In lieu of calculating the wastewater flow capacity required pursuant to ARSD § 74:53:01:20, Table 3 may be used to determine wastewater flow capacity for specific commercial or public service establishments when the amount of usage cannot be accurately determined. Flow projections, expressed as gallons per day (gpd), shall be calculated by multiplying total floor area in square feet of the commercial or public service establishment by the statistical factor given in Table 3.