1999-12-01_REVISION - M1977208 (2)

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rl~nir~~riirr~rr~~ , • ut2ANT -~. A SCIEN7ECN, fNG, Cnn~any November 5, 1999 Mr. Paul Banks Banks and Gesso, LLC 720 Kipling St., Suite 117 Lakewood, Colorado 80215 Subject: Additional HELP Modeling for CKD Disposal Site Dear Mr. Banks: RECEIVED DECO 1 1999 Division of Minerah & Geology Grant Environmental, Inc. (Gtant) is pleased to provide this summary of the results of the additional HELP modeling performed for the Southdown CKD disposal site. The HELP model input and output is included in the enclosed attachment. As requested by the Colorado Division of Minerals and Geology in their letter of October 18, 1999, Grant performed an additional HELP model run to simulate an open, partially-filled CKD disposal site without an interim compacted shale cap. The open C-Pit disposal site was simulated as apartially-filled, 7-acre disposal area with approximately 20 feet of disposed CKD. This is the approximate amount of CKD expected to be accumulated in a 3 to 5 year period. The CKD disposal site was simulated as an open landfill site, therefore precipitation run-off was not allowed to occur. Under this conservative model scenario, all precipitation that falls on the disposed CKD is either lost through natural evaporation or percolates through the disposed CKD. The default HELP model soil type used to simulate the disposed CKD (material texture 10) was the same as that used in previously submitted HELP model runs. Default evapotranspiration and precipitation data for Denver, Colorado 4vere also used in [he simulation. The results of this additional HELP model run indicate that the predicted flux of Ieachate through the disposed CKD in an open disposal site without an interim shale cap is about 0.34 inches per year. For the 7-acre disposal site, the predicted Ieachate flux is equivalent to about 8,581 cubic feet of Ieachate per year. The predicted leachate flux for the open, uncapped CKD disposal site is essentially the same as the leachate Flux predicted for an open CKD disposal site with an interim shale cap. A summary of the annual Ieachate fluxes generated under the various C-Pit disposal site configurations previously modeled and the results of [his analysis is provided in Table I . Table 1 Summary of the Predicted Leachate Fluxes for Various C-Pit Disposal Site Configurations For an Equivalent 7-Acre Disposal Site Area ^~ c~ ~~° - ~a ~~~ C-Pit Configuration ual Leachate Flux (inches) (cubic feet) Open, No Cap ,0.34 8,581 Open, Interim Cap 0.30 7,592 Closed, Final Cap - 0.74 18,803 Closed, InterimlFinal Ca 0.04 1,131 3.5 5 ,v ~~ - ., ?`i3x rt ', ; r~~