98011-0612

Report

To: Development Services Committee Item: Date of Report:

DS-07-174 June 13, 2007 From: Commissioner, Development File: Date of Meeting: Services Department E-6800 (9) June 18, 2007

Subject: Ward(s): All

Calcium Carbonate Formation in Foundation Drain Collector Systems

PUBLIC REPORT 1.0 PURPOSE The purpose of this report is to: (a) Advise Council of the results of a detailed investigation into the formation of calcium

carbonate within foundation drain systems in the City and; (b) To recommend a Council policy for future management of the issue. Report DS-06-76, dated March 1, 2006, advised Council of problems being experienced with the formation of calcium carbonate within foundation drain systems in the City. A copy of Report DS-06-76 appears as Attachment No. 1. On March 20, 2006, in response to Report DS-06-76, Council passed the following resolution: "That staff be authorized to retain Golder Associates Ltd. to investigate the cause of calcium carbonate formation in foundation drain collection systems at an estimated cost of $20,000 to be funded from 2006 operating contingency account." Golder and Associates Ltd. ("Golder") has recently completed its study and a copy of its Conclusions and Recommendations is provided as Attachment No. 2. The full report is available for viewing in Engineering Services (1st floor, Rundle Tower, attention Mike Sims). 2.0 RECOMMENDATION That the Development Services Committee recommend to City Council: 1. That, based on Report DS-07-174 dated June 13, 2007 regarding the formation of

calcium carbonate in foundation drains, Community Services initiate a regular cleaning program for foundation drain collector systems where calcium carbonate formation is known to be a problem.

2. That Community Services provide a cleaning service in 2007 for private property

foundation drain laterals at a cost not to exceed $30,000 to be funded from the 2007 corporate contingency.

Report to the Development Item: DS-07-174 Services Committee (Continued) - 2 - Meeting Date: June 18, 2007

3. That the Public Works Services 2008 budget submission be increased by $60,000 for

the annual costs of cleaning private property foundation drain laterals. 4. That residents currently known to be affected by calcium carbonate in their private

laterals be advised of Council’s policy. 5. That the Development Services Department consult with the Building Industry Liaison

Team (BILT) concerning the implementation of recommended measures to manage the formation of calcium carbonate in new developments and report back to Council should BILT have any major concerns.

3.0 EXECUTIVE SUMMARY Golder was retained by the City in March 2006 to investigate the formation of calcium carbonate in foundation drain systems and throughout 2006 undertook a number of field investigations to determine the cause of the problem. Golder's final report concludes that the natural groundwater within the impacted area is saturated with calcium carbonate and as the water flows through certain materials found beneath the basement floor slabs of homes in the area, the pH of the groundwater changes and its' ability to maintain the calcium and carbonate in solution is reduced, thus resulting in precipitation of the material in the foundation drain systems. Golder has recommended that the City: (a) institute a regular cleaning program for foundation drain collector mains and private property laterals where the formation of calcium carbonate is a problem; (b) Consider additional conditions of approval for new development to minimize the potential for future calcium carbonate problems. 4.0 INPUT FROM OTHER SOURCES

Public Works Services (Community Services Department) has provided input to the report and supports the Recommendation.

Finance Services (Corporate Services Department) has provided financial input to the

report. 5.0 ANALYSIS 5.1 Golder Study

As noted in Report DS-06-76 dated March 1, 2006 (see Attachment No. 1), calcium carbonate has been found in foundation drain systems in various parts of the City.

A study by Golder has focused on the Wilson Road/Clearsky Avenue area where

calcium carbonate formation is occurring on a fairly rapid basis.

Report to the Development Item: DS-07-174 Services Committee (Continued) - 3 - Meeting Date: June 18, 2007

Through 2006, Golder undertook field investigations in the Wilson/Clearsky area as follows:

Borehole drilling and monitoring wells were installed at eleven (11) different

locations. Groundwater level elevations were measured in each well in September 2006 and

December 2006. Water samples were taken from 4 wells in September 2006 for chemistry analysis. Various soil materials typically used on construction projects were tested. With the permission of the homeowners, boreholes were drilled through the

basement floors of 4 homes on Clearsky Avenue and underlying material was collected for analysis.

As a result of the investigation, Golder has concluded:

There are several areas within the area where the natural groundwater level is

within approximately 1 metre of the ground surface. The foundation drains on a number of homes are therefore persistently at or below the groundwater surface.

Groundwater within the area is saturated with respect to calcium carbonate. Golder believes this should be a fairly common occurrence in Oshawa as our soils are predominately derived from limestone. The pH of the groundwater was found to be in the 7.2 to 7.5 range.

The pH of the gravel layer beneath basement floor slabs was in the 8.6-9.8 range. As groundwater flows through and interacts with the gravel beneath the floor slab,

the pH of the groundwater rises and its ability to maintain calcium carbonate in solution is reduced, resulting in precipitation of the material in the drains.

Material found beneath the floor slabs was an unwashed clear stone backfill, which is permitted by the Ontario Building Code.

Golder has provided a series of recommendations to manage the issue in existing

developments and minimize the potential for problems in future development.

With respect to existing development, Golder has recommended that foundation drain systems (mains and private property laterals) be cleaned on a regular basis. Initially, it recommends that cleaning be carried out twice per year in the Wilson/Clearsky area. Golder believes the frequency of cleaning will decline over time to a point where it may no longer be required. The time frame for this to occur cannot be determined. Cleaning in other areas may not need to be as frequent, dependent on the rate of calcium carbonate formation.

With respect to future development, Golder recommends:

Chemical analysis should be performed on groundwater to assess the potential for

calcium carbonate formation where groundwater is anticipated to be within the depth of influence of new foundation drains.

The depth of footings below seasonal groundwater levels should be minimized as much as possible.

Report to the Development Item: DS-07-174 Services Committee (Continued) - 4 - Meeting Date: June 18, 2007

Where the potential for calcium carbonate formation is found, washed 19 mm clear stone should be used around new house footing drains and floor slabs.

The lateral connection between streetline and the home footing drain should be increased from 100 mm to 150 mm to facilitate cleaning and inspection.

Foundation Drain Collector (FDC) mains should be designed to minimize drop structures as the increased turbulence can also increase groundwater pH and cause subsequent calcium carbonate precipitation.

An inspection program should be put in place to examine FDC mains and lateral connections by the developer in order to monitor and manage any problems prior to assumption of the systems by the City.

5.2 Recommended Policy Measures

In order to implement Golder's recommendations, a number of new measures are proposed.

In developed areas where problems are being experienced, the following is

recommended:

A regular cleaning program be performed on City FDC mains. Funding in the amount of $35,000 was approved in the Public Works 2007 operating budget for this purpose. Financial needs for this program will be assessed and determined on an annual basis through the budget process.

A regular cleaning program be initiated on private property laterals where problems are identified. A few homes in the Wilson/Clearsky area have received this service while the study was underway using a local plumbing company at a cost of $300 per cleaning for the service. Based on a preliminary assessment on the scope of work in areas around the City, an estimated $60,000 would be required annually to provide this service.

The cleaning of laterals will require the City or its contractor to enter onto private

property to perform the work as the clean-out for the FDC is located within the basement of each home. This is similar to services the Region of Durham provides private homeowners for sanitary service connections.

While the City’s past practice has been to view the cleaning of private FDC connections

as a property owner responsibility, it is believed that the calcium carbonate issue is a unique circumstance in which the City should assist homeowners. Also, from a risk management perspective, providing the service to homeowners should also minimize claims against the City for damages to flooded basements arising from connections potentially impacted by calcium carbonate.

Report to the Development Item: DS-07-174 Services Committee (Continued) - 5 - Meeting Date: June 18, 2007

Within new development areas, the following is recommended:

The application of a standard condition of approval requiring a groundwater study and analysis that deals with the calcium carbonate issue.

New clauses in the City's Development Agreements which require:

- The use of washed 19 mm clear stone on applicable building lots; - The use of 150 mm pipe for house laterals; - Annual inspection of FDC by the developer's engineer with all systems to be

videoed and cleaned prior to City assumption.

Revisions to the City's Engineering Design Criteria and associated policies to reflect the above noted requirements, and:

- Design of development to minimize the extent of building footing drains below

the seasonal high groundwater table. - Design of systems to minimize areas that would create turbulent flow.

In addition to the above policy measures, a review will be undertaken by Development

Services, in conjunction with Community Services, on the benefits of continuing to use a separate foundation drain collector system as opposed to the connection of foundation drain laterals to a deeper storm sewer. An annual testing and monitoring program will also be established.

6.0 FINANCIAL IMPLICATIONS

The current estimated annual cost for cleaning City FDC system mains is $35,000. Funding was approved in the 2007 Public Works Services operating budget for this work.

An additional estimated $60,000 is required to perform semi-annual cleaning of private

house connections impacted by calcium carbonate formation. The 2007 Public Works Services budget did not include funding for the cleaning of private connections. If Council approves the undertaking of this work, the estimated cost of $30,000 for 2007 can be funded from the 2007 corporate contingency.

The 2007 budget for the corporate contingency is $187,900. As of June 11, 2007,

approximately $171,500 has been expended or committed (this includes $30,000 for the cleaning of the private laterals), leaving approximately $16,400 in funding available for the remainder of 2007.

The 2008 budget for Public Works Services will need to be increased by $60,000 to

fund the cleaning of private laterals if Council approves this report. It should be noted that the full scope of homes requiring cleaning is not fully known at this point in time and the overall budget for this service may need to change in the future.

Report to the Development Item: DS-07-174 Services Committee (Continued) - 6 - Meeting Date: June 18, 2007

7.0 RESPONSE TO THE COMMUNITY STRATEGIC PLAN

The investigation and recommended measures for the management and administration of the calcium carbonate formation in foundation drain collectors advances Goal A (A Vibrant, Strong and Progressive Community) and Goal C (A Caring and Responsive Community) of the City's Community Strategic Plan by promoting a positive City image and by ensuring accountability and effective City management.

M. J. Sims, P. Eng., Director Engineering Services Thomas B. Hodgins, B.E.S., M.A., R.P.P, Commissioner Development Services Department MJS/ls/c Attachments