Raw Material Stockpiles

Bulk materials are often stockpiled outdoors at industrial sites, mining locations, or transportation facilities, for example, coal stockpiled in coal terminals or power plants. In such cases, several impacts occur from discharges of untreated leachate generated by precipitation and/or contaminated stormwater runoff into surface or subsurface water bodies. Contaminants found in these discharges depend on the nature, purity, and time of exposure of the stockpiled bulky raw materials. There are two pathways, producing two types of contaminated wastewaters. First, when precipitation runoff occurs, it causes particulates to wash off and be carried away from the stockpile surface. Secondly, rainwater or snowmelt slowly percolates through the stockpile, dissolving some of the chemicals in addition to concentrating pile-bound particulates and

Pathways For Contaminated Wastes
Figure 9 Typical pathways for stormwater contamination. (Courtesy of O'Brien & Gere Engineers, Inc.).

appearing as leachate. There is a complex relationship between runoff and leachate; that is, in the outer crust of the stockpile, it is possible that the two terms become synonymous as runoff percolates below the surface and re-emerges to join the main surface streams. The quality of contaminated runoff from a stockpiling area or a bulk material transport terminal, in general, would not meet the federal or state criteria for discharges into a surface water body without treatment. The first approach to the problem should be prevention, collection, reduction of runoff and leachate volume, and the second, treatment of the resulting contaminated stormwater prior to leaving the industrial facility. Sheets of plastic and other material or permanent cover structures should be used for reduction of the volume and degree of contaminant concentration in the stormwater drainage or leachate. Lining of the stockpile areas and installation of collection and containment piping, ditches, berms, and other structures could alleviate problems and aid in the subsequent treatment of the stormwater, which will depend on the nature of contamination.

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