Rock soak-away for weeping tile

[pats1003]

We have a situation whereby we cannot connect a large residential dwelling storm sewer service (weeping tile drainage) to the existing storm sewer main in the street. The Municipality is allowing us to drain to a rock soak-away pit on the property. We are trying to size this soak-away (depth and diameter) and select the appropriate rock size to use. Dwelling has an 11,000 sf footprint and the watertable is below footing depth, therefore drainage would only occur during rain events. Any tips or references would be appreciated. Thanks.

 

[cvg]

so this is to drain seepage collected by the foundation drains only and this seepage is only from surface water runoff which soaks into the ground? Do you have granular or fine soils? How well do the soils percolate? Do you have good slopes draining the water away from the foundation? Do you have surface water flowing through your property from offsite? Where does the roof drainage go? How much rain do you get? Evaluate all of these and your soakaway might be very small or quite large depending on the answers.

 

[pats1003]

Yes, drainage is collected around foundation and seepage from surface runoff. Soils can be classified as well graded gravel with about 15 to 20% silt. Soil percolation at the deths required would be slow. Slopes away from the foundation would be considered fair. No surface water flowing through the propserty from off-site. Roof draiange discharging over land. Average yearly rainfall is 1200 mm.

How do you size the rock soak-away pit?

 

[cvg]

well graded gravel with slow percolation?

estimate the rainfall which will infiltrate and impact your foundation drain

Estimate a void ratio for your stone

Size the pit to hold the storm runoff within the voids in the stone

 

[bimr]

Here is a design guide for stormwater (soak-away pit):

http://www.ene.gov.on.ca/envision/gp/4329e_4.htm

The local stormwater utility should be able to provide some guidance.