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Home My WebLink About2021-09-13_Olson_RE_ (MH) stormwater key issue3 From: Olson.Erik To: "fanfh-carole(aleurooa.com" Subject: RE: (MH)stormwater key issue Date: Monday,September 13,2021 1:54:31 PM Hi Carole, Generally,when the code says that we must manage all stormwater"on the lot",it means two things: 1)Volume.The rate of stormwater runoff post-development does not exceed the rate of runoff or discharge from the lot prior to development.This does not mean all water must disappear into the ground on the lot. 2)Quality.Must meet water quality treatment standards. Also note that the stormwater code and stormwater manual requires infiltration of the 10-year storm to the maximum extent practicable,but that really starts to get into the technical part of the design.Please take a look at the stormwater code(LOC 38.25.120)and the stormwater management manual if you're interested in learning more about those specifics:httn://www.ci.oswego.or.us/nublicworks/stormwater-nrogram. I hope this is helpful,but please let me know if you have any other questions about this topic. Best, Erik Original Message From:fanfh-Carole@europa.com[mailto:fanfh-carole@.eurona.com] Sent:Thursday,September 09,2021 4:16 PM To:Olson,Erik<eolson@ci.oswego.or.us> Subject:RE: (MH)stormwater key issue >Hi Erik, I would like to try again-perhaps I can be more clear.Referring to the single sentence below that is in the memo for our MH meeting.Can you provide a description of what is meant by the phrase'manage all stormwater on the lot'. That is a key concept.I need to understand what that simple phrase actually,practically means.Can you help me with that or tell me who might explain it to me. Appreciate it, Thanks, Carole "The stormwater code requires that new developments and redevelopment >projects over a certain size manage all stormwater on the lot." 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 >Stay Connected I Facebook I Twitter I Instagram e-updates > 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 >PUBLIC RECORDS LAW DISCLOSURE This e-mail is a public record of the >City of Lake Oswego and is subject to public disclosure unless exempt >from disclosure under Oregon Public Records Law.This email is subject >to the State Retention Schedule.