Environmental Forensics Part II Flashcards
What do you understand by environmental forensic?
The systematic and scientific evaluation of physical, chemical and historical information is essential for developing defensible conclusions that will stand in courtroom/environment regarding the source of age of a contaminant.
When did environmental forensic evolved and why ?
Environmental forensic evolved in the 1980’s as a result of the potential liability of parties who allegedly released a contaminant into the environment
When were laws passed for environmental forensic?
Laws were first passed in the US in the 1980s the later, countries in the EU.
What is the application of EF
- Using science to identify pollutants, the responsibility for cleanup in areas of known pollution can be recognised.
- Identification of historical property owners that is responsible for a contaminant release.
- Developing the probability of the chemical exposure cause, manifest or latent injuries.
- To detect marine oil pollution and determining oil spill sources.
What is one thing forensics examiners need to understand before finding a Generic Forensic Techniques for
Contaminant Age-Dating and Source Identification?
There is NO technique that applies to ever chemical released at every site. As a result the investigator must identify the best method that will assist in reaching a valid
and defensible conclusions.
What is the use of Generic Forensic Techniques for
Contaminant Age-Dating and Source Identification?
- May be useful in determining source and age of a release of contaminant.
- Uses this for estimation of date, time and how much was released.
What are the two models used to track source identification?
(a) The Underground Storage Tank Corrosion Model
(b) Commercial Availability of a Chemical
What is the Underground Storage Tank Corrosion Model?
Tank corrosion models can provide probability statistics to estimate the release date of potential contaminants stored in an underground storage tank.
The UST Corrosion rate and piping is influence by ?
The corrosion rate of an underground storage tank and associative piping is influenced by the thickness of the metal and the electrical resistivity of the soil.
What are primary soil measurements typically used in
underground storage tank corrosion models?
- Soil moisture content
- Soil resistivity
- Water soluble chloride and sulfate concentrations (higher the chloride and sulfate concentration the greater, the corrosion rate for steel tanks)
- pH
- Bicarbonate concentration
How does soil resistivity affect UST corrosion?
Though rare, soil with resistivity values below 10,000Ωcm are extremely corrosive respective to steel while soil with resistivity values of 2000Ωcm are 5 times more corrosive than 10,000Ωcm soil.
What is the correlation between the resistivity of soil and UST corrosion?
Low resistivity soil = High corrosion
What are examples of the UST Corrosion Model?
- The Mean Time to Corrosion Failure (MTCF)
- Tank Environment Profiling (TEP)
- Tank Suitability Study (TSS) method
- Rossum Pitting Model
What is the basis of MTCF?
The MTCF relies upon characteristics of the tank backfill
material (eg soil moisture content, rho and sulfide content) along with the tank age.
What is the Mean Time to Corrosion Failure (MTCF)?
a statistical method for assessing and predicting when unsupported steel UTSs would fail based on soil variables surrounding the tanks.
When was MTCF developed?
In 1979
What are non invasive tank integrity assessment methods?
1)Mean Time to Corrosion Failure (MTCF) - Requires soil sampling and statistical prediction modeling;
- 2) Tank Environmental Profiling (TEP) - Requires soil sampling and statistical prediction modeling;
- 3) Petroscope - Requires video camera inspection with soil
sampling and statistical prediction modeling; - 4) Tank Suitability Study (TSS) - Requires soil sampling
and statistical prediction modeling.
What is Rossum Model?
The most frequently used model, because it gives a better estimation of when the underground storage tank began leaking.
Who is the Rossum model named after and why ?
John R. Rossum, who proposed in 1969 an expression to
estimate when an underground storage tank would result in
leakage.
What is the Rossum Pitting Model?
The Rossum Pitting Model provides a simplified expression for estimating when an underground storage tank began leaking and the number of leaks. It also provides the ability to use probability statistics to assign confidence levels to estimate when a leak first occurred.
What is the Rossum pitting model equation?
TL = ( p / 10 - pH) (z/ Kn Ka) ^1/n (1/A) ^ a/n
What is the meaning of the symbols in the Rossum pitting model equation?
TL is the time for the first leak to occur,
* A is the tank surface area associated with a pit depth of z
* p is the resistivity in ohms centimetre
* pH is a measure of the acidity or alkalinity of the soil
* z is the wall thickness of the metal in mil (1mil =0.001 inche. Also see thou )
* Kn and n are emperical constants based on whether the soil aeration is considered:
* Good (n=1/16 , Kn=170)
* Fair (n=1/3 , Kn=222)
* Poor (n=1/2 and Kn=355)
Ka is the relative pit depth and α is an emperical constant.
What is the equation Rossum provided as an s solution for the number of leaks that can occur at any time?
L = A ( [Kn/Ka]/ z) ^ 1/a ⋅ ( [t (10 - pH) ] / p ) ^ n/a
Considerations that affect or influence the results of a corrosion model:
- The presence of cathodic protection, (a sacrificial anode) which can retard the corrosion rate.
- The presence of interconnected tanks and piping of different composition and wall thickness.
- The presence of service coating on the exterior of the tank often similar to asphalt.
- Differences in corrosion mechanisms in undisturbed soils
as contrasted with backfilled excavations - Presence of a fluctuating ground water table which was in contact with the tank and associated piping for some portion of time each year
- Evidence that leakage occurred from tank over-filling or spills as opposed to corrosion.
