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ADDITIONAL ASSESSMENT WORKPLAN • JAMAR SERVICE,STOCKTON APRIL 2002 This field screening method consists of fillmg a Zip Lock plastic bag to about one-third of its capacity with soil and sealing the container After allowing sufficient time for the soil vapor to equilibrate with the containers headspace,the bag is opened enough to allow for the insertion of an organic vapor analyzer probe The field monitoring will be conducted using an Organic Vapor Analyzer(OVA)equipped with a photoionization detector(PID) The concentrations of organic vapors detected by the OVA will be recorded on the boring log Field screening will also include documenting visual indications for the presence of petroleum hydrocarbon contamination,such as staining, discoloration,and/or chemical sheens The groundwater monitoring wells will be constructed using 2-mch diameter Schedule 40 PVC casing and well screens Each of the soil samples collected will be descnbed according to the USCS The wells will be designed to provide 15-feet of screen below the saturated zone and 5- feet of screen in the unsaturated zone,to allow for seasonal fluctuations in water levels Based on the water level in the existing groundwater monitoring well located on-site,well depths are anticipated to be approximately 75-feet bgs The wells will be completed with 2-inch diameter, flush threaded, Schedule 40 PVC with 0 020- inch perforated and blank casing A threaded end cap will be placed at the bottom of the PVC casing,which will then be set m the open borehole Using the hollow stem augers as a tremmie pipe, #3 gram size RMC Lonestar sand will be poured in the annulus between the well casing and the auger to form the filter pack around the screened interval The sand will be extended 2-feet above the top of the screen Three-feet of 3/8-inch bentonite pellets will be placed above the filter pack as part of the annular seal These pellets will be hydrated with distilled water and allowed to sit for approximately 30 minutes The remaining annular space will be filled with a cement slurry mixture containing less than 5%bentonite To protect the integrity of the wells, the top of the wellhead assembly will be enclosed at the surface in a water tight,traffic-rated, flush-mounted well box All work will be performed in accordance with the County regulations, California Code of Regulations,Title 23, Section 2647 and 2648 and the California Department of Water Resources Bulletins 74-81 and 7490 A typical monitoring well construction detail is shown in Figure 5 Drill cuttings will be placed on plastic, covered and stored on-site until the soil is profiled for disposal Disposal of the cuttings will be completed by GHH