Agenda - Council - 09/13/1982 - Special

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I I I I weather conditions or poor operating practices can affect the extent of con- tamination. The second type of contamination can occur either during operation or afte~ closure of the landfill. 'If water is allowed to accumulate in a fill, hydrostatic pressure can build, forcing leachate to burst or seep out at weak points in the soil cover. Often, the settling of refuse causes the landfill cover to crack, and runoff of contaminated water may result. Although there is a risk that a landfill will contaminate surface waters, it can be considerably reduced if good operating procedures are established and followed. The most important factor in pre- venting degradation of surface water is planning the design and operation of the facility. Establishing appropriate storm water runoff management practices will help ensure good surface water quality. Installing tile, constructing storm water runoff ponds, replanting vegetation on the site as soon as possible after installing final cover, and grading of the site are possible ways of reducing the impact of waste disposal facilities on surface waters. A routine inspection and maintenance program is advisable to monitor the fill after clo- sure and is required for a limited time by the PeA. Any facilities for leach- ate treatment must meet applicable water quality standards' or land treatment requirements. ~ Groundwater Contamination One of the most serious environmental impacts of sanitary landfills is ground- water contamination. This may affect both the groundwater just below the sur- face within glacial drift or groundwater in the bedrock aquifers. Groundwater pollution occurs when leachate leaves the landfill and enters the groundwater. Leachate characteristics will-~ary over time because some waste materials are more degradable or soluble than others. Leachate can affect groundwater qual- ity so that it is unsuitable for either human or livestock consumption. In some cases, leachate may make the water unsuitable even for industrial or commercial use. The surficial water table is the groundwater nearest the surface, and in some areas it may be used for a potable water supply for either human or animal consumption. The surficial or shallow groundwater is always hydraulically connected to the groundwater in a drift aquifer. Contamination of the surfi- cial groundwater occurs when leachate leaves the landfill and enters the water table. The extent of contamination depends on the types of waste materials in the fill, the amount of leachate escaping from the fill, the degree to which soil particles can filter and adsorb pollutants in the leachate, the amount and flow of groundwater, the age of the fill, and whether it has reached field capacity (become totally saturated with water/. The contamination is poten- tially a long-term problem that may occur after the landfill is no longer in operation. The significance of groundwater contamination in the surficial water table depends On whether or not this groundwater is used as a water supply and whether it is connected hydraulically with bedrock aquifers. There are several bedrock aquifers underlying the Metropolitan Area. Confining layers that restrict the movement of water lie between some of these aquifers. The Prairie du Chien-Jordan is the most significant bedrock aquifer because it is one of the most productive in the Metropolitan Area. Over 75 percent of the groundwater pumped within the Metropolitan Area is drawn from this aquifer. The potential for contamination of a bedrock aquifer depends on many of the factors already identified and is a long-term ~roblem.