Exhibit 10.66


                        AMENDMENT NO. 5 TO LOAN AGREEMENT
                             DATED OCTOBER 25, 1996
               BY AND BETWEEN TANKNOLOGY-NDE INTERNATIONAL, INC.,
                           TANKNOLOGY/NDE CORPORATION,
                   TANKNOLOGY-NDE CONSTRUCTION SERVICES, INC.,
                      PROECO, INC. AND 2368692 CANADA, INC.
                                       AND
                              BANK ONE, TEXAS, N.A.

     This  Amendment No. 5 ("Fifth  Amendment")  to the Loan  Agreement,  by and
among  TANKNOLOGY-NDE  INTERNATIONAL,  INC. (formerly known as NDE ENVIRONMENTAL
CORPORATION)  ("NDE"), a Delaware  corporation,  TANKNOLOGY/NDE  CORPORATION,  a
Delaware corporation, PROECO, INC., a Delaware corporation, 2368692 CANADA, INC.
(formerly  known  as  TANKNOLOGY   CANADA  (1988)  INC.),  a  Canadian   federal
corporation, TANKNOLOGY-NDE CONSTRUCTION SERVICES, INC., a Delaware corporation,
and OUTBOUND SERVICES, INC., a California corporation (collectively, "Borrower")
and BANK ONE,  TEXAS,  N.A.,  a national  banking  association  (the  "Bank") is
entered into this 5th day of November 1998.

                              W I T N E S S E T H:

     WHEREAS,  Borrower and Bank entered into the Loan  Agreement on October 25,
1996,  as  amended  by the First  Amendment  dated  April 10,  1997,  the Second
Amendment  dated May 20, 1997, the Third  Amendment  dated December 23, 1997 and
the Fourth Amendment dated June 26, 1998 (the "Loan Agreement");

     WHEREAS,  NDE has  purchased all the  outstanding  common stock of Outbound
Services,  Inc. ("OSI") pursuant to that certain Stock Purchase  Agreement dated
August 7, 1998, by and among NDE, OSI and the  stockholders of OSI identified in
the signature  page of the Stock  Purchase  Agreement  (the "OSI Stock  Purchase
Agreement")  (the selling  stockholders  of OSI  hereinafter  referred to as the
"Sellers");

     WHEREAS, for consideration under the OSI Stock Purchase Agreement, NDE:

     (i)  executed that certain promissory note dated August 7, 1997 in the face
          amount of  $750,000  made  payable to the order of  Sellers  (the "OSI
          Unsecured Note");

     (ii) granted Sellers certain  non-transferable  rights to purchase up to an
          aggregate  of  500,000  fully paid and  nonassessable  shares of NDE's
          common stock as more fully described in that certain Warrant Agreement
          dated  August 7, 1998,  by and among NDE and Sellers (the "OSI Warrant
          Agreement");


                                       -1-

<PAGE>



     (iii) paid Sellers $700,000.00 in cash;

     (iv) transferred  stock  certificates  to Sellers for 250,000 shares of NDE
          common stock;

     (v)  agreed  to either  guarantee  or  advance  funds to OSI for OSI to pay
          certain  indebtedness  of OSI in an amount not to exceed  $335,000.00;
          and

     (vi) agreed to invest at least $500,000.00 in additional working capital in
          OSI.

     WHEREAS,  OSI  engages  in the  Maintenance  Service  Business--a  type  of
business unrelated to Borrower's  business prior to the closing of the OSI Stock
Purchase Agreement;

     WHEREAS, Borrower desires that OSI become a co-Borrower under the Revolving
Note;

     WHEREAS,   Borrower  desires  to  include  OSI's  accounts  receivable  and
inventory in the Borrowing Base calculation;

     WHEREAS,  Borrower has requested that Bank waive Borrower's  non-compliance
with certain  covenants,  insofar as such  non-compliance is the result of NDE's
(i)  acquisition of all the outstanding  stock of OSI, (ii)  indebtedness to the
Sellers  evidenced  by the OSI  Unsecured  Note,  (iii)  payment  to  Sellers of
$700,000.00  in cash,  (iv)  granting  of stock  warrants  under the OSI Warrant
Agreement,  (v) transfer of stock  certificates to Sellers for 250,000 shares of
NDE common stock, (vi) agreement to either guarantee or advance funds to OSI for
the  payment  of  certain  indebtedness,  (vii)  agreement  to  invest  at least
$500,000.00  in  additional  working  capital  in  OSI,  and  (viii)  Borrower's
engagement in the Maintenance Service Business, all in accordance with the terms
and provisions hereof;

     WHEREAS,  Bank is willing to agree to the foregoing in accordance with, and
subject to, the terms and conditions set forth herein;

     NOW, THEREFORE, in consideration of the promises herein contained, and each
intending to be legally bound hereby, the parties agree as follows:

         I.       Amendments to Loan Agreement.

     General. By its execution of the Fifth Amendment,  OSI's signature block is
hereby  deemed  added  to the  other  signature  blocks  at the end of the  Loan
Agreement, and, unless specified otherwise, is hereafter a co-Borrower under the
Loan Agreement,  as hereby amended, and does hereby assume,  ratify,  accept and
confirm all such obligations as co-Borrower under the Loan Documents.



                                       -2-

<PAGE>



     Article I, DEFINITIONS, is amended by adding the following definitions:

     "Borrower"  shall  have  the  meaning  ascribed  to it in the  introductory
     paragraph of the Fifth Amendment.

     "Fifth Amendment" means Amendment No. 5 to this Loan Agreement, executed by
     Borrower and Bank on November 5, 1998.

     "Maintenance  Service Business" shall mean activities  related to providing
     facility and equipment maintenance service management including maintenance
     call receiving,  maintenance  contractor  management,  maintenance cost and
     service performance analysis for third parties.

     "OSI" shall mean Outbound Services, Inc., a California corporation.

     "OSI Stock Purchase  Agreement" means that certain Stock Purchase Agreement
     dated August 7, 1998,  by and among NDE,  OSI and the selling  stockholders
     ("Sellers")  of OSI  identified in the signature page of the Stock Purchase
     Agreement.

     "OSI Unsecured  Note" shall mean that certain  promissory note dated August
     7, 1998  executed by NDE in the face amount of $750,000 made payable to the
     order of Sellers.

     "OSI Warrant  Agreement" means that certain Warrant  Agreement dated August
     7, 1998, by and among NDE and Sellers  wherein NDE granted  Sellers certain
     non-transferable  rights to purchase up to an  aggregate  of 500,000  fully
     paid and nonassessable shares of NDE's common stock as more fully described
     therein.

     "Revolving  Note" means that certain  promissory  note in the original face
     amount of $9,000,000.00 dated of even date with the Fifth Amendment made by
     the  Borrower  payable  to the  order of the Bank in the form  attached  as
     Exhibit  "A-1"  to  the  Fifth  Amendment,  together  with  all  deferrals,
     renewals, extensions, amendments,  modifications or rearrangements thereof,
     which  promissory note shall evidence  certain  advances to the Borrower by
     the Bank pursuant to Section 2.01 of the Loan Agreement.

     "Sellers" means those selling stockholders of OSI stock pursuant to the OSI
     Stock Purchase Agreement.

     Article II, THE LOAN, is modified by adding the following new sections:

          2.18 Obligations of OSI.  Notwithstanding anything contained herein to
          the contrary, while OSI is deemed a co-Borrower for all other purposes
          (except as otherwise noted herein), OSI is not a Borrower with respect
          to the Term Note.


                                       -3-

<PAGE>



     Article  IV,  REPRESENTATIONS  AND  WARRANTIES,  is  modified by adding the
following new section:

          4.19  Representations  and  Warranties  of OSI.  With  respect  to any
          representations  and warranties made by OSI with respect to the Notes,
          such  representations  and warranties  shall be applicable only to the
          Revolving Note.

     Article V, AFFIRMATIVE  COVENANTS,  of the Loan Agreement is hereby amended
by revising the following Section in its entirety to read as follows:

          5.19 Adjusted  Liabilities to Adjusted Net Worth.  Maintain a ratio of
          Adjusted  Liabilities  to Adjusted  Net Worth of not more than 2.25 to
          1.0 through  March 31, 1999;  thereafter  2.00 to 1.0 through June 30,
          1999;  thereafter 1.75 to 1.0 through March 31, 2000;  thereafter 1.25
          to 1.0 through September 30, 2000; and thereafter 1.0 to 1.0.

     Article V, AFFIRMATIVE  COVENANTS,  is modified by adding the following new
section:

          5.35  Affirmative  Covenants of OSI.  With respect to any  affirmative
          covenants  made by OSI with  respect  to the Notes,  such  affirmative
          covenants shall be applicable only to the Revolving Note.

     Article VI,  NEGATIVE  COVENANTS,  is modified by adding the  following new
section:

          6.17  Negative  Covenants  of OSI.  With  respect to the any  negative
          covenants  made  by OSI  with  respect  to the  Notes,  such  negative
          covenants shall be applicable only to the Revolving Note.

     Section  6.01 Other  Indebtedness,  as amended by the Third  Amendment,  is
hereby further amended by moving the word "and" immediately preceding subsection
(J) to the end of such subsection and is further amended by adding the following
subsection thereto:

          "(K) indebtedness as evidenced by the OSI Unsecured Note."

     Section 6.14 Capital Expenditures  Limitation,  as amended by the Third and
Fourth  Amendments,  is hereby  further  amended by replacing the clause therein
which reads  "$3,000,000.00 in the 1998 fiscal year" with  "$6,800,000.00 in the
1998 fiscal year".

     "Exhibit A-1," the form of Revolving  Note attached to the Loan  Agreement,
as replaced  pursuant to the Third Amendment and the Fourth  Amendment is hereby
replaced with Exhibit "A- 1" attached to this Fifth Amendment.


                                       -4-

<PAGE>



     "Exhibit  B," the  form of  Compliance  Certificate  attached  to the  Loan
Agreement,  as amended by the Third and Fourth  Amendments,  is hereby  replaced
with Exhibit "B" attached to this Fifth Amendment.

     "Schedule 1.01(a),  Collateral" attached to the Loan Agreement,  as amended
by the  Second,  Third and Fourth  Amendments,  is hereby  amended by adding the
following  information  to  the  end  of the  section  entitled  "Tanknology-NDE
International, Inc.", subpart "(a)":

          ", Outbound Services, Inc., a California corporation",

and is further  amended by adding the following  information  at the end of that
schedule:

          "Outbound Services, Inc.
               (a) Accounts Receivables
               (b) Inventory"

     "Schedule 3.10,  Collateral  Documents" attached to the Loan Agreement,  as
amended  by the Fourth  Amendment,  is hereby  amended  by adding the  following
information to each identified subpart:

         1. Stock Powers executed by Tanknology-NDE International, Inc.:
                  "e.    Outbound Services, Inc.;


         2. Security Agreements:
                  "e.  Outbound Services, Inc. dated November 5, 1998"

         3. Financing Statements:
                  "Outbound Services, Inc.
                  TEXAS: Secretary of State"

     "Schedule  4.01,  Jurisdiction  Information,  etc."  attached  to the  Loan
Agreement is hereby  amended by adding the following  information  to the end of
that schedule:

                  "Outbound Services, Inc.
                           State of Incorporation:       California"

     "Schedule 4.09,  Existing  Indebtedness"  attached to the Loan Agreement is
hereby amended by adding the following information to the end of that schedule:

          $750,000 promissory note dated August 7, 1998 executed by NDE and made
          payable to the order of Sellers, as defined in the Loan Agreement,  as
          amended.


                                       -5-

<PAGE>



     II. Certain Waivers. Bank hereby waives non-compliance by the Borrower with
the covenants set forth in Sections 6.01,  6.04, 6.07, 6.08 and 6.11 of the Loan
Agreement, but only to the extent that such non-compliance was the result of the
Borrower's acquisition of all the outstanding stock of OSI pursuant to the terms
under the OSI Stock  Purchase  Agreement.  Notwithstanding  anything that may be
contained  herein to the contrary,  no waiver or any other  provision  contained
herein shall serve to subordinate  any of Borrower's  Obligations to Bank to any
of Borrower's Obligations to any third party, including, but not limited to, any
of NDE's obligations to the Sellers.

     III. Certain  Consents.  Bank hereby consents to (i) the acquisition by NDE
of, and the additional  capital investment by NDE of up to $500,000 in, OSI as a
wholly owned  subsidiary of NDE, and (ii) the issuance of 500,000  shares of NDE
stock warrants pursuant to the OSI Stock Purchase Agreement.

     IV. Conditions to the Effectiveness of the Fifth Amendment.  As a condition
to the effectiveness of the Fifth Amendment by Bank,  Borrower has satisfied the
following conditions:

          A. Receipt of Amended and Restated Revolving Note, Fifth Amendment and
     Certificate  of  Compliance.  The Bank shall have  received the Amended and
     Restated  Revolving  Note (the form  which is  attached  hereto as  Exhibit
     "A-1"),  multiple  counterparts of this Fifth Amendment as requested by the
     Bank and the Compliance  Certificate duly executed by an authorized officer
     for each Borrower (the form of which is attached hereto as Exhibit "B");

          B. Collateral Documents.  As security for the payment of the Revolving
     Note  and  the  performance  of the  obligations  of  OSI  under  the  Loan
     Agreement,  Bank shall have  received the duly  executed  and  acknowledged
     Collateral Documents described on Schedule 1 attached hereto.

          C. Receipt of Certified Copy of Corporate  Proceedings and Certificate
     of  Incumbency.  The Bank shall have received from each Borrower  copies of
     all resolutions of its board of directors with respect to the  transactions
     set  forth  in this  Fifth  Amendment  and  the  execution  of  this  Fifth
     Amendment,  such copy or  copies to be  certified  by the  Secretary  or an
     Assistant  Secretary as being true and correct and in full force and effect
     as of the date hereof. In addition,  the Bank shall have received from each
     Borrower  a  certificate  of  incumbency  signed  by  the  Secretary  or an
     Assistant  Secretary setting forth (a) the names of the officers  executing
     this Fifth  Amendment,  (b) the  office(s)  to which such Persons have been
     elected  and in which they  presently  serve and (c) an  original  specimen
     signature of each such person.

          D.  Borrower's  Opinion of  Counsel.  Bank shall  have  received  from
     counsel  for  Borrower  a  written  opinion  in form  satisfactory  to Bank
     covering  the  matters  set  forth on  Exhibit  "D"  attached  to the Fifth
     Amendment.


                                       -6-

<PAGE>



          E. Delivery of OSI's Stock  Certificate.  Bank shall have received the
     stock  certificate  of  Outbound  Services,  Inc.  pursuant  to  the  Third
     Amendment to Pledge and Security Agreement by and between Borrower and Bank
     dated  of  even  date  herewith  as  part of the  security  for  Borrower's
     obligations under the Loan Agreement.

          F.   Satisfaction   of  Conditions  to  Fifth   Amendment.   Upon  the
     satisfaction  of  the  conditions  to  the   effectiveness  of  this  Fifth
     Amendment,  as set forth in this Article IV hereof,  Borrower shall execute
     and  deliver  to Bank a  Certificate  of  Compliance,  and if Bank has been
     reasonably  satisfied that such conditions have been fulfilled,  Bank shall
     contemporaneously  provide a letter to Borrower  stating "Bank One,  Texas,
     N.A. is satisfied  that the conditions set forth in Article IV of the Fifth
     Amendment to that certain Loan Agreement dated October 25, 1996,  among the
     Bank and  Tanknology-NDE  International,  Inc. et al. have been fulfilled,"
     whereupon this Fifth Amendment shall become effective.

     V. Reaffirmation of Representations and Warranties. To induce Bank to enter
into this Fifth Amendment, Borrower hereby reaffirms, as of the date hereof, its
representations and warranties contained in Article IV of the Loan Agreement, as
amended,  and in all other documents executed pursuant thereto, and additionally
represents and warrants as follows:

          A.  The  execution  and  delivery  of  this  Fifth  Amendment  and the
     performance by Borrower of its  obligations  under this Fifth Amendment are
     within  the  Borrower's   corporate  power,  have  received  all  necessary
     governmental  approval (if any shall be required),  and do not and will not
     contravene  or  conflict  with  any  provision  of law or of any  agreement
     binding upon the Borrower.

          B. The Loan  Agreement as amended by this Fifth  Amendment  represents
     the legal, valid and binding  obligations of Borrower,  enforceable against
     Borrower in  accordance  with its terms subject as to  enforcement  only to
     bankruptcy,  insolvency,  reorganization,  moratorium or other similar laws
     affecting  the  enforcement  of  creditors'  rights  generally  and general
     principles of equity.

          C. No Event of Default or Unmatured  Event of Default has occurred and
     is continuing as of the date hereof.

     VI. Defined  Terms.  Except as amended  hereby,  terms used herein that are
defined in the Loan Agreement shall have the same meanings herein.

     VII. Reaffirmation of Loan Agreement.  This Fifth Amendment shall be deemed
to be an amendment to the Loan  Agreement,  and the Loan  Agreement,  as amended
hereby,  is hereby  ratified,  approved and confirmed in each and every respect.
All  references  to  the  Loan  Agreement  herein  and in  any  other  document,
instrument,  agreement or writing shall hereafter be deemed to refer to the Loan
Agreement as amended hereby.


                                       -7-

<PAGE>



     VIII. Entire Agreement. The Loan Agreement, as hereby amended, embodies the
entire agreement  between Borrower and Bank, and supersedes all prior proposals,
agreements and  understandings  relating to the subject matter hereof.  Borrower
certifies  that  it is  relying  on no  representation,  warranty,  covenant  or
agreement except for those set forth in the Loan Agreement as hereby amended and
the other documents previously executed or executed of even date herewith.

     IX.  Governing Law. THIS FIFTH AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS AND THE APPLICABLE LAWS OF THE
UNITED STATES OF AMERICA.  This Fifth  Amendment has been entered into in Harris
County,  Texas,  and it shall be performable  for all purposes in Harris County,
Texas. Courts within the State of Texas shall have jurisdiction over any and all
disputes between Borrower and Bank, whether in law or equity, including, but not
limited  to,  any and all  disputes  arising  out of or  relating  to this Fifth
Amendment or any other Loan Document;  and venue in any such dispute  whether in
federal or state court shall be laid in Harris County, Texas.

     X.  Severability.  Whenever possible each provision of this Fifth Amendment
shall  be  interpreted  in  such  manner  as to be  effective  and  valid  under
applicable law, but if any provision of this Fifth Amendment shall be prohibited
by or invalid under  applicable  law, such provision shall be ineffective to the
extent of such prohibition or invalidity,  without invalidating the remainder of
such provision or the remaining provisions of this Fifth Amendment.

     XI. Execution in Counterparts.  This Fifth Amendment may be executed in any
number of counterparts  and by the different  parties on separate  counterparts,
and each  such  counterpart  shall be  deemed  to be an  original,  but all such
counterparts shall together constitute but one and the same agreement.

     XII.  Section  Captions.  Section captions used in this Fifth Amendment are
for convenience of reference only, and shall not affect the construction of this
Fifth Amendment.

     XIII.  Successors and Assigns.  This Fifth  Amendment shall be binding upon
the Borrower and Bank and their  respective  successors  and assigns,  and shall
inure to the benefit of the Borrower and Bank, and the respective successors and
assigns of Bank.

     XIV.  Non-Application  of Chapter 346 of Texas Finance Code. The provisions
of  Chapter  346 of the Texas  Finance  Code are  specifically  declared  by the
parties  hereto not to be applicable to the Loan  Agreement as hereby amended or
any of the other Loan Documents or to the transactions contemplated hereby.

     XV. Notice.  THIS FIFTH AMENDMENT  TOGETHER WITH THE LOAN AGREEMENT AND THE
OTHER LOAN DOCUMENTS  REPRESENT THE FINAL AGREEMENT  BETWEEN THE PARTIES AND MAY
NOT BE  CONTRADICTED  BY EVIDENCE OF PRIOR,  CONTEMPORANEOUS  OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL  AGREEMENTS  BETWEEN THE
PARTIES. `


                                       -8-

<PAGE>



     IN WITNESS WHEREOF,  the parties hereto have caused this Fifth Amendment to
be duly executed as of the day and year first above written.

                                     BORROWER:

                                     TANKNOLOGY-NDE INTERNATIONAL, INC.
                                     (formerly known as NDE ENVIRONMENTAL
                                     CORPORATION)

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                Jay Allen Chaffee
                                                Chairman of the Board

                                       TANKNOLOGY/NDE CORPORATION

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                Jay Allen Chaffee
                                                Chairman of the Board

                                       TANKNOLOGY-NDE CONSTRUCTION
                                       SERVICES, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                Jay Allen Chaffee
                                                Chairman of the Board

                                       PROECO, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                Jay Allen Chaffee
                                                Chairman of the Board

                                       2368692 CANADA, INC. (formerly known as
                                       TANKNOLOGY CANADA (1988) INC.)

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                               Jay Allen Chaffee
                                                President

                                       OUTBOUND SERVICES, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                               Jay Allen Chaffee
                                               Chairman of the Board

                               -9-

<PAGE>



                                       BANK:

                                       BANK ONE, TEXAS, N.A.


                                       By:   //s// JO LINDA PAPADAKIS
                                          ------------------------------------
                                               Jo Linda Papadakis
                                               Vice President

                                      -10-

<PAGE>



                                   Schedule 1

1.   Stock Power executed by Tanknology-NDE International,  Inc. with respect to
     its shares of Outbound Services, Inc., a wholly owned subsidiary.

2.   Third   Amendment   to  Stock  Pledge  and   Security   Agreement   between
     Tanknology-NDE International, Inc. and Bank One, Texas.

3.   Security Agreement between Outbound Services, Inc. and Bank One, Texas.

4.   Financing Statement

         Outbound Services, Inc.
         TEXAS: Secretary of State


                                       -1-

<PAGE>




                                  EXHIBIT "A-1"

                       AMENDED AND RESTATED REVOLVING NOTE

$9,000,000.00                                                   November 5, 1998

     FOR VALUE RECEIVED,  TANKNOLOGY-NDE INTERNATIONAL,  INC. (formerly known as
NDE ENVIRONMENTAL  CORPORATION) ("NDE"), a Delaware corporation,  TANKNOLOGY/NDE
CORPORATION,  a Delaware  corporation,  PROECO,  INC.,  a Delaware  corporation,
2368692  CANADA,  INC.  (formerly  known as TANKNOLOGY  CANADA  (1988) INC.),  a
Canadian federal  corporation,  TANKNOLOGY-NDE  CONSTRUCTION  SERVICES,  INC., a
Delaware corporation, and OUTBOUND SERVICES, INC., a California corporation, all
of the foregoing having an address at 8900 Shoal Creek, Bldg. 200, Austin, Texas
78757 (collectively,  "Borrower") unconditionally promise to pay to the order of
BANK ONE, TEXAS, NATIONAL ASSOCIATION, (herein called "Bank"), at its offices at
910 Travis,  Houston,  Texas 77001,  the principal  sum of NINE MILLION  DOLLARS
($9,000,000.00)  or,  if less,  the  aggregate  unpaid  principal  amount of all
Revolving  Loans  (as  defined  in the Loan  Agreement)  made by the Bank to the
Borrower  pursuant to the Loan  Agreement,  as shown in the records of the Bank,
outstanding on such date.

     The undersigned also promise to pay interest on the unpaid principal amount
hereof  from  time to time  outstanding  from the  date  hereof  until  maturity
(whether by acceleration  or otherwise) and, after maturity,  until paid, at the
rates  per annum and on the dates  specified  in the Loan  Agreement;  provided,
however,  that in no event  shall  such  interest  exceed the  Maximum  Rate (as
hereinafter defined).

     "Maximum Rate" means the Maximum Rate of  non-usurious  interest  permitted
from day to day by Applicable Law.

     "Applicable  Law" means that law in effect from time to time and applicable
to this Revolving Note which lawfully permits the charging and collection of the
highest  permissible  lawful,  non-usurious  rate of interest on this  Revolving
Note. To the extent federal law permits Bank to contract for,  charge or receive
a greater amount of interest, Bank will rely on federal law instead of the Texas
Finance  Code,  as  supplemented  by Texas  Credit  Title,  for the  purpose  of
determining the Maximum Rate.  Additionally,  to the maximum extent permitted by
applicable law now or hereafter in effect, Bank may, at its option and from time
to time,  implement  any other  method of  computing  the Maximum Rate under the
Texas  Finance  Code,  as  supplemented  by Texas Credit  Title,  or under other
applicable  law,  by giving  notice,  if  required,  to  Borrower as provided by
applicable  law now or  hereafter  in effect.  Notwithstanding  anything  to the
contrary  contained herein or in any of the other Loan Documents,  it is not the
intention of Bank to accelerate the maturity of any interest that has not

                                                                    ------------
                                                                     Initial for
                                                                  Identification
                                       A-1

<PAGE>


accrued at the time of such  acceleration or to collect unearned interest at the
time of such acceleration.

     In no event shall  Chapter 346 of the Texas  Finance Code (which  regulates
certain revolving loan accounts and revolving  tri-party accounts) apply to this
Note.  To the extent that Chapter 303 of the Texas Finance Code is applicable to
this Note, the "weekly ceiling"  specified in such Chapter 303 is the applicable
ceiling;  provided that, if any applicable law permits greater interest, the law
permitting the greatest interest shall apply.

     In no event shall the  aggregate  of the  interest  on this Note,  plus any
other  amounts  paid in  connection  with the loan  evidenced by this Note which
would under Applicable Law be deemed  "interest," ever exceed the maximum amount
of interest which, under Applicable Law, could be lawfully charged on this Note.
The Bank and the Borrower  specifically  intend and agree to limit contractually
the interest  payable on this Note to not more than an amount  determined at the
Maximum Rate. Therefore, none of the terms of this Note or any other instruments
pertaining to or securing this Note shall ever be construed to create a contract
to pay  interest  at a rate in excess  of the  Maximum  Rate,  and  neither  the
Borrower nor any other party liable herefor shall ever be liable for interest in
excess of that  determined  at the  Maximum  Rate,  and the  provisions  of this
paragraph  shall  control  over  all  provisions  of this  Note or of any  other
instruments pertaining to or securing this Note. If any amount of interest taken
or  received  by the Bank shall be in excess of the  maximum  amount of interest
which,  under  Applicable  Law, could lawfully have been collected on this Note,
then the excess shall be deemed to have been the result of a mathematical  error
by the  parties  hereto and shall be  refunded  promptly  to the  Borrower.  All
amounts paid or agreed to be paid in connection with the indebtedness  evidenced
by this Note which would under Applicable Law be deemed "interest" shall, to the
extent permitted by Applicable Law, be amortized, prorated, allocated and spread
throughout the full term of this Note.

     This Note is the  Revolving  Note  referred  to in and is  entitled  to the
benefits of a certain Loan  Agreement,  dated as of October 25, 1996, as amended
by that First Amendment  dated April 10, 1997,  that Second  Amendment dated May
20, 1997,  that Third  Amendment  dated December 23, 1997, the Fourth  Amendment
dated June 26, 1998 and the Fifth  Amendment dated of even date herewith (as the
same may be further amended, modified, supplemented, extended, rearranged and/or
restated  from time to time,  the "Loan  Agreement"),  entered into by and among
Tanknology-NDE  International,  Inc., (f/k/a NDE  Environmental  Corporation) et
al., as Borrower,  and Bank One, Texas,  National Association and secured by the
Collateral Documents (as such term is defined in the Loan Agreement).  Reference
is hereby made to the Loan  Agreement for a statement of the  prepayment  rights
and penalties and  obligations of the Borrower,  a description of the properties
and assets  mortgaged,  encumbered  and  assigned,  the nature and extent of the
security and the rights of the parties to the Collateral Documents in respect of
such security,  and for a statement of the terms and conditions  under which the
due date of this Note may be  accelerated.  Upon the  occurrence of any Event of
Default as specified in the Loan Agreement, the principal balance hereof and the

                                                                    ------------
                                                                     Initial for
                                                                  Identification
                                       A-2

<PAGE>



interest  accrued  hereon may be  declared  to be  forthwith  due and payable in
accordance with the Loan Agreement, and any indebtedness of the holder hereof to
the Borrower may be appropriated and applied hereon.

     In addition to and not in  limitation  of the  foregoing,  the  undersigned
further agrees, subject only to any limitation imposed by applicable law, to pay
all  reasonable  expenses,   including  reasonable  attorneys'  fees  and  legal
expenses,  incurred  by the holder of this Note in  endeavoring  to collect  any
amounts payable  hereunder which are not paid when due,  whether by acceleration
or otherwise.

     All parties hereto, whether as makers,  endorsees, or otherwise,  severally
waive presentment for payment,  demand, protest, notice of intent to accelerate,
notice of acceleration and notice of dishonor.

     This Note is issued in substitution for, and in replacement,  modification,
rearrangement,  renewal  and  extension  of, but not in  extinguishment  of, the
outstanding   principal   indebtedness   evidenced   by  that  certain  note  of
Tanknology-NDE  International,   Inc.  (f/k/a  NDE  Environmental  Corporation),
Tanknology/NDE   Corporation,   ProEco,   Inc.,  2368692  Canada,  Inc.  (f/k/a/
Tanknology Canada (1988) Inc.) and Tanknology-NDE  Construction Services,  Inc.,
dated  June 26,  1998,  payable  to the order of Bank One,  Texas,  N.A.  in the
original   principal  sum  of  $9,000,000.00,   (the  "Prior  Note");  it  being
acknowledged and agreed by Borrower that the indebtedness evidenced by this Note
constitutes an extension and renewal of the outstanding  principal  indebtedness
evidenced  by the Prior Note,  and that all security  interests  and other liens
which  secure  the  repayment  of the Prior Note  shall  continue  to secure the
indebtedness evidenced by this Note.

     THIS NOTE SHALL BE DEEMED TO BE A CONTRACT MADE UNDER THE LAWS OF THE STATE
OF TEXAS  AND  CONSTRUED  IN  ACCORDANCE  WITH THE LAWS OF THE  STATE OF  TEXAS,
WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF LAW.

     EXECUTED this 5th day of November, 1998.


                                       MAKER:

                                       TANKNOLOGY-NDE INTERNATIONAL, INC.
                                       (formerly known as NDE ENVIRONMENTAL
                                       CORPORATION)

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  Chairman of the Board


                                                        A-3

<PAGE>



                                       TANKNOLOGY/NDE CORPORATION

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  Chairman of the Board


                                       PROECO, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  Chairman of the Board


                                       2368692 CANADA, INC. (formerly known as
                                       TANKNOLOGY CANADA (1988) INC.)

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  President


                                       TANKNOLOGY-NDE CONSTRUCTION
                                       SERVICES, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  Chairman of the Board


                                       OUTBOUND SERVICES, INC.

                                       By:   //s// JAY ALLEN CHAFFEE
                                          ------------------------------------
                                                  Jay Allen Chaffee
                                                  Chairman of the Board



                                       A-4

<PAGE>



                                   EXHIBIT "B"


                             Compliance Certificate



     I,    ______________________,     the     ___________________________    of
TANKNOLOGY-NDE INTERNATIONAL,  INC. (the "Company"), pursuant to Section 5.05 of
the Loan  Agreement  dated as of  October  25,  1996,  as  amended  by the First
Amendment  dated April 10, 1997,  the Second  Amendment  dated May 20, 1997, the
Third  Amendment  dated December 23, 1997, the Fourth  Amendment  dated June 26,
1998,  and the Fifth  Amendment  dated  November  5, 1998 by and among BANK ONE,
TEXAS, N.A. ("Bank") and the Company et al. (the "Agreement") do hereby certify,
as of the date hereof, that to my knowledge:

     1.   No Event of Default (as defined in the  Agreement) has occurred and is
          continuing,  and no  Unmatured  Event of  Default  (as  defined in the
          Agreement)  has occurred and is  continuing  except for the  following
          events (include actions taken to cure such situations):
          ----------------------------------------------------------------------
          ----------------------------------------------------------------------
          ----------------------------------------------------------------------
          ----------------------------------------------------------------------
          ----------------------------------------------------------------------
          --------------------------;

     2.   No material adverse change has occurred in the condition, financial or
          otherwise, of the Company since ________________;

     3.   Except as otherwise stated in the Schedule,  if any,  attached hereto,
          each of the representations and warranties of the Company contained in
          Article IV of the Agreement is true and correct in all respects; and


                                       B-1

<PAGE>




     4.   The Company's  financial  condition for the month ending __________ is
          as follows:

<TABLE>
<CAPTION>

       Financial Covenant          Time Period           Required Ratio                                           Actual Ratio
<S>                               <C>             <C>                                                            <C>
================================= ==============  =============================================================  ==============
(a) Net Worth                      Term of Loan    Not less than the  Consolidated  Net  Worth as of  12/31/97,
                                                   with allowable  cumulative interim losses during fiscal year
                                                   1998 of not more than $1,000,000.00 (tested as of the end of
                                                   each calendar quarter),  and as of 12/31/98, and thereafter,
                                                   maintain  at least  the  Consolidated  Net  Worth in  effect
                                                   12/31/97  plus 70% of  Borrower's  Net Income (if  positive)
                                                   after 12/31/98.

(b) Capital Expenditures           Term of Loan    Not more than  $6,800,000 for fiscal 1998 and $2,000,000 for
                                                   each year thereafter.

(c) Debt Service Coverage Ratio    Term of Loan    Not less than 1.2 to 1.0

(d) Adjusted Liabilities to        Term of Loan    9/30/98 - 3/31/99 not more than 2.25 to 1.0;  4/1/99  
    Adjusted Net Worth                             6/30/99 not more than 2.00 to 1.0; 7/1/99 -  3/31/2000 not
                                                   more   than   1.75   to  1.0; 4/1/2000 - 9/30/2000 not more
                                                   than  1.25 to 1.0;  and after 9/30/2000  not more  than 1.0
                                                   to 1.0.

================================= ==============  =============================================================  ==============
</TABLE>




This certificate is executed this ___ day of ___________ 199__.


                                            TANKNOLOGY-NDE INTERNATIONAL, INC.


                                            ------------------------------------
                                            By: ________________________________
                                            Its: _______________________________



                                       B-2

<PAGE>



                                   EXHIBIT "C"

             There is no Exhibit C attached to this Fifth Amendment.

                                       C-1

<PAGE>



                                   EXHIBIT "D"

                     Form of Opinion of Counsel for Borrower
                              Baker & Botts, L.L.P.

     (1) OSI is a corporation  duly  organized,  existing,  and in good standing
under  the Laws of its  state  of  incorporation  [naming  such  states]  and is
qualified to transact business and is in good standing in those states where the
nature of business or property owned by it requires qualification,  as set forth
in  Schedule  4.01 of the Loan  Agreement,  as  amended,  attached to this Fifth
Amendment and made a part hereof,  and, to the knowledge of such counsel, is not
required to be qualified as a foreign corporation in any other jurisdiction;

     (2) OSI has the power to execute and deliver the Fifth Amendment, to borrow
money thereunder,  to grant the Collateral required  thereunder,  to execute and
deliver the Collateral Documents, and to perform its obligations thereunder;

     (3) All  corporate  actions by OSI and all  consents  and  approvals of any
Persons necessary to the validity of the Fifth Amendment and each other document
to be  delivered  hereunder  have been  duly  taken or  obtained,  and the Fifth
Amendment and the Collateral Documents, and such other documents do not conflict
with any provision of the charter or by-laws of OSI, or of any applicable  Laws,
or any other agreement  binding OSI or its property of which,  after  reasonable
inquiry, such counsel has knowledge; and

     (4) The Fifth Amendment and Collateral  Documents to be delivered hereunder
have been duly  executed by, and each is a valid and binding  obligation of OSI;
each of the  foregoing  documents is in all respects  sufficient  to achieve its
purported  function and is enforceable in accordance  with its terms,  except as
limited by bankruptcy, insolvency, reorganization,  moratorium, or other similar
laws affecting creditors' rights generally or by general equitable principles.

                                       D-1