ACTION MEMORANDUM Request for a Removal Action at the Sulphur Bank Mercury Mine Superfund Site, Clear Lake, Lake County ^Calif Ornia

XR0050 SFUm> RECORDS C7R 2142-00128

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION IX 75 Hawthorne Street San Francisco, Ca. 94105-3901

SDMSDocID 88124216 MEMORANDUM DATE: April 9, 1992 SUBJECT: ACTION MEMORANDUM Request for a Removal Action at the Sulphur Bank Mercury Mine Superfund site, Clear Lake, Lake County ^Calif ornia . s FROM: ad shpey^r on Scene Coordinator, Emergency Response Section, H-8-3 TO: Jeffrey Zelikson, Director, Hazardous Waste Management Division, H-l I. PURPOSE This site meets the criteria for a removal action under section 300.415 of the National Oil and Hazardous substances Pollution contingency Plan ("NCP"). The purpose of this Action Memorandum is to request and document approval of the proposed removal action described herein for the Sulphur Bank Mercury Mine Superfund site, Sulphur Bank Road, Clear Lake, Lake County, California. Category of Removal: Time Critical CERCLIS ID: CAD980893275 SITE ID: K2 II. SITE CONDITIONS AND BACKGROUND A. Site Description 1. Historical Background The Sulphur Bank Mercury Mine was one of the largest mercury producers of California, producing 4000-7000 tons of mercury over a 100 year operating history. Geothermal activity beneath the mine site created the rich mineral deposits. Mineral saturated hydrothermal fluids, rising up through fissures and faults, precipitated cinnabar (HgS) in rock formations below the water table. As the fluids rose above the water table the mercury content decreased and elemental sulfur was deposited near the ground surface. The Clear Lake area in general and the Sulphur Bank Mine site in particular, contain many geothermally active hot springs and gas vents, giving rise to the debate about whether or

Printed on Recycled Paper not mercury continues to be transported in significant quantities in the hydrotherxnal system beneath the site. Initial mining activities at the site commenced in 1865 with the open pit mining of surface sulphur deposits by the California Borax Company. Falling prices and refining difficulties caused by the presence of cinnabar ore at shallow depths forced a shutdown of the mine in 1868. During the quicksilver boom of the 1870's, California Borax reopened the mine for the production of mercury. Shaft mining of the mercury ore was periodically conducted by three successive companies until extreme heat and gases required the reimplementation of open pit mining techniques in 1915. The current owner, Bradley Mining Company (BMC), initially mined mercury at the site under a lease agreement with the G.T. Ruddock estate circa 1927. BMC obtained ownership in 1945 and continued intermittent, open pit mining activities until 1957. The mine, inactive since 1957, was not properly closed; therefore the mine workings, tailings, overburden waste rock and the open pit have been exposed to the elements since operations ceased. A detailed discussion of the operating history, physical setting and regulatory status at the site is provided in the RI/FS workplan and the site management plan, which are attached in appendix C to this Action Memorandum. 2. Physical location The Sulphur Bank Mine, situated on the eastern shore of the Oaks Arm of Clear Lake, is located approximately 90 miles North of San Francisco at an elevation of 1325 feet above sea level. The site is situated in the Clear Lake volcanic field, thought to be the youngest of several surface manifestations resulting from a mantle "hot spot" which is responsible for producing the geothermal resources of the Geysers-Clear Lake area. The site is approximately 5 miles north of the town of Clearlake (population 15,200), and 1/2 mile South, across the lake, from Clear Lake Oaks (population 2,677). The Elem Community of Porno Indians and a freshwater wetland area are situated directly North of the site. The Indian community has a fluctuating population of approximately 200. Several residential homes are located south of the site along Sulphur Bank Point. As shown in Figure 2, the southeastern boundary of the site is vaguely defined, however the roughly circular Clear Lake shoreline establishes the site boundary to the north and west. The waste rock piles that are the subject of this proposed removal action occupy approximately 1,320 feet of Clear Lake (Oaks Arm) shoreline that is also the western boundary of the mine site. 3. Site characteristics The main characteristics of the estimated 120 acre, inactive, privately owned mine site consists of massive overburden and waste rock piles, tailing piles and an unlined 23 acre impoundment (Herman Impoundment) that contains acidic water (pH=3) to a depth of 90 feet. Figure II-2 roughly distinguishes the relative size and location of these characteristics. The mine site has also significantly contributed to the mercury contamination in approximately five square miles of sediments in the Oaks Arm of Clear Lake. A substantial amount of site background material has been accumulated from over 20 years of data collection by the mine owner and several regulatory agencies and contractors. This is the first proposed removal action at the site. 4. Release or threatened release into the environment of a hazardous substance, or pollutant or contaminant Mercury and arsenic are designated hazardous substances under section 101(14) of CERCLA. The specific statutory sources for these hazardous designations under CERCLA are the Clean Water Act Section 307(a) and the Clean Air Act Section 112. Mercury is also a hazardous substance under RCRA Section 3001. High levels of mercury have been documented in sediment, fish and birds from Clear Lake. Mercury levels are significantly higher in sediments and fish in the Oaks Arm of the lake, which is the arm influenced by discharges from Sulphur Bank Mine. A December, 1986, Regional Water Quality Control Board (RWQCB) report concluded that sediment covering a five square mile area in the Oaks Arm has mercury levels in excess of 20 ppm, which is the state criterion for hazardous waste determination (California Hazardous Waste Control Act, 22 CCR Chapter 30, 1989). Organic mercury in sediments is taken up by aquatic organisms, converted to methylmercury and accumulated to levels that may be harmful to humans when consumed. Levels in edible fish tissue have exceeded maximum limits set by the U.S. Food and Drug Administration (FDA), prompting the issuance of a health advisory (1986) and fish consumption guidelines (1987) by the California Department of Health Services (DHS). The Environmental Resource Engineering department at Humboldt State University (HSU), under contract with RWQCB, completed an, "Abatement and Control Study: Sulphur Bank Mine and Clear Lake, 1/90" for the site, which estimated that various erosional processes affecting the steep, barren shoreline waste rock and overburden piles contribute at least 132 kg of mercury to the surface water and sediments of Clear Lake each year. Slope failure induced by wave undercutting was considered the most significant erosional process transporting mercury and arsenic contaminated sediments from the shoreline piles into Clear Lake. Fluvial transport, sheetwash and associated mass wasting processes had a calculated annual mercury contribution to Clear Lake of less than 10 kg, while groundwater transport was responsible for a negligible amount, estimated to be 0.0001 to 0.02 kg Hg/yr. Mercury levels in the shoreline waste rock and overburden piles have been documented in results from numerous site investigations. Not all of the data have adequate quality assurance because of various discrepancies in sampling and analytical procedures. However, the data overwhelmingly supports the conclusion that the shoreline waste rock piles are the most significant source of total mercury loading to the Oaks Arm of Clear Lake. The HSU report determined the statistical mean value for mercury concentrations in waste rock to be 87 ppm. This determination utilized data collected from three sources, HSU, CVRWQCB and Columbia Geoscience, which had respective mean values for mercury in waste rock of 164 ppm, 65 ppm and 55 ppm. In addition to the above information, EPA's Environmental Services Branch conducted sampling in June 1991. The data generated from this sampling event does have proper quality assurance/quality control and they document mercury levels in the shoreline waste rock piles ranging from 30 ppm to 443 ppm with a mean value of 155 ppm. Arsenic concentrations in the shoreline waste rock piles ranged from 30 ppm to 316 ppm with a mean of 114 ppm. These results are shown in Table 2. 5. NPL status Sulphur Bank Mine was listed on the NPL August 30, 1990. The Remedial Investigation/Feasibility Study (RI/FS) is currently being implemented by EPA and is discussed in detail in the attached RI/FS workplan. 6. Maps, pictures and other graphic representations This section contains referenced Figures 2, 3, II-2, and 10, Tables 2 and V-4 and four photographs showing the current status of the shoreline waste rock piles. These documents were extracted from other reports contained in the Administrative Record for this site. Documents for this section are contained in appendix A. A preliminary Index for the Administrative Record for this Removal Action is also attached (Appendix D). B. State and Local Authorities' Roles and Other Actions to Date Hundreds of fish tissue samples, collected by the California Department of Fish and Game (DFG) during the late 70's and early 80's, were found to contain elevated mercury levels in edible tissue. Growing public and regulatory concern led to the formation of the Clear Lake Mercury Task Force in 1983, which consisted of representatives from the California Department of Health Services (DHS), RWQCB, DFG, Elem Indian Reservation and several other county and local concerns. DHS conducted toxicological studies concerning the elevated mercury levels in Clear Lake fish, summarized in two reports: Methyl Mercury in Clear Lake Fish; Guidelines for Fish Consumption (May 1986) and Methyl Mercury in Northern Coastal Mountain Lakes; Guidelines for Sport Fish Consumption for Clear Lake (April 1987). In May 1986, DHS issued public health advisories recommending restrictions on consumption of Clear Lake fish, which have been incorporated in the California Sport Fishery Regulations for each subsequent year. Until the final NPL listing in August 1990, the Central Valley Regional Water Quality Control Board (RWQCB) was the lead regulatory agency at SBMM. Under the supervision of the RWQCB, Bradley Mining Company's consultant, Columbia Geoscience, has conducted several studies of the SBMM site. In 1985, they completed a preliminary site assessment. Under the Toxic Pits Cleanup Act (TPCA), BMC was required to conduct a hydrogeologic assessment of the contaminants in Herman Impoundment, which was completed in 1987. In December 1989, DHS determined that the bottom sediments of the Herman Impoundment might not be considered a hazardous waste under state law, as long as they remain in place. However, if removed, the sediments would be classified as a State-regulated hazardous waste. DHS indicated that the erosional sediments from the mine tailings might also be classified as a hazardous waste under state law, but more information would be required to be certain. Columbia Geoscience completed Phase I of the Hydrogeological Assessment Report (HAR) in late 1988, addressing the on-site ground water contamination. As a part of this study, several on- site groundwater wells were installed, water samples were collected, and field tests where conducted to determine aquifer characteristics. The HAR study includes an on-going groundwater monitoring program; Columbia Geoscience submitted the Phase II and Phase III reports in 1989 and 1990. Additionally, under a contract with RWQCB, Humboldt State University completed the Abatement and Control Study; Sulphur Bank Mine and Clear Lake in January 1990. The study identified the SBMM as the primary source of mercury contamination of Clear Lake and proposed methods to control further mercury inputs into the lake. Several abatement strategies were proposed to control both the erosion of waste piles and to address the contaminated mine sediments already present in Clear Lake. Following the completion of the Abatement and Control Study, the RWQCB issued Waste Discharge Requirements (WDRs) to BMC in February 1990 to address the erosion of mercury and arsenic contaminated sediments from the mine site. Under the WDRs, BMC was required to submit a plan for implementing erosion control measures. BMC's plan called for construction of a toe buttress and other measures to be implemented over a 5 year period. During September 1991, BMC met with EPA and RWQCB and indicated that they had financial problems that limited their ability to complete the work required by the RWQCB Order No. 90- 045. BMC was given a Notice of Violation by RWQCB on January 7, 1992. The Notice also informed BMC that EPA and DHS were being advised that a removal action may be appropriate to stabilize the shoreline piles at the Sulphur Bank Mine site. Subsequently, in a letter dated January 8, 1992, RWQCB requested that EPA, in consultation and coordination with the Department of Toxic Substances Control of Cal-EPA (DHS), take appropriate removal measures to stabilize the shoreline waste rock piles and prevent additional migration of mercury contaminated sediments into the Oaks Arm of Clear Lake. III. THREATS TO PUBLIC HEALTH OR WELFARE OR THE ENVIRONMENT, AND STATUTORY AND REGULATORY AUTHORITIES A. Threats to Public Health or Welfare or the Environment Aquatic organisms, especially fish, ingest and concentrate enough mercury to render them unsafe for food consumption in places where mercury has been released to the environment. The higher in the food chain an organism, the greater will be the concentration of mercury in its tissues (bio-accumulation). Long term exposure to either organic or inorganic mercury can permanently damage the brain, kidneys, and developing fetuses. The route of exposure and form of mercury to which exposed, determine which health affects are most severe. For example, organic mercury that is eaten in contaminated fish may cause greater harm to the brain and developing fetuses than to the kidney; breathed metallic mercury vapor may cause greater damage to the brain; and inorganic mercury salts that are eaten in food or drunk in water may cause greater harm to kidneys. Short-term exposure to high levels of inorganic and organic mercury will have similar effects, however once the body clears itself of the contamination, full recovery is more likely. Inorganic arsenic has been recognized as a human poison since ancient times, and large doses (above 60 ppm in food or water) can produce death. Ingestion at lower levels causes stomach and intestinal irritation with symptoms such as pain, nausea, vomiting and diarrhea. Other effects from swallowing arsenic include decreased production of red and white blood cells, abnormal heart function, blood-vessel damage, impaired nerve function and an increased risk of cancer in the liver, bladder, kidney, and lung. Long term oral exposure causes darkening of the skin and the appearance of small "corns" or "warts". The U.S. Department of Health and Human Services has determined that arsenic and certain arsenic compounds are known carcinogens. The threat presented by arsenic contamination in the shoreline piles has not been as fully characterized as that of mercury, however the proposed action will also mitigate the potential threat of continued arsenic migration from the shoreline piles into Clear Lake. The OSC has determined that a removal action is necessary because mercury and arsenic contaminated waste rock and overburden piles on the shoreline of the Oaks Arm of Clear Lake pose an unacceptable threat to public health, welfare and the environment. This determination is based on the following criteria, listed in 40 CFR Section 300.415(b)(2): i. Actual or potential exposure to hazardous substances or pollutants or contaminants by nearby populations or the food chain Mercury contamination in fish, birds and sediments from the Oaks Arm of Clear Lake is well documented in site literature. Subsistence fishing, a way of life for the adjacent Elem Indian community, is not uncommon in the local community at large. Fish consumption guidelines have been issued to keep mercury ingestion by humans below levels that are considered a threat to human health; however, it is not known to what extent the guidelines are understood or followed by consumers of fish taken from Clear Lake. The shoreline waste rock piles are considered the most significant source for future and past mercury and arsenic contaminated sediments. iv. High levels of hazardous substances or pollutants or contaminants in soils largely at or near the surface, that may migrate. The mercury contaminated shoreline waste rock piles are estimated to contribute greater than 100 kg of mercury each year to Clear Lake. The arsenic contribution has not been quantified. Two erosional processes impacting the piles and transporting mercury and arsenic contaminated sediments into Clear Lake are identified in site literature. These processes are, 1) slope failures and mass movement of waste materials into the lake associated with undercutting of waste rock slopes by wave action on Clear Lake; and 2) slope-wash erosion from precipitation and concentrated drainage flows that flow over the steep waste rock slopes. The HSU, Abatement and Control Study, 1/90, reported that, "direct field observations during precipitation events has revealed suspended sediment transport in rivulets running down the slope of the shoreline waste rock piles and subsequently forming a turbid plume along the shoreline (Walker 1989). Total mercury levels in samples taken from this turbid plume ranged from 150 to 1600 ug/1 with an average of about 750 ug/1." v. Weather conditions that may cause hazardous substances or pollutants or contaminants to migrate or be released The severity of weather impacting the exposed, unstable shoreline waste rock piles will affect the rate of erosion and transport of material from them. An extreme storm event may result in catastrophic landslides of mercury and arsenic contaminated sediments directly into Clear Lake. 8 vii. The availability of other appropriate federal or state response mechanisms to respond to the release The RWQCB has been unsuccessful in their attempts to Order the PRP stabilize the shoreline piles. Required actions clearly exceed the capacity of the state emergency reserve account. viii. Other situations or factors that may pose threats to public health or welfare or the environment None have been identified at this time. IV. ENDANGERMENT DETERMINATION Actual and threatened releases of hazardous substances from this site, if not addressed by implementing the response action selected in this Action Memorandum, will continue to present an imminent and substantial endangerment to public health, or welfare, or the environment. V. PROPOSED ACTIONS AND ESTIMATED COSTS A. Proposed Actions l. Proposed action description The proposed action consists of erosion control measures that target the stability of the shoreline waste rock piles. These measures are: a slope cut back in conjunction with base stabilization measures to prevent wave impact and create a more stable slope angle of repose; recontouring to control and direct runoff; and revegetation to minimize weather impact on the face of the slope and top surface of the piles. These erosion control measures are discussed in greater detail below. a. slope cut back The proposed slope cut back angle is 40% (2.5H:1V or 20 degrees). The slope will be cut back far enough so that the base of the piles are above the 100 year high water level. The 100 year high water level is 1331 feet; however, if extreme wave height, wave runup and wind surge are accounted for, then the appropriate design high water level is 1336 feet. The existing beach face, which has an approximate slope of 5H:1V (11 degrees), will be extended up to the 1336 foot level then stabilized with rip rap as necessary (some locations are already rip rapped and stabilized from natural processes). This creates a wider beach face to absorb wave energy in addition to the increase in elevation. At the 1336 foot level the 40% grade will be establish and continued to the tops of the piles. The 40% cut back and beach extension results in the on-site relocation of approximately 130,000 cubic yards of waste rock. Rocks from the excavated material that are determined to be suitable for rip rap will be separated and properly cleaned to remove loose soil that may contain mercury, prior to placement on the newly created beach area. Rocks that obviously contain cinnabar ore, as distinguish by a reddish color, will be avoided. This activity is intended to minimize the more expensive alternative of importing rip rap from an offsite location. The excavation activities will be implemented so that no material is allowed to migrate into Clear Lake. If necessary, barriers will be erected along the shoreline to prevent material from falling into the lake, however, the particular excavation methodology will be developed, under OSC oversight, by the contractor selected to conduct the work. The current plan calls for excavated waste rock material to be placed in the existing spillway that cuts through the waste rock piles, connecting Herman Impoundment to Clear Lake. A new drainage path will be constructed so that potential overflow from Herman Impoundment will be redirected around the southern end of the waste rock piles through an existing creek bed. The existing creek bed is pictured in Photo #1 and the approximate location of the new drainage path being proposed is shown in figure 3 (refer to appendix A). Excavated material in excess of that required to fill in the spillway will be placed into the western most section of Herman Impoundment, as shown in Figure 10. Concurrence with "support agencies will be obtained prior to filling in the existing spillway. If filling in the spillway is determined to be inappropriate, then the existing earth dam on the spillway will be refortified and elevated to help compensate for the displace impoundment capacity caused by filling with excavated waste rock. Excess rock may also be used as armor in the spillway to guard against severe erosion in case of the unlikely event of Herman Impoundment overtopping the spillway dam. The total capacity of Herman Impoundment is approximately 1100 acre feet. If all of the 130,000 cubic yards (80.6 acre feet) of excavated material were placed into Herman Impoundment, then the impoundment capacity would be decreased by less than 10%.

10 b. Recontouring A 1 foot berm will be constructed along the top edge of the newly configured piles to direct potential storm runoff back towards Herman impoundment. Existing trenches constructed by the PRP under the oversight of RWQCB will be left in place or reconstructed if disturbed by this action. The tops of the piles will be recontoured as necessary to restore disturb areas, fill in erosion gullies and direct and control runoff. c. Revegetation The newly established slope face, tops of the piles and other disturbed areas will be hydroseeded with native vegetation after all other activities have been completed. Appropriate soil testing will be conducted to determine the suitability of exposed surface material for growing and maintaining a vegetation cover. Nutrients may be added to the hydroseed mixture to compensate for deficiencies in the existing soil. Top soil will be imported if determined to be necessary by the OSC. 2. Contribution to remedial performance The proposed action is consistent with expected and proposed source control alternatives for this site. The partial filling of Herman Impoundment will provide information that may be useful in deciding it's ultimate fate, such as complete filling. This action may reveal additional alternatives for disposal of dredge spoils or waste rock and tailings piles that are associated with other site operable units. If, for some reason in the future, it is decided to remove all the piles, then this action will be a step towards that goal, while the construction of a toe buttress would not. (See discussion of alternatives below.) This action will also provide information regarding successful methods for revegetation, which is an alternative being considered for other areas of the site. It is important to note that there is complete agreement among the agencies and individuals concerned with this site that stabilizing the shoreline waste rock piles is a crucial component of any overall strategy to abate the site problems. The proposed action will accomplish this objective, while keeping all other options available for future cons ideration. The proposed action will mitigate the threat of continued erosion of the shoreline piles from wave impact, slope failure and sheetwash, which are considered the most significant erosional process affecting the piles. Other minor erosional processes, such as fluvial transport may continue at a reduced 11 rate, until the vegetation cover is established. Groundwater threats will not be addressed by this action, however, unlike the toe buttress, this action will not impede future groundwater studies or potential remedies. 3. Description of alternative technologies The HSU report describes a wide range of various alternatives considered. Cost estimates, although quite low by today's standards, do provide a good basis for comparison. These alternatives are summarized in Table V-4 which is presented in appendix A . Another alternative considered was the construction of a toe buttress at the base of the waste rock slopes. Design specifications and plans for the toe buttress were produced by Cornforth Consultants on behalf of BMC, in response to the RWQCB Order. These specifications and plans were found to be of sound design by reviewers from RWQCB, EPA, and EPA contractors. The buttress was to have been constructed over a three year period and did not include cutting back the slope unless deemed appropriate in the future. The toe buttress was designed to prevent wave impact and subsequent slope undercutting, which are also benefits realized from the selected remedy. The toe buttress was considered to be inconsistent with potential long term remedial actions. For instance, if it were necessary to remove or cut back the piles in the future, then the toe buttress would no longer serve a function and would therefore have been a waste of Superfund dollars. The toe buttress could also impede potential sediment removal in the Oaks Arm if that remedy is selected in the ROD. Cost estimates obtained by the PRP ranged from $500,000 to $1.2 million while the OSC estimated $1.7 million for ERGS with the RCMS. The total estimated costs with RCMS including TAT, PST and EPA exceeded $2 million for this alternative. 5. Applicable or Relevant and Appropriate Requirements (ARARs) A detailed discussion and preliminary list of ARARs for the entire site are provided in the attached RI/FS workplan. Potential ARARs determined to be associated specifically with the operable unit that this action applies to are listed below. This removal action is an interim measure to abate an imminent threat and thus does not represent a final decision by EPA on the complete scope of remedial actions needed to meet NCP requirements. The recommended Removal Action will comply with the following potential ARARs to the extent practicable, 12 considering the exigencies of the situation: FEDERAL Archeological and Historic Preservation Act. 16 U.S.C. Section 469 Establishes procedures to preserve historical and archeological data which might be destroyed through alteration of terrain as a result of a Federal construction project or Federally licensed activity or program. National Historic Preservation Act. 16 U.S.C. Section 470 Requires Federal agencies to take into account the effect of a Federally assisted undertaking or licensing on any district, site, building, structure, or object that is included in or eligible for inclusion in the National Register of Historic Places. Fish and Wildlife Coordination Act 16 U.S.C. Sections 661- 666 Requires Federal agencies involved in actions that will result in the control or structural modification of any natural stream or body of water, for any purpose, to take action to protect the fish and wildlife resources which may be affected by the action. Requires consultation with the US Fish and Wildlife Service prior to taking any action. Clean Water Act Section 404. 40 CFR part 230. 33 CFR part 320-330. 40 CFR Part 6. Appendix J Regulations to protect waters of the U.S. and wetlands, as defined by EPA and U.S. Army Corps of Engineers regulations, by prohibiting the discharge of dredged or fill material without a permit, and taking actions to avoid adverse effects, minimize potential harm and preserve and enhance wetlands to the extent possible. Endangered Species Act, 16 U.S.C Section 1531 et. seq Defines and provides a means for conserving various species of fish, wildlife, and plants what may be threatened with extinction, and provides for the designation of critical habitats essential to the conservation of a threatened or endangered species. Requires Federal agencies, in consultation with DOI and the National Marine Fisheries Service, to ensure that actions that they authorize, fund or carry out are not likely to jeopardize the continued existence of threatened or endangered species or adversely modify or destroy their critical habitats. Executive Order on Protection of Wetlands, Exec. Order No. 11990 Requires Federal Agencies to avoid, to the extent possible, the adverse impacts associated with the destruction or loss of wetlands and to avoid support of new construction in 13 wetlands if a practicable alternative exists. Surface Mining Control and Reclamation Act (SMCRA). 30 USC Sections 1201 et. seq.. establishes a regulatory program for surface coal mining operations. Although the SBMM site is not a coal mine, some of the SMCRA requirements may be relevant and appropriate. These regulations set requirements for mine sites to implement sediment control measures to minimize erosion and prevent additional contributions of sediment to stream flow or run-off, and require that measures instituted must attain State or Federal effluent limits. These regulations also require back- filling and regrading of the disturbed area to approximate original contour, minimize erosion, and achieve a stable slope. The disturbed area must also be revegetated with a species native to the area. For sulfide mine sites where there is a release or threatened release of acid, these regulations also set forth requirements to minimize the disturbance of the hydrogeologic balance within the permitted and adjacent area. RCRA Subtitle C (Hazardous Waste Management) RCRA Section 3001 and 40 CFR 261.4(b)(7) exempts certain solid wastes from specific ore and mineral processing operations. Wastes not exempted under the exclusion may be subject to RCRA subtitle C if determined to be a characteristic hazardous waste. Subtitle C regulations provide performance standards for the handling, transportation, storage, and disposal of hazardous wastes. RCRA requirements (either Subtitle D or C) may only be applicable if the wastes are solid wastes and will be actively managed. For the SBMM site, RCRA requirements may be relevant and appropriate, if not applicable. RCRA Subtitle D (State or Regional Solid Waste Plans) Mining wastes that are not regulated under Subtitle C (hazardous wastes) may be subject to Subtitle D requirements. Subtitle D includes requirements for nonhazardous solid waste facilities, such as surface impoundments, waste piles and landfills. The subtitle provides performance standards to be followed for disposal of solid wastes. These requirements address facility development, location, operation, closure, and post-closure maintenance. RCRA Waste Pile Design and Operating Requirements (40 CFR 264 Subpart L) A pile is defined as "any non-containerized accumulation of solid, nonflowing hazardous waste that is used for treatment or storage." Subpart L sets forth requirements for liners, leachate collection and removal, run-off management, groundwater protection (Subpart F), and closure, which may be relevant and appropriate for this site. 14 Rivers and Harbors Act. Section 10 and U.S. Army Corps of Engineers Regulations 33 U.S.C. 403. 33 C.F.R. 320-330 Sets forth regulations governing dredge or fill activities in navigable waters of the United States. Storm Water Discharge Requirements. 55 FR 47990, November 1, 1990 EPA recently promulgated the first of several regulations which will establish a permitting process and discharge regulations for storm water runoff which regulates storm discharges from municipal sewer systems, industrial discharges as well as from mining operations where storm runoff may come into contact with overburden, raw ore material, product or processing waste. Federal Mine Safety and Health Act 30 U.S.C. 801-962; Occupational Safety and Health Act. 29 U.S.C. 667 pertains to worker health and safety.

STATE California Fish And Game Code. Title 14, Chapter 2, Section 5650 States that it is unlawful to deposit in, permit to pass into, or place where it can pass into waters of the State any of the following materials, including: industrial refuse, slag, acid, or any substance or material deleterious to fish, plant life or bird life. California Hazardous Waste Control Act (HWCA). Health and Safety Code Section 25100-25395; 22 CCR Chapter 30 HWCA sets minimum standards for the management of hazardous and extremely hazardous wastes, for generation, transport, treatment, storage and disposal. California Hazardous Waste Criteria. 22 CCR Chapter 30 These regulations set forth State definitions and criteria for identifying hazardous waste. If the waste is determined to be hazardous under these criteria, the management of the waste must meet certain requirements. Porter Cologne Water Quality Act. Water Code 13000 et. seq. The RWQCB is required to develop Basin Management Plans to set enforceable water quality standards for the protection of the beneficial uses of State waters. Additionally, under WC Sections 13050 and 13172, the RWQCB is authorized to develop standards and regulations for the discharge of mining wastes.

15 6. Project schedule The project is expected to commence by the first of May, 1992 and be completed in approximately 60-90 days or by the end of July, 1992. The OSC intends to work 6 days per week, 10-12 hours per day. B. Estimated Costs The initial cost projection scenario, attached at the end of this document, was generated with the Removal Cost Management System. The total estimated cost for this project is $1,255,240.61. VI. EXPECTED CHANGE IN THE SITUATION SHOULD ACTION BE DELAYED OR NOT TAKEN Delaying the action until later in the summer may compromise safety concerns for dust emissions and heat stress. Mobilization in early spring is suggested because the weather and ground conditions can be expected to create a safer working environment. If the action were delayed a year or more, or not taken, the drought may end and Clear Lake would be expected to return to its normal level. The predicted consequences of this are: potential for increased erosion and subsequent mercury migration from the shoreline piles; and reduced beach area at the base of the piles, which impacts the work area and increases the potential of spillage into Clear Lake during excavation activities. VII. OUTSTANDING POLICY ISSUES Funding for this project may be obtained through a $50 million Remedial Action fund operated by EPA headquarters. The OSC is currently pursuing funding from this source. EPA's regional contracting officer is evaluating the appropriateness of a site specific contract for this action. If a site specific contract is selected, then the cost of the proposed action will be less than what is indicated on the provided cost projection. VIII. ENFORCEMENT The confidential, sensitive enforcement information is included in appendix B to this Action Memorandum.

16 IX. RECOMMENDATION This decision document represents the selected removal action for the Sulphur Bank Mercury Mine site, near Clear Lake, Lake County, California, developed in accordance with CERCLA as amended, and not inconsistent with the NCP. This decision is based on the administrative record for the site. Conditions at the site meet the NCP section 300.415(b)(2) criteria for a removal and I recommend your approval of the proposed removal action. The total project ceiling if approved will be $1,255,240.00. Of this, $1,006,818.00 comes from the Regional removal allowance, however the OSC is pursuing obtaining funding through a $50 million Remedial Action fund controlled by headquarters.

Approval Signature Date

Disapproval Signature Date

17 APPENDIX A Maps, Pictures and Other Graphic Representations (referred to in section 6 of the Action Memorandum) SOURCE : Ba»t trom USGS C>««rlik> O«k« and CU«fl«k> HghUndt Quadrangle*

CLEARLAKE. OAK*- GHOUNDWATER SUPPLY WELLS . ..

. CLEARLAKE OA^S WA6TEWATER TREATMENT PLANT

FRESHWATEfl WETLA* WIHOFLOWER POINT WATER DISTRICT SURFACE WATER WTAKE ruH liUnd

HAZARDOUS WASTE1 SITE-BOUNDARY %

and »nvhuftm«nt, Ing.

FIGURE 2 RI/FS RMu

Road

Overburden and Waste Rock

Tailings Undifferentiated Excavated Marenal , Andesite

Figure II-2 Classification and Spatial Distribution of Mine Wastes at Sulphur Bank Mine TABLE 2 Site Numbers, Site Locations, Sample Numbers and As and Hg Analytical Results For the June, 1991 Stratified Grid Surface Soil Sampling at the Sulphur Bank Mercury Mine Site

GRID SAMPLE # SAS As SASHg OTHER ANALYSES SAMPLE #s FOR SURFACE SOILS SITE Hg and As ANALYSIS ANALYSIS PERFORMED OTHER ANALYSES SITE NUMBERS LOCATION ANALYSIS mg/Kg mg/Kg (see data reports) AND COMMENTS SSG-1 tailings - grid #1 6399 Y- 18 238 110 SSG-2 tailings - grid #2 6399Y-19 60.1 145 SSG-3 tailings - grid #3 6399Y-20 93.9 362 TOC, pH, Cl, H2S SBR9-1 SSG-4 tailings - grid #4 6399 Y-21 41.7 72.5 SSG-5 tailings - grid #5 MYG220 29.2 65.1 RAS Metals SSG-6 tailings - grid #6 6399Y-22 48.9 188 TOC, pHt Cl, H2S SBR9-2 SSG-7 tailings - grid #7 6399Y-23 40.2 305 SSG-7D tailings - grid #7 6399Y-24 39.7 291 Duplicate of SSG-7 SSG-8 tailings - grid #8 6399Y-25 40.7 148 SSG-9 tailings - grid #9 6399Y-26 157 272 TOC, pH, Cl, H2S SBR9-3 SSG-10 tailings - grid #10 MYG221 13.6 107 RAS Metals SSG-1 1 tailings - grid #1 1 6399Y-27 7.5 1510 SSG-1 2 tailings - grid #12 6399Y-28 1.8 44.6 TOC, pH, Cl, H2S SBR9-4 SSG-1 3 tailings - grid #13 6399Y-29 35.1 246 SSG-14 tailings - grid #14 6399Y-30 30.2 112 SSG-1 5 tailings - grid #15 MYG222 11.3 744 RAS Metals LAB QC Sample TOC, pH, Cl, H2S SBR9-5 SSG-15D tailings - grid #15 MYG223 10.6 852 RAS Metals Duplicate of SSG-I5 TOC, pH, Cl, H2S SBR9-6 SSG-1 6 waste rock, grid 1 6399 Y-31 175 148 SSG-1 7 waste rock, grid 1 6399Y-32 316 230 SSG-1 8 waste rock, grid 1 6399Y-33 31.8 45.5 TOC, pH, Cl, H2S SBR9-7 SSG-19 waste rock, grid 1 6399Y-34 94.7 30.6 SSG-20 waste rock, grid 2 MYG224 273 125 RAS Metals SSG-2 1 waste rock, grid 2 6399Y-35 120 146 TOC, pH, Cl, H2S SBR9-8 SSG-22 waste rock, grid 2 6399Y-36 98.4 103 SSG-22 waste rock, grid 2 6399Y-37 115 103 Duplicate of SSG-22 SSG-23 waste rock, grid 2 6399Y-38 143 144 SSG-24 waste rock, grid 2 6399Y-39 93.4 270 TOC, pH, Cl, H2S SBR9-9 SSG-25 waste rock, grid 2 MYG225 41.6 83.4 RAS Metals SSG-26 waste rock, grid 2 6399Y-40 30.6 309 SSG-27 waste rock, grid 2 6399Y-41 79.5 116 TOC, pH, Cl, H2S SBR9-10 SSG-27 waste rock, grid 2 6399Y-42 48.6 88.0 TOC, pH, Cl, H2S SBR9-11 Dupe/SSG- SSG-28 waste rock, grid 2 6399Y-43 85.4 122 SSG-29 waste rock, grid 2 6399Y-44 50.9 128 SSG-30 waste rock, grid 3 MYG226 137 443 TOC, pH, Cl, H2S SBR9-12, RAS Metals Photograph #1 Photo by brad Shipley, January 3D, 1992. The southern end of the shoreline waste rock piles. The southern pile is approximately 55 feet high above ground surface. Evidence of slope failure (slump in middle of photo) and gully formation from runoff. Note that the lake is extremely lower than normal due to six years of drought in California. Sulphur Bank Mercury Mine Superfund site, Clear Lake, Lake County, California. "The ravine to the right of the waste rock pile is the existing dry creek bed to which Herman impoundment overflow will be directed." Photograph #2 Photo by Brad Shipley, January 30, 1992. These northern shoreline piles are approximately 70 feet high above ground surface. Sulphur Bank Mercury Mine, Superfund Site, Clear Lake, Lake County, CA. Photograph #3 Photo by Brad Shipley, January 30, 1992. These northern shoreline piles are approximately 70 feet high above ground surface. Sulphur Bank Mercury Mine, Superfund Site, Clear Lake, Lake County, CA. Photograph #4 Photo by Brad Shipley, January 30, 1992. These northern shoreline piles are approximately 70 feet high above ground surface. Sulphur Bank Mercury Mine, Superfund Site, Clear Lake, Lake County, CA. FIGURE 3: Approximate location of proposed new drainage nath from Herman Impoundment to Clear Lake. GAS DISCHAGE AREAS

Approximate location for placement of material excavated from the shoreline waste rock piles

i i* * *° iP *

* Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 10 Table V-4 Cost Estimates for Individual Source Control Strategies

StrateEV Objective^ Cost A. Cut Back Slope eliminate surficial failures & $126,000 to reduce erosion $168,000 B. 1) Revegetate Embankment reduce erosion & stabilize slope $11,000 2) Rcvcgctatc East Face of stabilize slope $5,200 Embankment 3) Revegetate Tributary reduce fluvial transport $25,100 Watersheds 4) Revegetate All Areas $41,300 C. Riprap Shoreline prevent undercutting at toe $130,000 to $290,000 D. 1) Grout Embankment reduce erosion & stabilize slope $209,000 2) Grout East Face of stabilize slope $477,000 Embankment 3) Grout Tributary Watersheds reduce fluvial transport $98.000 4) Grout All Areas $784,000 E. 1) Cap Embankment reduce erosion & stabilize slope $2,320,000 with Soil-Cement 2) Cap East Face of stabilize slope $5,300,000 Embankment with Soil-Cement 3) Cap Tributary Watersheds reduce fluvial transport $1,090,000 with Soil-Cement 4) Cap All Areas $8,710,000 with Soil-Cement F. 1) Cap Embankment reduce erosion & stabilize slope $770,000 with Flexible Geotextile 2) Cap East Face of stabilize slope $1,770,000 Embankment with Flexible Geotextile 3) Cap Tributary Watersheds reduce fluvial transport $360,000 with Flexible Geotextile 4) Cap All Areas $2,900,000 with Flexible Geotextile

Extracted from Humboldt State University's Abatement and Control Study Table V-4 (Continued) Cost Estimates for Individual Source Control Strategies

Stratetrv Objective Cost

G. 1) Cap Embankment reduce erosion & stabilize slope $200,000 with Concrete Blanket 2) Cap East Face of stabilize slope $470,000 Embankment with Concrete Blanket 3) Cap Tributary Watersheds reduce fluvial transport $90,000 with Concrete Blanket 4) Cap All Areas $760,000 with Concrete Blanket H. 1) Cap Embankment reduce erosion & stabilize slope $150,000 with Webbed Geotextile 2) Cap East Face of stabilize slope $350,000 Embankment with Webbed Geotextile 3) Cap Tributary Watersheds reduce fluvial transport $70,000 with Webbed Geotextile 4) Cap All Areas $570,000 with Webbed Geotextile I. Solidify All Wastes (Section A) eliminate erosion $50,000,000 J. Vitrify All Wastes (Section A) eliminate erosion $100,000,000 to $250,000,000 K. Excavate, Transport, and remove material $283,000,000 Dispose of All Wastes (Section A) L. 1) Add Spillway to Dam protect against failure during $3,000 overflow events 2) Armor Spillway Channel protect against severe channel $69,000 erosion during overflow events 3) Both $73,000

Extracted from Humboldt State University's Abatement and Control Study APPENDIX B Enforcement Confidential APPENDIX C Remedial Investigation/Feasibility Study Worfcplan and Site Management Plan Remedial Investigation/Feasibility Study Workplan

Sulphur Bank Mercury Mine Superfund Site

Clearlake, California

Prepared by U.S Environmental Protection Agency, Region 9 75 Hawthorne Street San Francisco, C A 94105

November 1991 WORKPLAN FOR THE EPA REGION 9 IN-HOUSE REMEDIAL INVESTIGATION/FEASIBILITY STUDY (RI/FS)

SULPHUR BANK MERCURY MINE SUPERFUND SITE Clear Lake, California

FINAL November 1991

Prepared by: Carolyn d'Almeida John Lucey Sharon Seidel Stewart Simpson Rich Freitas Vicki Rosen 1

1 TABLE OF CONTENTS CHAPTER PAGE 1.0 Executive Summary 1 1 2.0 Site Background 1 2.1 Site Location, Description & Potential Contaminants 2.2 History of Mine Operations 1 2.3 Regulatory Status: Enforcement and Investigations to Date 1 3 . 0 Site Physical Setting 5 " 3 . 1 Physiography 3 . 2 Climate 8 3 . 3 Regional Geology 3 . 4 Regional Hydrogeology 3 . 5 Site Geology 3 . 6 Site Hydrogeology 3.7 Surface Water 3.7.1 Herman Impoundment 3.7.2 Clear Lake 3.7.3 Springs and Ponds 1 4.0 Site Contamination Characteristics 14 4 . 1 Study Area 4.2 Herman Impoundment Water and Sediments 1 4.3 Site Soils 4.4 Mine Waste Rock and Tailing Piles 4.5 Clear Lake Surface Water and Sediments 4.6 Ground Water 5.0 Conceptual Model of Site Contamination 19 5 . 1 Potential Contamination Sources and Extent of Contamination 5.2 Contaminants of Concern i 5.3 Contamination Migration Pathways 5 . 4 The Methylation Process 5.5 Toxic Effects 5 . 6 Uses of Mercury and Prevalence in the Environment 5.7 Potential Receptors 5.7.1 Surrounding Populations 5.7.2 Ecological Concerns 5 . 8 Conceptual Model 6.0 Preliminary Identification of Remedial Alternatives 31 iMB 6.1 Source Control Alternatives 6.2 Pollution Abatement Alternatives

1 7.0 Data Management Requirements 34 7.1 Identification of Data Needs and Uses 7.2 Data Quality Objectives 8.0 Remedial Investigation 36 8.1 RI/FS Objectives 8.2 Project Planning and Management 8.3 Compilation and Review of Data 8.4 Development of ARARs 8.5 Development of CRP 8.6 Development of QAPjP 8.7 Development of HSP 8.8 Development of FSP 8.9 Field Investigation Activities 8.9.1 Herman Impoundment Operable Unit a. Surface water Geochemistry b. Groundwater Hydrology 8.9.2 Mine Waste Piles Operable Unit a. Sampling of Soil, Mine Waste and Vegetation b. Air Investigation 8.9.3 Lake Sediments Operable Unit a. Water/Sediment Sampling b. Ecological Assessment c. Mercury Geochemical/Bioaccumulation Models 8.10 Sample Analysis and Data Validation 8.11 Data Management and Interpretation

9.0 Risk Assessment: 46 Human Health Evaluation Ecological Assessment 10.0 Feasibility Study 47 10.1 Identification of Alternatives 10.2 Screening of Alternatives 10.3 Treatability Studies 10.4 Detailed Analysis of Alternatives 11.0 Remedial Investigation/Feasibility Study Reports 50 and Deliverables APPENDIX

I. Tentative RI/FS Schedule II. Compliance With Other Laws: Applicable, or Relevant and Appropriate Requirements (ARARs) A. Discussion B. Initial Identification and Screening of ARARs

II. Remedial Investigation A. Community Relations Plan (CRP) B. Quality Assurance Project Plan (QAPjP) C. Health and Safety Plan (HSP) D. Field Sampling Plan (FSP)

III. Risk Assessment Workplan A. Human Health Risk Assessment B. Ecological Assessment SULPHUR BANK MERCURY MINE RI/FS WORKPLAN

1.0 Executive Summary This workplan has been prepared for the In-House Remedial Investigation and Feasibility Study (RI/FS) for the Sulphur Bank Mercury Mine Superfund site located near Clear Lake, in Lake County, California. The objectives of the RI/FS will be to characterize the nature and extent of contamination at the site; identify the contaminants of concern, and their potential migration and exposure pathways; evaluate the adverse effects of actual or threatened releases upon human and ecological receptors; and evaluate the feasibility and cost-effectiveness of potential remedial alternatives in order to select a cleanup remedy. The Sulphur Bank Mine is located on the eastern shore of the Oaks Arm of Clear Lake, within a geothermally precipitated ore body of cinnabar (mercury sulfide) and native sulphur. During past open pit mining activities, waste rock excavated from the mine pit and ore processing wastes were directly disposed in Clear Lake. Erosion from the mine continues to add to the mercury contaminated sediments already present in the lake. Inor- ganic mercury in the lake sediments is biologically converted to methyl mercury, which bioaccumulates in the food chain. Tissue samples collected from fish and some birds indicates that mercury is concentrating in higher trophic level species. Many samples collected from Clear Lake fish contain mercury levels in excess of the U.S. Food and Drug Administration (FDA) guideline. Al- though the State has issued a public health advisory limiting the consumption of Clear Lake fish, the lake still supports an economically important sport and commercial fishery. The RI/FS will be conducted primarily in-house, using EPA personnel and expertise to the maximum extent possible. Work which cannot be readily carried out in-house will be assigned to contractors. RI/FS will be conducted in a phased approach, and will focus on investigating and developing remedial alternatives for three operable units: the mine pit, waste piles and contaminated soils, and contaminated lake sediments.

2.0 Site Background SOURCE : Base from Thomas Bros Maps

FIGURE 1 SITE LOCATION MAP SULFUR BANK MINE i 2.1 Site Location, Description, Potential Contaminants The Sulphur Bank Mercury Mine (SBMM) is located on the eastern shore of the Oaks Arm of Clear Lake, located in Lake County, California (Figures 1 & 2). The surrounding area is largely rural; the community of Clearlake Oaks (population 2,677) lies approximately 1/2 mile across the lake to the north of the mine site,* the larger town of Clear lake (population 15,200) lies approximately 5 miles to the south. The Elem colony of Porno In- dians is located immediately to the north of the site, a group of residential homes are located just south of the mine, along Sul- phur Bank Point. Clear Lake is the oldest and largest fresh water body lying entirely within California, and supports a highly productive commercial and sport fishery. Clear Lake is classified as a highly eutrophic lake, which supports large algal blooms during the summer months. Elevated mercury levels in Clear Lake were first detected in the 1970's by the California Department of Health Services (DHS). Since that time, hundreds of samples from fish and waterfowl tissues and water and sediment samples have been collected near the SBMM site and elsewhere in Clear Lake. The highest mercury levels found in Clear Lake were in the bottom sediments of the Oaks Arm, near the Sulphur Bank Mine. Mercury levels in Clear Lake fish often exceed the U.S. Food and Drug Ad- ministration (FDA) and National Academy of Sciences (NAS) guidelines for human consumption. The highest mercury levels tend to be found in fish caught in the Oaks Arm of the lake. The Sulphur Bank Mine has been identified as the most significant source of mercury contamination entering the Oaks Arm. The Sulphur Bank Mine, inactive since 1957, was one of the largest mercury producers in California and has been considered one of the world's most productive mineral deposits clearly related to hot springs (White & Roberson, 1962). The Sulphur Bank Mine is situated at the intersection of several regional faults and associated shear zones which serve as avenues for upward flow of hot mineralizing water and gas. Prior to mining, the ore body consisted of cinnabar (mercury sulfide, HgS) geothermally precipitated along fault lines, in rocks immediately below the water table. As the gasses produced by the springs rose above the water table the mercury content of the ore decreased, and elemental sulphur was deposited just below and at the ground surface. The mine site consists of approximately 120 acres of tailings and waste rock and an unlined pit (Herman Impoundment) which is filled with acidic water (pH 3) to a depth of up to 90 feet. The mine tailings and waste rock were disposed in the Oaks Arm of SOURCE : Basa from USGS Claarlake Oaks and Claarlak* Highlands Quadrangles

llrfun B.Hh

'«% . CLEARLAKE. OAKS- GROUNDWATER SUPPLY WELLS s;5^^fr^yL •*" TI'» , CLEARLAKE OAKS WASTEWATER TREATMENT PLANT

«» FrtESHWATErt WETLAF WIMDFLOWER POINT WATER DISTRICT SURFACE WATER INTAKE t rutt lilsnd

HAZARDOUS V SITE-BOUNDARY

ecology and envtfurtment, tnq.

FIGURE 2 the Lake along 1,320 feet of shoreline. The Herman Impoundment covers approximately 23 acres and is located 750 feet upgradient from the lake. (Figure 3)

2.2 History of Mine Operations The Sulphur Bank ore deposit was first discovered in 1857 by Dr. John Veatch of the California Borax Company. California Borax Company filed a mining claim on the ore deposit and began removing the sulphur from surface pits in 1865. The sulphur ore was hauled away in rail cars to a refinery where the ore was heated to a liquid state to drive off impurities, then cooled and shipped. Mining operations ceased in 1871 when market prices dropped and increasing cinnabar contamination increased the refining costs. Approximately 1,000 tons of sulphur were produced during this period. In 1872, California Borax Company reopened the mine for the production of mercury ore. The ore was mined from the Herman Shaft which was sunk to the 950 foot elevation (approximately 450 foot depth). The ore was heated with a fluxing agent in a Knox Osborne/Scott furnace to vaporize the mercury, which was drawn off, collected and cooled to a liquid state. Approximately 3200 tons of mercury were produced by California Borax by the time their operations ceased in 1883. sulphur Bank Quicksilver Mining Company resumed mine operations in 1887, sinking two new shafts: the Diamond shaft sunk to elevation 1140 feet, and the Babcock shaft to elevation 1210 feet. Approximately 400 tons of mercury were recovered by the time operations ceased in 1897. Empire Consolidated Mining Company assumed ownership in 1899 and operated until 1906. The three previous shafts caved in; Em- pire Consolidated sank the Empire shaft to the 1110 foot level, and the Parrot shaft to the 1230 foot level, producing about 20 tons of mercury. Underground mining operations ceased in 1905 due to extreme heat and gas. In 1915 to 1918, Sulphur Bank Association of San Francisco resumed mining operations using open pit mining techniques. They replaced the old Knox-Osborne/Scott furnace with a new rotary furnace. 80 tons of mercury were produced during a three year period. Bradley Mining Company began open pit mining at the site in 1927, under a lease from the G.T. Ruddock Estate. They also sunk two new shafts, which caved by 1944. With the introduction of power shovels and blasting techniques, 1200 tons of mercury were produced. Rock

Excavated Mamial Aadcsitt

Source: Humboldt State University - Abatement and Control Study FIGURE 3 SULPHUR BANK MERCURY MINE SITE GEOLOGY I I In 1945, following the end of World War II, Bradley Mining Company ceased operations, allowing the mine pit to fill with I rainwater and run-off, forming Herman Impoundment. Bradley Min- ing Company eventually assumed ownership of the mine and ten years later, in 1955, Bradley Mining Company drained the mine pit and resumed open pit operations, producing 120 tons of mercury during the final production period. Mine operations ceased in 1957, and the mine pit again filled with water, forming the existing Herman Impoundment. An estimated 4400 to 7000 tons of mercury were removed from the site, considering furnace losses and residual left behind in tailings and waste rock. Over 1,250,000 tons of material were estimated to have been removed, processed and disposed during nearly a century of mining activity.

2.3 Regulatory Status: Regulatory Enforcement and Investigations to Date Until the final NPL listing in August 1990, the Central Val- ley Regional Water Quality Control Board (RWQCB) was the lead regulatory agency at SBMM. Bradley Mining Company (BMC), the current property owner, which conducted open pit mining activities at the site during the last two productive periods (1922-1944 and 1955-1957) is the only surviving potentially responsible party identified to date. Hundreds of fish tissue samples were collected by the California Department of Fish and Game (DFG) during the late 70's and early 80's which were found to contain elevated mercury levels in edible tissue. Growing public and regulatory concern led to the formation of the Clear Lake Mercury Task Force in 1983, which consisted of representatives from the California Department of Health Services (DHS), RWQCB, DFG, Elem Indian Reservation and several other county and local concerns. DHS conducted toxicological studies concerning the elevated mercury levels in Clear Lake fish, summarized in two reports: Methyl Mercury in Clear Lake Fish; Guidelines for Fish Consumption (May 1986) and Methyl Mercury in Northern Coastal Mountain Lakes; Guidelines for Sport Fish Consumption for Clear Lake (April 1987). In May 1986, DHS issued public health advisories recommending restrictions on consumption of Clear Lake fish, which have been incorporated in the California Sport Fishery Regula- tions for each subsequent year. Under the supervision of the RWQCB, Bradley Mining Company's consultant, Columbia Geoscience, has conducted several studies of the SBMM site. In 1985, they completed a preliminary site assessment. Under the Toxic Pits Cleanup Act (TPCA), BMC was required to conduct a study of the contaminants in Herman Impound- ment, which was completed in 1987. In December 1989, DHS determined that the bottom sediments of the Herman Impoundment might not be considered a hazardous waste under state law, as long as they remain in place. However, if removed, the sediments would be classified as a State-regulated hazardous Waste. DHS indicated that the erosional sediments from the mine tailings might also be classified as a hazardous waste under state law, but more information would be required to be certain. Columbia Geoscience completed Phase I of the Hvdroaeoloqical Assessment Report (HAR) in late 1988, addressing the on-site ground water contamination. As a part of this study, several on-site groundwater wells were installed, water samples were collected, and field tests were conducted to determine aquifer characteristics. The HAR study includes an on-going groundwater monitoring program; Columbia Geoscience submitted the Phase II and Phase III reports in 1989 and 1990. Additionally, under a contract with the RWQCB, Humboldt State University completed the Abatement and Control Study; Sul- phur Bank Mine and Clear Lake in January 1990. The study identified the SBMM as the primary source of mercury contamination of Clear Lake and proposed methods to control further mercury inputs into the lake. Several abatement strategies were proposed to control both the erosion of waste piles and to address the contaminated mine sediments already present in Clear Lake. Following the completion of the Abatement and Control Study, the RWQCB issued Waste Discharge Requirements (WDRs) to Bradley Mining Company in February 1990 to address the erosion from the mine site. The WDRs did not address the problem of the contaminated lake sediments. Under the WDRs, Bradley Mining Company was required to implement erosion control measures over a 5 year period. In September 1991, Bradley Mining Company notified EPA and RWQCB that they would not be able to complete construction of the buttress to stabilize the shoreline slope of the waste piles due to financial difficulties. EPA intends to use it's emergency response authority to to complete the slope stabilization project in the event that Bradley Mining Company cannot complete the project. Concurrently, EPA will conduct a Remedial Investigation and Feasibility Study to characterize the potential threats posed by the SBMM site upon human health and the environment, and to examine the need for further remedial action.

3.0 Site Physical Setting I

I The Sulphur Bank Mine is located on the eastern shore of the Oaks Arm of Clear Lake, approximately 1.5 miles south of the community of Clearlake Oaks in Lake County, California. The mine is I associated with naturally occurring geothermal hot springs which have deposited various minerals at the site for thousands of years. The following sections present a summary of what is known about the site physical setting and the relationships between the I lake, the geothermal hot springs, and the mine site. I 3.1 Physiography The Sulphur Bank Mine property occupies approximately 203 acres of land adjacent to the shore Clear Lake. The lake is i naturally occurring and lies in a valley formed by a complex structural depression surrounded by mountains. Clear Lake is at a current elevation of about 1320 feet above mean sea level (MSL) i and the surrounding mountains vary in elevation from 2000 to 4600 feet above MSL. The lake is 18 miles long, covers an area of about 68 square miles, and is the largest freshwater lake en- i tirely within California. Clear Lake consists of an approximately circular northern main basin called the Upper Arm with two southern narrow arms, the Lower Arm and the Oaks Arm I (Figure 4). Communities surrounding the Sulphur Bank Mine include clearlake Oaks, residential homes located along Sulphur Bank Point, i and the Elem colony of the Porno Indians adjacent to the Sulphur Bank Mine. Many recreational resorts and communities are located on the shores of Clear Lake. Lake water is used for recreational i water sports, fishing, domestic purposes, and agricultural ir- rigation. Important economic activities in the Clear Lake area include cattle and sheep ranching, fruit orchards, recreational resorts, forestry harvesting, and mining. Clear Lake is ranked as i one of California's most productive sports fisheries, and is the only lake in California to support a commercial fishery.

3.2 Climate The climate and vegetation of the Clear Lake area is typical of Mediterranean climates. Moderate to heavy annual precipitation can locally exceed 100 inches in the mountains and can be as low as 20 inches in the Clear Lake basin. The mean annual precipitation at the Sulphur Bank Mine is estimated to be 24 inches, with 80% of the rain falling between the months of Novem- ber and March. Snow is common in the mountains above the 3,000 foot elevation. The mean annual lake evaporation is estimated to be 48 inches. Mean monthly precipitation usually exceeds mean monthly evaporation from November through February. Mean annual Source: Humboldt State University - Abatement and Control Study FIGURE 4 MAJOR SECTIONS OF CLEAR LAKE temperatures for the Clear Lake area are about 60 degrees Fah- renheit, with summer temperatures ranging above 100 degrees Fah- renheit and winter temperatures below freezing. Vegetation patterns are affected by climate, elevation, and soil type. Grassland, scrub oak, stands of cypress, manzanita, and other chaparral-type plants are distributed between the lowlands and moderately high ridges. Evergreen conifers and some deciduous plants, such as dogwood, are most common in the higher elevations and often are specific to soils developed on certain rock types, such as serpentine and rhyolite. Prevailing winds are from a northwesterly direction. Air pollution is not a common problem at the site.

3.3 Regional Geology The Clear Lake Area is located in the northern portion of the Coast Range geomorphic province. Clear Lake is approximately 60 miles east of the San Andreas Fault at the margin of the Pacific and North American Plates. The Coast Range is predominated by north west-trending faults and shear zones related to right-lateral stress of the San Andreas Fault system. Clear Lake is generally fault bounded and situated in a subsiding structurally controlled depression. The structure in the Clear Lake area is interpreted as a local development of the overall structural pattern of the San Andreas Fault system, overprinted by local deformations related to active volcanism. The subsiding Clear Lake basin is thought to be an extension of a graben structure related to movements along the San Andreas Fault system. The late Cenozoic history of Clear Lake is characterized by faulting and volcanic activity. Bedrock in the Clear Lake basin consists of the structurally broken and complex group of rocks known as the Franciscan Forma- tion. These rocks were formed approximately 65 million years ago during the Cretaceous time period when the sea floor in the Pacific Ocean was subducted beneath the North American continen- tal plate. Sediment and rock scraped from the top of the descen- ding Pacific plate, accumulated along the margin of the upper North American plate, and formed the Franciscan Formation. The Geysers-Clear Lake area has many occurrences of. geothermal activity believed to be related to a shallow magma source defined by geophysical evidence. The shallow magma chamber in this area is also thought to be related to the subduction of the Pacific plate beneath the North American Plate. The shallow magma chamber is located within and below the Franciscan Formation which acts as a cap rock to contain the magma. Geothermal activity is evidenced in the surface geology where the Franciscan Formation is thin or fractured and the magma chamber protrudes near the T«iMy «nd youngv fMttw and vtw rods o( *• Grart V«toy Uppv pUH o< *w COM fbngt *MI m SULPHUR txh wd youifv rada BANK tuhduc»ri Mora 3.0 m.y. «0>

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Source: McLaughlin, USGS Professional Paper 1141 (1981) FIGURE 5 MAJOR CRUSTAL FEATURES OF NORTHERN CALIFORNIA AND THEIR RELATION TO EMPLACEMENT OF MAGMA BENEATH THE GYESERS-CLEAR LAKE AREA surface. Commercial geothermal power plants are currently operating near Cobb Mountain and the Geysers steam field located about 15 miles southwest of Clear Lake.

3.4 Regional Hydrogeology There is relatively little background information available on the regional hydrogeology of the Clear Lake area, and the site hydrogeology has not been fully characterized. The regional ground water flow system primarily consists of relatively shallow ground water aquifers which flow down from the surrounding mountains into Clear Lake. It is believed that there is little ground water seepage lost from Clear Lake because the entire lake area is underlain by the impermeable, non-water bearing, Francis- can Formation. The regional ground water flow direction in the vicinity of the site is believed to be towards the North from the steep mountains towards Clear Lake. The U.S. Geological Survey has mapped numerous hot springs and associated faults throughout the Clear Lake area; many of them discharge directly into the lake. (See Figure 6)

3.5 Site Geology The geology of the Sulphur Bank Mine has been well documented in published literature. In general, the Herman Impound- ment area is the center of a pipeline zone of hydrothermal alteration where three faults and shear zones intersect. Geother- mal fluids moving upward along the faults altered the existing rock units and deposited various minerals. The original appearance of the deposit was described by Veatch who discovered it in 1856. The "hill of white powder" consisted of altered lava impregnated with abundant native sulphur. Hot vapors and sul- furous fumes escaped from cracks and fissures, and small springs rich in boric acid emerged from the south base of the hill. Prior to the first mining activity in 1856, the Sulphur Bank area consisted of hot springs and gas vents surrounded by thick deposits of native sulphur in a nearly pure form. As mining activities proceeded deeper and the water table was approached, the sulphur decreased and cinnabar became abundant. The principal ore bodies were at or below the water table and consisted of cinnabar, marcasite, pyrite, dolomite, calcite, quartz, metacin- nabar, and stibnite. There are four major rock types present at the site. The oldest rocks are metamorphic sandstones and shales of the Fran- ciscan Formation of late Mesozoic age. These are overlain uncon- formably by lake sediments and landslide debris of late Pleis- 8 Sulphur Bank Mine

Adapted from USGS Map MF-271, Sims & Rymer 1976 FIGURE 6 APPROXIMATE LOCATIONS OF GASEOUS SPRINGS AND ASSOCIATED FAULTS IN CLEAR LAKE tocene age. These rocks are overlain by an augite andesite lava flow, estimated to be less than 45,000 years old. The andesite flow is overlain locally by sands and gravels but the age and origin of these sediments are uncertain. Native soils at the site are thin, usually less than 30 centimeters, acidic, and generally derived by residual weathering of natural rock and mine waste rock. The four major rock types are described below: Franciscan Formation - In the Sulphur Bank area the Franciscan Formation is composed of contorted beds of graywacke and black shale with local chert-bearing zones. Evidence of low-grade metamorphism is present throughout the formation. In the eastern portion of the mine area and where the formation crops out at the surface in the western part of the mine, kaolinite/halloysite and hydrous sulfate alteration of the Franciscan rocks is observed. These white zones of alteration are often associated with the smell of sulphur-bearing gas and no vegetation is growing on these rocks. Lake Sediments and Landslide Debris - This grouping of sediments generally consists of two major units. The uppermost unit is a poorly bedded conglomerate and breccia, with many lenses of cross-bedded sandstone and other beds that are dominated by silt and sand. The conglomerates and breccias consist of blocks of sandstone and shale derived from the Franciscan Formation, in a shaly or sandy matrix. The angularity of these fragments sug- gests a landslide origin for these sediments. Underlying the coarser sediments is a thick section of blue-gray lake sediments consisting mainly of clay with minor silt and sand. Drilling near the site encountered about 60 feet of blue-gray clay. The entire grouping of lake sediments and landslide debris is as much as 200 feet thick in the south-central portion of the mine area. Augite Andesite Lava Flow - An augite andesite lava flow overlies the lake sediments. It mantles the area of about one square mile above lake level and averages close to 100 feet in thickness. The fresh lava is dark gray with irregular vesicles that are commonly more abundant in the upper part. The upper bleached zone is generally glaringly white without prominent megascopic structure. In places it is in sharp contact with the underlying boulder zone, but elsewhere the contact is gradational through a few feet. The bleached zone consists predominantly of opalized andesite, best explained as a product of attack by sulfuric acid, and corresponding to the near surface zone of bleaching in the older rocks. Post Andesite Sediments - The Andesite flow is overlain by sands and gravels of possible lacustrine origin as much as 50 feet above the lake level. Two small patches of coarse clastic sedi- Contact (Oatlw* wtitr* inftrrN)

Hot Andt*H« Flow (Variably altirid) Allltud* Herman Sorinc g s 111 1 1400' Shodn rVen.u*-t»^7t T^«*»: «•:•:•:•••••.•.•.•.'•JM .*. .* 4—fe2S^:t*i&l^ ti Prt-ondttUt FORMATION / »tdlm«nl»

Projtcttd outlinis of prtttnt pit ond oppro»imot« -—T— of H«rtnr| ShOft

200 40OFttt

Source: White & Roberson, 1962 FIGURE 7 GEOLOGIC MAP AND SECTION A - A% SULPHUR BANK MERCURY MINE I I ments as much as 75 feet above lake level were also described as lacustrine deposits. The origin and age of these rocks is uncer- I tain and has been debated. The mineral deposit at the the Sulphur Bank Mine is situated at the intersection of three sets of regional faults and shear I zones which serve as conduits for upward flow from depth of hot mineralized water and gas. Three sets of faults intersect at the mine: 1) The northwest trending fault associated with the ore body and soil mercury anomalies; 2) A set of two steeply dipping, I northwest trending faults exposed in the mine workings; and 3) the fault or shear zone delineated by as east-west line of gas leakage. The faulting and the associated discharge of mineral I bearing geothermal fluids which formed the ore deposit postdates the augite andesite lava flow. i The hydrothermal alteration and mineralogy of the ore and gangue are controlled to a major extent by the water table. The upper part of the augite andesite flow probably has always been above the water table and is extensively leached by sulfuric acid i formed by oxidation of hydrogen sulf ide in the hydrothermal fluid. Waters deep in the system appear to be neutral, but near the water table they become acidic because of mixing with super- i gene nonmeteoric waters containing sulfuric acid. Native sulphur was deposited at the surface down to the water table. The main ore deposit was restricted to depths near or below the inferred i position of the water table prior to mining. Rich ore bodies were found as veins and disseminated masses in the lower part of the andesite and in the lake and landslide deposits immediately below the contact. Some commercial grade ore was deposited in i the Franciscan Formation but in decreasing concentrations with depth . i The original location of geothermal springs and gas vents on the site have been altered or covered up by mining activities. It is likely that mining operations have altered the hydrothermal f system which previously existed at the site. i 3.6 Site Hydrogeology The major aquifer at the site is located -within the lake sediments and landslide debris deposit of late Pleistocene age. i The occurrence of ground water at the site generally corresponds with the contact between the lake sediments and landslide debris deposit and the overlying augite andesite flow. The occurrence of ground water in the augite andesite flow and the interconnec- i tion between the aquifer and Clear Lake is unknown. The shallow aquifer is unconf ined to semiconfined and is first encountered at depths of less than 1 foot near the shore of Clear Lake to 80 feet below the ground surface further away from the lake. The 10 shallow aquifer includes fractured rock of low permeability and lake sediments of moderate permeability consisting of silt, sand, a gravel alluvial deposits with thin clay layers. Wells screened in the aquifer generally have a low yield which may be attributed to a low hydraulic conductivity and because the aquifer averages only 75 to 100 feet in thickness. The permeability of specific layers in the alluvial deposits is highly variable and the extent to which individual layers are interconnected is unknown. It is also likely that ground water exists within the waste rock stock piles. The unsaturated zone at the site has not been characterized. Also, the elevation of the ground water at the site has been altered by mining activity and the existence of Herman Im- poundment . The presence of Herman Impoundment clearly alters the direction of regional ground water flow and most likely creates a ground water mound anomaly. Previous investigations have shown that ground water flows from the higher elevation Herman Impound- ment to the lower elevation Clear Lake. This flow direction is confirmed by ground water surface elevations and pH gradients, measured in three monitoring wells between Herman Impoundment and Clear Lake. Other monitoring wells have been drilled at the site, but their present conditions are unknown. The ground water flow characteristics on the north, south, and east sides of Her- man Impoundment are unknown. Local geothermal waters flow upward from depth along fault zones and are responsible for the formation of the Sulphur Bank Mine deposit. The hot geothermal waters have a unique metamorphic origin and generally follow a fault zone located at the bottom of Herman Impoundment, where previous mining activities and mineral deposits were concentrated. The shallow water table caused problems during early mining operations and has been altered by the formation of Herman Impoundment. The temperature and water chemistry of the shallow aquifer varies considerably over the site. Water temperatures as high as 400 degrees Farenheight have been measured at the site during previous geothermal investigations.

3.7 Surface Water The two major surface water features related to the site are Herman Impoundment and the Oaks Arm of Clear Lake. Some small seasonal ponds and springs are located in and around the mine site. Regional surface water drainage flows to the Herman Im- poundment and the Oaks Arm of Clear Lake; the majority of surface run-off at the mine site drains into Herman Impoundment. The water level in Herman Impoundment is several feet higher than lake level; potential overflow from Herman Impoundment would drain to Clear Lake. An earthen dam was constructed on the west 11 I

I end of Herman Impoundment to control drainage into Clear Lake. Three small drainage areas and the surfaces of steeply sloped tailings piles at the lake shore drain directly into Clear Lake. I Parts of these tailings piles extend into the lake and are exposed to erosion from wave action. i 3.7.1 Herman Impoundment Herman Impoundment is an unlined man-made excavation which i cuts through all four geologic rock units at the site, including the Franciscan Formation. Herman Impoundment is a highly unique acidic water body containing elevated trace metals and standard i mineral constituents. The unique geochemical character of the sediment and waters of Herman Impoundment is the result of a combination of diverse sources. These sources include discharge of natural geothermal fluids and gases, erosion of sediment from i waste rock and tailings, discharge of meteoric waters in contact with waste rock and tailings, and chemical reactions with the impoundment water and the pit wall-rock. An analysis of the gasses i issuing from a vent near the north shore of the pit reported 93.33% carbon dioxide, 5.46% methane and 0.13% (1300 ppm) hydrogen sulfide. The water in the pit contains dilute sulfuric i acid and has a pH of approximately 3.0. The acid is believed to be derived from oxidation of geothermal hydrogen sulfide gas venting into the bottom of the pit and mixing with impounded i water. The pit is approximately 90 feet deep and has a surface area of about 23 acres. The pit volume is approximately 700 acre i feet. Herman Impoundment is located 750 feet east of Clear Lake. The earthen dam was constructed in 1979 at the west end of the pit to provide sufficient freeboard to withstand overflow from a i 200-year flood event. Prior to construction of the dam, water from Herman Impoundment would overflow into Clear Lake seasonally and during large magnitude storm events. i Even though no perennial streams exist near Herman Impound- ment, there is an area immediately surrounding the pit that con- tributes surface water run-off during storm events. This area is i estimated to have a drainage area of approximately 88 acres, not including the surface water area of the pit, which varies from 21 i to 23 acres. Herman Impoundment is regulated under the Toxic Pits Cleanup Act (TPCA) due to hazardous levels of mercury found in the sediments. The Central Valley RWQCB maintains that the hazardous i materials found in Herman Impoundment, derived principally from mining activities, represent culturally disturbed or altered substances, and are therefore subject to state hazardous waste i management laws. i 12 i 3.7.2 Clear Lake Clear Lake is 18 miles long, and covers an area of about 68 square miles. Clear Lake consists of an approximately circular northern main basin called the Upper Arm, and two southern narrow arms, the Lower Arm and the Oaks Arm (Figure 4). The average depth of the Upper Arm is 7.1 meters, the Lower Arm is up to 10.3 meters deep, and the deepest part of the lake is the Oaks Arm with an average depth of 11.1 meters. Previous exploration drilling investigations performed by the USGS have recorded over 350 feet of accumulated sediments in the bottom of Clear Lake. The Clear Lake drainage basin covers an approximate area of 528 square miles (Figure 8). The main tributaries into the lake consist of seven creeks, all of which enter the northern Upper Arm. The lake drains from the south at Cache Creek on the Lower Arm. The level of lake water is controlled by a dam at Cache Creek; the lake is at a current elevation of about 1320 above MSL. Clear Lake is classified as a highly eutrophic lake and supports seasonal algae blooms of both blue-greens and dinoflagel- lates. Considerable nutrient concentrations, related principally to run-off from the drainage basin, sustain high levels of algae growth. Studies have also been performed which indicate that waste water treatment facilities at Clearlake Oaks and other communities are adversely impacting lake water quality. The algae blooms often appear to be concentrated in the Lower Arm and the Oaks Arm, which may be attributed to prevailing northwesterly winds that blow the algae blooms to the south and east ends of the lake. Seasonal water temperatures range between 6 and 27 degrees Celsius. The pH is of the lake water is basic and ranges from 7.5 to 9.0. Thermal stratification exists only weakly and intermittently for periods of up to a week during the summer. Bottom sediments may remain anoxic in the deepest locations during the summer and the fall. The shallow lake is generally turbid because surface and bottom waters are rapidly mixed by wind induced circulation. Three separate sub-basin drainage areas with a total surface area of 14 acres drain from the mine site directly into Clear Lake. Steeply sloped piles of wastes from mining operations are located adjacent to the lake shoreline and extend into the lake. The waste piles are in contact with about 2060 feet of shoreline, and run-off from these piles also drains into Clear Lake. Large storms are capable of producing strong wave activity on the lake which results in erosion at the base of the waste piles.

13 C*ch«Cr

Source: Humboldt State University, Abatement & Control Study 1990

FIGURE 8 CLEAR LAKE WATERSHED 3.7.3 Springs and Ponds Submerged springs have been mapped throughout the entire Clear Lake region (Figure 6). Several small seasonal springs and ponds are located in and around the mine site. The exact number and location of all the springs and ponds is unknown but several have been identified. fHvdroaeoloaical Assessment Report fHAR). coT.ujmi?j a Geoscience). The Green Pond is located within the tailings piles and is extremely acidic with a pH of 2.27. This pond acts as a retention basin for run-off from a portion of the surrounding steeply sloped drainage area. The temperature of naturally occurring springs in the vicinity of the site is variable, and associated with gas venting. The original mineral deposit at the mine was formed by thermal springs flowing upward along the faults. These springs are reported to still be actively discharging into the bottom of Herman Impoundment. Thermal springs have previously been reported at the mine site and near the lake shore but they have apparently been disrupted by mining operations or covered by tailings. It is likely that mining operations have altered the hydrothermal system that previously existed at the site.

4.0 Site Contamination Characteristics This initial evaluation of contamination at the site is based on a preliminary review of existing data concerning the site. Data limitations of the existing data will be identified and further investigated in order to completely characterize site contamination. This evaluation includes a description of the study area and contaminants at the mine site and in Clear Lake.

4.1 Study Area The SBMM site and surrounding areas which may be affected by site contamination are the primary focus of RI/FS activities discussed in this work plan. The SBMM property occupies approximately 203 acres of land. The study area consists of Herman Impoundment and the SBMM property, and surrounding areas which include but are not limited to, drainage areas contributing surface water run-off to the site, surface soils down-wind from mine smelting operations, the Oaks Arm of Clear Lake, the Elem Indian Colony located adjacent to the site, the community of Clearlake Oaks and other nearby residential areas. During the course of the investigation other areas may be discovered which need to be included in the study.

14 4.2 Herman Impoundment Water and Sediments The major surface water feature located on the mine site is Herman Impoundment. The contamination in the Herman Impoundment has been characterized in the Herman Lake TPCA Assessment report, completed by Columbia Geoscience in 1987, under contract with the Bradley Mining Company in compliance with the requirements of the California Toxic Pits Classification Act (TPCA). The purpose of the study was to characterize the chemistry of the water and bottom sediments of the mine pit to determine if it fell within the State definition of a toxic site. The field investigation was conducted in early November, 1987. Prior to sampling, a bathymetric survey of the mine pit was conducted using a recording fathometer along several straight-line transects. The bathymetric survey revealed a maximum bottom depth of 90 feet. Gas discharges were observed and recorded in several locations within the impoundment. (Figures 9 - 13) . Surface water temperature, pH, specific conductivity, and dissolved oxygen readings were taken from several near-shore locations. Pit sediments, thermal springs and ground water samples were collected within and adjacent to the Herman Impound- ment and analyzed for metals and selected anions. The results are tabulated in Tables 1 & 2. The TPCA report concluded that the water and bottom sediments of Herman Impoundment were below the toxic limits for all title 22 categories of the Toxic Pits Cleanup Act, except for mercury, which ranged from 9-46 mg/kg and averaged 26.33 mg/kg. (TPCA limit - 20 mg/kg). Bottom sediments were found to be up to 27 feet thick in some areas, have an estimated volume of 5,990,000 cubic feet, and contain an estimated 7.74 tons of mercury. Columbia Geoscience noted that the mercury concentrations observed in the pit sediments were much lower that the mercury levels observed in sediment cores taken from the Oaks Arm of Clear Lake, and elevated mercury levels occur naturally throughout the region. The major source of mercury in the pit sediments is likely associated with detrital accumulation from site surface water run-off. Less significant contributions may be attributed to pit wallrock-water reactions and precipitation from geothermal fluids entering the bottom of the pit. The water in Herman Impoundment is very acidic with a pH of about 3.0. The source of impoundment water is mostly from in- filtrating ground water and surface run-off. Pit water also contains high concentrations of sulfate, sodium, chloride, boron, and ammonia. Two filtered samples of pit water had 1.3 and 0.75 ug/1 of mercury which exceed the EPA No-Adverse-Response Level (SNARL) of 0.144 ug/1 and the EPA ambient Water Quality Standard 15 BATHYMETRY OF HERMAN LAKE, CALIFORNIA

STATISTICS LAKE VOLUHC )me»«*.«« cvfcic «««t (72*.l «CI«-t«ttl uucc ratrkcc me* »i4m.7» •«••(« *««t- CSO.t* •«•»( laztmiH DcroiCO 91.t s««t MBUI DCPTN J4.74 l««t MTCbWKtKT Of VOLUME . . . 1.1» RTLATITK DEPTH «.U f««t •MMU.tMt UMOTN «!«.« («tt 11.1« Btlct) •NOU.SMr MTKLOMCMT . . . l.tO

lUKil tsaM*et* « 4 .ft

• ItACLIV MIHIMO MIT B«Mh C*«t««r latcrval It P««t

Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 9 GAS DISCHAGE AREAS

Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 10 FATHOMETER RECORDS USED IN PREPARING HERMAN LAKE BATHYMETRY

o 10 to *0 I40 o«I"o 70 •0 •0

o 10 to so 40

IB«"0 .TO- •0- • •o.

Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 11 I f~\ I I « S-/ » VI I— II— » * • » «— I » IN PREPARING HERMAN LAKE BATHYMETRY

O 10 to 90 40 •0 •0 70 •0 •0 f . i

Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 12 FATHOMETER RECORDS USED IN PREPARING HERMAN LAKE BATHYMETRY 9._. 10 o 10- to so- 4O SO. S0> 70- SO- SO-

10 11

to SO !40 • SO' tso<

so so

Source: Herman Lake TPCA Assessment, Columbia Geoscience, 1987 FIGURE 13 T««» -I Qwrislry of w*Ur, MdM*. Ihenwl springs and ground-ttttr within wd adjacent In Henwn Lake. Sulphur Bank tertury Kvne. CW lake. California—1938 la KB7. (fepukktked lio* TPCA Asitiimtal Rtporl, Celt*** GwncMjM*, I9S7I.

So. Card. Ibtor in mlliaraK/liter. cores to •illiar«(A9 «*t wl Usis HUUtHWl IW S*f>W Sa*>k lab OtfrthTin, FteW U. FkW U. m Al Si02 B Ct Fe W* Li Hj Hi K h SM S2- Cl Ir MtMl HOQB u Inscription CM* 1 (•) (C) (urfu/a.) pH pH toUl W/CII/C1 K/ta Ll/fc L1/C1 \ n Proflk (ifcUr) MM. 1. 87 Z 9 19.7 (620 5600 102 2.6 .8< 110 33 270 189 «- 47 2.2 140 13 U 520 2800 a 13 320 1.7 HO 0 0.005 O.M3 0.026 0.004 0.006 2 17 Prafll* (UiUr) Nw. 87 1 23 JO. 3 65« 5600 3.03 2.6 !1.2 1W 3? 280 180 4k 48 2.2 MO 1? tt 530 270) 0.12 2» .7 WO 0 O.OOS 1.037 0.028 0.004 aOOB 3 W Proflk (U.Ur) MM. 87 3 13 20.0 6600 6600 - 2.6 4.7 1W 31 270 IBO «. 47 2.2 140 12 14 510 2900 0.12 310 .7 WO 0 0.006 0,870 0.0?7 0.004 0.007 4 P3 Ptottb («§t») MM. 87 . 4 26 20.0 6600 MOO - 2.6 !kO 1)0 31 280 180 4S 46 2.2 140 12 14 520 2900 0.13 310 .7 180 0 0.005 0.903 0.026 a004 0.007 S N Praftk (tbUr) MM. 87 S 4 20.0 6600 5600 - 2.6 !1.7 IW 32 260 170 44 47 2.2 140 12 14 490 2800 a 12 380 .8 WO 0 0.004 0.6M a028 0.004 0.005 6 P4 Profik OfcUr) MM. 87 6 24 20.0 6600 5600 - 2.6 !1.2 93 32 250 ISO » 46 1.9 120 11 12 480 2900 0.12 290 .6 180 0 aoos 0.862 ao» 0.003 aoos 7 K ftnoflk GhUr) MM. 1, 87 7 5 20.0 6650 5600 - 2.5 <.9 IW 31 270 1» 4» 46 2.2 140 12 14 SDO 2800 Osl2 290 .6 MO 0 0.005 0.931 a028 0.004 0.007

IMP (IMcr) Hg. 19.87 Cl. 6 - 110 - 270 180 - 47 2.1 ISO 12 15 490 - - - - - 0.835 0.030 0.034 a03S •9 \HP (UiUr) A*. W.87 W . 6 - - SM> - 2.8 - 49.9 253 159 31.2 - - 138 - - 40B 3374 - 323 - - ~0 0,783 10 K-H> QbUr) Aug. I9.B7 C2 6 - IW - 270 180 - 46 2.1 140 12 15 490 0.0300,004 0,062 11 *-W (UiUr) Aug. 19.87 tt 6 - - TOT - 2.4 - 52.044.2 373 333.6 - - W6 - - 172 »50 - 39.7 - - ~0 0.215 12 town Ptt (171) Am 27.X PI 6 21.0 - - 3,5 2.39 - - - 395 210 -86X71951921.68BD4430-205MI- 1.926 aoM 0.004 aow

13 K l"roHk (Caw) MM. . 87 11 23 «top 30 <• - - - - WOOD 2700 930 480 350DO 45 11.0 330 18M)64031001.00330M>190~ 2.818 0.017 0.033 M K Prtflk (Cora) MM. , 87 12 23 20 ai - - - - 31001400 230 190 44000 210 4.6 570 39 1200 380 4900 0.71 140 M) 140 .642X1570.012 0.032 18 M Profile (Cora) MM. .87 16 25 <»rid 20 at - - - - 3400 1900 200 180 44000 140 4.7 740 48 790 300 3500 0.91 IW M) 150 ~ .8182.6330.015 0.042 W M Praftk (Cora) MM. ,87 17 25

20 K Frank (Cora 1) MM. . 87 18 5 «tap 20 a* - - - - 36001500 180 220 SOOOti 0.61 4.8 730 53 3600 590 1800 1.2 110 H> 110 .636 6.101 0.008 a043 ?1 K Praflk (Cora 2) MM. . 87 19 5

23 9H Kelt MOMer) MM. 2, 87 f 15 - - 8100 - 6.4 - M) 33 15 490 U0.87 0.18 210 1.2 241100 1.3 a 13 2100 1.5 1.11800 7E-4M a037 a021 2C-04 9W6 24 SEN fell bMl(UaUr) JIM. 1964 - 497 160 - - - 6.05 - -5002 ---

27 S-f QhUr) Aug. 19.87 Q 6 ------660 - 47 560 - 570 0.47 200 13 M) 170 - - - - - ~0 0.002 28 S-f> (M«Ur) Aug. W.87 U3 6 - - 5930 2.8 - - 49 234 160 14.0 - - 139 - - 401 2960 - 285 - - 0 a821

29 Ihml Spring Mr. 26.57 - G 77 - TOO 7.5 - 72 660 7 - - 4.8 22 - 33 1WO 454 - 690 1.4 476 2960 0.0X0.956 0.03 aoo4 aoos 30 DiMwl Sfrti9-SM raotnaU g - 6 69.5 - - 6.8 I -0,14262020 - 0.1 - 55 0.2 23 1190 598 - 644 - 464 3290 a96? aoi9

ttaCIKKLWR; WTft»» 1 |M 0.05 6.05 0.1 0.1 0.0*. 0.05 6.0* 0.1 0.OS 50.25 0.3 6.65 » 1 to I (1987 /g»)y»s) 5£D!KMIS»» 5 5.00 2 W 5 0.05 2 W 0.5 500 ' 5 30 0.5 30 20 UO -

aobwUs: »- Sw Ubk 2 tor tdJitianil tract wUls. ml werell. for SUC (etchdik KUU «d 19R7 U reports K*IFOSMA MM.Y1IO1 UBORATORY) b- Amlysis ref. no's B to ]1.22.27.«d 28. s^plwd by UlifooiU teg. Utter (Xulity Control Puinh note wwvnt l*b mxr In 17 (B I Cl). c- Antlysts raf. no 12 by US. Gnlogic*! Survey and repurtcd by Thx|. 26 frm duMind drill rule Mttrr sm>ly (<««ct location U*n»*i) reported by Uiitt (1957). f- Analysis raf. no. 28 by U.S. Geological Survey (lk» 1985. Table 19). exact localKO not (irmukil. 9- Analysis raf.no 30 by US, Geological Survey (Uiite. 1957). exact location and (tab- nil |»uvKktl TeMt t Cwrtstrj of tejUr, Mdtant, tmnwl sprigs and gnanUrter within and adjacent to town Lake. Sulphur Bar* rareury Him. Ckar UU, California—1938 to 1987. lr«« TWA AtmuMaJ Htful, €•»*•**«• Kamcwuce, li«7|.

Utter in enlllgnw/llter; arcs hi irilllgraKAg «et «t basis «r. Sa*>k Saq>k Mh lab AtSbBafc CdCrCr*CoCuPb Mj fc Ni Se Ag In V* Z» W OMcrtpUM OeU M |

T K Praflk Qbur] MM. t. B 9 } ~M> ti anooaooGBaoo53 aoo6 w a?> 0.030 to aooaps to am M) M) Nb M) O.U 2 P2 Prvflk (U>Ur MM. 1, 87 a t Ml tO 0,01600,0068 M) 0.034 MX 0,27 0,034 M) 0.00)90 W 0.58 W M> Ml tO a90 3 P3 Praflk Otter MM. 1. 87 13 3 M> K) aOOSe 0.0057 0,0082 0.035 W a 27 ao?9 Mi O.OQOPS to ato w MI to to a si 4 P3 Praflk (Utter MM. 1. 87 26 4 in M) aoo95aoo56 m ao3s m 0,27 0.030 M> aontt w a 58 M) M) M) M) a82 S M Praflk (tbur MM. 1, 87 4 S W N> 0.0130 0.0066 W 0.033 MX 0.26 0.028 M) aOUOPS M) 0.59 to » to M) am 6 N Prank Otter MM. 1. 87 a i MI MI aoon 0.000 » 0.030 w 0.23 aoea to 0.0006? M) aso M) M) M) M) aTl 7 PS Praf1k Otter MM. I, U S 1 M> tO O.OOM 0.0056 tO 0,035 MX a 27 0.028 MI aooo32 M) aa MI MI M) MI an

I\MTOejter) fag. 19.87 a Ml M> 0.006S0.006B M) 0.036 - a2B 0.029 M) aooi3 to atf M) M) M> tO a87 9 1H» Otter) Aug. 19.87 M 10 K4f> Otter) Aug. 19,87 C2 tO tD 0.0065 0,0168 tO 0.036 - 0.30 0.028 MI aoooTs MI aea M) M> M) W aB7 11 K-4T Otter) Aug. 19.87 1C V Mm Pit (171) JVM 27.X 71 - aois - on _ - - - - }.?3

13 P2 Praflk (Cora) MM. 1, 87 23 11 M) M) 120 M) M) 17 MX 11 19 M) 21 W 6.3 M) M) M) 21 24 M P2 Praflk (Cora) MM. 1. 87 a 12 49 M) 1300 M) M) 15 t* 5,6 tt M) 9.0 tO 18 tO tO tD W 34 IS P3 Praflk (Cora) MM. 1. 87 n M tO tO VO tO tO 10 MX 4.0 9.0 M) 18 » 12 Ml M) M) 16 20 16 P3 Praftk (Cora) MM. 1. 87 27 13 ID tO 250 »» 26MXM) 16 tO 23 Ml 6.3 M) M) M) 29 12 17 P4 Praflk (Cora) MM. 1. 87 25 IS M) M) KD M) K) H W MJ 11 M) 19 » 5.3 tO tO IO 17 M W P4 Praflk (Cora) MM. 1, 87 25 M tD tO IW M) M) 16 MX 19 12 5.4 44 M) 11 M) M) M) 21 M 19 P4 Prafik (Cora) Mw. 1. 87 25 17 M) W » tO tO 13 NA » 11 6.2 46 U) 6.9 IO tO tO 21 15

20 PS Proflk (Cora) MM. 1. 87 S W tO tO WO tO M 26MX4.827 5.2 39 NO 13 M) Ml M) M 16 21 PS Praflk (Cora) MM. 1. 87 S 19 tO tO 90 tO tO KMX5.022 5.9 W to 13 W Ml N) 9.3 24 22 IW (Sail) Aug. 19.87, 6 C4 48 21 2800.48 tD 63 - 4.7 41 30 11.4 IO 17 M) M) Ml 62 27

23 SMthU (ttitar) MM. 2. 87 - B K> M> 2.B N> KD M) NA M) M) M) tO tO tO to aoo60 MI aow M> 24 SM fell BKIOttar) June, 1964 - - aois - - - aoao - 1.70 25 SW tttll BWOUer) JUM. 1964 - - & BMH*iVill(U»tar)OcU7, 3B - - 0(7) ~0(7) - - - '.'.".'. 0 - 27 S* Otter) Aug. 19.87 GO to to to aoow M> a 17 - i.oaooBi N) 0.0013 M) 0.65 to to to to u a S* 0tt«r) tat. ».» C W 29 ftmalSorl* Hwch. 57 6 - a« - 1.4 - . . . 3D IWnal Spring **» FaolMoU «, 6 - -

onicTKN iniTS: urtrs »» 0.10 aoso aoos 0.0010 0.0X0 0.010 0.010 0.010 aoos aoao 0.00020 aon aoo anaooso a« 0.010 aow (H87 Analyses) SUWOflS »» 40 40 10 a so a so i.o i.o 10 10 5,0 au w s.o 5.0 2.0 50 5.0 2.0 llt£ 22 VIOAIKNS AM) INTS»» 20 (OWES CM.*) ootnoUs: A«g iig o.oael «HH> WIB a-Atfer to table 1 for additional data, references, ard coring def*h Intervals. A»q ||g 26.33 «19H7 CUKtS to freshwater aquatic life of 0.012 ug/1. The pit water also exceeds drinking water standards for cadmium and ambient water quality goals to protect freshwater aquatic life for beryllium, copper, nickel, and zinc. Boron and ammonium concentrations exceed EPA estimated permissible ambient goals. Columbia Geoscience concluded that the acidic conditions of the Herman Impoundment were due to the large volume of hydrogen sulfide (H2S) in naturally discharging geothermal fluids reacting with oxygen, rather than due to oxidation of pyrite-bearing rock (Fes2), to form sulfuric acid (H2SO,), as is typical of acid mine drainage. The report also concluded that mercury ore continues to form in the mine pit and is not leaching from the sediments into the water. Columbia Geoscience sensed that the physical and chemical conditions in Herman Impoundment act as a natural treatment process, trapping the discharging geothermal fluids, and restricting solubility and confining the mercury to the bottom of the pit. Columbia Geoscience estimated that up to 8 tons of mercury may be present in bottom sediments of the Herman Impoundment, and more than 2,600 tons of mercury may exist within the ore bodies below the mine pit.

4.3 Site Soils The majority of contaminated soils at the site are associated with surface weathering of the mine waste piles. Con- tamination of the tailing piles and associated soils are discussed in the following section. Other soils at the site which could be contaminated are surface soils downwind from the mine smelting operations which were adversely impacted by airborne contaminants. The extent of these contaminated soils is unknown and will be investigated during the Remedial Investigation. A soil mercury survey was previously conducted at the site during geothermal exploration activities. Soil mercury anomalies are often associated with geothermal resources and can be used as an indicator during reconnaissance exploration. The mercury survey at the site indicated that the mercury bearing shear zone ex- tends both northeast and southwest of the mine and is at least two miles long. A study of wind currents at the site demonstrated that the soil mercury anomaly is not the result of downwind fall out from processing the mercury ore. Soil sampling at the site will be performed in order to determine the extent of naturally occurring mercury anomalies and establish background levels for the site.

4.4 Mine Waste Rock and Tailing Piles 16 ;:;:;:• TAILINGS AND MINE DUMPS SULPHUR BANK MIME Hg data In ppm

•a M 10 o PQ H O

C 0 U

CLEAR LAKE a 3 ex

0) 4J (0

(0 c o •H tn

H CO Two different types of mine wastes are found at the SBMM site, including the reddish tailings (wastes from ore processing) and waste rock, or unprocessed overburden excavated during mining operations, which are white in color. Based on volume estimates of existing tailings and waste rock piles on site, there is a minimum of 193,600 cubic yards of wastes on site. The mine tailings and waste rock extend 1,320 feet in the north-south direction, in contact with 2,060 feet of shoreline, and extend some 3,000 feet eastward from from the lake. Sampling conducted on-site indicate the mine waste piles contain elevated levels of mercury and arsenic. Samples collected by the RWQCB from all over the mine site during 1983-1984 contained concentrations of mercury ranging from 1 - 624 mg/kg, with a mean concentration of about 60 mg/kg (Figure 14). Subse- quent sampling conducted by the RWQCB found concentrations as high as 1000 mg/kg. Arsenic concentrations in the waste rock and tailings have been reported as high as 140 mg/kg, but have not been sufficiently characterized. However, surface water drainage from the mine site has been found to contain arsenic concentrations as high as six times the Maximum Contaminant Level (MCL) of 0.05 mg/1 (RWQCB, 1984). Subsequent sampling of mine tailings by HSU at various locations indicate the waste piles are uniform with respect to the distribution of mercury levels. Samples that contained fine grained material (clay and silt) had higher mercury concentrations than samples without fines, but using conventional statistical methods it is not possible to distinguish one sample type from another based on mercury levels. In other words, what "hot spots" do exist are as likely to occur in one area of the mine waste piles as another.

4.5 Clear Lake Surface Water and Sediments Elevated levels of mercury were first detected in Clear Lake in 1970 by the California Department of Health Services. Since that time hundreds of samples from fish and waterfowl tissue and from sediment and water in the vicinity of SBMM and in Clear Lake have been analyzed for mercury. These data indicate that the highest concentrations of mercury are found in the Oaks Arm of Clear Lake in the proximity of SBMM. Of the mercury already in the Oaks Arm, the largest amount (about 100,000 kg) is in the upper sediments, while the sediment blanket and the water column account for much smaller quantities of mercury (respectively 440 kg and 60 kg). The most significant outputs of mercury from the Oaks Arm are losses into the sediments; this amounts to ap-

17 proximately 100 kg of mercury per year. Losses to the atmosphere and flows out of the Oaks Arm each account for approximately 10 kg per year. Historical mine waste disposal practices have contributed mercury into the lake and appear to be the most likely source for the mercury stored in the upper sediments of the Oaks Arm. Mer- cury inputs from mining sources can be further subdivided into five major categories: 1) From mine water and sludge pumped into the lake during open pit mining operations; 2) Airborne inputs during ore smelting operations at the mine; 3) Disposal of wastes during smelting operations; 4) Erosion of detrital material from unstabilized waste piles and local drainages; and 5) Ground water discharge from Herman Impoundment into Clear Lake. Natural inputs from active geothermal systems have been documented in the vicinity of SBMM and throughout the Clear Lake area. The mercury in the deeper portions of lake sediments are associated with natural deposition prior to mining operations at the site. Mercury has a very low solubility in water; in Clear Lake, mercury levels in the water column are generally very low and near or well below the analytical detection limit of 5 ug/1. Based on sampling conducted by the RWQCB in 1984, mercury concentrations from lake bottom sediments in the Oaks Arm reportedly range between 11 mg/kg and 250 mg/kg (dry weight) with an average of 80 mg/kg. This is well above the state action level for mercury in sediments of 20 kg/mg. However, the validity of this data is suspect, and may contain even higher concentrations of mercury, based on sampling results from the waste piles along the shoreline. Bottom sediment samples collected concurrently in the rest of Clear Lake range from non-detect to 12 mg/kg with an average of 2 mg/kg (Figure 15). Short cores collected by both the RWQCB and the USGS from lake bottom sediments immediately off shore from the mine indicate that the highest levels of mercury are in the upper 50 to 60 cm of sediment, which corresponds with the last 100 years of lake deposition, during the period mining activity. Substantially lower amounts of organic matter and soil moisture coincide with this mercury peak, suggesting a changing lacustrine depositional environment with higher shore-derived detrital influx. The presence of pesticides from aerial spraying during the 1950s and 1960s in these upper sediments provide further evidence of recent deposition. Sediments below this mercury peak contain substantially lower concentrations of mercury, until a depth of about 4 meters is reached, where a natural mercury peak occurs (depositional age estimated to be about 6000 years before present).

18 MERCURY IN CLEAR fiTTB?ACE SSDH'IS

Regional Board Study Results Study Hesuits ' . 2/29/84-3/1/84 8/83 - results iii mg/kg Location 2; mgAs Rodman SI. Lower Lake Rattlesnake Is.' Sulfur Bank 430. Mine Tail.

TTTTS Study Results 7/70 Location Upper Ana. 3-7 Lower Arm 4.8 Oaks Ana 33-0

Source: Regional Water Quality Control Board FIGURE 15 High arsenic levels have also been detected in the bottom sediments of the Oaks Arm of Clear Lake. Concentrations from twenty samples ranged from less than the detection limit at 5 mg/kg to 95.9 mg/kg arsenic with an average of 27.9 mg/kg.

4.6 Ground Water Ground water contamination has been characterized by data collected from wells on site and nearby. Three monitoring wells are known to currently exist at the site. No domestic water wells in the vicinity of the site are known to have have detectable levels of mercury. Mercury levels in water, and specifically ground water, is dependent upon pH, Eh, chloride and sulfide levels, and temperature. Observed mercury levels in filtered and unfiltered samples from springs and wells near mercury deposits in north-central California are reported to range from non-detectable to 0.7 ug/1. The "Sulphur Bank" well is reported to have levels of 0.5 ug/1 in a 1973 survey. The HAR reports mercury levels at 0.2 ug/1 in the unused Bradley Mining Company well BM3 located on site. Humboldt State University (HSU) sampled three on-site ground water monitoring wells for the Abatement and Control Study completed under contract to the RWQCB. Mercury analysis of unfiltered samples from the monitoring wells ranged from about 7 to 130 ug/1 of total recoverable mercury. Analysis of two filtered samples from one single monitoring well were 0.4 and 0.6 ug/1 of mercury and 60 and 15 ug/1 for the other two wells. However, HSU considered the latter two results suspect due to improper filtration. As the water level in Herman Impoundment is approximately 3 to 10 feet higher than in Clear Lake, ground water flows is likely to be from the mine pit into the lake. The depth to the water table is approximately 10 feet. Two wells were installed by Humboldt State University between the Herman Impoundment and Clear Lake, and head and pH gradients were measured confirming this assumption. The pH gradient went from a pH of approximately 2.8 at Herman Impoundment to 3.9 in the well closest to the mine pit, to 4.1 in the well nearest the shoreline, to 6.9 in the lake. No domestic, stock or public water supply wells are located downgradient of the Sulphur Bank Mine., Mercury concentrations in water from other nearby wells were at or below detection limits at the date and time of measurement.

5.0 Conceptual Model of Site Contamination 19 I I f 5.1 Potential Contamination Sources and Extent of Contamination Mercury inputs into Clear Lake can be subdivided into two sources: mining activities and natural sources. The Sulphur Bank I Mine is not the only mercury mine in the Clear Lake area. The abandoned Bell Mine, and the nearby S-Bar-S quarry are both located in the vicinity of Mount Konocti. Other mercury mines in I Lake County include the Mirabel and Abbott Mines. At the SBMM site, contaminant sources directly resulting from mining activity include the mine tailings and waste rock I piles, which continue to erode into the lake, and the mercury contaminated sediments resulting from direct disposal into the lake. Acid water from the Herman Impoundment from groundwater or surface water discharges may also leach metals into Clear Lake I and impact water quality. High concentrations of mercury have been reported in the mine tailings and waste rock piles, ranging from 1 to over 1000 mg/kg mercury. Lake sediment samples col- I lected just off shore from the mine site have been found to contain as high as 250 mg/kg mercury (dry weight). Elsewhere in the lake, outside the Oaks Arm, bottom sediments have so far been I found to contain mercury levels ranging from non-detect to only as high as 12 mg/kg. (Figures 14 & 15) The state action level for mercury in sediments is 20 mg/kg. I Natural mercury inputs from active hydrothermal sources have also been documented within the immediate vicinity of SBMM. Hot springs have been observed discharging into the Herman Impound- I ment and elsewhere on the mine site. Historical accounts indicate that several large springs existed along the Clear Lake shoreline, before the hydrothermal system was disrupted by mining I activity. The U.S. Geological Survey has mapped numerous springs throughout the Clear Lake Area (Sims & Rymer, 1976). The contribution of these natural springs to the methylation and bioaccumulation of mercury in Clear Lake fish must be investigated I prior to selecting a cleanup remedy for the contaminated lake I sediments. 5.2 Contaminants of Concern I To date, mercury, in both it's inorganic and methylated forms, and arsenic have been identified as the primary contaminants of concern. Previous investigations have not sufficiently characterized the extent and significance of arsenic con- I tamination. Other metals may also be present in the sediments, tailings and waste rock, in concentrations which may effect water quality, but data collections to date have not been sufficient to I identify other metals as contaminants of concern. I 20 I 5.3 Contaminant Migration Pathways a) Shoreline Erosion: Approximately 2060 feet of Oaks Arm shoreline is in direct contact with mine wastes; of this, about 1240 feet of shoreline is in contact with very steep (up to €0 degrees), barren slopes made up of tailings and waste rock. Samples collected by Hum- boldt State University contained an average mercury level of 158 ppm. Two possible erosional processes for mercury transport from the shoreline deposits into Clear Lake include sheetwash erosion from the steep banks and slope failures due to undercutting of the slope by wave action. The shoreline slopes have well developed gully systems and talus cones, indicating sheetwash erosion and mass wasting processes are in progress. Humboldt State University (HSU) estimated the annual contribution of mercury due to mass wasting processes at > 132 kg/yr, based on field measurements made using an array of erosion pins and measurements of precipitation and soil properties. These measurements were taken during dry years (1988-1989); consequently, the normal erosion rates may be higher. b) Fluvial Transport In addition to shoreline erosion, drainage from the rest of the mine site is likely to carry additional mercury laden sediment into the lake. The possibility of failure of the dams containing the Herman Impoundment during heavy rains is of particular concern, and was addressed under the RWQCB order. Water samples collected from on-site ephemeral streams by RWQCB in 1989, contained mercury levels between 330 and 490 ug/1. Based on estimated annual discharge rates, Humboldt State University estimated the average annual mercury discharge from fluvial transport ranges from 1.24 to 18.6 kg/yr. c) Ground Water Transport The magnitude of ground water transport of mercury from Her- man Impoundment to Clear Lake is dependent on the elevation dif- ference between Herman Impoundment and Clear Lake, the hydraulic conductivity of the aquifer, the thickness and areal extent of the aquifer, and the mercury level in the ground water transposrt. Since the water level of Herman Impoundment is approximately 3 to 10 feet higher than the level of Clear Lake, it is likely that ground water flows from the mine pit to Clear Lake. The flow of ground water from Herman Impoundment to Clear Lake is further supported by the hydraulic head and pH gradient measured in the three on-site monitoring wells. The pH ranged from 2.8 at Herman Impoundment to 4.1 in the well near Clear Lake. 21 The aquifer between the Herman Impoundment and Clear Lake consists of 3 layers. The upper layer consists of the waste rock layer, which is underlain by a unit of quaternary sediments up to 35 feet thick, including silty lake sediments, landslide debris and beach sediments. Quaternary andesite volcanics, of unknown thickness, make up the bottom-most layer of the aquifer. Columbia Geoscience estimated hydraulic conductivities for these units through pump tests and lithologic interpretations. The hydraulic conductivity of the waste rock unit was estimated to range from 1.8 X IO"3 to 8.4 X 10"~4 cm/sec. For the quaternary sediment layer, hydraulic conductivities were estimated to range from 1 X IO"7 to 4.3 X 10~8 cm/sec, and for the andesite volcanics, 3.4 - 3.6 X 10 cm/sec. Mercury levels in groundwater are dependent upon pH, PE, temperature, and levels of chloride and sulfide. Samples collected from on-site wells (Columbia Geoscience - 1988) had reported mercury levels ranging from non-detectable (< 0.2 ug/1) to 0.2 ug/1. Unfiltered samples collected by HSU ranged from 7 to 130 ug/1 recoverable mercury. Filtered samples contained 0.4 and 0.6 ug/1 in one well and 60 and 15 ug/1 in the other two wells. HSU considered the latter two results suspect due to improper filtration. HSU and Columbia Geoscience reported estimated ground water transport rates for mercury ranging from 0.0001 - 0.02 kg/year. These estimates were based on computer modeling and an assumed mercury level of 0.5 ug/1 and calculated flow rates of 0.1 and 20 gpm. By these estimations, the contribution of mercury in the ground water from Herman Pit into Clear Lake is very low in comparison to other transport mechanisms such as shoreline erosion. d) Air Transport Previous investigations have not evaluated the air migration pathway. However, a mercury vapor survey was conducted on- site by the RWQCB in 1988. The survey was conducted using a Jerome Instruments mercury vapor analyzer. The results indicated that vapor concentrations throughout the site were well below the NIOSH recommended exposure limit (10 hour time weighted average, TWA) of 0.05 mg/cubic meter. The highest levels found, (0.012 mg/cubic meter) were found inside structures in the old mill processing area. Background concentrations were mostly between 0 and 0.002 mg/cubic meter, with occasional readings as high as 0.05 mg/cubic meter. Mercury vapor concentrations near the hot springs were not higher than for other areas.

22 During the daytime, prevailing winds blow in an easterly direction across the mine site. During the evenings, occasional wind reversals occur, blowing westward across the site towards the lake. The potential exists for particulates to be blown off-site. On windy days, hydrogen sulfide fumes can be smelled as far away as the mine gate. Both the on-site caretakers residence and several homes in the adjacent Elem community were constructed on mine waste. To date, indoor mercury concentrations in those homes have not been measured.

5.4 The Methylation Process The discovery of elevated mercury levels in certain aquatic species and subsequent findings that mercury tends to bioaccumulate and concentrate in higher life forms, with potentially serious toxic effects, spawned a surge of research into the behavior of mercury in the environment. Research has shown that while mercury in water and sediments is present predominantly in inorganic form, methylmercury is the form usually identified as being present in contaminated aquatic organisms. Both inorganic mercury and methylmercury may be absorbed by aquatic organisms, however, inorganic mercury is more likely to be excreted, and methylmercury is more likely to be retained in the tissues. Studies have shown that generally 80 - 95% of total mercury found in fish is in the form of methylmercury. Inorganic mercury is biologically converted to it's methylated form by microorganisms present in the water and sediments. Methylmercury may also be formed through abiotic processes, however abiotic transformation is neither well understood nor believed to be significant in aquatic environments. Inorganic mercury may enter natural waters from atmospheric deposition, geothermal sources, or from run-off as dissolved mercury bound to suspended solids, as detrital cinnabar, or in solu- tion. Inorganic mercury may be present in elemental form (Hg , metallic vapor) ionic form (Hg1+, formed by photochemical oxidation in air or possibly by methylation, or more commonly, Hg2+) or as a compound (e.g.: HgS). Metallic mercury and mercury compounds have low solubility in water (»1 ppm) and tend to sink below the sediment/water interface and become immobilized. Ionic mercury is more soluble, and may form organic species. In general, the speciation of mercury in natural waters is dependent on pH, redox potential, and availability of ligands or binding groups. Under most conditions, dissolved mercury is mainly bound to solids via surface layer adsorption to clays, hydrous oxides, and organic debris, so that at least 50%, and more likely 80-96% of total mercury is transported along with suspended solids. The 23 movement of mercury between the water column and surface sediment is rapid, reaching equilibrium within days, and is responsive to short-term physical and chemical changes. Inorganic mercury is converted to organic mercury in either the form of monomethylmercury (e.g.: methylmercuric chloride) or dimethylmercury. Dimethylmercury is the ultimate product, which may rapidly volatilize in the water column. Monomethylmercury is more stable and more likely to bioaccumulate. Methylation of mercury appears to occur primarily in the upper 5 to 15 cm of sediments under mildly to strongly reducing conditions; however, methylation has been shown to occur in the water column as well as in sediments. Levels of methylmercury may fluctuate seasonally as the lake bottom switches from aerobic to anaerobic conditions. Summertime anoxic conditions may enhance the solubility of mercury, increasing the availability of mercuric ion to form methylmercury. During the fall turnover, mixing of the lake waters disperses methylmercury throughout the water column. In addition to dissolved oxygen content, several other competing factors govern the methylation process, including temperature, pE, pH, type and concentration of bacteria present, and type and concentration of complexing organic and inorganic ligands and chelating agents (ie: reduced sulphur, chlorides, hydroxides, and suspended solids). Mercuric ions also tend to chemically adsorb to humic matter, forming soluble complex ions. While these complex ions may not be readily available for methylation by bacteria, they may be oxidized, or metabolized by benthic organisms, and thereby made available to bioaccumulate. The large seasonal algae blooms present in Clear Lake may serve as a temporary sink for mercury, by absorbing mercury from the water column. Fish may accumulate mercury by ingesting plankton, benthic organisms or other fish which have already absorbed mercury, or they may also absorb mercury directly from the water column through their gills, from the upper layer of sediments, and possibly they may also produce methylmercury within their own intes- tines from mercuric precursors. Once in the f.opd chain, mercury may bioaccumulate at levels exceeding FDA guidelines, particularly in the upper trophic level species. Numerous factors may effect methylation rate and bioaccumulation, which vary considerably between different aquatic systems. Sediment concentrations do not correlate directly with concentrations in biota. Some lakes may contain relatively low levels of mercury in sediments, and still may have elevated

24 levels of mercury in the fish. It is essential to develop a thorough understanding of the particular system before selecting a costly cleanup alternative. As numerous factors may potentially effect the methylation process, it may be possible to reduce the methylation rate in a given natural system by the manipulation of one or more factors. Several remedial strategies have been proposed to date, including: 1) Change the mercury binding characteristics of the sediment by adding a strong complexing agent (such as sulfide ions) in sufficient quantity to reduce the availability of mercuric ion for methylation. 2) Eliminate or reduce organic input in the benthic zone to stop or reduce biological activity. 3) Reduce the total inorganic mercury concentration by: a) dredging, treatment and off-site disposal of mercury contaminated sediments . b) covering contaminated sediments with a cap of sand, clay or gravel. c) using a getter system (mesh network treated with a complexing agent, such as sulphur) to adsorb mercuric ions and remove them from the: water column. In order to select the most appropriate remedial strategy for a particular system, it is essential to understand which factors control methylmercury production in the particular system of concern .

5.5 Toxic Effects A considerable amount of research has been conducted and data published on the toxic effects of mercury poisoning, particularly since the widespread outbreak of mercury poisoning in the fishing village of Minimata, Japan in 1953. For years, a plastics plant had directly discharged methyl mercury into the bay. Strange behavior and high death rates were first noted in cats, then neurological disorders, birth defects, and some deaths were reported in the human population. After intensive investigations, the cause of the epidemic vras found to be mercury poisoning from the consumption of local fish and shellfish. The source of the mercury was eventually traced to the plastics plant, where near-shore sediments were found to contain as high

25 as 2010 mg/kg mercury. (Sediments in the Oaks Arm of Clear Lake range from 11 to 250 mg/kg mercury, with an average concentration of 80 mg/kg.) Another case of mercury poisoning was reported in the early 1970's in Iraq, where homemade bread made from seed wheat that had been treated with a mercurial fungicide poisoned over 6500 children and adults. Over 500 hospital deaths were reported; many other deaths may have gone unreported. Patients experienced numbness in their hands, feet and around the mouth (paresthesia), loss of motor control (ataxia), slurred speech (disarthria), tun- nel vision and hearing loss. Symptoms of mercury poisoning include headaches, weakness, forgetfulness, aggressiveness and personality changes in its mildest form, and tingling skin, muscle numbness and slurred speech, to convulsions, delirium, respiratory failure, kidney failure, and death in its most severe forms. The milder symptoms of mercury poisoning, (headache, fatigue, memory loss, lack of concentration) may be reversible; the physical effects, (blurred vision, blindness, hearing loss, impaired motor control, numbness) are often irreversible. Mercury has been found to be a teratogen in all animal studies; there have also been reported cases of blindness, hearing loss and mental and physical defects in human babies exposed to mercury in the uterus. In most cases of fetal exposure, in- fants appear normal until the age of six months, then begin to show signs of slowed reflexes, poor motor control, delayed speech and cerebral palsy. Mercury kills brain cells and other nerve cells, possibly due to its tendency to form covalent bonds with sulfur, by deactivating sulfhydryl enzymes essential to cellular metabolism. In pregnant women, mercury tends to cross the placenta and concentrate in the fetus; breast milk may also contain concentrated levels of mercury. Mercury is toxic in both its organic and inorganic forms. Inorganic mercury most frequently effects the kidneys first, and may also damage the central nervous system with chronic exposure. Organic mercury tends to be retained in the body, particularly in the brain and the placenta. It attacks the central nervous system and is the form of mercury most often responsible for birth defects. Methyl mercury is the organic form of primary concern at SBMM. Inorganic mercury in lake sediments is converted biologically to methyl mercury, which enters the food chain and bioaccumulates and concentrates in higher trophic level species. Studies have shown that 98% of methyl mercury in food is absorbed by the tissues,, whereas only 1% of inorganic mercury is absorbed. At Clear Lake, high mercury levels in fish prompted the Califor- 26 nia Department of Health Services to issue a health advisory in May 1986 against consumption of all Clear Lake fish for pregnant women, nursing mothers, and children under age 6, and limiting fish consumption for all others. While fish consumption is a primary route of exposure, mercury poisoning can also occur through inhalation or ingestion of mercury dusts or vapors and skin contact with methyl mercury or organic salts. Although the U.S. Food and Drug Administration has issued an action level of l ppm (mg/kg) mercury in food, toxic effects are generally not seen until a level of 10 ppm is reached. The acceptable Daily Intake (ADI) for an average 70 kg adult is 30 ug methyl mercury per day. The World Health Organization (WHO) has established 10 ng Hg/ml (0.010 ppm) as a "safe" blood level, although the lowest blood level associated with adverse health effects found to date is 200 ng Hg/ml (0.2 ppm), taking into account the most sensitive populations. Methyl mercury has a half life of 70 days in most humans, however, in some individuals, it may take up to 120 days to excrete half of the toxin. Mercury levels can be measured in hair, blood and urine samples. While hair and blood data tend to correlate well, urine mercury levels cannot be used to calculate an exposure level, but can only be used to provide evidence of recent mercury exposure.

5.6 Uses of Mercury and Prevalence in the Environment Mercury has a number of industrial uses, including the manufacture of chlorine and caustic soda (chlor-alkali industry) and plastics manufacturing. It was formerly used as a slimicide in the paper manufacturing industry, and is still used in agriculture as a fungicide treatment for seeds. Mercury has also been used in paint, cosmetics, filters on sewage treatment plants, thermometers and scientific instruments, dental prepara- tions, amalgamation, and various mining extraction processes. Coal burning power plants also produce mercury vapor; mercury also occurs naturally in fossil fuels,, Although there are hundreds of potential uses for mercury, only about 18% is recycled. Most of it eventually ends up in the environment.

5.7 Potential Receptors 5.7.1 Surrounding Populations

27 I I The Elem community of Porno Indians is located on the north side of the SBMM site. The community consists of approximately 21 homes and a community center, half of them constructed on mine tailings and waste rock. While the residents formerly relied I heavily on subsistence fishing, most of them no longer eat much fish due to the health advisory. Residents still collect tules along the shoreline and eat the raw bulbs. Children frequently I play on the mine site and eat wild blackberries that grow on mine tailings. The community's drinking water wells are abandoned; water is now piped from Clear Lake Oaks. In addition to the Elem I community, the caretaker's residence is located on the mine site and was constructed on mine wastes; eight other homes are located just to the south of the mine. Most of the homes south of the mine along Sulphur Bank Point draw water from private intakes on I the lake. The nearby communities of Clear Lake and Clear Lake Oaks, I population 15,000 and 2,700 respectively, may also be affected. Residents may still be eating fish caught in the Oaks Arm of the Lake, also, residents have reportedly used algae from the lake as I compost for vegetable gardens. Samples of algae collected by EPA from the canals in Clearlake Oaks contained low levels of mercury, below 0.16 ppm (wet weight). The drinking water supply wells for Clear Lake Oaks are located near the Clear Lake I shoreline. The depth and screened intervals of the wells are presently unknown, but these wells could conceivably be pumping I lake water. Many of the nearby residents and tourists who come to the area swim in Clear Lake. As methyl mercury may also be absorbed through the skin, swimming provides another possible exposure I route. Beef cattle and sheep also graze near the mine site. While I health advisories have been issued against consumption of Clear Lake fish, there are currently four commercial fishing licenses issued for Clear Lake. Most of the fish are caught in the Upper I Arm and only a few species are marketed commercially, including Sacramento Blackfish, Carp, Clearlake Hitch and Goldfish (sold as Silver Carp). These fish are sold to Asian markets in the Bay I Area, Sacramento and Los Angeles. I 5.7.2 Ecological Concerns Clear Lake is host to a variety of terrestrial, aquatic and benthic communities. The surrounding area includes freshwater I marshes and seasonal wetlands containing sedges, rushes and grasses; riparian-woodlands dominated by hardwoods, pines, wil- lows and vines; and grassy chaparrals of shrubs and brush I species. These are home to deer, gray squirrels, raccoon, fox, I 28 I mink, jackrabbit, and many other small mammals, as well as egrets, great blue heron, the rare yellow-billed cuckoo, owls, and many other waterfowl and birds of prey. The U.S. Fish and Wildlife Service reports that federally endangered species found in Lake County include: American Peregrine Falcon (Falco pereorinus anatum) Bald Eagle (Haliaeelus leucouphalus) Northern Spotted Owl (Strix occidentalis caurina) Loch Lomond Coyote Thistle fErvncrium constancei) Other California rare, protected and endangered species and U.S. Forest Service sensitive species found in Lake County include: Black-shouldered Kite fElanus caeruleus) Northern Goshawk (Accipitier crentilis) Golden Eagle (Aquila chrysaetosl Prairie Falcon (Falco aexicanus) Blue Grouse (Dendragapus obscurusl Ringtail (Bassariscus astutus) Badger (Taxidea taxus)

Although various wildlife species may prefer one particular vegetative habitat type, many are dependent on other habitat for specific time intervals. For example, hawks may nest in the riparian-woodland areas but feed in other vegetative zones. The wetlands are particularly important in providing the nutrients for the growth of micro-organisms which are the base of of both aquatic and terrestrial food chains. The loss of wetlands due to past mining activity and the potential for future losses during remediation is an important ecological concern. Previous studies at Clear Lake have identified seven species of sport fish which live in Clear Lake. Upper trophic species include largemouth bass, channel catfish, and black and white crappie. Middle trophic fish include white catfish and brown bullhead. Lower trophic fish include Sacramento blackfish and hitch. Hundreds of fish tissue samples have been collected by the California Dept of Fish and Game since the late 70's; many fish, particularly the upper trophic species, contain levels of mercury in excess of the FDA guideline. A naturally occurring annual fish kill happens each year when the oxygen level in the water is too low for the fish to survive. The carcasses of the fish wash up on the lake shores where predatory and domestic animals eat the potentially contaminated fish. Also scavenger birds such as vultures feed on the dead fish. Tissue samples collected from two species of birds at Clear Lake indicate a potentially significant ecological impact of mercury contamination on the wildlife population. 29 I

I Samples collected from the fish-eating grebes contained mercury levels 70 times higher than those found in the strictly plant- I eating coots. The toxic effects of mercury on wildlife has been widely studied. In general, mercury is a known mutagen and teratogen, which adversely affects reproduction, growth and development, be- I havior, motor coordination and sensory perception in birds, mammals and aquatic organisms. The presence of pesticides in addition tc mercury tends to increase the toxic effects, whereas the I presence of selenium tends to counteract the toxic effects. In fish species, signs of acute mercury poisoning include I flared gills, increased respiratory movements, and loss of equilibrium. Chronic symptoms include emaciation, brain lesions, abnormal and diminished motor coordination, erratic behavior, and diminished response to changes in light intensity. Mercury tends I to be most concentrated in the liver, then the brain, and thirdly, in the carcass. Symptoms of severe poisoning appear at I relatively high concentrations (5 - 7 mg/kg in the whole body). Signs of mercury poisoning in birds include poor muscular coordination, falling, slowness, fluffed feathers, calmness, I withdrawal, drooping eyelids and hyporeactivity. Mercury levels in birds tend to be highest in the brain, then the liver, kidney, muscles and carcass, in that order. I In mammals, methyl mercury effects the central nervous system, causing sensory disturbances and diminished motor coordination in acute exposures, to brain damage, mental derangement, I coma and death following extreme exposures. Additional symptoms of acute exposure may include loss of appetite, belching, bloody diarrhea, and piloerection (hair more erect than usual). In I general, larger mammals tend to be more resistant than smaller mammals. Mercury tends to be most concentrated in the fur, fol- I lowed by the liver, kidney, muscle and brain. 5.8 Conceptual Model I The Sulphur Bank Mercury Mine Superfund Site consists of an abandoned mine pit (Herman Impoundment), 120 acres of mine tailings and waste rock, and contaminated sediments present in Clear I Lake as a result of mining activity. Children from nearby communities frequently play on the mine property, where soil mercury concentrations have been found as high as 1000 ppm. The potential exists for mercury contaminated particulates to be blown I off-site. Mercury does not appear to be volatilizing off the mine wastes, however, this pathway has not been thoroughly inves- I tigated. I 30 I The Sulphur Bank Mercury Mine has been identified as the most significant source of mercury entering the Oaks Arm of Clear Lake. Mine wastes were directly disposed in the lake, and erosion from the mine continues to contribute mercury through mass wasting and fluvial processes. The Oaks Arm is the most contaminated segment of the lake; sediments adjacent to the mine site contain mercury levels in excess of 250 ppm, whereas sediment samples in the rest of the lake range from non-detect to only as high as 12 ppm. Large mouth bass from the Oaks Arm also tend to have higher mercury levels than bass from other arms of the lake. The methylation of mercury from contaminated lake sediments, and the bioaccumulation of mercury in the food chain and ul- timately the human population, is a major concern. Numerous factors influence mercury methylation and bioavailability, namely the availability of mercuric ion, and availability of nutrients for bacterial growth. As natural springs may also discharge mercury into the lake, the speciation and bioavailability of mercury contributed by these springs would need to be evaluated in order to determine the significance of their contribution to the overall production of methylmercury and the bioaccumulation of mercury in fish. Groundwater migration of contaminants from the Herman Im- poundment may also impact Clear Lake water quality, although tc a lesser degree. There are currently no water supply wells downgradient of Herman Impoundment. The low pH of the surface water in the Herman Impoundment represents a physical hazard and may be of ecological concern.

6.0 Preliminary Identification of Remedial Alternatives Remedial Alternatives for this site will be developed and evaluated during the Feasibility Study, as described in Chapter 10. Remediation of site contamination will be dependent on establishing clean-up goals and standards, and results of the ecological and human health risk assessments. The relationship between remedial alternatives at the site and the actual reduction of exposure to the contaminants will be investigated during the RI/FS. Bench and/or pilot scale treatability studies may be needed to determine the effectiveness of proposed remedial alternatives . Considerable work has already been done in identifying and screening potential alternatives. The Abatement and Control Study prepared by Humboldt State University (HSU) focused on two primary objectives concerning remedial alternatives for the site: 31 1) Develop and evaluate source control alternatives to reduce or eliminate future mercury contributions from SBMM to Clear Lake; and 2) Develop and evaluate pollution abatement alternatives to reduce or eliminate human and wildlife exposure to mercury already existing in the water and bottom sediments if Clear Lake. The Abatement and Control Study did not consider or propose remedial alternatives to address the impact of ground water contamination from the Herman Impoundment. In order to ensure that all potential contamination problems are addressed, EPA has divided the investigation of the site into three parts, or operable units (OUs). The Herman Impoundment, soils and mine waste piles, and contaminated lake sediments will investigated separately, and remedial alternatives will be developed and screened for each operable unit. The source control and pollution abatement alternatives that have been identified to date are summarized below.

6.1 Source Control Alternatives Effective source control alternatives will have to consider the Herman Impoundment and the mine waste piles, and should focus on reducing rates of shoreline erosion. A total of 12 alternatives were evaluated during the detailed analysis in the Abate- ment and Control Study and are listed below: 1) Cut back the shoreline slope of tailing piles to reduce erosion and prevent slope failures 2) Revegetate all or part of the mine waste piles to reduce erosion 3) Riprap the Clear Lake shoreline to protect the base of the shoreline waste piles slope from wave action undercutting 4) Grout the waste piles 5) Cap the waste piles with soil-cement 6) Cover the waste piles with a flexible geotextile 7) Cover the waste piles with a concrete blanket 8) Cover the waste piles with a webbed geotextile 9) Solidify the waste piles 10) Vitrify the waste piles 11) Excavate and dispose of the mine waste piles 12) Raise the dam and/or construct a spillway on the Herman Impoundment to prevent overflow and dam failure The Abatement and Control study estimated the costs for these source control alternatives to range from approximately $200,000 for slope cutback and revegetation to $250,000,000 for vitrification.

32 Alternatives to address the groundwater pathway and the physical hazards of acid in the Herman Impoundment were not specifically addressed in the Abatement and Control Study, but could include: no action, draining and plugging the pit, deep underground injection of impoundment water, acid neutralization, or installing barriers to restrict groundwater. Any alternatives considered for the Herman Impoundment will have to account for the presence of natural springs. The Abatement and Control Study concluded that source control alternatives should focus on reducing shoreline erosion and on fluvial transport mechanisms for mercury contributions from SBMM to Clear Lake. The study recommended a combination alternative of riprapping the lake shoreline, reducing the shoreline slope to 20 degrees and revegetating to minimize erosion, and raising the Herman Impoundment dam and adding a spillway and channel, was recommended as the most cost-effective alternative.

6.2 Pollution Abatement Alternatives The pollution abatement alternatives for mercury in Clear- Lake water and bottom sediments evaluated in the Abatement and Control Study are: 1) Do Nothing 2) Implement a source control program on the mine site but do nothing in the lake 3) Dredge the entire Oaks Arm or only the most contaminated lake sediments 4) Cover all, or only the most contaminated sediments with clean sand or clay 5) Establish a bounty system to remove contaminated fish 6) Periodically remove and restock fish Costs for these alternatives ranged from $3,000,000 for dredging or covering the area of greatest contamination to $129,000,000 for periodic removal and restocking of fish. The most cost-effective pollution abatement alternatives will probably involve either dredging or covering the lake bottom sediments in the Oaks Arm with clay or sand. These approaches have proven to be satisfactory for sediment contamination problems in other areas, but will require additional study to verify their appropriateness for application in Clear Lake. Of particular concern is that the ultimate costs and efficacy of the lake pollution abatement alternatives can only be imprecisely quantified at present. Since these abatement alternatives will be very expensive, it is important that their costs and likelihood of success be more accurately assessed during the RI/FS. Understanding the mercury methylation and bioaccumulation 33 process in Clear Lake will be key in the development of a conceptual model for establishing sediment clean-up criteria that equate to acceptable mercury exposure levels. The technical im- pleroentability of these remedial alternatives will be studied during the Feasibility Study, and may require bench and/or pilot scale treatability studies to determine the potential effectiveness of these remedies.

7.0 Data Management Requirements The RI/FS objectives will be accomplished by collecting environmental data from soils, mine tailings, groundwater, lake water and sediments, lake biota, and air. The quantity and quality of data required will be determined by the establishment of Data Quality Objectives; the data requirements for the RI/FS and are identified and summarized below.

7.1 Identification of Data Needs and Uses To date, sampling at SBMM has not investigated the extent of arsenic contamination. Past soil and mine tailings sampling for mercury, performed by Columbia Geoscience, RWQCB/Central Valley, and Humboldt State University is extensive, but the data quality requires review. After reviewing the data, portions of the data may be incorporated into the RI/FS, limiting the amount of sampling needed. Data will be collected on the physical and chemical properties of the soil and tailings, as well as mercury speciation that might influence the effectiveness of remedial alternatives. Air transport of site contaminants by wind were neglected in the past since the prevailing strong winds would carry the mercury-laden dust away from Clear Lake (as referenced in the Humboldt State study). The potential for metals migration by air will be further evaluated in the RI/FS. If it is determined that this is a potential exposure route, air quality data will be collected along with contaminant emission rates and site meteorological data. Groundwater data was generated by Columbia Geoscience during their hydrogeological assessment of the site. Additional data to confirm and update their findings on groundwater contamination, geochemistry, hydraulic conductivity, groundwater flow rates and direction may need to be collected. The data will be used to examine the extent of contamination, and to assess the impacts on Clear Lake water quality.

34 The sediments and water column of the Oaks Arm of Clear Lake has been sampled extensively by Humboldt State University. Their data was used to estimate total mercury storage levels in the water column, sediment, and the interface between the two. This historical data can be used to assess the extent of contamination in the Oaks Arm which originated from the site. For the RI/FS, intensive seasonal water/sediment data will be required to develop a more detailed mass balance of methylmercury production. Data gaps exist in the mercury transport link between lake bottom sediments and edible lake fish. These data gaps will be filled under the objectives of the Ecological Assessment portion of the RI/FS. The data will be used to evaluate remedial alternatives pertaining to the Oaks Arm of Clear Lake. A centralized computer database will be set up to manage all historical data, as well as data to be collected for modeling and risk assessment purposes.

7.2 Data Quality Objectives Data Quality Objectives (DQOs) are qualitative and quantitative statements which specify the quality of data required to support the decisions reached from the RI/FS. DQOs are determined based on the end use of the data. During the RI/FS, the data collected will be used to characterize and model contamination at the site, to conduct a risk assessment, and to determine the feasibility of different remedial alternatives. To accomplish these tasks, specific levels of data quality are established by the procedures discussed below. DQOs are established in a three stage process as outlined in the EPA document, Data Quality Objectives for Remedial Response Activities (1987). The initial stage, which is covered in the preparation of this workplan, identifies the types of decisions that need to be made with the data. It includes an evaluation for existing data and development of a conceptual model of contamination at the site. In the second stage, the quantity and quality of data required to make the decisions from stage one is determined. The quantity and quality of the data are defined by factors such as the ARARs, acceptable risk levels, and the type of statistics and corresponding confidence intervals that will be used to evaluate the data. As a result of these factors, the target compounds, types of samples, required detection limits, the sampling and analysis approach, and precision, accuracy, and completeness goals will be determined. The second stage of the DQO process will be documented in the Quality Assurance Project Plan.

35 In the final stage of the DQO process, that actual procedures for obtaining data of acceptable quantity and quality are described. This includes specification of the exact type, number, and location of samples, and the procedures for collection and analyzing the samples, including the quality control measures. This information will be covered in the Field Sampling Plan.

8.0 Remedial Investigation 8.1 RI/FS Objectives The objectives of the SBMM Remedial Investigation is to gather sufficient information to characterize the nature and extent of the contamination at the site such that informed risk management decisions can be made. The purpose of the Feasibility Study will be to analyze and compare technological options for cleaning up the site and to evaluate their potential effectiveness. The goal of the clean-up at SBMM will be to reduce the risk or potential risk to public health and the environment, if the risks are found to be unacceptable and if workable and effective mitigation alternatives can be identified.

8.2 Project Planning and Management The RI/FS will be conducted in three parts, and will consist of three separate, but integrated studies on three operable units (OUs): the Herman Impoundment, the soils and mine waste piles and the lake sediments. Each Operable Unit Feasibility Study (OUFS) will characterize the nature and extent of contamination, potential threats posed to human health and the environment, and to further evaluate remedial alternatives for each OU. Each OUFS will be conducted in phases. In general, Phase I investigations will be designed to collect data for screening and site characterization purposes in order to determine Phase II data needs. Phase II investigations will be designed to collect statistically strong, high quality data for use in risk assessment and to support remedy selection. The schedule for specific RI/FS activities may be found in Chapter 12 of this workplan. The Sulphur Bank Mercury Mine RI/FS has been selected to be conducted in-house. Portions of the investigation will be conducted by EPA staff, with possible assistance from other federal and state agencies; however, due to the level of effort required for the three operable units, some of the work will be conducted entirely or in part by contractors.

36 The overall RI/FS project will be directed by the Remedial Project Managers with technical direction from members of the SBMM Technical Support Team. Individual members of the Technical Support Team will be responsible for planning various portions of the project and preparing sample plans and final reports. Other Team members will have advisory responsibilities. Table 3 presents the project organization.

TABLE 3 SBMM Project Organization Management; Remedial Project Manager Carolyn d'Almeida John Lucey On-Scene Coordinator Brad Shipley Regional Counsel Dan Reich Community Relations Vicki Rosen Contract Management: Project Officer Sherry Nikzat Contract Officer Jeri Simmons Technical Team: Ecologist/Superfund-ORD liaison Joe Greenblott Hydrogeologist Rich Freitas Toxicologist Stan Smucker Engineer Ken Erikson Field Investigation Stewart Simpson Quality Assurance/Quality Control Stewart Simpson Quality Assurance Officer Kent Kitchingman Techn i ca1 Advisorv: Public Health Gwen Eng (ATSDR), Bob Schlag, (DHS Epi-Studies) Ecology Jim Lazorchak, (EPA: EMSL-Cincinnati) Dave Charters, (EPA-ERT) Eco. Assess. Group Risk Assessment Support EPA: ECAO-Cincinnati OH Feasibility study Support EPA: RREL-Cincinnati OH RI Support/Modeling Bob Ambrose (EPA: CEAM-Athens GA) Site Specific Tech. Support Scott Walker (CAL-EPA) Emmanuel Mensah (CAL-EPA) Contractors; RI/FS ICF Technology Inc Ecological Assessment U.C. Davis

37 I I Most of the contracted RI/FS work will be conducted by ICF Technology, under the ARCS contract. Additionally, University of California - Davis has been contracted to conduct an Ecological Assessment to define the extent of contamination in the biota of I Clear Lake and to further investigate the factors controlling methylmercury production and bioaccumulation in Clear Lake and the lingering effects of mercury in the ecosystem, in order to I determine if attempts to remediate the contaminated lake sediments will be effective. I As the contamination problems at the SBMM site are very similar to the Carson River Superfund Site which is also currently beginning an RI/FS, SBMM team members will work closely with the Carson River RPM and technical team to ensure consis- I tency . Some work related to the SBMM RI/FS may also be carried out I by other agencies, including the US Bureau of Mines and natural resource trustees, including the US Fish and Wildlife Service, and/or California Department of Fish and Game. Health studies may also be conducted by the California Department of Health I Services, Office of Epidemiological Studies (DHS), the Agency for Toxic Substances and Disease Registry (ATSDR) and local health I agencies. The Lake County Flood Control Agency is currently beginning a study of the algae problem in Clear Lake under an EPA grant. I As the algal blooms may have an effect on the mercury methylation process, the SBMM team will follow up on the progress of that in- I vestigation. I 8.3 Compilation and Review of Data Throughout the investigation, the SBMM team will continue to review and compile existing information on the SBMM site, the I sources and extent of mercury contamination in Clear Lake, on- going research concerning the mercury methylation and bioaccumulation processes in freshwater ecosystems, and attempts elsewhere to mitigate mercury contaminated river and lake sediments. I The scope of the investigations will continue to be refined throughout the course of the RI/FS to adapt to the growing body of knowledge concerning the site and the behavior of mercury in I the environment. I 8.4 Development of Applicable or Relevant and Appropriate I Requirements (ARARs) I 38 I ARARs are legal requirements or standards which will effect the remedy selection process and the final design and implementation of the cleanup at SBMM. An in-depth discussion and preliminary list of potential ARARs is included in the Appendix. The procedure for development of ARARs is to first identify potential ARARs, then evaluate them. The identification of ARARs is an on-going process as more information is learned about the site. However, there are two points in the RI/FS process where formal requests for ARARs identification will be sent to the State, other Federal Agencies and EPA divisions. The first point is at the beginning of the RI/FS where potential ARARs can be identified using the data from past investigations. Potential ARARS will be identified for each of the possible remedial alternatives. Towards the end of the investigation, the same offices will be contacted again and the ARARs list will be further defined for the alternatives to included in the detailed analysis for the feasibility study reports. The following offices will be contacted: 1) State of California Department of Health Services 2) State of California Regional Water Quality Control Board 3) California State Clearing House 4) Lake County Environmental Health Department 5) U.S. Fish and Wildlife Service 6) U.S. Army Corps of Engineers 7) U.S. EPA Region 9 Water Management Division Air and Toxics Division RCRA Program Health and Safety Office Once potential ARARs are identified, and potential remedial alternatives are further defined and screened, the Regional Coun- sel and the Remedial Project Manager will analyze each proposed ARAR in relation to the pertinent facts about the chemicals present, and the location of and the types of action/technology under consideration. The analysis and screening of ARARs will be included in the final feasibility study reports.

8.5 Development of the Community Relations Plan A Community Relations Plan (CRP) will be developed as part, of the RI/FS, in accordance with the guidance document Community Relations in Superfund. A Handbook (1988). Contents of the CRP are further discussed in the Workplan Appendix. 8.6 Development of the Quality Assurance Project Plan I

39 I I I A Quality Assurance Project Plan (QAPjP) will be prepared for all data collection activities during the RI/FS. The QAPjP will be prepared according to the regional document, U.S. EPA Region 9 Guidance for Preparing Quality Assurance Project Plans for Superfund Remedial Projects (1989). Contents of the QAPjP are further described in the Appendix.

8.7 Development of a Health And Safety Plan A Health and Safety Plan (HSP) will be prepared for all field activities during the RI/FS. The HSP will be prepared according to the regional document, Field Health and Safety Manual, U.S. EPA Region 9. The Health and Safety Plan is further discussed in the Appendix..

8.8 Development of a Field Sampling Plan A Field Sampling Plan (FSP) will be prepared for each phase of field sampling during the RI/FS. The FSP will be prepared according to the regional document, Preparation of a U.S. EPA Region 9 Sample Plan for EPA-Lead Superfund Projects (1989). The required elements of the FSP are discussed in detail in the Ap- pendix.

8.9 Field Investigation Activities The objective of the Remedial Investigation is to obtain information needed to complete site characterization, ecological and human health risk assessments and treatability studies. An overview of the types of samples which may be collected, and other tests and surveys which may be required is presented in this section. Types of data to be collected for the human health risk assessment is also discussed in the Appendix. The RI/FS has been divided into three operable units, the Herman Impoundment, the mine waste piles and the contaminated lake sediments, which will each be investigated separately, as part of an integrated study. Data collected for one operable unit may be used in planning investigations for another operable unit. The field activities will be conducted in phases, and are subject to change in light of new information obtained throughout the course of the RI/FS. The activities to be conducted under each operable unit are discussed below.

8.9.1 Herman Impoundment Operable Unit

40 The primary concerns associated with this operable unit are human and ecological direct contact hazards associated with acidic water in the mine pit and potential surface and groundwater discharges of acid and metals into the lake. While groundwater in the vicinity of the mine is not used for drinking, acid conditions may enhance groundwater migration of metals which may adversely impact Clear Lake water quality. Possible remedial alternatives for this operable unit include: no action; adding lime to the pit to neutralize the acid; draining and plugging the pit, possibly combined with acid neutralization and underground injection to dispose of impoundment water; or installing barriers to re-route or block groundwater flow. Bradley Mining Company has already conducted an assessment of the Herman Impoundment to comply with requirements of the California Toxic Pits Cleanup Act, as well as several groundwater studies. EPA will conduct field investigations as necessary to confirm the information and conclusions of these reports and collect any additional data which may be necessary to characterize the significance of the problem and select a remedy. Confir- matory sampling will be performed on Herman Impoundment water and sediment to characterize the chemistry of the impoundment, and additional ground water samples will be collected to provide validated data to model contaminant transport. If necessary, a few additional wells may be installed as part of this study.

8.9.2 Mine Waste Piles Operable Unit The primary concerns associated with this operable unit are physical hazards and the potential for soil ingestion by children playing on the mine, ingestion of tules, wild berries or garden vegetables growing on the mine site or in mercury contaminated soils adjacent to the mine, possible air exposure to mercury and arsenic vapor and particulates, and the continuing erosion of mine wastes into the lake. Bradley Mining Company has been ordered by the RWQCB to construct erosion controls to stabilize the mine site. These controls include riprapping the shoreline and constructing a toe buttress on the waste piles to stabilize the slope, gully work to minimize erosion, and improving the Herman Impoundment dam. Ad- ditional remediation may be required to adequately protect human health and the environment. Potential alternatives for the mine waste piles operable unit may include: no action beyond the RWQCB controls; cutting back the slope of piles along the shoreline; capping the waste piles with soil and revegetating to minimize erosion; or on-site reburial of mine wastes in the Herman Pit. 41 Other possible alternatives for this operable unit are discussed in Section 6.1. Field investigations for this operable unit will include soil sampling, air monitoring and some sampling of on- site vegetation. a. Sampling of Soil, Mine Waste and Vegetation Additional mine tailings and waste rock samples will be collected to confirm existing data, and to provide validated data for the human and ecological risk assessments. Samples will be collected from areas with the greatest potential for human exposure (i.e.: samples to be collected near homes, children's play areas, areas where tules, blackberries or vegetables are grown, as well as grid samples. Samples will be analyzed for mercury and arsenic, an identified contaminant of concern at the site which has not been adequately characterized. Mine waste samples will also be analyzed for pH, chloride and sulfide in order to predict the dominant mercury species present, and to roughly predict the potential mobility of the mercury in the tailings and overburden , under both the groundwater and lake sediment scenarios. A full metals analysis will be performed on a per- centage of samples to more completely characterize the nature of the contamination and to define the analytical parameters for subsequent sampling. Data from the surface soil investigation will be used in the preparation of the human health risk assessment, to evaluate the risks associated with soil ingestion exposure . Samples will also be collected from tules and berries growing on the mine site to evaluate vegetative uptake for the Ecological Assessment and provide data for the Human Health As- sessment. b. Air Investigation EPA will conduct air monitoring in homes for mercury vapor, and ambient monitoring for mercury vapor and particulates to characterize the air migration pathway and to collect Risk As- sessment data. The analytical parameters for the air investigations will be determined from the soil data. Additional meteorological data will also need to be collected as part of this study, . .

8.9.3 Lake Sediments Operable Unit The primary concern associated with this operable unit is methylmercury production and bioaccumulation. Methylmercury produced in contaminated sediments enters the aquatic food chain, concentrating in the tissues of higher trophic level species. Humans and terrestrial wildlife may accumulate potentially harm- 42 ful levels of mercury through fish consumption. Methylmercury may also be absorbed through the skin; swimming may also be a potential exposure route. The alternatives most likely to be considered for this operable unit are: no action; dredging all, or only the most contaminated sediments; or covering all, or only the most contaminated sediments with clean sand or clay. Mercury methylation, cycling and bioaccumulation in aquatic ecosystems is highly complex and controlled by numerous competing factors such as temperature, dissolved oxygen, pH, redox potential, nutrients and biological productivity, bacteria count, and availability of organic and inorganic ligands and binding agents. Sediment mercury concentrations do not directly correlate with mercury concentrations in biota. Due to the potentially high costs of remediation and the extreme complexity of the problem, it is essential to develop an understanding of the system prior to selecting a remedy. The field investigations will include seasonal sampling of the sediment/water interface to evaluate the relationship between sediment mercury concentrations and methylmercury production, and aquatic tissue sampling under the Ecological Assessment to evaluate the pathways and the extent of mercury uptake in biota. The results of the investigations will be used to construct a detailed mass balance of mercury and methylmercury fluxes between sediments, water column and biota. Full target compound list (TCL) screening will be perform initially on tailings and overburden samples under the waste piles operable unit, which will be used to determine if there are any other metal contaminants of concern which should be evaluated in the sediment investigation. a. Water/Sediment Sampling EPA will be collecting seasonal lake water and sediment samples to develop a detailed mass balance of mercury speciation, as well as to collect data for use in both the human and ecological risk assessments. As the mercury methylation process tends to be cyclic, with seasonal variations, EPA will conduct frequent seasonal sampling of the bottom sediments and the lowest portion of water column near the mine and in background locations in order to detect seasonal fluctuations in the levels of methylmercury produced. The investigation will require intensive seasonal monitoring of the sediment/water interface to measure concentrations of elemental mercury (Hg°), reactive mercury (Hg2+) and methylmercury (MeHg), which is primarily responsible for mercury bioaccumulation. Physical tests, (measuring grain size, water con- 43 tent, organic content, pH, etc) will be conducted to characterize the physical nature of the sediments, as well as bulk and elutriate chemical tests to evaluate the partitioning of contaminants . Factors effecting the methylation process, i.e.: temperature, pH, pE, dissolved oxygen, concentrations of methylating bacteria, sulfide ion availability, etc., will also be monitored in an attempt to determine which factors are controlling the methylation of mercury in Clear Lake. The specific parameters to be included in the seasonal monitoring will be selected in the sampling plan. The investigation is expected to take two years to complete. Frequent (i.e. monthly) sampling at established monitoring stations is required as previous studies on other lakes have shown methylmercury production may peak sharply in response to seasonal changes; the peaks may be missed with less frequent sampling. The sampling schedule and specific details of the water column/sediment investigation will be defined in the Field Sam- pling Plan. During the sample plan preparation for the seasonal sediment/water sampling EPA will investigate and attempt to identify possible springs discharging into the Oaks Arm Clear Lake. A fathometer will be used to look for gas discharges during the selection of sampling stations. Areas of identified gas discharges will be included in the sampling program to characterize methylmercury production near natural springs. During the second phase of the project, grid core samples will be collected from the Oaks Arm sediments to further define the depth and extent of the contaminated area. b. Ecological Assessment Methylmercury is the species of mercury most responsible for bioaccumulation; once mercury enters the food chain, it becomes concentrated in the higher trophic level fish, and may become even more concentrated in terrestrial species consuming the fish: birds, mammals and humans. Seasonal tissue sampling of aquatic organisms is necessary in order to evaluate the routes of exposure and bioaccumulation pathways and to characterize and compare the degree of bioavailability of mercury from the contaminated Oaks Arm sediments with background sources. To be included in these investigations are selected species of benthic organisms, plankton and fish. Benthic flora and fauna (infauna and epifauna) absorb mercury directly from the sediments, are relatively stationary, and form the basis of the food chain for bottom feeding fish. Plankton (zooplankton and phytoplankton) are free-floating microorganisms which may absorb methylmercury from the water column, and form the base of the food chain for 44 water column feeders. Several fish species will be selected for sampling to represent various trophic levels, including small plankton-eating fish as well as larger piscivorous fish. The benthic mercury bioconcentrations and community structure in the vicinity of the mine will be compared to similar benthic communities elsewhere in the lake to assess the ecological impacts from the mine. Additional sampling of terrestrial species, including birds and mammals may also be incorporated into the Ecological Assessment as Phase II studies, if warranted. The Ecological Assessment will be designed primarily to determine the significance of the SBMM as a source of bioavail- able mercury in Clear Lake, in order to determine whether or not the contaminated sediments should be remediated. The specific tasks to be conducted will be further defined in the Ecological Assessment Workplan. c. Mercury Geochemical/Bioaccumulation Model During the course of the investigation, EPA's Office of Research and Development (ORD) will develop a computer model which will be used to incorporate and interpret the data collected under these studies to aid in evaluating remedial alternatives for the lake sediments operable unit. EPA's Center for Ex- posure Assessment Modeling (CEAM) located in Athens, Georgia proposes to link several existing models, including a mercury cycling model under development by the Electric Power Research In- stitute, and a sediment transport and resuspension model (WASP4), and bioaccumulation model (FGETS) already developed by CEAM - Athens. The model will be designed to establish a mass balance budget of mercury and methylmercury present in the sediments, water column and biota of the lake. Once the mass balance has been established, the model will be used to estimate the effects of various remedial strategies and sediment cleanup levels on the fate, transport, and bioaccumulation of mercury in Clear Lake.

8.10 Sample Analysis and Data Validation Samples collected in the field will be analyzed by the EPA Region 9 laboratory, or a Contract Lab Program (CLP) laboratory, using standard EPA methods whenever practicable. Specific analytical, quality control, and documentation requirements will be specified in the FSP. In the event that the CLP program is not capable of handling certain types of samples or analyses, a non-CLP lab offering special analytical services will be retained. Water column mercury speciation analyses in particular will require non-standard, super-clean analytical techniques. Labs and analytical methods will be selected based upon data 45 quality objectives. The CLP program will be used to analyze screening samples; non-CLP labs offering special analytical services will be considered for crucial samples. Validation of laboratory data will be conducted by the US EPA Region 9, Quality Assurance Management Section and their contractor. Data validation will be conducted according to the current EPA functional guidelines for validation of CLP data. Generally, all laboratory data will receive full data validation. Data used for field screening purposes may receive only a partial data validation; the use and extent of partial data validation will be discussed in the QAPjP or FSP.

8.11 Data Management and Interpretation Existing data, and data collected during the field investigation will be validated and interpreted to define the nature and extent of contamination, the degree of bioaccumulation, and to assess exposure pathways. Data and information collected during each phase of the project will be used to direct the focus of subsequent sampling events, and will be used in making managerial decisions regarding interim and long-term remedial action.

9.0 Risk Assessment The Comprehensive Environmental Response, Compensation and Liability Act of 1980, as amended, (CERCLA) requires that EPA action at Superfund sites be protective of human health and the environment. In order to meet this objective, EPA is required to perform both human and ecological risk assessments to characterize the magnitude of impacts of actual or potential releases of contaminants upon human health and the environment. Baseline Risk Assessments will be conducted to characterize the threats posed by the site in absence of any remedial action; the remedial alternatives that are developed during the feasibility study will also be evaluated in terms of their effectiveness in reduction of risk. Both the Ecological Assessment and the Human Health Risk Assessment will be performed in accordance with the Risk Assess- ment Guidance for Superfund. vols I & II (RAGS, 1989). Individual workplans for the Human Health Risk Assessment and Ecological Assessment are being prepared separately; the workplan for the Human Health Assessment may be found in the Ap- pendix to this workplan. Data collection for the Human Health Assessment will be incorporated into the field investigations, as summarized in section 8.9. Ecological Assessment will constitute a major portion of the Lake Sediments RI/FS; field data 46 collection requirements for the Ecological Assessment are discussed in detail in section 8.9.3. The Ecological Assessment workplan will be developed by the EA contractor.

10.0 Feasibility Studies The objective of Feasibility Studies (FS) is to develop and evaluate appropriate and cost-effective remedial alternatives to clean up contamination at SBMM. The investigation of the Sulphur Bank Mercury Mine has been divided into three parts, or operable units, which will separately develop and evaluate alternatives for the Herman Impoundment, the mine waste piles and the contaminated sediments in the lake. Decisions made during the FS process are based on information gathered during the Remedial Investigation. Feasibility Studies consist of three major components: 1) development and screening of alternatives; 2) detailed analysis of alternatives; and 3) final report and selection of a preferred remedial alternative. Feasibility Studies will be conducted in accordance with EPA OSWER Directive 9355.3-01, Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA.

10.l Identification of Alternatives Chapter 6 described remedial alternatives for source control at the mine site and pollution abatement of existing contamination in Clear Lake that were proposed in the Abatement and Source Control Study prepared by Humboldt State University. Section 8.9 also summarized the remedial alternatives which appear most likely to be considered for each of the three operable units, as follows: Operable Unit 1: HERMAN IMPOUNDMENT - no action; adding lime to the pit to neutralize the acid; - draining and plugging the pit/acid neutralization and underground injection to dispose of impoundment water; - installing barriers to re-route groundwater flow.

Operable Unit 2: MINE WASTE PILES - no action beyond slope stabilization measures - cutting back the slope of piles along the shoreline; - capping the waste piles with clean soil and revegetating to minimize erosion; - on-site reburial of mine wastes in the Herman Pit 47 Operable Unit 3: LAKE SEDIMENTS - no action; - dredging all, or only the most contaminated sediments; - covering all, or only the most contaminated sediments with clean sand or clay. Other alternatives, including those originally identified in the Abatement and Control study will be more thoroughly considered in the initial screening.

10.2 Screening of Alternatives During the initial screening, the number of potential remedial alternatives is reduced by evaluating each alternative with respect to technical implementability. Information from the site characterization is used to determine if a specific technology is appropriate for site remediation. Alternatives for remediation are developed by assembling combinations of appropriate technologies retained from the initial screening. Specific technology options are screened on the basis of whether or not they could meet a particular remedial action objective. During the screening, each alternative is evaluated for the following criteria: 1. Effectiveness - Alternatives will be evaluated as to whether they (1) adequately protect human health and environment, (2) attain federal and state ARARs or other criteria, or guidance, (3) significantly and permanently reduce the toxicity, mobility, or volume of hazardous constituents, and (4) are technically reli- able or are effective in other respects. 2. Implementability - Alternatives will be evaluated as to (l) the technical feasibility and availability of the technologies each alternative would employ, (2) the technical and institu- tional ability to monitor, maintain, and replace technologies over time, and (3) the administrative feasibility of implementing the alternative. 3. Cost - The costs of construction and any long-term costs to operate and maintain the alternatives will be evaluated. A detailed cost analysis will not be conducted at this stage, however, during the initial screening, cost will be an important factor when comparing alternatives.

10.3 Treatability Studies

48 Treatability studies may be conducted during the course of the Feasibility Study in order to: i) provide sufficient data to allow alternatives to be fully developed and evaluated during the detailed analysis, and to support the remedial design of the selected alternative; ii) evaluate the potential effectiveness of proposed remedial alternatives; and iii) reduce cost and performance uncertainties for alternatives to acceptable levels so that a remedy can be selected. Treatability studies are particularly appropriate for the lake sediments operable unit, to test the potential effectiveness of the sediment cover alternative. Toxicity testing may be needed in conjunction with treatability studies in order to develop cleanup criteria for the contaminated sediments, determine the extent of the area to be remediated, and predict the ecosystem's response to remediation. The toxicity tests /treatability studies will be closely tied to the Ecological As- sessment . Treatability studies can be performed on a either a bench or pilot scale. Bench-scale testing is usually performed in a laboratory setting; larger pilot studies are performed in the field and are usually not conducted until after the detailed analysis of the alternatives has been nearly completed. Bench scale studies could be conducted in a laboratory microcosm setting; several experiments could be designed to simulate the conditions in Clear Lake and to test the effects of various sediment concentrations on different selected species, in order to establish cleanup criteria. Microcosms could also be used to test the effectiveness of various cover materials or thicknesses, or possibly to simulate the effects of bottom disturbance during dredging. Tc test the cover alternative, bench or pilot studies will probably be required to ensure their effectiveness in Clear Lake. In particular, such treatability studies should be designed to provide the following information: 1) Test the degree to which the covering material will lie on top of the sediment and not mix with it; 2) Test the susceptibility of covered sediments to move downslope and re-expose contaminated layers; 3) Determine the effectiveness of alternative covering materials and depths of coverage in controlling the mercury transport; 4) Quantify the amount of resuspension that would take place and the extent of other environmental problems associated with the covering of bottom sediments; 5) Determine the impacts of wave action during winter storms upon cover maintenance; and, 6) Account for the presence of possible springs and evaluate their potential impacts on the cover, 7) Measure the effects that covering the sediments will have on the uptake of mercury in biota.

49 I I 10.4 Detailed Analysis of Alternatives The detailed analysis of alternatives will consist of the analysis and presentation of the relevant information needed to I allow decision makers to select a site remedy; it is not the decision-making process itself. Each alternative will be assessed against the nine evaluation criteria described in the I RI/FS guidance. The results will be arrayed to compare the alternatives and identify the key tradeoffs. The nine evaluation criteria include the following: I 1. overall protection of human health and the environment ("protectiveness"); 2. compliance with ARARs; I 3. long-term effectiveness and permanence; 4. reduction of toxicity, mobility, or volume through treatment; I 5. short-term effectiveness; 6. imp lenient ab i 1 i ty; 7. cost; 8. state acceptance; I 9. community acceptance. The evaluations conducted during this phase will build on I previous evaluations conducted during the development and screening of alternatives. This phase will incorporate any treatability study data and additional site characterization in- I formation. If necessary, the alternatives will be further defined. Each will be reviewed to determine if additional definition is required in order to apply the evaluation criteria I consistently and to develop detailed cost estimates. Once the alternatives have been described and individually assessed against the nine criteria, a comparative analysis will I be conducted to evaluate the relative performance of each alternative in relation to each specific evaluation criterion. The purpose is to identify the advantages and disadvantages of each I alternative relative to one another so that key tradeoffs can be I identified. 11.0 Remedial Investigation/Feasibility Study Reports I and Deliverables The RI/FS will consist of three separate, but integrated studies focusing on the Herman Impoundment, mine waste piles and the contaminated lake sediments. Two separate Operable Unit I Feasibility Study (OUFS) reports will be completed to characterize the nature and extent of contamination, assess the migra- I tion potential of contamination and the associated risks, and to I 50 I evaluate potential remedial alternatives for the Herman Impound- ment and the mine waste piles operable units. Both the Herman Impoundment OUFS and the mine waste piles OUFS are scheduled to be completed simultaneously in 1993, to ensure the selection of compatible remedies for the two on-site operable units. The overall RI/FS will be completed with the investigation of the contaminated lake sediments, which is expected to be completed in 1994. The OUFS and RI/FS reports shall be prepared in accordance with the Guidance for Conducting Remedial Investigations and Feasibility Studies under CERCLA (EPA/540/g-89/004). The Human Health Risk Assessment Report will integrate the human exposure and risk assessment for all three operable units into one report which will embody the human health evaluation for the overall site. The pertinent sections from the Human Health Risk Assessment will then be incorporated into each OUFS or RI/FS report. A separate Ecological Assessment Report will also be prepared, which will be incorporated into the overall RI/FS report.

51 RI/FS WORKPLAN APPENDIX Sulphur Bank Mercury Mine Superfund Site Appendix I: Tentative RI/FS SCHEDULE

Overall RI/FS; RI/FS Workplan - Final November 1991 Quality Assurance Plan - Final May 1991 Health and Safety Plan - Final May 1991 Community Relations Plan - Final January 1992 Human Health Risk Assessment: OU1 & OU2 - Winter 1992-1993 Overall Human Health Risk Assessment - Winter 1994 OU 1; Herman Impoundment; Herman Impoundment/Groundwater sampling - Spring 1992 OUFS Report - Spring 1993 Proposed Plan Public Comment Period - Summer 1993 Record Of Decision - Winter 1993-1994

OU 2; Mine Waste Piles: Phase I Sampling: soil - Summer 1991 Phase II Sampling: air, soil, vegetation - Summer 1992 OUFS Report - Spring 1993 Proposed Plan Public Comment Period - Summer 1993 Record of Decision - Winter 1993-1994

OU 3; Lake Sediments; Water Column/Sediment Sampling - Spring 1992 - Winter 1993-1994 Ecological Assessment Sampling - Spring 1992 - Winter 1993-1994 Toxicity Testing/Treatability Studies - Summer 1992 - Fall 1993 Final RI/FS Report - Summer 1994 Proposed Plan Public Comment Period - Summer 1994 Record of Decision - Winter 1994-1995 Appendix II COMPLIANCE WITH OTHER LAWS: APPLICABLE, OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARS) A. Discussion Under Section 121(d) of the Comprehensive Environmental Response Compensation and Liability Act (CERCLA), 42 U.S.C. Sec- tion 121(d) remedial actions at Superfund sites must, at a minimum, attain the level or standard of control set by requirements of other environmental laws, standards or requirements that are found to be either "applicable" or "relevant and appropriate" to the conditions and circumstances found at the site. Guidance for identifying ARARs may be found in the National Contingency Plan (55 FR 8741 et. seq., March 8,1990) and CERCLA Compliance With Other Laws Manual. Part I. Overview RCRA. Clean Water Act, and Safe Drinking Water Act. OSWER Directive 9234.1-01 (August 1988 and CERCLA Compliance with Other Laws Manual Part II. Clean Air Act. State Requirements and Other Environmental Statutes. OSWER Directive 9234.1-02 (August 1989). "Applicable" requirements are defined as those cleanup standards, standards of control, and other substantive environmental protection requirements, criteria or limitations promulgated under Federal or State Law that specifically address or regulate a hazardous substance, pollutant, contaminant, remedial action, location or other circumstance at a CERCLA site. "Applicability" implies that the remedial action or the circumstances at the site satisfy all of the jurisdictional prerequisites of a requirement. "Relevant and Appropriate" requirements are defined as those standards of control, and other substantive environmental protection requirements, criteria or limitations promulgated under Federal or State law, that, while not "applicable" to a hazardous substance, pollutant, contaminant, remedial action, location or other circumstance at a CERCLA site, address problems or situations sufficiently similar to those encountered at the CERCLA site that their use is well suited to the particular site or to the remedial action alternatives. For example, requirements may be relevant and appropriate if they would be "applicable" but for jurisdictional restrictions associated with the requirement. In addition to legally binding laws and regulations, EPA or the State may identify other advisories, criteria or guidance as "To Be Considered Material" (TBCs). These are non-promulgated advisories or guidance issued by Federal or State government that do not have the status of potential ARARs. These are evaluated along with ARARs as part of the site assessment to establish protective cleanup goals and to help identify remedial action alternatives. After completion of the risk assessment, if no ARARs address a particular situation, or if existing ARARs do not ensure protectiveness, then advisories, criteria or guidelines are to be considered (TBCs) to set cleanup goals. I Under SARA, all Federal requirements may be ARARs for a par- I ticular site; State requirements may be considered ARARs provided that they are: (1) Promulgated standards, with full weight of law; I (2) More stringent than Federal requirements; (3) Identified to EPA in a timely manner; (4) Found not to result in a statewide prohibition on land I disposal; and (5) Consistently applied statewide. I Section 121(e) implicitly states that no Federal, State, or local permits (administrative requirements) are required for remedial actions conducted entirely onsite. These onsite remedial actions must, however meet the substantive requirements of any ARARs. I Any action which takes place off-site, however, is subject to the full requirements of Federal, State, and local regulations. I ARARs have been divided into three categories: (1) chemical- specific (2) location-specific, and (3) action-specific requirements. Chemical-specific requirements are usually health or risk-based numerical values or methodologies that set limits on I concentrations of specific hazardous substances, pollutants and contaminants in the environment. Location-specific requirements set restrictions on conduct of activities due to the geographic I or physical location of the site, such as in a wetland, floodplain, wildlife reserve or historic site. Action-specific ARARS are technology or activity-based requirements which set I limitations on actions taken with respect to removal, treatment or disposal of hazardous substances. CERCLA Section 121 provides that under certain circumstances I ARARs that are non-statutory requirements may be waived for on- site remedial actions. Waivers which may be invoked are provided I by CERCLA Section 121(d)(4) and include such circumstances as: * interim remedial actions * compliance may result in greater risk to human health and the I environment * compliance is technically impracticable * situations where ARAR specifies a particular operating design or standard, but where equivalent or better results could be I obtained using an alternative design or method of operation * State ARAR which has not been consistently applied * Fund Balancing: compliance would entail such high cost, I without justifiable added protection or reduction of risk, such that funding of remedial action at other sites may be I jeopardized. ARARs and TBCs will be identified, screened and refined I throughout the Remedial Investigation/Feasibility Study process. B. Initial Identification and Screening of ARARs I 3 I Some potential ARARs and TBCs for the SBMM site have already been identified and are discussed below. Chemical-Specific Requirements: 1. gafe Drinking Water Act (SDWA) Maximum Contaminant Levels fMCLsl; 40 CFR 141. Standards for 30 toxic compounds have been adopted as enforceable standards for public drinking water systems. MCLs for non-carcinogens are based in part on the allow- able lifetime exposure to the contaminant for a 70 kg adult who is presumed to consume 2 liters of water per day. In addition to health factors, and MCL is required to reflect the feasibility of removing the contaminant from the water supply. EPA has established an MCL of 0.002 mg/1 for mercury, and 0.05 mg/1 for arsenic. 2. SDWA Maximum Contaminant Level Goals; (MCLG) 40 CFR 141 These standards are nonenforceable health-based goals for public water supplies. They are derived from chronic toxicity information, but do not acknowledge technical or economic feasibility as do the MCLs. The MCLG level for suspected human carcinogens has been set at zero. CERCLA 121 states that MCLGs will be attained to the greatest extent possible. MCLGs may be a TBC for this site. 3. Resource Conservation and Recovery Act (RCRA) Maximum Concentration Limit; (40 CFR 264 Subpart F) These are standards adopted under the RCRA groundwater protection program which provide groundwater monitoring and response requirements for RCRA permitted facilities. The baseline protection standard is the background level of the constituent or the MCL, whichever is higher. The SBMM site is not a RCRA facility; although these requirements would not be directly applicable to the SBMM site, they may be relevant and appropriate. 4. Clean Water Act (CWA) Ambient Water Quality Criteria; 40 CFR 100 - 149 Section 304(a) of the Clean Water Act requires EPA to develop ambient water quality criteria related to protection of human health and aquatic life. These standards are not directly enforceable and therefore not "applicable" but may be considered relevant and appropriate under the circumstances of the release or threatened release of contaminants from the site. 5. U.S. Food and Drug Administration fFDAl guideline for human, consumption of mercury in fish; The U.S. FDA has established an action level of 1 ppm for mercury in fish for human consumption. 6. California Hazardous Waste Control Act fHWCA). Health and Safety Code Section 25100-25395; 22 CCR Chapter 30 HWCA sets minimum standards for the management of hazardous and extremely hazardous wastes, for generation, transport, treatment, storage and disposal. I 7. California Hazardous Waste Criteria. 22 CCR Chapter 30 I These regulations set forth State definitions and criteria for identifying hazardous waste. If the waste is determined to be hazardous under these criteria, the management of the waste must I meet certain requirements. 8. Porter Cologne Water Quality Act. Water J2ode 13000 et. seq. The RWQCB is required to develop Basin Management Plans to set I enforceable water quality standards for the protection of the beneficial uses of State waters. Additionally, under WC Sections 13050 and 13172, the RWQCB is authorized to develop standards and I regulations for the discharge of mining wastes. 9. California Safe Drinking Water Act. Health and Safety Code I Section 4026 The State (DHS) has developed drinking water action levels as guidelines for the protection of drinking water systems. These levels are advisory, not regulatory and are used I where corrective action may be required. 10. Safe Drinking Water and Toxics Enforcement Act (Prop. 65). Health and Safety Code Chapter 6.6 This law was passed to I protect the people of California against chemicals that cause cancer, birth defects or reproductive harm, and requires notification and the development of safe-use numbers to ensure I protection of human health. I Location specific Requirements: 1. Archeological and Historic Preservation Act. 16 U.S.C. Section 469 Establishes procedures to preserve historical and I archeological data which might be destroyed through alteration of terrain as a result of a Federal construction project or Federally licensed activity or program. I 2. National Historic Preservation Act. 16 U.S.C. Section 470 Requires Federal agencies to take into account the effect of an Federally assisted undertaking or licensing on any district, I site, building, structure, or object that is included in or eligible for inclusion in the National Register of Historic I Places. 3. Fish and Wildlife Coordination Act 16 U.S.C. Sections 661-666 Requires Federal agencies involved in actions that will result in the control or structural modification of any natural stream or I body of water, for any purpose, to take action to protect the fish and wildlife resources which may be affected by the action. Requires consultation with the US Fish and Wildlife Service prior I to taking any action. 4. Clean Water Act Section 404. 40 CFR part 230. 33 CFR part I 320-330. 40 CFR Part 6. Appendix J Regulations to protect wetlands, as defined by U.S. Army Corps of Engineers regulations, by I prohibiting the discharge of dredged or fill material without a I permit, and taking actions to avoid adverse effects, minimize potential harm and preserve and enhance wetlands to the extent possible. 5. Endangered Species Act. 16 U.S.C Sections 1531 et. seq Defines and provides a means for conserving various species of fish, wildlife, and plants what may be threatened with extinction, and provides for the designation of critical habitats essential to the conservation of a threatened or endangered species. Requires Federal agencies, in consultation with DOI and the National Marine Fisheries Service,, to ensure that actions that they authorize, fund or carry out are not likely to jeopardize the continued existence of threatened or endangered species or adversely modify or destroy their critical habitats. 6. Executive Order on Protection of Wetlands. Exec. Order No. 11.990 Requires Federal Agencies to avoid, to the extent possible, the adverse impacts associated with the destruction or loss of wetlands and to avoid support of new construction in wetlands if a practicable alternative exists. 7. California Fish And Game Code. Title 14. Chapter 2. Section 5650 States that it is unlawful to deposit in, permit to pass into, or place where it can pass into waters of the State any of the following materials, including: industrial refuse, slag, acid, or any substance or material deleterious to fish, plant life or bird life.

Action Specific Requirements: 1. Surface Mining Control and Reclamation Act (SMCRA). 30 USC Sections 1201 et. seq., establishes a regulatory program for surface coal mining operations. Although the SBMM site is not a coal mine, some of the SMCRA requirements may be relevant and appropriate. These regulations set requirements for mine sites to implement sediment control measures to minimize erosion and prevent additional contributions of sediment to stream flow or run-off, and require that measures instituted must attain State or Federal effluent limits. These regulations also require back- filling and regrading of the disturbed area to approximate original contour, minimize erosion, and achieve a stable slope. The disturbed area must also be revegetated with a species native to the area. For sulfide mine sites where there is a release or threatened release of acid, these regulations also set forth requirements to minimize the disturbance of the hydrogeologic balance within the permitted and adjacent area. 2. RCRA Subtitle C (Hazardous Waste Management) RCRA Section 3001 and 40 CFR 261.4(b)(7) exempts certain solid wastes from specific ore and mineral processing operations. Wastes not exempted under the exclusion may be subject to RCRA subtitle C if determined to be a characteristic hazardous waste. Subtitle C regulations provide performance standards for the handling, transportation, storage, and disposal of hazardous wastes. RCRA requirements (either Subtitle D or C) may only be applicable if the wastes are solid wastes and will be actively managed. For the SBMM site, RCRA requirements may be relevant and appropriate, i: if not applicable. 3. RCRA Subtitle D fstate or Regional Solid Waste Plans) Mining wastes that are not regulated under Subtitle C (hazardous wastes) I may be subject to Subtitle D requirements. Subtitle D includes requirements for nonhazardous solid waste facilities, such as surface impoundments, waste piles and landfills. The subtitle I provides performance standards to be followed for disposal of solid wastes. These requirements address facility development, siting, operation, closure, and post-closure maintenance. 1 3(a). RCRA Surface Impoundment Design and Operating Requirements (4 0 CFR 264 Subpart K) Surface Impoundment requirements set forth under RCRA may be relevant and appropriate for this site. I These requirements set standards for design, operation, groundwater monitoring (under subpart F) and closure for surface I impoundments. 3(b). RCRA Waste Pile Design and Operating Requirements (40 CFR 264 Subpart L) A pile is defined as "any non-containerized accumulation of solid, nonflowing hazardous waste that is used for I treatment or storage." Subpart L sets forth requirements for liners, leachate collection and removal, run-off management, groundwater protection (Subpart F), and closure, which may be I relevant and appropriate for this site. 4. Rivers and Harbors Act. Section 10 and U.S. Army Corps of En- I gineers Regulations 33 U.S.C. 403. 33 C.F.R. 320-330 Sets forth regulations governing dredge or fill activities in navigable waters of the United States. I 5. Storm Water Discharge Requirements. 55 FR 47990. November 16. 1990 EPA recently promulgated the first of several regulations which will establish a permitting process and discharge regula- I tions for storm water runoff which regulates storm discharges from municipal sewer systems, industrial discharges as well as from mining operations where storm runoff may come into contact I with overburden, raw ore material, product or processing waste. 6. Underground Injection Control Program. 40 CFR Part 144 Es- tablishes classifications for underground injection wells and I permitting requirements, as well as standards for construction, operating, monitoring and closure of injection wells. Also sets forth promulgated treatment levels for hazardous constituents of I wastes to be disposed through underground injection. 7. National Ambient Air Quality Standards for Criteria Pol- lutants (NAAOS) 40 CFR Part 50 These standards set national I limitations on ambient concentrations of carbon monoxide, lead, I nitrogen dioxide, particulate matter, ozone and sulfur oxides. I Attainment and maintenance of NAAQS is a responsibility of States, and is achieved through State Implementation Plans, and. through regulation of major sources. Although the SBMM site may not be considered a "major source", these regulations may be considered relevant and appropriate for controlling particulate emissions from the site. 8. Federal Mine Safety and Health Act 30 U.S.C. 801-962; Occupa- tional Safety and Health Act. 29 U.S.C. 667 pertains to worker health and safety.

8 I Appendix III RI/FS PLANNING DOCUMENTS

A. Community Relations Plan The Community Relations Plan (CRP) will be developed during the early phases of the RI/FS to meet the following objectives: 1. Give the public opportunity to comment on and provide input to technical decisions. 2. Inform the public of planned or ongoing actions. 3. Establishing an information repository and administrative record. Community relations activities will follow the requirements and policies specified in the National Contingency Plan, CERCLA and SARA. At a minimum, community relations activities to be conducted include the following: * Conducting community interviews. * Developing a community relations plan. * Establishing an information repository and administrative record. * Providing notice and analysis of the RI/FS and proposed plan. * Providing a public comment period on the RI/FS and proposed plan. * Providing a public comment period on consent decrees for enforcement sites. * Providing an opportunity for a public meeting. * Discussing pre-ROD significant changes. * Preparing a responsiveness summary. * Publishing a notice after the selection of an alternative. * Publishing a notice of the proposed settlement in the Federal Register and providing a comment period on settlement actions. * Revising the community relations plan after the ROD is signed, if necessary. * Publishing an explanation of significant changes. * Preparing a fact sheet on the engineering design and making it available to the public during the remedial design.

B. Quality Assurance Prelect Plan fOAPnP) The Quality Assurance Project Plan (QAPjP) will be prepared to cover all data collection activities to be conducted during the RI/FS, which shall specify procedures for sample collection, packaging and handling, equipment decontamination, analytical methods, as well as data quality objectives. The QAPjP will include the following: 1) Project Description. The background sections of this workplan will be incorporated into the QAPjP. 2) Data Quality Objectives. The QAPjP will discuss in detail the DQOs according to the guidelines in section 7.2 of this workplan. 3) Project Organization. The QAPjP will identify individuals who are responsible for quality assurance, field and laboratory activities, and project management; it will also identify key data users (individuals or organizations). 4) Sample Collection. This element will be covered by referencing the Field Sampling Plan. 5) Sample Custody. The QAPjP will describe chain-of custody procedures. 6) Analytical and Quality Control Procedures. The QAPjP will include a list of analytical methods and target compounds appropriate to the RI/FS and will briefly discuss the routine quality control measures that will be made in the field and laboratory. This section will also describe preventative maintenance of field analytical instruments. Detailed quality control requirements for the field and laboratory will be covered by referencing the Field Sampling Plan. 7) Data Quality Management. The QAPjP will outline the project data management scheme. It will trace the path of data from the field or laboratory to storage of the final reported from; and it will describe record keeping, document control, and data validation. 8) QA Oversight. The QAPjP will describe performance and system audits, and corrective action procedures. The QAPjP will also identify the frequency, content, and distribution of reports to management on project status, audit results, and quality assurance assessments. The QAPjP will initially address data collection activities required to fill data gaps on soil and groundwater contamination at the site. As needed, the QAPjP will be amended to cover any new field tasks that are outside the scope of the original QAPjP, and which have not yet been determined to be required at the site, such as air sampling. Prior to conducting any field activities, the QAPjP and any amendments to the QAPjP must be reviewed and approved by the Regional Quality Assurance Officer and the Remedial Project Managers.

C. Site Health And Safety Plan CHSP)

10 I Health and Safety Plans (HSPs) shallbe prepared to cover all I site visits and sampling activities at the site, including soil, vegetation, air, ground water and surface water sampling, and well drilling, construction and development, and any other data I collection activities involving on-site field work. Elements of the HSP will include site background, personnel responsibilities, training and medical monitoring requirements, personal protective equipment to be used, procedure for visitors, site control I measures, decontamination plan, and emergency contingency plan. All HSPs prepared by EPA staff must be approved by the Regional Health and Safety Officer prior to conducting any field ac- I tivities. When field activities are conducted by a contractor, the I contractor will prepare their own HSP. Contractor HSPs will be prepared according to the manuals Standard Operating Safety Guides (US EPA. 1988) and Occupational Safety and Health Guidance Manual for Hazardous Waste Site Activities. (NIOSH/OSHA/USCG/EPA I 1985). I D. Field Sampling Plan fFSP) A separate Field Sampling Plan will be prepared for each I sampling phase or event to be conducted. Separate FSPs will be prepared for soil/mine waste/vegetation sampling, air sampling, ground water sampling, surface water sampling, lake water and I sediment sampling, and ecological assessment tissue sampling. I The following elements will be included in each FSP: 1) Sampling Objective. The FSP will include specific objectives for the sampling effort that describe the intended uses of the data and that relate directly to the data quality objectives out- I lined in the QAPjP. 2) Background. Appropriate parts of section I of this work plan I will be included in the FSP for site background. 3) Rationale for Sample Locations. Numbers of Samples, and I Analytical Parameters. The FSP will discuss the locations and numbers of samples being collected in the field, and the analyses to be performed on each sample. A rationale for the sampling and analytical scheme, and maps containing proposed sample locations I will be included. 4) Sample Analyses. The FSP will describe the analytical I methods, quality control parameters, and documentation requirements to be followed by Contract Laboratory (CLP) or EPA I laboratories.

I 11 I 5) Field Methods and Procedures. The FSP will describe field procedures and quality control requirements for collecting samples. It will include or reference documentation of procedures for any well construction and well development activities to be conducted. 6) Health and Safety Plan. An approved Health and Safety Plan will accompany the FSP. Separate FSPs will be prepared for each major sampling episode. Existing FSPs will be amended when new sampling activities are within the scope of an existing FSP. The FSP must be reviewed and approved by the Regional Quality Assurance Of- ficer and the Remedial Project Managers prior to conducting any field sampling activities.

12 IV. RISK ASSESSMENT WORKPLAN A. Human Health Risk Assessment Introduction The purpose of the Human Health Risk Assessment (HHRA) is to provide an evaluation, in accordance with the Risk Assessment Guidance for Superfund (RAGS, July 1989) of the potential threat to human health in the absence of any remedial action at the site. The HHRA will consist of two sections; (1) the Baseline Risk Assessment and (2) the Remedial Criteria. The purpose of the Baseline Risk Assessment is to evaluate the potential risks to human health and the environment that might exist currently and in the future if no remedial action is taken at the site. The Remedial Criteria section will then establish cleanup goals for each contaminant in each media, based on the exposure and toxicity assumptions used in the Baseline RA and the determined impact of site contaminants on potential receptors. guidance Documents The following documents constitute the main sources of risk assessment guidance for CERCLA/Superfund projects in Region 9 and will be the main sources of guidance for the Sulphur Bank site risk assessment: 1) Risk Assessment Guidance for Superfund, Human Health Evalua- tion Manual, Part A. Office of Solid Waste and Emergency Response. OSWER Directive 9285.701a (July 1989). This specifically supersedes the older guidance in the Superfund Public Health Evaluation Manual. EPA 540/1-86/060 (October 1986). 2) U.S. EPA Region IX Recommendations, Risk Assessment Guidance for Superfund, Human Health Risk Assessment (Interim Final), 15 December 1989. These are Region 9 supplemental guidelines which are intended to highlight components of RAGS thought to be especially important to Region 9 or address issues not covered in RAGS. 3) Exposure Factors Handbook. Office of Health & Environmental Assessment, EPA 600/8-89/043 (July 1989). 4) Superfund Exposure Assessment Manual. EPA 540/1-88/001 (April 1988) . Toxicity information for use in the risk assessment will be obtained primarily from the following sources: 1) Integrated Risk Information System (IRIS). IRIS is an EPA database containing toxicity values approved for risk assessment on an Agency-wide basis. IRIS is the ultimate database for EPA

13 risk assessment information; only if information is not available on IRIS for a chemical being evaluated should any other sources be consulted. 2) Health Effects Assessment Summary Tables (HEAST). HEAST sum- marizes toxicity values for chemicals for which Health Effects Assessments (HEAs), Health and Environmental Effects Documents (HEEDs), Health and Environmental Effects Profiles (HEEPs), Health Assessment Documents (HADs) or Ambient Air Quality Criteria Documents (AAQCDs) have been prepared. HEAST is updated on a quarterly basis. 3) EPA Criteria Documents. Criteria documents include Drinking Water Criteria Documents, Drinking Water Health Advisory sum- maries, Ambient Water Quality Criteria Documents and Air Quality Criteria Documents; they contain general toxicity information that can be used to develop toxicity values for risk assessment. 4) Agency for Toxic Substances and Disease Registry (ATSDR) Toxicity Profiles.

Baseline Risk Assessment The following elements will comprise the activities in preparation of the Baseline Risk Assessment: Preliminary Evalua- tion, Data Collection, Data Evaluation, Identification of Chemi- cals of Concern, Exposure Assessment, Toxicity Assessment and Risk Characterization. a. Preliminary Evaluation 1) Site Inspection Site inspections will be conducted with the goal of identifying relevant geographic, climatic and demographic features for the risk assessment. An important goal will be to identify populations potentially at risk, including both current and future populations. The Elem Indian Rancheria is a population of specific concern in this regard, since these people reside in close proximity to the site. 2) Historical Assessment of Potential Contaminants at the Site In conjunction with the Remedial Project Manager (RPM), the site history will be reviewed with the goal of indentifying chemicals expected to be present as contaminants, along with expected locations of contaminants. The site is an abandoned mercury mine and the major contaminant profiled to date is mercury. Arsenic has also been tentatively identified as a contaminant of concern based on historical data collected at the site. The historical review will seek to identify historical contaminants, the

14 expected locations (geographic and media) of contamination and transformation products of potential concern, e.g., methylmercury in fish and biota. 3) Preliminary Identification of Exposure Pathways Based on the site visit and the historical review of operations at the site, a preliminary identification of exposure pathways will be made. This task will concentrate on identifying complete exposure pathways and areas of potential human contact, taking into consideration both current and future conditions at the site. Pathways may include exposure through the following media: air (outdoor and indoor), surface soil, subsurface soil, surface water, sediment, groundwater and the foodchain, including fish ingested from Clear Lake and locally grown foodstuffs which may be impacted by site-related contamination. 4) Preliminary Sampling to Assess Potential Current Health Impacts from the Site Preliminary interviews with the Elem Indian community have tentatively identified several exposures of potential immediate concern. A preliminary data collection round is suggested to address these potential current health concerns and includes the following: a. Surface soil sampling on the mine site in the areas where children are known to play. Contaminants suggested for initial analysis: mercury and arsenic. b. Surface sediment sampling at Clear Lake waterfront near the Elem community and on Rattlesnake Island which serves as a destination point for children swimming in the lake. Con- taminants suggested for initial analysis: mercury and methyl mercury. c. Sampling of Clear Lake water near the mine site where children are known to swim. Contaminants suggested for initial analysis: mercury and methyl mercury (filtered and unfiltered water). d. Sampling of the tubers of the tules growing along the edge of Clear Lake near the Elem community and which serve as a foodstuff in the community. Contaminants suggested for initial analysis: mercury and methyl mercury. e. Indoor air sampling of Elem homes which are built over mine overburden and waste rock. Contaminant suggested for initial analysis: mercury. f. Sampling of the drinking water supply at the Elem community. The source of this water is the Clear Lake Oaks Water District which draws water from two wells located approximately 50 feet from Clear Lake in a shallow aquifer. The water supplies 15 for the Clear Lake Oaks community and the Windflower Water Dis- trict, the latter using direct surface water withdrawal in the Oaks Arm of Clear Lake, should be included in the preliminary sampling analyses for mercury. Contaminants suggested for initial analysis: mercury and methyl mercury.

b. Data Collection - Remedial Investigation The risk assessor will provide technical support for data collection in the remedial investigation phase of the project. The goal of this technical support will be to ensure that data collected in the Rl will be sufficient to support a meaningful assessment of potential human health risks posed by contamination at the site. 1) Need for Random/Purposive Samples Based on the site visit and historical review of operations at the site, a determination will be made of the need to collect samples in a random and/or purposive (directed) manner. Typi- cally, a directed approach will be used to indicate general areas of concern, i.e. those areas likely or thought to be affected by contamination. A random approach will then be used for collection of specific samples within these areas of concern. Data from random sampling is preferred for risk assessment as it can be meaningfully summarized by standard statistical methods. It should be noted that the type of sampling may differ for different media and/or locations. 2) Need for Filtered/Unfiltered Water Samples A determination will be made concerning the need for filtered and/or unfiltered water samples in the RI. If unfiltered water is of potable quality, data from unfiltered samples should be used in the exposure assessment; if not, it may be appropriate for the exposure assessment to focus on filtered sample data. In considering this need, attention will be paid to potential exposures to distant receptor populations (e.g., public water supply consumers, consumers of fish). 3) Meteorological and Physical/Chemical Data Needs In this element, the risk assessor will consult with Region 9 hydrogeologists, appropriate personnel at the Center for Ex- posure Assessment Modeling and the project manager to identify meteorological and soil/water chemistry data needs for risk assessment. The goal of this element is to ensure that appropriate data are gathered in the RI to support modeling of the environmental fate and transport of the contaminants at the site.

16 Climatic data will be sought from the U.S. Meteorological Service. Data needs are expected to include precipitation, temperature, wind speed, wind direction and atmospheric stability class on an hourly basis. The local airport will also be investigated as a possible source of meteorological data. The need for site-specific data on airborne particulates (concentration and size distribution) and/or windblown dust is probable at this site. The feasibility of collecting data for total air particulates and the respirable (PM10) fraction of airborne particulates on-site and in the Elem community will be determined. 4) Background Sample Collection The risk assessor will consult with personnel involved in environmental fate and transport modeling, a statistician and the project manager in order to identify appropriate locations, types and number of samples to be taken for evaluation of background levels for contaminants at the site. The goal of this element is to provide sufficient data on natural and ubiquitous levels of the chemicals identified at the site to distinguish site-related versus "other" contributions to the levels of contaminants detected in the RI. This is a crucial component of the RI at this site, where geothermal activity has contributed to a natural background level of mercury. 5) Statistical Analysis Support The risk assessor will consult with a statistician regarding the appropriate statistical procedures for summarizing data collected in RI in order to provide meaningful analyses for risk assessment purposes. The risk assessor and the statistician will advise the project manager regarding the appropriate number and type of samples to be collected in the RI in order to support risk assessment needs. 6) Adequacy of Detection Limits Detection limits for the analytical procedures used on samples collected in the RI will be reviewed from a risk assessment perspective. The goal of this review is to ensure that the analytical procedures in the RI are sufficiently sensitive to detect contaminant levels potentially posing significant risks to human health or the environment. 7) Advise Re: Additional/Enhanced Sampling or Analysis The risk assessor will review actual locations and types of samples collected in the RI to determine if the sampling effort is sufficient to evaluate exposure pathways for potential exposure to contaminants in the vicinity of the site. If necessary, the risk assessor will advise the project manager of any additional sampling needed to support the risk assessment. This 17 advice will be based on the risk assessor's review of location/type of samples and the adequacy of detection limits for the analytical procedures. 8) Demographics of Potential Receptor Populations In this element, the assessor will undertake efforts to characterize populations potentially at risk and activity patterns at and/or adjacent to site. This investigation will focus on both current and future land uses and activities at the site; the possibility of future residential development of the site will be a specific concern. Local planning departments will be contacted for future land use projections and ordinances. Any regulations specifically addressing future development will be reviewed. The local association of governments will be contacted to obtain population statistics for census tracts within a two mile radius of the site. Current population data will be summarized, as well as projections for the future (the year 2020 will serve as a target date). U.S. Census data for 1980 (1990 if available) will be used to determine demographic parameters such as age distribution.

c. Data Evaluation In this phase of the risk assessment, the data collected in the RI will be reviewed and evaluated for its applicability for risk assessment. Any data not of sufficient quality (accuracy, precision, etc.) or of a nature inappropriate to risk assessment will be eliminated. The goal of this phase will be to interpret the RI data in a risk assessment context, specifically focusing on the following issues: - type and distribution of contaminants - identification of non-site-related contamination in the area - estimation of background levels of "contaminants" - contaminant exposure pathways - potential exposure levels at points of human contact 1) Data QA/QC A quality analysis/quality control review of the RI data will be obtained from the Region Environmental Services Branch and reviewed by the risk assessor. Any data not meeting quality objectives stated in RAGS will be eliminated from further consideration for the risk assessment. 2) Statistical Analysis

18 Statistical analysis of the data will be performed using a computerized statistical package; the analysis may include, but is not limited to: - test for normality - description of central tendency (esp. arithmetic & geometric means) - description of variability (standard deviation, etc.) - tests for comparison (esp. to background) - trend analyses over time, season, distance, depth, etc. Summary tables or databases will be prepared as necessary. A statistician will be consulted as part of this element to ensure that appropriate statistical procedures are employed. In addition, personnel involved in environmental fate and transport modeling (e.g., hydrogeologists, air modelers) will be consulted to determine their needs regarding statistical analysis and summary.

d. Identification of Chemicals of Concern This phase of the project will identify those chemicals which will be carried through the detailed risk assessment for the site. A corollary goal is to eliminate from further consideration those chemicals posing a risk that is clearly de minimus. 1) Establish Selection Criteria The characteristics of the site and the RI data will be reviewed in the context of risk assessment guidance and standard-of-practice to set criteria for inclusion/exclusion of chemicals for further analysis. Criteria to be considered will include, but not be limited to: - frequency of detection - adequacy of detection limits - comparison to background - comparison to laboratory/blank contamination - toxicity potential - risk potential. A screening level risk analysis may also be performed to identify any chemicals clearly posing a de minimus risk; these may also be eliminated from further consideration. A rationale will be stated in the risk assessment report for each chemical eliminated as part of this element of the project. Class A chemicals, Known Human Carcinogens, will generally be included as chemicals of concern, regardless of other selection criteria.

19 Based on preliminary data collected to date, chemicals currently expected to be included in the detailed risk assessment include mercury, methyl mercury and arsenic.

e. Toxicity Assessment 1) Toxicity Profiles Standard risk assessment databases will be searched for relevant toxicity information on the chemicals of concern. A toxicity summary will be provided for the individual chemicals of concern along with relevant environmental fate and transport data, based on appropriate literature citations. 2) Toxicity factors Reference doses (RfDs) and cancer potency factors/slope factors (CPF/SF) will be obtained from the following hierarchy of sources as noted in Section 2.0: - Integrated Risk Information System (IRIS) - Health Effects Assessment Summary Table (HEAST) - EPA Criteria Documents 3) Development/Solicitation of Toxicity Values Toxicity values "missing" from the standard sources may be derived by the risk assessor or solicited from the Agency's En- vironmental Criteria Assessment Office (ECAO) or other sources,. This may be necessary for some of the potential contaminants of concern, e.g., mercury and/or methylmercury, should exposure routes such as inhalation and dermal absorption be determined to be of concern at the site. The source or derivation of all toxicity values will be documented. Uncertainties in the toxicity values for the chemicals of concern will be noted in the discussion of uncertainties in the risk assessment. f. Exposure Assessment The goal of this phase of the project is to identify and quantify known and hypothetical exposure pathways relevant to an assessment of public health risk at the site. Potential exposure pathways associated with the site will be reviewed and evaluated with regard to completeness, plausibility and importance relative to public health and environmental considerations. Potentially important pathways are identified and quantitative estimates of exposure are developed for a subsequent, detailed characterization of risk potential. 1) Identify Exposure Pathways

20 I This project element will identify exposure pathways to be I evaluated in the detailed risk assessment. Exposure pathways must be complete and must consider both current and future land uses. Complete pathways consist of the following (all elements I must be present): (1) a source and mechanism for release (2) a retention or transport medium/media I (3) a point of potential human contact with the contaminated medium/media (4) an exposure/intake route at the point of human I contact. Identification of exposure pathways will consider potential releases from the site into soil, surface water/sediment, air and I groundwater.Minor pathways, those creating a clearly de minimus risk, may be eliminated for some or all chemicals based on I screening risk analyses. Specific tasks under this element include, but are not I limited to: 1. Water Well Inventory An inventory of water wells, including municipal and private I drinking water wells and agricultural/industrial wells, will be conducted to identify the location, depth of completion and type of water wells in the area. Wells located within approximately a I two mile radius of the site will be located on topographic maps. Local regulations regarding the installation and use of private I wells may also be reviewed. 2. Assessment of Groundwater Exposure Potential Potential exposure pathways that may be considered relative I to groundwater wells include, but are not limited to: - ingestion as drinking water I - inhalation from domestic uses - food chain exposures from agricultural uses - atmospheric volatilization from agricultural/industrial I uses 3. Surface Water Uses I The uses of Clear Lake for drinking water, agriculture and recreation (e.g., fishing, swimming), will be documented. Ephemeral bodies of surface water, such as run-off ponds, and as- I sociated sediment will also be considered. Clear Lake supports a large commercial fishery which supplies fish, e.g., blackfish and carp, to markets known to include I Sacramento and the Bay Area. The feasibility of investigating levels of contaminants in representative commercial catches of I 21 I fish from Clear Lake will be investigated. Additional analyses for potential contaminants in fish will be performed as necessary to supplement the existing database on mercury in fish in Clear Lake. Municipal and private water systems which withdraw water directly from the Oaks Arm of Clear Lake, e.g., the Windflower Water District, will be considered for contaminant analysis. Agricultural withdrawal systems, e.g., the Orchard Shores system, will be similarly evaluated. Additional potential exposure pathways that may be considered relative to surface water bodies include, but are not limited to: - incidental ingestion of surface water - dermal contact with surface water - food chain exposures from agricultural uses - incidental ingestion of sediment - dermal contact with sediment ^Agricultural uses are reported to include soil enrichment of local gardens with algae which blooms densely in much of Clear Lake. This pathway will be further investigated and data collection undertaken as necessary, e.g., saunpling of algae for contaminants of concern such as mercury. 4. Potential Air Pathways The environs of the site will be examined tidentify potential and likely pathways and locations relevant to potential airborne exposures. Potential exposures that may be considered relative to the air pathway include, but are not limited to: - inhalation of chemicals volatilized from the soil and/or vadose zone - inhalation of soil particulates Both outdoor and indoor exposures may be considered. Indoor exposure considerations will specifically include homes of the Elem community which are constructed over mine overburden and waste rock. 5. Potential Soil Exposures The environs of the site will be examined to identify potential and likely pathways and locations relevant to potential exposures to contaminants in soil and/or dust. Potential soil/dust exposures that may be considered include, but are not limited to: - incidental ingestion of soil - dermal contact with soil Both outdoor and indoor exposures may be considered. 22 2) Environmental Fate and Transport Analysis In this element of the project, appropriate environmental fate and transport models will be used when necessary to estimate concentrations of contaminants that may be expected to occur at points of potential human contact. Exposure modeling techniques utilized for the Sulphur Bank site may range from simple al- gebraic equations to complex computer models. Upon consultation with appropriate guidance documents and personnel, relevant models will be identified for estimation of environmental fate and transport of the contaminants at the site. The main sources of guidance are expected to be hydrogeologists in the Technical Support Section, the Superfund Exposure Assess- ment Manual and the Center for Exposure Assessment Modeling (CEAM) at Athens, GA. Choice of appropriate exposure models will be based on site-specific factors and the nature of the data obtained in the RI. The models selected for exposure assessment should be able to reasonably simulate the environmental conditions in the area of the site and the constituent transport processes. Preference will be given to models which generate results consistent with available site-specific observations. Models initially considered for use at this site will be simple or screening-level models, many of which are described in the Superfund Exposure Assessment Manual. Fate and transport analyses which may require a computer modeling effort at this site may include, but not necessarily be limited to, atmospheric dispersion of airborne contaminants, groundwater plume modeling and uptake of contaminants in the foodchain. 3) Quantification of Exposures The goal of this phase of the project is to calculate chemical-specific intakes for the exposure pathways selected for quantitative evaluation in the risk assessment. The general equation for estimation of intake levels is: I = (C X CR X EFD) / (BW X AT) Where: I «= daily contaminant intake (mg/kg/d) C = contaminant concentration contacted over the exposure period CR = contact rate with contaminated medium EFD = exposure frequency and duration term BW •= body weight AT = period over which exposure is averaged. 1. Define Exposure Scenarios

23 Two exposure scenarios will be evaluated for each of the exposure pathways identified for inclusion in the risk assessment. The Risk Assessment Guidance for Superfund specifies that the overall risk characterization, integrated across all relevant contaminants and exposure pathways at the site, will be evaluated for a Reasonable Maximum Exposure (RME) scenario. Definition of this RME scenario requires evaluation of both Average and RME scenarios for each individual exposure pathway. The overall RME scenario is then defined as a reasonable combination of pathway- specific Average and RME exposures to account for additive exposures to more than one pathway. The average pathway-specific exposure scenario is based on average contaminant levels in the environment and average values for exposure assumptions such as contact rate, exposure frequency and duration, etc. The RME pathway-specific scenario is based on the upper 95% confidence limit of the mean contaminant levels in the environment and on upper 90-95th percentile levels, or best professional judgment, for exposure assumptions such as contact rate, exposure frequency and duration, etc. A third exposure scenario, Worst Case, may be used to to initially screen out media, exposure pathways or contaminants that pose a risk to public health that is clearly de minimus. Exposure assumptions used in the Worst Case scenario are typi- cally unrealistic maximal levels chosen to ensure an overestimate of the actual exposure potential at the site. 2. Identify Exposure Assumptions Numerical values for variables in the general equation for estimation of intake levels are obtained chiefly from two sources. The Exposure Factors Handbook is the primary source for exposure assumptions and the Risk Assessment Guidance for Super- fund is the secondary source. Additional guidance is issued periodically as OSWER Directives, such as the interim final guidance on soil ingestion (OSWER Directive 9850.4). Other sources may be consulted for parameters not addressed in any of the above; documentation will be provided in the risk assessment report. If site-specific data on exposure parameters were collected as part of the RI, these should preferentially be used in the intake equations. 3. Quantitative Evaluation of Exposure Scenarios Actual or potential exposure to contaminants at the site will be calculated according to the general equation for estimation of intake levels, as discussed above. Specific forms of

24 I this equation are presented in Risk Assessment Guidance for Su- I perfund for many of the standard exposure pathways at Superfund I sites (see Chapter 6: Exposure Assessment, section 6.6). 4. Quantitatively Evaluate Overall RME Site Exposure Potential I Reasonable combinations of individual exposure pathways will be identified and quantitatively evaluated in order to generate an overall RME estimate of exposure potential. A table summariz- I ing exposure estimates, exposure assumptions and pathway combinations for the various scenarios will be created for the risk as- I sessment report. 4) Additional Health Studies Under Consideration Additional public health studies may be considered for in- I clusion in the health assessment. These may include a study of blood mercury levels in children and other members of the Elem community near the site. Such studies would be coordinated with I the California Department of Health Services. I g. Risk Characterization In this final phase of the Baseline Risk Assessment, the toxicity and exposure assessments are integrated into quantita- I tive or qualitative expressions of risk. To characterize the non-cancer toxicity potential projected contaminant intakes are compared to reference doses, which represent daily intakes ex- I pected to be without significant risk of toxicity. Potential cancer risks are estimated by multiplying the projected daily contaminant intakes by the appropriate cancer potency factors. Separate risk evaluations will likely be performed for current I and future land use scenarios. Separate evaluations may also be performed for pathways and/or populations which are not expected to overlap (e.g., exposure via off-site consumption of municipal I water may not overlap with exposure to on-site surface water/sediments).

I h. Uncertainties A discussion will be developed for the report of the uncer- I tainties in the risk assessment. These may include, but are not limited to, uncertainties related to: I - toxicity assessment - exposure assumptions - future land use assumptions I - cancer potency factor or RfD derivation - RI data.

I 25 I To the extent possible, an evaluation should be made of the potential impacts on the overall risk assessment of these various uncertainties. It is recognized this evaluation may be highly judgmental and may be of either a qualitative or quantitative nature.

i. Summary for Report The Risk Assessment report should contain summary discus- sions, with tables, on the following: 1. Cancer risk estimates and hazard indices for both average and reasonable maximum exposure scenarios for each pathway and for an aggregate RME scenario for the entire site. Prior to summation of the aggregate risk, estimated cancer risks should be segregated by weight of evidence category for the contaminants at the site. 2. These tables should include comments highlighting any unusual factors that may influence interpretation of the risk estimates (such as: "Risk primarily due to assumed drinking water use of a non-potable aquifer." or "Metals at levels below background contribute significantly to the estimated risk." or "Risk primarily due to X, which is present at levels below its MCL."). 3. Exposure assumptions for each scenario, with documentation of source or rationale for use (see exhibit 6-20 of RAGS for an example of a table summarizing exposure assumptions). 4. Exposure estimates (estimated daily intakes) with comments on the major contributing factors. 5. Reference dose (RfD) and cancer potency factor (CPF) values (and any other toxicology criteria used in the risk assessment). CPFs and estimates of the upperbound excess lifetime cancer risk should be accompanied by the weight of evidence appraisal for each chemical. 6. Contaminant levels at the site (include mean, upper 95% confidence limit of the mean, maximum, # detected/** samples).

j. Report Format The risk assessment report is expected to follow Exhibit 9-1 • of the Risk Assessment Guidance for Superfund, Suggested Outline ™ for a Baseline Risk Assessment Report,.

26 I I B. Ecological Assessment (EA) The Ecological Assessment will be performed to evaluate the I impacts of contamination from the SBMM site on fish and wildlife populations in order enable EPA to make ecologically-based remedial decisions. The primary exposure pathway of concern for I biota is the aquatic pathway; mercury contaminated mine sediments present in the Oaks Arm of the lake may contribute significantly to the bioaccumulation of mercury in fish, which are a major food I source for many terrestrial species in the area. The objectives of the EA are to: 1. Determine if mercury contaminated sediments from the mine I that are present in the lake have resulted in adverse ecological impacts. I 2. Assess whether or not remediation of contaminated lake sediments may be effective in reducing the bioaccumulation of mercury in Clear Lake fish. I 3. Provide a basis for developing cleanup criteria for contaminated sediments present in the lake. I The Ecological Assessment Workplan will be prepared separately by the EA contractor and will be incorporated by I reference into the overall RI/FS workplan. I I I I I I I I 27 I APPENDIX D Preliminary Administrative Record Index Page 1 02/14/92

SULPHUR BANK MERCURY MINE SUPERFUND SITE Lake County, California *** Draft Administrative Record Index *** Removal Action No. 1

DOC # AR # DATE AUTHOR ADDRESSEE SUBJECT yy/mm/dd

2142-00013 R1- j 86/12/01 CA Regional Water Quality Summary of mercury data collection Control Board - Central at Clear Lake Valley Region

2142-00015 R1- 7 87/00/00 James Luzier. Albert Bradley Mining Co Herman Lake TPCA assessment Waibel w/appendices A, 1 & 2 & w/o Columbia Geoscience appendix B (for appendix B, see doc #2142- )

2142-00161 R1- 87/00/00 Columbia Geoscience Bradley Mining Co Appendix B: Lab data sheets to Herman Lake TPCA assessment (goes w/document #2142-00015)

214Z-00052 R1- LJ 87/04/00 James Stratton, et al Methyl mercury in northern coastal CA Dept of Health mountain lakes: Guidelines for Services sport fish consumption for Clear Lake...Lake Berryessa...Lake Herman...

2142-00017 R1- 88/07/00 Columbia Geoscience Bradley Mining Co Hydrogeological assessment rpt w/o plates 1 - 3 & appendices 1-2 (for appendices, see #2142-00018 & #2142-00021)

2142-00018 R1- (0 88/07/00 Columbia Geoscience Bradley Mining Co Hydrogeological assessment rpt appendix 1: Section 13: Sampling & analysis data & misc rpts (for rpt, see doc #2142-00017) (redacted FOIA ex 4 & 5)

2142-00019 R1- 88/08/00 Columbia Geoscience Bradley Mining Co Executive summary findings & recommendations fr 1985 evaluation of mercury sources, 1987 Herman Lake TPCA assessment, 1988 hydrogeological assessment

2142-00031 R1- ' 88/08/18 David Clark William Lewis Site assessment rpt (cont #68-01- Ecology & Environment, Environmental Protection 7368, TAT #098808-T-0006, TDD Inc Agency - Region 9 #T098806-018, PAN #TCA0584-SAA) w/appendix A: Photographic documentation

2142-00113 R1- 88/08/31 David Clark Wi Hi am Lewis Technical Assistance Team Ecology & Environment, Environmental Protection stabilization feasibility study, Inc Agency - Region 9 TAT #098808-T-0015, TDD #T098806- 018, PAN #TCA0584-SAA, cont #68-01- 7368 w/attchs Page 2 02/14/92

SULPHUR BANK MERCURY MINE SUPERFUND SITE Lake County, California *** Draft Administrative Record Index *** Removal Action No. 1

DOC # AR # DATE AUTHOR ADDRESSEE SUBJECT yy/mm/dd

2142-00021 R1- 89/07/00 Columbia Geoscience Bradley Mining Co Hydrogeological assessment rpt appendix 2: Section 10 - monitoring systems (for rpt see doc #2142- 00017) (redacted FOIA ex 4 & 5)

2142-00022 R1- j / 89/11/00 Columbia Geoscience Bradley Mining Co Hydrogeological assessment rpt appendix 3: Update (for rpt, see doc #2142-00017)

2142-00023 90/01/00 Charles Chamberlin, et CA Regional Water Quality Abatement & control study: Sulphur al Control Board Bank Mine & Clear Lake w/appendices California State Univ, A - D Humboldt

2142-00106 R1- / 7 90/11/00 Randall Hill, Erik Bradley Mining Co Erosion control - remedial action Mikkelsen design plans & construction Cornforth Consultants, schedule w/maps 1,2,4,5 (missing Inc map 3)

2142-00045 R1-/fs{ 90/11/26 Andrew Vessely, Randall Frederick Bradley Ltr: Waste discharge requirements - Hill Bradley Mining Co construction of erosion control Cornforth Consultants, measures impoundment dam & culverts Inc w/site plans & limitations of rpt

2142-00109 R1-/-t 90/11/28 Neil I Butcher Environmental Protection Site assessment rpt, TAT #099011-T- Ecology & Environment, Agency - Region 9 006. TDD #T099010-048, PAN Inc #ECA0584-SA w/marginalia, attch A: Photos & attch B: Analysis & QA/QC work plan

2142-90073 R1-i 90/12/11 Scott Walker Frederick Bradley Ltr: Comments on construction of CA Regional Water Quality Bradley Mining Co temporary erosion control measures Control Board - Central rpt Valley Region

2142-90075 R1- }fj 91/01/03 Scott Walker Frederick Bradley Ltr: Comments on erosion control CA Regional Water Quality Bradley Mining Co remedial action design plan & Control Board - Central construction schedule, per Waste Valley Region Discharge Order #90-045

2142-00105 91/04/00 Cornforth Consultants, Oversized Maps: Erosion control Inc measures 10 sheets (map case drawer #18)

2142-00047 91/05/00 Cornforth Consultants, Bradley Mining Co Construction quality assurance plan Inc - erosion control measures Page 3 02/14/92

SULPHUR BANK MERCURY MINE SUPERFUND SITE Lake County, California *** Draft Administrative Record Index *** Removal Action No. 1

DOC # AR # DATE AUTHOR ADDRESSEE SUBJECT yy/mm/dd

2142-00046 91/05/01 Cornforth Consultants, Bradley Mining Co Final design memo - riprap/rockfill Inc buttress erosion control measure w/appendices, TL to Frederick Bradley fr Randall Hill & Erik Mikkelsen 5/1/91

2142-00032 91/06/14 Stewart Simpson Field sampling plan (FSP) for Environmental Protection surface soil sampling 6/10-14/91 Agency - Region 9 w/map

2142-90080 91/06/20 Carolyn d'Almeida Scott Walker Ltr: Comments on construction Environmental Protection CA Regional Water design plans for slope Agency - Region 9 Pollution Control Board stabilization

2142-00029 R1- ..O 91/08/01 James Luzier Bradley Mining Co Interim rpt: WDR monitoring results Luzier Hydrosciences (1990-91) - sediment, surface water & groundwater monitoring

2142-00110 91/08/09 C Babbitt, et al John Lyons Ltr: Bid package for erosion Riedel Environmental Landels, Ripley & Diamond control project w/proposed Services, Inc schedules

2142-90152 91/08/29 Eric Zalas Anthony Garvin Ltr: Reevaluation of proposed scope Riedel Environmental Landels, Ripley & Diamond of work for erosion control project Services, Inc

2142-90151 R1-' 91/09/26 Daniel Reich, Scott Anthony Garvin TL: Erosion control cost estimates Walker Landels, Ripley & Diamond Environmental Protection Agency - Region 9

2142-90150 91/09/30 Howard Dashiell Frederick Bradley Ltr: Proposal pursuant to telephone Mitchell & Heryford Bradley Mining Co call re possible mutually beneficial transfer of spoils fr aggrelite quarry to provide slope protection for mine

2142-90153 R1-<5t<5" 91/10/16 Scott Walker Frederick Bradley Ltr: Erosion control cost estimates CA Regional Water Quality Bradley Mining Co Control Board - Central Valley Region

2142-00114 91/10/25 Margie Weiner Data validation rpt Case SAS #16614 ICF Technology, Inc Memo #1 Analyses: RAS metals w/TL to Stewart Simpson fr Victoria Taylor 10/25/91 Page 4 02/14/92

SULPHUR BANK MERCURY MINE SUPERFUND SITE Lake County, California *** Draft Administrative Record Index *** Removal Action No. 1

DOC # AR # DATE AUTHOR ADDRESSEE SUBJECT yy/mra/dd

2142-00119 R1-j>£) 91/18/28 Lisa Hanusiak Data validation rpt Case SAS #6399Y ICF Technology, Inc Memo #2 Analyses: SAS arsenic & mercury w/TL to Stewart Simpson fr Victoria Taylor 10/28/91

2142-90154 R1-,J/ 91/10/28 Stewart Simpson Data summary tables (refers to Environmental Protection document 2142-00014) Agency - Region 9

2142-00111 91/10/31 Theresa Brandabur Carolyn D1Almeida Ltr: Data assessment Itr rpt, cont ICF Technology, Inc Environmental Protection #68-W9-0059, Work Assignment #59- Agency - Region 9 11-9KL2 w/o computer diskettes & w/rpt w/appendices A - D (draft)

2142-00102 R1- 91/11/00 Carolyn d'Almeida, et al Final workplan for EPA-9 in-house Environmental Protection Remedial Investigation/Feasibility Agency - Region 9 Study (RI/FS)

2142-00112 91/11/07 Scott Walker Water quality data & inspection CA Regional Water Quality summary rpt w/appendices A - E & Control Board - Central w/o computer diskette Valley Region

214a-00121 R1-.35" 91/12/02 Avram Franklin Brad Shipley Preliminary workplan & cost Ecology & Environment, Environmental Protection estimate, TDD #T099111-0001, TAT Inc Agency - Region 9 #099012-T-002, PAN #ECA0584-SBA, cont #68-WO-0037 w/marginalia

2142-00120 91/12/10 Margie Weiner Data validation rpt Case Sulphur ICF Technology, Inc Bank Memo #3 Analysis: TOC, pH, chloride & sulfide w/TL to Stewart Simpson fr Victoria Taylor 12/10/91

2142-90155 R1- 91/12/23 Brad Shipley File Memo: Why TAT preliminary workplan Environmental Protection & cost estimates for anticipated Agency - Region 9 erosion control measures not accepted, & TDD for this TAT project terminated

2142-90156 92/01/08 William Crooks Environmental Protection Ltr: BMC not meeting requirements CA Regional Water Quality Agency - Region 9 of Waste Discharge Order #90-045 & Control Board - Central NOV transmitted to BMC w/ltr to BMC Valley Region fr Thomas Pinkos 1/7/92 re NOV

2142-90157 92/02/04 Brad Shipley Agenda for meeting to resolve Environmental Protection issues pertaining to scope of work Agency - Region 9 w/list of attendees Page 5 02/14/92

SULPHUR BANK MERCURY MINE SUPERFUND SITE Lake County, California *** Draft Administrative Record Index *** Removal Action No. 1

DOC # AR # DATE AUTHOR ADDRESSEE SUBJECT yy/mm/dd

2142-90158 92/02/04 Brad Shipley Field notes & calculations Environmental Protection (handwritten) Agency - Region 9

2142-99998 92/02/06 Environmental Protection List of US EPA guidance documents Agency - Region 9 consulted during development & selection of response action for Removal Action #1

No. of Records: 41 \ardraft.rpt

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