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August 22, 2024
Brian Conde, Airport Director
Garfield County Regional Airport
2375 County Road 352, Bldg. 2060
Rifle, Colorado 81650
RE: Conceptual Drainage Report
Vantage Aviation, LLC
Proposed Hangar Development on Lease Parcel A5/A6
Dear Brian,
The purpose of this letter is to describe the existing and proposed drainage conditions for Lease Lots A5 and A6 at
the Garfield County Regional Airport. As you are aware, Vantage Aviation, LLC is proposing to develop these lots
with a 39,993 square foot hangar and a connected 5490 square foot terminal. With this development will be the
requisite parking and landscape areas as well as ties to the adjacent taxiway B-4 (with ramp areas) and access to
Betty Clark Way located south of adjacent Lot A7.
We have attached the following:
1. Existing Conditions map of Lease Lots A5/A6
2. Concept Grading and Drainage Plan of Lease Lots A5/A6
3. Garfield County Airport’s May 2023 Stormwater Map as prepared by Armstrong Engineers
Existing Drainage Patterns:
Lots A5 and A6 are bounded on the west by Taxiway B-4 that is sloping down to the north. It has a borrow ditch
on each side of the taxiway where the taxiway sends water from the east edge of pavement to the west borrow
ditch. The west borrow ditch slopes to the north and west to the major drainage swale on the south side of
Taxiway A. Water then drains to the west along Taxiway A to exit the airport at the west end of the airport
property. The east borrow ditch slopes to the north and east beyond the east end of the airport property into the
receiving drainage of Mamm Creek. Along the south side of Lot A7 is Betty Clark Way complete with borrow
ditches on each side to transport waters to the east borrow ditch of Taxiway B-4. Drainage from Betty Clark way
borrow ditches flow to the east Taxiway 4 borrow ditch where it is then transported north to a that traverses the
airport facilities to the north and east of the airport property to discharge into Mamm Creek. For the access
road. Finally, along the east side of Lots A5/A6, drainage sheet flows to the northwest to the east borrow ditch of
Taxiway B-4 for eventual discharge into Mamm Creek as well. These drainage patterns are generally reflected on
the May 2023 Stormwater Map by Armstrong.
Proposed Drainage Patterns:
Grading and drainage design for Lots A5/A6 is proposing to not change the roadway and taxiway improvements
as they currently exist. Given that, for roadway access, a paved access road will be constructed from Betty Clark
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Way along the east Lease line of Lots A5-A7. Drainage from the roadway and tributary offsite areas east of the
roadway will be directed north to the swale directing water to Mamm Creek. Drainage on Lot A5/A6 will be
directed to the north west for discharge into the adjacent east borrow ditch of Taxiway B-4 for eventual transport
to Mamm Creek as well. Ramp and apron improvements (including de-icing facilities) will be designed to be
captured with surface and piping improvements to treat and direct flows as appropriate for eventual transport to
Mamm Creek. Therefore, the drainage improvements are proposed to mimic those of the existing conditions.
Obviously, with the increase in impervious surfaces, the peak rates of runoff are expected to increase and
receiving drainage facilities will be evaluated to assure that the capacity of those facilities are capable of handling
that runoff. If any improvements to throttle peak flows to the capacity of existing conditions are needed, those
will be provided. Likewise, any treatment of stormwater prior to release that may be necessary will be designed
as well.
It is the intent of the proposed drainage and grading plans to meet the following bullet points:
· The Surface Water Management Plan will remain in effect.
· Surface water will be properly routed to the main drainage swale to transport flows to Mamm Creek as
exists now
· Piping/culverting, borrow ditches, treatment and detention (as necessary) will be properly implemented
to assure the drainage facilities are capable of properly transporting the design flows in compliance with
the Surface Water Management Plan for the airport.
Upon your receipt and review of this report as part of the submittal application for development on Lot A2, if you
have questions, concerns or modifications to the proposed conceptual drainage plan, please don’t hesitate to
contact me.
Sincerely,
SGM
Jefferey S. Simonson, PE
Principal
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