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Former Fayette Manufacturing Page 2 of 2 <br /> 7675 West Eleventh Street March 18, 2013 <br /> Tracy, California <br /> • Although Cardno ATC proposes to collect air samples over a period of six to eight <br /> hours, the EHD directs that the sampling time be at least eight hours. The Department <br /> of Toxic Substances Control (DISC) in Final Guidance for the Evaluation and Mitigation <br /> of Subsurface—Vapor Intrusion-toIndoar-Air(Vapor Intrusion-Guidance)-dated-Octaber <br /> 2011, recommends for the first sampling event that indoor air samples be collected over <br /> a twenty-four-hour period to ensure diurnal fluctuations in vapor intrusion and indoor air <br /> concentrations are included in the sampling period. <br /> • Although Cardno ATC proposes to collect the outdoor ambient air sample approximately <br /> one-hundred feet up-gradient from the site structure, the EHD believes the distance is <br /> excessive considering the Vapor Intrusion Guidance states that ambient air samples <br /> should be collected at a distance equal to twice the height of the building. Please <br /> reconsider the proposed location of the ambient air sample; and <br /> • Soil gas and air concentrations of chemicals of concern that exceed Environmental <br /> Screening Levels (ESLs) and California Human Health Screening Levels (CHHSLs) and <br /> undergo the Tier 2 modeling program must be evaluated for an excess cancer risk of <br /> one-in-a-million (1 X 10-6) as well as a hazard quotient of 1.0. <br /> With these conditions the EHD approves the work plan. Please submit the boring permit <br /> application and fees and complete the field work by 15 May 2013. If you have any questions <br /> concerning this matter, please contact Vicki McCartney at (209) 468-9852 or by email at <br /> vmccartney(a)sicehd.com. <br /> Sincerely, <br /> e, <br /> Victoria L. McCartney, RENS Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental HealtSpecialist Engineering Geologist <br /> c: Ms. Jeanne Homsey, PE, ATC Associates Inc., 1117 Lone Palm Avenue, Suite 201, <br /> Modesto, California 95351 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central <br /> Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br /> I <br />