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t WEISS ASSOCIATES 23 GROUND WATER MONITORING WELL INSTALLATION, DEVELOPMENT, AND SAMPLING A ground water monitoring well was installed in the vertical borings adjacent to each vault Each well was constructed to monitor the upper-most water-bearing zone, which was encountered at about 71 ft depth in each boring The well screens extend 10 to 15 ft above the static ground water level and 15 to 16 ft below the static water level to 85 to 89 ft depth in each well j WA constructed the wells of 4-inch ID,0 02-inch slotted, flush threaded Schedule 40 PVC well screen and blank casing Lonestar #3 Monterey sand filter material occupies the annular ' space from the approximate bottom of the borings to about two ft above the top of the well screens One to two ft of bentonite pellets was placed on top of the sand pack to prevent infiltration of grout into the sand pack and disturbance of the sand pack by tremied grout The borehole was backfilled to ground surface with cement grout containing 3-5% bentonite powder The well heads are secured with locking plugs and finished at-grade with protective vaults On January 29, 1991,P C Exploration and WA environmental technicians David Charles and Paul Cardoza developed the three wells with a surging bailer and air lift evacuation to remove drilling residues, reduce the sediment content of water entering the well, and improve the monitoring well performance Each well was developed with at least two episodes of surge block agitation followed by removal of sediments by air lift evacuation Each well was purged until five times the volume of water in the well plus the water in the sand pack had been removed,and the water was as free of fine-grained sediments as possible All equipment which may have contacted ground water during well development was steam-cleaned before use and after developing each well On January 31, 1991,WA environmental technician Paul Cardoza collected ground water samples from the wells Prior to sampling, at least three well-casing volumes of ground water were removed from each well using a steam-cleaned PVC bailer Water samples were collected ' with steam-cleaned Teflon bailers and the samples transferred to appropriate sample containers The samples were refrigerated and a chain-of-custody was maintained until the samples were delivered to the laboratory for analysis Prior to well sampling,the bailers used to purge and sample the wells were washed with D lALL1331DWG1331R1MA1 WP Page 9