sinking leach field

Anyone ever heard of a drain bed type leach field settling to the point it slopes downward from the head pipe to the end at a slope of 33" over 44 feet? It is a fairly new drain bed installed a little over two years ago. I dug up observation holes at the head pipe, mid way on the distribution pipes, and at the ends of each of the three lines. I then had a friend come over with survey equipment and we measured the pipes at each observation point and recorded 33" drop from the head pipe to the ends (44 feet length).

Any insight from industry experts would certainly be appreciated.

well lets see......

1/4'' per foot x 44'= 11''

the slope of your pipe is to extreme,

A pipe will not drop in elevation in its entirety, sections may drop causing bellies in the pipe
but the whole 44' sinking at the same rate is,,,impossible

your line was installed incorrectly, it is not sinking

Frodo,

I agree with you completely. I believe the contractor installed the drain bed with a pre-exisiting slope (I suspect approximately 3% grade....which is wildly illegal per our county code) and since then the drain field has continued to settle and shift due from what I believe are a variety of poor construction techniques. Its important the note that the header pipe is completely level from end to end. Its the distribution pipes that have settled and shifted to what is now a 6% grade from header pipe to the end of the distro lines.

It is also important to note that the entire drain bed was installed into pretty significant compound slope in our yard. It appears to my un-untrained eye that only a portion of the drain bed was actually dug into the existing slope and the the majority of the drain bed was installed into a make-shift "raised" bed to compensate for the existing slope of my yard. Coincidently, the most severe evidence of shifting and settling is associated with the "raised" bed portion and that same shifting/settling appears to be in the general direction of the natural compound slope of my yard.

A follow up question/opinion for you Frodo. Is it, in your experience, normal to create drain bed in which part of it would be dug into the natural slope of the terrain and have the remainder of it built onto a "raised" drain bed? I hope my question makes sense, its difficult to describe the situation in my yard.

Thanks much!

http://www.floridahealth.gov/enviro...ewage/forms-publications/_documents/64E-6.pdf

64E-6.014 Construction Standards for Drainfield Systems [starts on pg 41]

5. ASTM F 810-99, Standard Specification for Smoothwall Polyethylene (PE) Pipe for Use in Drainage and Waste Disposal Absorption Fields (1999), herein incorporated by reference. Materials used to produce this pipe shall meet ASTM D 3350-98a (1998), Standard Specification for Polyethylene Plastics Pipe and Fittings Materials, Cell Classification 32442C or E, herein incorporated by reference. (b) Corrugated or smooth wall fittings (elbows, tees and crosses) shall be acceptable for gravity flow headers. Header pipe interior shall be smooth. Header pipe shall have a minimum inside diameter of 4 inches for gravity flow applications. Header pipe shall not be perforated. (c) The header pipe shall be laid level with direct, connections to each drainfield line and the septic tank outlet pipe. When installed in a drainfield which uses mineral aggregate, the header pipe shall be encased in mineral aggregate, and shall be included as part of the drainfield area. Gravity flow header pipes, when installed within the mineral aggregate drainfield, may be non-watertight but shall be soil tight. Snap connections are acceptable. On non-mineral aggregate systems, header pipe must be supported by soil. All connections shall be such that all joints or fittings are firmly connected to pipes. When a drainfield system is a pumped system, the header pipe and fittings shall be smooth-walled and watertight. Where the header pipe is not within the absorption surface area it shall not be included in drainfield size calculations, but shall be considered part of the system. The header pipe shall be designed to distribute effluent as equally as practical to each individual drainline and shall be supported so that the header is laid level. (

(h) Depending on the type of drainfield system being utilized, the drainfield absorption surface shall be constructed level or with a downward slope not exceeding one inch per 10 feet. Drain lines shall be placed at the same slope as the drainfield absorption surface. (