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<br />well paint, 30 or 36 inches long, fastened to joints of 2 <br />• inch schedule 40 black steel pipe was placed inside the <br />hollow auger and driven,. to final depth by a 140 pound drop <br />hammer, normally employs d in soil testing. The well points <br />were fitted with #80 mes s,4reens. The casing was driven by <br />employing standard soil`tration test procedure: 30 <br />inches fall of a 140 pound hammer and recording the number <br />of blows to advance the casing one foot (BPF). Blow counts <br />ranged from 3 to 23 BPF for tailings to 30 to 70 BPF for the <br />underlying gravel. The final determination of the tailings - <br />subbase contact was by the distinctly different penetration <br />characteristics of the two materials. The objective was to <br />drive the casing until the top of each well point was 3 feet <br />below the base of the tailings; however, this was not <br />possible in wells M2C, M3A and M3B due to the presence of <br />large boulders, resulting in as many as 94 blows without <br />obtaining appreciable advance of the casing. This resulted <br />in the partial buckling of the casing in wells M2C and M38. <br />Blow counts were not recorded at wells M7A and MIB. Instead <br />the base of the tailings was projected from logs of the <br />drill holes completed in 1980. <br />After driving the casing to depth, the annulus between the <br />casing and the well bore was sealed by pumping cement slurry <br />into the hole while withdrawing the hollow stem augers. The <br />cement slurry conformed to API Class B, 6% Bentonite Cement, <br />• consisting of a mir.ture one 90 lb. sack of Type II (sulfate <br />resistant) cement, 6 pounds of bentonite and 9 gallons of <br />water per sack of cement. The cement seal was placed <br />throughout the exposed length of casing (i.e. to surface) in <br />two stages. Prior to placing the seal, a 1 foot column of <br />high viscosity bentonite slurry was pumped in the hole to <br />prevent the seepage of the thinner cement slurry into the <br />screened zone. <br />Three observation wells (P2, P3 & P4) were drilled on the <br />north and west crest of the new pond dike to measure water <br />levels in the dike. The wells are cased with 2" diameter pvc <br />pipe perforated and wrapped with mirifi geoter.tile along the <br />bottom 10 feet. The bottoms of these wells are 2 to 3 feet <br />above the base of the tailings dam. (Refer to Plate II, <br />Sheet 1). <br />In addition, four monitor wells (MW1, MW2, MW3 & MW4) were <br />constructed, near the north and west toes of the tailings <br />dam. The construction of these wells is identical to that of <br />the previously described observation wells. The use of <br />hollow stem augers greatly facilitated the installation of <br />casing in the unconsolidated alluvium, which frequently <br />caved. These monitor wells were installed to provide early <br />• -6- <br /> <br />