Sub-module 5A, page 5

If you explored PCP via the Level I model, the RAIS site, and the NSC site, you probably discovered some contradictions. (There is very important mistake in the NSC site, extra credit for anyone who caches it.) But it seems clear that the PCP is either a solid on the ground, mixed into the top layer of soil,or bound to the organic carbon in the soil. It is not volatile, nor in its present state, particularly water soluble. We don't know, at least so far, if it is in the vegetation on the site. Let's assume it is not. Also the problem statement did not mention if the soil was bare between the stunted vegetation.

We quickly see that exposure via the soil and or dust could be a problem. Our level 1 model indicated that there could be some PCP in the sediment of the lake, we don't know. I'll go through these with my comments in red. You may have some different ideas. That's fine. In real life this would be an iterative process and with each pass through our data we would recognize other data we need before me make a decision.

Step 1. Characterize the Exposure Setting

Physical Setting

• Geology Consider topography: land forms, slope, distance to water bodies We did not talk about the slope of the land. Could runoff of rainwater with entrained soil spread the contaminant?
• Hydrogeology Number and use of aquifers, groundwater flow direction.The groundwater table is probably high, given the lake surface close-by. We don't know about the groundwater flow. No drinking water wells are nearby, that we know about.
• Climate Temperature and precipitation, relation of seasons to land use.If this was Alaska, kids might swim one or two months each year, if it was Mississippi they might swim 8 or nine months.
• Meteorology Prevailing wind direction, storms We have the prevailing wind. Is the site subject to storms? Have there been storms since the PCP was left on the site?
• Vegetation Soil cover, potential for dust, food chain exposure.We are not sure about the vegetation now, but if the lot is sold to another contractor, they are liable to disturb the vegetation and stir up the soil.
• Soil type Chemical binding and leaching potential. We need to know the organic carbon content of the soil.

Identification of potential receptors

• Residents Of the subdivision
• Workers The blueberry farm and cemetery have workers. Also, if the gravel pit is reactivated, there will be workers there.
• Trespassers The kids who swim in the lake are probably legally trespassers. There may be others, since there is no fence.
• Recreational Users We know about the kids who swim. Are there bike paths, trails?
• Special: children, elderly ages, present population, future population Kids for sure.
• Activity patterns: season activity, portion of time spend in exposed locations. Summer swimming, fishing.

Step 2. Identify Exposure Pathways and Potential Intake Routes.

Chemical Sources and release mechanisms.

• Types of Chemicals:chemical properties, solid, liquid, persistence It is a solid, in or on the soil. The one reference indicated PCP is not persistent. I think it is.
• Source: leaking drums, contaminated soil At this time, soil is the source. We might assume that some time ago there was a "primary source" that spilled on to the soil, and perhaps the lake, but today the soil is the source.
• Releases: past, present, future We assume large amounts were release some time ago. At present PCP may be transported from the site a variety of ways. We will have to consider that if the site is disturbed by reactivating the pit, there may be dust released in large quantities.

Exposure Points

• On site Yes, people might be exposed on site, kids as it is, workers later.
• Off site It is plausible that people will be exposed off site at several places.

Exposure routes through which intake of the contaminant might occur

• Ingestion of Water: deliberate drinking from ground or surface water sources. Incidental ingestions of surface water during swimming and recreation. Since we have not found any in the lake and there is no local groundwater use, there is unlikely to be exposure from this route. Are we sure? (No, we would need to do some monitoring of the groundwater under the site just to be sure, but let's keep this simple for now.)
• Dermal contact with Water: Recreations, showering See above
• Ingestion of soil or sediments. If soil is exposed, consider vegetation and paving. Soil is ingested by hand to mouth transfer. Sediment ingestion is less frequently an issue, unless water bodies dry up or during recreation.For now, Kids play near the site and we know soil is ingested (we will talk more about this. Some kids eat soil directly, but we all ingest dust.)
• Dermal contact with soil and sediments. Yes, there could be contact with the soil.
• Inhalation exposure. both vapor phase, particle phase The PCP has a low vapor pressure so inhalation of the vapor is probably not a problem. However inhaling dust particles may be an exposure route.
• Exposure to biota. Plants and animals (which includes an evaluation of how it got into the biota.) Since the lake is not known for its fishing, even though kids sometimes do catch a fish, we can neglect fish. How about PCP dust on the blueberries? Yes.

For both steps 1 and 2, you must 

When identifying the pathways an potential intake routes, you must consider both the present and the future.

• Changes in land use. From industrial to residential, from uninhabited to inhabited. We have focused on the expected transition from inactive to active gravel pit. However there may be nothing preventing the future use of the land for a subdivision, housing.
• Changes in the concentration of contaminant.We don't have data that indicate the concentration in the soil will go down. It is unlikely to go up.
• Transport of the contaminant. Migration over time to distant sites.Dust can blow quite a distance. But let us assume it does not go further than the region we are discussing. How about the blueberries?
• Transport of the contaminant to different media. Soil washed into a river. Here we don't know if the PCP has been washed into the lake and is now in the sediments.
• Accumulation in plants and animals over time.Is PCP in the blueberries?
• Uses of the media. Soil for crops, water for irrigation or drinking. We have not tested the soil in the blueberry farm.

Land use. Here are some common land uses:

• Agricultural The site itself is not agricultural, but there is a farm close-by.
• Residential Again, close-by.
• Commercial
• Industrial
• Recreational The recreation potential is probably limited to the casual swimming.
• Mining The extraction of gravel is technically mining. It could also be considered industrial.
• Mixed: Often the case. Must focus on the use that will result in the highest most exposure
• Unused

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