At a glance
Location: Washington
Geology: Silty sand
Contaminant(s): BTEX, GRO
ETEC Solution(s): CBN, DO-IT system, PetroBac
Unique challenge(s): Ecologically sensitive area, Mixed contaminant types, Off-site
Site Summary
A costal former fuel site in Washington state was remediated to MCTA A goals for BTEX using bioremediation with groundwater recirculation. Despite free-product being present at the remediation startup, the recirculation system - along with dissolved oxygen, nitrate, nutrients, active hydrocarbon-degrading cultures, and rhamnolipids - resulted in 97% reduction in BTEX and 95% reduction in GRO.
Site conditions and remedial goal
At a former fueling facility in Washington, historical gasoline, diesel, and heating oil releases from ASTs onsite impacted soil and groundwater. Limited soil excavation was performed at the site. Free-product was present at remediation startup. The total impacted groundwater area measured 7,500 square feet, with the highest groundwater concentration of GRO & DRO combined being 74,470 µg/L. The groundwater gradient at the site was flat, causing the groundwater plume to extend in all directions, including off-site. The soil at the site consisted of sand and silty sand. The depth to water at the site varied seasonally, ranging from 1 to 5 feet bgs, with annual fluctuations to the extremes.
ETEC Solution
For the treatment of the groundwater plume residing both onsite and offsite, dissolved oxygen, nitrate, nutrients, active hydrocarbon-degrading cultures, and rhamnolipids were distributed using consistent groundwater recirculation. A 10-gpm DO-IT system was used to oxygenate the water and to control the extraction and injection. Activated carbon pretreatment was used prior to reinjection.
Due to the shallow depth to water at the site, horizontal injection trenches were used to apply the recirculated groundwater. The trenches were placed at approximately three to four feet bgs and were 15 feet in length. Five vertical extraction wells were used for extraction along the perimeter of the plume. MW-10 was later converted to an extraction well in the center of the impacted area.
Remedial outcome
Over 66 months, the DO-IT system recirculated:
- 7 million gallons of groundwater
- 2,600 lbs dissolved oxygen
- 29,200 lbs CBN nutrients containing 17,520 lbs nitrate
- 335 gallons hydrocarbon-degrading cultures
- 395 gallons rhamnolipids
The results included:
- 97% reduction in BTEX
- 95% reduction in GRO