Soil Mix Calculation

[hockeyfan960]

I have a project on which I want to do soil blending.

The soil currently has 38.9mg/kg of arsenic in about 1,250cf of soil (for the first 6")....the underlying soil (12"-18" depth) has an arsenic reading of 16.3 and 9.18 respectively.

How do I calculate the depth to which I need to blend to bring the arsenic reading below the threshold of 20mg/kg..???

Thanks in advance.

 

[civilperson]

Need to go deeper than 18". Average of top 18" is 21.5.

 

[TDAA]

As far as I was aware, the adding of a clean material to a polluted material was not typically allowed. The thought being that you are really not cleaning anything up. You still have the same amount of pollutant.

I worked on a project that utilized soils from a brown field. We were not able to justify keeping a “hot” load (PCB, lead, arsenic, dro, gro, plenty of other things) because it would be mixed with 500 other trucks. And this was being used at a landfill site, under the final cover.

 

[hockeyfan960]

The current DEP regulations in my area allow for soil blending. I need to make a recommendation as to how deep to do the blending. Of course the $$ are bigger the deeper you have to go, so I am trying to justify the blending depth. The machine to be used has the ability to blend down to 40", of course this is all trial and error as it will have to be retested after the blending, but I do not want to be the one to tell the client to blend again because the first time did not bring down the concentration below 20mg/kg

 

[fattdad]

Dilution is not the solution to pollution. This a quote from several decades ago. I'd check with the local/state environmental agency to see if this is allowed. Bear in mind if the arsenic is mobile, you are doing nothing to attenuate the potential leaching of the arsenic into the underlying ground water using this method (i.e., infiltration will pass through the same number of arsenic molecules whether it's in a 1 ft layer or a 2 ft layer.

(Maybe I should first ask, are you looking at total or TCLP arsenic levels?)

f-d

¡papá gordo ain’t no madre flaca!

 

[hockeyfan960]

What is happening is that the project site is an agriculture farm field and the "hot spot" is the low spot in the field, so all of the stormwater collects in the low spot and thus that is the area with the largest concentration of As. It is only above the 20mg/kg in the first 6" as I have readings from 12" and 18" which are 16 and 9.5 respectively. What I need to do is to determine the blending depth in order to bring the first 6" into compliance. All of this is irrelevant as I will be placing 36" of structural fill over top of this topsoil to develop the site, but the bank will want to see a clean Phase I before approving the loan.

 

[fattdad]

Are you fully aware of how the arsenic got to this portion of the site? Is it related to some agricultural chemical or past industrial use of the land? Is it related to some "unknown" site activity? For what it's worth, these are the questions that would lead to a "clean" Phase I ESA (from my perch on the fence). If your environmental regulators are o.k. then blend away. I'd use a weighted averging method to get the answer.

f-d

¡papá gordo ain’t no madre flaca!