EXHIBIT 10.27

                              AMENDED AND RESTATED
                                    AGREEMENT


         THIS AGREEMENT  ("Agreement")  is made as of November 3, 1997,  between
EMCON, A California corporation, (the "Company"), and R. Michael Momboisse, (the
"Employee").  Unless otherwise indicated,  certain of the capitalized terms used
herein are defined in Exhibit A and shall have the meaning as assigned.

                                    RECITALS

         A. The Company  recognizes  that the possibility of a Change of Control
Event  exists and that the  Employee  possesses  an  intimate  knowledge  of the
Company. The Board of Directors of the Company (the "Board") believes that it is
necessary  that the Company be able to call on the  Employee for advice upon the
occurrence  of a Change of  Control  Event.  The Board  also  believes  that the
existence of this  Agreement  will enhance the Company's  ability to call on and
rely upon such Employee.

         B. The Company and the Employee  desire to enter into this Agreement in
order to  provide  additional  compensation  and  benefits  to the  Employee  in
recognition  of past services and to encourage  Employee to continue  employment
with the Employer.

         C. It is intended by the parties that the  provisions  of  paragraphs 2
and 3 of this Agreement shall be effective during the eighteen (18) month period
following a Change of Control Event.

                                    AGREEMENT

         NOW, THEREFORE,  for good and valuable consideration,  receipt of which
is hereby acknowledged, the Company and Employee agree as follows:

         1. Term:  Operation of Agreement.  Except as provided in paragraph 1(a)
below, this Agreement shall be effective immediately, and, except as provided in
paragraph 1(b) below,  shall terminate on the eighteenth (18) month  anniversary
following any Change of Control Event.

                  (a) The provisions of paragraphs (2) and (3) of this Agreement
shall not become  effective  unless  (i) there is a Change of Control  Event and
(ii) the Employee is employed by the Company  immediately prior to the Change of
Control Event.  Notwithstanding the foregoing, if the Employee's employment with
the  Company  is  terminated  within  the  ninety  (90) day  period  immediately
preceding a Change of Control Event and such termination  would have constituted
a  Termination  as defined in Exhibit A if  termination  had occurred  after the
Change of Control Event, the termination will be deemed to have occurred the day
after the  Change  of  Control  Event,  such  that  paragraphs  2 and 3 shall be
effective as to such termination.

                  (b)      This Agreement shall terminate on the first to occur
of the following:

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                           (i)      The termination of the Employee's employment
with the Company prior to a Change of Control Event unless such  termination  is
deemed to occur the day  after  such  Change of  Control  Event as  provided  in
paragraph 1(a) above.

                           (ii)     Subject to the provisions of paragraph 3(f) 
below,  the  termination  of the  Employee's  employment  following  a Change of
Control Event is due to any of the  following:  (a)  termination  by the Company
with Cause, (b) death of the Employee,  (c) Permanent Disability of the Employee
or (d) voluntary termination of employment by the Employee without Good Reasons.

         2. Service.  Once a Change of Control Event occurs,  the Employee shall
not voluntarily terminate his employment with the Company until ninety (90) days
after such Event has occurred.  Following a Change of Control Event, the Company
shall not  terminate  the  Employee's  employment  with the  Company,  except in
accordance  with this  Agreement  and the  Company  shall  provide not less than
ninety (90) days prior written notice of such Termination to the Employee.

         3.       Payments and Benefits Upon Termination.  The Employee shall be
entitled to the following payments and benefits following Termination:

                  (a)  Termination  Payment.  The Company shall pay the Employee
within ten (10) days of the date of  Termination  an amount  equal to the sum of
twenty-four  (24) months cash  salary and a prorated  cash bonus,  if earned and
otherwise due.

                  (b) Welfare Plan  Benefits.  The Employee shall be entitled to
continuation of medical insurance  coverage under the Company's  Continuation of
Benefits  Program for Former Senior  Executives  (originally  implemented by the
Company on January 1, 1993). The Company shall pay the cost of medical insurance
coverage for a period equal to the lesser of (i)  twenty-four  months  following
the date of  Termination  or (ii)  until the  Employee  is  provided  by another
employer with medical insurance benefits.  The Employee shall notify the Company
within ten (10) days of any  employment  by the  Employee  during the period the
Company is paying for medical  insurance  coverage  pursuant  to this  paragraph
3(b).

                  (c) Vesting of Benefits.  Employee  shall  become  immediately
vested  in  full  in  any  and  all  employment  benefits,   including,  without
limitation:

                           (i)  Employee's interest in the EMCON Shared Savings 
and Profit Sharing Plan, including the Company match portion; provided that if 
such action is found to be a violation of ERISA,  the Company  shall have the 
option of instead  paying the Employee an amount which after taking account for 
applicable withholding, equals the unvested balance of the Company match portion
of the Employees account.

                           (ii)  all amounts payable as salary continuation and 
noncompetition payments under the salary  continuation  agreements  between the
Employee  and the  Company  dated January  1993,  November  1994;  and  November
9, 1996,  as well as any similar agreements that have been or may hereafter be 
entered into between  Employee and the Company;  provided that (A) the portion 
of such payments representing salary continuation payments shall be immediately

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due  and  payable  upon  full  vesting  and  (B) the  portion  of such  payments
representing  noncompetition payments shall be paid to Employee in equal monthly
installments over a three-year period commencing from the date of departure from
the  Company  and for so long  during the  subsequent  three-year  period as the
Employee is not employed by a competitor or potential competitor of the Company.
For purposes of the  foregoing,  a competitor  or  potential  competitor  of the
Company  shall  be  defined  as  an  environmental  engineering,  consulting  or
construction  company not affiliated  with the Company.  (iii) all incentive and
non-qualified  stock  options to purchase  the  Company's  (or its  successor's)
capital stock, and

                           (iv)   all restricted stock agreements.

                  (d) Continued Right to Exercise Options. Employee shall retain
the right to exercise all of the incentive and  nonqualified  stock options held
by Employee and referred to in paragraph  3(c)(iii)  above for a period of up to
three years after  Employee's  departure from the Company or, if earlier,  until
expiration of the original term of the  respective  option  agreements,  and for
these purposes Employee shall be considered a continuing employee of EMCON.

                  (e) No  Mitigation.  All  payments  and  benefits to which the
Employee is entitled  under this  Agreement  shall be made and provided  without
offset,  deduction or  mitigation  on account of income the Employee may receive
from other employment or otherwise, except as provided in paragraph 3(b) above.

                  (f)  Death of the  Employee.  In the  event of the  Employee's
death  subsequent  to  Termination,  all payments and benefits  required by this
Agreement   shall  be  paid  to  the   Employee's   designated   beneficiary  or
beneficiaries  or, if he has not designated a beneficiary or  beneficiaries,  to
his estate.

         4. Arbitration.  Any claim, dispute or controversy arising out of or in
any way relating to the parties'  employment  relationship  (including,  but not
limited  to,  any  claims  of  wrongful   termination   or  age,  sex  or  other
discrimination),  this Agreement,  the  interpretation  of this Agreement or the
alleged breach thereof shall be submitted by the parties to binding  arbitration
by the  American  Arbitration  Association  in  San  Mateo  County,  California;
provided,  however,  that  this  arbitration  provision  shall  not apply to any
disputes or claims relating to or arising out of the misuse or  misappropriation
of the Company's trade secrets or confidential and proprietary information.

         5.  Conflict in  Benefits.  This  Agreement  amends and  restates  that
certain  Agreement  between the Employee and the Company dated November 30, 1995
and shall supersede all other prior  arrangements,  whether written or oral, and
understandings  regarding  the  subject  matter  of  this  Agreement;  provided,
however,  that this Agreement is not intended to and shall not affect,  limit or
terminate  (i) any plans,  programs,  or  arrangements  of the company  that are
either in  writing  or  regularly  made  available  to a  significant  number of
employees of the Company,  (ii) any agreement or  arrangement  with the Employee
that has been  reduced  to  writing,  or (iii) any  agreements  or  arrangements
hereafter entered into by the parties in writing.


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         6.       Miscellaneous.

                  (a) Notices. Any notice or other communication provided for in
this Agreement or contemplated  hereby shall be  sufficiently  given if given in
writing and personally  delivered or delivered by certified mail, return receipt
requested, and addressed, in the case of the Company, to the Company at:

                           EMCON
                           400 S. El Camino Real, Suite 1200
                           San Mateo, CA  94402
                           Attn:  Chairman of the Board

and, in the case of the Employee, to the Employee at:

                           R. Michael Momboisse
                           1920 Polk Court
                           Mountain View, CA  94040

Either  party may  designate a  different  address by giving  written  notice of
change of address in the manner provided above.

                  (b) Waiver.  No waiver or  modification in whole or in part of
this Agreement,  or any term or condition hereof, shall be effective against any
party  unless in writing  and duly signed by the party  sought to be bound.  Any
waiver of any breach of any provision  hereof or any right or power by any party
on one occasion shall not be construed as a waiver of, or a bar to, the exercise
of such right or power on any other  occasion  or as a waiver of any  subsequent
breach.

                  (c)  Binding  Effect;  Successors.  This  Agreement  shall  be
binding upon,  inure to the benefit of, and be  enforceable  by, the Company and
the Employee and their respective heirs, legal  representatives,  successors and
assigns.  For purposes of the  foregoing,  the  successors  to the Company shall
include,  without  limitation,   successors  (whether  direct  or  indirect,  by
purchase,  merger,  consolidation,  or otherwise) to all or substantially all of
the  business or assets of the Company (a "Company  Successor").  If the Company
shall be merged into or consolidated with another entity, the provisions of this
Agreement shall be binding upon and inure to the benefit of the entity surviving
such  merger  or  resulting  from such  consolidation.  The  provisions  of this
paragraph  6(c)  shall  continue  to apply to each  subsequent  employer  of the
Employee  hereunder  in the event of any  subsequent  merger,  consolidation  or
transfer or assets of such subsequent employer.

                  (d)  Separability.  Any provision of this  Agreement  which is
unenforceable  or  invalid  in any  jurisdiction  shall be  ineffective  in such
jurisdiction to the extent that it is unenforceable or invalid without affecting
the remaining  provisions hereof, which shall continue in full force and effect.
The  unenforceability  or  invalidity  of a provision  of this  Agreement in one
jurisdiction shall not invalidate or render  unenforceable such provision in any
other jurisdiction.

                  (e)  Controlling  Law. This Agreement shall be governed by and
construed in accordance  with the laws of the State of California  applicable to
contracts made and to be performed therein.

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         IN WITNESS  WHEREOF,  the Company and the Employee  have  executed this
Agreement as of the day and year first above written.

                                    COMPANY:
                                    EMCON, a California Corporation



                                    By: /s/ Douglas P. Crane 
                                        ---------------------------------------
                                        Douglas P. Crane, Chairman of the Board


                                    EMPLOYEE:



                                    By: /s/ R. Michael Momboisse
                                        ------------------------
                                        R. Michael Momboisse


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                                    EXHIBIT A
                                   DEFINITIONS

         As used in this Agreement,  and unless the context requires a different
meaning, the following terms mean:

         (i)  "Cause"  means  (a)  theft,  dishonesty  or  falsification  of any
employment  or  Company  records;  (b)  improper  disclosure  of  the  Company's
confidential  or proprietary  information;  (c) any  intentional act by Employee
which has a material detrimental effect on the Company's reputation or business;
or (d) failure to perform any reasonable  assigned duties,  which failure is not
cured within thirty (30) days following  written notice of such failure from the
Company.

         (ii) "Change of Control  Event" means an Ownership  Change of which the
shareholders of the Company before such Ownership Change do not retain, directly
or indirectly, at least seventy percent (70%) of the beneficiary interest in the
voting stock of the Company  after such  transaction  or in which the Company is
not the surviving corporation.

         (iii) An  "Ownership  Change"  shall be deemed to have  occurred in the
event any of the following events occurs with respect to the Company;

                  A.       the direct or indirect sale or exchange by the 
shareholders of the Company of all or substantially all of the stock of the 
Company;

                  B.       a merger or consolidation in which the Company is a 
party;

                  C.       the sale, exchange, or transfer of all or 
substantially all of the assets of the Company; or

                  D.       a liquidation or dissolution of the Company.

         (iv) A voluntary  termination  of  employment by the Employee for "Good
Reasons"  means a termination  of employment  following:  (a) a Deemed  Demotion
which  results  without  the  Employee's   express  written  consent  and  which
continues,  for a period of twenty (20) days after written notice thereof to the
Company  from the Employee  with a "Deemed  Demotion"  being  defined as (i) the
assignment to the Employee of any duties,  or any  limitation of the  Employee's
responsibilities,   inconsistent   with  the   Employee's   positions,   duties,
responsibilities  and status with the Company  immediately  prior to the date of
the  Change  of  Control  Event,  or (ii) a  removal  of the  Employee  from the
Employee's  position with the Company held by the Employee in contemplation of a
Change of  Control  Event,  except in  connection  with the  termination  of the
employment  of the Employee by the Company for Cause or as a result of the death
or Permanent Disability of the Employee;  (b) any failure by the Company to pay,
or any reduction by the Company of, the  Employee's  base annual salary or bonus
compensation  in effect  immediately  prior to the date of the Change of Control
Event;  (c) any failure by the Company to (i)  continue to provide the  Employee
with the  opportunity to  participate,  on terms no less favorable than those in
effect  immediately  prior to the date of the  Change of Control  Event,  in any
benefit plans and programs,  including,  but not limited to, the Company's life,
disability, health, dental, medical, bonus savings and retirement plans in which
the Employee was  participating  immediately  prior to the date of the Change of

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Control Event, or their equivalent,  or (ii) provide the Employee with all other
fringe  benefits  (or their  equivalent)  from  time to time in  effect  for the
benefit of any executive,  management or administrative  group which customarily
includes a person holding the employment  position with the Company then held by
the Employee; (d) without the Employee's express written consent, the relocation
of the principal  place of the Employee's  employment to a location that is more
than 20  miles  further  from  the  Employee's  principal  residence  than  such
principal  place of  employment  immediately  prior to the date of the Change of
Control  Event,  or the  imposition of travel  requirements  on the Employee not
substantially  consistent with normal  day-to-day travel  requirements  existing
immediately  prior to the date of the Change of Control  Event and/or (e) a good
faith determination by the Employee, in his sole judgment, that the continuation
of the Employees  employment with the company is no longer in the best interests
of the Company.

         (iv) "Permanent Disability" means, as applied to the Employee, that (a)
he has been  totally  incapacitated  by  bodily  injury or  disease  so as to be
prevented thereby from engaging in any occupation or employment for remuneration
or profit,  (b) such total  incapacity  shall have continued for a period of six
consecutive  months  and (c) such total  incapacity  will,  in the  opinion of a
qualified  physician,  be permanent and  continuous  during the remainder of the
Employee's life.

         (v)  "Termination"  means  any  termination  of the  employment  of the
Employee following the occurrence of any Change of Control Event, by the Company
without  Cause or by the  Employee  for Good  Reason;  provided,  however,  that
"Termination"  shall  not  include  any  termination  of the  employment  of the
Employee  (a) by the  Company  as a result of the  Permanent  Disability  of the
Employee or (b) as a result of the death of the Employee.



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