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ADDITIONAL ASSESSMENT WORKPLAN JAN AR SERVICE, STOCKTON DECEMBER 2001 i The sampler will be driven by a 140-pound hammer with a 30-inch drop according to ASTM Methods D 1586-84 Split Barrel Sampling in Soil and the resulting blow counts will be recorded in 6-inch intervals after every sampling event The middle of the three brass tubes in the sampler will be selected for submittal to the laboratory for analysis To preserve the sample,the liners at each end will be sealed using Teflon sheeting secured by tight fitting plastic caps The samples will be stored in a chilled cooler at 4 degrees Centigrade for transport to a California State certified laboratory for analysis To provide a preliminary indication of the presence of petroleum hydrocarbons, a portable organic vapor detector will be used to monitor for the presence of organic vapors in soil collected from the borings This field screening method consists of filling a Zip Lock plastic bag to about ane-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 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-inch diameter Schedule 40 PVC casing and well screens Each of the soil samples collected will be described 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 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 in the open borehole Using the hollow stem augers as a tremmie pipe, 43 grain 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 318-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 traffic-rated, flush-mounted well box All work will be performed in accordance with the County regulations,Califorma Code of Regulations,Title 23, Section 2647 and 2648 and.the California Department of Water Resources Bulletins 74-81 and 74- 90 A typical monitoring well construction detail is shown in Figure 5 • 5