Final Formosa Mine Superfund Site OU1 Remedial Investigation
Total Page：16
File Type：pdf, Size：1020Kb
Formosa Mine Superfund Site Douglas County, Oregon FINAL OU1 REMEDIAL INVESTIGATION REPORT Report January 31, 2012 VOLUME I – TEXT This page intentionally left blank Executive Summary The Formosa Mine Superfund Site (Site) encompasses the abandoned Formosa and Silver Butte mines and portions of Upper Middle Creek and South Fork Middle Creek. These creeks are severely affected by acid rock drainage (ARD) and associated releases of contaminants of potential concern (COPCs). ARD generating mine materials are present on the surface and within the underground mine. Mine materials contain naturally enriched concentrations of COPCs such as arsenic, cadmium, copper and zinc. COPCs in source materials are associated with pyrite, a sulfide mineral that generates ARD when exposed to oxidizing conditions and percolating water. The ARD process results in dissolution of COPCs from solid mine materials, transport in surface water and groundwater, subsequent contamination of stream sediments and soil, and severe effects to the aquatic ecosystem. The purpose of the remedial investigation (RI) is to characterize physical characteristics, nature and extent of contamination, fate and transport processes, and risks to human health and ecological receptors in sufficient detail to support the feasibility study (FS). The RI/FS process will identify the best approaches to remediate ARD and associated environmental contamination. This RI was prepared for the US Environmental Protection Agency (EPA) in accordance with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and associated regulations and guidance. Cooperating agencies include the US Bureau of Land Management (BLM), Oregon Department of Environmental Quality (ODEQ), and United States Geological Survey. Introduction The Site is located in Douglas County, Oregon, within the Coast Range Klamath Mountains at elevations ranging from 3,200 to 3,700 feet (ft) above mean sea level (amsl). Historic underground mining occurred during the 1920’s and 1930’s. Exploration activities occurred intermittently after historic mining, and modern mining was conducted by Formosa Exploration Inc. (FEI) during 1990 to 1993. Copper was the primary payable metal, and some gold and silver was produced as a byproduct of copper production. Reclamation was conducted by FEI and cooperating agencies during 1993 to 1994, but the reclamation was not successful in mitigating ARD generation. EPA, BLM and ODEQ have conducted ARD management activities at the Site since that time. Previous work assessing contamination at the Site was conducted prior to and after modern mining; however, the most comprehensive work was conducted during the late 1990’s and early 2000’s by BLM, ODEQ, and EPA. This work demonstrated adverse effects to the environment caused by ARD generation, and supported listing of the Site on the National Priorities List in 2007. Previous work is compiled and summarized in a Z:\3380-New RAC8\221 - Formosa\RI Report\Text\Final\Formosa RI Executive Summary Final.docx ES-1 Executive Summary Data Summary Report (CDM 2008). The previous work was used to scope the RI, prevent duplication of efforts, and focus RI investigations. During the RI, the Site was subdivided into two operable units, Operable Unit 1 (OU1) and Operable Unit 2 (OU2). OUs are management tools used during the CERCLA process. The OUs are described as follows: . OU1 includes surface and subsurface mine materials and contaminated soils located outside of the underground mine workings; and . OU2 includes all remaining media and site contamination, including surface water, stream sediment, groundwater, underground workings, and adit water drainage. This RI report is focused on OU1, but also describes data collected to date associated with OU2. The OU1 data are sufficient to support the OU1 FS, which is in progress. The OU2 data are useful to understand adverse effects of OU1 source materials on media included in OU2 such as surface water and groundwater. Study Area Investigations Two sampling and analysis plans (SAPs) were developed during the RI, SAP1 (CDM 2009) and SAP2 (CDM 2010). These SAPs define investigation activities that address both OU1 and OU2. During the course of these investigations, EPA and other cooperating agencies decided to focus RI work on OU1 to expedite Site remedial action. Some RI work was conducted that primarily addresses components of OU2 including surface water and groundwater sampling. However, additional RI work is required to fully characterize OU2 in sufficient detail to support a subsequent OU2 FS. Investigations completed to date included: . Geochemical characterization and spatial delineation of OU1 mine materials; . Sampling of seeps, springs, surface water and groundwater; and . Sampling of potentially affected and background soils. These data were validated in accordance with EPA protocol. The data are usable for the purpose of the RI with limited exceptions as described in Section 2 of the OU1 RI report. Physical Characteristics Physical characteristics were assessed to support FS evaluations in accordance with CERCLA guidance. The OU1 RI evaluated physical characteristics of the following: . Mining infrastructure, former mining facility locations and characteristics, waste rock dumps (WRDs), underground mine characteristics, adit water drainage, and reclamation; . Climate, surface water hydrology, and groundwater hydrology; and ES-2 Z:\3380-New RAC8\221 - Formosa\RI Report\Text\Final\Formosa RI Executive Summary Final.docx Executive Summary . Ecology, land use, and demographics. Mining was conducted primarily by underground methods, which resulted in construction of a network of underground voids, partial backfill of underground voids with ARD generating mine materials, and placement of ARD generating mine materials on the surface. Reclamation of the mine between 1993 and 1994 included removal of former mineral processing facilities, haulage of low grade ore and tailings into the underground mine, re-grading of waste rock and other mine materials located on the surface, construction of a tailings repository in a former water storage pond (the encapsulation mound), and revegetation. Major site features include: . OU1 mine materials located on the surface, which contain ARD generating source materials and cover an area of approximately 25 acres; . The underground mine, which includes the underground voids and OU2 mine materials present within the voids; . The adit water diversion system, which collects mining influenced water (MIW) from the Formosa 1 adit and Silver Butte 1 adits and diverts the water to an overland flow drainfield; . Watersheds and drainages including Upper Middle Creek and South Fork Middle Creek, which are affected by MIW; and . Historic mining features such as the former crusher, shop, milling, water and tailings storage areas, and the encapsulation mound. Previous mine reclamation is not effectively mitigating contaminant generation and transport from the former mine into the environment. The Formosa 1 adit discharges MIW on a perennial basis, the encapsulation mound (a capped repository that stores strongly acid generating tailings and ore) is leaking to groundwater at rate estimated to be 17 percent of precipitation, and surface mine materials are generating ARD and contributing to surface water and groundwater contamination. The Site is located in rugged mountainous terrain near the headwaters of Upper Middle Creek and South Fork Middle Creek, two perennial streams that flow from the mine area downstream to Cow Creek. Precipitation ranges from 15 to 70 inches per year in the general area, and falls primarily in the late fall and winter. Average precipitation for the area is 34.5 inches based on data from a weather station near the Site at an elevation of 3,973 ft amsl. Snow is present on an intermittent basis during winter months, and summers are characterized by mild temperatures and low precipitation. Stream flow varies seasonally in relation to precipitation patterns with highest flows occurring during late fall and winter. Groundwater discharges to surface water from alluvial and fracture-controlled bedrock aquifers in headwaters of Upper Middle Creek and South Fork Middle Creek. Vegetation in the mine area ranges from mining-denuded areas largely devoid of vegetation to coniferous forest dominated by Douglas fir. The forest is habitat for wildlife including black bear, deer, and a variety of birds. Creeks near the site provide aquatic habitat for chinook salmon, coho salmon and other species. The northern spotted owl, a federally threatened species, has been Z:\3380-New RAC8\221 - Formosa\RI Report\Text\Final\Formosa RI Executive Summary Final.docx ES-3 Executive Summary reported in the area, and designated critical habitat for the northern spotted owl is present in a portion of the Site. Land uses in the area are primarily logging and recreational. Land ownership includes a mixture of private lands and federal land managed by BLM. Nature and Extent of Contamination Evaluation of nature and extent of contamination considered: . OU1 mine materials and soil; . Surface water; and . Groundwater. OU1 Mine Materials and Soil The Formosa Mine exploited an ore body called a volcanogenic massive sulfide, which is a natural deposit of rock that is strongly enriched in metals. The mining process exposed these rocks to surface weathering through construction of tunnels and haulage of broken rock to the surface. Mine materials such as waste rock, tailings, and mixtures