Forensic Techniques for Establishing the Origin and Timing of a Contaminant Release
- submitted by:
- Robert D. Morrison, Ph.D.
R. Morrison & Associates, Inc.
201 E. Grand Avenue, 2B
Escondido, CA 92025
- Common issues in environmental coverage cases include
determination of the origin of the contaminant release, the timing of the release, the
distribution of the contamination in the subsurface, and the reasonableness of the alleged
remediation costs. Of these issues, the origin and timing of a release are pivotal and
frequently the most difficult to resolve. The timing of a release and whether it is sudden
and accidental is especially relevant given that it is foundational as to when a
particular insurance policy is "triggered". The selection of triggering theories
such as "exposure" (when the property was exposed to hazardous waste),
"manifestation" (discovery of the contamination), "injury in fact"
(the date at which the property damage occurred) and "continuous trigger" (the
continuous damage to property throughout all policy periods) is influenced by
the ability to identify the timing of a release.
In instances where conclusive evidence is lacking to identify the timing or origin of a
release, forensic review of the environmental data may provide this important information.
Techniques available include aerial photography interpretation, identification of the date
the chemical was commercially available, association of the chemical with a manufacturing
process, chemical profiling, chemical degradation models, and groundwater modeling. These
techniques individually, or in concert with other information, can provide the evidence
needed to identify the timing and origin of a release.
Aerial Photography Interpretation
Interpretation of aerial photographs can provide convincing evidence in establishing the
timing of a contaminant release. The successful use of this technique is dependent on
acquiring a complete list of coverage dates and retaining an expert in aerial photographic
interpretation. The latter is important because the interpretation of aerial photographs
is dependent on both the sophistication of the diagnostic equipment as well as the
experience of the interpreter.
Acquisition of a complete list of aerial photographs requires a firm that specializes in
such acquisitions. Public sources of aerial photographs include the Summary Record System
maintained by the United States Geological Survey, the United States Department of
Agriculture, the National Archives, the United States Forest Service, the National Oceanic
and Atmospheric Administration, the Army Corps of Engineers and local state Highway
Departments. Specialized firms are aware of and can access private collections and brokers
of photography (Chinese and Russian satellite imagery) which can provide the crucial
evidence for identifying a surface feature that is consistent with a release.
Wherever possible, acquisition of stereo pairs is required as it allows features such as
stream channels, barrels, disposal areas, pits, above ground tanks, drainage ditches,
lagoons, or settling ponds to be examined three dimensionally. The presence of dark
staining in areas of known contamination is also useful in establishing a causal
relationship for arguing that a release occurred within a time period established with the
Commercial Availability of a Chemical
If the chemical of concern is known, the date of its commercial availability can identify
the earliest time period that it could have been present. Chlorinated hydrocarbons,
chemicals associated with fuel additives, pesticides, herbicides, fungicides, and
insecticides are especially amenable to this type of dating analysis. Knowledge of the
synomyns and trade names of the chemical is necessary to perform this analysis because a
chemical can have numerous trade names with no similarity to the chemical name. Numerous
texts are available for this examination (1). Exhibit 1 summarizes when
selected chemicals became commerically available in the United States.
Exhibit 1 Commercial Availability of Selected Chemicals
|1,1,1 trichloroethane (1,1,1 TCA)
|1,1,2 trichloroethane 1941-3
- Chemicals Unique to a Manufacturing Process
An understanding of a site's manufacturing processes and material - handling systems can
provide insight into probable locations of a release. For a semiconductor manufacturing
site, likely locations where chlorinated solvents can enter the subsurface include
neutralization sumps, corroded sewer and transfer piping, and chemical storage areas. The
chemical distribution of chlorinated solvents in the subsurface in relation to these
features can then assist in developing a causal relationship between these features and
the observed contamination.
The spatial association of a particular chemical with various unit processes at the
facility is used to further define the origin of the release. Chemicals, such as
chlorinated solvents, uniquely associated with particular equipment can provide insight
into probable source locations. An example is the use of chlorinated solvents in
degreasing operations. In 1970, trichloroethylene (TCE) accounted for 82 percent of all
chlorinated solvents used in vapor degreasing; by 1976, its share had declined to 42
percent. (2). A degreaser is also designed to handle solvents only within a
certain boiling range; obtaining the manufacturer's operating manual for the degreaser can
provide information concerning the inclusion or exclusion of chemicals used by the
degreaser. This information, coupled with a knowledge of when the degreaser commenced
operation and its historical location, can help identify where and when a release of a
particular chlorinated solvent occurred.
Using information on a chemical's application to identify the timing of a release is also
helpful for soil contamination by polychlorinated biphenyls (PCBs). PCBs are listed on
laboratory reports with a numbered designation, such as PCB-1254; 12 refers to the number
of carbon atoms and 54 refers to the number of chlorines. Different carbon and chlorine
combinations are manufactured for specific uses during discrete time periods. For example,
PCB-1016 was manufactured between 1971 and 1976 and used as an insulator fluid for
electric condensers and as an additive in high-pressure lubricants. PCB-1254 was used as a
secondary plasticizer in the manufacture of polyvinyl chloride and in capacitors; it was
produced from 1957 to 1977 (3). The date of manufacture of PCBs can therefore
be combined with its' particular use to bracket the date at which it was available and
identify the location of the equipment at the facility that would use a particular PCB
Chemical fingerprinting is used to describe the ability to distinguish the age and often
the origin of a chemical. It is most commonly used in hydrocarbon contamination cases. In
its simplest form, chemical fingerprinting identifies the type of hydrocarbon (e.g.,
diesel, gasoline, jet fuels, kerosene, mineral oil, Stoddard solvent) as a means to
identify the source and timing of a release. More sophisticated techniques to identify the
age of the hydrocarbon include the examination of the composition of fuels as a function
of the time of formulation or the identification of additives associated with a discrete
time period. These techniques can often determine whether a chemical release was a single
event, a series of events, or a continuous release.
Techniques used to identify the age of a hydrocarbon release include analysis of
proprietary additives, the composition of antiknock formulations, trace metals analysis,
hydrocarbon profiling, physical characteristics, and degradation models. Some are
Proprietary additives are compounds added to hydrocarbon products for specific purposes.
Additives often have discrete time intervals during which they were introduced into a
formulation. The use of additives for hydrocarbon fingerprinting requires a prior
knowledge of the additive package and the ability to detect a unique additive that is not
masked by other chemicals or obscured by degradation.
Gasoline additives include antiknocks, antioxidants, metal deactivators, corrosion
inhibitors, anti-icers, lead scavengers, and oxygenates. Exhibit 2 lists examples of each.
Exhibit 2: Examples of Gasoline Additives
|Type of Additive
||p-phenylenediamine; alkyl-substituted phenols
||Carboxylic acids and diimides
||Short-chained n-alcohols (freeze point depressants);
amines and ethoxylated alcohols with long hydrocarbon chains.
||Methanol, methyl-tertiary butyl ether (MTBE)
- The composition of additive packages vary with time. For example,
a typical additive package for gasolines formulated in the 1980s was 62 percent tetraethyl
lead, 18 percent ethylene dibromide, and 2 percent inactive ingredients such as stability
improvers, dyes, and antioxidants.
Diesel fuels also contain additive packages. Diesel often contains quality-enhancing
additives such as diesel ignition and stability improvers, corrosion inhibitors and
surfactants that can similarly be associated with discrete periods of time (5).
Alkyl leads are the most frequently encountered antiknock additive. The first reported use
of a lead antiknock additive was in 1923 by the General Motors Development Company in
Dayton, Ohio, which used tetraethyl lead. By 1950, most gasolines in the United States
were leaded; in 1960, tetramethyl lead was marketed. Consumption of all lead alkyls peaked
in 1969 (6). For premium-grade gasolines, these concentrations were as much as
2.9 grams per gallon. Subsequent reductions in lead concentrations in gasoline occurred
from the late 1970s to 1985 due to regulatory concerns. Tetraethyl lead was reportedly the
only alkyl lead added to leaded fuels after 1980. Only tetraethyl lead is currently used
as an additive in leaded gasoline in amounts up to two orders of magnitude less than that
added before 1980. The history of lead additives to gasoline frequently provides a basis
for bracketing the age of the gasoline in the soil or groundwater.
The most common organic lead alkyl additives are tetraethyl, triethylmethyl, methyldiethyl
and tetramethyl lead. Redistribution reactions of equimolar amounts of tetraethyl and
tetramethyl leads can also produce trimethyl, trimethylethyl, dimethyldiethyl, and
methyltriethyl lead  . Older gasolines included these lead compounds, along
with lead scavengers such as ethylene dibromide and 1,2-dichloroethane; these additives
were first introduced in 1928. Exhibit 3 summarizes the concentration of leads in a leaded
Exhibit 3 Concentrations of Lead in Leaded Gasoline
|Leaded Gasoline Additive
- The concentration of organic lead in a sample has been argued as a
means to determine when the fuel was released into the subsurface. In 1982, the allowable
levels of lead in leaded gasoline was 4.2 grams per gallon, which was changed by the
Environmental Protection Agency (EPA) in 1984 to a maximum of 0.1 gram per gallon. This
concentration applies to the average quarterly production from a refinery or "pool
standard." The pool standard is based on the total grams of lead used by a refinery
in a given time period divided by the total amount of gasoline manufactured by the
refinery in that time frame. As a result, individual batches of gasoline can contain 4.2
grams per gallon per EPA requirements and 0.8 grams per gallon in California. It has been
argued that these guidelines can be used to predict the time frame during which the
product was manufactured. A challenge to this argument is that the lead content of an
individual sample is not conclusive because the lead content for any given time frame is
based on the pool standard. The consequence of this practice is that individual gasoline
samples can vary from batch to batch and therefore cannot be used to date the year of
A recent technique forwarded to age-date is the examination of lead isotope ratios in
gasoline-impacted soil or water samples. It is based on the premise that the use of one
particular source of lead with distinctive high isotopic ratios increased progressively
from the late 1960s to the late 1980s. High-precision lead isotope ratio analysis is used
to calibrate these changes as a function of time. It is reported that this technique
allows one to established the time of formulation to within one to five years. Examples of
the degree of resolution for different time periods using this analysis is: one to two
years for 1969-1982, two to three years for 1982-1990, and three to five years for
Other antiknock ingredients used in fuels include iron-based compounds. The most
well-known metal compound is iron pentacarbonyl, which was marketed in the 1930s. Another
is the manganese additive, methyl cyclopentadienyl manganese tricarbonyl (MMT), which was
introduced in the United States in 1957 as an antiknock and lead alkyl supplement and
later commercialized as a supplement to tetraethyl lead. Although MMT can
be age- diagnostic, its absence in gasoline does not necessarily indicate a basis for
age-dating because it was not routinely added by all manufacturers. It is currently an
additive in Canadian gasolines.
Oxygenates are added to gasoline to increase the oxygen content and reduce carbon monoxide
emissions. Oxygenated compounds used for this purpose include methanol, methyl tertiary
butyl ether (MTBE), ethanol and tertiary butyl alcohol, tertiary methyl ether (TAME), and
ethyl tertiary butyl ether (ETBE). MTBE is used to improve the octane rating and/or
improve the tolerance for moisture in gasoline. MTBE has been an additive in gasoline
since about 1979; current unleaded gasolines contain as much as 15 percent by volume. MTBE
was introduced into East Coast, Gulf and Midwest gasolines after 1980 and into West Coast
gasolines after 1990 .
The changing formulation of fuels over time also provides opportunities for dating a
release. Prior to 1975, diesel was primarily straight-chained, while post-1975 diesel was
thermally cracked. This distinction can be determined analytical with a small volume of
product, thereby providing a time frame for when the product was available.
Trace metal analysis may be useful in the confirmation of waste oil, which is more likely
to contain lead, zinc, chromium, copper, or aluminum from the abrasion of an engine than
from a fuel.. Metals can also be additives to a hydrocarbon fuel; the addition of barium
and zinc to motor oil is an example. Vanadium and nickel are also associated with fuels;
concentrations can range from 100 to 400 parts per million. While not a trace metal, boron
was a common gasoline additive in use from 1956 to 1981 and, if detected with gasoline,
may provide an indicator of a pre-1981 formulation. Another example is the addition of
borates to gasoline in the 1960s by ARCO.
Chemical profiling is used to identify the individual components of a soil or liquid
sample. This information is then used to estimate how long a chemical has been in the
subsurface. The presence of gaseous hydrocarbons, isobutane, n-butane, iso-pentane, and
n-pentane in a sample contaminated with gasoline can be used to determine whether a
gasoline released into the subsurface is "fresh" or "weathered." Fresh
gasolines normally contain n-hexane and n-heptane in higher concentrations than
methylcyclohexane (MCH) and n-octane. After the gasoline weathers in the subsurface, the
MCH concentration increases relative to n-hexane and n-heptane and carbon seven (C7)
normal paraffins. The difficulty with this analysis and testimony is that
"fresh" and "weathered" are relative terms that allow a wide range of
interpretations by forensic geochemists.
Chemical Degradation Models
Chemical degradation models are used to estimate the length of time that a hydrocarbon or
chlorinated solvent has been in the subsurface as a means for developing allocation models
in environmental insurance cases. The following are commonly used degradation models used.
The degradation of specific petroleum fractions in a fuel has been proposed as a means to
age-date a hydrocarbon . One approach relies on the volatilization and
dissolution of BTEX (benzene, toluene, xylene, and ethylbenzene) compounds in groundwater
as an qualitative indicator of how long the product has been in the subsurface. The normal
sequence of loss of these compounds in groundwater is that benzene diffuses most rapidly
out of free- phase gasoline and partitions into groundwater followed by toluene,
ethylbenzene, and xylene. The reverse occurs with BTEX in soils. Toluene, ethylbenzene and
xylenes are preferentially retained by soil relative to benzene; ethylbenzene and xylenes
are also more resistant to degradation than benzene or toluene. Calculating ratios between
these four compounds has been argued in environmental insurance cases as a means to
identify the relative age of a hydrocarbon release.
In BTEX impacted soils, the concentration ratio of benzene plus toluene to ethylbenzene
plus xylene changes from about 0.8 in the original fuel to about 0.4 in five years. For
BTEX-impacted groundwater, if the ratio between benzene plus toluene to ethylbenzene plus
xylene is between 1.5 to 6.0 near a suspected source, the release probably occurred within
the last five years. This ratio decreases exponentially with time because of the
preferential transport of benzene and toluene, which increases the less soluble
ethylbenzene and xylene concentrations. The degradation of benzene and toluene with time
also results in a reduction of the BTEX ratio.
Significant uncertainty is inherent using these ratios for age-dating due to the variation
of BTEX compounds in the original gasoline as well as environmental alterations to the
product. For example, under anaerobic conditions, toluene may be more rapidly degraded
than benzene. These uncertainties can result in a wide range of ratios for identically
aged spills, especially in different soils. A knowledge of the range of BTEX in fresh and
weathered gasolines illustrates the uncertainties associated with such ratio analyses.
Exhibit 4 summarizes BTEX ranges in different grades of dispensed gasoline and ranges of
BTEX hydrocarbons in free product, water, and soils. 
Exhibit 4. BTEX Ranges (mg/ml) in Gasolines
- BTEX Ranges in Environmentally Altered Gasolines
- A more quantitative approach is reliance on the biodegradation
half-life of hydrocarbon compounds in the soil or groundwater. The estimated half-life is
the time required for one half of the compound to biodegrade. Exhibit 5 summarizes the
biodegradation rates of selected BTEX and polynuclear aromatic hydrocarbons (PAHs)
compounds measured at 25 degrees Celsius:
Exhibit 5. Biodegradation Half-Lifes for Selected Hydrocarbons
Compound Biodegradation Half-Life (hours)
|o, m, p-xylene
The degradation of diesel in the subsurface over time can also
provide a qualitative indicator as to whether the diesel is "fresh" or
"aged". For example, examination of chromatograms from fresh and aged diesel
samples shows that n-alkane compound peaks associated with fresh diesel are diminished or
non-existent in weathered diesel. Similarily, while the n-alkane compounds in diesel
readily degrade, other compounds such as pristane and phytane remain in weathered samples.
Consequently, the concentration of these compounds increases as the diesel ages.
The presence of chlorinated solvents and their breakdown products has been proposed as a
means of identifying how long a chemical has been in the subsurface. This argument is
usually based on laboratory-measured degradation rates between chlorinated solvents,
primarily for the parent compounds tetrachloroethene (PCE), trichloroethane (TCA), and
carbon tetrachloride (PCM) The presence or absence of a particular breakdown product is
argued as evidence that the parent compound was present for a particular period of time.
For example, the compound 1,1-dichloroethene is a breakdown product of both TCA and PCE,
while chloroethane is a degradation product of only TCA or 1,2-dichloroethane. The
presence of chloroform can indicate the presence of carbon tetrachloride; it is not an
associated product of either PCE or TCA. A variation to this dating approach is that if
the original concentration of a chlorinated solvent introduced into the subsurface is
known along with measured values in the soil or groundwater, a knowledge of the half-life
for that chemical can provide a basis for estimating when the chemical was released into
Several arguments to these approaches are available. One is that site-specific information
is rarely available to compare to laboratory-derived degradation rates. A wide range of
half-lives are also reported in the published literature. For example, published
half-lives for PCE at 100 to 250 C range from 0.7 to 1.3 X 106
years.  For 1,1,1-trichloroethane, published half-lives at 100
to 250 C range from 1.1 to 12 years. . Furthermore, the
heterogeneity of the physical and chemical systems at a site introduces tremendous
uncertainty into degradation rates. A simple example is whether site-specific information
is available to determine whether soils are anaerobic or aerobic; this determination is
significant as to whether the chlorinated solvent can be degraded.
The presence of these compounds in the subsurface can also inhibit the microbial
degradation that may otherwise occur. For example, the anaerobic degradation of carbon
tetrachloride is reported to be inhibited at concentrations between 80 and 250 µg/L; for
TCE anaerobic inhibition was observed at concentrations of 150 µg/L. These types of
complications introduce further uncertainty in the use of degradation rates as an
indicator of the timing of a release. 
Impurities in the original product can similarily introduce uncertainty with the use
of degradation rates for chlorinated solvents as an age-dating technique. It is not
uncommon for industrial-grade PCE to contain impurities of one to three percent which can
include the degradation products of PCE. Degradation can also occur prior to a release
into the subsurface (e.g., degradation within a clarifier or sewer pipe).
Groundwater modeling is a frequently used technique to establish the timing and origin of
a release. Reverse modeling is a type of modeling used specifically for this purpose and
is commonly encountered in insurance cases.
Reverse modeling uses the direction and velocity of groundwater to predict, in reverse,
when and where a contaminant entered a groundwater system. This technique is called
"reverse" or "backward extrapolation groundwater modeling".
In its simplest application, the observed length of a contaminant plume and a
representative groundwater velocity are used to estimate the timing of the release.
Reverse modeling relies on various hydrogeologic and contaminant characteristics to
mathematically simulate the origin and timing of a release. Hydrogeologic variables used
in reverse modeling include the groundwater gradient, soil porosity, velocity, and
horizontal and transverse dispersivity. The reliability of these values is due in part to
whether they are measured in the field or laboratory or are obtained from published
numbers. For example, it is generally recognized that the most representative measurements
for determining the hydraulic conductivity of a formation are from a pump test, while less
reliable values are associated with slug tests, sieve analyses, and laboratory
measurements of soil cores. Given that variables such as the gradient of the groundwater
table and changes in soil porosity differ significantly with soil texture, a
scientifically defensible approach is to use a range of values for each parameter and to
develop a corresponding range in the groundwater velocity.
Dispersivity is a hydrogeologic characteristic used in reverse modeling. It is the three-
dimensional spreading of a contaminant plume in groundwater and is primarily dependent on
the aquifer characteristics and the geometry of the contaminant source area. Dispersivity
is a fitted parameter that allows considerable latitude in calibrating or adjusting a
reverse model to fit a prescribed result. Dispersivity values are used in both a
longitudinal and transverse direction relative to the center of mass of a contaminant
plume. In reverse modeling, it is used to fit the shape of the plume to the observed plume
at one point in time. Longitudinal dispersivity values used with solute transport models
are commonly in the range of 90 to 300 feet, while horizontal dispersivity values can be
as much as 150 feet. There is little physical evidence for using such large numbers other
than the fact that groundwater models are able to simulate contaminant concentrations that
compare favorably with observed values in monitoring wells. In cases where no data exist
to estimate dispersivities, EPA recommends multiplying the length of the plume by 0.1 to
estimate the horizontal dispersivity .
Contaminant properties used in modeling affect the modeled transport of a contaminant and
include variables such contaminant density and viscosity, retardation, and biodegradation.
The retardation of a selected chemical in groundwater is an example of a fitted parameter
that is commonly used in litigation where reverse modeling is employed .
If groundwater flow is six feet per day and a selected retardation coefficient for
PCE (perchloroethylene) is two, then PCE is assumed to be transported at a rate of three
feet per day. Given that published values for the retardation of PCE in sand and gravel
aquifers is between one (no retardation) and five, one can vary the
retardation rate to fit the observed detection of PCE at a monitoring well to fit a
selected time of release. While retardation values for TCE (trichloroethylene) are
reported as less than ten and usually between one and two and a half  these
values can similarily be adjusted to correspond to a prescribed time of release of TCE.
An argument against the use of reverse groundwater models is that the direction of
groundwater flow and velocity at time periods prior to the first measurement are unknown.
Similarily, the rate of transport of a contaminant as compared to groundwater is unknown
with certainty. These factors introduce significant uncertainty and variability in terms
of when the contaminant entered groundwater. As parameters such as the retardation of a
chemical and the dispersivity of the groundwater are usually not measured but rather
fitted parameters, these values can significantly bias the modeling results. A successful
challenge to reverse modeling usually is based on on the representativeness of these
hydrogeologic and chemical parameters and the lack of information to verify the accuracy
of the results given that the data are not available at this earlier point in time.
A Case Study
Selected forensic techniques in identifying the origin and date of release for allocation
purposes was used in T. H. Agriculture & Nutrition Co. Inc., v. Aceto Chem. Co.,
Inc., et al.. The case dealt with a pesticide manufacturing facility
located in Fresno, California. A number of parties had formulated a variety of pesticides,
herbicides, fungicides and defoliants from 1951 to 1982. Building materials, soil, and
groundwater were contaminated with numerous types of chemicals throughout site. Allocation
of discrete areas of contamination to responsible parties was the focus of the technical
Techniques used for identifying the origin and timing of releases by both parties included
aerial photography interpretation, determining when a chemical was first commercially
available, association of chemicals with a formulation process, chemical degradation
models, and reverse groundwater modeling.
Aerial photographic interpretation was key in identifying certain activities and areas of
contamination with specific time periods. For example, the presence of several landfills,
numerous above ground storage tanks, buildings, railroad spur lines, cisterns, and a
concrete sump associated with soil and groundwater contamination provided a means to
associate these features and subsurface contamination with a particular time period. The
location of specific activities, such as the preparation of defoliants, was confirmed by
aerial photography by identifying the associated equipment used in these formulations in a
Hundreds of chemicals were used at the site. An analysis of when these chemicals first
became commercially available in the United States provided the basis for identifying the
earliest time that the chemical could have been present. For example, Diphenamid and
Bromacil were available after 1960 and 1963, respectively, thereby providing the basis for
the association of these chemicals with a particular operator. Other chemicals, such as
DDT (available in 1942), were used throughout the operational history.
Examination of degradation models and the resulting by-products were examined to identify
patterns that could be associated with a particular feature or chemical that was known to
be used by a particular owner. For example, chloroform was detected in groundwater about
one mile downgradient of the site and was a chemical of concern. Chloroform was allegedly
used as a laboratory solvent and discharged into a brick cistern. Chloroform is also a
degradation product by hydrolysis and bacteria of carbon tetrachloride; analysis was
therefore performed to distinguish whether the chloroform detected in groundwater was
associated with carbon tetrachloride degradation. This issue was also relevant because
chemicals such as DDT, DDE, toxaphene, dieldrin, and other pesticides preferentially
dissolve into chloroform. This phenomena is known as cosolvation. The chloroform thereby
transports these chemicals to depth in the soil column or into the groundwater; these
chemicals otherwise are strongly sorbed by soil and remain shallowly distributed in the
Cosolvation was similarily argued to be responsible for the distribution of DDT and
dieldrin at depth in soil near a railroad loading dock due to the release of xylene onto
contaminated soil. The volume of DDT contaminated soil at depth, resulting from the
release of xylene and subsequent cosolvation of the DDT, depth was argued to be allocated
to the operator responsible for the xylene spillage.
Another technique used was association of a chemical or group of chemicals with a specific
activity. For example, the chemical ethylene dichloride (1,2-DCA) was a chemical detected
in downgradient monitoring wells. It is a lead scavaneger in unleaded gasoline as well as
a component in food fumigants. The detection of 1,2-DCA in samples also contaminated with
hydrocarbons or fumigants provided the basis for associating the ethylene dichloride to a
particular activity and time period.
Reverse modeling was employed to link groundwater contamination with particular source
areas, such as cisterns and drainage lines, as well as a time period. An assumption of the
model is that the direction of groundwater flow and velocity has remained generally
unchanged for approximately 45 years. Challenges to the approach included the inability to
model groundwater for a 30 year period for which no groundwater velocity values were
available. Changes in the direction and velocity of groundwater flow over time due to the
influences of a nearby irrigation canal and a high capacity irrigation well introduced
uncertainity. The shape of the chloroform plume was also more consistent with a known
source of chloroform from a cistern than with leakage from a sewer line which would
produce a more diffused plume shape. The time required for the chloroform to reach the
groundwater after discharge into the cistern was also unknown thereby introducing
additional uncertainty regarding the accuracy of the model.
When the testimonial and historical information was combined with the results from these
dating techniques, the ability to allocate many of the contaminated buildings and soil to
a particular time period was possible.
Absent direct testimony or other conclusive evidence, various forensic techniques are
available to identify the timing and origin of a contaminant release. When used in concert
with other evidence, they can provide convincing information regarding the origin and
timing of a release that forms the basis for allocation. Techniques such as reverse
groundwater modeling and the use of BTEX ratios should be scrutinized to determine whether
they are scientifically defensible.
1. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans,
Halogenated Hydrocarbons, Volume 20, International Agency for Research on Cancer, October
United States Environmental Protection Agency, 1971, EPA Compendium of Registered
Pesticides, Volume III, Washington, D.C., United States Government Printing Office.
Groundwater Chemicals Field Guide., 1995. J. Montgomery. Lewis Publishers, Chelsea, MI.
2. J., Blackford, J., 1975, "Trichloroethylene," Chemical Economics Handbook,
Stanford Research Institute, Menlo Park, CA, 697.301A-697.302Y.
3. Monsanto, Polychlorinated Biphenyls, A report on Uses, Environmental and Health Effects
and Disposal, White Paper, p. 18.
4. I. Kaplan, and Y. Galperin, 1996, How To Recognize a Hydrocarbon Fuel in the
Environment and Estimate Its Age of Release. Groundwater and Soil Contamination:
Technical Preparation and Litigation Management, Thomas Bois and Bernard Luther, eds.
John Wiley & Sons Inc, New York, pp. 145-200.
5. L. Lee et al., 1992, Partitioning of Polycyclic Aromatic Hydrocarbons from Diesel Fuel
into Water, Environmental Science and Technology, 26:2104-2110.
Global Geochemistry Corp., 1991, Characterizing petroleum contaminants in soil and water
and determining source of pollutants, p. 37.
6. R. Rhue et al., 1992, "The Fate and Behavior of Lead Alkyls in the Environment: A
Review," Critical Reviews in Environmental Control. 22(3/4): 169-193.
7. P. Cline et al., 1991, "Partitioning of Aromatic Constituents into Water from
Gasoline and other Complex Solvent Mixtures." Environmental Science and Technology,
8. L. Gibbs, 1993, "How Gasoline has Changed," SAE Technical Paper Series
(Fuels and Lubricants Meeting and Exposition, Philadelphia, PA, (October 18-21, 1993).
9. R. Hurst et al., 1996, "The Lead Fingerprints of Gasoline Contamination," Environmental
Science and Technology,Vol. 30, No. 6., p. 304-307.
10. T. Russell, 1988, "Petrol and Diesel Additives". Petroleum Review,
(October 1988), The Institute of Petroleum, pp. 35-42.
J. Faggan et al., 1975, An evaluation of manganese as an antiknock in unleaded gasoline.
SAE Automobile Engineering Meeting, Detroit, MI, (October 13-17, 1975), p. 21.
11. J. Walker et al., 1976. Biodegradation Rates of Components of Petroleum. Canadian
Journal of Microbiology, 22:1209-1213.
12. R., Raymond et al., 1976. Oil Degradation in Soil. Applied and Environmental
Microbiology, 31(4) 522-535.
I. Kaplan et al., 1995, Pattern of Chemical Changes in Fugitive Hydrocarbon Fuels in the
Environment. Society of Petroleum Engineers, SPE 29754, SPE/EPA Exploration &
Production Environmental Conference, Houston TX (March 27-29, 1995).
13. W., Haag and T. Mill, 1988, "Effect of Subsurface Sediment on Hydrolysis of
Haloalkanes and Epoxides", Environmental Science and Technology, 22:658-663.
14. P. Jeffers et al., 1989, "Homogeneous Hydrolysis Rate Constants for Selected
Chlorinated Methanes, Ethanes, Ethenes, and Propanes". Environmental Science and
P. Cline and J. Delfino, 1989, "Transformation Kinetics of 1,1,1-trichloroethane to
the Stable Product 1,1-dichloroethene," Biohazards of drinking water treatment.
(R.A. Larson, ed.) Chelsea, MI: Lewis Publishers, Inc., pp. 47-56.
15. W. Dilling et al., 1975, "Evaporation Rates and Reactivities of Methylene
Chloride, Chloroform, 1,1,1, Trichloroethane, Trichloroethylene, Tetrachloroethylene, and
other Chlorinated Compounds in Dilute Aqueous Solutions". Environmental Science
and Technology, 9:833-838.
P. Howard, et al., Handbook of Environmental Degradation Rates. Lewis Publishers,
16. M. Alexander, 1985, Biodegradation of Organic Chemicals. Enviornmental Science and
17. A. Kezsbom and A. Goldman, 1991, "The Boundaries of Groundwater Modeling under
the Law: Standards for Excluding Speculative Expert Testimony," Environmental
Claims Journal, Vol 4, No. 1 (Autumn 1991).
I. Kornfeld, 1992. "Comment to the Boundaries of Groundwater Modeling under the Law:
Standards for Excluding Speculative Expert Testimony," Tort and Insurance Law
Journal, Vol. 28, No. 1. (Fall 1992).
R. Morrison and R. Erickson, 1995, Chapter 7, "Groundwater Investigations". Environmental
Reports and Remediation Plans: Forensic and Legal Review. John Wiley & Sons, Inc.,
New York, p. 155.
18. J. Wilson, et al., 1981, "Transport and Fate of Selected Organic Pollutants in a
Sandy Soil", Journal of Environmental Quality, 10:501-506.
A. Lallemand-Barres and P. Peaudecerf, 1978, Recherche de reltions entre les valeurs
mesurees de la dispersivite macroscopique d'un milieu aquifere, ses autres
caracteristiques et les conditions de mesure. Etude bibliographique. Bull. Bur. Rech.
Geol. Min (BRGM), Ser. 2, Sec. III, No. 4, pp. 277-284.
19. U.S. Environmental Protection Agency, 1985, Water Quality Assessment: A screening
Procedure for Toxic and Conventional Pollutants in Surface and Ground-water, Parts I and
II (revised 1985), EPA/600/6-85-002a (Part I, 609 p.), EPA/600/6-85/002b (Part II, 444 pp)
Environmental Research Laboratory, Athens, GA.
Carrier Corp. v. Detrex Corp., No. C-703625, Cal. Super. Ct. Los Angeles, County,
20. T. H. Agriculture & Nutrition Co. Inc., v. Aceto Chem. Co., Inc., et al.,
No. CV-F-93-5404 OWW/DLB, E.D. Cal., (1996).
R., Schwarzenbach, et al., "Behavior of Organic Compounds during Infiltration of
River Water to Groundwater. Field Studies." Environmental Science and Technology,
17, (1983), p. 472-479.
21. L. Barber, et al., "Long-term Fate of Organic Micropollutants in Sewage
Contaminated Groundwater, " Environmental Science and Technology, 22 (1988),
D., Mackay, "Characterization of the Distribution and Behavior of Contaminants in the
Subsurface", Ground Water and Soil Contamination Remediation: Toward Compatible
Science, Policy, and Public Perception, Washington, DC, National Academy Press,
(1990), p. 70-90.
M. Mehran, et al., "Distribution Coefficient of Trichloroethylene in Soil-Water
Systems," Ground Water, 25, (1987) 275-282.