EXHIBIT 10.35

                                 NINTH AMENDMENT
                               TO CREDIT AGREEMENT

THIS NINTH AMENDMENT TO CREDIT  AGREEMENT (this "Ninth  Amendment")  dated as of
December 22, 1998, 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 to 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 commitment amount of $13,785,713 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:

                  ""Termination 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) February 1, 1999,  for the Line of Credit;  or (c) June
30, 2001 for the Term Loan."

3.       Effectiveness of the Ninth amendment. This Ninth 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  Ninth  Amendment,  duly  executed  by
          Borrower;

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

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 executive,  delivery and performance of the Ninth 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
         Ninth  Amendment  which  constitutes  or would  constitute  an Event of
         Default under the Agreement.

6.       Governing  Law.  This  Ninth  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  Ninth  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/  David Jackson                             By:  /s/ Eugene M. Herson
- - -------------------------                           ----------------------------
Title:  Vice President                              Title:  CFO & President 



                                                    By:  /s/  R. Mike Momboisse
                                                    ----------------------------
                                                    Title:  CFO and VP Legal 



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                                 PROMISSORY NOTE
                                   (BASE RATE)


Borrower Name:  EMCON

Borrower Address:                         Office  70061
400 SOUTH EL CAMINO  REAL,  STE 1200      Loan Number  259-668-7520  0081-00-000
SAN MATEO, CA 94402                       Maturity Date FEBRUARY 1, 1999
                                          Amount  $10,000,000.00

$10,000,000.00                            Date  DECEMBER 31, 1998
- - --------------                            -----------------------

FOR VALUE RECEIVED, on FEBRUARY 1, 1999, the undersigned  ("Debtor") promises to
pay to the order of UNION BANK OF CALIFORNIA, N.A. ("Bank"), as indicated below,
the principal sum of TEN MILLION AND NO/100 Dollars ($10,000,000.00), or so much
thereof as is disbursed, together with interest on the balance of such principal
from time to time  outstanding,  at the per annum rate or rates and at the times
set forth below.

1. INTEREST PAYMENTS. Debtor shall pay interest at maturity. Should interest not
be paid when due, it shall become a part of the  principal  and bear interest as
herein  provided.  All computations of interest under this note shall be made on
the basis of a year of 360 days, for actual days elapsed.

         a.  BASE  INTEREST  RATE.  At  Debtor's  option,   amounts  outstanding
         hereunder  in  minimum  amounts  of at  least  $100,000.00  shall  bear
         interest  at a rate,  based on an index  selected  by Debtor,  which is
         1.50% per annum in excess of Bank's  LIBOR-Rate for the Interest Period
         selected by Debtor, acceptable to Bank.

         No Base  Interest  Rate may be changed,  altered or otherwise  modified
         until the  expiration of the Interest  Period  selected by Debtor.  The
         exercise of  interest  rate  options by Debtor  shall be as recorded in
         Bank's  records,  which  records  shall be prima facie  evidence of the
         amount  borrowed  under either  interest  option and the interest rate;
         provided,  however,  that failure of Bank to make any such  notation in
         its records shall not discharge  Debtor from it obligations to repay in
         full with interest all amounts borrowed. In no event shall any Interest
         Period extend beyond the maturity date of this note.

         To exercise this option,  Debtor may, from time to time with respect to
         principal  outstanding  on which a Base  Interest Rate is not accruing,
         and on the expiration of any Interest  Period with respect to principal
         outstanding  on which a Base Interest Rate has been accruing  select an
         index  offered by Bank for a Base  Interest  Rate Loan and an  Interest
         Period by telephoning an authorized  lending officer of Bank located at
         the banking office identified below prior to 10:00 a.m.,  Pacific time,
         on any Business Day and  advising  that officer of the selected  index,
         the  Interest   Period  and  the   Origination   Date  selected  (which
         Origination   Date,  for  a  Base  Interest  Rate  Loan  based  on  the
         LIBOR-Rate, shall follow the date of such selection by no more than two
         (2) Business Days).

         Bank will mail a written  confirmation of the terms of the selection to
         Debtor  promptly  after the  selection  is made.  Failure  to send such
         confirmation  shall not affect Bank's rights to collect  interest at at
         the rate selected. If, on the date of the selection, the index selected
         is  unavailable  for any  reason,  the  selection  shall be void.  Bank
         reserves  the  right to fund the  principal  from any  source  of funds
         notwithstanding any Base Interest Rate selected by Debtor.

         b. VARIABLE INTEREST RATE. All principal outstanding hereunder which is
         not bearing  interest at a Base  Interest Rate shall bear interest at a
         rate per annum of equal to the Reference Rate, which rate shall vary as
         and when the Reference Rate changes.

         At any  time  prior  to the  maturity  of  this  note,  subject  to the
         provisions  of  paragraph  4, below,  of this note,  Debtor may borrow,
         repay and reborrow  hereon so long as the total  outstanding at any one
         time does not exceed the  principal  amount of this note.  Debtor shall
         pay any  amounts  due under  this note in  lawful  money of the  United
         States at Bank's NORTHERN CALIFORNIA COMMERCIAL BANKING Office, or such
         other office as may be designated by Bank, from time to time.

2.       LATE  PAYMENTS.  If any  payment  required by the terms of this note
shall  remain  unpaid ten days after same is due, at the option of Bank,  Debtor
shall pay a fee of $100 to Bank.


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3.       INTEREST RATE  FOLLOWING  DEFAULT.  In the event of default,  at the
option of Bank, and, to the extend  permitted by law,  interest shall be payable
on the  outstanding  principal under this note at a per annum rate equal to five
percent (5%) in excess of the interest rate specified in paragraph 1.b.,  above,
calculated  from the date of default  until all amounts  payable under this note
are paid in full.

4.       PREPAYMENT.

         a. Amounts outstanding under this note bearing interest at a rate based
         on the  Reference  Rate may be prepaid in whole or in part at any time,
         without penalty or premium. Debtor may prepay amounts outstanding under
         this note bearing  interest at a Base Interest Rate in whole or in part
         provided  Debtor  has given Bank not less than five (5)  Business  Days
         prior written notice of Debtor's  intention to make such prepayment and
         pays to Bank the liquidated damages due as a result. Liquidated Damages
         shall  also  be  paid,  if  Bank,  for  any  other  reason,   including
         acceleration or  foreclosure,  receives all or any portion of principal
         bearing interest at a Base Interest Rate prior to its scheduled payment
         date.  Liquidated Damages shall be an amount equal to the present value
         of the product of: (i) the difference  (but not less than zero) between
         (a) the Base Interest Rate applicable to the principal  amount which is
         being  prepaid,  and (b) the return  which Bank could obtain if it used
         the amount of such  prepayment  of  principal  to purchase at bid price
         regularly  quoted  securities  issued  by the  United  State  having  a
         maturity  date most  closely  coinciding  with the  relevant  Base Rate
         Maturity Date and such  securities were held by Bank until the relevant
         Base Rate Maturity Date ("Yield Rate"); (ii) a fraction,  the numerator
         of  which  is the  number  of days in the  period  between  the date of
         prepayment and the relevant Base Rate Maturity Date and the denominator
         of which is 360;  and (iii)  the  amount of the  principal  so  prepaid
         (except in the event that  principal  payments are scheduled  under the
         terms of the Base  Interest  Rate Loan  being  prepaid,  then an amount
         equal to the lesser of (A) the amount  prepaid or (B) 50% of the sum of
         (1) the amount prepaid and (2) the amount of principal  scheduled under
         the  terms  of  the  Base  Interest  Rate  Loan  being  prepaid  to  be
         outstanding  at the relevant  Base Rate Maturity  Date).  Present value
         under  this note is  determined  by  discounting  the above  product to
         present value using the Yield Rate as the annual discount factor.

         b. In no event shall Bank be obligated to make any payment or refund to
         Debtor,  nor shall  Debtor be  entitled  to any  setoff or other  claim
         against  bank,  should the return  which Bank could  obtain  under this
         prepayment formula exceed the interest that Bank would have received if
         no prepayment had occurred.  All  prepayments  shall include payment of
         accrued  interest  on the  principal  amount  so  prepaid  and shall be
         applied to payment of  interest  before  application  to  principal.  A
         determination by Bank as to the prepayment fee amount, if any, shall be
         conclusive.

         c. Bank shall  provide  Debtor a  statement  of the  amount  payable on
         account of prepayment.  Debtor acknowledges that (i) Bank establishes a
         Base  Interest  Rate upon the  understanding  that it apply to the Base
         Interest  Rate  Loan  for the  entire  Interest  Period,  and  (ii) any
         prepayment may result in Bank incurring  additional costs,  expenses or
         liabilities;  and Debtor  agrees to pay these  liquidated  damages as a
         reasonable  estimate of the costs,  expenses  and  liabilities  of Bank
         associated with such prepayment.

5.       DEFAULT AND ACCELERATION OF TIME FOR PAYMENT.  Default  shall  include,
but not be limited to, any of the  following:  (a) the failure of Debtor to make
any payment required under this note when due; (b) any breach, misrepresentation
or other default by Debtor, any guarantor,  co-maker endorser,  or any person or
entity  other  than  Debtor  providing   security  for  this  note  (hereinafter
individually and  collectively  referred to as the "Obligor") under any security
agreement,  guaranty or other  agreement  between Bank and any obligor;  (c) the
insolvency  of any Obligor or the failure of any Obligor  generally  to pay such
Obligor's debts as such debts become due; (d) the commencement as to any Obligor
of  any  voluntary  or  involuntary   proceeding  under  any  laws  relating  to
bankruptcy, insolvency,  reorganization,  arrangement, debt adjustment or debtor
relief;  (e) the  assignment  by any Obligor  for the benefit of such  Obligor's
creditors;  (f) the  appointment,  or  commencement  of any  proceeding  for the
appointment  of a receiver,  trustee,  custodian or similar  official for all or
substantially  all  of any  Obligor's  property;  (g)  the  commencement  of any
proceeding  for  the  dissolution  or  liquidation  of  any  Obligor;   (h)  the
termination  of  existence or death of any Obligor;  (i) the  revocation  of any
guaranty or subordination  agreement given in connection with this note; (j) the
failure of any Obligor to comply with any order, judgment,  injunction,  decree,
writ or  demand  of any  court or other  public  authority;  (k) the  filing  or
recording against any Obligor,  or the property of any Obligor, of any notice or
levy,  notice to withhold,  or other legal process for taxes other than property
taxes;  (l) the  default  by any  obligor  personally  liable for  amounts  owed
hereunder on any obligation  concerning the borrowing of money; (m) the issuance
against any Obligor,  or the property of any Obligor, of any writ of attachment,
execution,  or other  judicial lien; or (n) the  deterioration  of the financial
condition of any Obligor  which  results in Bank  deeming  itself in good faith,
insecure. Upon the occurrence of any such default, Bank, in its discretion,  may
cease to advance funds hereunder and may declare 

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all obligations under this note immediately due and payable;  however,  upon the
occurrence  of an  event of  default  under  d, e, f, or g,  all  principal  and
interest shall automatically become immediately due and payable.

6.      ADDITIONAL  AGREEMENTS  OF DEBTOR.   If  any  amounts  owing  under this
note are not paid  when due,  Debtor  promises  to pay all  costs and  expenses,
including  reasonable  attorneys'  fees,  incurred by Bank in the  collection or
enforcement of this note.  Debtor and any endorsers of this note for the maximum
period  of time and the full  extent  permitted  by law,  (a)  waive  diligence,
presentment,  demand,  notice of  nonpayment,  protest,  notice of protest,  and
notice of every  kind;  (b) waive the right to assert the defense of any statute
of limitations to any debt or obligation hereunder;  and (c) consent to renewals
and  extensions  of time for the payment of any amounts due under this note.  If
this note is signed by more than one party,  the term "Debtor"  includes each of
the undersigned and any successors in interest  thereof;  all of whose liability
shall be joint and several.  Any married  person who signs this note agrees that
recourse  may be had  against  the  separate  property  of that  person  for any
obligations  hereunder.  The  receipt  of any check or other  item of payment by
Bank,  at its option,  shall not be  considered a payment on account  until such
check or other  item of payment is honored  when  presented  for  payment at the
drawee  bank.  Bank may  delay the  credit of such  payment  based  upon  Bank's
schedule of funds availability,  and interest under this note shall accrue until
the funds are deemed  collected.  In any action  brought under or arising out of
this note,  Debtor and any  Obligor,  including  their  successors  and assigns,
hereby consent to the  jurisdiction  of any competent  court within the State of
California, as provided in any alternative dispute resolution agreement executed
between  Debtor  and Bank,  and  consent  to  service  of  process  by any means
authorized by said state's law. The term "Bank"  includes,  without  limitation,
any holder of this note.  This note shall be  construed in  accordance  with and
governed by the laws of the State of California.  This note hereby  incorporates
any  alternative  dispute  resolution  agreement  previously,   concurrently  or
hereafter executed between Debtor and Bank.

7.        DEFINITIONS.  As  used  herein,  the  following  terms shall have  the
meanings  respectively  set forth below:  "Base  Interest  Rate" means a rate of
interest  based on the  LIBOR-Rate.  "Base  Interest  Rate Loan"  means  amounts
outstanding  under this note that bear interest at a Base Interest  Rate.  "Base
Rate  Maturity  Date" means the last day of the Interest  Period with respect to
principal  outstanding  under a Base Interest Rate Loan.  "Business Day" means a
day on which Bank is open for business for the funding of corporate loans,  and,
with respect to the rate of interest  based on the LIBOR Rate, on which dealings
in U.S. dollar deposits  outside of the United States may be carried on by Bank.
"Interest  Period" means with respect to funds bearing  interest at a rate based
on the LIBOR  Rate,  any  calendar  period of one,  three,  six,  nine or twelve
months. In determining an Interest Period, a month means a period that starts on
one  Business  Day in a month and ends on and  includes  the day  preceding  the
numerically corresponding day in the next month. For any month in which there is
no such numerically  corresponding day, then as to that month, such day shall be
deemed to be the last  calendar  day of such month.  Any  Interest  Period which
would  otherwise  an on a  non-Business  Day  shall  end on the next  succeeding
Business  Day  unless  that is the first  day of a month,  in which  event  such
Interest Period shall end on the next preceding Business Day. "LIBOR Rate" means
a per annum rate of interest (rounded upward, if necessary, to the nearest 1/100
of 1%) at which dollar  deposits,  in immediately  available funds and in lawful
money of the United Sates would be offered to Bank, outside of the United Sates,
for a term  coinciding  with the Interest  Period  selected by Debtor and for an
amount  equal to the amount of  principal  covered  by  Debtors'  interest  rate
selection,   plus  Bank's  costs,  including  the  costs,  if  any,  of  reserve
requirements.  "Origination  Date" means the first day of the  Interest  Period.
"Reference  Rate"  means  the rate  announced  by Bank  from time to time at its
corporate  headquarters  as its Reference  Rate.  The Reference Rate is an index
rate  determined  by Bank  from  time to time  as a  means  of  pricing  certain
extensions  of credit  and is  neither  directly  tied to any  external  rate of
interest  or index nor  necessarily  the lowest  rate of  interest  or index nor
necessarily the lowest rate of interest charged by Bank at any given time.

EMCON             

By:  /s/  Eugene M. Herson                           

Title:  CFO and President                            

By:  /s/ R. Michael Momboisse                        

Title:  CFO and VP Legal                             

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