JWM&A Letter 08-28-07 001JWM&A
Jerome W. Morrisseae 8 Associates Inc., P.S.
I ]00 Cooper Point Road SW, #9-2, Olympia, WA 98502-1110
^60)352-94561 FA%13607352-9990
August 28, 2007
Mr. Jim Gibson, PE
Development Review Engineer
P.O. Box 479
Yelm, WA 98597
Re: Yelm High School/Portable Classrooms
Dear Mr. Gibson:
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The intent of this letter is to help obtain an occupancy permit for two portable classroom
buildings at Yelm High School by way of addressing the ability of an existing STEP tank to
accommodate the sanitary sewage flow from the portable classroom buildings. The buildings are
located southerly of the main building and westerly of the Auto-Shop. The existing STEP tank
noted above currently serves only the Auto-Shop. The portable buildings are identified "A" and
"B" on the attached Sheet C3.0.
Each classroom building houses two classrooms. Each classroom will be able to accommodate
30 students. Although the buildings aze plumbed, the only plumbing fixtures in the buildings
will be I hand wash sink per classroom. The students that will be in these buildings aze now
accommodated in several aeeas within the Main Building, Commons, Career Planning, and
Performing Arts. When the portable classrooms are available, the students will still be primarily
in the Main Building and will use the restrooms in the main building. Adding the portable
classroom buildings does not add to the total student load on campus. Adding the portable
classroom buildings does allow utilization of the Commons, Cazeer Planning, and Performing
Arts areas within the Main Building for their intended purposes rather than as classroom areas.
"fhe sanitary sewage generation rate at these portable classroom buildings will be considerably
less than at Main Building since only hand wash sinks and no lavatories are provided in the
classroom building.
The anticipated peak daily wastewater generation rate from the 4 hand wash sinks in [he 2
classroom buildings is:
20 sec wash lime/capita x Imin./60 sec x 2.2 gal./min. x 4 room x 30 capita/room = 88 gal.
o Where 20 second hand wash time is the recommended time for handwashing by
the Center for Disease Control. Also a short survey of J.W. Morrissette
employees disclosed an average handwash time of 20 seconds with water running
Mr. Jim Gibson, PE
August 28, 2007
Page 2 of 2
when the employees were asked to thoroughly wash their hands without being
told the purpose of the exercise.
o Where the Federal Energy Policy Act of 1992 requires kitchen type faucets and
lavatory type to dischazge 2.2 gpm at 60 psi.
o Where it is acknowledged that most student and staff handwashing at schools
occurs in restrooms and that relatively few persons wash their hands at
handwashing sinks in classrooms.
The existing 1,500 gallon STEP tank currently serves the Auto Shop. The approved design
calculations for wastewater generation at the Auto Shop noted that for the 37 students and staff
(capita), the design flow was 37 capita x 16 gallons per capita per day = 592 gpd.
The total design flow for the two classroom buildings and the Auto Shop and is 88 gpd + 592
gpd = 680 gpd. Using the same criteria as the sizing calculation as was used for the Auto Shop
alone, the required STEP tank volume is 680 gpd z 1.5 = 1,020 gallons. Since the existing STEP
tank has a volume of 1,500 gallons, it has adequate volume to accommodate the 4 sinks in the 2
classroom buildings.
Should you have any questions or comments, please do not hesitate to contact me.
Very truly yours
Je~ro~/m)e W. Morrissette & Associates Inc., P.S.
„ ~y. ~~~~
Doug Eklund, P.F,.
Senior Project Engineer
Attachment