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In order to calculate munici al return flows, it is necess to se a ate water use into its indoor and p azY t~ g outdoor components. Table 3.3 and Figure 3.1 show the distribution of monthly usage under both the baseline and future demand scenarios. Using the monthly distribution of annual use over the last 10 years as provided in the Pearse & Associates (1995) report, a uniform indoor use was calculated for baseline conditions as the average usage over the winter months of November through March when little or no outdoor usage would be expected. Similarly, indoor use was calculated for future conditions using the demand projections discussed in Section 2 of this Appendix. The horizontal lines on Figure 3.1 represent the calculated indoor use components. For the months of November through March, it is assumed that no outdoor use occurs. For April through October, outdoor use was calculated as the portion of total use greater than indoor use (i.e., the portion of use above the lines on Figure 3.1). The District's water use pattern is unusual in that usage does not fluctuate as greatly, nor is outdoor .use as great, as that typically found in other municipal water systems. Table 3.4 and Figure 3.2 provide a comparison of the District's water use pattern to the patterns for the cities of Denver and Louisville, Colorado. The percentages in the table and figure are expressed as percent of annual demands in order to easily compare the values. Overall demands for these communities are significantly different than those for the District, with Denver's being much greater and Louisville's much less than the District's. The usage patterns for both Denver and Louisville are nearly identical and typical of a municipal system, with outdoor use increasing significantly during the summer months and representing approximately 40 percent of the total annual demand. However, outdoor use does not increase nearly as much during the summer in the District's system, and outdoor use represents less than 20 percent of the annual demand. The primary reason for this is that significant irrigation water other than that supplied by the District is available and utilized within the District's service area and the District's rate structure discourages use of potable water for irrigation purposes. Annual return flows for Denver and Louisville are generally in the range of 60 to 70 percent of total annual use. With indoor use proportionately greater in the District's system, larger return flow percentages would be expected. Offsetting the effect of the indoor use, however, is the effect of a proportionately larger number of septic systems in the Ute Water District. The exact percentage of the District's users which utilize septic systems is not known; however, the District has indicated that a reasonable estimate is that 50 percent of the users under the baseline year demand levels were on septic systems. It is also a reasonable assumption that most future users will be incorporated into the wastewater systems rather than septic, and that any new septic system installations would be offset by the conversion of existing septic systems to the wastewater system; so the total water use associated with septic systems should remain fairly constant at the baseline level. With the assumption of no future net increase or decrease in septic system usage, the actual percentage chosen for the baseline scenario is inconsequential to the future net depletion calculation and return flows from septic systems will be identical in both the baseline and future scenarios. Tables 3.5 and 3.6 present an evaluation of the District's municipal return flows under both the baseline and future demand conditions. The return of water used in municipal water supply systems to river systems has been a component of water rights transfers in Colorado for some time, particularly in Water Divisions 1 (South Platte River) and 2 (Arkansas R.iver). Numerous transfer ,; decrees in these divisions have included provisions for recognizing credits to the stream system due CDM Camp Dresser & McKee 0:8047-IIO~DOCIAPPEND-B.DOC B-7