EXHIBIT 5



[LETTERHEAD OF GRAY CARY WARE & FREIDENRICH LLP]
400 Hamilton Avenue, Palo Alto, CA  94301-1825
Phone:  650-328-6561       Fax:  650-327-3699        www.gcwf.com

August 10, 1998

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C.  20549

Ladies and Gentlemen:

As legal counsel for EMCON, a California  corporation  (the  "Company"),  we are
rendering this opinion in connection with the registration  under the Securities
Act of 1933, as amended, of up to 1,000,000 shares of the Common Stock,  without
par value,  of the  Company  which may be issued  pursuant  to the  exercise  of
options under the 1998 Stock Option Plan (the "Option Plan").

We have examined all instruments, documents and records which we deemed relevant
and  necessary  for the  basis of our  opinion  hereinafter  expressed.  In such
examination,  we  have  assumed  the  genuineness  of  all  signatures  and  the
authenticity of all documents submitted to us as originals and the conformity to
the  originals of all  documents  submitted to us as copies.  We are admitted to
practice  only in the State of California  and we express no opinion  concerning
any law other than the law of the State of California and the federal law of the
United States.

Based on such  examination,  we are of the opinion that the 1,000,000  shares of
Common Stock which may be issued upon  exercise of options under the Option Plan
are duly  authorized  shares of the  Company's  Common  Stock,  and, when issued
against receipt of the consideration  therefor in accordance with the provisions
of the Option  Plan will be validly  issued,  fully paid and  nonassessable.  We
hereby  consent to the filing of this opinion as an exhibit to the  Registration
Statement  referred to above and the use of our name wherever it appears in said
Registration Statement.

Respectfully submitted,


/s/ GRAY CARY WARE & FREIDENRICH LLP
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GRAY CARY WARE & FREIDENRICH LLP


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