Report to: General Committee Report Date: December 7, 2009

SUBJECT: West Thornhill Stormwater Flood Remediation Class Environmental Assessment

PREPARED BY: Phoebe Fu, Manager, Capital of Right-of -Way, Ext.3010

Yanli Xu, Senior Stormwater Management Engineer, ext.2894

RECOMMENDATION:

1) THAT the report entitled “West Thornhill Stormwater Remediation Class Environmental Assessment” be received;

2) AND THAT Council’s direction of the preferred alternative solution - 100 year level of protection for the West Thornhill stormwater system improvements be reaffirmed;

3) AND THAT Asset Management staff be authorised to file the Environmental Assessment Report for the 30 day public review commencing January 12, 2010;

4) AND THAT staff report back to Council on implementation strategy for the preferred alternative solution;

5) AND THAT staff be authorized and directed to do all things necessary to give effect to this resolution.

EXECUTIVE SUMMARY:

Not applicable

1. Purpose 2. Background 3. Discussion 4. Financial

5. Others (HR, Strategic, Affected Units) 6. Attachment(s)

PURPOSE:

The purpose of this report is to seek Council’s endorsement for the preferred alternative solution, the 100 year level of protection, to improve the stormwater system performance in West Thornhill and to obtain the Council’s authorization to file the Class EA report for the 30 day public review.

BACKGROUND:

West Thornhill (Attachment A – Study Area) like many other older areas in Markham is vulnerable during severe storm events to significant surface and building flooding. Rainfall events that excess the level of protection available in the municipal infrastructure such as that which occurred in August of 2005 have the potential to cause flooding of many basements and damage to the Town's infrastructure such as culverts, storm sewers and watercourses.

In response to the damages that occurred from the 2005 storm event, the Town of Markham initiated, in February 2008, a Municipal Class B Environmental Assessment study to assess the existing stormwater system capacity, explore alternative solutions and to arrive at a preferred alternative solution to improve the level of protection in West Thornhill.

On March 23, 2009, Staff presented to General Committee a detailed presentation on the background of the area, the characteristics of the rainfall event, causes of basement flooding, modeling results of various simulations and the new infrastructure required to improve the level of protection to the 5, 25 and 100 year level. Included also was the estimated cost for these improvements. Council authorized staff to proceed to host Public Information Centre (PIC) No. 1.

PIC No.1 was held on April 27, 2009 and approximately 150 residents attended the meeting.

On June 2, 2009 at a Special Development Services Meeting (SDSC), staff presented the alternative solutions, evaluation criteria / methodology, funding options, Town-wide financial implications, application for the federal infrastructure stimulus funding and next steps pending results from the stimulus announcement. Staff were directed to hold Public Information Centre (PIC) No. 2 and present the draft preferred alternative solution: "#4 - 100 year level of protection" to increase the level of flood protection in West Thornhill Area.

At the Council meeting on June 3, 2009, there were further discussions and clarification on the rational why staff were recommending a 5 year level of protection as the preferred solution and it was explained that:

· West Thornhill, like many other older area of town, was built with 2 year storm sewer system without overland flow routes. This was a standard level of service across the Province when the community was originally developed. This level has served the community well with only a few incidences of flooding over the years.

· The storm event that occurred in August 2005 was a very intense storm with a return probability of over 150 years. Given the large storm that occurred, the storm system performed extremely well with only several hundred homes flooded in the area of over 8000 properties. The likelihood of another rainfall of this intensity hitting this particular area is low. Under frequent rain events, the area is relatively well protected.

· There was concern about the cost to implement a program to transform a community’s infrastructure to the extent of a 100 year design storm. It was communicated that a more modest increase to a 5 year level would be more affordable and management on a Town-wide basis initially with options available in the future to increase this level further using in-line storage or other environmental techniques. It was clarified that the 100 year level of protection does not provide 20 times more protection compared to the 5 year level of protection, but rather only twice as much. The rainfall volume of the 100 year is only 40% more than the 5 year design storm.

· It was explained also that flooded basements can be caused by a lot of factors including lot grading issues, drain problems and building foundation defects that are outside the scope of the improvements identified and beyond the control of the municipality.

· The sanitary sewer system responds in proportion to the rainfall intensity and there will be a larger cost to protect against sanitary sewer surcharging to this higher level of protection. This is not part of this Class EA study but staff had communicated some of the potential costs.

· The infrastructure upgrades identified in the study were established on the basis of alleviating flooding in areas where flooding occurred to a cluster of homes. Individual properties flooded in the upper reaches of the drainage area due to back falling driveways or particularly low basement elevations were not addressed in the study due to the high cost. Therefore not all vulnerable basements will be protected with extent of the infrastructure established in the study.

On June 5 2009, it was confirmed that the Town was not successful in the infrastructure stimulus funding application. On June 22 2009, Staff reported to General Committee with the project update report. In the report, staff indicated that “once Council makes the decision on the level of protection, staff will move forward to host the Public Information Centre #2 in the fall of 2009.” General Committee confirmed its position on the 100 year level of protection.

At the June 23, 2009 Council meeting, Council further discussed the report, “West Thornhill Stormwater Flood Remediation Class Study Update”. At this meeting Council reconfirmed its position on the 100 year level of protection and directed staff to proceed to host PIC No.2 and present the draft preferred alternative solution – the 100 year level of protection.

PIC No. 2 was held on October 14, 2009 and approximately 170 residents attended the meeting.

PUBLIC / REGULATORY AGENCY CONSULTATION:

A Public Liaison Committee was established which included ratepayer groups, regulatory agencies, neighbouring municipalities, Councillors and Town’s staff. Four Liaison Committee meetings were held to review the study findings.

Notice of Commencement, and notices for PIC No.1 and No.2 were placed in both the Markham Economist & Sun and the Thornhill Liberal. Notice of the public meetings was also mailed/e-mailed to the Liaison Committee members, stakeholders and residents. Participants were invited to review display boards and were then given a formal presentation on the study. The presentation was followed by a question and answer period.

PIC No.1 was held on April 27, 2009, 109 attendees signed in while approximately 150 residents attended the meeting and 33 comment sheets were received. PIC No.2 was held on October 14, 2009, 121 attendees signed in while approximately 170 residents attended and 4 comment sheets were received. In response to the public comments, the study team communicated with individual residents via e-mail or telephone and the comments will be documented in the Class EA report comments at both meetings. The comments focused on a preference for a 100 year protection and concerns on the financing options.

OPTIONS/ DISCUSSION:

After the presentation of alternative solutions to Council on March 23 and to the public at the PIC#1 on April 27 2009, four evaluation criteria were used to evaluate and select preferred alternative solution. The evaluation criteria included:

· Technical and Engineering Considerations – minimize potential for basement flooding / protection of human and built environment / reduce cost of flooding for residents;

· Economic Environment Considerations – Minimize capital, operating and maintenance costs;

· Natural Environment Considerations – Minimize impacts to natural habitats / peak flow / creek erosion / sediment transport / water quality; and

· Social and Cultural Environment. – Minimize community disruption.

Extensive technical analysis and evaluation was conducted. Following the presentation of the draft preferred alternative, the 100 year level of protection, at the PIC No.2, there was only one objection to the draft preferred alternative received on a comment sheet. Based on the Class EA process and the direction of Council, the 100 year level of protection is carried forward and recommended as the preferred alternative solution for flood prone areas within West Thornhill (Attachment B). The 100 year level of protection includes:

· downspout disconnections,

· Installations of inlet control devices (to reduce surface flows into storm sewers where these is limited capacity),

· Installation of new catchbasins (to increase surface flow into storm sewers where there is capacity) and

· New infrastructure (twinning or diversion) for flood prone areas only.

The cost estimated for the preferred alternative is $40 millions as shown on Attachment C.

The recommended alternative of raising the level of service to 100 year design storm in the flood prone areas within West Thornhill has a number of implications:

TOWNWIDE IMPLICATIONS: The majority of the storm system infrastructure in West Thornhill, like many other older areas across the Town, was built accommodate a 2 year storm with no provision for overland flow routes. This was the accepted and affordable design criteria at the time the homes that were developed. Although the design standards for stormwater systems have changed significantly, these systems have performed reasonably well over the past 50 years. However, due to the severe rainfall event on August 19, 2005, West Thornhill encountered flooding problems in certain areas. If the other older areas across the Town were to experience the same rainfall, similar flooding problems would likely occur. It is assumed that if the West Thornhill area is upgraded to a higher level of protection then a similar program would be adopted by Council to upgrade other older areas of Town. This would require significant additional funding. Further discussions regarding Town-wide implication will be part of a future implementation report.

SANITARY IMPROVEMENTS: Basement flooding is also caused by surcharge in the sanitary sewers. The estimated cost for sanitary improvements required in West Thornhill is estimated to be $37.5M, which includes sanitary sewer replacements and inflow / infiltration (I/I) reductions. This will have a corresponding financial impact if adopted across the Town.

Upon approval of the Class EA and as per Council direction, staff will report back to General Committee on an implementation strategy including resource requirements, financing options, Town-wide implications, phasing strategies, value engineering, and a detailed design and construction schedule for the initial phases.

FINANCIAL CONSIDERATIONS AND TEMPLATE:

The precedent of raising the level of protection to 100 year design storm in flood prone areas within West Thornhill has significant financial impacts to the Town. Estimated costs (including sanitary improvements) for Town-wide (as presented at Jun 2, 2009 Special DSC) are as follows:

Level of Protection	West Thornhill	Rest of Town (Projected)	Total Cost
Stormwater – 100 year level of protection	$40 Million	$ 77 Million	$117 Million
Sanitary	$37.5 Million	$ 72 Million	$109.5 Million
Total	$77.5 Million	$149 Million	$226.5 Million

The cost associated with the rest of Town is an estimate only, based on prorating the cost of the Thornhill area and applying it to the rest of the Town. The actual cost may be substantially different depending on the results of future detailed studies.

HUMAN RESOURCES CONSIDERATIONS

Not applicable

ALIGNMENT WITH STRATEGIC PRIORITIES:

This report is consistent with the Building Markham’s Future Together strategic priority on the “Environment” as it considers sustainability on the built environment.

BUSINESS UNITS CONSULTED AND AFFECTED:

Not applicable

RECOMMENDED

BY:

________________________ ________________________

Steve Andrews Brenda Librecz

Director, Asset Management Commissioner, Community and Fire Services

ATTACHMENTS:

Attachment A – Study Area

Attachment B – Preferred Alternative Solution – 100 Year Level of Protection

Attachment C – Preliminary Cost Estimate for 100 Year Level of Protection

Q:\Asset Management\CAPITAL RIGHT OF WAY\Design\08-004_Thornhill Storm Water Flood Remediation Study\Admin\council report\GC Nov 30 09\West Thornhill Stormwater Flood Remediation Class EA_GC Dec7 09_FINAL.doc