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r California Regional Water Quality Control Board <br /> Central Valley Region 0 <br />,wcrelary <br /> Lloyd,PhD Robert Schneider,Chair far Sacramento Main Office Arnald Sc6warzenegger <br /> Environmental Internet Address http/Avww awrcb ca gpvhwigcb5 RECEIVED Governor <br /> Protection 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-6114 MAY <br /> n rya <br /> Phone(916)464-3291 MA V 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 /> REPORTS/WORKPLANREVIE W, CLEANUP AND ABATEMENT ORDER (CAO)NO. 5-00-707, <br /> FORMER UNION OIL COMPANY OF CALIFORNIA (UNOCAL)STATION#5098 AT <br /> 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE AT <br /> 5400 PACIFICA VENUE,STOCKTON,SAN JOAQUIN COUNTY, <br /> I reviewed the Amendments to Monitoring and Reporting Program CA 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 Monitoring and Remediation Status Report(1 st 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 I"Quarter 2005 Report <br /> data was electronically submitted to GeoTracker on 29 April 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 /> O B-zone, at 50 to 70 feet bgs <br /> G C-zone,at 85 to 90 feet bgs, and <br /> is 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 majority 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 April 2005phone discussion with Robert L'Heurex, ENSR Project 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 /> The Is`Quarter 2005 Report states the maximum analytical results(MW-3)were- Total Petroleum Hydrocarbons <br /> f as Gasoline(TPHg), 15,000 micrograms per Liter(pg/L),Benzene(B),2,500 pg/L, <br /> California Environmental Protection Agency <br /> $p R.,ymkd Paper <br />