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t Of-Site Groundwater Investigation Work Plan Page 7 Rainwater Car Wash, Manteca, California 95336 May 30, 2012 Soil samples from the remaining soil borings will be collected at 5-foot intervals from ground surface to terminal depth and logged for lithologic analysis only.Drilling activities will be conducted to minimize cross- contamination of groundwater between water zones. Wooden plug and rubber gaskets will be fitted at the auger joints to minimize groundwater intrusion into the augers during drilling activities. ' Soil samples from hollow-stem drilling activities will be collected by driving a California-modified split-spoon sampler 18 inches into the undisturbed soil. The AA&A field geologist,under the supervision of the PG,will describe the soil in accordance with the Unified Soil Classification System.A portion of the soil sample collected will be screened for volatile organic compounds(VOCs)by headspace analysis,using a to photo-ionization ' detector(PID)calibrated to 100 parts per million(ppm)isobutylene.For each sampling interval,approximately 200 grams of soil will be placed in a plastic bag that will be sealed to allow organic vapors to volatize for several minutes prior to each measurement.After the soil and the atmosphere in the sealed plastic bag are allowed to equilibrate,the probe tip of the PID will be inserted into the plastic bag,and VOCs(in ppm)will be recorded. The boring number, sample depth, lithologic description, discolorations,and PID readings will be documented on the boring log. ' 5.3.3 Well Installation The dual-nested monitoring wells will be installed in accordance with the DWR Water Well Standards Bulletin ' 74-90. The wells will consist of a 0.02-inch,perforated PVC(Schedule 40)screen and Blank 2-inch-diameter PVC casing.The wells will be surged to allow the sand filter pack to settle. Additional filter pack material may be added as needed. A locking water-tight cap will be installed on the casing. The surface will be completed with a ' traffic-rated well box. The well construction diagram is illustrated on Figure 4. Well construction details for the groundwater wells are summarized in Table 1. Depths of the well casing may be adjusted in the field according to lithology. ' 5.3.4 Well Survey After the well installation,the well elevations will be surveyed by a California-licensed surveyor. The top of the ' well casings,cover of the wells,and the ground surface will be measured in feet relative to the North American Vertical Datum of 1988. The survey report will also include longitude and latitude coordinates for each well. The well elevation survey report will be included in the report. 5.3.5 Well Development and Groundwater Sampling ' In accordance with the SJCEHD's Well Standards a minimum of 12 hours will be allotted between the placement of the annular seal in each dual-nested groundwater monitoring well and well developments activities. The wells will be developed to remove suspended solids and/or other drilling fluids and materials using a rig-mounted surge block and bailer and a hand-bailer. Development will be accomplished by mechanically moving the rig bailer and surge block gently up and down the well casing to remove drilling fluids,suspended solids, settled solids, and other fine-grained materials that could inhibit well yield from the well screen. ' Approximately five well volumes of water will be purged from each well using a submersible water pump. The purged water will be monitored for turbidity,pH,specific conductance and temperature using instruments calibrated in advance in accordance with the manufacturer's instructions, and the data will be recorded in a field ' logbook. The purging will continue until approximately five well volumes of water have been removed or the water quality parameters have stabilized. Groundwater samples will be collected from each well following well development. Groundwater samples will be ' collected by a dedicated, disposable high-density polyethylene bailer.A bottom-emptying device will be attached, Ami Arora SAssocinCes.inc.