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i 1 SOFAf4®R%��' Environmental Technology Inc groundwater sampling, neither free product nor sheen was noticed in any of the ' monitoring wells Dedicated bailers were used for sampling activities at each of the wells, in order to prevent possible cross contamination ' The six water samples collected were stored in an ice chest maintained at 4 degrees Celsius Appropriate chain of custody was prepared prior to transporting to a State certified laboratory Del Mar Analytical, Irvine, CA performed the laboratory analyses All the water samples were analyzed for Total Petroleum Hydrocarbons (TPH) as gasoline (Volatile Fuel Hydrocarbons) and Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) following EPA Methods 8015/8020 The test data are presented in Table 2 ' All laboratory analytical results including QA/QC are enclosed with this letter report Table 2 also includes the historical data for wells MW-1 through MW-6 ' The groundwater level observations (Table 1) indicated a consistent increase of approximately 5 1 to 5 2 Feet during the reporting period (12/1/94 to 2/22/95) Groundwater elevations in all six monitoring wells are currently above the ' screened intervals of the respective wells Due to this the laboratory data should be reviewed with caution because the water sample collected, even after purging may not represent the underlying aquifer water quality conditions It should also be noted that the fluctuation in groundwater level is a common occurrence in the Stockton area as reported in Applied Consultants report dated April 9, 1994 If during the monitoring event for the second quarter of 1995 the groundwater levels are still above the screened intervals then SOTA will pump adequate volumes of water at the requisite flow rates to lower the groundwater level below ' the top of the screened interval A water sample will be collected for laboratory analysis after adequate recharge occurs Such a sampling event will represent the underlying aquifer water quality conditions Depth to water level will be ' measured using an electronic water level probe Figure 2 presents the groundwater contour map The general groundwater flow direction at the site is towards the west The gradient for the monitoring event ' conducted on February 21, 1995 is [-51 30-(-51 45)j / 98 = 0 0015 feet/feet The gradient for the monitoring event that was conducted on December 1, 1994 is 1-46 00-(46 30)] /121 = 0 0025 feet/feet ' During the reporting period 12/94 through 2/95, TPH (gasoline) conc.entiations in MW-1 deci eased from 5 300 to 2,100 parts per billion (ppb) MW-2 ' decreased from 1,100 to 480 ppb MW-3 increased from 5GO ,o 630 ppb MW-4 increased from 2,200 to 24,000 ppb MW-5 increased Froin 420 to 630 ppb, and MW-6 decreased from 1,200 to 78 ppb A TPH concentration contour map is presented in Figure 3 ' During the reporting period 12/94 through 2/95, Benzene concentrations in MW-1 decreased from 64 to 47 ppb MW-2 decreased from 54 to 9 2 ppb MW- 3 remained unchanged at 97 ppb MW-4 increased from 33 to 4,700 ppb MW- 5 decreased from 40 to 17 ppb, and MW-6 decreased from 240 to I 1 ppb 1