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L ,./ -- immediately placed in a cooler, packed with ice, and transported under chain of '�- custody to Geotest, a State of California certified hazardous waste testing laboratory located in Long Beach, California. 4.3 SOIL SCREENING Soil samples collected during the field investigation were screened in the field for organic vapor content using a photoionization detector; specifically, a Thermo Environmental Instruments Model 580B Organic Vapor Monitor (OVM) which has _ a manufacturer's reported detection limit of 0.5 parts per million (ppm). The OVM was calibrated prior to conducting field activities using a 250 ppm isobutylene standard. Plastic bags were partially filled with soil from the samplers, sealed, and allowed to warm and volatilize into the headspace. The organic vapor concentration of each soil sample was determined by inserting the probe of the OVM into the headspace of the sample and recording the highest sustained reading. The results of the field screening are presented in the boring logs contained in Appendix B. 4.4 MONITORING WELL INSTALLATION After borings MWA, MW-2, and MW-3 were drilled, they were completed as monitoring wells. The monitoring wells were constructed with threaded, 2-inch diameter Schedule 40 PVC casing, and slotted Schedule 40 PVC screen (slot widths of 0.010 inches). Fifteen feet of screen, with a screw-on PVC end cap was placed in each well. Five feet of blank casing was extended from the top of the screen to the ground surface, and a water-tight locking cap was installed on the top of the well casing. All lengths of casing were steam cleaned prior to use. Sand pack consisting of RMC Lonestar No. 2/16 sand was then placed in the annular space between the well casing and the borehole wall. The sand pack extended from the bottom of the borehole to one foot above the top of the screen. At this point the monitoring wells were developed. A stainless steel bailer was used to surge at specific depth intervals from the bottom to the top of the water column in order to compact and clean the filter pack. This bailer was then used to remove groundwater, sand and sediment, and establish representative groundwater movement through the well. Approximately fifteen gallons (seven well casing volumes) of groundwater were removed from each well and placed in a 55-gallon drum. The drums were labeled and stored on-site pending laboratory analytical results of the groundwater samples. PSI will arrange for the disposal of these drums upon closure of this site. Upon completion of well development, a one foot thick layer of Baroid 3/8-inch bentonite pellets was placed immediately above the sand pack and hydrated with potable water. Two feet of Ready-mix cement / bentonite grout was then 7