For more than two decades, TCAS has been retained in cases involving LNAPLs.
We have considerable experience in establishing the source(s), age and characteristics
of LNAPL. Additionally, we have performed LNAPL risk assessments on behalf of individuals, private
industry and government agencies (New York State DEC, New Jersey DEC and others). We
have offered unbiased toxicological opinions on behalf of both defendants and plaintiffs, based on objective and analytical evidence.
We are experienced with the methodologies required to produce reports and demonstratives
suitable for peer review or for presentation in court. We work closely with clients
and attorneys to ensure that all pertinent analytical and toxicological issues related
to LNAPL are addressed thoroughly in our reports and in expert testimony.
What is LNAPL?
LNAPL (Light Non-Aqueous Phase Liquid) refers to a group of organic chemical substances
(often petroleum) which are relatively insoluble and less dense than water. These characteristics cause them to form a layer
at or near the surface of a water table.
LNAPL can pose significant environmental and toxicological
issues with respect to both short- and long-term exposures. LNAPL analyses can involve
aspects of analytical and reconstructive chemistry as well as modeling of liquid
behavior, migration and fate. Consequently, scientifically credible LNAPL analyses frequently require the combined
efforts of a qualified hydrogeologist working in concert with an analytical toxicologist.
U.S. EPA provides general guidance1,2 with respect to
LNAPL analyses, health impacts and remediation of contamination. Generally-recognized attributes
of LNAPL include:
- LNAPL may float on water or co-exist with water in the pore network within an
- LNAPL only partially fills the aquifer pore space. LNAPL saturations decrease
with depth until water fills all the pores.
- The degree of LNAPL saturation is dependent upon the soil and fluid properties,
site history and the volume of LNAPL released.
- The variation of LNAPL saturation in soil with depth can generally be predicted.
- The total free LNAPL volume, migration potential and recoverable volume can also
LNAPL Toxicological Components
LNAPL analytical toxicology is a complex subject owing to the wide range of constituent
chemicals that may be present. LNAPL can contain any of a variety of substances
such as gasoline, diesel, crude or waste oil and other types of petroleum-based
fuels. LNAPLs can also include more toxic chemicals such as benzene, toluene and
tetraethyl lead. A state-of-the-art LNAPL analysis involves characterization, source
and age determination supported by a compilation of laboratory results of free product
and water samples. Such a compilation can include P-I-A-N-O analysis (Paraffins, Isoparaffins,
Aromatics, Naphthenes and Olefins), high-temperature distillation and other specialized
Constituent chemicals are assessed according to concentrations and composition.
LNAPL laboratory analyses can includes tests for chemicals such as methyl-t-butyl
ether (MTBE), ethyl-t-butyl ether (ETBE), diisopropyl-ether (DIPE), t-amyl-methyl
ether (TAME), t-butyl alcohol (TBA), ethanol, organic lead additives, manganese
additives (MMT) and others. Ultimately, TCAS has been highly successful
in the identification and characterization of LNAPL including its source and age.
Hydrological Properties of LNAPL Contamination
LNAPL laying above the water table tends to move slowly over time, changing location,
concentration and composition as different chemicals age and dissociate. Only a
qualified hydrologist can accurately assess the behavior, migration, transport and
fate of underground LNAPL over time. Expert toxicologists and hydrologists
work closely together to characterize the petroleum and determine its source and
Normally, the hydrological model is supported by water and free product samples
collected at multiple depths and in multiple locations within the area of concern (AOC).
Combining sample results with the hydrological model creates a realistic picture
of the scope of LNAPL contamination — an important requirement for an impartial
toxicological risk assessment.
LNAPL Vapor Intrusion
Some constituent chemicals in LNAPL possess sufficient volatility to produce soil
vapors which may infiltrate into basements and other subterranean structures. This
vapor intrusion can occur when transformed LNAPL liquids vaporize and migrate through
soil layers over time. Vapor concentrations can be detected near the ground surface
as well using specialized soil gas monitoring techniques. In cases where vapors
are present, the scope of LNAPL vapor inhalation must also be determined as inhalatlon
is an additive component in a toxicological risk assessment.
LNAPL Source Identification
Characterization and source identification of LNAPL contamination presents as a
complex and challenging field of study. Identification of the composition, source
and age of LNAPL contamination is central to identification of the responsible party.
A hydrogeological model of LNAPL contamination, validated by free product soil and
water samples and coupled with state-of-the-art analytical methodology, greatly
assists in the creation of an objective source identification.
The same analytical methodology can often identify the LNAPL source(s) with reasonable
scientific certainty, particularly if free product soil and water samples are collected
over time. LNAPL contaminants can sometimes be segregated and type-matched to specific
sources by virtue of their composition, additives and documented historical factors.
For example, if a chemical compound found in a LNAPL mixture was manufactured only
for a specific period of time or was in use only by a particular, known source,
this information can help to eliminate other candidates as sources of origin. Great
attention to detail and strict compliance with generally-recognized, peer-reviewed
analytical methodologies are required as weight-of-evidence (WOE) determinations
can greatly impact the outcome of any case involving LNAPL.
Total Petroleum Hydrocarbons
A comprehensive toxicological risk assessment will typically include objective analyses
and determination of total petroleum hydrocarbons (TPH). This includes all undifferentiated
hydrocarbons for aromatic and aliphatic carbon compounds C5 through C35. These substances
have significant toxicological relevance when assessing the potential health effects
of petroleum hydrocarbons in soil, water, food and atmospheric vapors, as varying
molecular weight ranges of hydrocarbons each exhibit different potential adverse
Target Organ/Critical Effects
Decreased body weight4,5
Decreased body weight, liver3
Hematological system, liver3
Health effects from TPH exposures depend on many factors and the compounds in different
TPH fractions impact the body in different ways. Toxicological variables include
(but are not limited to) the types of chemical compounds present in contamination,
exposure dose, duration and pathways. Some TPH compounds, particularly the smaller
compounds such as benzene, toluene, and xylene (which are present in gasoline) impact
the human central nervous system. However, human studies are lacking for the majority
of TPHs and the documented toxicity and effects of some TPH compounds are presently
based largely on animal studies. Thus, in human health risk assessments, the expert
toxicologist must rely upon animal and human epidemiological studies of TPH mixtures
with respect to identifying specific potential adverse health effects.6
LNAPL Contamination Liability
From a forensic toxicological perspective, scientifically credible determination
of the age and source of LNAPL contamination is critical with respect to liability.
Since LNAPLs are lighter than water, they frequently tend to form a layer on top
of the water over time (and may subsequently migrate). Compounds with densities
greater than that of water (such as TCE) can form dense non-aqueous phase layers
known as DNAPL.
LNAPL layer(s) can persist over long periods of time, even decades. There are numerous
locations in the US where industrial LNAPL contamination has created underground
layers of petroleum products of various ages floating on top of underground water
tables and reservoirs. TCAS has assessed cases in which LNAPL was suspended
on residential water tables as a consequence of contamination from multiple sources
over many decades. Forensic toxicological analyses in such cases involved the use
of specific scientific methods to identify the characteristics, additives, source
and age of the LNAPL plume. These are all critical issues with respect to matters
It should be pointed out that LNAPL contamination remediation is seldom a short-term
project. Toxicologists may work closely with legal personnel to set achievable goals
consistent with regulatory requirements and human health risk assessments, both
in realistic timeframes and within reasonable budgets. However, LNAPL contamination
imposes some unique, practical considerations. For example, LNAPL is hydraulically
recoverable if the rate of recovery (using conventional hydraulic methods such as
pumping, skimming, etc.) is technically and economically feasible at the contamination
site and if applying such recovery methods does not introduce new health hazards.
However, only some sites will warrant such an investment in recovery apparatus and
personnel. Similarly, a toxicological assessment can identify health-based considerations
which, in turn, may suggest specific approaches for medical monitoring and treating
residents during and after remediation. U.S. EPA publications and state regulatory
guidance can assist decision-makers with making good choices and addressing health-based
factors most appropriate to the impacted community.
An objective LNAPL toxicological assessment involves compositional chemistry analyses
designed to assess source and age, followed by a comprehensive health risk assessment
based on a quantitative evaluation of water ingestion, vapor intrusion and other
factors. It is highly recommended that in view of the scope of potential liabilities
associated with LNAPL, any individual, company or government agency engaged in LNAPL
litigation matters always retain an experienced expert toxicologist and hydrologist.
TCAS has performed numerous LNAPL assessments and provided objective reports
as well as expert opinions and expert witness consults for many types of LNAPL and
Notes and References
- U.S. Environmental Protection Agency, "Light Non-Aqueous Phase Liquids
- U.S. Environmental Protection Agency, "A
Decision-Making Framework for Cleanup of Sites Impacted With Light Non-Aqueous Phase
- Massachusetts Department of Environmental Protection, "Updated
Petroleum Hydrocarbon Fraction Toxicity Values for the VPH/EPH/APH Methodology,"
November 2003, Bureau of Waste Site Cleanup.
- Louisiana Department of Environmental Quality, "Risk Evaluation Corrective
Action Program (RECAP)," 2003.
- State of Ohio, "Guidance for Assessing
Petroleum Hydrocarbons in Soil," September 22, 2004, Number DERR-00-DI-033.
- ATSDR, Division of Toxicology and Environmental Medicine, "Public
Health Statement for Total Petroleum Hydrocarbons (TPH)," September, 1999.
- Adapted from U.S. EPA, "Understanding
Light Non-Aqueous Phase Liquid (LNAPL) Behavior in Soil"
- Adapted from Delin and others; 1998 USGS Fact Sheet FS-084-98G