Lawnnymph, I have never heard of this concern before, prohibiting fertilization of the plants growing on a leach field. Not once, in my long career (26 years) in designing, installing, and operating septic tank/soil absorption systems, have I experienced negative consequences in the function of a leach field by applying lawn fertilizer on the grass growing on the surface.
One should NOT, however, over-irrigate the grass on the leach field. Actually, it really depends upon the type of soil that covers the leach field, the type of soil that is below the leach field, the groundwater table elevation, and the annual precipitation in your area. These variable factors determine which direction the majority of the septic tank effluent is going after being applied to the leach field, up or down. If the percolation of the effluent through the soil is rapid, then the application of the typically aerobic irrigation water would have a beneficial effect on the soil absorption system. If the percolation rate of the soil is slow, and a large percentage of the effluent is dispersed through evapotranspiration from the surface of the ground, and dispersed through the plants growing on the leach field, then there should not be a need for irrigation of the leach field area.
The other variables certainly should be considered, but the reality is, if your grass on the leach field is turning brown, I recommend that you fertilize and irrigate the grass!
John Aldrich (Septic Tank Yank) Septic System Consultant Advanced Professional Engineering, Inc. Fort Collins, Colorado firstname.lastname@example.org
» This message has been edited by John Aldrich on 30 August 2002