One of the critical factors in mound design is the sand specification for the clean sand layer. This will determine the dimensions of the infiltration bed.In Minnesota, most of our mounds are designed assuming a soil-sizing factor of 0.83 square feet per gallon per day, which is equivalent to a loading rate of 1.2 gallons per square foot per day. This number is based on early mound research conducted in Wisconsin where they determined that if a clean sand was loaded no more than 1.2 gallons per day per square foot, pathogens would be removed in less than 2 feet
