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California conal Water Quality Co rol Board <br /> Central Valley Region <br /> Katherine Hart,Chair <br /> Arnold <br /> Linda S. Adams 11020 Sun Center Drive#200,Rancho Cordova,California 9 <br /> Secretary for 1 '\"� n D Schwarzenegger <br /> Phone(916)464-3291 •FAX(916)4644645 U \VVI Governor <br /> Environmental htipJ/www.waterboards.ca.gov/centralvalley <br /> Protection <br /> t9AY 0 3 .Lui0 <br /> 30 April 2010 <br /> NUtRONI•AEN7 HEALTH <br /> Ms. Stephanie McKenna Mr. Jay All nPERMIT/SERVICES <br /> Chevron Environmental Management Company Stone <br /> Pa othersfic Management <br /> Avenue, to Company <br /> 6001 Bollinger Canyon Road 5757 Stockton, CA 95207 <br /> San Ramon, CA 94583 <br /> DOCUMENT REVIEW, MONTGOMERY WARDS AND UNOCAL STATION #5098, 5400- <br /> 5606 PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY, CASE NOS. 390258 AND <br /> 390014 <br /> 1 reviewed the Semi-Annual Groundwater Monitoring and Remediation Status Report (Report) <br /> received 29 April 2010 from Chevron Environmental Management's consultant AECOM. The <br /> Report evaluates the second soil vapor extractionlair sparging treatment system (SVE/AS) <br /> rebound test conducted from 28 December 2009 until semi-annual groundwater sampling on <br /> 19 February 2010, and estimates approximately 0.11 pounds of benzene and 356.1 pounds of <br /> total petroleum hydrocarbons as gasoline (TPHg) remain in soil and groundwater. Maximum <br /> groundwater concentrations were TPHg, 2,100 micrograms per Liter (ug/L); benzene, 5 ug/L; <br /> toluene, 5 ug/L; ethylbenzene, 31 ug/L; and xylenes, 25 ug/L. Groundwater concentrations <br /> rebounded in February 2010 and exceeded the concentration limit for permanently shutdown <br /> of the SVE/AS. The Report recommends leaving the SVE/AS off until the soil vapor wells are <br /> sampled on 12 May 2010, then run SVE/AS until just prior to the next groundwater monitoring <br /> event scheduled for early August 2010 (third quarter of 2010). If groundwater concentrations <br /> show a declining trend, then the SVE/AS will be shut down permanently and a no further <br /> action report will be submitted for consideration of case closure. If the data show rebound <br /> continuing, then an additional groundwater monitoring event will occur in the fourth quarter of <br /> 2010 and SVE/AS may be resumed as appropriate. The second semi-annual monitoring <br /> report is due 30 October 2010. <br /> The recommendations are acceptable and approved. Please provide an email status report <br /> by 15 September 2010 consisting of the August 2010 monitoring data relevant to the SVE/AS <br /> rebound testing. You may contact me regarding questions by phone at(916) 464-4615; or by <br /> e mail at 'barton waterboards.ca. ov. <br /> James L.L. Barton, P.G. <br /> Engineering Geologist <br /> cc: Judy Reid, SWRCB, UST Cleanup Fund (Commingled Plume Program), Sacramento <br /> Mike Infurna, San Joaquin County Environmental Health Division, Stockton <br /> Nichole Gleason, Downey Brand, 621 Capitol Mall, 18th Floor, Sacramento 95814 <br /> Jennifer Johnston, AECOM, 10461 Old Placerville Rd, Ste 170, Sacramento 95827 <br /> Jim Brake, Geocon Inc., 3160 Gold Valley Dr., Ste. 800, Rancho Cordova 95742 <br /> California Environmental Protection Agency <br /> Ca Recycled Paper <br />