<PAGE>
                                                                    EXHIBIT 10.8

                           LEASE AMENDMENT NUMBER ONE

         This Lease Amendment Number One (the "Amendment") is entered into this
1st day of May, 2002 by and between SKY HARBOR ASSOCIATES LIMITED PARTNERSHIP, a
Michigan limited partnership, whose address is 74 East Long Lake Road,
Bloomfield Hills, Michigan 48304 ("Landlord"); and CET ENVIRONMENTAL SERVICES,
INC., a California corporation whose address is 7032 South Revere Parkway,
Englewood, CO 80112 ("Tenant").

        The facts upon which this Amendment is based are:

        A.     Landlord and Tenant entered into a certain Lease Agreement dated
               March 1, 1999, for the premises located at 7032 South Revere
               Parkway (the "Original Premises"), Englewood, Colorado 80112.
               That Lease Agreement, including all addenda, exhibits, riders,
               attachments, and amendments thereto shall hereafter be referred
               to as the "Lease";

        B.     To date, Tenant has remained in occupancy of the Premises; and

        C.     Landlord and Tenant desire to amend the Lease in order to provide
               for, among other things, the further extension of the Lease Term,
               the increase in the base rental rates, the reduction of the
               square footage and the construction of certain tenant
               improvements for the Premises, but all only in accordance with
               and subject to the terms and conditions of this Amendment.

        NOW, THEREFORE, in consideration of the mutual covenants and conditions
contained herein, and for other good and valuable consideration, the receipt and
sufficiency of which is hereby mutually acknowledged, the parties hereby agree
as follows:

1.     Incorporation of Recitals. The recitals contained in Paragraphs A through
       C above, both inclusive, are incorporated herein and made a part of this
       Amendment.

2.     Defined Terms. Terms used herein shall have the same meaning as defined
       in the Lease, unless otherwise defined herein. The following specific new
       terms are hereby enumerated:

         "New Commencement Date" as used herein shall mean June 1,2002..

         "New Expiration Date" as used herein shall mean May 31, 2005..

         "Original Premises" as used herein shall mean the original 12,000
         square feet which comprise the entire rentable square feet in Building
         7032.

         "Premises" as used herein shall mean the reduced premises of
approximately 6,000 square feet that comprise the southern half of Building 7032
as cross hatched on Exhibit A.

3.     Tenant Improvements. Landlord shall provide those improvements to the
       Premises as indicated below with the location of the improvements to be
       mutually determined and acceptable by Tenant and Landlord. Landlord shall
       be responsible for the initial $4,000 (Four Thousand and 00/lOO Dollars)
       of Tenant Improvements costs. Any costs incurred, either soft or hard,
       including, but not limited to architectural fees, engineering fees,
       construction management, actual costs of construction, materials and
       labor, which shall exceed $4,000 shall be the mutual and equitable
       responsibility of Tenant and Landlord.

                 a)       A warehouse demising fire wall.
                 b)       Installation of two fire doors.
                 c)       A fire wall closure in the front hall.
                 d)       Tenant, at its expense, agrees to provide the
                          refrigerator and microwave for the common area
                          kitchen and shall provide janitorial service for
                          the common area kitchen, hall and restrooms
                          (until such time as another tenant occupies the
                          south end of building 7032 and can share in the
                          janitorial expense.
                 e)       And such other improvements that may be required
                          either by the appropriate governing entity or the
                          Landlord.

<PAGE>


4.   Base Rent. Commencing on the New Commencement Date, Tenant shall pay to
     Landlord Base Rent in monthly installments in advance on the first day of
     each calendar month during the Term, as follows:

<TABLE>
<S>                                 <C>                       <C>                       <C>
06/01/02 - 05/31/03                 $7.67 PSF/NNN             $3,835.00 Monthly         $46,020.00 Annually
06/01/03 - 05/31/04                 $7.92 PSF/NNN             $3,960.00 Monthly         $47,520.00 Annually
06/01/04 - 05/31/05                 $8.17 PSF/NNN             $4,085.00 Monthly         $49,020.00 Annually
</TABLE>

Tenant shall continue to be responsible for Tenant's proportionate share of
taxes, insurance and common area maintenance as enumerated in the Lease.

5.   Utilities. Tenant shall promptly pay its proportionate share of the utility
     costs, to include gas and electricity, based on Tenant's historical
     use/consumption of such services over the entire Original Premises, then
     reduced by one-half. Landlord shall be responsible for the utility costs in
     the vacated portion of Building 7032 until such time as another tenant
     shall occupy the south end of Building 7032 and assume that responsibility.

6.   Incorporation of Lease Terms. With the exception of the foregoing
     provisions of this Amendment, Tenant and Landlord shall be subject to all
     terms, covenants and conditions of the Lease, and the same shall remain in
     full force and effect as therein stated. In the event of any express
     conflict or inconsistency between the terms of this Amendment and the terms
     of the Lease, the terms of this Amendment shall prevail.

7.   Ratification: Except as expressly modified by this Amendment, all other
     terms and conditions of the Lease are hereby expressly approved, ratified
     and affirmed.

         Intending to be legally bound, the parties have signed this Amendment
upon the date first written above.

<TABLE>
<S>                                           <C>
LANDLORD                                      TENANT

SKY HARBOR ASSOCIATES                         CET ENVIRONMENTAL
LIMITED PARTNERSHIP                           SERVICES, INC


By:  Diversified Development Corporation,     By:
      its General Partner                        -----------------------------------
                                                           Dale W. Bleck


By:                                           Its:
   ------------------------------------           ----------------------------------
         Keith J. Pomeroy, President                            CFO

Date:                                         Date:
     ----------------------------------            ---------------------------------
</TABLE>