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=:"- SOMA Working To Restore Nature ' 1990, an additional subsurface investigation in October and November 1990, and quarterly groundwater monitoring The results of these Fnvestigatxons are presented in the reports listed at the end of this report. A soil vapor extraction test was conducted at the site by RESNA in November 1992 (RESNA, January 1993) Investigations have shown that the majority of petroleum hydrocarbons in the soil were present from 0 to approximately 25 feet below grade and within a radius of about 20 feet of the former 1,000 gallon gasoline UST tank pit. A soil ' vapor extraction system was constructed at the site and began operating July 23, 1993 Quarterly groundwater monitoring results have shown detectable levels of petroleum hydrocarbons in the monitoring wells in the past (Table 1) 1 GROUNDWATER SAMPLING AND GRADIENT EVALUATION ' RESNA personnel performed the latest quarterly groundwater monitoring of monitoring wells on December 27, 1993 Mr. Michael Collins of SJCPHS was present on-site to observe RESNA ' sampling techniques Field work consisted of measuring depth-to-water (DTW) levels in wells MWA through MW-6, collecting groundwater samples from wells MW-1, MW-2, and MW-6, and submitting groundwater samples for laboratory analysis Water level measurements were collected from wells MW-1 through MW-6 The depth to water P ranged from 68 42 to 69 06 feet below top of well casing elevation. In general, groundwater ! elevations have increased an average of 2 59 feet since September 2, 1993 The water level data were used to develop the groundwater elevation contour map (Plate 3) Assuming that horizontal ' isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed in an easterly direction The hydraulic gradient on December 27, 1993 was calculated to be 0.0011 ft/ft or about 6 feet/mile These data indicate no change when compared with the previous quarterly monitoring results for gradient flow and direction. A summary of groundwater monitoring data is presented in Table 2 Groundwater elevations are referenced to feet mean sea level. ' Groundwater samples were collected from three shallow groundwater monitoring wells, MW-1, MW-2, and MW-6 Prior to collection of groundwater samples a minimum of three well casing, ' volumes were purged The depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected No evidence of measurable floating product or hydrocarbon vapor was noted in the water samples Samples ' were then collected from each well using disposable bailers Purge water was contained in 55 gallon DOT approved drums and stored on-site ' The groundwater samples collected from each well were submitted with Chain of Custody Record to Sequoia Analytical Laboratories of Redwood City, California, a State Certified laboratory (State Hazardous Waste Testing Laboratory Certification No 1210) Samples were analyzed for total petroleum hydrocarbons as gasoline (TPHG), total petroleum hydrocarbons I 3400561QUAR'TL,Y14QMR1993 FNL 2