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September 21, 1992 S E P z 4 1992 SEACOR <br /> ENVIRONMENTAL HEALTH <br /> Ms, Mary Meays <br /> San Joaquin County Public Health Services <br /> Post Office Box 2009 <br /> Stockton, California 95201 <br /> RE: 429 WEST LOCKEFORD STREET, LODI, CALIFORNIA, SITE CODE 1.354 <br /> Dear Ms. Meays: <br /> On behalf of Mr. Mardee Kidd, Science & Engineering Analysis Corporation (SEACOR) has <br /> prepared this letter to respond to specific comments presented in your letter to Mr. Kidd dated <br /> September 15, 1992 regarding the above referenced site. In the September 15, 1992 letter, you <br /> request additional groundwater monitoring wells be installed at the site to confirm groundwater flow <br /> direction and evaluate the lateral extent of groundwater contamination. SEACOR believes that <br /> additional groundwater investigation is not necessary based on the following: <br /> 1. At the time of underground storage tank(UST)removal, no evidence of holes or other signs <br /> of obvious integrity loss were observed. This suggests that the release(s) was probably the <br /> result of a slow leak and/or overfilling and not a catastrophic release. <br /> 2. Detectable levels of fuel hydrocarbons were measured in soil samples collected within 40 feet <br /> of the ground surface directly beneath the former underground storage tanks (USTs). The <br /> maximum hydrocarbon concentration (5,100 ppm) was detected in a soil sample collected <br /> from a depth of 19 feet below ground surface in a boring advanced within the boundary of <br /> the former UST excavation. Hydrocarbon concentrations in soil attenuate with depth and <br /> were non-detectable below 40 feet. Significant lateral migration of fuel hydrocarbons in the <br /> vadose zone did not occur as evidenced by the absence of detectable fuel hydrocarbons in <br /> soil borings drilled outside the boundaries of the former UST excavation. Since beginning <br /> site investigations in May 1991,the depth to groundwater measured in the existing monitoring <br /> well has ranged from 44.4 to 46.8 feet. <br /> 3. Given that the source of potential groundwater contamination (e.g. adsorbed phase <br /> hydrocarbons in the vadose zone) is limited to soils underlying the USTs, the point of <br /> maximum groundwater impact would be expected at or very near the source area. <br /> Groundwater samples collected from a monitoring well installed directly beneath the source <br /> area indicate that groundwater quality has not been significantly degraded. Furthermore, <br /> groundwater monitoring results for February, May, and August 1992 show that fuel <br /> hydrocarbon concentrations have decreased to non-detectable to trace levels, well below <br /> drinking water standards for aromatic hydrocarbons. <br /> 4. Based on San Joaquin County Flood Control and Water Conservation District groundwater <br /> elevation maps and surface topography, the regional groundwater flow direction in the site <br /> vicinity is believed to be towards the south. Because the former USTs were located directly <br /> north of the current shopping center building, the nearest feasible downgradient well location <br /> is over 100 feet from the former USTs. 100 Pine Street <br /> Suite 2025 <br /> San Francisco, CA 94111 <br /> (415)296-7877 <br /> (415)677-9694 FAX <br />