Graywater for irrigation of small avocado orchard

[bicyclemichaela]

Dear People:
I’m not an engineer yet. But my master’s project in civil engineering from Norwich University (online degree) is a new residential installation of a septic system and a graywater system to save potable water in the irrigation of about 70 avocado trees. There is currently a San Diego Co. DEH approved lot layout for the septic system’s leach field. The DEH specified leach pipes 2’ deep on top of 3’ of gravel in a 5’ deep trench.
The trenches for the septic system could be placed down slope from each row of trees and branched drain fed, mulch basins for the graywater could be placed upslope of each row of trees. The soil has low permeability. The average is 27 mpi, but some spots were >240 mpi. With the new, more liberal, graywater regulations in California coming up, this may, if the local agency agrees to use them, make the installation easier.
Well that hopefully gives an idea of what I’m doing. Any specific or general suggestions are most welcome. Here are two specific questions:
1) If by whatever means it is determined that the graywater is over watering the avocado trees, what would be a good way to have the systems configured so that the graywater flows can be turned down or off and the flows be rerouted for disposal or use in areas with ornamental irrigation? What I'm thinking of is using 3 way valves to divert the graywater to the septic system.
2) How can mulch basins be put in around mature orchard trees with well developed root structures? I guess it depends if the tree has developed deep or shallow roots. I’ll have to find that out. Shallow feeder roots could make it difficult to build the mulch basin because digging the basin could significantly harm the tree. But if the roots are deep, then digging the basin wouldn’t harm the trees. Watch a video on graywater that shows what mulch basins are at

http://www.youtube.com/watch?v=PBMpaWq4EKE

.
Thanks.
Michael Roth

 

[bpattengale]

Excavation and Construction around trees can be difficult. A lot of it depends on the tree. The general rule of thumb is no disturbance within the dripline of the tree or 1.5*Diamter of the tree at chest height in inches. So if the tree has an 8" diameter then you'd want to leave an undisturbed area with a diamter of 12' at the minimum. Some trees are more succeptable to root zone disturbances so I'd suggest talking to an arborist. Also note that if you destroy some of the root zone you'll need to trim the tree back in proportion to the amount of the root zone that was destroied.

In my area of the country this defacto standard when trying to save trees during construction.

One last thing is you'll want to limit the size of the equiment working around the trees to prevent the soil from becoming overly compacted.

 

[bimr]

You really have two separate issues.

The first is to treat the sewage to a quality suitable for irrigation. A septic field is not going to provide wastewater treatment such that the effluent is suitable for irrigation of food plants used for human consumption. That wastewater treatment would typically include filtration and disinfection of the wastewater.

The second part of your question involves irrigation of plants. The equipment required to do this is just the standard irrigation equipment that is used in the agriculture industry.