HomeMy WebLinkAboutFile Documents.614 North St.0248.2017 (51).ARBK
592 Highway 133 • Carbondale, CO 81623 • 517.282.3656 • www.rfeng.biz •
adamr@rfeng.biz
From: Adam Racette, PE
Principal
Roaring Fork Engineering
(517) 282-3656
adamr@rfeng.biz
To: Justin Forman, PE, CFM
Senior Project Manager I
City of Aspen Engineering Department
(970) 429-2783
Justin.forman@cityofaspen.com
February 28, 2018
Permit No. 0248.2017.ARBK
614 W. North Street – BMP Memorandum
Justin,
This memorandum outlines the stormwater Best Management Practice’s (BMP’s) analyzed and
implemented for the 614 W. North Street project in Aspen, CO. Below is a summary of the analysis for
this specific site.
The lot size for this property is 4,065 square feet (sf), with a total impervious area of 2,293 sf that will be
required to be captured and detained per the City of Aspen Urban Runoff Management Plan (URMP)
requirements. Pervious paver areas were utilized as much as possible to reduce runoff volumes. It is a
requirement on this site to fully detain the collected runoff since there is no public storm infrastructure
servicing this area and there is no path to route stormwater offsite without affecting neighboring
properties. The irrigation ditch located along North Street cannot be used as an overflow path. Since full
detention is required, this omits the possibly of the following BMP’s to be utilized for detention:
- Sedimentation Vault
- Grass Swales
- Bioretention Pond
- Planter Boxes
- Grass Buffers
- Water Quality Vault
Due to the site constraints, a limited amount of onsite BMP’s can be utilized in order to fully detain
stormwater runoff. Below are BMP’s that are not feasible for the site due to size constraints:
- Constructed Wetland Channel
- Extended Detention Basin
- Constructed Wetlands Basin
2/27/2018
614 W. North Street BMP Memo February 28, 2018
Page 2 of 2
In order to reduce the amount of runoff from impervious areas, pervious pavers were utilized for both of
the east and southeast patios. Roaring Fork Engineering analyzed screened rock beds for full detention
under the pervious paver patios. However, the east patio is located near the proposed foundation and a
neighboring residence. With the requirement to infiltrate a minimum 10 feet from a proposed structure, a
screened rock bed on the east side of the residence cannot be implemented. The pervious paver patio on
the southeastern corner of the residence cannot provide enough storage or infiltration area to completely
drain in 24 hours for full detention of a 100-year storm event. It is also within 10’ of the proposed
foundation.
The east and west sides of the residence are very close to the property line and neighboring homes. This
removes the potential for any BMP’s on the east and west sides of the residence since stormwater is not
allowed to infiltrate towards neighboring structures.
The north side of the residence is also very close to the property line and all utility services, besides
water. The driveway will not be removed and replaced with this project. The northern side of the property
cannot support full detention BMPs.
The south to southeast portion of the property has the driplines of two large, existing trees that are located
in the North Street ROW. These trees cannot be removed. The existing water service line is also a
constraint within the southern edge of the property. This leaves the southwestern corner of the property as
the only feasible area for a subsurface BMP to be implemented.
Since the collected runoff is required to be fully detained, a drywell is the only potential BMP to be
utilized for this project after reviewing the approved BMP’s within the City of Aspen URMP and the site
constraints. None of the previous locations discussed can support a drywell, besides the southwest corner
of the property. The drywell cannot be located anywhere on the property where it is not 10 feet from a
foundation or property line/right-of-way.
The proposed drywell will be required to have a diameter of 5-feet and a depth of 16-feet, since the
storage depth is the area within the drywell from the lowest invert to the bottom. The drywell will be lined
on the side facing the residence so that water will not infiltrate towards the foundation of the residence.
All runoff will infiltrate from the bottom and the side facing the North Street ROW of the drywell.
Feel free to call with any questions.
Adam Racette
2/27/2018