<PAGE>

Exhibit 10.4

                           SECOND AMENDMENT AGREEMENT

     This Second Amendment Agreement is made this ______ day of April, 1999, 
by and between Grays Ferry Cogeneration Partnership, a partnership 
("SELLER"), and PECO Energy Company ("PECO ENERGY") (collectively, the 
"PARTIES").

                                  BACKGROUND

     SELLER and PECO ENERGY are parties to an Agreement for Purchase of 
Electric Output dated July 28, 1992 ("Original Agreement"), pursuant to which 
SELLER agreed to sell, and PECO ENERGY agreed to purchase, the NET ELECTRIC 
OUTPUT to be generated by SELLER from a cogeneration facility ("FACILITY") to 
be constructed by SELLER.

     By an Amendment Agreement signed January 31, 1994, SELLER and PECO 
ENERGY amended the Original Agreement to reflect SELLER's desire to construct 
the FACILITY in two phases. Thus, the Original Agreement was substituted with 
(1) an Agreement for Purchase of Electric Output (Phase I) from SELLER's 
cogeneration FACILITY up to 31 megawatts, and (2) an Agreement for Purchase of 
Electric Output (Phase II) from SELLER's cogeneration FACILITY up to 119 
megawatts ("Revised Agreements").

     In addition, SELLER and PECO ENERGY entered into two Contingent 
Capacity Purchase Addendums to the Agreements for Purchase of Electric Output 
(for Phase I and Phase II) dated as of September 17, 1993 ("Capacity 
Addendums"). Under these Capacity Addendums, SELLER agreed to sell, and PECO 
ENERGY agreed to purchase, electric capacity from the 31 megawatt and 119 
megawatt FACILITIES under certain circumstances.

     In early 1998, a dispute arose between the PARTIES concerning the 
payments to be made by PECO ENERGY under the Revised Agreements and the 
Capacity Addendums. A lawsuit was filed in the Philadelphia Court of Common 
Pleas at April Term, 1998 No. 544 against PECO ENERGY and Adwin (Schuylkill) 
Cogeneration, Inc. by SELLER and the following entities: Trigen-Schuylkill 
Cogeneration, Inc. and NRGG (Schuylkill) Cogeneration, Inc., two of the 
partners of SELLER, and Trigen-Philadelphia Energy Corporation (the "Grays 
Ferry action"). The Chase Manhattan Bank ("CHASE") and Westinghouse Power 
Generation, a Division of CBS Corporation ("WESTINGHOUSE"), provided 
financing to SELLER for construction of the FACILITY. CHASE intervened as a 
plaintiff in the Grays Ferry action, and WESTINGHOUSE filed a separate action 
against PECO ENERGY at May Term, 1998 No. 3454, which was consolidated with 
the Grays Ferry action (the consolidated actions are referred to as "the 
LITIGATION").

     The PARTIES have now reached an amicable resolution of their disputes 
and have entered into an agreement to settle the LITIGATION, as provided in 
the Final Settlement Decree and Order. As a term of the settlement of the 
LITIGATION, the PARTIES have agreed to amend the Revised Agreements and 
Capacity Addendums as follows and CHASE and WESTINGHOUSE have consented to 
the PARTIES' amendment of the Revised Agreements and Capacity Addendums.

<PAGE>

     All capitalized terms not defined herein shall have the meanings 
ascribed to them in the Revised Agreements and the Capacity Addendums

     NOW, THEREFORE, in consideration of the above, and intending to be 
legally bound hereby, the PARTIES agree that the Revised Agreements and 
Capacity Addendums are hereby amended as follows:

     1.   Section 4.1 AMOUNT PURCHASED of the Agreement for Purchase of 
          Electric Output (Phase I) is deleted in its entirety and replaced 
          with the following language:

                    4.1 AMOUNT PURCHASED. Commencing on the DATE OF INITIAL 
               OPERATION, and thereafter during the term of the AGREEMENT, 
               SELLER shall sell and deliver to PECO ENERGY exclusively, and 
               PECO ENERGY shall purchase and accept delivery of, the 
               PROJECT's NET ELECTRIC OUTPUT. Subject to Section 3.1 
               AVAILABILITY of the Capacity Addendum, as amended, PECO ENERGY 
               has the exclusive right to purchase all of the NET ELECTRIC 
               OUTPUT of the FACILITY throughout the term of this AGREEMENT; 
               provided, however, that PECO ENERGY shall not be required to 
               purchase or accept delivery  of NET ELECTRIC OUTPUT from the 
               PROJECT in excess of the lesser of (a) 31 megawatts or (b) the 
               amount of electric output for which the FERC has certified the 
               FACILITY as a QUALIFYING FACILITY. SELLER shall notify the 
               person designated by PECO ENERGY by 10:00 a.m. at least one 
               business day prior to delivering NET ELECTRIC OUTPUT in excess 
               of 150 megawatts per hour (31 megawatts per hour per Phase I, 
               119 megawatts per hour per Phase II), and PECO ENERGY will 
               purchase and accept such NET ELECTRIC OUTPUT from SELLER 
               unless PECO ENERGY notifies SELLER by 12:00 p.m. noon at least 
               one business day prior to delivery that it will not purchase 
               and accept such NET ELECTRIC OUTPUT, in which case SELLER 
               shall have the right to sell such NET ELECTRIC OUTPUT in 
               excess of 150 megawatts per hour to third parties. Should PECO 
               ENERGY elect to accept NET ELECTRIC OUTPUT in excess of 150 
               megawatts per hour, SELLER has no obligation to provide such 
               excess electric output in the amount identified during each 
               hour of the period for which PECO ENERGY has agreed to accept 
               the excess energy.

          Section 4.1 AMOUNT PURCHASED of the Agreement for Purchase of 
          Electric Output (Phase II) is deleted in its entirety and replaced 
          with the following language:

                    4.1 AMOUNT PURCHASED. Commencing on the DATE OF INITIAL 
               OPERATION, and thereafter during the term of the AGREEMENT, 
               SELLER shall sell and deliver to PECO ENERGY exclusively, and 
               PECO ENERGY shall purchase and accept delivery of, the 
               PROJECT's NET ELECTRIC OUTPUT. Subject to Section 3.1 
               AVAILABILITY of the Capacity


                                      2

<PAGE>

               Addendum, as amended, PECO ENERGY has the exclusive right to 
               purchase all of the NET ELECTRIC OUTPUT of the FACILITY 
               throughout the term of this AGREEMENT; provided, however, that 
               PECO ENERGY shall not be required to purchase or accept 
               delivery of NET ELECTRIC OUTPUT from the PROJECT in excess of 
               the lesser of (a) 119 megawatts or (b) the amount of electric 
               output for which the FERC has certified the FACILITY as a 
               QUALIFYING FACILITY. SELLER shall notify the person designated 
               by PECO ENERGY by 10:00 a.m. at least one business day prior 
               to delivering NET ELECTRIC OUTPUT in excess of 150 megawatts 
               per hour (31 megawatts per hour per Phase I, 119 megawatts 
               per hour per Phase II), and PECO ENERGY will purchase and 
               accept such NET ELECTRIC OUTPUT from SELLER unless PECO ENERGY 
               notifies SELLER by 12:00 p.m. noon at least one business day 
               prior to delivery that it will not purchase and accept such 
               NET ELECTRIC OUTPUT, in which case SELLER shall have the right 
               to sell such NET ELECTRIC OUTPUT in excess of 150 megawatts 
               per hour to third parties. Should PECO ENERGY elect to accept 
               NET ELECTRIC OUTPUT in excess of 150 megawatts per hour, 
               SELLER has no obligation to provide such excess electric 
               output in the amount identified during each hour of the period 
               for which PECO ENERGY has agreed to accept the excess energy.

     2.   Section 4.3(c) of both Revised Agreements is deleted in its 
          entirety and replaced with the following language:

               "(c) Commencing after the FINAL PROJECTION DATE of December 
               31, 2000 and through December 31, 2004, the Output Purchase 
               Payment shall be ninety-eight percent (98%) of the PJM VALUE."

     A new Section 4.3(d) is added to both Revised Agreements after the 
     revised Section 4.3(c) as follows:

               "(d) Commencing on January 1, 2005 and through December 31, 
               2017, the remaining term of the AGREEMENT, the Output Purchase 
               Payment shall be eighty-seven percent (87%) of the PJM VALUE."

     3.   A new Section 4.3(e) is added to both Revised Agreements after the 
          new Section 4.3(d) as follows:


                                      3

<PAGE>

               "(e) Notwithstanding the other provisions of this Section, 
               payment for NET ELECTRIC OUTPUT in excess of 150 megawatts per 
               hour from the combined Phase I and Phase II FACILITY shall be at 
               the PJM VALUE, unless SELLER fails to provide PECO ENERGY with 
               the notice required by Section 4.1 in which case payment for 
               NET ELECTRIC OUTPUT in excess of 150 megawatts per hour shall 
               be ninety-eight percent (98%) of the PJM VALUE through 
               December 31, 2004, and eighty-seven percent (87%) of the 
               PJM VALUE through December 31, 2017."

     4.   The following language is added to the end of Section 3.1 
          AVAILABILITY of both of the Capacity Addendums:

               "SELLER shall be entitled to sell to third parties any 
               capacity from the FACILITY in excess of the NOMINATED 
               CAPACITY of 150 megawatts."

     5.   Line 10 of Section 6.9 DISPATCH of both Capacity Addendums is 
          revised as follows:

          "twenty (20)" shall be deleted and replaced with "fifty (50)", so 
          that the third sentence of Section 6.9 DISPATCH as revised, 
          reads in its entirety: "The scheduling of DISPATCH PERIODS shall 
          be at the sole discretion of PECO, except that (A) a DISPATCH 
          PERIOD shall not exceed sixteen (16) hours in duration and (B) 
          PECO shall not schedule more than fifty (50) DISPATCH PERIODS 
          in a CALENDAR YEAR."

     6.   Other than the amendments stated above, the Revised Agreements and 
          the Capacity Addendums shall remain unchanged.

     7.   This Second Amendment Agreement may be executed in counterparts 
          each of which shall constitute an original and all of which 
          together shall constitute one Agreement.

     This Second Amendment Agreement shall become effective upon its 
execution by authorized representatives of the PARTIES, CHASE and WESTINGHOUSE, 
and upon the entry of the Final Settlement Decree and Order by the Court in 
the LITIGATION.


                                      4

<PAGE>

     IN WITNESS WHEREOF the PARTIES have caused this Second Amendment 
Agreement to be executed as of the day and year first above written.


                                           PECO ENERGY COMPANY


Attest:  /s/ [ILLEGIBLE]                   By: /s/ Michael J. Egan
       ------------------------------         --------------------------------
        Secretary                             MICHAEL J. EGAN, SENIOR VICE
                                              PRESIDENT-FINANCE AND CHIEF 
                                              FINANCIAL OFFICER


                                           GRAYS FERRY COGENERATION
                                           PARTNERSHIP
                                           By Trigen-Schuylkill Cogeneration, 
                                           Inc., its Managing General Partner
Attest:                                    By: /s/ [ILLEGIBLE]
       ------------------------------         --------------------------------
        Secretary                              President



CONSENTED TO:
                                           THE CHASE MANHATTAN BANK


Attest:  /s/ Deborah [ILLEGIBLE]           By: /s/ Cathryn A. Greene   4/27/99
       ------------------------------         --------------------------------
       Assistant Treasurer                    Cathryn A. Greene



CONSENTED TO:
                                           WESTINGHOUSE POWER GENERATION


Attest:                                    By:
       ------------------------------         --------------------------------
       Secretary


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