SW_Review_Comments.pdf
City of Edmonds
TH
121 5 AVENUE NORTH
EDMONDS, WA 98020
(425) 771-0220
FAX(425) 771-0221
Website: www.ci.edmonds.wa.us
DEVELOPMENT SERVICES DEPARTMENT
Planning Building Engineering
Stormwater Review Comments
Permit : Date:
# BLD20071100 11/28/2007
Project Name/Address:
Ben Holt 1141 Sea Vista Place
Contact Person/Address/Fax:
Ben Holt/22508 76TH AVE W Edmonds, 98026/Phone:
__
(425) 775-4616.
Reviewer: Division:
Blaine Chesterfield Engineering
During review of the subject submittal it was found that the following information,
corrections, or clarifications will need to be addressed:
1.
There are several concerns related to this type of system at this location. The
National Cooperative Soil Survey shows these soils as Alderwood-Urban land
complex, 8 to 15 percent slopes. 1) The Alderwood soils usually have an
impermeable silt layer about 20 to 40 inches below the surface. Per the DOE 1992
Stormwater Management Manual III-3.3.2 General Limitations 2 (GL-2) Depth to
Bedrock, Water Table, or Impermeable Layer: The base of all facilities shall be
located at least three feet above the seasonal high water mark, bedrock (or hardpan),
and/or impermeable layer. If there is not at least three feet it could result in the BMP
not functioning as designed. The silt/hardpan layer, if present, needs to be located
and included in the existing geotechnical report. The existing geotechnical report
should include (soils log) soil types, depths, composition, and depth of silt/hardpan
layer if present. Provide a soils log including the depth of the silt layer or water
table if present.
2.
The drainage plans shows the overflow spreader trench drainage sheetflowing
to the west towards Seavista Place. The overflow will need to have a direct
connection to the catch basin about 100 feet to the Northwest in the cul-de-sac
of Seavista Place.
3.
The calculations check done, during the review, produced a higher peak flow
rate than the Sea Vista drainage report indicated for the 100-yr, 24 hour design
storm. The city uses the Santa Barbara Urban Hydrograph when calculating
the peak discharge rate of the site. The Time of Concentration used in the
calculations was not apparent during the review. Please provide as much
detail as possible to improve the review results and time to completion. For
infiltration designs use the 100-year, 24-hour design storm total precipitation
(3.0 inches in City of Edmonds).
Please resubmit three copies of the revised plans/documents to a Development
Services Coordinator. You may contact me at 425-771-0220 if you have specific
questions regarding these plan corrections.