A Stochastic Modeling Approach to Address Hydrogeologic Uncertainties in Modeling Wellhead Protection Boundaries in Karst Aquifers¹

Abstract

Development of any numerical ground‐water model is dependent on hydrogeologic data describing the subsurface. These data are obtained from geologic core analyses, stratigraphic analyses, aquifer performance tests, and geophysical studies. But typically in remote areas, these types of data are very sparse and site‐specific in terms of the aerial extent of the resource to be modeled. Uncertainties exist as to how well the available data from a few locations defines a heterogeneous surficial aquifer such as the Biscayne Aquifer in Miami‐Dade County, Florida. This is particularly the case when an exceptionally conductive horizontal flow zone is detected at one site due to specialized testing that was not historically conducted at the other at sites that provided data for the model. Not adequately accounting for the potential effect of the high flow zone in the aquifer within a ground‐water numerical model, even though the zone may be of very limited thickness, might underpredict the well field protection capture boundaries. Applied Stochastic ground‐water modeling in determining well field protection zones is steadily becoming important in addressing the uncertainty of the hydrogeologic subsurface parameters, specifically in karstic heterogeneous aquifers. This is particularly important in addressing the uncertainty of a 60‐day travel time capture zone in the Northwest Well Field, Miami‐Dade County, where a predominantly high flow zone controls much of the flow in the production wells. A stochastic ground‐water modeling application along with combination of pilot points and regularization technique is presented to further consolidate the uncertainty of the subsurface.

Hydrologic conditions in urban Miami-Dade County, Florida, and the effect of groundwater pumpage and increased sea level on canal leakage and regional groundwater flow

“…Other numerical models of Miami-Dade County include (1) surface-water flow models, (2) groundwater flow models, and (3) coupled surface-water and groundwater flow models. Published groundwater flow models include those by Merritt (1996bMerritt ( , 1997, Langevin (2001), Giddings and others (2006), Guha (2008), Guha and Panday (2012), and Brakefield and others (2013). Numerous surface-water flow models have been developed to evaluate how the surface-water system might respond during storm events.…”

Quantifying flow and remediation zone uncertainties for partially opened wells in heterogeneous aquifers

“…Varljen and Schafer, 1991;Franzetti and Guadagnini, 1996;2292 C.-F. Ni et al: Quantifying flow and remediation zone uncertainties Lessoff and Indelman, 2004;Indelman et al, 2006;Riva et al, 2006;Kunstmann and Kastens, 2006;Guha, 2008). The MCS is conceptually straightforward for determining stochastic remediation zones in heterogeneous aquifers.…”

Application of Numerical Tools to Investigate a Leaky Aquitard beneath Urban Well Fields

“…Such numerical tools apply mathematical equations to calculate aquifer system responses to forcing conditions such as pumping, stream-stage variation, and rainfall events [18]. Besides groundwater models, several other numerical tools and techniques are developed to post-process the flow equations and the results of numerical models, to improve our understanding of the studied groundwater system [19][20][21][22][23][24][25][26][27].…”