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6 Support the well cover by installing a concrete pad according to project requirements Pads are <br /> commonly square-shaped with a thickness of 4 inches (102 mm) and sides measuring 24 inches (610 <br /> mm)or greater Finish the pad so that the edges slope away from the center to prevent ponding of surface <br /> water on the well cover <br /> 7 Fill the inside of the well cover with sand up to approximately 2 to 3 inches(51 to 76 mm)from the top <br /> ' of the PVC pipe with locking cap <br /> 6.0 WELL DEVELOPMENT <br /> Polyethylene Tubing <br /> "The development serves to remove the finer 318 in o0 <br /> (TB25L) <br /> grained material from the well screen and fil- t <br /> ter pack that may otherwise interfere with <br /> water quality analyses, restore groundwater <br /> properties disturbed during the installation 1 Oscillate tubing up and <br /> (probing)process,and to improve the hydrau- down to bring sample to the <br /> he characteristics of the filter pack and hydrau- surface or <br /> 2 Insert Check Valve <br /> lic communication between the well and the (without check ball)to <br /> hydrologic unit adjacent to the well screen," sampling interval Drop <br /> (ASTM D 5092) check ball in tubing from <br /> surface Check valve is <br /> sealed Retrieve and collect <br /> The two most common methods of well de- sample from poly tubing <br /> ' velopment are purging (bailing or pumping) <br /> and mechanical surging <br /> Check Ball <br /> (GW421) <br /> 61 Purging involves removing at least Water Level <br /> three well volumes of water with either <br /> a Tubing Bottom Check Valve (Fig <br /> ' 6 1), Stainless Steel Mint-Bailer As- <br /> sembly or Peristaltic Pump Include the <br /> entire 3 6-inch(9 l mm)diameter of dis- Tubing <br /> turbed soil at the screen interval when Bottom <br /> Check <br /> ' calculating the well volume valve <br /> (GW42) <br /> 62 Mechanical Surging uses a surge <br /> block which is attached to extension <br /> rods and lowered inside the riser to the FIGURE 6 1 <br /> screen interval The extension rods and Sampling with Polyethylene Tubing and a <br /> surge block are moved up and down, Tubing Bottom Check Valve <br /> forcing water into and out of the screen <br /> Water and loosened sediments are then <br /> removed using one of three methods listed in 6 1 <br /> NOTE Mechanical surging may damage the well screen and/or reduce groundwater flow across the filter pack <br /> if performed incorrectly or under improper conditions Refer to ASTM D 5521, "Standard Guide for <br /> Development of Groundwater Monitoring Wells in Granular Aquifers" for a detailed discussion of me- <br /> chanical surging <br /> Development should continue until consecutive samples yield representative water "Representative water is <br /> • assumed to have been obtained when pH,temperature,and specific conductivity readings stabilize and the water <br /> is visually clear of suspended solids," (ASTM D 5092) <br /> ' Standard Operating Procedure Page 22 1 0-m x 2 5-in OD Prepack Screen Monitoring Well <br />