Sewer separation projects

[SMIAH]

I am trying to find a way to estimate the equivalent population of a combined sewer separation.
Well it's not my idea but I have to do it

Using :
Area (road) = 1000 m length x 10 m wide.
Rainfall = 10 mm of rain on a 3-hour duration Chicago storm
CN = 98 (road)
Initial abstraction Ia = 2.5 mm
Lag time = 10 min

I get:
Total rainoff volume = 44 m3
Peak runoff = 0.018 m3/s

Then using a unit consommation of 320 l/p*d avec a hourly peak factor of 4 : 1 pers. = 0.015 l/s.

Removing this 1000 m of road =
Peak flow = 18/0.015 = 1 200 pers.
Daily volume = 55 pers.

I find the results not really convincing as with a 1 000 m road separation project, we would be able to add a population of 1 200 pers.

Any thoughts on this (over-simplistic) method?

 

[dicksewerrat]

If you are looking to reduce I/I, then calculate the water removed from the system by separating the roadway. If you are really looking at this, then you have to take a look at the runoff from the buildings along that road. If they are dumping all the rainwater into the street you have more. Separation is not a SIMPLE process. The idea is. Rain water in the sanitary causes floods. Reduce flooding by removing rainwater.
1000 m times 10 m times .01m equals 100 cubic meters of water removed. If you have high density bldgs., then maybe 50 percent of the rain off road is coming there also. Say the first 100 m on each side of the road and average of 10 meters of rain per year. Now you have 1000 times 110 times 10 equals 1.1 million cubic meters of removal. If your treatment costs alone are $3.00 per cubic meter, you saved $3.3 million. I think that is the number to look at first. then look at how many more people can get sanitary sewage service.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[SMIAH]

Interesting.

For now, I am more interested in a separation vs development but the treatment cost has to be in the equation somewhere (if it doesn't go back in the combined sewer).

 

[cvg]

in order to separate the flows, you need to build a separate storm sewer drain. the $3.3 million you saved pays for the storm drain.

you do need to include adjacent property which drains directly to the road.

assuming you store and treat all combined sewer flows, then just calculate the total volume of storm runoff and convert that to a population by using your per capita sewage generation number.

 

[SMIAH]

I just think that the results are very good in terms of developpment.
Suppose we have to add a relatively big developement of population = 1 200, then we could remove 1 km of road (and probably less if I take adjacent property)!
In terms of flow rate, this sounds good. A little less in terms total volume.