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Jerry l.ile Page 2 March 3,2005 Slough and the Stockton Channel. HERD has participated in numerous meetings and teleconferences, reviewed numerous documents,and provided written or oral comments on issues related to preparing an acceptable human health risk assessment(HHRA). DOCUMENT REVIEWED HERD reviewed the February 25,2004 'Work Plan for Soil Vapor Assessment, Stockton Parcel 2A, L&M Operable Unit, 666West Weber Avenue, Stockton, Califomle"prepared by Secor in Rancho Cordova, Caliiomia and received by HERD on February 28, 2005. COMMENTS 1. The soil vapor sampling is proposed to be conducted consistent with DTSC guidance(DTSC & LARWQCB, 2003; DISC, 2004),therefore the baseline data should be acceptable for use in a predictive indoor air human health risk assessment. 2. HERD recommends the following modifications to fill active soil gas and geotechnlcal data gaps In the area of the SVE system under apartment buildings for the HHRA. a. Use 6 liter summa canisters, except for methane analyses where the IL are sufficient. b. Use glass lined summa canisters for hydrogen sulfide analyses. c. Use EPA Method TO-15 SIM, rather than TO.15. d. Include sample collection and analysis for hydrogen sulfide via EPA Method 16. e. Ensure detection limits are 500 times less than acceptable indoor air concentrations (DTSC, 2004). f. Sample locations: 1) Locate proposed SV-2 under the building (in location of SV-11 on Figure 2 of the July 14, 2004 HRA). 2) Locate proposed SV-3 under the building (between locations of SV-13 and SV-14 on Figure 2 of the July 14, 2004 HRA). 3) Locate proposed SV-4 under the building_ 4) Locate proposed SV-5 under the building but ensure it is outside the zone of influence of the DPE system (in general location of SV-15 on Figure 2 of the July 14, 2004 HRA). 050303JLdoc