STORM1_BLD20190651_714 13th Way SWTo:Applicant
Date:July 5, 2019
Project Name:Jenkins Lot 3
Permit Number:BLD20190651
Address:714 13th Way SW
Review Type:Building (SFR)
Submittal Date:6/4/2019
Reviewer: Zack Richardson, PECity of Edmonds, Stormwater Engineer
Recommendation:I recommend that BLD20190651 be withheld until the comments below are adequately addressed.
Review Comments:
It appears the proposal for this lot has increased the impervious area and decreased the drywall volume since the previous plat approval; the minimum value now used (by simplified sizing)
meets code but represents a revision from the previously approved drainage planwhich requires additional attention, most notably the potential for generating an overflow at this location.
Simplified sizing to meet MR #5 does not ensure that a regular overflow will not occur here; for this reason these systems require a piped overflow. If system remains as currently designed,
update plans to provide a piped overflow connection to the city system.
Alternatively, the applicant can demonstrate that the system achieves 100% infiltration, typically requiring a WWHM model with the field measured infiltration rate.
As an alternative to the WWHM model, the City will accept a system which doubles the minimum sizing per simplified sizing (similar to the original approved design) in order to be considered
100% infiltration.
For the high infiltration rates at this site, the drywells may not need upsizing when design with a true infiltration rate, however it is a documentation step which the engineer must
complete in lieu of the double volume condition.
It appears the callout for 31 LF-6” PVC is no longer pointing to an improvement; updated as needed.
Add a note to the plans to make more clear the need to grade the driveway to discharge toward, and align with the flow line of, Tract 999.
Show protective construction fencing around the drywell areas.
If fencing cannot be feasibly located during construction, add notes to over excavate and obtain geotech approval of the subgrade prior to backfilling drywells.
Provide detail or specification enough for contractor to install soils meeting the requirements of BMP T5.13 (City detail SD-642).
Update drywell details to be SD-638 or update plan details to provide more of the required and shown elements from the City version:
Update “marked center” to provide an observation pipe to the bottom of the facility with detail as/where needed for construction.
Extend distribution pipe through entire width of drywell and bring to surface with clean-out with detail as/where needed for construction.
Callout/show a push-on tee or downturned elbow in the yard drain upstream of the drywells with detail as/where needed for construction.
Identify 12” minimum cover depth, provide a bottom of rock elevation, and ensure the two are consistent with proposed finish grade.