DRAFT

2.0 SITE HISTORY AND SITE DESCRIPTION

2.1 Site Description and Background

Park City, Utah has a rich historic mining history since the discovery of lead-silver ore in the 1870's. Mine and mill tailings were dumped for many years at the SMC site, although there was little mining at the site itself. The SMC site consists of tailings from inactive, historic high grade silver milling and reprocessing operations since the 1880s. Tailings were processed at the Ontario Mill and Pacific Bridge mills in Park City and stored in tailings impoundments at the location of the Silver Creek Tailings (SCT) site (the current Prospector Square) and downstream at Richardson Flats. Prospector Square is located upstream of the site where milling of the ore had also taken place. These tailings were covered and developed for homes and commercial development in the 1970s. Historical aerial photography for 1962 and 1967 indicates tailings/fill materials were transported downstream via Silver Creek onto the BLM-administered parcel, the SMC, by sluicing, flooding and by dumping of low grade ore by truck (Weston, 1989). Unprocessed ore was also reported to be stockpiled along Silver Creek (Weston, 1989).

From 1906 through 1926 E. J. Beggs filed claim notices on the Beggs placer mining claims that included SMC. In 1915, the Beggs Milling Company constructed a mill thought to be on the present SMC near the main beaver pond area to reprocess tailings. Prior to 1916, tailings from all the mills were sluiced into Silver Creek and carried downstream as far as seven miles. Because of farmer’s complaints the Ontario Mining Company was forced to construct tailings dams (SAIC, 1992).

During the late 1970s and 1980s, a residential subdivision and commercial development was built directly on the SCT Site (Weston, 1989). Work performed by USGS and others indicates that Prospector Square Tailings are impacting the groundwater in the unconsolidated valley fill and water quality of Silver Creek for cadmium, manganese and zinc (USGS, 1989).

2.1.1 Site Location

SMC is located in Summit County, Utah in lands administered by the BLM Salt Lake Field Office. The site is located immediately east of the town of Park City at an elevation of approximately 6,700. Figure 1 presents the location of the site and watershed as shown on the State’s map.

The site is located downstream from Prospector Square. The area is popular for hiking, biking, jogging, and wildlife viewing along the “Rail Trail.” The Rail Trail was developed by Union Pacific as the Historic Railroad Grade and managed by the Utah Division of State Parks and Recreation.

Topography surrounding the site of the Silver Creek watershed ranges in altitude from approximately 5,400' at the valley bottom to 6,700' at the site to about 8,000' at the highest peak in the drainage. Diverse flora and fauna occupy the riparian zone where tailings are not exposed. The vegetation includes sedges, rushes, willows, cattails and cottonwoods. There are several active beaver ponds.

Surface water features include Silver Creek which flows through the site in the flood plain and wetland which narrows to a canyon onsite. Silver Creek is in Hydrologic Unit Code 16020102 and has a drainage area of 17.4 square miles, principally occupied by urban and ski area land uses (Figure 1). Typical Silver Creek flows are 1 cubic foot per second (cfs) west to east through the site. In May, the USGS measured 3.2 cfs at the east end of the site, and in August, BLM personnel estimated 0.95 cfs at the same location. According to Kolm (2004), Silver Creek through SMC is a gaining stream during low flow periods, but it appears to have a losing reach near the east boundary. Silver Creek at Silver Creek Junction five miles north of the site ranged in flow from 2.62 to 39.2 cfs, with a median of 3.53 cfs during the period October 2001 through July 2002, with the peak flow on April 2, 2002 (USGS, 2002a). Silver Creek is classified by the State of Utah for the following uses: secondary contact (2B), aquatic life (3A), and agriculture (4). Silver Creek is listed in the State’s 303(d) list of water quality-impaired waterbodies for which a Total Maximum Daily Load (TMDL) is high priority. Zinc and cadmium are the water quality limiting parameters (Utah DWQ, 2004). The target annual reductions for zinc and cadmium in the draft TMDL for Park City are 65% and 92%, respectively. The Park City reach is inferred to include SMC.

The second main feature is a 7.5 acre jurisdictional wetland fed by Silver Creek and groundwater with several beaver ponds and well-established plant communities of cattail (Typha), sedges (Carex), rushes (Juncus) and willow (Salix). This wetland is classified by the USFWS National Wetland Inventory Program as palustrine, scrub-shrub/emergent, seasonally flooded; the ponds in SMC are classified as palustrine, aquatic bed, intermittently exposed. Wetlands perform a variety of important ecological functions including storage of floodwaters, recharging groundwater, discharging groundwater, stabilizing shorelines and streambanks, maintaining water quality, removing contaminants and sediments from the flow, promoting ecosystem health, and providing recreational, educational and research opportunites (Mitsch and Gosselink, 1993).

The hydrology on site is complicated by inflows from Pace Homer ditch, Prospector drain and groundwater. Pace-Homer Ditch, an irrigation ditch, flows easterly onto and through the site via a pipeline at about 4-5 cfs. Pace Homer irrigation ditch is piped and behind the retaining wall for Highway 248. During the summer irrigation period, Pace Homer ditch leaks irrigation water into Silver Creek on site in several places, and joins Silver Creek just below the site and increase flows in Silver Creek to approximately 2 cfs. Another feature, the Prospector Square subsurface drain (PD), enters the site underwater inside the west property boundary according to BLM surveys. This drain was constructed in about 1976 to help drain shallow groundwater associated with buried tailings in the eastern portion of Prospector Square tailings (Dames and Moore, 1975) and discharges into SMC underwater in the wetland. Another feature is a sanitary sewer that parallels Silver Creek and passes through the site to the wastewater treatment plant. This sewer line is constructed in the tailings.

To better understand the hydrology and contaminant sources affecting the site, BLM tasked USGS to perform a tracer injection study with synoptic sampling during May, 2002. USGS reported that the hydraulic residence time of the wetland is 12.5 hours (USGS, 2003) and the volume and flow velocity of the wetland is 486,000 gallons/day 1.9 feet/minute. According to the Flood Insurance Rate Map for the City of Park City, the entire wetland area up to the Rail Trail is situated in the 100 year flood plain (FEMA, 1987).

The site covers approximately 13.0 acres situated on 2 inactive, unpatented placer mining claims (BLM, 1985). The site is surrounded by a locked fence or state highway. Tailings occur throughout the wetland portion of the site (except perhaps the northeast portion) and are mostly submerged by the wetland. Small tailings piles are exposed above the mean water level. The buried tailings are up to 11 feet in thickness and most are isolated physically and geochemically beneath more recent sediments and surface water. Work from the RSI indicates the primary concerns for the site are the elevated metals concentrations in Silver Creek and exposed mine tailings with high concentrations of heavy metals, specifically arsenic, cadmium, copper, lead, mercury, and zinc.

2.1.2 Geology and Groundwater

This discussion of geology and groundwater at the site is taken from USGS (1989), Crittenden et al (1966) and Kolm et. al. (2004). Consolidated sedimentary rocks in the mountains range from Pennsylvanian to Tertiary age, and consist of quartzite, limestone, shale and sandstone. These rocks were structurally deformed in Late Cretaceous

time resulting in folding and faulting. Dips range from 35-40 degrees north to northwest. The specific bedrock units of interest for the Silver Maple Claims area are the Thaynes Formation, the Park City Formation, and the Woodside Shale. The Thaynes Formation is a fine-grained sandstone/siltstone formation interbedded with fossiliferous limestone that occupies the hills north and west of the site. The Thaynes provides the major source of municipal water for the town of Park City.

The Park City Formation outcrops to the south of the site. The formation is about 670 ft thick with a highly variable lithology, mostly composed of limestone with a phosphatic horizon near the middle, but also containing sandstone and thin shale beds and some cherty limestone. The Park City Formation partially underlies the unconsolidated alluvium along the southern boundary of the SMC site. This bedrock unit may be a significant contributor of subregional groundwater to the SMC site, but its role in the SMC hydrology is not well established. The Park City limestone at the SMC site is recharged by upward or lateral flow from the subregional system. This allows water from the Park City bedrock aquifer to enter into the Silver Maple Claims alluvial hydrologic system as originally conceptualized by Kolm and Yan (2004). Kimball et. al. (2004) observed that two reaches of Silver Creek in the Silver Maple Claims area are significantly gaining reaches, near the western SMC boundary and at the main beaver pond.

The nearly impermeable Woodside Shale underlies the valley fill at SMC and is a confining layer. The Woodside Shale is uniform thin-bedded red shale, with some sandy sections. The base of the unit forms a sharp contact between the red shale and the underlying Park City limestone. In the Park City area, the Woodside shale thickness was estimated to be between 680 and 985 ft by various authors. The Woodside shale underlies most of the unconsolidated units at the Silver Maple Claims site. This bedrock unit has minimal transmissivity and storage, and it is considered a confining unit in the SMC hydrologic system.

Unconsolidated valley fill of Quaternary age and tailings occupy the SMC site and consist of alluvial deposits. The area of the fill narrows from the Park City area to a neck in the canyon at SMC. The fill ranges from a few feet at the base of the mountains to at least 260 feet near the Pacific Bridge well and pinches out in the neck of the canyon. The fill ranges from about 13 feet at the west SMC boundary (this study) to only about four feet thick in the eastern boundary of the SMC area. The hydraulic conductivity is expected to be similar to that in the Prospector Square area, 1‑14 feet per day (USGS, 1989). Groundwater in the unconsolidated units is also recharged laterally from the Prospector Square site valley fill upstream and at the western boundary of the site.

BLM has recently completed initial groundwater flow modeling for SMC ( Kolm and Yan, 2005). An analysis of mass balance reveals that approximately 30% of the alluvial ground water flowing under Prospector Square is captured by the Prospector Drain, with the remaining amount moving directly or indirectly into the SMC site. According to Kolm and Yan, the SMC flow system is conceptualized as having four components: (1) flow from the bedrock aquifer of the Park City Formation into unconsolidated materials and tailings and then into lower Silver Creek; (2) flow due to infiltration and leakance from the lower Pace-Homer Ditch into the unconsolidated materials and tailings that enters lower Silver Creek or exits the groundwater system at the eastern boundary of the site; (3) flow from the Prospector Square alluvial/tailings directly into the Silver Maple Claims alluvium; and (4) flow from the Prospector Square tailings drainage pipe directly into the ponds, Silver Creek and the alluvium (Kolm and Yan, 2005).

Shallow groundwater flows easterly in this area and exists at the surface elevation at SMC (6,700'), suggesting that Silver Creek is a gaining stream during the spring (Kolm, 2004). Groundwater seepage was observed entering the wetland from the south at various points in the Park City Formation during May, 2002 and is supported by Kolm et al (2004). However, observations during late August 2002 indicated Silver Creek was dry near the east boundary of the site, suggesting that portion of Silver Creek is a losing stream during summer conditions due to a drop in the water table below the bottom of the drainage (see also USGS, 1989). The shallow groundwater gradient is approximately 1.3 feet per 100 feet in the area of Prospector Square (USGS, 1989), flowing to the east. Figure 1B is a conceptual groundwater model for SMC (Kolm and Yan, 2005).

One shallow monitoring well (PS-MW-10) was installed in 1987 and sampled four times in 1987-1988 by USGS and others as part of the larger Prospector Square study. This well was apparently destroyed and no longer exists. The following data was summarized from USGS (1989). The well was located north of the main beaver pond near Highway 248. It was installed in shallow sands and gravels and encountered bedrock shale (Woodside Shale) at 11.5 feet. Water levels ranged from 0.3 to 1.8 feet during 1987-1988. Dissolved metals concentrations ranged from <1 to 28 ug/L for arsenic, 2-8.6 ug/L for cadmium, 15-43.3 ug/L for lead and 610-1950 ug/L for zinc. Concentrations reduced by half during the winter. Split samples among USGS, EPA, and the State showed variability, especially for arsenic and mercury. The results are similar to monitoring wells in the SCT (wells 4-8) located in the main SCT, except arsenic and lead are higher in MW-10, and cadmium and zinc are higher in MW-8. Mason (USGS, 1989) suggested the arsenic and lead were due to exposed tailings located upgradient of well MW-10.

Soils

Soils in the vicinity of the site are classified by the United States Soil Conservation Service as Typic Fluvaquents, with 0 to 3% northeast-trending slope (SCS, 1977). The soil is typically very deep and poorly drained. These soils are found on floodplains along Silver Creek and Parleys Park, Utah. The soils are described as having formed from sand-textured mine tailings of 18-26 inches in thickness. They have been spread or subsequently washed over a black to dark gray-brown, silty clay loam (the original wetland hydric soil). Permeability is rapid through the sands (i.e. tailings) and much less rapid through the silty clay loam. Surface runoff is rated slow, and the erosion hazard is only slight. The thickness of various units and the texture of the soil are not described due to the great variability in this unit over short distances. Except for near the west boundary where tailings are found, data collected on this soil group during the wetland delineation found the soils to have a sulfidic odor, aquic moisture regimes, and reducing conditions typical of hydric or developing hydric soils (Attachment 3).

2.1.3 Surrounding Land Use and Populations

The nearest town to the site is Park City, Utah, located immediately adjacent and to the west of the site. Park City is a resort community known for skiing and other winter sports and was the site of several 2002 Olympic venues. Park City had a permanent population of 7,371 in 2000. Approximately one-half mile west and upstream of the site is the SCT site, which has been the focus of previous CERCLA studies and has been developed with hotels, homes and a city park. Downstream (east) of the site are undeveloped wetlands owned by Park City and private owners, and the Richardson Flat NPL site. Immediately north of the SMC is State Highway 248 with a concrete retaining wall (see cover photograph). As mentioned previously, parallel and immediately south of the site is the Rail Trail, a State Park easement managed by the Utah Division of State Parks and Recreation that receives significant hiking, jogging and cycling use. The site is fenced.

2.1.4 Sensitive Ecosystems

There are no known wildlife species in the SMC area that have received protection under the Endangered Species Act (Attachment 3). However, the site is a wetland and contains many wetland species of plants and animals. Diverse flora and fauna occupy the riparian and wetland zone where tailings are not exposed. The vegetation species includes willow (Salix), cottonwood (Populus), cattail (Typha), sedge (Carex), and rush (Juncus). Three beaver ponds are also found in the wetland. Wetlands are protected under Executive Order 11990.

2.1.5 Meteorology

According to the Western Regional Climate Center, the average minimum and maximum temperatures for Park City are 30.8 and 56.3 degrees F, respectively. Average annual precipitation is 21.4 inches, including 138 average inches of snowfall. Precipitation is distributed evenly throughout the year with slightly higher amounts in January and December. Snowpack accumulates in the upper part of the watershed which is developed as ski areas. Snow melts and runs off during spring with a peak in April to May.

2.2 Site Waste Characteristics

There are four principal waste sources affecting SMC. In no particular order, these are:

· Upstream sources, notably the Silver Creek Tailings and associated surface water and groundwater that flows into SMC.

· The Prospector Drain, a subsurface drain constructed in Prospector Square that collects groundwater and drains into SMC. The drain-water contains high metals concentrations.

· Exposed onsite tailings leaching acid rock drainage (ARD) distributed in surface pockets that are visible (Figures 2 and 3). The visible tailings are white to tan in color and are mostly acidic. Sample results from BLM, (2004), USGS (1989) and Weston (1989) indicate concentrations of lead and zinc in the 5,000-10,000 ppm range and arsenic in the 400 ppm range in tailings.

· Saturated buried onsite tailings with similar concentrations. Comparing the current aerial photograph with the 1962 aerial photograph (Figure 4) shows where the tailings are exposed and where they are buried.

Acid rock drainage is caused by the action of sulfide oxidation bacteria, oxygen, and water on pyrite (iron sulfide) mine waste according to the following simplified equation (Ford 2003):

4FeS₂ +15O₂ + 14H₂O → 4Fe(OH)₃ + 8H₂SO₄

Oxygen is necessary for the weathering and oxidation of pyrite, producing hydrogen ions (that decrease pH) and the oxidation of sulfide to sulfuric acid and sulfate. It is important to understand this reaction because leaching is greatly magnified by acid pH and conditions producing ARD. This condition is known to occur in most of the exposed tailings on site. The reaction can be reversed by excluding oxygen and this concept has been employed in constructed anaerobic bioreactors (sometimes called treatment wetlands) that use sulfate reducing bacteria (SRBs) to precipitate iron and the ancillary metals as sulfides. There is evidence the ARD process is occurring in the sediments of the SMC wetland.

According to Nordstrom and Alpers (1999) and Nimick and Moore (1991), another related process, sometimes overlooked, plays an important role in the environmental consequences of mining: the formation of soluble, efflorescent salts. Efflorescent salts are highly soluble, hydrated, heavy-metal sulfate compounds that have been shown to be very important for storing heavy metals and acid during dry periods in acid mine drainage settings. During rain storms or spring melting of snow packs, these salts readily dissolve and release large amounts of heavy metals and acid to the watershed. These salts often appear as white, blue-green, yellow to orange or red efflorescent coatings on surfaces of waste rock, tailings, and in underground or open-pit mines. At SMC, as the water level rises, metals are leached; as the water level lowers, metal sulfates are stranded on the surface in the form of visible salts that are subsequently mobilized in rain or high water events.

2.3 Previous Investigations and Actions

The Silver Maple Site has undergone previous study by the BLM (BLM, 1985) and EPA. In 1984, a Preliminary Assessment was performed followed by two Site Inspections, one in 1992 and the other in 1994. EPA issued a NFRAP (No Further Remedial Action Planned) in 1994 after the Site Inspection was completed by Weston for the BLM. In 1999 the State of Utah and the EPA reopened the Silver Maple case when it formed an “Upper Silver Creek Stakeholders Group” to review and study contamination problems in the entire Silver Creek drainage. In 2001, a regional study was completed by EPA. To answer questions concerning sources of metals loading to Silver Creek, in 2002 the USGS performed a tracer injection and synoptic sampling study at the site.

Various watershed investigations of water quality in Silver Creek in the vicinity of Silver Maple Claims have been reported (USGS, 1989, EPA 2001, USGS, 2001, USGS, 2003). Results shown in Table 1 vary over time and seasonally and not all sampling stations are in the same exact locations. But there are trends apparent in the data. For example, in 1987-1988, the USGS (1989) found zinc to increase downstream of Silver Maple during April but not July. EPA (2001) found a similar trend, but USGS in 2000 found the opposite trend although its downstream station was near Highway 248. In most cases, SMC concentrations are greater during low flow periods. This would suggest the contribution of proportionately more groundwater contamination to surface water in the SMC wetland during low flow periods, consistent with Silver Creek being a gaining stream in the SMC reach (Kolm, 2004). Note various authors have labeled Silver Creek gaining or losing, depending on the time of year or exact reach. The wetland contains standing water year-round, but the eastern boundary of SMC sometimes dries up during the summer. Table 1 shows zinc averages about a 2-fold exceedance of the water quality standard, while cadmium is uncertain due to detection limits.

The USGS 2002 sampling was the most intensive for the site and was part of the RSI. The details of the 2002 water quality investigation are in the full USGS report (Attachment 1). Using the USGS 2000 sample results, the zinc hardness-adjusted water quality standard for Silver Creek was 0.39 mg/L. Silver Creek water quality results indicate that zinc concentration varies through SMC. In the USGS study, dissolved zinc concentrations enter SMC at about 0.7 mg/L, spike downstream of PD to about 1.8 mg/L, decrease to about 1.2 mg/L in the next 300 meters, then increase below the main beaver pond to 1.9 mg/L, then exits SMC at 1.57 mg/L (USGS, 2003, Figure 8). PD is the largest source of zinc loading in SMC. The overall report indicates that, excluding the effect of PD, SMC itself serves as a source and a sink for zinc loads, but that the area of the main beaver pond is the largest source within SMC (excluding PD). This is consistent with a surface tailings hotspot of metals contamination potentially associated with the former 1915 Beggs Mill found at and just below the main beaver pond. It is likely that the hotspot contributes to this loading.

In separate action, in September 2003, BLM conducted an interim time-critical removal action at an area near the main beaver pond to cap a soil contamination hotspot. A geotextile fabric, followed by 3-5 inches of limestone gravel, followed by six inches of topsoil, were installed over the ¼ acre area to prevent direct contact/soil ingestion exposure to site visitors. The barrier was not intended as a long-term solution, but as an interim action pending access to a local mine waste repository.

3.0 SITE CHARACTERIZATION OBJECTIVES AND PROCEDURES

3.1 Data Quality Objectives

The data quality objective (DQO) process is a series of planning steps based on the scientific method that is designed to ensure that the type, quantity, and quality of environmental data used in the decision making are appropriate for the intended purpose and will be sufficient in the evaluation of risk and applicable, relevant and appropriate requirements (ARARs). DQOs clarify the study objective, define the most appropriate type of data to collect, establish the most appropriate conditions from which to collect the data, and specify tolerable limits on decision errors that will be used as a basis for estabilishing the quantity and quality of data needed to support project decisions.

The current investigation was conducted to obtain the data necessary to further characterize the site and extent of contamination, evaluate human and ecological risk, and to evaluate the functioning of the wetland and its potential to remove contaminants. Because the principal exposure pathways that are complete with receptors are the surface water and soil/sediment pathways, these served as focus for the RSI. Groundwater sampling was not investigated in this field effort as there were no receptors using shallow groundwater, and because it had been investigated by others (USGS,1989; Kolm, 2004). For purposes of this investigation, the site is defined by the BLM property boundaries. The chemical and physical properties of tailings were assessed to evaluate the degree of removal required.

The activities performed to obtain these data were as follows: soil/tailings sampling for arsenic, copper, lead, mercury, zinc and other metals, acid/base accounting (ABA), leaching and sorption potential, and geophysical studies and soil borings to assess tailings volumes. In addition, trace level mercury and methylmercury sampling was performed and biological studies were performed to evaluate the health of the wetland. Each of these sampling activities is described in detail in the sections to follow. Objectives of the sampling investigation were as follows:

· Determine the locations and volume of tailings;

· Determine the chemical characteristics of the tailings

· Conceptually assess wetland metal removal processes

· Determine the biological and hydrological functioning of the wetland

· Determine the presence of mercury and methylmercury, and

· Perform a streamlined risk assessment.

The specific USEPA and other analytical methods for chemical analyses that were used are as follows:

· 6200 - Field portable x-ray fluorescence spectrometry (XRF)including measures for quality assurance and confirmation sampling

· 6010 - Metals analysis by inductively coupled plasma (ICP)

· 1312 - Synthetic precipitation leaching procedure (SPLP)

· Nevada meteoric water mobility procedure (NMWMP)

· 1631 - Trace level mercury and methylmercury analyses.

The work was conducted under the Silver Maple Claims Sampling and Analysis Plan (BLM, 2002).

3.2 Chemical Analysis of Tailings and Soils

XRF Analysis

Weston analyzed 26 soil and sediment samples at SMC in 1988 and found high concentrations of arsenic, cadmium, lead and other metals (Weston, 1989). They did not analyze for zinc or other non-RCRA metals. To further define the spatial distribution of contaminants in the tailings and adjacent native soils, the 2002 surficial samples (0-2") were collected and analyzed for arsenic, cadmium, copper, lead, mercury, zinc and other metals via x-ray fluorescence spectrometry (XRF). The locations of these samples focused on identifying the location and extent of surficial tailings, contaminated sediments, and any conditions that have the potential to vary the chemical properties of contaminants.

All samples were collected in accordance with the criteria specified in the Compendium of ERT Soil Sampling Procedures (EPA/540/P-91/006). Samples were collected using a steel sampling tube, hand auger or PVC plastic core and analyzed via XRF. XRF analyses were conducted using a Niton model 702 portable analyzer using EPA method 6200 and analyzed for the six metals listed above, plus nickel, chromium, iron, manganese and selenium. Cadmium is not measured with the cadmium 109 detector. Detection limits were from 25-50 mg/kg.

At selected locations, samples were collected at ground surface and at intervals below ground surface, depending on site conditions. Upon collection, wet samples were placed on paper plates, air-dried, sieved and analyzed. Dry samples were analyzed in a ziplock bag. These steps were taken to ensure that the most accurate and precise results are generated by XRF analyses.

A sampling grid was laid out using a tape measure. Sample locations were established along eleven transects perpendicular to Silver Creek spaced at approximately 250 foot intervals where vegetation permitted. Within each transect, XRF analysis of surface soils, and sediment and resistivity data (see below) were collected every 50 feet. Six confirmation soil borings were conducted as described earlier.

Upon collection, samples were dried, labeled and analyzed in the field via XRF or stored for later XRF analysis. The information provided on the sample labels included: time and date the sample was collected; sampling location; preservative used; initials of person who collected the sample; and a unique sample number. Finally, all sampling activities and locations were recorded in the field notebook. Figure 2 shows the sampling and geophysical transect locations.

Leaching and Sorption Studies

To assist in evaluating leaching characteristics, four representative samples were selected from the core soil samples and analyzed for the following parameters: acid/base accounting (ABA) was used to assess the acid neutralizing or acid generating potential of the tailings; EPA Method 1312 Synthetic Precipitation Leaching Procedure (SPLP) samples were collected to evaluate the leaching characteristics of the tailings/soil samples; and total organic carbon and cation exchange capacity.

One surface water sample SW-1 was collected from the main beaver pond for sorption studies. This sample was analyzed for dissolved metals concentrations and dissolved organic carbon.

3.3 Geophysical Survey

A geophysical survey was performed to map the location and extent of tailings in the wetland area. An Advanced Geosciences Inc. Sting^TM electrical resistivity meter was used with a Swift control box and automated cable in a schlumberger array. Each line consisted of at least 6 electrodes over a 250 foot transect to acquire horizontally continuous data. Five transect lines were acquired at the same locations as used for the XRF sampling. Field XRF results were used for confirmation of tailings horizons. Analytical software (RSXIP2DI) developed by INTERPEX of Golden, Colorado was used in plotting of results. Geoprobe soil borings and sampling for resistivity and metals content were performed in December 2002 to confirm field resistivity results for thickness of buried tailings. Attachment 4 contains the soil boring logs and resistivity profiles.

3.3 Wetland Assessment

As mentioned in EPA’s Data Interpretation Report for the Silver Creek watershed (EPA, 2001), there are a number of environmental processes that affect the fate and transport of contaminants in a wetland. It is well established that wetlands can serve as natural treatment systems to remove and sequester contaminants from the environment. Wetlands have other functions in addition to water quality improvement such as fish and wildlife habitat, floodwater storage, aesthetics, biological productivity groundwater recharge, erosion and sediment control (Dynamac, 2002). Further, wetlands are considered sensitive environments and by law, any net loss of wetlands must be mitigated by creating or restoring other wetlands. Executive Order 11990 requires federal agencies to avoid long- and short-term adverse impacts associated with the destruction or modification of wetlands whenever there is a practical alternative. EPA (1994) recommends that a wetland functional assessment be performed as a part of the ecological assessment of the site. Therefore, in order to determine the relative health of the SMC wetland, an assessment of the hydrological and biological functioning of the Silver Creek wetland was performed by Dynamac Corporation in August 2002 using the Summit Wetland Assessment methodology (Dynamac, 2002).

Background data were gathered for both the Silver Maple wetland complex and a reference wetland complex (Negro Hollow). These data included existing topographical, wetland, and vegetation mapping, as available. Additional data included applicable soil survey information, surface water and ground-water reports, meteorological data, and previous analytical work.

A routine jurisdictional wetland delineation of the Silver Maple wetland complex was performed using U.S. Army Corps of Engineers (USACE) protocols prescribed in their 1987 Wetland Delineation Manual. Jurisdictional wetlands are protected under the jurisdiction of Section 404 of the Clean Water Act. Attachment 3 contains the full report. This included defining a wetland-upland boundary, photographic documentation of the boundary, and GPS of boundary points with which a map of the boundary was produced. Plant communities present within the wetland complex were identified and mapped. This effort included photo- and GPS-documentation of sampling points.

Field measurements were also made using an Horiba U-10 meter to measure pH, conductivity, temperature, dissolved oxygen, turbidity, and salinity of surface waters associated with the wetland complex.

The Summit Wetland Assessment Method, derived by the USACE et al. from work in Summit County, Colorado, was used to perform the assessment procedure. It uses a modified version of the Hydrogeomorphic (HGM) Approach developed by Brinson (1993). Data were assessed for dynamic flood storage, flood flow attenuation, production export/aquatic food chain support, nutrient and pollutant removal/sediment retention, shoreline stabilization/sediment control, wildlife habitat, rare species habitat, and endangered species habitat. Qualitative ratings were assigned for each of these data types and were related to similar ratings for a reference wetland. In addition, four composite samples were collected from pondweed (1), willow (2), cattail (1), and one moose scat sample, Figure 2. All were collected near the main beaver pond in August 2002, and analyzed for total metals by ACZ Laboratory of Steamboat Springs, Colorado.

3.5 Macroinvertebrate Characterization

Benthic macroinvertebrates are larval insect stages and other invertebrates found in the aquatic environment. Macroinvertebrates are excellent indicators of stream health. Previous work by USGS has been performed on Silver Creek (but not at SMC). This investigation found that the aquatic invertebrate assemblages in this location appeared to be impaired due to higher than ambient metal concentrations in Silver Creek (USGS, 2001). Macroinvertebrate samples were collected by BLM and personnel from Utah State University at the SMC site to determine the abundance and diversity of macroinvertebrates and to help determine the health of Silver Creek in this reach. In addition, one composite sample each was collected in December 2002 of macroinvertebrates and fish by Utah State University personnel for whole body metals analysis from the main beaver pond and analyzed by ACZ Laboratory of Steamboat Springs, Colorado.

3.6 Surface Water Characterization

Except for water sample SW-1 for the sorption studies, and three trace-level mercury in water samples, no additional laboratory samples of surface water in Silver Creek were collected as USGS and others have completed more detailed studies of water quality at this site and in the watershed. Complete USGS methods and results are contained in Attachment 1.

3.7 Site Mapping

GPS and aerial photograph maps of the site were prepared showing the stream features, visible tailings piles, site boundary, XRF/geophysical transects, plant communities, and sampling locations. The coordinates of all locations and notable features were recorded with a Trimble Pro XRS GPS unit.

3.8 Quality Assurance/Quality Control

Quality assurance and quality control (QA/QC) measurements were observed to ensure the integrity of the XRF sampling data using EPA Method 6200. The QA/QC samples consisted of analysis of certified standards, blank samples, and laboratory confirmation XRF split samples on a 1:20 basis. The confirmation samples were compared to XRF results per EPA method 6200. Attachment 2 shows the QA/QC summary.

4.0 ANALYTICAL RESULTS

This section discusses the results of the site characterization conducted during July and December 2002.

4.1 Chemical Analysis of Tailings, Sediment and Soils

4.1.1 Surficial Soil, Tailings and Sediment XRF Results

The surface grid encountered three types of samples. Most prevalent were sediment and mixed tailings taken from below the water column, then uncontaminated sediment samples and soil samples from the northeast area of the parcel, and least prevalent were visible tailings samples. Native, fluvial sediments were the first solid material below the water column and are described as fine, black, light-fluffy organic material with a sulfide odor. Figure 2 shows the location of the sampling transects with shading of these three sample types. Table 2 shows the XRF analytical results for the grid. Where the metal results were mostly undetected, 25 mg/kg was substituted for the non-detections to compute a mean. Background results from Weston (1989) are also shown. Since there is no discernible pattern to the surficial contamination, the concentration data were not mapped. The arithmetic mean lead, arsenic, zinc and copper concentrations were 2,090, 162, 7,550, and 107 mg/kg, respectively. Applying the Method 6200 laboratory correction for lead and zinc modifies these means to 2,675 and 6,419 mg/kg, respectively.

Table 2 and Figure 2 were evaluated and samples of tailings (1A, 1D, 1E, 2A, 5C, 7A, 8A, 10B) and obvious uncontaminated dry soils (10C, 10D, 11C, 11D) were deleted and the metals means computed for sediments, but the means did not change significantly, hence are not shown. Tailings samples have a chemical signature. They normally contain arsenic and copper, appear to have a ratio of zinc to lead of <2:1, whereas sediment has a ratio of about 4:1. Pure sediment samples were low in iron and high in manganese, and tailings showed the reverse pattern. Some samples show a combination signature, indicating mixed tailings and sediment.

Some of the exposed tailings are visible but much larger quantities are present in subsurface areas that are not currently visible. Review of aerial photographs from 1962 (Figure 4) show extensive disturbed areas assumed to be tailings and mine waste and much less vegetation. During the July 2002 investigation, a hotspot was located near the center of the site along the Rail Trail (grid node 7A). The hotspot had maximum arsenic, lead and zinc concentrations of 5,600 ppm, 79,000 ppm and 80,000 ppm, respectively, more typical of mill concentrates, potentially from the Beggs Mill. About 70% of the hotspot is located inside the fence, and the remainder is located outside the fence along the Rail Trail. This area was the subject of an interim removal action (Section 2.3).

Table 3 shows the analytical results for the depth and miscellaneous other samples. Depth samples were taken at 1A-B, 7C, and 10B. Sample 1A-B was collected at the 50' interval of the geophysical transect in a sandy material of suspected tailings. This sample did not show any pattern with depth. Sample 7C was collected from sediment in the center of the beaver pond on transect 7. This sample did show a definite increase in concentration of all metals and a decreased zinc:lead ratio with depth. Sample 10B appeared to be tailings at the surface, but at 24 inches was black colored and sandy with stones indicating tailings mixed with flood plain sediment but did not show a concentration increase with depth. Additional depth samples were taken from six boreholes during December 2002 and analyzed via XRF (Attachment 4).

Four samples were split for laboratory confirmation according to EPA Method 6200 and evaluated for data usability (Attachment 2). The laboratory and XRF results were compared using linear regression and the results indicated good correlation (>0.9). Lead XRF results were underestimated by 28% and the zinc results were overestimated by 15%.

4.1.2 Laboratory Results

Tables 4 and 5 show the laboratory results for four representative samples of tailings and sediment from the site. The visible exposed tailings are white, tan or yellow in color, with the yellow color normally indicating acidic conditions. These appear at the following grid locations: 1A, 1D, 1E, 2A, 5C, 7A, 8A, 10B. Sample 1D was an unsaturated, oxidized sample that visually appeared to be tailings with iron staining and salt crusting indicating acidic pH. Its pH is 2.1 and its acid base potential is -230 indicating high sulfide content and a strongly acid potential. Total metals in this sample were high for arsenic, lead and zinc. SPLP results showed the greatest concentrations for copper at 1.27 mg/L and zinc at 33.8 mg/L. Dividing SPLP results by total metal results gives the fraction leachable. Among the four samples, this sample leached the highest absolute amount of metals even though its initial concentrations were not the highest. The fraction leachable was 0.006 and 0.0034 for cadmium and zinc, respectively.

Oxidized tailings sample 65' E of 7A had even higher initial concentrations of metals, but a neutral pH and positive acid base potential, indicating less inherent acidity and lesser leaching. This sample was from the main beaver pond area and is either a Beggs Mill concentrate or highly weathered (removing acid potential) or originally a carbonate host rock (e.g. Thaynes or Park City Formations). The fraction leachable for this sample was 0.00005 and 0.000001 for cadmium and zinc, respectively, or about two orders of magnitude less leachable than 1D on a mass basis.

Sample 10B was collected from a 24" depth and is representative of the saturated, reduced zone of tailings. This sample was black, saturated and fine-grained. This is confirmed by lower concentrations in the SPLP results. Reduceing conditions sample 10B showed a higher acid base potential (-330) than 1D but a low leaching potential. The fraction leachable for this sample was 0.00004 and 0.000005 for cadmium and zinc, respectively, or about two orders of magnitude less leachable than 1D on a mass basis. Because of anoxic conditions, this sample had not been exposed to oxygen long enough to produce acid rock drainage. It is likely that 18 hours of the SPLP test was not sufficient to mobilize the acidity and leach metals. Weathering can take months when exposed to air using kinetic testing. This is a key point in understanding the leaching characteristics of the exposed versus buried tailings – air must be available to produce acid rock drainage.

Sample 6B is representative of non-tailings surface sediment from the site. It was light, fluffy, black with a sulfide odor. Sample 6B had high organic carbon (6.4%) neutral pH (6.9) and a positive acid base potential (34) which tended to reduce leaching potential. Based on the Wetland Assessment (Attachment 3) and chemical samples, sediments/soils in the wetland were mostly fine-grained, dark black (with high organic matter), saturated with a sulfide odor, indicative of anoxic or reducing conditions. Sediment thickness at the site ranged from 0-18 inches and averaged about six inches. Table 5 shows the percent total organic carbon (TOC) and cation exchange capacities (CEC) of five wetland samples. The mean CEC and TOC are 39.8 meq/100g and 6.43%, respectively. High TOC and high CEC leads to more sorption sites for positively charged cations such as lead, zinc and cadmium. The fraction leachable for sample 6B was 0.00002 and 0.00004 for cadmium and zinc, respectively, or about two orders of magnitude less leachable than 1D on a mass basis. The sediments interact with the water column to gain metals by complexation with organic ligands, sedimentation, plant decay and adsorption, and metal sulfide burial (EPA, 1999), hence the concentration pattern of sediments is more similar to surface water than the tailings. The tailings are high in arsenic, iron, lead and zinc, whereas the sediments are high in cadmium, zinc and manganese with reduced arsenic and lead concentrations, Table 4.

Lesser-contaminated soils collected in the northeast part of the parcel were dry, brown, clayey soils (8D, 9C, 9D, 10C, 10D, 11C, 11D) possibly imported, although similar in appearance to the Woodside Shale.

From these results, it is concluded that among the mine wastes onsite, the exposed, oxidized, low pH tailings such as sample 1D, represent a major on-site source of metals to Silver Creek, both by erosion and leaching. These materials appear to be mostly acidic except near the 7A hotspot. The buried tailings (represented by sample 10B) are covered by oxygen-excluding organic sediment and water, conditions known to prevent or reverse acid rock drainage conditions, and have neutral pH and low leaching results. Sediment, represented by sample 6B, did not leach detectable metals except for zinc, and despite a high total zinc concentration of 10,100 mg/kg and 18 hours of mixing in an acidic environment, leached only 0.37 mg/L zinc or slightly below the water quality standard of 0.39 mg/L (hardness adjusted).

Sorption studies are contained in Attachment 5. Both compost and Iron 2 (porous iron aggregate high in zero-valent iron) were highly effective in adsorbing zinc at low concentrations with calculated sorption coefficients in the range of 2800-4545 assuming a linear adsorption isotherm. These coefficients indicate sediment can sorb 2800-4545 times the water concentration of zinc on a mass basis. These results suggest one reason why the zinc concentration of the sediment (which has physical properties similar to compost) is high - sorption. Compost material has the additional advantage of eventually removing a much larger amount of zinc from the water column via anaerobic sulfate reduction as microorganisms utilize the sulfate for energy and convert zinc to the insoluble sulfide state.

Figure 5 contains a conceptual model for biogeochemical metals cycling at the site. Direct and indirect evidence presented in this RSI and the tracer study suggest: (1) oxidation of exposed tailings with water and oxygen to form ARD, (2) leaching of metal loads during high flows, and (3) visual evidence indicates metals are wicked from the exposed tailings during lower flows, leaving metal salt residues. Metals in the water column are often complexed with dissolved or suspended organic matter and clay particles where they eventually sink via sedimentation and accumulate in the sediment. Different redox processes take place in the sediment (EPA, 1999). Decaying plants provide organic matter, create reducing conditions and neutralize pH. The sediment at SMC is high in organic matter and anaerobic conditions are evidenced by the H₂S odors when disturbed. This reducing environment favors reducing reactions, e.g. metal sulfide removal mediated by sulfate-reducing bacteria. Sulfides are very insoluble in neutral pH. Also, organic matter provides many sorption sites for metals. These wetland processes: neutral pH, reducing conditions, and organic matter, explain how the sediment becomes contaminated with metals from the water column and why the metals bound in the sediment are less mobile. Metals in buried tailings are likewise less mobile for these reasons. Metals from the buried tailings are believed to be largely isolated from oxygen because of anaerobic conditions in the sediment and submersion in surface water.

These data indicate that the exposed tailings are likely to contribute more metals to the wetland than the buried tailings because of the oxygen-excluding aspect of the water and sediment. The results, together with the loadings tracer study also indicate the sediment is a sink for the cadmium, zinc and other dissolved metals in the water column (Sections 4.6- 4.7).

4.2 Geophysics and Tailings Volume Estimates

4.2.1 Exposed Tailings Volumes

Figure 2 shows the location and area of exposed tailings based on aerial photos and XRF sampling. The total area is 40,886 square feet (0.9 acre). The average depth of the tailings to ground water is approximately 2.5 feet, so therefore the exposed estimated volume is approximately 3,785 cubic yards (cy).

4.2.2 Buried Tailings Volumes

In 1989, Weston estimated a volume of 145,200 cy for an 18 acre area assuming an average depth of five feet based on information related to installing the Snyderville Basin sewer line through SMC. Weston did not use the correct property boundary. The area of the SMC affected by tailings is less than 13 acres, based on current information.

A geologic characterization of the Silver Maple Claims was necessary for defining the determination of tailing thickness and volumes. This effort was accomplished in two phases, starting in July 2002, BLM initiated a non-intrusive surface geophysics survey which was followed by confirmation drilling in December 2002. The National Science and Technology Center (NSTC) of BLM conducted the geophysical survey and contracted the drilling to Dynamac Corporation. A detailed discussion of this effort is presented in the Attachment 4 and the following is a summary of the effort and its findings.

The geophysical survey consisted of five electrical resistivity survey lines which transected the site, south to north, at various locations. Because the wetland environment severely limited access of a drill rig, only six boreholes were drilled to confirm the presence of tailings, the degree of heavy metal contamination via XRF analysis, tailing thickness, and depth to bedrock. Information from the borings was also used to correlate with resistivity results which provide thickness estimates in areas inaccessible by the drill rig. The six borings were placed near two resistivity lines (SM-1a and SM-7).

Both drill logs and resistivity profiles indicate some interbedding of sediments and a depth to bedrock varying from 4.5 to 11 ft. Across the site, bedrock is a chocolate, reddish-brown shale known as the Woodside Shale. XRF results of the bedrock material did not show any elevated heavy metal concentrations. Both the drilling and the resistivity indicate gravel lying on top of the shaley bedrock, and because of the more continuous lateral coverage provided in a resistivity profile, the shape of these deposits is observed as lenses or piles of gravel. This observation is consistent with historical aerial photographs which show dump-truck piles of gravel in the wetland area of the site. These gravel piles have been buried by finer grained sediments, primarily tailings, as confirmed by drilling logs and XRF sample results.

Because of the excellent correlations between the drill logs and resistivity data (1' error or less), accurate thickness estimates of tailings can be made where drilling was not possible. Both drill logs and resistivity profiles indicate some interbedding of sediments, and tailings typically extending from ground surface to the top of bedrock. XRF results of the borehole samples indicate elevated heavy metal concentrations in nearly all of the fine-grained sediments and most of the gravel deposits. XRF results of the bedrock material did not show significant heavy metal concentrations. The majority of the resistivity survey lines crossed saturated soils or was sub-aqueous, typically being submerged 2' or less, but to as much as 4' in the beaver pond (SM-7). Though the surface water had a specific conductance of 1,800 umho/cm and capable of being detected, its thickness was typically insufficient to cause interpretation problems. In areas where the depth of water was greater (3' or more) the resistivity reading was very similar to that of the tailings, but due to the interbedding of the tailings, the two could be differentiated.

Throughout the site the thickness of tailings extends from the ground surface to the top of bedrock. There is a slight thinning of the tailings in the downstream direction, starting at 11' in the west end and ending with 4.8 to 7' at the east end of the site. Though some native sediment interbedding may occur, the natural mixing of these native uncontaminated sediments with tailings has rendered all of the fine-grained sediments contaminated. The source of the gravel piles which exist on top of the bedrock is unknown, and based upon the XRF results contain elevated concentrations of heavy metals. These deposits were assumed to be alluvium or waste rock and are included in the total volume calculations of the tailings.

After resistivity survey data were correlated with six drill logs and XRF data, results were evaluated and interpreted within ESRI’s ArcGIS, ArcMap applications software utilizing an extension called, “Geostatistical Analyst”. The data analysis method employed was “Ordinary Kriging”, within this modeling method “Covariance” and “Spherical” interpretation were used, dataset selection included all data points using nearest neighbor, 6 neighbors being used with “Shape Type” being full quadrant analyses. The prediction error had a mean of 0.01778 of 1% of total dataset, and a root-mean square standardized at 0.8832 of 1% of total dataset.

The study area was divided into three Areas (A, B, C). Several volume estimates of the tailings were generated in order to provide a range of possible scenarios. This is necessary to address the changing tailing thickness and some uncertainty of the lateral extent of the tailings in the northeast side (Area-C) of the drainage where neither drilling nor resistivity was implemented. The division between Area-A and –B occurs at SM-6, with an average thickness of 11ft of tailings being applied toward the western segment (Area-A) and 7ft to the east. Based upon the above, the total volume of tailings ranges from 141,651 cy to 177,541 cy, as depicted in Plate 1 of Attachment 4. The difference in the two estimates is Area C. Because this area is uncontaminated at the surface, no geophysics was performed in this area and the borehole scheduled for this area failed due to field conditions.

4.3 Summary of Wetland Assessment

4.3.1 Findings

The first objective of this assessment was to determine if the Silver Maple wetland complex assessment area was judged to be a jurisdictional wetland. Jurisdictional wetlands are protected under the jurisdiction of Section 404 of the Clean Water Act. Attachment 3 contains the full report. The SMC wetland was found to be a jurisdictional wetland of approximately 7.5 acres. It should be noted that probable jurisdictional wetlands lie both up- and downstream of the study area along Silver Creek. The focus of this delineation and functional assessment was to consider BLM-administered lands only. The wetland/upland boundary is quite distinct, featuring a floristic transition from dominant willows, rushes, sedges, and cattails in the wetland, to stands of more mesic grasses, forbs, and small shrubs in the upland. The site has been mapped for wetlands under the USFWS National Wetland Inventory (NWI) program. The site is classified by NWI as palustrine, scrub-shrub/emergent, seasonally flooded with characteristic hydric soils. The ponds within the site are classified as palustrine, aquatic bed, intermittently exposed. The field mapping of the jurisdictional boundary compares favorably with the NWI map for the area. Aerial photos reveal the characteristic wetland hydrology for the site, as well as plant communities dominant in this area.

The second objective was to determine the biological and hydrological functioning of the wetland. This report concluded the Silver Maple wetland received an overall functional assessment rating of high. This rating is based on the following functions this wetland offers:

· excellent potential to store and release water into the surrounding aquatic ecosystem,

· excellent potential to detain and/or store floodwaters during high flow events,

· excellent producer of biomass and connection to downstream ecosystem allows for aquatic food chain support,

· well placed system for both nutrient removal from nearby anthropogenic sources and for heavy metal pollutant retention and assimilation from the historic mining activity,

· beaver activity, macro topography, and dense vegetation act to stabilize shorelines and provide sediment control for Silver Creek,

· provides a reasonable area for wildlife habitat, featuring robust plant and animal diversity, and fair habitat connectivity, and

· may provide limited habitat for rare and endangered species, though none have been documented for this site with this assessment.

The Silver Maple wetland appears to be in good functional order despite the proximity of Park City, and also despite the historic mining wastes that were deposited upstream and within the wetland itself. There is no visible sign of vegetative stress, or poor vegetative cover within the jurisdictional boundary. There are unvegetated tailings piles on the periphery and as small inclusions within Silver Maple wetland. They exhibit elevated heavy metal concentrations, but they were not mapped as part of the jurisdictional wetland.

The continuing function of this wetland is important for wildlife at the site, for aquatic and terrestrial life downstream, and for human recreation in Park City.

4.3.2 Plant and Animal Communities

Four plant communities were mapped at the site. The Typha latifolia (cattail) community consists of at least three significant stands in the western half of the Silver Maple wetland complex. These plants were standing in shallow (0-6”) water at the time of the fieldwork. These stands are dense, with few other species occurring within their midst. The Juncus arcticus (rushes) community occurs in at least six significant stands within the delineated wetland boundary, and they occur virtually throughout the whole wetland system in lesser profusion. This community also features a variety of other graminoids, including Agrostis spp. (bentgrass), and Eleocharis palustris (spikerush). The mixed sedge community includes the species Carex aquatilis (water sedge), C. nebrascensis (Nebraska sedge), and C. utriculata (beaked sedge). The mixed willow community is dominated by Salix exigua (coyote willow), but also includes S. monticola (Rocky Mtn. willow), S. boothii (Booth willow), S. eriocephala (yellow willow), and perhaps others. The willows were difficult to key to species level in late August, due to the lack of reproductive structures (catkins) present.

The field reconnaissance of Silver Maple Wetlands documented a total of 66 species of plants. This total included three tree species (box elder, peach-leaved willow, and narrow-leaved cottonwood), eleven shrub species (including six species of willow), forty-seven species of herbaceous plants (including four species of sedge, one species of rush, ten species of grasses), four species of aquatics, and several dense stands of broad-leaved cattail. Of the 66 plant species identified, 36 were within the wetland boundary (i.e., hydrophytes or wetland species), while the other 30 species were primarily upland or transitional wetland/upland species.

A cursory reconnaissance for animal species in Silver Maple Wetland revealed a total of 31 species. This list included at least seven species of invertebrates, nine species of mammals (including moose [Alces alces]), one amphibian a northern leopard frog (Rana pipiens, one reptile a common garter snake (Thamnophis sirtalis), and at least 12 bird species and unidentified fish (later identified by Utah State University to be in the Family Cyprinidae, probably a chub or shiner species). Warm water temperatures observed during the assessment (>20^o C) may inhibit coldwater fish species at the site. Of special note are the abundance of sora rails (Rallus limicola), mallards (Anas platyrhyncus), and red-winged blackbirds (Agelaius phoeniceus), all of which utilize and depend on the cattail plant community of Silver Maple Wetland, and barn swallows (Hirundo rustica) aerially feeding on insects above the wetland. A complete listing of animal species identified at Silver Maple Wetland is provided in Attachment 3.

The most significant organism contributing to the structure and function of this wetland complex is the American beaver (Castor canadensis), which is largely responsible for the vegetative structure and hydrologic regime of the system. A total of two major beaver lodges and one bank den were identified during the site fieldwork, all of which appeared active, based upon fresh cuttings of willow, prints in sediment, and the obvious recent maintenance of dams and lodges within each system. For the Silver Maple wetland, this would translate into a total of 5-15 animals, including adults, yearlings, and juvenile offspring. (Note: a beaver kit was observed by BLM in SMC in June 2003). Beaver in Silver Maple wetland are probably feeding primarily on willow species (bark, buds, leaves, and twigs) in winter months, and on aquatic and terrestrial herbaceous vegetation during spring and summer months.

During the wetlands assessment, five plant and two animal samples were collected and analyzed for the metals arsenic, cadmium, copper, lead, mercury and zinc. Table 6 shows the results. Pondweed (Potamogeton sp.) is elevated in most metals. Potamogeton is also known to be an significant metals accumulator, especially for cadmium and zinc (Condoyannis, 1994). Another finding, that of cadmium in willow, was anticipated based on previous work at other BLM sites and other authors (Ford, 2001). The other samples, including one sample of moose scat, showed much lower concentrations.

In addition, as part of the wetlands assessment, mercury sampling of aquatic biota was performed on December 4, 2002. Mercury was found near the detection limit in macroinvertebrates (0.04 mg/kg) and was undetected in the fish sample. EPA has recently published a new ambient water quality criterion for methylmercury for the protection of aquatic life. The criterion is 0.3 mg/kg mercury in fish tissue instead of a water concentration. Comparing this criterion to the fish and macroinvertebrate mercury concentration indicates mercury is not significantly bioaccumulating in the aquatic food chain (EPA, 2000b).

4.3.3 Conclusions and Recommendations

Dynamac’s recommendations for management and potential enhancement of Silver Maple wetland function include the following:

· Consider removal or in-situ treatment of existing tailings piles that border the wetlands and which are unvegetated. If the tailings are removed, clean fill can replace them, and this material can be planted with native wetland species to increase habitat and macro topography of the wetland.

· Consider a conservation plan to increase habitat connectivity between Silver Maple wetland and other habitats, such as wetlands ½ mile northwest near Pace-Homer Ditch, and uplands to the north and south of the wetland. The barriers to wildlife travel include the substantial wall and traffic lanes of Utah State 177 to the north, and the raised bed of the Rail Trail to the south of the wetland. This connectivity might be enhanced by placement of culverts that promote movement of reptiles, amphibians, and especially for medium mammals.

· Other sections of this report discuss data from USGS synoptic of surface water sampling (USGS, 2004) and BLM sampling (this report) and USGS sampling of sediments (USGS, 2001) above, within, and below the Silver Maple wetland complex that indicate pollutant uptake/removal in this ecosystem. The data collected during the functional assessment provide many indicators that this function probably is occurring.

· Preparation of a simple integrated weed management plan for use in controlling the invasive species identified at Silver Maple. This will promote the maintenance of native species diversity, and improve wildlife habitat. Weedy species of particular concern include Canada thistle, dalmation toadflax, scotch thistle, musk thistle, bull thistle, tamarisk, and stinging nettle. The official Utah State list of noxious weeds includes musk and scotch thistles.

4.4 Macroinvertebrate Characterization

Aquatic invertebrates in the vicinity of the Silver Maple Site were investigated by the USGS in 1998-2000 (USGS Water Resource Investigations Report 01-4213). This investigation found that the aquatic invertebrate assemblages in this location appeared to be impaired due to higher than ambient metal concentrations in Silver Creek. The BLM National Aquatic Monitoring Center at Utah State University sampled the aquatic invertebrates at the site in July 2002 and again on December 4 (USU, 2002). The purpose of the work was to (1) provide an initial assessment of the aquatic macroinvertebrate assemblage and compare our findings to samples collected previously by the USGS (2001); and (2) provide guidance on future sampling to evaluate changes to aquatic macroinvertebrate assemblages as reclamation work is conducted in the future.

4.4.1 Methods

A single sample of macroinvertebrates was collected using a dipnet in pondweed (Potamogeton) at the main beaver impoundment in Silver Creek at the site. The sampling location was located about half-way between the USGS’s 1998-2000 sampling location numbers 1 and number 2, (Figure 3, USGS 2001). Riparian and wetland vegetation consisted of cattails, bulrush, sedges, mullen and clover. Filamentous algae and pondweed (Potamogeton) were abundant on the surface of the beaver pond.

Aquatic macroinvertebrates were collected with a rectangular kicknet (457 x 229 mm) with a 500 micron mesh net. Samples were collected by the BLM’s Hazardous Materials personnel. The goal of the sampling was to collect a minimum of 500 invertebrates. Invertebrates were collected from submergent vegetation in the main beaver pond and separated from organic and inorganic debris in the field. Invertebrates were preserved in 90% ethanol and returned to the laboratory for identification and enumeration. The December sampling was collected for metals analysis. Samples were placed in vials without ethanol and submitted for laboratory analysis.

All of the organisms removed during the field sorting process were identified to the lowest practical taxonomic level and counted. The data were then entered into a computer data base. All invertebrates were composited into a single museum-grade glass screw‑top vial with a polypropylene lid and polypropylene liner. Sample labels were written with fade proof permanent black carbon ink on waterproof paper. Information on each label included the sampling location, sampling date and a unique catalog number.

4.4.2 Results

Invertebrates were very abundant at the sample collection location in the beaver pond. Aquatic invertebrate assemblage measures or metrics are typically calculated to summarize and compare complex lists of taxonomic information (Table 8). The measures calculated for this sampling location are shown in Table 9. The summarized metric values and the individual taxa that were collected suggest that this site was moderately impaired compared to unimpacted sites that Utah State University has sampled in this region. The primary evidence for this was total number of different taxa (taxa richness) and the types of organisms that we collected at this site. The low number of mayflies (Ephemeroptera) was particularly diagnostic of potential heavy metal contamination. Mayflies are a diverse and generally abundant part of aquatic invertebrate assemblages in northern Utah. They have also been shown to be particularly sensitive to heavy metal contamination. Only a single tolerant genera of mayflies, Callibaetis, was collected at this site. The complete lack of caddisflies (Trichoptera) and stoneflies (Plecoptera), from the sampled habitat also point to water quality impairment. Taxa generally tolerant of impaired water quality included the snail, Pysella. The assemblage was also dominated (45%) by individuals generally considered to be tolerant of moderate pollution levels and no taxa generally considered to be intolerant of moderate or slight pollution levels were collected.

The overall findings, based on this single sampling event, were that the aquatic invertebrate assemblage appeared to be impaired due to elevated metal concentrations, derived from upstream tailing areas. In December, upstream at the small pond receiving the Prospector Drain, aquatic invertebrates were absent, probably due to the metals concentrations at this site. The macroinvertebrates for ecological analysis were collected from Potamogeton in the beaver pond which is itself a metals accumulator, hence the sample may not be representative of the entire wetland. In December 2002, one each sample of macroinvertebrates and one chub/shiner fish sample was sent for mercury analysis by ACZ Laboratories. These results are shown in Table 6 and are discussed further below.

As restoration work progresses in this area, additional monitoring of the aquatic macroinvertebrate assemblages should be conducted. For better data comparability, samples should be collected at the sites sampled by the USGS in 1998-2000. Annual sampling, preferably in the fall, should be adequate to evaluate impacts and track recovery of aquatic invertebrate assemblages following restoration of the site.

4.5 Mercury Investigations

Mercury can be methylated by sulfate reducing bacteria (SRB) in anoxic sediments to methylmercury. Methylation of inorganic mercury is important because it greatly increases the bioavailability and toxicity of mercury and increases the exposure of wildlife and humans to methylmercury. Fish accumulate methylmercury by 10⁶to 10⁷ -fold (Wiener, et al, 2002). Recent research clearly indicates sulfate, SRBs and anoxic conditions are associated with mercury methylation in wetlands (King, et al, 2001, Wiener, 2002, EPA, 2002). Factors such as increased pH, alkalinity, sunlight, and sediment sulfide concentrations demethylate or reduce mercury methylation and factors such as increased aqueous sulfate and dissolved organic matter tend to increase methylation and fish bioaccumulation of mercury (EPA, 2002, Wiener, 2002).

Since one potential remediation alternative is to enhance the metal removal capabilities of the Silver Maple wetland, it was necessary to evaluate the amount of methylmercury present at the site. SRBs are expected to be present and active at the wetland as Silver Creek provides an excess of sulfate and because of the aforementioned sulfide odor. Mercury is not only methylated by bacteria, but can be demethylated by bacteria, depending on sediment chemistry, microbial interactions, and macrophyte contributions. In one study, the aquatic macrophyte Potamogeton (pondweed) actually promoted demethylation of mercury (King, et al 2001). Potamogeton is very abundant in the SMC main beaver pond.

USGS sampled Silver Creek in 2000 above the site at Bonanza Drive and above Richardson Flat for total (THg) and methylmercury (MHg) in sediment and water (USGS, 2001), but did not sample SMC. Table 7 indicates that water quality standards for total mercury were exceeded at both locations, but by a larger magnitude above Richardson Flat. Some critical values for piscivorous wildlife range from (0.1 ppm methylmercury in fish tissue to 0.05 ng/L methylmercury in water (Yeardley et al 1998, EPA, 1997). Note that while SMC lies between the sampling locations, so does a contaminated reach of Silver Creek that is over one mile long and at least twice as long as SMC, hence a significant portion of the concentrations were potentially due to this reach that is outside of SMC. The USGS data show more methylmercury in sediment, but not in water upstream of the site. Clearly, there are important upstream sources and SMC is only a partial contributor to mercury and methylmercury in Silver Creek. Because USGS did not sample the SMC site, BLM sampled the SMC site using the EPA analytical method 1631 in 2002.

Co-located surface water and sediment samples were collected by BLM in December 2002 at the west property boundary near the Prospector Drain, at the main beaver pond, and at the east property boundary, Figure 2. Aqueous water samples were analyzed by ACZ Laboratories using the EPA trace detection method 1631. Methylmercury analyses were analyzed by Frontier Geosciences of Seattle. Table 7 shows the BLM SMC results are similar to or less than the USGS results from upstream Silver Creek at Bonanza Drive. Comparing the USGS and BLM data, a ten-fold increase in water total mercury occurs offsite somewhere between the east boundary of SMC and east of Richardson Flat. It may be seen that the surface water samples slightly exceed the Utah water quality standard for total mercury of 12 ng/L.

4.6 Summary of USGS Quantification of Metal Loading to Silver Creek

In May 2002, the USGS performed a tracer injection study and synoptic water quality sampling to characterize the water quality at the site and to determine loading sources in a 1,420 meter reach of Silver Creek (USGS, 2003). Twenty-nine of the total 46 samples were collected within the SMC site and water flows were determined by tracer injection. All samples were analyzed for complete water chemistry, and metal loadings were computed. The full report is included in the RSI by reference in Attachment 1. Among the samples collected within SMC was Prospector Drain. PD drains groundwater from the existing upstream SCT tailings that are still in place and conveys this water into the Silver Maple Claims site near location 1B (Figure 2).

USGS uses terms of “total load” and “cumulative load” in its report. Total load is figured at each sampling location and increases or decreases according to sources and sinks (losses) at the location. Cumulative load includes only the positive loads (sources) but not losses (sinks) from natural wetland processes.

Table 8 of the USGS report shows that for the reach from the Park City injection downstream to Wanship, a substantial amount of the zinc load occurs from sources upstream of SMC (7.07 kg), the greatest mass of zinc loading occurred at the Prospector Drain (8.91 kg (correction from 10.2 kg (Kimball, 2004)), and a substantial amount of zinc loading occurs within SMC (8.49 kg). These three loads account for 14%, 18% and 17% of the zinc loading to Silver Creek (down to Wanship) based on cumulative loads. However, Table 8 and Figure 11 of the USGS report also shows total load losses of 7.5 kg zinc occur in the SMC wetland (USGS, 2003), in effect canceling out the sources within the wetland and is attributed to attenuation in the pond area (USGS, 2003). Cadmium follows a very similar pattern. These losses are likely due to complexation, adsorption, sedimentation, sulfide metal removal via SRBs, and bioaccumulation, Figure 5.

USGS uses cumulative instream load to discuss inputs of loading mostly for two reasons.

First, although there may be “credits” for losses (particularly for a wetland like SMC), according to Kimball, the losses generally are seasonal and annually there is a flush out of the area that does contribute to the entire load. Note however, the injection study was performed during spring runoff and may reflect seasonally high loadings. This strategy has mostly been applied to streams that build up floc on the streambed over the summer and it is flushed with snowmelt runoff. It is possible that Silver Creek through SMC does not fit that at all. So the losses may be retained, and the values in the report “count” as removal. Second, even if metal load is lost it most likely is lost in a way that keeps it as part of the problem, such as in the sediment which is available to the food web (Kimball, 2004).

Whether the total load or cumulative load is considered, the wetland appears to be functioning to attenuate or remove a substantial amount metal loading and accumulations of cadmium and zinc are occurring in sediment. The ecological risk associated with sediment is discussed in Section 5.5.

Table 8 of the USGS report can also be used to investigate the effect of removal actions to meet TMDL goals. The TMDL targets a zinc and cadmium loading reductions of 65% and 92%. The sum of the PD load (8.9 kg), the upstream load (7.07 kg) and the SMC load (8.49 kg) equals 24.5 kg. Less sixty-five percent removal of each of these sources leaves 8.6 kg, likely attainable with cost-effective removal actions with or without loading credits from wetland processes discussed above. Eighty-one percent of the cadmium load from upstream sources and SMC comes from upstream sources and PD, so attaining 92% removal is contingent on high removal efficiencies of these sources.

4.7 Summary of Waste Sources

The USGS tracer study results show that the sources listed below are contributing to the loading of Silver Creek. The following lists the major sources and the percent of cumulative zinc loading to Silver Creek to Wanship (Kimball, 2004):

· Prospector Square drain is supplying about 18% of the loading to the reach or 6.9 kg/day to SMC,

· Upstream sources are supplying about 14 % of the loading to the reach or 8.9 kg/day to SMC,

· SMC is contributing about 17% percent of the loading to the reach or 8.5 kg/day and recaptures 7.5 kg/day.

Cumulative loads do not account for losses of load due to natural wetland process in SMC. Total zinc loads in SMC are much less than cumulative loads apparently based on natural wetlands treatment processes such as complexation, sedimentation, adsorption and precipitation.

Excluding PD and upstream sources, it is likely that the approximately 3785 cy of exposed tailings contribute most of the SMC cadmium and zinc load based on leaching ARD geochemistry, tracer results and higher aqueous concentrations at the hotspot near the main beaver pond. ARD leaching of metals requires oxygen, water and sulfidic waste (Ford, 2003), all present in the exposed tailings. Using zinc for example, calculations show the exposed tailings alone have the potential to increase the cumulative load within SMC. Seasonal rise in the ground and surface water levels exacerbate ARD formation by providing water. The exposed tailings volume (3785 cy or 5.11x10⁶ kg assuming 1.48 ton/cy) was multiplied times the SPLP zinc concentration of 33.9 mg/L for sample 1D. This yields a theoretical daily load of 173 kg zinc. Even with the dilution factor in the SPLP, the exposed tailings have the capacity to leach more zinc than shown in the tracer study (8.5 kg/day) for all of SMC. Acidic, exposed tailings are found at locations downstream of the Prospector Drain and at the east SMC boundary that coincide closely with locations of zinc loads shown in Figure 11 of USGS (2003). The hotspot exposed tailings, while not acidic, are of very high concentration and, combined with acidic exposed tailings on the north side of the main beaver pond, may account for the major point of zinc loading downstream from the main beaver pond (segment S13, USGS, 2003). Similar zinc loading from USGS Figure 11 occurs near the east boundary where exposed tailings are in contact with Silver Creek.

The 141,651 to 177,541cy of buried tailings are believed to contribute much less to the Silver Creek metal loadings because they are isolated from air by surface water and thick sediment layers and because they are in a reduced oxidation state. Overlying the tailings is an average 6 inch blanket of organic-rich sediment that creates anaerobic conditions (based on black color and H₂S odor). The sediment effectively excludes oxygen from the buried tailings and promoting sulfide removal using SRBs. Leaching and acid rock drainage processes require oxygen. In their reduced state, acid-base accounting and leaching samples show the buried tailings have near neutral pH and metal leaching 100 times less than that of the exposed tailings (based on conservative SPLP results in the presence of oxygen). It is possible that seasonally lower water tables may reduce this protection, although the sediment would tend to stay moist and anaerobic. USGS well PS-MW-10 showed a lowest water level of just 1.7 feet below ground surface.

5.0 STREAMLINED RISK ASSESSMENT

Removal actions do not require the intensive level of risk assessments performed for CERCLA National Priorities List sites. EPA guidance calls for a streamlined risk assessment that uses available criteria and standards for assessing risk at the removal site evaluation stage to determine if further action is warranted (EPA, 1993).

Mining activities from the upstream Silver Creek and at SMC has probably influenced Silver Creek since the late 1800s. Tailings generated from mining activity have contributed acidity and heavy metals into water, stream sediments and soils. The area currently serves as wildlife habitat and wetlands and viewing area for hikers and cyclists on the Rail Trail. Recreational demands are fairly intensive, but access is restricted by a fence and signs.

To address these issues, BLM developed acceptable multi-media risk management criteria (RMC) for the chemicals of potential concern (COPCs) as they relate to human use and wildlife habitat on or near BLM lands (Ford, 2004). The primary objective of this section is to perform a streamlined risk assessment for the site and to establish the magnitude of risk to human health and wildlife. RMCs for soil, sediment, fish and water protective of human receptors for the metals of concern were developed using available toxicity data and standard U.S. Environmental Protection Agency (EPA) exposure assumptions. Acceptable soil and sediment concentrations protective of wildlife receptors (ecological RMCs) for the metals of concern were developed using toxicity values and wildlife intake assumptions reported in the current ecotoxicology literature.

The COPCs were identified from historical information, the TMDL process, and site evaluation. The COPC selection process focused on chemicals documented to have been released to surface water at or near water quality standards and observed contamination in sediment and tailings at the site exceeding RMCs. Background soil concentrations in mg/kg for arsenic, cadmium, lead, mercury, and selenium were <20, 3, 50, 0.35, <1, respectively. Copper and zinc in soil and sediment were added based on comparison to RMCs. For aquatic life protection, Utah water quality standards for Class 3A waters (aquatic life protection) and sediment criteria (Probable Effects Concentration) were also used to establish COPCs (EPA, 2000b). Human and ecological COPCs for SMC are: arsenic, cadmium, copper, lead, mercury, and zinc in tailings and sediment; cadmium, mercury and zinc in surface water (based on the TMDL and exceedances of mercury in this report.

Potential receptors, receptor exposure routes, and exposure scenarios were identified from on-site visits and discussions with BLM personnel. To be complete, a pathway must have a source, transport through an environmental medium, a point of exposure, a route of human exposure and an exposed population. Representative wildlife receptors at risk were chosen using a number of criteria, including likelihood of inhabitation, and availability of data. Figure 6 is a site conceptual model for human and ecological exposure to mining waste at the site. The risk assessment focuses on surface water and soil/sediment pathways as these pathways are complete and have human and/or ecological receptors. The fishing pathway is rated as potential but incomplete (ATSDR, 2004).

5.1 Human Health Risk Assessmenttc \l3 "5.1 Human Health Risk Assessment

Several on-site human exposure scenarios were developed to provide realistic estimates of the types and extent of exposure which individuals might experience to the metals of concern in the water, soils, and sediments on BLM property. The camping scenario often used for evaluation of BLM sites assumes 14 days of exposure. Such exposures might occur to individuals who use the site and adjacent contaminated areas for hiking, bird-watching, and fishing. The principal exposure pathway that normally contributes the large percentage of risk is incidental soil ingestion to users of the Rail Trail. Hikers may carry contaminated mud on their shoes or dust on their clothing to the home. Dogs may carry mud home. Young children may rest and sit or play in the contaminated soil and ingest soil from toys or hand-to-mouth activities. Inhalation of dust from these areas during dry weather may contribute a minor amount of risk. Exposure to sediments is less likely because of the fence and because most people do not want to enter the wetland. Fishing is also not permitted in the wetland.

The RMC correspond to either a target excess cancer risk level of 1 x 10^-5, or a target noncancer hazard index of 1.0. In the case of metals posing both carcinogenic and noncancer threats to health, the lower (more protective) concentration was selected as the RMC. The concept behind the RMC is that people will not experience adverse health effects from metal contamination on BLM lands in their lifetimes, while exposure is limited to soil, sediments, and waters with concentrations at or below the RMC. A target excess cancer risk of 1 x 10^-5 means that for an individual exposed at these RMC, there is only a one in a hundred thousand chance that he would develop any type of cancer in a lifetime as a result of contact with the COPCs. A hazard index of <1.0 means that the dose of noncancer metals assumed to be received at the site by any of the receptors in a medium is lower than the dose that may result in any adverse noncancer health effects. The RMC are protective for exposures to multiple chemicals and media. Lead RMC for the child receptors were determined from EPA's Integrated Exposure Uptake Biokinetic Model and other EPA regulations and guidance.tc \l3 "Lead RMC for the child receptors were determined from EPA's Integrated Exposure Uptake Biokinetic Model and other EPA regulations and guidance.

The human health assessment did not evaluate mercury exposure from fish ingestion because this is not a complete exposure pathway at the site. Fish accumulation of methylmercury is dependent on fish size, diet and trophic position. The site is not believed to support game fish of any numbers or size and access is restricted by a fence and signs. Recently, EPA established a methylmercury criterion of 0.3 ppm in fish tissue (EPA, 2001). The composite fish tissue sample analyzed for mercury was found to be less than the criterion and is discussed below.

5.2 Screening Level Problem Formulation and Ecological Risk Assessment

EPA guidance recommends the use of a problem formulation approach to ecological risk assessment (EPA, 1997), including:

· environmental setting and contaminants present,

· contaminant fate and transport,

· contaminants ecotoxicity and receptors

· complete exposure pathways

· selection of endpoints to screen for ecological risk.

Figures 5 and 6 contain conceptual models showing the environmental setting, biogeochemical cycling of metals, and present a problem formulation model relating exposure pathways to ecological receptors at the site. These biogeochemical processes explain how metals are released onsite, how they are transported, stored, and attenuated in the wetland, and important routes of exposure to receptors. The figure does not include upstream sources. Free-swimming aquatic life forms are exposed in the water column and benthic organisms are exposed in the sediment. Higher trophic level birds and mammals are exposed by consuming aquatic food items and sediment.

The Wetland Functional Assessment was used to help evaluate the biological resources at the site, Section 4.3 and Attachment 3 (Dynamac, 2003). Five plant communities were mapped at the site, Figure 7. The Typha latifolia (cattail) community consists of at least three significant stands in the western half of the Silver Maple wetland complex. These plants were standing in shallow (0-6”) water at the time of the fieldwork. These stands are dense, with few other species occurring within their midst. The Juncus arcticus (rushes) community occurs in at least six significant stands within the delineated wetland boundary, and they occur virtually throughout the whole wetland system in lesser profusion. This community also features a variety of other graminoids, including Agrostis spp. (bentgrass), and Eleocharis palustris (spikerush). The mixed sedge community includes the species Carex aquatilis (water sedge), C. nebrascensis (Nebraska sedge), and C. utriculata (beaked sedge). The mixed willow community is dominated by Salix exigua (coyote willow), but also includes S. monticola (Rocky Mtn. willow), S. boothii (Booth willow), S. eriocephala (yellow willow), and perhaps others. The fifth community is floating and submergent aquatic plants including Potamogeton (pondweed) and Lemma (duckweed).

At SMC, pondweed is an important metals accumulator, but may also serve to demethylate mercury (King, 2001). Lesser amounts of metals are bioaccumulated in cattail and willow where they become available for herbivores such as mallard ducks, beaver, and moose. Metals can also be bioconcentrated into macroinvertebrates, and into higher trophic levels such as fish and birds. Fish, in turn, may be consumed by piscivores, e.g. herons, racoons and mink.

The potential exposure pathways include aquatic bioconcentration, soil and sediment ingestion, vegetation ingestion, surface water ingestion. Ecological RMCs have been established for metals in soil and sediments. This has been accomplished using the best data available, including: ecotoxicological effects data for the metals of concern, wildlife receptors representative of the southern Rocky Mountains ecosystem, body weights and food intake rates for each receptor, and soil ingestion rates for each receptor. The site lies within the southern Rocky Mountain Steppe (Bailey, 1995). The wildlife receptors typical for this area include aquatic life, beaver, mallards, red-winged blackbirds, and swallows. Various mammals may also use the area, such as raccoons, mink, and moose.

The streamlined assessment endpoint evaluated chronic adverse effects on terrestrial and aquatic life. The measurement endpoints include comparison to aquatic life water quality standards, comparison to probable exposure concentrations (PECs - in sediment), macroinvertebrate community diversity, wetland functioning (vegetation), and for wildlife, comparison to ecological RMCs.

In deriving wildlife RMCs, the literature was surveyed for toxicity data relevant to either wildlife receptors at the site or to closely related species, including waterfowl. In the absence of available toxicity data for any receptor, data were selected on the basis of phylogenetic similarity between ecological receptors and the test species for which toxicity data were reported. Soil ingestion data for each receptor were obtained from a recent study on dietary soil content of wildlife from the U.S. Fish and Wildlife Service (Beyer, et. al., 1994). Where no dietary soil content data were available for a particular receptor, the soil content was assumed to be equal to that of an animal with similar diets and habits. The amount of soil ingested by each receptor was estimated as a proportion of their daily food intake (Beyer, et. al., 1994). The food intake in grams for each receptor was calculated as a function of body weight (Nagy, 1987).

RMCs were calculated for each chemical of concern based upon assumed exposure factors for the selected receptors, and species- and chemical-specific toxicity reference values (TRVs). Essentially, the TRVs represent daily doses of the metals for each wildlife receptor that will not result in any adverse toxic effects (no observed adverse effect level (NOAEL)). TRVs were computed by metal of concern for each wildlife receptor/metal combination for which toxicity data were available. Phylogenetic and intraspecies differences between test species and ecological receptors have been taken into account by the application of uncertainty factors in derivation of critical toxicity values. These uncertainty factors were applied to protect wildlife receptors which might be more sensitive to the toxic effects of a metal than the test species. The uncertainty factors were applied to the test species toxicity data in accordance with a method developed by BLM. In accordance with this system, a divisor of two (Ford, 1993) was applied to the toxicity reference dose for each level of phylogenetic difference between the test and wildlife species, i.e. individual, species, genus, and family. Wildlife RMC methodology and values are found in Ford (1996-online and 2004).

5.3 Uncertainty Analysis

Toxic doses for each metal were selected from the literature without regard to the chemical speciation that was administered in the toxicity test.

The process of calculating human health RMC, using a target hazard quotient and target excess lifetime carcinogenic risk, has inherent uncertainty. The COPCs may have synergistic (or antagonistic) effects on human or wildlife receptors. Cumulative effects from multiple COPCs and pathways were quantitatively dealt with for the human assessment, although not all metals are elevated. Additionally, it is improbable that human receptors would be exposed concurrently via all possible exposure pathways, although this has been assumed for conservatism (Ford, 2004). There is uncertainty in deriving wildlife RMCs due to the lack of toxicity data for these species.

tc \l1 "The COCs may have synergistic (or antagonistic) effects on human or wildlife receptors. Cumulative effects were quantitatively dealt with for the human assessment, although not all metals are elevated. Additionally, it is improbable that human receptors would be exposed concurrently via all possible exposure pathways, although this has been assumed for conservatism (Ford, 1996). There is uncertainty in deriving wildlife RMCs due to the lack of toxicity data for these species. A standard uncertainty factor approach was used for interspecies extrapolation (Ford, 1996). 5.4 Risk Assessment Results - Human Health

Table 11 compares the maximum, mean, and representative media concentrations for COPCs at the site with the selected appropriate RMCs. For tailings, a maximum value was selected to show the risk to human health at the hotspot near the Rail Trail. The ratio of the environmental media concentration to the RMC is analogous to a hazard quotient of 1.0; that concentration that should present negligible risk. Media concentrations exceeding RMCs for humans or wildlife greater than 1.0 are flagged "+"; these occurrences may pose a chronic threat. Media concentrations exceeding RMCs by more than 10 and 100-fold for humans or wildlife are flagged as “++” and “+++”, respectively. Because camping is unlikely on the site, comparison to the camper RMC is conservative. This RMC allows for 14 days exposure via several media, however, it is possible that recreational users might use the Rail Trail 14 days per year and is thus retained for comparison.

Using sample 65' E of 7A, taken from the near the gate, the most significant tailings exceedances are for arsenic, lead and zinc where RMCs are exceeded by more than 10-fold, placing the site in the high risk category for site visitors, and leaching potential to Silver Creek. Visitors exposed to direct contact or dust entrained at this location may be exposed to high concentrations of arsenic, lead and zinc. In 2003, this material was covered with a temporary barrier to minimize direct contact and dust exposure to visitors, and to help reduce a source of mercury exposure to aquatic life as this area had the highest mercury levels found at the site. Tailings near 1A and within Prospector Park west of 1D and 1E are also near areas where visitors may contact tailings.

In November, 2004, the Utah Department of Health and Utah Department of Environmental Quality issued a fish advisory for Silver Creek, because of arsenic concentrations in trout collected downstream of Richardson Flat, recommending limits on fish consumption (UDH, 2004). No other metals were found to warrant an advisory. The concentrations found averaged less than the arsenic screening value (0.027 mg/kg) using a wet weight basis (ATSDR, 2004). ATSDR classified the fish pathway as only a potential exposure pathway because of a lack of evidence of an exposed population (lack of fishers). BLM’s composite fish (not trout) sample arsenic results (0.3 mg/kg) are dry weight basis; adjusting to wet weight using a 0.15 conversion factor, yields 0.045 mg/kg, greater than the ATSDR screening value.

In summary, the hotspot near 7A, exposed tailings near 1A, and similar tailing inclusions throughout the site pose risk to recreational visitors via direct contact, especially where located near the Rail Trail. The fence may not stop some visitors in approaching the water’s edge and pets may even swim in the wetland. Removal of these tailings can practically eliminate risk to human health. Fish consumption from SMC is also subject to the fish advisory for arsenic.

5.5 Risk Assessment Results - Ecological Receptors

For the purposes of a streamlined assessment, this section summarizes the measurement endpoints from the wetland and macroinvertebrate assessments, and compares sample results to water quality standards for the protection of aquatic life, ecological RMCs, and for sediment chemistry PECs (EPA, 2000a). For sediment risk, the sediment quality triad of chemistry, toxicity and biology was observed to the degree possible considering the nature and scope of a streamlined risk assessment for removal actions (EPA, 1993).

Wetland Assessment: The wetland functional assessment rated the quality of the wetlands as high with excellent potential to: store and release water into the surrounding aquatic ecosystem; detain and/or store floodwaters during high flow events; produce biomass, connect the downstream ecosystem and support aquatic food chains; remove nutrients from nearby anthropogenic sources and for heavy metal pollutant retention and assimilation from the historic mining activity; support beaver activity, macro topography, and dense vegetation; stabilize shorelines and provide sediment control for Silver Creek; and provide area for wildlife habitat, featuring robust plant and animal diversity, and fair habitat connectivity. Five robust plant communities are present with evidence of survival and reproduction similar to the reference wetland. Most of the wetland appears to have been established after 1962 based on aerial photography. Approximately 7.5 acres are a jurisdictional wetland to be protected. Warm summer-time temperatures (>20^o C) observed during the assessment may inhibit coldwater fish species.

Macroinvertebrate Assessment: Although these conclusions are from a single composite sample, it was chosen to be collected from portion of SMC expected to be highly contaminated because of the high loadings and exposed tailings at the hotspot. The macroinvertebrate findings indicated the aquatic invertebrate assemblage appeared to be impaired (or absent near Prospector Drain) due to elevated metal concentrations, derived from upstream tailing areas. The primary evidence for this was total number of different taxa (taxa richness) and the types of organisms collected at this site. The low number of mayflies (Ephemeroptera) was particularly diagnostic of potential heavy metal contamination. Mayflies are a diverse and generally abundant part of aquatic invertebrate assemblages in northern Utah. They have also been shown to be particularly sensitive to heavy metal contamination. Only a single tolerant genus of mayflies, Callibaetis, was collected at this site. The complete lack of caddisflies (Trichoptera) and stoneflies (Plecoptera), from the sampled habitat also point to water quality impairment. The assemblage was dominated (45%) by taxa generally considered to be tolerant of moderate pollution levels and no taxa generally considered to be intolerant of moderate or slight pollution levels were collected. The impairment is probably due to both exceedance of water quality standards and exceedance of sediment criteria (Table11) leading to high metal concentrations in pondweed with which macroinvertebrates associate.

Water quality: Table 11 shows two water samples taken from the main beaver pond. USGS SCS0684 is representative the larger USGS data-set for the SMC site for spring run-off conditions. Based on exceedances shown in Table 11, zinc and cadmium are the metals most likely to cause toxicity to fish at the site. Zinc toxicosis affects freshwater fish by destruction of gill epithelium and consequent tissue hypoxia. In general, zinc is more toxic to embryos and juveniles than to adults, to starved animals, at elevated temperatures, in the presence of cadmium and mercury, in the absence of chelating agent, under conditions of marked oscillations in ambient zinc concentrations, all potentially present at the site. Conversely, zinc toxicity to Daphnia magna is mitigated by increased dissolved organic carbon, water hardness and alkalinity (Heijerick, 2004) also found at the site. Dissolved oxygen (10 mg/L, Attachment 3), hardness (400 mg/L), dissolved organic carbon (7 mg/L) and pH (neutral to 8.5) are all optimum to reduce aquatic life toxicity at the site.

Dissolved zinc concentrations measured by various investigators since 1988 show that, on average from Table 1, zinc immediately below SMC exceeds Utah water quality standards by about 2-fold during high-flow periods and about 4-fold during low flow periods. Comparing concentrations at the upstream boundary to the downstream boundary, zinc sometimes decreases at the downstream boundary of SMC. Cadmium had similar but lower exceedances. There is evidence that the low-flow exceedances are also found upstream of SMC and that there is groundwater inflow into Silver Creek and SMC from SCT and PD. Minnow fish are found and were collected in the main beaver pond at SMC, but no inventory or species identification has been conducted. Sample SW-1 collected in December 2002 from the main beaver pond did not exceed zinc water quality standards. Although Silver Creek is classified as a cold-water fishery, summer temperatures may be too high to support cold-water species.

As described in Section 4.5, USGS and BLM results for total mercury (THg) and methylmercury (MHg) in sediment and water onsite and off-site indicated that the Utah water quality standard for total mercury was slightly exceeded at upstream and onsite locations, but were exceeded by a much larger magnitude downstream above Richardson Flat. The results indicate that the SMC site is not the source of the large increase near Richardson Flat.

Because of the proximity of the exposed tailings to Silver Creek, RMCs were developed based on leaching characteristics of the waste, specifically unsaturated, exposed, acidic tailings based on sample 1D. The exposed acidic tailings produce leachate concentrations 100 times that of reduced tailings and sediment (Section 4.1.2). The leaching RMC is intended to protect aquatic life from leaching of metals and was derived with the equation below using Utah water quality standards (UWQS) and available analytical results. This equation considers the ratio of the amount of total metal to the amount leaching and computes the maximum total metal concentration in mine waste that will not exceed UWQS. A dilution-attenuation factor (DAF) was applied using EPA’s Soil Screening Level guidance except that a factor of 10 for surface water was used instead of 20 for groundwater (EPA, 1996). The leaching RMCs were computed for copper, cadmium, lead and zinc according to the formula below and are shown in Table 10.

Leaching RMC=UWQS*total metal*DAF/SPLP

Since tailings concentrations are much greater than leaching RMCs, especially for cadmium and zinc, these results show the importance of removing the exposed tailings.

Sediments: Table 11 shows mean and a representative sediment sample results for comparison to RMCs. Tables 7 and 11 show results from sediment sampling indicate exceedances of EPA’s Probable Effects Concentration for mercury at all three SMC sites and one upstream and one downstream site. But onsite sediment mercury and methylmercury concentrations are less than or equal to upstream and much less than downstream concentrations. Aquatic macroinvertebrate and fish samples also showed low concentrations of mercury. Mercury may be converted by anaerobic bacteria to the more toxic methylmercury that is known to bioaccumulate in aquatic food chains. EPA (1997, 2002) reported that bioaccumulation of methylmercury is reduced by alkaline pH and dissolved organic matter. Both conditions are present at the SMC wetland. The ability of the SMC wetland to methylate mercury in the food chain appears to be low based on these data.

Table 11 also shows exceedances of PECs and mallard RMCs for arsenic, cadmium, lead and zinc. PECs are based on sediment-dwelling invertebrates in the Great Lakes. Comparison to lead and zinc RMCs show exceedances greater than 10-fold and would be generically be classified in the moderate to high risk range, although the RMC conservatively assumes 100% bioavailability and 100% SMC habitat use. The RMC is very conservative as sediment bioavailability is probably much smaller based on SPLP and TOC results and the home range for the mallard probably exceeds the size of the SMC wetland. These factors may be used to modify the RMC in more detailed studies (Ford, 2004). It should also be noted the mallard RMC is based on a conservative NOAEL and that lowest effect levels may be 3-10 times higher without affecting survival or reproduction.

Wildlife: Effects to higher trophic level animals can be evaluated by bioaccumulation in the food chain and dietary concentrations of sensitive receptors such as avian species. Aquatic plants, macroinvertebrates and fish were sampled at the site. Elevated cadmium was found in willow (Salix) and pondweed (Potamogeton), but not cattail (Typha) plants at the site. While it is known that cadmium bioaccumulates in these two species more so than other plants and that cadmium in the willow diet has been associated with toxicity to one species (ptarmigan - Larison, et al, 2000), there is little firm evidence that cadmium in soil or other plants is associated with toxic effects to terrestrial wildlife (Beyer, 2000).

The remaining elevated metals concentrations in pondweed (especially lead and zinc) may help explain the impairment to macroinvertebrates as the macroinvertebrates were collected from pondweed at the same sampling location in the main beaver pond. The macroinvertebrate chemical analyses reflect the pondweed and sediment results at location 7C, where the highest values are also seen for lead and zinc. Pondweed and associated periphyton provide food and cover for macroinvertebrates, so it is not surprising to see a correlation. Mercury was not found to be accumulating to any great degree in composite fish and macroinvertebrate samples, despite the fact that the highest mercury concentrations are found near the main beaver pond where the samples were collected.

Birds may be affected by ingestion of contaminants in sediment and diet. Mallards, red-wing blackbirds and swallows are abundant at the site and use it for feeding and some nesting. These birds have different feeding strategies. According to Henny (2002) in the Lower Coeur d’ Alene watershed, waterfowl have higher risk of exposure to contaminated sediment than any other birds because of their higher rate of sediment ingestion. Ingestion of lead in contaminated river sediment was found to have adverse effect on waterfowl (e.g. ducks) in the Coeur d’ Alene River in Idaho with a lowest effect level (LEL) of 530 mg/kg lead in sediment and some mortality at 1800 mg/kg (Beyer et al, 2000a). The sediment lead LEL for the typical mallard is probably greater than 530 mg/kg since the 530 mg/kg level is for swans ingesting sediment at the 90% percentile and swans are more sensitive to lead. Beyer (2000a) states that the blood lead to sediment lead relationship is site-specific, species-specific, sediment ingestion rate specific and depends on bioavailability.

Mallard drakes (Anas platyrhynchos) were fed 1, 5, or 25 ppm lead nitrate for 12 weeks (Finley et al, 1976). No mortality occurred, and the pathologic lesions usually associated with lead poisoning were not found. After 3 weeks, ducks fed 25 ppm lead exhibited a 40% inhibition of blood delta-aminolevulinic acid dehydratase (ALAD) activity that persisted through 12 week exposure. After 12 weeks of treatment, similar enzyme inhibition was present in the ducks fed 5 ppm lead. At 3 weeks there was a small accumulation of lead (less than 1 ppm) in the liver and kidneys of ducks fed 25 ppm lead; no further increases occurred throughout the exposure. No significant accumulation of lead occurred in the tibiae or wing bones. After 3 weeks on clean diet, ALAD activity and lead concentrations in the blood returned to pretreatment levels.

The above results were for lead salts where lead is assumed to be 100 percent bioavailable. Lead in sediment is believed to have a much lower bioavailability. In a subchronic feeding study with mallards, 3,400 mg/kg lead in Coeur d’ Alene River, Idaho sediment was fed to mallards mixed with feed at doses of 3-24% of the diet in pellets, resulting in ten percent mortality at the 24% dose (Heinz et al, 1999). The 3% dose (102 ppm lead) did not cause mortality, but decreased ALAD and increased blood lead to approximately 1 ug/g, a level consistent with lead poisoning. Necropsies and histopathology of these birds did not show signs of lead poisoning. In a similar feeding study, 3950 mg/kg lead from Coeur d’ Alene River sediment fed at 24% of diet in mute swans did not cause mortality, but did show multiple signs of lead poisoning (Beyer, 2003). Using the 2,675 mg/kg mean SMC sediment lead concentration and a sediment ingestion rate of 4% (Beyer, 2005), the estimated dietary concentration is 107 ppm, approximately equal to the concentration of Idaho sediment known to have caused lead poisoning in mallards in the feeding study. It should be noted in the Heinz study, that when fed in mash form, the ducks were able to wash and reduce their sediment and lead intake, as they might in a natural setting.

Table 11 exceedances of the conservative mallard RMC (based on a NOAEL and assuming 100% bioavailability) and the conservative 530 mg/kg LEL for Idaho (Beyer 2002), suggest risk to waterfowl or other birds feeding in the aquatic food chain at SMC is possible, although further studies of the home range and dietary bioavailability of metals in site-specific sediment and food items would be needed to further assess this (Beyer, 2002).

Swallows are members of a different feeding guild than ducks as they eat emergent insects, and ingest little if any sediment. Lead affected blood chemistries of tree swallows feeding on emergent insects from the Arkansas River, another site contaminated by mining wastes (Custer et al, 2002), with mean lead concentrations of 12.5 mg/kg in diet (insects) and in the Tri State Mining District (Beyer, 2004) with 80 mg/kg in macroinvertebrates, although it is not known if the swallows were feeding on these macroinvertebrates. Like at the Arkansas River, swallows are abundant feeders at SMC. Lead concentrations in the composite aquatic macroinvertebrate sample from the SMC site contained 29.7 mg/kg, more nearly matching the Custer study results. However, neither study identified any carefully measured dose-response effects on survival or reproduction.

Comparison to the RMCs for higher trophic levels (such as the swallow and mallard) does not account for the size of a species’ home range. The avian species mentioned above are migratory and only spend at most about half of their lives on or near the site, although they may reproduce there. Each of these species may have home ranges larger than the site and may feed in aquatic habitats outside of the site. It is common practice in ecological risk assessment to use a home range adjustment. If an adjustment was made for home range, the criteria exceedances would not be as large.

Waterfowl may also be at risk from zinc poisoning. Beyer (2004) found evidence of zinc poisoning (pancreatitis) in the Tri-State Mining District where sediment zinc concentrations ranged up to 25,000 mg/kg, but the minimum exposure associated with effects has not been identified. Cadmium also exceeds the mallard RMCs, but high concentrations of zinc interfere with the absorption of cadmium and the high zinc to cadmium ratio (150:1) probably reduces cadmium toxicity (Beyer, 2004).

Additional study of sediment ecological risk should be performed prior to natural resource damage and restoration or removal action decisions pertaining to sediment or buried tailings removal at SMC. Such studies are normally beyond the scope of removal response actions, but could include: sampling of waterfowl feces to estimate exposure, bioavailability studies, sediment pore-water, acid-volatile sulfide-simultaneous metals extraction, sediment bioassays, avian tissue analyses, macroinvertebrates, etc.

In summary, the data show concentrations of cadmium, zinc and mercury in the SMC water column are occasionally slightly higher than water quality standards, especially during low-flow periods when groundwater is suspected to be the major water source to the SMC wetland. Exceedances are not always the case and upstream sources are major contributors. Lead and other metals do not generally exceed water quality standards. Sediment concentrations of arsenic, cadmium, lead, mercury and zinc may have potential to affect benthic aquatic life, although multiple lines of evidence (wetland functioning, water quality and macroinvertebrate data) show only low to moderate impairment. Of the COPCs in sediment, lead and zinc have the greatest exceedances of criteria. Some minnow fish species are abundant but it is not known whether trout are totally absent or if they are limited due to contaminants, temperature or other stresses. Although no sick or dead birds were found at SMC, some risk to waterfowl or other birds feeding in the sediment or aquatic food chain at the site is possible. At minimum, studies of exposure, home range and dietary bioavailability of metals in sediment would be needed to further assess this risk (Beyer, 2002). Sediment lead bioavailability to the aquatic food chain at the SMC site may differ from other sites. The choice of endpoint (effects) to be studied is important. Adverse effects are often identified in tissue or pathology studies that may not affect survival or reproduction. The overall rating of the wetland health was high, suggesting that contaminants were not having a major adverse effect on the ecological structure and function of the wetland.

5.6 Removal Action Considerations

5.6.1 Upstream Sources

In evaluating removal actions for SMC and the Silver Creek watershed, it is important to consider objectives of the action, and the effect of the upstream sources, such as SCT on the removal action. The SCT area is already developed and those tailings are not likely to be removed. Modeling shows SCT serves as a source of contaminated groundwater and surface water to SMC via the Prospector Drain and through contaminated groundwater inflow at the west SMC boundary and interactions with Silver Creek. Unless the upstream sources are treated, removal actions at SMC will be subject to re-contamination over time from the interaction of ground and surface waters originating from upstream sources and entering the SMC wetland. The USGS report shows that unless upstream sources including PD are removed, water quality standards will not be met at SMC regardless of what actions are taken within the wetland. This would be particularly true if the saturated subsurface tailings are excavated, removed and new fill is brought in to restore the wetland. Based on the loading studies conducted by USGS, TMDL loads and water quality standards can probably be met by less-intrusive removal actions such as removing or treating upstream sources, Prospector Drain and removal of exposed tailings. Sediment metals concentrations should also gradually decrease as the metals loadings from upstream sources, Prospector Drain and exposed tailings are reduced.

5.6.2 TMDL Loads

The TMDL loading reductions should be re-evaluated with respect to total or cumulative loads. If total loads are used, credit for wetlands processes (e.g. metal sulfide removal) and compliance with the TMDL is more attainable than if no credit for wetlands processes is given. As discussed in Section 4.6, TMDL or Utah water quality standards can likely be met by cost-effective removal actions based on the USGS tracer study, but upstream sources, including PD are essential to meeting water quality standards at SMC.

The highest zinc loadings, and tailings and sediment samples for metals were found immediately southeast of the main beaver pond where the Beggs Mill may have been located. This area also harbors a large population of Potamogeton that has been shown to accumulate metals and potentially contribute to food chain ecological risk. Risk at this location could be reduced by removal of Potamogeton on a regular basis as a method of phytoextraction, removal of exposed tailings, by draining the pond and partially filling with soil.

Removal of exposed tailings will not only reduce metals in the water column, but will reduce sediment metals concentrations by reducing metals loading to the wetland.

Removal of tailings or sediments below the waterline may require a Section 404 permit and wetland restoration.

5.7 Removal Site Inspection Summary

Section 40 CFR 300.415 prescribes the elements of a removal preliminary assessment/site inspection and is summarized in the sections below.

5.7.1 Source and Nature of the Release

Section 4.1 summarizes the source and nature of the release. The Prospector Drain and upstream sources are considered important contaminant sources to Silver Creek with additional contributions from exposed tailings.

5.7.2 Threat to Public Health and Environment

Threat to human health is limited by fencing and the gravel barrier at the hotspot. Visitors are not likely to drink the water at the site because of the fencing and proximity to Park City. However, the portions of the tailings of concern are found outside the fence in the area of the gate near the main beaver pond. A gravel cap was placed over this area as a time-critical measure in 2003. Arsenic and lead in the tailings in this area were the primary metals of concern. The site is located near the Rail Trail and is frequented year-round by recreational users. Arsenic is a human carcinogen and lead has a variety of toxic effects to humans. There are other areas of exposed tailings. Recreational users may come into contact with the tailings by several exposure pathways. Although the site is fenced and posted, Silver Creek has an arsenic fish advisory and a composite fish sample from SMC exceeded the screening value. Adults may accidently ingest soil by hand-to-mouth activities including eating, drinking and smoking; and small children may ingest larger amounts of soil than adults. Inhalation of dust during dry periods may contribute lesser risk.

Risk to aquatic life is also posed by sediment as ecological probable effects concentrations (PECs) are exceeded particularly for cadmium, lead and zinc. Some risk to waterfowl or other birds feeding in the aquatic food chain at the site is possible, although at minimum, further studies of exposure, home range and dietary bioavailability of metals in sediment would be needed to further assess this.

In surface water, zinc and cadmium are the principal contaminants of concern at the site to aquatic life, with lesser contributions from other metals. Zinc is non-toxic to humans, but very toxic to fish. Zinc toxicosis affects freshwater fish by destruction of gill epithelium and consequent tissue hypoxia. In general, zinc is more toxic to embryos and juveniles than to adults, to starved animals, at elevated temperatures, in the presence of cadmium and mercury, in the absence of chelating agent, under conditions of marked oscillations in ambient zinc concentrations, all present at the site. Zinc toxicity is mitigated by high dissolved oxygen, dissolved organic matter, and water hardness and alkalinity also found at the site. Utah water quality standards are occasionally exceeded for the cadmium, zinc and mercury.

5.7.3 Factors Relating to the Need for a Removal Action

40 CFR 300.415 (a) (2) cites other factors to be considered in determining the need for a removal action:

1. Actual or potential exposure to nearby human populations, animals or the food chain from hazardous substances, pollutants or contaminants: Threat to human health is limited by fencing. Visitors are not likely to drink the water or have much soil contact at the site because of the fencing. However, the portions of the tailings are found outside the fence in the area of the gate near the main beaver pond. The site is located in Silver Creek, a water quality-impaired watershed and coldwater fishery. There is a fish advisory for arsenic on Silver Creek. Risk to ecological receptors is low to moderate based on water quality, sediment and biological data, but further studies could refine the risk.

2. Actual or potential contamination of drinking water supplies or sensitive ecosystems:

Besides metal contamination of Silver Creek, the site has a highly rated jurisdictional wetland and serves as a wildlife corridor. It is popular as a bird-watching and other recreational and scenic uses for residents and visitors of Park City.

3. Hazardous substances or pollutants, or contaminants in drums, barrels, tanks or other bulk storage containers that may pose a threat of release: No storage containers found on site.

4. High levels of hazardous substances, pollutants or contaminants in soils largely at or near the surface that may migrate: The site contains exposed tailings and contaminated drain-water with high concentrations of arsenic, lead, zinc, and other metals that are migrating into surface water; some metals are transferred into aquatic food chains.

5. Weather conditions that may cause hazardous substances, pollutants or contaminants to migrate or be released: No unusual risks from weather. The site is subject to periodic inundation from flooding which entrains contaminants into Silver Creek.

6. Threat of fire or explosion. Not applicable.

7. Availability of other appropriate federal or state response mechanisms to respond to the release. EPA and the Utah Department of Environmental Quality have been notified, however they will not be available to respond.

8. Other situations or factors that may pose threats to public health or welfare or the environment. None.

5.8 Recommendation

Based on the foregoing, it is concluded that further action is warranted at this site that would include, at minimum, removal of the exposed tailings. This action would practically eliminate human health risk, reduce ecological risk and, with control of upstream sources, help meet TMDL goals and water quality standards.
6.0 APPLICABLE, RELEVANT AND APPROPRIATE REQUIREMENTS

The lead Federal agency is responsible for the identification of applicable or relevant and appropriate requirements (ARARs) of all environmental laws that pertain to any CERCLA removal actions. As defined in the Guidance on Consideration of ARARs During Removal Actions (EPA 1991), ARARs are:

Applicable requirements are cleanup standards, standards of control, and other substantive requirements, criteria or limitations promulgated under Federal environmental or State environmental or facility siting laws that specifically address a hazardous substance, pollutant, contaminant, remedial action, location or other circumstances found at a CERCLA site.

Relevant and appropriate requirements are cleanup standards, standards of control, and other substantive requirements, criteria, or limitations promulgated under Federal environmental or State environmental or facility siting laws that, while not “applicable” to a hazardous substance, pollutant, contaminant, remedial action, location or other circumstances at a CERCLA site, address problems or situations sufficiently similar to those encountered at the CERCLA site and are well‑suited to the particular site.

Other information To Be Considered (TBC) generally falls within three categories: health effects information with a high degree of credibility; technical information on how to perform or evaluate site investigations or response actions; and policy.”

Typical ARARs identify the major Federal and State environmental laws as follows:

· Chemical specific standards established for specific chemicals found on the site,

· Location specific restrictions based on the location of the site, and

· Action specific limitations on “actions” associated with a CERCLA removal action.

The process of identifying ARARs will continue in consultation with the State as removal action alternatives are further developed and selected.

The principal state ARAR are water quality standards and stream classifications are found in Utah Administrative Code (UAC) Title R317-2, Standards of Quality for Waters of the State. Important federal ARARs are Sections 303d and 404 of the Clean Water Act. Section 303d requires listing of impaired water bodies and preparation of a TMDL. The 404 program prohibits discharge of dredged or fill material if a practicable alternative exists that is less damaging the aquatic environment or if the nation's waters would be significantly degraded. Excavation would require a permit. Compensatory mitigation, such as wetlands restoration or enhancement may be required.

Parameter	Acceptance	Arsenic	Lead	Zinc
Blanks	0 ppm	0 ppm	0 ppm	0 ppm
%D	+/- 20	28.4	0.7	7.2
%RSD	+/- 20	18.7	5.6	6.9
Regression R²	>0.7	0.43	0.95	0.96
Regression		Lab=0.42*XRF	Lab=1.28*XRF	Lab=0.85*XRF

Analyte	Silver Creek Water	RSPLP-1	RSPLP-2	RSPLP-3	RSPLP-4	RSPLP-5	RSPLP-6
Sorbent ratio		Compost 1 g/L	Compost 0.1 g/L	Iron 1 g/L	Iron 0.1 g/L	Iron2 1g/L	Iron 2 0.1 g/L
Arsenic	<0.04	<0.04	<0.04	<0.04	<0.04	<0.04	<0.04
Cadmium	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005	<0.005
Copper	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
Lead	<0.04	<0.04	<0.04	<0.04	<0.04	<0.04	<0.04
Mercury	<0.0002	<0.0002	<0.0002	<0.0002	<0.0002	<0.0002	<0.0002
Zinc	0.32	0.06	0.25	0.25	0.32	0.06	0.22
Zinc K_D		4333	2800	280	0	4333	4545

Day	1	2	3	4	5	6	7	8	9	10
Total Alkalinity	1400	1420	1200	1260	1260	1220	1120	979	894	839
Unionized NH3	2.28	1.48	0.84	0/9	0.67	0.84	0.66	0.5	0.6	0.4
Ammonia N	190	123	70	75	81	70	55	44	34	26
Orthophosphate	3.2	3.1	2.97	3.6	3.93	3.4	3.5	3.3	3.2	2.9