Formatted Title
Investigation and Combined Remedies Approach of CVOC Plumes in Soil and Multiple Fractured Bedrock Horizons
Background/Objectives
The site is a former manufacturing facility in western Pennsylvania. Soil in and around the source area and groundwater flowing through multiple fractured bedrock horizons was affected by chlorinated volatile organic compounds (CVOCs). Investigation of the lateral and vertical extent of the impacts to soil and groundwater were completed in an iterative manner. An innovative combined remedies approach was implemented based upon the outcomes of the investigation to address soil, sub slab soil gas, and groundwater impacts at the site. Source area remedies included targeted excavations, soil vapor extraction, phytoremediation, in situ bioremediation, and in situ chemical reduction. Dissolved phase CVOCs were identified to be migrating in shallow (up to 15 feet below ground surface [ft bgs]) surface soils and in the upper portions of fractured marine unit bedrock (approximately 15-35 ft bgs) and underlying fractured sandstone (up to 85 feet deep) migrating over 1,200 feet downgradient from the source area and onto the adjacent downgradient property. This talk will focus on the iterative investigative steps taken to define the lateral and vertical extent of impact within the source area as well as within fractured bedrock and the design and deployment of the combined remedial actions to address CVOC impacts in soil, soil gas, and groundwater.
Approach/Activities
The lateral and vertical extent of impact to soil, soil gas, and groundwater was completed in an iterative approach using a combination of direct push, air rotary, air core, and sonic drilling techniques. Downhole geophysics and dual packer pumping tests defined inflow zones in fractured bedrock and provided the data needed to set well screens to isolate flow zones. Multiple day pumping tests provided details on the hydraulics and interaction between zones needed to design the remedial action plan. Remedial actions included traditional technologies including soil removal and soil vapor extraction using both horizontal and vertical extraction points, as well as an innovative combination of phytoremediation via the TreeWell technology to address impacts to groundwater in soil and two fractured bedrock zones, and enhanced in situ bioremediation (EISB) and in situ chemical reduction (ISCR) to address impacts at the soil/bedrock interface and in three fractured bedrock horizons.
Results/Lessons Learned
Detailed site characterization activities led to the design and implementation of the combined remedies approach to address groundwater containing total CVOC concentrations that exceeded 830,000 µg/L at the source. A pilot study planting of 52 TreeWells approximately 125 feet downgradient of the source area resulted in total CVOC concentrations being reduced by more than 50% within 4 years of implementation. A second planting of 166 TreeWells along the downgradient property line was installed to address residual CVOC concentrations in groundwater prior to exiting the site. EISB and ISCR injections in 117 locations into four different horizons has significantly reduced the plume size and geometry and CVOC concentrations. TCE at the source has been reduced from 46,300 µg/L immediately before EISB/ISCR injection to 6.4 µg/L 2.5 years following injection. Installation and operation of an SVE system beneath the building slab has resulted in the removal of over 1,500 pounds of total VOCs since 2009. Groundwater monitoring data collected following remedial action implementation have demonstrated that the combined remedial approach has been an effective and efficient means of addressing CVOC impacts in soil and fractured bedrock at this site.