Exhibit 10.23.3 THIRTY-SEVENTH AGREEMENT AMENDING NEW ENGLAND POWER POOL AGREEMENT THIS THIRTY-SEVENTH AGREEMENT AMENDING NEW ENGLAND POWER POOL AGREEMENT, dated as of August 15, 1998 ("Thirty-Seventh Agreement"), is entered into by the signatory Participants to amend the New England Power Pool Agreement (the "NEPOOL Agreement"), as amended. WHEREAS, the NEPOOL Agreement as in effect on December 1, 1996 was amended and restated by the Thirty-Third Agreement Amending New England Power Pool Agreement dated as of December 1, 1996 (the "Thirty-Third Agreement") in the form of the Restated New England Power Pool Agreement ("Restated NEPOOL Agreement") attached to the Thirty-Third Agreement as Exhibit A thereto, and the Thirty-Third Agreement also provided for the NEPOOL Open Access Transmission Tariff ("Tariff") which is Attachment B to the Restated NEPOOL Agreement; and WHEREAS, the Restated NEPOOL Agreement and the Tariff have subsequently been amended by five supplements dated, respectively, as of February 7, June 1, September 1, November 1 and December 31, 1997 and by three additional amendatory agreements dated, respectively, as of September 1, 1997, November 15, 1997 and July 20, 1998; and WHEREAS, the signatories hereto desire to amend the Restated NEPOOL Agreement, as amended by the Thirty-Sixth Agreement Amending New England Power Pool Agreement, dated July 20, 1998, to amend the definition of "Power Year" and to make certain related changes. NOW, THEREFORE, the signatory Participants agree as follows: SECTION 1 AMENDMENT TO RESTATED NEPOOL AGREEMENT 1.1 AMENDMENT OF SECTION 1.77. Section 1.77 of the Restated NEPOOL Agreement is amended to read as follows: POWER YEAR is (i) the period of twelve (12) months commencing on November 1, in each year to and including 1997; (ii) the period of seven (7) months commencing on November 1, 1998; and (iii) the period of twelve (12) months commencing on June 1, 1999 and each June 1 thereafter. 1.2 AMENDMENT OF SECTION 1.104. Section 1.104 of the Restated NEPOOL Agreement is amended to read as follows: WINTER PERIOD in each Power Year is (i) the seven-month period from November through May and the month of October for the Power Year commencing on November 1 in 1997 or a prior Power Year; (ii) the seven-month period from November through May for the Power Year commencing on November 1, 1998; and (iii) the eight-month period from October through May for the Power Year commencing on June 1, 1999 and each June 1 thereafter. 1.3 AMENDMENT OF SECTION 12.2(A)(1), DEFINITION OF "I". The definition of "I" in Section 12.2(a)(1) of the Restated NEPOOL Agreement is amended to read as follows: I for the Participant for the month is the percentage which represents the weighted average (using the Installed Capability of each Installed Capability Entitlement for such month for the weighting) of the Four Year Installed Capability Target Availability Rates of the Installed Capability Entitlements which are included in the Participant's Installed System Capability during the hour of the coincident peak load of the Participants for the month. The Four Year Target Availability Rate for an Installed Capability Entitlement for any month is the average of the monthly Target Availability Rates for the forty-eight months which comprise the period of four consecutive calendar years ending within the Power Year which includes such month, as determined on the basis of the Target Availability Rates for each of the forty-eight months, and as applied on a basis which is consistent with the fuel or maturity status of the unit for each of the forty-eight months; provided, however, that for the purpose of determining the Four Year Target Availability Rate (i) for months included within the Power Year which commences June 1, 1999, the determination shall be made for the months of June through October on the basis of the calendar years 1995 through 1998, and shall be made for the months of November through May on the basis of the calendar years 1996 through 1999, and (ii) for months included within the Power Year which commences June 1, 2000, the determination shall be made on the basis of the calendar years 1996 through 1999. The Target Availability Rates shall be those utilized by the Management Committee in its most recent determination of NEPOOL Objective Capability pursuant to Section 6.14(e). 1.4 AMENDMENT OF SECTION 12.2(A)(1), DEFINITION OF "H". The definition of "H" in Section 12.2(a)(1) of the Restated NEPOOL Agreement is amended to read as follows: H for the Participant for the month is the percentage which represents the weighted average (using the Installed Capability of each Installed Capability Entitlement for such month for the weighting) of the Four Year Actual Availability Rates of the Installed Capability Entitlements which are included in the Participant's Installed System Capability during the hour of the coincident peak load of the Participants for the month. The Four Year Actual Availability Rate for an Installed Capability Entitlement for any month is the percentage which represents the average of the amounts determined for H{1} for the four applicable Twelve-Month Measurement Periods within the forty-eight months which comprise the period of four consecutive calendar years ending within the Power Year which includes such month; provided, however, that for the purpose of determining the Four Year Actual Availability Rate (i) for months included within the Power Year which commences June 1, 1999, the determination shall be made for the months of June through October on the basis of the calendar years 1995 through 1998, and shall be made for the months of November through May on the basis of the calendar years 1996 through 1999, and (ii) for months included within the Power Year which commences June 1, 2000, the determination shall be made on the basis of the calendar years 1996 through 1999. A Twelve-Month Measurement Period is a period of twelve sequential months. For purposes of this sequence, the first month in the four years and the immediately succeeding months shall be considered to follow the forty-eighth month in the four-year period. The four applicable Twelve-Month Measurement Periods to be used in the determination of H{1} for an Installed Capability Entitlement shall be the four sequential Twelve-Month Measurement Periods out of the twelve possible combinations which yield the highest H{1}. 1.5 AMENDMENT OF SECTION 12.2(A)(1), DEFINITION OF "R". The definition of "R" in Section 12.2(a)(1) of the Restated NEPOOL Agreement is amended to read as follows: R for the month is the phase-out factor for the month, which shall be as follows: R=0.75 for the Power Year beginning November 1, 1997. R=0.50 for the 12 month period beginning November 1, 1998. R=0.25 for the 12 month period beginning November 1, 1999. R=0 for the 12 month period beginning November 1, 2000 and all subsequent 12 month periods. SECTION 2 MISCELLANEOUS 2.1 Following execution by the requisite number of Participants in accordance with the Restated NEPOOL Agreement, this Thirty- Seventh Agreement shall become effective November 1, 1998, or on such other date or dates as the Commission shall provide that the amendments provided for in this Agreement shall become effective; provided that such amendments shall not become effective if Participants having the requisite number of Voting Shares give notice in accordance with Section 21.11 of the Restated NEPOOL Agreement that they object to the amendments. 2.2 Terms used in this Thirty-Seventh Agreement that are not defined herein shall have the meanings ascribed to them in the Restated NEPOOL Agreement. 2.3 This Thirty-Seventh Agreement may be executed in any number of counterparts and each executed counterpart shall have the same force and effect as an original instrument and as if all the parties to all the counterparts had signed the same instrument. Any signature page of this Thirty-Seventh Agreement may be detached from any counterpart of this Thirty-Seventh Agreement without impairing the legal effect of any signatures thereof, and may be attached to another counterpart of this Thirty-Seventh Agreement identical in form thereto but having attached to it one or more signature pages. IN WITNESS WHEREOF, each of the signatories has caused a counterpart signature page for this Thirty-Seventh Agreement to be executed by its duly authorized representative as of August 15, 1998. COUNTERPART SIGNATURE PAGE TO THIRTY-SEVENTH AGREEMENT AMENDING NEW ENGLAND POWER POOL AGREEMENT IN WITNESS WHEREOF, the undersigned has caused this counterpart signature page to the Thirty-Seventh Agreement Amending New England Power Pool Agreement, dated as of August 15, 1998, to be executed by its duly authorized representative as of August 15, 1998. Boston Edison Company________________ (Participant) By:/s/ Douglas S. Horan______________ Name: Douglas S. Horan Title: Senior Vice-President Central Maine Power Company__________ (Participant) By:/s/ Arthur Adelberg______________ Name: Arthur Adelberg Title: Exec VP Connecticut Municipal Electric Energy Cooperative (Participant) By:/s/ Maurice R. Scully_____________ Name: Maurice R. Scully Title: Executive Director COMMONWEALTH ENERGY SYSTEM COMPANIES_ (Participant) Cambridge Electric Light Company Canal Electric Company Commonwealth Electric Company By:/s/ James J. Keane________________ Name: James J. Keane Title: Vice President Energy Supply & Engineering Services EASTERN UTILITIES ASSOCIATES COMPANIES Blackstone Valley Electric Company Eastern Edison Company Newport Electric Company (Participants) By:/s/ Kevin A. Kirby________________ Name: Kevin A. Kirby Title: Vice President Fitchburg Gas and Electric Light Company (Participant) By:/s/ David K. Foote________________ Name: David K. Foote Title: Senior Vice President Hingham Municipal Lighting Plant_____ (Participant) By:/s/ Joseph K. Spadea, Jr._________ Name: Joseph K. Spadea, Jr. Title: G.M. Granite State Electric Company_______ (Participant) By:/s/ John G. Cochrane______________ Name: John G. Cochrane Title: Assistant Treasurer Massachusetts Electric Company_______ (Participant) By:/s/ John G. Cochrane______________ Name: John G. Cochrane Title: Treasurer The Narragansett Electric Company____ (Participant) By:/s/ John G. Cochrane______________ Name: John G. Cochrane Title: Treasurer New England Power Company____________ (Participant) By:/s/ Cheryl A. Lafleur_____________ Name: Cheryl A. Lafleur Title: Vice President North American Energy Conservation, Inc. (Participant) By:/s/ William J. Wagers_____________ Name: William J. Wagers Title: Director, Electric Wholesale Marketing NORTHEAST UTILITIES SYSTEM COMPANIES_ The Connecticut Light and Power Company Holyoke Power and Electric Company Holyoke Water Power Company Public Service Company of New Hampshire Western Massachusetts Electric Company (Participants) By:/s/ Frank P. Sabatino_____________ Name: Frank P. Sabatino Title: Vice President of Wholesale Marketing SOUTH HADLEY ELECTRIC LIGHT DEPARTMENT (Participant) By:/s/ Wayne D. Doerpholz____________ Name: Wayne D. Doerpholz Title: Manager PG&E Energy Trading-Power, L.P.______ (Participant) By:/s/ Sarah M. Barpoulis____________ Name: Sarah M. Barpoulis Title: Senior Vice President Strategic Energy Ltd.________________ (Participant) By:/s/ John E. Molinda_______________ Name: John E. Molinda Title: Director, Electricity Market & Strategy Development The United Illuminating Company______ (Participant) By:/s/ Stephen Goldschmidt___________ Name: Stephen Goldschmidt Title: VP Planning & Information Resources Unitil Resources, Inc._______________ (Participant) By:/s/ James G. Daly_________________ Name: James G. Daly Title: President Unitil Power Corp.___________________ (Participant) By:/s/ David K. Foote________________ Name: David K. Foote Title: Senior Vice President Velco________________________________ (Participant) By:/s/ Richard M. Chapman____________ Name: Richard M. Chapman Title: President and CEO Pres/CEO _____________________________________ (Participant) By:__________________________________ Name: Title: