SITE INFORMATION AND CORRESPONDENCE

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Shockey Trucking May 24 2010 850 Milgeo, Manteca Page 2 of 3 3. The CAP contains evaluations of two soil remedial alternatives; soil excavation with on-site treatment or off-site disposal, and soil vapor extraction (SVE) with on-site ' treatment of vapor. AGE does not recommend soil excavation, but does recommend SVE. AGE stated, "the method is most effective on volatile hydrocarbon (TPH-g/BTEX) in permeable soil and to a lesser degree in semi- permeable soil types." Numerous soil and ground water samples have been collected and analyzed and it has been demonstrated that TPH-d is present in high concentrations and the more volatile components of diesel fuel are absent. The EHD is concerned regarding the potential effectiveness of SVE.for reducing TPH-d contamination with low volatility in a reasonable amount of time; point source removal of TPH-d contaminant mass would probably be more effective. 4. Three ground water remediation alternatives were evaluated and compared in the CAP including ground water extraction with treatment; in-situ chemical oxidation (ozone injection and RegenOx injection); and monitored natural attenuation, In October 2002, six ozone sparge wells were installed by AGE and were later used to inject ozone into ground water during a pilot study. The pilot study was conducted from March 31, 2003 to July 10, 2003. Ground water contaminant concentrations were not significantly affected during the pilot study; no evident t. decrease in TPH-d concentration occurred in MW-4 in the source area or in MW-1 off-site although dissolved oxygen concentrations increasing in the ground water. It is not clear to EHD if the ozone injection rate was sufficient enough to address the contaminant mass or that the test duration was long enough to affect the mass. The second remedial alternative evaluated by AGE is RegenOx. This treatment will require injection of an estimated 45,000 pounds of RegenOx to mitigate the contaminant mass (10 gallons or 73 pounds of THP-d) in the ground water plume. This approach would require that a Waste Discharge Report be submitted to the Central Valley Regional Water Control Board (CVRWQCB) for approval. It is not clear to the EHD if the added cost for the CVRWQCB permit and discharge requirements were considered in the CAP. Monitored natural attenuation (MNA) was also considered, but discounted as having little benefit. AGE estimated 25-50 year duration for MNA with a cost between $2,500 and $45,000 annually. Even using the lower estimate of 25 years, it would seem to be an unreasonable amount of time to invest in MNA. 5. The EHD agrees with the CAP recommendation to conduct a sensitive 'receptor survey specifically for your site. The survey should be conducted to identify all receptors within a 2,000- foot radius of the site. 6. The EHD does not concur at this time with the recommendation for an additional deep MW installation and additional soil sampling northwest of MW-4, the location of former UST-1. In January 2008, AGE completed boring B-23; 8 soil samples and 2 ground water samples were collected and analyzed. Boring B-23 was completed approximately 20 feet northwest of MW-4. No contaminants were reported in soil samples collected from 25 to 50 feet below ground surface (BGS) and no contaminants were reported in the water samples collected from two deep water bearing Units at 40 feet and 50 feet BGS from B-23. If threatened receptors are identified in the -pending sensitive receptor survey, further ground water i assessment may be warranted to the northwest beyond MW-7. I