Monday, April 20, 2009: 11:30 a.m.
Canyon Suites I/II (Hilton Tucson El Conquistador Golf & Tennis Resort )
June T. Fabryka-Martin, Ph.D.
,
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM
Ardyth Simmons
,
Environmental Programs, Los Alamos National Laboratory, Los Alamos, NM
Since 1998, more than 40 wells have been drilled in and around Los Alamos National Laboratory in order to understand potential contaminant pathways and eventually to become part of a site-wide monitoring network. The complex geologic setting and extreme depth of the regional aquifer necessitate the use of drilling fluids and additives. Groundwater data quality and detection monitoring of contaminants have been compromised in some of these wells as a result of incomplete removal of drilling products from lost-circulation zones and from screened intervals during well development. The residual drilling products manifest as elevated concentrations of soluble constituents in water samples. More significant are the consequences of residual organics immobilized in the subsurface, where they fuel the growth of microbial populations and the concomitant development of reducing conditions. Reducing conditions that evolve to the sulfate-reducing stage tend to persist for years. Associated mineralogical changes near the screen are another recalcitrant condition. A protocol was developed for evaluating historic and new water-quality data to assess which data could be considered to be reliable and representative of predrilling conditions. To optimize efficiency and reproducibility of the results, the protocol was semi-automated as a Data Qualification module linked to the facility’s water-quality database. The module compares analytical data for each water sample against threshold levels for about 30 indicator species to identify the presence of specific categories of drilling effects: residual drilling products, reducing conditions, shifts in the carbonate system, enhanced adsorption, and corrosion of stainless-steel components. The threshold levels are defined based on levels measured in background samples considered representative of local groundwater quality. Based on the category of effects determined to be present, data are then flagged if suspect. Although the test threshold values are tailored for local conditions, the protocol should be implementable at any groundwater location.
