EXHIBIT 10.25

                                FOURTH AMENDMENT
                               TO CREDIT AGREEMENT

THIS FOURTH  AMENDMENT TO LOAN AGREEMENT (this "Fourth  Amendment")  dated as of
June 24,  1997,  is made and entered  into by and between  EMCON,  a  California
Corporation ("Borrower"), and UNION BANK OF CALIFORNIA, N.A. ("Bank"), successor
in interest to the Bank of California, N.A.

                                    RECITALS:

A.   Borrower  and Bank are  parties to that  certain  Credit  Agreement  dated
     February 29, 1996 as amended from time (the "Agreement"), pursuant to which
     Bank agreed to extend credit to Borrower.

B.   Borrower  is  currently  indebted  to  Bank  under  the  Agreement  in the
     aggregate  principal  amount of  $15,928,571  and  Borrower has no defense,
     offset or  counterclaim  against  Bank or any other  person or entity  that
     diminishes such indebtedness.

Now,  therefore,  in  consideration  of the  above  recitals  and of the  mutual
covenants and conditions contained herein, Borrower and Bank agree as follows:

                                   AGREEMENT:

1.   Defined  Terms.  Initially  capitalized  terms  used  herein  which 
     are not otherwise defined shall have the meanings assigned thereto
     in the Agreement.

2.   Amendments to the Agreement.

     (a)  In  ARTICLE 1 -  DEFINITIONS,  "Termination  Date" is  amended  in its
          entirety to read as follows:

              ""Terminate  Date"  means  the  earlier  of (a) the date  Bank may
              terminate  making  Advances or  extending  credit  pursuant to the
              rights of Bank under  Article 7; or (b) May 29,  1998 for the Line
              of Credit; or (c) June 30, 2001 for the Term Loan."

     (b)  In ARTICLE 1 - DEFINITIONS,  "Permitted Liens" is amended by adding
          the following:

         "(vii) Deed of Trust on that certain real  property the common  address
         of which is 725 Friendship Drive, New Concord, Ohio".

         "(viii) Liens created pursuant to that certain Security Agreement dated
         as of April 4, 1996 among Organic Waste Technologies,  Inc. ("OWT") and
         its subsidiaries and Charter One Bank F.S.B. in support of that certain
         $4,850,000  Equipment Term Loan of same date to OWT (the "OWT Equipment
         Loan")."

     (c) Section 2.1.1 (a) Advances is hereby  amended by  substituting  in line
         six the amount "$100,00.00" for the amount "$10,000.00".

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     (d) Section 5.2 (b) Tangible Net  Worth/Debt to Worth is hereby  amended by
         substituting the amount "Forty-One  Million Dollars  ($41,000,000)" for
         the amount "Thirty Six Million Dollars ($36,000,000)".

     (e) Section 5.4 (b)  Year-End  Financial  Statements  is hereby  amended by
         deleting in line four the words "and consolidating".

     (f) Section 5.4 (e) Financial Projections is hereby amended in its entirety
         to read as follows:

         "As soon as available, but no later than December 31 of the prior year,
         a complete copy of Borrower's annual,  company-prepared projections for
         the  ensuing  fiscal  year,  which  shall  include   consolidating  and
         consolidated statements of income."

     (g) Section 6.7 Loans/Investments is hereby amended by adding the 
         following:

         "(j)  The OWT Equipment Loan"

         "(k) A mortgage on that  certain real  property  the common  address of
              which is 725 Friendship  Drive,  New Concord,  Ohio in a principle
              amount not to exceed One  Million  Two  Hundred  Thousand  Dollars
              ($1,200,000)."

     (h) Section 6.8 Limitation on Capital Expenditures/Leases is amended in 
         its entirety to read as follows:

              "Expend or be committed to expend,  on a consolidated  basis, Four
              Million  Dollars  ($4,000,000)  or more in the  aggregate  for the
              acquisition  of gross fixed assets or the lease or rental of gross
              fixed  assets  under  capital  leases  during  the  term  of  this
              Agreement;  provided, however, Borrower may obtain operating lease
              lines to be used  solely  for the  purpose of  financing  leachate
              evaporation  systems  projects  in an  amount  not  to  exceed  an
              aggregate of Five Million Dollars  ($5,000,000) and so long as the
              creation  of such lease  lines does not cause a  violation  of any
              financial covenants set forth in Section 5.2 of this Agreement."

3.   Effectiveness of the Fourth  Amendment.  This Fourth Amendment shall become
     effective  as of the date  hereof  when,  and only  when,  Bank  shall have
     received all of the following, in form and substance satisfactory to Bank:

     (a)  The counterpart of this Fourth Amendment, duly executed by Borrower;

     (b)  The Promissory Note, duly executed by Borrower;

     (c)  Such other documents, instruments or agreements as Bank may reasonably
          deem necessary.

     (d)  A non-refundable  fee of Fifteen  Thousand  Dollars  ($15,000) for the
          Line of Credit.

4.   Ratification.  Except as  specifically  amended  hereinabove,  the 
     Agreement  shall  remain in full force and effect and is hereby ratified 
     and confirmed.

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5.   Representations and Warranties.  Borrower represents and warrants as 
     follows:

     (a)  Each of the representations and warranties contained in the Agreement,
     as may be amended hereby, is hereby reaffirmed as of the date hereof,  each
     as if set forth herein;

     (b)  The execution,  delivery and  performance of the Fourth  Amendment and
     any other  instruments  or  documents  in  connection  herewith  are within
     Borrower's power, have been duly authorized,  are legal,  valid and binding
     obligations  of  Borrower,  and are not in  conflict  with the terms of any
     charter,  bylaw, or other organization  papers of Borrower or with any law,
     indenture,  agreement  or  undertaking  to which  Borrower is a party or by
     which Borrower is bound or affected;

     (c)  No event has  occurred  and is  continuing  or would  result from this
     Fourth Amendment which  constitutes or would constitute an Event of Default
     under the Agreement.

6.   Governing Law. This Fourth  Amendment and all other  instruments or 
     documents in connection  herewith shall be governed by and construed 
     according to the laws of the State of California.

7.   Counterparts.  This  Fourth  Amendment  may be executed  in two or more  
     counterparts,  each of which shall be deemed an original and all of which 
     together shall constitute one and the same instrument.

WITNESS the due execution hereof as of the date first above written.



UNION BANK OF CALIFORNIA, N.A.         EMCON

By:      /s/William C. Hinch              By:   \s\Eugene M. Herson
        -------------------------               ------------------------------
Title:   Vice President                Title:    CEO and President
        -------------------------               ------------------------------
                                       By:      \s\R. Michael Momboisse
                                                ------------------------------
                                       Title:   CFO and Vice President, Legal
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