SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Mr. Gregory Torlai, Jr. ' -2 - • 29 April 2009 H&H Marina amyl methyl ether (TAME). The highest petroleum hydrocarbon detections in soil in boring B-24 occurred between the ground surface and 20 feet below ground surface (bgs). TBA was the constituent with the highest concentration and was detected at a maximum concentration of 13 milligrams per kilogram (mg/kg) at 15 feet bgs. Depth to first encountered (shallow) groundwater was five to six feet below natural grade at the time of the investigation. Shallow groundwater was sampled from all borings except B-24. The contaminant with the maximum detection in first groundwater was MTBE, which was detected at 47 micrograms per liter (pg/L) in B-21. This boring is located about 120 feet cross gradient of the AGTs.and about 200 feet downgradient of the former underground storage tanks (USTs). Deep groundwater was sampled in all completed borings at depths ranging from 48 to 60 feet bgs. B-24 contained the maximum contaminant detection in deep groundwater, which was TPHg at 140 pg/L. This boring is equidistant between the September 2007 gasoline AGT spill collection sump and extraction well EW-2. Groundwater monitoring and reporting requirements for the Site are set forth in Monitoring and Reporting Program (MRP) No. R5-2004-0828. Groundwater monitoring is conducted quarterly. Monitoring for the fourth quarter 2008 was conducted on 12 December 2008. The Annual Report shows that the highest concentrations of TPHg and MTBE were in monitoring well MW-2 at 40,000 pg/L and 230 pg/L, respectively. Benzene, toluene, ethylbenzene, and xylene (collectively BTEX) were detected at 12 pg/L, 40 pg/L, 60 pg/L, and 760 pg/L, respectively. These December 2008 MW-2 concentrations are distinctly lower than last September's and one to three orders of magnitude less than the initial spike in concentrations observed in September 2007. Although not shown on Table 3, the laboratory analytical results show that the lead scavenger, 1,2-dichloroethane (1,2-DCA), was present at 20 pg/L in MW-2. Central Valley Water Board staff conducted split sampling with AGE from MW-2 on 2 April 2009 to verify the drastically reduced concentrations of contaminants of concern (CDCs) observed in MW-2. The analyte list for our splits included volatile organics. compounds (VOCs) by Method 8260B, TPHg and TPHd by Method 8015M, and total heterotrophic plate counts by Method SM9215. H & H could not replicated the Central Valley Water Board staffs Method SM9215 sample because they did not have a sample vessel preserved with sodium thiosulfate. To mitigate the pre-September 2007 spill, H & H conducts groundwater remediation by extracting groundwater from a 6-inch diameter extraction well (EW-1) and routing it through a granular activated carbon (GAC) treatment system. Operation of this interim remedial measure (IRM) system commenced in June 2005 under general National Pollutant Discharge Elimination System (NPDES) Permit No. CAG915001., Order No. 5- 00-11938. To address the.soil and groundwater pollution caused by the September 2007 spill, H & H excavated and disposed of the contaminated soil, partially backfilled and shored the excavation, and installed a sump pump. H & H commenced groundwater extraction from the sump and routed the groundwater to the existing IRM treatment system. The IRM remains in operation to the present. However, due to