At a glance
Location: Colorado
Geology: Coarse (sand/gravel)
Contaminant(s): TCE
ETEC Solution(s): CarBstrate, ISD system
Unique challenge(s): Active business, Ecologically sensitive area, Under structure
Site Summary
An operating manufacturing plant, a sensitive receptor (stream), and limited remediation runtime created unique challenges to remediate TCE-impacted groundwater with concentrations as high as 54,900 µg/L. The chosen solution was ERD using groundwater recirculation. After 18 months of runtime, 98% reductions were observed, and successful site closure was achieved.
Site conditions and remedial goal
A release of 110 gallons of trichloroethene (TCE) was documented on the upgradient side of a manufacturing plan still in operation, while suspected releases may have occurred within the building footprint near a parts washer during decades of use.
The total impacted groundwater area spanned 15,000 square feet, with the highest groundwater concentration of TCE being 54,900 µg/L. Negligible Enhanced Reductive Dechlorination (ERD) was occurring naturally, as evidenced by low cis-1,2-DCE and vinyl chloride concentrations. Redox conditions at the site were oxidative (>100 mV) prior to the ERD activities.
ETEC Solution
To treat the groundwater plume beneath the building footprint, 10,300 lbs. of CarBstrate, a soluble, nutrient-amended substrate (carbohydrate-based), was distributed using consistent groundwater recirculation. A 10-gpm ISD In-Situ Delivery system was used to control the extraction and injection. An SVE system was also operated continuously to remove any TCE from the vadose soil.
To minimize operational disruptions, only seven vertical injection wells and five vertical extraction wells were used for the groundwater recirculation activity. Remediation wells were strategically placed to avoid disrupting business activities. Three separate groundwater recirculation cells were created to better control the distribution of the soluble substrate. Conveyance piping was not winterized, so active remediation was restricted to the summer months at a rate of approximately 5-gpm. A total of 4.5 million gallons of groundwater was recirculated. The active groundwater remediation occurred over three summers, spanning less than 18 months in total.
Remedial outcome
Negative redox conditions sitewide were created within 6 months of operation. A 98% reduction of chlorinated solvents was achieved sitewide. NFA was received for the site.
