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ENGEO INCORPORATED Well Installation Work Plan / River Islands Z/OS Lathrop, CA This well installation work plan outlines field procedures to be employed during the course of completing quarterly groundwater sampling at River Islands. Monitoring Wells: We propose to utilize the services of a licensed drilling contractor to construct the following: • Ten (10) groundwater monitoring wells within the site using a truck-mounted drill rig. The wells will extend to depths of approximately 22 feet below existing grade. • At least 48 hours prior to drilling the borings, we will mark the site for an Underground Service Alert(USA) utilities check. • Drilling will include using 8 to 10-inch-diameter hollow stem augers. • Soil samples will be collected for field soil classification only. Well screen intervals will be between 10 and 20 feet below the ground surface (bgs). • The well screens will consist of 4-inch-diameter, Schedule 40 PVC pipe with 0.010- inch-wide machined slots and flushed-threaded connections. The bottom of the well shall be comprised of 2 feet of solid casing, which is sealed with a flush-threaded PVC cap. • Based on grain size distribution analyses of soil samples collected during our geotechnical explorations at local sites, #3 clean, kiln-dried, silica sand filter pack material will be placed in the annular space around the well screens up to 3 feet above the highest screen slot. • A surge block will then be used to consolidate the filter pack. A two-foot-thick layer of bentonite pellets with be placed over the filter pack and clean water will be added to hydrate the pellets for 30 minutes prior to sealing the remainder of the borehole with neat cement. • 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 will be installed later. Protective barriers or equivalent shall be installed around the monitoring well. At least 48 hours after completion of the well installations, each monitoring well will be developed through purging groundwater to maximize the hydraulic connection between the well and the surrounding aquifer material and remove fine sediment. A minimum of three well casing volumes will be purged from the well using a 12-volt pump while monitoring stabilization of groundwater parameters (temperature,pH and electrical conductivity). Purging will continue during well development until flowing water is visually clear(at least 1.5 hours per well). Since pervious investigations have indicated that groundwater is not contaminated at the site, the purge water will not be containerized.