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ACZ Mr. Randall P. Price March 24, 1992 Page Two III IIIIIIIIIIIIIIII trench). The proposed replacement monitoring well would consist of a double casing design with an outer four inch schedule 40 PVC casing enveloping an inner two inch PVC casing. A clean, graded sand would be placed in the annular space between the two casings and will serve as a filtering mechanism which will restrict sediment from entering the two inch casing. The outer four inch casing will serve the same purpose as a borehole wall in competent material, had the well been installed in a boring. The trench would be backfilled with the excavated soil. This design allows the screened interval to be packed with a highly permeable material (sand) which will remain in place during backfilling of the trench. In order to reduce the potential influence from surface waters, a number of steps would betaken; 1) the outer casing would not be slotted from ground surface to a depth of three feet, 2) the trench backfill would be compacted to the extent practical, and 3) the trench azea would be "domed-up" to deflect surface runoff. The doming of soil would extend at least two feet beyond the perimeter of the trench and at most one foot above grade level at the well casing. The soil in the area is dominated by a clay matrix and is expected to possess a relatively low permeability rate once compacted. The placement of a seal, bentonite for example, across the entire trench area is not viewed as practical or necessary if the above steps are taken. The timing for replacement of Well AO-2 is dependent upon weather and associated ground conditions. The ground must provide a solid foundation to allow access of any equipment. This solid foundation, in the specific location of Well AO-2, exists only when the ground is frozen to a considerable depth or the water table has dropped and the ground dried enough to provide a firm footing. Kerr personnel have indicated that the frost zone has already melted and, therefore, it is unlikely that the well can be installed before late fall (if ground dries out) or next winter. Kerr will install the proposed Well AO-2 as soon as possible to facilitate ongoing water sampling as outlined in the water monitoring plan. ACZ believes that this method of monitoring well installation will provide an adequate means for Kerr to generate the required groundwater data with a minimum impact or disturbance to the site. No revision to permit sections or pages is required as the reestablishment of Well AO-2 is required for maintenance and will not add to or otherwise alter existing permit conditions. Sincerely, ~/ S- F. Jay James Project Engineer FJ1:cmc enclosure cc: George Patterson ~~~~.~ 0/Lf93 On