HomeMy WebLinkAbout20240815 6584 Staging Yards Drainage Memo
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Memo
Date: Wednesday, August 14, 2024
Project: 6584 TLine: Mitchell (MITC) - Rifle (UTER) Electric Transmission Line Rebuild - McLin and Murray
Staging Areas.
To: Garfield County
From: Brian Brown – HDR Engineering
Subject: Drainage Memo for Staging Yards – Murray and McLin
Public Service Company of Colorado (PSCo), a Colorado corporation conducting business as Xcel Energy
(Xcel), is proposing to rebuild a 25-mile segment of a 69-kilovolt (kV) overhead transmission line from
the Mitchell Creek Substation within the City of Glenwood Springs and unincorporated Garfield County,
Colorado to the Rifle Ute Substation in unincorporated Ga rfield County.
In support of this line rebuild, Xcel has secured two staging/material yards to store equipment, perform
limited equipment assembly, and provide a meeting place for construction crews .
The impact to surface drainage at the Murray Yard and the McLin Yard is the focus of this memo. See
Site plans submitted in support of this project for a figure that includes location of the line and the
Murray and McLin s taging yards.
Existing Conditions:
The Murray Yard (36 acres) and McLin Yard (15 acres) are both in Garfield County and are undeveloped
parcels with varying slopes from gentle to nearly level and vegetation density from sparse (majority of
the Murray Yard) to moderately dense (McLin Yard). While both yards have had utility improvements,
buried gas and overhead power for Murray and buried irrigation for McLin, neither yard has existing
improvements that substantively impact surface stormwater flow or change the surface flow type or
direction.
Proposed Temporary Conditions:
The proposed improvements for both the Murray and McLin Yards will be temporary with the
installation of a 2-acre aggregate surfaced Stabilized Staging Area (SSA) at each yard that will be
constructed to generally match the existing grades of the site. The SSA is to minimize impacts to water
quality by minimizing rutting and uncontrolled surface disturbance that can lead to sediment transport
off-site and track out onto adjoining roads. The SSA is temporary and will be removed once construction
is complete and the site topsoil will be restored to generally match pre -construction grades. After the
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seeding and mulch and with adequate moisture and time for germination and vegetation growth, the
slopes, soil types, and vegetation cover will generally match the pre -construction conditions.
The portion of the Yard outside of the SSA will remain in the pre -construction condition and will be
accessed without grading modification. Access will be overland in a manner described as ‘drive and
crush’. This limited drive and crush access will temporarily impact surface foliage but generally keeps the
plant ’s root structure in place which maintains current soil loss rates (erosion rates) and allows for a
rapid rebound of the plant community. This drive and crush approach typically maintains the current
surface runoff rates and flow types.
Outcome:
At the closure of the County Grading Permit and the State Stormwater Management Plan (SWMP)
Permit, the site grades and vegetation density will generally match the pre -construction conditions.
Therefore, there will be no permanent change to surface drainage within either the Murray Yard nor the
McLin Yard compared to pre-construction surface drainage. This project will not permanently change
the existing surface water flow paths, overall slopes, impervious surface area, nor time of concentration
and therefore will not change the runoff volume, runoff peak, nor conveyance path for either Yard.
HDR Engineering
Brian Brown, PE
CO PE 41644
08/15/2024
41644