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Farmington Groundwater Recharge Program STC Work Plan—Hammer Site 1. INTRODUCTION This Survey, Testing, and Construction.(STC) Work Plan (WP) summarizes the scope and schedule for upcoming field investigation activities at the Hammer property (the site) for the Farmington Groundwater Recharge Program (the Program). Specifically, this WP describes preparation, operation, and monitoring activities during future field investigation. This document is presented as part of Task 4 of contract DACW05-01-D-0013 between the U.S. Army Corps of Engineers (USACE) and MWH. The site, shown in Figure 1, is approximately 17.2 acres in size and is located '/2 mile north of Highway 12 and 750 feet west of North Tretheway Road in eastern San Joaquin County. The site is located within the North San Joaquin Water Conservation District. 1.1. Background Information Due to a long history of predominantly sole reliance on groundwater (for primarily agricultural use), severe groundwater overdraft conditions exist in the eastern portion of San Joaquin County. Long-term groundwater pumping in excess of natural replenishment has dramatically lowered groundwater levels and allowed the intrusion of saline water to portions of the aquifer. Continued groundwater overdraft will exacerbate saline water intrusion, resulting in the demise of the groundwater resource. Increased economic losses will be experienced by those urban and agricultural sectors dependent on groundwater as a water supply. Stockton East Water District (SEWD) and the USACE in a cost share agreement have created the Program with the intent of replenishing the aquifer system to insure future groundwater supply and to protect against saltwater intrusion. The goal of the program is to obtain 25-30 parcels of land totaling 1,200 acres for the purposes of directly recharging surface water to the groundwater aquifer. It is estimated that the development of these parcels into recharge facilities may return approximately 35,000 acre-feet of water per year into the overdrafted groundwater basin in eastern San Joaquin County. This site represents one parcel which may be used as a recharge facility. Pursuant with this effort, SEWD and the USACE are screening other locations within eastern San Joaquin County for the purposes of developing other recharge facilities. SEWD and USACE have employed MWH to assist in this program. As part of this program MWH is to provide planning, investigation, design, oversight of field activities and performance monitoring services to adapt the site for non-flood season groundwater recharge. 1.2. Work Plan Overview The goal of this STC WP is to document site preparation and establish an operation and monitoring plan to evaluate the site for the purposes of converting to a long-term recharge facility. Specifically, the WP will provide guidance for implementation of field investigation activities. The goal of these investigation activities is to collect data necessary to: • Explore of the nature,thickness, and permeability of the unsaturated zone in the area; • Estimate infiltration rates; • Examine pilot scale groundwater recharge test data; • Evaluate the feasibility of the site for future long-term use. MWH 1-1 July 2004