Section 905.55  Subsurface Seepage System Design Requirements

When designing a subsurface seepage system the absorption capacity of the soil shall be determined by subsection (a) or (b) of this Section as follows:

a)         Soil Investigation.

1)         Soil investigations shall be conducted in the following manner:

A)        Determination of soil characteristics on sites proposed for development with private sewage disposal systems shall be based on soil boring data collected by a soil classifier or an Illinois licensed professional engineer.

B)        There shall be a minimum of 3 borings per soil absorption system site.  The soil borings shall be at least 50 feet apart, and the proposed subsurface seepage system shall be located within the area where the soil borings were located.  More soil borings may be necessary for accurate and appropriate evaluation of a site where there is some concern about the consistency of the soil materials.  One of the borings shall be made at the lowest elevation of the proposed absorption field area.  Borings shall extend a minimum of 60 inches below the natural ground surface.  An observation pit shall be used in gravelly materials.

C)        Observation and determination of soil characteristics may be also determined from a pit dug by a backhoe or other excavating equipment.  The Department or local authority may require soil pits (backhoe excavation) in cases where ground is frozen, where the soil materials are considerably varied in texture, where there has been previous or current fill material, cutting of soils, or where gravelly soils are encountered.  Such soil pits shall be prepared at the perimeter of the expected soil absorption area to minimize damage to natural soil structure.  Soil pits shall extend a minimum of 60 inches below the natural ground surface.

D)        Site characteristics to be described include zones of seasonal and permanent water saturation, U.S.D.A. soil textural changes, U.S.D.A. soil structural features, slope, compaction and depth, soil coloration, depth of limiting layer, depth of soil mottling (depth to low chroma equal to or less than 2 and a value of 4 or more - Munsell Color System), internal drainage classification, and permeability range, and other limiting soil characteristics that may reduce permeability.

2)         The following persons are qualified to conduct soil investigations:

A)        any person who meets the definition of soil classifier in Section 905.10;

B)        a licensed professional engineer;

C)        an employee of a local health department who has 3 years of experience in designing or approving private sewage disposal systems using soil classification information and 6 semester hours of soils related coursework;

D)        an employee of a local health department with 5 years experience designing or approving private sewage disposal systems using soil classification information under the direct supervision of those persons listed in subsection (A), (B) or (C) of this subsection (a)(2).

            A list of qualified persons will be available from the Department upon request.

3)         If conflicting soils investigation information is provided about a given site, an NRCS soil scientist may be requested to provide professional information.

b)         Percolation Tests.

1)         Performance of Percolation Tests.  At least 3 separate percolation tests, a minimum of 50 feet apart, shall be performed at the site of each proposed subsurface seepage system.

2)         Procedure for Performing Percolation Tests.  Percolation tests shall be performed in accordance with the procedure outlined in Appendix A: Illustration G of this Part.  Alternate procedures for performing percolation tests may be submitted to the Department for review.  If determined to be as stringent as that described in Appendix A: Illustration G of this Part, the alternate procedure shall be approved.

3)         If soils information, permits for private sewage disposal systems in close proximity to the proposed site, direct observations or other information show conditions which will impact the design, construction, installation, modification or performance of the private sewage disposal system, the Department or local authority shall cause the determination of the seasonal high water table, fill, soil compaction, poor soil structure, high bulk density, dense unleached glacial till, fragipans, sodic horizons or other limiting soil characteristics that may reduce permeability or impact on design, construction or location of a subsurface seepage system.

(Source:  Added at 20 Ill. Reg. 2431, effective March 15, 1996)