Wisconsin Mound Soil Absorption System and Area FillPractice Exam

For an area fill mound system, the coarse sand should not have more than what percentage of fines?

1. 2%

2. 5%

3. 8%

4. 10%

The correct answer is: 5%

In the context of an area fill mound system, maintaining a low percentage of fines in the coarse sand is crucial for ensuring proper drainage and function of the system. Fines are small particles that can impede water flow and lead to premature saturation of the system. A concentration of more than 5% fines can promote clumping and reduced permeability, making it difficult for wastewater to be effectively treated as it passes through the sand layer. Choosing 5% as the maximum acceptable percentage of fines ensures that the coarse sand retains enough porosity to facilitate adequate effluent movement and oxygen exchange, both of which are necessary for optimal biological treatment processes. Therefore, keeping fines to this level is considered best practice in the design and function of mound systems in Wisconsin, where soil absorption systems must meet specific criteria for effective wastewater treatment.