9344

• UCREFRP Catalog Number: 9344
• Author: Camp Dresser & McKee Inc.
• Title: Replacement of the Plateau Creek Pipeline.
• USFW Year: 1996.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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to return flows from both indoor and outdoor uses of water. This has not et become a significant
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issue in Water Division 5 (Colorado River), but will likely be similar to precedents set in Water
Divisions 1 and 2. In-house consumptive use has typically been accepted to be at a rate of 5 percent
of in-house total use, with the remainder returning to the system via the wastewater collection and
treatment system. Returns from outdoor use, primarily lawn irrigation, have been recognized at rates
ranging from 10 percent to 38 percent. For this analysis, a reasonably conservative value of
15 percent has been selected, which includes 2 percent as immediate surface runoff and 13 percent
as deep percolation.
Using these return flow factors, surface and groundwater returns for indoor and outdoor use were
calculated. Wastewater from indoor water use associated with septic systems will also eventually
return to the streams, but both the volume and timing of such returns is dependent on the location,
type and configuration of the septic systems, characteristics of the intervening alluvium between the
septic systems and the receiving stream, and consumption via evapotranspiration from area
vegetation. For this analysis, it was assumed that the lagged return flows of total indoor use
associated with septic systems and returned to area streams is 13 percent. .
Under the baseline ear demand return flows are ex ected to avera e a relative) low 46.6 ercent
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of total usage (see Table 3.5), because 50 percent of the users are estimated to be on septic systems
where return flows do not accrue at the same level as from wastewater system users. Depletions to
the river basin are therefore reduced by 3,236 ac-ft/yr in return flows under baseline conditions.
Future.return flows would be expected to increase to 71.8 percent of demand (see Table 3.6), due
to the increased returns from additional users incorporated into the wastewater collection system.
Depletions under future conditions are therefore offset by the 20,527 ac-ft/yr in municipal returns
under future conditions.
Another factor that affects the municipal return flow calculation is the issue of replacement reservoir
return flow credits. It is the position of the USFWS that return flows from within Ute Water's
system associated with replacement reservoir releases must be credited to the replacement reservoir
rather than the project proponent under Section 7 consultation. As a result, the replacement reservoir
releases must be subtracted from Ute Water's use prior to calculation of return flows for both
baseline and future conditions. Therefore, return flow volumes are reduced to 2,910 ac-ft/yr and
18,236 ac-ft/yr of municipal returns for the baseline and future condition, respectively (see Tables
r 3.1 and 3.2).
Ute Water does not agree with the USFWS position on return flow credits from replacement
reservoirs and believes that this position is contrary to Colorado water law. However, Ute Water
accepts the USFWS position in this case because it affects only the project depletion for calculation.
3.2.8 Depletion Summary
Each of the above factors was evaluated and incorporated into the depletions analysis for the District,
as summarized in Tables 3.1 and 3.2. Total Colorado River Basin depletions under baseline
conditions average 4,628 ac-ftlyr. This number is expected to increase to 7,823 ac-ft/yr. Though
demand will increase significantly, this increase will be offset to a large degree by future municipal
CDM Camp Dresser & McKee B-8
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