HomeMy WebLinkAbout2021-08-30_Olson_RE_ (MH) stormwater key issue From: Olson,Erik
To: "fanfh-carole(aleurooa.com";Sieael,Scot
Cc: bobandmianon(cacomcast.net;randvarthur7(caamail.net
Subject: RE: (MH)stormwater key issue
Date: Monday,August 30,2021 2:31:18 PM
Carole,
I agree that more could be said about stormwater in the Key Issues document;unfortunately,given the large scope
of the issues presented to the MHCAC for consideration by Council/the Planning Commission,we were forced to
focus the discussion on elements within the Community Development Code that could be modified to better address
stormwater concerns.While any recommendation the Committee makes to place limitations on impervious surface
or require landscaping would be consistent with the Stormwater Code and best management practices for
stormwater generally,a re-examination of the Stormwater Code itself would generally be outside of the scope of this
Committee's work.
Regardless,the Committee could certainly identify the Stormwater Code as a topic for further discussion that may
be unable to be fully addressed in our meetings but should still remain on the radar as the project proceeds.We had
discussed a system to identify topics like this previously,but please let me know if there are any other
recommendations you may have to ensure we don't lose sight of potential solutions outside the scope of what we
have been tasked to cover.
With respect to the specific situation you are referring to,I'll just quickly point out that those pipes are part of the
design of stormwater facilities to generally ensure that post-development runoff rates do not exceed pre-
development runoff rates;one of these pipes manages stormwater discharge from the lot,and the other is an
emergency overflow for when the facility is clogged.The owner is generally responsible for making sure the facility
operates correctly and are required to sign a maintenance agreement which runs with the land.
If the Committee requires further information or additional background on this issue I'm happy to coordinate with
Sonja Johnson in Engineering for a more complete response.
Thank you,
Erik Olson
Senior Planner
City of Lake Oswego
PO Box 369
Lake Oswego,OR 97034
tel: 503.697.6524
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Original Message
From:fanfh-carole@europa.com[mailto:fanfh-carole@.eurona.com]
Sent:Tuesday,August 17,2021 2:45 PM
To:Olson,Erik<eolson@ci.oswego.or.us>; Siegel,Scot<ssiegel@ci.oswego.or.us>
Cc:bobandmignon@comcast.net;randyarthur7@gmail.net
Subject:(MH)stormwater key issue
Hi Erik,
Knowing that stormwater is likely shifted to our Aug.24th MH meeting,I would like to cover an item in the staff
Key Issue#3 memo.A quote from the memo below:
"...The stormwater code requires that new developments and redevelopment projects over a certain size manage all
stormwater on the lot.These requirements are triggered for any project that creates more than 1,000 square feet of
new impervious surface area,and any remodel that alters
3,000 square feet or more of existing imperious area.The code requires applicants to submit a site assessment,
stormwater system design,and other analyses to demonstrate compliance with the code...."
This functionally tells our committee a message about structures,sizing,and stormwater,that when it comes to
code,LO has got it taken care of on site or the development doesn't happen.That certainly gives us as committee
members a sense of reliance and security when it comes to new builds in our neighborhoods.However the statement
I have quoted seems to be lacking something,because it is not covering a current stormwater reality.I have attached
the image for your reference.
In this new build,you will see that there are two pipes openings in the cement stormwater holding tank.All site
generated stormwater is directed into this holding tank.The top pipe opening is an infill for a french drain off a to be
poured driveway.The lower pipe opening has been trenched to pour into the sensitive lands on the far side of the
alley.
5.2.Downstream Conveyance
Treated stormwater runoff leaving the lined vegetated flow through planter will be routed through a 0.50-inch flow
control orifice prior to being conveyed to the new outfall on the east side of the public alley.The planned storm
outfall location will direct stormwater to the existing Tryon Creek drainage. Should the planters' flow control orifice
become plugged,overflow stormwater will be conveyed through the planter via an overflow riser located within the
planter.
I have reviewed the required stormwater report.This approach was staff approved.The developer was not told to
right size the building for the lot such that expected development created runoff would be contained on site.The
developer was given permission to run all site stormwater through a pipe into existing Tryon Creek drainage in an
area that is sensitive lands. So back to my comment,that apparently there is more that needs to be said about
stormwater code that is not in the Key Issues#3 statement.
I prefer the committee get a full understanding of our stormwater code approach before we start making
recommendations about other code that directs development right sizing.We need to understand when staff
approves systems for handling stormwater that is not contained on site especially when the runoff is onto sensitive
lands.I'm not arguing you shouldn't put stormwater runoff from a new home into sensitive lands.What I am saying
is that there is something missing from the description of LO code as stated and perhaps we can get more delineation
before the meeting next week.It would be good for our committee to walk though this example next week with
understanding rather than confusion.
Thanks,
Carole