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rz <br /> 16 Fourth Quarter 1992 Mondonng Report <br /> Coca-Cola Enterpnses- West <br /> ' February 10, 1993 <br /> Page 2 <br /> ' Several environmental investigations have been conducted since tank removal Including a soil <br /> gas survey In May 1990, a subsurface environmental Investigation in August and September <br /> ' 1990, an additional subsurface investigation in October and November 1990, and quarterly <br /> groundwater monitoring from August 1990 to November 1991 The results of these <br /> investigations are presented in the reports listed at the end of this report A soil vapor extraction <br /> ' test was conducted at the site by RESNA in November 1992, in order to collect data for design <br /> and construction of a soil vapor extraction system The report of this pilot test has been <br /> prepared and will be submitted under separate cover Investigations have shown that the <br /> ' majority of petroleum hydrocarbons in the soil were present from 0 to approximately 25 feet <br /> below grade and within a radius of about 20 feet of the former 1,000 gallon gasoline UST tank <br /> pit Quarterly groundwater monitoring results have shown detectable levels of petroleum <br /> ' hydrocarbons in the monitoring wells (Table 1) No known monitoring has occurred at the site <br /> since November 1991, primarily due to the fact that Coca-Cola was in the process of selecting <br /> new consultants <br /> GROUNDWATER SAMPLING AND GRADIENT EVALUATION <br /> 1P <br /> RESNA personnel performed the latest quarterly groundwater monitoring and sampling of <br /> monitoring wells on December 17, 1992 Mr Michael Collins of San Joaquin County Public <br /> ' Health Services - Environmental Health Division (SJCPHS-EHD) was present on-site to observe <br /> RESNA sampling techniques Field work consisted of measuring depth-to-water (DTW) levels <br /> in wells MW-1 through MW-6, collecting groundwater samples from wells MWA, MW-2, and <br /> ' MW-6, and submitting groundwater samples for laboratory analysis as stated in the November <br /> 24, 1992 correspondence from RESNA to SJCPHS-EHD <br /> ' Water level measurements were collected from wells MW-1 through MW-6 Water levels <br /> ranged from 73 96 to 74 46 below top of well casing elevation In general, groundwater <br /> ' elevations have decreased an average of 3 76 feet since November 21, 1991 The water level <br /> data were used to develop the groundwater elevation contour map (Plate 3) Assuming that <br /> horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site <br /> ' flowed in a northeasterly direction The hydraulic gradient on December 17, 1992 was <br /> calculated to be 0 002 ft/ft or about 11 feet/mile These data are consistent with previous results <br /> for gradient and flow direction A summary of groundwater monitoring data is presented in <br /> ' Table 2 Groundwater elevations are referenced to feet above mean sea level <br /> Groundwater samples were collected from three shallow groundwater monitonng wells, MW-1, <br /> MW-2, and MW-6 Prior to collection of groundwater samples, the depth-to-water, pH, <br /> electrical conductivity, and temperature were measured in the monitoring wells and recorded <br /> ' 40MR1992 FNL <br /> I <br />