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0J 1 <br /> A <br /> 3} The dissolved hydrocarbon plume is stable. All off-site wells except <br /> MW-4, had no detectable concentrations of TPPH-g or benzene during <br /> the most recent groundwater monitoring event. There has been no <br /> MtBE detected at this site. Groundwater will continue to be impacted <br /> by capillary fringe or smear zone soils. However, eight years of <br /> monitoring data strongly suggests the groundwater plume is naturally <br /> attenuating. Additional data could not provide any stronger argument <br /> than 32 quarters of groundwater samples. <br /> 4) A well survey completed by Applied GeoSystems in 1990 identified the <br /> nearest municipal water supply well as being approximately 800 feet <br /> north of the site (crossgradient). <br /> 5) Soil contamination has been defined on site. Groundwater has <br /> historically been at depths of 35 to 50 feet below ground surface. It is <br /> highly unlikely that any basements or utility trenches extend to these <br /> depths. <br /> In conclusion, the majority of the source material has been removed, the extent of <br /> contamination is defined, the groundwater plume has been stable for several years, and <br /> there are no drinking water wells near the site. Given these facts, it is Unocal's technical <br /> opinion that this site poses no significant threat to human health and safety or the <br /> environment. Further site assessment and active corrective action are not needed, and the <br /> site is suitable for closure as a low-risk groundwater case. If you have any questions or <br /> concerns, please call me at (510) 277-2334. <br /> Sincerely, <br /> Robert Boust <br /> cc: Andrew Lehane, PEG <br /> Elizabeth Thayer, CVRWQCB <br /> Mel7acobo, SWRCB <br />