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} The drilling will be directed by a qualified ASE geologist. Undisturbed soil <br /> samples will be collected continuously for subsurface ill bedrog r bed <br /> tion and possible chemical analysts. The samples <br />� <br /> description <br /> by the ASE geologist according to the USCS. The samples will be collected <br /> f in brass tubes using a split-barrel drive sampler advanced ahead of t h e <br /> auger tip by successive blows from a 140-1b. hammer dropped 30-inches. <br /> Each sample will be itnrnediately removed from the sampler, trimmed, <br /> sealed with Teflon tape and plastic caps, secured with duct tape, labeled <br /> Nvith the site location, san-iple designation, date and ti���e the sample ,vas <br /> collected, and the initials of the person collecting the sample. The <br /> samples will be placed into an ice chest containing wet ice for delivery <br /> under chain of custody to a CAL-EPA certified analytical laboratory. <br /> - Soil from the remaining tubes not sealed for analysis will be removed for <br /> h dro eologic description and will be screened for volatile compounds <br /> Y g b P <br /> with an OVM. The soil will be. screened by emptying soil from one of the <br /> tubes into a plastic bag. . The bag will be sealed and placed in the sun for <br /> approximately 10 minutes. After the hydrocarbons have been allowed to <br /> volatilize, the OVM will measure the vapor through a small hole punched <br /> in the bag. These OVM readings will be used as a screening tool only since <br /> v these procedures are not as rigorous as those used in an analytical <br /> laboratory. ' <br /> a <br /> The wells will be constructed within the hollow-stem augers using 2-inch 1 <br /> diameter, flush-threaded,; schedule 40, 0.020-inch slotted PVC well screen <br /> and blank casing. The wells will be screened in the vadose zone only. <br /> Based on the boring logs and depth to groundwater (6.5-feet bgs) during <br /> the previous drilling at this site, ASE estimates that these wells will be <br /> screened between approximately 4 and 6-feet bgs. The well casing will be <br /> lowered through. the augers and #2/12 filter pack sand will be placed in <br /> the annular space between the well casing and the borehole from the <br /> bottom of the boring 'to approximately 0.5-feet above the screened <br /> interval. Approximately X0.5-feet of bentonite pellets will be placed on t o p <br /> of the sand pack prior to placing '° the cement sanitary seal. Since the <br /> bentonite seal will be placed in the unsaturated zone, the bentonite will be <br /> hydrated with potable water prior to placing the cement sanitary seal. <br /> Cement mixed with 3 to 5 percent bentonite powder by volume will be <br /> used to fill the annular space between the bentonite layer and the surface <br /> to prevent surface water. from infiltrating into the well. The seal will b e . <br /> placed by simply pouring the seal into the boring. The well heads will be <br /> protected with a locking well plug beneath an at-grade, traffic-rated well <br /> box (See Figure 6 - Typical Vapor Extraction Well). <br /> 574 West Grand.Line Road, Tracy, CA Workplan — April 2001 <br /> -9- <br /> 1 <br />