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California Re'Ronal Water Quality C ntrol Board <br /> Central Valley Region /� <br /> Alan C.Lloyd,PhD _ Robert Schneider,Chair /�// � � <br /> Secretary for Sacramento Main Office rze�iftnegger <br /> Environmental Internet Address: http:// .swrcb.ca.gov/rwgcb5 04y - or <br /> w <br /> Protection 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-61147�Q5 <br /> Phone(916)464-3291 �R <br /> 3 May 2005 % T ��/C fS rH <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 /> REPORTSIWORKPLAN REVIEW, 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 PACIFIC AVENUE,STOCKTON,SAN JOAQUINCOUNTY, <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 Monitoring and Remediation Status Report(1st 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 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 /> • 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 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 1"Quarter 2005 Report states the maximum analytical results(MW-3)were:Total Petroleum Hydrocarbons <br /> as Gasoline(TPHg), 15,000 micrograms per Liter(µg/L);Benzene(B), 2,500 µg/L; <br /> California Environmental Protection Agency <br /> Co Recycled Paper <br />