SITE INFORMATION AND CORRESPONDENCE

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Fernando's Place - 3 - 29 September 2016 1201 South Center Street Stockton, San Joaquin County ozone injection in wells OZ-1 through OZ-3. However, while the intermediate ozone wells are screened between 66-70 feet bgs, MW-3A is screened between 100-105 feet bgs, and thus cannot be used to evaluate effectiveness of the injections conducted 30 feet shallower. Decreases observed in MW-3B appear to be part of a declining trend that began prior to the implementation of ozone, with little effect observed during or after the pilot test. Both TPHg and benzene in MW-3B have rebounded to concentrations higher than prior to implementation of ozone. As there does not appear to have been a positive effect on groundwater contaminant concentrations as a result of the ozone pilot test, and the construction of ozone wells does not address hydrocarbon impacts between 70 and 198 feet bgs, I do not believe that ozone is an effective remedial technology for cleaning up groundwater pollution at this Site. It should be noted that in the Review Summary Report—Additional Work Fifth Review_ — November 2013 and in a letter dated 17 February 2014, respectively, the State Water Resources Control Board Cleanup Fund and San Joaquin County Environmental Health Department staff both noted concerns regarding the use of ozone at this Site prior to and during the implementation of the pilot test. While AGE has proposed the use of peroxide, several alternative remedial technologies to target groundwater pollution should be evaluated, one of which may be peroxide. By 30 November 2016, please submit a Feasibility Study which evaluates at least three (3) remedial technologies that have a high likelihood of achieving cleanup goals and includes estimates of cost and time to reach WQOs for each evaluated option, with a recommendation for the preferred remedy. 3. The Site is currently being used as an automotive repair facility. Following the completion of the pilot test, significant increases in TPHg concentrations have been observed in MW-1. The concentration of 729,000 ug/L reported in June 2016 is over 2.5 times the previous historical maximum of 290,000 ug/L reported in May 2005, and is an order of magnitude above the March 2015 concentration of 78,000 ug/L. A concentration of 600,000 ug/L in December 2015 indicates that the recent high concentration is not anomalous. Additionally, other constituents such as benzene, toluene, ethylbenzene, and xylenes (BTEX) have not increased along with TPHg in this well. Chlorinated solvents, such as trichloroethylene (TCE) and tetrachloroethylene (PCE), elude within the same time period as petroleum hydrocarbons during gas chromatography-mass spectrometry (GC/MS) analysis by EPA Method 8260B. As such, elevated TPHg concentrations without accompanying concentrations of BTEX constituents may indicate the presence of chlorinated solvents, which are likely to be used at an automotive repair facility. During the next semi-annual groundwater sampling event (fourth quarter 2016), please analyze groundwater samples collected from Site wells for TCE and PCE. Please include the results in a semi-annual Groundwater Monitoring Report due 30 January 2017. 4. Soil gas samples have been collected off-site to assess soil vapor intrusion risk to nearby residences. Samples were collected in the sidewalk near residences at 36 West Jackson Street adjacent to the Site to the west, 21 and 27 West Jackson Street across Jackson Street from the Site, and 21 East Jackson Street to the northeast of the Site.