E.F.A. I
IDENTIFICATION OF BIASED ENVIRONMENTAL DATA
An expert opinion is worth no more than the factual data upon which it is based. The critical review of
environmental data is therefore essential for judging the reliability of the factual information. Environmental data
relied upon to form an opinion should be of a sufficient known quality to withstand the scientific and legal
challenges relative to the purpose of the data collection.
In most instances, only a small percentage (about 10 to 15%) of the data in an environmental investigation
contains elements susceptible to bias. These elements are usually associated with the geologic investigation and
sample collection, analytical testing, and interpretation of the horizontal and vertical extent of soil and
groundwater contamination.
An important task in the forensic review of environmental data is the determination of whether a pattern of bias
(systematic error) exists. This bias can be due to factually incorrect information, errors, or intentional
manipulation. The Figure below illustrates bias and data variability (random error) based on a sample population
whose true concentration is about 20 parts per million (ppm). As depicted in the Figure, data can be biased
negatively or positively. Three specific types of biases and/or errors are defined as follows:
1. Positive bias: In a data sufficiency context, a positive bias arises when a test incorrectly indicates
contamination or an increase in contamination when there is none.
2. Negative bias: In a data sufficiency context, a negative bias occurs when monitoring fails to detect
contamination or an increase in the concentration of a hazardous material.
3. Erratic data: Erratic data are anomalous values which make it statistically impossible to develop
meaningful trends and/or correlations
These biases result from investigative, sampling, analytical, and statistical errors. Ultimately, expert witness
opinions based on incorrect information can result.
1 Identification of Biased Environmental Data| Environmental Forensic Analysis I
, E.F.A. I
Graphical representation of sample bias and variability. (From Mishalanie, E.,in Proc. of the National Environmental Forensic Conference:
Chlorinated Solvents andPetroleum Hydrocarbons, August 27–28, College of Engineering and Engineering Professional Development,
University of Wisconsin, Madison, 1998, p. 27. With permission.)
Geologic Characterization
The geologic characterization component of a site investigation provides insight regarding contaminant
distribution and transport. Components of a geologic investigation usually include:
Drilling and logging of the boreholes and/or trenches
Soil retrieval for textural classification and/or physical testing
Soil sampling for chemical analysis
The first step is to acquire and review the original field borings and/or trench logs. Compare the information on
the field logs and final logs in the report for consistency. If geologic cross-sections or fence diagrams are included
in the report, examine them for consistency with the field log/trench descriptions.
When reviewing boring logs, examine their placement relative to historical information, especially areas of known
or suspected contamination. This review often provides insight as to whether additional borings and/or sampling
are necessary. Given that site access agreements among multiple parties are usually required in order to perform
additional sampling, the sooner the data sufficiency of the geologic information is identified, the sooner the site
access agreements and sampling can proceed. The sufficiency of existing geologic information can be determined
via the following steps:
Ascertain whether the drilling method employed allows an accurate description of the subsurface.
Determine whether the number of soil borings is sufficient to characterize the geologic environment
relative to litigation allegations.
Decide whether the borings are sufficiently deep to characterize the geology of interest.
Decide whether the borings are spatially located so as not to preclude developing useful information for
geologic characterization.
The drilling technology impacts the geologist’s ability to describe the soil and/or geologic setting. Reliance solely
on mixed drill cuttings from air or mud rotary drilling, for example, precludes the ability to provide detailed
descriptions of stratigraphic changes. Continuous hollow stem augering and/or most push technologies that
retrieve an in situ soil sample provide this level of detail.
Groundwater Characterization
The hydraulic properties of an aquifer are commonly estimated or measured as part of a groundwater
characterization investigation. The determination of how these properties are measured and their reliability is one
factor in evaluating contaminant transport and risk assessment models. Hydraulic properties and their definitions
include:
Hydraulic conductivity: The rate of flow of water in gallons per day through a cross-section of 1 ft2 under a
unit hydraulic gradient at a prevailing temperature.
Hydraulic gradient: The rate of change in total head per unit of distance of flow in a given direction.
Permeability: The property or capacity of a porous rock, sediment, or soil to transmit a fluid.
2 Identification of Biased Environmental Data| Environmental Forensic Analysis I
IDENTIFICATION OF BIASED ENVIRONMENTAL DATA
An expert opinion is worth no more than the factual data upon which it is based. The critical review of
environmental data is therefore essential for judging the reliability of the factual information. Environmental data
relied upon to form an opinion should be of a sufficient known quality to withstand the scientific and legal
challenges relative to the purpose of the data collection.
In most instances, only a small percentage (about 10 to 15%) of the data in an environmental investigation
contains elements susceptible to bias. These elements are usually associated with the geologic investigation and
sample collection, analytical testing, and interpretation of the horizontal and vertical extent of soil and
groundwater contamination.
An important task in the forensic review of environmental data is the determination of whether a pattern of bias
(systematic error) exists. This bias can be due to factually incorrect information, errors, or intentional
manipulation. The Figure below illustrates bias and data variability (random error) based on a sample population
whose true concentration is about 20 parts per million (ppm). As depicted in the Figure, data can be biased
negatively or positively. Three specific types of biases and/or errors are defined as follows:
1. Positive bias: In a data sufficiency context, a positive bias arises when a test incorrectly indicates
contamination or an increase in contamination when there is none.
2. Negative bias: In a data sufficiency context, a negative bias occurs when monitoring fails to detect
contamination or an increase in the concentration of a hazardous material.
3. Erratic data: Erratic data are anomalous values which make it statistically impossible to develop
meaningful trends and/or correlations
These biases result from investigative, sampling, analytical, and statistical errors. Ultimately, expert witness
opinions based on incorrect information can result.
1 Identification of Biased Environmental Data| Environmental Forensic Analysis I
, E.F.A. I
Graphical representation of sample bias and variability. (From Mishalanie, E.,in Proc. of the National Environmental Forensic Conference:
Chlorinated Solvents andPetroleum Hydrocarbons, August 27–28, College of Engineering and Engineering Professional Development,
University of Wisconsin, Madison, 1998, p. 27. With permission.)
Geologic Characterization
The geologic characterization component of a site investigation provides insight regarding contaminant
distribution and transport. Components of a geologic investigation usually include:
Drilling and logging of the boreholes and/or trenches
Soil retrieval for textural classification and/or physical testing
Soil sampling for chemical analysis
The first step is to acquire and review the original field borings and/or trench logs. Compare the information on
the field logs and final logs in the report for consistency. If geologic cross-sections or fence diagrams are included
in the report, examine them for consistency with the field log/trench descriptions.
When reviewing boring logs, examine their placement relative to historical information, especially areas of known
or suspected contamination. This review often provides insight as to whether additional borings and/or sampling
are necessary. Given that site access agreements among multiple parties are usually required in order to perform
additional sampling, the sooner the data sufficiency of the geologic information is identified, the sooner the site
access agreements and sampling can proceed. The sufficiency of existing geologic information can be determined
via the following steps:
Ascertain whether the drilling method employed allows an accurate description of the subsurface.
Determine whether the number of soil borings is sufficient to characterize the geologic environment
relative to litigation allegations.
Decide whether the borings are sufficiently deep to characterize the geology of interest.
Decide whether the borings are spatially located so as not to preclude developing useful information for
geologic characterization.
The drilling technology impacts the geologist’s ability to describe the soil and/or geologic setting. Reliance solely
on mixed drill cuttings from air or mud rotary drilling, for example, precludes the ability to provide detailed
descriptions of stratigraphic changes. Continuous hollow stem augering and/or most push technologies that
retrieve an in situ soil sample provide this level of detail.
Groundwater Characterization
The hydraulic properties of an aquifer are commonly estimated or measured as part of a groundwater
characterization investigation. The determination of how these properties are measured and their reliability is one
factor in evaluating contaminant transport and risk assessment models. Hydraulic properties and their definitions
include:
Hydraulic conductivity: The rate of flow of water in gallons per day through a cross-section of 1 ft2 under a
unit hydraulic gradient at a prevailing temperature.
Hydraulic gradient: The rate of change in total head per unit of distance of flow in a given direction.
Permeability: The property or capacity of a porous rock, sediment, or soil to transmit a fluid.
2 Identification of Biased Environmental Data| Environmental Forensic Analysis I
