No KCAL9, that's not what the results mean. Part 4

Okay Bowman, you are confusing me.  How can 101 mg/kg of lead in the soil possibly make it a hazardous waste, but 400 mg/kg in the soil make it acceptable for children to live at?

That don't make no sense!

What makes a physical solid material a hazardous waste for lead is based on the idea that if the lead leaches out at or above 5 mg/L it could get into the groundwater and be consumed above the maximum contaminate level (MCL).

The STLCs and TTLCs, originally proposed in 1978, were intended to identify those wastes that “pose a substantial threat to human health and the environment if not disposed in a controlled and systematic manner.  ...the STLC for lead focused on ingestion of drinking water as the route of exposure, considering the exposure pathway of drinking water derived from groundwater or surface water. The STLC was developed by applying a 100-fold attenuation factor to the maximum contaminant level (MCL) for lead, which was 50 µg of lead/L of drinking water at the time the threshold was developed. (Page 4-4)

What makes soil containing less than 400 mg/kg of lead "not hazardous" is based on a risk assessment related to children and the concentration of lead in the blood.

The idea that 5 mg/L of lead leaching from soil is hazardous is archaic. But it is how the regulations require a determination of "hazardous waste" be met.  Would soil that leaches out 5 mg/L of lead create a hazard for the public - children in particular - ??  I don't know.  My guess is that based on what we know now, probably not.

But you are more interested in why up to 400 mg/kg of lead in the soil is okay for a backyard where children play.

That value of 400 mg/kg is based on a complex risk assessment, which is based on how much lead would increase the blood-lead level in a child:

Briefly, within the context of the §403 risk analysis, individual risks refer to the risks associated with a young child’s exposure to specified levels of environmental-lead. Once environmental-lead levels were specified for each medium, the model-predicted blood-lead concentration at these levels, along with the assumption that blood-lead concentrations have a lognormal distribution with a specified variability, were used to estimate the percentage of children exposed to the specified set of environmental-lead levels that would have elevated blood-lead concentrations (i.e., at or above 10 µg/dL). 

Then, those sets of environmental-lead levels associated with estimated elevated blood-lead percentages of 1%, 5%, and 10%... The IEUBK model was used to identify soil-lead concentrations associated with these elevated blood-lead percentages (at specified dust-lead loadings), while the Rochester multimedia model was used to identify (wipe) dust-lead loadings associated with these elevated blood-lead percentages (at specified soil-lead concentrations).  (source)

Told you it was complex!

California looks at lead a bit differently than the EPA, which offers even more confusion when trying to understand why.

One of California’s hazardous waste standards is the total threshold limit concentration (TTLC). The TTLC for lead is intended to protect receptors from direct exposure, primarily through ingestion, which is the type of exposure of greatest concern with lead and certain sensitive receptors. The TTLC in use today assumes that 1,000 mg/kg is protective of children likely to ingest soil containing lead. However, as shown by the recently developed health-based screening values for soils at school sites and near residential lead-paint sites, soil-lead concentrations that protect children who are exposed to lead in soil range from 255 mg/kg to 400 ppm, depending upon the model and assumptions used. The models and assumptions used to develop these values consider the most recent information regarding the health effects of lead and the exposure likely to occur.

California lowers that threshold to 80 mg/kg for children:

The Department of Toxic Substances Control’s Leadspread model (DTSC, 2007) was used to estimate blood lead concentrations in children. The Leadspread model considers exposure to lead in soil by three pathways: ingestion, re-suspension and inhalation, and dermal contact. The Leadspread model was queried for the soil lead concentrations that would give rise to a 90th percentile estimate of increase in blood lead of 1 µg/dL using the “goal seek” function in Excel

The point of all this is this.  The lead concentrations Randy Paige found using the XL2 XRF are above 400 ppm.  This is concerning, especially if the California model is correct.

What needs to happen now is to look at the blood-lead levels in these children.  That would indicate the potential for health concerns.

No need to scare people with "hazardous waste."  That's a whole different wacky world that does not apply to these folks living in Vernon near the Exide facility.

tl;dr: Stop saying "hazardous waste"!!


Thanks for reading.

Jeff

No KCAL9, that's not what the results mean. Part 3

Is soil that contains 1000 ppm of lead - as detected by a Niton XL2 XRF - a hazardous waste?

Probably not.  But I cannot say for sure without running a TCLP on the soil.

But it contains 100 ppm of lead!  The regulatory limit for lead as a hazardous waste is 5 ppm!  That's 200 times more lead in that soil than a hazardous waste!

Whales are aquatic.  Fish are aquatic.  Whales are not fish.

XL2 XRF reports a ppm for lead.  TCLP reports a ppm for lead.  These ppm results mean two different things.  You cannot use the XL2's ppm to state "hazardous waste."

And here is where it gets really wacky!

The XL2 is telling us a ppm based on surface area and depth.  I do not know how this correlates to a ppm we use in environmental determination of regulatory compliance or cleanup levels.  I am going to assume that the ppm reported aligns with mg/kg - the standard way we discuss ppm when looking at lead in soil.

So let's just accept that a reading of 1000 ppm determined by Randy Paige when using the XL2 in the yard near the bike detected 1000 mg of lead per kg of soil.

1000 mg is 200 times more than 5 mg (the hazardous waste threshold).

Yeah...but..1000 mg per kilogram of soil versus 5 mg per liter of liquid (the leachate).

They do not correlate.  With one exception...

If we were to run a totals constituent analysis on that soil, and we obtained 1000 mg/kg of lead, this would cause us to consider the soil as possibly being a hazardous waste.  This is due to a concept we call "the rule of 20."

If a waste is 100% solid, as defined by the TCLP method, then the results of the total constituent analysis may be divided by twenty to convert the total results into the maximum leachable concentration. This factor is derived from the 20:1 liquid-to-solid ratio employed in the TCLP.

So now we have ourselves a dilemma.

If the ppm reported by the XL2 correlates to a totals analysis result in mg/kg.  1000 ppm detected by the XL2 is way above "the maximum theoretical concentration in the leachate could have" which is 20 times the TC regulatory value of 5 mg/L - or 100 ppm.

If the soil contains less than 100 ppm of lead from a totals analysis, then theoretically, because of the 20 to 1 dilution - it could not leach more than 5 mg of lead per liter of leachate.

Too many numbers Bowman!  Boring!

Okay...so work with me here.  We are told 1000 ppm in the backyard by the bike. Let's assume that 1000 ppm reported by the XL2 meter is the same result we would get if we took a soil sample to a laboratory.  1000 ppm is greater than 100 so we cannot rule out this soil - in this backyard - by this bike - does not meet the definition of a hazardous waste.

Here we get wacky!

The EPA threshold for lead in the soil of residential property is 400 ppm.

But...400 is four times higher than 100 - the theoretical value!  How can the EPA say that up to 400 ppm is a safe level for children?

Because what makes something a hazardous waste relates to risk of a particular health impact and not the health impact that is present.

Confused?


No KCAL9, that's not what the results mean.  Part 4