BACKGROUND: Site an industrial/office building in Burlington Ontario, Canada. Past site use includes environmental service businesses; abutting property past use includes, automobile parts/service industries. Principal Contaminants-of-Concern (COC) are chlorinated volatile organic compounds (cVOC); 1,1,1-Trichloroethane (TCA) and breakdown products Dichloroethylene (DCE) and Dichloroethane (DCA), documented in subslab soils. Groundwater solute plume migrating downgradient, off-site, in concentrations above Ontario Ministry of Environment (MOE) Table 2 criteria. Concentrations total cVOCs range 10 ug/L to 500 ug/L (presumed source zone); maximum [TCA] 240 ug/L, [DCA] 11 ug/L, and [DCE] 170 ug/L. Groundwater flows southerly, towards Lake Ontario. Site soils reddish brown silty-sand to a depth of ≈26ft below ground surface (bgs), assumed 25% effective porosity.

OBJECTIVES: May 2013, G2S Environmental, Inc. (G2S) of Burlington Ontario initiated in-situ treatability program to evaluate biostimulation as passive, safe, sustainable remedy to destroy groundwater and residual mass cVOCs. Secondary data regarding distribution capabilities also evaluated. Additive used a carbon, carbohydrate, macro-micro nutrient biostimulant ERDENHANCED™; patented, distributed by TerraStryke Products LLC.

APPROACH/ACTIVITIES: Five injection nodes (INJ) were installed within ≈17m x 8m treatment zone (TZ); vertical impact estimated to extend 5m (10ft to 25ft bgs), total volume ≈680m3. Each injection node 2-inch diameter PVC; extending ≈3-4m bgs, bottom five-feet screened. Each node assumed to generate ≈5-6ft (≈10m2) Area-of-Influence (AOI); therefore, ≥50m2 of 135m2 TZ estimated to be amended. Total 294 pounds additive/100 gallons water deployed via gravity. Two deployment events; May 29, June 28, 2013. Each node amended with ≈40-Liters additive slurry per event. Groundwater monitoring points located within, lateral, downgradient TZ. Groundwater sampled annually over three-plus year period.

RESULTS: Pre-deployment concentration total cVOCs ([cVOCTOTAL]) within the TZ ranged 97.5 µg/L to 911.1 µg/L. Post-deployment [cVOCTOTAL] ranged from 4.4 ug/L to 193.2 ug/L. Decreases in [1,1,1-TCA], the parent TZ cVOC, averaged 87.4%: with specific reductions; 97.3% (BH102), 92.9% (BH110), 95.8% (BH111) and 63.7% at upgradient location BH101. One monitoring downgradient location (BH2) was sampled throughout the evaluation period; located outside the TZ ≈5m from INJ4, documented a 75.0% decrease in [cVOCTOTAL] after a 71.1% increase indicating apparent additive enhanced reductive dechlorination outside the TZ. Specifically, at the downgradient location BH2, [1,1,1-TCA] decreased 77.7% from peak bioavailability, while [1,1-DCA] decreased 90.9% and [1,1-DCE] decreased 92.6%. Contaminant mass destruction is demonstrated by reductions in Parent:Parent-Daughter Molar Ratios (P:PD). Three years-post deployment, total moles cVOCs decreased an average 85.2%; with 77.2% reduction at monitoring well BH101, 83.9% BH102 and BH110, and 95.8% at BH111 (located proximate TZ center). In general, P:PD decreased throughout the evaluation period, realizing maximum decreases of 86.4% (BH102) and 87.4% (BH110).

CONCLUSIONS: Performance data indicates passive amendment of the treatment zone with minimal amounts of ERDENHANCED™ facilitated enhanced reductive dechlorination by native microbials throughout the treatment zone. Evaluation demonstrated greater than anticipated distribution capabilities, documented expedited cVOC biotransformation and overall decreases in Site [COCs] while realizing significant mass destruction, evidenced by reductions in Parent:Parent-Daughter Molar Ratios. The evaluation affirmed biostimulation; and specifically, ERDENHANCED™ a cost-effective, safe, and sustainable strategy to passive-aggressively destroy cVOC contaminants with minimal Site impacts.

Primary Author/Conference Presenter:
Kent Armstrong
TerraStryke Products, LLC
Andover, New Hampshire

Geoff Bell; G2S Environmental Inc., Project Manager, Burlington Ontario Canada