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a) Measured depth is 2 to 3 feet (0,6 to 0,9 m) less than riser length- This indicates that unstable Extension Rod Handle conditions have resulted in formation collapse A (AT69) natural grout barrier was formed as material col- Extension Rod (AT67 or AT671) lapsed around the PVC riser when the probe rods were retracted This commonly occurs in sandy formations No further action is required Proceed with Section 5 5 and perform Step 2 (unstable for- mation) ' b) Measured depth is equal to or greater than riser length: This indicates that stable conditions ' are present The probe hole has remained open and void space exists between the riser (and possibly the screen)and formation material Clean sand must t be placed downhole to provide a suitable grout bar- ner Continue with Step 2 2 Begin slowly pouring 20140 grade sand down the ' annulus between the PVC riser and probe rod string Reduce spillage by using a funnel or flexible con- tamer as shown in Figure 5 10 Add approximately ' l 3 gal (5,0 L)for each 5-foot(1,52 m)screen sec- tion,plus 0 9 gal (3,4 L) for a 2-foot(0,6 m)layer of sand above the screen section 3 Measure the annulus depth after each 1,5 liters of sand The sand may not fall all the way past the screen due to the tight annulus and possible water Extension Rod intrusion This is acceptable, however, since the (AT67 or AT671) prepacked screens do not require the addition of screen push Adapter sand The important thing is that a sand barrier is (Gw1535) provided above the screens 4 Sand may also bridge within the annulus between the risers and probe rods and consequently fail to reach total depth(Fig 5 10) This most likely oc- FIGURE 5 9 curs when the sand contacts the water table during Using Extension Rods to ' deep well installations Wet probe rods also con- tap Out Wedged Screens tribute to sand bridging If the annulus is open, skip to Section 5 5, Step 1 if bridging is evident, t continue with Step 5 5 In case of a sand bridge above the screens(wet rods,high water table,etc ),insert clean extension rods into the well annulus to break up the sand (Fig 5 10) Simultaneously retracting the probe rods ' usually helps Check annulus depth again If sand is no longer bridged,proceed to Section 5 5 if bridging is still evident,continue with Step 6 ' 6 If the sand bridge cannot be broken up with extension rods,inject a small amount of clean water into the annulus using a Geoprobe GS500 or GS1000 Grout Machine and 318-in (9,5mm)OD polycthy- ' Standard Operating Procedure Page 16 1 0 in x 2 5 in OD Prepack Screen Monitoring Well