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Attachment A <br />reduction of the sulfate to sulfide. Such treatment in constructed wetlands would require <br />the constant addition of organic constituents and iron to promote the reaction. In <br />addition, since this reaction can only occur in reducing conditions, the system would have <br />to be either in an enclosed bio-reactor, which would require constant maintenance, or an <br />up-flow type of constructed wetlands, requiring all flow to be routed through subsurface <br />piping. This type of system would be prone to clogging and would require the frequent <br />addition of organic material and on-going maintenance. <br />OOSI conducted field testing by percolating retort water through a series of vessels <br />containing different media mixtures (the subject of Technical Revision No. 3). A portion <br />of this work involved consultation by Mr. Jim Gusek, who is well known for his work in <br />the field of passive treatment of mine discharge waters. After evaluating the retort water <br />chemistry data, Mr. Gusek recommended a sulfate reducing bioreactor (SRB) field test <br />using a mixture of alfalfa, sawdust, woodchips, manure, and pea gravel. The bioreactor <br />was constructed in a 1,700 gallon polyethylene container. In addition, OOSI conducted <br />other field tests in 5 gallon containers using media including mixtures of zero-valent iron <br />(iron fillings), Ferrophos®(iron product), manure, and the SRB compost described. <br />Retort water was percolated through the test vessels at a rate to maximize residence time. <br />The experiments were run for 3 to 4 months. <br />The results of the experiments did not show a notable improvement in the removal of <br />sulfate. The removal of key hydrocarbons (BTEX) was not evaluated as it was assumed <br />that these volatile compounds would be removed through any moderately aerobic <br />treatment method. Phenols were also expected to show significant removal by way of <br />adsorption or degradation through reactions with organic media. Because of the failure <br />of these tests to remove conservative inorganic solutes, namely sulfate, the application of <br />a bioreactor or treatment wetland was not considered a viable treatment alternative. <br />Based on our review of currently available biological passive technologies, it does not <br />appear that any type oflow-maintenance or passive removal process would be suitable <br />for reducing sulfate concentrations in water seeping from the former oil shale retort area. <br />Since neither of these types of biological treatment systems has been proven for this type <br />of application, and both would require a high degree of monitoring and maintenance, it is <br />unlikely that either system would be effective compared to the existing evaporation <br />system. <br />Groundwater Barriers and Intercept Drains <br />Preventing groundwater from coming in contact with the former retort azea would <br />involve either intercepting the groundwater before it comes in contact with the retort area, <br />which would require a major on-going groundwater extraction or diversion program to <br />dewater the area; or by creating some sort of subsurface barrier to groundwater flow, <br />either by solidifying the entire retort area to reduce the permeability of the mass, or by <br />constructing a grout curtain around the perimeter of the retort area to isolate it from the <br />groundwater system. As discussed below, neither of these alternatives is considered to be <br />practical for long-term application in this azea. <br />7 <br />