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HomeMy WebLinkAboutAppendix F.1 - Conceptual Engineering LetterAugust 29, 2018 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S O PRIS E NGINEERING • LLC civil consultants Richard Shaw Design Workshop 120 E Main Street Aspen, CO 81611 rshaw@designworkshop.com RE: Gorsuch Haus- Conceptual Engineering Letter SE Job # 15101.05 Dear Richard, This letter summarizes our initial findings as it relates to the recently revised site plan associated with the Gorsuch Haus. The purpose of this review was to understand some of the recent revisions to the proposed site plan that are being considered in support of allowing Lift 1A to move further down the hill. This review is provided to demonstrate that the elements of civil engineering will be able to be met in respect to Utilities, Access and Drainage. Further coordination and design efforts will be pursued as the project progresses through the accelerated PD Development Review process. A conceptual site plan highlighting some of the changes (Exhibit A) has been provided as an attachment to this letter for illustrative support. Utilities Since the previous Engineering Report was published a significant amount of utility improvements have been installed along S. Aspen Street in support of the recent development of the One Aspen Project. In addition, further discoveries have been identified as noted below: Water: The water main improvements along S. Aspen Street have been installed and extend south from Durant Avenue to the southern end of S. Aspen Street. The approved construction drawings actually included the extension of the water main to continue east along Hill Street and re-connect to the existing system just east of S. Monarch Street; however prior to this section being installed it was determined that the proposed alignment creates complications to the Lift One Lodge and Gorsuch Projects and therefore the City agreed to defer the final 500+ feet until after revised site plans for the Gorsuch and Lift One Lodge were available to determine if a better alignment could be provided. As such, the recent site revisions associated with the Gorsuch Project provides an opportunity to improve the previously proposed alignment for this final section of water main. The proposed re-alignment is illustrated on Exhibit A and places the 16-inch water main along the south side of the remaining Hill Street ROW which will require a 8-ft+/- wide easement through the northern portion of Gorsuch Haus Lot 1, running parallel to the remaining Hill Street ROW. This easement along with the remaining Hill Street ROW will provide the required 30-ft easement through this section of water line replacement. A 30-ft easement will also be required through Gorsuch Haus Lot 2. This improved alignment avoids conflicts with structures, reduces the amount of bends and provides additional separation between proposed structures which improves future access and maintenance to the water main. The proposed water service for this project will tap into this new 16” water main and will likely entail a combined service line to provide domestic and fire flow requirements. Since the development extends above the City’s 8040-Greenline the applicant will have to provide a private water pressure boosting system to ensure adequate pressures and fire flow requirements are maintained. Final designs of the extended water main, booster pumps, service lines and fire suppressant systems will be provided at time of building permit application. APPENDIX F.1 - GORSUCH HAUS CONCEPTUAL ENGINEERING LETTER 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S OPRIS E NGINEERING • LLC civil consultants 2 | P a g e Sewer: Aspen Consolidated Sanitation District (ACSD) is the supplier of sanitary sewer service to the subject property and surrounding area. Sewer service to the project will be tapped from the recently installed sewer main (8” and 12”) that extends south from Durant Avenue to the southern end of S. Aspen Street. The size of the line will be verified prior to permit application. Grease interceptors will be provided for any and all food processing establishments and a sand/oil interceptor will be provided within the proposed parking garage. Ejector pumps are anticipated for portions of the project given the depths and use of the proposed below grade space. Abandonment of all existing sewer services shall comply with ACSD specifications and final terminations will need to be inspected by ACSD personnel. All work associated with Aspen Consolidated Sanitation District infrastructure shall be in accordance with their rules and regulations. Since the previous report was published it has been determined that there is an existing 8” sewer service that runs up Aspen Mountain and serves Ruthie’s Restaurant. Based on available mapping it appears that this existing service line will need to be re-aligned to avoid the proposed building and then re-connected to the recently installed sanitary sewer main that runs up S. Aspen Street. A conceptual alignment is illustrated on Exhibit A and runs along the east side of the building. Several manholes are proposed for change of direction and future maintenance which will be an improved condition as compared to what exists today. The proposed service for the Gorsuch Haus is currently shown tapping into the Ruthie’s new sewer service which will either require extending the Districts mainline 65-ft+/- to the east or a shared service line agreement will need to be pursued between Aspen Ski Company and the applicant. This will be further evaluated as the project design progresses with final alignments and designs being provided in support of any future building permit applications. ACSD has provided an Ability to Serve Letter which is attached to this report. Electric: Holy Cross Energy is the supplier of electric service in this area. Numerous coordination meetings have occurred to better understand the improvements that were installed and how to best serve the project. In summary, new primary electric lines were installed with the S. Aspen Street improvements. These primary lines extend to the southern end of S. Aspen Street and serve the existing transformer (3468P1) located north of Lift 1A, a recloser located adjacent to this transformer, a recently installed switch gear, a transformer (3128P1) serving the Shadow Mountain Townhomes and then existing infrastructure serving Aspen Mountain. The proposed improvements associated with the Gorsuch Project will require relocating the existing recloser and transformer located near Lift 1A. In addition, the recently installed switch gear may also need to be relocated given the close proximity to the proposed building. Furthermore, the existing primary line that feeds infrastructure further up Aspen Mountain will likely need to be re-routed to accommodate the proposed building. The proposed location of the transformers to serve the project and the relocated infrastructure mentioned above are illustrated on Exhibit A; however alternative locations are currently being explored to improve access for future maintenance. Further coordination with the design team, City and Holy Cross Energy is anticipated as the project design evolves and the project proceeds through the review process. A will serve letter from Holy Cross has been provided as an attachment to this letter. Gas: As noted in the previous Engineering Report Black Hills Energy is the provider of natural gas in the area. Since the previous Engineering Report was published a new 6” gas main has been extended to the southern end of S. Aspen Street. A new service line will be extended from this gas main to serve the proposed 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S OPRIS E NGINEERING • LLC civil consultants 3 | P a g e development. The size of the proposed service will be determined prior to building permit. All natural gas improvements/infrastructure shall conform to Black Hills rules and regulations. Telephone: Century Link is the provider of telephone service within the area. New service to the proposed building will be extended from the recently installed main line infrastructure that was installed as part of the S. Aspen Street improvements. Cable: Comcast is the provider of cable service within the area. New service to the proposed building will be extended from recently installed main line infrastructure that was installed as part of the S. Aspen Street improvements. A will serve letter prepared by Comcast has been attached to this report. With the exception of the City Water Department, will serve letters from all utility providers are included as attachments to this report. Further coordination and refining pedestal, transformer and service alignments may occur as the project progresses into detail design with a final plan being submitted when a Building Permit Application is pursued. Access The new site plan includes a much improved cul-de-sac that will serve as the primary pick up/drop off and access to the site as well as emergency turn around. This cul-de-sac will be dedicated to the City as ROW and meets their minimum dimensional requirements as stated within Title 26.580.020 of the City of Aspen’s Land Use Code as well as Section 4.2.3 of the City’s Engineering Standards. The cul-de-sac also provides 24-ft of width for vehicular circulation as well as a 12.5 ft wide drop off aisle which will provide primary ADA access to the property. As illustrated on the attached Exhibit A the cul-de-sac accommodates an Aerial Fire Truck. It should be noted that under the revised site plan the lift will be moved further down the hill and therefore the cul-de-sac will no longer be used as primary access to the lift which will reduce the overall impacts to the area. Site Drainage The revised site plan reduced the overall footprint of the proposed building and hardscape areas resulting in a reduction of impervious area of approximately 25% as compared to the previous site plan. This reduction will simplify the stormwater mitigation requirements by reducing the amount of water quality treatment volume that will be required as well as a reduction of post development peak runoff rates and volumes. Stormwater mitigation strategies have not been completely vetted at this time however green roofs are being considered to further reduce impervious areas. Final green roof coverage will be determined prior to building permit application. Other potential stormwater mitigation infrastructure includes permeable pavers and underground water quality treatment vaults. The site plan is currently showing two underground treatment vaults that have dimensions capable of providing a combined volume of approximately 600 cubic feet. This amount of volume can accommodate water quality treatment for approximately 28,000 sf of impervious area which is approximately 80% of the overall roof and hardscape area currently proposed on the subject property. Based on discussions with the City it is our understanding that this project will not be required to provide onsite detention given the recent storm sewer improvements installed along S. Aspen Street. Our office will continue to work with the design team and City to identify and address any concerns that may arise during the PD review process. 502 Main Street • Suite A3 • Carbondale, CO 81623 • (970) 704-0311 • Fax (970) 704-0313 S OPRIS E NGINEERING • LLC civil consultants 4 | P a g e Conclusions In summary, it is our opinion that the revised site plan provides improved access to the site, it is consistent with the previous application as it relates to utility services to the building, provides for a better alignment for the required 16- inch water main and results in an overall reduction of impervious area which will simplify stormwater mitigation requirements as compared to the previous site plan. All utilities serving the proposed development including water supply, wastewater collection, and the shallow utilities (power, gas, phone, data/communication) are proposed to have essentially the same delivery and connection routes as outlined within the previous application dated March 2016. In addition, since the publication of the previous engineering report the majority of utility upgrades along S. Aspen Street have been completed. Our office will continue to work with the design team and City to further develop utility, grading and drainage designs and address any concerns that may arise as the project continues through the City’s review process. Please let us know if you have any questions or if you need additional information. Sincerely, SOPRIS ENGINEERING, LLC Jesse K. Swann, PE Sopris Engineering, LLC 970-704-0311 Encls. Exhibit A Utility Provider Will Serve Letters