ARCHIVED REPORTS_XR0012879 CASE 1

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Mr Wade Broughton General Mills June 9, 1992 Page 2 were not detected in soil samples MW-1-35, MW-2-35, or MW-3-35 Analytical results for soil samples collected on May 12, 1992, are compiled in Table 1 Laboratory analytical reports of these soil samples are included in Enclosure C Well Installation/ Development Monitoring wells MW-1, MW-2, and MW-3, installed on May 12, 1992, were constructed with 2-inch diameter, flush-threaded, Schedule 40 polyvinyl chloride(PVC) pipe Monitoring wells were screened from 30 to 50 feet below the surface with 0 02-inch wide slots The annular space of each well was filled with No 3 Monterey sand from the bottom of the well to approximately 2 feet above the screened interval A 2-foot thick bentonite seal was placed above the sand pack The remaining annular space was filled with cement grout containing 3-5 percent bentonite The top of the well casings were sealed with locking, water tight, expansion caps and were completed at the surface with traffic-rated well covers Complete well construction details are included in Enclosure D Monitoring wells MW-1, MW-2, and MW-3 were developed by raising and lowering a surge block to remove fines from the sand pack After surging, each well was purged of 6 well volumes of ground water in order to remove sediment and to ensure collection of a representative ground water sample Ground Water Level Measurements Ground water levels were measured in monitoring wells MWA through MW-3 on May 13, 1992, and found to be approximately 40 feet below the surface Ground water level data are compiled in Table 2 Depth to ground water measurements collected on May 13, 1992, and the top of the well riser elevations surveyed on May 21, 1992 (Enclosure A), were used to calculate ground water table elevations and construct the ground water table contour map shown in Figure 4 The primary direction of ground water flow is toward the south-southwest with a hydraulic gradient of approximately 0 005 Ground Water Analytical Results Ground water analytical results collected from monitoring wells MW-1 through MW-3 on May 13, 1992, are compiled in Table 3 Total petroleum hydrocarbons as diesel and BTEX were not detected in groundwater samples collected from monitoring wells MW-I through MW-3 Copies of certified laboratory reports for ground water samples collected in May 1992 are included in Enclosure E Discussion Laboratory results of soil samples collected at 35 feet below grade (immediately above ground water) from soil borings MW-1, MW-2, and MW-3, were found not to contain petroleum hydrocarbon constituents Laboratory results of ground water samples collected from momtorsng wells MW-1, MW-2, and MW-3, located cross-gradient and down-gradient of the former fuel oil storage tank location were found not to contain petroleum hydrocarbons constituents Based on these soil and ground water analytical results, Delta recommends that no further environmental actions be taken regarding this tank basin There is no evidence that subsurface soils or ground water have been impacted by petroleum hydrocarbons