API PUBL 4657 : 1997

This report, sponsored by the American Petroleum Institute (API), presents the results of laboratory and field studies on field methods for the measurement of geochemical indicators of intrinsic bioremediation.

Intrinsic bioremediation is a risk management strategy that relies on naturally occurring biodegradation for mitigation of the potential risks posed by subsurface contaminants. Various technical articles and protocols offer guidance on the groundwater parameters and properties that should be measured to characterize intrinsic bioremediation of petroleum hydrocarbons. These include dissolved oxygen (DO), nitrate, sulfate, ferrous iron, methane, carbon dioxide, alkalinity, oxidation/reduction potential (ORP), pH, conductivity, and temperature. Measurement of these parameters is being performed at an increasing number of petroleum hydrocarbon sites. However, there is a lack of guidance on appropriate sampling and analytical procedures to ensure that these measurements generate quality data. This lack of guidance is cause for concern because the extent to which intrinsic bioremediation is ultimately embraced will depend, to a large degree, on the valid characterization of site conditions.

The project consisted of a laboratory study, which allowed comparison of sampling methods under controlled conditions, as well as field studies, which allowed verification of laboratory results on sampling methods under actual field conditions. The field studies also incorporated a comparison of commercial laboratory and field analytical methods. Field analytical methods are of interest because their use makes possible rapid sample analyses, thus reducing the potential for changes in the composition of the sample during sample shipment and storage, and allowing for "real time" data evaluation in the field.

Based on these studies, a companion document (CH2M HILL, 1997) was prepared to provide guidance on the selection and use of field sampling and analytical methods for measuring geochemical indicators of intrinsic bioremediation.

The primary objective of this report is to document and discuss the findings of the laboratory and field studies. This report should not be interpreted as providing endorsement of a particular sampling or analytical method. Guidance on the selection and use of sampling and analytical methods used to support intrinsic bioremediation site characterizations is presented in the companion document (CH2M HILL, 1997).

Site data on indicators of intrinsic bioremediation can be used in a variety of ways, ranging from very qualitative uses (e.g., comparison to background data) to very quantitative uses (e.g., input parameters to numerical fate and transport models). The ultimate data use dictates the data quality objectives. The data quality obtained through the various sampling and analytical methods, and effects on data use, are discussed in this report. This report should not be interpreted as providing endorsement of any particular data use.

The field studies described in this report were conducted at petroleum hydrocarbon sites, and the report focuses on applications of intrinsic bioremediation at petroleum hydrocarbon sites. However, the observations and findings presented will generally be applicable to any site where biodegradable organic constituents exist.