EXHIBIT 10.5




                                February 29, 1996

EMCON
400 South El Camino Real, Suite 1200
San Mateo, CA  94402
Attn:  R. Michael Momboisse, CFO

                  RE:      EURODOLLAR RATE OPTION AGREEMENT

Dear Mr. Momboisse:

          As of this date,  EMCON has entered into a Credit  Agreement  with The
Bank of  California,  N.A.  ("Bank")  pursuant  to which EMCON has (i) a line of
credit  facility  in the  maximum  principal  amount of  $10,000,000  and (ii) a
$10,000,000 term loan facility (collectively,  the "Credit Facility"), the terms
and conditions of which are governed by the Credit  Agreement,  a Line of Credit
Note,  a Term Loan Note,  and various  other  documents  ("Loan  Documents).  In
conjunction  with your current Credit  Facility,  Bank is pleased to offer you a
chance to participate in a special commercial pricing program.

                  1.       AVAILABILITY AND MATURITY

          Bank  usually  extends  financing  based on a  fluctuating  rate  that
changes  with the rate Bank  announces  to be in effect from time to time as its
prime rate ("Prime Rate"). The Prime Rate is a rate set by Bank based on various
factors,  including  general  economic and market  conditions,  and is used as a
reference point in pricing certain loans.  Bank may price its loans at, above or
below the Prime Rate.

          In  contrast,  Bank's  "Eurodollar  Rate" is a fixed rate (more  fully
defined below) Bank offers from time to time which, if you accept this proposal,
will apply to all or such portion of the principal amount  outstanding under the
Credit  Facility  ("Covered  Amount")  and for such time periods as you and Bank
shall  mutually  agree.  Pricing tied to the  Eurodollar  Rate is available  for
periods of 1, 2, 3, 6, 9 or 12 months (each a "Period"); provided, however, that
no Period shall have a maturity date  subsequent to the scheduled  maturity date
for the Credit Facility with respect to which the Covered Amount  relates.  This
pricing  may be  applied  to Covered  Amounts  in a minimum  of  $1,000,000  and
additional increments of $500,000 outstanding under the Credit Facility.

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          Bank's  "Eurodollar Rate" is, for each Period, a rate comprised of (a)
the rate of interest at which Dollar deposits for such period and in such amount
would be offered to Bank in the Eurodollar Market at a time selected by Bank two
(2) Banking Days (as defined  below) prior to the  commencement  of the relevant
Period,  adjusted  for the  then  maximum  reserve,  capital  adequacy,  deposit
insurance,  and  similar  requirements  that  under  any  circumstance  could be
applicable to Bank pursuant to applicable law or  regulation,  and other amounts
associated with Bank's costs and desired return;  plus (b) a margin equal to one
and one-half percent (1.50%).  The Eurodollar  Market is the market in which the
buying and selling of United States Dollar  deposits  booked  outside the United
States of America occurs among the international banking community.

          Bank's  Eurodollar  Rate is available  and may be accepted only at the
time quoted by Bank for the  applicable  Period  beginning  two (2) Banking Days
hence. Due to changes in legal, regulatory,  economic or market conditions, Bank
may at any time  determine  that  pricing  based on the  Eurodollar  Rate is not
available, and thus, may be unable to offer such a rate.

          2. QUOTE, EURODOLLAR RATE, AND PAYMENTS

          For a quote  of  Bank's  Eurodollar  Rate  which  would  apply  to the
specified  Covered  Amount and Period,  you may call  Bank's San Mateo  Regional
Office  between 8:00 a.m.  and 11:00 a.m.  Pacific time on any day on which such
office and Bank's San Francisco  main office are open for business to the public
(each a "Banking  Day").  As the Eurodollar  Rate is established two (2) Banking
Days prior to the first day of the requested Period,  you must call at least two
(2)  Banking  Days prior to such date.  If you accept the  Eurodollar  Rate when
offered,  that rate will apply to such Covered Amount for the applicable Period.
Interest  shall be  calculated  for actual days  elapsed on the basis of a three
hundred and sixty (360) day year.

          During any Period,  you agree to pay interest on the Covered Amount at
the Eurodollar  Rate on the last day of each  consecutive  month,  beginning the
first such date after the commencement of the Period,  until the last day of the
Period,  whether scheduled or accelerated ("Maturity Date"). During each Period,
you must maintain under your Credit Facility a principal  balance which is not a
Covered Amount under any of your rate option  agreements with Bank sufficient to
cover each scheduled instalment of principal coming due during such Period under
the  Credit  Facility.  Should  you have any  obligation  under any  other  Loan
Document to repay any portion of the Credit Facility  ("Obligation")  that would
conflict  with  your  obligation  under  the  preceding  sentence  ("Maintenance
Obligation"), you shall nevertheless comply with the Obligation and not with the
Maintenance  Obligation,  and you  shall not be  deemed  in  default  hereunder.
Nonetheless,  payment of the Obligation shall be deemed to be a "Prepayment", as
defined below,  to the extent it repays a portion of a Covered Amount under this
or any of your other rate option agreements you may have with Bank.

          If,  prior to a Maturity  Date and while the Credit  Facility is still
available,  you and Bank have not agreed that a new rate tied to the  Eurodollar
Rate shall apply to a Covered Amount,  then, if the term of your Credit Facility
extends beyond such Maturity Date, Bank's Prime Rate plus the applicable margin,


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if any,  under  the  terms  of  your  Credit  Facility  shall  be  automatically
applicable to such Covered Amount.

          Bank's records of the date, Covered Amount,  Period,  Eurodollar Rate,
Maturity Date, and all payments of principal and interest and all other payments
and amounts due under this letter  agreement  shall be conclusive and binding on
you, absent obvious error.

          3. PREPAYMENT LIMITATION

          Do not sign this  letter  agreement  before you read it.  This  letter
          agreement  provides for payment of  liquidated  damages if you wish to
          repay  the  loan  (Covered  Amount)  prior to the  date  provided  for
          repayment under the Credit Facility.

          Bank  establishes the Eurodollar Rate with the  understanding  it will
apply to the Covered Amount for the entire scheduled  Period. If for any reason,
including,  without limitation,  acceleration,  foreclosure or prepayment,  Bank
receives all or any portion of a Covered Amount (each a  "Prepayment")  prior to
the scheduled Maturity Date, then in consideration thereof you shall pay to Bank
on demand:

          a. The amount,  if any, by which the  additional  interest which would
          have been payable on the  Prepayment  exceeds the interest  which Bank
          would  receive  had it placed an amount  equal to the  Prepayment,  in
          United States  Dollars,  on deposit in the  Eurodollar  Market (or, at
          Bank's sole discretion, invested such amount in a domestic certificate
          of deposit issued by an institution rated at least "investment  grade"
          or "A" by Moody's or any successor  rating  agency) for a period equal
          to the period of time  remaining  until the maturity of the applicable
          Period.  Should the  scheduled  maturity  fall between two periods for
          which rates are quoted or  available to Bank,  then Bank,  in its sole
          discretion, shall interpolate this rate; and

          b. Any other out of pocket  costs to Bank  associated  with funding or
          maintaining the Covered Amount.

          Bank shall provide you a statement of the amount payable on account of
each Prepayment, which statement shall be a conclusive and binding determination
of the  amount  owed by you for  such  Prepayment,  absent  obvious  error.  All
Prepayments,  subject to this  Section  3,  shall be applied on the most  remote
instalment or instalments of principal then unpaid on the Credit  Facility being
prepaid.

          You  acknowledge  that any  Prepayment  may  result in Bank  incurring
additional  costs,  expenses  or  liabilities.  Therefore,  you agree to pay the
above-described  liquidated  damages and agree that said amount is a  reasonable
estimate of the costs,  expenses and  liabilities of Bank  associated  with each
Prepayment.

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          4. SPECIAL FUNDING PROVISIONS

          If at any time Bank determines that:

          a. United States Dollar  deposits in principal  amounts similar to the
          Covered Amount bearing interest at the Eurodollar Rate and for periods
          equal to the  relevant  Period  are not  available  in the  Eurodollar
          Market;

          b. The  Eurodollar  Rate does not  cover  the cost to Bank of  making,
          funding or  maintaining  the  Covered  Amount at the  Eurodollar  Rate
          during any Period;

          c. Any  change in  financial,  political  or  economic  conditions  or
          currency exchange rates makes it impractical for Bank to make, fund or
          maintain the Covered Amount at the Eurodollar  Rate during any Period;
          or

          d. Any change in applicable law or regulation or in the interpretation
          thereof  (whether or not having the force of law) makes it unlawful or
          impractical  for Bank to make,  fund or maintain the Covered Amount at
          the Eurodollar  Rate,  then Bank shall promptly give notice thereof to
          you and as of the date  stated in such  notice,  the  Eurodollar  Rate
          option  shall  terminate,  and Bank's  Prime Rate plus the  applicable
          margin under the terms of your Credit Facility shall be  automatically
          applicable  to the  relevant  Covered  Amount  through  the end of the
          relevant Period.

          5. RESERVES, DEPOSIT INSURANCE, CAPITAL ADEQUACY

          You  shall  additionally  compensate  Bank upon  demand  for all costs
incurred,  or losses suffered,  including  without  limitation lost profits,  by
reason of:

          a.  any and all  increases  in  reserve,  deposit  insurance,  capital
          adequacy or similar  requirements  against (or against any class of or
          change in or in the  amount  of) the  assets or  liabilities  of Bank,
          deposits with or for the account of Bank, or loans by Bank, imposed by
          any  governmental or regulatory  authority  (whether or not having the
          force of law) in connection with a Covered Amount bearing  interest at
          the Eurodollar Rate; or

          b. compliance by Bank with any direction,  requirement or request from
          any  governmental or regulatory  authority  (whether or not having the
          force of law) in connection with a Covered Amount bearing  interest at
          the  Eurodollar  Rate to the  extent  any  such  costs  have  not been
          previously blended or adjusted into the Eurodollar Rate.



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          Bank  shall  provide  you with a written  statement  of the amount and
basis of its request for compensation under this Section,  which statement shall
be a  conclusive  and binding  determination  of the amount owed by you,  absent
obvious error.

          6. TAXES

          a. If at any time any taxes,  fees or other  charges of any nature are
          imposed by any  governmental or regulatory  authority on any aspect of
          the  transactions  referred  to in  this  letter  agreement  including
          without  limitation all stamp or documentation  duties  (collectively,
          "Taxes"),  you shall pay such Taxes  directly,  or compensate Bank for
          such payment, as set forth below, except for such Taxes as are imposed
          on Bank's net income.

          b. In the event you are  prohibited  by  operation  of law from making
          payments or  reimbursements  to Bank without making such deductions or
          paying,  or  causing to be paid,  any and all Taxes,  you shall pay to
          Bank upon demand such additional  amounts as may be necessary in order
          to reimburse  Bank for Taxes paid by Bank on your behalf such that the
          aggregate  net amounts  received by Bank shall equal the amounts which
          would have been received if such deduction or withholding had not been
          required.

          c. You shall confirm that all applicable Taxes shall have been paid to
          appropriate  taxing  authorities  or agencies by sending  official tax
          receipts or notarized  copies of such  receipts to Bank within  thirty
          (30) days after  payment of any Taxes.  Should Bank receive  notice of
          any such liability for Taxes, Bank will promptly so inform you.

          7. GENERAL PROVISIONS

          a. To the extent interest rates,  prepayment  provisions and times for
          payment of  interest  established  under  this  letter  agreement  are
          different  than the terms of the note or notes  evidencing  the Credit
          Facility,  the terms of this letter agreement shall prevail. All other
          provisions of the Loan Documents remain in full force and effect.

          b. This letter agreement shall be governed by the laws of the State of
          California.

          c. This letter agreement,  and all confirmations  provided  hereunder,
          evidence the entire  agreement  of the parties on the matters  covered
          herein, and supersede all prior understandings and agreements.



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          If you would like to  participate  in Bank's  Eurodollar  Rate  Option
program,  please  execute  the  enclosed  duplicate  original of this letter and
return it to Bank,  on or before  February  29,  1996,  at which time the option
granted in this letter will otherwise expire.

          The Bank is pleased to serve you.

                            Very truly yours,

                            THE BANK OF CALIFORNIA, N.A.


                            By:     /s/
                                   -------------------------
                                    Marie T. Wiseman, V.P.


ACCEPTED AND AGREED:

EMCON


By:     /s/
       ---------------------
Name:  R. Michael Momboisse
Title: CFO & V.P. - Legal

Dated:  February 29, 1996

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