SITE INFORMATION AND CORRESPONDENCE

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TUSD Delta Island School - 2 - 17 June 2016 Stockton, San Joaquin County (PID). Soil samples will be sent to a California —certified analytical laboratory and analyzed for TPH-d by United States Environmental Protection Agency (USEPA) Method 8015. The collection of five groundwater samples is also proposed in the vicinity of the former transformer pad. Five borings will be advanced approximately two feet into groundwater and then temporary well casing will be inserted into the boring. Grab groundwater samples will be collected and sent to a California —certified analytical laboratory and analyzed for TPH-d by USEPA Method 8015. A report documenting the completion of the work proposed in the Work Plan will be submitted to the Central Valley Water Board approximately 30 days after receipt of laboratory analytical results. The Work Plan notes that the Report will include an evaluation of the analytical results and a comparison to the San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs). Comments Central Valley Water Board staff comments on the Work Plan are below: 1. The Work Plan alludes to a previous removal action conducted by Tracy Unified School District to address the petroleum hydrocarbon contaminated soil but does not include any information regarding when this activity occurred, the volume of soil removed, or the final disposition of the removed material. Information pertaining to the timing, volume of soil removed and location of this soil should be provided in the report that will document the work proposed in the Work Plan. 2. The Work Plan proposes to compare analytical data from soil and groundwater samples collected at the Site to California San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs). The ESLs are not generally acceptable screening values for the Central Valley Regional Water Quality Control Board. Cleanup goals for TPH in the Central Valley Region are typically determined on a case by case basis using multiple lines of evidence that provides an overall reduction in risk to human health and the environment and restores the beneficial uses of groundwater. The following are some acceptable approaches for determining appropriate TPH cleanup levels: use of background values; EPA Regional Screening Levels, DIWET analysis to see if the extractant exceeds the Water Quality Objectives or use VLEACH° or similar type models to determine the TPH leaching potential to groundwater and/or surface water. The actual groundwater cleanup levels generally will depend upon the age of the TPH and its chemical composition and may consider other environmental or geochemical factors. 3. Pursuant to the Geologist and Geophysicist Act (Business and Professions Code §§ 7800 — 7887), all geologic plans, specifications, reports, or documents shall be prepared by a professional geologist or registered certified specialty geologist, or by a subordinate employee under his or her direction. In addition, they shall be signed by the professional geologist or registered certified specialty geologist or stamped with his or her seal, either of which shall indicate his or her responsibility for them.