HomeMy WebLinkAboutASPEN HEIGHTS STUDENT HOUSING - FDP - FDP130010 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT (6)Aspen Heights Student Housing 9/16/2013
Storm Water Management & Erosion Control Plan
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ASPEN HEIGHTS STUDENT HOUSING
FORT COLLINS, COLORADO
STORM WATER MANAGEMENT PLAN
and
EROSION CONTROL PLAN
Site and Project Description
The project site, which is currently vacant, comprises a total of approximately 31.00 acres,
located at the southwest corner of the intersection of Conifer St. and Redwood St. in Fort
Collins, CO. It is part of the SW ¼ of Section 1, Township 7 North, Range 69 West of the 6th
Principal Meridian, City of Fort Collins, Larimer County, Colorado. The site is bounded on the
north by Conifer St., on the east by Redwood St., on the south by the future alignment of New
Vine Dr., and on the west by vacant land. Adjacent developments and land uses, beyond the
abutting streets, include residential and commercial to the north (Evergreen Park), residential to
the east (Redwood Meadows), residential to the south (Old Town North), and commercial
beyond the vacant land to the west.
The site also surrounds on three sides (north, west and south) a parcel of land owned by the
City and designated for development of a regional stormwater detention facility. This City-
owned parcel comprises approximately 9.5 acres, and will be the site of the interim detention
facility, to serve the Aspen Heights development, pending development of the ultimate detention
facility.
The proposed development of the site will include 130 two-story, cottage-style residences; a
clubhouse and recreation / amenities area; off-street surface parking, accessed via a network of
local public streets and private driveways; and landscaped open-space areas and pedestrian /
bicycle paths. Buildings will account for approximately 21% of the site area; paved roads,
sidewalks and parking areas will account for a further approximately 30% of the site; and
landscaped areas will account for approximately 49% of the developable area of the site. The
balance of the site (approximately 4.9 acres) will be either dedicated to the City for the
construction of New Vine Drive (3.1 ac), or left in it’s current natural state (1.8 ac).
Specific construction activities to be completed during the course of development will include
overlot grading; excavation, shaping and grading of a storm drainage channel and detention
basin; installation of underground utility services; construction of concrete curb and gutter and
drainage pans; asphalt paving of public streets, drive aisles and parking areas; construction of
project buildings; development of exterior amenities areas; final grading; and installation of
landscaping materials. The layout of the proposed development is shown on the attached
Erosion Control Plan.
The site slopes relatively uniformly from northwest to southeast at an average gradient ranging
between 0.5% – 1.0%. A remnant of the Dry Creek channel lies within a tongue of the site,
southeast of the proposed right-of-way for New Vine Drive. This portion of the site (approx. 1.84
ac) is effectively undevelopable, so the Dry Creek channel will not be impacted by the proposed
development, other than to a small extent by the construction of New Vine Drive. In addition to
the remnant Dry Creek channel, there is currently a drainage ditch that traverses the property
from north to south, along an alignment located approximately 40% of the width of the property
from the west boundary. This ditch is approximately five to six feet deep and conveys runoff
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through the property from tributary areas to the north. This ditch will be widened, reshaped and
regraded, as part of the development improvements, to continue to convey runoff through the
site to the proposed detention facility. There is also currently a branch ditch that extends from
the northwest corner of the property to a confluence with the main north-south ditch, at a point
approximately 30% of the distance from the north property line to the south boundary of the site.
This lateral ditch will be eliminated and replaced by a piped storm drain, as part of the
development of the site. The Lake Canal Irrigation Company channel passes to the south of the
site, and is closest to the site at a point approximately 550 feet east of the south east corner of
the property.
The native soils underlying the site consist primarily of lean clays, with varying amounts of silt
and sands, ranging to depths of 3 – 8 feet below existing grade, underlain by well-graded and
poorly-graded sand with silt and gravel, ranging to depths of approximately 20 feet below
existing grade. These soils fall within NRCS Hydrologic Soil Group C. Ground water was
encountered at depths ranging from approximately four to seven feet below existing grade, at
the time of drilling. After three days, the depth to the water table had stabilized at between five
and six feet below grade, throughout the site.
Flood plain mapping for the vicinity of the development site shows a FEMA-designated
floodplain and floodway (the Dry Creek Floodplain) that extends into the southeast corner of the
undevelopable portion of the site and the City-owned detention basin site. The floodway
extends along a portion of the Dry Creek channel, with some extension of the floodplain north
along the alignment of the not-yet-constructed portion of Redwood Street, north of the proposed
alignment of New Vine Drive. The floodplain and floodway boundaries are delineated on FEMA
FIRM Panel # 08069C0977G, dated June 17, 2008.
For the current vacant state of the site, the Runoff Coefficient would range between
approximately 0.2 and 0.5, depending on storm intensity. Upon completion of the proposed
development, the composite 100-yr Runoff Coefficient for the site, “C100”, is calculated to be
0.57 and the composite Percent Imperviousness of the site is calculated to be 44.15%.
The general sequence of development activities at the site will include construction of the
interim detention basin; removal and stockpiling of existing topsoil; overlot grading; installation
of underground utilities; construction of new concrete curb and gutter, paved roadways,
driveways and parking areas; construction of the buildings and exterior paved amenities areas;
final grading; and landscaping of the open-space areas of the site. During the course of
development, at one time or another, the majority of the site will be disturbed, however,
progressive development of the site will limit the scope of the area of disturbance, such that not
more than approximately 50% of the site is likely to be disturbed at any one time.
The primary source of potential surface water contamination that may result from development
of the site is sediment that will be liberated due to construction operations. Other lesser
potential sources of contamination may include hydrocarbons from on-site fueling and servicing
of construction vehicles and equipment, as well as particulate and trace chemicals from
concrete and building construction activities. There are no other known or anticipated sources
of contamination that may impact the site runoff and downstream receiving waters.
Runoff from the site will be collected and conveyed to the interim detention basin, which has
been sized to provide storm attenuation and water quality enhancement for the developed site,
and which will be constructed as an initial part of the construction program. Site runoff
accumulated in the detention basin will eventually be discharged from the outlet control
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structure at the southeast corner of the site and conveyed to the discharge point at the Lake
Canal channel, and from there, ultimately into the Cache La Poudre River.
Construction Activities
As indicated above, as much as 50% of the site (a total of approximately 16 acres) will likely be
disturbed, at any one time, during the course of site development, building construction, final
grading and landscaping. There will not likely be a surplus of excavated soil from the
construction activities, so on-site stockpiling of soil, other than topsoil, will be limited. There will
be a need to haul fill material onto the site, but that material will be deposited and immediately
spread in its final location, without stockpiling. Topsoil stockpile(s) will be limited in height, and
will be located as far as possible from any permanent or interim drainage ways.
Construction materials will generally be delivered to the site as they are required, and stored in
close proximity to the work area or immediately incorporated into the permanent construction.
Imported construction materials, with the exception of import fill, will, for the most part, be non-
polluting (steel, concrete, brick, clean fill or construction aggregate, lumber, finishing materials,
etc.). There will not likely be any dedicated asphalt or concrete batch plants on-site.
Wherever possible, excavated native soils will be used for site fill and trench backfill, and this
material will be placed, spread and compacted immediately or stockpiled adjacent to the
excavation and reused as quickly as practicable in a tight operation. Precautions will be taken,
as described below, to limit erosion and transport of temporarily stockpiled material.
Best Management Practices (BMPs) for Erosion Control and Stormwater Pollution Prevention
Erosion and sediment transport from disturbed areas of the site present the most significant
potential for contaminant migration during construction activities at the site. Several structural
BMPs, common to most construction sites, will be implemented to limit this potential and to
mitigate impacts, as follows:
Silt fencing will be installed along the perimeters of the site, prior to initiation of any soil
disturbance. The silt fences will be maintained throughout the course of construction
activities.
Additional silt fencing and/or temporary diversion berms may also be installed along the
uphill perimeter of localized on-site disturbance areas, in order to minimize the inflow of
runoff from outside areas to the respective active construction areas.
Within the disturbed areas, the surface of exposed soils will be roughened along an
alignment that follows the site contours, to limit the flow path length of runoff water and to
promote infiltration of stormwater into the exposed soils.
Where deemed necessary, exposed soils will be stabilized with mulch or other approved
methods, to stabilize the exposed surface and limit erosion.
Temporary drainage swales will be established within the site, as necessary, to intercept
and divert storm runoff, and temporary sediment traps (silt fence, wattles, or other approved
materials) will be installed at appropriate intervals along the lengths of these temporary
swales to slow the velocity of runoff flows and to promote deposition of sediment and other
suspended solids.
The permanent stormwater detention basin, which will have capacity to detain the runoff
expected from the 100-year storm impacting the entire tributary area of the site, will serve as
a temporary sediment trap during the construction period. All runoff from the site will be
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directed to the detention basin, and discharge from the detention basin will be controlled. A
silt-fence sediment trap will be constructed within the detention basin, immediately upstream
of the outlet control structure, to intercept sediment and confine it to the detention area. This
sediment trap will be regularly maintained and accumulations of sediment generated from
the site will be removed and properly disposed of.
Inlet protection will be installed at all storm drain inlets into which runoff from the site might
flow.
A vehicle tracking control pad will be constructed at the site construction access point (to be
determined) to limit transport of mud or soil clods from the site onto the public streets via
truck tires.
Existing pavement will be swept and/or flushed, as necessary, to remove dirt and/or debris
that might be tracked beyond the site by local traffic.
In addition to the structural BMPs listed above, several non-structural BMPs will also be
implemented as part of the construction program, in order to limit erosion and sediment
transport.
The construction activities will be advanced in a manner designed to maintain a compact
scope of construction activities within the site at any given time.
Construction activities will be kept tight and excavations will be backfilled as promptly as
practical, in order to limit the number and extent of exposed temporary soil stockpiles.
Soil stockpiles and other exposed soils will be wetted, as necessary, to control dust
generation.
Where it is necessary to have soil stockpiles or other significant areas of exposed soil on
site for an extended period of time, consideration will be given to applying synthetic covers
or durable, membrane-forming surfactants on these surfaces, to limit the potential for
erosion or dust generation.
In addition to soil erosion and sediment transport, a further, but considerably lesser risk of
contaminant migration may be presented due to spills or leaks during equipment fueling and
maintenance, materials handling and storage, or waste disposal. Equipment fueling and
maintenance will be ongoing daily activities, throughout the course of construction activities.
However:
On-site storage of bulk fuels, lubricants and solvents will be minimized.
Where practicality and efficiency necessitate having a certain supply of such potential
contaminants on-site, they will be stored in approved containers and at locations well
removed from drainage flow paths.
If bulk fuel is stored on-site, approved secondary containment facilities will be established at
the storage location.
Fueling and servicing of vehicles and equipment will be conducted in areas that are away
from drainage swales and other potential runoff flow paths.
In the event of a spill or leak during fueling or servicing, contaminated soils will be promptly
collected and properly secured or disposed of in an approved facility. In addition,
appropriate notification will be given and documentation of the cleanup maintained. Contact
numbers for project personnel are provided at the end of this SWMP.
Materials and supplies will be delivered to the site on an ongoing basis to support construction
activities. Appropriate handling and storage procedures will be implemented to limit any
potential for contamination of storm water being discharged from the site.
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Most materials will be delivered to the site as they are needed, and will be promptly
incorporated into the permanent works.
There will be very little on-site materials storage, and only a small percentage of those
materials that are stored on-site will constitute a potential source of contamination.
If it becomes necessary to store potentially hazardous or contaminating materials on-site,
they will be stored in a secure, protected area to minimize the risk of exposure or migration.
As necessary, indoor or covered storage will be provided, and secondary containment will
be established.
Handling and disposal of waste and debris will also be regulated in order to avoid creation of
unnecessary sources of potential contamination.
All subcontractors will be required to maintain a neat and tidy operation, regularly cleaning
up and removing excess materials, construction spoil and debris.
Sanitary waste facilities (Porta-Potties) will be located away from drainage channels and will
be regularly maintained and serviced.
All subcontractors will be required to dispose of construction waste in approved, covered
containers, which will be regularly removed from the site to an approved waste disposal
facility.
Clean-up or decontamination of construction equipment, including washout of concrete
mixers, will be performed in a designated area of the site, well removed from drainage paths
and storm water management facilities.
Potential contaminants from such activities will be contained and, if necessary, collected for
appropriate disposal.
Final Site Stabilization and Long-Term Storm Water Management
As soon as practicable after completion of construction activities in a given area of the site,
permanent landscaping will be installed including trees, shrubs, seeding, sodding, weed barrier,
mulch and plant materials, per the approved Landscape Plan.
If climatic conditions, at any given time, are not suitable for planting and timely establishment of
new vegetation, interim measures will be taken to limit the potential for erosion and sediment
transport, and such measures will be maintained until permanent actions can be effectively
implemented. Such interim measures may include mulching or application of erosion mats
and/or surfactants, particularly on areas that may be prone to erosion.
Inspection and Maintenance of Storm Water Management Facilities
All BMPs, and the site in general, will be inspected at least every 14 days, as well as after
significant storm events throughout the construction period, in order to assess the condition of
storm water management facilities and identify any need for maintenance, repair or replacement
of such facilities, to ensure their continued effectiveness. The frequency of regular inspections
will be not less than bi-weekly. During such inspections, particular attention will be given to
BMPs and other preventative measures where the risk or consequence of a failure is greatest
(e.g., in proximity to materials of significant concentration or toxicity, or closest to the site
discharge point, etc.). All inspections will be fully documented and records will be maintained
on site for reference and confirmation.
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If a need for maintenance, repair or replacement of BMP’s is identified, the nature of the
problem will be documented, along with recommended actions and a timeline for completion of
the work. A follow-up inspection will be made to ensure that appropriate actions have been
taken and to ensure the continued adequacy and effectiveness of the construction stormwater
management system. The follow-up inspection will also be documented and filed with the
original inspection report.
Specific inspection and documentation will also be implemented after any extraordinary incident
or event, such as a spill or leak, with appropriate follow-up to ensure effective containment and
clean-up. The documentation of such an event will also address measures or procedures to be
implemented to avoid a recurrence.
In addition to inspection and incident reports, storm water management system records will also
include:
Documentation of the implementation or removal of BMPs.
Records of communications or correspondence with regulatory personnel
Details of and authorization for modifications to the SWMP
Maintenance and repairs records
Details of preventative maintenance activities
Pertinent photos, sketches and field memos.
Contact Information
The following individuals will be available for contact in the event of an on-site incident, or to
respond to questions regarding the implementation and/or compliance with this SWMP. In the
event that these individuals are no longer associated with the project, or when changes or
additions are made to the relevant contact information, an addendum to this SWMP will be
prepared providing updated information, and that addendum will be incorporated into the
original and all copies of the document.
Owner:
Breckenridge Group Fort Collins Colorado, LLC
1301 S. Capital of TX Hwy
Building B, Suite 201
Austin, TX 78746
(512) 369-3030
Att’n: Ryan Fetgatter
Contractor
Connell Resources, Inc.
7785 Highland Meadows Pkwy, Suite 100
Fort Collins, CO 80528
(970) 223-3151
Att’n: TBD – Project Mgr. (Phone) / Site Sup’t (Phone)
Civil Engineering Consultant
Owen Consulting Group, Inc.
3715 Shallow Pond Drive
Fort Collins, CO 80528
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970-226-0264
Att’n: Mr. Larry Owen, P.E.
In addition to the personnel listed above, the following agencies may/should be contacted in
certain situations:
For emergencies, always dial 911