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Ms. Christine Holm, ARU Kennedy/Jenks Consultants <br /> 19 December 1994 <br /> Page 3 <br /> USTU Constituents of Concern <br /> A groundwater sample collected from monitoring well MW-1 was analyzed for TPH-gasoline, <br /> TPH-diesel and BTEX. The analytical results from the fourth quarter 1994 as well as previous <br /> sampling events are listed in Table 4. Elevated concentrations of all constituents were detected <br /> as compared with results from previous sampling events. Because current sampling results <br /> indicate chemicals of concern at concentrations 10 to 100 times greater than historic data, a <br /> re-analysis of the groundwater sample was conducted. Results of the re-analysis indicated a <br /> decrease in the concentrations of these constituents. However, it should be noted that re- <br /> analysis was conducted 18 days after the normal holding time had expired and therefore these <br /> results may confirm the presence of chemicals of concern. Since TPH-gasoline and TPH-diesel <br /> had not been present at such elevated concentrations following the removal of the <br /> underground tank, it is possible that an unidentified or offsite source is contributing to <br /> groundwater contamination at MW-1. <br /> RECOMMENDATIONS <br /> Agricultural Regulatory Unit <br /> As requested by the ARU during a telephone conversation, conclusions or recommendations <br /> regarding the finding of agricultural chemicals is not provided in this letter report. <br /> Underground Storage Tank Unit <br /> The groundwater sample collected from monitoring well MW-1 contained elevated <br /> concentrations of petroleum hydrocarbons. Because historic data from MW-1 does not support <br /> the high levels at which the chemicals were detected and because samples were not collected <br /> from the other on site monitoring wells, the potential source(s) of this contamination can not <br /> be ascertained. It is recommended that additional groundwater samples from all five <br /> groundwater monitoring wells be collected to confirm the results obtained for this sampling <br /> event and to evaluate the potential for an off-site source. <br /> If you have any questions regarding the results of our latest sampling event, or if you would <br /> like to discuss our recommendations, please contact me at (916) 362-3251. <br /> Sincerely, <br /> KENNEDY/JENKS CONSULTANTS <br /> Kelye McKinney <br /> Projec anager <br /> attachments <br /> cc: Elizabeth Thayer, RWQCB <br /> Catherine Whitworth, Trustee <br /> Diane Hinson, San Joaquin County <br />