SITE INFORMATION AND CORRESPONDENCE

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Morita Brothers 814 E. Charter Way, Stockton Page 2 of 3 largely removed through over-excavation in 1993, and was interpreted to present no significant risk to human health or the environment. An estimate of the residual contaminant mass in soil was not provided as GTI believed the data to be too sparse. Recent groundwater analytical data from the shallow and intermediate well zones have yielded less than detectable concentrations to low concentrations of total petroleum hydrocarbons as gasoline (TPH-g), methyl tert-butyl ether (MTBE) and tertiary butyl alcohol (TBA) which GTI interprets to indicate a submerged source of impacted soil on site slightly impacting groundwater and an off-site source of contaminants that are commingling with the subject site plume. The contaminants GTI believes to be commingling with the on-site plume are attributed to the unauthorized UST release on the 749 E. Charter Way site. GTI interpreted the site data to indicate that the plume of groundwater impacted by the on-site UAR attenuates to undetectable concentrations within 220 feet of the source in the down-gradient direction and has a total mass of approximately 1 pound. Fuel oxygenates concentrations are characterized as not warranting remedial action. GTI was concerned that utilization of a pump and treat remedial action would accelerate migration of the plume believed to be migrating from the 749 E. Charter Way site, a plume GTI characterized as unstable. In the SCM, the residual gasoline plume is characterized as posing a negligible risk to human health or the environment; no sensitive receptors were identified within a radius of 2,000 feet of the subject site. The SCM ends with a recommendation to grant site closure. The EHD notes that of the nineteen monitoring wells installed to monitor the plume of impacted groundwater, seven have not been significantly impacted, seven impacted wells have declining contaminant concentration trends, four have no distinct contaminant concentration trends but do appear to be stable, and one (MW-208) has a trend of increasing contaminant concentrations. Also, of the nineteen monitoring wells, seven occasionally or regularly exceed maximum contaminant levels (MCLs), water quality objectives (WQOs) or actions levels (ALs); of those seven, three exhibit a trend of declining contaminant concentration, three have no discernable trend, and one well (MW-208) has an increasing contaminant concentration trend. With the exception of MW-208, the plume of impacted groundwater appears to be stable and diminishing. With some differences of interpretation, in large measure the EHD concurs with most of the conclusions in the SCM, but there are a few items that should be addressed before the EHD can concur with the site closure recommendation. Recently, the Central Valley Regional Water Quality Control Board (CVRWQCB) has required that sites proposed for closure that have residual contamination in place must have the residual soil and groundwater contaminant concentrations evaluated for risk posed to human health and the environment. Currently, the San Francisco Bay Regional Water Quality Control Board's (SFBRWQCB)