Illinois Administrative Code
Title 77 - PUBLIC HEALTH
Part 905 - PRIVATE SEWAGE DISPOSAL CODE
Appendix A - Illustrations and Exhibits
ILLUSTRATION G - Instructions for Conducting Percolation Tests
Current through Register Vol. 48, No. 12, March 22, 2024
Percolation tests shall not be made in frozen ground or ground that has been filled in the preceding 12 months. Percolation tests shall be performed in accordance with the following procedures:
1. Number and Location of Percolation Tests. Select an area where the seepage field will be located. When digging the holes, avoid animal burrows, large root channels, etc. At least 3 separate percolation tests shall be performed at the site of each proposed disposal area. The percolation test holes shall be at least 50 feet apart. At least one hole shall be located at the lowest elevation of the proposed absorption field area. The 2 holes with the highest results shall be used to determine percolation rate.
2. Depth of Percolation Test Hole. Dig or bore the holes with horizontal dimensions approximately 4 to 6 inches in diameter to the depth of the proposed seepage field or seepage bed.
3. Preparation of Test Hole.
4. Saturation and Swelling of Soil: It is important to distinguish between saturation and swelling. Saturation means the void spaces between soil particles are full of water. This can be accomplished in a very short period of time. Swelling is caused by the intrusion of water into the individual soil particle. This is a slow process, especially in a clay type soil and is the reason for requiring a prolonged soaking period.
5. Recording of Results. Record results of all tests as the total minutes required for the last 6 inches of seepage. If the last 6 inches of water has not seeped away at the end of 6 hours, the soil must be considered unsuitable for seepage field disposal and the appropriate statement marked on the results form. If there is more than a 30 minute difference between the highest 2 percolation tests, use the larger result or perform additional percolation tests.
6. Calculating the Percolation Rate. Add the total minutes required for the last 6 inches of water to fall from the 2 holes with the highest result and divide by 2. If the average is less than 60 minutes, use the percolation rate of 60 minutes. If the average is greater than 60 minutes, refer to Section 905.Appendix A: Illustration H of this Part. Locate in the first column (Time (minutes) required for last 6 inches of water to fall) where the highest 2 hole average fits and use the next highest result as the percolation rate for sizing and design. An example of this procedure is as follows: If 3 percolation tests are conducted with results of 120 minutes, 140 minutes, and 155 minutes, the highest 2 hole average would be (140 + 155)/2 or 147.5 minutes. Looking at Section 905.Appendix A: Illustration H of this Part, the next highest result would be 150 minutes. The 150 minute rate would be used to size and design the subsurface seepage system.
7. Distribution of Results. The results of the percolation tests shall be given to the homeowner and shall be retained by the contractor for at least 5 years. The percolation test data report shall be returned to the appropriate regional office or local authority.
TEST HOLE:
TEST HOLE #1 |
TEST HOLE #2 |
TEST HOLE #3 |
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READING # |
TIME (in min.) |
WATER LEVEL (in inches) |
TIME (in min.) |
WATER LEVEL (in inches) |
TIME (in min.) |
WATER LEVEL (in inches) |
1 |
0 |
0 |
0 |
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2 |
30 |
30 |
30 |
|||
3 |
60 |
60 |
60 |
|||
4 |
90 |
90 |
90 |
|||
5 |
120 |
120 |
120 |
|||
6 |
150 |
150 |
150 |
|||
7 |
180 |
180 |
180 |
|||
8 |
210 |
210 |
210 |
|||
9 |
240 |
240 |
240 |
|||
10 |
270 |
270 |
270 |
|||
11 |
300 |
300 |
300 |
|||
12 |
330 |
330 |
330 |
|||
13 |
360 |
360 |
360 |