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Mr. James L. Barton <br /> June 20, 2008 <br /> Page 3 <br /> Technical Basis for Scope of Work <br /> Remediation effectiveness will focus on monitoring wells with higher concentrations of dissolved constituents. <br /> To ultimately achieve system shut-down, decreasing trends in these wells must be evident. To determine <br /> potential system optimization needs, concentrations of petroleum hydrocarbon constituents, TPHg and <br /> benzene, (from the laboratory analyses of groundwater samples)will be charted and compared to remediation <br /> goals, which are as follows: <br /> • Reduce dissolved concentrations of petroleum hydrocarbons (TPHg and benzene) in source area <br /> monitoring wells by more than one order of magnitude. This will achieve residual TPHg and benzene <br /> concentrations below 1,000 pg/L and 100 pg/L, respectively. <br /> • Establish decreasing concentration trends in monitoring wells without active remediation to support <br /> subsequent achievement of closure criteria via MNA in a reasonable time frame. <br /> While decreasing trends of dissolved concentrations are indicators of remediation effectiveness, dissolved <br /> concentrations in groundwater may not change significantly in a relatively short period of time because of <br /> aquifer heterogeneity and physical processes such as contaminant desorption from solids. Application of <br /> CSIA can identify microbial activity and whether or not biodegradation is being enhanced. CSIA is an <br /> analytical technique capable of producing isotopic characterizations of compounds. Since biodegradation <br /> produces an isotopic change in compounds, CSIA unambiguously quantifies if biodegradation of the fuel <br /> hydrocarbons is occurring, and can to some degree provide an estimate on the rate of biodegradation. The <br /> advantages of CSIA for evaluating processes associated with groundwater remediation have been recognized <br /> in the technical literature. A technical publication that describes, in greater detail, the analytical technology <br /> associated with CSIA, the fundamentals of stable isotopes with regard to contaminant removal in <br /> groundwater, and examples of CSIA application to a variety of groundwater contaminants, including fuel <br /> hydrocarbons, is available at the following web-site: http://www.microseeps.com/pdf/csia.pdf. <br /> BioTrap®samplers can passively collect microbial communities and provide a more representative <br /> understanding of the microbial response to the active remediation. The application of these samplers is more <br /> advantageous than traditional soil/groundwater samples because the microbial activity represents a"real time <br /> snapshot" of the most active bacterial community, whereas results from soil samples could portray older <br /> communities than are metabolically dormant. BioTrap®samplers are devices that can be deployed in a <br /> monitoring well below the water table for a defined time period, commonly 30 days, and can compensate for <br /> the inherent variability in collecting groundwater samples. BioTrap®samplers contain unique beads designed <br /> to allow for the adsorption of contaminants, which attracts microbes to the bead matrix rather than "free <br /> floating' in the groundwater. Once retrieved, the samplers can be analyzed using a variety of microbial <br /> analyses. Additionally, the BioTrap®samplers can be "baited" for a specific compound, such as benzene, <br /> and subsequently through analyses, can demonstrate that the actively colonizing bacteria are seeking and <br /> bioremediating benzene. One such analysis is the phospholipids fatty acid analysis (PLFA). The PLFA can <br /> show which percentage of the bacteria used benzene as an electron donor. <br /> By deploying BioTrap®samplers before start-up of the upgraded AS/SVE system, the current difference, if <br /> any, between a"background"well like MW-10 and a "hot'well like MW-2 or MW-81D can be identified. The <br /> "background" well should preferably be a well that is located as close as possible to the hot area but is one <br /> that has not been impacted and likely will not be impacted in the future. Given the distance between <br /> monitoring wells and the migration of the contaminants with the influence of the irrigation well, an ideal <br /> 01231-154 ENSR AECOM <br />