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Plans are currently being developed to permanently seal this exploratory core hole, pending <br />DRMS approval of a Technical Revision to the permit. The objective is to accomplish this <br />task before the pond permanently freezes over for the winter (hopefully before the end of <br />December 2010). <br />In the future, it will be important to try to schedule remedial investigation activities involving <br />excavation of alluvial fill material during the months of August and September, and to <br />complete such activities prior to mid-October when Ralston Creek historically begins <br />flowing again adjacent to the alluvial fill and recharging groundwater tables. This will <br />minimize potential problems associated with groundwater management and help to facilitate <br />successful remedial efforts. <br />Management of Alluvial Groundwater and Associated Water F-wraction/Treatment <br />Systems <br />The primary issues surrounding unintended onsite releases of raw alluvial groundwater were <br />the additions of groundwater collection sumps in response to water quality data from a nearly <br />dry creek bed, sedimentation generated by construction disturbance, a coincident and sudden <br />appearance of water flowing again in Ralston Creek (beginning October 12, 2010), and a <br />subsequently rapid recharge of groundwater tables in the alluvial fill. <br />Above-ground construction of alluvial groundwater extraction and water treatment systems <br />began in July 2010. Major trenching for piping and electrical systems burial/winterization <br />was initiated in September when Ralston Creek was essentially dry and groundwater tables in <br />the alluvium were at the lowest possible levels. Completion of the trenches and new sumps <br />was significantly complicated and delayed by necessary system design/configuration changes <br />and the reappearance of water flow in Ralston Creek and the associated sudden rise in <br />alluvial water tables which began running in the trenches. <br />Sedimentation issues are believed to have been eliminated with completion of pipe/conduit <br />burial and installation of alluvial groundwater extraction sumps in accordance with <br />construction permit specifications (designed to prevent intrusion of sediment into the sumps). <br />No related problems have occurred since October 14, 2010. Temporary run-permissive <br />systems were installed shortly after that date and have since been replaced by permanent <br />systems. All sump and related piping system construction was completed on November 19, <br />2010 and no further problems related to construction and associated mobilization of <br />sediments are expected. <br />If future remedial activities at the site were to require treatment of water with the potential to <br />contain significant amounts of sediment, there are now three preventative measures in place <br />to prevent water treatment plant overflows: (1) permanent run-permissive systems for each <br />sump pump; (2) parallel sand filters in the building that can be quickly brought on line to <br />prevent intrusion of solids into the surge tank; and (3) secondary containment within the <br />building that would direct any system overflows into a building sump with any excess <br />automatically pumped into structural containment within the north concrete Barren Pond. <br />7