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Phase III - In-Situ Groundwater Remediation <br />' After soil excavation, disposal and backfilling is completed, the slurry wall <br />construction will resume. Due to the need for equipment and soil staging during <br />the slurry wall construction, the groundwater monitoring wells will need to be <br />abandoned. The wells will either be filled with clean silica sand to the top of the <br />' screen interval followed by hydrated bentonite, or the PVC well casings will be <br />removed by pulling then from the ground. Immediately upon completion of the <br />slurry wall, new groundwater monitoring wells will be installed to determine the <br />extent of residual gasoline impacts on both sides of the slurry wall. It is expected <br />that dissolved phase BTEX will be present in groundwater. Based on the level <br />and extent of residual gasoline impacts, a groundwater remediation system will <br />be designed for expedited installation. The goal of the remediation system will <br />be to eliminate the exposure pathways by dissolved phase groundwater to the <br />surrounding surface water bodies. When dissolved phase BTEX concentrations <br />have been remediated to below the Basic Colorado Groundwater Standards, the <br />' remediation system will be shut off for monitoring. If groundwater is shown to be <br />successfully remediated for a period of four quarters after system shut-off, the <br />system will be removed and a petition for no further action will be submitted. <br />' Summary <br />' Excavation and off-site disposal of gasoline impacted soils should eliminate <br />exposure pathways for impacts in soils to surface water bodies and groundwater <br />aquifers. After gross removal of gasoline impacts in soils have been completed, <br />groundwater conditions will be fully characterized and a remediation program will <br />' be designed to eliminate human and environmental exposure pathways due to <br />residual gasoline impacts in groundwater. <br />B. A map identifying areas to be remediated, the area where the remediation <br />system will be located if it differs from the contaminated areas, the locations of <br />' confirmation samples, the locations of monitoring wells, areas where <br />contaminated media will be temporarily be stored, and areas where contamination <br />will not be actively remediated. <br />' See Figure 7. <br />C. A plan meeting the level of community interest in, and concerns about, the <br />' corrective action facility. <br />The site is undeveloped at this time. Based on the rural location and limited <br />' extent of the clean-up operations within the limits of an active, major construction <br />site with ongoing major construction activities for the next 2 or more years, <br />community impact and interest is expected to be minor to negligible. Due to the <br />close proximity of the release to the St. Vrain River and other surface water <br />' bodies, we request the cleanup begin immediately and the public comment <br />period be waived. <br /> <br /> <br />22 <br />