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w � lea_. , '"'� rr�r � +yae��A - * Si' �: �,''•_; � .a �� xe -r� q' ..� �,e ..� �.�. M y � 9+� �"� prsiyt 4 Monitoring Well Construction A groundwater monitoring well was installed in each bcrehole by inserting 4-inch- inside-diameter, Schedule 40, polyvinyl chloride casing with 20 feet of 0.020-inch slotted well screen (0.020-inch slots) attached to the bottom. The perforated casing extends approximately 16 feet Ln-low the water table and 4 feet above the water table in order to accommodate water table fluctuations, and to detect free-floating product. A bottom plug was installed at the bottom of the perforated interval. To gravel pack the well, coarse aquarium sand was pourer: directly through the augers as the augers were gradually removed from the borehole. A bentonite seal was placed immediately above the gravel pack and the augers were then removed from the borehole. The remaining annular space of each well was filled with corcrete. Each well was completed at grade with a watertight utility box. The construction details for each well ate included in Appendix B. On January 26, 1988, each well was developed by pumping and surging the well with a centrifugal pump. Throughout development, pH, specific conductance, and temperature of the discharged water were measured, and development was continued until these parameters had stabilized and until the water was- relatively sediment-free. Approximately -' 55 gallons of water were removed from each well prior to sample collection. Each well was then .sampled with a Teflon bailer equipped with a bottom-emptying valve. The sample was then drained directly from.the bottom valve into four 40-milliliter glass bottles with Teflon-lined septa and intp one 112-liter plastic bottle containing nitric acid preservative. The samples were stored- on ice from the time of collection through delivery to the Eureka laboratory. The samples were analyzed for BETX by EPA Method 602, total petroleum fuel hydrocarbons by EPA Mcthod 8015, mortified, and total lead by EPA Method 6010. All groundwater produced during well development and sampling was contained and temporarily stored on site in 55-gallon drums pending results of the analytical tests. The hollow-stem augers were steam-cleaned prior to use at each borehole. All soil and groundwater sampling equipment was washed with laboratory-grade detergent and tap water then rinsed with deionized water prior to each use. Groundwater Gradient On February 2, 1988, each new well was surveyed,for ground surface and top-of-casing (TOC) elevations. Groundwater levels were measuref..•at all existing monitoring wells for the site with an electronic water level indicator to determine the groundwater elevations r.tative to the TOC elevations. The static groundwater gradient and flow direction were determined based on these elevations. The groundwater flow direction for January th*%-l3gh mid-April 1988 was to the northeast, and the gradient was an average of 8.5 feet per mile, or 0.16 percent. Since late April 1988, the groundwater flow direction has been influenced by the recovery System which has been functioning continuously since early April. Ground-water �. contours for April 14, May 5, and July 8, 1988, are shown on Figures 3, 4, and 5, respectively.