TSM352: Land and Water Management Systems

Due 3/26/12

Advantages of Using Septic Systems

  • Minimum maintenance: Pumping once every couple years
  • Cost effective: The cost of individual septic tanks less than central wastewater collection and treatment systems.
  • Low technology: Septic tanks are not difficult to operate
  • Low energy requirements

Disadvantages of Using Septic Systems

  • Potential for groundwater pollution: This potential is related to incorrect siting based on density, soil characteristics, or both. EPA recommends a density less than or equal to 40 per square mile.
  • Require proper maintenance: Although the maintenance requirements are not much, the maintenance schedule has to be strictly adhered to.
  • Careful cleaning required: Very often, the cleaning process may result in groundwater contamination.
  • Requires large land areas.

Principal Pollutants

  • Nitrates and Phosphates
  • Heavy Metals
  • Inorganic Ions
  • Fecal and Coliform Bacteria
  • Possible Synthetic Organic Chemicals

Suitable Sites for Septic Systems

Site not prone to flooding: Septic systemss should not be located in gullies, flood plains or hollows.

Slope less than 10 - 15 %

Limiting layer more than 4 - 6 ft below drain field: The separation is required to provide adequate distance for aerobic treatment for occur.

High water table more than 4 ft below drain field

No trees

Sufficient area for absorption

Down-gradient of wells, particularly drinking water wells.

Percolation within suitable range:

Acceptable : 3 - 60 min/in

Marginal (too fast) : 1 - 3 min/in

Marginal (too slow) : 60 - 120 min/in

Unacceptable : < 1 or > 120 min/in

Percolation Test for Septic Tanks

  1. Dig a relatively small hole between 4 and 6 inches in diameter. The hole should be as deep as the required depth of drain field
  2. If necessary, scarify the sides of the hole to remove smearing.
  3. Put 2 inches of gravel in bottom.
  4. Fill up to about 12 inches and all the level to fall 6 inches.
  5. Measure the rate at which the water level drops.
  6. Proceed until three consecutive measurements give the same rate. It may be necessary to refill the hole during the test.

Sizing Drain Fields

The sizing of drain field in Illinois is governed by the Private Sewage Disposal Code. The required absorption area is dependent on the size of the house being treated and the percolation rate.

Gravel System

Time (minutes) required for last 6 inches of water to fall / FOR RESIDENTIAL USE Required Absorption Area (sq ft)/bedroom) / FOR INSTITUTIONAL OR COMMERCIAL USE Allowable application rate (GPD/sq ft) (5) / Recommended depth from bottom of the trench to the limiting layer
18 - 60 / 200 / 1.0 / 3 feet
90 / 210 / .95
120 / 235 / .85
150 / 265 / .75
180 / 290 / .69 / 2 feet
240 / 320 / .62
300 / 350 / .57
360 / 385 / .52
NOTE:
1. / Absorption area is figured as trench bottom area in absorption trenches and bottom area in seepage beds.
2. / Seepage beds require 1½ times the seepage field absorption area specified.
3. / Over 360 is unsuitable for subsurface seepage systems.
4. / Under 18 is unsuitable for subsurface seepage systems.
5. / Divide the required total gallons per day by this number to get the number of square feet required

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

Gravelless System

Time (minutes) required for last 6 inches of water to fall / FOR RESIDENTIAL USE Required Absorption Area (sq ft)/bedroom) / FOR INSTITUTIONAL OR COMMERCIAL USE Allowable application rate (GPD/sq ft) (5) / Recommended depth from bottom of the trench to the limiting layer
8 inch / 10 inch / 8 inch / 10 inch
18 – 60 / 100 / 70 / 2.00 / 3.00 / 3 feet
90 / 105 / 70 / 1.90 / 2.86
120 / 120 / 80 / 1.66 / 2.50
150 / 135 / 90 / 1.48 / 2.22
180 / 145 / 100 / 1.38 / 2.00 / 2 feet
240 / 160 / 110 / 1.25 / 1.82
300 / 175 / 120 / 1.14 / 1.66
360 / 195 / 130 / 1.0 / 1.54
NOTE:
1. / Over 360 is unsuitable for subsurface seepage systems.
2. / Under 18 is unsuitable for subsurface seepage systems.
3. / Divide the required total gallons per day by this number to get the number of lineal feet required.

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

Laboratory Exercise

Percolation test

  1. Use the auger supplied to make a hole in the middle of the bin. The hole should be at least 12 inches deep.
  1. Use the bottle and the rule to make a measuring stick. When in use, the measuring stick should be vertical.
  1. Fill the hole with water and allow the water level to fall 3 to 6 inches.
  1. Depending on the rate of fall, determine the time it takes for the water level to fall 0.5 or 1 inch intervals.
  1. Determine the percolation rate at steady state or after 50 minutes, whichever comes first.

Depth (in)

/

Time

/

Depth (in)

/

Time

Excel Template (Individual Activity)

Develop a template for sizing drain fields for residential locations.

Inputs

  1. Distance the water table falls (e.g. 0.5 inches)
  2. Time over which the level fell (e.g. 17 minutes)
  3. Number of bedrooms (e.g. 3 bedrooms)
  4. Type of system (e.g. Gravelless 8-inch )
  5. Width of trench (e.g. 8 inches)

Outputs

  1. Percolation rate (e.g. 34 minutes/ inch)
  2. Suitability for septic systems (e.g. Suitable)
  3. Required absorption area per bedroom (e.g. 280 sq. ft.)
  4. Total absorption area required (e.g. 840 sq. ft. )
  5. Trench length required ( e.g. 1260 ft)

Turn in the template, alongwith the lab report for your lab grade