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CAdIIIIIIIIIIIQL�_ �Pp =014 PEA Work Plan N G I a 1 R I N G Martin Metals Finishing Inc. (Former) Stockton, California 3 SCOPE AND OBJECTIVES The objectives of the PEA are to delineate the extent of contamination at the Site, estimate potential threat to human health and the environment, determine if action is required to reduce the threat, identify data gaps and to develop a Site mitigation strategy. 3.1 Preliminary Conceptual Site Model CDIM developed a Conceptual Site Model(CSM)for potential exposure pathways to understand the Site's potential risk to human health and the environment and to inform the PEA Work Plan. A documented historic release of hazardous substances from the MMF building to the storm drain and to soil near the storm drain outfall in Mormon Slough occurred in 1989 at the latest,over 30 years ago. MMF operations have ceased,and associated hazardous materials were removed from the Site. Commercial and industrial workers occupy the MMF building and buildings surrounding the Site. FIP prevents trespasser access to the Slough by filing letters with law enforcement and requesting the clearing of persons from the FIP property; however, trespassers are often observed in Mormon Slough. Factors related to the soil, water, and air pathways were assessed in accordance with the PEA Guidance Manual (DTSC, 1994). The CSM Receptor Network as it is currently understood is presented in Figure 4. • Soil Pathway Factors: Topography at the Site is flat with a gentle slope to the north towards Mormon Slough. Site soils are gravelly loam, sandy loam, and clay loam with slow infiltration rates; cemented soils underlying the loam restrict the downward movement of water. Site access is restricted by a locked gate, which surrounds the entire FIP property, and the Site and surrounding FIP property is paved or occupied by building foundation slabs. No school, day care, or terrestrial sensitive environments are present within 200 feet of the Site. • Water Pathway Factors: The Site is in the San Joaquin Basin of the Central Valley hydrologic region, and groundwater in the basin is critically over drafted (California Department of Water Resources, 2020). Groundwater in the vicinity of the Site is not used for drinking water (DTSC, 1998) due to overdraft and salt-water intrusion, and no drinking water wells are mapped within one mile of the Site (EDR, 2022; Appendix B). Depth to the shallowest aquifer is approximately 50 ft bgs (DTSC, 1998), and shallower confining layers retard surface water infiltration to the aquifer. There is no suspected release of hazardous substances to groundwater at the Site. The Site is located in an area with reduced flood risk outside of the 500-year flood and protected by levee from the 100-year flood, according to the Federal Emergency Management Agency(FEMA) National Flood Hazard Map.' The San Joaquin River is approximately 3.5 miles west and hydrogeologically upgradient of the Site, and no drinking water intakes,fisheries, or wetlands are located along the surface water migration path. Hazardous substances were discharged to the Slough over 30 years ago, and there is no suspected recent release of hazardous substances to surface water at the Site. The slope between the Site and Mormon Slough towards the north is ' https://hazards-fema.maps.arcgis.com/apps/webappviewer/index.html?id=8bOadb51996444d4879338b5529aa9cd. Accessed June 24, 2022. CDIM—Fairgrounds Industrial Park Page 7