Where the underlying soil has a percolation time of 20 minutes, what is the minimum area of a Type B dispersal bed if the total daily design flow is 1 600 L?

Where the underlying soil has a percolation time of 20 minutes, what is the minimum area of a Type B dispersal bed if the total daily design flow is 1 600 L?

• A. 40
• B. 60
• C. 80
• D. 100

Answer: (C)

Sizing a Type B dispersal bed hinges on matching the daily design flow to how much soil area can absorb it, using the percolation test result as the guide for how much water can pass through per unit area. With a percolation time of 20 minutes, the Type B table gives a loading rate of 20 L per day per square meter. To get the required area, divide the total daily flow by this rate: 1600 L/day ÷ 20 L/day/m^2 = 80 m^2. So the minimum area is 80 square meters. Faster infiltration (shorter percolation time) would allow a higher loading rate and a smaller area, while slower infiltration would require more area. The other numbers don’t fit the calculation for this loading rate.

Sizing a Type B dispersal bed hinges on matching the daily design flow to how much soil area can absorb it, using the percolation test result as the guide for how much water can pass through per unit area. With a percolation time of 20 minutes, the Type B table gives a loading rate of 20 L per day per square meter. To get the required area, divide the total daily flow by this rate: 1600 L/day ÷ 20 L/day/m^2 = 80 m^2. So the minimum area is 80 square meters. Faster infiltration (shorter percolation time) would allow a higher loading rate and a smaller area, while slower infiltration would require more area. The other numbers don’t fit the calculation for this loading rate.