CORRESPONDENCE_1984-1989 - Laserfiche WebLink

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0 • A second problem which faces the installation of the lysimeters is the drifting of the augers in deep angled boreholes and, in this case, the possible puncturing of the clay liners. Presuming an accurate drilling location can be ascertained for Trenches 2 and 4, angle drilling to the south at a specified angle will result in the drifting of the auger to the right of the drilling rig and to the south at a greater angle than that originally specified due the resistance of the strata and the inherent play between the augers. This drifting may be compensated for by placing the hole ata greater distance from the original location, however, the amount of drifting is unknown and incalculable. A third problem which must be mentioned is simply the lack of room to the north of Waste Management Unit A to offset the boreholes and also position the drilling rig. The offset distance required for the borehole under trench 2, for example, is 10 feet, not counting extra distance needed for the drifting of the augers. The length of the rig to be positioned in a north-south orientation is an additional 35 feet. The amount of usable working space north of the WMU up to the property line is only 50 feet, not enough room to place the lysimeters from the north of the WMU and to continue to allow incoming traffic to pass. A possible alternative to angle drilling in order to place lysimeters under the sumps in Trenches 2,3 and 4 may be to drill a vertical hole as close to the risers along the north side of the WMU as possible. This would not be as risky to the integrity of the liner as angle drilling, but the lysimeters could be placed within 10 feet of the bottom of the sump at a horizontal offset of up to 140 feet. This alternative, however, may not prove anything valuable in terms of the level of contamination under the sump. Another alternative may be to place the lysimeter under Trench 1, as previously mentioned, and to make several shallow boreholes on the west side of Trench 4 to determine the western boundary of that trench. Once the western edge is known, a second lysimeter may be placed, angled to the east, and installed under the western bottom edge of the trench in the same manner as was under Trench 1. This would allow vadose zone monitoring for the most recent and the oldest trenches in Waste Management Unit A and, if the laboratory results show no leakage has or is occurring, no other lysimeters may be needed. I