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To: Sandra Pinel Anoka County Sector Representative Date: May 8, 2000 From: Kyle L. Colvin, PE Municipal Services Section RE: Second Response to Ramsey Councilmember Hendriksen question City of Ramsey CP sanitary sewer projections The following is a brief response to the follow-up question posed by Terry Hendriksen via email dated April 26,2001. It is a follow-up to questions asked by Terry in an email dated April 10. Ql: "Explain the process used to project the sewer volume generated from an acre of the following land uses. Residential, commercial, industrial, and mixed use. " Rl: Residential: In projecting sewer volume for residential developments it is first important to determine or establish the type of residential development we're dealing with and the density ofthe dwelling units within the development. The unit flow per residential dwelling unit varies across the Twin City metropolitan area. However, the standard that most communities/developers/ engineers/planners will use is between 250 and 300 gallons per dwelling unit per day. Ramsey's comprehensive plan uses 270 gallons per residential dwelling unit per day, which is within this standard range and is appropriate for this area ofthe metropolitan area. Typically the unit flow is the same regardless if the dwelling unit is a single family home, townhouse, condominium, or high-end apartment. We do see some reduction in the unit flow for those apartment units that lack individual amenities such as dishwashers, clothes washer and dryer, and garbage disposals. In these types of units, the unit flow can be up to 80% of a single family discharge rate. There are also some variations of discharge rate due to the demographics of the occupants in the development. Typically single family housing that attracts established families would generate more sewer per day than housing that attracts seniors, or single occupants. Therefore, in order to "project" the total sewer volume generated from a residential development, one needs to review the local zoning/land use regulations and determine the allowable density for the area and consider typical demographic conditions within the City. These factors should enable someone to estimate the number of potential dwelling units of each type of housing unit, then using the unit flow rate for each housing unit type, calculate the average daily flow from the development. CommerciallIndustrial: The method used to calculate sewer discharge for commercial/Industrial uses is basically the same as the method used for projecting residential flow. Typically, density assumptions for commercial and industrial uses are fairly consistent across the metro area and most communities use a flat rate of discharge for each type of development. The City's comprehensive plan uses a discharge rate of 1,300 gallons per acre for both commercial and industrial uses. This rate is also consistent with those rates used by other communities in the metro area. Therefore, in order to project the total sewer discharge from a commercial or industrial or a commerciaVindustrial zoned area, one would simply multiply the number of acres under that land use by the City's figure of 1,300 gallons per day per acre.