Anaerobic Bioremediation of Chlorinated Solvent DNAPL in Groundwater Stephen D. Richardson, Ph.D., P.E.; Jessica Keener, P.G.; M. Tony Lieberman, R.S.M. (Solutions-IES, Inc., Raleigh, NC) Kirsten M. Hiortdahl; Robert C. Borden, Ph.D., P.E. (North Carolina State University, Raleigh, NC) Adria Bodour, Ph.D. (Air Force Center for Engineering and the Environment [AFCEE], San Antonio, TX)

Introduction Source areas with DNAPLs are some of the

most difficult and expensive sites that

AFCEE must manage. DNAPLs generate a

disproportionately large component of

remediation costs and are major obstacles

for sites striving to achieve remedy-in-place.

Conventional DNAPL remediation technologies such as surfactant flushing, in situ

chemical oxidation, and thermal treatment are expensive, are often less effective than

desired, and are not consistent with AFCEE’s Green and Sustainable Remediation

initiatives. Anaerobic bioremediation has the potential to increase the effective solubility of

chlorinated solvents, resulting in more rapid bioremediation of DNAPL source areas.

Solubility enhancement factors of up to six times have been demonstrated for tetrachloro-

ethene (PCE) and trichloroethene (TCE) (Yang & McCarty, 2000; Sleep et al., 2006).

Several technical challenges can limit anaerobic bioremediation of PCE or TCE DNAPL:

(Source: UK Environment Agency, 2003)

Challenges of DNAPL Bioremediation

Scope of Work

Laboratory Column Studies Site Characterization Results

Conclusions & Going Forward

Literature Cited

Field Demonstration

► MIP data from boring SB-2 (a, b) and HPT data from boring HPT-2 (c)

► Analytical data from soil boring SB-11

► Site SS-36, Joint Base McGuire-Dix-Lakehurst

Air Force Base (Joint Base), New Jersey

► DNAPL must first dissolve in the aqueous phase for biodegradation to occur

► High chlorinated solvent concentrations can be toxic to dechlorinating bacteria

► Poor contact between the DNAPL source and injected electron donor

► Rapid dechlorination produces HCl, creating a sub-optimal pH for dechlorination

Demonstrate the bioremediation of PCE or TCE DNAPL by

injecting emulsified vegetable oil (EVO) formulated with an

alkaline pH buffer and a bioaugmentation culture

Objectives & Rationale

► Introduce buffered EVO product through the DNAPL zone

► Partition PCE or TCE into micro-EVO droplets o Higher surface area for greater bacterial growth & dissolution

o Reduced toxicity by PCE / TCE partitioning into EVO

► Integrated buffer neutralizes HCl where it is produced o Maintains pH in optimal range for dechlorination activity

► All bacterial requirements met at single location

Proposed Strategy + Emulsified Oil

Preliminary Lab Study

“Proof of Concept”

(NCSU)

Field Site Identification

& Characterization

Single Injection

Distribution Test

Field Demonstration &

Data Analysis

Column Design

► Four upflow 1-in. diameter, 5-ft long clear PVC columns

► Each packed with masonry sand

► 1 ml of neat PCE was injected above each column inlet

Treatments

► 1. Commercial EVO product (EOS® Remediation, LLC)

► 2. EVO formulation with 5% solid alkaline buffer

► Treatments bioaugmented with Dehalococcoides sp. (DHC)

► pH maintained between 6.5 and 8 (Eaddy, 2008) for the buffered EVO treatment

► Maximum PCE solubility enhancement factors of 4 to 5 observed

► Significant formation of cis-DCE observed; minor amounts of VC and ethene formed

Treatments

Injected

PCE Aqueous

Solubility

► Install 3-4 downgradient monitoring wells

► Inject buffered EVO throughout test area

► Perform long-term performance monitoring (as above)

Full-scale Demonstration (May 2012)

► Test area (30’ x 30’) and injection interval identified o Membrane Interface Probe (MIP)

o Hydraulic Profile Technology (HPT)

o Soil cores PCE, TCE analytical; soil pH and buffer capacity

Site Characterization (completed November 2011)

► Inject buffered EVO into center of test area (near SB-2) o Designed for approx. 5 ft radius of influence (ROI)

o Collect soil cores within ROI to confirm buffer distribution

o 1, 3, and 6 month performance monitoring at downgradient well

(e.g., cVOCs, geochemical indicators, DHC abundance)

Single Injection Distribution Test (December 2011) Approx. GW direction

► Eaddy, A. (2008). Scale-Up and Characterization of an Enrichment Culture for Bioaugmentation of the P-Area Chlorinated Ethene

Plume at the Savannah River Site. M.S. Thesis, Clemson University.

► Sleep, B.E. et al. (2006). Biological Enhancement of Tetrachloroethene Dissolution and Associated Microbial Community Changes,

Environ. Sci. Technol., 40:3623-3633.

► Yang, Y. & P.L. McCarty (2002). Comparison between Donor Substrates for Biologically Enhanced Tetrachloroethene DNAPL

Dissolution, Environ, Sci. Technol., 36:3400-3404.

► Injection of buffered EVO in laboratory columns resulted in 1) PCE DNAPL partitioning

into oil, 2) generation of PCE daughter products, and 3) optimal pH for dechlorination.

► A suitable test site at Joint Base was identified with significant TCE concentrations,

indicative of DNAPL presence

► A single injection test will be conducted in December 2011 to evaluate distribution of

alkaline buffer away from the injection point.

a b c

Depth (ft bgsground surface)

Analyte 16 18 20 22 24

TCE (mg/kg) 130 430 230 110 360

cis-DCE (mg/kg) 6.1 6.3 4.3 0.28 0.48

TOC (mg/kg) 570 3,800 4,600 6,400 7,400

pH 4.48 4.48 4.24 4.31 3.96

► MIP and HPT analyses of the test area identified: o A zone of significant VOC contamination between 13 to 25 ft below ground surface (bgs)

o Stratigraphy consisting mainly of silt and clayey silt

o A sand interval between 20 and 22 ft bgs, which could influence EVO distribution during injection.