What two factors determine the size of a drainfield?

The size of a drainfield is primarily influenced by the sewage loading and the long-term soil acceptance rate. Sewage loading refers to the expected volume of wastewater that will be processed by the drainfield, which is critical in determining the required area to effectively treat the sewage without overwhelming the soil's absorption capacity. The long-term soil acceptance rate is a measure of how well the soil can absorb and treat the effluent over time. It takes into account the soil characteristics, which can affect the infiltration and percolation of the effluent into the surrounding environment.

When the sewage loading is too high for the soil's acceptance capacity, it can lead to system failure or environmental contamination. Therefore, understanding these two factors is essential for the proper sizing of a drainfield to ensure sustained operation and compliance with health and environmental standards.

The other options, while they mention important aspects related to drainage and sewage treatment, do not directly address the fundamental criteria necessary for accurately determining drainfield size.