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•� California Regional WaterQuality Control Board <br /> Central Valley Region <br /> C.Lloyd,PhD Robert Schneider,Chan <br /> retaryfor Sacra�eato Main Office Arnold Schwarzenegger <br /> TVironmentaI Internet Address httpJ/www awrcb ca ggvhwgcb5 RECEIVED Governor <br /> Protection 11020 Sun Center Drive 0200 Rancho Cordova,CA 95670-6114 <br /> PhY <br /> Mono(916)464-329 k <br /> 05 M <br /> 3 May 2005 <br /> Mr John Fray Mr Jay Allen <br /> Union Oil Company of California Stone Brothers Management Company <br /> 276 Tank Farm Road 1024 W Robinhood Dr <br /> P O Box 1069 Stockton, CA 95207 <br /> San Luis Obispo, CA 93406 - <br /> REPORTSIWORAPLAN REVIEW, CLEANUP AND ABATEMENT ORDER (CAO)NO. 5-00-707, <br /> FORMER UNION OIL COMPANY OF CALIFORNIA (UNOCAL)STATION#5098 AT <br /> 5606 PACIFIC A VENUE,AND FORMER MONTGOMERY WARDS A UTO SER VICE AT <br />' 5400 PA CIFIC A VENUE,STOCKTON,SAN JOA QUIN COUNTY, <br /> I reviewed the Amendments to Monitoring and Reporting Program CAO No 5-00-707 and Work Plan to Install <br /> an Additional Air Sparge Well within the Deeper Aquifer Zone(near MW-3) and Convert Monitoring Well <br /> MW-23S into an Air Sparge Well(Workplan),received 1 April 2005, the Updated Site Conceptual Model, <br /> Quarterly Monitonng and Remediation Status Report(I"Quarter 2005 Report), received 15 April 2005, and the <br /> • Addendum to Work Plan to Install an Additional Air Sparge Well within the Deeper Aquifer Zone(near MW-3) <br /> and Convert Monitoring Well MW-23S into an Air Sparge Well(Remedial Alternatives Report),received <br /> 29 March 2005,submitted by ENSR International(ENSR)on behalf of Unocal The 1"Quarter 2005 Report <br /> data was electronically submitted to GeoTracker on 29 Apnl 2005 and received by me on 2 May 2005 <br /> Depth to water at A-zone MW-19S (shallow well near MW-23S)was 36 28 feet on 14 January 2005 There are <br /> four identified interconnected hydrogeologic groundwater units <br /> • A-zone, at 30 to 50 feet below ground surface(bgs) <br /> • B-zone, at 50 to 70 feet bgs <br /> • C-zone,at 85 to 90 feet bgs, and <br /> • D-zone,at 97 to 103 feet bgs <br /> Groundwater in all four zones generally flows towards the east through the southeast. Soil Vapor Extraction <br /> (SVE)/AS, the current active groundwater remediation, has been effective for reducing petroleum hydrocarbon <br /> concentrations over a majonty of the site <br /> The Workplan was submitted in response to my letter of 23 February 2005,which requested a report of additional <br /> remedial alternatives with a workplan to address residual petroleum hydrocarbons in groundwater In a <br /> 7 Apn12005phone discussion with Robert L'Heurex,ENSR Protect Engineer,I was informed that the Remedial <br /> Alternatives Report would be submitted separately from the Workplan As stated in the title, the Workplan <br /> proposes the C-zone installation of one air sparge(AS-33)well screened 85 to 90 feet bgs near monitoring well <br /> MW-3 (Figure 2) The Workplan also proposes the conversion of C-zone monitoring well MW-23S <br /> (also screened 85 to 90 feet bgs)into an AS well, The new AS wells will address a portion of a B-zone <br /> petroleum hydrocarbon hot spot located beneath Robinhood Drive not currently treated by the existing SVE/AS <br /> system <br /> 0 The I"Quarter 2005 Report states the maximum analytical results(MW-3)were Total Petroleum Hydrocarbons <br /> Ias Gasoline(TPHg), 15,000 micrograms per Liter(pg/L); Benzene(B), 2,500µg2, <br /> California Environmental Protection Agency <br /> ja Reeyckd Paper <br />