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9 y�. :. '7i „` -p"uT^ .i � ,�k`� '•°n.. ,. . n'F'r S�ti� ..r: "`'.Lti9S� Mr... . .. �' .��"��.� :. �� _.�`G Awa. �': w ,,:_� � <br /> Mr. Dave Heinrich <br /> August 15, 1989 <br /> 202/150-4150 <br /> Page :i <br /> lenses. Groundwater beneath the site was encountered between 29 <br /> and 30 feet below grade, with a gradient of approximately 0.4 <br /> f percent to the past (Figures 3 and 4) . <br /> Laboratory analyses of soil samples recovered from drilling <br /> operations indicated that sail beneath the site has been <br /> impacted. TPH--G concentrations ranged from 1,900 parts per <br /> million (ppm) to below practical quantitation levels (<PQL) . <br /> Benzene concentrations ranged from ?.1 ppm to <PQL (Attachment <br /> II) . The majority of the impacted samples ranged in dept,t from <br /> i5 to 30 feet below grade. During drilling operations, free <br /> product was observed in angle boring 1 (AD-1) and in MW-1. Upon <br /> completion of the monitoring wells, an- interface probe was used <br /> to determine the thickness of the product in MW-1. on May 26, <br /> 1989, the product thickness was 4.70 feet. On June 16, 1989, the !� <br /> product thickrps, had decreased to X5.65 -'Fee}-. lr <br /> Laboratory analyses of groundwater samples indicated dissolved <br /> TPH-G ranging from 17,000 parts per billion (ppb) to 350 ppb <br /> (Figure 5) . Dissolved benzene concentrations ranged from 5,300 <br /> ppb to 9 ppb (Figure 6) . Laboratory reports of groundwater <br /> analyses are presented in Attach,uent TI. <br /> To further ascertain the extent of the dissolved hydrocarbon <br /> plume and subsurface soil conditions beneath the site, GTI <br /> proposes that the following work steps be performed: <br /> " Drill seven borings into groundwater and install seven <br /> monitoring wells (MW-6 through MW-12) around the site <br /> to investigate the extent of the hydrocarbon plume <br /> (Figure 7) . <br /> ` Drill three additional borings and install mon:_torinq <br /> wells in them if needed to further define the extent of <br /> the hydrocarbon plume. <br /> ` Develop the monitoring wells and obtain representative <br /> water samples ror laboratory analyses following <br /> California Regional Water Quality Control Board, <br /> jentral Valley Region (CRWQCB-CVR) guidelines. <br /> Professionally survey all new well-'-lead elevations and <br /> lccatiuns for vertical and horizontal control. <br /> ` monitor the wells to determine depth to groundwater and <br /> to detect the presence of free floating hydrocarbons. <br /> CoIl.ect water samples from all monitoring wells not <br /> GROUNIMATER <br /> TECHNOLOGY,INC. <br /> ®r r <br />