Laserfiche WebLink
amec— <br /> microbe). <br /> According to Li and Logan (1999), transport distances with this range of <br /> sticking coefficients would be limited to less than 3 feet from the injection well at pore <br /> velocities of approximately 30 feet per day. <br /> • Groundwater velocity, which controls the number of collisions per unit distance (less <br /> collisions at higher velocities), is another key factor. Efforts to maximize groundwater <br /> velocity during injection such as increasing the injection rate will result in greater <br /> transport distances (Li and Logan, 1999). <br /> Equation 1 could be used to calculate the mobility of specific injected microbes upon injection <br /> if all relevant parameters are known a priori, however, this information is usually not available. <br /> Site-specific data on microbial transport would have to be collected before the well spacing is <br /> finalized. For the purposes of this feasibility evaluation, AMEC is assuming that the target in <br /> situ concentration of 104 cells/mL could be achieved within 3 feet of each injection location. <br /> 2.4.4 Geochemistry of ambient groundwater conditions <br /> The growth and long-term viability of the injected microbial population is a key consideration <br /> for the effectiveness of bioaugmentation. For dehalorespiring microbes (those needed for TCE <br /> reduction), groundwater needs to be oxygen-depleted with an excess of organic carbon. <br /> These conditions are generally present in the WWTP, based on the assessment of Intrinsic <br /> Remediation discussed in Technical Attachment#3 to FS Addendum #2. Therefore, for the <br /> purposes of this evaluation, the groundwater geochemical conditions near the WWTP are <br /> assumed to be appropriate for bioaugmentation based on existing data. Additional <br /> geochemical assessments (collection groundwater samples for analysis of nutrients, organic <br /> carbon and electron acceptors) and microbiological studies (in situ microbial community <br /> assessments and microcosm studies) would be conducted if a full-scale bioaugmentation <br /> program were to be implemented. <br /> 3.0 TECHNOLOGY EVALUATION <br /> 3.1 TREATMENT AREA <br /> In the WWTP area, the highest VOC concentrations have been reported for groundwater <br /> samples from monitoring wells in the Intermediate Aquifer M-1 7C1, M-20C1, M-30C1 and M- <br /> 31 Cl; Figure B.2-1). This area of elevated VOC concentrations in groundwater (greater than <br /> 100 µg/L) of the Intermediate Aquifer is estimated to be approximately 120 acres in size, <br /> based on the locations of these monitoring wells, not including the area directly beneath the <br /> WWTP facility, which is assumed to be underlain by clean groundwater (Figure B.2-1). The <br /> sands and gravels of the C1-zone of the Intermediate Aquifer would be targeted for <br /> bioaugmentation, not the silts and clays that also comprise a substantial portion of the <br /> Intermediate Aquifer. The C1-zone appears to be approximately 15 feet in vertical thickness at <br /> monitoring well M-30C1, therefore, this is the minimum saturated thickness that is assumed to <br /> AMEC Geomatrix, Inc. <br /> \\oad-fs1\doc_safe\9000s\9837.006\4000 REGULATORYTFS Assessment_Apx B_01 2711\Attachment B.2\Attach B-2.doc 132-7 <br />