Influence of Fracture Fabric and Gradients on Contaminant Migration at the Savage Well Superfund Site

Fuller, Andrew

Influence of Fracture Fabric and Gradients on Contaminant Migration at the Savage Well Superfund Site

Monday, September 23, 2013: 10:35 a.m.

Andrew Fuller, PG , Weston Solutions Inc., Concord, NH

Bette L. Nowack, PE , Weston Solutions, Inc., Concord, NH

James Soukup, PG, RG, LSP , Weston Solutions Inc, Concord, NH

Historical use of tetrachloroethene at the Savage Well Superfund Site in Milford, New Hampshire impacted both the overburden and bedrock aquifers underlying the site, including the nearby municipal overburden water supply well. Although the municipal well was taken offline, residences to the north of the source area are serviced by private bedrock water supply wells. Site geology consists of transmissive glacial outwash and a discontinuous till unit overlying fractured crystalline bedrock.

A multi-phased approach including well installations, borehole geophysics, packer interval sampling, and a pumping test was employed to develop a conceptual site model for the fractured bedrock aquifer at the site. Borehole geophysics and a 76-hour pumping test were utilized to evaluate fracture frequency, strike, and dip, identifying hydraulically active fractures within each monitoring well, and determining the anisotropy of the bedrock aquifer.

The investigation identified a competent bedrock fabric with a limited number of hydraulically active fractures that were moderately to steeply dipping (median 66º), with a predominant strike to the north-northeast. The pumping test data displayed a similar trend with a clear north-northeast anisotropy to the cone of depression. However, static hydraulic head distribution indicated easterly flow across the aquifer, almost perpendicular to the predominant strike of the fractures and anisotropy. To further complicate interpretation, hydraulic conditions at the site had been modified over the years as a result of the installation of a slurry wall barrier and groundwater extraction system in the overburden. It was not initially clear whether the fracture fabric or the hydraulic gradient had greater control over contaminant migration. Determining the actual direction of contaminant migration was essential to determining whether residential wells to the north of the site were at risk. This presentation will discuss the investigation, the final conceptual model for the site, and the fate of the residential wells.

Andrew Fuller, PG, Weston Solutions Inc., Concord, NH

Andrew Fuller is a professional geologist with seven years of experience investigating and remediating hazardous waste sites. He has worked on several fractured rock sites in New England, including remedial investigations, remedial actions, and O&M.

Bette L. Nowack, PE, Weston Solutions, Inc., Concord, NH

Bette Nowack has more than 20 years of environmental engineering and consulting experience involving a wide variety of environmentally-focused projects, including groundwater and soil contamination assessment and remediation, water and wastewater treatment, and hazardous waste site remediation. Nowack has a bachelor’s degree in Biology from Lafayette College and a master’s degree in Environmental Engineering from the University of New Hampshire. She has managed large multidisciplinary projects for the Air Force, Army Corps of Engineers, EPA, and the New Hampshire Department of Environmental Services for the last 18 years as a project manager at Weston Solutions Inc.

James Soukup, PG, RG, LSP, Weston Solutions Inc, Concord, NH

James Soukup is a registered professional geologist with over 25 years consulting experience specializing in environmental investigation and remediation. His current focus is on the design and implementation of in situ groundwater remediation projects including chemical oxidation and enhanced biodegradation.