WSP09394

• File Number: 8220.106
• Description: Animas-La Plata
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 9/1/1997
• Title: Animas-La Plata Project Summary Information
• Water Supply Pro - Doc Type: Project Overview

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Ridges Basin Dam would be constructed in two stages: (I) foundation preparation and
(2) embankment placement. During the first phase, the footprint of the dam would be
excavated, and the necessary grouting of the abutments and foundation would occur.

Based on the Service's post research study Biological Opinion, the size of the dam and
reservoir would be determined, and the dam and pumping plants could be sized
accordingly. 11

In lieu of Long Hollow Tunnel and Dry Side Canal, which would not be constructed if
future ESA consultations do not allow additional depletions, the La Plata Rural M&I
Pipeline would be constructed to deliver municipal water from Ridges Basin Reservoir to
the La Plata rural area.

The pipeline would have a capacity of 4 cfs and would extend approximately 15,000 feet
from Ridges Basin Pumping Plant to a high point in the La Plata rural area. Future
treatment, storage, and distribution systems for the water would be the responsibility of
the water users.

Ridges Basin Pumping Plant would also deliver water to supply rural subdivisions west
of Durango. Raw Project water would most likely be delivered to a central water
treatment plant and then pumped to high points northwest of Ridges Basin Reservoir via
Shenandoah M&I Pipeline. Future treatment, storage, and distribution systems for the
water would be the responsibility of the water users, and the system may require
additional NEP A compliance prior to construction.

Phase I, Stage A - Operation

Operation of Phase I, Stage A as an independent facility assumes:

· An annual average depletion of57,100 acre-feet per year of water from the
San Juan River system is the maximum allowable under the 1991 and 1996
RP As for the Project.

· A total average annual diversion of 80, 100 acre-feet would be required to
fully satisfY the M&I demand. The Project proponents have agreed that the
supply would be used for M&I, although Phase I, Stage A would not fully
satisfY the requirements of the Settlement Act.

· A full average annual diversion of 80, 100 acre-feet with the associated
return flows of26,300 acre-feet equates to an annual 53,800-acre-feet
depletion. In addition, a depletion of3,300 acre-feet would occur as a
result of evaporation from Ridges Basin Reservoir, resulting in an average
annual 57,100 acre-feet allowable depletion to the San Juan River.

2 Final sizing of the features would be determined following consideration of the post research study Biological Opinion.

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