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Vice-President Legislative Report
John Perales
Well
it's time for another ASPE convention I do hope all the members of The
Orange County Chapter get to come out to the EPE. I could not tell you when the next time
this is event will be in the Southern California region. So please come out and enjoy all the
festivities. I will include in next
month's newsletter a summary of the results of the by-law and officer
elections as well as a few stories of the fun we are having in the
evenings.
I
thought I would use this section of my article to post up the results and
some discussions of the IAPMO vote to repeal the FOG sizing in the new
code. This vote
went about 200 - 4 in favor of retaining the new sizing method used
in the 2006 UPC. A group of manufactures
are trying to revert to using the 'Meals per Hour' way of sizing Gravity
Grease Interceptors. Here are some
arguments for the continued use of table 10-3 in the 2006 UPC, used to make
the arguments which secured the overwhelming victory in the last IAPMO
meeting.
Debunking the Arguments Supporting Chapter 10 -
Item #152 Sizing of Gravity Grease Interceptors (GGIs)
I. Argument #1 - DFU’s do not equal GPMs
A. If
this were true, then Table 7-5 and Hunter’s curve would be flawed since
DFUs are equated to flow capacity (GPMs) in order to determine pipe sizes.
While there may not be a singular value equivalent of GPM per DFU, there is
a range that varies with the number of fixture units and associated
diversity that allows the correlation between fixture units, GPM, and the
associated pipe size for both water and waste. This correlation has worked
flawlessly for over 80 years.
B.
The original Table 10-3 developed during the
2005 FOG Task Group meetings was an expanded table that showed GPMs
(below). This expanded table was a
significant element of the substantiation.
The 2005 FOG Task Group chose to shrink the final table because the
expanded table was not necessary for the users of the Code. The 2007 FOG Task Group supported this as
well. If the Technical Committee prefers the expanded Table, it could be
used to replace the abbreviated Table 10-3 presently in the 2006 UPC.
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Table 10-3 Expanded
GRAVITY GREASE
INTERCEPTOR SIZING
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DFUs
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Pipe Size
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Slope
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Flow (1)
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Calculated Size
(2)
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Nominal Size
(3)
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8
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2"
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2%
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10 gpm
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300 gallons
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500 gallons
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35
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3"
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2%
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29 gpm
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870 gallons
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1,000 gallons
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172
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4"
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1%
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44 gpm
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1,320 gallons
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1,500 gallons
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216
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4"
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2%
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62 gpm
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1,860 gallons
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2.000 gallons
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342
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5"
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1%
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80 gpm
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2,400 gallons
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3,000
gallons
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428
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5"
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2%
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120 gpm
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3,600 gallons
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4,000
gallons
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576
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6"
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1%
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140 gpm
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4,200 gallons
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5,000
gallons
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720
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6"
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2%
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190 gpm
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5,700 gallons
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7,500
gallons
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Notes:
(1)
Based on UPC “Useful Tables” for flow in half-full pipes (ref: Mohinder Nayyar Piping
Handbook)
(2)
Based on 30 minutes retention time (ref:
Metcalf and Eddy 3rd Edition, Small and Decentralized
Wastewater Management Systems, 1998)
(3)
Rounded up to nominal capacity
II. Argument #2 - Full pipe flow should be
used instead of half-full pipe flow to determine main drain flow into the
interceptor
A. Since
GGIs are centrally located (i.e., not connected to one fixture and not
located in close proximity to the fixtures), the resultant flow that they
carry represents a combination of all the connected fixtures. This
combination has an inherent diversity that results in a maximum of
half-full pipes that is the basis of Table 7-5.
B.
The GGI never sees the momentary full pipe
flow that can sometimes be experienced immediately downstream of an
individual fixture when it is drained at full volume.
C.
Half-full pipe flow is a very conservative
assumption based on the actual flows experienced at restaurants (Ref: North Carolina restaurant flow study data
attached)
III. Argument #3 - Item #152 GGI fixture capacity sizing example
A. The
example fixture with a volume of 44.9 gallons cannot produce 1,500 gallons
in 30 minutes. It will not remain
full and it will not continue to flow after emptying its contained volume.
The flow rate after draining its volume would be the flow rate of the
faucet, if left running, which is generally 2.2 GPM. So the 30 minute flow
volume produced by this one fixture would be approximately:
44.9 gallons + (2.2 GPM x 29
minutes) = 110 gallons
IV. Argument #4 - Item #152 GGI sizing table “Bigger is Better”
A. This
would create serious problems related to over-sizing of GGIs. Item #152 would result in most GGIs being
4,000 gallons or larger. In fact,
this would be worse than the old Appendix H sizing table which was the
original problem that the 2005 FOG Task Group corrected. Examples of problems directly related to
over-sized GGIs are as follows:
a.
Low pH and sewer system corrosion
b.
Hydrogen sulfide generation due to septic
conditions developing in the GGI
i.
Rotten Egg Odors
ii.
Dangerous (sometimes lethal) conditions for
pumpers, plumbers, and sewer maintenance workers
c.
The larger the interceptor, the less likely
it will be properly maintained
i.
Complaints from numerous pumpers/haulers and
sewering agencies regarding unnecessarily large
GGIs
V. Argument #5 – The November 29, 2007
FOG Task Group did not consist of balanced interests or expertise
In summary, the Task Group consisted of the following
balance:
Hydromechanical GI / Grease
Removal Device Reps 6
Gravity Grease Interceptor Representatives 4
Sewering Agency
Representatives 3
Manufacturer - Other 2
Plumbing Engineers 2
Code Consultant 1
Plumbing Inspector 1
IAPMO 2
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