SITE INFORMATION AND CORRESPONDENCE_1987-1992

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LEEDSHILL•HERKENHOFF. INC. CHAPTER 4 ' RESULTS ' 4. 1 Groundwater Gradient and Direction ' Three municipal wells and three of the four monitoring wells are located along the western edge of LVC, along Gettysburg Place. LVMD well #1 and monitoring well #4 are approximately fifty feet apart; however, static water ' levels in the municipal wells are roughly twelve to fourteen feet lower than static water levels in the monitoring wells. The municipal wells are over 150 feet deeper than the monitoring wells and are perforated in a water ' bearing sand layer located at a depth of approximately 175 to 200 feet below the ground surface. This hydrogeologic data supports the theory that the municipal and monitoring wells are constructed in different zones, with the municipal wells tapping into a semi-confined aquifer; while the monitoring ' wells tap into an, upper water bearing zone. The groundwater direction and gradient of the upper water bearing zone is ' generally easterly to northeasterly with little slope (the fall is approxi- mately 1'/500' , or 0.2%) . Figure 4.1 shows June 1988 groundwater elevation contours for the upper water bearing zone beneath Lincoln Village Center. Based on limited data, the localized direction of groundwater flow in the ' semi-confined layer was found to be toward the cone of depression created by the active pumpage of LVMD wells #1 and #2. ' 4.2 Groundwater Sampling Results Analysis of the monitoring well water samples and confirmation sample col- lected from MW#4 revealed PCE and TCE contamination in monitoring well #4, but not in monitoring wells #1, #2, or #3. The initial sampling at monitor- ing well #4 contained 1900 ppb of PCE and 110 ppb of TCE; the confirmation sample contained 2500 ppb of PCE and 190 ppb of TCE. All other samples were ' non-detect for purgeable halocarbons. (See Appendix C for individual laboratory data sheets. ) ' Given the direction of groundwater flow in the upper water bearing zone (as measured at the time of this investigation), there are no downgradient domestic wells within a 1-mile radius of the site. In fact, there are only two down gradient wells within one-half mile of the site. One of these ' wells is a deep municipal supply well whose highest perforation is located at a depth of 237 feet and is therefore drawing water only from the lower aquifer. The other well is the Chevron monitoring well located in the ' upper water bearing unit, which is approximately 900 feet down gradient from LVMD #1. This well , which was sampled by RWQCB staff in January 1987, showed non-detectable levels of PCE and TCE. 4-1