Percolation pit/trenches close to slopes

[Okiryu]

Hi, we have a building site which is in a terrace area surrounded by steep vegetated slopes (~30%). The site soils are sandy silts / silty sands. The site is in an undeveloped area and the city office is "encouraging" us to use infiltration systems to manage rainfall water. We are planning to use permeable pavements, paver block parking lots and percolation pits and trenches. My question is about what are the considerations for placing percolation systems such as percolation pits and trenches close to the top of the slopes. Are any typical recommendations for setback? We need to do a slope stability analysis but just wondering if there are any standard guidelines. Also, I just found a design guideline for San Diego City, CA and it says: "maintain a 15-foot setback from all parts of the disposal trench to daylight on the slope." This may be a good start point.

For example, for building foundations, we do not want to install percolation pits closer than 10-foot from the foundations. This is a standard recommendation.

 

[oldestguy]

In a situation like this I'd want some on-site test studies of just what would be going on for then establishing some standards. Flow nets supplemented by observation wells at a typical test site along with the stability studies would be involved. Lab tests for permeability of "undisturbed" (as close as you can) samples needed. Then you have ammunition for setting standards for the special situation you have..

 

[Okiryu]

Hi OG, thanks for the input. Yes, we are doing some field percolation tests and start from there. You are right, we will need to consider seepage in our slope stability analysis...

 

[dik]

I've done this using an impervious clay... also proprietary units like Ecoflow (sp?)

Dik