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<br /> <br />A <br />NATIVE GRASSES AND SHRUBS <br />PRESSURE RELEASE SYSTEM <br />4" 0 OBSERVATION WELL RECLAIMED <br />TOPSOIL LAYER LEACH PAD P <br />UPPER SAND LAYER 3 <br />1 ~ <:..:: <br />. - .SUBSTRATE LAYER..:.. _ _ - PADMCOLLECCTION <br />~~ ~ ...;:.~~~ `~ .;. - _ SYSTEM <br />~-~ ~ EXISTING HDPE <br />BIOPASS SYSTEM LOWER SAND LAYER LINER SYSTEM <br />CELL DETAIL <br />SEE FlGURE 3 <br />SGLE IH FEE7 <br />0 10 20 40 <br />FIGURE 2 <br />BIOPASS SYSTEM CROSS SECTION <br />3.2 Biological and Cherti~ Processes <br />The most important feature of the Biopass <br />System is the organic layer into which the pad <br />drainage is directed, if it occurs. This layer <br />contains the necessary' nutrients and organic <br />substrates to support the growth of a diverse <br />population of microorganisms, principally <br />anaerobic and facultative bacteria. Since the <br />layer is placed many feet below the vegetated <br />surface, anoxic or anaerobic conditions are <br />established along with a chemically reducing <br />environment, as the organic matter is degraded <br />and the residual oxygen is depleted. The <br />anaerobic and chemically reducing <br />environments promote the growth of the <br />bacterial population capable of uptake, <br />treatmen[, sorption, and/or precipitation of <br />cyanide, nitrate, sulfate, and metals, the <br />primary constituents of concern. <br />The initial chemical process that occurs as the <br />drainage enters the Biopass System involves <br />physical sorption of a portion of the metals and <br />complexed metal cyanides within the organic <br />layer, for example azsenic, copper cyanide, and <br />mercury. The sorption of metals on both <br />inactivated and living biomass, even from <br />solutions containing elevated to[a] dissolved <br />solids levels, is well documented and forms the <br />basis of several specialized treatment systems, <br />such as AIgaSO1tB and BIO-FIX, a treatment <br />process being evaluated by the U.S. Bureau of <br />Mines and Department of Interior (Darnall and <br />Gabel, 1989; Ferguson and Jeffers, 1991). <br />The sulfate entering the organic layer, which <br />contains the necessary organic substrate, <br />nutrients, and bacterial seeds, is slowly <br />converted to sulfide by one of several strictly <br />anaerobic and chemoheterotrophic bacteria <br />which utilize sulfate as a terminal electron <br />acceptor and organic matter as their carbon <br />source. The genus and species of bacteria mos[ <br />commonly associated with sulfate reduction are <br />named Desulfovibno and D. desu~ricans. The <br />basic sulfate reduction reaction is as follows <br />-7- <br />