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1315 Oakridge Drive, Suite 120
Fort Collins, CO 80525
ditescoservices.com
Drainage Memorandum
Date: March 24, 2016
Project: Timberline Center
2133 Timberline – Lot 11 / 3rd Filing – Lot 1
Attn: Stormwater Staff
City of Fort Collins Utilities
Stormwater Engineering
700 Wood Street
Fort Collins, CO 80521
To Whom It May Concern:
The purpose of this drainage memorandum is to summarize the proposed drainage design changes as
compared to the original Final Drainage and Erosion Control Report for the Timberline Center Subdivision
as prepared by North Star Design; February 2006 - (North Star Report), describe project conformance to
LID standards, and provide an erosion control report.
Site Imperviousness:
Lot 1, 3rd Filing of the Timberline Center Subdivision changed since the original North Star Report which
was approved by the City of Fort Collins (COFC) on May 23, 2006. The original lot configuration for that
filing served a drive through bank and associated parking. Both the lot and site design have been
adjusted to serve an office building/restaurant use with associated parking areas. There is no increase in
impervious area from the approved 2006 report. In fact, there is a net decrease of approximately 4,500
square feet. The summary of impervious and pervious areas for both the North Star Report and this
submitted memorandum are tabulated below in Table 1 and shown visually in Appendix A.
TABLE 1: Impervious/Pervious Area Summary
2133 Timberline Lot 1 - Current Design 2133 Timberline Lot 1 - 2006 Approved Design
Impervious Area Summary Impervious Area Summary
Area Description Area-SF Area Description Area-SF
Asphalt 20,728 Asphalt 32,550
Sidewalks 3,990 Sidewalk/Building 7,050
Building Footprint 10,325 Total Area 39,600
Total Area 35,0 3
5
Page 2 of 3
2133 Timberline Lot 1 - Current Design 2133 Timberline Lot 1 - 2006 Approved Design
Pervious Area Summary Pervious Area Summary
Area Description Area-SF Area Description Area-SF
Islands At Parking Lot 815 Islands At Parking Lot 1,753
Islands at Sidewalk 1,182 Islands at Sidewalk 1,377
Planters at Building 5,942 Open Area/Detention Pond 21,676
Open Area/Detention Pond 21,458 Total Area 24,840
Total Area 29,397
Impervious Percentage 61.5%
Impervious Percentage 54.4%
As the new site plan and design provides additional landscaped area when compared to the initial 2006
site design, this site remains in compliance with the original approved North Star Report. Additionally,
a site specific Erosion Control Report has been developed for Lot 11 and is included in Appendix B.
Drainage Basin Compliance:
The site slopes from the west to east from the high point ridge designed as part of the Ascent site plans
which is exactly consistent with the grading plan presented in the North Star Report. As there is lower
impervious area in the new site plan than originally shown in the North Star Report, this site does not
increase runoff quantity relative to the previous approved plan.
Low Impact Development Compliance:
Low Impact Development (LID) requirements per Section 3.1 of the Urban Drainage and Flood Control
District Manual (Fort Collins 2012 Amendments) (UDFCD) include Section 3.1(a)(1) - a higher degree of
water quality treatment for 50% of new impervious area and Section 3.1(a)(2) - 25% of new paved areas
must be pervious. As an alternative to these requirements, per City of Fort Collins Ordinance No. 007,
2016; 75% of a newly developed area may be treated using a combination of LID techniques to achieve
compliance. A summary LID Compliance Table in Appendix C is provided for clarity. This project meets
the 75% treatment requirement through the following means:
The project is proposing a total impervious area of 35,053 square feet (0.80 Acres) through a
combination of traditional asphalt pavement, curb and gutter, sidewalks, ramps, pans and building roof
area. At 75% treatment, this requires a treated area of 26,290 square feet (0.60 Acres). These areas will
be treated through a combined method of rain garden treatment, bio-swale treatment, and release of
partial roof collection area to roof catchment infiltration areas. Appendix C shows areas highlighted and
delineated for treatment types.
Rain Garden Treatment – A combined area of 13,125 square feet (0.30 Acres) of impervious area are
routed to a restricted entry to a 480 square foot partial-infiltration rain garden adjacent to the
northwest corner of the building envelope. This restriction allows storm water to enter the rain garden
during the 2-year event and allows larger event flows to continue past into the existing inlet at the north
end of the concrete pan. The rain garden is designed to hold a maximum of one foot of standing water
Page 3 of 3
above rain garden grade prior to infiltration per LID design standards. At that elevation, storm water
overtops the curb and is routed to the existing inlet at the north end of the concrete pan.
Bio-Swale Treatment – A combined area of 8,015 square feet (0.18 acres) of impervious area are routed
to a geo fabric-lined cobble bio-swale with 100-year storm event capacity. The swale is 6 feet wide with
4:1 side slopes and 1% longitudinal slope. All contributing drainage is routed through the front of the
drainage swale and progresses through approximately 95 linear feet of swale before outfalling into the
existing detention basin.
Release to Roof Catchment Infiltration Areas – The east side of the building roof, an area of 5,524 square
feet (0.13 acres) will be routed through roof drains to the roof catchment infiltration areas on the east
side of the building. This storm water will filter through depressed landscaped areas, infiltrating
through soil and filter rock to a perforated subdrain system which outlets into the detention basin.
In summary, this project complies with applicable Urban Drainage and Flood Control District Manual
(Fort Collins 2012 Amendments) requirements. The total LID treatment area of 0.61 acres is in excess of
the required treatment area of 0.60 acres.
If you have any questions regarding this submittal, please do not hesitate to contact me by email at
bill.renz@ditescoservices.com or by phone at 970-219-0157. Thank you for your attention and
assistance in this matter.
Sincerely,
Bill Renz, EI Keith Meyer, PE
Enc. Appendix A – Impervious Areas Comparison
Appendix B – Erosion Control Report
Appendix C – 3rd Filing Lot 1 LID Treatment Areas
2133 TIMBERLINE - 3rd FILING - LOT 1
Appendix A Impervious Areas Comparison
155.09'
SOUTH TIMBERLINE ROAD
FF= 4946.80
309
C603
FND #4 REBAR
w/ RPC LS 37987,NE
FND #4 REBAR
FND #4 REBAR w/ RPC LS 33106,KSI
FND #4 REBAR w/ RPC LS 33106,KSI
w/ RPC LS 37987,NE
FND #4 REBAR
w/ RPC LS 34995,KSI
FND NAIL & SHINER
LS 34995,KSI
EXISTING 8" WIDE
MASONRY WALL
3' CONCRETE PAN
PROPOSED BIO SWALE
CHANNEL
1' CURB CUT
MATCH EXISTING
PROPOSED STEPS
(SEE SHEET C402)
PROPOSED RAIN
GARDEN
(SEE SHEET C402)
PROPOSED STEPS
(SEE SHEET C402)
PROPOSED
TRANSFORMER
PROPOSED SCREEN WALL
(SEE DETAIL)
314
C604
PROPOSED SEAT WALL
(SEE DETAIL)
313
C604
308
C603
PROPOSED SEAT WALL
(SEE DETAIL)
PROPOSED 10" PVC DRAIN
9 LF @ 1.22%
313
C604
PROPOSED 10" PVC DRAIN
15 LF @ 1.2%
PROPOSED 2'
SIDEWALK CHASE
(0.86' DEEP)
PROPOSED BIKE PARKING
9'x9' OPEN CELL PAVERS
PROPOSED 3' WIDE PATH;
CRUSHER FINES
(SEE DETAIL)
310
C603
EXISTING SIDEWALK
49'-10"
2133 TIMBERLINE - 3rd FILING - LOT 1
Appendix B Erosion Control Report
2133 TIMBERLINE - LOT 11
PROJECT ECR
Page 1 of 5
APPENDIX A – EROSION CONTROL REPORT
A. Proposed Construction Area
i. Developed Conditions – The proposed site is located at the northwest corner of the
Timberline Rd. and Nancy Gray Ave., in Fort Collins. Currently, the proposed site
development area contains an established detention pond and outlet along the eastern
edge of the site. The proposed building will have an 85’ setback from Timberline road.
Vegetative Cover has been established in the detention pond.
ii. Rainfall Erodibility – Rainfall erosion will be controlled through use of temporary
construction BMPs until permanent vegetative cover has reached 70% percent of
groundcover. Opportunities for rainfall erosion include sheet flow across the site during
earthwork operations and utility installations.
iii. Proposed Rainfall Erosion and Sediment Control Methods – Primary methods will
include silt fence installation on the east and south lot limits and inlet and channel
protection with gravel bags to both slow and filter runoff water before it enters any
structures or channel outletting to the detention pond. A stabilized construction
entrance will be utilized at the site ingress/egress point.
iv. Site Phasing and BMP Installation Schedule – The site construction will take place in the
following order:
1. Installation of site BMPs
i. Stabilized Construction Entrance
ii. Silt Fence
iii. Inlet protection on existing inlets
2. Site Utility Installation
i. Installation of inlet control in new inlets and channels as they are
finished
3. Building Foundation and Earthwork
4. Vertical building construction and ongoing utilities
5. Finished site grading, hardscaping and paving
6. Landscaping and Irrigation installation
B. Stormwater Management Controls
i. SWMP Administrator
1. During construction, the SWMP administrator will be the earthwork and utility
contractor. Until such time as that contractor has been selected, the SWMP
Administrator will be Bill Renz, Project Manager-Ditesco. He will be responsible
2133 TIMBERLINE - LOT 11
PROJECT ECR
Page 2 of 5
for developing, implementing, maintaining, and revising the SWMP and will
address all aspects of the site SWMP.
i. Bill Renz – Ditesco Project Manager
1315 Oakridge Drive, Suite 120
Fort Collins, CO 80525
970.219.0157
ii. Identification of Potential Pollution Sources
1. All disturbed and stored soils – there will be disturbed soils onsite through
excavation and vehicle/equipment movement. Soils will be
stockpiled/permanently embanked onsite. Excess soil will be transported
offsite. Soil stockpiles left undisturbed for a period greater than 30 days will be
mulched and seeded.
2. Vehicle tracking of sediments – most vehicle and equipment travel will risk
sediment tracking until final pavement is installed. A stabilized construction
entrance will be used for the site. Surrounding roadways will be swept if
sediment is tracked onto the roadway.
3. Management of contaminated soils – soils may be contaminated through spills
during fueling operation or equipment oil leaks. The contractor will keep spill
kits onsite during the project and will excavate and remove contaminated kit
materials and soil and dispose through the proper waste stream.
4. Loading and unloading operations – Loading and unloading operations will take
place within the site for materials to be incorporated in the project. Vehicles
will use the stabilized entrance for ingress/egress.
5. Outdoor storage activities (building materials, fertilizers, chemicals, etc.)
Storage of materials will be in a designated area. Any chemicals used during
construction, concrete cure, etc., will be stored on secondary containment.
6. Vehicle and equipment maintenance and fueling – Maintenance and fueling will
be done in the field at the location of the equipment on grade. Spills will be
addressed through item 3 of this section.
7. Significant dust or particulate generating processes – dust may be generated
from vehicle tracking or portions of backfill operation. The site will be kept from
producing dust through watering of any exposed soils.
8. Routine maintenance activities involving fertilizers, pesticides, detergents, fuels,
solvents, oils, etc. – Fueling, lubrication, and maintenance operations will take
place within the project limits on grade. No fertilizers pesticides or detergents
are planned for use on site.
9. On-site waste management practices (waste piles, liquid wastes, dumpsters,
etc.) Roll-off Dumpsters will be utilized for the site and will be hauled off at
2133 TIMBERLINE - LOT 11
PROJECT ECR
Page 3 of 5
regular intervals. Any liquid waste generated will be contained. Concrete
process water will be addressed through the next item in the section.
10. Concrete truck/equipment washing, including the concrete truck chute and
associated fixtures and equipment – A concrete wash out will be utilized for all
concrete placement operations. A sign will be posted clearly showing the
washout location.
11. Dedicated asphalt and concrete batch plants – no asphalt or concrete batch
plants will be erected onsite.
12. Non-industrial waste sources such as worker trash and portable toilets –
Portable toilets will be staged onsite. Trash receptacles will be emptied
regularly.
13. Other areas or procedures where potential spills can occur – No other areas
qualify for this section.
C. Dryland Vegetation
i. All areas will be hardscaped, sodded, or mulched. Existing open areas have already
been seeded.
D. Detailed Sequence of Construction Activities
i. It is anticipated that this project will begin construction during 2016 and will be
completed within a year.
ii. Installation of site BMPs
1. Stabilized Construction Entrance
2. Silt Fence
3. Inlet protection on existing inlets
iii. Site Utility Installation
1. Installation of drainage facilities
2. Installation of inlet control/BMPs in new inlets and channels as they are finished
iv. Building Foundation and Earthwork
v. Vertical building construction and ongoing utilities
vi. Finished site grading, hardscaping and paving
vii. Landscaping and Irrigation installation
1. Seeding and mulching
2. Tree planting
3. Shrub planting
viii. Vegetative cover establishment period
ix. Removal of silt fence and inlet protection
x. BMPs will be inspected for effectiveness and maintained after each runoff event and
every 14 days at a minimum during construction.
E. Erosion Control Security Calculations
2133 TIMBERLINE - LOT 11
PROJECT ECR
Page 4 of 5
Project: Disturbed Acres: 1.31
EROSION CONTROL BMPs Units
Estimated
Quantity
Unit
Price
Total
Price
LF 440 $2.50 $1,100.00
EA 3 $150.00 $450.00
EA 1 $750.00 $750.00
EA 1 $1,100.00 $1,100.00
Sub-Total: $3,400.00
1.5 x Sub-Total: $5,100.00
Amount of security: $5,100.00
Total Acres x Price/acre: $1,299.99
$995.00 Sub-Total: $1,299.99
1.5 x Sub-Total: $1,949.98
Amount to Re-seed: $1,949.98
Minimum escrow amount: $3,000.00
Erosion Control Escrow: $5,100.00
Reseeding Amount
Miniumum Escrow Amount
Timberline Lot 11
Unit Price of Seeding per acre:
“The amount of the security must be based on one and one-half times the estimate of the cost to install the approved measures, or one and one-half times
the cost to re-vegetate the disturbed land to dry land grasses based upon unit cost determined by the City's Annual Revegetation and Stabilization Bid,
whichever is greater. In no instance, will the amount of security be less than one thousand five hundred dollars ($1,500) for residential development or three
thousand dollars ($3,000) for commercial development”
Inlet Protection (IP)
Concrete Washout (CW)
(add all other BMPs for the site in this list)
Final Escrow Amount
Example Erosion and Sediment Control Escrow/Security
Calculation for The City of Fort Collins
BMP Amount
Silt Fence (SF)
Vehicle Tracking Control (VTC)
SOUTH TIMBERLINE ROAD
SF
SF
VTC
CIP3
IP
IP
FND #4 REBAR
w/ RPC LS 37987,NE
DESIGN BY OTHER
(FOR REFERENCE ONLY)
FND #4 REBAR
FND #4 REBAR w/ RPC LS 33106,KSI
FND #4 REBAR w/ RPC LS 33106,KSI
w/ RPC LS 37987,NE
FND #4 REBAR
w/ RPC LS 34995,KSI
FND NAIL & SHINER
LS 34995,KSI
DESIGN BY OTHER
(FOR REFERENCE ONLY)
FF= 4946.80
LOT 1
TIMBERLINE CENTER
THIRD FILING
TRASH ENCLOSURE
15'
UTILITY
&
DRAINAGE
EASEMENT
PROPOSED EASEMENT
EXISTING 8" WIDE
CONCRETE WALL
GS
GS
GS
GS
PROPOSED RAIN GARDEN
(SEE SHEET C402)
SLOPE &
DRAINAGE EASEMENT
(TO BE VACATED; SEE PLAT)
UTILITY, DRAINAGE, ACCESS EASEMENT
C301
6
EROSION CONTROL PLAN
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what's
R
City of Fort Collins, Colorado
Date
Date
Date
Date
Date
Date
City Engineer
Traffic Engineer
2133 TIMBERLINE - 3rd FILING - LOT 1
Appendix C - LID Treatment Areas
SOUTH TIMBERLINE ROAD
DESIGN BY OTHER
(FOR REFERENCE ONLY)
EXISTING 8" WIDE
MASONRY WALL
3
2
FF= 4946.80
LOT 1
TIMBERLINE CENTER
2ND FILING
PROPOSED EASEMENT
SLOPE & DRAINAGE
EASEMENT
15'
UTILITY
&
DRAINAGE
EASEMENT
UTILITY, DRAINAGE, ACCESS
& EMERGENCY EASEMENT
PROPOSED 10" PVC DRAIN
9 LF @ 1.22%
PROPOSED 10" PVC DRAIN
15 LF @ 1.2%
C701
14
DRAINAGE EXHIBIT
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
Know what's
R
City of Fort Collins, Colorado
Date
Date
Date
Date
Date
Date
City Engineer
Traffic Engineer
Parks & Recreation
Stormwater Utility
Water & Wastewater Utility
SHEET NO.
15-01-29
PROJECT NO.
SHEET INDEX
DESIGNED BY:
DRAWN BY:
APPROVED BY:
SCALE:
SHEET SUBSET:
LOT 1, TIMBERLINE CENTER,
THIRD FILING DATE:
NONE
February 4, 2016
K. Meyer
R. Bunner
K. Meyer
NOT FOR CONSTRUCTION
1"=30'
30' 0 30' 60' 90'
LEGEND:
NOTES:
A
A
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
LID COMPLIANCE TABLE QTY UOM QTY UOM
New Impervious Area
Traditional Pavement Area 17,621 SF 0.405 AC
Other Impervious Surfaces (Roofs, Concrete Walks, Etc.) 17,376 SF 0.399 AC
Required Minimum Impervious Area to be Treated (75%) 26,248 SF 0.603 AC
Rain Garden LID Treatment
Rain Garden Area 480 SF 0.011 AC
Run-on area for Rain Garden 13,125 SF 0.301 AC
Impervious Area Treated by Rain Garden 13,125 SF 0.301 AC
Bio Swale LID Treatment
Bio Swale Area (6' Width) 600 SF 0.014 AC
Run-on area for Bio Swale 8,015 SF 0.184 AC
Impervious Area Treated by Rain Garden 8,015 SF 0.184 AC
Impervious Area Treated by LID Roof Catchment
East Roof Area 5,524 SF 0.127 AC
Total Impervious Area 34,997 SF 0.803 AC
Total Impervious Area Treated 26,664 SF 0.612 AC
Total Impervious Area Treated Percentage 76.20%
High
Point
High
Point 1
0.23 AC
2
0.18 AC
3
0.15 AC
4
0.07 AC
5
0.03 AC
6
0.13 AC
7
0.01 AC
RAIN GARDEN TREATMENT
BIOSWALE TREATMENT
RELEASED TO LID ROOF CATCHMENT AREAS
UNTREATED
WATER QUALITY TREATMENT LEGEND
RAIN
GARDEN
BIO
SWALE
BIO SWALE
6" PVC 6" PVC 6" PVC
Parks & Recreation
Stormwater Utility
Water & Wastewater Utility
SHEET NO.
15-01-29
PROJECT NO.
SHEET INDEX
DESIGNED BY:
DRAWN BY:
APPROVED BY:
SCALE:
SHEET SUBSET:
LOT 1, TIMBERLINE CENTER,
THIRD FILING DATE:
NONE
March 24, 2016
K. Meyer
R. Bunner
K. Meyer
NOT FOR CONSTRUCTION
1"=20'
20' 0 20' 40' 60'
LEGEND:
SF
VTC
NOTES:
IP
GS
PROPOSED 2'
CONCRETE PAN
THRU ISLAND
1' CURB CUT
DESIGN BY OTHER
(FOR REFERENCE ONLY)
DESIGN BY OTHER
(FOR REFERENCE ONLY)
LOT 1
TIMBERLINE CENTER
THIRD FILING
TRASH ENCLOSURE
PROPOSED EASEMENT\
BUILDING ENVELOPE
315
C604
39.98'
INV: 40.4
4" PERFORATED PVC
LATERALS (TYP) AT
ALL DOWNSPOUTS
LOCATIONS.
COORDINATE WITH
LANDSCAPE PLAN
FOR LID ELEMENTS
AT EACH
DOWNSPOUT.
155 LF, 6" SOLID PVC @2%
CLEANOUT
INV: 43.5
50 ft