A primary objective of the WIPP EM pre-disposal baseline phase was to quantify the background environmental levels of the radionuclides and inorganic non-radioactive constituents that are known or expected to occur in the wastes deposited at the WIPP. These data serve as a basis for comparison against data collected for the same constituents after the WIPP began operation, and extending into the post-operational phase. A true quantification requires application of specialized methods, particularly in radiochemistry, to produce data that are free of non-detect values.
It is also important to note that the objective requires sampling designs that provide data to characterize the spatial variation in the analytes of interest across the natural landscape in the vicinity of the WIPP, and the temporal variation in the analytes of interest with respect to seasonal and interannual ecosystem fluctuations. For example, the background concentrations of Pu in aerosols in the vicinity of the WIPP span a range of values that may be dependent on such factors as localized soil type and seasonal weather variations that impact resuspension.
The WIPP EM incorporates analyses of a variety of inorganic substances as part of the routine monitoring design. According to information contained in the waste acceptance criteria for the WIPP (DOE/WIPP-069, November 8, 1999), the mixed waste to be placed at the WIPP may contain arsenic, barium, beryllium (powder), cadmium, chromium, copper, lead, mercury, nickel, selenium, and silver. These constituents are naturally-occurring elements, and are also produced as contaminants from other anthropogenic sources, so quantification of pre-operational levels in the WIPP region was needed to evaluate potential future releases. Some of these trace elements are of concern due to possible toxicological effects for humans and ecosystems. From a practical standpoint, they are also very important and useful in the WIPP EM project as chemical tracers. The sources for these metals are reasonably well known, even on global scales (Nriagu, J. O. and J. M. Pacyna, 1988, Nature, 333:134), and they are readily determined in various types of environmental media.
If contaminant releases from the WIPP were known or suspected, it would become critical to predict the movements of the contaminants within the ecosystem. A second major objective of the WIPP EM baseline studies was to gather information concerning the basic structural/chemical composition of environmental media and ecosystem processes that could be applied in such predictive modeling. Concurrent analyses of naturally occurring radionuclides, non-radioactive elements, and target ions (such as nitrate and sulfate), provide an understanding of the complex and interlocking biogeochemical cycles that characterize the WIPP surface environment. Such characterization provides the basis for modeling of ecosystem processes that determine the fate and transport of contaminants of concern.
The following sections present a brief description of the basic sampling design for each major environmental medium in the WIPP EM, including some primary considerations that serve as the basis of the design. In addition to the core sampling and analyses, information is provided on ancillary studies that are planned or in progress.