The Village of DePue: The ethics of drawing a line - Part 11

Looking at the 125 samples collected in OU-4, I found that a number of them exceed the level of concern.

Arsenic, in particular, creates the most problem for establishing a "safe" level at which to leave the soil in OU-4.  Because OU-4 is the area where exposure can take place.

The problem with arsenic is not the poison part we all associate it with, but instead our knowledge that it may cause cancer at low concentrations.

The problem with contaminants that are suspected to cause cancer is that we are told:

The underlying presumption for carcinogens is that the introduction of even one molecule of the contaminant can cause cancer in an individual even if the probability is very low. This conservative, “non-threshold” concept is used because it is presumed that there is no level of exposure to a carcinogen that does not pose a certain level of risk.

That's from Illinois' TACO's Fact Sheet.  That statement is one of the presumptions we hold as true when we look at risk of exposure to a chemical.

You can see the bind that puts us in.  If we say exposure to "even one molecule of the contaminant can cause cancer in an individual" setting a "safe" concentration is, well, not possible.  Instead we draw a line in the sand and say:

You see how they put us risk calculating types between a rock and a hard place?  For exposure to a contaminant in soil, I have to come up with a concentration that theoretically will show no more than one excess cancer per 1,000,000.  That number, based on what we know today, is calculated to be no more than 0.39 mg of arsenic in a kg of soil (0.39 mg/kg).

Now there is no way on God's green earth that you will ever find soil at less than 0,39 mg/kg of arsenic.  Arsenic is a naturally occurring element.  It is everywhere.  Because it is everywhere, we are constantly exposed to it.  In this case, we cannot reasonably ask that soil be cleaned up to a standard lower than what good ol/ mother nature has exposed us to.  So we settle on a background concentration as our cleanup objective.

According to the regulations in Illinois (742.Appendix A, Table G) the background for arsenic in soil at 11.3 in non-metropolitan areas.  Therefore, we are now going to live with this:

But this creates a sense of foreboding when the levels exceed background.  What is the probability of added risk?

In OU-4 there are 98 samples out of 125 that are at or above the background concentration of 11.3 mg/kg arsenic.  The spreadsheet provided by Cleanup DePue shows the average amount of arsenic in OU-4 to be 19.6 mg/kg of arsenic.

Now anyone can see that 19.6 is higher than 11.3.  Does that constitute a "way-above-normal concentrations?"

As I discussed in my last post, what we need to look at is the amount of exposure above normal.  In this case, on average, the soil in OU-4 is 8.3 mg/kg higher in arsenic than the regulatory background limit.

If, and this is a big if, a citizen of DePue is exposed to that soil for 350 days a year for 70 years, by my estimate, that would bring about a probability of 1.8 excess cancers in 10,000.

Now anyone can see that a probability of 1.8 in 10,000 is much higher than 1.0 in 1,000,000.  But that probability of 1.8 in 10,000 is based on coming in direct contact with the soil and having the arsenic in that soil enter into the body.  You must also have that happen each day for 350 days a year for 70 years.  It is also based on a theoretical slope factor that we guestimate will show cancer at a particular concentration.

So how close is that added probability of 1.8 excess cancers in 10,000 to what might actually happen?  Possible?  Maybe.  Probable?  Not even close.

That puts me between a rock and hard place.  One one hand I accept the "even one molecule of the contaminant can cause cancer" presumption and on the other I can soundly state that ya' got nothin' to worry about in OU-4.

And here is where it get's all ethical on us...or at least for me.

• If I accept the "even one molecule of the contaminant can cause cancer" presumption then exposure to any molecule above zero presents a risk.
• If I accept one in one million as being an acceptable level of risk, then I accept as "safe" a concentration that will not present a risk of no more than one excess cancer in one million as my threshold.
• If I accept the premise that arsenic - like chromium, cadmium, and lead - are naturally occurring in the soil, then I must accept the fact that I will always be exposed to some concentration of those contaminants when I come in contact with soil.
• If I accept that there is a concentration of contaminant in the soil that is low enough to be considered "safe" then my responsibility to cleanup my mess will end when that threshold is met.

That last one is the premise of "how clean is clean?"  Since we are concerned about a risk of acute and chronic health problems because of our exposure to the soil in OU-4, we must draw a line in the sand and say on this side it is clean.

That side is determined by doing a risk assessment.  Apparently, Nancy Loeb, the director of the Environmental Advocacy Clinic at Northwestern University School of Law’s Bluhm Legal Clinic, has told the folks in DePue that this risk assessment is flawed:

“The companies spent millions of dollars on consultants in an attempt to show that this SuperFund site poses no significant risks, and they delivered a superficial plan that barely touches many of the contaminated areas, leaves the slag pile and other waste in place, does nothing to stop contamination from seeping into the groundwater, and leaves backyards, playgrounds and Lake DePue without real remediation.”

Ms. Loeb claims that the "safe" line is not set low enough.  She offers no calculations or explanation to support that claim, but, nonetheless, that's her contention.

I am going to look for this plan that she speaks of to see what those cleanup levels and remediation methodologies are to see if they are indeed lacking.

Right now, all I have is a bunch of data that shows an average concentration of arsenic in the soil in OU-4 to be 8.3 mg higher than the legal background concentration established by Illinois in  742.Appendix A, Table G.

Regardless of what I think the true risk is.  Regardless of whether or not 8.3 is to be considered "way-above-normal," the one fact that remains is this.  If I am going to draw a line in the sand that says "clean" then I must do something about the soil that has a concentration above that threshold.

I need to see what is proposed for OU-4.  In particular, I need to see how they are addressing arsenic above background.

Ethically, if I use a concentration to make the statement of clean soil, then I have a responsibility to do something about soil that falls above that level designated as "safe."  I have an obligation regardless as to whether or not the soil above that line presents a risk or not.

This is the double-edged sword we live by.  If I draw a line in the sand to say "safe" and therefore my responsibility is ended, then I have an ethical responsibility to rectify those areas that are above that threshold.

Since Illinois has stated that background may be used as a cleanup objective, anything above background must be remediated.  This is the ethical contract we must adhere to if we are to use the benefit it provides in establishing a level of "safe."  If my responsibility can be terminated at a particular concentration, then ethically I need to be responsible for areas above that.  I cannot accept background when it suits me and discount it when it does not.

Ms. Loeb seems to indicate that the bar of what is "safe" has been moved to allow for exposure to higher concentrations then she thinks is "safe."  What I need to see is how the soil screening levels are being calculated and what constitutes a "safe" concentration.

At this point, 98 samples are above background concentrations for arsenic in OU-4.  The Illinois regulators have drawn a line in the sand and said that background is an appropriate cleanup objective.

Is that legal background concentration in 742.Appendix A, Table sacrosanct?

If we have an ethical duty to reduce the risk for the people living, working, and playing in OU-4, then establishing what a "safe" level of exposure is becomes critical.  This, if I had to guess, is the main sticking point with Ms Loeb.

Not sure if I can get a hold of that information, but I am going to start looking.


Next post: The Village of DePue:  What's in store for OU-4 - Part 12

The Village of DePue: Theoretical Cancer Risk at Background - Part 10

The theoretical cancer slope factor (CSF) that has been set for Arsenic is 1.5 (mg/kg)/day.

So...theoretically:

• The soil screen level that will achieve a risk of one additional cancer in one million for arsenic is 0.39.
• A person exposed for 350 days a year, for 70 years, to 0.39 mg/kg of arsenic in soil would have a 33.3334 percent chance of getting cancer in their lifetime
• A person not exposed to 0,39 mg/kg of arsenic in soil will have a 33.3333 percent chance of developing cancer in their lifetime.
• The difference is 0.0001 percent or a probability of 0.000001 (1 in a million)

This is how we look at chemicals suspected to cause cancer.  There is no "safe" dose, so we calculate the risk based on a chronic exposure to a set amount.

We feel that one in one million is an acceptable risk and the amount of arsenic in soil that would be expected to produce the chronic daily intake (CDI) necessary to show a one in one million risk is 0.39 mg of arsenic per kg of soil.

All of this is theoretical.  But for purposes of setting a cleanup standard, it is the best we have so we will make the assumption that 0.39 mg/kg is the "safe" limit.

That, as we discussed in a previous post, is a value that is unable to be obtained in nature.  That is, there is a natural amount of arsenic that we are exposed to.  We call that "background" and it is set based on what we "normally" see in places where we live.

Illinois has set the background for arsenic in soil at 11.3 in 742.Appendix A, Table G.

11.3 is quite a bit higher than the theoretical "safe" value we want which is 0.39 mg/kg.

There is nothing we can do about background, so we ignore the theoretical what we want, and accept the background as "safe."

So...11.3 mg/kg is "safe."

In OU-4 we have 102 samples that exceed the background concentration that Illinois has said is acceptable.

What do those exceedances  mean in terms of additional risk?

Let's look at this from EPA's Integrated Risk Information System (IRIS) perspective:

IRIS

IRIS shows that the concentration of 0.02 μg of arsenic per liter of drinking water is the "safe" amount that will increase the risk of cancer from 33.3333 to 33.3334 percent.

If you increased the concentration 100 fold, from 0.02 μg to 2.0 μg per liter of water, the risk would move from 33.3333 to 33.3433 percent.

100 times more arsenic consumed increases the risk from 33.3334 percent to 33.34 percent.

Okay, so what does this mean for the people who live in DePue?  It depends on how one wants to look at it.

First off, the slope factor used to calculate the risk is very conservative which means it most likely over-estimates the risk.  Second, the amount of arsenic that enters into the body from soil fluctuates wildly.  Our calculations of how much are based on a consistent amount of arsenic entering into the body 350 days a year for 70 years.  Third, we are looking at excess cancer above and beyond the one in three chance of getting cancer in a 70 year lifetime.

But let's ignore all of that and focus solely on establishing a threshold where on one side it is "safe" and on the other side there is "risk."

The Illinois background level for arsenic has been set at 11.3 mg/kg.  This level is a cleanup objective that Illinois assumes presents a "safe" environment if the arsenic is at or below that amount.

For all intents and purposes, we will assume 11.3 or less to present no excess cancers above the norm of a 33.3333 percent chance of getting cancer in a 70 year lifetime.

That assumption means, theoretically, that exceeding the value of 11.3 presents an additional risk.  So...how much are we talking about?

The average exceedance of the background threshold of 11.3 mg/kg was 1.7 times the background for an average amount of arsenic in the soil in OU-4 (where the people live) of  19.6 mg/kg.

19.6 mg/kg exceeds the threshold of 11.3 mg/kg by 8.3 mg of arsenic.  So...8.3 mg of additional arsenic exposure is what we will estimate the additional cancer risk on.

Here is where it gets fun.

The EPA's soil screening level (SSL) for arsenic is 0.39 mg/kg.  0.39 mg of arsenic in the soil is assumed to present a risk of no more than one additional cancer in one million cancers for a person exposed 350 days a year for 70 years.

EPA's IRIS has calculated the chronic daily intake (CDI) for arsenic to be 0.02 μg of arsenic per liter of drinking water for a risk of one additional cancer in one million cancers  .

Since the average person is assumed to consume 2 liters of water per day, the amount of arsenic that will theoretically bring about a risk of one additional cancer in one million is 0.04 μg per day for 70 years.

So...we can assume that exposure to 0.39 mg/kg of arsenic in soil, for 350 days a year, for 70 years, will equate to a CDI of 0.04 μg of arsenic.

0.04 μg of arsenic.consumed each day for 70 years will theoretically result in no more than one additional cancer in one million.

0.39 mg/kg exposure = 0.04 μg of arsenic consumed.  That's our line in the sand.

On average, in OU-4, the soil exceeds background by 8.3 mg of arsenic per kg of soil.

Okay...take a break and relax.  Here is a picture of a kitten and a puppy to help...before we do more math and take on more assumptions.

Source

Feeling better?  Okay, let's continue.

8.3 mg is 21 times higher than 0.39.  Therefore, the CDI at 8.3 mg of arsenic exposure would - theoretically - be 21 x 0.04 = 0.84 μg of arsenic consumed.  That's based on the SSL calculations the EPA used.

So what is the risk of consuming 0.84 μg of arsenic per day for 70 years?

In my previous post I showed this calculation:

Source

Here is what we know:

• The NSRL is the uptake - 0.84 μg which is equal to 0.00084 mg
• The the slope factor (qhuman) is 1.5 (mg/kg-day)-1
• The body weight we use is 70 kg.

Basic algebra here with the math.  We need to solve for the risk "R"

(0.00084 x 1.5) / 70 = 0.00018 or 1.8 excess cancers in 10,000.

Here is what the TACO's fact sheet says about that:

The risk of cancer due to exposure to a contaminant is commonly expressed in exponential terms, e.g., 10-6 and 10-4. These terms equate to a risk of 1 in 1,000,000 and 1 in 10,000 respectively. Adding a 10-6 risk would increase the probability of an individual getting cancer to 0.333334. With the addition of a 10-4 risk, the probability of an individual getting cancer would be 0.333433.

On average, in OU-4, the probability of an individual getting cancer would be 0.333453.

What that means is one's normal probability of cancer in a life-time of 0.333333 becomes 0.333453 if exposed to that soil for 350 days a year for 70 years.  This is based on contact with the soil so that the soil enters into the body.

Although it is possible, it is highly improbable that any one in DePue would have an uptake of soil over a lifetime that would equate to a risk of 1.8 excess cancers in 10,000.

Based on how conservative these formulas are, and how theoretical the slope factor is, I do not see any reason to be concerned about the amount of arsenic in the soil in OU-4.

But that raises and ethical question.

Should the citizens of DePue be exposed to any risk above one in one million?

Next Post: The Village of DePue:  The ethics of drawing a line - Part 11

.

The Village of DePue: By how much and how many - Part 9

Tis the day after Christmas, and Excel sorting I will go....

Okay, it took me a few more days to get through all this....

In my last post I looked at the Illinois requirement for residential use which told me to meet Appendix B, Table A objectives.

Based on the data in the Excel files I downloaded from the Cleanup DePue website, six contaminants were found in OU-4 - the area where people have access to, that were above the Illinois cleanup objective concentrations in Appendix B, Table A.

I now need to sort the data to see by how many of them are over the objectives.  This, along with how much the exceedance is, will give me a good indication of risk.  I am only concerned with OU-4 because that is where exposure can take place.

Right now, I have a ton of data from soil samples collected in OU-4.  What I don't know is what the plan addresses.  What I do know is that the plan is much more complicated  in evaluating risk than what I am doing here.  What I am trying to do in these posts is make an assessment as to the claim of  "way-above-normal concentrations of pollutants at hundreds of contaminated sites" so don't go telling people "Bowman says you only need to clean it up to this level."

With that in mind, lets do some sorting...

Ahh, but first we need to get some things out of the way first.

1. csv_post_date is 1996 and 2009
2. Thallium is identified as less then "<" a value.  Therefore less than 10 will mean it is below TACO Appendix B, Table A objectives.  I am removing thallium from the CoC list.
3. Other values identified with "<" will be assumed to be the number below it.
4. Only one sample exceeded the mercury objective of 23 mg/kg.  Since the analytical value is only 24.4 I am going to remove it from the CoC list.

Now that I have it sorted, of the 125 soil samples:

• 102 exceed the objective for one of the chemicals, arsenic, barium, cadmium, or lead. 
• Of these 102 OU-4 samples, all but five exceed the objective for arsenic, which is set at background.
• Only two samples show exceedance for all four of the CoCs.

How, then, do I make sense out of this data?  That's what's missing from the Cleanup DePue's web site.  Tons of data and no context.  This is where I need to be careful in how I describe what I see.  I don't have access to the plan so I cannot speak on the validity of the risk calculations.  I also do not know what the remediation plan is for OU-4.  If they are going to leave the soil in place, well maybe these folks in DePue have something to beef about.  If these "hot spots" are going to be removed, then what I say from this point on is moot.

Oh how I wish I knew what Cleanup DePue and Nancy Loeb, director of the Environmental Advocacy Clinic at Northwestern University School of Law’s Bluhm Legal Clinic and pro-bono counsel for the Village of DePue want.  All I know is they think the plan insufficient to protect them.

The other thing missing from their site is what cleanup levels do they think are health protective and what areas do they want these levels met?  I have been writing these previous posts trying to answer my own curiosity about "way-above-normal concentrations of pollutants at hundreds of contaminated sites"

My problem is that I don't know what they construe as "way-above-normal concentrations."  I am missing some important pieces here.  Since I don't now how the remediation plan is addressing the soil in OU-4, I can only look at what I see from the sample data that I have.

Right now, arsenic is where my focus is because of the number of OU-4 samples where it exceeds the threshold - or cleanup objective in Section 742 Appendix A, Table G.

What I see when I sort the OU-4 soil sample concentrations is that arsenic shows up like this:

• 27 of the samples are more than twice background
• Two samples are three times background (3.0 and 3.3)
• One sample is 4.2 times above back ground
• The average exceedance is 1.7 times background with a median exceedance of 1.6.

Depending on how one looks at it, twice the amount could be seen as "way-above-normal concentrations of pollutants at hundreds of contaminated sites."  Unfortunately, that's not how it works out in this case with arsenic.

Arsenic is set at background because natural background concentrations of arsenic are often well above the health-based, direct-exposure goals in soil.  That's a bit confusing.  On one hand you tell me the "safe" concentration in soil for arsenic is 0.39 mg/kg and then you tell me you only need to clean it up to background.

Yeah...that's what we are telling you.  Our health-based cleanup goals (objectives) are theoretical erring on the conservative side.  Because we suspect arsenic to be a human carcinogen, we set the acceptable risk for an adverse health affect to no more than one additional cancer out of one million cancers.

I'll let TACO's explain that:

For carcinogens, risks are estimated as the probability of an individual developing cancer over a lifetime as a result of exposure to a contaminant.

What we are looking at is a probability of cancer, in the case of soil, we set that probability of a "safe" level at a concentration that we expect to see no more than one additional cancer out of one million cancers over a 70 year lifetime.  We do this with a calculation involving our good friend the slope factor:

This value is known as a slope factor (SF), and it converts daily intakes of a carcinogen averaged over a lifetime directly to the upper bound risk of an individual developing cancer.  That is, risk is equal to chronic daily intake (CDI) averaged over 70 years (lifetime) multiplied by the SF. (page 4 of TACOs)

Figuring out the dose that will give you no more than one additional cancer in one million is quite simple:

Source

Calculating how low a concentration of a contaminant needs to be in soil to bring about that dose is a bit more complicated.  For risk, we are assuming that ingestion, dermal contact, and inhalation of dust for getting the chemical into to human receptor.  We know that as little Suzy grows from a toddler to an adult she will come in contact with that contaminated soil.  We assume that little Suzy will be in contact with that soil for some period of time each year for 70 years (default is 350 days/year).  We know, through a bunch of different studies, that people like little Suzy and adult Suzy will ingest a certain amount of soil in a day.  The question becomes how much contaminant in that ingested soil needs to be there to bring about a probability of one additional cancer in a million.

Remember this bad boy calculation?

Source

That's how it is calculated.  When you see "IFS" it is "age-adjusted soil ingestion factor." DFS is the "age-adjusted soil dermal factor."  These formulas take into account the differences in body weight and uptake as little Suzy goes from a toddler to an adult.  They are very, very conservative and very, very protective.

So for arsenic, the amount in soil that will bring about no more than a one in one million probability of an additional cancer is 0.39 mg of arsenic per one kilogram of soil.  Why show y'all this?  Because that's how we come up with a "safe" threshold for a contaminant we suspect to be a carcinogen.  You need to see that in order to understand the next part of the calculation.

If little Suzy is exposed to 0.39 mg of arsenic in one kilogram of soil for 350 days a year for 70 years, we expect her to have a one in one million chance of developing cancer.  This is a probability based on assumptions which are all worst case.  The biggest assumption is the Slope Factor (SF or CSF):

The SF is derived through the plotting of a curve that compares dose to response. Statistical procedures usually calculate the SF as the upper 95th percent confidence limit of the slope of the dose-response curve (i.e., there is only a 5% chance that the cancer risk could be greater). Because this is the upper bound risk, the actual risk is between that value and zero. The SF is roughly equivalent to the risk per unit dose, expressed as (mg/kg/d)-1. As with the RfD, the SF is provided by the U.S. EPA. (page 4 of TACOs)

And what is the SF provided by the EPA for arsenic?  1.5 as it stands today.  With that, we can calculate the chronic daily intake (CDI) for arsenic to get us a one in one million risk probability.  We can use the method described in the California equation above:

• We know the risk (R) we want is one in one million or 1.0 x 10-6 or 0.000001.
• We know the slope factor (qhuman) is 1.5 (mg/kg-day)-1
• We know the average weight of the human is 70 kg

So, a little math...and we can calculate the intake level (I) or CDI

I = (0.000001 x 70 kg) / 1.5 mg/kg-day = 0.000047 mg/day or 0.05 μg/day.

0.05 μg of arsenic consumed for 365 days a year for 70 years should see no more than one additional cancer per one million cancers.  What does that mean?  Here is how Illinois describes it in the TACO's Fact Sheet:

The risk of cancer due to exposure to a contaminant is commonly expressed in exponential terms, e.g., 10-6 and 10-4. These terms equate to a risk of 1 in 1,000,000 and 1 in 10,000 respectively. In the benzene example, the risk estimate of 1.5 x 10-5 means that 1.5 additional cases of cancer above background might occur among 100,000 exposed persons (or 15 cases in 1,000,000 persons) as a result of benzene exposure. The background cancer rate is 1 in 3, meaning that over a lifetime, an American’s probability of getting cancer is 0.333333. Adding a 10-6 risk would increase the probability of an individual getting cancer to 0.333334. With the addition of a 10-4 risk, the probability of an individual getting cancer would be 0.333433.

Confused?  Focus on the numbers here:

The slope factor is a value that is a very conservative number.  It is very, very protective of public health in and by itself.

• The probability of cancer risk is based on a CDI of that concentration of arsenic each day for 70 years.
• The probability of consuming that amount over 70 years and getting cancer is one in one million.
• The chance of getting cancer in your lifetime is one in three - 33.3333%.
• If we expose you to soil with 0.39 mg/arsenic per kg of soil for 350 days a year for 70 years, the chance of getting cancer increases to 33.3334%

Now if you have stayed with me to this point, you might be asking "what is the risk of cancer at the background concentration of arsenic?"

Good question.

Next post: The Village of DePue:  Theoretical Cancer Risk at Background  - Part 10

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

I'm still trying to support Cleanup DePue's Press Release claim that:

Contaminated debris blows onto public and private property throughout the village and surrounding natural areas, exposing residents -- more than a quarter of whom are children under the age of 16 -- and local wildlife to arsenic and heavy metals such as lead, mercury and cadmium. Visit www.CleanUpDePue.org to see an interactive map that details the way-above-normal concentrations of pollutants at hundreds of contaminated sites.

I did visit their site and I have been looking at the data to see where these "way-above-normal concentrations of pollutants at hundreds of contaminated sites."

I thought possibly that it might be arsenic and chromium leading this charge since every single one of the samples in OU-4 - where the people of DePue live, work, and play, were above the screening levels for these two compounds.

Then I remembered that Chemicals of Concern (CoCs) that are carcinogens are calculated differently and calculate considerably lower levels than background concentrations making them impracticable to use for remediation goals.

On the Cleanup DePue's website they write about background concentrations:

"For each parameter whose sampling results demonstrate concentrations above those , 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.

Yes that is true.  But background levels are not the sole remediation goal, and I believe that may be where the confusion lies and why Nancy Loeb, director of the Environmental Advocacy Clinic at Northwestern University School of Law’s Bluhm Legal Clinic states in the Press Release:

“The companies spent millions of dollars on consultants in an attempt to show that this SuperFund site poses no significant risks, and they delivered a superficial plan that barely touches many of the contaminated areas, leaves the slag pile and other waste in place, does nothing to stop contamination from seeping into the groundwater, and leaves backyards, playgrounds and Lake DePue without real remediation.” 

The issue, as I think I am now coming to understand, is twofold.

1. They are leaving the contaminated areas in place and moving contaminated media to these areas.
2. They are not remediating the area, specifically OU-4, to background levels in Section 742 Appendix A, Table G of Title 35 of the Illinois Administrative Code or groundwater down to MCL/MCLG levels.

Loeb also criticized CBS and ExxonMobil for their totally unrealistic methods for looking at risk:

“In determining whether a person is exposed to potentially harmful levels of toxic pollutants, CBS and ExxonMobil are counting each exposure as if it were an isolated incident, and pretending that residents are exposed only to a single contaminant and only in one area of the town. The reality is that children are growing up here, eating from home gardens, playing in parks and ball fields, boating in the lake, and later working and living as adults in DePue. Any realistic assessment of health risks has to take these multiple, constant and long-term exposures into account.”

I do not have access to the plan, but I am pretty sure that the Illinois EPA is making CBS and ExxonMobil cleanup to a level consistent with the "Tiered Approach to Corrective Action Objectives":

Source

...or more affectionately called "TACOs"

I know nothin' about this thing called TACOs.  All I know is what any other person reading up on this topic and trying to understand it gets to look at on the interwebs.  What I do know about my industry, including the regulators that oversee it, is that they overkill everything when you attach the words "Superfund" and "Town" together.

I am pretty sure that the remediation plan CBS and ExxonMobil put together meets TACOs.  If Cleanup DePue thinks it does not, I will need to see their reasoning.  All I have is a Press Release stating that the plan is not a "realistic assessment of health risks," and a bunch of analytical data.

So let's get back to the question of are there "way-above-normal concentrations of pollutants at hundreds of contaminated sites?"  And, are the levels found high enough to present a concern?

TACOs tells us this:

The purpose of these procedures is to provide for the adequate protection of human health and the environment based on the risks to human health posed by environmental conditions while incorporating site related information.

With that in mind, we must assume that meeting TACOs meets adequate protection of human health and the environment.  If one wants to make an argument that it does not, let me know why in the comments.  For the most part, TACOs gets you to the same place that EPA's soil screening level calculations do.  They will spit out basically the same remediation goals.

Here is how TACO is designed to work:

Source

You can read more about TACOs by going here.

OU-4 will be samples collected in residential areas so that's the path we will go down.  This requires Appendix B Table A and Table E objectives.  Based on the values in Table A, the new CoC list looks like this:

I still show that some of the OU-4 CoCs exceed the Table A objectives (the one's in purple).  Also note how Illinois goals match closely in some cases with EPA's SSLs.

So, based on the data in the Excel files I downloaded from the Cleanup DePue website, six contaminants were found in OU-4 - the area where people have access to - that were above the Illinois cleanup objective concentrations in Appendix B, Table A.

My next quest will be to see by how much over the objectives as well as how many sample points are elevated.


Next post: he Village of DePue:  By how much and how many  - Part 9


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