SITE INFORMATION AND CORRESPONDENCE FILE 2

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�✓ y Interstate Shell Page 2 620 West Charter Way April 14, 2011 Stockton, California 95206 • It is unlikely that groundwater in the vicinity of this site will be used for potable water in the near future since the Water Quality Objective (WQO) for sodium is 20 mg/L and sodium was detected at concentrations between 27.8 and 727 milligrams per liter (mg/L) in groundwater samples collected from the on- and off-site monitoring wells in July 2010. • The most impacted soil from the five CPT borings was found below 30 feet bsg. • The most impacted groundwater was detected in Zone B at approximately 46 to 51 feet bsg. • Impacted soil and groundwater are delineated vertically and horizontally in Zone B, the zone with the highest concentrations of chemicals of concern. • An estimated 4,275 pounds of total petroleum hydrocarbons quantified as gasoline (TPHg) and 8.1 pounds of benzene may be present in the vadose and saturated soil at this site. • It is not necessary to collect soil gas samples since "the bulk of TPHg mass is in Zone B." • Human exposure pathways are functionally incomplete for direct contact .with petroleum hydrocarbon contamination in soil and groundwater at this site. • Soil within approximately ten feet of ground surface contains little to no contaminants of concern. • Concentrations of contaminants of concern in groundwater collected from the Zone A monitoring wells in May 2010 do not exceed the Environmental Screening Levels (ESLs) established by the San Francisco Bay Regional Water Quality Control Board. • Comparison of site specific soil data to ESLs has not been completed since soil ESLs for petroleum constituent do not exist for vapor intrusion risk. • The remaining contaminant concentrations at this site do not pose a risk of vapor intrusion into structures at this site. The EHD questions the determination presented by CRA that it is unlikely.that groundwater at this site will be used for potable water based on the sodium concentrations detected in groundwater. CRA states that the WQO for sodium is 20 mg/L. In an e-mail dated 08 April 2011, CRA provided the source for the WQO for sodium as A Compilation of Water Quality Goals, August 2003 with tables updated August 2007, prepared by the California Environmental Protection Agency Central Valley Regional Water Quality Control Board. In this document there is no Primary nor Secondary Maximum Contaminant Level (MCL) listed for sodium. The 20 mg/L concentration for sodium is listed under the column titled Drinking Water Health Advisories or Suggested No-Adverse-Response Levels (SNARLs) (for toxicity other than cancer risk). A footnote (57) associated with the 20 mg/L concentration states the "Guidance level to protect those individual restricted to a total sodium intake of 500 mg/day. " It seems reasonable that the sodium concentrations detected in the groundwater at this site are acceptable drinking water concentrations for the general public since only 2 of the 19 groundwater samples collected in July 2010, and none of the 9 groundwater samples collected in December 2010 were detected with sodium concentrations greater than 500 mg/L. (The National Academy of Sciences' Institute of Medicine has recommended the maximum intake of sodium at 1500 mg per day.) Based on this information, the EHD directs that sodium be removed from the analytical list. The EHD is in general agreement with the remaining bullets listed above.