SITE INFORMATION AND CORRESPONDENCE

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Donna Heran 325 S. EI Dorado Street December 16, 1999 Page 2 The site is located five blocks south of the eastern end of the Stockton Deep Water Channel, and four blocks north of Mormon Slough. The soils to groundwater in this, and surrounding areas, are predominantly Gays. According to the San Joaquin County Flood Control District Maps, groundwater is located approximately thirty feet below ground surface. Previously on this site, an area contaminated with heavy metals and oil was identified as the site of an old auto-disman#'ling center. The dismantling center existed over thirty years ago. The soil was tested to find the limits of contamination, excavated and hauled to an appropriate dumpsite. Evidence of transport of the contaminant was.not present, as the area required only four feet (4') of vertical —'excavation,*even after thirty.years This is mentioned.as-a=basis--of-comparison as4o -� the lack of movement of contaminants through the soils at this site. A recent study was sponsored by the State Water Resources Board (SWRB) on the cleanup practices for leaking underground storage tanks (LUFTs). The study found that low risk leaks are stabilized by microorganisms consuming the fuel, referred to as passive remediation, thereby stabilizing the plume. The study also showed that benzene, the most dangerous component, does not travel far from the source, even over time. The study supports the option of passive cleanup for low risk sites with shallow groundwater as opposed to the traditional aggressive methods. The contaminated soil under one end of the twelve foot (12') tank does not qualify as a typical fresh or high-risk spill. The test results are more indicative of an old leak, possible after the tank was predominantly emptied, as no BTEX or MTBE were detected at any of the sampling locations. Tests of the first tank removed were clean, also indicative of an isolated leak that is not spreading. Resistance to transport at this site is supported by the presence of predominantly clay soils, and lack of transport of oil and metal contamination at adjacent location. Additionally, this tank was located immediately adjacent to EI Dorado Street. Any attempts to excavate material from the site would°jeopardize the integrity of the street: k Even with shoring and supports, El Dorado Street could suffer significant damage. It is also important to note that this site is commercially zoned and that the Agency has approved a project (plans available on request):that will provide for complete coverage of the property. The project will consist of single story retail facilities and parking. Either building improvements or asphalt paving will cover the entire site and there will be no opportunity for migration of contamination due to percolation of surface water. Considering the specifics of this site, the low levels of contamination, the trend by the SWRB towards passive methods for low risk sites, the potential risks to EI Dorado Street, and the proposedimprovement project on this site; we would request this site.be allowed to remain in place and undergo passive remediation. t . t