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El90 FN <br /> Work Plan for Re-excavation May 3, 1989 <br /> Former Texaco Service Station, Manteca, California AGS 36053--1 <br /> Because concentrations of TPH remain in the soil at 18 feet below <br /> grade, which is the limit of the initial excavation, Applied <br /> GeoSystems recommended re-excavating the currently backfilled <br /> tank cavity to the ground-water surface. In addition, because <br /> the underground product-delivery lines were not removed <br /> concurrent with removal of the tanks, the California Regional <br /> Water Quality Control Board, Central Valley Region, requested <br /> that the product lines be removed and soil samples collected from <br /> beneath the former locations of the product lines. <br /> Furthermore, it is the opinion of Applied GeoSystems that <br /> a quarterly monitoring of ground-water quality should be initiated <br /> after removal of the contaminated soil to evaluate contaminant <br /> trends over a period of 1 year. If hydrocarbon concentrations do <br /> --------------------------- <br /> not increase during this period, we recommend the site be re- <br /> evaluated. <br /> GEOLOGY AND HYDROGEOLOGY <br /> The site is located in the San Joaquin Valley geomorphic province <br /> J of California. The valley has been a sedimentary trough since <br /> pre-cretaceous time. Most of the pre-Cretaceous to mid-Tertiary <br /> sediments in this portion of the valley are of marine origin, <br /> 6 <br /> AP,011-00' G600SYSMOMS <br />