36 PLUS CONTROLS ON POROSITY AND HYDRAULIC CONDUCTIVITY

Knowledge of spatial distribution of porosity, hydraulic conductivity and other engineering properties within carbonates and evaporites is critical to cost effective groundwater exploration, evaluation and development projects. This information is also needed to formulate and test hydro-geologic conceptual, flow and transport models, site critical facilities, e.g. dams, WIPP, Asse II repository, and advance understanding of geologic processes, karst features and events. Unlikely controlling variables can be eliminated when investigating new project sites. This allows for design and initiation of more cost-effective site characterization efforts.

Petrographic features attributed to deposition, lithification and diagenesis are primary properties. Lithology and stratigraphic sequences can be altered. Deformed secondary controls on hydraulic properties include topographic setting and relief, base level and paleo-base level, water table and paleo-water table levels, unconformities, systematic and non-systematic joints and fractures, faults, folds, fracture trace-and lineament-scale zones of fracture concentration, weathering under existing and paleo-climatic conditions, recharge rates, position within the drainage network, hydrodynamics and water chemistry among others. Anthropomorphic features also must be included.

First, second and lower order controls on hydraulic properties may be indicated by the presence and scale of groundwater troughs and mounds, pumping stresses, effluent-influent stream segments, size and abundance of springs, seasonal changes in flow and chemistry. Petrographic analysis contributes to understanding of hydraulic properties but can be less revealing when compared to controlled wells tests normalized for exposed borehole length, diameter, test duration and well losses. Who would expect yields of shale and limestone wells to be similar!

Experiments intended for one-off analysis of yield contributions by independent variables are time consuming, costly and constrained by data availability. Exceptions include grid drilling projects for strategic facilities, but often with only limited geographic coverage allowing evaluation of but just a few of many possible variables. Publishing existing data sets would help advance this agenda.