Building a drain at Base of Hill

[dnonnema]

I have a water issue with my house--it sits at the base of a large hill and my back yard is very wet. My sump pump runs frequently.

I recently installed a french drain at the base of the hill, approximately 20 feet from my foundation (3ft deep, 4" perforated pvc pipe wrapped with fabric sleeve, surrounded with 3/4" clean stone). The drain is working great--water has been flowing out of the outlet pipe constantly since i put it in.

One problem--my sump pump is still running just as much as it ever did. I'm talking about a lot of water--the pump is 3/4hp, 1.5" outlet pipe, runs for about 40-50 minutes every 3 hours.

My question--should I have dug my drain deeper? Do i need to take the base of the drain down to the basement floor foundation level to keep the sump pump from running so much? Should I build a new, deeper french drain parallel (closer to my house) to the first drain I dug?

Also, should I wait for the ground to dry up before I excavate again?

Also, apparently my footing drains are blocked. Is their any way to clean out the footing drains without draining my bank account? :-D

 

[Focht3]

Check out my reply in this thread:

thread158-60100



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[SirAl]

With the sump discharge rates that you reference, it sounds like your weeping tile is performing well. Was the tile line scoped? Are you having moisture problems in your basement?

How and where does your sump discharge? Make sure you are not recycling water from sump and french drain discharges being too close to the house. Ensuring that roof downspouts drain onto splash pads or extensions that carry roof discharge well away from the basement foundation wall is also important. Finally, positive lot grading away from your foundation is important. A minimum of 5% grade for a distance of at least 10' is what I commonly recommend.

One last comment - I would like to know what the ground water table elevation (relative to the footing elevation) is. This will have an affect upon any subsurface drain recommendations that I may have.

 

[dnonnema]

Thanks. The basement is damp (not unusual in my experience) No leaks though. Both the French drain and the sump outlet pipes are 50+ feet down grade from the house. Roof downspouts drain into leaders that drain 50+ft from the house also. My grade also is adequate, per your suggestions.

How would I go about figuring the ground water table elevations vs. the footing elevation

 

[SirAl]

Thanks for the reply to the above dnonnema. I appears that you have taken good steps to minimize surface water related problems. The above link that Focht3 referenced will take you to a related discussion. Refer to my June 17 post that explains a basic standpipe installation. This is an effective method of establishing the ground water table. Do you have a walk-out style of basement?

 

[dnonnema]

Thanks again! Even without the piezometer, I believe i have a groundwater issue--when i was digging the french drain i hit water at about 2.5' depth. I will install one, but i'm afraid it will look a little like old faithful.

I finished about 1/2 of the 80 foot trench on day 1. When i went out the next morning, the entire 40 foot trench was filled with water. The house is not a walkout

 

[dicksewerrat]

With that much water being pumped, I'd say the ground water is being recharged by the water in the hill. You may want to drive some sand points horizontally into the hill starting at 5 feet from the face of the hill all the way back to 20 feet from the face. Place these across the entire width of the house plus 10 feet. This will cut off the water from your house. Pipe the water that comes from these hor. wells downslope. This system works with gravity, the only thing the gov't doesn't tax. If you can drill holes into the hill and place a perforated pipe covered with a geotextile filter, the pipe will take more water.

 

[dnonnema]

Thanks for all your help. How do i go about finding a geotechnical consultant in my area? I'm in Northwest NJ. Thanks!

 

[Focht3]

You have several options.

Contact the American Society of Civil Engineers at 800-548-ASCE and ask for a contact at the local ASCE Branch. Contact that person (who should be a civil engineer) and ask for a list of contacts in your area. That will get you in touch with individuals - not just firms.

Check with your local public works department. They will know who is active in your area, too. But you will miss some of the smaller firms that way.

Finally, check the Yellow Pages. There are enough in north New Jersey - I'd expect a separate heading for them - "Geotechnical Engineers." Also look under "Foundation Engineers."

Good luck -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[dnonnema]

dicksewerrat..thanks for the info. What exactly are sand points?

 

[BigH]

Expensive.

 

[dicksewerrat]

They are the section of a well pipe that has ascreen on it. They are constructed to drive by hand or machine. The screen allows the water to enter but not the soil. For driving horizontally, I would use a jackhammer with a special head made for diving sand points.

 

[Focht3]

Sand points are not appropriate where the soils contain a lot of clay - they tend to clog fairly quickly. And knowing how far to drive them, how much screen to use, spacing, etc. isn't exactly obvious or intuitive. And they are expensive.

I still think you need to hire a consultant; I'm not convinced that a "shotgun" approach to addressing your concerns is a good use of either your time or your money -



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[dicksewerrat]

You can price the sandpoints at most 'Farm and Home' type store. Sears, Tractor Supply.