ADMINISTRATIVE CODE

TITLE 77: PUBLIC HEALTH
CHAPTER I: DEPARTMENT OF PUBLIC HEALTH
SUBCHAPTER r: WATER AND SEWAGE
PART 906 PRIVATE SEWAGE MOUND CODE

Section 906.10 Applicability

Section 906.20 Definitions

Section 906.25 Incorporated Materials

Section 906.30 Soil and Site Requirements

Section 906.40 Fill Material

Section 906.50 Mound Design

Section 906.60 Distribution System (for sewage flows of less than 800 gallons per day)

Section 906.70 Distribution System (for sewage flows in excess of 800 gallons per day)

Section 906.APPENDIX A Illustrations and Exhibits

AUTHORITY: Implementing and authorized by the Private Sewage Disposal Licensing Act (Ill. Rev. Stat. 1987, ch. 111½, pars. 116.301 et seq.)

SOURCE: Adopted at 13 Ill. Reg. 12608, effective August 1, 1989)

Section 906.10 Applicability

a) This Part is promulgated by the Illinois Department of Public Health in order to establish requirements for the design and construction of mounds in Illinois which are to be used as private sewage disposal systems. All such mounds must be constructed in accordance with the requirements of this Part.

b) Plan approval must be obtained from the Department or local authority prior to beginning any construction of a mound system in accordance with Section 905.190 of the Private Sewage Disposal Code (77 Ill. Adm. Code 905). All individuals who construct such systems must be licensed as a Private Sewage Disposal System Installation Contractor.

Section 906.20 Definitions

"Absorption Area" means the area of coarse aggregate in the absorption bed or trenches in a mound.

"Basal Area" means the area of natural soil under a mound which is effective in absorbing effluent.

"Depression" means an area that is sunk below its surroundings.

"Dosing" means the application of sewage under pressure to a sewage disposal system at constant intervals or in constant amounts per application.

"Drainageway" means a natural or artificial channel for the discharge of surface water through a given tract of land or region.

"Flood plain" means the land bordering a stream, built up of sediments from overflow of the stream and subject to inundation when the stream is at flood stage.

"Mound" means a soil absorption sewage treatment system that is elevated above the natural ground surface in a suitable fill material as defined in 906.40.

"Perched Water Table" means groundwater which is trapped above a normal water table by an impervious formation.

"Percolation Rate" means the downward movement of water through a saturated soil.

"Permeable Soil" means soil which has a percolation rate between 18 and 180 minutes. (See Appendix A, Illustration G of the Private Sewage Disposal Code for meaning of percolation rate and percolation test procedure.)

"Shallow Permeable Soil" means pervious soil over creviced or porous bed rock, 5½ feet or less in thickness.

"Slowly Permeable Soil" means soil having a percolation rate of between 180 and 360 minutes.

Section 906.25 Incorporated Materials

a) The following federal and state regulations, standards and statutes are incorporated or referenced in various sections of this Part.

1) 1986 Annual Book of ASTM Standards:

American Society for Testing and Materials

1916 Race Street

Philadelphia, PA 19103

2) American Society for Testing and Materials (ASTM) required standards for approved plastic pipe and published by:

American Society for Testing and Materials

1916 Race Street

Philadelphia, PA 19103

b) All incorporations by reference of federal regulations and the standards of nationally recognized organizations refer to the regulations and standards on the date specified and do not include any additions or deletions subsequent to the date specified.

c) All materials incorporated by reference are available for inspection and copying at the Department's Central Office, Division of Environmental Health, 525 West Jefferson, Springfield, Illinois 62761.

Section 906.30 Soil and Site Requirements

In order to be suitable for mound construction, the site shall meet the following requirements and those listed in Appendix A, Exhibit A.

a) Percolation Rates. Percolation rates shall be used to determine the suitability of the site for accepting effluent. Percolation tests shall be performed according to the procedure outlined in Appendix A, Illustration G of the Private Sewage Disposal Code (77 Ill. Adm. Code 905). Excepting that, percolation tests shall be performed at a depth of 20-24 in. from the natural surface. However, in cases where a more slowly permeable soil horizon is above this depth the percolation tests shall be conducted in the more slowly permeable soil horizon. Those results shall be used in the design of the mound. For shallow permeable soils over pervious bedrock, the percolation test shall be run at a depth of 12-18 in. below the natural surface. For permeable soils with high water tables, the percolation test shall be run at a depth of 20-24 in. below the natural surface.

b) Depth to Pervious Rock or Seasonal High Water Table. There shall be a minimum of 24 in. of unsaturated soil between the soil surface and pervious bedrock or the seasonal high water table, including a perched water table, at the proposed mound site. High water tables can be determined by direct observation or by soil mottling. Occurrence of grey and red soil mottling patterns can be used to indicate periodic saturation with water.

c) Rocky Soils. If the soil contains 50% rock fragments or more by volume in the upper 24 in. of soil, the mound basal area shall be 25% larger than that normally required.

d) Slopes. The mound shall be placed upslope and not at the base of the slope of the existing ground. On a site where there is a complex slope, (two directions), the mound shall be situated such that the liquid is not concentrated in one area downslope. Upslope runoff shall be diverted around the mound. For the more permeable soils where the percolation rate is 18-179 min., slopes shall not exceed 12%. For tighter soils where the percolation rate is 180-360 min., slopes shall not exceed 6%.

e) Flood Plains. Construction of mound systems shall not be allowed in flood plains, drainage ways or depressions.

f) Sites with Trees and Large Boulders. Sites with large trees, numerous smaller trees or large boulders are unsuitable for the mound system. If no other site is available, the trees shall be cut off at ground level, leaving the stumps. An increase in mound basal area shall be required where stumps are involved, so that sufficient soil is available to accept the effluent. The increase in mound area shall equal the surface area of the stumps on the mound site.

g) Site Preparation

1) Vegetation shall be cut and removed from the site prior to construction. The site must then be plowed with a mold board plow 7-8 in. deep with the plowing done perpendicular to the slope. Plowing shall not be done with the furrow running up and down the slope. Chisel plowing may be used in place of mold board. Roto tilling is prohibited. However, roto tilling may be used to incorporate the vegetative cover in unstructured soil such as sand.

2) Site preparation shall not take place when the soil is too wet. The soil shall be considered too wet when a soil sample taken at a depth of 7-8 in. beneath the surface can be rolled between the palms of the hands into a continuous ribbon of soil. If the soil crumbles, site preparation can then proceed.

3) Once the site is plowed, all construction machinery and other vehicles shall be kept off the mound site. The fill material shall be deposited on the site with a backhoe or pushed on from the side, using a track type tractor, keeping 6 in. of fill beneath the tracks. At no time shall ruts be made in the plowed area. The fill shall be placed immediately after site preparation to avoid the possibility of precipitation falling on the plowed area.

4) All work shall be performed from the ends and upslope side, especially on fine textured soils.

Section 906.40 Fill Material

a) Below Absorption Area

1) A mound system shall be provided with a fill material beneath the absorption area (trenches or bed). One of the following fill materials shall be used.

A) FA-1

B) FA-2

C) FA-3

D) FA-8

E) FA-9

2) These materials are classified and graded in accordance with Illinois Department of Transportation, Division of Highways specifications for fine aggregate. These materials shall meet the gradation specifications as shown for these five fine aggregates in Appendix A, Exhibit B.

b) Above the Absorption Area. The cap (area above the bed or trenches) shall consist of a topsoil to allow plant growth. Sands are not allowed since they drain rapidly and allow more infiltration of precipitation into the absorption area. Topsoil shall be placed to a depth of 6 in. over the entire mound to promote good vegetation cover. The cap soil shall be seeded and fertilized.

Section 906.50 Mound Design

a) A mound system shall include a septic tank for pre-treatment of sewage. The septic tank and piping between the septic tank and the pumping chamber shall conform to the applicable rules in the Private Sewage Disposal Code (77 Ill. Adm. Code 905).

b) The design of the mound shall be based upon the expected daily waste water volume using the data contained in Appendix A, Illustration A, of the Private Sewage Disposal Code, (77 Ill. Adm. Code 905) and the soil percolation rate. Mounds shall be sized such that they can accept the daily waste water flow without surface seepage, and the basal area, which is the natural soil area beneath the mound, shall be sufficiently large to conduct the effluent into the underlying topsoil. The system shall also be designed to avoid encroachment of the water table into the mound.

c) For homes having up to and including 4 bedrooms or for flows less than 800 gallons per day the mound shall be designed in accordance with 906.60. For homes with 5 or more bedrooms or for flows greater than or equal to 800 gallons the mound shall be designed in accordance with 906.70.

d) Design of the Absorption Area

1) Sizing the absorption area. The size of the absorption area is dependent upon the daily waste water flow. The design infiltration capacity of the fill material shall be 1.2 gal/ft²/day.

2) Absorption Area Design

A) System configuration. The absorption area within the mound shall be constructed as trenches or beds. An illustration of construction using trenches and bed is shown in Appendix A, Illustration A through D. The location of the water table and soil permeability will dictate whether a trench or bed shall be used. In slowly permeable soils, two or three narrow parallel trenches shall be used instead of a bed. Trench widths shall be between 24 and 48 inches. For permeable soils either a narrow rectangular bed or two or three narrow parallel trenches may be used. Bed widths shall not be greater than 10 ft.

B) On sloping sites, the trenches and beds shall be situated perpendicular to the slope in order to prevent the concentration of effluent into a small area as it moves laterally downslope. Sufficient basal area shall be provided so all the effluent infiltrates into the natural soil before it reaches the toe of the mound. With a trench system, the trench spacing shall be such that the effluent from an upslope trench shall be absorbed by the natural soil before reaching the area under the next trench downslope.

C) The bottom of the absorption area within the bed and trenches shall be level and at the same elevation.

e) Mound Dimensions

1) Mound height. The mound height shall consist of the fill depth (D & E), the trench or bed depth (F), and the cap and topsoil depth (G & H) as shown in Appendix A, Illustration A through D for trench and bed construction respectively. A minimum of 1 foot of fill is required under the bed or trenches. For sites where the soil depth is less than 3 feet over creviced bedrock, the fill depth (D) shall be a minimum of 2 feet.

2) Bed or trench depth (F). The depth of the bed or trenches shall be at least 10 inches. A minimum of 6 in. of aggregate shall be placed beneath the distribution pipe. Clean, ½-2 inch stone shall be used. The use of soft limestone is prohibited.

3) Cap and topsoil (H & G). The depth of soil over the aggregate at the apex (H) shall be a minimum of 1.5 ft. For a 3 parallel trench system, the depth shall be a minimum of 2 ft. At the outer edge of the gravel the cap and topsoil shall be at least 1 ft. deep. The cap shall be topsoil or finer textured subsoil. A minimum of 6 inches of topsoil shall be placed over the entire mound. The topsoil shall be seeded with grass seed to control erosion.

4) Side and end slopes. Side and end slopes shall be no steeper than one foot vertical rise in 3 feet horizontal.

f) Basal Area

1) The basal area is the natural soil-fill interface of the mound. The basal area required shall be dependent upon the soil and site conditions. For level sites, the total basal area beneath the mound can be used. For sloping sites the only basal area which may be considered for design is the area beneath and downslope of the bed or trenches (see Appendix A, Exhibit C). The percolation rate of the natural soil shall determine the mound area required. For the percolation rates shown the following design loading rates shall be used:

A) 60 min – 1.2 gal/ft²/day

B) 180 min – .74 gal/ft²/day

C) 360 min – .24 gal/ft²/day

2) If sufficient basal area is not available for the given design and site conditions, additional fill shall be used to make the mound wider for a level site or the fill used to extend the downslope width on a slope site until sufficient area is available.

Section 906.60 Distribution System (for sewage flows of less than 800 gallons per day)

a) Piping System. The piping distribution system for the mound shall consist of a manifold pipe and small diameter laterals with perforations. The perforations shall be drilled at 30"-36" intervals along with the invert of the lateral. Perforations shall be installed perpendicular to the pipe axis. Perforation diameters shall be between 3/16" and ¼". If the distance between the end of the lateral and the nearest perforation is greater than ½ the perforation spacing used, another hole shall be installed in or near the end cap of the lateral. A typical distribution system of a mound is shown in Appendix A, Illustration E. For a trench system, one lateral shall be required per trench; for a bed system, up to 3 laterals may be used. Laterals shall extend to within 6 inches of the end of the bed or trench. Lateral spacing shall be a maximum of 3 ft. for beds in small mounds only (1-4 bedroom sized system). Pipe diameter will depend upon the length of bed or trenches. The allowable lateral lengths for various size diameter pipes and various hole spacings are given in Appendix A, Exhibit D. The system shall be designed and placed so that the laterals and manifold drain after every dosing. If the mound is downslope of the pumping chamber, the manifold shall be on top of the laterals so the manifold drains, or cross-to-cross construction used. For systems which are to treat a flow of more than 800 gallons per day, the manifold and lateral network must be designed in accordance with Section 906.70. All piping shall be Schedule 40 Polyvinyl Chloride (ASTM Standard D1785/76) or Schedule 40 Acrylonitrile/Butadiene/Styrene (ASTM Standard D1527/77).

b) Pumping System. The components of the pumping system shall consist of the pumping chamber, pump, pump controls and alarm system as shown in Appendix A, Illustration F. The dosing volume shall be ten times the total lateral pipe void volume or one-fourth the estimated daily sewage flow, whichever is greater. Appendix A, Exhibit F lists the void volumes for various sizes of pipe. The daily volume of sewage shall be determined using Appendix A, Illustration A of the Private Sewage Disposal Code (77 Ill. Adm. Code 905).

1) Pumping Chamber Requirements.

A) Pumping Chamber. Appendix A, Illustration F gives a cross-section of a typical pumping chamber. The volume shall be sufficient to provide the desired dosing volume, space for controls, space for setting the pump on a pedestal, and extra volume for a malfunction and flow-back after pump shuts off. Appendix A, Exhibit G establishes pumping chamber sizes for the various sized systems. Larger tanks may be used, but they may limit the flexibility of adjusting the desired dosing quantity. Sufficient volume must be available to provide for the dose volume, pump pedestal and controls.

B) The pumping chamber shall be waterproof. Waterproofing shall consist of sealing all joints and coating the outside of the tanks. The pumping chamber shall be filled with water after being installed and back filled to prevent the pumping chambers from floating out of position due to hydrostatic pressures, unless the tank is installed in dry soil. A riser pipe shall extend at least 6 in. above the ground surface. All electrical controls shall be mounted outside the tank. The pump disconnect shall be accessible for easy pump removal in the event of pump failure.

2) Pump Selection. The pump shall be a submersible pump designed for corrosive liquids and shall be capable of maintaining at least 2 feet of head at the distal ends of the laterals. The pump switch shall be controlled by a float in the pumping chamber, set so that the required dosing volume is discharged during each pumping cycle. A check valve between the pump and the piping network manifold shall not be allowed.

3) Pump and Alarm Control. The control system for the pumping chamber shall consist of a control for operating the pump and an alarm system to detect when the system is malfunctioning. Pump controls shall be selected which give flexibility in adjusting the on-off depth. Example of acceptable controls are shown in Appendix A, Illustration F. Pump controls shall be adjusted to pump the required dose of sewage plus the volume of sewage which flows back to the pumping chamber after shut-off.

4) Electrical and Alarm System. The alarm system shall consist of an audible and visual alarm in the home or facility building. This system shall be on a circuit separate from the pump. The electrical controls shall be placed outside the pumping chamber.

5) Siphons. Siphons can be designed where elevation exists between the mound and the siphon chamber. However, the siphon shall be designed to deliver the same flow rate at the same head at the distribution system as a pump system. The distribution system consisting of manifold and laterals shall be designed so that it will drain after each siphon. This shall be accomplished by placing the manifold above the laterals.

Section 906.70 Distribution System (for sewage flows in excess of 800 gallons per day)

a) Design criteria for laterals.

1) The variation in discharge rates from the perforations in any lateral shall not exceed ten percent.

2) The variation in discharge rates between the perforations of any two laterals shall not exceed 15%.

3) The pressure at the distal ends of the lateral shall be at least 2.5 feet of water.

b) Perforations. The perforation requirements of this Section shall be used in place of those of Section 906.60.

1) The perforations shall be spaced uniformly along the laterals and at an interval not to exceed 10 feet.

2) Perforations shall be installed perpendicular to the centerline of the lateral and along the lateral invert.

3) Perforation diameter shall be between ¼ and ⅝ inches.

4) To facilitate the draining of laterals between dosing cycles, a perforation shall be installed at the distal end of each lateral near the crown of the pipe.

c) Network Configuration

1) The laterals shall be installed in seepage beds. The lateral spacing shall equal the perforation spacing. The perforations of adjacent laterals in the bed shall be staggered.

2) Mounds employing multiple beds may be used. Also, multiple mounds may be employed. If bed elevations are not all equal, then this fact must be considered in the design of the pipe network in order to provide uniform dosing of effluent.

3) Manifold-to-lateral connections shall be made using tee-to-tee construction, with the manifold below the laterals (see Appendix A, Illustration G). If the design is such that the manifold does not drain between dosing cycles, then insulation or some other means shall be provided to prevent freezing. In addition, provisions shall be made for manual draining of the manifold.

4) Two separate distribution networks may be employed, with each network receiving alternate doses of effluent through the use of alternating pumps, valves, or siphons.

5) Siphons or siphon breaks shall be used in networks where the low water level in the pumping chamber is above the lateral inverts.

d) Pumping Chamber

1) Dosing volume. Dosing volume shall be determined by dividing the average daily sewage flow by the dosing frequency for the particular soil type, as is shown in Appendix A, Illustration H. Dosing volume shall be at least five times the pipe volume of the network. The dosing volume is the amount of liquid pumped or siphoned during each cycle minus the amount which drains back from the system after each dose.

2) Reserve capacity. If a single pump is used, a reserve capacity equal to one day's average sewage flow shall be provided. A reserve capacity is not required if multiple pumps or siphons are used.

3) A high water alarm switch shall be installed 2-3 inches above the pump or siphon activation level. The switch shall be on a circuit separate from the pump controls.

4) The pump or pumps shall be of a submersible type, designed for corrosive liquids. The control switches shall be corrosion resistant. All electrical contacts and relays shall be mounted outside the chamber. Provisions shall be made to prevent gases in the chamber from following the electrical conduits into the control box.