API Publication 4658:1997 pdf download

API Publication 4658:1997 pdf download.METHODS FOR MEASURING INDICATORS OF INTRINSIC BIOREMEDIATION: GUIDANCE MANUAL.
This section presents an overview of the key considerations in sampling and analytical methodology. Information is presented on how sampling and analytical methodology can alter data on geochemical indicators of intrinsic rernediation. The general factors that should be considered in selecting sampling and analytical methods are reviewed.
WHY BE CONCERNED WITH SAMPUNG AND ANALYI’ICAL METHODOLOGY?
The characterization of key geochemical parameters of groundwater is a tool that has emerged in recent years for evaluating intrinsic bioremediation. Microbial metabolism of petroleum hydrocarbons has predictable geochemical consequences (Wilson et al., 1994). For example, respiration of hydrocarbons may result in the loss of oxygen, nitrate, and sulfate, and the conversion of iron from the ferric to ferrous oxidation state. Petroleum hydrocarbons may also be biodegraded by an anaerobic process that results in the production of methane (i.e., methanogenesis). Measuring the trends in the distribution and concentration of these and other parameters can help to qualitatively establish hydrocarbon biodegradation activity. Data on the spatial distribution of these parameters, together with hydrogeologic and stoichiometric data, are also sometimes used to support the quantitative estimation of contaminant biodegradation rates and the prediction of plume migration.
Why be concerned with sampling and analytical methodology? The uses of geochemical data previously described will be valid only to the extent that measurements of these parameters are representative of geochemical conditions in the groundwater system sampled. Sampling and analytical methodology can significantly affect measurements of key geochemical indicators of intrinsic bioremediation, as described below.
Geochemical Considerations
To understand how sampling and analytical methods may impact results one must first have a basic understanding of the geochemistry of the groundwater being sampled, and recognize that the geochemical condition of groundwater from biologically active zones is typically not stable during and after extraction from the subsurface.
In recent years, it has become widely recognized that microorganisms can have profound effects on groundwater quality. This is particularly true where large masses of biodegradable organic compounds, such as petroleum hydrocarbons, are present in the vadose and groundwater zones. Hydrocarbon biodegradation involves microbiologically mediated oxidation coupled with reduction of an electron acceptor through the biological process of respiration. The reduction of highly oxidized electron acceptors (e.g., DO) results in an overall decrease in the oxidizing potential of the groundwater. As species with the highest oxidizing potential are exhausted, the oxidizing potential of the groundwater system is progressively reduced, and the next most highly oxidized electron acceptor is used Thus, a general sequence of electron acceptor utilization and lowering of the oxidizing potential of the groundwater is as follows.