The Village of DePue: "A" is for Arsenic - Part 7

T'was the day before Christmas...
And I'm looking at sample data.

Last post I looked at all the 125 samples collected in OU-4.  These samples I surmised, represented the potential exposure for the people who live in DePue.

Yellow = Chemicals of Concern for public health.  Red indicates the highest concentration found that exceeds the soil screening level for residence chronic health.  If the highest value is not in red, there were no samples that exceeded the SSL and those sites do not pose a human health risk for that chemical at that concentration.

I found that seven of the contaminants exceeded the screening level threshold.  That being the case, I need to look to see how many samples exceeded it and if that exceedance elevates my concern for a risk to public health.

The one that caught my eye was arsenic.  If you are going to make a statement of "way-above-normal concentrations" that one might fit the bill.  What's important here is to see how many of the 125 soil samples from OU-4 exceed the Soil Screening Level (SSL).

So I go back to the Excel file, sort on arsenic, and...they all do!

Well that can't be right.  No where have I read that arsenic was a chemical of concern for this site.  Yet all 125 samples are above the screening level establish for inorganic arsenic!

In 1992 - before any cleanup had begun, the Illinois EPA said this about the site:

All residential soil samples showed elevated levels of cadmium when compared to samples taken in Tiskilwa. All but two samples showed elevated levels of zinc. Thirteen samples showed elevated levels of barium. Other samples showed elevated levels of arsenic, lead, copper, mercury, and selenium.

Okay, so arsenic is identified there.  But they go on to say:

Many of the contaminants are naturally occurring in soil at lower concentrations. Based on this first round of sampling, cadmium appears to be the main contaminant of concern.

Wait...cadmium is the main CoC, not arsenic?  Okay...so if cadmium is elevated and it is being dispersed in dust, then one would expect the other metals to follow along with it.  But we have only 26 that are elevated for cadmium, with the average concentration at 91 mg/kg - which is very close to the cadmium SSL of 70 mg/kg.

Something isn't right here.  I would think the Illinois EPA would be making much more of a concern over arsenic and chromium since the SSL is exceed considerably for both those compounds.  Why focus on cadmium?

Oh..."many of the contaminants are naturally occurring in soil."

What are the screening levels for arsenic and chromium based on?  Cancer (ca).

Oh yeah...carcinogens are calculated differently.  If you will recall from previous posts, cancer risk is based on the number of excess cancers we are willing to accept.  In the case of soil screening levels, the cancer risk plugged into the formula that spits out that number uses a value of one additional cancer in one million cancers (1.0E-6).

Source

This creates a problem for us.  Our formula that calculates a SSL does so based on the parameters and values we assign.  If we tell it to spit out a SSL for a contaminant we classify as a carcinogen, it will use the slope factor and the target cancer risk of 0.000001.  Here is what those calculations look like:

Source

Aren't you glad the computer does those calculations for you?  Trust me on that one.  I had to do these by Excel which is way easier than the poor chaps who had to do them with a paper and a calculator.

Don't get bogged down on those formulas.  What I want you to see is that these calculations use the cancer slope factor (CFO) and the target cancer risk (TR) of one in one million in their calculation of the soil screening level.  If you want to know more about the cancer slope factor see my previous posts.

So...based on these two parameters, CFO and TR, we get SSLs that are very...very...very low for suspected carcinogens.  They are that low because our margin of safety is less than one additional cancer in one million over a 70 year lifetime - based on a theoretical dose from the cancer slope factor.

The point is, our SSL for aresenic is lower than what our background exposure to that compound will be.  Arsenic and chromium are natural elements (yes, I know chrome VI is not, I used the most toxic form and assume that all of the chromium they detected is chrome VI).  In other words, what we theoretically want to see is not the reality of the world we live in.  In this case, we can ignore the calculated SSL and set the SSL to background.

That's what California does:

Source

And that's how the Illinois EPA does it as well:

IL EPA Soil Background Level: The standards used to compare soil samples are the Illinois EPA's background concentrations of inorganic chemicals in counties outside metropolitan statistical areas, as published in Section 742 Appendix A, Table G of Title 35 of the Illinois Administrative Code (starting on page 89 of this document). The standard states that "For each parameter whose sampling results demonstrate concentrations above those in Appendix A, Table G, the [responsible party] shall develop appropriate soil remediation objectives in accordance with this Part." The Illinois EPA considers these background standards an appropriate measure by which to compare soil samples.

That came from the Cleanup DePue's website.  Table G looks like this:

Source

...and with that table, as well a MCLs, we get a whole bunch of confusion as to what level is "safe."  The Cleanup DePue webpage writes:

The standard states that "For each parameter whose sampling results demonstrate concentrations above those in Appendix A, Table G, the [responsible party] shall develop appropriate soil remediation objectives in accordance with this Part." The Illinois EPA considers these background standards an appropriate measure by which to compare soil samples.

I'll need to look into that statement.  If that is what it states, then it is looking at risk incorrectly when requiring a cleanup plan be developed.  And since this is a Superfund site, there's this thing we call ARARs that are taken into consideration.  Oh goody.  Looks like I will be posting into the double digits before I get through with this series.


Next post: The Village of DePue:  Mmm....TACOs  - Part 8