bld20130919-Meadowview Estates-E2-storm.pdf
From:Shuster, Jerry
To:kent@halvorsonconstruction.com
Cc:Lien, Kernen; McConnell, Jeanie
Subject:BLD20130919 -Halvorson - Stomwater Review
Date:Tuesday, January 14, 2014 2:45:18 PM
Attachments:15625_75th_PL_W.pdf
20131212 HWA Meadowview Peer Review.pdf
For this permit I reviewed the following:
Large Site Drainage Report , Meadowdale Estates, LDC, Inc. November 14, 2013
Plan Sheets RD-01, RD-04, and DT-01
Drainage Report
Section 4, Flow Control Analysis – Exhibit 3 shows an offsite contribution area for the City
system to be 0.96 acres. This is not correct. In 2009, a new home was built just
downstream of this proposed development at 15631 75TH PL W. The applicant had a
downstream capacity analysis performed to try and get a detention waver. That analysis
used a 14.6 acre drainage basin area for the City system. This estimate is in line with past
City basin plans. That analysis also found that the downstream pipe with the smallest
capacity was the one between your node # 8 and node #9 at 4.2 cfs compared to your 5.1
cfs (see enclosed). Note that this was done under the previous stormwater code (25-year
peak flow standard).
The analysis for the Halvorson site does not include: Time of Concentration exhibits and
calculations, rainfall values, and nodes 1 through 5 are not shown on the exhibits. These
should be included. Also, the manhole just west of node #0 receives flow from the south,
which need to be accounted for in the calculations.
Due the steepness of the proposed storm pipes on the site (up to 15.4%) and where it
th
connect to the City system on 75 Ave N., high velocities of flow may cause surcharging of
CBs. Please calculate hydraulic grade lines for the system from the proposed development
down to node #8.
Plan Sheets
RD-01 – An additional set of catch basin should be placed on the driveway there it turns
towards the north and they should be connected to the proposed downstream system. The
spacing between catch basis is current too long for a 12% + slope. This could cause bypass
and flooding down the proposed driveway to existing garage.
RD-04 – The pipe material used should be on the plans.
DT-01 – The Stomfilter detail needs to include the data from the Drainage Report: the
number of cartridges, the media in the cartridges, and the design flow rate. This detail does
not include the 22 inch tall cartridges that can handle 9 gpm specified in the Drainage
Report.
Also, please respond to the last comment on page 4 from the enclosed HWA report regarding
geotechnical issues related to construction of the proposed stormwater system.
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Jerry.Shuster@edmondswa.gov