Effluent pipe size? 1

[beameupscotty]

For a sanitary sewer between the primary septic tank of a single-family residential dwelling and the secondary treatment facility (Orenco AX-100 or like for 11 dwellings) what method is acceptable for sizing. The average max flow per dwelling is 450 gpd around here. Is this the flow I would use with a Manning's equation (I have gravity flow to the treatment facility). Does this take into account solids removed by the primary septic tank?

Thanks for any help.

 

[waterexpert]

Firstly the flow:

I would suggest you use a slightly more rigourous anlaysis of likely flows, based upon numbers of bedrooms. Here in the UK we have guidelines for this, to prevent th ecommon undersizing of these units. You can get them free at the following link:

http://www.britishwater.co.uk/COP_Flows___Loads_2_-_final_-_6_page_version-22Jun05.pdf

Having established the flow you need to consider whether the pipe will be running full, and having done that, and gather data on pipe materials, condition, fittings, length and proposed diameter, you could do worse than use the appropriate on-line tool at the following site:

http://www.lmnoeng.com/

Hope that helps

Seán

http://www.expertise-limited.co.uk

 

[bimr]

You do not really have to worry about sizing the pipe. The minimum size for a residential sewer is 4" dia.

A 4" sewer at minimum slope of 1% grade has a maximum capacity of 85 gpm.

Use mannings equation.

 

[beameupscotty]

I understand the hydraulics and plumbing code for residential into public sewer. It's the actual quantity of flow out of each individual septic tank that I'm after. Our DEQ has a table that lists typical residential use as 450 gpcd (avg max). This number converts to 0.0007 cfs, which is nothing. I'm connecting 6 and 5 dwellings, respectively, to 2 common sewers that each connect at a manhole and then go combined in a sewer to the treatment facility. So, I'm trying to size each sewer. I was planning on using 6" ASTM D3034 SDR 35, but that seems like overkill to me. Maybe it would be preferable for cleaning out though.

Thanks for any experience-guided help

 

[bimr]

It is not clear what you are trying to do. The distances between facilities and elevations have also not been provided.

As far as flows go, if you have a normal house residence, you can figure 350 gpd average flow per house, and a peak flow of 4 times that.

If you have six houses on one line, that would be 2,100 gpd average flow, and a peak flow of 8,400 gpd.

A 4" diameter building sewer on 1/4" slope per foot can hand 216 fixture units. A 4" diameter building sewer on 1/4" slope per foot flowing half full will discharge approximately 76,900 gpd.

A normal residential bathroom consists of 6 fixture units. One fixture unit equals about 35 gal per 8 hour.

A building sewer is defined as that part of the building drainage system that extends from the septic tank or a public sewer to a point 3 ft out from the foundation wall. Separate sewers are generally required for new construction.

Most areas have regulations that require a minimum size of 8 inch for public sewers.

However, if all of your development is a private system, then a 4-inch diameter sewer from the septic tank is adequate for the flow. As far as cleaning goes, going to a 6" is probably not going to help much. Lower flows in the larger sewer may cause solids to drop out in the sewer.