# Presentation: 577605

## Permeable Reactive Barriers for Inorganic Contaminants and Treatment of Acid Rock Drainage

**	**

- USEPA Scientist - to - Scientist MeetingLas Vegas, NevadaJune 14 - 15, 2000
**Robert W., Ph.D. ****U.S. EPA, National Risk Management Research Laboratory, ****Ada, Oklahoma**

## What?

**	****A Permeable Reactive Barrier (PRB):**
**A permeable zone creating a reactive treatment area oriented to intercept and remediate a contaminant plume **
**Removes contaminants from groundwater flow system by physical, chemical, or biological processes**

## Why Use a PRB?

**Treatment occurs in the subsurface**
**Treatment is passive**
**Lower costs than conventional methods**
**Allows full economic use of a property**
**Robust**
**Monitoring can be focused**

## PERMEABLE REACTIVE BARRIERS (PRBs)

**Notes:**
Notes:

An in situ permeable reactive wall is installed downgradient of a groundwater containment plume.  The wall will intercept and react with contaminated groundwater.  The process represents a low-cost, low-maintenance, remedial alternative for groundwater treatment.

The barrier material consists of a reactive medium that will degrade or retain the containment plume.  Construction specifications for the barrier are based on the retention time required for specific contaminants.

Some reactive walls containing zero valent iron have been used to dechlorinate solvents dissolved in groundwater such as trichloroethylene and dichloroethylene.

## Permeable Reactive Barriers for In-Situ Remediation of Inorganic Contaminants 

**Task 1061 Inhouse Project - PRB for Cr and TCE - Elizabeth City Full-Scale PRB for a mixed waste plume. **
**WA SF - 1 - 4 - PRB for Nitrate and Arsenic Contaminated Groud Water**
**Task 5851  Inhouse Project - PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants **

## Elizabeth City PRB Site

- United States Coast Guard
- Support Center
- Elizabeth City, North Carolina

**North Carolina**

- Elizabeth City

- Vicinity Map

- 0

- STATUTE MILES

- 1

- 2

- 3

- 4

**Nixonton**

- TCE / Chromium Plume Site
- United States Coast Guard
- Support Center, Elizabeth City

**Weeksville**

**Hospital**

**Elizabeth City**

**U.S.C.G.**
**Support Center,**
**Elizabeth City**

**Pasquotank**
**River**

**17**

**156**

**20**

**158**

**343**

**168**

**34**

**17**

- N

## Elizabeth City Site Plan View 

**Fe Fence**

**Hanging Iron Wall**
**Full Scale**
**Demonstration**

- Approximate extent

- of chromium contamination

- in shallow groundwater

- ,

- dashed where inferred

- Approximate location

- of former chromic acid tank

- TCE

- Plume

- Axis

- MW

-  13

- MW52

- MW

-  48

- MW

-  38

- MW

-  18

- Approximate Scale in Feet

- 30’

- 20’

- 10’

- 0

- 30’

- Asphalt Pavement

**12**

**2**

**1**

**8**

**10**

**5**

**1**

**1**

**9**

**4**

**3**

- Pasquotank River

- 1790

- RX core location

- Multi-layer sampler

- Compliance

- monitoring well

- LEGEND

**N**

- MW46

- MW35D

- MW47

- MW51

- MW50

- MW49

## USEPA - USCG Full-Scale       Demonstration Results

**First site to use continuous wall design**
**more cost effective than funnel & gate**
**more efficient at plume capture**
**After 4 years continues to meet remedial objectives (MCL’s)**
**No evidence of decrease in performance**
**First wall to remediate both chlorinated solvents and chromium**

## US EPA -  USCG  Full-Scale Demonstration Results (cont)

**Most intensively monitored PRB in the world**
**Continues to serve as foundation for follow-on research efforts**
**Final Report completed Sep 1999 available from CERI, Kerr lab,internet @ www.epa.gov/ada/kerrcenter.html**

## PRB’s for Nitrate -  Project Status

**Work on nitrate complete**
**Work on arsenic to continue **
**column tests**
**other reactive media**
**more basic studies to explore surface reactions**

## Objectives - PRB’s for Nitrate

**To evaluate nitrate reduction kinetics in zero-valent iron media**
**To study nitrate transformation in organic compost media**
**To evaluate the potential use of iron and organic compost as permeable reactive barrier materials for in situ remediation of nitrate in groundwater**
**To derive mechanisms of nitrate degradation**

## Conclusions - PRB’s for Nitrate

**Nitrate removal via biological denitrification in compost was more rapid than abiotic reduction in the zero-valent iron media**
**Nitrate reduction and transformation in compost media was predominantly a biotic process **
**Zero-valent iron may be useful for in situ remediation of nitrate in groundwater only when the denitrification conditions are not favorable **
**Technology transfer interest**

## Objectives - PRB’s for Arsenic

**To evaluate removal kinetics of arsenate and arsenite in the zero-valent iron media and iron oxides media**
**To evaluate the potential use of iron and iron oxides as permeable reactive barrier materials for in situ arsenic remediation in groundwater**
**To derive mechanisms of arsenic interaction with the permeable reactive barrier media**

## Anion Effect on As Removal by Feo

**Sulfate at 0.001 M did not affect arsenate removal by Peerless Fe****o**** compared to 0.01 M NaCl**
**Phosphate at 0.001 M significantly reduced the rate of arsenate removal by Peerless Fe****o**** compared to 0.01 M NaCl **
**Other anions that may affect As removal are being tested including nitrate, carbonate, borate, molybdate, and chromate. Both As(V) and As(III) will be tested further.**

##  Removal of As by Metal Oxides

**On a mass basis, goethite was the most effective sorbent**
**All the added As(III) in the birnessite suspension was oxidized to As(V) that resulted in the almost identical sorption envelopes for both added As(V) and As(III)**
**As(III) was oxidized significantly to As(V) in the magnetite and hematite suspensions at pH > 6. Minor amounts of manganese dioxide present in the Fe oxides might be responsible for the oxidation**

## Conclusions -  PRB’s for Arsenic

**All the zero-valent iron samples and iron oxides showed effective removal of both As(V) and As(III) from water**
**Surface adsorption was likely the major process of As removal (at least initially)**
**Arsenic redox reactions seem occur at the surface of iron and iron oxides following adsorption**
**Phosphate inhibited As sorption with sulfate showing no effect**
**Field testing initiated in April, 2000**

## PRB Strategies and Performance Monitoring for Remediation of Inorganic Contaminants Task 5851 (Wilkin, Puls)

**Sub tasks:**
**Long-term performance monitoring**
**AMD strategies**
**Remediation of As-contaminated GW**

## Objectives: AMD Strategies

**Evaluate metal removal rate and neutralization rate of AMD using:**
**Fe° mixtures w/**
**Clinoptilolite (natural zeolite)**
**Ca sulfide, compost**
**Carbonate**
**Steel slag**
**Evaluate metal uptake mechanisms**

## Status

**Batch and Column studies in progress**
**Synthetic AMD solution**
**pH 2.3, Fe, Al, As, Cu, Cd, Zn, Pb, Co, Ni**
**Connelly Iron, Fisher Iron**
**Zero-valent iron is useful for in situ remediation of AMD but other components required for iron removal**
**Sorption to both Fe metal/Fe-O coatings and “free” precipitates**

## SummaryNRMRL/SPRD Research on PRB’s

**Leader in PRB research, development, training and technology transfer**
**InHouse research focus has been on inorganic contaminants**
**Mining problems naturally fit under SPRD-led NRMRL Ecosystem Restoration Program**
**PRB’s likely component of large-scale remedial measures for mine wastes**

## PRB Strategies and Performance Monitoring for Remediation of Inorganic ContaminantsTask 5851 (Wilkin, Puls) 

- Sub tasks:
- 	Long-term performance monitoring
- 	AMD strategies
- 	Remediation of As-contaminated GW

## Objectives: AMD Strategies

**Evaluate metal removal rate and neutralization rate of AMD using:**
**Fe° mixtures w/**
**Clinoptilolite (natural zeolite)**
**Ca sulfide, compost**
**Carbonate**
**Steel slag**
**Evalaute metal uptake mechanisms**

## Status

**Batch and Column studies in progress**
**Synthetic AMD solution**
**pH 2.3, Fe, Al, As, Cu, Cd, Zn, Pb, Co, Ni**
**Connelly Iron, Fisher Iron**
**Zero-valent iron is useful for in-situ remediation of AMD but other components required for iron removal**
**Sorption to both Fe metal/Fe-O coatings and “free” precipitates**
**Secondary ppt problem**

## EPA/ITRC/RTDF Permeable Reactive Barrier Short Course

**David Blowes, Ph.D., (University of Waterloo, Waterloo, Canada**

**EPA/ITRC/RTDF ****Permeable Reactive Barrier Short Course**

## Acid Mine Drainage and Sulfate Reduction

## Wall Reactions of Interest

**SO****4****2-**** + 2CH****2****O **** H****2****S + 2HCO****3****-**
**Me****2+**** + H****2****S **** MeS****(s)**** + 2H****+**

## Nickel Rim Site, Canada

**Sulfate****	****	****	****	****2000 - 4000 mg/L**
**Iron****	****	****	****	****200 - 1200 mg/L**
**pH****	****	****	****	****	****slightly acidic (pH < 6)**
**Alkalinity****	****	****	****c. 50 mg/L**
**Reactive mixture****	****	****compost, limestone**

## Results:  Nickel Rim Site, Canada

**The reactive wall is removing >95% of the dissolved iron**
**Water exiting the wall has changed from acid producing to acid consuming**
**Sulfate significantly reduced**

## Cost:  Nickel Rim Site, Canada

**Size****	****	****	****	****15 x 8 (4 + 4) x 4 m**
**Materials****	****	****	****$15,400**
**Installation****	****	****	****$15,500**
**Site Restoration****	****	****$1,300**
**Total****	****	****	****	****$32,200 (Cdn$)**