backflow prevention: let the civil engineer deal with it

Presentation to the 2016 ASPEConvention & Expo

Let the Civil Designer Deal with theContainment 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.

http://www.awwa.org/

http://fccchr.usc.edu/

https://www.aspe.org/

• 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

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

https://www.safe-t-cover.com/blog/dc-vs-rpz-backflow-prevention-devices

2 types of backflow Preventers:

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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)

DC: Low hazard?

Public (Supply)

side

Property(Private)

side

Flow

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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.


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RPZ: Fail-safe against returning water

Flow

Property(Private)

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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.


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.

Flow Stop

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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.


Loss of pressure

#2 valve blocked#2 valve blocked

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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!



#2 Valveblocked

#1 valve Failure

#1 valve Failure

Normal delivery pressure

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But with this imbalance in the system, changes in demand tend to rock the remaining valves open and closed sporadically.


Demand


#1 Valvefailure

#1 valve Failure

#1 valve Failure

Blockage relief valve

Blockage relief valve

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Demand


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.


Blockage Relief Valve

#1 Valvefailure

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No demand



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.


Above ground in an enclosure Inside a building Inside a vault – Click here for more

3 options for backflow preventer placement

2. Placement Practices

Inside a building Above ground in an enclosure – Click here for more Inside a vault



Inside a building Above ground in an enclosure Inside a vault



Inside a building3 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

Inside a building



This flood occurred in a hospital mechanical room causing over $1M in damage. You are looking at two sides of one wall.



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.




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.




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.




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.




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.


3 .The Real Flood Risks of indoor RPZs


He concludes that regarding indoor RPZs…




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

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




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.




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.)




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




$1,000

$1,120

$1,800

$3,920

$3,266

$1,200

$1,800

$6,266




Indoor CBPA

$3,920.00 plus assembly



Owner’s Cost: 3” Domestic line




“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 $11,357.2310 $1,248.55 $12,849.6715 $1,412.62 $14,538.2220 $1,598.25 $16,448.6625 $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




No more DCs on commercial or industrial properties.

Chicagoland, IL

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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.

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Atlanta Area, GARoswell, 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


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Atlanta Area, GARoswell, 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.


And the outdoor method mandates an enclosure that is ASSE-1060 compliant.

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Delaware, June 2013

Columbus Area, OH


North central Texas

AlpineBedfordBoerneCarrolltonCleburneCollege StationDenisonFarmingtonFarrisFranklinGrand PrairieHaltomTexarkanaWacoWaskomWhite Settlement

AddisonArlingtonBudaCedar HillColleyvilleCrowleyDentonDuncanvilleFort WorthFranklinGainesvilleHighland VillageMidlothianRoanokeRound RockSaginaw

Same language added to muni code

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Fort Worth added this in 2010, since then many cities have added it as well.

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Central VA

Lynchburg, 2008

Lynchburg has required RPZs on all non residential connections for almost a decade. This includes domestic, irrigation, and fire lines.


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RPZ

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.


Seattle, WA

Raleigh, NC

Charlotte, VAAustin, TX

Nashville, TN

Albuquerque, NM

Long Island, NY

Denver, CO

Las Vegas, NV

Lynchburg, VA

Columbus, OHChicago. 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….)

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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.

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


1. Define your discipline. 2. The presentation added to my knowledge


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 backflowpreventer installation.

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


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