ARCHIVED REPORTS_XR0004210 - Laserfiche WebLink

Home Browse Search

Mr. David DeWitt Page 3 November 2, 1993 • Unocal Corporation During the process of dispersion of contamination from a source Point, contamination could travel in the upgradient and cross gradient directions, prior to intersecting the ground water table. Also, due to the relatively flat historical gradient and the enhanced flow in permeable units overlying lower permeability layers, some ground water flow in other than the directly downgrad- ient direction can occur. The relatively low levels of contamination that exist a short distance both upgradient and cross-gradient from the suspected release point (as seen in the soil samples collected from MW6 at 60 and 74 feet below grade and occasionally in the ground water samples collected from MW2 ) , do not appear to require a second source. It is important to note that the aforementioned detected concentrations in both soil and ground water are relatively minor . REGIONAL GROUND WATER ELEVATION INVESTIGATION In their letter dated November 1992 , the SJCPHS also requested that Unocal investigate the historical ground water depth at and in the vicinity of the sub3ect site. On January 18 , 1993 , KEI reviewed the depth to water measurement collected for the City of Lodi Wells 0 #1, #1R, #6R, #81 012 , and #22 Ground water elevation data for the aforementioned wells was available for the period of 1972 to 1991. Data was recorded on individual graphs for each well (see Appendix A) . Based on the depth to water data collected and graphed for each well, annual cycles appear to exist within each separate year. However, an overall slow deepening trend of the ground water is .illustrated. This trend indicates that the ground water depth is more a function of ground water pumping (usage) and only slightly influenced by annual rainfall. Due to the fact that well construc- tion and screening intervals differ between the City of Lodz wells and Unocal ' s wells, the individual ground water depths may not correlate between the two sets of wells. However, the documented regional trend indicates that the vertical distance from the ground water table to the previously detected residual soil contamination at the subject site will continue to expand. POTENTIAL RECEPTOR AREAS In January of 1993 , KEI conducted a survey of water wells located within a 1/2-mile radius of the sub3ect site in order to identify the location of potential ground water contaminant receptor areas. The survey indicated the existence of five domestic wells and three sites with monitoring wells. The well locations were determined by a review of the California Department of Water Resources (CDWR) records. The water wells identified in the study area, along with well information, survey numbers, owners, and locations, are listed i