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r <br /> J California Regional Water Quality Control Board <br /> Central Valley Region. <br /> Robert Schneider,Chair (0 <br /> Winston H.Hickox Gray Davis <br /> Secretaryfor Sacramento Main Office Governor <br /> Environmental - Internet Address: http://www.swrcb.ca.gov/mgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> TO: Brian Newman FROM: James Barton <br /> Senior Water Resources Control Engineer Engineering Geologist <br /> UST—LOP Enforcement Unit US —LOP Enforcement Unit <br /> Gordon Lee Boggs SIGNATURE: L <br /> Underground Tank Program Manager <br /> Thomas R. Pinkos <br /> Executive Officer <br /> DATE: 22 October 2003 <br /> SUBJECT: REVIEW OF UPDATED SITE CONCEPTUAL MODEL AND THIRD QUARTER 2003 <br /> MONITORING AND REMEDIA TION REPORT, FORMER UNOCAL STATION#5098 AT <br /> 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE AT <br /> 5400 PACIFIC AVENUE,STOC%TON, <br /> CLEANUP AND ABATEMENT ORDER NO.. 5-00-707,.SAN IOAQUIN COUNTY <br /> I reviewed the 2 October 2003 Updated Site Conceptual Model And Third Quarter 2003 Monitoring And <br /> Remediation Report(Report) submitted by Environmental Audit,Incorporated(EAI) on behalf of Unocal. <br /> Unocal is the primary responsible party for this commingled plume site. The Report provides the results of the <br /> groundwater sampling(3 to 5 August 2003) and Soil Vapor Extraction(SVE) system influent sampling <br /> (8 September 2003). During the third quarter of 2003, the SVE system operated for 173 hours, while the Air <br /> Sparging(AS) system cycled on and off during alternating weeks for a total of 627 hours. Groundwater <br /> concentrations of Total Petroleum Hydrocarbons as gasoline (TPHg)remained stable or continued to decline, <br /> with the exception of B-zone monitoring wells MW-11 (TPHg, 15,000 µg/L) and MW-12 (TPHg, 1,500 gg/L), <br /> which increased one to three orders of magnitude,respectively. Table 1 shows a general downward <br /> concentration trend for all monitoring wells, including MW-11 and MW-12,with occasional concentration <br /> spikes. The Report correlates the rise in concentrations with the winter months. Groundwater levels dropped <br /> three feet since May 2003. Groundwater flow direction is towards the east <br /> The following are my comments to the Report recommendations requiring approval under CAO No. 5-00-707: <br /> 1. The Report recommends continuing the Air Sparging without running the Soil Vapor Extraction, since <br /> only 6 pounds of petroleum hydrocarbons were removed from April through September 2003. <br /> I concur with the recommendation to suspend the SVE portion of the treatment system. I recommend <br /> that: 1)the SVE system remain in place, and 2)continue quarterly monitoring of the individual SVE <br /> wells,using the appropriate laboratory methods for soil gas analysis versus the current method of Photo <br /> Ionization Detection field readings. I recommend using TO-series methods or an approved laboratory <br /> California Environmental Protection Agency <br /> Recycled aper <br /> The energy challenge facing California is real. Every Californian needs to rake immediate action to reduce energy consumption. <br /> For a list of simple ways you can reduce demand and cut your energy costs,see our Website at hnp://w swrcb.ca.gov/mgcb5 <br />