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4. COMPREHENSIVE REVIEW OF STORM AND SANITARY SERVICE BACKWATER VALVES – COUNCIL MOTION 71/11
PLAN DE VALORIZATION DE L’EAU
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Committee recommendation
That Council approve an amendment to the City’s Sewer Design Guidelines to require the installation of a backwater valve on the sanitary service lateral for all new home construction.
RECOMMANDATION DU COMITÉ
Que le Conseil approuve les modifications apportées aux Lignes directrices de la Ville d’Ottawa concernant la conception des égouts afin d’imposer l’installation d’un clapet anti-refoulement sur la conduite secondaire des égouts séparatifs pour toutes les nouvelles constructions de maison.
DOCUMENTATION
1. Deputy City Manager’s report Infrastructure Services and Community Sustainability dated 17 May 2010 (ACS2010-ICS-INF-0006).
Report to/Rapport au :
Planning and Environment Committee
Comité de l'urbanisme et de l'environnement
and Council / et au Conseil
Submitted by/Soumis par : Nancy Schepers, Deputy City Manager/
Directrice municipale adjointe, Infrastructure Services and Community Sustainability/Services d 'infrastructure et Viabilité des collectivités
Contact Person/Personne ressource : Wayne Newell, General Manager/Directeur général, Infrastructure Services/Services des infrastructures
(613) 580-2424 x16002, Wayne.Newell@ottawa.ca
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Ref N°: ACS2010-ICS-INF-0006 |
That the Planning and Environment Committee recommend Council approve an amendment to the City’s Sewer Design Guidelines to require the installation of a backwater valve on the sanitary service lateral for all new home construction.
Que le Comité de l’urbanisme et de l’environnement approuve les modifications apportées aux Lignes directrices de la Ville d’Ottawa concernant la conception des égouts afin d’imposer l’installation d’un clapet anti-refoulement sur la conduite secondaire des égouts séparatifs pour toutes les nouvelles constructions de maison.
EXECUTIVE SUMMARY
Assumptions and Analysis:
On 24 July, 2009, the City experienced a significant rainfall event that resulted in approximately 1500 occurrences of basement backups, with a majority in the west end. Of this number, backwater valves (BWV) placed on the storm sewer service laterals for 119 of the homes were identified to be the likely source of the flooding.
At its meeting of 2 September, 2009, Council approved Motion No. 71/11 directing staff to conduct a thorough assessment of backwater valves on storm and sanitary services. A comprehensive review was undertaken to determine the mode of failure of the BWV in the July 24th event, investigate City standards with regard to current industry technology and practices, gauge the City’s requirements relative to peer municipalities and recommend a plan for moving forward to reduce the potential for future occurrences of basement backups related to failure of BWV. The following 5-step plan for moving forward is recommended:
1. Continue with Sewer System Improvements
The City’s current Sewer Design Guidelines are based on preventing storm sewers from surcharging, thus reducing the reliance on BWVs on perimeter foundation drains. In this case, the BWVs serve as a second line of defence instead of being the primary means of protection as is the case in communities built prior to the implementation of this standard.
A Wet Weather Infrastructure Management Plan is being developed and this plan will identify other areas of the City that could also be vulnerable to flooding. This plan is expected to be completed in 2010. The intent is to identify opportunities to increase the level of protection in these existing communities. Taking a systems approach is the most effective means of reducing the risk of flooding.
2. Expand Installation of Backwater Valves
The review identified opportunities to increase the level of protection against sanitary sewer backups. Recommended changes include amending the City’s Sewer Design Guidelines to include the mandatory installation of a BWV on the sanitary service lateral for all new home construction.
3. Increase Homeowner Awareness
Through various discussions with property owners, it is apparent that many are not aware of the existence or maintenance requirements for BWVs and other measures to reduce the risk of basement flooding (i.e. not connecting sump pump outlets to internal sanitary plumbing systems, directing eaves trough outlets away from the home). The following measures are recommended:
a. Work with homebuilders and real estate agents on check lists and information to be shared with new homeowners related to maintenance of BWVs, sump pumps (where applicable) and other measures to reduce the risk of basement flooding.
b. Develop an annual campaign focused on measures residents can consider to reduce the risk of basement flooding. This could be conveyed through print and radio ads, highlighted on the City’s website and/or included with the tax or water bill.
c. Update information available on the City’s web-site.
4. Maintain Backwater Valve Inspection Practices
The City already includes 2 BWV inspections at different stages of construction, which is considered a best practice when compared to peer municipalities. Through the building and plumbing permit application processes, there is an opportunity to increase awareness with contractors and homeowners of the benefits of BWVs and other measures to reduce the risk of basement flooding.
5. Consult with Backwater Valve Manufacturers
The review identified technical differences related to the test pressure for the cap of a storm BWV. Follow up discussions will take place with manufacturers to raise this issue along with including maintenance literature with the BWV.
Legal/Risk Management Implications:
From the risk management perspective, the installation of BWV’s on both storm and sanitary service laterals with new home construction provides a consistent city-wide enhanced level of protection against basement flooding.
Financial Implications:
Requiring the installation of a BWV on sanitary sewer service laterals, as part the initial new construction, would have minimal impacts on costs to the homebuilder. When installed with new home construction, the cost of a storm or sanitary BWV is approximately $250, as compared with retrofit costs of approximately $1,400 under the City’s Residential Protective Plumbing Program. There is a clear benefit to having this protective device installed at the time of original construction.
Staff from Infrastructure Services Department, Environmental Services Department and Building Code Services Branch provided technical input and review in the background study for this report.
A presentation was made to the Stittsville community on 17 February, 2010 to update residents on the flooding investigation. The presentation also included an update on the status of the BWV review.
City staff outlined the key changes at the Development Engineering Liaison Sub-Committee at its meeting of 26 February, 2010.
RÉSUMÉ
Hypothèses et analyse:
Le 24 juillet 2009, la Ville a reçu une importante pluie qui provoqué environ 1500 cas d’inondation de sous-sol, dont la majorité dans la partie ouest. De ce nombre, les clapets anti-refoulement placés sur les conduites secondaires des égouts pluviaux dans 119 des maisons affectées ont été identifiés comme la source de l’inondation.
À sa réunion du 2 septembre 2009, le Conseil a approuvé la motion no 71/11 demandant que le personnel effectue une évaluation exhaustive des clapets anti-refoulement installés sur les services d’égouts pluviaux et séparatifs. Un examen complet a été entrepris pour déterminer les circonstances à l’origine du non-fonctionnement des clapets anti-refoulement dans le cas de l’événement du 24 juillet, pour évaluer les normes de la Ville en matière de technologie et de pratiques sectorielles actuelles, étudier les critères établis par la Ville relativement aux municipalités comparables et recommander un plan pour aller de l’avant et réduire les possibilités d’occurrences futures d’inondations de sous-sol liés au mauvais fonctionne des clapets anti-refoulement. Le plan suivant en cinq étapes est recommandé:
1. Continuer d’améliorer le réseau d’égout
Les Lignes directrices de la Ville d’Ottawa concernant la conception des égouts sont fondées sur la prévention de toute forme de surcharge des égouts pluviaux, réduisant ainsi la dépendance des clapets anti-refoulement sur les drains de fondation périmétriques. Dans ce cas, le clapet anti-refoulement sert de moyen de défense plutôt que d’être l’unique moyen de protection, comme c’est le cas dans les communautés construites avant la mise en œuvre de cette norme.
Nous élaborons actuellement un Plan de gestion de l’infrastructure des eaux pluviales, qui permettra notamment de cibler d’autres secteurs de la Ville qui pourraient être vulnérables aux inondations. Ce plan devrait être finalisé en 2010. L’objectif est de trouver des moyens d’accroître le niveau de protection dans ces collectivités. L’adoption d’une démarche systématique est le meilleur moyen de réduire le risque d’inondation.
2. Augmenter les installations de clapets anti-refoulement
L’examen a relevé de nombreuses possibilités d’accroître le niveau de protection contre les refoulements dans les égouts séparatifs. Diverses modifications ont été recommandées, notamment modifier les Lignes directrices de la Ville d’Ottawa concernant la conception des égouts afin d’inclure l’installation de clapets anti-refoulement sur la conduite secondaire de l’égout séparatif pour toutes les nouvelles constructions de maison.
3. Sensibiliser davantage les propriétaires de maison
Après nombre de discussions avec les propriétaires, il semble évident qu’un grand nombre d’entre eux ne savent pas qu’il existe des clapets anti-refoulement , qu’il faut en faire l’entretien et ne connaissent pas non plus les autres mesures visant à réduire le risque d’inondation dans le sous-sol (c.-à-d. ne pas raccorder l’orifice de refoulement de la pompe d’assèchement au réseau interne de plomberie sanitaire, orienter les orifices des gouttières pour que l’eau s’écoule dans la direction opposée à la maison). Les mesures suivantes sont recommandées:
a. Collaborer avec des constructeurs de maison et des agents immobiliers pour l’élaboration de listes de vérifications et de renseignements qui seront distribués aux nouveaux propriétaires de maison, concernant notamment l’entretien des clapets anti-refoulement, les pompes d’assèchements (s’il y a lieu) et d’autres mesures visant à réduire le risque d’inondations dans le sous-sol.
b. Préparer une campagne annuelle axée sur les mesures qui peuvent servir aux résidents pour réduire le risque d’inondations dans le sous-sol. Cette information pourrait être distribuée au moyen d’annonces dans les journaux et à la radio, affichée sur le site Web de la Ville et/ou incluse dans la facture de taxe ou des services d’eau.
c. Mettre à jour l’information disponible sur le site Web de la Ville.
4. Conserver les pratiques d’inspection des clapets anti-refoulement
La Ville a déjà inclus deux inspections de clapets anti-refoulement à différentes étapes de la construction, ce qui est considéré comme une meilleure pratique par rapport aux municipalités comparables.
Dans le cadre du processus de demande de permis pour travaux de construction et de plomberie, il y a une possibilité de sensibiliser davantage les entrepreneurs et propriétaires sur les avantages des clapets anti-refoulement et d’autres mesures pour réduire le risque d’inondation dans le sous-sol.
5. Effectuer une consultation auprès des fabricants de clapets anti-refoulement
L’examen a permis de constater qu’il existe des différences techniques relatives à la pression d’essai pour le chapeau d’un clapet anti-refoulement. Des discussions de suivi auront lieu avec les fabricants à ce sujet et aussi pour parler de la possibilité de joindre de la documentation expliquant l’entretien avec les clapets anti-refoulement.
Incidences juridiques / concernant la gestion des risques:
Du point de vue de la gestion des risques, l’installation d’un clapet anti-retour sur les deux branchements d’égout pluvial et sanitaire dans le cadre de l’aménagement de nouvelles résidences assure un niveau de protection uniforme et amélioré à l’échelle de la ville contre les inondations de sous-sol.
Répercussions financières:
Le fait d’imposer l’installation d’un clapet anti-refoulement sur les conduites secondaires des égouts séparatifs, dans le cas de nouvelles constructions, n’aurait qu’une incidence financière minime pour le futur propriétaire. Lorsqu’ils sont installés pendant la construction d’une maison neuve, les clapets anti-refoulement ne coûtent que 250 $ environ par unité, comparativement à des coûts de rattrapage de l’ordre de 1 400 $ dans le cadre du programme de subventions à l'installation de dispositifs anti-refoulement de la Ville. Il est définitivement plus avantageux de procéder à l’installation de ces dispositifs au moment de la construction.
Le personnel des Services d’infrastructure, des Services environnementaux et des Services du code du bâtiment a fourni des renseignements techniques et ont effectué les analyses qui ont servi dans l’étude préliminaire qui a servi à al préparation du présent rapport.
Une présentation a été effectuée devant la communauté de Stittsville le 17 février 2010 pour informer les résidents des résultats de l’étude sur les inondations. La présentation comprenait également une mise à jour sur l’état de l’examen du système de clapet anti-refoulement.
Le personnel de la Ville a présenté les modifications principales à la réunion du 26 février 2010 du sous-comité technique de liaison.
On 24 July, 2009, parts of the City of Ottawa experienced a significant rainstorm (over 100
mm of rain in a 24-hour period in some areas) resulting in nearly 1,500 flooded basements,
overflows at two sewage pumping stations, and seven culvert failures. These occurred
primarily in the City’s west end, mainly in Ward 4 - Kanata North (Beaverbrook), Ward 5 -
West Carleton-March (Carp Village), Ward 6 - Stittsville, and Ward 23 - Kanata South (Katimavik and Glen Cairn).
Of the nearly 1500 flooded basements, backwater valve (BWV) placed on the storm sewer service lateral for 119 of the homes were identified to be the likely source of the flooding.
Currently, as stipulated in the City's Sewer Design Guidelines, the installation of a BWV, or backflow prevention device, is required on new foundation drain systems connected to a City storm sewer and on service laterals connected to a combined sewer system. BWVs, as a retrofit application, are also installed on sewer laterals as part of the City's Residential Protective Plumbing Program (RPPP).
At its meeting of 2 September, 2009, Council approved Motion No. 71/11 directing staff to conduct a thorough assessment of BWVs to consider items like:
In addition, the assessment was to review:
The purpose of this report is to respond to Motion No. 71/11.
Storm Backwater Valve Performance
In late August 2009, staff from the City’s Building Code Services Branch conducted inspections on a representative sample of storm BWV for 29 properties, about 25% of the 119 properties, identified as having had BWV failures during the July 24th flooding event.
A summary of their findings follows:
City staff determined that the main mode of failure of the BWV was likely through the valve cover (or cap). Either the cover had not been installed correctly, could have dislodged during the flooding event or the cover had not been screwed in place tightly. Staff also confirmed that of the 29 properties investigated, there was no failure of either the valve body or flapper mechanism that controls the flow of water.
Current Situation – City of Ottawa
Installation requirements
The City’s current requirements, as defined in the Sewer Design Guidelines, requires BWV to be installation on the perimeter foundation drain connected to the storm sewer system and on service laterals connected to the combined sewer system. A check valve is also required on the discharge of sump pumps.
Inspection Practices
During new home construction, the City’s current practice requires inspection of the BWV at two stages. The BWV is inspected after the piping has been placed, and again after the BWV has been encased in concrete. At both stages a visual inspection is undertaken by City staff to ensure that the valve is properly oriented. The plumber has the only contact with the valve, and for the second inspection is required to open the cover and screw the cover back on.
Residential Protective Plumbing Program
In 2005, Council approved Bylaw 2005-209, the Residential Protective Plumbing Program for Sewer Backup Protection By-law (RPPP). The RPPP is a grant program for homeowners to retrofit their service laterals to protect their basements from sewer backups as a result of sewer surcharging events. At the time, this program was limited to the installation of BWV on sanitary service laterals in areas of the City that had experienced basement flooding (typically on combined sewers and partially separated sewer systems). This program was established to respond to sewer backups and to mitigate the potential for future occurrences.
In 2006, the program was amended to increase from 80% to 100% the grant coverage for properties that had previously experienced basement flooding (Bylaw 2006-390). The amendment also included a higher maximum limit for properties with flat roofs (from $4,000 to $7,500).
The program was again amended in 2009 and 2010 to include the following provisions:
· To broaden funding at the 100% level for homes located immediately adjacent to homes that have experienced a basement backup and on the same sewer system as homes that have experienced a backup, due to sewer system surcharging.
· If the engineering study recommends the installation of a sump pump, the maximum amount is increased to $7500 when otherwise qualifying for 100% funding, and $3750 when otherwise qualifying for 50% funding.
The current program includes the following key provisions:
· 100% of the cost of the work to a maximum of $4,000 (including taxes) where a basement or cellar has previously flooded resulting from a City Sewer Backup; or
· 50% of the cost of the work to a maximum of $2,500 (including taxes) for a house that has not experienced flooding resulting from a City Sewer Backup but is located in an area with a history of flooding.
The amount approved under the Bylaw for residential dwellings having to address drainage from a flat roof represents:
· 100% of the cost of the work to a maximum of $7,500 (including taxes) where a basement or cellar has previously flooded resulting from a City Sewer Back-up; or
· 50% of the cost of the work to a maximum of $3,750 (including taxes) for a house that has not experienced flooding resulting from a City Sewer Back-up but is located in an area with a history of flooding.
To date, under the RPPP, approximately 900 BWV have been installed and there have been no reported failures.
Backwater Valve Technology and Industry Experience
On sanitary sewer service laterals, the City only permits the use of “normally open” BWV devices that permit venting of the internal plumbing system of a building (as per Ontario code requirements). During a sanitary sewer surcharging event, the BWV will close and prevent backup through to the internal plumbing of the building. Based on experience with the RPPP and information provided by other municipalities, the BWV installed to date have proved to be reliable for use on the sanitary service lateral.
On storm sewer service laterals, the City permits several types of BWV; some suitable for interior installation on the building and some intended for an external application. Some storm BWV can operate in “normally open”, as discussed above but most operate as “normally closed” configurations. Valves that operate as “normally closed” permit drainage from the weeping tile system to flow into the storm sewer, but prevent surcharging storm sewer flow from entering the weeping tile system.
In reviewing the technical specifications, the test pressure for storm BWV caps is less than for clean-out caps. The test pressure for the cap of a storm BWV is 5 psig, but it is 15 psig for the cap on a sewer cleanout. The cap on a full-port sanitary BWV also has a 15 psig test pressure. Having a higher test pressure could reduce the impacts associated with valves caps that may not be fully closed.
Cost of Technology
Typically, the cost to install a storm and sanitary BWV at the time of construction is approximately $250 per valve.
When considered relative to costs associated with basement flood damages, social impacts, inconvenience to the homeowner and grant costs for retrofit protective plumbing programs offered by the municipality, the cost to install as part of initial construction is negligible.
Practices of Peer Municipalities and Other Organizations
A peer review was undertaken to investigate and document the practices of peer municipalities related to the use of BWV and basement backup occurrences. The review included municipal governments in 4 provinces (5 in Ontario, 2 in Quebec, 2 in Saskatchewan and 1 Alberta), some of which had experienced basement flooding recently.
Protective Plumbing Installations
The assessment identified a range of practices that can be summarized as follows:
Enhanced Retrofit Protective Plumbing Programs
In the City of Toronto, a decision was made recognizing that “the whole City is declared at risk of basement flooding in the event of unusually severe precipitation”. A requirement was also made that any applicant for a Plumbing Permit related to a sewer drain where there is a below grade living area, anywhere in the City of Toronto, be required to install a BWV on the sanitary sewer lateral.
Building Code Provisions
The National Building Code of Canada requires every new home to have a BWV installed on both the storm and sanitary sewer service laterals, but municipalities follow their respective Provincial building codes. The Ontario Building Code (OBC) permits the installation of BWV on building drains provided the BWV is “normally open”. In Ontario, under the OBC, the installation of BWV on new homes is an option but not mandatory. In Ottawa, the requirement for the installation of backwater valves is defined in the City’s Sewer Design Guidelines.
Other organizations like Canadian Water and Wastewater Association, Association of Municipalities of Ontario, Ontario Municipal Benchmarking Initiative and InfraGuide were scanned for relevant experience but were silent on the BWV issue.
In summary, of the peer municipalities reviewed, all have implemented various strategies and programs, including specific requirements for use of BWV. The City of Ottawa’s current practices are generally consistent with the peer municipalities, with the exception of requiring BWV on sanitary sewer service laterals on new house construction.
Inspection Practices
Based on the information received, peer municipalities require a certified plumber to install the BWV and they typically perform one inspection after the BWV has been installed in new or existing homes.
Recommended Measures
A comprehensive review was undertaken to determine the mode of failure of the BWV in the July 24th event, investigate City standards with regard to current industry technology and practices, gauge the City’s requirements relative to peer municipalities and recommend a plan for moving forward to reduce the potential for future occurrences of basement flooding related to failure of BWV. The following 5-step plan for moving forward is recommended.
1. Continue with Sewer System Improvements
The City’s current Sewer Design Guidelines are based on preventing storm sewers from surcharging, thus reducing the reliance on BWVs on perimeter foundation drains. In this case, the BWVs serve as a second line of defence instead of being the primary means of protection as is the case in communities built prior to the implementation of this standard.
A Wet Weather Infrastructure Management Plan is being developed and this plan will identify other areas of the City that could also be vulnerable to flooding. This plan is expected to be completed in 2010. The intent is to identify opportunities to increase the level of protection in these existing communities. Taking a systems approach is the most effective means of reducing the risk of flooding.
2. Expand Installation of Backwater Valves
The review identified opportunities to increase the level of protection against sewer backups. Recommended changes include amending the City’s Sewer Design Guidelines to include the mandatory installation of a BWV on the sanitary service lateral for all new building construction. There is already a requirement in the guidelines to install a BWV on the storm sewer service lateral (perimeter foundation drain and on sump pump outlets). The additional material cost for a BWV installed in a new home at the time of construction is significantly less than in a retrofit situation (approximately $250 compared to $1,400).
3. Increase Homeowner Awareness
Through various discussions with property owners, it is apparent that many are not aware of the existence or maintenance requirements for BWVs and other measures to reduce the risk of basement backups (i.e. not connecting sump pump outlets to internal sanitary plumbing systems, directing eaves trough outlets away from the home). The following measures are recommended:
a. Work with homebuilders and real estate agents on check lists and information to be shared with new homeowners related to maintenance of BWVs, sump pumps (where applicable) and other measures to reduce the risk of basement backups.
b. Develop an annual campaign focused on measures residents can consider to reduce the risk of basement backups. This could be conveyed through print and radio ads, highlighted on the City’s website and/or included with the tax or water bill.
c. Update information available on the City’s web-site.
4. Maintain Backwater Valve Inspection Practices
The City already includes 2 BWV inspections at different stages of construction, which is considered a best practice when compared to peer municipalities. Through the building and plumbing permit application processes, there is an opportunity to increase awareness with contractors and homeowners of the benefits of BWVs and other measures to reduce the risk of basement backups.
5. Consult with Backwater Valve Manufacturers
The review identified a difference between the test pressure for the cap of a storm BWV (5 psig) and the cap for a cleanout (15 psig). The cap on a full-port sanitary BWV also has a higher pressure test standard (15 psig) than the cap on a storm BWV. Follow up discussions will take place with manufacturers to raise the following issues:
a. The cap on storm BWV should be able to sustain a surcharge pressure of 15 psig; the same standard as a clean-out cap and the cap used on the BWV for the sanitary service lateral (Mainline Fullport BWV). This will assist in reducing the risk of a failure of the cap should the City sewer experience surcharged conditions.
b. Include maintenance literature with the BWV.
Except where properties are connected to municipal storm and sanitary sewer systems in rural villages, this report is not applicable.
Staff from Infrastructure Services Department, Environmental Services Department and Building Code Services Branch provided technical input and review in the background study for this report.
A presentation was made to the Stittsville community on 17 February, 2010 to update residents on the flooding investigation. The presentation also included an update on the status of the BWV review.
City staff outlined the key changes at the Development Engineering Liaison Sub-Committee at its meeting of 26 February, 2010.
From the risk management perspective, the installation of BWV’s on both storm and sanitary service laterals with new home construction provides a consistent city-wide enhanced level of protection against basement flooding.
CITY STRATEGIC PLAN
This report is consistent with the Service Delivery priority of the City Strategic Plan.
N/A
Requiring the installation of a BWV on sanitary sewer service laterals, as part the initial new construction, would have minimal impacts on costs to the homebuilder. When installed as part of new home construction, the cost of a BWV is approximately $250, as compared with retrofit costs of approximately $1,400 under the City’s RPPP. There is a clear benefit to having this protective device installed at the time of original construction.
Infrastructure Services Department will:
Environmental Services Department will:
· Provide educational material for distribution to the public and Client Service Centres and the City’s web-site for the operation and maintenance of back water valves and other measures to reduce the risk of basement backups.