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' M LEEDSHILL•HERKENHOFF, INC. <br /> CHAPTER 5 <br /> CONCLUSIONS <br /> 5.1 Conclusions <br /> Contamination of the upper water bearing zone by PCE and TCE has been con- <br /> firmed through samples obtained from MW#4. None of the other monitoring <br /> wells (MW #1, 2, or 3) contained detectable chemical concentrations. The <br /> direction of groundwater flow in the upper water bearing zone is generally <br /> ' easterly to northeasterly. No downgradient domestic wells exist within one <br /> mile of the site. A monitoring well located 900 feet downgradient from <br /> LVMD #1 did not contain detectable concentrations of PCE or TCE. Available <br /> data indicates that the direction of groundwater flow in the deeper semi- <br /> confined aquifer is generally toward the cone of depression created by the <br /> pumpage of LVMD wells #1 and #2. Currently, there is a static water level <br /> differential of approximately 12 feet between the upper and lower water <br /> bearing zones. Based on the hydrogeological data obtained during this <br /> ' investigation, and the available wells logs, these water bearing zones <br /> appear to be hydraulically separate. <br /> ' Contamination of the upper water bearing zone probably occurred through <br /> leakage of PCE/TCE contaminated wastewater through joints in the existing <br /> ' sewer lines. From the soil and sewage sampling conducted, these sewer <br /> system discharges probably occurred over a long period of time, and were not <br /> the result of a single large discharge event. There are several factors <br /> ' (which are summarized pictorally on Figure 5.1) which have contributed to <br /> the contamination problem: <br /> 1 . As discussed in Section 2.7 and illustrated on Figure 2.5, the <br /> entire Lincoln Village Center sewage flow is combined at MW#4, <br /> before being routed into the San Joaquin County sewer system which <br /> passes within 30 feet of LVMD well #1. <br /> Figure 2.7 showed the location of eleven sewer joints between MH#4 <br /> and Gettysburg Place which required pressure grouting due to <br /> excessive water loss. Once the PCE/TCE contaminated wastewater <br /> ' leaked through the sewer joints, the continued sewer leakage (even <br /> after contaminated water discharges ceased) provided the driving <br /> ' 5-1 <br />