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i • • 6 Support the well cover by installing a concrete pad according to project requirements Pads are commonly square-shaped with a thickness of 4 inches (l 02 mm) and sides measuring 24 inches (610 mm)or greater Finish the pad so that the edges slope away from the center to prevent ponding of surface water on the well cover 7 Fill the inside of the well cover with sand up to approximately 2 to 3 inches(51 to 76 mm)from the top of the PVC pipe with locking cap 6.0 WELL DEVELOPMENT Polyethylene Tubing ment serves to remove the finer 3/8-in OD "The development (TB25L) grained material from the well screen and fil- ter pack that may otherwise interfere with water quality analyses, restore groundwater properties disturbed during the installation t Oscillate tubing up and ' (probing)process,and to improve the hydrau- down to bring sample to the lic characteristics of the filter pack and hydmu- surface or 2 Insert Check Valve he communication between the well and the (without check ball)to hydrologic unit adjacent to the well screen," sampling interval Drop ' (ASTM D 5092) check ball in tubing from surface Check valve is sealed Retrieve and tolled The two most common methods of well de- sample from poly tubing velopment are purging (bailing or pumping) and mechanical surging Check Ball (GW42t) 61 Purging involves removing at least Water Level three well volumes of water with either a Tubing Bottom Check Valve (Fig ° 6 1), Stainless Steel Mini-Bailer As- sembly or Penstaltic Pump Include the entire 3 6-inch(91 mm)diameter of dis Tubing turbed soil at the screen interval when Bottom ' calculating the well volume check oal e (GW42) 62 Mechanical Surging uses a surge ' block which is attached to extension rods and lowered inside the riser to the FIGURE 61 screen interval The extension rods and Sampling with Polyethylene Tubing and a surge block are moved up and down, Tubing Bottom Check Valve forcing water into and out of the screen Water and Ioosened sediments are then removed using one of three methods listed in 6 1 NOTE: Mechanical surging may damage the well screen and/or reduce groundwater flow across the filter pack if performed incorrectly or under improper conditions Refer to ASTM D 5521, "Standard Guide for ' Development of Groundwater Monitoring Wells in Granular Aquifers" for a detailed discussion of me- chanical surging Development should continue until consecutive samples yield representative water "Representative water is assumed to have been obtained when pH,temperature,and specific conductivity readings stabilize and the water is visually clear of suspended solids,"(ASTM D 5092) Standard Operating Procedure Page 22 1 0-in x 2 5-in OD Prepack Screen Monitoring Wel!