ARCHIVED REPORTS_XR0004193 - Laserfiche WebLink

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1 1 Drilling Procedures We contacted Underground Service Alert at least 48 hours before drilling to delineate Public utility lines at the site Before drilling, we hand augered each borehole to 3 to 5 feet below grade A licensed well driller drilled the borings using a truck-mounted drill rig equipped with 8- inch-diameter or 10-inch-diameter hollow-stem augers The drilling was performed under the guidance of a field geologist The earth materials were logged using visual and manual methods and classified according to the Unified Soil Classification System A photolonization detector (PID) was used to evaluate soil samples for gasoline hydrocarbons Field instruments such as the PID are useful for indicating relative levels of gasoline hydrocarbon vapors but do not detect the concentration of gasoline hydrocarbons present with the same precision as laboratory analyses Any subjective evidence of gasoline hydrocarbons such as soil discoloration or obvious odor was noted Collecting Soil Samples During drilling, soil samples were collected at 5-foot or other appropriate intervals using a California-modified, split-spoon sampler equipped with clean brass sleeves Samples were collected by drilling the boring to a point gust above the sampling depth and then driving the sampler into the soil through the hollow center of the auger The sampler was driven 18 inches with a standard 144-pound hammer dropped 30 inches The number of blows required to drive the sampler each successive 6-inch interval was counted and recorded on the field boring log to give an indication of soil consistency Soil samples were identified and evaluated for relative levels of gasoline hydrocarbons using a PID when appropriate Borings not converted to wells were backfilled with a slurry of cement, bentonite, and water Construction of Vapor-Extraction Wells Vapor-extraction wells were constructed of thread-jointed, 4-inch-diameter schedule polyvinyl (PVC) chloride casing No chemical cements, glues, or solvents were used in well construction The screened portion of the wells consisted of factory-perforated casing with 0 020-inch-wide slots No 3 sand was placed in the annular space opposite the screen to approximately 1 foot above the top of the slotted casing A 2-foot bentonite plug was placed above the sand pack, and a cement-bentonite slurry was used to fill the remaining annulus to the surface A traffic-rated cast-aluminum utility box with a PVC apron was placed over each wellhead and set in concrete flush with the surrounding concrete pad This box has a watertight seal to protect against surface water infiltration and is opened with a special wrench The design of the box discourages vandalism and reduces the possibility of accidental disturbance of the well soocia-$