Defending the Rights of Metals: How to Distinguish Naturally High Groundwater Concentrations from...

Defending the Rights of Defending the Rights of Metals:Metals:

How to Distinguish Naturally How to Distinguish Naturally High Groundwater High Groundwater

Concentrations from Site-Concentrations from Site-Related ContaminationRelated Contamination

Karen Thorbjornsen and Jonathan Myers, Karen Thorbjornsen and Jonathan Myers, Ph.D.Ph.D.

Shaw Environmental, Inc.Shaw Environmental, Inc.

22

Typical Definitions of Metals Typical Definitions of Metals Contamination in Groundwater Contamination in Groundwater

Concentrations that exceed MCLsConcentrations that exceed MCLs

Concentrations that exceed risk-Concentrations that exceed risk-based screening levelsbased screening levels

Concentrations that exceed Concentrations that exceed background screening values, or fail background screening values, or fail other statistical comparisons to other statistical comparisons to background data setsbackground data sets

33

Typical Definitions of Metals Typical Definitions of Metals Contamination in Groundwater Contamination in Groundwater

Chromium in Unfiltered Groundwater, Sewage Treatment Site, Alabama

CH

RO

MIU

M (ug/L)

BG(n=424; ND=63%) Site(n=18; ND=25%)0.1

1.0

10.0

100.0

1000.0

10000.0

44

Problems With These Standard Problems With These Standard ApproachesApproaches

Trace elements in groundwater can have Trace elements in groundwater can have naturally large ranges (3 to 4 orders of naturally large ranges (3 to 4 orders of magnitude)magnitude)

Distributions are highly skewed (lognormal)Distributions are highly skewed (lognormal)

Insufficient number of background samplesInsufficient number of background samples

Unequal sample sizes (site [n] >> background Unequal sample sizes (site [n] >> background [m])[m])

Geochemical processes are ignoredGeochemical processes are ignored

55

……Unnecessary monitoring, risk Unnecessary monitoring, risk assessment, or remediation can ensue assessment, or remediation can ensue

if metals in site groundwater are if metals in site groundwater are erroneously identified as contaminants.erroneously identified as contaminants.

Geochemical evaluation should be Geochemical evaluation should be performed to properly distinguish performed to properly distinguish

actual contamination from actual contamination from naturally high background.naturally high background.

66

Reasons for Elevated MetalsReasons for Elevated MetalsConcentrations in Groundwater Concentrations in Groundwater

Suspended particulatesSuspended particulates

Reductive dissolutionReductive dissolution

pH effectspH effects

ContaminationContamination

77

Effects of Suspended Effects of Suspended Particulates Particulates

Most common suspended particulates in Most common suspended particulates in groundwater are clay minerals, hydrous groundwater are clay minerals, hydrous aluminum oxides, aluminum hydroxides; and aluminum oxides, aluminum hydroxides; and iron oxides, iron hydroxides, iron oxyhydroxidesiron oxides, iron hydroxides, iron oxyhydroxides

In neutral-pH water, Al concentrations > 1 mg/L In neutral-pH water, Al concentrations > 1 mg/L indicate suspended Al-bearing minerals (clays)indicate suspended Al-bearing minerals (clays)

((––) ) surface chargesurface charge

In neutral-pH, moderate to oxidizing redox In neutral-pH, moderate to oxidizing redox conditions, Fe concentrations > 1 mg/L indicate conditions, Fe concentrations > 1 mg/L indicate suspended iron oxidessuspended iron oxides

(+) (+) surface chargesurface charge

88


Trace elements are associated with specific Trace elements are associated with specific suspended particulates, yielding good suspended particulates, yielding good correlations for trace-vs.-reference element correlations for trace-vs.-reference element concentrations in uncontaminated samplesconcentrations in uncontaminated samples

Oxyanionic elements – negatively charged Oxyanionic elements – negatively charged speciation under oxidizing conditionsspeciation under oxidizing conditions

Arsenic (V):Arsenic (V): HAsOHAsO4422−−, H, H22AsOAsO44

−−

Antimony (V):Antimony (V): Sb(OH)Sb(OH)66−−

Selenium (VI):Selenium (VI): SeOSeO4422−−

Vanadium (V):Vanadium (V): HH22VOVO44−−, HVO, HVO44

22−−

Iron Iron oxides oxides

(Fe)(Fe)

99


Cationic elements – positively charged speciationCationic elements – positively charged speciation

Barium:Barium: BaBa2+2+

Lead:Lead: PbPb2+2+

Nickel:Nickel: NiNi2+2+

Zinc:Zinc:ZnZn2+2+

Mixed elements – multiple charges at equilibriumMixed elements – multiple charges at equilibrium

Chromium (III):Chromium (III): Cr(OH)Cr(OH)22++, Cr(OH), Cr(OH)33

oo, Cr(OH), Cr(OH)44−−

Clays (Al) and/or Clays (Al) and/or manganese oxides manganese oxides

(Mn)(Mn)

1010

Effects of Reductive DissolutionEffects of Reductive Dissolution

Releases of organic contaminants Releases of organic contaminants (fuel, solvents) can establish local (fuel, solvents) can establish local reducing environments via anaerobic reducing environments via anaerobic microbial activitymicrobial activity

These conditions drive the dissolution These conditions drive the dissolution of iron oxides and manganese oxides, of iron oxides and manganese oxides, thereby mobilizing trace elements that thereby mobilizing trace elements that were adsorbed on the oxide surfaceswere adsorbed on the oxide surfaces

1111

Effects of Reductive DissolutionEffects of Reductive Dissolution Identified by correlations of metals with Identified by correlations of metals with

indicators of local redox depression:indicators of local redox depression:

Low ORP and DOLow ORP and DO

Elevated dissolved Fe and MnElevated dissolved Fe and Mn

Lower sulfate and nitrateLower sulfate and nitrate

Detectable sulfide and ammoniaDetectable sulfide and ammonia

Detectable hydrogen, methane, ethene, ethaneDetectable hydrogen, methane, ethene, ethane

Anaerobic Cl-solvent degradation productsAnaerobic Cl-solvent degradation products

((ciscis-1,2-DCE, vinyl chloride)-1,2-DCE, vinyl chloride)

1212

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

Iron (ug/L)

Alu

min

um

(u

g/L

)

Background Site

Site 1 (Alabama): Aluminum vs. Site 1 (Alabama): Aluminum vs.

Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater n = 16 (m = 300)

pH: 4.9 to 8.3

mean = 6.6

DO: 1.1 to 6.9 mg/L

mean = 5.2 mg/L

ORP: +148 to +272 mV

mean = +212 mV

R2 = 0.96

1313

Site 1 (Alabama): Unfiltered Site 1 (Alabama): Unfiltered Aluminum vs. Filtered/Unfiltered Aluminum vs. Filtered/Unfiltered

RatioRatio

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1E-07 1E-06 0.00001 0.0001 0.001 0.01 0.1 1 10

Filtered/Unfiltered Ratio

Un

filt

ered

Alu

min

um

(u

g/L

)

1414

Site 1 (Alabama): Unfiltered Iron Site 1 (Alabama): Unfiltered Iron

vs. Filtered/Unfiltered Ratiovs. Filtered/Unfiltered Ratio

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1E-07 1E-06 0.00001 0.0001 0.001 0.01 0.1 1 10


Un

filt

ered

Iro

n (

ug

/L)

1515

0.1

1

10

100

1000

10000

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

Iron (ug/L)

Ch

rom

ium

(u

g/L

)

Background Site

Site 1 (Alabama): Chromium vs. Site 1 (Alabama): Chromium vs. Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater

R2 = 0.99

1616

Site 1 (Alabama): Unfiltered Site 1 (Alabama): Unfiltered Chromium vs. Filtered/Unfiltered Chromium vs. Filtered/Unfiltered

RatioRatio

1

10

100

1,000

10,000

0.0001 0.001 0.01 0.1 1 10


Un

filt

ered

Ch

rom

ium

(u

g/L

)

1717

0.1

1

10

100

1000

10000

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07

Iron (ug/L)

Van

adiu

m (

ug

/L)

Background Site

Site 1 (Alabama): Vanadium vs. Site 1 (Alabama): Vanadium vs. Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater

R2 = 0.99

1818

Site 1 (Alabama): Unfiltered Site 1 (Alabama): Unfiltered Vanadium vs. Filtered/Unfiltered Vanadium vs. Filtered/Unfiltered

RatioRatio

1

10

100

1,000

10,000

0.0001 0.001 0.01 0.1 1 10


Un

filt

ered

Van

adiu

m (

ug

/L)

1919

Site 2 (Georgia): Aluminum vs. Site 2 (Georgia): Aluminum vs.

Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater n = 352

pH: 4.3 to 8.4

mean = 5.9

DO: 1.3 to 12.6 mg/L

mean = 8.4 mg/L

0.01

0.1

1

10

100

1000

10000

0.01 0.1 1 10 100 1000 10000

Iron (mg/L)

Alu

min

um

(m

g/L

)

2020


Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater n = 30 (m = 300)

pH: 5.8 to 6.2

DO: 0.9 to 10.4 mg/L

ORP: -210 to +82 mV

1

10

100

1,000

10,000

100,000

1,000,000

10 100 1,000 10,000 100,000 1,000,000

Iron (ug/L)

Alu

min

um

(u

g/L

)

Background Site

2121

Site 3 (Alabama): Mercury vs. Iron Site 3 (Alabama): Mercury vs. Iron

in Unfiltered Groundwaterin Unfiltered Groundwater

0.01

0.1

1

10

100

10 100 1,000 10,000 100,000 1,000,000

Iron (ug/L)

Mer

cury

(u

g/L

)

Background Site

2222


Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater

10

100

1,000

10,000

100,000

10 100 1,000 10,000 100,000

Iron (ug/L)

Alu

min

um

(u

g/L

)

Background Site

n = 43 (m = 300)

pH: 5.0 to 12.7

mean = 7.7

DO: 0.7 to 5.7 mg/L

mean = 3.0 mg/L

ORP: -270 to +268 mV

mean = +104 mV

2323

Site 4 (Alabama): Arsenic vs. Iron Site 4 (Alabama): Arsenic vs. Iron

in Unfiltered Groundwaterin Unfiltered Groundwater

1

10

100

1,000

10,000

10 100 1,000 10,000 100,000

Iron (ug/L)

Ars

enic

(u

g/L

)

Background Site

2424

Site 5 (Virginia): Aluminum vs. Site 5 (Virginia): Aluminum vs.

Iron in Unfiltered GroundwaterIron in Unfiltered Groundwater

n = 407 (m = 11)

TDS: 153 to 25,800 mg/L

mean = 4,350 mg/L

pH: 4.9 to 10.6

mean = 7.0

DO: 0.1 to 13.6 mg/L

mean = 5.1 mg/L

ORP: -421 to +344 mV

mean = -21 mV

1

10

100

1,000

10,000

100,000

10 100 1,000 10,000 100,000 1,000,000

Iron (ug/L)

Alu

min

um

(u

g/L

)

Site Background

2525

Site 5 (Virginia): Unfiltered Site 5 (Virginia): Unfiltered Aluminum vs. Filtered/Unfiltered Aluminum vs. Filtered/Unfiltered

RatioRatio

1

10

100

1,000

10,000

100,000

0.0001 0.001 0.01 0.1 1 10


Un

filt

ered

Alu

min

um

(u

g/L

)

Site Background

2626

Site 5 (Virginia): Unfiltered Iron Site 5 (Virginia): Unfiltered Iron


10

100

1,000

10,000

100,000

1,000,000

0.001 0.01 0.1 1 10


Un

filt

ered

Iro

n (

ug

/L)

Site Background

2727

Site 5 (Virginia): Copper vs. Site 5 (Virginia): Copper vs. Aluminum in Unfiltered Aluminum in Unfiltered

GroundwaterGroundwater

0.1

1

10

100

1000

1 10 100 1,000 10,000 100,000

Aluminum (ug/L)

Co

pp

er (

ug

/L)

Site Background

2828

Site 5 (Virginia): Unfiltered Copper Site 5 (Virginia): Unfiltered Copper


0.1

1

10

100

1000

0.01 0.1 1 10


Un

filt

ered

Co

pp

er (

ug

/L)

2929

ConclusionsConclusions Geochemical evaluation is a cost-effective Geochemical evaluation is a cost-effective

approach for determining if metals approach for determining if metals contamination of groundwater has occurredcontamination of groundwater has occurred

Uses existing data (requires Al, Fe, Mn analyses)Uses existing data (requires Al, Fe, Mn analyses)Does not require a valid background data setDoes not require a valid background data setLowers the probability of a false-positive Lowers the probability of a false-positive determinationdeterminationIdentifies the mechanism(s) responsible for elevated Identifies the mechanism(s) responsible for elevated metals concentrationsmetals concentrations

Geochemical evaluation complements Geochemical evaluation complements statistical site-to-background comparisonsstatistical site-to-background comparisons

If an element in the site data set fails a statistical If an element in the site data set fails a statistical test, then a geochemical evaluation should be test, then a geochemical evaluation should be performedperformed

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