HomeMy WebLinkAboutFile Documents.1010 E Hyman Ave.0025-2022-BCHO (16) RI VERC rnY
C O N S U LTA N T S
MEMORANDUM
Re: 1010 E. Hyman Avenue,Aspen: Drywell Setback Variance Request
To: Carly McGowan, E.I.T., Project Manager II, City of Aspen Engineering Department
From: Paul Southworth, P.E. River City Consultants
Date: February 24, 2023
River City Consultants has prepared Grading and Drainage plans for site revisions to accommodate
proposed remodel at 1010 E. Hyman Avenue,Aspen, under separate cover. This memorandum is to
request a variance to City requirements for setbacks for drywells installed for storm water management.
The Property at 1010 E. Hyman Ave,Aspen, Colorado, is a 6000 square foot lot with a residential duplex
and associated utilities, landscaping, and hardscape. The existing structure had significant water
infiltration into the lower level below grade. The primary impetus of the drainage system design is to
maximize conveying drainage from the site surface runoff, and particularly the roof drainage,to an on-
site drywell for subsurface disposal. Because of this significant problem with the existing structure,the
design exceeds the City of Aspen requirements,to remedy the existing condition of water entering the
below-grade level of the duplex.The primary drywell was engineered to maximize the infiltration
capacity as far away from the foundation as possible to alleviate the lower level infiltration to the
maximum extent practicable. In additions,there is a separate drywell provided for discharge of sub-
surface foundation drain to provide separation of surface and subsurface drainage, which eliminates the
potential for primary drainage to backup into the foundation drains, which is in accordance with
engineering best practices.
Kumar&Associates prepared a soils report for the project, September 2021 that recommended
temporary shoring methods for the proposed work to prevent impact to adjacent improvements. This
report also recommended drywells be located a minimum of 5-feet off foundations. The report noted
soils are free draining granular soils with a percolation rate of 2-minutes per inch.The dry wells are
designed to discharge no higher than the basement floor level per the soils report recommendations.
Due to the small footprint available for stormwater improvements,the need to not disturb property
owned by abutters (including the duplex owner of 1014 E Hyman Ave),the existing structure locations of
the duplex and neighboring property, and to preserve mature pine trees and shrubs at the site, an
acceptable limits of disturbance was established for site improvements and a micro pile wall was
constructed at limits of disturbance to contain all site work. This requirement limited available area for
drywell construction to the southwest corner of the site.
The resultant available area for construction of the two drywells, after consideration of existing site
dimensions, structural improvements, mature vegetation, and micro pile wall construction, resulted in
setbacks to foundation and property lines less than the 10-foot required by City of Aspen.The two
drywells were sited within the allowable limits of disturbance to meet a minimum 5-foot setback to
foundation as noted in the soils report. This resulted in setbacks from drywells to E. Hyman prop E(l EI ED
03/01/2023
ASPEN
BUILDING DEPARTMENT
rllPilLRIVERCITY
C O N S U L T A N T S
line (right-of-way) of 4.5-feet, to foundation at 5.7-feet and to west property line at 5.3-feet. To
eliminate the potential for underground cross lot water flow,the western half of the primary drywell
will have its perforations plugged by a coating of hydraulic waterproofing cement on the inside of the
drywell.The foundation drywell is further than 10-ft from the west property line and will not have its
perforations sealed. Calculations provided in the drainage report prove that the percolation area
requirement can still be met when subtracting out the stone on the western side of the primary dry well
as well as the stone that overlaps with the 4-foot foundation drain dry well percolation area.
A variance is requested to approve these reduced setbacks as noted, and as shown on attached Exhibit,
to accommodate all site constraints and meet stormwater management requirements. Due to the
distance to street improvements in E. Hyman (16-feet to sidewalk and 24-feet to asphalt) and due to the
fast-draining subsoils as noted in the soils report, reduced setbacks will not have detrimental impact to
adjacent properties.
Attachments: Exhibit 1—Setback Distances
_` ���'A`,, Reviewed by Engineering
pDO U� 411b 03/24/2023 9:35:19 AM
Ar ram. 0*s0U.c:/fr
"It should be known that this review shall not
5 Cr:.0 ti:y.FQ �j relieve the applicant of their responsibility to
i r�� °�; j comply with the requirements of the City of
i i.f 6012 —:, Aspen.The review and approval by the City is
0 -( e +,1 offered only to assist the applicant's
�,••�2y/23. _ understanding of the applicable Engineering
AN, .. ..0 -v 47 requirements."The issuance of a permit based
1I1illi dat shall
k.s/0f ALe .e.— not prevent the City of Aspen from‘Ac., 4.-7 on construction documents andh rer equiring the
correction of errors in the construction
Paul J. Southworth, P.E. documents and other data.
CO Professional Engineer No 60123
RECEIVED
03/01/2023
ASPEN
BUILDING DEPARTMENT
84" DIA DRYWELL
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(DOWNSPOUTS)
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48" DIA DRYWELL III
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GENERAL NOTES
1. Drywells shall be surrounded by 18-inches of 3/4", washed,
4 0 2 4 crushed stone and wrapped in a non-woven, geotextile.
-
Bottom of drywells shall be set at Elev. 7927.25. 1.
Perforations shall not extend above elevation 7931.25.
( IN FEET ) The perforations on the western half of the 84" drywell
CONTOUR INTERVAL = 1 FOOT shall be sealed with hydraulic cement (shaded region).
1010 East Hyman Avenue Figure RED IVED
Exhibit 1 RIv 9 J �?3
DATE: 24.FEB.2023 1" = 4' ASPEN
S:\PROJECTS\2008 Monique Agnew Architecture\001 1010 Hyman\Design\DWG\05—Sheet\2008-001 Variance Exhibit.dwg LEX 1J 2/26/202BUILDING DEPARTMENT