Groundwater electron acceptor concentrations

After start-up, the system should be checked at least weekly, with some observations, notably in the early phases, requiring daily monitoring. Information such as ground-water levels, extraction and injection flow rates, groundwater electron acceptor concentrations, nutrient concentrations, pH, and conductivity should be recorded at least on a weekly basis. Complete records of rates, concentrations, electrical usage, and other operational data can be invaluable when evaluating operational efficiency or documenting unit costs. 

Extraction wells are usually necessary to maintain hydraulic control of the plume and to ensure that the plume does not migrate into clean areas or accelerate migration toward sensitive receptors. Placement of extraction wells is especially important with systems that use nutrient injection wells or infiltration galleries. These sources of fluids can alter natural groundwater flow patterns, which may cause contaminant migration in an unintended direction or rate. If the natural groundwater system has a sufficient concentration of electron acceptors and nutrients, to achieve remediation at an acceptable rate, it may not be necessary to add any additional materials. 

Without appropriate cleanup measures, BTEX often persist in subsurface environments, endangering groundwater resources and public health. Bioremediation, in conjunction with free product recovery, is one of the most cost-effective approaches to clean up BTEX-contaminated sites [326]. However, while all BTEX compounds are biodegradable, there are several factors that can limit the success of BTEX bioremediation, such as pollutant concentration, active biomass concentration, temperature, pH, presence of other substrates or toxicants, availability of nutrients and electron acceptors, mass transfer limitations, and microbial adaptation. These factors have been recognized in various attempts to optimize clean-up operations. Yet, limited attention has been given to the exploitation of favorable substrate interactions to enhance in situ BTEX biodegradation. 

Figure 6 Distribution of reported organic matter turnover under the various TEAPs in pristine surface water sediments and groundwater aquifers (a) and landfill-leachate contaminated groundwater (b). The respiration rates in pristine groundwater ((a) middle and right panels) were modeled using total electron acceptor species concentration (geochemical) and carbon isotope fractionation (isotopic constraints) (after Murphy and Schramke, 1998 and...

A role of microbial processes in release of arsenic into groundwater concomitant with the reductive dissolution of Fe(ni) oxyhydroxides has been suggested based on the observed correlation between dissolved arsenic and bicarbonate concentrations (94,95). Increased bicarbonate concentrations are attributed to the oxidation of organic matter with Fe(III) oxyhydroxides as the terminal electron acceptor. Like oxidative dissolution, reductive dissolution may be kinetically limited. Rates of microbial reduction may be limited by the supply (and nature) of organic carbon. 

Electrokinetics may conceivably be used in six general ways for hazardous waste site remediation (a) concentration and dewatering of waste sludges (b) extraction of pollutants from soUs, sediments, and groundwater (c) creation of hydraulic flow barriers (d) injection for dehvery of nutrients or electron acceptors to enhance bioremediation (e) injection of grouts or cleanup chemicals or (f) improvement of the effective permeability of a soil mass (Parker, 1992). 

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