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g. �M Appendix A. Responsiveness Summary Martin Metals Finishing Inc. (Former) Stockton, California Response to Department of Toxic Substances Control (DTSC) Comments for CDIM's Preliminary Endangerment Assessment (PEA) and Supplemental Site Investigation (SSI)Work Plan (Work Plan), Martin Metal Finishing Inc. Stockton California, dated July 25, 2022. Comment Response MMF-SS-07 through MMF-SS-09. These PEA and SSI Work Plan. borings could ultimately reduce the number of future step-out locations. • The addition of one soil boring adjacent One boring, MMF-SS-11, was added just (preferably just downgradient)to the downgradient of the old stormwater outfall, presumed location of the"old stormwater and one boring, MMF-SS-08, was added outfall" and one soil boring adjacent to the adjacent to the central portion of the storm storm drain leading from the MMF building drain (Figure 5). Soil samples will be collected to Mormon Slough (in between the storm from 5, 10, and 15 feet below ground surface drain inlet and boring MMF-SS-05). Soil (ft bgs) and analyzed for metals, hexavalent samples should be collected from these chromium, soil pH, and volatile organic borings at the same depth intervals as compounds (VOCs) as described in text. MMF-SS-03 through MMF-SS-06 and be submitted for the same laboratory analyses as well. • The GSB recommends the addition of three Three soil borings were added to the scope of soil borings inside the former MMF building. work inside the MMF building: MMF-SS-03 at These borings should be located in the the former sludge drying and storage area, former sludge drying and storage area, the MMF-SS-05 at the former plating area, and former plating area, and the center of the MMF-SS-04 in the center of the building building. Soil samples should be collected (Figure 5). Soil samples will be collected from from these boring at the same depth 5, 10, and 15 ft bgs and analyzed for metals, intervals as MMF-SS-01 and MMF-SS-02 hexavalent chromium, soil pH, and VOCs as and be submitted for the same laboratory described in text. analyses as well. • The GSB recommends the collection of soil In Figure 5 and text Section 3.4, CDIM has vapor samples in addition to sub-slab vapor. proposed finishing the five borings located The GSB suggests that the five interior soil inside the MMF building as dual-nested soil borings be competed as dual-nested soil gas wells (MMF-SV-01 through MMF-SV-05) vapor probes, with implants placed at 5 and with probes set at 5 and 15 ft bgs. Four 15 feet bgs. Following installation, these soil additional dual-nested soil vapor probes are vapor probes should be sampled in proposed north of the MMF building in the accordance with the DTSC's 2015 Advisory- vicinity of the storm drain and former Site Active Soil Gas Investigations (the operations to assist with delineation of Advisory). The collected soil vapor samples constituents detected in soil vapor within the should be submitted for laboratory analysis building. All soil vapor samples will be of VOCs. The GSB further recommends that analyzed for VOCs, oxygen, and helium as CDIM consider the installation and sampling described in text Section 3.5—Laboratory of between two and four exterior soil vapor Analysis. Sampling protocols are described in probes. Based on the overall size of this the QA/QC Plan. scope of work, installing and sampling these probes may prove beneficial in delineating any potential impacts to soil vapor. Page A-4