<PAGE>


                     TERMINATION AGREEMENT CONCERNING THE
                         FIRST AMENDED LEASE AGREEMENT


     This TERMINATION AGREEMENT CONCERNING THE FIRST AMENDED LEASE AGREEMENT, 
is by and between DESTEC PROPERTIES LIMITED PARTNERSHIP ("Destec"), a Nevada 
limited partnership, and THE DOW CHEMICAL COMPANY, a Delaware corporation 
("Dow").

     WHEREAS, Destec Ventures, Inc. and Dow entered into a Lease Agreement 
effective December 29, 1989 concerning certain fee simple, leasehold and 
other property interests, including options to acquire fee or determinable 
fee ownership, in various lignite-containing lands in Texas; and

     WHEREAS, the Lease Agreement was amended, superseded and replaced in its 
entirety by the First Amended Lease Agreement effective the 1st day of 
January, 1990; 

     WHEREAS, Destec Ventures, Inc. assigned all its rights, title and 
interest in the Lease Agreement and the First Amended Lease Agreement to 
Destec Properties Limited Partnership by an Assignment executed as of 
December 17, 1991;

     WHEREAS, Destec Ventures, Inc. conveyed its fee simple properties 
covered by the First Amended Lease Agreement to Destec Properties Limited 
Partnership;

     WHEREAS, Destec Ventures, Inc. assigned its leases covered by the First 
Amended Lease Agreement to Destec Properties Limited Partnership; and

     WHEREAS, Dow and Destec now mutually desire to terminate the First 
Amended Lease Agreement because Dow has exercised its option to purchase all 
of Destec's interests in all of the reserves covered by the First Amended 
Lease Agreement;

     NOW THEREFORE, in consideration of their mutual covenants and 
undertakings Dow and Destec agree as follows:

     1.  FIRST AMENDED LEASE AGREEMENT.  Effective as of the Effective Time, 
     as such term is defined in the Agreement and Plan Of Merger dated 
     February 17, 1997, by and among Destec Energy, Inc., Dow, NGC Corporation
     and NGC Acquisition Corporation II, the First Amended Lease Agreement is
     terminated; provided however, any remedies of either party for any breach
     of the other party's obligations under that Agreement shall survive
     termination of that Agreement.
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     This Agreement has been duly executed by authorized representatives of 
the parties.


DESTEC PROPERTIES LIMITED PARTNERSHIP

BY: DESTEC PROPERTIES, INC.
    GENERAL PARTNER

By:  /s/ Enrique M. Larroucau
    ---------------------------
Name:   Enrique M. Larroucau
Title:  Senior Vice President, Chief
        Financial Officer and Treasurer


THE DOW CHEMICAL COMPANY

By:  /s/ B.G. Taylorson
    ---------------------------
Name:   B.G. Taylorson
Title:  Corporate Director, Mergers & Acquisitions


WITNESSES: (as to Destec)              WITNESSES: (as to Dow)

/s/ Marian M. Davenport                /s/ Jane M. Gootee
------------------------------         ------------------------------

/s/ David T. Pendergast                /s/ Marc F. Sperber
------------------------------         ------------------------------


STATE OF NEW YORK

COUNTY OF NEW YORK

     On this 17th day of February, 1997 before me and the two witnesses 
indicated above appeared Enrique M. Larroucau, who, being duly sworn, stated 
that he is the Senior Vice President, Chief Financial Officer and Treasurer 
of Destec Properties, Inc., General Partner of Destec Properties Limited 
Partnership, a Nevada limited partnership, and that the above Termination 
Agreement Concerning the First Amended Lease Agreement was signed on behalf 
of and is the free act and deed of said limited partnership.


                                       /s/ Stephen F. Arcano
                                       -----------------------------------
                                       NOTARY PUBLIC
                                       STATE OF NEW YORK
                                       MY COMMISSION EXPIRES 

STATE OF NEW YORK

COUNTY OF NEW YORK

     On this 17th day of February, 1997 before me and the two witnesses 
indicated above appeared B.G. Taylorson who, being duly sworn, stated that he 
is the Corporate Director, Mergers & Acquisition of The Dow Chemical Company, 
a Delaware corporation, and that the above Termination Agreement Concerning 
the First Amended Lease Agreement was signed on behalf of and is the free 
act and deed of said corporation.

                                       /s/ Laura Heiman
                                       -----------------------------------
                                       NOTARY PUBLIC
                                       STATE OF NEW YORK
                                       MY COMMISSION EXPIRES