August 5, 2009 Ptarmigan Substation Public Open House

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WELCOME

Public Open House

Public Service Company of ColoradoProposed Ptarmigan Electrical SubstationSilverthorne, COAugust 5, 2009

Welcome to the August 5, 2009 Ptarmigan Substation Public Open House. This OpenHouse will provide the public with an update of our siting process for this project. TheOpen House meeting format will be comprised of four informational stations staffed by

company representatives to provide information regarding important aspects of theproposed Ptarmigan Substation Project. The subject matter areas to be discussed atthese stations are as follows:

Purpose and NeedTransmission EngineeringSubstation EngineeringSiting and Permitting

PSCo has also assembled several questions and answers below to help provide youwith a greater understanding of some of the more significant issues that have been

identified by the public. Please take some time to read this information. We alsoencourage you to visit the various stations, ask additional questions and gather moreinformation concerning this important project.

Q. What has PSCo done since the February Open House?

A. Following last February’s Open House, PSCo compiled written public commentsprovided at that meeting and also those submitted to the company by mail and e-mail. After reviewing those comments and performing additional design analysis,PSCo elected to introduce “gas insulated switchgear” (GIS) technology into thesubstation design, thus substantially reducing the overall footprint of the facility. ThisGIS design is non-traditional and very costly, but is being proposed to help addresscertain potential impacts of the Project. With this fundamental change, the sitingstudy data was revisited for the possible availability of additional sites that might nowbe suitable due to the smaller GIS substation footprint. Two potential sites wereidentified and preliminary site plans and photosimulations developed for this PublicOpen House.



Q. Why can’t the Dillon and Summit Substations be expanded and additional feedersconstructed to the Silverthorne area?

A. The existing Summit Substation site is too small to be expanded. To add another

transformer, the entire substation would need to be rebuilt and adjoining land usesmake expansion problematic. There are also complications with supporting theelectric load to the Frisco area during a rebuild. Furthermore, the 115kV line thatsupplies the substation is near capacity.

The Dillon Substation has already been expanded to its existing physical limits.Expanding it even further would require new Summit County and US Forest Servicepermits and the expansion would extend onto an old land fill, which makesexpansion even more problematic.

The idea behind the proposed project is to shorten the feeder distance to the

Silverthorne area to improve the electric system integrity while also providingoperational flexibility. Installing additional feeders from the Summit or DillonSubstations does not aid with either of these important issues. In addition, the loadgrowth has been growing northerly in the Silverthorne area, thus requiring the newsubstation being placed in a location to best serve this trend.

Q. Can the substation be located near the dam or the Dillon water tank?

A. PSCo is proposing a facility to best address the present and future needs of theSilverthorne area and also areas growing to the north. Ideally, the feeder linesemanating from the substation need to be less than four miles long. Sites south of

the siting study area may be under four miles to the load center, generally identifiedas the intersection of HWY 9 and I-70, but feeders will exceed four miles in length toserve areas in the north part of the Silverthorne community and beyond, wheregrowth patterns are extending.

Q. Why can’t the substation be located north of the town limits?

A. PSCo’s study area for the substation best addresses the present and future electricneeds of the Silverthorne area and areas north. As described, it is ideal that feeder lines be four miles long or less. Sites north of the siting study area may be under four miles long to the north part of Town, but exceeds the four mile threshold to theload center.

Q. Why can’t the site be located on federal lands?

A. Approval of a substation on federal lands requires certain permitting requirementsincluding compliance with the National Environmental Policy Act. Following



communications about land use policy with the US Forest Service, PSCo elected toconsider federal lands as less suitable due to the presence of suitable alternativesites located on private lands.

Q. Why isn’t the PSCo owned parcel of land located in the Town of Silverthorneconsidered a more suitable site?

A. The placement of a substation on the vacant PSCo property located in the Townwould require the construction of an overhead transmission line that would have tocross the Blue River Valley, Highway 9, and parts of the Town. PSCo feels that thevisual impacts associated with this transmission line make the site less suitablecompared to alternative sites on the east side of the valley.

Q. Why can’t the transmission line be buried?

A. An underground transmission line would need to be constructed in a buried ductbank along a gently sloped route comparable to a major county road. The duct bankwould likely consist of 6-inch diameter conduit laid within in a 3’x3’ duct bankconfiguration. Large vaults would be required every ½ mile to pull cable sectionsand splice them together. Additionally, at each vault an approximately 12,000square foot leveled surface is required for the pulling and splicing equipment. Theoverall cost of burying an electric transmission line can be up to 10 times more thanoverhead construction costs and this area’s mountainous terrain can be prohibitiveto constructing transmission lines underground. In addition, a 10,000 square footswitching station facility would be required at the tap point of the existing overhead

transmission line.

Reliability challenges associated with underground lines include therepair/replacement time needed in the event of a transmission line cable fault. If oneof the cables requires repair/replacement, the substation would potentially need tobe on a radial feed for months during work activities, increasing the risks of extendedoutages.

Q. How has the Lower Blue Master Plan been considered?

A. The siting study takes into consideration applicable local and regional plans,depending on the jurisdiction at each site. PSCo recognizes that protection of theLower Blue River Basin’s rural character is a theme of the Lower Blue Master Planand each candidate site under the county jurisdiction is being evaluated for itspotential impacts to this theme. Important aspects of the plans that were analyzedinclude, among others, land use designations, open meadows, irrigated haypastures, prominent hillsides and ridgelines, ranch lands and environmentallysensitive areas.



Documents

August 5, 2009 Ptarmigan Substation Public Open House