Laserfiche WebLink
July 28, 1992 <br /> Former Texaco Station, Manteca, California <br /> In December 1989, RESNA began quarterly ground-water monitoring. The direction of <br /> ground-water flow across the site was to the northwest with an average gradient of 0.0012. <br /> Ground-water samples collected during the subsequent year of monitoring (1990) indicated <br /> that concentrations of dissolved hydrocarbons had decreased to concentrations below <br /> Maximum Contaminant Levels(MCL's) established by the California Department of Health <br /> Services for drinking water. The groundwater fl o direction and gradient had remained <br /> fairly consistent(Applied GeoSystems,December 18, 1990,Report No.38053-2). Therefore, <br /> RESNA recommended the wells be sampledsemi-annually during 1991 to verify <br /> hydrocarbon concentrations remained below MCL' for over 1 year. Data collected during <br /> the June 1991 monitoring event indicated hydrocarbons were not detected in ground-water <br /> samples and the ground-water flow direction remained constant. <br /> WORK IN PROGRESS <br /> Environmental work has not been conducted during the first and second quarters of 1992. <br /> DISCUSSION AND RECOMMENDATIONS <br /> In recent years, the land use in and.around Manteca has changed. Much of the land has <br /> been sold for development and is no longer being i rigated;and flood irrigation is no longer <br /> being used_ These changes in land use and irrigation prevailing drought conditions have <br /> slowed the recharge of the water-table aquifer in this- area. Water is still being pumped <br /> from these aquifers for agricultural and, industrial uses. Due to the depletion of ground- <br /> water in the water-table aquifer and the greatly rec,uced recharge, groundwater may never <br /> recharge to the level where hydrocarbons were previously detected. <br /> Dissolved hydrocarbon concentrations have been either not detectable or below their <br /> respective MCL's since March 1990, which was after the soil containing hydrocarbons was <br /> removed by excavation. Because dissolved hydrocarbon concentrations have remained below <br /> MCL°s for nearly 2 years and the ground water table never return to previous levels, we <br /> recommend on behalf of Mr. Gary Brophy, we request a meeting with personnel of the <br /> California Regional Water Quality Control Board, Central Valley Region and the San <br /> Joaquin County Public Health Services Department to further discuss the need for <br /> additional work.at this site. <br /> 0701gbro 2 <br /> � 38053-4 <br />