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6.4. ] Drill Borings for the Installation of Vapor Extraction Wells On August 14, 2001, Gregg Drilling of Martinez, California drilled borings VE-1 and VE-2 at the site using a Mobile B-61 drill rig equipped with 8 - inch diameter hollow-stem augers (Figure 4). Vapor extraction wells VE-1 and VE-2 were subsequently constructed in these borings. The drilling was directed by ASE associate geologist Erik Paddleford. Undisturbed soil samples were collected continuously as drilling progressed for lithologic and hydrogeologic description and for possible chemical analysis. The samples were collected by driving a split-barrel sampler lined with 6-inch diameter brass tubes using repeated blows from a 140-1b hammer dropped 30-inches. Selective soil samples were immediately trimmed, sealed with Teflon tape and plastic end caps. labeled, and stored on ice for transport to Kiff under chain of custody. Soil from the remaining tubes was described by the site geologist using the USCS and was screened for volatile compounds using an OVM. The soil was screened by emptying soil from one of the sample tubes into a plastic bag. The bag was then sealed and placed in the sun f o r approximately 10 minutes. After the volatile compounds were allowed to volatilize, the OVM measured the vapor in the bag through a small hole r punched in the bag. OVM readings are used as a screening tool only, since the procedures are not as rigorous as those used in the laboratory. The OVM readings are listed on the boring logs presented in Appendix D. Drilling equipment was cleaned with a TSP solution between sampling intervals to prevent potential cross-contamination. 6.4.2 Vapor Extraction Well Construction The vapor extraction wells were constructed within the hollow-stem augers using 2-inch diameter flush-threaded, schedule 40, 0.020-inch slotted PVC well screen and blank casing. The wells were screened between 4 and 6-feet bus to allow for vapor extraction throughout the entire vadose zone. In each well, the well casing was lowered through the augers and 42112 filter pack sand was placed in the annular space between the well casing and the borehole from the bottom of the boring to 0.5-feet above the screened interval. A 0.5400t thick layer of bentonite pellets was placed on top of the sand pack. The bentonite was hydrated with water prior to placing the cement sanitary seal. Cement was used to fill the annular space between the bentonite layer and the surface to prevent surface 574 West Grant Line Road CAP — January 2002