Section 3129B Rapid Sand Pressure Filters
In addition to the requirements for all filters as indicated in Section 3128B, the following apply to rapid sand pressure filters.
The filtration rate shall not exceed 3 gallons per minute per square foot (122.24 L/m per m2) of filter area. The backwash rate shall not be less than 15 gallons per minute per square foot (611.2 L/m per m2) of filter area.
The filter shall contain not less than a 20-inch (508 mm) depth of media and not less than a 10-inch (254 mm) depth of filter gravel above the underdrain system.