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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
Effects of Suspended Effects of Suspended Particulates Particulates
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
Effects of Suspended Effects of Suspended Particulates Particulates
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
Filtered/Unfiltered Ratio
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
Filtered/Unfiltered Ratio
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
Filtered/Unfiltered Ratio
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
Site 3 (Alabama): Aluminum vs. Site 3 (Alabama): Aluminum vs.
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
Site 4 (Alabama): Aluminum vs. Site 4 (Alabama): Aluminum vs.
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
Filtered/Unfiltered Ratio
Un
filt
ered
Alu
min
um
(u
g/L
)
Site Background
2626
Site 5 (Virginia): Unfiltered Iron Site 5 (Virginia): Unfiltered Iron
vs. Filtered/Unfiltered Ratiovs. Filtered/Unfiltered Ratio
10
100
1,000
10,000
100,000
1,000,000
0.001 0.01 0.1 1 10
Filtered/Unfiltered Ratio
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
vs. Filtered/Unfiltered Ratiovs. Filtered/Unfiltered Ratio
0.1
1
10
100
1000
0.01 0.1 1 10
Filtered/Unfiltered Ratio
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