1990-04-18_REVISION - M1977493 (4)

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BLACK & V EAT• Colorado Department of Health B&V Project 6913.007 Mr. Phil Hegeman 2 April 16, 1990 As depicted on Figure 2, the tailing deposition area encompasses over 350 acres, 172 of which have received a 12 to 18-inch layer of soil as part of the interim reclamation process. Sludge would only be applied to those areas which have first received the soil. Following sludge application, Climax will incorporate the sludge into the soil via scarification, plant their seed mixture, and establish a high-altitude vegetative cover to stabilize the soil. The vegetation would not be utilized as feed for domestic animals. In accordance with the Colorado's Domestic Sewage Sludge Regulations, a soil sample was obtained and the results of the laboratory analyses are presented in Attachment A. The County has also prepared sludge screening and application analyses and these are presented in Attachment B. As with many wastewater sludges in Colorado, the sludge is classified as Grade 2 due to its copper content. All other heavy metal concentrations fall within the Grade 1 criteria. Attachment C presents the details of Climax's standard seed mix for the vegetative cover that will be established on the soil. As detailed in Figure 3, the surface of the tailing area is about 160 feet above the underdrain that runs along the former valley floor. Based on Climax's monitoring wells, actual ground water levels are about 20 feet below the underdrain providing a total height of about 180 feet from the surface of the tailing area to the top of the ground water table. PROGRAM DESCRIPTION The essence of the County's program will be to haul and apply aerobically digested waste activated sludge which has been thickened to about seven percent solids. This sludge would then be land applied and mixed with the soil already at the site. Since the slopes on the application site are less then three percent, the State's regulations will allow the sludge to be spread on frozen or snow-covered ground. Consequently, the County and Climax intend to provide year-round access so that all sludge produced by the Snake River WWTP, about 180 dry tons per year, can be applied at the site. If at any time the local soil and weather conditions are unsuitable for application on the tailing area, the County will haul its sludge to the Front Range via Liquid Waste Management. Use of the tailing area would resume as soon as site conditions again became suitable. SLUDGE APPLICATION RATES On March 28, 1990, the County and Climax met with you to review the preliminary letter of intent. At that time, you indicated an initial sludge application rate of up to 25 dry tons per acre could be used to ammend the soil prior to planting. You further stated that after establishment of the vegetative cover, a maintenance application rate of up to six dry tons per acre per year would be acceptable. Based on our own experience, we agree with the initial reclamation rate of 25 dry tons per acre. We suggest, however, that a lower maintenance rate of 2.5 dry tons per acre per year be used to guard against the potential long-term migration of nitrates into the groundwater.