Nearby Targets
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Only two factors are evaluated: nearby individual and population within 1 mile. These two target types are treated and evaluated for potential exposure rather than actual exposure.
Nearby Individual: Look at HRS Table 5-9, page 51649. What is the maximum value that can be assigned? ANSWER
- Population within 1 mile: Examine HRS Table 5-10, 55 FR, page 51649 carefully. Compare the value assigned for 1,200 people within 1/4 mile travel distance (41) with the value assigned in HRS Table 3-12, page 51604 for 1,200 people who receive drinking water from a well within 1/4 mile (1,633).
The value for the nearby targets in the soil exposure pathway receive only 1/40 the value of potential targets in the drinking water threats (ground water or surface water). This difference results from the exposure scenarios that underlie the different exposure routes.
QUESTION: What is the estimated value for population within 1 mile at a rural site with a population density of 100 people per square mile? Assume that the areas within the three distance rings are 0.2, 0.6, and 2.6 square miles respectively. ANSWER
EXERCISE: Lets complete the nearby population threat with some quick what-if calculations based on the following site information. The site is a small, bankrupt wood preserver with observed contamination documented in the process area and drip yard for a total of about 50,000 square feet. The maximum toxicity value for wood-treating substances found in the sampling is 10,000. The site is not secured from access. There are no resident targets. ANSWER
There are two teaching points buried in this exercise:
- Back-of-the-envelope or what-if scoring is relatively easy to do and can focus your attention on the factors that can make a change in the pathway score.
- How much effort will you spend at the site inspection trying to shore up documentation like area of observed contamination, recreational use of the site, or location of the nearby individual?
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