French Drain Installation in Fallbrook

French Drain Installation questions from Fallbrook customers

My property isn't on a street with a storm drain. Where can a French drain legally discharge?

County minor-grading standards call for drainage facilities that carry surface water to the nearest practical street, storm drain or other watercourse, and require the point where a drain discharges onto natural ground to be protected from erosion. On a large unincorporated parcel that usually means a daylight outlet on the same property with erosion protection. The County also allows only rainwater into streets and storm drains.

Would a dry well work instead of running the line out to daylight?

It depends which soil is under the yard. Within the Fallbrook area, SSURGO maps Bonsall and Placentia as major components rated hydrologic group D. The Bonsall series is described as having very slow permeability with 35 to 50 percent clay in the upper 20 to 40 inches. A pit dug into that holds water instead of releasing it. Fallbrook and Ramona components rate group C; group A soils appear in only a few map units.

We're on septic. How close can a French drain run to the leach field?

County septic design criteria set leach line setbacks of five feet from property lines, eight feet from structures, 50 feet from the top of bank of a drainage course, 100 feet from the top of bank of a flowing stream, and a 5:1 horizontal setback from the top of a cut slope. A subsurface drain that creates a new discharge point interacts with those distances, and FPUD notes much of its sewer service area is on septic.

How deep can a trench go before it hits rock?

Depth to weathered granite varies by soil across one sloping lot. The Fallbrook series is described with 40 to 60 inches to a paralithic contact of decomposed granite; the Vista series runs 20 to 40 inches; Cieneba only 4 to 20 inches, and it is mapped on slopes of 9 to 85 percent. Below that contact the material is described as loamy coarse sand to gravelly coarse sand.