Environmental CSI:
Chl i t d Solvent
Chlorinated
S l
t Releases
R l
Alan Jeffrey, Ph.D.
DPRA/Zymax Forensics
600 S. Andreasen Drive
Escondido, CA 92029
[email protected]
Chlorinated Solvents
„
„
„
„
„
PCE – dry
dr cleaning
solvent
TCE – vapor
degreasing solvent
TCA – degreasing
solvent
Dissolve in
groundwater; migrate easily
Vapors intrude into overlying buildings
Chlorinated Solvent
Issues
„
Is the chlorinated solvent in a plume from
one or more sources?
„
Is the chlorinated solvent in separate plumes
from the same source or different sources?
„
Is TCE in a PCE plume from degradation of
the PCE or from a separate TCE source?
Chlorinated Solvent
Characterization
„
PCE, TCE etc are single compounds
„
Different sources are chemically identical
„
May be stable isotopic differences
„ 13
C/ 12C,
C 37Cl/ 35Cl,
Cl D/H ratios differ depending
on feedstock and manufacturing process
Carbon Isotopes
6P
6N
6P
7N
6P
8N
Mass 12
(stable)
12C
Mass 13
(stable)
13C
Mass 14
(radioactive)
14C
I nature
In
t
approximate
i
t ratios
ti for:
f
D/H:
1/6500
37Cl/35Cl:
13C/12C:
1/3
1/99
Compound Specific Isotope Analysis
„
Volatiles isolated from g
groundwater and soil
on a Solid Phase Micro Extraction (SPME)
fibre
„
Volatiles desorbed in inlet of GC/Isotope
Ratio Mass Spectrometer
„
Carbon isotope ratios measured as δ13C in
parts per mil (o/oo) referenced to PDB
standard (0 o/oo)
GC/IRMS Instrument
Schematic
CASE STUDIES
„
Progression
g
from simple
p to more complex
p
„
Carbon isotope
p ratios,, little biodegradation
g
„
Carbon isotope ratios, biodegradation
„
Carbon and Chlorine isotope ratios, multiple
aquifers
if
„
C b
Carbon,
Chl
Chlorine,
i
and
d Hydrogen
H d
isotope
i t
ratios
Case 1: Offsite PCE Source?
„
Retail Store
„
Possible offsite dry
y cleaning
g source
„
Possible onsite/offsite solvent cleaning
g source
„
Single or Multiple Sources?
„
Time(s) of release
GROUNDWATER
δ13 C of Chlorinated Hydrocarbons
PCE
SAMPLE
TCE
IDENTIFICATION
‰
ug/L
‰
ug/L
MW 108
MW-109
MW 102
MW 117
MW 1
-26.4
6
-25.8
-30.4
-30.4
-28.1
28 1
2580
580
1960
109
100
372
-30.8
30 8
-30.0
71
63
0.9
4
21
-32.0
-31.5
31 5
PCE δ13C
-30.4
-30.4
-28.1
-26.4
-25.8
Conclusions
„
At least two PCE sources
„
Lik l offsite,
Likely
ff it more work
k needed
d d tto
establish this
„
Plumes p
possibly
y mixing
g downgradient
g
in the site
„
Time of release
Case 2: Multiple
p PCE Releases?
„
Dry
y Cleaning
g Operation
p
„
Two Operators
p
1968-1978
1968-
„
Current Operator 19781978-Present
„
PCE in soil and groundwater
„
Single or Multiple Sources?
Conclusions
„
Fairly uniform PCE δ13C ratios
„
N evidence
No
id
for
f multiple
lti l sources
„
Possible that different operators used
PCE from the same distributor
„ 37
Cl/ 35Cl can now provide additional
way to distinguish plumes
Case 3: Offsite TCE Source?
„
Manufacturing operation
„
Degreasers used onsite
„
TCE, some PCE in groundwater
„
Offsite, onsite sources?
GW Flow
Direction
GROUNDWATER
PCE δ13C
-19.2
-25.4 -23.6
-24.8
-24.5
-28.6
28.6
-31.8
-23.7
Conclusions
„
Two TCE plumes
„
Off it TCE source, migrating
Offsite
i
ti onsite
it
„
Onsite PCE/TCE source ?
„ 37
Cl/ 35Cl can now provide additional
way to distinguish plumes
Case 4: PCE Degradation?
„
PCE releases
„
Two potential sources
„
Mixing of plumes?
„
Delineate sources
PCE Degradation
g
As PCE degrades
degrades,
isotopic ratio
changes
h
TCE
PCE Degradation
12C
– X Bonds are weaker than 13C – X Bonds
In a chemical reaction, 12C – X Bonds break faster
than 13C – X Bonds
If reaction proceeds to completion – all PCE goes to TCE isotope ratio in product is the same as in starting material
If reaction is partially completed, 12C is
product, and 13C is concentrated
concentrated in p
in starting material
Product (TCE) becomes more negative; starting material
(PCE) becomes less negative
PCE Sources
PCE δ13C
δ 13C
GROUNDWATER
δ13C of Chlorinated Hydrocarbons
PCE
SAMPLE
TCE
cis-DCE
IDENTIFICATION
‰
ug/L
/L
‰
ug/L
/L
‰
ug/L
/L
MW 1A
-11.6
20
-36.4
7
n/a
n/a
MW-4A
-17.4
33
-31.1
46
-39.9
2
MW-5A
-27.0
28
-32.1
11
-29.1
<1
MW-7A
-23.4
73
-36.2
54
n/a
<1
MW-10A
-28.7
2800
-42.2
82
-24.9
<1
MW-15D
-24.4
35
-38.9
16
n/a
n/a
MW-16D
-28.4
76
-35.7
22
-32.5
2
MW-18D
-29.1
8
-28.9
76
-46.5
6.6
MW-20D
-29 6
-29.6
4
-32 1
-32.1
38
-35 8
-35.8
1
MW-21D
n/a
3.
-27.6
110
n/a
8
PCE Degradation
If isotope ratios and concentrations of daughter
products are known
known, isotope ratio of initial PCE can be
calculated
Initial PCE δ 13C =
PCE δ 13C x conc + TCE δ 13C x conc + DCE δ 13C x conc
PCE + TCE + DCE conc
Assuming no loss of PCE, TCE, DCE or other daughter
products from the system
Calculated Initial PCE δ13C
Conclusions
„
„
„
„
Potential upgradient undegraded PCE
source
PCE degraded in some downgradient
wells
I iti l PCE carbon
Initial
b isotope
i t
ratios
ti for
f
degraded PCE consistent with the
undegraded
d
d d source
Must be consistent with hydrogeology
Case 5: Contamination in Multiple Aquifers
• Upper and lower aquifers have PCE
contamination
• Only
O l traces
t
off TCE and
d DCE - little
littl apparentt
degradation
• Isotope ratios not altered by degradation
• Multiple sources in upper aquifer?
• Different sources in upper and lower aquifer?
PCE Concentrations in Upper Aquifer
ug/L
260
1,100
,
210
180
PCE Concentrations in Lower Aquifer
ug/L
140
PCE Isotope Ratios in Upper Aquifer
δ13C
δ37Cl
-28
28.9
9
-2
2.0
0
-29.9
-1.6
-29.3
-0.5
-29.6
29 6
-0.8
08
PCE Isotope Ratios in Lower Aquifer
δ13C
-27.0
27 0
δ37Cl
-0.2
02
PCE in Multiple Aquifers
δ13C
δ37Cl
-29.6
-0.8
-27.0
.
-0.2
.
PCE in Multiple Aquifers
Upper
Lower
Conclusions
• Some differences in carbon and chlorine
isotopes in upper aquifer
• Possibly
P
ibl different
diff
t sources
• Significant
g
differences between upper
pp and
lower aquifers in the same well
• Definitely different sources
Case 6: Multiple PCE, TCE Sources
„
PCE and TCE releases
„
Multiple PCE sources?
„
TCE from degradation of PCE
release
l
or from
f
TCE release?
l
?
3,300
,
<10
7,100
110
440
50
3,300 PCE concentration ug/L
7,100 TCE concentration ug/L
<10
1,200
1 900
1,900
370
-25.8
5.8
-27.5
-27.2
-27.7 PCE Carbon Isotope Ratio o/oo
-25.4
-27.7
27 7
-0.2
.
-0.2 PCE Chlorine Isotope Ratio o/oo
-0.2
-1.7
17
-36.1
-29.0
-28.5
-28.9
-29
29.0
0 TCE Carbon Isotope Ratio o/oo
D/H Ratio and TCE
Source
„
TCE
Is TCE in a PCE plume from degradation of
the PCE or from a separate TCE source?
„
„
„
D/H ratio of H in TCE can discriminate
H in degraded
g
TCE comes from H2O in
groundwater
H in manufactured TCE has very different
D/H ratio
+68
+400
+55
+400 TCE Hydrogen Isotope Ratio o/oo
Conclusions
• Two PCE sources – confirmed by Carbon and
Chlorine isotope ratios
• Possible
P
ibl migration
i
ti pathway
th
• TCE source – limited migration
g
• Other TCE from PCE degradation – confirmed
by hydrogen isotope ratios
Monitoring Degradation
1 As PCE degrades
1.
degrades,
isotopic ratio
changes
h
TCE
Monitoring Degradation
„
„
PCE MTBE
PCE,
MTBE, BTEX compounds
compounds, nitrate
M
Measure
δ13C or δ15N over ti
time or along
l
plume
„
If ratios change
g and become less
negative, degradation is occurring
„
Useful to confirm natural attenuation
CONCLUSIONS
„
„
„
„
„
„
„
Measure Carbon and Chlorine ratios for more
definitive evidence
Hydrogen ratios if source of TCE is an issue
Select samples to adequately characterize the
plume
If the budget is limited, use a 2 phase approach:
Li it d survey to
Limited
t detect
d t t any isotopic
i t i differences
diff
within plume pointing to multiple sources
More detailed survey to delineate components of
a mixed plume
Don’t assume that all that PCE on your site is
your client’s
y