ALTALINK INVESTMENTS, L.P. CAPITAL MARKETS PLATFORM THIRD SUPPLEMENTAL INDENTURE Dated as of December 15, 2010 ALTALINK INVESTMENTS, L.P. SENIOR PLEDGED BOND, SERIES 2 CAPITAL MARKETS PLATFORM THIRD SUPPLEMENTAL INDENTURE

WHEREAS by a Master Trust Indenture dated as of November 21, 2005 among the Issuer, the General Partner and the Trustee (as supplemented from time to time, the "Master Indenture"), provision was made for the issuance of Bonds in one or more Series, unlimited as to aggregate principal amount but issuable only upon the terms and subject to the conditions therein provided;

AND WHEREAS the Issuer, The Toronto-Dominion Bank (the "Former Agent') and the lenders party thereto are party to that Amended and Restated Credit Agreement dated December 16, 2009 (such agreement, as amended by a first amending agreement dated as of December 23, 2009, the "Existing Credit Agreement').

AND WHEREAS pursuant to a second supplemental indenture dated June 28, 2006 (the "Second Supplemental Indenture") under the Master Trust Indenture a Senior Pledged Bond, Series 1 was issued in respect of the obligations owing under the Existing Credit Agreement.

AND WHEREAS the Issuer wishes to amend and restate the Existing Credit Agreement pursuant to the Credit Agreement (as defined below) between the Issuer, Royal Bank of Canada, as the Agent and the Lenders party thereto, in order to, inter alia, increase the maximum principal amount of the credit facility thereunder and replace the Existing Agent with the Agent.

AND WHEREAS in respect of the Credit Agreement the Issuer wishes to create and issue under the Master Indenture and a Third Supplemental Indenture a Senior Pledged Bond, Series 2 (the "Senior Pledged Bond, Series 2") in the principal amount of Three Hundred Fifty Million Dollars ($350,000,000) in lawful money of Canada;

AND WHEREAS this Supplemental Indenture is executed pursuant to all necessary authorizations and resolutions of the Issuer to authorize the creation, issuance and delivery of the Senior Pledged Bond, Series 2 and to establish the terms, provisions and conditions of the Senior Pledged Bond, Series 2;

AND WHEREAS the foregoing recitals are made as representations and statements of fact by the Issuer and not by the Trustee;

NOW THEREFORE THIS SUPPLEMENTAL INDENTURE WITNESSES that in consideration of the premises, covenants and agreements herein contained, the parties hereto agree as follows:

This Third Supplemental Indenture is supplemental to the Master Indenture and shall be read in conjunction therewith. Except only insofar as the Master Indenture may be inconsistent with the express provisions of this Third Supplemental Indenture, in which case, subject only to section 2.8 of the Master Indenture, the terms of this Third Supplemental Indenture shall govern and supersede those contained in the Master Indenture only to the extent of such inconsistency, this Third Supplemental Indenture shall henceforth have effect so far as practicable as if all the provisions of the Master Indenture and 'this Third Supplemental Indenture were contained in one instrument The expressions used in this Third Supplemental Indenture and the Senior Pledged Bond, Series 2 shall, except as otherwise provided herein, have the respective meaning ascribed to such expressions in the Master indenture.

The Issuer hereby creates and issues a Bond under the Master Indenture to be designated as the Senior Pledged Bond, Series 2 in the principal amount of Three Hundred and Fifty Million Dollars ($350,000,000) in lawful money of Canada. The Senior Pledged Bond, Series 2 shall be dated as of the date of authentication and delivery thereof (the "date of issue") as determined by Written Order of the Issuer to the Trustee and shall be payable as to principal, interest thereon and premium (if any) at the office in Toronto, Ontario of the Trustee at which the Senior Pledged Bond, Series 2 is registrable. The Senior Pledged Bond, Series 2 shall bear interest as provided in Section 2.4 of this Third Supplemental Indenture and shall have the other terms and characteristics set forth or referred to in the Master Indenture and in Schedule "A" hereto.

The Senior Pledged Bond, Series 2 shall be delivered by the issuer pursuant to the bond delivery agreement attached hereto as Schedule "B" (the "Bond Delivery Agreement") in connection with, and as fixed, general, and continuing security for the due payment and performance of all present and future indebtedness, liabilities and obligations of the Issuer under the Credit Agreement and the Loan Documents (as defined in the Credit Agreement) (such indebtedness, liabilities and obligations, collectively, the "Obligations").

The Senior Pledged Bond, Series 2 shall be payable on demand therefor pursuant to and in accordance with the terms and conditions of the Master Indenture and the Bond Delivery Agreement.

The Senior Pledged Bond, Series 2, shall bear interest on the amount outstanding under the Credit Agreement from the date of issue at the applicable rate of interest per annum payable by the Issuer under the terms of the Credit Agreement, payable at the place and on the dates provided in the Credit Agreement, as well after as before demand, default and judgment with interest on overdue interest at the same rate and payable in like money at the same place and on the same dates.

The Senior Pledged Bond, Series 2 shall be issued as a fully registered Bond without coupons.

The Trustee's certificate of authentication shall be in the form annexed to the form of Bond attached hereto as Schedule "A".

The Senior Pledged Bond, Series 2 is a Senior Bond. The Senior Pledged Bond, Series 2 is a Pledged Bond securing all of the Obligations including, for greater certainty, all debts, liabilities and obligations of the Issuer under the Existing Credit Agreement are debts, liabilities and obligations of the Issuer under the Credit Agreement and constitute "Obligations" for the purposes of the Third Supplemental Indenture and the Senior Pledged Bond, Series 2. Each of this Third Supplemental Indenture, the Senior Pledged Bond, Series 2, and the Bond Delivery Agreement is a Loan Document (as defined in the Credit Agreement).

The Senior Pledged Bond, Series 2 in the principal amount of Three Hundred and Fifty Million Dollars ($350,000,000) in lawful money of Canada shall be executed by the Issuer and delivered to the Trustee. The Senior Pledged Bond, Series 2 shall thereupon be authenticated by the Trustee, registered in the name of the holder as may be specified in a Written Order of the Issuer and returned by the Trustee to the Issuer for delivery to the holder in accordance with the Bond Delivery Agreement without any further action and formality on the part of the Issuer but nevertheless only upon satisfaction of the conditions precedent set forth in Section 2.4 of the Master Indenture.

The parties hereto confirm that upon the issuance of the Senior Pledged Bond, Series 2, the Senior Pledged Bond, Series 1 shall be cancelled.

ALTALINK INVESTMENTS, L.P. (herein called the "Issuer") for value received hereby acknowledges that it is indebted to and promises to pay to the registered holder hereof upon demand the sum of Three Hundred and Fifty Million Dollars ($350,000,000.00), in lawful money of Canada at the office of the BNY Trust Company of Canada (the "Trustee") in the City of Toronto, Ontario, Canada and to pay interest thereon in accordance with the Credit Agreement, such interest to accrue from the date hereof, or in the case of any amounts in default from the date of default, at the applicable rates of interest per annum as set out in Section 2.4 of the Third Supplemental Indenture (defined below), as well after as before demand, default and judgment with interest on any such interest overdue at the same rate in like money at the same place and on demand.

This Bond is one of a duly authorized series of Altalink Investments, L.P. Capital Markets Platform Bonds, issued and to be issued under a trust indenture (herein called the "Master Indenture") made as of November 21, 2005, among the Issuer, the General Partner and the Trustee, as supplemented by the Third Supplemental Indenture (the "Third Supplemental Indenture") dated as of December 15, 2010, between the same parties as each may be amended, supplemented or otherwise modified from time to time.

Terms used in this Bond which are defined in the Master Indenture or the Third Supplemental Indenture shall, except as otherwise provided herein, have the respective meanings ascribed to them in the Master Indenture or the Third Supplemental Indenture, as applicable.

Reference is hereby made to the provisions of the Master Indenture (including, without limitation, section 2.8 thereof) and, where applicable, the Third Supplemental Indenture and the Bond Delivery Agreement, as to the rights of the holder of this Bond, the rights of the holders of the Altalink Investments, L.P. Capital Markets Platform Bonds issued and to be issued under the Master Indenture and of the Issuer and of the Trustee in respect thereof and the terms and conditions upon which this Bond and the Altalink Investments, ~.P. Capital Markets Platform Bonds are issued or may hereafter be issued, all to the same effect as if the provisions of the Master Indenture and, where applicable, the Third Supplemental Indenture and the Bond Delivery Agreement, were herein set forth, to all of which provisions, terms and conditions the holder of this Bond agrees by acceptance hereof.

The Bond shall be transferable only in accordance with the provisions, terms and conditions of the Master Indenture and the Third Supplemental Indenture. No transfer of this Bond shall be valid unless made on the register kept by and at the office of the Trustee in the City of Toronto, Ontario pursuant to the provisions of the Master Indenture.

This AltaLink Investments, L.P. Capital Markets Platform Bond is one of the Bonds referred to in the Master Indenture within mentioned and is the Senior Pledged Bond, Series 2 issued under the Third Supplemental Indenture within mentioned.

WHEREAS by a trust indenture (the "Master Indenture") dated as November 21, 2005 among the Issuer, AltaLink Investment Management Ltd., as general partner, and the Trustee (as defined herein), provision was made for the creation and issue of Bonds of the Issuer,

AND WHEREAS the Issuer, the General Partner, the Agent and the lenders party thereto entered into an amended and restated credit agreement dated as of the date hereof (such agreement, as amended, amended and restated, supplemented or otherwise modified from time to time referred to herein as the "Credit Agreement');

AND WHEREAS pursuant to the Third Supplemental Indenture dated as of the date hereof among the Issuer, the General Partner and the Trustee (the ''Third Supplemental Indenture"), the Issuer created and issued the Senior Pledged Bond, Series 2 (as defined herein);

AND WHEREAS pursuant to the Master Indenture and the Third Supplemental Indenture, the Issuer executed and delivered the Senior Pledged Bond, Series 2 to and in favour of the Agent;

AND WHEREAS the parties hereto are entering into this Agreement for the purpose of delivering the Senior Pledged Bond, Series 2 to the Agent on the terms and conditions of this Agreement;

NOW THEREFORE THIS AGREEMENT WITNESSES THAT in consideration of the premises, the covenants and agreements herein contained, the parties hereto agree as follows:

All capitalized terms used herein shall, unless otherwise indicated, have the respective meanings ascribed to them in the Master Indenture or the Third Supplemental Indenture. In this Agreement, the following terms shall have the respective meanings indicated below:

"Senior Pledged Bond, Series 2" means the Senior Pledged Bond, Series 2 Capital Markets Platform Bond in the principal amount of Three Hundred and Fifty Million Dollars ($350,000,000) issued by the Issuer pursuant to the Master Indenture and the Third Supplemental Indenture and duly authenticated by the Trustee as required by the Master Indenture.

The inclusion of headings in this Agreement is for convenience of reference only and shall not affect the construction or interpretation hereof

Whenever in this Agreement a particular Article, Section or other portion thereof is referred to then, unless otherwise indicated, such reference pertains to the particular Article, Section or portion thereof contained herein.

The Issuer hereby delivers the Senior Pledged Bond, Series 2 to the Agent to be held by the Agent as continuing collateral security for the Obligations of the Issuer (as defined in the Third Supplemental Indenture).

The Agent is hereby authorized, upon the occurrence of an Event of Default under the Credit Agreement and for so long as such Event of Default continues, to demand payment, in accordance with the Credit Agreement, of the Senior Pledged Bond, Series 2, without notice to, consent of or control by the Issuer. Notwithstanding that the Senior Pledged Bond, Series 2 is expressed to be payable on demand, the Agent shall have no right to and shall not demand payment unless or until an Event of Default under the Credit Agreement shall have occurred and be continuing. No payment of principal on account of any of the obligations of the Issuer under the Credit Agreement shall reduce the principal amount of the Senior Pledged Bond, Series 2. Notwithstanding the principal amount of the Senior Pledged Bond, Series 2, or the rate of interest expressed to be payable thereon, or that the Senior Pledged Bond, Series 2 is expressed to be payable on demand, the Senior Pledged Bond, Series 2 shall constitute a liability of the Issuer to the Agent only to the extent of the lesser of (i) the Obligations of the Issuer under the Credit Agreement outstanding at the

time of calculation, and (ii) the principal amount of the Senior Pledged Bond, Series 2 and interest accrued thereon, and such liability shall be payable only in accordance with the payment provisions of the Credit Agreement.

All proceeds of the Senior Pledged Bond, Series 2 including, without limitation, any distributions in respect thereof by the Agent, shall be applied on account of the obligations of the Issuer under, and in accordance with, the Credit Agreement without prejudice to any claim on the Issuer for any deficiency.

Upon full, final and irrevocable satisfaction of the obligations of the Issuer under the Credit Agreement, the Agent shall, at the request and expense of the Issuer, deliver the Senior Pledged Bond, Series 2 to the Trustee for cancellation.

The Senior Pledged Bond, Series 2 shall not be transferable or negotiable except to a successor of the Agent pursuant to the Credit Agreement

The Senior Pledged Bond, Series 2 shall not be considered as satisfied, discharged or redeemed by any intermediate payment or satisfaction of the whole or any part of the Obligations or by reason of the account of the Issuer having ceased to be in debit.

Notwithstanding the principal amount of the Senior Pledged Bond, Series 2, the holder of the Senior Pledged Bond, Series 2 shall only be entitled to that number of votes at any meeting of Bondholders or in respect of any Special Bondholders' Resolution, Extraordinary Resolution or Majority Resolution to which would be entitled the holder of an Obligation Bond in a principal amount equal to the lesser of (i) the outstanding Obligations of the Issuer at the time of calculation, and (ii) the principal amount of the Senior Pledged Bond, Series 2 and interest accrued thereon. All of the rights of the holders of the Senior Pledged Bond, Series 2 may be divisible with respect to the entire Obligations of the Issuer, provided that such rights, other than voting rights, may only be exercised by the Agent or its agent and that voting rights relating to

the Senior Pledged Bond, Series 2 may only be exercised by the Agent or any Person or Persons duly appointed as proxy for voting the Senior Pledged Bond, Series 2.

The Senior Pledged Bond, Series 2 shall not operate to merge any of the obligations of the Issuer under the Credit Agreement and no judgment recovered by or on behalf of the Agent shall operate to merge or in any way affect the security constituted by the Senior Pledged Bond, Series 2, which is in addition to and not in substitution for any other security now or hereafter held by the Agent or the Trustee.

The Issuer shall not amend, modify or supplement the provisions of the Senior Pledged Bond, Series 2 or any other delivery agreement relating to any other series of bond issued pursuant to the Master Indenture except as provided in the Master Indenture. No amendment or waiver of this Agreement shall be binding unless executed in writing by the party to be bound thereby. Nothing contained herein, in the Senior Pledged Bond, Series 2, in the Master Indenture or in the Third Supplemental Indenture shall amend, modify, vary or otherwise change the rights of the Agent under the Credit Agreement or the obligations of the Issuer thereunder or shall limit the rights of the Agent under or in respect of such obligations.

Upon the delivery of the Senior Pledged Bond, Series 2 pursuant to Section 2.1 hereof, the Senior Pledged Bond, Series 2 shall have the following legend conspicuously noted thereon:

"This AltaLink Senior Pledged Bond, Series 2 is subject to the terms and conditions of a bond delivery agreement dated as of December 15, 2010 among Altalink Investment Management Ltd. as general partner of AltaLink Investments, L.P., AltaLink Investment Management Ltd. and Royal Bank of Canada, as Agent."

Any Bond issued under the Master Indenture in substitution for or in replacement of the Senior Pledged Bond, Series 2 shall have conspicuously noted thereon the legend referred to in this Section 3.5.

The provisions hereof shall be binding upon and shall enure to the benefit of the Issuer and the Agent under the Credit Agreement and their respective permitted successors and assigns.

The Issuer shall forthwith and from time to time on demand, execute and do or cause to be executed or done· all assurances and things which 'in the opinion of the Agent may be necessary or of advantage to give the Agent so far as may be possible under any applicable law the benefit of the Senior Pledged Bond, Series 2, the Third Supplemental Indenture and the Master Indenture to secure the payment and performance of the obligations of the Issuer under the Credit Agreement.

Except where otherwise expressly provided in the Credit Agreement, all amounts In this Agreement are stated and shall be paid in Canadian currency.

In this Agreement, unless the context otherwise requires, words importing the singular include the plural and vice versa and words importing gender include all genders.

Each of the provisions contained in this Agreement is distinct and severable and a declaration of invalidity or unenforceability of any such provision or. part thereof by a court of competent jurisdiction shall not affect the validity or enforceability of any other provision thereof.

No waiver of any provision of this Agreement shall constitute a waiver of any other provision of this Agreement or constitute a continuing waiver unless otherwise expressly provided.

This Agreement shall be governed by and construed in accordance with the laws of the Province of Alberta and the laws of Canada applicable therein and the Issuer hereby irrevocably attorns to the non-exclusive jurisdiction of the courts of the Province of Alberta.

The Issuer is a limited partnership formed under the Partnership Act (Alberta), a limited partner of which is only liable for any of its liabilities or any of its losses to the extent of the amount that such limited partner has contributed or agreed to contribute to its capital and such limited partner's pro rata share of any undistributed income.

IN WITNESS WHEREOF the parties hereto have duly executed this Agreement as of the date above written.