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GEOTECHNICAL ENVIRONMENTAL WATER RESOURCES ENGEO CONSTRUCTION SERVICES Expect Excellence— COASTAL/MARINE GEOTECHNICS Project No. 5044.500.101 September 12, 2023 Ms. Susan Dell'Osso Califia, LLC 73 Stewart Road Lathrop, CA 95330 Subject: River Islands Lathrop, California WORK PLAN FOR REMOVAL OF MONITORING WELLS MWR-27 THROUGH MWR-30 Dear Ms. Dell'Osso: As requested, ENGEO has prepared this work plan to remove existing monitoring wells that will be decommissioned at the subject project located in Lathrop, California. The wells to be removed are identified as MWR-27, MWR-28, MWR-29, and MWR-30 (Figure 1). The wells were installed in 2005 for the purpose of monitoring groundwater levels and collection of water quality samples at the site. The wells are included in the City of Lathrop Central Valley Regional Water Quality Control Board (RWQCB) Waste Discharge Requirements and Master Reclamation Permit (Order No. 2016-0028-01). The work scope described below will be performed in general accordance with the City of Lathrop Waste Discharge Requirements and Master Reclamation Permit (Order No. R5 2016-0028-01) and San Joaquin County well destruction standards. PROJECT DESCRIPTION The overall River Islands Project is located on Stewart Tract in the southwestern portion of Lathrop, just south of the San Joaquin and Old Rivers, northeast of Paradise Cut, and northwest of the Union Pacific Railroad. MWR-27 and MWR-28 are located on APN 213-61-005, and MWR-29 and MWR- 30 are located on APN 213-63-001. SCOPE OF WORK Well Destruction Prior to demolition, a well destruction permit will be obtained from the San Joaquin County Environmental Health Department. Well destruction will be performed in general accordance with the California Department of Water Resources Standards for destruction of groundwater wells, as well as applicable County well standards. The well destruction will include either completely overdrilling the wells to remove existing well materials and tremie backfilling the hole with neat cement (MWR-27), or by pressure grouting the wells (MWR-28, MWR-29 and MWR-30), while under the observation of a San Joaquin County Environmental Health representative. We will coordinate with a licensed drilling contractor to overdrill the wells to bottom depth. Drilling will be accomplished using a truck-mounted hollow stem or mud rotary drill rig equipped with minimum 8-inch-diameter augers in order to remove the annular seal around the well. Given that the subsurface material is not suspected to be contaminated, drilling cuttings will be discharged on the ground surface near the well. 17278 Golden Valley Parkway, Lathrop CA 95330 • (209)835-0610 • Fax(888)279-2698 www.engeo.com