20070404 PW Ltr 06032010June 3, 2010
Gorclon Thomas Honeywell
Attn: William'T. Lynn
1201 Pacific Ave S. Ste. 2100
"Tacoma, WA 98402
Public Works Department
Physical Address: 901 Rhoton Road SE
Mailing Address: 105 Yelm Ave West
Yehn, WA 98597
(360) 458 -84oG Fax: (360) 458 -8417
Web: www.cr yelmma.us
Re: Creek Street Mixed -Use Rater and Seiner Issues
Dear Mr. Lynn,
The City of Yehn Public Works Department has reviewed your letter of May 4, 2010 and responds as
follows regarcling the above referencecl project.
Watcr SysWni Backf ow Protection :.
WAG 246 -290 -490, gives the purveyor the option to establish Cross Connection Control program
requirements that are more stringent then the requirements specified in the WAC 246 -290 -490. The City
has required a reduced pressure backflow assembly (RP13A) for multi- family buildings since the Crass
Connection Control Program was implemented.
1. A reduced pressure back{low assembly has two inclependent check valves with a relief valve.
Iu case the cheek valve would fail during a backflow, the relief valve will open, discharging
the water from the assembly and not allow the water to rc -enter the distribution system.
2. In the Cross Connection Control Manual, Sixth Edition, Chapter 5, Tall Buildings (over 30
feet), it states: 'T is not necessmy for the water distribution system pressure to fall to zero for
a bacicflow to occur. The potential backpressure on the purveyor's disnribution system which
could be cxerted by the water in the customer's plumbing system is a fametion of the height of
the piping in the customer's system. Some tall building use booster pumps to provide
adequate pressure to upper floors, or to fill covered roof storage tanks. The booster pumps
may be equipped with hydropneumatic tomes, that also provide limited water storage.
Wheneve� the water pressure (I�ydrazdic gradient) falls below the elevation of a plumbing
fixture, bucksiplz017ag6 conditions occur. The taller the building, the greater the likelihood
that backpressure could be exerted when there is a reduction in the pressure in the
distribution system. This increased prohability of back low, increases the risk assessment f )
tall building. "
Due to the height of the building, our analysis concluded that a bachllow assembly is
required.
_Setiyer Tank_Sir.in
The City again reviewed the calculations for tank sizing criteria provided by Timothy D. I lolderman, P.E.
with Sound Gigineering (enclose(i). We find the assumptions and recommendation (provided by the
applicant) consistent with our City Development Guidelines and are not able to alter the sizing and
configuration of the tanks as requested in your May 4 °i letter.
If you have any further questions in this regard, please contact me at (360) 458 -8499.
Sincerely,
Tim Peterson
Public Works Director
Cc: Grant Beck, Conununity Development Director
Jim Doty, Wastewater Treatment Plant Manager
Kevin Ray, Goss Connection Control Specialist
Amy I -lead, Shea Carr.lewell
Gnel: Sound I;ogineering, Inc. Report, January 12, 2010