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Re: Basement Drainage - Sump

From: info@builderswebsource.com
Category: Drainage/Waterproofing
Remote Name: 63.198.181.43
Date: 14 Jun 2001
Time: 10:39 PM

Comments

First, let's look at how the drainage system works. The perimeter drainage system (called a french drain) picks up groundwater near the footing which could otherwise enter the basement. In order to direct this water to a common location, a sump is installed where the water can collect. A sump pump discharges the water and the cycle repeats.

It's common for sumps to also have holes in them. Sometimes there is a liner wrapped with filter fabric to prevent dirt and debris from entering. You mention that most of the water is coming from the bottom of the sump, as opposed to the french drain.

This would indicate that you have a significant water problem around your house, either due to natural causes or man-made causes.

The first thing to note is that you should always follow these minimum guidelines:

1) Make sure that your exterior ground slopes away from the house, not towards it. This will help to keep water away from the foundation in the first place.

2) Make sure any irrigation (sprinklers) or downspouts properly drain well away from the foundation. Watering the foundation is just asking for trouble.

3) Verify that there is no broken water pipe that could be causing excessive moisture.

4) Determine where the sump is draining. If it is discharging the water anywhere near the house, you'll just keep recycling the water, wearing out your pump. The discharge should be 20-30 feet away from the house or more if possible. Ideally, it should flow to the street into the gutter.

5) It's also possible that your pump is not properly sized or adjusted. Pumps have something called hysterisis. This is the difference between the "on state" and the "off state." For example, a typical pump might turn on when the water level reaches, say 7-10", but not turn off until the water level is back down to 3". If the difference between the trip points is too close, the pump will continue to cycle on and off at an excessive rate.

However, if the pump is properly adjusted, then you may have a case where there is excessive ground water, such as a natural spring or a very high water table. You may want to consult with a civil engineering company (or the original builder) to understand what kind of unique conditions your property may have.

Increasing the size of the sump pit will allow more water to flow in before reaching a certain height...but the key is to identify the actual source of the water...and to what extent it is natural or self-induced.

The reason you don't see much water coming through the french drains is that the water may be coming from the water table itself...and it will tend to flow to the point of least resistance, which is the bottom of the sump. As a result, the water level never has a chance to reach the height of the footings because it enters the sump first through hydrostatic pressure.

At best, all you need is a simple adjustment to your sump (or a different type of pump with variable settings). At worst, your property has a chronic water problem that may require more engineering investigation. Please keep us posted on what you find out so we can help our other readers who may be experiencing a similar problem.

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