Retardance of Rainwater-Retardance of Rainwater-Leached Metals in Amended Leached Metals in Amended

Soil Systems:Soil Systems:

A Case Study A Case Study

John D. Harden, P.G., Ph.D.John D. Harden, P.G., Ph.D.Robert E. Pitt, P.E., Ph.D., BCEE, D.WRERobert E. Pitt, P.E., Ph.D., BCEE, D.WRE

Department of Civil, Construction & Environmental Department of Civil, Construction & Environmental EngineeringEngineering

The University of AlabamaThe University of AlabamaTuscaloosa, AlabamaTuscaloosa, Alabama

Presentation OverviewPresentation Overview

Goal and Scope of ResearchGoal and Scope of Research BackgroundBackground Ash and Soil ClassificationAsh and Soil Classification Batch StudiesBatch Studies Column StudiesColumn Studies ConclusionsConclusions Future WorkFuture Work

Research GoalResearch Goal

Identify a readily available agricultural Identify a readily available agricultural soil amendment to reduce the mobility soil amendment to reduce the mobility

of metals at Chromated Copper of metals at Chromated Copper Arsenate (CCA)-treated wood burn sites.Arsenate (CCA)-treated wood burn sites.

Iron sulfate, agricultural lime, and gypsum Iron sulfate, agricultural lime, and gypsum were studied. The results for gypsum were studied. The results for gypsum

(CaSO(CaSO44·2H·2H22O) are presented. O) are presented.

Scope of ResearchScope of Research

What are the potential environmental What are the potential environmental effects on soil and water resulting effects on soil and water resulting from the burning of CCA-wood?from the burning of CCA-wood?– What is the composition of the ash?What is the composition of the ash?– What is the fate of the ash in soil?What is the fate of the ash in soil?– How effectively are metals leached from How effectively are metals leached from

the soil/ash by rainwater?the soil/ash by rainwater?

Can the leaching rates be reduced by Can the leaching rates be reduced by the addition of soil amendments?the addition of soil amendments?

BackgroundBackgroundWhat is CCA?What is CCA?

Chromated Copper Arsenate (CCA) Chromated Copper Arsenate (CCA) wood preservativewood preservative

Designed for the humid Southeastern Designed for the humid Southeastern U.S. where wood is prone to insect and U.S. where wood is prone to insect and fungal attack fungal attack – CuCu - serves as a fungicide - serves as a fungicide– AsAs - serves as an insecticide - serves as an insecticide– CrCr - a fixing agent for bonding Cu & As - a fixing agent for bonding Cu & As

to woodto wood

Used in residential-use wood until 2004Used in residential-use wood until 2004

Very large amounts of wood were Very large amounts of wood were treatedtreated

Pictures: www.google.com/search?q=pictures+of+CCA+wood

Statistics on CCA Production Statistics on CCA Production ~1lb CCA preservative/3 ft~1lb CCA preservative/3 ft33 treated wood treated wood

1997: 450 x 101997: 450 x 1066 ft ft33 of CCA-wood products of CCA-wood products

Service life of CCA-wood 20-50 yearsService life of CCA-wood 20-50 years

CCA-treated wood waste will increase fromCCA-treated wood waste will increase from 5 to 32 x 105 to 32 x 1066 ft ft33/yr by 2015/yr by 2015

AsAs in CCA-wood waste: 31,000 metric tons in CCA-wood waste: 31,000 metric tons introduced into Florida environment over the introduced into Florida environment over the past 30 yearspast 30 years

Burning of waste/old CCA-treated wood has Burning of waste/old CCA-treated wood has been common practicebeen common practice

Metal Species in Metal Species in CCA-Wood/AshCCA-Wood/Ash

NameName

SymbolSymbol

OxidatioOxidationn

StateState

Cation/Cation/

AnionAnionSpeciesSpecies CharacteristicsCharacteristics

CopperCopper

CuCuCu(II)Cu(II) CationCation

CuCu+2+2

CuOHCuOH++

CuCu22(OH)(OH)44--

varying toxicityvarying toxicity

varying solubilityvarying solubility

varying mobilityvarying mobility

ChromiuChromiumm

CrCr

Cr(III)Cr(III) AnionAnionCr HydroxidesCr Hydroxides

Cr(OH)Cr(OH)44--

less toxicless toxicless solubleless solubleless mobileless mobile

Cr(VI)Cr(VI) AnionAnion

ChromateChromate

CrOCrO44-2-2

DichromateDichromate

CrCr22OO77-2-2

more toxicmore toxicmore solublemore solublemore mobilemore mobile

ArsenicArsenic

AsAs

As(III)As(III) AnionAnionArseniteArsenite

AsOAsO33-3-3

more toxic (25-60 more toxic (25-60 times)times)

more solublemore solublemore mobilemore mobile

As(V)As(V) AnionAnionArsenateArsenate

AsOAsO44-3-3

less toxicless toxicless solubleless solubleless mobileless mobile

Investigations to Quantify Investigations to Quantify Metals and Evaluate MobilityMetals and Evaluate Mobility

Produce ash & Quantify metals in CCA-ashProduce ash & Quantify metals in CCA-ash

How mobile are the metals?How mobile are the metals?– Batch Leaching ExperimentsBatch Leaching Experiments

Accelerated leach studiesAccelerated leach studies Regulatory classification of CCA-ashRegulatory classification of CCA-ash Leaching of CCA-ash & a soil/CCA-ash mixtureLeaching of CCA-ash & a soil/CCA-ash mixture Potential contamination of water by CCA-metalsPotential contamination of water by CCA-metals

Effect of CaSOEffect of CaSO44 on metals mobility on metals mobility– Optimization StudyOptimization Study

Column Leaching ExperimentsColumn Leaching Experiments Evaluate CaSOEvaluate CaSO44 performance versus natural soil performance versus natural soil Measure the pH range of the leach eventsMeasure the pH range of the leach events

Burn Site

Down-gradient 10’ & 16’

Sample pointsScale

1ft

Upgradient Sampling:

200’ (baseline) & 10’

CCA-metals at Burn SiteAs (12.2±1.2)Cr (17.4±1.4)Cu (14.5±0.5)

mg g-1 site soil ± 95% CI

LakeTuscaloosa

Sampling Points & CCA-Sampling Points & CCA-metals Concentration at metals Concentration at

Burn SiteBurn Site

Alabama

Burn Site

Soil & CCA-ash Soil & CCA-ash

Soils in US & Proportions of Major Adsorbed Cations on Surface Layers

Soil Order Typical location H+ and Al+3 Ca+2 Mg+2 K+ Na+

Oxisols Hawaii 85 10 3 2 trace

Spodosols New England 80 15 3 2 trace

Ultisols Southeast U.S. 65 25 6 3 1Alfisols PA to WI 45 35 13 5 2

Vertisols AL to TX 40 38 15 5 2

Mollisols Midwest U.S. 30 43 18 6 3

Aridisols Southwest U.S. 65 20 10 5

Adapted from Brady, 1990          

Cr, 76mg 33%

Cu, 86mg 37%

As, 70mg 30%

Total CCA-metals in 1g CCA-Total CCA-metals in 1g CCA-ashash

1000mg CCA-ash contains 232mg (23%) CCA-1000mg CCA-ash contains 232mg (23%) CCA-metalsmetals

Microwave digestion & ICP

CCA-metals

As Cu

Cr

Batch LeachingBatch Leaching

Establish preliminary leaching trends for column design

Metals Present and Metals Present and Leached from Soil/Ash Mixture (mg gLeached from Soil/Ash Mixture (mg g-1-1 & &

%)%)

0.01

0.1

1

10

100

1000

1 2 3 4

Mass % Leached

Log

Met

als

(mg

g-1

Ash

)

Total Metal (mg) Leached Metal (mg)

232

6.9

86

0.03

76

4.2

70

2.6

3.0% 0.03% 5.5% 3.7%

Cu Cr As

Leaching Trend : Cr>As>Cu

Regulatory Classification ofRegulatory Classification ofCCA-ash by RCRA-TCLPCCA-ash by RCRA-TCLP

As - Regulated Haz. Waste (RCRA) As - Regulated Haz. Waste (RCRA) TCLP Limit:TCLP Limit: 5.0 mg L 5.0 mg L-1-1 CCA-ash by TCLP: CCA-ash by TCLP: 578578±44.7 mg L±44.7 mg L-1-1

Cr - Regulated Haz. Waste (RCRA) Cr - Regulated Haz. Waste (RCRA) TCLP Limit Cr(VI): TCLP Limit Cr(VI): 5.0 mg L 5.0 mg L-1-1 CCA-ash Cr(VI+III) by TCLP:CCA-ash Cr(VI+III) by TCLP: 0.7190.719±0.057 mg L±0.057 mg L--

11

Cu - Not regulated under RCRACu - Not regulated under RCRA CCA-ash Cu by TCLP:CCA-ash Cu by TCLP: 6.726.72±0.713 mg ±0.713 mg

LL-1 -1

Results reported in mg LResults reported in mg L-1-1 ± 95% CI± 95% CI

Therefore CCA-ash is classified as a regulatedTherefore CCA-ash is classified as a regulated

RCRA Haz. WasteRCRA Haz. Waste due to Asdue to As

0.446

17.1

0.0290.010

4.23

0.369

2.60

10.1

1.02

0.0

0.1

1.0

10.0

100.0

1 2 3

Leach Samples

Log

Leac

hed

Met

al m

g g

-1 A

sh Cu LeachedCr LeachedAs Leached

Cu

As

Cr

Ash-Only Leach

Ash-Soil Leach

Ash-Soil Releach

Batch Leaching of Batch Leaching of CCA-ash & Soil/CCA-ash CCA-ash & Soil/CCA-ash

MixtureMixture

Therefore natural soil retards Cr & As mobilityTherefore natural soil retards Cr & As mobility

75% Lower

74% Lower

280% Higher

250% Decrease

1150% Decrease1550% Increase0.01

0.1

1.0

10

100

Potential Contamination of WaterPotential Contamination of Water by CCA-metals by CCA-metals

MetalMetal LeachedLeached (µg g(µg g-1-1ash)ash)

Regulatory Regulatory Level (µg LLevel (µg L--

11))L gL g-1-1 ash ash

CuCu 11301130 10*10* 113***113***

CrCr 29002900 100**100** 29***29***

AsAs 47004700 10**10** 469***469***

Batch Leach (5 Leachings)1.45 g CCA-ash, 8.25 g Test Soil, 465 mL Total Rainwater

* Cu based on toxicity to freshwater clams, Harrison, et al. 1984** SDWA-MCL*** Volume of Water Contaminated to Regulatory Level

CaSOCaSO44 Optimization Batch Optimization Batch StudyStudy

A 1:1 to 3:1 ratio of CaSO4:CCA-ash was acceptable

1.90

0.1640.0470.0470.023

1.77

2.53

3.213.11

1.241.57

2.83

0

1

2

3

4

-50 0 50 100 150 200 250 300 350 400 450

Gypsum Addition (mg)

Le

ac

he

d C

CA

-me

tal (m

g g

-1 C

CA

-

as

h)

Cu

Cr

As

1:1 4:1 16:1

ash

)

Column Leaching Column Leaching ObjectivesObjectives

Evaluation of CaSOEvaluation of CaSO44 performance performance

Accelerated leaching equivalent to annual rainfall at Accelerated leaching equivalent to annual rainfall at the burn sitethe burn site - 19 Rainfall events = 130 cm yr- 19 Rainfall events = 130 cm yr-1-1

Evaluation of metals leached mass determined for Evaluation of metals leached mass determined for each rainfall eventeach rainfall event

- 49 g CCA-ash, 68 g CaSO- 49 g CCA-ash, 68 g CaSO44, 231 g soil, 231 g soil - 1.6:1 Ratio of Ca- 1.6:1 Ratio of Ca+2+2 to CCA-metals to CCA-metals

Measure leachate pH for each rainfall eventMeasure leachate pH for each rainfall event - pH Range: 7.3 to 8.0- pH Range: 7.3 to 8.0

Mobility Reducing Mobility Reducing MechanismsMechanisms

Negative Surface Charge on Soil Particle

Inner-Sphere Complex

Outer-Sphere Complex Diffuse Ion

- - - - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - -

Soil/CCA-ash/CaSOSoil/CCA-ash/CaSO44 System System Ultisol SoilUltisol Soil

– Low Cation Exchange Capacity (CEC), 35% efficiencyLow Cation Exchange Capacity (CEC), 35% efficiency– Low to moderate Anion Exchange Capacity (AEC)Low to moderate Anion Exchange Capacity (AEC)

CCA-ashCCA-ash

– XO => X(OH)XO => X(OH)22 => XCO => XCO3 3 , where X = Ca, Mg, Cu, Cr, As, where X = Ca, Mg, Cu, Cr, As

General Mechanisms from CaSOGeneral Mechanisms from CaSO44 Amendment Amendment

– CaCa+2+2 replaces Al replaces Al+3+3, increases CEC efficiency, increases CEC efficiency

– Increased Al(OH)Increased Al(OH)33 and Cr(OH) and Cr(OH)33 precipitation precipitation

– Increased CaIncreased Ca+2+2 concentration and negative surface concentration and negative surface charge produces greater adsorption and coprecipitation charge produces greater adsorption and coprecipitation of As and Cr. Increased Cu mobility due to competition of As and Cr. Increased Cu mobility due to competition with Cawith Ca+2+2 for adsorption sites and increased mobility of for adsorption sites and increased mobility of Cu-bound organic compoundsCu-bound organic compounds

Accelerated One-Year Mass Leach of Accelerated One-Year Mass Leach of MetalsMetals

Accelerated One-Year Mass LeachAccelerated One-Year Mass LeachControl vs CaSOControl vs CaSO4 4

MetaMetall

CombinationCombination MassMass(mg g(mg g-1-1))

±± %%

AsAsControl Control 2.532.53

  -77%-77%CaSOCaSO44 0.5780.578

  

CrCrControlControl 4.314.31

  -72%-72%CaSOCaSO44 1.201.20

  

CuCuControl Control 0.0120.012

  400%400%CaSOCaSO44 0.0480.048

• CaSO4 reduces mobility of As by a further 77% and Cr by 72% over soil alone

• Cu mobility increases by a small mass compared to the large reduction in As and Cr mobility

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 500 1000 1500 2000

Cumulative Leach Volume (mL)

Lea

ched

Cr

mg

g-1

Ash

Control

CaSO4

Cr

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 500 1000 1500 2000

Cumulative Leach Volume (mL)

Leac

hed

As

mg

g-1

Ash

Control

CaSO4As

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0 500 1000 1500 2000

Cumulative Leach Volume (mL)

Lea

ched

Cu

mg

g-1

Ash

Control

CaSO4

Cu

ConclusionsConclusions Unamended soil retards leaching of As & Cr from Unamended soil retards leaching of As & Cr from

CCA-ash while increasing Cu mobilityCCA-ash while increasing Cu mobility

CaSOCaSO44 amendment of soil further reduces mobility amendment of soil further reduces mobility of As by 77% and Cr by 72%of As by 77% and Cr by 72%

Optimization study revealed 3:1 ratio of CaSOOptimization study revealed 3:1 ratio of CaSO44

to CCA-ash mass is recommendedto CCA-ash mass is recommended

A higher ratio of CaSOA higher ratio of CaSO44 to CCA-ash mass would to CCA-ash mass would serve as a continued source of Caserve as a continued source of Ca+2+2 cations for cations for long-term stabilization of As & Crlong-term stabilization of As & Cr

CaSOCaSO44/Soil/CCA-ash system: 7.3 to 8.0 pH/Soil/CCA-ash system: 7.3 to 8.0 pH

Ongoing Work & Future Ongoing Work & Future PotentialPotential

Soil and Sediment ContaminationSoil and Sediment Contamination journal journal has published two articles from this research has published two articles from this research on CCA- metals adsorption/desorption on CCA- metals adsorption/desorption mechanisms in amended soil systems and a mechanisms in amended soil systems and a third article is under review in another third article is under review in another journaljournal

The future of metals immobilization in soil The future of metals immobilization in soil by the use of common soil amendments by the use of common soil amendments could involve the manufacture of could involve the manufacture of “enhanced” soil amendments to improve “enhanced” soil amendments to improve the performance of immobilization the performance of immobilization mechanismsmechanisms

Presentations

Parts of the research results have been presented at the following:

EWRI-World Environmental & Water Resources Congress 2008

Honolulu, HI American Water Resources

Association 2010 Annual Conference Philadelphia, PA

Questions ?

jharden1947@charter.net