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The process of risk assessment for identifying hazardous materials at a site, classifying human activities, determining cancer and hazard quotients, and developing remediation plans. It includes examples of calculations for beryllium and other substances using intake factors and slope factors from the epa.
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Kennedy Space Center
Toxic Waste Remediation
at the Kennedy Space Center!
Mathematics for Engineering Technology
Industrial and Management Environmental Geology
Materials
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Aerial view of Swartz Road old and new landfill.
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Part 1 Risk Assessment 101
Like many high technology applications, NASA’s Shuttle operations can emit toxic materials into the environment. Because of this, the need to clean up these materials is a big concern to NASA. The risk assessor’s job is to analyze, both scientifically and mathematically, a potentially polluted area to determine if the site should be cleaned up. The risk assessor also works with other scientists to help determine how the site should be cleaned up. In order to complete the analysis, the risk assessor needs to consider many factors. He/she needs to determine:
a) the hazardous materials which exist at the site, b) whether or not the presence of these materials presents a potential risk to human health, and c) whether or not the contamination at the site is so bad that it needs to be cleaned up and, if so, then how “clean” does the site need to be?
To determine what hazardous materials exist in an area, soil and water samples are taken from the site. A lab then analyzes these samples to determine if any hazardous materials are present. Hazardous materials fall into two general classes:
Hazardous materials can be present in:
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To determine whether the presence of hazardous materials might become a risk to human health, the risk assessor needs to determine the ways in which a polluted site will be used. Will the polluted site be used for industrial, residential or recreational purposes? The risk assessor classifies the type of human activity that is occurring or may occur after NASA has left the site. Here is a list of typical classifications from which the risk assessor can choose: i) Industrial Worker ii) Adolescent Trespasser iii) Adult Recreator iv) Child Recreator v) Adult Resident vi) Child Resident
For each kind of human activity at the site, the risk assessor needs to determine whether the carcinogenic materials at the site pose a cancer risk to humans. For each carcinogenic material present at the site, the risk assessor calculates a value called the Cancer Risk due to this material. He/she then adds up the Cancer Risks for all carcinogenic materials found at a site, and this becomes the total Cancer Risk for the identified type of human activity at the site. If this number
is larger than 10 −^6 , the risk of cancer from these materials is considered unacceptable.
The risk assessor will also calculate the risk to human health due to each non-carcinogenic material at the site. He/she does this by calculating the Hazard Quotient for the hazardous material at the site. He/she then adds up Hazard Quotients for all non-carcinogenic materials found at a site, and this becomes the total Hazard Quotient for the identified type of human activity at the site. If this number is larger than 1, the risk from these materials is considered unacceptable.
After determining the total Cancer Risk and the total Hazard Quotient, the risk assessor will work with other scientists and managers to determine what type of clean up plan (called the Remediation Plan) should be developed. There are many options for remediation at a site. These options include:
a) Do Nothing : In this case you would leave the site alone, and the hazardous materials will be left to decompose. Of course this is the cheapest method of clean up, but it does not do anything to change the risk of human contact with hazardous materials. b) Prevent Human Contact : You could put up a fence around the site and have it guarded. Like the first option, this does not clean up the site, but it also does not cost very much. c) Low Cost Remediation : In this option you would bring the site up to standards that are minimally acceptable for human health. This is more expensive than the previous options. d) High Cost Remediation : In this option you would bring the site up to standards that exceed the minimally accepted standards. This type of remediation is the most expensive.
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Part 2 Doing a Risk Assessment
Now that you have completed Risk Assessment 101 , your next step is to undertake a risk assessment of a particular site. This site is a landfill at the Kennedy Space Center (KSC) located in an area which is closed to the public.
Hansom Landfill
This site is approximately one mile east of the Visitors Information Center. The landfill began operation in 1964 during the initial construction of KSC by NASA. During its period of operation, the landfill received unspecified waste which was placed in unlined trenches that were 600 ft x 30 ft x 10 ft. While no records of the type or quantity of materials at the landfill were maintained, it is likely that the site received a variety of hazardous waste materials. This land was also used to stockpile scrap metal and other materials on a temporary basis.
With this particular site under consideration, we first address the question of who will use the site. Since the site is an interior location at KSC in an area which is closed, we may eliminate usage by recreators or residents. Therefore, we will consider the scenario of an industrial worker at the site.
Recall from the previous section that the Cancer Risk and the Hazard Quotient are numbers that the risk assessor uses to determine a course of action. These numbers need to reflect all the factors which have an effect on the amount of risk present. Therefore, the calculations of Cancer Risk and Hazard Quotient are, by their very nature, quite involved. They will require formulas, variables, calculations, and units. We will go through the calculations one step at a time, and stop along the way to organize the information in table format. This process is presented in the following steps:
Intake Rates and Exposure Assumptions
Calculating Intake Factors (eating, drinking and breathing)
Risk Calculations A. Ingestion of Soil B. Inhalation of Airborne Soil C. Ingesting Water
Writing a Report
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Intake Rates and Exposure Assumptions
Recall from the previous section that hazardous materials can be present in the soil and water at a site. These hazardous materials can threaten people who may eat or breathe in contaminated soil or drink contaminated water. Table 1 lists amounts that are considered reasonable maximum Intake Rates (IR) for an industrial worker at the site. It is important to note that these Intake Rates refer to the contaminated substance (soil, air, or water) and not to the hazardous material itself.
Table 1 - Intake Rates Intake Rate of ingesting (taken in orally) contaminated soil (IR) 100 mg/day Intake Rate of breathing air containing contaminated soil particles (IR) 1.9 m^3 /hour Intake Rate of drinking contaminated groundwater (IR) 1 l /day
ACTIVITY 1: Translate the units for each Intake Rate into a verbal phrase. For example, mg/day would be milligrams per day. Discuss the amounts given and why these are reasonable maximum rates.
To determine the amount of contaminated substance ingested by an individual, we need to take into consideration not only the Intake Rate but also how often the individual was at the site and over what period of time. This leads to two more quantities referred to as Exposure Frequency and Exposure Duration.
Now we are ready to use a formula to calculate the amount of contaminated substance ingested over a certain amount of time:
Amount Ingested = (Intake Rate) × (Exposure Frequency) × (Exposure Duration)
Using variables, the formula is:
AI = IR × EF × ED
To determine this calculation for our industrial worker, let’s say he/she will be working at the site for 25 years. The Exposure Duration would then be 25 years, but what about the Exposure Frequency? Risk assessors typically use the worst case scenario. If the worker only gets
weekends and a few holidays a year off from work, then 250
days year
can be used for Exposure
Frequency.
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ACTIVITY 4: In order to organize the data we have accumulated so far, complete the following table by filling in the empty cells. Notice in Table 2 that the value and units for Amount Ingested by eating have been converted from mg to kg. You should verify the conversion.
Table 2 Exposure Assumption Reference Variable
Units Reasonable Maximum Exposure Value
Intake Rate
mg/day m^3 /hr l /day Exposure Time ET 8 Exposure Frequency Exposure Duration years
Amount Ingested
kg m^3 l (^) 6.250E+
Calculating Intake Factors (eating, drinking, and breathing)
Since the numbers we have calculated for Amount Ingested are based on a 25 year time frame, the risk assessor includes an averaging time to calculate the Intake Factor. The Intake Factor is a value that indicates the present level of danger to an individual. The impact of the Amount Ingested by an individual is influenced by the size of that the individual. In other words, a child’s system would be impacted more severely than an adult’s because the larger body mass of the adult allows a higher tolerance to the same level of exposure. The Intake Factor is calculated using the following formula.
Intake Factor =
Amount Ingested (Body Weight) (Averaging Time)
Recall that the type of individual we are considering is an industrial worker. We will consider that the individual weighs 70 kg. (Just for fun, what is the person’s weight in pounds?)
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Since carcinogens may remain in the body for many, many years before they might cause cancer, the averaging time for carcinogens is taken to reflect an entire average lifetime of 70 years times 365 days per year. Thus, the Carcinogenic Intake Factor for eating would be:
Carcinogenic Intake Factor (CIF)
6.25E 01kg 70kg 25,550days
kg kg - day
For non-carcinogens, the averaging time is the Exposure Duration (ED) times 365 days per year. The Non-carcinogenic Intake Factor for eating would be:
Non - carcinogenic Intake Factor (NIF) =
6.25E 01kg 70kg days
kg kg - day
Note: In the above formulas, the units
kg kg - day
signify kilograms of the contaminated substance
that the industrial worker ingests for each kilogram of his/her body weight per day. We have not canceled kilograms to emphasize that the kg in the numerator refers to the contaminated substance, but in the denominator kg refers to body weight.
ACTIVITY 5: Calculate CIF and NIF for drinking and breathing, and fill in the empty cells in Table 3.
Table 3 Intake Factor Reference Variable
Units Value
kg/kg-day 3.495E-
Carcinogenic Intake Factor
kg/kg-day 9.785E-
Non-carcinogenic Intake Factor
Our calculations so far have dealt with the contaminated substance – soil, air, or water. Now we can consider calculations involving the actual contaminants (hazardous materials).
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Verify the following calculations for Cancer Risk and Hazard Quotient due to beryllium from ingesting soil at this site. Use the scientific notation display mode on your calculator.
Cancer Risk = (2.16E 01)
mg kg
kg kg - day
kg - day mg
Hazard Quotient =
mg kg
kg kg - day
5.00E 03 mg kg - day
Notice that all units cancel in both calculations. This means that Cancer Risk and Hazard Quotient do not have a unit label. This makes the comparison more straightforward.
ACTIVITY 6: Using the last equation as an example, compute the Hazard Quotient for thallium ingested at the site by eating soil, and enter the result in the appropriate cell of Table 4. (Thallium is not carcinogenic when ingested so there is no need to compute Cancer Risk.)
Table 4 - Pathway Sums for Ingesting Soil Metal Cancer Risk Hazard Quotient Beryllium 3.246E-07 4.227E- Thallium ---- Pathway Sums
ACTIVITY 7: Add the values in the Cancer Risk and Hazard Quotient columns and enter the sums, called Pathway Sums , in the bottom row of Table 4.
B. Inhalation of Airborne Soil
To calculate the Cancer Risk and Hazard Quotient for breathing contaminated air, we use the following formulas:
Cancer Risk =
(Chemical Concentration) (CIF) Inhalation Risk) (Volatilization Factor)
Hazard Quotient =
(Chemical Concentration) (NIF) Volatilization Factor) (Reference Concentration)
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Table 5 summarizes the data necessary to calculate Cancer Risk and Hazard Quotient for inhalation of airborne soil. If a box contains dashed lines, this indicates that a value in this category is not relevant. For example, since there is no Reference Concentration indicated for cadmium, we do not calculate a Hazard Quotient for cadmium.
Table 5 Hazardous Material Chemical Concentration in mg/kg
Inhalation Risk in kg-day/mg
Reference Concentration in mg/kg-day
Volatilization Factor in m^3 /kg Beryllium 2.16E-01 8.4E+00 5.00E-03 9.66E+
Cadmium 8.66E-01 6.3E+00 ---- 4.63E+
Chromium 1.57E+01 4.2E+01 ---- 4.63E+
4-Methyl-2-Pentanone 6.07E-04 ---- 2.3E-02 7.36E+
ACTIVITY 8: Using the values given in Table 5 above and our previous calculations of Cancer Risk and Hazard Quotient as examples, fill in the appropriate cells of Table 6.
Table 6 - Pathway Sums for Inhaling Airborne Soil Hazardous Material Cancer Risk Hazard Quotient Beryllium Cadmium ---- Chromium ---- 4-Methyl-2-Pentanone ---- Pathway Sums
ACTIVITY 9: Referring to Table 6, add the values in the Cancer Risk and Hazard Quotient columns, and enter the sums in the last row labeled Pathway Sums
C. Ingesting Water
To calculate the Cancer Risk and Hazard Quotient for drinking contaminated water, risk assessors use the following formulas:
Cancer Risk=(ChemicalConcentration)×(CIF)×(Slope Factor)
Hazard Quotient =
(Chemical Concentration) (NIF) (Reference Dose)
