Evaluating Water Quality with Data from Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Cameron Tana is giving a talk today at the CA-NV AWWA Spring Conference in Anaheim. The talk is at 2:45 PM in the Water Well Technology committee’s session. Here is the abstract:

Evaluating Water Quality with Data from Dynamic Dye Tracer and Sampling Techniques Used in Production Wells

Cameron Tana1, Nicholas Byler1, Haleemah Qureshi1, David Van Brocklin2, and Derrik Williams1

1 HydroMetrics Water Resources Inc., Oakland, CA
2 Perth, Western Australia

The U.S. Geological Survey (USGS) has developed a technique for characterizing depth dependent flow in water supply wells (Izbicki et al. 1999) that is commonly used to evaluate well water quality issues. The technique involves injecting a dye tracer at various depths in the well and using travel times to estimate velocity and cumulative flow at various intervals in the well. To evaluate well water quality, depth-discrete samples are collected in conjunction with the dye tracer study. Sample concentrations and flow data from the dye tracer technique are used to estimate contaminant mass flux and aquifer concentrations over depth. These estimates often inform plans for well modification or other strategies to improve water quality produced by the well.

However, the resolution of the data obtained from the dye tracer technique is limited since the technique only provides average velocities and flows over depth intervals in the wells. If the data’s resolution limitations are not addressed, flows and therefore contaminant mass fluxes and chemical concentrations may be assigned to the wrong depth interval without acknowledging the potential error.

Data interpretation should address the resolution limits of the technique by fitting estimated travel times and well concentrations to the raw data. One approach is to calculate a mass balance that fits the obtained data (Halford et al., 2010). A second approach is to use an axi-symmetric model based on Langevin (2008) such as AnalyzeHOLE (Halford 2009) and calibrating to the obtained data. We will present case studies of wells affected by Chromium VI that show how plans to address well water quality can change when using a data interpretation approach that addresses the data’s resolution limits.

We also recommend two field strategies for improving the resolution of using the dye tracer technique with depth-discrete sampling: 1) injecting the dye tracer at different depths within blank casings between screens, as flows should be uniform within the blank and 2) sampling at different depths than the dye injection depths to increase spatial resolution of obtained data. We will use the case studies to present an evaluation of these strategies.

References:
Halford, K., 2009. AnalyzeHOLE-An integrated wellbore flow analysis tool, U.S. Geological Survey Techniques and Methods 4-F2.
Halford, K.J., Stamos, C.L., Nishikawa, T., and P. Martin, 2010. Arsenic management through well modification and simulation, 48, no. 4. 526-537
Izbicki, J.A., 2004. A small diameter sample pump for collection of depth-dependent samples from production wells under pumping conditions, U.S. Geological Survey Fact Sheet FS 2004-3096, September.
Izbicki, J.A., Christensen, A.H., and R.T. Hanson, 1999. U.S. Geological Survey combined well-bore flow and depth-dependent water sampler, U.S. Geological Survey Fact Sheet FS 196-99, October.
Langevin, C.D., 2008. Modeling axisymmetric flow and transport, Ground Water, 46, no. 4, 579-590.

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