For a perc test, after the presoak, how long should the water be left before taking readings?

The correct duration for leaving the water in a perc test after the presoak is three minutes. This timeframe allows the water to sufficiently infiltrate the soil and lets you obtain a more accurate reading of the soil's absorption rate.

During a perc test, the presoak phase is important because it helps to saturate the soil, creating conditions that reflect the actual absorption capabilities of the soil rather than its immediate reaction to water. Once the presoak has occurred, waiting for three minutes ensures that any rapid absorption has taken place, allowing for a more stable and reliable measurement of how quickly the water level drops. This is crucial for determining the soil's percolation rate, which directly affects the design and implementation of septic systems. Measurements taken too soon might not accurately represent the soil's characteristics, potentially leading to improper system sizing or placement.

Other durations, like one, two, or four minutes, do not provide the appropriate balance between allowing for sufficient infiltration and accuracy in measurement. Each of these timeframes either rushes the readings or does not align with standard procedures established for conductively testing soil percolation rates effectively.