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A <br /> ENVIROINCENTAL HEALTHSEPARTMENT <br /> PQM," SAN JOAQUIN COUNTY <br /> Donna K. Heran, R.E.H.S. Unit Supervisors <br /> Director 304 East Weber Avenue,Third Floor Carl Borgman,R.E.H.S. <br /> Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. <br /> c.,.. <br /> q .. �'P Program Manager Telephone: (209)468-3420 Douglas W.Wilson,R.E.H.S. <br /> iFSa <br /> Margaret Lagorio,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellan, R.E.H.S. <br /> Website:www.sjgov.org/ehd/ .Jeff Carruesco,R.E.H.S. <br /> JOHN FRARY APR 1 0 2006 <br /> UNION OIL COMPANY <br /> 270 TANK FARM ROAD <br /> P O BOX 1069 <br /> SAN LUIS OBISPO CA 93406 <br /> RE: Former Unocal #0187 <br /> 437 E. Miner Street <br /> Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the "Conceptual <br /> Site Model' dated January 2006 and the "Quarterly Groundwater Monitoring and Ozone <br /> Microsparge System Status Report, Fourth Quarter 2005' dated January 6, 2006, prepared by <br /> ENSR for the above referenced site and provides the following comments. <br /> When monitoring wells were first installed at this site in 1994, the depth to first groundwater was <br /> approximately 47 feet below ground surface (bgs)and water from monitoring wells U1, U2 and <br /> U3 contained petroleum contaminants. In August 1994, the water sample from U3 had 51,000 <br /> ug/I of total petroleum hydrocarbons as gasoline (TPH-g) and 9700 ug/I of benzene. By March <br /> 1998 there had been a significant reduction in contaminant concentrations in the water samples <br /> from U1, U2 and U3 and water had risen above the top of the screened interval (30 to 50 feet) <br /> of these monitoring wells. By May 1999 with the continued rise in groundwater, the depth to first <br /> water was approximately 25 feet bgs. Water samples from U1 and U2 were non-detect for <br /> contaminants. Water samples from U3 contained 18,000 ug/I of TPH-g and 2600 ug/I of <br /> benzene. This reduction of contaminant concentrations was probably the result of dilution from <br /> the rising groundwater. <br /> Water from the nested piezometer wells NP1 and NP2 with screen intervals that intersect first <br /> water and two deeper intervals, as well as water from U3 contained concentrations of petroleum <br /> contaminants when the ozone system was started in December 2000 (with NPl-65 and NP2-60 <br /> having high concentrations of contaminants). In December 2000 water from NPl-65 had <br /> 34,000 ug/I of TPH-g and 1710 ug/I of benzene and water from NP2-60 had 20,400 ug/I of TPH- <br /> g and 5580 ug/I of benzene. <br /> By August 2005 contaminant concentrations had declined in water from NPl-65 to 2500 ug/I of <br /> TPH-g and 21 ug/I of benzene and in water from NP2-60 to 1400 ug/I of TPH-g and 99 ug/I of <br /> benzene. Concentrations of contaminants in water samples from U3, N131-22, NPl-111, N132- <br /> 22 and NP2-116 had also declined. In the Gettler-Ryan "Ozone Microsparge System Pilot Test <br /> Status Report" dated November 19, 2003, which was their final report for this site, they <br /> concluded that the ozone microsparging system had been effective in reducing the dissolved <br /> hydrocarbon concentrations in the groundwater and they included graphs of the concentration of <br /> benzene and TPH-g in NP1-22, NP1-65, NP1-111, N132-22, NP2-60, NP2-116, U3 and U10 <br /> from June 2000 to September 2003. EHD supports the Gettler-Ryan conclusion that the ozone <br /> system was effective in reducing the groundwater contaminant concentrations near these wells. <br />