Sizing an Underground Disposal Field 1

[SharkswithLasers]

A contractor is proposing to dispose of 250 GPM of pumped groundwater to an underground infiltration disposal gallery (piping to gravel bed) below frost line in the vadose zone (4 foot frost depth, 30 feet to water table, fairly uniform silty sands below 4 foot depth). The pumpout will occur over a long period of time (greater than five years).

The size of the disposal field/infiltration gallery recommended by the contractor is much less than I expected. Using an estimated long term soil acceptance rate, I estimated aproximately 4 acres needed (based on permeability 10E-4) and hydraulic loading (250 gal/min). The contractor (who has much experience with these matters) calculates 1/2 acre needed.

The main difference appears to be in the long-term soil acceptance rate or permeability and the way the soil will actually accept the water. We have no field tests yet, but we will be conducting some soon. We will use actual field test data to determine if proposed size is acceptable.

Has anyone designed/sized a similar underground disposal field? What are the equations and guidelines for such a system? Examples? I think I am missing something here because 4 acres is so much diffeent than 1/2 acre.


Any help you can offer is greatly appreciated.

 

[glenns]

http://www.state.nj.us/dep/dwq/pdf/techguid.pdf

 

[cdale]

I have a similar question as yours, I checked out the link provided by glenns I was wondering if you ended up using the equation provided in that text? If not what did you do and how is your project working out?