HomeMy WebLinkAboutFile Documents.534 E Cooper Ave.0003.2017 (24).ACBKJanuary 31, 2020
Mike Horvath, P.E.
City of Aspen Engineer II
201 N. Mill Street
Aspen, CO 81611
Subject: 534 East Cooper (0003.2017.ACBK)
Request for Variances
SE Project No. 16022
Dear Mr. Horvath,
The proposed primarily onsite drainage and water quality mitigation strategy for the above
referenced project is to route all roof drainage to a new drywell within beneath the
basement of the proposed structure. The proposed drywell was designed to comply with
the requirements of Section 8.5.4.2 of the City of Aspen's Urban Runoff Management
Plan, 2014 (URMP). The proposed mitigation strategy and detention design were reviewed
and approved by City Staff as part of the building permit approval process.
Subsequent to building permit approval, Sopris Engineering expressed concerns that the
perforated riser pipe within the intermediate drywell lid may artificially constrict design
flows entering the lower chamber, causing the emergency overflow pumps to engage
during smaller storm events than designed. SE presented these concerns to City Staff and
a site visit was performed on October 9, 2019 to witness a flow test of the drywell installed
as designed with the original permit documents. During this site visit all parties agreed that
a revision to the City's detail for the interior overflow "gooseneck" to increase the available
flowrate into the lower drywell chamber would be prudent. Please see the attached
revision implemented. All other components of the drywell to include the 10- and 100 -year
overflow pumps as well as the emergency alarm float remain unchanged.
Additionally, SE was made aware that the installed foundation drain lines were connected
to the proposed stormwater drywell, without prior consultation. The basement slab
elevation is approximately 7916.5+/-, while the top of footing elevations are constructed
just below the slab, at an elevation of approximately 7915.8+/-. The constructed dry well
sump elevation is well below the footings, at an elevation of 7902.1+/ Furthermore, there
are is a duplex pump system with control floats designed to discharge flows that exceed
the capacity of the dry well. Both float elevations that control the overflow pumps are set
in excess of 2.5' below the bottom of footing. Please refer to the attached document that
illustrates the relationship between existing footers and recently installed dry well. The
contractor has performed routine inspections of the existing foundation drains and has not
observed any water to date, including a period of heavy rain where the proposed
hardscape had yet to be installed around the building. Lastly, the existing dry well that
was replaced with the new construction had footing drains connected within it. Historically
there were no issues nor where there any areas of concern identified during the recent
demo work. Accordingly, SE does not see any issues with terminating the foundation
drains within the recently installed dry well and is requesting a variance given the nature of
the project; however we also understand that this approval shall not set a precedent for
future projects and that the City typically will not allow this cross connection to occur.
Sincerely,
Sopris Engineering, LLC
Jesse K Swann, PE
Principal
Encl: Dry Well Riser Detail
Foundation Drain/Dry Well Detail
Pn
DATE 2/fir 22Zo
BY
502 Main Street • Suite A3 • Carbondale, CO 81623 •
(970) 704.0311 • Fax (970) 704-0313
SOPRIS
ENGINEERING 9
LLC
civil consultants
DRY WELL RISER PIPE DETAIL
534 E COOPER-BOOGIES
ASPEN, STATE OF COLORADO.
SHEET 1 OF 2
6" GOOSE NECK & RISER
HIGH WATER
PIPE; RE, TO BLOW UP
ALARM
DETAIL SHEET 2 OF 2
FLOAT
FLOAT
TREE
DUAL
PUMPS
SOPRIS ENGINEERING - LLC
CIVIL CONSULTANTS
S02 MAIN STREET, SUITE A3
CARBONDALE, COLORADO 81623
(9)D) 7040311
G'A2016A16022VCIVILACIVIL DWGSVPL07VC6.0 STE DETAIL£.oev_-
DRY WELL RISER PIPE DETAIL
534 E COOPER -BOOGIES
ASPEN, STATE OF COLORADO.
SHEET 2 OF 2
EXTEND 6" PERFORATED PVC TO
HIGH WATER ALARM FLOAT. WRAP
ENTIRE RISER PIPE & GOOSE NECK
WITH FILTER FABRIC: RE.. TO NOTES
5" PVC TEE WI 90° BEND TO
CREATE GOOSE NECK TURN
DOWN 8 RISER PIPE _Tr�
6" PVC RISER WI (2) 90°
BENDS TO CREATE GOOSE
<' 2„ NECK SET 12" FROM TOP
..
_T 12"
LID', RE. TO RISER
Z" NOTES
2'•
INTERMEDIATE LID
6' THREADED COUPLING CAST IN LID
RISER NOTES.
1. PERFORATE & PVC WITH 1" HOLES @ 2" O.C. (X&V).
2. PLACE A SINGLE WRAP OF FILTER SOCK AROUND RISER PIPE AND ZIP TIE IN
PLACE WITHOUT COVERING PIPE INTAKE @ GOOSE NECK.
3. NON -WOVEN FABRIC TO BE MIRAFI Mscape E (OR PRE -APPROVED EQUAL)
SOPRIS ENGINEERING - LLC
CIVIL CONSULTANTS
502 MAIN STREET, SUITE A3
CARBONDALE, COLORADO 81623
(9]0)104-0311
Dry Well Foundation Drain
534 E COOPER -BOOGIES
ASPEN, STATE OF COLORADO.
SHEET 1 OF 1
TOP OF
EXISTING
FOOTER ITOP OF SLAB
EXISTING
FOUNDATION DRAIN
INTERCEPTED UNDER
SLAB & ROUTED TO
NEW DRY WELL
7916.5+
HW ALARM = 7914.65
-X100-YR PUMP ON/OFF= 7914.11
s10 YR PUMP ON/OFF=7913.11
gPUMPS OFF = 7912.61
2W QSE = 7912.12
- o c
091aSN40[e]1,11440IP[eng114
CIVIL CONSULTANTS
502 MAIN STREET, SUITE A3
CARBONDALE, COLORADO $1623
(970) 7040311
STC NT -113 ._._