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TECHNICAL MEMORANDUM CH2MHILL <br />Appendix B - Demand Forecasting Procedure <br />PREPARED FOR: City of Longmont Water Conservation Master Plan <br />PREPARED BY: <br />COPIES: <br />DATE: April 23, 2008 <br />The following technical memorandum (TM) describes the methodology for forecasting <br />treated water demand for the separate water use segments for the City of Longmont's Water <br />Conservation Master Plan Update. Forecasting water demand is important for a variety of <br />reasons including estimating future treated and raw water demands. The City has regularly <br />updated the Treated Water Master Plan (TWMP), last updated in 1990, and the Raw Water <br />Master Plan (RWMP), last updated in 2004. The RWMP used population growth rates from <br />the 1990 TWMP, but adjusted the population projections based on more recent census data <br />and estimated buildout populations. Water demands in the 2004 RWMP were based on the <br />1990 TWMP with modifications to account for the adjusted population and input from large <br />industrial customers. Since the RWMP update in 2004, trends in water use and development <br />continue to change. Treated water demand forecasts, for the purposes of this Water <br />Conservation Plan, were revised based on metered water usage through 2006. <br />Future treated water use forecasts were developed to estimate total annual water use and <br />peak daily and monthly treated water demands for the City and all its customers. Annual <br />water demand is used to evaluate the availability of water within the City's water rights <br />portfolio, whereas peak daily and monthly water demand is used to evaluate current and <br />future water treatment and delivery capacity. <br />The following TM provides a more detailed description of the forecasting methodology and <br />is a supporting document to the Water Conservation Plan. Forecasting methodology is <br />described for each metered water use segment: residential, multifamily, small commercial, <br />industrial, irrigation, and City. <br />Raw water irrigation, which is currently used by the City to maintain various parks, school <br />grounds, arterials, golf courses and other City facilities, is not consistently metered. <br />Therefore, there is not an estimate of current raw water use, let alone future raw water use. <br />The best current estimate of raw water use on the 27 parks, two golf courses, 13 schools, and <br />other City facilities, which cover about 580 irrigated acres is about 1,450 acre -feet per year, <br />assuming about 30 inches of water is applied each year. Since an increase in raw water use <br />would be offset by a reduction of treated water use, future forecasts do not included <br />increases in future raw water irrigation, per se. Additional raw water irrigation that will be <br />implemented by the City in the future will be offset by a reduction in treated water demand <br />with a net effect of reducing unaccounted for water and water use at the treatment plant <br />(totaling about 13.7% of total treated water demand). As previously indicated, forecasting <br />B -1 <br />