Formatted Title

Evolving Lifecycles with High Resolution Site Characterization (HRSC) and Three-Dimensional Conceptual Site Models in Complex Geology 

Background/Objectives

Traditional site investigation data collection methodologies have historically provided inadequate data density, data quality and data interpolation to overcome site heterogeneity leading to improper field geologic and hydrogeologic applied methods. This deficiency in data often leads to repeated and/or incomplete investigations during initial stages of a site’s lifecycle and can result in the development of incomplete or an incorrect conceptual site model (CSM). Incomplete CSMs often lead to flawed environmental system interpolations of geologic/hydrogeologic and microbiological-biochemistry systems, leading to unsuccessful remedial strategies, yielding to a greater potential to increase lifecycles and costs. 

A specialty chemical manufacturing facility located in South Carolina entered into a consent order in 1986 beginning environmental investigations during the late 1980s where the site later entered into the USEPA NPL site listing in 1990. The site published an initial ROD in 1993, which was subsequently amended over the next 23 years for alternative remediation technologies that included; source excavation, soil vapor extraction, groundwater pump and treatment (P&T) and in situ chemical oxidation (ISCO). Site investigations identified primary contaminants of concern as 1,4-dioxane and tetrahydrofuran with imposed Remediation Action Levels (RALs) established as the Minimum Contaminant Levels (MCLs). With the approved ROD, remediation strategies of ISCO (e.g., ozone injection) and a groundwater P&T system and their associated groundwater Sampling and Analysis Plan (SAP) have been operational in perpetuity with a monetized liability lifecycle of $30MM placed in reserve.

Approach/Activities

In 2021, the site’s historical investments with investigations and remediation in the form of existing and new data were migrated to a Geographic Information System (GIS) and EarthSoft’s EQuIS database and exported for data-visualization using C Tech’s Earth Volumetric Studio (Studio). Prior geophysical and hydrogeologic pumping test data were used to generate a geologic model of overburden and fractured rock. A voluntary high resolution site characterization (HRSC) investigation was completed to verify any presence of residual source area contamination and vertically profile downgradient contaminants of concern adjacent to a surface water stream and  along the property boundary to aid in understanding the shallow hydrogeology in association with the contaminant mass flux at the site.

After completion of the HRSC, in-well passive diffusion bag sampling devices were deployed to vertically profile recovery wells down to 90 ft below ground surface (bgs). Surface water gauges were installed within the onsite stream and shallow piezometers all used for collection of enhanced water level measurements across the site. Down well data loggers were also installed across the groundwater monitoring and recovery well networks. Over the course of twelve months, the 3D-CSM was enhanced with a limited suite of geophysics along with the high-resolution data sets and concluded the following: 1.)  Identified technical data gaps in the geologic and hydrological systems 2.) Identified flawed remediation designs 3.) Provided for a collaborative medium for stakeholder engagement with data-driven strategy decisions.

Results/Lessons Learned

The incorporation of a 3D-CSM and completion of HRSC provided a tool for enhanced, data-driven decisions to support a change in remediation closure strategies. Currently, an approved pilot study has been obtained to shut down the remediation systems (ISCO, P&T) and conduct a hydraulic study under non-pumping conditions. A separate micro-biological bench-scale treatability study was competed that yielded positive results for an emerging innovative technology.  As a result, a field pilot study has commenced with results expected in nine-twelve months. With the results of the hydraulic study, field pilot studies and an updated risk assessment leading site monitoring optimization cost lifecycle savings upwards of $15MM towards an alternatively evolved best available technology remediation closure strategy.