ARCHIVED REPORTS XR0012566 - Laserfiche WebLink

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��'. yY»�,x-"r¢�� ':w •e.r. .rfv - ��,Wr.e�,_ •�� - - : y 7Y ... r-.0 �: -�, u e sr . JJJ hUm 7ue S �i 6� I �q KtEI\FELDER The lateral extent of the plume affected with gasoline could not be assessed with the three wells installed during this investigation. It is apparent that the plume of contaminated ground water extends beyond IMW-1, 30 feet east of the excavation. Several additional wells should be installed in a downgradient position,possibly off site, to assist in evai=ting the extent of the plume. At least one upgradient well should also be installed to assess, the potential for onsite migration of petroleum hydrocarbons from an offsite source. `A Additional wells may also be needed to evaluate the extent of the product on the ground water. In addition, the: depth to ground water should be monitored to assess the ground a' water flow direction over time and to evaluate if the tidal changes in the Port of Stockton ' are affecting ground water in this area. Based on concerns by the SJCEHD that the plume of impacted ground water may have affected wells in the area, a well location was conducted. Ten wells within 2000 feet of the i d site were Iocated by reviewing agency files and conducting a +,round survey. The wells can be grouped into two areas. Four monitoring wells are located northwest of the site near i the intersection of Pershing Street and Navy Drive, while five domestic wells and an I..t industrial well are within a rural/residential area south of the site (Plate 7). Both groups of wells are within, approximate 2,000 feet from the site, and are not in a direct downgradient position. l 1.1 Efforts should be made to remediate both the soil and ground water affected by gasoline beneath the site. Gasoline and its constituent compounds being highly volatile may be i= l remedlated by using vapor extraction technology. Vapor Extraction Systems (VES) remediates soil by extracting vapors in the soil pores that are in equilibrium with the absorbed and dissolved constituents and free product. VES systems, operating under t favorable conditions, may also be effective in reducing volatile petroleum constituents from I contaminated ground water. 40 Soils Be nth the;site consist predominkni y of silt anti fine sands.,Soil permeability tests of t:1 three samples from the site were made to evaluate the vapor extraction potential beneath and surrounding the tank excavation. One soil sample collected from the ur:satur,ted zone in each of the three monitoring wells was tested for soil permeability (Table 6, Appendix G). The average permeability ranged from 7.5 x 10-7 to 7.2 x I0'a centimeters/sec. The higher permeabilities appear to occur at depths below 25 feet. As most of the affected soil " is in the v.L"dose zone between 23 feet and grour;d water (at a depth of approximately 33 F feet),VES remedial alternatives are being pursued. Because ground water beneath the site F18-91-62 11 Copyright 1991 Kleinfelder, Inc.