EXHIBIT 10.6




                                February 29, 1996

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

         RE:      FIXED RATE AMORTIZING 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 a $10,000,000
term loan facility ("Term Loan"), the terms and conditions of which are governed
by the Credit  Agreement,  a Term Loan Note, and various other documents  ("Loan
Documents").  In conjunction with your Term Loan, 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 the 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 Amortizing Term Loan Fixed Rate ("ATLF Rate") is a
fixed rate (more fully  defined  below) the 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 Term Loan  ("Covered  Amount")  and for such time
periods as you and Bank shall mutually  agree.  Pricing tied to the ATLF Rate is
available for one period of 12 to 84 months duration (the  "Period");  provided,
however,  that the last  day of the  Period  must  coincide  with the  scheduled
maturity date of the Term Loan.  This pricing may be applied to Covered  Amounts
in a minimum of $1,000,000  and  additional  increments of $500,000  outstanding
under the Term Loan.

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          Bank's ATLF Rate is a rate comprised of (a) the blended rate per annum
which Bank calculates in good faith, at which funds in the amount of the Covered
Amount with an amortization schedule comparable to that required by the terms of
the Term  Loan  would be  available  to Bank in the  ordinary  course  of Bank's
business on the first day of the 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 ATLF Rate is available and may be accepted only at the time quoted
by Bank.  Due to changes in legal,  regulatory,  economic or market  conditions,
Bank may at any time determine  that the ATLF Rate is not  available,  and thus,
may be unable to offer such a rate.

         2.       QUOTE, THE ATLF RATE, AND PAYMENTS

          For a quote of the  ATLF  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. If you accept the
ATLF Rate when  offered,  that rate will  apply to such  Covered  Amount for the
entire Period.

          During the Period,  you agree to pay interest on the Covered Amount at
the ATLF Rate on the last day of each  consecutive  month,  beginning  the first
such date after the  commencement of the Period,  and continuing  through and on
the maturity date for the Term Loan, whether scheduled or accelerated ("Maturity
Date"). Each regularly scheduled principal payment date under the Term Loan is a
"Principal  Payment Date." During each Period, you must maintain under your Term
Loan a portion of the 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 under the Term  Loan.  Should you have any
obligation  under any other Loan  Document to repay any portion of the Term Loan
("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.

          Bank's records of the date, Covered Amount, ATLF Rate, Period, 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.


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         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 Term Loan.

          Bank establishes the ATLF Rate with the understanding it will apply to
the Covered Amount for the entire 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 Maturity  Date
(but excluding  each payment of principal  required under the Term Loan which is
paid on its applicable  Principal Payment Date), then in consideration  thereof,
you shall pay to Bank on demand:

          a. The amount ("Prepayment  Liquidated Damages"), if any, by which the
          additional  interest  that would have been  payable on the  Prepayment
          exceeds the  interest  the Bank would  receive had it placed an amount
          equal  to the  Prepayment  in the  types  of  United  States  Treasury
          securities described in the calculation below. The date the Prepayment
          is received by Bank in immediately  available funds is the "Prepayment
          Effective Date". The amount of Prepayment  Liquidated  Damages will be
          calculated  in  accordance  with  the  following  formula,   with  all
          Prepayments  applied  first to the remote  instalment(s)  of principal
          then unpaid under the Term Loan:

                  Prepayment Liquidated Damages = P x (L-T) x N

                  Where

                           P =    the total dollar amount of the Prepayment;

                           N =    the  weighted  average  number  of  years
                                  remaining  to maturity  from the  Prepayment
                                  Effective Date for P, where each  successive
                                  year   ("Year")   used  to  calculate  N  is
                                  measured at its  midpoint  (i.e,  0.5 years,
                                  1.5 years, 2.5 years,  etc.) and is weighted
                                  by   the   cumulative   dollar   amount   of
                                  Prepayments   applied   during   that  Year,
                                  rounded to the next highest half-year;

                           L =    the ATLF Rate expressed in annualized decimal
                                  form ("annualized" means not modified for 
                                  number of days);

                           T =    the  "annualized"  fixed rate for a United
                                  States  Treasury  security  with a  maturity
                                  equal  to N where  the rate is  quoted  on a
                                  bond equivalent basis (that is, the security
                                  is deemed to  require  semi-annual  interest
                                  payments  with  interest  calculated  on  an
                                  actual 365/366-day basis) in decimal form. T
                                  will  be  calculated  by  interpolating  the


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                                  rates  for  Treasury   constant   maturities
                                  included  in the  H.15  statistical  release
                                  published  by the  Federal  Reserve  for the
                                  latest weekly period prior to the Prepayment
                                  Effective Date.

 

          Bank may rely  upon  reports  transmitted  by the Dow  Jones  Telerate
          service,  the  Bloomberg  Financial  Markets,  Commodities,  and  News
          service, or any other news service it deems reputable to timely obtain
          values for rates on Treasury  constant  maturities.  If the prepayment
          calculation  requires the rate for a maturity that is not available in
          the  H.15  Treasury  constant  maturities  or if the H.15  release  is
          unavailable,  Bank at its discretion  may substitute  market yields on
          United States Treasury  securities that it deems to be a current issue
          with the appropriate maturity required to obtain the interpolated rate
          defined by T. In a case where market yields on current issue  Treasury
          securities  are utilized,  Bank will use yield values for the business
          day prior to the  Prepayment  Effective  Date and may depend upon such
          values reported by a financial news service Bank deems reputable.

          If T is  greater  than or equal to L at the  time of  calculation,  no
          payment of any kind is required.

               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.

          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.

         4.       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,


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          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 ATLF 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 ATLF Rate to the extent  any such  costs have not been  previously
          blended or adjusted into the ATLF Rate.

          Bank shall provide you 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.

         5.       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  evidencing  the Term Loan,  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.

          If you would  like to  participate  in the  Bank's  ATLF  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.

          Bank is pleased to serve you.


                      Very truly yours,

                      THE BANK OF CALIFORNIA, N.A.

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


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                              ACCEPTED AND AGREED:

EMCON


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

Dated: February 29, l996


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