Footing Drains with Sump Pumps and One-way Valves

[KatiLynSki]

Hello to All-

I am currently reviewing a subdivision plan with 173 housing units, which is in close proximity to wetlands. In order to prevent the footing drains from daylighting in the protected wetland buffer, the designer has opted to do two different options.
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OPTION 1) Use a sump pump to daylight the pipe. (Approximately 58 of the 173 units)

Example A. Basement elevation: 482 ft. Daylight elevation: 488.5 ft.

Example B. Basement elevation: 481 ft. Daylight elevation: 483.5 ft.

Option 1 Question: Are there any constraints or specific considerations I should take into account with the use of a sump pump?
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OPTION 2) Tie the footing drains into a catch basin. (Approximately 60 of the 173 units)

Example C (basement lower than invert out of catch basin, no sump pump called out on plans). Basement elevation: 491 ft. Catch basin invert out: 493.19 ft.

Example D (basement not much higher than invert out of catch basin). Basement elevation: 484 ft. Catch basin invert out: 483.8 ft.

Example E (basement higher than invert out of catch basin). Basement elevation: 495 ft. Catch basin invert out: 489.29 ft. Catch basin top of frame: 495.8 ft.

Option 2 Question: Example E seems to make conceptual sense to me that it would work but I am hesitant on the other two. We have requested that the designer submit a hydraulic grade line analysis to prove that the water will not backup from the catch basins into the basements in a storm event. The designer has stated that they do not want to do a hydraulic grade line analysis and they would rather add sump pumps and one-way valves in cases such as Examples C and D. Does anyone have any experience in a similar scenario?
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Any insight will be greatly appreciated.

Thank you,
Kati

 

[KatiLynSki]

Option 1 should additionally read:

Use a sump pump to daylight the pipe outside of the wetland buffer.

-Kati

 

[cvg]

the hydraulic grade line of the catch basin should be below the floor of the basement. In fact you should require some freeboard also. So I would like to see calculations and would require that the crown of the storm drain pipe be maybe a foot below the floor elevation of the basement.

sump pumps should also daylight into a drain system manhole and above the hydraulic grade line to prevent flow backing up through the pump lines into the basements (in case the check valve fails to close. Make sure your sump pumps don't pressurize the gravity outlet drain.

 

[GeoPaveTraffic]

I agree with cvg, and would add that examples C and D should not be constructed under any conditions.

 

[KatiLynSki]

cvg-

Thank you for your response. As I was looking over the plans more carefully I realized that many of the units that connect to the catch basins do in fact fall under examples C and D which is why the designer did not see the need to do an HGL analysis since he already knows that they will have a problem.
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Which leads me to the next comment...

GeoPaveTraffic-

Thank you for your response. I am beginning to think that I agree with your instinct that Examples C and D should not be constructed. Originally I believed that the intent of connecting into the storm drainage was to eliminate the need for a sump pump but if there is going to need to be a mechanical device relied upon then I would rather have it daylight to ground instead of in a catch basin.
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Any further insight would always be appreciated.

-Kati

 

[GeoPaveTraffic]

The vast majority that I have seen constructed, just daylight to ground. This includes when a sump pump is installed. One thing to consider is once the water is on the ground surface "where is it going?" Always look at the path that the water will take, this also applies to the downspouts from the roof.

 

[DMcGrath]

There are also the "what-ifs" to consider concerning the sump pumps and options C - E. What happens during storms with lots of rain? The power goes out, of course, and sump pumps won't pump without a backup power supply. This may be a headache down the road for the local public works department who gets to answer all the calls about flooded basements, only to tell the homeowner that it is not the government's problem.

The other "what if" is what is the anticipated high water level in the catch basin. This should be more telling than the pipe inverts alone.

 

[DRC1]

Question 1 What is wrog with daylighting the foundations into the wetland buffer?
Question 2 If the soil is sandy, has any consideration been given to dischaging to dry wells?

 

[KatiLynSki]

Answer 1 Nothing is wrong with daylighting the foundations into the wetland buffer. Except that the plan had already been accepted by the Wetland Commission with a note saying that if the final footing drain design daylights in the wetland buffer the application would have to go back in front of the Wetland Commission for approval since that is not the plan they approved. So to avoid having to go back in front of the Wetland Comission they have chosen not to daylight in the wetland buffer.

Answer 2 The soil is anything but sandy and there is a very high water table on the site. Therefore drywells are not an option.

-Kati

 

[jheidt2543]

So, instead of daylighting some of the drains, the design will saddle the home owners with a permenent maintaince problem of sump pumps? This just doesn't seem like the right thing to do. Bite the bullet and send the plan back with a design solution that works without the hazards and maintenence others have noted above.