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Scientific Investigations Report 2009–5239

Prepared in cooperation with the Naval Facilities Engineering Command Southeast

Groundwater Hydrology and Chemistry in and near an Emulsified Vegetable-Oil Injection Zone, Solid Waste Management Unit 17, Naval Weapons Station Charleston, North Charleston, South Carolina, 2004–2009

By Don A. Vroblesky, Matthew D. Petkewich, Mark A. Lowery, Kevin J. Conlon, and Clifton C. Casey

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ABSTRACT

The U.S. Geological Survey and the Naval Facilities Engineering Command Southeast investigated the hydrology and groundwater chemistry in the vicinity of an emulsified vegetable-oil injection zone at Solid Waste Management Unit (SWMU) 17, Naval Weapons Station Charleston, North Charleston, South Carolina. In May 2004, Solutions-IES initiated a Phase-I pilot-scale treatability study at SWMU17 involving the injection of an edible oil emulsion into the aquifer near wells 17PS-01, 17PS-02, and 17PS-03 to treat chlorinated solvents. The Phase-I injection of emulsified vegetable oil resulted in dechlorination of trichloroethene (TCE) to cis-1,2-dichloroethene (cDCE), but the dechlorination activity appeared to stall at cDCE, with little further dechlorination of cDCE to vinyl chloride (VC) or to ethene. The purpose of the present investigation was to examine the groundwater hydrology and chemistry in and near the injection zone to gain a better understanding of the apparent remediation stall. It is unlikely that the remediation stall was due to the lack of an appropriate microbial community because groundwater samples showed the presence of Dehalococcoides species (sp.) and suitable enyzmes. The probable causes of the stall were heterogeneous distribution of the injectate and development of low-pH conditions in the injection area. Because groundwater pH values in the injection area were below the range considered optimum for dechlorination activity, a series of tests was done to examine the effect on dechlorination of increasing the pH within well 17PS-02. During and following the in-well pH-adjustment tests, VC concentrations gradually increased in some wells in the injection zone that were not part of the in-well pH-adjustment tests. These data possibly reflect a gradual microbial acclimation to the low-pH conditions produced by the injection. In contrast, a distinct increase in VC concentration was observed in well 17PS-02 following the in-well pH increase. Adjustment of the pH to near-neutral values in well 17PS-02 may have made that well relatively favorable to VC production compared with much of the rest of the injection zone, possibly accounting for acceleration of VC production at that well. Following a Phase-II injection in which Solutions-IES, Inc., injected pH-buffered emulsified vegetable oil with an improved efficiency injection approach, 1,1-dichloroethene, TCE, and cDCE rapidly decreased in concentration and are now (2009) undetectable in the injection zone, with the exception of a low concentration (43 micrograms per liter, August 2009) of cDCE in well 17PS-01. In August 2009, VC was still present in groundwater at the test wells in concentrations ranging from 150 to 640 micrograms per liter. The Phase-II injection, however, appears to have locally decreased aquifer permeability, possibly resulting in movement of contamination around, rather than through, the treatment area.

First posted January 21, 2010

For additional information contact:
Director
USGS South Carolina Water Science Center
720 Gracern Road, Suite 129
Columbia, SC 29210
http://sc.water.usgs.gov/

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Suggested citation:

Vroblesky, D.A., Petkewich, M.D., Lowery, M.A., Conlon, K.J., and Casey, C.C., 2010, Groundwater hydrology and chemistry in and near an emulsified vegetable-oil injection zone, Solid Waste Management Unit 17, Naval Weapons Station Charleston, North Charleston, South Carolina, 2004–2009: U.S. Geological Survey Scientific Investigations Report 2009–5239, 31 p.



Contents

Abstract

Introduction

Purpose and Scope

Methodology

Groundwater Hydrology

Groundwater Chemistry

Aquifer Terminal Electron-Accepting Processes

Groundwater and In-Well pH

Contributing Factors Affecting the Stall in Dechlorination Activity Following the Phase-I Emulsified Vegetable-Oil Injection

Recent Data on Contaminants and Water Movement in and near the Injection Zone

Summary and Conclusions

References Cited

Appendixes


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