Former Dry Cleaner

A pilot scale remedial event was conducted in Durham, NC at a former dry cleaner site to exhibit the efficacy of a proposed remedial design. The site was identified as having impacted soils and groundwater due to the historical use of tetrachloroethylene (PCE).

In April 2011, an 18' self-contained mobile injection trailer was used to deliver the remedial materials via permanent injection wells. Open rock wells were utilized to deliver materials from 30' to 40' and create a pilot scale permeable reactive barrier.

The injection program consisted of three injection wells utilized to inject a mixture of remedial materials containing blue green algae, sodium sulfite, calcium propionate, zero valent iron, and soluble kelp.

A single inflatable TMA 350 packer system was used to inject the materials below 25' bgs. The remedial mixture was designed to be a pilot scale remedial action at the site to restrict plume migration while also reducing CVOC concentrations locally via enhanced reductive dechlorination.

The pilot scale program was designed to act as a proof of concept and promote anaerobic conditions in the groundwater, thereby enhancing bacterial populations within the anoxic groundwater.

Monitoring well MW-26 is located within the pilot scale remedial treatment area, immediately downgradient of the three injection points and screened between 27-37.5 feet bgs.

Vinyl chloride increased from below detection to 20 µg/L, which is normal as it is a byproduct of cis-1,2-DCE. Continued reductive dechlorination is expected in the pilot area.

This Durham pilot project demonstrates IET's innovative use of novel organic electron donors — blue green algae, sodium sulfite, calcium propionate, and soluble kelp — combined with zero-valent iron (ZVI) for enhanced reductive dechlorination (ERD) of chlorinated solvents. The amendment cocktail was delivered via three injection wells using an inflatable TMA 350 packer system to isolate the treatment interval below 25 feet bgs, creating a pilot-scale permeable reactive barrier (PRB) in the open rock well setting.

The multi-substrate approach leverages staggered fermentation profiles: calcium propionate provides rapid hydrogen release (0–100 days), soluble kelp provides intermediate-release fermentation (60–500 days), and blue green algae provides sustained long-term electron donor capacity. The ZVI component contributes both abiotic reductive dechlorination and ferrous iron that precipitates sulfide — protecting dechlorinating bacteria from sulfide toxicity in sulfate-rich aquifers. Sodium sulfite serves as an oxygen scavenger to rapidly establish anaerobic conditions needed for reductive dechlorination.

The pilot-scale design — three injection wells, one monitoring well (MW-26), and 9 months of post-injection monitoring — provided the performance data needed to evaluate whether to scale to a full-site deployment. The 97.2% total CVOC reduction and 99.74% PCE reduction at MW-26 within 9 months demonstrate the effectiveness of the amendment formulation, with the expected vinyl chloride increase (a normal dechlorination byproduct) indicating active biological treatment progression toward complete dechlorination to ethylene.

Durham, North Carolina is located in Durham County within the Durham Triassic Basin physiographic province. The shallow geology consists of Triassic-Jurassic age sedimentary rocks of the Durham Basin — predominantly sandstone, siltstone, and mudstone of the Chatham Group, with localized diabase intrusions. Groundwater in this setting occurs primarily in fractures within the bedrock and in the overlying saprolite (weathered rock), creating a fractured rock aquifer system that presents unique challenges for in-situ remediation.

The use of an inflatable TMA 350 packer system for injection below 25 feet bgs is specifically adapted to fractured rock hydrogeology — the packer isolates discrete fracture intervals, allowing targeted amendment delivery into the productive fracture zones rather than the rock matrix. This approach maximizes treatment efficiency in fractured settings where conventional open-hole injection would distribute reagent unevenly across both productive and non-productive intervals. The pilot PRB approach — creating a reactive barrier perpendicular to groundwater flow in the fracture network — is designed to restrict plume migration while reducing CVOC concentrations locally, providing both source zone treatment and downgradient plume control from a single injection event.