Exhibit 10.5

                  This  Amendment  No. 4, dated as of December 16, 1996,  to the
Amended and Restated Decommissioning Trust Agreement (PVNGS Unit 2), dated as of
January 31, 1992,  as amended by Amendment No. 1 thereto dated as of November 1,
1992,  Amendment No. 2 thereto dated as of November 1, 1994, and Amendment No. 3
thereto dated as of June 20, 1996 (the "Decommissioning Trust Agreement";  terms
used herein as therein defined),  is entered into between Arizona Public Service
Company ("APS"),  State Street Bank and Trust Company, as successor to The First
National Bank of Boston, as Owner Trustee and as Lessor,  and Mellon Bank, N.A.,
as Decommissioning Trustee ("Decommissioning Trustee").

                                R E C I T A L S:
                                - - - - - - - - 

                  WHEREAS,  the parties hereto wish to amend the  limitations of
the parties' ability to modify the Decommissioning Trust Agreement under certain
circumstances;

                  NOW, THEREFORE,  in consideration of the premises and of other
good and valuable  consideration,  receipt and  sufficiency  of which are hereby
acknowledged, the parties hereto agree as follows:

                              A G R E E M E N T S:
                              - - - - - - - - - - 

                  SECTION 1. Amendments.

                  The  Decommissioning  Trust  Agreement  is hereby  amended  by
adding the  following as the last sentence of Section 15:  "Notwithstanding  the
foregoing, this Agreement may not be amended or modified in violation of Section
468A of the Code or the regulations thereunder."

                  SECTION 2.  Effectiveness.

                  This  Amendment  No. 4 shall  become  effective as of the date
hereof upon the execution and delivery of a counterpart  of this Amendment No. 4
by each of the parties hereto.

                  SECTION 3.  Miscellaneous.

                  (a)      Full Force and Effect.

                  Except as expressly provided herein, the Decommissioning Trust
Agreement shall remain unchanged and in full force and effect. Each reference in
the  Decommissioning  Trust Agreement and in any exhibit or schedule  thereto to
"this Agreement," "hereto," "hereof" and terms of similar import shall be deemed
to refer to the Decommissioning Trust Agreement as amended hereby.
<PAGE>
                  (b)      Counterparts.

                  This  Amendment  No.  4 may  be  executed  in  any  number  of
counterparts,  all of which taken  together  shall  constitute  one and the same
instrument,  and any of the parties  hereto may execute this  Amendment No. 4 by
signing any such counterpart.

                  (c)      Arizona Law.

                  This Amendment No. 4 shall be construed in accordance with and
governed by the law of the State of Arizona.

                  IN WITNESS  WHEREOF,  the  parties  hereto  have  caused  this
Amendment No. 4 to the Decommissioning Trust Agreement to be duly executed as of
the day and year first above written.

                                        ARIZONA PUBLIC SERVICE COMPANY


                                        By       NANCY E. NEWQUIST
                                           -------------------------------------

                                        Title    Treasurer
                                             -----------------------------------

                                        MELLON BANK, N.A., as
                                        Decommissioning Trustee


                                        By       EARL G. KLECKNER
                                           -------------------------------------
                                                 Earl G. Kleckner
                                        Title    Vice President
                                             -----------------------------------


                                        STATE STREET BANK AND TRUST COMPANY,
                                        as Owner Trustee under a Trust Agreement
                                        with Security  Pacific  Capital  Leasing
                                        Corporation   and  as  Lessor   under  a
                                        Facility   Lease  with  Arizona   Public
                                        Service Company


                                        By       ERIC DONAGHEY
                                           -------------------------------------

                                        Title    Assistant Vice President
                                             -----------------------------------
                                      -2-
<PAGE>
                                        STATE STREET BANK AND TRUST COMPANY,
                                        as Owner Trustee under a Trust Agreement
                                        with  Emerson  Finance Co. and as Lessor
                                        under  a  Facility  Lease  with  Arizona
                                        Public Service Company


                                        By       ERIC DONAGHEY
                                           -------------------------------------

                                        Title    Assistant Vice President
                                             -----------------------------------



STATE OF ARIZONA         )
                         )  ss.
County of Maricopa       )

                  The foregoing  instrument was acknowledged before me this 16th
day of December,  1996, by Nancy E.  Newquist,  the Treasurer of ARIZONA  PUBLIC
SERVICE COMPANY, an Arizona corporation, on behalf of said corporation.


[Official Seal]                         MARIA R. MARRS
                                        -------------------------------
                                        Notary Public

My commission expires:
July 21, 1998



STATE OF PENNSYLVANIA    )
                         )  ss.
County of Allegheny      )

                  The foregoing  instrument was acknowledged before me this 16th
day of October,  1996, by Earl Kleckner, a Trust Officer of MELLON BANK, N.A., a
corporation having trust powers, as Decommissioning  Trustee,  on behalf of said
corporation.


[Official Seal]                         STEPHANIE RIEGER
                                        ---------------------------------
                                        Notary Public

My commission expires:
May 12, 1997
                                      -3-
<PAGE>
Commonwealth of Massachusetts       )
                                    )  ss.
County of Suffolk                   )

                  The foregoing  instrument was acknowledged before me this 13th
day of December,  1996, by Eric Donaghey,  the Assistant Vice President of STATE
STREET BANK AND TRUST COMPANY, a Massachusetts trust company, in its capacity as
Owner Trustee under a Trust  Agreement  with Security  Pacific  Capital  Leasing
Corporation,  and as Lessor under a Facility  Lease with Arizona  Public Service
Company, on behalf of said association in such capacities.


[Official Seal]                            SCOTT KNOX
                                           ---------------------------------
                                           Notary Public

My commission expires:
July 12, 2002


Commonwealth of Massachusetts       )
                                    )  ss.
County of Suffolk                   )

                  The foregoing  instrument was acknowledged before me this 13th
day of December,  1996, by Eric Donaghey,  the Assistant Vice President of STATE
STREET BANK AND TRUST COMPANY, a Massachusetts trust company, in its capacity as
Owner Trustee under a Trust  Agreement  with Emerson  Finance Co., and as Lessor
under a Facility Lease with Arizona Public  Service  Company,  on behalf of said
association in such capacities.


[Official Seal]                             SCOTT KNOX
                                            ---------------------------------
                                            Notary Public

My commission expires:
July 12, 2002
                                       -4-