1.
Presentation to the 2016 ASPE
Convention & Expo
Let the Civil Designer Deal with the
Containment Backflow Preventers
The water engineering community has been
struggling with new professional liability risk
involving the location of premise isolation
backflow preventer systems; Not because of new
design practices, but because of new information
about the old practices. There has been a slow
trickle of warnings for years, but in the past 3
years important organizations and industry
leaders have added new warnings with much
stronger language that not only change
recognized best practices, but actually challenge
the fitness and safety of older placement
methods altogether.

2.
• Water Districts NEED
Containment in order to
fulfill their EPA
mandate; and
Bottom Line:
“…. The return of any water to the
public water system after the water
has been used for any purpose on
the customer’s premises or within the
customer’s piping system is unacceptable
and opposed by AWWA.…”
• Containment design details and specifications need to be provided to civil
engineers because of their general familiarity with standard details and
their comparable lack of familiarity with backflow systems.
AWWA’s preamble to the Cross Connection Control Manual,
published by EPA
Introduction

3.
1. Design differences DC vs. RPZ; Why it matters
2. Current placement practices
3. The real flood risks of indoor RPZs
4. The real cost of indoor containment
5. The explosive growth of the RPZ and how it impacts M/P Engineers
6. How do we encourage transitioning this task to the civil engineering discipline?
Today We’ll Cover…
Let the Civil Designer Deal with the Backflow
System

4.
2 types of backflow Preventers:
DesigndifferencesDCvs.RPZ
Double-Check Valve
Assemble, DC or DCDA
Reduced Pressure Zone
Valve Assembly, RP RPDA
A designer may specify one of two types of BFPs for premise isolation. Up until
recently, the decision for which assembly to specify was based solely on the
perceived hazard to the waste water system created by the processes of the end
user. High hazard (better named, high waste-hazard) uses were required to utilize an
RPZ. Uses that did not pose a risk to the waste water were allowed to use a DC.
For example, a medical facility or a chemical plant triggered the requirement for an
RPZ while an office or simple retail user would be allowed to use a DC or, depending
on the municipality, no premise isolation system at all.
1. Design Differences (and why it matters)

5.
DC: Low hazard?
Public
(Supply)
side
Property
(Private)
side
Flow
DesigndifferencesDCvs.RPZ
The Double-check assembly was developed in the 1950s for the fire industry. And for
many years it was regarded as a satisfactory solution. The design is simple. Any time
system-water pressure on the property (private) side exceeds the system pressure on the
city (public) side, two redundant check valves close and water stops flowing backwards.
But no remedy exists in the event of a malfunction of the valve closures or if debris in the
water line causes the valves to not close completely. Additionally, The DC is a closed, or
blind system making detection of any failure impossible without a field test performed by
a licensed tester. Today, millions of DCs are in service that may have failed. When a Florida
city began its annual testing program in 2010, it found 52% of the valves in service had
failed with no way to determine how long they had been inoperable.
1. Design Differences (and why it matters)

6.
DesigndifferencesDCvs.RPZ
RPZ: Fail-safe against returning water
Flow
Property
(Private)
side
Public
(Supply)
side
The RPZ emerged in the 1970s as a remedy to the double-check limitations. Like the DC, it
incorporates 2 redundant check valves. But unlike the DC, the RPZ incorporates a
hydraulically operated differential relief valve directly beneath the # 1 check valve. It is
this relief valve’s placement (along with the universal laws of hydraulics) that make this a
fail-safe solution for water purveyors. As elegant as the design is, it comes at a cost. And
that cost is the surrounding area.
1. Design Differences (and why it matters)
As the DC reveals, valves fail. But when they fail in an
RPZ, the assembly is designed to create a deluge
event directly under the assembly so that no
contaminated water returns to the public water
supply. Because of the danger of contamination, no
water from the relief valve may be piped directly
from the assembly. It must release into the
atmosphere away from any piping. Watch this short
video revealing an actual discharge.

7.
Flow Stop
DesigndifferencesDCvs.RPZ
RPZ: Fail-safe against returning water
In a flow-stop situation the water
between the check valves will often
drain out the relief valve. Some think
that that event defines the limit of
what water can ever flow into a drain.
Not so.
1. Design Differences (and why it matters)

8.
Loss of pressure
#2 valve
blocked
#2 valve
blocked
DesigndifferencesDCvs.RPZ
Consider a flow-stop situation, one that
might naturally occur at the end of the day.
If you look closely, you can see that a small
pebble has lodged in the #2 check valve.
Now let’s say there’s a fire around the
corner that causes back siphon at this point
in the system.
Because the # 2 check valve is not closing,
all the water that has been delivered to the
building will continue to flow out the relief
valve until the private lines are cleared. If
this is a four story building, that’s a lot of
water!
RPZ: Fail-safe against returning water
1. Design Differences (and why it matters)
#2 Valve
blocked

9.
#1 valve
Failure
#1 valve
Failure
Normal
delivery
pressure
DesigndifferencesDCvs.RPZ
Now consider a failure of the #1 check
valve. Under normal operating conditions,
this failure would go unnoticed. After all,
water is being called for by the user
through the opening of taps. The water
flows in undeterred.
But with this imbalance in the system,
changes in demand tend to rock the
remaining valves open and closed
sporadically.
RPZ: Fail-safe against returning water
Demand
1. Design Differences (and why it matters)
#1 Valve
failure

10.
#1 valve
Failure
#1 valve
Failure
Blockage
relief
valve
Blockage
relief
valve
DesigndifferencesDCvs.RPZ
RPZ: Fail-safe against returning water
Demand
Normal
delivery
pressure
This creates the conditions for the “perfect
storm” scenario. The imbalance created by
the # 1 failure makes the relief valve more
prone to opening momentarily, allowing
debris to block the closure of that valve.
Under such conditions, a constant flow of
delivered water will begin to flow directly
out the relief valve. This reduces water
pressure for the user, but delivery will
continue.
1. Design Differences (and why it matters)
Blockage
Relief
Valve
#1 Valve
failure

11.
DesigndifferencesDCvs.RPZ
No
demand
Normal
delivery
pressure
RPZ: Fail-safe against returning water
The real damage begins when the user
stops using water such as at the end of a
work day.
With the relief valve blocked open and the
# 1 valve inoperative, all the water that the
purveyor can provide will flow unabated
out the relief valve wherever it might be,
and continue until the water source is
interrupted.
This is the scenario that must be avoided:
the perfect storm.
1. Design Differences (and why it matters)

12.
 Above ground in an enclosure
 Inside a building
 Inside a vault – Click here for more
3 options for backflow preventer placement
2. Placement Practices

13.
 Inside a building
 Above ground in an enclosure – Click here for more
 Inside a vault
3 options for backflow preventer placement
2. Placement Practices

14.
 Inside a building
 Above ground in an enclosure
 Inside a vault
3 options for backflow preventer placement
2. Placement Practices

15.
 Inside a building
3 options for backflow preventer placement
1. Professional liability: indoor flooding
Here’s what the American Society of
Plumbing Engineers advise about indoor RPZs.
“Before an RPZ is located, consideration should be
given to both how much water will be discharged,
and where it will drain. Consideration must be given
to the drain system to assure the drainage system
can handle the load. If a drain is not capable of
accepting the flow, other choices as to the location
of the valve, such as outside in a heated enclosure,
should be made.”
-2006 ASPE Plumbing
Engineering Design Handbook, vol 2, p 70
3. The Real Flood Risks of indoor RPZs

16.
 Inside a building
3. The Real Flood Risks of indoor RPZs
3 options for backflow preventer placement
This flood occurred in a hospital mechanical room causing over $1M in damage. You are
looking at two sides of one wall.
1. Professional liability: indoor flooding

17.
 Inside a building
3 options for backflow preventer placement
On the left, we see that the sudden water flow and volume moved the wall into the next
room (right photo), which happened to be a telephone and low-voltage wiring room.
1. Professional liability: indoor flooding
3. The Real Flood Risks of indoor RPZs

18.
 Inside a building
3 options for backflow preventer placement
The insurer sought recovery from all the risk holders including the engineer, architect,
contractor, subcontractor, and even the most recent recorded tester; While the details
of who paid what were not made public, we do know that the property insurer was
made whole by one or more of the listed defendants.
1. Professional liability: indoor flooding
3. The Real Flood Risks of indoor RPZs

19.
 Inside a building
3 options for backflow preventer placement
In times past, this event would have been seen as an unforeseeable casualty, a pipe
burst. But insurers have been listening to the next part of the discussion. This
commentary from experts changed everything.
1. Professional liability: indoor flooding
3. The Real Flood Risks of indoor RPZs

20.
 Inside a building
3 options for backflow preventer placement
So if an RPZ is designed to dump water, then drain
capacity is the issue. The chart on the right is from
the manufacturer of the BPA seen in the previous
flood photos. It illustrates the anticipated flow rate
from the relief valve at various pipe sizes and at
various pressures. Note that the assembly shown will
flow 375 GPM at 85 PSI. A 4” drain pipe with a 1%
fall rate evacuates clean water at a maximum rate of
93 GPM. If that device is flowing at 375 GPM and
your clearing 93, then you are flooding at a rate of
282 GPM.
1. Professional liability: indoor flooding
3. The Real Flood Risks of indoor RPZs

21.
 Inside a building
3 options for backflow preventer placement
An article published June 2013 in the
Chicago chapter of the American
Society of Plumbing Engineers written
by David DeBord, a former president of
that organization, and current
Education chair of the national ASPE,
states all these facts better than I can.
He uses the Manufacturer’s data
supplied by a different manufacturer,
and he uses a 65 PSI instead of my 85,
but he actually does the math in the
article and offers FLOOD rates or 219
GPM for 2 1/2 and 3”; and flood rate of
482 GPM for 4” and above.
1. Professional liability: indoor flooding
3 .The Real Flood Risks of indoor RPZs

22.
 Inside a building
3 options for backflow preventer placement
He concludes that regarding
indoor RPZs…
1. Professional liability: indoor flooding
3. The Real Flood Risks of indoor RPZs

23.
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility
The space provided for an indoor BPA is
routinely inadequate as provided by the
architect. That’s because giving up space that
would otherwise add value is being allocated
as non-revenue space. Non-revenue space is
the enemy of every development project.
The BPA pictured cost tens of thousands in
property value. Even a mere 3” indoor BPA will
cost a developer $6,000 to $9,000 more than
an outdoor installation in a heated enclosure.
4. The Real Cost of Indoor BPAs

24.
Charlotte: 32.000 SF
Columbus: 36.000 SF
Suffolk Cty: 33.333 SF
Arlington: 32.000 SF
Average: 33.325 SF
Consider the average square footage required
for just a 3-inch indoor in-line backflow
preventer. To the right, four representative
cities are represented. The average required
space is 33.325 SF.
Assuming a discount rate of 9%, rent value of
$30 per foot annually, and a 25 year life, the
net present value of that space to the property
owner is $12, 156.48.
Arlington, TX: 32 SF
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

25.
Average: 33.325 SF
Annual Rent Value
(based on Class A Office
@ $30/sf)
$999.75
25-year Cash Flows
(based on 2.5% inflation)
$34,149.22
Net Present Value
(based on 9% discount
rate)
$12,156.48
Assuming a discount rate of 9%, rent value of
$30 per foot annually, and a 25 year life, the
net present value of that space to the property
owner is $12, 156.48.
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

26.
NPV:
Landlord has lost this amount of value
by placing CBPA inside.
$12,156.48
CONSIDER:
1.If space is recaptured for rental value, what will my alternative cost be?
2.Will placing the system outside cost more or less than $12,156.48?
3.If it’s less, then how much less? (I don’t like the look of a box outside.)
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

27.
Aboveground heated enclosure
for 3” BPA with heat.
Option A:
Use conventional model
e.i., Watts 957 NRS
Safe-T-Cover 300-AL-H
$3,266.00
72 X 38 X 22 = 60K CI
Option B:
Use new ”n-type” model
e.i., Watts 957N NRS
Safe-T-Cover 200SN-AL-H
$1,120.00
46 X 38 X 19 = 33K CI
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

28.
$1,000
$1,120
$1,800
$3,920
$3,266
$1,200
$1,800
$6,266
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

29.
Indoor
CBPA
$3,920.00
plus assembly
$6,266.00
plus assembly
$12,156.48
plus assembly
Owner’s Cost: 3” Domestic line
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

30.
“How much more value does my building have with the additional
rent?”
ANSWER:
Year Annual Rent*
1 $999.75
PropertyValue*
$10,289.09
5 $1,103.54 $11,357.23
10 $1,248.55 $12,849.67
15 $1,412.62 $14,538.22
20 $1,598.25 $16,448.66
25 $1,808.27 $18,610.15
* - Today’s dollars: Assumptions: Annual rent growth of 2.5%; 5% vacancy; 35% operating expenses;
capitalization rate of 6%.
Owner’s Property Value
4. The Real Cost of Indoor BPAs
 Inside a building
3 options for backflow preventer placement
2. Space allocation/Accessibility

31.
No more DCs on
commercial or industrial
properties.
Chicagoland, IL
TheexplosivegrowthoftheRPZ
Elgin, October 2012
5. The Explosive Growth of the RPZ
Naperville, April 2013
Naperville already required RPZs on their commercial irrigation systems, but after
Elgin’s action, they too outlawed DCs, and in fact, extended mandatory RPZ use on
fire line systems as well.

32.
TheexplosivegrowthoftheRPZ
Atlanta Area, GA
Roswell, August, 2014
Roswell detailed two methods of RPZ
placement, one indoors for small sizes,
and one outdoors for larger sizes.
The drawings for the indoor method
explicitly address drain system
requirements and force designers to
reconcile the flood rate risks with
specific drainage system capacities
5. The Explosive Growth of the RPZ

33.
TheexplosivegrowthoftheRPZ
Atlanta Area, GA
Roswell, August, 2014
The chart shows that unless the
designer is willing to install an 8”
drain system all the way to the
sewer inlet, he cannot utilize an
indoor solution for any pipe size
larger than 2 inches.
5. The Explosive Growth of the RPZ
And the outdoor method mandates an
enclosure that is ASSE-1060 compliant.

34.
TheexplosivegrowthoftheRPZ
Delaware, June 2013
Columbus Area, OH
5. The Explosive Growth of the RPZ

35.
North central Texas
Alpine
Bedford
Boerne
Carrollton
Cleburne
College Station
Denison
Farmington
Farris
Franklin
Grand Prairie
Haltom
Texarkana
Waco
Waskom
White Settlement
Addison
Arlington
Buda
Cedar Hill
Colleyville
Crowley
Denton
Duncanville
Fort Worth
Franklin
Gainesville
Highland Village
Midlothian
Roanoke
Round Rock
Saginaw
Same language added to muni code
TheexplosivegrowthoftheRPZ
5. The Explosive Growth of the RPZ
Fort Worth added this in 2010, since then many cities have added it as well.

36.
TheexplosivegrowthoftheRPZ
Central VA
Lynchburg, 2008
Lynchburg has
required RPZs on all
non residential
connections for almost
a decade. This includes
domestic, irrigation,
and fire lines.
5. The Explosive Growth of the RPZ

37.
TheexplosivegrowthoftheRPZ
Mountain West
Denver, February, 2013
In 2013 Denver Water
added new standard
details for 3” and larger
RPZs to be installed
outdoors.
They also call for double
checks for public park
drinking fountains to be
installed above ground in
a heated enclosure.
5. The Explosive Growth of the RPZ

38.
Seattle, WA
Raleigh, NC
Charlotte, VA
Austin, TX
Nashville, TN
Albuquerque, NM
Long Island, NY
Denver, CO
Las Vegas, NV
Lynchburg, VA
Columbus, OH
Chicago. IL
Forth Worth, TX Roswell, GA
Longview, WA
Arlington, TX
Gwinnett Cty, GA
Chesapeake, VA
Olympia, WA
Kent, WA
Franklin, TN
All these cities have made changes
whereby RPZ use has been
expanded either by lowering or
eliminating the hazard threshold
for use on domestic water lines in
the past 5 years. (These are the
cities we know of….)
TheexplosivegrowthoftheRPZ
5. The Explosive Growth of the RPZ

39.
Consider the ‘worst case scenario’ of a
water volume discharge of a
containment backflow prevention,
namely, an uncontrolled discharge
caused by a failure of the #1 check
valve contemporaneous with the relief
valve being stuck or propped open by
debris. If there is no faucet demand
within the commercial premise, such
as over night, then this perfect storm
produces an unmitigated flow of all
available water through the relief valve
continuously. The management of this
sudden water deluge is a significant
hazard. As severe as the most severe
storm water runoff event.
Special Insert
This hazard is clearly work found within
the civil engineering discipline rather than
the plumbing engineering discipline.
Designing and specifying any outdoor
containment BPA – even if it is placed
within the jurisdictional boundaries of the
plumbing engineer, is asking for trouble.
Watch a video of an RPZ doing what it’s designed to do here.

40.
A survey of 1869 civil and mechanical
engineers was conducted by Safe-T-
Cover and EnviroDesign Management
over a 22-month period ending in
Spring, 2016. The survey followed a
professional learning module
delivered by EnviroDesign and was
managed and tabulated by Benchmark
Email Services. Excluding delivery
failures, 1220 were delivered and
opened. The following 2 slides show
the questions in the short survey and
the responses.
6. How do we Encourage transition to Civil
Engineers

41.
6. How do we Encourage transition to Civil
Engineers
1. Define your discipline. 2. The presentation added to my
knowledge

42.
6. How do we Encourage transition to Civil
Engineers
3. The information causes me to
rethink my perspective on
containment backflow preventer
placement
4. The local water guidelines for
commercial and industrial
construction lack needed standard
details for above-ground backflow
preventer installation.

43.
 Develop a firm-level policy
 ASPE local chapter dialog with local water purveyor
 Encourage best practices learning
 Publish standard details and drawings consistent with
best practices
6. How do we Encourage transition to Civil
Engineers

44.
 Plumbing engineers are facing new liability risks from insurance carriers, revealed by new warnings
and commentary from industry leadership regarding indoor containment RPZs.
 Because of the need for pure water in the public water supply and the undetectable nature of the
DCs, purveyors are demanding more RPZs and ignoring the legacy hazard guidance.
 RPZs are designed to engulf the immediate surrounding area.
 Indoor placement of 3” & larger RPZs adds irrational risk for PO & designer.
 Placing the CBPA inside costs PO $000s more than outside.
 The need to address sudden flood water flows disqualifies MEP from CBPA Design.
 Your local water district must be encouraged to adopt new details and guidelines that promote best
practices and adoption by CEs.
Take-Aways