Contaimated Soil

[Hockeyfan960]

Can anyone help me with a soil dilution calculation..???

I have a volume of soil (1,250ft3) with a concentration of arsenic at 38mg/kg and I need to mix it so that the concentration is below 20mg/kg.

Can some one give me a starting point...???

 

[RIP - VTEnviro]

I would suggest first finding your total mass of arsenic present.

Volume of soil x density of soil x concentration = total mass of As.

20 mg As/kg soil = total mass of As / X kg soil. Find your mass of soil needed in the diluted condition.

Divide by density to determine total volume of soil in the diluted condition.

Subtract your original soil volume (1250 ft3) from the total volume to determine the amount of clean mix soil to add.

 

[Guest]

I hate these kind of questions, because as a regulator they send my flags up !!! :lmao:

VTE's response is correct provided the dilutant soil is 'clean' (e.g. As = 0 mg/kg).

However, in my experience:

1. Concentrations of As in soil are never zero, and in fact, are almost very close to regulatory criteria.

2. Regulatory criteria for As in Florida = 2.1 mg/kg (residential) and 12 mg/kg (commercial/industrial).

Therefore, even if you can dilute the soil to 20 mg/kg, the contaminated media is STILL hazardous. That means if you try to move it ... you are gonna get nailed !!! I wish these !@#$%*&$ prepatory test materials would give 'real' problems and not these ... let me pull a rabbit out of my hat types of examples.

/rant off

:17:

JR

 

[udpolo15]

In Illinois I'd recommend placing an engineered barrier over the soil and and call it a day.

 

[FusionWhite]

In Illinois I'd recommend placing an engineered barrier over the soil and and call it a day.

We just capped some contaminated soil at a site which is going to be warehouse. The lawyers had to do more work then we did to get that approved.

 

[snickerd3]

In Illinois I'd recommend placing an engineered barrier over the soil and and call it a day.

Depends on how the site is classified...the CERCLA/federal facility program doesn't recognize the use of engineered barriers as a remedy...the Illinois soil regs are not promulgated so they are only To-be-considered guidence for my section... make life so much fun.

 

[Hockeyfan960]

I hate these kind of questions, because as a regulator they send my flags up !!! :lmao:
VTE's response is correct provided the dilutant soil is 'clean' (e.g. As = 0 mg/kg).

However, in my experience:

1. Concentrations of As in soil are never zero, and in fact, are almost very close to regulatory criteria.

2. Regulatory criteria for As in Florida = 2.1 mg/kg (residential) and 12 mg/kg (commercial/industrial).

Therefore, even if you can dilute the soil to 20 mg/kg, the contaminated media is STILL hazardous. That means if you try to move it ... you are gonna get nailed !!! I wish these !@#$%*&$ prepatory test materials would give 'real' problems and not these ... let me pull a rabbit out of my hat types of examples.

/rant off

:17:

JR

So how do I handle the problem if my soil to be mixed "clean soil" has a background value of 10mg/kg...???

 

[Guest]

So how do I handle the problem if my soil to be mixed "clean soil" has a background value of 10mg/kg...???

If you have a soil that is contaminated with 38 mg/kg As and you want to 'dilute' it to a concentration of 20 mg/kg As and the 'clean' soil has a concentration of 10 mg/kg As, then this simplifies to a weighted average problem.

20 mg/kg As = { (38 mg/kg As)*(1250 ft3) + (10mg/kg As)*(x ft3) } / { 1250 ft3 + x ft3 }

Solve the equation for x (ft3)

Does that make sense ??

JR

 

[Hockeyfan960]

If you have a soil that is contaminated with 38 mg/kg As and you want to 'dilute' it to a concentration of 20 mg/kg As and the 'clean' soil has a concentration of 10 mg/kg As, then this simplifies to a weighted average problem.
20 mg/kg As = { (38 mg/kg As)*(1250 ft3) + (10mg/kg As)*(x ft3) } / { 1250 ft3 + x ft3 }

Solve the equation for x (ft3)

Does that make sense ??

JR

That makes sense, but should there be some sort of conversion for the metric to SI units....or does it not matter since the math will get the metric value to cancel out...???

 

[Guest]

That makes sense, but should there be some sort of conversion for the metric to SI units....or does it not matter since the math will get the metric value to cancel out...???

You are correct - you do not have to convert to get consistent units because the mg/kg terms cancel on either side leaving you with ft3

JR

 

[Slugger926]

If you have a soil that is contaminated with 38 mg/kg As and you want to 'dilute' it to a concentration of 20 mg/kg As and the 'clean' soil has a concentration of 10 mg/kg As, then this simplifies to a weighted average problem.
20 mg/kg As = { (38 mg/kg As)*(1250 ft3) + (10mg/kg As)*(x ft3) } / { 1250 ft3 + x ft3 }

Solve the equation for x (ft3)

Does that make sense ??

JR

That is why I stated an algebra book. I didn't have time to dig into a more in depth answer. In Biosystems Engineering, besides environmental problems like this, you may be mixing a volume one level of grain (has sand and dirt mixed in) with another volume of a high grade clean grain to meet the most profitable level you can for your contaminated grain (or fruit).

The problem has applications in many industries. It is just stated differently for different materials.