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North County Recycling Center & Sanitary Landfill Department of Public Works/Solid Waste First Semiannual 2025 Groundwater Monitoring Report ©2025 COUNTY of San Joaquin. All Rights Reserved 1 1 INTRODUCTION 1.1 General This First Semiannual 2025 Groundwater and Surface Water Monitoring Report for the North County Recycling Center and Sanitary Landfill (NCRC&SL) is submitted in compliance with Waste Discharge Requirements (WDR) and Monitoring and Reporting Program (MRP) Order No. R5-2010-0016. The NCRC&SL is located at 17720 East Harney Lane, approximately nine (9) miles east of Lodi (Figure 1). Land uses within 1,000 feet of the facility are primarily agricultural and livestock grazing. The average precipitation near the landfill is 17.5 inches per year. The NCRC&SL is a single solid waste management unit, designated Class III, accepting non- hazardous municipal solid waste and inert waste, as defined in §20164 of Title 27. The site is 185 acres in area, comprised of lined areas (previously designated “modules”), each constructed on an as-needed basis. The total capacity of the landfill is 41.2 million cubic yards. The average rate of disposal during the reporting period was less than 27,000 tons per month (Table 1). 1.2 Hydrogeology The sediments underlying the NCRC&SL consist of inter-bedded sands, silts and clays with occasional gravelly layers. The measured hydraulic conductivity of the unsaturated zone soils is between 1 x 10-4 and 2 x 10-7 centimeters/second. Groundwater is first encountered at a depth ranging from 165 to 185 feet below ground surface (bgs). Groundwater elevations range from -50 to -70 feet National American Vertical Datum of 1988 (NAVD 88), fluctuating seasonally approximately 6 feet. The groundwater is unconfined. 1.3 Construction Details of construction are contained in the WDRs for this site. Lined Area 1 (previously designated “Modules 1 and 2”) was constructed in 1991 (Figure 2). This Area was excavated to an elevation of approximately 88 feet NAVD 88, which is approximately 30 feet below original grade. This Area is provided with a 60-mil High-Density Polyethylene (HDPE) liner installed over a 6-inch (minimum) thick layer of compacted native soil. NCRC&SL was not designed to meet Title 27 and RCRA Subtitle D criteria since these regulations were not in effect at the time of construction. Lined Area 3 was constructed in 1995, excavated to an elevation of approximately 60 feet NAVD 88, which is approximately 60 feet below original grade. This area is provided with a composite liner comprised of a geocomposite clay layer (GCL) under a 60 mil HDPE membrane. This liner design was approved as an engineered alternative to the prescriptive composite liner of Title 27 and RCRA Subtitle D.