What is the formula for calculating the perc rate?

The correct answer involves using the amount of time it takes for a certain volume of water to be absorbed into the soil, which is measured in inches. The perc rate, or percolation rate, is determined by observing how many inches of water percolate into the soil over a specific period of time.

In practice, the formula takes the total amount of water that has been absorbed in inches and divides it by the time it took for that absorption to occur. This helps in assessing the soil's absorption capacity, which is crucial when designing a septic system. The perc rate is typically expressed in terms of minutes per inch, indicating how quickly or slowly the soil allows water to move through it.

The other options misrepresent the relationship needed to calculate perc rate either by using feet or time units that do not align with the standard practice in septic system evaluations. Therefore, focusing on the measurement of inches over time is essential for an accurate understanding of soil drainage characteristics.