SITE INFORMATION AND CORRESPONDENCE_FILE 1

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July 17, 1996 NEW Pale 2 detected in Wells MW-2 through MW-5, or MW-7. MtBE was detected in Well MW-6 at a concentration of 8.4 parts per billion (ppb). MtBE concentrations will continue to be monitored at the site to establish trends regarding this gasoline additive. Issue 2: The depth to gi-oiurdwalet-ha.v significantly itici-eased i+,ithin the last niw years and a number of monitoring Wells are screened beloii,first Water. Please include a ` summary of i+,ell construction details and an ei aluation of the current monitoring ccipabilities. Well construction details, recent groundwater depths, and total petroleum hydrocarbons calculated as gasoline (TPH-g) concentration data are presented in the attached well summary (Table 1). The summary indicates that groundwater elevations are higher than the top of the screen interval in each of the groundwater monitoring wells'at the site. PACIFIC performed an analysis of groundwater concentrations relative to the ground- water elevations and screened interval. With the exception of Well MW-2, the site wells had exhibited a trend of decreasing concentrations, and generally did not contain hydro- carbon concentrations at the time the well screens became drowned. The analysis was therefore centered on Well MW-2. In general, the TPH-g concentrations in site wells are denoted by the laboratory as discrete single peaks and not indicative of gasoline. There- fore, TPH-g was not used in the analysis. The well screens in Well MW-2 were submerged initially during the June 1994 sampling event. Water levels decreased slightly following that, such that the well screens were exposed during the October and November 1994 sampling events. During the March 1995 sampling event the wells were again submerged, and have been submerged during subsequent sampling events. The well screens have been submerged by more than two feet since the May 1995 sampling event, and there may be a correlation between that event and hydrocarbon concentrations. However, a trend of decreasing hydrocarbon concentra- tions was observed prior to May 1995, suggesting that the current low concentrations in Well MW-2 may be attributable to natural attenuation. Additionally, as hydrocarbons have been detected in Well MW-2 subsequent to screen submergence, the well is functioning as an indicator of hydrocarbon trends, and should be adequate to evaluate future trends of hydrocarbon concentrations. The June 29, 1995 CAP recommended the placement of a monitoring well downgradient of Well MW-2. An existing building is currently situated on the proposed well location. Therefore, the installation of this monitoring well has been postponed. Issue 3: As a rationale for long term monitoring as a corrective action methodology, the proposal included regular analysis of groundHwier parameters to confirm the remedia- tion of hydrocarbons through natural processes. Please include a list of parameters that Would be used to monitor the remediation through natural processes... 3201357C/CAPADD