When analyzing the percolation times from tests, you take

• A. The Fastest Percolation Time
• B. The Slowest Percolation Time
• C. The Average Percolation Time
• D. The Median Percolation Time

Answer: (B)

In percolation testing, you design for the least favorable infiltration rate by using the slowest percolation time from the tests. A longer percolation time means the soil absorbs water more slowly, so the drainage field needs more area to handle the effluent safely. By basing the design on the slowest time, you account for the worst-performing portion of the soil and prevent issues like ponding or inadequate treatment under real conditions. Using a faster time would assume quicker drainage and could lead to underdesign, while the average or median might still miss the slowest spot. So, the slowest percolation time provides a conservative, protective basis for sizing the system.