HomeMy WebLinkAboutGrading Plans - 10/21/2019� I NORTH ERN
ENGINEERING
B1907998 & B1908348
Lot 3 Blk 322 Capitol Hill
Grading plan and drainage memo accepted and permits
released 10/21/2019 DJM
Drainage Memo — 227 West Street
Date: October 21, 2019
Project: 227 West Street
Fort Collins, CO
Attn: Stormwater Staff
City of Fort Collins Stormwater Utility
700 Wood Street
Fort Collins, CO 80521
Stormwater Staff:
Project No. 1685-001
This letter serves to document the proposed drainage impacts of a home addition proposed at
227 West Street in Fort Collins, Colorado.
Project Overview
The project proposes to construct an addition to an existing 1-story home located on the
property.
Existing Site
The existing site functions as a"B" Lot, with drainage sheet flowing from the home to both the
front, back and side lot lines, which then convey the drainage to both the front and back of the
lot. Existing grades in the front yard range between 1%-2%, and grades in the back of the home
vary between 1% and 5%. In addition to the existing home, the existing lot consists of a
concrete pad and small sidewalk from the rear of the house and a 2' sidewalk that connects to
West street. The remainder of t11e site is a grass lawn and 3 mature trees.
The total existing impervious area for the lot is 1,722 sf.
Pro�osed Site
The proposed site will continue to function as a'B' Lot, with drainage from the new residence
being directed to the side lot lines, and then to both the front and back of the lot via "swales"
along the lot line. There are two proposed additions consisting of a detached garage adjacent to
the alley and an extension of the existing home toward West Street. The proposed garage will
replace the current concrete pad that is behind the home and the extension of the main building
will extend into the grass lawn.
FORT COLLINS: 301 North Howes Street, Suite 100, 80521 � 970.221.4158
GREELEY: 820 8t" Street, 80631 � 970.395.9880 � WEB: www.northernengineering.com
� I NORTH ERN
ENGINEERING
The total proposed impervious area for the lot is 3,362 sf. This is an increase of 1,640 sf. The
increase in runoff as a result of this will be negligible, and no adverse impacts to adjacent
properties are anticipated.
Alley Drainage
City staff has noted drainage issues with alleys in the Old Town area. If greater than 350 sf of
imperviousness is added to the alley drainage, additional analysis is required to show adequate
conveyance. For this specific site, an existing concrete pan and connecting sidewalk are being
removed (-506 sf) and being replaced with a garage, patio, and concrete pan (+572 sf). The net
increase in impervious areas is +66 sf, therefore, additional analysis is not required.
Detention
The proposed project is located within the Old Town Master Drainage Basin. Since the
impervious area increases less than 5000-sf, no detention is required for the site.
Water Qualit�
Water Quality for the site is being provided by releasing concentrated flows from the roof into
landscaped areas that allow stormwater runoff to infiltrate surrounding soils. Stormwater that
is unable to infiltrate is slowly passed through vegetated areas, further removing stormwater
contaminates before stormwater leaves the property.
An exhibit has been provided to illustrate the existing and proposed impervious areas. Please
feel free to contact us if you have any questions.
Sincerely,
Mason Ruebel
Project Engineer
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Danny Weber, PE
Project Engineer
FORT COLLINS: 301 North Howes Street, Suite 100, 80521 � 970.221.4158
GREELEY: 820 8t" Street, 80631 � 970.395.9880 � WEB: www.northernengineering.com
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