HomeMy WebLinkAboutA2_Drainage_Report
www.sgm-inc.com
GLENWOOD SPRINGS 118 West Sixth St, Suite 200 | Glenwood Springs, CO 81601 | 970.945.1004
Page | 1
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 A2
Dear Brian,
The purpose of this letter is to describe the existing and proposed drainage conditions for Lease Lot A2 at the
Garfield County Regional Airport. As you are aware, Vantage Aviation, LLC is proposing to develop this lot with a
25,042 square foot hangar and a connected 5453 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 John
Sullivan Road (access and parking improvements).
We have attached the following:
1. Existing Conditions map of Lease Lot A2
2. Concept Grading and Drainage Plan of Lease Lot A2
3. Garfield County Airport’s May 2023 Stormwater Map as prepared by Armstrong Engineers
Existing Drainage Patterns:
Lot A2 is bounded on the west by John Sullivan Road that is a paved roadway sloping down to the north. It has a
borrow ditch on each side of the roadway where the crown of the road sends water from centerline to both the
east borrow ditch and the west borrow ditch. The borrow ditches slope 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 exist the airport
at the west end of the airport property. Along the south side of Lot A2 is Betty Clark Way complete with borrow
ditches on each side to transport waters to the east borrow ditch of John Sullivan Road. Finally, along the east
side of Lot A2 is Taxiway B-4 where the taxiway also slopes to the north to Taxiway A. Borrow ditches exist on
both sides of B-4 and direct water to the Taxiway A swale. Lot A-2, itself, slopes to the north and west to
ultimately end up in the east borrow ditch of John Sullivan Road and then to the swale for Taxiway A. These
drainage patterns are generally reflected on the May 2023 Stormwater Map by Armstrong.
Proposed Drainage Patterns:
Grading and drainage design for Lot A-2 is proposing to not change the roadway and taxiway improvements as
they currently exist. Given that, the grading improvements will continue to provide full access from the roadway
for access and parking as well as provide full access from the taxiway for aircraft. With no reconstruction or
modifications of the existing conditions, the drainage patterns for the proposed conditions will remain as is.
www.sgm-inc.com
GLENWOOD SPRINGS 118 West Sixth St, Suite 200 | Glenwood Springs, CO 81601 | 970.945.1004
Page | 2
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.
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 along the south side of Taxiway A
· Piping/culverting, borrow ditches 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
HY
D
HYD
HYD
HYD
ICV
W
W
ICV
ICV
Graphic Scale
In Feet: 1" = 50'
0 25 50 100
Re
v
i
s
i
o
n
#
Dwg No.
Job No.
Drawn by:
Print Date:
File:
PE:QC:
2024-346.001
ES
8/21/2024
ES
Existing Conditions Mapping
XX
11
8
W
e
s
t
S
i
x
t
h
S
t
r
e
e
t
,
S
u
i
t
e
2
0
0
Gl
e
n
w
o
o
d
S
p
r
i
n
g
s
,
C
O
8
1
6
0
1
97
0
.
9
4
5
.
1
0
0
4
ww
w
.
s
g
m
-
i
n
c
.
c
o
m
Da
t
e
By
:
2
Of :
Pr
o
j
e
c
t
M
i
l
e
s
t
o
n
e
:
2
PR
E
L
I
M
I
N
A
R
Y
N
O
T
F
O
R
C
O
N
S
T
R
U
C
T
I
O
N
Ri
f
l
e
A
i
r
p
o
r
t
Drainage and Grading
Plan - A2
Va
n
t
a
g
e
A
v
i
a
t
i
o
n
Title:
HY
D
HYD
HYD
HYD
ICV
W
W
ICV
ICV
Graphic Scale
In Feet: 1" = 50'
0 25 50 100
Re
v
i
s
i
o
n
#
Dwg No.
Job No.
Drawn by:
Print Date:
File:
PE:QC:
2024-346.001
ES
8/21/2024
ES
Existing Conditions Mapping
XX
11
8
W
e
s
t
S
i
x
t
h
S
t
r
e
e
t
,
S
u
i
t
e
2
0
0
Gl
e
n
w
o
o
d
S
p
r
i
n
g
s
,
C
O
8
1
6
0
1
97
0
.
9
4
5
.
1
0
0
4
ww
w
.
s
g
m
-
i
n
c
.
c
o
m
Da
t
e
By
:
2
Of :
Pr
o
j
e
c
t
M
i
l
e
s
t
o
n
e
:
2
PR
E
L
I
M
I
N
A
R
Y
N
O
T
F
O
R
C
O
N
S
T
R
U
C
T
I
O
N
Ri
f
l
e
A
i
r
p
o
r
t
Drainage and Grading
Plan - A2
Va
n
t
a
g
e
A
v
i
a
t
i
o
n
Title: