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California yjgional Water Quality Co4ol Board <br /> Central Valley Region <br /> Katherine Hart, Chair <br /> Linda S.Adams Arnold <br /> Secretary for 11020 Sun Center Drive#200, Rancho Cordova,California 9 IVE D Schwarzenegger <br /> Environmental Phone(916)4643291 •FAX(916)4644645 Governor <br /> Protection http://ww .waterboards.ca.gov/centralvalley <br /> DEC 28 2010 <br /> 27 December 2010 <br /> ENVIRONMENTAL HEALTH <br /> Ms. Stephanie McKenna Mr. Jay AIIspMIUSERVICES <br /> Chevron Environmental Management Company Stone Brothers Management Company <br /> 6001 Bollinger Canyon Road 5757 Pacific Avenue, Suite 220 <br /> San Ramon, CA 94583 Stockton, CA 95207 <br /> DOCUMENT REVIEW, MONTGOMERY WARDS AND UNOCAL STATION#5098, 5400-5606 <br /> PACIFIC AVENUE, STOCKTON, SAN JOAQUIN COUNTY, CASE NOS. 390258 AND 390014 <br /> 1 reviewed the Report on Soil Vapor Sampling and Human Health Risk Assessment (Report) received <br /> 20 December 2010 from Chevron Environmental Management's consultant AECOM. The Report <br /> provides the results of the September 2010 and October 2010 soil vapor sampling in a Human Health <br /> Risk Assessment. Total petroleum hydrocarbons as gasoline (TPHg) and benzene concentrations <br /> initially failed (TPHg, May 2010 and September 2010; benzene, May 2010) the San Francisco Bay <br /> Regional Water Quality Control Board Environmental Screening Levels (ESLs) and the California <br /> Human Health Screening Levels (CHHSLs); however, all constituents passed the ESLs and CHHSLs <br /> during the October 2010 soil vapor sampling event. A Tier 2 Johnson and Ettinger Model, which used <br /> the highest soil vapor results to determine the risk, determined that benzene (64.5 micrograms per <br /> cubic meter, or ug/m3) and the elevated detection limits value for naphthalene (<310 ug/m3) did not <br /> present a risk to human health in a commercial setting. However, TPHg (470,000 ug/m3) presented an <br /> unacceptable risk. The Report identified tentatively compounds (TICS) from the September 2010 and <br /> October 2010 samples. When quantified by carbon range, the TICS were identified primarily as the <br /> less toxic TPHg components; therefore, the Report states TPHg does not pose a significant risk to <br /> human health or the environment. Land use (commercial) is not changing in the foreseeable future. <br /> The Report requests site closure and states the closure report requested in my 3 November 2010 letter <br /> will be submitted by 30 April 2011. <br /> Removal of the above-ground soil vapor extraction/air sparging treatment system (requested in <br /> November 2010) is now appropriate. Please submit a well abandonment work plan, a draft fact sheet, <br /> a parte! map of all properties within 400' of_the hto tank sites, and as address list of all prnrnerty, <br /> owners and tenants to be notified by public participation by 30 April 2011 with the closure report, which <br /> is to be written in accordance with the Appendix A— Tri-Regional guidance obtained at <br /> http://www.waterboa rds.ca.gov/centralvalley/water_issues/u nderg round_storage_tan ks/tri- <br /> regionals_appendix_a.pdf. The draft fact sheet for public participation will be submitted as a MS Word <br /> document to me at the following email address. You may contact me regarding questions by phone at <br /> (916) 464-46115/x; or by e�-mail at Ibarton(&waterboards.ca.gov. <br /> James L.L. Barton, P.G. <br /> Engineering Geologist <br /> cc: Mike Infurna, San Joaquin County Environmental Health Division, Stockton <br /> Breda Miller, AECOM, 1220 Avenida Acaso, Camarillo 93012 <br /> Jim Brake, Geocon Inc., 3160 Gold Valley Dr., Ste. 800, Rancho Cordova 95742 <br /> California Environmental Protection Agency <br /> CA Recycled Paper <br />