Using Geology to Follow the Groundwater, Follow the Flow to Successful Remediation

Recently in our industry there has been a developing best practice that focuses on the geology to define the subsurface “plumbing”, which can make or break groundwater remediation programs. The subsurface provides the greatest uncertainty when addressing complex contaminated groundwater sites. “It’s dark down there” and the data from boring logs represent only a small fraction of the subsurface and do not present a complete picture. To increase our understanding of the subsurface, Environmental Sequence Stratigraphy (ESS) is an established methodology that focuses on 1) a critical understanding of the sedimentary depositional environment, 2) formatting of lithology data to emphasize vertical grain-size distribution, and 3) a stratigrapher’s knowledge of facies models and related grain-size pattern recognition. These components result in an interpretation and prediction of the geology between boring logs that significantly reduces the uncertainty and provides the framework for characterizing contaminant migration pathways and defining the conceptual site model (CSM). ESS is considered an emerging best practice for complex site CSMs by US EPA and US Air Force (AFCEC).

 

Examples will be presented that show the efficacy of ESS as a critical path to complex site investigation and remediation. The methodology has been successfully applied at numerous complex contaminated groundwater sites throughout the US, including over 25 US DOD facilities. The case studies will provide examples of best practices in applying geology to CSMs and provide “rules of thumb” to test the efficacy of your CSM, such as the following questions.

• Is groundwater flow, and the contaminant plume, controlled by geologic features (e.g., buried sand channels)?
• Does the CSM adequately define the geologic features?
• What tools are available to define the geologic features that carry groundwater contamination?
• How do buried sand channels and other geologic features affect source identification?
• How do they affect remedial design?