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In late 1993, it became apparent that four permanent wells were becoming <br /> unusable for monitoring purposes. These four wells, PW4-113, PW6-149, PW8-76 <br /> and PW10-138, consistently pumped dry and recovered either very slowly or not <br /> at all between sampling attempts. The wells were replaced by nearly identical <br /> wells in February/March, 1994 and the original wells were abandoned in March, <br /> 1995. <br /> Also in March, 1995, the three wells of the PW17 well cluster were <br /> abandoned due to commercial development near the cluster site. These wells <br /> were located on privately owned land approximately three quarters of a mile to the <br /> northwest of the groundwater remedial system. The wells were not replaced <br /> because it was determined that they were no longer needed to monitor the <br /> remedial program. <br /> As a result of these changes, the monitoring well network now consists of <br /> a total of 62 PW wells. The monitoring wells are typically arranged in clusters of <br /> three wells to monitor the different aquifer zones. <br /> 2.2 Site Information <br /> The unconfined aquifer system below the facility is classified as a "loosely <br /> coupled production zone system", which has been divided into three permeable <br /> zones for the purposes of the remedial program. The shallow zone of the aquifer <br /> lies approximately between the depths of 31 and 83 feet beneath the ground <br /> surface (bgs), the intermediate zone between 84 and 150 feet bgs and the deep <br /> zone lies approximately between 151 and 218 feet bgs. A confined hydrologic <br /> zone is located below the Corcorran clay layer at approximately 300 feet bgs. <br /> 3 <br />