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California Regional Water Quality Control Board Central Valley Region (a _ Robert Scltnefder,Chair C Lloyd,PhD Arnold Schwarnnegger cretary for Sacramento Main Office RECEIVED Governor ' uvironmental - - y _- Intent AddresshttpJ/www swrcb ca gpv/wgcb5 - - - Protection— 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-6114 MAY-0 5-20 - T Pbone(916)464-3291 3 May 2005 Mr John Fray Mr Jay Allen ' Union Oil Company of California Stone Brothers Management Company 276 Tank Farm Road 1024 W Robinhood Dr P O Box 1069 _ Stockton,CA 95207 San Luis Obispo, CA 93445 _ ' REPORTSIWORKPLANREVIEW, CLEANUPAND ABATEMENT ORDER (CAO) NO. 5-00-707, FORMER UNION OIL COMPANY OF CALIFORNIA (UNOCAL)STATION#5098 AT 5606 PACIFIC AVENUE,AND FORMER MONTGOMERY WARDS AUTO SERVICE AT 3400 PA CIFIC A VENUE,STOCKTON,SAN JOA QUIN COUNTY, 1 reviewed the Amendments to Monitoring and Reporting Program CAO No 5-00-707 and Work Plan to Install 1 an Additional Air Sparge Well within the Deeper Aquifer Zone(near MW-3) and Convert Monitoring Well MW-23S into an Air Sparge Well(Workplan),received 1 April 2005, the Updated Site Conceptual Model, Quarterly Monitoring and Remediation Status Report(1"Quarter 2005 Report),received 15 April 2005, and the Addendum to Work Plan to Install an Additional Air Sparge Well within the Deeper Aquifer Zone(near MW-3) ' and Convert Monitoring Well MW-23S into an Air Sparge Well(Remedial Alternatives Report),received 29 March 2005, submitted by ENSR International(ENSR)on behalf of Unocal The I"Quarter 2005 Report data was electronically submitted to GeoTracker on 29 April 2005 and received by me on 2 May 2005 —Depth to_water_at_A-zone MW_19S (shallow well near MW,23S)was 36 2$ feet on 1_4 January 2005 -There_are-- _ four identified interconnected hydrogeologic groundwater units• •---A-zone;at-30 to 50 feet below-ground surface(bgs) - -- —= -- - O B-zone, at 50 to 70 feet bgs C-zone,at 85 t6_90 feet bgs,and - a 0 D-zone, at 97 to 103 feet bgs Groundwater in all fora zones generally flows towards the east through the southeast. Soil Vapor Extraction (SVE)/AS, the current active groundwater remediation,has been effective for reducing petroleum hydrocarbon econcentrations over a majonty of the site The Workplan was submitted in response to my letter of 23 February 2005, which requested a report of additional ' remedial alternatives with a workplan to address residual petroleum hydrocarbons in groundwater In a 7 April 2005phone discussion with Robert L'Heurex,ENSR Project Engineer,I was informed that the Remedial Alternatives Report would be submitted separately from the Workplan As stated in the title, the Workplan 1 proposes the C-zone installation of one air sparge(AS-33)well screened 85 to 90 feet bgs near monitoring well MW-3 (Figure 2) The Workplan also proposes the conversion of C-zone monitoring well MW-23S (also screened 85 to 90 feet bgs)into an AS well The new AS wells will address a portion of a B-zone - e petroleum hydrocarbon hot spot located beneath Robinhood Drive not currently treated by the existing SVE/AS system 0 The I"Quarter 2005 Report states the maximum analytical results(MW-3)were- Total Petroleum Hydrocarbons ' as Gasoline(TPHg), 15,000 micrograms per Liter(pg/L),Benzene(B), 2,500µg/L, California Environmental Protection Agency ' Reeyrkd Paper