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Case Study Exercise
Now that you’ve finished the exercise on carbon tetrachloride in private well water, use what you’ve learned to define exposure units and compile data for them in the following case study exercise.
This case study exercise will focus on working with the arsenic data for soil at the daycare center of the GLC site.
Review the GLC site information.
Site Information: GLC used chromated copper arsenate (CCA) as a wood preservative. The CCA contained arsenic, chromium VI, and copper. The facility placed the CCA-treated lumber on an uncovered drip pad, and CCA-contaminated drippings dropped to the ground. In 2005, Sunshine Playcare Center (a daycare facility) began operating off site, next to a part of the old drip pad.
In December 2015, EPA collected 18 discrete surface soil samples to check for CCA components on the daycare center property. All samples were from the top 2 inches of soil.
Children aged 3 months to 5 years attend the daycare, but only those ≥1 year play in the outside area. They can access all portions of the property. One or two children at the daycare likely engaged in pica behavior for acute or intermediate durations. Pica behavior is the intentional ingestion of non-food items, like soil. Adults and children are present at the daycare facility for five days/week over a maximum of 50 weeks/year (school is closed for two weeks/year for holidays). Some adults have worked at the daycare facility for up to 25 years.
Look at the following GLC site map.
The legend shows the sample location numbers that correspond with the laboratory sampling data. All samples were collected on the daycare property.
The GLC site map shows the locations where EPA collected 18 surface soil samples in December 2015 to see if CCA components were present around the Sunshine Playcare Center.
The map legend shows the full sample location number and the number used on the map to show each location.
Choose one of the following:
- One exposure unit for the entire outside area of the daycare center.
- Different areas of the property as separate exposure units.
The correct answer is “A.”
Option “B” is not correct because you would not define different areas of the property as separate exposure units. This decision is based on our knowledge that children may access all portions of the daycare property.
Specifically, we compiled the arsenic data for the surface soil samples from PHAT Module 6 into the table shown here.
| Sample Location | Date Sampled | Arsenic (mg/kg) |
|---|---|---|
| SS-GL-DC-1 | 12/12/15 | 1.3 |
| SS-GL-DC-2 | 12/12/15 | 350 |
| SS-GL-DC-3 | 12/12/15 | 400 |
| SS-GL-DC-4 | 12/12/15 | 2.6 |
| SS-GL-DC-5 | 12/12/15 | 31 |
| SS-GL-DC-6 | 12/12/15 | 350 |
| SS-GL-DC-7 | 12/13/15 | 560 |
| SS-GL-DC-8 | 12/13/15 | 280 |
| SS-GL-DC-9 | 12/13/15 | 290 |
| SS-GL-DC-10 | 12/13/15 | 550 |
| SS-GL-DC-11 | 12/13/15 | 520 |
| SS-GL-DC-12 | 12/13/15 | 460 |
| SS-GL-DC-13 | 12/14/15 | 840 |
| SS-GL-DC-14 | 12/14/15 | 1,020 |
| SS-GL-DC-15 | 12/14/15 | 950 |
| SS-GL-DC-16 | 12/14/15 | 430 |
| SS-GL-DC-17 | 12/14/15 | 360 |
| SS-GL-DC-18 | 12/14/15 | 270 |
Note: Remember that this exercise has been simplified for training. At real sites, you need to make sure you compile data for each exposure unit, considering data for each potential contaminant of concern and exposure pathway of interest.
You’ve now completed the exposure unit primer. Click next to go to the primer for exposure point concentration.