Primary Author / Conference Presenter:
Kent Armstrong
TerraStryke Products, LLC
Andover, NH, USA

Barbara Forslund, Advanced GeoServices, West Chester, PA, USA

Incidental releases of trichloroethene (TCE) at former electronics manufacturer in east-central Ohio impacted shallow overburden-bedrock groundwater. Hydrogeology includes 15 to 20 feet of alluvial silty clay or gravelly sand overlying fractured sandstone with estimated 10-foot thick interval of dense non-aqueous phase liquid (DNAPL) trapped in primary/secondary porosity of shallow bedrock. Baseline [TCE] in bedrock ranged from 55-550 milligrams per liter (mg/L), up to ≈30% of TCE’s aqueous solubility limit; dechlorination byproduct cis-1,2-dichloroethene (cis-1,2-DCE) at ≤15 mg/L and Vinyl chloride (VC) not detected above method detection limits (0.25-10 mg/L). Pump & treat system operates to manage plume migration. Responsible party desires low-impact, low-cost and sustainable strategy to achieve enhanced reductive dechlorination (ERD) which targets DNAPL destruction.
Proof-of-Concept (POC) study in 2012 evaluated ERDenhanced™, a carbon-carbohydrate based biostimulant formulated with proprietary blend of macro-micro nutrients, with a purpose to determine the additives ability to enhance native microbial populations, stimulate enhanced reductive dechlorination, and optimize syntropic relationships between dechlorinators and fermenters to increase rate and effect residence time of additive enhanced dechlorination. Additional benefits include increased biosurfactant production/biofilm development, expedited solubilization, and an increase in the bulk fraction of dechlorinating bacteria. Bioaugmentation was not performed; [Ethene] detected at all test wells prior to start, demonstrating dechlorinators/genes required for complete TCE biotransformation present. Results of three-year study indicate, at additive amended locations: 1) 80-99.9%reduction [TCE], 2) consistent indicator parameters for biotic dechlorination pathway; 3) increased [Ethene] demonstrating reaction completion; and, 4) presence of Dehalococcoides mccartyi and dehalogenase genes tceA, bvcA, vcrA. Together, 10 and 20 results indicate additive enhanced native dechlorinators are expressing necessary beneficial genes to facilitate complete dechlorination of TCE to Ethene.
In 2015 Pilot Study was performed to determine the transferability of POC study data and collect pre-design data for full-scale remedy. Two bedrock injection wells and performance network of eight bedrock wells were utilized. Results of the 20-month evaluation documented the following within the amended zone: 1) 70-99%reduction [TCE] at eight performance wells from baseline concentrations of 130 mg/L or, ≈10% TCE’s aqueous solubility. In fact, four of the eight wells exhibited ≥99%reductions; 2) 95%reduction [cis-1,2-DCE] at six of eight wells, evidence of no “cis-stall”; 3) [VC] either decreased or remained constant at five of eight wells; 4) up to two orders-of-magnitude increase in [chloride] at seven of eight wells, results consistent with the active dechlorination of a TCE DNAPL; 5) [Ethene] detected during 40-80% of post-injection sampling rounds for all eight wells demonstrating complete dechlorination; 6) [diss.Fe]/[diss.Mn] increased at all eight wells indicating Redox conditions decreased to at least ferrogenic/manganogenic reduction; and, 7) while pH significantly depressed at a few wells, values generally returned around neutrality.
Recent performance data from monitoring wells within amended zones at the POC and PS locations proves biostimulation with ERDenhanced™ provides robust and complete TCE DNAPL dechlorination without “cis stall” by optimizing the syntropy between dechlorinators and fermenters. Site data through 2020 demonstrates biostimulation with ERDenhanced™ expedited rates of dechlorination, extended effect-residence times (8+ years), to realize three Orders-of-Magnitude reductions in cVOC contaminant mass