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Central Valley Regional Water Quality Control Board 6793.4.001.01 North Lathrop Properties May 20, 2005 WORK PLAN FOR GROUNDWATER STUDIES Page 2 SCOPE OF SERVICES Our project scope is described below and is comprised of activities related to the construction and sampling of shallow groundwater monitoring wells to characterize the shallow aquifer. Groundwater Wells We will coordinate with a licensed drilling contractor to construct five groundwater monitoring wells within the site at the locations shown on Figure 2. Drilling will be accomplished using a truck-mounted hollow stem auger drill rig equipped with 8-inch diameter augers. These proposed wells will extend to depths of approximately 20 feet below existing grade. Each monitoring well will be constructed of 2-inch diameter PVC screen and blank casing. This will allow for an annular seal of three inches between the well casing and the edge of the borehole. Well casings will be installed with manufactured well screens that are positioned between 10 and 20 feet below the ground surface (bgs). The screen interval was selected to the length of the annular seal in each well. A two-inch bottom well cap will be threaded on the bottom of each well screen section. The slot screen size is proposed to be 0.010 with #2/12 sand to be used as filter pack material. Granular material will be placed in the annular space beginning at the bottom of the borehole and extending to approximately 2 feet above the top of the well screen. Each well will be surged, following placement of the filter pack and prior to installation of the bentonite seal to obtain optimal filling of the annual space. We propose to install the bentonite annular seal from seven to eight feet bgs. The annular seal will be constructed of neat cement grout that extends from ground surface to seven feet bgs. The exact depth of the final well screen may vary depending on site conditions during drilling. A typical well construction diagram is attached. We will extend the well casing between 2 to 3 feet above the ground surface and install a steel standpipe to protect the well casings and the data logging equipment that be installed later. At least 48 hours after completion of the well installations, each monitoring well will be developed through the use of purging and surge blocks to maximize the hydraulic connection between the well and the surrounding aquifer material. Wells will be purged of a minimum of three casing volumes using a using a 12-volt pump while monitoring stabilization of groundwater parameters (temperature, pH and electrical conductivity). Purging will continue during well development until sediments are minimized. Purge water will be discharged to land onsite. At least 48 hours prior to drilling the borings, we will mark the site for an Underground Service Alert (USA) utilities check. Monitoring well permits will be obtained and well construction activities will be conducted in accordance with San Joaquin County requirements.