ARCHIVED REPORTS XR0003296 - Laserfiche WebLink

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WEISS ASSOCIATES monitor the first water-bearing zone encountered The soil boring will be advanced to approximately 20 ft below the water table to allow construction of a well with a 20-foot screened section, unless a confining layer of fine-grained sediment greater than two ft thick ' is encountered below the water table if a confining layer is encountered, the boring will be terminated, the hole will be back-filled to the top of the confining layer with bentonite pellets, ' and the well constructed in the water-bearing unit above the confining layer with a screened section shortened to the appropriate length ' The well will be constructed of 4-inch diameter, 0 02-inch slotted PVC well screen and solid PVC casing The bottom of the well screen will be placed no more than 20 ft below the lowest expected water level in the shallowest water-bearing zone The well screen will extend approximately two ft below the top of the water-bearing unit to a maximum of 10 ft into ' unsaturated soil Sand filter material will be placed in the annulus around the well screen, from the bottom of the boring to about one to two ft above the top of the well screen One to two ft of bentonite pellets will be 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 will then be backfilled to ground surface with cement grout containing three to five percent bentonite powder The well will be completed with a protective vault installed flush with ground surface A typical well construction diagram and boring log is shown in Figure 6 The groundwater monitoring wells will be developed to remove drilling residues,reduce ' sediment content of water entering the well, and improve the monitoring well performance Each well will be developed with at least two episodes of surge block agitation followed by ' removal of sediments by air lift evacuation This will settle the sand pack and draw fine- grained sediments through the sand pack and into the well Purging the well will also remove the sediments brought into suspension by drilling and development activities The well will be purged until five times the volume of water in the well plus the water in the sand pack has been removed, and the water is as free of fine-grained sediments as possible In calculating the purge volume, the assumed porosity of the sand pack is 30 percent Ground water will be sampled at least 24 hours after well development Prior to sampling, at least four well volumes of ground water will be removed from each well using a cleaned PVC bailer Water samples will be collected with cleaned Teflon bailers and the samples transferred to appropriate sample containers The samples will be refrigerated at 4° C and a chain of custody maintained until delivery to the laboratory for analysis ' D \ALL\331DWG\331P1SE0 WP Page 18