ISB and ISCO Pilot Testing and Full-Scale Remedy Design for VOC Impacted Groundwater in Shallow Bedrock

Omer J. Uppal, Paul McAndrew, Stewart H. Abrams, Daniel Yu, Jerry Zambrella, Matthew J. Ambrusch Langan Engineering & Environmental Services, Inc., 619 River Drive Center 1, Elmwood Park, NJ 07407

ABSTRACT In-situ bioremediation (ISB) and in-situ chemical oxidation (ISCO) pilot tests were performed to support a full-scale remedial design for the treatment of chlorinated volatile organic compounds (VOCs) impacted groundwater at a state-mandated cleanup program site located along the west side of the lower Hudson River in northeastern New Jersey. The soils and groundwater at the site are impacted with chlorinated VOCs, primarily tetrachloroethene (PCE), and its degradation daughter products (i.e., trichloroethene [TCE], cis-1,2-dichloroethene [cis-1,2-DCE], and vinyl chloride). Pilot testing activities were performed to evaluate enhanced reductive dechlorination via in-situ biostimulation and alkaline activated persulfate oxidation technologies for the treatment of VOC impacted groundwater in shallow fractured bedrock. Pilot testing activities were performed at the site in April 2012. The ISB and ISCO pilot tests were performed in two separate areas at the site. The ISB pilot testing activities included injection of approximately 1,250 pounds (lbs) of the electron-donor solution consisted of a water-soluble oil (EDS-ERTM) mixed with 2,385 gallons of potable water and 35 gallons of nutrients (NutimensTM) into the subsurface using ten shallow injection wells (i.e., wells up to approximately 25 feet deep) and subsequent post-injection groundwater monitoring. The ISCO pilot testing activities included injection of approximately 1,600 lbs of sodium persulfate oxidant mixed with 865 gallons of potable water and 700 lbs of sodium hydroxide (activator reagent) into the subsurface using one shallow injection well followed by post-injection groundwater monitoring. The ISB pilot test was successful in reducing the groundwater concentrations of PCE in the targeted areas by approximately 90%. Notably, the highest groundwater concentration of PCE in the targeted area was decreased significantly (from 1,500 micrograms per liter [µg/L] to non-detect) within two months after injection. Analytical results showed that aquifer conditions rapidly became more reducing and favorable for anaerobic biodegradation within the first month after injection. Prior to the ISB pilot test, an acclimated population of dechlorinating bacteria (e.g., Dehalococcoides spp.) and functional genes were present at the site, but was limited by the availability of carbon. Electron-donor and nutrients were injected in the groundwater to stimulate and facilitate the growth of indigenous microbial populations capable of sequential reductive dechlorination of site contaminants. The observed trend of declining PCE concentrations, water quality parameter measurements, and the presence of degradation products demonstrated that anaerobic biodegradation was notably enhanced as a result of the electron-donor and nutrients injection. The post-injection groundwater monitoring data collected approximately two months following the oxidant injection showed a decrease in PCE concentrations; however, the data from the subsequent post-injection sampling rounds performed from July through October 2012 indicated a significant increase in PCE concentrations to levels higher than the baseline sampling event. The observed increase in PCE concentrations after the oxidant injection suggests that VOCs mass in the shallow fractured bedrock was likely released and contributed to increased groundwater concentrations as a result of the injection activities. The presentation discusses the results of the pilot testing activities and how field-derived parameters were used to formulate an integrated full-scale remedial design strategy using ISB with ISCO to facilitate treatment of VOCs impacted groundwater in a cost-effective and sustainable manner.

• Targeted Areas: o Historic Source Area 2 – Three Injection Wells, ISB

Pilot Test o Historic Source Area 3 – Seven Injection Wells, ISB

Pilot Test o Historic Source Area 1 – One Injection Well, ISCO

Pilot Test

• ISB Injection Solution Composition: o ~ 1,250 lbs of the electron-donor solution

consisted of a water-soluble oil (EDS-ERTM) with 2,385 gallons of potable water

o ~ 35 gallons of nutrients (NutimensTM)

• ISCO Injection Solution Composition: o ~ 1,600 lbs of sodium persulfate oxidant mixed

with 865 gallons of potable water o ~ 700 lbs of sodium hydroxide (activator reagent)

PILOT TEST ACTIVITIES

• Approximately 90% reduction in groundwater PCE concentrations • Electron-donor and nutrients injection stimulated the growth of

dechlorinating bacteria (e.g., Dehalococcoides spp.). • Sequential Reductive Dechlorination Lines of Evidence:

o Declining VOC concentration trends o Water quality parameter measurements (anaerobic and

reducing conditions - decreasing DO and ORP levels) o Post-injection presence of degradation products

• VOC concentrations at the majority of wells have decreased to below the applicable NJDEP Groundwater Quality Criteria (GWQC), with the exception of 2-Butanon, a metabolic product of emulsified vegetable oil.

• 2-Butanone is expected to be consumed by microorganisms as carbon source.

ISB PILOT TEST FINDINGS

• Temporary decreases in groundwater PCE concentrations observed immediately following injection

• The July and October 2012 indicated a significant increase in PCE concentrations (Observed Rebound)

• VOC mass in the shallow fractured bedrock was likely released and contributed to increased groundwater concentrations as a result of the injection activities.

ISCO PILOT TEST FINDINGS

• Proposed Monitored Natural Attenuation (MNA) for the Historic Source Areas 2 and 3 • Proposed additional groundwater monitoring at the Historic Source Area 1 to evaluate if

supplemental injections would be beneficial

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