Texas SWPPP Requirements

[GoldDredger]

I've recently come across an issue for one of my projects regarding a SWPPP requirement in Texas. The TPDES permit has a published requirement that any site with more than 10 acres of disturbed land 'should' have temporary sedimentation basin(s).

The guidelines for the basin sizing according to the TCEQ (Tex Commish. on Env. Quality) is as follows:

"..must provide sufficient storage to contain a calculated volume of runoff from a 2-year 24 hour storm event"

It goes on to say:

"Where rainfall data is not available, the sedimentation basin must provide at least 3,600 cu. ft of storage per acre drained..."

The guidelines make no mention of the rational method, storage times, release rates, runoff coefficients, or whether it is intended to be detention or retention.

So I contacted TCEQ to get some guidelines but they don't really know or understand the requirement. I've now got a City inspector who wants 'calculations' but can't explain what calculations <snicker>

Anyway, has anyone come across this issue before? The site has no proposed detention pond otherwise it would be a non issue. I figure the intent is to hold the runoff temporarily so any solids can settle out of solution.

 

[bimr]

On page 31, the permit actually says "where feasible". So you have to document why a detention pond may or may not be feasible.

http://www.tceq.state.tx.us/assets/...rquality/attachments/stormwater/txr150000.pdf

That means you don't necessarily have to put a pond in. You may be able to achieve the same results by filtering the runoff.

One would think that you will be constructing some type of stormwater detention on your project anyway.

In addition, "Where rainfall data is not available or a calculation cannot be performed", the sedimentation basin must provide at least 3,600 cubic feet of storage per acre drained until final stabilization of the site.

There are plenty of loopholes there.

Regarding the permit calculations, since the permit does not have a stated procedure that you have to use, you can a method to calculate storm runoff that is most advantageous to your client.

 

[francesca]

The Tennessee EPSC manual has details and calculations.

http://www.state.tn.us/environment/wpc/sed_ero_controlhandbook/