Volume 56, Issue 2 p. 317-336
Case Study/

Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix

by Allen M. Shapiro

Corresponding Author

Allen M. Shapiro

Corresponding author: U.S. Geological Survey, 12201 Sunrise Valley Drive, Mail Stop 431, Reston, VA 20192; 703-648-5884; fax: 703-648-5832; [email protected]Search for more papers by this author
Claire R. Tiedeman

Claire R. Tiedeman

U.S. Geological Survey, Menlo Park, CA 94025

Search for more papers by this author
Thomas E. Imbrigiotta

Thomas E. Imbrigiotta

U.S. Geological Survey, Lawrenceville, NJ 08648

Search for more papers by this author
Daniel J. Goode

Daniel J. Goode

U.S. Geological Survey, Lawrenceville, NJ 08648

Search for more papers by this author
Paul A. Hsieh

Paul A. Hsieh

U.S. Geological Survey, Menlo Park, CA 94025

Search for more papers by this author
Pierre J. Lacombe

Pierre J. Lacombe

U.S. Geological Survey, Lawrenceville, NJ 08648

Search for more papers by this author
Mary F. DeFlaun

Mary F. DeFlaun

Geosyntec Consultants, Princeton, NJ 08628

Search for more papers by this author
Scott R. Drew

Scott R. Drew

Geosyntec Consultants, Princeton, NJ 08628

Search for more papers by this author
Gary P. Curtis

Gary P. Curtis

U.S. Geological Survey, Menlo Park, CA 94025

Search for more papers by this author
First published: 05 September 2017
Citations: 12
Article impact statement: Chloroethene mobilization from the rock matrix after bioremediation in a sedimentary rock is quantified using groundwater fluxes.

Abstract

A mass balance is formulated to evaluate the mobilization of chlorinated ethene compounds (CE) from the rock matrix of a fractured mudstone aquifer under pre- and postbioremediation conditions. The analysis relies on a sparse number of monitoring locations and is constrained by a detailed description of the groundwater flow regime. Groundwater flow modeling developed under the site characterization identified groundwater fluxes to formulate the CE mass balance in the rock volume exposed to the injected remediation amendments. Differences in the CE fluxes into and out of the rock volume identify the total CE mobilized from diffusion, desorption, and nonaqueous phase liquid dissolution under pre- and postinjection conditions. The initial CE mass in the rock matrix prior to remediation is estimated using analyses of CE in rock core. The CE mass mobilized per year under preinjection conditions is small relative to the total CE mass in the rock, indicating that current pump-and-treat and natural attenuation conditions are likely to require hundreds of years to achieve groundwater concentrations that meet regulatory guidelines. The postinjection CE mobilization rate increased by approximately an order of magnitude over the 5 years of monitoring after the amendment injection. This rate is likely to decrease and additional remediation applications over several decades would still be needed to reduce CE mass in the rock matrix to levels where groundwater concentrations in fractures achieve regulatory standards.