µg/L

In Situ Chemical Reduction of Hexavalent Chromium in Soils and Groundwater Using Ferrous Sulfide (FeS)

NanotechnologyRichard H. Christensen, PhD, LPG Indianapolis, INSteven R. IrvinJim V. Rouse (MWH)

Site Location -- Muncie, IN

Source Areas

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Chrome Platingat its best!

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Site OverviewSite Conditions

First investigation – 2005

AcuityES - 2008

Status:Equipment DeconnedBuilding Demolished

FOLLOWING SLIDES- GEOLOGY- HYDROGEOLOGY- REMEDIAL APPROACH- RESULTS

A’

A

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Geology

FORMER BASEMENT

SOURCE AREA

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Hydrogeology

Unconfined Aquifer

Sands & fine gravels

Static Water at 15’ bgl

Saturated thickness5’ in SE to

> 25’ in NW

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Soil Impacts

Two Adjacent Source Areas5,400 cubic yards of impactPerched water sand stringers

Max Cr+6 concentration:7,900,000 µg/Kg

3,600,000 µg/Kg Cr+6 at 12’ bgl

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Groundwater Impacts

Groundwater CoCsCr+6, Sb, As, and Ni

On-SiteCr+6

800,000 µg/L

9,700,000 µg/L

66,000 sq ft PlumeOffsite Cr+6 at 58,800 µg/L

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Selected ISCR for Remediation Enhanced what was already occurring at Site

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Chemical Reductant – FeSBENCH TESTED

•Ferrous Sulfide

•CaSx

•Sodium Thiosulfate

•Sodium Metabisulfite

•Zero Valent Iron

•Organosulfates

SELECTED –FeS

Liquid suspension of 7% FeSFeS - With additional 2% free Sulfide

to simulate CaSx

Nanoscale: 98% crystals <5 microns

Cation (Iron) & Anion (sulfide) Reaction

4 H2O + Cr042-+ 3 Fe2- + 4 OH-

3 Fe(OH)3+ Cr(OH)3 (1)

17 H2O + 8 Cr042- + 3 HS-

3 S + 8 Cr(OH)3 + 12 OH- (2)

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In-Situ Soil Blending

Dual Axis Blender – 15’ PlungeTotal Area – 130’ x 110’

GPS Grid Network – 10’ x 10’Deep to 15’ & Shallow to 5’

Computerized Dosing

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In-Situ Soil Blending

Dual Axis Blender

FeS - 5% admix (15 gals/yd3)

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In-Situ Soil Blending

Thorough Mixing to 15’ BGL

Note: Cement barrier for uncompaction

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In-Situ Soil BlendingCompleted in 2 weeksTotal FeS = 78,300 gallonsSubsequent stabilization with aglime required

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Confirmation Sampling

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Groundwater Injections – FeS

THE NUMBERS

155 Inject Pts

15 ft ROI

3% by volume

25 gals / LF

6 wks complete

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Groundwater Injections

DifficultInjections

Boulder Fields

6’ caliche

Lodgement till

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GroundwaterInjections

FeS Injection Totes35,385 gallons injected

Rotosonic DrillingTop Down Injection – 5ft intervals

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Groundwater Injections

CommunitySensitivityRequired

ResidentialHours

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Preferential Flow Paths15 – 20’ bglSand Unit

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Preferential Flow Paths20 - 25’ bglSand Unit

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Pre-Treatment Cr+6

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1st Q Post-Treatment Cr+6

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2nd Q Post-Treatment Cr+6

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3rd Q Post-Treatment Cr+6

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On-Site Monitoring Wells - Cr+6

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Off-Site Monitoring Wells - Cr+6

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Summary of Cr+6 Reduction

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Pre-Treatment Antimony

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1st Q Post-Treatment Antimony

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2nd Q Post-Treatment Antimony

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3rd Q Post-Treatment Antimony

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Other Constituents of ConcernNickel – off-Site up to 4,100 µg/L

on-Site up to 50,000 µg/LSame footprint as AntimonyComplete 100% Reduction by 1st Quarter

Arsenic – Overall reduction in pervasiveness.Occurrence generally coincides with Cr+6

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Lessons Learned 1. Forced to use Rotosonic over direct push

- Budget for the unexpected

2. Chemical injection instead of GW recirculation- Can’t wear blinders when considering delivery

method options for chemicals

3. Agency onboard for the technology- Relationship, communication, education

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QUESTIONS?

Thank you!!

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