Drywell Design/Installation

[RobS]

I’m going to put in a few drywells to take our roof runoff and eventually one for the washing machine. Anyone have any tips on sizing and construction?

I did some preliminary calcs on the rainwater and came up with a whopping 2800 gallons for the biggest one! That was based on 4 inches of rain. Even a reasonable ¼ inch of rain amounts to 175 gallons the way I’ve got the downspouts routed. Our soil is quite sandy so it drains well. I don’t expect to handle the worst-ever storm but how big should I make it to keep the rains under control?

As far as construction, I’ve seen anything from pre-fab kits to drilled out plastic barrels. Generally covered in landscape fabric and surrounded by stone with a surface overflow. I’ll probably use the barrel/plastic trash can approach to keep costs down.

So that’s what I’m up against for the springtime. Hoping to use this (along with a list of other projects) to partially justify a backhoe for my tractor. Of course, the main justification will always be recreation/entertainment value to keep my sanity. Any and all suggestions/experiences welcome /forums/images/graemlins/smile.gif

 

[gerard]

I wouldn't be too concerned about making sure the capacity can handle all the runoff, just make sure the top of the dry well is below the level of the top of the drain pipe from the downspout, a foot or more differential should be fine, more is better. That wil give you head, ie pressure. When the dry well fills quicker than the ground can absorb it the water will just seep up through the grass and run off the surface. I use that system for the overflow from my koi pond. Just make sure you locate the drywell at a place that when the water oozes up it will flow in the direction you want /forums/images/graemlins/smile.gif

 

[ejb]

If you are going to go to all that trouble of building a huge drywell to catch roof runoff, why not build a cistern instead?

Then with the addition of a pump you can use the water for outdoor things like the garden...

 

[gerard]

Also I don't know what the plastic barrel does? I just dug a hole, ran the pipe in, filled it with gravel, laid down some landscape fabric on top of the gravel and topped with about 6 inches of dirt and planted grass seed. I have seen systems that have a grate which is flush with the ground and the pipe runs into a box just below the grate. That way the water just flows up and out the grate and across the ground. Both ways work, one is just a little cheaper and better hidden!

 

[djradz]

Just a couple of thoughts. Why not just route the downspouts under ground a little ways from the house and let them natuarlly drain on the lawn, soil, whatever. I've been doing this for years in clay and still no problmes. Also, my experience with a dry well for washing machine is not too good. The soil quickly becomes clogged with all that soap and nothing seems to break it up. Plugged up two drywells that way. Reverted to dumping it into the sump and draining it on the lawn also. Maybe not code however, but works fine.

 

[Rubintropfen]

A previous owner of my land started building here about 20 years before me. He died before he finished, and I bulldozed over the remains of the foundation, but that's not important. His footer drain went out the front of the hill, just like mine, but he built a dry well for the downspouts. I have never understood why, because there is plenty of grade to daylight a pipe downhill from the house. It seems to me that he could have done a little more trenching for the cost of the pit he dug and filled with stone. Especially since the soil is mostly clay and doesn't drain well at all.

I guess I'm trying to say a dry well only seems like a good option to me if there is no other reasonable way to get rid of the water. If it is too close to your house you risk a wet basement or even foundation damage.

There are some design criteria in this document: NJ Standard for Dry Wells.

 

[RobS]

Good link, thanks Rubintropfen. And thanks for the other ideas everyone else. The main reason I (think) I want drywells is because our property is basically flat. I've already buried the downspout drains and they route well away from the house and septic. Because the land is so flat though, the drain lines now slope upward at the tail end to emerge from the ground. This was a temporary solution from the beginning. To maintain some pitch and prevent water backup/freeze I need to terminate the line underground. At the same time, I don't want to create a bunch of mudholes for the kids to get into. Thus, the drywell idea. Take the normal rainwater underground and keep it there. Heavier rains will bubble up and that's not a problem /forums/images/graemlins/smile.gif

 

[CTyler]

I have been considering doing this as well but for a different reason. The water will be stored for future use like watering the lawn, garden, washing mud off the tractor, etc.. The reason is to cut down well water usage for all that stuff.

I have not looked into this very hard other than pricing some underground plastic tanks. What is a good inexpensive option? What about controlling algea, bugs, etc? I was thinking a very large tank as well.