08-27-2021

In-Situ Chemical Reduction And Enhanced Bioremediation

Technical Webinar

To Treat A Comingled TCE And Hexavalent Chrome Plume

Background/Objectives

Site groundwater was impacted by a TCE plume co-mingled with a Hexavalent Chromium
(Cr[VI]) plume. High Cr(VI) concentrations inhibit the biodegradation of TCE, complicating
remedies for mixed plumes. The selected remedy employed sequential applications of
In-situ Chemical Reduction (ISCR) with calcium polysulfide (CPS) to initially reduce Cr(VI)
concentrations followed by enhanced anaerobic bioaugmentation (EAB) and ISCR to
degrade TCE.

Approach/Activities

Calcium precipitation is common during CPS injections resulting in negative impacts to soil
permeability, injection equipment, well screens, and radius of influence. Our work focused on
bench-scale development of pH-adjusted CPS solution and field implementation of the CPS
solution to reduce unacceptable secondary impacts to soil permeability and groundwater
geochemistry. Subsequent EAB was combined with ferrous lactate ISCR to polish off residual
Cr(VI) concentrations.

Results/Lessons Learned

After the CPS injection, Cr(VI) concentrations within the injection area ranged from
non-detected to about 1 mg/L. Cr(VI) concentration rebound was not observed
3 years after injection. Three years after the ISCR/EAB injection, TCE and Cr(VI)
plumes continue to shrink and rebound has not occurred. Geochemistry continues
to remain in the pH neutral anoxic range conducive to biotic and abiotic degradation.

About The Presenter

Kristi Diller, PG, RG Kristi is a project geologist with Parsons specializing in in-situ groundwater remediation. She has more than 13 years of experience in environmental investigations and remediation for Federal and industrial clients.

About The Presenter

Jim Leu, Ph.D., PE, LEED AP, QSD, QSP Jim has more than 30 years of experience designing, managing, directing, and executing soil and groundwater investigation and remediation projects. He is a Parsons Fellow and senior project manager.

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