EXHIBIT 10.29

                                      EMCON

                          REGISTRATION RIGHTS AGREEMENT

     THIS REGISTRATION  RIGHTS AGREEMENT is entered into as of April 3, 1998, by
and  among  EMCON,  a  California  corporation  ("EMCON")  and  the  undersigned
shareholders  of Advanced  Analytical  Solutions,  Inc., a Colorado  corporation
("A2S")  (collectively,  the "Shareholders"),  such Shareholders having received
certain rights to register  shares of EMCON common stock to be received upon the
merger (the "Merger") of A2S with and into Advanced Analytical Solutions,  Inc.,
a Delaware  corporation  and a  wholly-owned  subsidiary of EMCON ("Sub") as set
forth in the  Agreement  and Plan of  Reorganization  dated  April 3,  1998 (the
"Merger Agreement") among EMCON, A2S, Sub and the Shareholders.

                                    RECITALS:

     Pursuant to the terms of the Merger Agreement, EMCON desires to provide the
shareholders certain registration rights as provided for in this Agreement.


                                   AGREEMENT:

     In  consideration   of  the  mutual  promises,   covenants  and  conditions
hereinafter set forth, the parties hereto mutually agree as follows:

         1.       Registration Rights.

                  1.1      Certain  Definitions.  As used in this  Agreement,  
the  following  terms  will have the following respective meanings:

                           (a)      "Commission"  will mean the Securities  and 
Exchange  Commission  or any other federal agency at the time administering the 
Securities Act.

                           (b)      "Exchange  Act" will  mean  the Securities  
Exchange  Act  of  1934, as  amended,  or any similar  federal  statute and the
rules and regulations thereunder, all as the same will be in effect at the time.

                           (c)      "Holder" will mean any person or persons to 
whom  Registrable  Securities  were originally issued.

                           (d)      "Securities  Act" will mean the Securities
Act of  1933, as amended,  or any  similar  federal  statute and  the rules and
regulations thereunder, all as the same will be in effect at the time.

                           (e)      "Registrable  Securities"  means (i) all 
shares  of  EMCON  Common  Stock issued to the  Shareholders in connection with
the Merger,  including  shares of Common  Stock  issued in  connection  with the
Earnout Payments (as defined in the Merger  Agreement),  but excluding shares of
EMCON Common Stock issued to the  shareholders in the Merger that have been sold
or otherwise  transferred by the Shareholders who initially received such shares
in the

                                       55
<PAGE>


Merger;  (ii) all  shares of  capital  stock  issued in lieu of any of the stock
referred to in clause (i) in any reorganization, which have not been sold to the
public;  and (iii) all shares of capital  stock  issued in respect of any of the
stock  referred to in clauses (i) or (ii) as a result of any stock split,  stock
dividend, recapitalization or the like, which have not been sold to the public.

                           (f)      The  terms "register",  "registered" and 
"registration"  refer  to  a registration  effected  by  preparing  and filing a
registration   statement  in  compliance   with  the  Securities  Act,  and  the
declaration or ordering of the effectiveness of such registration statement.

                           (g)      "Registration   Expenses"  will  mean  all 
expenses  incurred  by  EMCON  in  complying  with this  Section 1,  including,
without  limitation,  all registration,  qualification and filing fees, printing
expenses,  escrow fees, fees and  disbursements  of counsel for EMCON,  blue sky
fees and expenses and the expense of any special audits  incident to or required
by any such registration (but excluding the compensation of regular employees of
EMCON which will be paid in any event by EMCON).

                           (h)      "Selling   Expenses"   will  mean  all   
underwriting  discounts  and  selling  commissions  applicable to the sale of
the  Registrable  Securities  and all fees and  expenses of legal  counsel for a
Holder.

                  1.2      Piggyback Registration

                           (a)      If at any time or from time to time,  EMCON 
will  determine  to  register  any  of  its  securities,  other  than  (i) a
registration  relating  solely to  employee  benefit  plans on Form S-1,  S-8 or
similar forms which may be promulgated in the future,  or (ii) a registration on
Form S-4 or similar forms which may be promulgated in the future relating solely
to a Commission Rule 145 transaction, EMCON will:

                                    (A)    promptly give to each Holder written
notice thereof; and

                                    (B)    include  in such  registration  (and 
     any related qualification under blue sky laws or other compliance),  and in
any underwriting involved therein, all the Registrable Securities specified in a
written request or requests,  made within twenty (20) days after receipt of such
written  notice  from EMCON,  by any Holder or  Holders,  except as set forth in
Subsection 1.2(b).

                           (b)      Underwriting.  If  the  registration  of  
which  EMCON  gives  notice is for  a  registered  public offering  involving an
underwriting,  EMCON will so advise the Holders as a part of the written  notice
given pursuant to Subsection 1.2(a)(i). In such event the right of any Holder to
registration pursuant to this Section 1.2 will be conditioned upon such Holder's
participation   in  such   underwriting  and  the  inclusion  of  such  Holder's
Registrable  Securities in the underwriting to the extent provided  herein.  All
Holders proposing to distribute their securities  through such underwriting will
(together  with EMCON and the other  shareholders,  if any,  distributing  their
securities  through such underwriting)  enter into an underwriting  agreement in
customary form with the  Underwriter  selected for such  underwriting  by EMCON.
Notwith-standing  any other  provision of this  Section 1.2, if the  Underwriter
determines  that marketing  factors require a limitation of the number of shares
to be  underwritten,  the  Underwriter  may limit the amount of securities to be
included in the registration and underwriting by EMCON's shareholders or exclude
such  securities  entirely.  The number of shares  that may be  included  in the
registration and underwriting by the Holders will be allocated among the Holders
in proportion to

                                       56
<PAGE>


the number of Registrable  Securities then held by each. If any such shareholder
disapproves  of the terms of any such  underwriting,  he may  elect to  withdraw
therefrom  by  written  notice to EMCON  and the  Underwriter.  Any  Registrable
Securities  excluded or withdrawn from such  underwriting  will be excluded from
such registration.

                  1.3  Expenses  of  Registration.   All  Registration  Expenses
incurred  in  connection  with any  registration,  qualification  or  compliance
pursuant to Section 1.2 will be borne by EMCON. All Selling Expenses relating to
securities  registered  by the  Holders  will be  borne by the  Holders  of such
securities  pro rata on the basis of the  number of  Registrable  Securities  so
registered.

                  1.4 Registration Procedures. In the case of each registration,
qualification or compliance effected by EMCON pursuant to this Agreement,  EMCON
will,  upon  request,  inform  each  Holder  as  to  the  status  of  each  such
registration, qualification and compliance. At its expense EMCON will:

                           (a)      Keep  such  registration,  and any  
qualification  or  compliance  under  state  securities  laws  which  EMCON
determines to obtain, effective for a period of one hundred eighty (180) days or
until the Holder or Holders have  completed  the  distribution  described in the
registration statement relating thereto, whichever first occurs;

                           (b)      Furnish such number of prospectuses  and 
other documents  incident thereto as a Holder from time to time may reasonably 
request; and

                           (c)      Use its efforts to register  and  qualify 
the  securities  covered  by  such  registration  statement  under  such  other
securities  or blue  sky  laws of such  jurisdictions  as  shall  be  reasonably
requested by the Holders, provided that EMCON will not be required in connection
therewith  or as a  condition  thereto to qualify  to do  business  or to file a
general consent to service of process in any such states or jurisdictions.

                  1.5 Delay of  Registration.  No Holder  will have any right to
take any action to restrain, enjoin or otherwise delay any registration pursuant
to Section 1.2 hereof as a result of any controversy that may arise with respect
to the interpretation or implementation of this Agreement.

                  1.6      Indemnification.

                           (a)     EMCON will indemnify each Holder, each of its
officers,  directors,  employees,  partners,  legal  counsel  and  accountants,
and each person  controlling such Holder within the meaning of Section 15 of the
Securities  Act,  with  respect  to which  any  registration,  qualification  or
compliance has been effected  pursuant to this Agreement,  and each underwriter,
if any,  and each  person who  controls  any  underwriter  within the meaning of
Section 15 of the Securities Act, against all expenses,  claims, losses, damages
and liabilities (or action in respect  thereof),  including any of the foregoing
incurred in settlement of any litigation,  commenced or threatened,  arising out
of or based on any untrue statement (or alleged untrue  statement) of a material
fact contained in any registration statement,  prospectus,  offering circular or
other  document,  or any amendment or supplement  thereof,  incident to any such
registration, qualification or compliance, or any omission (or alleged omission)
to state therein a material  fact required to be stated  therein or necessary to
make the  statements  therein not  misleading,  or any violation by EMCON of any
rule or regulation promulgated under the Securities Act, Exchange

                                       57
<PAGE>


Act or state  securities  laws  applicable  to EMCON and  relating  to action or
inaction   required  of  EMCON  in  connection   with  any  such   registration,
qualification  or compliance,  and will reimburse each such Holder,  each of its
officers,  directors,  employees,  partners, legal counsel and accountants,  and
each person  controlling such Holder,  each such underwriter and each person who
controls any such underwriter,  for any legal and any other expenses  reasonably
incurred in  connection  with  investigating,  preparing or  defending  any such
claim, loss, damage, liability or action; provided, however, that EMCON will not
be liable in any such case to the  extent  that any such  claim,  loss,  damage,
liability  or  expense  arises  out of or is based on any  untrue  statement  or
omission  made in  reliance  upon and in  conformity  with  written  information
furnished to EMCON by an instrument duly executed by or on behalf of such Holder
or underwriter and stated to be specifically for use therein.

                           (b)      Each Holder will, if  Registrable Securities
held  by  such  Holder  are  included  in  the  securities  as  to  which  such
registration,  qualification  or compliance is being effected,  indemnify EMCON,
each  of  its  directors,  officers,  employees,  partners,  legal  counsel  and
accountants,  each underwriter,  if any, of EMCON's securities covered by such a
registration  statement,  each  person who  controls  EMCON or such  underwriter
within the  meaning of Section  15 of the  Securities  Act,  and each other such
Holder, each of its officers, directors,  employees, partners, legal counsel and
accountants,  and each  person  controlling  such  Holder  within the meaning of
Section 15 of the  Securities  Act,  against  all  claims,  losses,  damages and
liabilities  (or  actions in  respect  thereof)  arising  out of or based on any
untrue  statement (or alleged untrue  statement) of a material fact contained in
any  such  registration  statement,   prospectus,  offering  circular  or  other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated  therein or necessary to make the  statements  therein not
misleading,  and will reimburse EMCON, such Holders,  such directors,  officers,
employees,  partners,  legal  counsel,  accountants,  persons,  underwriters  or
control  persons  for any legal or any other  expenses  reasonably  incurred  in
connection  with  investigating  or  defending  any such  claim,  loss,  damage,
liability  or action,  in each case to the  extent,  but only to the extent that
such  untrue  statement  or  omission  is made in such  registration  statement,
prospectus,  offering  circular  or  other  document  in  reliance  upon  and in
conformity  with written  information  furnished to EMCON by an instrument  duly
executed  by or on behalf of such Holder and stated to be  specifically  for use
therein.  Notwithstanding the foregoing, in no event will a Holder be liable for
any such claims, losses,  damages, or liabilities in excess of the proceeds, net
of  underwriting  discounts  and  commissions,  received  by such  Holder in the
offering, except in the event of fraud by such Holder.

                           (c)      Each  party   entitled  to  indemnification 
under  this  Section  1.6  (the  "Indemnified  Party") will  give  notice to the
party required to provide  indemnification  (the "Indemnifying  Party") promptly
after  such  Indemnified  Party has  actual  knowledge  of any claim as to which
indemnity may be sought,  and will permit the  Indemnifying  Party to assume the
defense of any such claim or any litigation resulting  therefrom,  provided that
counsel for the  Indemnifying  Party, who will conduct the defense of such claim
or litigation,  shall be approved by the Indemnified  Party (whose approval will
not unreasonably be withheld), and the Indemnified Party may participate in such
defense at such party's  expense,  and provided  further that the failure of any
Indemnified  Party to give  notice  as  provided  herein  will not  relieve  the
Indemnifying Party of its obligations under this Agreement,  unless such failure
is prejudicial to the Indemnifying  Party in defending such claim or litigation.
No  Indemnifying  Party,  in the defense of any such claim or litigation,  will,
except  with the  consent  of each  Indemnified  Party,  consent to entry of any
judgment or enter into any settlement which does not include as an unconditional
term thereof the giving by the claimant or plaintiff to such  Indemnified  Party
of a release from all liability in respect to such claim or litigation.  Subject
to the foregoing, the Indemnifying Party will promptly


                                       58
<PAGE>


advance all expenses  incurred by the  Indemnified  party in connection with the
investigation  and  defense  of any  claim as to which  indemnity  may be sought
pursuant to this Agreement after written  request  therefor (but no earlier than
incurred) by the Indemnified  Party to the  Indemnifying  Party. The Indemnified
Party  will  repay  such  amounts  advanced  if  and to the  extent  that  it is
ultimately   determined   that  the   Indemnified   Party  is  not  entitled  to
indemnification or contribution under this Agreement.

                           (d)      If the indemnification provided for in this 
Section  1.6  is  held  by  a court of competent  jurisdiction to be unavailable
to an Indemnified Party with respect to any loss,  liability,  claim,  damage or
expense  referred  to  therein,   then  the  Indemnifying   Party,  in  lieu  of
indemnifying such Indemnified  Party  thereunder,  will contribute to the amount
paid or payable by such Indemnified  Party as a result of such loss,  liability,
claim,  damage or expense in such  proportion as is  appropriate  to reflect the
relative fault of the Indemnifying  Party on the one hand and of the Indemnified
Party on the other in connection with the statements or omissions which resulted
in such loss, liability,  claim, damage or expense as well as any other relevant
equitable  considerations.  The relative fault of the Indemnifying  Party and of
the  Indemnified  Party will be  determined by reference to, among other things,
whether  the  untrue or  alleged  untrue  statement  of a  material  fact or the
omission or alleged  omission to state a material  fact  relates to  information
supplied by the Indemnifying  Party or by the Indemnified Party and the parties'
relative intent, knowledge,  access to information and opportunity to correct or
prevent such statement or omission.

                           (e)      Notwithstanding   the   foregoing,  to  the
extent  that  the  provisions on  indemnification  and contribution contained in
any underwriting  agreement  entered into in connection with the relevant public
offering are in conflict with the foregoing  provisions,  the  provisions in the
underwriting agreement will be controlling.

                  1.7 Lockup  Agreement.  In consideration for EMCON agreeing to
its obligations under this Section 1, each Holder agrees, in connection with the
registration  of  EMCON's  securities,  that  upon the  request  of EMCON or the
Underwriter,  such Holder will not sell, make any short sale of, loan, grant any
option for the purchase of, or otherwise  dispose of any Registrable  Securities
(other  than those  included  in the  registration)  without  the prior  written
consent of EMCON or  Underwriter,  as the case may be, for a period of up to 180
days after the effective date of such registration; provided, however, that such
Holder will have no  obligation  to enter into the  agreement  described  herein
unless all executive  officers and directors of EMCON are required to enter into
similar agreements.

                  1.8 Information by Holder.  As a condition to the inclusion of
their Registrable  Securities,  the Holder or Holders of Registrable  Securities
included in any registration  will furnish to EMCON such  information  regarding
such Holder or Holders and the  distribution  proposed by such Holder or Holders
as EMCON may request in writing and as will be reasonably required in connection
with any registration,  qualification or compliance  contemplated in Section 1.2
of this Agreement.

                  1.9 Rule 144 Reporting. With a view to making available to the
Holders the benefits of certain rules and  regulations of the  Commission  which
may  permit  the  sale  of the  Registrable  Securities  to the  public  without
registration, EMCON agrees to:

                           (a)      Make and keep public information  available,
as those terms are understood and defined in Rule 144 under the Securities Act;

                                       59
<PAGE>



                           (b)      Use its best  efforts  to file  with the  
Commission  in  a  timely  manner all  reports and other  documents  required of
EMCON under the Securities Act and the Exchange Act;

                           (c)      So long as a Holder owns any unregistered  
Registrable   Securities,  furnish  to  such  Holder  upon  request a written
statement by EMCON as to its compliance with the reporting  requirements of said
Rule 144, and of the  Securities  Act and the  Exchange  Act, a copy of the most
recent annual or quarterly report of EMCON, and such other reports and documents
of EMCON as such Holder may reasonably request in availing itself of any rule or
regulation  of the  Commission  allowing  a Holder  to sell any such  securities
without registration.

                  1.10  Termination of Registration  Rights.  The obligations of
EMCON pursuant to this Section 1 will terminate with respect to any Holder, when
all of the Registrable Securities of such Holder may be sold under Rule 144 in a
three-month period.

         2.       Miscellaneous.

                  2.1 Waivers and Amendments.  With the written consent of EMCON
and the record holders of a majority of the outstanding  Registrable Securities,
any  provision  of  this  Agreement  may be  waived  (either  generally  or in a
particular  instance,  either  retroactively or  prospectively  and either for a
specified period of time or indefinitely) or amended,  and with the same consent
EMCON, when authorized by its Board of Directors, may enter into a supplementary
agreement for the purpose of adding any  provisions to or changing in any manner
or eliminating any of the provisions of this Agreement. Any waiver, amendment or
supplement to which such consents are obtained will be binding upon all Holders.
Upon the effectuation of each such waiver,  amendment or supplement,  EMCON will
promptly  give  written  notice  thereof to the Holders who have not  previously
received  notice  thereof or consented  thereto in writing.  In  addition,  each
Holder,  as to such  Holder  only,  may  consent in writing to any such  waiver,
amendment or supplement,  which will be binding upon such Holder.  No amendment,
waiver or supplement  to this  Agreement  will be effective  unless agreed to in
writing by the party against whom  enforcement  is sought or, in the case of any
Holder,  by such Holder or Holders of a majority of the outstanding  Registrable
Securities.

                  2.2  Governing  Law.  This  Agreement  will be governed in all
respects  by the laws of the State of  California  as such laws are  applied  to
agreements  between  California  residents  entered  into  and  to be  performed
entirely within California.

                  2.3  Successors  and Assigns.  Except as  otherwise  expressly
provided  herein,  the  provisions  hereof  will inure to the benefit of, and be
binding upon, the successors,  assigns,  heirs,  executors and administrators of
the parties hereto.

                  2.4 Entire  Agreement  This  Agreement,  the  exhibits to this
Agreement and the other documents  delivered  pursuant hereto or incorporated by
reference  herein  constitute  the full and entire  understanding  and agreement
between the parties with regard to the subjects hereof and thereof and supersede
all prior oral and written  understandings,  agreements  and  commitments  by or
between the parties hereto.

                  2.5  Notices,   etc.  All  notices  and  other  communications
required  or  permitted  hereunder  will be in  writing  and will be  mailed  by
certified or registered mail, postage prepaid,

                                       60
<PAGE>


addressed  (a) if to a party other than EMCON,  at the address of such party set
forth on such party's signature page to this Agreement, or at such other address
as such party  furnishes to EMCON in writing,  or (b) if to EMCON,  at 400 S. El
Camino Real, Suite 1200 San Mateo, CA 94402, Attention: Chief Financial Officer,
or at such  other  address  as EMCON  furnishes  to the  other  parties  to this
Agreement.

                  2.6 No  Waivers.  No  failure  on the  part  of any  party  to
exercise  or delay in  exercising  any right  hereunder  will be deemed a waiver
thereof,  nor will any such failure or delay, or any single or partial  exercise
of any such right,  preclude any further or other  exercise of such right or any
other right.

                  2.7 Separability.  If any provision of this Agreement,  or the
application  thereof,  is for any reason and to any extent determined by a court
of competent jurisdiction to be invalid or unenforceable,  the remainder of this
Agreement  and  the   application   of  such   provision  to  other  persons  or
circumstances  will be interpreted so as best to reasonably effect the intent of
the parties hereto.  The parties agree to use their best efforts to replace such
void or  unenforceable  provision of this Agreement with a valid and enforceable
provision  which will achieve,  to the extent greatest  possible,  the economic,
business and other purposes of the void or unenforceable provision.

                  2.8  Titles and  Subtitles.  The  titles of the  sections  and
subsections of this Agreement are for  convenience of reference only and are not
to be considered in construing this Agreement.

                  2.9 Counterparts. This Agreement may be executed in any number
of  counterparts,  each of which will be an original,  but all of which together
will constitute one instrument.

                  2.10  Attorneys'  Fees.  In the event of any  action,  suit or
proceeding for the breach of this Agreement or  misrepresentation  by any party,
the prevailing  party will be entitled to reasonable  attorneys' fees, costs and
expenses incurred in such action, suit or proceeding.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

  


                                       61
<PAGE>



         IN WITNESS WHEREOF,  the parties hereby have executed this Agreement on
the date first above written.


                                            EMCON



                                             By:\o\ R. Michael Momboisse
                                                ------------------------------

                                             Its: CFO and VP Legal
                                                  ----------------------------


                                             SHAREHOLDERS:



                                             \o\ William J. Hengemihle
                                             ---------------------------------
                                             William J. Hengemihle

                                             51 Casselberry Drive
                                             Audubon, Pennsylvania 19403


                                             \o\ Christopher M. Wittenbrink
                                             ---------------------------------
                                             Christopher M. Wittenbrink

                                             2715 South Pierce Street
                                             Denver, Colorado 80227


                                             \o\ Timothy M. Keaten
                                             ---------------------------------
                                             Timothy M. Keaten

                                             3048 East Clairton Drive
                                             Highlands Ranch, Colorado 80126



                                       62