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• • - <br /> VERTICAL EXTENT OF GROUND WATER CONTAMINATION <br /> The existing monitoring well network is designed to provide detection <br /> monitoring of the uppermost water—bearing unit. Gasoline contamination <br /> has been identified in ground water from this uppermost water—bearing <br /> zone. The RWQCB requested limited detection monitoring of ground water <br /> from a deeper zone or the second water—bearing zone. The objective of <br /> installing this well is to prove or disprove the existence of an aquitard <br /> at about 40 feet below grade and a subsequent second aquifer below this <br /> zone. In addition a chemical analysis of the ground water in this zone <br /> will provide an indication of the vertical extent of contamination. <br /> To provide access for obtaining samples of ground water from the deeper <br /> zone, a single monitoring well will be installed. The well will be <br /> positioned down—gradient from the former location of the underground <br /> storage tank area within the southwest quadrant of the property. The well <br /> will be designed to screen the deeper water—bearing zone exclusively. To <br /> preclude the introduction of contamination by drilling from the uppermost <br /> water—bearing zone into the deeper zone the well will be drilled in two <br /> steps utilizing a large diameter (12—inch to 14—inch) PVC surface casing. <br /> The actual well will be installed through the surface casing. The surface <br /> casing will be keyed into a clay layer located between the uppermost <br /> water—bearing zone and the deeper zone. The annulus between the surface <br /> casing and the bore hole will be grouted. The well will then be fully <br /> developed and sampled. The collected water samples will be analyzed for <br /> total petroleum hydrocarbons and BTXE by a California State—certified <br /> laboratory. All soil cuttings and purged water will be containerized. <br /> The RWQCB has requested this well installation and agreed in principal to <br /> the construction methods employed. A well permit will be obtained prior <br /> to installation from the San Joaquin County Health District. Plates 1 and <br /> 2 show in a flow diagram format the steps necessary to proceed from <br /> installation of the deep zone monitoring well through implementation of an <br /> interim onsite ground water remediation system. <br /> OFFSITE GROUND WATER CONTAMINATION <br /> The RWQCB has requested additional detection monitoring wells located <br /> offsite to provide assessment of the limits of contamination in a <br /> direction which is down—gradient (south to southwest) from existing <br /> monitoring well MW-2. Additional monitoring wells will not be required <br /> west of the site, between existing monitoring well locations MW-6 and <br /> MW-1, because of the presence of Pacific Avenue. The proposed offsite <br /> monitoring wells will be installed after ground water quality has been <br /> assessed from the deep zone. The RWQCB will allow installation of offsite <br /> wells to occur concurrently with the proposed interim onsite ground water <br /> remediation program. Moving forward with the installation of offsite <br /> wells is contingent on obtaining permission from property owners. The <br /> logic and sequence of these tasks is shown on Plate 1. <br /> A work plan will be developed for offsite monitoring in the near future. <br /> Well permits will be obtained from the San Joaquin County Health District <br /> prior to drilling. <br /> KLEINFELDER 9795 Business Park Drive, Suite C, Sacramento, CA 95827 (916) 366-1701 <br />