M E M O / N O T E D E S E R V I CE |
|
|
To /
Destinataire |
Chair and Members
of the Environment Committee
/ Président et membres du Comité de l’environnement |
File/N° de
fichier: ACS2011-ICS-ESD-0023-IPD |
|
From /
Expéditeur |
Dixon Weir, General Manager /
Directeur général Environmental Services / Services environnementaux Infrastructure Services and Community Sustainability / Services d’infrastructure et Viabilité
des collectivités |
Contact
Person / Personne-ressource : Michel Chevalier, Manager / Gestionnaire, Wastewater Services / Services des eaux usées 613-580-2424 x 22335 Michel.chevalier@ottawa.ca |
|
Subject / Objet |
2010 Annual Combined
Sewer Overflow Control Period Reporting/ Rapport annuel de 2010 sur les débordements
d’égouts unitaires durant las période de surveillance |
Date: June 3, 2011
/ Le 3 juin 2011 |
The purpose of this memo is to provide Council with an update on the 2010
performance of the City’s Combined Sewer System during the April 15 through
November 15 Control Period.
The information attached to this memo has also been submitted to the
Ministry of the Environment (MOE) as a part of the Province’s annual regulatory
reporting requirements for all municipalities with a combined sewer system,
including the cities of Kingston, London, Toronto and Hamilton.
Background – Regulatory Framework
The primary purpose of the City’s wastewater
collection system is to protect public health through the collection and
conveyance of sanitary wastes away from neighbourhoods and communities. The oldest portion of the City’s wastewater
collection system is a combined sewage collection system that conveys both
sanitary and storm flows in a single pipe.
This type of collection system evolved over time, first to partially
separated systems in the 1950s and then to fully separated systems in the early
1960s.
The design and operating philosophy of these older combined or partially
combined collection systems is that during wet weather events when the
collection system is operating at its design peak flow, a portion of the
combined sewage (diluted by the addition of large amounts of stormwater) will be overflowed into a nearby body of water
to minimize the risk of flooding in the neighbourhoods serviced.
These types of combined sewage collection systems are common
characteristics of as many as 700 older communities in North America.
Recognizing the number of combined sewer systems and, therefore, the
need for combined sewer overflows to mitigate the risk of residential flooding,
the MOE has developed a procedure entitled, “Determination of Treatment
Requirements for Municipal and Privately Combined and Partially Separated Sewer
Systems.” This procedure establishes
the framework within which these systems must operate in order to protect
public and environmental health. Since
2006, the MOE has requested that Ottawa provide an annual combined sewer system
discharge report to the Ministry on the City’s collection system performance
during the Annual Control Period (April 15 through November 15) as defined by
the MOE procedure. This memorandum
summarizes the details submitted to the Ministry in correspondence dated 13
April 2011. A copy of that more detailed
report is available upon request at this time and will be posted on the City’s
website in the future.
Overview of Report to Province Regarding 2010 Annual Control Period
Events
Since May 2008, the City staff have been informing City Council of all
sanitary sewage and combined sewer overflow discharges as close to the
occurrence as possible. Included with
these preliminary event notifications were estimated volumes of discharges into
the Ottawa River. The volumes and event
notifications reported below are refinements of the information previously
provided to Council, and they form part of the annual report to the MOE.
A summary of the 2010 report indicates the following:
·
Total
Combined Sewage overflow volume for the 2010 Control Period is estimated to be 424,000
m3;
·
Percentage
of Collected Sewage Treated to Secondary Level – 99.5%;
·
Total
Volume of Wastewater Collected Citywide During Control Period – 84,256,000 m3;
·
Total
Volume of Wastewater Treated at the R.O. Pickard Environmental Centre During
Control Period – 83,832,000 m3;
·
Collection
System Sanitary Sewage Spills:
o
Number of
Discharge Events – 1;
o
Estimated
Total Volume – 2060.8 m3;
·
Total
Number of Sewage Collection System Bypasses[1]
– 0 Bypass Events;
·
Total
Number of individual CSO events, as defined by MOE Policy F-5-5, was 69 Eventsc; and
·
Rainfall
During the Control Period – 646 mm, approximately 24% above the “Average”
Control Period rainfall of 522 mm.
It is important to note that with a Control Period CSO volume of 424,000
m3 in 2010, this is the lowest Combined Sewage Overflow volume
reported in the five years of preparing these reports.
Looking more
specifically at the individual CSO sites, the following are the major sites at
which overflows occurred:
|
|
2009 |
2010 |
||
|
Location |
Number of Events |
Estimated Volume (m3) |
Number of Events |
Estimated Volume (m3) |
|
Booth Street Sewer Overflow (Lloyd Booth Regulator) |
53 |
268,000 |
13 |
122,000 |
|
Rideau River Collector Overflow (Keefer
Regulator) |
30 |
164,000 |
23 |
59,100 |
|
Rideau Canal Interceptor |
54 |
114,000 |
44 |
146,000 |
|
Cave Creek Collector |
10 |
29,000 |
10 |
19,000 |
|
Manor Park Overflow |
34 |
18,000 |
48 |
25,800 |
|
Bolton Street Overflow (Cathcart Regulator) |
29 |
15,000 |
28 |
24,700 |
|
TOTAL Volume of CSO’s from Listed Sites |
|
608,000 |
|
397,000 |
|
TOTAL COMBINED SEWER SYSTEM OVERFLOW |
|
632,000 |
|
424,000 |
These six overflow sites represent
collectively approximately 94 per cent of the total volume of combined sewer
overflows during the Control Period. The steps the City is taking to reduce
these volumes further are described below in the Ottawa River Action Plan
section.
The
most significant rainfall of the Control Period was the August 15-16 rainfall
event that caused approximately 30 per cent of the total CSO volume for the
Control Period. Just less than 44 mm of
rain was recorded by Environment Canada’s Experimental Farm rain gauge for that
event and that followed previous day rainfalls of 16 mm.
Attached to this memo is a table depicting the
2010 Control Period Combined Sewer Overflows on both a volumetric and event
basis for each of the active overflow locations.
As always, it is important to note that all combined sewer overflows are
located downstream of the City’s drinking water production plant intakes and as
such do not affect drinking water quality.
·
Ottawa
River Action Plan
In February 2010, Council approved the comprehensive multi-year $251
million Ottawa River Action Plan. A
major component of that Plan is reducing both the frequency and volume of
combined sewage overflows. Major
advances in this area have been made in 2010 and include:
· The
implementation of Real Time Control;
· Ongoing combined
sewer separation; and
· Advanced
planning for the construction of major combined sewage overflow storage
facilities.
Over the course of 2010, the City’s Real Time
Control program reached construction completion. All sites are now operational and discharges
to the Ottawa River will now occur only in situations when the Ottawa River
Interceptor is at maximum carrying capacity.
2011 will be the first year that these sites will be in full operation
throughout the Annual Control Period. As such, further reductions in combined
sewage overflows are projected for this year.
As well, work continues with the West Nepean Collector which should
offer system performance improvement through reduced volumes.
The City continues with combined sewage
separation projects. The City’s long
term goal is to separate combined sewage collection systems to the point that
only that area of the City within the Ultimate Combined Sewage Area has
combined sewers. (For details on the
Ultimate Combined Sewage Area, please see the attached map). For 2011, sewer separation work centres in
the Rockliffe Park area.
To
address combined sewage that is collected from within the Ultimate Combined
Sewage Area, work is advancing well on the requisite Environmental Assessment
phase of the CSO Storage project. The
purpose of the CSO Storage Tank is to receive combined sewage during rainfall
events when the Ottawa Interceptor/ Collector (OIC) Sewer is conveying sewage
at maximum capacity. The storage
facility will store combined sewage until the Ottawa Interceptor/Collector
Sewer is no longer flowing at maximum capacity.
Once peak demands have receded, and conveyance capacity exists within
the OIC, combined sewage collected within the storage facility will then be
directed to the R. O. Pickard Environmental Centre for sewage treatment. This
storage facility is being designed to eliminate the discharge of any combined
sewage during an average year of rainfall’s Annual Control Period.
For
the Manor Park Overflow site, final commissioning is expected to conclude this
spring. It is expected that these
improvements will eliminate CSOs from this site for all but very large rain
events.
·
Strengthened
Communications Protocol
In 2010, a revised and strengthened
communication protocol was established that made combined sewage overflow
information available on a per event basis on the City’s website. That practice will remain in place for 2011.
For 2011, we have moved to improved immediate
reporting accuracy by using uniquely calculated CSO volumes at each of the five
(5) primary CSO sites. The sixth site, that of the Manor Park Overflow/Sandridge
facility, will be similarly calculated, when fully commissioned. These flows will be more accurate than the
rainfall vs. flow nomograph that has been used in the
past.
With the final commissioning of the flow
monitoring equipment at each overflow site, which is currently anticipated in
late 2011, we will transition from calculated volumes to actual flow monitored
results. We will provide notification to
Council and various stakeholders when this change in reporting methodology
occurs.
That being said, we want to bring to your attention the difference
between volumes reported immediately after the event and volumes based on more
rigorous analysis and interpretation of monitoring data and simulation
results. For the 2010 Control Period, the
sum of “immediate” CSO Volume reports was roughly 910,000 m3, or
roughly double the volume obtained through better estimates and presented in
this report. This confirms our common understanding that immediate reports are
conservative. This difference is
primarily due to the following:
·
“Immediate, next
day” reported CSO volumes (i.e. during the Control Period) were calculated
using un-calibrated daily RADAR rainfall data and, a simple and conservative nomograph method, as derived for the entire combined sewer
area. While using a nomograph
and un-calibrated rainfall data permits ready next day reporting of CSO
volumes, such a method cannot then account for area specific and variable
rainfall event locations, durations or intensities.
·
“Immediate, next
day” reported CSO volumes (i.e. during the Control Period) were not determined
using installed temporary or permanent flow monitoring equipment so as to
ensure that complete reporting was made for all possibly active CSO sites (most
of which do not have flow monitoring equipment installed from which data could
be retrieved or interpreted in a timely same or next day fashion).
·
The CSO volumes
provided herein are derived using more rigorous and lengthy analysis and
interpretation of both monitoring data and model simulation results using
detailed sewer shed specific calibrated rainfall information.
·
The nomograph based “immediate, next day” CSO volume
determination methodology was deliberately designed to be conservative to
reduce the risk that CSO volumes were underreported.
The change in CSO volume determination has
been implemented. As noted previously, the
City of Ottawa’s more detailed 2010 Annual Report to
the Ministry of Environment on Combined Sewer Overflows (CSO) will be available
at Ottawa.ca / Sewers and Wastewater / Combined Sewer Overflows / Reports and
Related Information or upon request by contacting my office at extension 22610.
Should you have any further
questions, please do not hesitate to contact either myself or Michel Chevalier,
Manager, Wastewater Services at (613) 580-2424, extension 22335.
Yours truly,
Dixon Weir, P.Eng.
General Manager
Environmental Services Department
cc: Nancy Schepers, Deputy City Manager,
Infrastructure Services and Community Sustainability
Executive
Management Team
Isra
Levy, Medical Officer of Health, Public Health Department
Wayne
Newell, GM, Infrastructure Services Department
Michel Chevalier, Manager, Wastewater and
Drainage Services
Attachments: Map – Current Combined Sewershed Areas: CSO Location, Frequency and Volumes for the
2010 Control Period
Table – Combined Sewer Overflows for
Control Period – Average Year, 2006 – 2010
Map – Current Status of
Separation Program (End 2010)