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• Pumping and treatment of contaminated ground water in the Idaho Springs area, <br /> • Providing alternate sources of drinking water where required, and <br /> • Capping or physical barriers, and institutional controls for select mine waste piles such as <br /> the Golden Gilpin Mill Site. <br /> The selected remedy for OU3 was intended as an interim action with further response actions <br /> planned. Additional response actions for the Superfund Site are outlined in the Central <br /> City/Clear Creek Superfund Site Operable Unit 4 Record of Decision (CDPHE 2004) and the <br /> Central City/Clear Creek Superfund Site Amendment to the Operable Unit 3 and Operable Unit <br /> 4 Records of Decision (CDPHE 2006). <br /> III. CONSTRUCTION ACTIVITIES <br /> The objective of construction activities at the Golden Gilpin Mill Site was to minimize <br /> environmental threats caused by elevated levels of metals in the mine waste. Contaminants in <br /> the waste pile posed several threats to North Clear Creek, including those caused by run-off of <br /> mine waste into the creek during storm events, continued undercutting of the embankment <br /> between North Clear Creek and the tailing ponds that could lead to slope failure and subsequent <br /> erosion of mine waste into North Clear Creek, and leaching of contaminants from the tailing <br /> ponds into North Clear Creek. The project design was guided by these goals. <br /> Project design began with the selection of an engineering consultant. In March 2004, WRC <br /> Engineering, Inc. (WRC) and Smith Environmental were selected to perform design engineering <br /> on behalf of CDPHE. The design team was tasked with preparing a reclamation design and <br /> construction documents and performing construction quality assurance for both the Golden <br /> Gilpin and the Chase Gulch#2 sites. <br /> During the design process for the Golden Gilpin Mill Site, a number of issues had to be <br /> considered to achieve an acceptable set of construction plans. The Golden Gilpin Mill Site <br /> maintains a permit with the Colorado Division of Reclamation Mining and Safety(DRMS). Due <br /> to the active mine permit, the project design was structured to allow for either complete or partial <br /> reclamation of the waste pile. The design allowed for capping and revegetation of the entire <br /> waste pile or alternatively, capping only the side slopes of the waste pile. Following additional <br /> agency consultation, EPA advised CDPHE to omit capping the top of the waste pile with the <br /> intent that the property owner would be responsible for that action in the future. This approach <br /> also provides the property owner with the option to use the pile for future mine-related activities <br /> under a DRMS permit. <br /> Previous investigations at the site had determined a portion of the mine waste pile to be <br /> marginally stable to unstable. Failure of the waste pile slope would result in significantly <br /> increased erosion of mine waste into North Clear Creek. Therefore, one of the design objectives <br /> was to stabilize the bank of North Clear Creek. <br /> The final construction plans were completed after careful consideration of the project objectives <br /> and the property owner's needs. The plans specified that storm water run-off issues would be <br />