56 ANNUAL REPORT 2012 The defned beneft obligations and beneft cost levels will change as a result of future changes in the actuarial methods and assumptions the membership data the plan provisions and the legislative rules or as a result of future experience gains or losses none of which have been anticipated at this time Emerging experience differing from the assumptions will result in gains or losses that will be revealed in future accounting valuations As a result of the uncertainty associated with these estimates there is no assurance that the plans will be able to earn the assumed rate of return on plan assets Furthermore market driven changes may result in changes to discount rates and other variables which would result in the Company being required to make contributions to the plans in the future that may differ signifcantly from estimates As a result there is a signifcant amount of measurement uncertainty involved in the actuarial valuation process This measurement uncertainty may lead to potential fuctuations in fnancial results attributable to the selection of actuarial assumptions and other accounting estimates involved in the determination of pension expense and obligations A signifcant actuarial and accounting assumption impacting the reporting of pension plans is the discount rate assumption As at December 31 2012 the Company used a discount rate of 375 in its pension plan calculations for fnancial statement purposes The impact of a 05 decrease in the discount rate assumption would have resulted in an increase in the pension beneft obligation of approximately 2400 at December 31 2012 and an increase in the estimated 2013 pension expense of approximately 100 23 CONTINGENCIES The Company is involved in various disputes and litigation both as plaintiff and defendant In the opinion of management the r esolution of disputes against the Company including those provided for see Note 17 will not result in a material effect on the consolida ted fnancial position of the Company As part of regular operations the Company has the following guarantees and letters of credit outstanding GUARANTEES AND LETTERS OF CREDIT PROJECT DECEMBER 31 2012 DECEMBER 31 2011 Guarantees Surety bonds guaranteed joint and severally to cover construction and concession related performance obligations advance payment bond and retention release bond Quito Airport Project 122779 125964 Letters of credit In support of various project contingencies Quito Airport Project 32785 36462 Financial and performance issued in the normal conduct of business Various 179525 107788 Under the terms of many of the Companys joint venture contracts with project owners each of the partners is jointly and sever ally liable for performance under the contracts As at December 31 2012 the value of uncompleted work for which the Companys joint venture p artners are responsible and which the Company could be responsible for assuming amounted to approximately 2252847 December 31 20 11 1669950 a substantial portion of which is supported by performance bonds In the event the Company assumed this additional work it would have the right to receive the partners share of billings to the project owners pursuant to the joint venture contract NOTES TO THE CONSOLIDA TED FINANCIAL ST A TEMENTS DECEMBER 31 2012 AND 2011 IN THOUSANDS OF CANADIAN DOLLARS EXCEPT PER SHARE AMOUNTS