Project Abstract

Remediation of Chlorinated Solvents at the Bachman Road Site Using Innovative Technologies: Microbial Halorespiration and Surfactant-Enhanced Aquifer Remediation

Principal Investigators

Peter Adriaens, Babu Z. Fathepure, Linda M. Abriola, and Kim F. Hayes
University of Michigan
E-mail: adriaens@engin.umich.edu

James M. Tiedje, Frank E. Loffler, and Shannon J. Flynn
Michigan State University
E-mail: tiedjej@pilot.msu.edu

Kurt D. Pennell
Georgia Institute of Technology
E-mail: kurt.pennell@ce.gatech.edu

Introduction

Groundwater at the Bachman Road Residential Wells site (Oscoda, Michigan) is contaminated predominantly with tetrachloroethene (PCE) and trichloroethene (TCE), presumably orginating from former and current drycleaning operations. A remedial investigation identified two chlorinated solvents plumes:

plume A (the northern-most plume) contains PCE and TCE at concentrations of 4,200 and 2,300 microns g/L, respectively, as well as low concentrations of cis- and trans- DCE, indicative of intrinsic dechlorination activity;
plume B contains chlorinated solvents and elevated PCE concentrations of up to 18,000 microns g/L.

Though no free product has been demonstrtated upon repeated sampling, the concentrations found near the source areas of plumes A and B may be indicative of residual non-aqueous phase liquid (NAPL). Whereas a pump-and-treat system has been recommeded to remediate the site, its implementation will depend on the outcome of the current evaluation of innovative in situ methods to remediate the source and dissolved plume regions.

Study Objectives

The overall goal of phase I is to investigate and evaluate the feasability of surfactant enhanced aquifer remediation (SEAR) of the source area of the contamination, and of stimulating halorespiration to remediate the dissolved contaminant plume. Halorespiration is a respiratory process whereby microorganisms conserve metabolic energy from reductive dechlorination of chlorinated compounds, and is a much superior microbial process over cometabolic dechlorinations.

Site Characterization

Initially reports from previous field studies conducted by several environmental consultants at the site were assembled and reviewed to develop a sampling strategy for source characterization. A number of groundwater samples were collected at the Bachman site from locations surrounding the former N.S.I. dry cleaners (the suspected origin of plume B). The highest PCE concentrations were found at sampling points located in the parking lot directly in front of the building, suggesting that the entrapped PCE may lie beneath the building.

Laboratory Studies

Laboratory studies are being conducted to gain valuable and necessary information on the soil properties at the Bachman site, to study and evaluate surfactant/soil and surfactant/PCE interactions, and to study the potential influence of field heterogeneities on SEAR performance.

Initial surfactant screening studies have been completed. Selected solubilizing and mobilizing surfactants are being combined with PCE to examine the potential for macro-emulsion formation. Preliminary investigations into the use of additives to dissipate these emulsions have also been performed.

Batch microcosms and continuously-fed columns were constructed using aquifer solids collected near monitoring well 6/6A. Initial screening studies have evaluated the potential of native microorganisms to dechlorinated PCE, TCE, cis-DCE, or VC added as electron acceptor and amended with a variety of electron donors.

Fresh coring was done in the vicinity of monitoring well 6/6A and new microcosms were established to confirm the presence of halorespiring bacteria. Microcosms were constructed from the aquifer solids that was repeatedly washed with phosphate buffer to remove any dissolved alternative electron acceptors such as nitrate, sulfate, and bicarbonate. These and other experiments have clearly demonstrated the presence of halorespiring organisms at the Bachman aquifer.

Mathematical Modeling

Mathematical simulators can provide a capability for the prediction and evaluation of SEAR performance in the field setting. Two simulators will be used for surfactant performance prediction and assessment. The first, MSURF2D, was developed at the University of Michigan to simulate rate-limited surfactant solubilization in heterogeneous formations. The second simulator, UTCHEM, was developed at the University of Texas for oil recovery applications. The latest version of this code has been obtained and is being installed onto the University of Michigan computer system and benchmarked for numerical verification.