Ion Tracer to Quantify Drill Fluid Impact During Vertical Aquifer Profiling
A case study is presented where an ion tracer was added to drilling fluid to assess the impact of drilling fluid on groundwater samples during vertical aquifer profiling (VAP). VAP involves collecting and analyzing discrete groundwater samples at a mobile on-site laboratory, providing near-real time data for guiding site characterization. At sites where drilling fluids are required, a method is needed to evaluate whether water introduced during advancement of the boring impacts the quality of (or dilutes) the discrete groundwater samples. This presentation will cover the design and implementation of the tracer method along with lessons learned to effectively implement this approach for future work. It will cover the background information of the specific project, including drilling equipment used, sampling equipment, mobile laboratory requirements, aquifer type, and specific problems encountered to better assist others in implementation of this method.
Use of the tracer in the drilling fluid allowed for determining whether discrete groundwater samples were representative of field conditions or diluted by the drilling fluid during VAP. By introducing the tracer at a known concentration into the drilling fluid, then screening the groundwater samples in a field laboratory prior to analysis for contaminants, we were able to estimate the percentage of the sample that was comprised of drilling fluid. With a threshold of ten percent or less, we could confidently analyze the samples for target contaminants knowing that they were not compromised by the introduction of drilling fluid. The detection of tracer compound was also used as a criteria during development of monitoring wells placed in the same boring.