Iowa Administrative Code › Agency 567 - Environmental Protection Commission › Title IV - Wastewater Treatment and Disposal › Chapter 69 - Private Sewage Disposal Systems › Rule 567-69.9 - Secondary Treatment-subsurface Soil Absorption Systems

Current through Register Vol. 47, No. 3, July 24, 2024
Subsurface soil absorption systems are the best available
				  treatment technology and shall always be used where possible.
(1)
General requirements.
a.
Locations.
All subsurface
				soil absorption systems shall be located on the property to maximize the
				vertical separation distance from the bottom of the absorption trench to the
				seasonal high groundwater level, bedrock, hardpan or other confining layer, but
				under no circumstances shall this vertical separation be less than 3
				feet.
b.
Soil
				evaluation.
A percolation test or professional soil analysis is
				required before any soil absorption system is installed.
(1)
Percolation test.
The
				percolation test procedure is outlined in Appendix B.
(2)
Alternative analysis.
If
				a professional soil analysis is performed, soil characteristics such as soil
				content, color, texture, and structure shall be used to determine a loading
				rate.
(3)
Acceptable
				percolation rate.
An area is deemed suitable for conventional soil
				absorption if the average percolation rate is 60 minutes per inch or less and
				greater than 1 minute per inch. However, if an alternative soil absorption
				system is proposed (e.g., mound system), then the percolation test should be
				extended to determine whether a percolation rate of 120 minutes per inch is
				achieved.
(4)
Confining
				layer determination.
An additional test hole 6 feet in depth or to
				rock, whichever occurs first, shall be provided in the center of the proposed
				absorption area to determine the location of groundwater, rock formations or
				other confining layers. This 6-foot test hole may be augered the same size as
				the percolation test holes or may be made with a soil probe.
c.
Groundwater.
If the seasonal high groundwater level is present within 3 feet of the trench
				bottom final grade and cannot be successfully lowered by subsurface tile
				drainage, the area shall be classified as unsuitable for the installation of a
				standard subsurface soil absorption system. The administrative authority shall
				be consulted to determine an acceptable alternative method of wastewater
				treatment.
d.
Site
				limitations.
In situations where specific location or site
				characteristics would appear to prohibit installation of a soil absorption
				system, design modifications which could overcome such limitations may be
				approved by the administrative authority. Examples of such modifications could
				be the installation of subsurface drainage, use of shallow or at-grade
				trenches, drip irrigation, or mound systems or use of pretreated
				effluent.
e.
Prohibited
				drainage.
Roof, foundation and storm drains shall not discharge into
				or upon subsurface absorption systems. Nothing shall enter the subsurface
				absorption system which does not first pass through the septic tank.
f.
Prohibited construction.
There shall be no construction of any kind, including driveways, covering the
				septic tank, distribution box or absorption field of a private sewage disposal
				system. Vehicle access should be infrequent, primarily limited to vegetation
				maintenance.
g.
Driveway
				crossings.
Connecting lines under driveways shall be constructed of
				Schedule 40 plastic pipe or equivalent and shall be protected from
				freezing.
h.
Easements.
No wastewater shall be discharged upon any property under
				ownership different from the ownership of the property or lot upon which the
				wastewater originates unless easements to that effect are legally recorded and
				approved by the administrative authority.