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c �H m I PEA Work Plan N G I a 1 R I N G Martin Metals Finishing Inc. (Former) Stockton, California approximately 1%. Discharge of MMF wastewater ceased before 1990. The pathway to surface water from MMF residuals will be assessed via sediment in Mormon Slough. • Air Pathway Factors: No sampling data exists to document a release of hazardous substances to the atmosphere. The air pathway is assessed due to the potential for contaminated surface soils at the Site, resulting in the potential for vapor intrusion. Surface soils are not subject to wind dispersal, evaporation,or dispersal from fire/explosion, as the Site and surrounding area is paved or has revegetated since the potential historic release to soil over 30 years ago. The Site is mapped in an area with a population density of 5,000 to 9,999 persons per square mile. No sensitive receptors such as schools, day cares, hospitals, medical centers, or nursing homes have been identified within 1/4 mile of the Site. 3.2 Identified Data Gaps Based on a review of the preliminary CSM and sampling results, CDIM identifies the following data gaps which will be addressed during the PEA: • Concentrations of constituents of primary concern (COPCs) in subsurface soil at the Site have not been established; • Concentrations of volatile COPCs, including toluene, in soil vapor at the Site have not been established; and • Concentrations of COPCs in Mormon Slough have not been fully delineated. 3.3 Data Quality Objectives Data quality objectives (DQOs) for the Site are established using EPA's seven-step DQO process (USEPA, 2006) as described in the Quality Assurance/Quality Control (QA/QC) Plan contained in Appendix C. The problem at the Site is the potential presence of COPCs in soil and soil vapor including cadmium, chromium,copper, lead,zinc, and volatile organic compounds(VOCs)due to historic plating operations and waste disposal to the storm drain trench and Mormon Slough. The PEA Work Plan proposes (1) sediment sampling within the storm drain, (2) shallow and subsurface soil sampling onsite and offsite along the storm drain and in Mormons Slough, and (3) sub-slab and subsurface soil vapor sampling onsite. Data generated will be compared to the screening criteria below in order to estimate potential threat to human health and the environment: • DTSC Human Health Risk Assessment(HHRA) Commercial/Industrial Screening Levels (DTSC- SLs; DTSC, 2020)for soils; • The USEPA Industrial Regional Screening Levels (RSLs)for soil will be applied (USEPA, 2022) for constituents with no established DTSC-SL; • San Francisco Regional Water Quality Control Board (SFRWQCB) Terrestrial Habitat Environmental Screening Levels (ESLs; SFRWQCB, 2019) for Mormon Slough samples only; and, CDIM—Fairgrounds Industrial Park Page 8