If you explored PCP via the Level I model and the RAIS site,
you probably discovered some contradictions. 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 I 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? Slope of land may indicate direction of groundwater flow.
- Hydrogeology Number and use of aquifers, groundwater
flow direction. The groundwater table is probably high,
given the lake surface is 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.
Also, soil type can indicate a relative scale of permeability.
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 ingestion 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 and 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 exposure.
- Unused.
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