Messages and Online Forum Q&A

Re: Dry Well

From: info@builderswebsource.com
Category: Plumbing
Date: 19 Jun 2000
Time: 21:32:39
Remote Name: 63.198.181.43

Comments

You can build your own dry well or purchase a ready-made plastic version. In either case, the concept is the same: to create a designated area where surface drainage (or, in this case, an outdoor shower) can percolate naturally into the surrounding soil.

Technically, several factors are required to properly engineer a satisfactory dry well. Among these include the expected flow in gallons per minute (assume 3 gpm for a shower), total expected flow, soil type (to estimate percolation rate), and basin size (accounting for drainage rock).

Without knowing the above, it would only be a guess. However, if you assume a worst-case situation where the soil is clay (which drains very slowly), then we can assume that the effective outgoing flow rate is zero during the period in which the shower is on. Assuming a 3 gallon per minute flow rate and a 15-20 minute shower, that's 50-60 gallons of water you'll need to disperse. Let's assume that a dry well filled with #2 gravel has 25% available liquid volume. You'd need a pit equivalent to approximately 200-250 gallons, or approximately 33 cubic feet (1 gallon = 0.1337 cubic feet). This would be equivalent to a 4-foot diameter hole nearly 3 feet below the inlet level.

Of course, if your flow rate is different from the above assumptions, then this would impact the calculation.

Also, it's a good idea to prevent silt from entering the dry well by using a landscape filter fabric on the dry well perimeter. A comprehensive Tech Note on drainage is available here in printable PDF format.

To avoid "gumming up" your dry well, avoid using soaps and shampoos which can leave unwanted residues. If you must use a cleansing agent, use something that's biodegradable and mild.

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