An Integrated Approach to Identify Predominate Flow Zones within Fractured Shale Bedrock

Musgrove, Kristen

An Integrated Approach to Identify Predominate Flow Zones within Fractured Shale Bedrock

Tuesday, September 24, 2013: 2:10 p.m.

Kristen Musgrove , Brown and Caldwell, Nashville, TN

Scott Blanchard , Brown and Caldwell, Columbus, OH

An integrated approach was used to identify predominate flow zones within a fractured shale bedrock to understand its hydrogeologic relationship to the underlying regional sandstone aquifer system. The site is located in the Midwest and the fracture shale unit is impacted by a release of chlorinated solvents. The integrated approach included bedrock coring using roto-sonic techniques, borehole geophysics, and interval packer testing for groundwater quality and hydraulic head measurements.

Bedrock core borings were advanced using roto-sonic drilling to assess the potential presence of chlorinated solvent contamination within the fractured shale bedrock. An extensive borehole geophysical suite, including flowmeter logs, was run in each bedrock core boring, and is capable of identifying fracture flow zones. Fracture flow zones have the ability to provide principal groundwater flow pathways that constitute the discrete aquifer units of a bedrock formation (Michalski and Britton 1997). Borehole geophysics offers a suite of tools able to characterize bedrock flow zones. Additionally, interval packer testing was conducted during the advancement of each core boring. The interval packer testing provided an assessment of groundwater quality within discrete bedrock zones. The interval packer testing also provided an opportunity to measure hydraulic heads within each interval sampled. When completed across the site, the core borings provided sufficient hydrogeologic characterization to connect potential groundwater flow zones.

Multiple lines of evidence support the findings that contaminants of concern (COCs) were not present below the overburden water-bearing zone. These multiple lines of evidence include: no detection of COCs in the wells screened in the shallow bedrock water-bearing zone; geophysical data and hydraulic head measurements indicating limited potential for vertical (downward) migration of COCs in groundwater; and negligible to very low hydraulic connection among depths within the core borings.

Kristen Musgrove, Brown and Caldwell, Nashville, TN

Kristen Musgrove has six years of experience with Brown and Caldwell as a hydrogeologist. Her experience includes providing technical support on a full range of environmental services including environmental site assessments, soil sampling, groundwater sampling, conducting hydraulic/geological investigations for CERCLA, RCRA, and state regulated facilities. Musgrove holds her undergraduate and graduate degrees in Geology from South Illinois University.

Scott Blanchard, Brown and Caldwell, Columbus, OH

Scott Blanchard is a Principal Geologist with Brown and Caldwell and has over 19 years of experience in the successful implementation and completion of various hydrogeological and environmental projects, ranging from UST investigations to technical support for U.S. EPA and the U.S. Department of Justice on CERCLA RI/FS and RCRA projects. In addition to his on-the-job experience, Blanchard has taught and lectured several college level environmental and geology courses. He holds an undergraduate degree in Geology from Denison University.