Engineered soils

[dpa]

I have a project where the native soil is very porous sand and gravel. The county officials have raised the question of whether it will be necessary to place engineered soils to prevent wastewater and stormwater runoff from reaching the ground water too quickly.

I have heard the term before but have no idea what those soil mixes are or in what quantity and depth they should be applied.

For some reason the engineers in the area are all overloaded with work this year so hiring a local geotech any time soon will probably not be possible. Much of my work this year has come from their overflow even though I am located 175 miles away.

Any help would be appreciated.

Thanks,
DPA

 

[BigH]

dpa - first explain your project, please, in a bit of detail. Are you generating wastewater and stormwater runoff - such as in a parking lot for the latter? As to the concern of the county officials, have they ever raised this issue before? If so, why? What is their real concern - real or imagined?

If stormwater runoff is not contaminated by percolating through the upper reaches, then I would think it would be a good thing, in general. If you have a large parking area, then this would normally influence the precipitation entering into the groundwater (and usually lowering the groundwater level). In such cases as you seem to indicate, the project would use soak-pits to continue to introduce the water into the groundwater regime so as not to influence unduly the normal groundwater levels. As to wastewater - this may be contaminated - are you using septic fields? If so, they would have a concern as some time is needed for filtration. Please advise.

 

[dpa]

Hi BigH,

Thanks for the quick response. I was out for several hours and didnt get to answer your questions right away.

The design is for a non-ferrous metals recycling facility. The site gathers metal scrap, sorts it and sends it out of town for recycling. There will be a restroom on-site for the workers. Chances are some of the public will also end up using the restroom even though that is not the intent.

There are two designs here both related to the native soil problem. One is storm water retention. The parking lot will be about one quarter acre gravel. In addition we are required to catch the runoff from the adjacent county road and the roof of the new building and divert it to an on-site retention facility. I am not sure how much contamination there will be from oil leaks in cars and trucks. I am a bit concerned about any oil, antifreeze leaks etc getting into the groundwater directly through the parking lot surface before it ever reaches the retention pond.

The other design is for a septic system. I do not know how far it is to the water table or how much it varies with the seasons but it is likely fairly high during the spring melt.

Since posting this message I have found some information on slowing the rate of infiltration by using frequent very small doses in sand lined trenches using ASTM C33 sand. Maybe that is the trick. I wish I could get a geotech in on this job but everyone is booked up solid and the existing facility must move as soon as possible because their present location is a code violation.

Thanks for your help.

DPA

 

[Focht3]

Hmmm,

You need help. And the contamination issue is a serious one.

Where is the site located?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[cvg]

You may need to consider an oil/water separator for your retention pond

As far as septic system design, you do need to verify ground water depth / levels in order to get your permits, or face more code violations...

 

[dirtsqueezer]

I'd say you're doing well for yourself thinking of these issues ahead of time.

This is an interesting problem! Now that the jurisdiction's involved, it seems like if you were to make everybody happy and end up with a squeaky-clean conscience, you would need some subsurface routing of the groundwater to drain to some contaminant-cleaning facility, which you would then need to have serviced and maintained for the life of your business. My thought is, if you already have in mind the oil/antifreeze that comes from this scrap, why not just impliment some stringent policy with the employees to drain these fluids as the scrap arrives? It seems like this might be a more practical solution, and may possibly cost a lot less in the long run.

The other option would just be adding infastructure to your lot (asphalt and storm drains), to drain to your detention pond. Obviously more costly, but a cheaper variety like chip-seal or ATB would definitely do the job, as well as appease the county. I imagine it would cost some time & materials, but this way, there would be no question. You might just call your local asphalt company for a ballpark.

Good luck!

 

[mubash]

The problem seems to be of treating the effluent so that it is not harmfull and do not contaminate ground water and there is no violation of codes also.I do not think it is very essential to provide engineered soil to get desired result.By treating nd separating the harmfull contamination it could be done easily.