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USE OF DRILLING FLUIDS IN MONITORING WELL NETWORK INSTALLATION: LANL AND OPEN DISCUSSION
Citation:
FORD, R. G. USE OF DRILLING FLUIDS IN MONITORING WELL NETWORK INSTALLATION: LANL AND OPEN DISCUSSION. Presented at EPA Regional Site Manages Meeting on DOE Issues, Richland, WA, October 25, 2005.
Impact/Purpose:
To inform the public.
Description:
Personnel at the EPA Ground Water and Ecosystems Restoration Division (GWERD) were requested by EPA Region 6 to provide a technical analysis of the impacts of well drilling practices implemented at the Los Alamos National Laboratory (LANL) as part of the development of their ground-water monitoring program. The focus of this review involved analysis of the impacts of bentonite- and organic polymer-based drilling fluids during the drilling and construction of regional aquifer wells installed to characterize the hydrogeologic setting beneath Los Alamos. The questions which were posed for this analysis centered on the capability of the existing hydrogeologic characterization wells to provide representative ground-water samples for all site-related constituents of concern. Based on review of well installation records and water chemistry data provided by LANL, it was concluded that intrusion of bentonite and organic-based polymer drilling fluids into the aquifer adjacent to well screens posed a potential problem for monitoring the transport of reactive contaminants of concern. For organic-based polymer drilling fluids, the primary impact could be attributed to microbial degradation of the drilling fluid components leading to alteration of aquifer mineralogy via iron- and sulfate-reduction. In general, both drilling fluids introduce new reactive solid phases within the screened interval that may retard contaminant transport relative to un-impacted zones within the aquifer that the screened interval is intended to sample. This could result in the delay or failure to recognize contaminant migration from source zones into the regional aquifer. Recommendations were made relative to proposed steps forward to 1) characterize the extent of alterations to aquifer geochemistry and 2) potentially rehabilitate impacted well screens for use in the ground-water monitoring program.