver = Creek

 

Silver Creek flows approximately 500 feet from the = main=20 embankment along the west edge of the Site.  The headwaters of Silver Creek = are=20 comprised of three signifigant drainages in the Upper Silver Creek = Watershed;=20 the Ontario Canyon, the Empire Canyon=20 and Deer=20 Valley.  Flows from Ontario and Empire Canyons occur in the late spring to early = summer=20 months in response to snowmelt and rainfall, while Deer = Valley flows appear to be = perennial and=20 originate from snowmelt and springs (RMC, 2000b).  The largest contributor to = water flow in=20 Silver Creek near the Site is the Pace‑Homer (Dority Springs) = Ditch, which=20 derives most of its flow from ground water (USEPA, 2001).  The outflow from the = Pace‑Homer Ditch=20 enters Silver Creek at several locations below the Prospector Square area.  Significant riparian zones and = wetlands=20 exist near the Site in areas that consist of accumulated tailings piles. =

 

5.2.2 = Hydrogeology

 

Ground water of concern at the Site occurs in = shallow=20 aquifers below the original ground surface.  These aquifers are primarily = fed from=20 local surface water recharge and are small and local in nature.  They generally flow from = southeast to=20 northwest toward Silver Creek.  =20 Below these shallow aquifers, at varying depths, lies the bedrock = aquifer=20 of the Keetley Volcanics, which contains varying amounts of ground water = depending upon local conditions.  = The hydraulic gradient in all aquifers is generally upward, but = the=20 connection between the bedrock aquifer and the shallow aquifers is = weak.    

  =

The Site is located in a low gradient valley = surrounded by=20 small hills.  The erosion = and=20 weathering of these hills, also part of the Keetley Volcanics, formed = the=20 original soil surface upon which the tailings were placed, as well as = the soils=20 used to cover the impoundment after its closure.  These soils are rich in clay = and exhibit=20 a very low permeability, making them very important to the ground water = and=20 surface water hydrology of the Site. =20 Beneath the tailings, the original ground surface acts as a = confining=20 unit for ground water movement, preventing water in the tailings from=20 infiltrating downward into the shallow aquifers, as well as preventing = water in=20 the shallow aquifers from moving upward into the tailings.  On the surface, the soils used = to cover=20 the tailings function as a nearly impermeable cap, effectively = preventing=20 infiltration of surface water into the tailings.  The tailings are effectively=20 encapsulated above and below by low permeability, clay rich soil.  At present, the surface of the = impoundment is convex and forms a closed basin, so precipitation that = falls=20 directly on the impoundment remains there until it evaporates or is used = by=20 plants.  Spring snow melt = and heavy=20 rains cause a large, temporary area of ponded water on the east side of = the=20 impoundment.  This ponded = area=20 remains for a significant duration after snow melt, with little recharge = from=20 precipitation, which shows the effectiveness of the cover soil in = preventing=20 significant infiltration into the tailings.   The very small amount of = water=20 that does infiltrate into the tailings eventually seeps through the main = embankment into a small wetland.   

 

The diversion ditch is also critical to the = Site=92s=20 hydrology.   The = diversion=20 ditch serves as a barrier to both surface water and shallow ground water = and=20 captures water that flows toward the impoundment.  The captured water is = channeled around=20 the impoundment, through a small retention pond, and into the small = wetland at=20 the foot of the main embankment.  = Here it mixes with water from Silver Creek and the small amount = of water=20 seeping through the embankment.  = All=20 of this water is eventually used by plants in the wetland or flows north = away=20 from the Site as surface water or shallow ground water in the alluvium = of Silver=20 Creek. 

   =20            &nbs= p;            = ;            =             &= nbsp;           &n= bsp;           &nb= sp;      =20

5.3 SAMPLING STRATEGY

 

Sampling events for the RI took place in 2001 and = 2002.  The RI was designed to augment = existing=20 data that were collected in previous Site investigations and to collect=20 additional data for the Ecological Risk Assessment.  During these events each media = was=20 sampled as a separate entity. =20 Samples were collected from the various site media, including = surface=20 water, ground water, Area A and B tailings, Area A and B soil cover, and = lastly,=20 sediments in the south diversion ditch and wetlands area. 

 

Surface and Ground Water=20 Sources

Surface water

Sample locations were chosen to provide sufficient = data to=20 characterize seasonal water quality and quantity in the South Diversion = ditch=20 and the two unnamed drainages flowing into the South Diversion Ditch, = and Silver=20 Creek.  Data were also = collected to=20 determine the effects of the Site on Silver Creek and the metal = concentrations=20 in the surface water of the South Diversion Ditch.  When sampling was not limited = due to=20 lack of flow, data was collected monthly at each location through one = complete=20 seasonal time period.  All = dissolved=20 metal concentration data were screened against Utah Water Quality=20 Standards.  The most = stringent of=20 these standards are the Class 3A Aquatic Wildlife Chronic Criteria = (AWCC).  These standards are dependent = on=20 hardness and are adjusted appropriately for an average hardness measured = at each=20 sample location.

 

Ground water =20

Due to the amount of historic ground water data, = additional=20 data collection required the addition of two new monitoring wells which = were=20 installed adjacent to Silver Creek up and down gradient of the = Site.  These were established to = determine any=20 shallow alluvial groundwater impacts caused by the tailings.  Samples were also taken from = established=20 wells close to the South Diversion ditch to determine the metals = concentrations=20 within the ground water associated with the Area B tailings, and to = determine=20 the hydraulic gradient

 

Tailings

Area A

Three test pits were created within Area A to = sample the=20 tailings.  The test pits = allowed for=20 observation and documentation of the physical characteristics and = spatial=20 configuration of the interface. =20 Additionally, at each location, five discrete samples were = collected at=20 one foot vertical increments to a depth of five feet below the soil = cover.  Acid/base potential data was = used to=20 assess the geochemical characteristics of the tailings materials.

 

Area B

Sampling in this area was completed first to = determine the=20 extent of the tailings outside of the main impoundment.  The sample data were used in = combination=20 with areal photographs and historical information to determine the study = area=20 boundary.  Backhoe test = pits (63=20 total) and a series of hand tool excavations were completed in order to = gather=20 analytical and visual samples. =20 Visual samples were used to establish the location of the = tailings/clay=20 layer interface.  This = sample data=20 was also used to assess the thickness of the soil cover on top of the = tailings=20 in Area B.  Analytical = data was used=20 to confirm the visual data.  = At=20 seven sample locations one sample was taken from the tailings and one = sample was=20 taken from the clay layer below the tailings.

 

Soil cover

Area A

Soil samples (41 samples total, 0-2" each) were = collected for=20 analysis.  The holes were = dug down=20 until tailings were collected from below the main impoundment soil cover = to=20 determine the depth of the soil cover and the chemistry of the surface=20 soils.  Samples were = analyzed for=20 lead and arsenic while 20% of the samples were analyzed for RCRA metals = plus=20 copper and zinc.

 

Area B

The same excavation and hand tool sampling = techniques that=20 were described in the Area B tailings section were used to determine = soil cover=20 thickness in this area. =20 Additionally, this area was sampled to assess the extent and = impact of=20 windblown tailings.  A = series of=20 samples were collected from three transects (28 total) and analyzed for = lead and=20 arsenic.

  =

South = Diversion=20 Ditch Sediments

Six locations were chosen for sediment sample=20 collection.  Data were = used to=20 identify the source of zinc loading to the surface water found in the = diversion=20 ditch and to evaluate ecological risk. =20

 

Background=20 Soils

Background surface soil samples (0-2") were = collected from=20 areas that have not been affected by tailings, found at least a mile = away from=20 the Site in all directions.  = All=20 samples were analyzed for lead and arsenic, while 2 samples were = analyzed for=20 RCRA metals plus copper and zinc. =20

 

Study = Area=20 Boundary

Study area boundary samples were collected from two = areas=20 south of the tailings found outside the impoundment, and on the west and = east=20 perimeter of the main impoundment. =20 These samples analyzed for lead and arsenic to aid in determining = the=20 study area boundary. 

 

Ecological=20 Sampling

Additional sampling was necessary to facilitate the = completion of a thorough ecological risk assessment.  Surface water and sediment = sample data=20 were collected from locations in the wetland area, site pond, and South=20 Diversion Ditch.  = Vegetation samples=20 and fish and macroinvertebrate samples were also taken.  An analysis of these samples = was=20 necessary to complete the ecological risk assessment.

           =20

5.4 KNOWN AND SUSPECTED SOURCES OF=20 CONTAMINATION

 

As previously described, the Silver Creek watershed = is=20 contaminated with heavy metals resulting from years of heavy mining = activity in=20 the Park City District.  = Surface=20 water from the Site enters Silver Creek after passing through a wetland = area in=20 the northwest corner of the Site. =20 There are three main sources of contamination at the Site: (1) = the=20 tailings contained within the tailings impoundment (Area A), (2) the = tailings=20 south of the diversion ditch (Area B) and (3) the tailings within the = wetland=20 area. 

 

Metal contamination resulting from wind blown = tailings=20 distribution was investigated.  = Soil=20 samples were taken along three transects (running west to east) that = were=20 oriented perpendicular to the prevailing wind direction. One transect = was=20 located north of the impoundment while the remaining two were located = south of=20 the impoundment.  These = samples were=20 collected to determine the extent of wind blown tailings contamination = and to=20 aid in the study area boundary determination.  The samples were analyzed for = arsenic=20 and lead and for eight RCRA metals, including zinc.  Samples taken along transect = two (south=20 of the impoundment) had higher concentrations of lead than transects one = and=20 three.  It is possible = that these=20 sample locations were not covered with top soil, while the other sample=20 locations were.  Sample = locations=20 with the highest concentrations of lead are included in the study area=20 boundary.

 

5.5 TYPES OF CONTAMINATION AND AFFECTED = MEDIA

 

The Site is contaminated with heavy metals, = primarily zinc,=20 lead and arsenic which are associated with the tailings found in the = three=20 locations described in Section 5.4. =20 The media that are affected by these metals include the sediments = and=20 surface water of the south diversion ditch, the site wetland, and Silver = Creek. 

 

Surface water =

Conclusions drawn from the sample data show that = zinc exceeds=20 the water quality criteria in some parts of the South Diversion Ditch, = however,=20 surface water zinc concentrations are below the criteria where the = diversion=20 ditch meets the wetland area.  = A=20 Comparison of surface water data collected from Silver Creek to the AWCC = shows=20 that zinc exceeds the criteria at both sample locations.  Peak concentrations of zinc = appear=20 during spring run-off conditions.

 

Ground = water

Data gathered from the monitoring wells were used = to=20 determine the metals concentrations within the ground water associated = with the=20 Area B tailings, and to determine the hydraulic gradient. After data = gathered=20 from these two areas were compared to Primary and Secondary Drinking = Water=20 Standards (PDWS and SDWS) and Treatment Technology Requirement (TTR) = they were=20 also compared to each other to determine whether the Site tailings are=20 contributing zinc or other metals to the Silver Creek alluvial = aquifer.  Results show that ground water = within=20 the Area B tailings had lower concentrations of metals than the Silver = Creek=20 alluvial aquifer. Dissolved zinc concentrations from the Area B tailings = are=20 approximately 500 times lower than the zinc concentrations measured in = the up=20 gradient Silver Creek alluvial aquifer. =20 Lastly, there is no hydraulic connection between ground water = stored in=20 the Area A tailings and the underlying aquifers.

  =

Tailings Metals=20 Concentrations

Area A

The average lead concentration in the Area A = tailings was=20 4,530 ppm, while the average arsenic value was 265 ppm. 

 

Area B

The average lead and arsenic concentrations in the = tailings=20 above the clay layer were 10,434 ppm and 412 ppm respectively, while the = average=20 lead and arsenic concentrations in the clay layer below the tailings = were 52 ppm=20 and 9 ppm.  Average lead = and arsenic=20 concentrations in the clay layer below the tailings in Area B are well = below the=20 background soil concentration.

 

Area A and = B tailings=20 data analysis

Based on the data presented above it appears that = there are=20 higher metals concentrations in the tailings in Area B as compared to = Area=20 A.  However, metal = concentrations in=20 the clay layer below the tailings in Area B are lower than in background = soil=20 concentrations.  = Furthermore, the=20 composition of the clay layer below Area B tailings is the same as the=20 composition of the clay layer below the main impoundment. This leads to = the=20 conclusion that the clay layer below the tailings is serving as an = adequate=20 barrier to metals migration in Area B and A.        =

 

Soil Cover

Area A

Sample data indicate that the range of thickness of = the soil=20 cover is 0.5 to 4 feet.  = Analytical=20 results show the average lead concentration to be 385 ppm, while the = average=20 arsenic concentration was 22 ppm. =20 As there are no regulatory criteria for metals in soils, this = data was=20 used to analyze the risk of surficial soil exposure to recreational = users and=20 ecological receptors at the Site. =20

 

Area B

A series of samples were collected from three = transects (28=20 total) and analyzed for lead and arsenic. =20 Five of the samples were analyzed for eight RCRA metals plus zinc = and=20 copper.  In conclusion, = Transect 2=20 had a higher average concentration of lead and arsenic (1,446 ppm Pb, 75 = ppm As)=20 than transects 1 and 3, however, samples taken from this area may not = have been=20 covered by soil, causing the results to represent concentrations of lead = and=20 arsenic associated with the tailings that were already there, rather = than=20 concentrations associated with windblown tailings.

 

South = Diversion=20 Ditch Sediments

Analytical results show that the average = concentrations for=20 lead, arsenic and zinc are 2,578 ppm, 138 ppm and 7,878 ppm = respectively.  Concentrations are highest in = the sample=20 location found in the lower portion of the diversion ditch just east of = the site=20 pond.

 

 

Background=20 Soils

The average lead concentration for the background = soils is=20 43.3 ppm.  The average = arsenic=20 concentration is 9 ppm.  = None of the=20 background soil samples had elevated metals concentrations.

 

Study = Area=20 Boundary

Study area boundary samples were collected from two = areas=20 south of the tailings found outside the impoundment, and on the west and = east=20 perimeter of the main impoundment. =20 These  were = analyzed for lead=20 and arsenic to aid in determining the study area boundary.  Analytical sample results were = used to=20 delineate the Study area Boundary. =20 The boundary is drawn where background lead concentrations appear = in the=20 sample results.

 

Ecological=20 Sampling

Additional sampling was necessary to facilitate the = completion of a thorough ecological risk assessment.  Surface water and sediment = sample data=20 was collected from locations in the wetland area, Site pond, and South = Diversion=20 Ditch.  Vegetation samples = and fish=20 and macroinvertebrate samples were also taken.  The resulting data was used to = determine=20 risk to ecological receptors in the Site area.  A summary of the Ecological = Risk=20 Assessment including the findings from the ecological sampling is = presented in=20 section 7.2.

 

5.6 LOCATION OF CONTAMINATION AND POTENTIAL = ROUTES OF=20 MIGRATION

 

5.6.1 = Surface water=20 and Sediments

 

Sediments and surface water impacted by the = tailings in Area=20 A and B are found in the South Diversion Ditch and in the Wetland = area.  The contamination in these = media is=20 potentially affecting ecological receptors found in the area.  Importantly, metal = concentrations in the=20 surface water of  Silver = Creek are=20 higher than metals concentrations found in the surface water of the = diversion=20 ditch.  Therefore, = contaminated=20 surface water found within the wetland is not adversely affecting Silver = Creek.

 

South Diversion = Ditch

Elevated concentrations of lead, arsenic, zinc and = some=20 cadmium were found in all water and sediment samples taken.  The South Diversion Ditch is a = dynamic=20 environment, where elevated concentrations of metals, particularly zinc, = fluctuate with seasonal runoff and correspond with peak groundwater=20 elevation.  Likely sources = of=20 elevated metals concentration found in surface water and sediments in = the=20 Diversion Ditch include the tailings located in the bottom if the ditch, = the=20 small pond area south of the Site, or from the tailings in Areas A or = B.   

 

Wetlands

Although concentrations of metals in the surface = water and=20 sediment of the wetland area are lower than those of the South Diversion = Ditch,=20 they are very likely to have impacts on the ecological environment at = the=20 Site.  The average = concentrations of=20 lead, arsenic and zinc are just below those in the South Diversion = Ditch.  There is a mixing of surface = waters that=20 occurs in the wetland area; while water from Silver Creek enters the = northern=20 portion of the wetland, surface water also flows in from the Diversion = Ditch in=20 the southern portion of the wetland. =20 Sample results indicate that water entering the wetland area from = Silver=20 Creek contains higher metals concentrations than the surface water of = the South=20 Diversion Ditch. 

 

5.6.2 = Ground=20 water

 

  • Ground water sampling results indicate that the Site = ground=20 water has much lower concentrations of metals than the ground water = within the=20 Silver Creek alluvial ground water. =20 A large amount of this ground water is captured in the South = Diversion=20 Ditch.  Based on this = data, it=20 does not appear that the Site ground water is impacting the Silver = Creek=20 alluvial aquifer.=20
  • As a result of the native clay layer found beneath = the Area A=20 tailings there is no hydraulic connection between the ground water = associated=20 with these tailings and the shallow alluvial aquifers or the = underlying=20 Keetley Volcanic aquifers.=20
  • Sample results from ground water within the wetland = area=20 indicate that there are no significant impacts from the contamination = found in=20 the wetland, the embankment or the Area A tailings.

 

5.6.2 Soils

 

In the = previous=20 sections on Background Soils and Soil Cover (Section 5.5) it is made = clear that=20 impacts to the soils at the Site are minimal.  Most contamination is in the = form of=20 tailings that were deposited within Area A and in some small areas = within Area=20 B.  Migration of metals = away from=20 these small areas within Area B is extremely limited.  Most of the small tailings = deposits=20 within Area B have been previously covered with topsoil.  Any soils within Area B that = have high=20 concentrations of metals are included in the Study Area Boundary are = addressed=20 by the selected remedy.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SECTION 6

 

CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE=20 USES

 

This=20 section describes the current and reasonably anticipated future land = uses and=20 current and potential beneficial ground and surface water uses at the=20 Site.

 

Current = Land=20 Use

 

The Site=20 is located in a rural area within a broad valley of mostly undeveloped = rangeland=20 within the Silver Creek Watershed, approximately two miles outside the=20 Park=20 City limits.  The Deer Valley=20 and Park=20 City ski resorts = sit at the=20 top of the watershed and serve as recreational use areas for skiers in = the=20 winter and bikers/hikers in the warmer months.  As Silver Creek passes through = Park=20 City and into the = surrounding suburban areas, the land use is primarily residential and=20 commercial, changing to recreational and agricultural in the areas = surrounding=20 Richardson Flat.  Most of = the land=20 around the Site is undeveloped open space.

 

Mining=20 activities at the Site ceased in 1982. =20 Since that time, the Site has not been used and has remained open = space.  A small = recreational trail=20 skirts the Site along Silver Creek.  =20 There are a few small industrial operations in the vicinity of = the Site,=20 including a concrete plant on a nearby parcel.  Park City and other resort-like = residential=20 developments are expanding in the general area, but none are closer than = one=20 mile away.

 

Reasonably=20 Anticipated Future Land Use

 

The=20 Site, and much of the surrounding area, is privately owned by UPCM.  UPCM has consistently = indicated a desire=20 to retain title and limit future use to recreational activities at the=20 Site.  While no final = decision has=20 been made, uses that range from open space wildlife habitat to athletic = fields=20 are currently being discussed.  = Any=20 type of recreational use is consistent with surrounding land uses, and = both=20 Park City and Summit County have indicated general = agreement=20 with recreational proposals. =20 Park=20 City is proactive = in=20 obtaining and preserving open space. =20 There is no indication that higher uses of the land, such as = residential,=20 are reasonably foreseeable.

 

Ground and=20 Surface Water Uses

 

The=20 surface water features at the Site, including the south diversion ditch, = the=20 wetlands area below the embankment, the Site pond and Silver Creek are = used as=20 habitat by a limited number of vegetative species, fish, and = wildlife.  All of the surface water and = shallow=20 ground water on the Site eventually discharges to Silver Creek.  Silver Creek is classified by = the State=20 of Utah as a=20 potential drinking water source, a recreational use feature, a cold = water=20 fishery, and a potential irrigation source. At present, Silver Creek is = used for=20 irrigation and recreational fishing only, and no changes are = expected.  The State of Utah is = considering=20 issuing an advisory against fishing due to elevated metal levels in = Silver=20 Creek.  Silver Creek is = listed on=20 the State=92s Clean Water Act Section 303(d) list of impaired water = bodies because=20 zinc and cadmium levels exceed chronic standards for protection of = aquatic=20 wildlife.  =

 

Silver=20 Creek has been impacted by the legacy of mining activities, though the = remedial=20 investigation confirmed that the Site is not, at present, a significant=20 contributor of metals to the creek. =20 The goal is to remediate the entire watershed, improving the = ecological=20 quality of the area, thereby allowing for continued beneficial use of = the=20 watershed and the Site by a variety of living organisms. 

 

Ground=20 water in the immediate area is used only for private wells, and no wells = are=20 known to be located within a half mile of the Site.   Most area drinking water = wells are=20 finished in the deeper consolidated sedimentary rocks that can sustain = aquifers=20 and produce sufficient yields for culinary wells.  In the Site area, these = formations are=20 very deep and are covered by the Keetley volcanics.  The volcanic rocks are = generally not=20 suitable to sustain aquifers and serve as more of a confining unit.  The shallow ground water at = the Site is=20 generally associated with the alluvial system of Silver Creek.  This water is very high in = solids and is=20 also often contaminated due to water quality in Silver Creek and = tailings that=20 are present along the Creek in many areas. =20 There are no known uses for this water at this=20 time.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SECTION 7

 

SUMMARY OF SITE = RISKS

 

A baseline human health risk assessment (BHHRA) and = a=20 baseline ecological risk assessment (BERA) were performed to evaluate = the=20 potential for adverse human health and ecological effects that might = occur from=20 exposure to Site-related contaminants. =20 Current and future risks were estimated for the baseline scenario = (i.e.,=20 risks that might exist if no remediation or institutional controls were=20 applied).  The BHHRA and = the BERA=20 aided in drafting the remediation goals by providing a basis for taking = action=20 at the Site.  The = Chemicals of=20 Concern and the exposure pathways were also identified through these = risk=20 assessments.

 

7.1 HUMAN HEALTH RISK = ASSESSMENT

 

7.1.1 Identification of Chemicals of=20 Concern

 

The BHHRA identified two contaminants, lead and = arsenic, as=20 chemicals of potential concern (COPC=92s) at the Site through a four = step=20 selection process.  Risks = to human=20 health posed by exposure to these chemicals have been studied = extensively=20 through risk assessments completed at other Superfund sites in = Utah and = throughout the=20 country.  Currently, the = Site has a=20 soil cover that has a depth of 4 feet in some areas.  Because of this soil cover, = exposure=20 pathways to these COPC=92s are limited or interrupted.  However, if the integrity of = this soil=20 cover were threatened in any way by forces of nature or human = intervention, the=20 exposure pathways could become complete. =20 Because of the high human health risk associated with lead and = arsenic,=20 and because of the potential exposure to recreational Site visitors if a = remedy=20 were not in place, lead and arsenic were selected as chemicals of = concern=20 (COC=92s) and risk drivers for the Site. =20 The COC=92s are summarized in Tables 7-1,7-2, and=20 7-3.

 

7.1.2 Exposure Assessment

 

The exposure assessment identifies scenarios = through which=20 people could be affected by the COCs in Site media and estimates the = extent of=20 exposure Site users could endure. =20 The conceptual site model illustrates the media and exposure = pathways=20 that were evaluated in the BHHRA (Figure 5).  Media selected for evaluation = in the=20 BHHRA were soil/tailings, surface water, sediment, and air = particulates.  Because land use will be = limited to=20 recreational visitors, two separate recreational use scenarios were=20 considered.  An evaluation = of the=20 exposure pathways is also presented in Figure 6.

 

Low intensity User

The first scenario includes low intensity users, = such as=20 hikers, bikers and picnickers, ranging in age from young children to=20 adults.  Exposure pathways = evaluated=20 were ingestion of soil/tailings, surface water and sediment, dermal = exposure to=20 surface water and inhalation of particulates in air.  

High Intensity User

Scenario two includes high intensity users such as = horseback=20 riders, ATV users, dirt bikers and team sports players.  High intensity users were = assumed to=20 exclude younger children and include teenagers and adults.  The exposure pathways a high = intensity=20 user may be subjected to include ingestion of soil/tailings and = inhalation of=20 particulates in air.

 

7.1.3 Toxicity Assessment     =

 

The purpose of the toxicity assessment is to review = and=20 summarize the potential for each COC to cause adverse effects in exposed = individuals.  The toxic = effects of a=20 chemical generally depend on the inherent toxicity of a chemical, the = route of=20 exposure (ingestion, inhalation, and dermal), and the duration of = exposure=20 (subchronic, chronic or lifetime).

 

There is a positive relationship between dose = (chemical=20 intake through an exposure pathway), and adverse effect, so as dose = increases=20 the type and severity of adverse reponse also increases.  Chemical toxicological = information=20 derived from either animal or human studies is used to estimate toxicity = criteria which are numerical expressions between dose (exposure) and = response=20 (adverse health effects).  = Toxicity=20 criteria are developed for the assessment of carcinogenic and = non-carcinogenic=20 health effects.  Toxicity = criteria=20 include the EPA online Integrated Risk Information System (IRIS) and = EPA=92s=20 Health Effects Assessment Summary Tables (HEAST).

 

Toxicity criteria for carcinogens are provided as = cancer=20 slope factors (CSF=92s) in units of risk per milligram of chemical per = kilogram of=20 body weight per day (mg/kg-day).  = CSF=92s are based on the assumption that no threshold exists for=20 carcinogenic effects and that any dose is associated with some finite=20 carcinogenic risk.  The=20 chemical-specific CSF is multiplied by the estimated chemical intake to = provide=20 an upper-bound estimate of the increased likelihood of cancer resulting = from=20 exposure to the chemical.  = This risk=20 would be in addition to any background risk of developing cancer over a = lifetime=20 due to other causes.  = Consequently,=20 the risk estimates in the BHHRA are referred to as incremental or excess = lifetime cancer risks.  = Based on=20 data from IRIS and other published data, arsenic is classified as a = known human=20 carcinogen (EPA weight of Evidence A). Table 7-4 shows the cancer = toxicity=20 criteria for ingestion of arsenic. =20 Lead toxicity is evaluated using other methodologies such as the=20 Integrated Exposure Uptake Biokinetic (IEUBK) model.  Estimated blood lead levels = are compared=20 to target blood-lead concentrations to assess possible risks.

 

Toxicity = criteria for=20 noncarcinogens are provided as reference doses (RfDs) and represent the = daily=20 exposure to a chemical that would be without adverse effects, even if = the=20 exposure occurred continuously over a lifetime.  The RfD is provided in units = of=20 milligrams per kilogram per day (mg/kg-day) for comparison with chemical = intake=20 into the body.  Chemical = intakes=20 that are less than the RfD are not likely to be of concern even to = sensitive=20 individuals.  Chemical = intakes that=20 are greater than the RfD indicate a possibility for adverse = effects.  Noncancer toxicity values for = COCs for=20 ingestion/dermal exposures are presented in Table 7-5.

 

EPA has not = published=20 toxicity criteria for lead.  = This is=20 because available data suggest that there is no threshold for adverse = effects=20 even at exposure levels that might be considered background.  Any significant increase in = exposure=20 above background levels could represent a cause for concern.  Instead of evaluating risk = using typical=20 intake calculations and toxicity criteria, EPA has developed other = methodologies=20 for evaluating lead exposures.  = One=20 such methodology is the Integrated Exposure Uptake Biokinetic (IEUBK) = model, a=20 computer model used to predict blood-lead levels in children exposed to = lead=20 from a variety of sources, including soil, dust, ground water, air, = diet,=20 lead-based paint, and maternal blood. =20 Estimated blood-lead levels are compared to target blood-lead=20 concentrations to assess possible risks. =20 The IEUBK model is intended for use only for children up to the = age of=20 seven, as these are the most sensitive receptors to lead exposure.  The model assumes daily = exposure in a=20 residential setting.

 

There are = circumstances=20 in which adjustments to toxicity criteria should be made to account for = the=20 relative bioavailability of a chemical due to its chemical form or its = reactive=20 form or the particular medium in which it is found.  The issue of bioavailability = is=20 especially important when dealing with media from mining sites because = metals in=20 these media may exist in insoluble media. =20 These chemical and physical properties may tend to influence = (usually=20 decrease) the adsorption or bioavailability of the metals when = ingested.  Because no site specific data = are=20 available for the bioavailability of arsenic in soils/tailings the = default value=20 of 0.8 was applied to the arsenic toxicity criteria.

 

Adverse Effects of Arsenic=20 Exposure

Noncancer Effects

Oral = exposure to acute=20 and chronic ingestion of lower levels of arsenic often include diarrhea, = vomiting, decreased blood cell formation, injury to blood vessels, = damage to=20 kidney and liver, and impaired nerve function.  The most diagnostic sign of = chronic=20 arsenic exposure is an unusual pattern of skin abnormalities, including = dark and=20 white spots and a pattern of small "corns," especially on the palms and = soles=20 (ATSDR 1991).

 

Carcinogenic Effects

There have = been a number=20 of epidemiological studies in humans which indicate that chronic = inhalation=20 exposure to arsenic is associated with increased risk of lung cancer = (USEPA=20 1984, ATSDR 1991).   = In=20 addition, there is strong evidence from a number of human studies that = oral=20 exposure to arsenic increases the risk of skin cancer (USEPA 1984, ATSDR = 1991).  The most common = type of=20 cancer is squamous cell carcinoma, which appears to develop from some = skin=20 corns.  Although the = evidence is=20 limited, there are some reports which indicate that chronic oral arsenic = exposure may also increase risk of internal cancers, including cancer of = the=20 liver, bladder and lung, and that inhalation exposure may also increase = risk of=20 gastrointestinal, renal or bladder cancers (ATSDR 1991).

 

Adverse Effects of Lead = Exposure

Noncancer=20 Effects

Excess exposure to lead can result in a wide = variety of=20 adverse effects in humans.  = Chronic=20 low-level exposure is usually of greater concern for young children than = older=20 children or adults.  = The=20 effect of lead that is usually considered to be of greatest concern in = children=20 is impairment of the nervous system. =20 The effects of chronic low-level exposure on the nervous system = are=20 subtle and normally cannot be detected in individuals, but only in = studies of=20 groups of children.  = Common=20 measurement endpoints include various types of tests of intelligence, = attention=20 span, hand-eye coordination, etc. =20 Such effects on the nervous system are long-lasting and may be=20 permanent.  = Additionally,=20 studies in animals reveal that high blood lead levels during pregnancy = can cause=20 fetotoxic and teratogenic effects. =20 Further,=20 a characteristic effect of chronic high lead exposure is anemia stemming = from=20 lead-induced inhibition of heme synthesis and a decrease in red blood = cell life=20 span. 

 

Cancer=20 Effects

Studies=20 in animals indicate that chronic oral exposure to very high doses of = lead salts=20 may cause an increased frequency of tumors of the kidney (USEPA 1989b, = ACGIH=20 1995).  However, there is = only=20 limited evidence suggesting that lead may be carcinogenic in humans, and = the=20 noncarcinogenic effects on the nervous system are usually considered to = be the=20 most important and sensitive endpoints of lead toxicity (USEPA = 1988). 

 

7.1.4 = Risk=20 Characterization

 

The BHHRA = characterized=20 the risk to low and high intensity recreational users through exposure = to the=20 COCs at the Site.   =

 

7.1.4.1 = Evaluation of=20 Carcinogenic Risk

 

For = carcinogens, risks=20 are generally expressed as the probability of an individual developing = cancer=20 over a lifetime as a result of exposure to the Site-related = contaminants.  This is described as =93excess = lifetime=20 cancer risk=94 because it is an addition to the risk of cancer from = other=20 causes.  Exposure to Site = COPCs was=20 evaluated by multiplying chemical specific exposure estimates (i.e. = average=20 lifetime dose) by the chemical and route specific CSF.  The result was a unitless = measure of=20 probability (e.g., 1E-4) of an individual developing cancer as a result = of=20 chemical exposures at the Site.  = A=20 cancer risk of 1E-04 refers to an increased chance of one in ten = thousand of=20 developing cancer as a result of site related exposure to a carcinogen = over the=20 expected duration.  = Typically, the=20 USEPA considers remedial action at a site when estimated total excess = cancer=20 risk to any current or future population exceeds the range between one = in ten=20 thousand (1E-04) and one in a million (1E-06).  Estimated carcinogenic risks = for=20 reasonable maximum exposure (RME) scenarios are presented in tables 7-6 = and=20 7-7.  Estimates of average = risks are=20 presented in the BHHRA.

 

Low = Intensity=20 Users

RME excess = cancer risks=20 were calculated for potential low intensity recreational users, which = include=20 hikers, bikers and picnickers. =20 Risks were evaluated for the ingestion, inhalation and dermal = exposure=20 pathways.  Risk from = inhalation and=20 ingestion of sediments, soils/tailings and surface water and dermal = exposure to=20 surface water were estimated to fall below EPA=92s threshold cancer risk = of=20 1E-06.  Risk from = ingestion of=20 soil/tailings was estimated to be 2E-05 for the RME scenario.  This risk falls into EPA=92s = acceptable=20 range of 1E-04 and 1E-06.            &nbs= p;            = ;=20            &nbs= p;            = ;           =20

           &nbs= p;            = ;            =            =20

High = Intensity=20 Users

RME excess = cancer risks=20 were calculated for high intensity recreational users which include = horseback=20 riders, ATV users, dirt-bikers, and sports (soccer, baseball) players. = Risks=20 were evaluated for the ingestion of soil/tailings and the inhalation of = soil as=20 dust exposure pathways.  = Risk from=20 inhalation of soil as dust was estimated to fall well below the = threshold cancer=20 risk of 1E-06.  Risk from = ingestion=20 of soil/tailings was estimated to be 1.1E-05, which falls into EPA=92s = acceptable=20 range of 1E-04 and 1E-06.  =20

 

7.1.4.2 = Evaluation of=20 Noncarcinogenic risks

 

The potential = for=20 noncarcinogenic effects due to exposure to a particular chemical is = expressed as=20 the hazard quotient (HQ).  = An HQ was=20 calculated by dividing the dose (estimated chemical intake) of a = chemical by the=20 RfD.  The HQ calculation = assumes=20 that there is a threshold level of exposure below which no adverse = effects will=20 occur.  An HQ less than = one=20 indicates that there is little potential for adverse noncancer effects, = even in=20 sensitive individuals, while an HQ greater than one indicates the = potential for=20 adverse noncancer effects.

The hazard = index (HI) is=20 equal to the sum of all the HQs.  = A=20 HI less than one indicates there is little potential for adverse effect = from=20 exposure to all COCs at a site.  = An=20 HI greater than one indicates the potential for adverse noncancer = effects from=20 exposure to all COCs, assuming that all chemicals have the same toxic = effect and=20 that toxic effects would be additive. =20 Estimated RME noncancer hazards for populations evaluated in the = BRA are=20 presented in Tables 7-8 and 7-9.  = Please refer to the BHHRA for estimates of average noncancer = hazards=20 across the Site.

 

Low = Intensity=20 Users

Noncancer = hazards were=20 quantified for exposure to arsenic via ingestion of soils/tailings, = surface=20 water and sediment. The risk associated with inhalation of soil as dust = and=20 dermal contact with surface water was also considered.  The HI was the sum of all HQs = associated=20 with the Site for the low intensity user. =20 The RME HI was 9.2E-02 related to arsenic exposure through the = various=20 pathways.  This falls = below EPA=92s=20 acceptable range for exposure to non-carcinogenic contaminants, which = means that=20 it is not a human health concern by EPA=92s standards

 

High = Intensity=20 Users

Noncancer = hazards were=20 quantified for exposure to arsenic via ingestion of soils/tailings, and=20 inhalation of soil as dust for the high intensity recreational = user.  The HI, the sum of the HQs, HI = was=20 5.8E-02, which falls below EPA=92s acceptable range for exposure to=20 non-carcinogenic contaminants, which means that it is not a human health = concern=20 by EPA=92s standards

 

7.1.4.3 = Evaluation of=20 Risks from Lead

 

Risks from = lead are=20 usually evaluated by estimation of the blood levels in exposed = individuals and=20 compared to blood lead levels within an appropriate health based = guideline.  The USEPA and CDC have set a = goal that=20 there should be no more than a 5% chance that a child should have a = blood level=20 over 10=B5g/dL.   The = BHHRA used=20 the IEUBK model to first evaluate risks to a hypothetical nearby = resident of a=20 child=92s age (0-6 years).  = Second,=20 risks to a residential child engaged in low-intensity recreational = activities at=20 the Site were evaluated.  = The risk=20 to residential children engaged in recreational activity is higher than = the risk=20 to children who live nearby but don=92t engage in recreational = activity.  However, the geometric mean = values are=20 relatively low, and children engaging in recreational activities have = less than=20 a 5% chance of exceeding a blood lead level of 10=B5g/dL.

 

Risks for = exposure to=20 lead in Site media were also evaluated for teenage and adult = recreational=20 visitors using the Bowers model.  = Low and high intensity recreational visitor exposure scenarios = were=20 examined.  Results showed = that high=20 or low-intensity recreational use at this Site is not predicted to cause = high=20 blood lead levels which exceed a target concentration of = 11.1=B5g/dL.  The 11.1=B5g/dL standard is a = health=20 criterion based on the blood lead concentration that is acceptable for a = pregnant adult. 

 

7.1.5 = Assessment of=20 Uncertainties

 

Several assumptions used in the evaluation of lead = risks at this=20 Site may introduce uncertainty into the presented findings.  Although in most cases, = assumptions=20 employed in the risk assessment process to deal with uncertainties are=20 intentionally conservative; that is, they are more likely to lead to an=20 overestimate rather than an underestimate of risk, it is nevertheless = important=20 to take these uncertainties into account when interpreting the risk = conclusions=20 derived for this Site. =20 Uncertainties presented in the risk assessment include: = uncertainty in=20 lead concentrations estimates, uncertainty in lead absorption from soil, = and=20 uncertainty in the modeling approach.

 

Uncertainty in Lead Concentration=20 Estimates

Evaluation of human health risk at any particular = location=20 requires accurate information on the average concentration level of a = COPC at=20 that location.  Because = estimating=20 the mean is more difficult when aggregating data over a large exposure = area,=20 such as the Site, the true mean could be underestimated.  Here, the 95th = Upper=20 Confidence Limit soil lead concentration was used to evaluate risks from = lead.  This approach is = reasonable=20 for use at the Site where lead concentrations in onsite soil/tailing = materials=20 range from 14 to 5,875 mg/kg.  = This=20 conservative approach for estimating exposure to lead at the site may overestimate the actual risks = from lead=20 for the Site, ensuring that all of the risk estimates are more likely to = be high=20 than low.      =20

 

Risks from exposure to lead were evaluated based on = surficial=20 soil data.  This decision = was based=20 on the assumptions that recreational users are most likely to be exposed = to=20 surficial soils based on their activities. =20 Based on the depth distribution observed for lead, risks from = exposure to=20 subsurface soils will be similar or less than those observed for surface = soils.  However, if = concentrations=20 for lead are ever found to increase as a function of depth, the risks = based on=20 surface soil exposure will underestimate risks for those=20 individuals exposed to buried materials. =20 The maximum lead concentration in soil/tailings observed at the = Site at=20 any depth is 21,380 mg/kg.

 

Uncertainty in Lead Absorption = from=20 Soil

 

Another important source of uncertainty regarding = the risk=20 from lead in soil is the degree of absorption (RBA) within the = gastrointestinal=20 tract.  For the risk = assessment=20 performed at the Site, a default relative bioavailability factor for = lead of=20 0.60 has been applied.  = This=20 introduces uncertainty, and causes either an over or underestimation of = risk=20 because the selected value is not based on actual measurements for site=20 soils.  Soils are complex = by nature=20 and may have numerous attributes which influence overall absorptions=20 characteristics. 

 

Uncertainty in Modeling = Approach

 

All predictive models, including the IEUBK model = and the ISE=20 model, are subject to a number of limitations.  First, there is inherent = difficulty in=20 providing the models with reliable estimates of human exposure to=20 lead‑contaminated media.  = For=20 example, exposure to soil and dust is difficult to quantify because = human intake=20 of these media is likely to be highly variable, and it is very difficult = to=20 derive accurate measurements of actual intake rates.  Second, it is often difficult = to obtain=20 reliable estimates of key pharmacokinetic parameters in humans (e.g., = absorption=20 fraction, distribution and clearance rates), since direct observations = in humans=20 are limited.  Finally, the = absorption, distribution and clearance of lead in the human body is an = extremely=20 complicated process, and any mathematical model intended to simulate the = actual=20 processes is likely to be an over‑simplification.  Consequently, model = calculations and=20 predictions are generally rather uncertain.

 

The Bowers model used to assess lead exposures in = youths and=20 adults requires a composite toxicokinetic parameter (the biokinetic = slope=20 factor) to predict the effect of exposure on blood lead levels.  This value is derived mainly = from=20 studies in adult males, and it is not certain that the value is accurate = for=20 youths or for women (especially pregnant women).  Also, the exposures being = modeled with=20 the Bowers model are intermittent rather than continuous, so blood lead = levels=20 in the exposed populations are expected to show temporal variability. = Toxicity=20 data are not adequate to estimate the level of health risk associated = with=20 occasional (rather than continuous) elevations in blood lead level due = to=20 intermittent exposures to elevated lead levels in the environment.  However, since the observed = lead levels=20 in soil/tailings result in predicted blood lead levels that are well = below the=20 established level of concern, these uncertainties in the modeling = approach do=20 not cast serious doubt on the accuracy of the conclusion that lead = levels at=20 this Site are not of concern to older children or adults. 

 

7.2 = ECOLOGICAL RISK=20 ASSESSMENT

 

Tailings = released to the=20 environment from ore milling operations generally contain metals that = can,=20 depending on the concentration and level of exposure, be toxic to = ecological=20 receptors.  In accord with = the=20 eight-step process recommended by USEPA for evaluating ecological risks = the=20 ecological risk assessment process at this Site was initiated by = performing a=20 Screening‑Level Ecological Risk Assessment (SLERA) (USEPA, 2003a), = which was=20 followed by the Baseline Ecological Risk Assessment (BERA, January, = 2004).  These ecological risk = assessments were=20 completed to describe the likelihood, nature, and extent of adverse = effects to=20 ecological receptors resulting from present and potential exposure to = the COCs=20 at the Site.  The SLERA = was intended=20 to provide a preliminary evaluation of the potential for adverse effects = to=20 three classes of ecological receptors (aquatic, terrestrial, = wildlife).  Because a SLERA normally uses = a number=20 of simplifying assumptions and approaches and is intentionally = conservative, the=20 SLERA was not intended to support any final quantitative conclusions = about the=20 magnitude of the potential ecological risks.  The SLERA was also used to = identify=20 additional data that needed to be gathered in order to complete the = BERA.  Once the additional data was = compiled it=20 became possible to perform a more complete risk assessment, addressing = the COC=92s=20 and the risks posed through the various ecological exposure pathways = within the=20 exposure areas of the Site.  = The=20 BERA was conducted using the problem formulation approach, which is an = iterative=20 process that allows risk assessors to refine the assessment as new = information=20 becomes available and to make qualitative conclusions about Site risks = by using=20 a weight of evidence evaluation.  The various methods used to = assess=20 exposure and risk under the problem formulation approach as well as a=20 description of the combined results of the SLERA and the BERA are = described in=20 the sections that follow.

 

7.2.1 = Identification=20 of Chemicals of Concern

 

Chemicals of = concern=20 (COCs) at the Site were identified through a weight of evidence = evaluation=20 that began in the SLERA.  = In this=20 process, the maximum concentration of each detected metal was compared = to the=20 screening level benchmark (SL) for that metal.  If this concentration was = greater than=20 the SL, the chemical was considered a chemical of potential concern = (COPC) and=20 was retained for further evaluation in the BERA.  Additionally, the Site was = divided into=20 exposure areas for the purpose of the risk assessment.  These areas are based on the = Site=20 characteristics and include Silver Creek (upstream and downstream), Site = diversion ditches, the wetlands area, Site pond, and Area A and Area B=20 tailings.  By examining = the=20 ecological receptors and the COPCs associated with the environmental = media=20 within each exposure area, a risk management decision was made to = determine the=20 COCs for the Site.  As a = result of=20 this approach, the following COCs are described based on the = environmental media=20 and the ecological receptor associated with that media.  Cadmium and zinc (dissolved) = were the=20 COCs identified for surface water and aquatic receptors at the = Site.  Within the bulk sediment, = cadmium,=20 copper, mercury and zinc were considered COCs if benthic organisms were = the=20 receptors.  Lead = associated with the=20 sediment was found to be a COC if waterfowl were the ecological = receptors. The=20 COCs, arsenic and zinc (dissolved), associated with sediment porewater = could be=20 toxic to benthic organisms.  = Lastly,=20 aluminum, lead, mercury and zinc were named COCs and considered toxic to = plants=20 and soil invertebrates in contact with the soils and tailings at the = Site. The=20 COCs are summarized in Tables 7-10 through 7-14.  These COC=92s have the = potential to=20 adversely affect growth, diversity, reproduction and survival of the = various=20 species that populate the Site. =20

 

7.2.2 = Exposure=20 Assessment

 

When = examining exposure=20 to ecological receptors at the Site it is important to note that in = accordance=20 with the State of Utah surface water code, the Weber River from the = Stoddard=20 diversion to its headwaters (including Silver Creek) is classified as a = cold=20 water fishery (3A) and is protected for cold water species of game fish = and=20 other cold water aquatic life, including the necessary aquatic organisms = in the=20 food chain.  Because the = Site=20 provides possible habitat for fish, aquatic invertebrates, terrestrial = plants,=20 terrestrial invertebrates, mammals, birds, reptiles and amphibians, = those were=20 the receptors included in the SLERA.

 

Figure 7 = presents the=20 ecological conceptual site model (CSM) for the Site.   As indicated in the = Ecological=20 CSM, ecological receptors that may be exposed at the Site include = aquatic=20 receptors (fish and benthic macroinvertebrates), amphibians and = reptiles,=20 terrestrial receptors (plants and soil invertebrates), and wildlife = receptors=20 (birds and mammals).  Each = receptor=20 class may be exposed to chemical contamination via contact with one or = more=20 environmental media, including surface water, sediment, seeps, aquatic = food=20 items, soil/tailings, and terrestrial food items.   However, not all of = these exposure=20 pathways are likely to be of equal concern.  Pathways that were supported = by adequate=20 data became the primary focus of the BERA and were included in the = quantitative=20 risk evaluation.  An = explanation of=20 the elimination of certain pathways can be found in the BERA and for the = purposes of this ROD, only the pathways of high ecological concern are = described=20 below. =20

 

Aquatic=20 Receptors (Fish)

 

The main = pathways of=20 exposure for fish and benthic invertebrates are direct contact with = surface=20 water and sediment.  Each = of these=20 pathways were evaluated quantitatively.

 

Terrestrial=20 Receptors (Plants and Invertebrates)

 

The primary = exposure=20 pathway for both terrestrial plants and soil invertebrates is direct = contact=20 with contaminated soils.  = This=20 pathway was evaluated in the SLERA; however, additional data were not = collected=20 for the BERA, so further analysis of this pathway was not conducted. It = is=20 assumed from the SLERA that direct contact with contaminated soils is a = complete=20 pathway and one of potentially high risk to terrestrial receptors.

 

Wildlife Receptors=20 (Birds and Mammals)

 

Birds and = mammals may be=20 exposed by ingestion of food web items (either from the terrestrial = environment=20 and/or from the aquatic environment). =20 Wildlife receptors may also ingest soil or sediment during = feeding,=20 especially for soil‑ or sediment‑dwelling prey items.  Although these exposure = pathways are=20 complete and of potential concern (USEPA, 2003a), no new data are = available for=20 contaminant concentrations in soil or in terrestrial food items, and it = is=20 expected that remedial actions planned for the site will largely address = potential risks to terrestrial (upland) wildlife receptors from = exposures to=20 contaminants on the main impoundment and in off-impoundment areas (RMC,=20 2003).   Therefore,=20 quantitative risk characterization for the BERA focused on exposures of=20 aquatic/semi-aquatic wildlife receptors in the wetlands area, and risks = to=20 upland terrestrial wildlife receptors were not re-evaluated in the = BERA.

 

7.2.3 = Ecological=20 Effects Assessment

 

Assessment and=20 measurement endpoints are part of the problem formulation approach used = to=20 examine ecological risk at the Site. =20 Again, the problem formulation method is an approach to risk = assessment=20 that is designed to provide risk managers with adequate qualitative and=20 quantitative information.  = As a=20 result, risk managers can make decisions that lead to protection of the=20 ecological environment.

 

Assessment = endpoints are=20 explicit statements of the characteristics of the ecological system that = are to=20 be protected.  Assessment = endpoints=20 are either measured directly or are evaluated through indirect = measures.  Measurement endpoints = represent=20 quantifiable ecological characteristics that can be measured, = interpreted, and=20 related to the valued ecological components chosen as the assessment = endpoints=20 (USEPA 1992, 1997).

 

Table 7-15 = presents the=20 assessment and measurement endpoints used to interpret potential = ecological=20 risks for the Site that were evaluated in the BERA.  These measurement endpoints = can be=20 divided into three basic categories: (1) hazard quotients (HQs), (2)=20 site‑specific toxicity tests, and (3) observations of population = and community=20 demographics.

 

Hazard = Quotients

 

Hazard = Quotients (HQ=92s)=20 are generally used by the EPA to determine whether remedial action is=20 warranted.  For example, = in human=20 health risk assessment for non-carcinogenic effects, remedial action is=20 warranted if the HQ for a COC is greater than 1 for a particular site = user.  However, for the purposes of = the BERA,=20 HQs were used as one part of the weight-of-evidence evaluation along = with the=20 other factors including toxicity testing and population = observations.   A HQ is the ratio of the = estimated=20 exposure of a receptor at the Site to a "benchmark" exposure that is = believed to=20 be without significant risk of unacceptable adverse effect:

 

HQ =3D=20 Exposure / Benchmark

 

Exposure may = be=20 expressed in a variety of ways, including:

 

=B7          =20 Concentration in an environmental medium (water, sediment, soil,=20 diet)

=B7          =20 Concentration in the tissues of an exposed receptor

=B7          =20 Amount of chemical ingested by a receptor

 

In all = cases, the=20 benchmark toxicity value must be of the same type as the exposure = estimate.

 

If the value = of an HQ is=20 less than or equal to 1, risk of unacceptable adverse effects in the = exposed=20 individual is judged to be acceptable. =20 If the HQ exceeds 1, the risk of adverse effect in the exposed = individual=20 is of potential concern.

 

When = interpreting HQ=20 results for ecological receptors, it is important to remember that the=20 assessment endpoint is usually based on the sustainability of exposed=20 populations, and risks to some individuals in a population may be = acceptable if=20 the population is expected to remain healthy and stable.  In these cases, population = risk is best=20 characterized by quantifying the fraction of all individuals that have = HQ values=20 greater than 1 and by the magnitude of the exceedences.

In = interpreting HQ=20 values and distributions of HQ values, it is always important to bear in = mind=20 that the values are predictions, and are subject to the = uncertainties=20 that are inherent in both the estimates of exposure and the estimates of = toxicity benchmarks.  = Therefore, HQ=20 values should be interpreted as estimates rather than highly precise = values and=20 should be viewed as part of the weight‑of‑evidence along = with the results of=20 site‑specific toxicity testing and direct observations on the = structure and=20 function of the aquatic community (see below).

 

 

Site‑Specific=20 Toxicity Tests

 

Site‑specific toxicity=20 tests measure the response of receptors that are exposed to Site = media.  This may be done either in the = field or=20 in the laboratory using media collected on the site.  The chief advantage of this = approach is=20 that site‑specific conditions which can influence toxicity are = usually accounted=20 for.  A potential = disadvantage is=20 that, if toxic effects occur when test organisms are exposed to a Site = medium,=20 it is usually not possible to specify which chemical or combination of = chemicals=20 is responsible for the effect. =20 Rather, the results of the toxicity testing reflect the combined = effect=20 of the mixture of chemicals present in the Site medium.  In addition, it is often = difficult to=20 test the full range of environmental conditions which may occur at the = Site=20 across time and space, either in the field or in the laboratory, so = these=20 studies are not always adequate to identify the boundary between = exposures that=20 are acceptable and those that are not.

 

Population and Community Demographic = Observations

 

A third = approach for=20 evaluating impacts of environmental contamination on ecological = receptors is to=20 make direct observations on the receptors in the field, seeking to = determine=20 whether any receptor population has unusual numbers of individuals = (either lower=20 or higher than expected), or whether the diversity (number of different = species)=20 of a particular category of receptors (e.g., plants, benthic organisms, = small=20 mammals, birds) is different than expected.  The chief advantage of this = approach is=20 that direct observation of community status does not require making the = numerous=20 assumptions and estimates needed in the HQ approach.  However, there are also a = number of=20 important limitations to this approach. =20 The most important of these is that both the abundance and = diversity of=20 an ecological population depend on many site‑specific factors = (habitat=20 suitability, availability of food, predator pressure, natural population = cycles,=20 meteorological conditions, etc.), and it is often difficult to know what = the=20 expected (non‑impacted) abundance and diversity of an ecological = population=20 should be in a particular area. This problem is generally approached by = seeking=20 an appropriate "reference area" (either the site itself before the = impact=20 occurred, or some similar site that has not been impacted), and = comparing the=20 observed abundance and diversity in the reference area to that for the=20 site. 

 

7.2.4 = Risk=20 Characterization

 

As noted = above, each of=20 the measurement endpoints has advantages but also has limitations.  For this reason, conclusions = based on=20 only one method of evaluation may be misleading.  Therefore, the best approach = for=20 deriving reliable conclusions is to combine the findings across all of = the=20 methods for which data are available, taking the relative strengths and=20 weaknesses of each method into account. =20 If the methods all yield similar conclusions, confidence in the=20 conclusion is greatly increased.  = If=20 different methods yield different conclusions, a careful review must be=20 performed to identify the basis of the discrepancy and to decide which = approach=20 provides the most reliable information.

 

 

 

 

Risk = to Aquatic=20 Receptors

 

As discussed = above,=20 aquatic receptors (fish, benthic invertebrates) may be exposed to Site=20 contaminants in surface water and sediment at a number of exposure areas = including Silver Creek, the south diversion ditch, the wetlands area, = Site pond,=20 and an unnamed drainage which flows into the south diversion ditch.  Evaluation of potential risks = by the HQ=20 approach, site-specific toxicity testing, and population surveys are = summarized=20 below.

 

Risk to Aquatic = Receptors

 

 

Exposure Pathway

 

Line of Evidence

 

Findings

 

Direct Contact with Surface Water

 

Estimated HQs from measured surface water=20 concentrations

 

Surface water concentrations of cadmium and zinc = in Silver=20 Creek are probably adversely impacting aquatic receptors.  Zinc may also be of = concern to=20 aquatic receptors in the Site diversion ditch and wetlands = area.  Concentrations of = several metals=20 may be above a chronic level of concern in the unnamed drainage = which=20 flows into the Site diversion ditch.

 

Direct Contact with Sediment

 

Estimated HQs from measured bulk sediment=20 concentrations

 

Wide-spread, and potentially severe, toxicity to = benthic=20 invertebrates may be occurring in Silver Creek, the site diversion = ditch,=20 the wetlands area, and the site pond due to multiple metals in = bulk=20 sediment.

 

Estimated HQs from measured sediment porewater=20 concentrations

 

Sediment porewater concentrations of arsenic and = zinc=20 (antimony, cadmium and lead to a lesser extent) in the wetlands = area,=20 especially in the northern portion of the wetlands, may be of = concern to=20 benthic invertebrates.

 

Sediment toxicity tests (Hyalella = azteca)

 

Statistically significant decreases in survival = were seen=20 for 5 of 8 stations in the wetlands area.  100% mortality was seen = in 3=20 sampling stations located in the northern part of the wetlands=20 area.

 

 

All exposure pathways combined

 

Tissue burden evaluation

 

Measured tissue levels of zinc suggest that = benthic=20 invertebrates and snails in the wetlands area may be adversely = impacted=20 due to site exposures.  = Fish=20 in the Site pond may also be adversely impacted based on the = elevated=20 tissue levels of aluminum, lead, and zinc.

 

Aquatic community evaluation

 

No recent data are = available.

 

Weight of evidence=20 conclusions

Based on = these lines of=20 evidence, metals in the wetlands area and the Site diversion ditch are = probably=20 having an adverse effect on aquatic receptors (fish and aquatic=20 invertebrates).  Antimony, = arsenic,=20 cadmium, lead, and zinc found in sediment, sediment porewater or surface = water=20 may adversly impact the aquatic receptors in the exposure areas = mentioned above.=20

 

For Silver = Creek,=20 dissolved metals (especially cadmium and zinc) are likely to pose a = significant=20 risk to aquatic receptors.  = Because=20 risks are elevated in surface water collected upstream of the Site, it = is=20 evident that sources in addition to the Site contribute to the = toxicity.  The headwaters of Silver Creek = originate=20 in the mountains south of Park City, a location that is = influenced by=20 several historic mining operations such as the Little Bell and Daly = Mines.  According to the findings of = the Upper=20 Silver Creek watershed evaluation (USEPA, 2001a), the Silver Maple = Claims=20 (Pace-Homer Ditch) was the largest contributor of zinc for the lower = reaches of=20 Silver Creek.  Zinc loads = from the=20 Site south diversion ditch are reported to contribute only 0.03 lbs/day = to=20 Silver Creek (USEPA, 2001a).  = Based=20 on this information, it appears that the Site is currently only a minor=20 contributor to the current level of metal contamination in Silver = Creek.  However, if the metals present = in=20 sediments and/or surface water are reduced in Silver Creek as a result = of=20 off-site clean up activities, it may be possible that discharges from = the Site=20 could recontaminate these media and become a more dominant influence on = metal=20 loading in the future.

 

Risk = to Wildlife=20 Receptors

 

The SLERA = evaluated=20 risks to terrestrial and aquatic/semi-aquatic wildlife and concluded = that=20 ingestion exposures from most media were potentially above a level of=20 concern.  Because no new = data are=20 available for contaminant levels in soils or terrestrial food web items, = and=20 because it is expected remedial activities will address concerns over=20 soil-related pathways, terrestrial (upland) wildlife exposures were not=20 re-evaluated.  New data = for surface=20 water, sediment, and aquatic food web items were gathered, therefore, = exposures=20 of aquatic/semi-aquatic wildlife from these pathways were quantitatively = evaluated as described below.

 

Selection = of=20 representative species

It is not = feasible to=20 evaluate exposures and risks for each aquatic/semi-aquatic avian and = mammalian=20 species potentially present at the Site. =20 For this reason, several species were selected to serve as = representative=20 species (surrogates) of several different semi-aquatic feeding = guilds.  Selection criteria for = representative=20 wildlife species include trophic level, feeding habits, and the = availability of=20 life history information. =20 Representative wildlife receptors selected for the Site = include:

 

 

 

 

 

 

 

Wildlife Receptors and = Exposure=20 Pathways Evaluated

 

Feeding Guild

 

Representative = Species

 

Exposure Pathways=20 Evaluated

 

Mammalian = piscivore

 

Mink

 

Ingestion of surface water, sediment, and=20 fish

 

Avian = piscivore

 

Belted = Kingfisher

 

Avian omnivore

 

Mallard Duck

 

Ingestion of surface water, sediment, aquatic=20 invertebrates, and aquatic = plants

 

Avian = insectivore

 

Cliff Swallow

 

Ingestion of surface water, sediment, and = emerging aquatic=20 insects

 

Weight of = evidence=20 conclusions

Based on the = estimated=20 HQs and Hazard Indexes (HIs) from ingested dose, it was concluded that=20 incidental ingestion of lead, manganese and zinc in sediments from the = wetlands=20 area, the south diversion ditch, and Site pond are likely to be causing = adverse=20 effects in waterfowl and other birds which feed in these areas.  Concentrations of lead, and = possibly=20 zinc and manganese, in aquatic food items may also cause adverse effects = in=20 birds that consume fish, aquatic invertebrates, or aquatic plants from = the=20 Site

 

Risk to Wildlife=20 Receptors

 

Exposure = Pathway

 

Line of = Evidence

 

Findings

=

 

Ingestion of surface water, sediment, and = aquatic food=20 items

 

Estimated HQs and HIs from ingested dose = (calculated from=20 measured data)

 

Risks = to birds are=20 likely to be of potential concern in the wetlands, diversion = ditch, and=20 pond, primarily from lead in sediment and also from these lead in = aquatic=20 food items. 

 

Risks to the cliff swallow may be above a level = of concern=20 from manganese and zinc in aquatic invertebrates and = sediment.  However, correlation of = manganese=20 in sediment compared to manganese in invertebrates is = inconsistent, so=20 predicted risks may not be site-related or may reflect an overly=20 conservative TRV. =

 

7.2.5 Ecological = Cleanup=20 Levels

 

A review of the lines of evidence and numerical=20 calculations presented in the BERA suggests that lead is a clear driver = of=20 ecological risk at the RFT Site.  =20 HIs for incidental ingestion of lead in sediment by wildlife = receptors=20 (primarily waterfowl) are generally higher than those for other COCs, = pathways,=20 and receptors.   In = this=20 regard, lead can be used to establish a cleanup standard that is=20 conservative.   = Rather than=20 establishing cleanup levels for all COCs, a cleanup level that is = protective=20 relative to incidental ingestion of lead in sediment by wildlife is = considered=20 sufficiently protective of other COCs, pathways, and receptors. 

 

EPA selected an ecological cleanup level of 310 = ppm lead in=20 sediment.  This value is = based on a=20 low-end threshold Toxicity Reference Value (TRV) from the species = sensitivity=20 distribution (SSD) for all birds, and hence it is likely to be the most=20 appropriate value to ensure protection of all waterfowl.  This approach assumes that the = variability in TRVs between different species of waterfowl is similar to = the=20 variability for other types of birds. =20 While there is considerable uncertainty, it is expected that = attainment=20 of this numerical level would reduce HI=92s for lead in sediment to less = than=20 one.

 

7.2.6=20 Uncertainties

 

Quantitative = evaluation=20 of ecological risks is generally limited by uncertainty regarding a = number of=20 important data.  This lack = of=20 knowledge is usually circumvented by making estimates based on whatever = limited=20 data are available, or by making assumptions based on professional = judgment when=20 no reliable data are available. =20 Because of these assumptions and estimates, the results of the = risk=20 calculations are themselves uncertain, and it is important for risk = managers and=20 the public to keep this in mind when interpreting the results of a risk=20 assessment.  Uncertainties = related=20 to the BERA are summarized in Table 7-16.

 

7.3 HUMAN HEALTH AND ECOLOGICAL = RISK=20 CONCLUSIONS

 

The BHHRA, = which is=20 based on present conditions at the Site, determined there are currently = no=20 unacceptable risks from lead and arsenic to the targeted use population=20 (recreational visitors) at the Site. =20 However, remedial action is necessary to maintain and improve the = soil=20 cover that was placed on the tailings. =20 Disturbances to the present soil cover could allow for exposure = to the=20 underlying tailings.

 

There is = substantial=20 risk to ecological receptors at the Site from exposure to zinc, cadmium, = lead=20 and arsenic found in the various environmental media at the Site.  Exposure pathways include = direct contact=20 with the sediments within the South Diversion Ditch and the wetlands = area.  These exposure areas also = present risks=20 to ecological receptors through contact or ingestion of surface water = and=20 sediment porewater found at the Site.

 

 

 

 

 

 

 

 

 

 

 

SECTION=20 8

 

REMEDIAL=20 ACTION OBJECTIVES

 

8.1 NEED = FOR REMEDIAL=20 ACTION

 

The measures undertaken voluntarily by UPCM over = the past two=20 decades have significantly reduced the risks presented by contaminants = at the=20 Site.   These = measures, while=20 incomplete, have effectively isolated most of the contaminated materials = from=20 the environment and generally made the Site safe for recreational = use.   However, the ecological = risks=20 identified and described in the previous sections, along with the = physical=20 conditions present at the Site, necessitate additional remedial = action.  In its current state, the Site = presents=20 unacceptable risks to aquatic wildlife receptors, both in the wetland = below the=20 embankment and in the south diversion ditch.   Similarly, the Site=92s = physical=20 characteristics create the potential for significant migration of heavy = metals=20 off the Site and into Silver Creek, as well as the potential for future = exposure=20 to recreational users.  = The Remedial=20 Action Objectives (RAOs) for the Site focus on mitigating existing = ecological=20 risks and maintaining or improving the physical conditions to prevent or = minimize future releases and exposures. =20

  =

8.2 = REMEDIAL ACTION=20 OBJECTIVES

 

To address the existing and potential risks, as = well as=20 accommodate the anticipated future recreational and ecological use of = the Site,=20 EPA has developed nine RAOs:

 

  1. Reduce risks to wildlife receptors in the wetland = area and=20 south diversion ditch such that hazard indexes for lead are less than = or equal=20 to one.=20
  2. Ensure that recreational users, including children, = continue=20 to have no more than a 5% chance of exceeding a blood lead level of 10 = micrograms per deciliter from exposure to lead in soils=20
  3. Ensure that recreational users, including children, = continue=20 to have no more than 1 x 10-4 chance of contracting cancer = from=20 exposure to arsenic in soils.=20
  4. Eliminate the risk of catastrophic failure of the = tailings=20 impoundment.
  1. Ensure that surface water discharged from the Site = meets=20 applicable Utah water quality standards.=20
  2. Eliminate the possibility of future ground water use = and=20 withdrawal at the Site.  =
  3. Allow for a variety of future recreational uses.=20
  4. Allow for future disposal of mine tailings from the = Park = City area within the tailings=20 impoundment until the remedy is complete. 
  5. Minimize post-cleanup disturbance of tailings and = contaminated=20 soil.  Provide controls = that=20 ensure any necessary disturbance at the Site follows prescribed = methods. 

 

 

 

SECTION=20 9

 

DESCRIPTION=20 OF ALTERNATIVES

 

In the FFS, four specific alternatives for remedial = action,=20 as well as a No Action alternative, were brought forward for detailed=20 analysis.  These = alternatives are=20 described in the subsections below.

 

9.1 = DESCRIPTION OF=20 REMEDY COMPONENTS

 

9.1.1 = Alternative 1-=20 No Action

 

It is a requirement of CERCLA and the NCP that the = EPA=20 evaluate the consequences of taking no action at the Site.  This alternative is designed = to=20 establish a baseline of current conditions upon which other alternatives = can be=20 compared.  Alternative 1 = does not=20 provide any additional protection of human health or the environment. =

 

9.1.2 = Alternative 2-=20 Soil Cover, Institutional Controls and Wedge Buttress

 

Alternative 2 entails increasing the depth of cover = over=20 tailings in the Study Area, implementing institutional controls to = manage human=20 contact with Site materials, and installing a wedge buttress to a = portion of the=20 main embankment of the tailings impoundment.  The South Diversion Ditch and = wetland=20 areas will be left undisturbed. =20

 

Major Components =

 

  • All tailings are left in current location=20
  • Existing soil cover is augmented to achieve a depth = of at=20 least 18 inches of soil above tailings both inside and outside the = impoundment=20
  • Embankment is fortified to prevent catastrophic = failure=20
  • Institutional controls (easements and land use = restrictions)=20 to protect soil cover and prevent ground water use=20
  • Ongoing surface water monitoring=20
  • Mine waste from the Park City area will be placed = inside the=20 impoundment before the soil cover is augmented.

 

9.1.3 = Alternative 3-=20 Source Removal, Soil Cover and Wedge Buttress

 

Alternative 3 includes source removal and covering = of Area B=20 tailings, placing clean soil over the tailings impoundment, installation = of a=20 wedge buttress, covering of contaminated sediments in the diversion = ditch,=20 removing contaminated sediments in the wetland, and placing of = restrictions on=20 future land and groundwater use.

 

 

 

Major Components =

 

  • Tailings in critical areas outside the impoundment = (Area B)=20 are excavated and moved inside the impoundment=20
  • Existing soil cover is augmented to achieve a depth = of at=20 least 18 inches of soil above tailings=20
  • Sediments in diversion ditch are covered with clean = gravel=20
  • Contaminated sediments and soils in the wetland = below the=20 embankment are excavated and material is placed within the impoundment =
  • Mine waste from the Park City area is placed within the = impoundment during implementation of the remedy=20
  • Embankment is fortified to prevent catastrophic = failure=20
  • Institutional controls (easements and land use = restrictions)=20 to protect soil cover and prevent ground water use=20
  • Ongoing surface water monitoring

 

9.1.4 = Alternative 4-=20 Excavation, Treatment and Offsite Disposal

 

This alternative entails excavating the = contaminated material=20 from the impoundment and from an area south of the diversion ditch, = stabilizing=20 it onsite, and disposing of it in a non-hazardous waste (Subtitle D) or=20 hazardous waste (Subtitle C) landfill. =20 Following treatment, the material would be tested using Toxicity=20 Characteristic Leaching Procedure (TCLP) methods and disposed of in the = proper=20 landfill depending on its classification as either hazardous or = non-hazardous=20 waste.  Once treatment and = disposal=20 processes are complete the site would be reclaimed by grading the area, = applying=20 six inches of topsoil and seeding the new soil with a native mix.

 

Major Components =

 

  • All tailings are excavated=20
  • Tailings treated on-site through stabilization = process to=20 limit release of metals=20
  • Tailings disposed of at off-site landfill

 

9.1.5 = Alternative 5-=20 Excavation, Treatment and Onsite Disposal

 

This alternative would include excavating the = contaminated=20 material from the impoundment and south of the diversion ditch and = stabilizing=20 it in a temporary treatment facility located adjacent to the = impoundment.  The treated materials would = then be=20 disposed of in a repository space within the impoundment.  Upon completion of treatment = and=20 disposal activities the impoundment would be reclaimed.  The Site will be graded to = prevent=20 surface water accumulation, thus reducing infiltration.  Following the remedial = activities, 18=20 inches of soil will be applied, including 12 inches of a low = permeability soil=20 and 6 inches of top soil.  = The top=20 soil will be seeded with a native mix.

 

 

 

 

Major Components =

 

  • All tailings are excavated=20
  • Tailings treated on-site through stabilization = process to=20 limit release of metals=20
  • Tailings replaced into impoundment and covered with = 18 inches=20 of soil=20
  • Institutional controls (easements and land use = restrictions)=20 to protect soil cover and prevent ground water use=20
  • Ongoing surface water monitoring

 

 

9.2 = COMMON ELEMENTS=20 AND DISTINGUISHING FEATURES OF EACH ALTERNATIVE

 

Alternatives 1, 2, and 3 all involve managing the = tailings in=20 place to varying degrees, with alternatives 2 and 3 adding increased = levels of=20 response.  The RI has = shown that the=20 existing soil cover and the Site=92s hydrogeologic setting have = effectively=20 isolated the tailings from the environment, so it is clear that each of = these=20 alternatives, even the No Action Alternative, will be effective to some=20 degree.   This type = of managed=20 repository for low-toxicity mine wastes is standard industry practice = and can be=20 considered a presumptive remedy.  = The design requirements for all alternatives are small and the = time to=20 implement each alternative is no more than two years.   

Alternative 3 is distinguished from Alternative 2 = by the=20 increased protectiveness and risk reduction achieved by (1) excavating = wastes in=20 critical areas outside the impoundment, and (2) covering the diversion = ditch=20 sediments with gravel.  = Both=20 alternatives 2 and 3 provide the opportunity for placement of mine waste = from=20 other locations in the Upper Silver Creek Watershed at the Site.

 

Alternatives 4 and 5 both involve excavation and = treatment of=20 all contaminated materials.  = These=20 alternatives add additional protectiveness and limit future maintenance = and=20 management requirements such as monitoring.   The design requirements = for these=20 alternatives are larger, involve significant bench and pilot testing, = and the=20 time to implement these alternatives are in excess of five years.  Alternative 5 is distinguished = from=20 Alternative 4 in that treated wastes will remain on-site, as opposed to = being=20 disposed of in an off-site landfill. =20

 

9.3 = EXPECTED OUTCOMES=20 OF EACH ALTERNATIVE

 

Alternative 1 - No=20 Action

 

  • Immediately safe for recreational use=20
  • Ecological risks not addressed=20
  • Potential for increased future releases and = exposures,=20 including catastrophic failure of embankment=20
  • No=20 additional improvements in water quality=20
  • Potential for unacceptable future ground water = exposures=20

 

Alternative 2 - Soil Cover, = Institutional=20 Controls and Wedge Buttress

 

  • Ready for recreational use in approximately two = years=20
  • Ecological risks not addressed=20
  • Potential for catastrophic failure of embankment = eliminated=20
  • Site could be used for disposal of mine waste from = other=20 locations in the Watershed during implementation of the remedy=20
  • Limited additional improvements in water quality=20
  • Future ground water use restricted and potential for = future=20 exposures eliminated=20
  • Ongoing monitoring and management required =

 

Alternative 3 - Source Removal, = Soil Cover=20 and Wedge Buttress

 

  • Ready for recreational use in approximately two = years=20
  • Ecological risks mitigated=20
  • Potential for catastrophic failure of embankment = eliminated=20
  • Site could be used for disposal of mine waste from = other=20 locations in the Watershed during implementation of the remedy=20
  • Significant improvements in water quality=20
  • Future ground water use restricted and potential for = future=20 exposures eliminated=20
  • Ongoing monitoring and management required =

 

Alternative 4 - Excavation, = Treatment and=20 Offsite Disposal

 

  • Ready for unlimited use no sooner than five years=20
  • Ecological risks mitigated=20
  • Potential for catastrophic failure of embankment = eliminated=20
  • Significant improvements in water quality=20
  • Potential for future ground water exposures = eliminated=20
  • No future Site management or monitoring

 

Alternative 5 - Excavation, = Treatment and=20 Onsite Disposal

 

  • Ultimate land-use potential unknown, but no use = sooner than=20 five years=20
  • Ecological risks mitigated=20
  • Potential for catastrophic failure of embankment = eliminated=20
  • Significant improvements in water quality=20
  • Potential for future ground water exposures likely = eliminated=20
  • Limited Site management and monitoring required =

 

 

SECTION = 10

 

SUMMARY OF=20 COMPARATIVE ANALYSIS

 

The NCP sets forth nine criteria for use in a = detailed,=20 comparative analysis of alternatives. =20 This section summarizes the detailed analysis found in the FFS = with=20 specific discussion for each criterion followed by a summary and ranking = table=20 (10-1, 10-2).

 

10.1 = QUALITATIVE=20 EVALUATION OF EACH CRITERION

 

Overall Protection of Human Health = and the=20 Environment

 

This criterion addresses whether each alternative = provides=20 adequate protection of human health and the environment and describes = how risks=20 posed through each exposure pathway are eliminated, reduced, or = controlled.

 

Alternatives 1 and 2 do not provide adequate = protection of=20 human health and the environment. =20 Neither alternative addresses risks posed by contaminated = sediments in=20 the diversion ditch and wetland areas.   Alternative 1 also does = not=20 improve physical conditions at the Site, making future releases and = exposures=20 likely. 

 

Alternatives 3, 4, and 5 all provide adequate = protection of=20 human health and the environment.  =20 Alternative 3 addresses risks posed by contaminated sediments in = the=20 diversion ditch and wetland areas through a combination of source = removal and=20 containment.   = Alternatives 4=20 and 5 provide additional protectiveness through treatment of = contaminated wastes=20 and soils.   = Alternatives 3, 4,=20 and 5 also improve physical conditions at the Site, minimizing or = eliminating=20 the potential for future releases.  =20 Alternative 3 accomplishes this with a wedge buttress, soil = cover, and=20 institutional controls to better contain the tailings.  Alternatives 4 and 5 = accomplish this=20 primarily through treatment of contaminated wastes and soils.  

 

Compliance with Applicable or = Relevant and=20 Appropriate Requirements

 

Section 121(d) of CERCLA and NCP Section = 300.430(f)(1)(ii)(B)=20 require that remedial actions at CERCLA sites at least attain legally = applicable=20 or relevant and appropriate federal and state requirements, standards, = criteria,=20 and limitations which are collectively referred to as =93ARARs,=94 = unless such ARARs=20 are waived under CERCLA Section 121(d)(4).

 

Applicable requirements are those cleanup = standards,=20 standards of control, and other substantive requirements, criteria, or=20 limitations promulgated under Federal environmental or State = environmental or=20 facility siting laws that specifically address a hazardous substance, = pollutant,=20 contaminant, remedial action, location, or other circumstance found at a = CERCLA=20 site.  Only those state = standards=20 that are identified in a timely manner and that are more stringent than = federal=20 requirements may be applicable.

 

Relevant and appropriate requirements are = those=20 cleanup standards, standards of control, and other substantive = requirements,=20 criteria, or limitations promulgated under federal environmental or = state=20 environmental or facility siting laws that, while not applicable to a = hazardous=20 substance, pollutant, contaminant, remedial action, location, or other=20 circumstance at a CERCLA site, they nonetheless address problems or = situations=20 sufficiently similar to those encountered at the CERCLA site such that = their use=20 is well-suited to the particular site. =20 Again, only those State standards that are identified in a timely = manner=20 and that are more stringent than Federal requirements may be relevant = and=20 appropriate. 

 

Site ARAR=92s are summarized in Table 10-3.  Alternatives 1 and 2 will not = comply=20 with all of the ARAR=92s, while alternatives 3, 4 and 5 will.  Additionally, the Action = Specific=20 hazardous waste ARAR=92s dealing with federally-defined hazardous wastes = under=20 RCRA are not applicable to Bevill-exempt solid waste, but may be = relevant and=20 appropriate.  The = majority, if not=20 all, of the mine waste at Richardson, = and most=20 mining waste that is transported from other Park City mining areas is considered=20 Bevill-exempt solid waste under federal exemptions.  Therefore, the Action Specific = hazardous=20 waste ARARs apply to any hazardous waste associated with the Site that = is not=20 Bevill-exempt, however, it is not anticipated that any hazardous waste = will be=20 placed at the Site.

 

Long-Term Effectiveness and=20 Permanence

 

Long-term effectiveness and permanence = refers to=20 expected residual risk and the ability of the remedy to maintain = reliable=20 protection of human health and the environment over time, once cleanup = levels=20 are met.   This = criterion=20 includes the consideration of residual risk that will remain on-site = following=20 remediation and the adequacy and reliability of controls.

 

Due to UPCM=92s prior voluntary efforts, each = alternative=20 provides some degree of long-term protection, though Alternatives 1 and = 2 do not=20 adequately address all risks posed by the Site.   Alternatives 2 and 3 = improve upon=20 Alternative 1 through the use of physical improvements and institutional = controls to reduce the risk of future releases from the Site, with = Alternative 3=20 including provisions that address the risks posed by the diversion ditch = and=20 wetlands.   However, = both these=20 alternatives require on-going institutional controls and monitoring to = ensure=20 their continued efficacy. =20 Alternatives 4 and 5 largely eliminate this concern through = treatment of=20 all contaminated wastes and soils. =20

 

Reduction of Toxicity, Mobility, = or Volume=20 through Treatment

 

Reduction of toxicity, mobility, or volume = through=20 treatment refers to the anticipated performance of the treatment=20 technologies that may be included as part of a remedy.

 

Only Alternatives 4 and 5 contain provisions for = active=20 treatment.  Both = alternatives would=20 reduce, though not eliminate, the toxicity and mobility of the = contaminants=20 through stabilization treatment technologies in a similar fashion.  The technologies considered = are proven=20 for mine wastes, but their effectiveness varies from site to site based = upon the=20 physical characteristics of the waste. =20 However, neither alternative would reduce the volume of material = required=20 to be managed, which may actually increase slightly due to the addition = of=20 necessary reagents.

 

Short-Term=20 Effectiveness

Short-term effectiveness addresses the = period of time=20 needed to implement the remedy and any adverse impacts that may be posed = to the=20 workers, the community, and the environment during construction and = operation of=20 the remedy until cleanup levels are achieved. 

 

Each alternative can be implemented safely with = proper=20 engineering controls, though the degree of short-term risk varies = considerably=20 among the alternatives.   =20

 

Alternatives 2 and 3 can be completed in a = relatively=20 short-time period of approximately two or three construction = seasons.  These alternatives involve = only limited=20 on-site earthmoving and any risks would be limited to workers and=20 trespassers.  These risks = are easily=20 controlled through institution of safe work practices and engineering=20 controls.

  =

Alternatives 4 and 5 would take substantially more = time to=20 complete - perhaps in excess of ten years. =20 Both alternatives not only include more earthwork than = Alternatives 2 and=20 3, but both also involve the operation of treatment systems and the use = of=20 slightly toxic reagents.   =20 These factors serve to increase the risk to workers.  Alternative 4 also involves = off-site=20 transportation and disposal, which increases the risk to the community = as waste=20 is hauled via highway.  = Again, these=20 risks could be managed, though not as easily, or likely as effectively, = as those=20 in Alternatives 2 and 3.  =

 

Implementability

 

Implementability addresses the technical and = administrative feasibility of a remedy from design through construction = and=20 operations.  

 

All of the alternatives involve technology that is = relatively=20 basic.  Alternatives 2 and = 3 involve=20 only on-site earth moving, and all of the resources are available = locally.  Alternatives 4 and 5 are = somewhat more=20 difficult to implement due to the inclusion of treatment = technologies.  However, these technologies = are well=20 established, and all of the resources necessary for implementation are = readily=20 available. 

 

Cost

 

The estimated present worth costs for the = alternatives, not=20 including Alternative 1, range from $2,295,398 for Alternative 2 to = $343,234,058=20 for Alternative 5.  = Alternatives 4=20 and 5 both involve on-site treatment, are considerably more expensive = than=20 Alternatives 2 and 3, which do not involve treatment.  Cost summaries are found in = Tables=20 10-2.

 

State = Acceptance

 

The UDEQ has expressed its support for Alternatives = 3, 4, and=20 5.  However, UDEQ also = recognizes=20 that Alternatives 4 and 5 are significantly more costly.

 

 

Community Acceptance =

 

This criterion considers whether or not the local = community=20 agrees with EPA=92s analyses and preferred remedial alternative.  Comments received on the = Proposed Plan=20 are important indicators of community acceptance.  This is a balancing = criterion.

 

During the Proposed Plan public comment period, one = set of=20 written comments was received that related to the transportation of = waste from=20 other areas within the Watershed to the Site.  Specifically, the comments = were directed=20 to the chosen transportation route. =20 Some comments on the preferred alternative were made by Utah = Department=20 of Fish and Wildlife and they are addressed in the Responsiveness = Summary.  All verbal questions raised at = the=20 public meeting were addressed at the meeting by EPA staff.  A transcript of the meeting is = available=20 on the website and in the information repository. 

 

10.2 = SUMMARY AND=20 RANKING TABLE  =

 

A comparison summary and the rankings are found in = table 10-1=20 and 10-2.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SECTION=20 11

 

PRINCIPAL=20 THREAT WASTE

 

The NCP establishes an expectation that EPA will = use=20 treatment to address principal threats posed by a site wherever = practical.  A principal threat concept is = applied to=20 the characterization of =93source material=94 at a Superfund site.  A source material is material = that=20 includes or contains hazardous substances or pollutants, or contaminants = that=20 act as a reservoir for migration of contamination to ground water, = surface=20 water, or air, or acts as a source for direct exposure.  EPA has defined principal = threat wastes=20 as those source materials considered to be highly toxic or highly mobile = that=20 generally cannot be reliably contained or would present a significant = risk to=20 human health or the environment should exposure occur.

 

The waste at the Site is considered a high volume, = low=20 toxicity source material in that the risk levels at the Site under the = current=20 conditions are near or within the acceptable range.  This is true for existing = conditions, as=20 well as for reasonably anticipated future recreational land uses.  Similarly, past experience at = similar=20 mining-related sites has shown that low-toxicity mine wastes can be = reliably=20 contained.  As such, = though=20 treatment was considered as an alternative, no materials at the Site = were=20 considered principle threat wastes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SECTION = 12

 

THE SELECTED=20 REMEDY

 

 

12.1 = SUMMARY OF THE=20 RATIONALE FOR THE SELECTED REMEDY

 

Several basic questions guide the development of = the ROD and=20 the ultimate selection of a remedy:

  • What risks does the Site present?=20
  • To what degree and how will those risks be = mitigated?=20
  • Which alternative best meets the nine remedy = selection=20 criteria set forth by the NCP?

 

EPA has considered these questions, as set forth in = the=20 previous sections of the ROD and in the supporting FFS, and has = determined that=20 Alternative 3, =93Source Removal, Soil Cover and Wedge Buttress,=94 is = the selected=20 remedy for the Site.  = Alternative 3=20 mitigates risks to a sufficient degree, meets all threshold standards = and=20 criteria, and has the best balance of tradeoffs with respect to = balancing and=20 modifying criteria.  =20 Alternatives 1 and 2 do not sufficiently mitigate risks and are = not=20 satisfactory candidates for a final remedy.  Alternatives 4 and 5 = sufficiently=20 mitigate risks, meet all threshold standards and criteria, and offer = increased=20 protection of human health and the environment, but the costs of = implementation=20 are dramatically higher than Alternative 3.  The greater costs are not = justified by=20 the relatively small improvements in overall protection of human health = and the=20 environment offered by Alternatives 4 and 5. 

 

12.2 = DETAILED=20 DESCRIPTION OF THE SELECTED REMEDY

 

The selected remedy has several key components that = are=20 described in detail below:

 

Source = Removal

 

Tailings and contaminated soils in Area B and in = the wetland=20 below the main embankment will be excavated and relocated to the = low-lying area=20 within the impoundment.  = The areas=20 of concern will be over-excavated by 6 inches or to the depth required = for=20 removal of visible mine tailings and materials with lead concentrations = greater=20 than 310 ppm lead.  Areas = selected=20 for excavation include: (1) contaminated materials in low-lying portions = (subject to seasonal ponding or interaction with shallow ground water) = of Area=20 B, and (2) all of the sediments in the wetland below the = impoundment.  The wetland may not be = excavated until=20 upstream source areas along Silver Creek, specifically Empire = Canyon, Silver Maple Claims, and = the=20 =93flood plain=94 tailings just above the Site, are remediated.  This is to ensure that clean = areas are=20 not re-contaminated, and is consistent with the overall cleanup plan for = the=20 Upper Silver Creek Watershed.  =

 

Soil Cover

 

A minimum 12 inch thick low permeability soil cover = will be=20 placed on all areas where tailings or contaminated materials are left = in-place,=20 including the impoundment.  = The=20 cover will build upon the existing soil cover and utilize similar=20 materials.   The = cover would be=20 placed in 6 inch lifts and compacted. =20 Upon completion of the impermeable soil cover, 6 inches of = topsoil cover=20 will be added to provide for an 18 inch soil cover in total.  The final surface would be = graded to=20 control surface storm water runoff and drainage and re-vegetated with a = native=20 seed mix to minimize erosion. =20 Drainage swales and runoff channels may be installed where = required to=20 direct surface runoff toward the diversion ditch.  Where applicable storm water = runoff=20 control structures will be constructed using erosion resistant materials = such as=20 geotextile fabric and rip-rap.        =20

 

Wedge Buttress          =20

 

A wedge buttress will be installed along the = over-steepened=20 portion of the embankment (for about 400 feet of the total embankment = length of=20 800 feet).  Fill will be = placed=20 along the toe of the embankment to a height of approximately 10 feet = above the=20 toe and extending horizontally out from the embankment face = approximately 30=20 feet, or to other dimensions designed to provide an increase in = stability of at=20 least 50%.   Prior to = construction, the upper soil and existing vegetation and organic matter = will be=20 removed.  Drain material = and a=20 filter blanket (if required) will be placed prior to the buttress = fill.  Seep water currently emanating = from the=20 embankment will be diverted to the South Diversion Ditch.  The buttress fill material = will be=20 compacted to at least 95% of the maximum dry density as determined by = ASTM D-698=20 at moisture content within two (2) percent of optimum.  At the end of construction the = buttress=20 fill will be protected from erosion by re-vegetation.

 

Sediment = Cover

 

Clean gravel (12 inches) will be placed over = sediments in the=20 south diversion ditch.

 

Institutional=20 Controls

 

Two primary institutional controls (ICs) will be = implemented=20 to mitigate potential risks and ensure the long-term efficacy of the = remedy:

 

1.  = Ground water=20 use restrictions within the Site boundary.   The goal is to preclude = any use of=20 shallow ground water, as well as eliminate any significant alteration of = the=20 existing hydrogeologic system, such as mixing of aquifers.  This IC will be in the form of = a deed=20 restriction and will be the responsibility of the owner of the Site.

 

2.  = Land use=20 restrictions within the Site boundary. =20 The goal is to preclude non-recreational uses and to ensure the = soil=20 cover, or similar protections, are maintained.    This IC will be in = the form=20 of an Environmental Covenant and will be the responsibility of the owner = of the=20 Site.

 

Placement of Additional Mine Waste = at the=20 Site

 

There are several reasons why the Richardson Flat = Site is an=20 appropriate location for the placement and consolidation of mine wastes = from=20 cleanups conducted at other locations in the Watershed.  First, the nature of the mine = wastes=20 found throughout the watershed is similar. =20 Second, the volume of waste from other locations is extremely = small=20 relative to the volume of wastes already present in the = impoundment.  The impacts from such a small=20 contribution would be negligible. =20 Lastly, the RI has shown that the mine tailings at the Site are = well=20 contained and present no unacceptable risks to human health.  The selected remedy will = ensure=20 conditions remain this way and that all other Site risks are = addressed.   These factors make the = Site an=20 acceptable long term repository, and, in conjunction with these factors=20 anoff-site rule determination was made and agreed upon in date.

    =

Monitoring

 

Water quality samples will be collected at the = mouth of the=20 diversion ditch quarterly for two years after construction completion to = ensure=20 discharges into Silver Creek meet applicable water quality = standards. 

 

12.3 = SUMMARY OF THE=20 ESTIMATED REMEDY COSTS

 

A summary of the selected remedy costs can be found = in table=20 12-1.  The present worth = cost of=20 this remedy is $3,675,868 and is presented in detail in table 12-2.

 

12.4 = EXPECTED=20 OUTCOMES OF THE SELECTED REMEDY

 

Land=20 Use

 

The selected remedy allows for a variety of = recreational=20 uses.  Such uses may = include=20 low-intensity uses, such as open space, or more high-intensity uses such = as=20 athletic fields.  Any=20 construction/development activities occurring on the soil cover must be = designed=20 to maintain at least 18 inches of clean soil (12 inches of low = permeability soil=20 plus 6 inches of topsoil) between the tailings and the surface and = minimize=20 infiltration through the use of low-permeability clay or other = engineering=20 controls.  Future changes = in land=20 use may be contemplated but would require a reassessment of=20 risk.

 

In=20 the short-term, the selected remedy allows for placement of mine wastes = from=20 other cleanup locations in the Watershed at the Site.  This will reduce the cost to = implement=20 other cleanups (by eliminating the need to haul wastes to a landfill) = and aid in=20 the overall cleanup of the Watershed.   Only select locations in = the=20 impoundment (generally low spots that require fill) will be used for = this=20 purpose.

 

Ground Water and=20 Surface Water Use

 

The selected remedy restricts ground water use = only within=20 the impoundment.   = This shallow=20 ground water is very low in volume and of poor quality and will not be=20 considered a potential drinking water source.   Deeper ground water = below and=20 around the impoundment that may be considered a future drinking water = source is=20 not affected. =20

 

All surface water from the Site discharges to = Silver Creek=20 and is expected to be acceptable for all designated uses of the = creek.   No drinking water uses = are=20 expected.

 

Final = Cleanup=20 Levels and Residual Risk

 

Several media are affected at the Site, but the = nature of=20 the Site and the remedy mean that most cleanup decisions were based upon = physical characteristics of the Site rather than media-specific = concentrations=20 of COCs:

 

    In surface water, discharges from the south = diversion ditch=20 are expected to be consistently below the appropriate water quality = standards=20 for protection of aquatic wildlife.    For zinc, the = most=20 critical metal, this value is dependent upon water hardness, but is = generally=20 between 0.1 and 0.8 ppm.  = Water=20 discharging from the Site is expected to continue to be of better = quality than=20 Silver Creek, and will create a net improvement in water quality=20 downstream.   = Surface water=20 conditions in the wetland are contingent upon upstream remediation = activities=20 and are impossible to predict at this time.  No human health risk is = associated=20 with surface water from the Site.=20 In sediments, all contaminated sediments are = expected to be=20 addressed.  All = sediments in the=20 diversion ditch will be covered with clean fill.  Contaminated sediments in = the wetland=20 will be excavated and replaced with clean fill as necessary.  Again, this is based upon = the physical=20 dimensions of these features, rather than on concentrations within the = media.   To ensure = that all=20 contaminated sediments are removed in the wetland, a remediation goal = of 310=20 ppm lead was established.  =20 Soils will be over-excavated, as necessary, and sampling will = be=20 conducted to ensure to EPA=92s satisfaction that sediments with = concentrations=20 of lead greater than 310 ppm have been adequately addressed.    This is expected = to bring=20 all HI=92s for aquatic wildlife below one. =20 It is impossible to predict eventual sediment concentrations as = the=20 system comes to equilibrium over time, but they are expected to be of = equal=20 quality or of improved quality than sediments in Silver Creek and = protective=20 of aquatic wildlife.=20 In soils, all contamination (e.g. the entire = impoundment and a=20 few small areas outside of the impoundment) will be covered with at = least=20 eighteen inches of clean soil (12 inches of low permeability soil plus = 6=20 inches of topsoil), so there should be no appreciable residual human = health=20 risk due to incidental exposure if the soil cover is maintained.   As an additional = measure, soils=20 will be sampled and no soils with concentrations greater than 500 ppm = lead=20 will be left exposed.  = Such a=20 level is far below any calculated remediation goals for recreational=20 uses.  Some risks will = be=20 associated with potential disturbance of buried tailings, but these = are=20 considered minimal and manageable with ICs.=20 In ground water, only water within the impoundment = is=20 affected.   This = water is not=20 expected to be used as a drinking water source, but IC=92s will = prevent any=20 exposure.  =

 

Socioeconomic=20 impacts

           =20

  • No significant socioeconomic impacts are = expected. 

 

 

SECTION=20 13

 

STATUTORY=20 DETERMINATIONS

 

Under CERCLA =A7121 and the NCP, the lead agency = must select=20 remedies that are protective of human health and the environment, comply = with=20 applicable or relevant and appropriate requirements (unless a statutory = waiver=20 is justified), are cost-effective, and utilize permanent solutions to = the extent=20 practicable.  In addition, = CERCLA=20 includes a preference for remedies that employ treatment that = permanently and=20 significantly reduces the volume, toxicity, or mobility of hazardous = wastes as a=20 principal element and a bias against off site disposal of untreated = wastes.  The following sections discuss = how the=20 selected remedy meets these statutory requirements.

 

13.1 = PROTECTION OF=20 HUMAN HEALTH AND THE ENVIRONMENT

 

The selected remedy ensures both short-term and = long-term=20 protection of human health and the environment in several ways:

 

Protection of Human=20 Health

 

  • The baseline human health risk assessment, as = discussed in=20 Section 7 of this ROD, shows that the Site, under current and = reasonably=20 anticipated future uses, presents no unacceptable risks to human = health. 
  • Remedial actions will ensure that these conditions = are not=20 significantly altered in the future. =20 The existing soil cover will be enhanced to ensure that the = mine=20 tailings do not migrate and that future exposure to mine tailings does = not=20 occur.   The = impoundment wall=20 will be buttressed to ensure that no catastrophic failure occurs.   Institutional controls = will be=20 established to ensure that only recreational uses are allowed, that = ground=20 water within the impoundment is not extracted, and that the soil cover = remains=20 intact.=20
  • Implementation of the remedy is simple and = straightforward,=20 and engineering controls will be implemented to ensure that workers = are=20 protected.   =

 

Protection of the=20 Environment

 

=B7        =20 The RI showed that surface water = discharged from=20 the Site currently meets the appropriate Utah Water Quality Standards = for all=20 metals.   The Site is = only a=20 minor contributor to metal loading in Silver Creek.   Remedial actions will = ensure that=20 metals discharged from the Site will be further reduced, helping to = further=20 enhance water quality in Silver Creek. =20 Area B tailings, which apparently influence water quality in the=20 diversion ditch, will be excavated and placed inside the = impoundment.  The impoundment will be graded = to=20 further reduce infiltration into tailings.

=B7        =20 The BERA, as discussed in Section 7 of = this ROD,=20 showed that contaminated sediments in the wetland and diversion ditch = present=20 unacceptable risks to aquatic receptors and wildlife.   In the diversion ditch, = the=20 sediments will be covered with clean fill material, breaking the = exposure=20 pathway.   In the = wetland,=20 which is a natural and critical habitat, the contaminated sediments in = the=20 entire wetland will be removed and the wetland restored.   These actions are = expected to=20 reduce risks to acceptable levels.

=B7        =20 Future land uses, all recreational in = nature, are=20 expected to largely preserve the habitat value the Site provides. 

=B7        =20 Engineering controls will be established = to=20 ensure no cross-media contamination during implementation.   Remedial actions will = ensure no=20 future migration of contamination, either within or between media.  The existing Site conditions = and=20 enhanced soil cover will isolate and contain the tailings.   The buttress on the = impoundment=20 will ensure no catastrophic failures and release occur.  A well-ban will ensure no = cross=20 contamination of aquifers or discharge of contaminated water. 

 

13.2 = COMPLIANCE WITH=20 APPLICABLE, RELEVANT AND APPROPRIATE REQUIREMENTS

 

The = selected remedy=20 is compliant with all ARARs associated with the Site.   Site ARARs are = summarized in Table=20 10-1.  The Action Specific = hazardous=20 waste ARAR=92s are not applicable to Bevill-exempt solid = waste.  The majority, if not all, of = the mine=20 waste at Richardson, and any mine waste = that is=20 transported from other Park City mining areas to the Site = most likely=20 is or will be Bevill-exempt solid waste. =20 Therefore, the Action Specific hazardous waste ARAR=92s apply to = any=20 hazardous waste associated with the Site that is not Bevill-exempt, = however, it=20 is not anticipated that any hazardous waste will be placed at the = Site.

 

13.3 COST = EFFECTIVENESS

 

The NCP mandates that the selected remedy be=20 cost-effective.  It does = not mandate=20 that the most cost-effective alternative be selected, only that the = alternative=20 that is selected meets a few basic criteria for cost-effectiveness.  The nature of the Site (high = volume of=20 waste, low toxicity waste, limited number of suitable cleanup = technologies)=20 makes this determination somewhat simple. The five alternatives = evaluated can be=20 broken down into three basic categories: =20

 

  • No Action (Alternative 1)=20
  • Containment-Based =20 (Alternatives 2 and 3)=20
  • Treatment-Based (Alternatives 4 and 5)

 

Alternatives 1 and 2 did not meet minimum standards = for=20 protectiveness, and hence cannot be considered cost effective.   Alternatives 4 and 5, = while adding=20 increased protectiveness and satisfying the statutory preference for = treatment,=20 increase the costs relative to Alternative 3 up to two orders of = magnitude =96=20 hundreds of millions of dollars.  = The relatively small increase in protectiveness for such a large = cost=20 increase is not warranted.   = Alternative 3 is somewhat more expensive than Alternative 2, but=20 addresses all Site risks.  = It is=20 simple to implement and the basic technology is consistently used for = tailings=20 pile closures.  The = overall=20 effectiveness of Alternative 3 is clearly proportional to its overall=20 effectiveness.  Tables = 13-1, 13-2,=20 13-3 and 13-4 summarize the costs of each alternative besides = alternative 1, the=20 No Action Alternative.

 

 

 

13.4 = UTILIZATION OF=20 PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT FOR RESOURCE RECOVERY = TECHNOLOGIES=20 TO THE MAXIMUM EXTENT PRACTICABLE (MEP)

 

The selected remedy represents the best balance of = trade-offs=20 among the alternatives evaluated. Because the waste at the Site is = comprised of=20 naturally occurring inorganic minerals and metals, it is impossible to=20 completely rid it of toxicity through treatment.  It cannot be burned or = significantly=20 altered.   Because of = this,=20 some degree of containment must be contemplated for the materials = whether they=20 are treated or not =96 either on-site or off-site containment.  All of the alternatives, with = the=20 exception of the No Action alternative, include containment components, = and are=20 thus not fundamentally different in this regard.   Alternatives 4 and 5, = while they=20 may be considered slightly more =93permanent=94 than Alternative 3 = because of the=20 reduction in toxicity and use of a managed, off-site landfill, are far = more=20 costly to implement.   = Clearly,=20 on-site containment is the most permanent solution that is = practicable.

 

No resource recovery technologies are applicable = for the=20 Site.  The tailings have = already=20 been processed for metal recovery during initial mining, and current = economic=20 conditions do not warrant further metal recovery at the very high cost = such=20 actions would require.

 

13.5 = PREFERENCE FOR=20 TREATMENT AS A PRINCIPLE ELEMENT

 

As stated in Section 11, there are no principle = threat wastes=20 present at the Site.  The = waste is=20 high volume, low toxicity.  = As such,=20 there is no waste that is particularly critical to treat.  The waste can be treated, but = the=20 exceedingly high cost with relatively low reduction in toxicity is not=20 warranted.  Because of = this,=20 treatment is not a principle element of the selected remedy.   

 

13.6 = FIVE-YEAR REVIEW=20 REQUIREMENTS

 

Because the selected remedy will result in = hazardous=20 substances remaining on-site above levels that allow for unlimited use = and=20 unrestricted exposure, a statutory review will be conducted within five = years=20 after initiation of remedial action to ensure the remedy is, or will be, = protective of human health and the environment.  Such reviews will continue = every five=20 years indefinitely to ensure the remedy remains protective over = time.

 

 

 

 

 

 

 

 

 

 

 

 

SECTION 14

 

DOCUMENTATION OF SIGNIFICANT=20 CHANGES

 

 

The proposed plan was released for public comment = in=20 September of 2004.  It = identified as=20 the preferred alternative the same alternative as the selected remedy = identified=20 in this ROD.  This remedy = includes=20 removing small potions of tailings in Area B and disposing of them = within the=20 impoundment, installing a wedge buttress to support the main embankment, = removal=20 of sediments within the wetland area and finally capping the main=20 impoundment.  The = preferred=20 alternative did not change between the issuance of the proposed plan and = the=20 ROD.