Theme: 01. Remediation Technology Innovations

Topic Area: 01a. Abiotic and In Situ Biogeochemical Processes: Applications and Lessons Learned

Formatted Title:

Enhanced Reductive Dechlorination with Intentional Overdosing to Support Limited Site Accessibility and Dosage Longevity

Background/Objectives:

Historical dry cleaners located within a busy commercial strip mall located in Northern New Jersey contained soil and groundwater contamination consisting of chlorinated volatile organic compounds (cVOCs) with primary contaminant of concern, tetrachloroethene (PCE), with a downgradient cVOC plume encompassing the congested parking lot. Site PCE concentrations within the known source area (front entrance) exceed 17,000 micrograms per liter (µg/L), with downgradient concentrations exceeding 250 µg/L. Site soils consist of varying tight sandy silts with high organics. An additional source area was suspected within the dry cleaner’s boundary; however, due to the current operations, further delineation was unfeasible and injection accessibility was only available within the known source area located at the front entrance of the cleaners and highly active parking lot, making future accessibility limited. The remedial design accounted for these considerations, and dosage longevity was determined to be paramount.

The remedial goal is to significantly reduce Site cVOC mass and facilitate reductive conditions throughout the plume to support mass destruction and consistent downward concentration trends.

Approach/Activities:

Enhanced reductive dechlorination (ERD) was the chosen remedial application utilizing small droplet emulsified vegetable oil (EVO), micro - zero valent iron (ZVI), and bioaugmentation inoculum. The remedial design encompassed a total of thirty (30) temporary injection points, installed via a track mounted direct push rig. The temporary injection points would be oriented within two downgradient barrier arrays (BAs), source area treatment and an upgradient BA to address residual delineation gaps within the source interior. Each injection point was installed via direct push in a bottom-up method, targeting a 5- to 20-foot below ground surface (bgs) treatment interval. Each treatment interval received the prescribed remedial amendments, followed by anerobic chase water with bioaugmentation inoculum.

A key project goal was to implement as few injection events as practical while reaching the remedial objectives. Injection sequence and scheduling was crucial to maintaining remedial efficiency. Chemical deliveries and injection logistics were coordinated by the consultant and subcontractor, ensuring parking spots were closed for designated days, drill rig access to the source interior (cleaners), and maintaining vehicle and pedestrian traffic control. An injection manifold was utilized to reduce oversaturation of the subsurface, improve injection productivity and reduce surfacing of remedial material.

Results/Lessons Learned:

In total approximately 7,500-gallons of diluted EVO and ZVI and 20 liters of bioaugmentation inoculum was injected into the subsurface throughout the injection event. Lower than anticipated injection flow rates were attributable to the below average freezing temperatures, tight formation acceptance and reagent daylighting.

Based on three (3) quarters of analytical data, total cVOC reduction rates compared to baseline samples are 99.6%. Based on Q3 analytical data, a slight spike of vinyl chloride (VC) has been observed; however, this is attributed to the rapid methanogenesis occurring within the highly reductive subsurface.

Additionally, an elevated spike in methyl ethyl ketone (MEK) has been observed and is being attributed to low transmissivity within the formational materials and the designed amendment overdose implemented based on the Site access constraints, accessibility, soil organics and data gap assumptions. However, these spikes are expected to be temporary based on the rapid methanogenesis occurring within the highly reductive subsurface and are being monitored accordingly by the consultant.

Kassandra Lacerda

Affiliation

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(Group 2, Poster Board #188) Enhanced Reductive Dechlorination with Intentional Overdosing to Support Limited Site Accessibility and Dosage Longevity