We have recently performed a number of Monte Carlo based studies of uncertainties associated with characterization of wellhead protection areas. This work is based on recognition that heterogeneity can lead to significant local variation in groundwater velocities. Perhaps most importantly, anisotropy in the SPATIAL DISTRIBUTION OF SEDIEMNTS can lead to STATISTICAL anisotropy in the conductivity field which can lead to dramatic errors in estimating the orientation and extend of a wellhead capture zone.
Details of this work may be found in several publications, including the dissertation by Bryce Cole (1997), and the following publications:
Cole, B.E., and S.E. Silliman, "Utility of simple models for capture zone delineation in heterogeneous unconfined aquifers", Ground Water, 38(5), 665-672, 2000
Silliman, S.E. and G. Mantz, "Incorporating data related uncertainty in the definition of wellhead capture zones", in Interdisciplinary Perspectives on Drinking Water Risk Assessment and Management, IAHS Publication No. 260, 53-56, 2000.
Cole, B., and S. Silliman, "Capture zones for passive wells in heterogeneous unconfined aquifers", Ground Water, 35(1), 1997.
Cole, B. and S. Silliman, "Estimating the horizontal gradient in heterogeneous, unconfined aquifers: Comparison of three-point schemes", Ground Water Monitoring and Remediation, Spring, 1996, 84-91.
Analysis of Depth to Water Data
We are also actively pursuing a new field technique for the analysis of water level data. Among the capabilities of this technique, currently termed the LGE or Local Gradient Estimator, are assessment of local variability in the hydraulic gradient, identification of data errors, and identification of local anomalies in local aquifer hydraulics. Information on this technique may be found in:
Silliman, S.E. and G. Mantz, "The Effect of Measurement Error on Estimating the Hydraulic Gradient in Three-Dimensions", Ground Water, 38(1), 114-120, 2000.
Silliman, S.E., and C. Frost, "Monitoring of the hydraulic gradient using a three-point estimator", Journal of Environmental Engineering, 124(6), 517-523, 1998.