BOREHOLE IMAGE, FLOW, AND HEAD ANALYSIS AND INSIGHTS INTO HYDRAULIC CONNECTION AND CONTAMINANT MIGRATION IN FRACTURED BEDROCK

Integrated analysis of borehole image, vertical-flow, and hydraulic-head measurements has provided insights into hydraulic connections and migration of contaminants at fractured-bedrock sites in the Appalachian Plateau, Newark Basin, and Hudson Lowland. Borehole images collected with acoustic and optical televiewers were analyzed along with gamma logs and observations from cores, quarries, and outcrops to determine lithostratigraphic correlations and fracture-and-bedding relations and orientations. Borehole flow and fluid-property logs collected under ambient and quasi-steady-state stressed (pumping or injection) conditions were analyzed to estimate transmissivity and hydraulic head of fractured zones. Transient flow responses measured during cross-borehole pumping and recovery were analyzed to delineate flow-zone connections. Hydraulic-head profiles measured in cluster-well, packer-and-port, and liner-and-port monitoring installations, which were designed based on image, gamma, and flow logs, were analyzed to verify and further define head relations between flow zones.

In the sedimentary bedrock at the Appalachian Plateau and Newark Basin sites, hydraulic connection and contaminant migration occurred along specific beds susceptible to fracturing and (or) solutioning. In the metasedimentary bedrock at the Hudson Lowland sites, hydraulic connection and contaminant migration occurred along subhorizontal to moderately dipping fractured zones and conjugate fracture sets oriented parallel to bedding strike. Hydraulic gradients in the clastic and carbonate sedimentary and metasedimentary bedrock generally were downward, except immediately adjacent to surface discharge areas with significant head differences occurring across non-fractured beds. At the Appalachian Plateau site in carbonate bedrock, widely spaced and near-vertical fractured and solutioned zones appeared to provide localized hydraulic connection, focused recharge, and discrete pathways for downward contaminant migration. At the Hudson Lowland site in metamorphosed shale, a less fractured interval between parallel dipping fractured zones provided for a secondary hydraulic connection between the zones, and displayed high contaminant concentrations due to the lack of natural flushing.