ARCHIVED REPORTS XR0010526 - Laserfiche WebLink

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4 0 RESULTS 4.1 Depth to Groundwater and Groundwater Flow Direction The depth to groundwater on August 19 ranged from 28 54 to 29 07 feet below grade (Table 1) These depths are approximately 2 feet greater than those that were measured on June 13, 2002, and the decline is typical of the seasonal change in the depth to groundwater Using the three-point method to contour these values yields a groundwater elevation (piezometric surface) map with a uniform gradient of 0 003 ft/ft to the southeast (Figure 3) This result confirms the flow direction that was reported as tentative in the Second Quarter 2002 Report It is therefore evident that the regional groundwater elevation maps that are prepared semi-annually by the San Joaquin County Flood Control District may not accurately depict the local flow direction The 1993,map indicated that groundwater flow'at the site is to the northeast 4.2 Laboratory Results No hydrocarbons were detected this quarter in JLM-4, in the previous quarter, concentrations were very low and ranged from 1 to 2 micrograms per liter(µg/1 =parts per billion) (Table 2) TPH-g, benzene, toluene, ethylbenzene, and xylene were all detected in JLM-5, at concentrations that are nearly identical to those reported in June In contrast, concentrations were significantly lower in JLM-3 than those reported in June In , June, JLM-3 was purged and sampled after JLM-5, whereas the sequence was reversed in August This suggests the possibility that the June sample from JLM-3 was cross- contaminated by the pump when it was transferred from JLM-5 In the future, JLM-5 will be the last well to be purged and sampled Hydrocarbons in the diesel range were again} detected in both JLM-3 and JLM-5, and concentrations were similar to those reported in June No recognizable pattern was evident in the chromatograms f As previously reported, gasoline oxygenates are not a major component of the groundwater contamination Very low concentrations of TBA and/or MTBE were again detected in JLM-3 and JLM-5, and 1,2-DCA was also detected at concentrations that are essentially identical to those reported in June 5.0 DISCUSSION AND CONCLUSIONS Water-elevation data collected in August confirm the southeastward groundwater flow direction that was reported in the second quarter, implying that additional investigation of the extent of groundwater contamination is required to the southeast of JLM-3 One boring(JLM-11) and one well (JLM-13) were proposed in this area in the Second Quarter 2002 Report, and both are again recommended here As proposed in our August 21 Work Plan Addendum, boring JLM-11 should be drilled deep enough to reach the • second aquifer to determine whether it has been impacted by any of the petroleum hydrocarbons that are present in the first aquifer 4