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Effective April 28, 2015 Chapter Four Subsurface Sewage Treatment System Regulations <br />SECTION 12 SEWAGE FLOW DETERMINATION <br />12.1 Design Phase II: System Design. <br />Completion of tasks outlined in Section 12 to Section 21 is considered the second phase of SSTS design. <br />12.2 Design Flow. <br />The estimated design flow for any dwelling must provide for at least two (2) bedrooms. For multiple or multifamily <br />dwellings, the design flow must be calculated according to Section 12.4 to 12.6. <br />12.3 Design Flow by Bedrooms. <br />The estimated design flow for dwellings is determined by Table I. For more than six bedrooms, the design flow is <br />determined by multiplying the number of bedrooms by 150 gallons per day. <br />Table I <br />Number of <br />Bedrooms <br />Gallons Per <br />Da <br />2 <br />300 <br />3 <br />450 <br />4 <br />600 <br />5 <br />750 <br />6 <br />900 <br />12.4 Sum of design flow for existing dwellings. <br />The design flow for MSTS serving existing dwellings is determined by the following calculation in conjunction <br />with Section 12.3: <br />Total flow from the ten highest flow dwellings + (total flow from the remaining dwellings X 0.45) <br />12.5 New housing developments. <br />For new housing developments to be served by a common SSTS, the developer shall determine and restrict the total <br />number of bedrooms for the development and determine the design flow by multiplying the total number of <br />bedrooms by 150 gallons per day. If the ultimate development of phased or segmented growth meets or exceeds <br />10,000 gallons per day, the initial system or systems and all subsequent systems require a state disposal system <br />permit. <br />12.6 Additional Capacity. <br />If construction of additional dwellings or bedrooms, installation of water -using devices, or other factors likely to <br />increase the flow volumes can be reasonably anticipated, the MSTS must be designed to accommodate the <br />additional capacity as determined by the Department. <br />12.7 Design Flow Determination for Other Establishments <br />Design sewage flow and waste concentration levels for other establishments with a flow of 5,000 gallons per day or <br />less are determined by methods in item (1) or (2): <br />(1) The design flow of sewage for other establishments is estimated using Table II. <br />(2) The measured design flow of sewage for other establishments is determined by averaging the <br />measured daily flows for a consecutive seven-day period in which the establishment is at maximum <br />capacity or use. <br />Table II — Estimated Design Sewage Flow from Other Establishments <br />43 Washington County Development Code <br />