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• S ECOR - • Ms. Devra Lewis April 8, 2005 Page 2 3. The nomenclature of the SVE wells needs to be consistent. On Figure 3, the SVE wells are labeled as "ASVE," and on Figure 5 the SVE wells are labeled as "SVE." Furthermore, identifying the soil vapor monitoring points as "SV"is confusing based on previous active soil gas samples with the same label. The L&M OU needs to label the proposed soil vapor monitoring points with an identifier that has not already been used for sample identification. On Figure 5 there are wells SVE-1 through SVE-11 — these represents the SVE wells installed in the excavation. The apartment wells ASVE-1 through ASVE-6 are not shown. We have updated the soil vapor points to the following — PSV-1 —for permanent soil vapor (PSV) and shown SVE lines and permanent soil vapor probes on Figure 1. 4. We do not concur with the monitoring schedule provided on Page 8 of the Work Plan. The scheduled monitoring does not propose sampling until six months after the startup of the SVE system and proposes to eliminate a sampling point after one round of non-detectable results. This is not sufficient. Increased monitoring is • needed for the first three months of operation. After the initial rounds of sampling from the soil vapor monitoring points, the L&M OU may propose performance based monitoring or a set time schedule. Sampling of the vapor points has been increased to monthly for the first 3 months the quarterly thereafter. 5. The Work Plan needs to include monitoring for the methane and polynuclear aromatic hydrocarbons. Vapor points will also be sampled for methane by ASTM D 1946. PAH are semi-volatile, and not likely to be present in soil gas, especially in high quantities; therefore they are not proposed as part of the SVE system operation. 6. The L&M OU needs to provide a discussion of the proposed leak test during sample collection, which is mentioned on page 8. Two types of leak checks will be conducted. First, a vacuum test will be conducted from the Summa canister to the most distant valve on the sampling train. Once connected to the canister, the furthest valve is shut, and for 10 minutes the sampling train is held at vacuum to determine if any leaks are present. Second, DTSC guidance suggests the use of a tracer compound, like isopropyl alcohol, which is sprayed in the vicinity of the tracer apparatus. That tracer compound is then analyzed in the sample. If it is detected above any background level, then a leak occurred. . 7. The locations of the five proposed soil vapor monitoring points are not sufficient to determine the radius of influence for the SVE system. At least one soil vapor Stockton Parcel 2A:Agency Response Letter 6-10-04. SECOR International Incorporated