20190278 SCJ LTR 06.28.2019From: Derek McCoy
Sent: Friday, June 28, 2019 9:51 AM
To: Charlie Severs, P.E. (charlie.severs@scjalliance.com)
Subject: YCS Facilities & Maintenance Bldg
Attachments: Sewer Details.pdf; Trap Pond - 1.jpg; Trap Pond - 2.jpg; Trap Pond - 3.jpg;
Water Details.pdf
Charlie,
The Civil Plan Review is almost complete and I expect to send the formal comment letter and markups
out early next week. There are a couple of items that I am attaching that I hope will assist you in a quick
turnaround. The City is in the middle of updating our Development Guidelines and Standard Details.
While we haven’t gotten to updated Transportation details we have more current Sewer and Water
details. They are included in the attachments.
While reviewing the WWHM Report in the Stormwater Site Plan I noticed that there were quite a few
“Fails” in the Duration Flows section of the report. I also noticed that while 100% infiltration was being
shown, there was still 0.003 ac-ft of flow going through the theoretical riser.
Bottom Line Up Front (BLUF): The proposed pond is acceptable but some minor correction in the Design
Calculations (WWHM Report) will better support it.
The Trapezoidal Pond Module assumes a flat bottom so you enter in the 4 Side Slopes, Top, Bottom,
Left, and Right. 0 (0.000001:1) was entered in the Top Side Slope box reflecting a vertical side wall. This
does not match with the proposed pond contours. Precipitation should also be applied to the pond for a
more conservative model. I suspected that the proposed pond design would achieve 100% infiltration
with 0 flow through the riser so I played around in WWHM to test this. I have included three screenshots
of different iterations I tried.
· Trap Pond - 1: This is where I tested that I had entered the data to get the same results in your
WWHM Report. The only part that wasn’t readily apparent from the report was that
precipitation nor evaporation were being applied to the pond.
· Trap Pond - 2: I entered 3 in the Tope Side Slope box and applied precipitation and evaporation
to the pond and got 100% - 0 flow. While I did not include a screenshot of it, I also ran a more
conservative trial with only precipitation being applied to the pond and got the same successful
result.
· Trap Pond -3: I also tested a 7’ rather than 7.25’ bottom length and noticed that this also
passed.
As of today I am only waiting for comments from Sewer and Building/Fire but I don’t anticipate there to
be anything to complicated so I hope to be able to complete the review process and have the comment
letter sent out middle of next week.
Hope you had a good week and great weekend!
Derek M. McCoy, P.E.
Community and Economic Development - Civil Review Engineer
City of Yelm | 106 2nd Street SE | Yelm, WA 98597
Office: (360) 458-8132 | Cell: (253) 278-2937
Email: derekm@yelmwa.gov
Website: www.yelmwa.gov