<PAGE>
 
                                                                   Exhibit 4(b)


                     FOURTH AMENDMENT TO LOAN INSTRUMENTS


     THIS FOURTH AMENDMENT TO LOAN INSTRUMENTS (the "Fourth Amendment") is dated
as of this ____ day of December, 1994 by and among GDC ENGINEERING, INC., a
Louisiana corporation ("Borrower"), KATHLEEN J. ELNAGGAR in her capacity as
trustee (the "Trustee") of the testamentary trust for the benefit of Tarek
Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie Elnaggar (the "Trust") created
by the Last Will and Testament of Hameed Ahmed Elnaggar dated March 20, 1988
(the "Will"), which Will was probated in THE SUCCESSION OF HAMEED AHMED
ELNAGGAR, PROBATE NO. 56829, NINETEENTH JUDICIAL DISTRICT, PARISH OF EAST BATON
ROUGE, STATE OF LOUISIANA (the "Succession"), KATHLEEN JORDAN ELNAGGAR, one and
the same as Kathleen J. Elnaggar, individually and in her capacity as
usufructuary under the Will, a person of the full age of majority and a resident
of Baton Rouge Parish, Louisiana ("K. Elnaggar") (each of Borrower, the Trustee,
the Succession and K. Elnaggar are sometimes hereinafter referred to
individually as an "Obligor" and collectively as the "Obligors"), and GREYHOUND
FINANCIAL CORPORATION, a Delaware Corporation ("Lender").

     WHEREAS, there is in effect a Loan Agreement dated December 30, 1992
between Borrower and Lender, as amended by Amendment to Loan Instruments dated
June 30, 1993 among Obligors and Lender, Second Amendment to Loan Instruments
dated October 26, 1993 among Obligors and Lender, Third Amendment to Loan
Instruments dated April 1, 1994 among Obligors and Lender (collectively,
together with this Fourth Amendment, the "Loan Agreement"), pursuant to which
Lender committed to loan to Borrower an amount not to exceed the principal sum
of $4,900,000 to refinance existing debt of Borrower and $4,000,000 to fund
certain capital expenditures (the "Loan");

     WHEREAS, the Loan is evidenced by the Loan Agreement and a promissory note
dated December 30, 1992 from Borrower payable to Lender in the principal sum of
$8,900,000 (the "Note"), and secured by, among others, a Security Agreement and
Shareholder Pledge Agreement dated December 30, 1992 from the Succession and K.
Elnaggar in favor of Lender and a Subordination and Stand-By Agreement dated
December 30, 1992 among the Succession, K. Elnaggar, Borrower and Lender;

     WHEREAS, the $4,000,000 commitment to fund certain capital expenditures
expired unused;

     WHEREAS, Borrower has requested Lender's consent to the sale of all of the
Borrower BCI Capital Stock owned by Borrower to the existing BCI management;

     WHEREAS, Lender has agreed to consent to the sale of all of the Borrower
BCI Capital Stock owned by Borrower to the existing BCI management, upon the
terms and conditions contained herein;

     WHEREAS, the administration of the Succession has been completed and
Judgement of Possession was signed in the Succession on October 4, 1994, a copy
of which is attached hereto 
<PAGE>
 
as Exhibit A and incorporated herein by this reference, which said Judgment of
Possession recognizes certain rights and puts the legatees under the Will in
possession of the assets of the Succession;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein, and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Obligors and Lender,
intending to be legally bound, agree as follows:

     1.   Definitions.   Except as otherwise defined herein, all capitalized
          -----------                                                       
terms used herein shall have the meanings ascribed thereto in the Loan
Agreement.

     2.   Recitals.  The Recitals set forth above are true and accurate and are
          --------                                                             
incorporated herein by this reference.

     3.   Amounts Outstanding.  Obligors hereby acknowledge and agree that (a)
          -------------------                                                 
as of November 1, 1994, the principal amount of the Loan outstanding is
$____________ and there is no accrued and unpaid interest, and (b) as of the
date of execution hereof by Obligors, there are no defenses, claims or offsets
to payment of such principal amount and the other indebtedness evidenced by the
Note.

     4.   Loan Agreement Definitions.  The definitions of, and references to,
          --------------------------                                         
"Assignment of Interest Hedge Contract" and "Interest Hedge Contract" in Section
1.1 of the Loan Agreement are hereby deleted in their entirety and the
definitions of "Operating Cash Flow" and "Working Capital Loan" is hereby
deleted in its entirety and the following is inserted therefor:

          Operating Cash Flow:  for any period, the net income of
          -------------------
          Borrower for such period:

               (i)  plus the sum of the following, to the extent
          deducted in determining net income for such period:

                    (A)  interest paid or accrued on Indebtedness,
               including, without limitation, interest on Capitalized
               Leases that is imputed in accordance with GAAP;

                    (B)  Depreciation and amortization of assets; and

                    (C)  extraordinary losses from sales or
               dispositions of Property outside of the normal course
               of Borrower's Business;

               (ii) minus the sum of the following, to the extent
                    -----
          included in determining net income for such period:

                                      -2-
<PAGE>
 
                    (A)  all payments made by Borrower during such
               period with respect to Capital Expenditures, other than
               Subsequent Advance Expenditures;

                    (B)  extraordinary gains from sales or
               dispositions of Property outside the ordinary course of
               Borrower's Business; and

                    (C)  for purposes of Excess Cash Flow payments
               pursuant to Section 2.9.2 hereof only, fifty percent
               (50%) of all payments received by Borrower from
               Occidental Chemical Corporation or its successors or
               assigns ("Oxy Chem") pursuant to that certain agreement
               dated September 21 and 28, 1994 between Borrower and
               Oxy Chem, a copy of which is attached hereto as EXHIBIT
               2.9.2 and incorporated herein by this reference.

          Working Capital Loan:  shall mean a revolving loan to be made by
          --------------------                                            
          Working Capital Lender to Borrower in an amount of not less than
          $750,000.

     5.   Additional Defined Terms.  Section 1.1 of the Original Loan Agreement
          ------------------------                                             
is hereby amended by adding the following definitions in the appropriate
alphabetical order:

          Approved BCI Sale: shall mean a sale, transfer conveyance or
          -----------------                                           
          assignment of all or substantially all of the assets of BCI or
          all or substantially all of the Borrower BCI Capital Stock owned
          by Borrower to the existing BCI management, which is consummated
          on or before December 31, 1994 and which results in the receipt
          by Borrower of a net sales amount of not less than $45,000.00.

          Annual Site Inspection Expenses: shall mean all costs and 
          -------------------------------                                   
          expenses incurred by Lender with respect to Lender's annual
          inspections of the Business premises (all locations) by Lender or
          a representative of Lender pursuant to Section 6.2 hereof, but
          not to exceed $2,500 per year.

     6.   Prepayments.  Subsection 2.9.2 of the Loan Agreement is hereby
          -----------                                                    
amended to add the following:

          (E)  PROCEEDS FROM AN APPROVED BCI SALE.  Upon the 
               ----------------------------------    
          consummation of an Approved BCI Sale, Borrower shall pay to
          Lender $45,000, which shall be applied as a prepayment of the

                                      -3-
<PAGE>
 
          Principal Balance of the Loan.

     7.   Interest Hedge Contract.  Subsection 4.2.1 of the Loan Agreement is
          -----------------------                                            
hereby deleted in its entirety and the following is inserted therefor:

          4.2.1 INTENTIONALLY DELETED.

     8.   Annual Statements.  Section 6.3.3 of the Loan Agreement is hereby
          -----------------                                                
amended to add the following:

          As soon as available and in any event within 120 days after the
          end of each calendar year, Borrower shall cause K. Elnaggar to,
          and K. Elnaggar shall, provide to Lender a personal financial
          statement as of December 31 of the immediately prior calendar
          year, in a form and with a certification satisfactory to Lender,
          and a true, correct and complete copy of K. Elnaggar's Federal
          tax return, as filed, for the immediately prior calendar year.

     9.   Interest Hedge Contract.  Section 6.17 of the Loan Agreement is hereby
          -----------------------                                               
deleted in its entirety and the following is inserted therefor:

          6.17 INTENTIONALLY DELETED.

     10.  Appraisal.  Section 6 of the Loan Agreement is hereby amended to add
          ---------                                                          
the following:

               6.18 APPRAISAL.  On or prior to December 15, 1994, 
                    ---------    
          Borrower, at Borrower's sole cost and expense, shall provide
          Lender with an appraisal conducted by an appraiser acceptable to
          Lender, which appraisal shall reflect a net orderly liquidation
          value of Borrower's environmental and remediation machinery and
          equipment and a fair market value of Borrower's rotary kiln
          incineration system, more particularly described as item 102 ER
          on page 20 of the GDC Engineering, Inc. Appraisal dated December
          7, 1992.

               6.19 GUARANTY. K. Elnaggar shall execute and deliver to 
                    --------     
          Lender a continuing guaranty in the form attached hereto as Exhibit 
                                                                      -------
          6.19 and incorporated herein by this reference (the "K. Elnaggar
          ----
          Guaranty"), together with an opinion of counsel as to the
          enforceability of the K. Elnaggar Guaranty in form and substance
          and from counsel satisfactory to Lender.

     11.  Sale or Transfer of Assets.    Section 7.9 of the Loan Agreement is
          --------------------------                                         
hereby deleted in its entirety and the following is inserted therefor:

                                      -4-
<PAGE>
 
          7.9  Sell, lease, assign, transfer or otherwise dispose of any
          Property except Borrower may dispose of (i) inventory in the
          ordinary course of business, (ii) Property which is not material
          to or necessary for the continued operation of Borrower's
          Business, (iii) items of equipment which promptly are replaced
          with new items of equipment of like function and comparable value
          to those of equipment when the same were new, and (iv) the assets
          or Capital Stock of BCI pursuant to an Approved BCI Sale;
          provided, however, that in the event of an Approved BCI Sale,
          Borrower shall pay to Lender $45,000, which Lender shall apply to
          the Loan in accordance with subsection 2.9.2(e) hereof. As soon
          as practicable after Lender's receipt of such funds, Lender shall
          release its lien on the BCI assets more particularly described on
          pages 11 and 12 of the GDC Engineering, Inc. Appraisal dated
          December 7, 1992.

     12.  Fees.  Article X of the Loan Agreement is hereby amended to add the
          ----                                                                  
following:

          10.3 Site Inspection Expense.  Upon demand, Borrower agrees to 
               -----------------------      
          pay to Lender the Annual Site Inspection Expenses with respect to
          inspections as provided for in Section 6.2 hereof.

     13.  Notices.  Section 11.1 of the Loan Agreement with respect to the copy
          -------                                                              
of notices to Lender is hereby deleted in its entirety and the following
inserted therefor:

          Copy to:  Greyhound Financial Corporation
                    Dial Tower/Dial Corporate Center
                    Phoenix, Arizona 85077
                    Attention:  Vice President, Law
                    Telecopy No.: (602) 207-5036

                    and

                    Greyhound Financial Corporation
                    10 South LaSalle Street
                    Suite 2121
                    Chicago, Illinois 60603
                    Attention:  Adolph G. Letke
                    Telecopy No.: (312) 855-1779

                                      -5-
<PAGE>
 
                    and

                    Fennemore Craig
                    Two North Central Avenue
                    Suite 2200
                    Phoenix, Arizona 85004-2390
                    Attention:  Jay S. Kramer
                    Telecopy No.: (602) 257-8527

     14.  Representations, Acknowledgments, and Agreements of Obligors.  As
          ------------------------------------------------------------     
material inducements to Lender to enter into this Fourth Amendment, and
acknowledging Lender's reliance upon the truth and accuracy thereof, Borrower,
with respect to subsections (a), (b), (d), (g), (j) and (n), the Trustee with
respect to subsections (c), (e), (h) and (k) and K. Elnaggar, individually and
as usufructuary under the Will, with respect to subsections (f), (i) (l) and
(n), represent, warrant and covenant that:

          (a) Borrower is a corporation, duly organized, validly existing and in
good standing under the laws of the State of Louisiana.

          (b) This Fourth Amendment has been duly authorized by all necessary
corporate action and has been duly executed and delivered by an authorized
officer of Borrower, and the Fourth Amendment constitutes a legal, valid and
binding agreement enforceable against Borrower in accordance with its terms;

          (c) This Fourth Amendment, the K. Elnaggar Guaranty and the Pledge
Agreement have been duly authorized by all necessary action and have been duly
executed and delivered by the authorized Trustee of the Trust, and the Fourth
Amendment, the K. Elnaggar Guaranty and the Pledge Agreement constitute legal,
valid and binding agreements enforceable against the Trust in accordance with
their terms;

          (d) As of the date hereof, Borrower is not the subject of a pending
bankruptcy proceeding and Borrower is not aware of any threatened bankruptcy
proceeding against Borrower nor is Borrower presently contemplating filing such
a proceeding;

          (e) As of the date hereof, the Trustee is not the subject of a pending
bankruptcy proceeding and the Trustee is not aware of any threatened bankruptcy
proceeding against the Trust nor is the Trustee presently contemplating filing
such a proceeding;

          (f) As of the date hereof, K. Elnaggar is not the subject of a pending
bankruptcy proceeding and K. Elnaggar is not aware of any threatened bankruptcy
proceeding against her nor is K. Elnaggar presently contemplating filing such a
proceeding;

          (g) Except as disclosed to Lender in Exhibit 5.8.A hereof, there are
                                               -------------                  
no lawsuits pending or threatened against Borrower, or instituted by Borrower in
which the party defendant has counterclaimed against Borrower;

                                      -6-
<PAGE>
 
          (h) There are no lawsuits pending or threatened against the Trust, or
instituted by the Trust in which the party defendant has counterclaimed against
the Trust;

          (i) There are no lawsuits pending or threatened against K. Elnaggar,
or instituted by K. Elnaggar in which the party defendant has counterclaimed
against K. Elnaggar;

          (j) The execution and delivery of this Fourth Amendment and any other
instruments executed and delivered to Lender concurrently herewith, and the full
and complete performance of the provisions hereof will not result in any breach
of, or constitute a default under, or result in the creation of any lien, charge
or encumbrance upon any property or assets of Borrower under any indenture,
mortgage, deed of trust, bank loan or credit agreement or other instrument to
which Borrower is a party or by which Borrower is bound;

          (k) The execution and delivery of this Fourth Amendment and any other
instruments executed and delivered to Lender concurrently herewith, and the full
and complete performance of the provisions hereof will not result in any breach
of, or constitute a default under, or result in the creation of any lien, charge
or encumbrance upon any property or assets of the Trust under any indenture,
mortgage, deed of trust, bank loan or credit agreement or other instrument to
which the Trust is a party or by which the Trust is bound;

          (l) This Fourth Amendment, the K. Elnaggar Guaranty and the Pledge
Agreement have been duly executed and delivered by K. Elnaggar, individually.
The execution and delivery of this Fourth Amendment and any other instruments
executed and delivered to Lender concurrently herewith, and the full and
complete performance of the provisions hereof will not result in any breach of,
or constitute a default under, or result in the creation of any lien, charge or
encumbrance upon any property or assets of K. Elnaggar under any indenture,
mortgage, deed of trust, bank loan or credit agreement or other instrument to
which K. Elnaggar is a party or by which K. Elnaggar is bound;

          (m) This Fourth Amendment, the K. Elnaggar Guaranty and the Pledge
Agreement have been duly authorized by all necessary action and have been duly
executed and delivered by K. Elnaggar, as usufructuary under the Will, and the
Fourth Amendment, the K. Elnaggar Guaranty and the Pledge Agreement constitute
legal, valid and binding agreements enforceable against K. Elnaggar, as
usufructuary under the Will, in accordance with their terms;

          (n) Borrower has all requisite corporate power and corporate authority
and all necessary licenses, governmental authorizations and permits, including,
without limitation, all licenses, authorizations and permits required for the
operation of Borrower's business under all Environmental Laws.

     15.  No Misrepresentation.  Each Obligor respectively represents, warrants
          ---------------------                                                
and covenants that no representation or warranty made by said Obligor and
contained herein or in the other Loan Instruments, and no certificate,
information or report furnished or to be furnished by said Obligor in connection
with any of the Loan Instruments or any of the transactions contemplated hereby
or thereby, contains or will contain a misstatement of material fact, or omits
or will omit to state a material fact required to be stated in order to make the
statements contained 

                                      -7-
<PAGE>
 
herein or therein not misleading in the light of the circumstances under which
such statements were made. There is no fact known or reasonably foreseen by said
Obligor that will materially adversely affect said Obligor or her or its
respective financial conditions, operations, Property, business, prospects,
profits or the ability of said Obligor to consummate the transactions and
perform her or its obligations pursuant to the Loan Instruments that has not
expressly been disclosed to Lender in writing.

     16.  Reaffirmation of Security Interest.  Obligors hereby confirm and agree
          ----------------------------------                                    
that Lender's Security Interests, and Lender's lien priority, in all of the
Collateral previously pledged, assigned, transferred or granted to Lender shall
continue to secure the payment and performance of Obligors' obligations
following the execution, delivery and effectiveness of this Fourth Amendment and
the documents, instruments and agreements contemplated hereby and thereby.

     17.  No Waiver of Defaults.  This Fourth Amendment is not a waiver of any
          ---------------------                                               
future default of Obligors or a release or relinquishment of any Lien, Security
Interest, rights or remedies securing payment and performance of Obligors'
obligations or the enforcement thereof.  Such Liens, Security Interests, rights
and remedies are hereby ratified, confirmed, preserved, renewed and extended by
Obligors in all respects.

     18.  Release.
          ------- 

          (a) Each Obligor and her or its officers, directors, shareholders,
employees, predecessors, personal representatives, executors, executrixes,
heirs, successors and assigns, each hereby fully release, remise and forever
discharge Lender and all past and present officers, directors, agents,
employees, servants, partners, shareholders, attorneys and managers of Lender,
and all of their respective heirs, personal representatives, predecessors,
successors and assigns, for, from and against any and all claims, demands,
causes of action, controversies, offsets, obligations, losses, damages, and
liabilities of every kind and character whatsoever, including without limitation
any action, omission, misrepresentation or other basis of liability founded
either in tort or contract and the duties arising thereunder that said Obligor,
or any of her or its respective predecessors, successors and assigns, or any one
or more of them, has had in the past, or now has, whether known or unknown,
whether currently existing or hereafter asserted, relating in any manner to, or
arising from or in connection with, the indebtedness evidenced by the Note, any
negotiations, loan administration, exercise of rights and remedies, payment,
offset with respect to, or other matter relating to such indebtedness, any
Collateral securing payment and performance of such indebtedness, or any matter
preliminary to the execution and delivery by Obligors and Lender of this Fourth
Amendment, or any statement, action, omission or conduct of Lender or any of its
officers, directors, agents, employees, servants, partners, shareholders,
attorneys and managers relating in any manner to such indebtedness, Collateral
or this Fourth Amendment; provided, however, that the foregoing release and
discharge shall not apply to the obligations of Lender expressly set forth in
this Fourth Amendment or first arising after the date of this Fourth Amendment.

          (b) Obligors acknowledge and agree that Lender's commitment to advance
the Remaining Portion has expired unused by Borrower, and Lender is not, and
shall not be, obligated in any way to continue or undertake any loan, financing
or other credit arrangement with Obligors, including, without limitation, any
renewal of the indebtedness evidenced by the 

                                      -8-
<PAGE>
 
Note, beyond the maturity date thereof as set forth therein.

     19.  Modifications.  No amendment, modification, change, waiver, release or
          -------------                                                         
discharge hereof or hereunder shall be effective unless evidenced by an
instrument in writing signed by the party against whom enforcement is sought.

     20.  Severability.  If any provision hereof is invalid or unenforceable,
          ------------                                                       
the other provisions hereof shall remain in full force and effect and shall be
liberally construed in favor of Lender in order to effectuate the other
provisions hereof.

     21.  Binding Nature.  The provisions of this Fourth Amendment shall be
          --------------                                                   
binding upon, and inure to the benefit of, the respective successors and assigns
(including without limitation, any receiver, debtor in possession or trustee in
bankruptcy) of Lender and any of Obligors.

     22.  APPLICABLE LAW.  THE OBLIGATIONS OF OBLIGORS HEREUNDER, UNDER THE LOAN
          --------------                                                        
AGREEMENT, AS MODIFIED HEREBY, AND UNDER THE OTHER LOAN INSTRUMENTS, ARE TO BE
PERFORMED IN, AND THIS FOURTH AMENDMENT IS, AND THE LOAN AGREEMENT AND OTHER
LOAN INSTRUMENTS HAVE BEEN, EXECUTED, DELIVERED AND ACCEPTED IN, AND THIS FOURTH
AMENDMENT, THE LOAN AGREEMENT, AS MODIFIED HEREBY, AND THE OTHER LOAN
INSTRUMENTS SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE INTERNAL
LAWS AND DECISIONS OF, THE STATE OF ARIZONA (WITHOUT REGARD FOR ITS CONFLICTS OF
LAW PRINCIPLES), AND BY EXECUTION HEREOF OBLIGORS AND LENDER EACH AGREE THAT
SUCH LAWS AND DECISIONS OF THE STATE OF ARIZONA SHALL GOVERN THIS FOURTH
AMENDMENT, THE LOAN AGREEMENT, AS MODIFIED HEREBY, AND THE OTHER LOAN
INSTRUMENTS, NOTWITHSTANDING THE FACT THAT THERE MAY BE OTHER JURISDICTIONS
WHICH MAY BEAR A REASONABLE RELATIONSHIP TO THE TRANSACTIONS CONTEMPLATED
HEREBY; PROVIDED, HOWEVER, THAT WITH RESPECT TO PROCEDURAL AND SUBSTANTIVE
MATTERS RELATING ONLY TO THE CREATION, PERFECTION AND ENFORCEMENT BY LENDER OF
ITS RIGHTS AND REMEDIES AGAINST ANY REAL OR PERSONAL PROPERTY COLLATERAL LOCATED
IN ANY STATE OTHER THAN ARIZONA, SUCH MATTERS SHALL BE GOVERNED BY THE LAWS OF
THE STATE IN WHICH SUCH PROPERTY IS LOCATED.

     23.  JURISDICTION AND VENUE.  OBLIGORS HEREBY AGREE THAT ALL ACTIONS OR
          ----------------------                                            
PROCEEDINGS INITIATED BY OBLIGORS, OR ANY OF THEM, AND ARISING DIRECTLY OR
INDIRECTLY OUT OF THE LOAN INSTRUMENTS SHALL BE LITIGATED IN THE SUPERIOR COURT
OF ARIZONA, MARICOPA COUNTY DIVISION, OR THE UNITED STATES DISTRICT COURT FOR
THE DISTRICT OF ARIZONA OR, IF LENDER INITIATES SUCH ACTION, IN ADDITION TO THE
FOREGOING COURTS, ANY COURT IN WHICH LENDER SHALL INITIATE SUCH ACTION, TO THE
EXTENT SUCH COURT HAS JURISDICTION.  OBLIGORS HEREBY EXPRESSLY SUBMIT AND
CONSENT IN ADVANCE TO SUCH JURISDIC-

                                      -9-
<PAGE>
 
TION IN ANY ACTION OR PROCEEDING COMMENCED BY LENDER IN ANY OF SUCH COURTS, AND
HEREBY WAIVE PERSONAL SERVICE OF THE SUMMONS AND COMPLAINT, OR OTHER PROCESS OF
PAPERS ISSUED THEREIN, AND AGREE THAT SERVICE OF SUCH SUMMONS AND COMPLAINT OR
OTHER PROCESS OR PAPERS MAY BE MADE BY REGISTERED OR CERTIFIED MAIL ADDRESSED TO
OBLIGORS, OR ANY OF THEM, AT THE ADDRESS TO WHICH NOTICES ARE TO BE SENT
PURSUANT TO THE LOAN AGREEMENT. OBLIGORS EACH WAIVE ANY CLAIM THAT PHOENIX,
ARIZONA OR THE DISTRICT OF ARIZONA IS AN INCONVENIENT FORUM OR AN IMPROPER FORUM
BASED ON LACK OF VENUE. SHOULD OBLIGORS, OR ANY OF THEM, AFTER BEING SO SERVED,
FAIL TO APPEAR OR ANSWER TO ANY SUMMONS, COMPLAINT, PROCESS OR PAPERS SO SERVED
WITHIN THE NUMBER OF DAYS PRESCRIBED BY LAW AFTER THE MAILING THEREOF, SUCH
BORROWER(S) SHALL BE DEEMED IN DEFAULT AND AN ORDER AND/OR JUDGMENT MAY BE
ENTERED BY LENDER AGAINST SUCH BORROWER(S) AS DEMANDED OR PRAYED FOR IN SUCH
SUMMONS, COMPLAINT, PROCESS OR PAPERS. THE EXCLUSIVE CHOICE OF FORUM FOR
OBLIGORS SET FORTH IN THIS SECTION SHALL NOT BE DEEMED TO PRECLUDE THE
ENFORCEMENT, BY LENDER, OF ANY JUDGMENT OBTAINED IN ANY OTHER FORUM OR THE
TAKING, BY LENDER, OF ANY ACTION TO ENFORCE THE SAME IN ANY OTHER APPROPRIATE
JURISDICTION, AND OBLIGORS HEREBY WAIVE THE RIGHT TO COLLATERALLY ATTACK ANY
SUCH JUDGMENT OR ACTION.

     24.  WAIVER OF RIGHT TO JURY TRIAL.  LENDER AND OBLIGORS ACKNOWLEDGE AND
          -----------------------------                                      
AGREE THAT ANY CONTROVERSY WHICH MAY ARISE UNDER ANY OF THE LOAN INSTRUMENTS OR
WITH RESPECT TO THE TRANSACTIONS CONTEMPLATED THEREBY WOULD BE BASED UPON
DIFFICULT AND COMPLEX ISSUES AND, THEREFORE, THE PARTIES AGREE THAT ANY
LAWSUIT ARISING OUT OF ANY SUCH CONTROVERSY SHALL BE TRIED IN A COURT OF
COMPETENT JURISDICTION BY A JUDGE SITTING WITHOUT A JURY.

     25.  Amendment.  This Fourth Amendment and the other Loan Instruments
          ---------                                                       
executed prior or pursuant hereto constitute the entire agreement between the
parties hereto with respect to the transactions contemplated hereby or thereby
and supersede any prior agreements, whether written or oral, relating to the
subject matter hereof.  Except as specifically amended herein, the Loan
Agreement shall remain in full force and effect.  In the event of any conflict
between the terms and provisions of this Fourth Amendment and the terms and
provisions of the Loan Agreement, the terms and provisions of this Fourth
Amendment shall govern and prevail. Nothing contained in this Fourth Amendment
is intended to or shall be construed as relieving any person or entity, whether
a party to this Fourth Amendment, or not, of any of such person's or entity's
obligations to Lender.

     26.  All Loan Instruments.     Each of the other Loan Instruments is
          --------------------                                           
amended so that any reference therein to a definition or agreement amended
hereby shall be deemed to be a reference to such definition or agreement, as
applicable, as amended hereby.

                                      -10-
<PAGE>
 
     27.  Effectiveness. This Fourth Amendment shall not become effective unless
          -------------                                                         
and until:

          (a)  Delivery of Documents:  The applicable Obligor has delivered to
               ---------------------                                          
Lender the following, each of which shall be in form and content satisfactory to
Lender:

               (1) this Fourth Amendment;

               (2) a corporate resolution and incumbency certificate of Borrower
authorizing the execution and delivery of this Fourth Amendment;

               (3) evidence of K. Elnaggar's authority to execute and deliver
this Fourth Amendment on behalf of the Trust;

               (4) the K. Elnaggar Guaranty;

               (5) a Security Agreement and Shareholder Pledge Agreement (the
"Pledge Agreement"), together with assignments separate from certificate in
blank, and all certificates evidencing the shares of capital stock pledged, from
Trustee and K. Elnaggar, individually and as usufructuary under the Will;

               (6) an opinion of counsel satisfactory to Lender; and

               (7) such other documents and instruments as Lender may require.

          (b)  Payment of Fees.     Borrower shall have paid or reimbursed
               ---------------                                            
Lender for Lender's attorneys' fees and costs incurred in connection with this
Fourth Amendment.

                       [THE REMAINDER OF THIS PAGE
                       IS LEFT INTENTIONALLY BLANK]

                                      -11-
<PAGE>
 
     IN WITNESS WHEREOF, this Fourth Amendment is executed as of the date first
above written.

                                    LENDER:

                                    GREYHOUND           FINANCIAL 
                                    CORPORATION, a Delaware corporation

                                    By:_______________________________________
                                    Name: Ward B. Carr
                                         -------------------------------------
                                    Title: Vice President
                                           -----------------------------------

 
                                    OBLIGORS:

                                    GDC ENGINEERING, INC., a Louisiana 
                                    corporation

                                    By:_______________________________________
                                    Name:_____________________________________
                                    Title:____________________________________



                                    __________________________________________
                                    TRUST FOR THE BENEFIT OF TAREK ELNAGGAR,
                                    SHARIF JOSEPH ELNAGGAR AND JEANNE-MARIE
                                    ELNAGGAR, CREATED BY THE LAST WILL AND
                                    TESTAMENT OF HAMEED AHMED ELNAGGAR DATED
                                    MARCH 20, 1988, APPEARING THROUGH AND
                                    REPRESENTED BY ITS DULY QUALIFIED TRUSTEE,
                                    KATHLEEN J. ELNAGGAR



                                    __________________________________________
                                    KATHLEEN JORDAN ELNAGGAR, individually and
                                    as Usufructuary under the Last Will and
                                    Testament of Hameed Ahmed Elnaggar dated
                                    March 20, 1988

                                      -12-
<PAGE>
 
                              EXHIBIT 5.8.A

                            PENDING LITIGATION

     The following are all the actions, suits, arbitration proceedings or claims
pending or threatened against or maintained by Borrower in which the party
defendant has counterclaimed against Borrower:

     1.   R. Troy Boone, et al v. GDC Engineering, Inc., et al., Docket No. 
          ----------------------------------------------------- 
          93-967-B- MS, United States District Court, Middle District of
          Louisiana.

     2.   EEOC claim filed against Borrower by Irvin E. West, claiming violation
          of the Age Discrimination Act.

     3.   EEOC claim filed against Borrower by Edward St. Romain, alleging
          violation of the Americans With Disability Act.

     4.   EEOC claim filed against Borrower by Ricky LaGrange alleging racial
          discrimination.

     The following are all the actions, suits, arbitration proceedings or claims
pending or threatened against or maintained by the Succession in which the party
defendant has counterclaims against the Succession.

     NONE.

     The following are all the actions, suits, arbitration proceedings or claims
pending or threatened against or maintained by K. Elnaggar in which the party
defendant has counterclaimed against K. Elnaggar.

     NONE.
<PAGE>
 
                               EXHIBIT 6.19

                           CONTINUING GUARANTY


     THIS CONTINUING GUARANTY (the "Guaranty") is made as of December ___, 1994
by KATHLEEN J. ELNAGGAR, in her capacity as trustee of the testamentary trust
for the benefit of Tarek Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie
Elnaggar (the "Trust") created by the Last Will and Testament of Hameed Ahmed
Elnaggar dated March 20, 1988 (the "Will"), which Will was probated in The
Succession of Hameed Ahmed Elnaggar, Probate No. 56829, Nineteenth Judicial
District, Parish of East Baton Rouge, State of Louisiana, and KATHLEEN JORDAN
ELNAGGAR, one and the same as Kathleen J. Elnaggar, individually and in her
capacity as usufructuary under the Will, a person of the full age of majority
and a resident of Baton Rouge Parish, Louisiana (collectively, "Guarantor"), in
favor of GREYHOUND FINANCIAL CORPORATION, a Delaware corporation ("Lender").

     WHEREAS, there is in effect a Loan Agreement dated December 30, 1992
between GDC Engineering, Inc., a Louisiana corporation ("Borrower"), and Lender,
as amended by Amendment to Loan Instruments dated June 30, 1993 among Borrower,
The Succession of Hameed Ahmed Elnaggar, Probate No. 56829, Nineteenth Judicial
District, Parish of East Baton Rouge, State of Louisiana, appearing through and
represented by its duly qualified executrix, Kathleen Jordan Elnaggar (the
"Succession"), Guarantor (each of Borrower, the Succession, the hereinafter
defined Trustee and Guarantor are sometimes hereinafter referred to individually
as an "Obligor" and collectively as the "Obligors") and Lender (the "First
Amendment"), Second Amendment to Loan Instruments dated October 26, 1993 among
Obligors and Lender (the "Second Amendment"), Third Amendment to Loan
Instruments dated April 1, 1994 among Obligors and Lender (the "Third
Amendment") and Fourth Amendment to Loan Instruments of even date herewith among
the Borrower, Guarantor,individually, as Trustee under the Last Will and
Testament of Hameed Ahmed Elnaggar dated March 20, 1988 (the "Will") and as
usufructuary under the Will, and Lender (the "Fourth Amendment and, together
with the First Amendment, Second Amendment and Third Amendment, the "Loan
Agreement"), pursuant to which Lender committed to loan to Borrower an amount
not to exceed the principal sum of $4,900,000 to refinance existing debt of
Borrower and $4,000,000 to fund certain capital expenditures (the "Loan"). All
capitalized terms used in this Guaranty but not otherwise defined herein shall
have the meanings ascribed thereto in the Loan Agreement;

     WHEREAS, the Loan is evidenced by the Loan Agreement and a promissory note
dated December 30, 1992 from Borrower payable to Lender in the principal sum of
$8,900,000 (the "Note"), and secured by, among others, a Security Agreement and
Shareholder Pledge Agreement dated December 30, 1992 from the Succession and
Guarantor in favor of Lender and a Subordination and Stand-By Agreement dated
December 30, 1992 among the Succession, Guarantor, Borrower and Lender;

     WHEREAS, the $4,000,000 commitment to fund certain capital expenditures
expired unused;
<PAGE>
 
     WHEREAS, Borrower desires to sell all or substantially all of the assets or
capital stock of BCI, which sale requires the consent of Lender pursuant to the
Loan Instruments;

     WHEREAS, Guarantor owns or controls 100% of the issued and outstanding
capital stock of Borrower and, accordingly, Guarantor has a direct financial
interest in inducing Lender to consent to the Approved BCI Sale (as defined in
the Fourth Amendment);

     WHEREAS, one of the conditions precedent to the obligation of Lender to
consent to Approved BCI Sale is the execution by Guarantor of this Guaranty and
the performance by Guarantor of her obligations hereunder.

     NOW, THEREFORE, in order to induce Lender to modify the Loan in accordance
with the terms and provisions set forth in the Fourth Amendment and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, Guarantor hereby agrees as follows:

     1.   Definitions.   Except as otherwise defined herein, all capitalized
          -----------                                                       
terms used herein and in the recitals above shall have the meanings ascribed
thereto in the Loan Instruments.

     2.   Guaranty of Payment and Performance.  Guarantor hereby unconditionally
          -----------------------------------                                   
and irrevocably guaranties to Lender the punctual payment and performance when
due, whether at stated maturity or by acceleration or otherwise, of Borrower's
Obligations (the obligations and liabilities of Guarantor hereunder and under
the Shareholder Pledge Agreement and the Shareholder Subordination Agreement and
any other instruments or agreements previously, concurrently or hereafter
executed and delivered by Guarantor in favor of Lender are sometimes hereinafter
referred to as the "Guarantor Obligations").  Guarantor agrees that this
Guaranty is a present and continuing guaranty of payment and not of
collectability, and that Lender shall not be required to prosecute collection,
enforcement or other remedies against Borrower, any other guarantor of
Borrower's Obligations or any other Person, or to enforce or resort to any of
the Collateral or other rights or remedies pertaining thereto, before calling on
Guarantor for payment. Guarantor agrees that if, for any reason, either
Borrower, any other Obligor or any other guarantor of Borrower's Obligations
shall fail or be unable to pay, punctually and fully, any of Borrower's
Obligations, Guarantor shall pay such obligations to Lender in full immediately
upon demand. Guarantor agrees that one or more successive actions may be brought
against Guarantor, as often as Lender deems advisable, until all of Guarantor's
Obligations and/or Borrower's Obligations are paid and performed in full.
Guarantor hereby further unconditionally guarantees to Lender the punctual and
faithful performance by Borrower of all duties, agreements and obligations of
Borrower contained in the Loan Instruments.

     3.   Continuing Guaranty.  Guarantor agrees that the obligations of
          -------------------                                           
Guarantor pursuant to Section 1 above and any other provision of any of the Loan
                      ---------                                                 
Instruments shall be primary obligations, shall not be subject to any
counterclaim, set-off, abatement, deferment or defense based upon any claim that
Guarantor may have against Lender, Borrower, any other guarantor of Borrower's
Obligations or any other Person, and shall remain in full force and effect
without regard to, and shall not be released, discharged or affected in any way
by, any circumstance or condition (whether or not Guarantor shall have any
knowledge thereof) including, without 

                                   -2-
<PAGE>
 
limitation:

          (a)  any lack of validity or enforceability of any of the Loan
     Instruments;

          (b)  any termination, amendment, modification or other change in any
     of the Loan Instruments;

          (c)  any furnishing, exchange, substitution or release of any
     Collateral, including, without limitation, any furnishing, exchange,
     substitution or release of any Collateral which may be effected pursuant to
     the terms of Section 7.9 of the Loan Agreement, or any failure to perfect 
                  -----------    
     any Lien in any of the Collateral;

          (d)  any failure, omission or delay on the part of Borrower,
     Guarantor, any other guarantor of Borrower's Obligations or Lender to
     conform or comply with any term of any of the Loan Instruments or any
     failure of Lender to give notice of any Incipient Default or Event of
     Default;

          (e)  any waiver, compromise, release, settlement or extension of time
     of payment or performance or observance of any of the obligations or
     agreements contained in any of the Loan Instruments;

          (f)  any action or inaction by Lender under or in respect of any of
     the Loan Instruments, any failure, lack of diligence, omission or delay on
     the part of Lender to enforce, assert or exercise any right, power or
     remedy conferred upon Lender in any of the Loan Instruments, or any other
     action or inaction on the part of Lender;

          (g)  any voluntary or involuntary bankruptcy, insolvency,
     reorganization, arrangement, readjustment, assignment for the benefit of
     creditors, composition, receivership, liquidation, marshalling of assets
     and liabilities or similar events or proceedings with respect to Borrower,
     Guarantor or any other guarantor of Borrower's Obligations, as applicable,
     or any of their respective Property or creditors, or any action taken by
     any trustee or receiver or by any court in any such proceeding;

          (h)  any merger or consolidation of Borrower, Guarantor or any other
     guarantor of Borrower's Obligations into or with any Person, or any sale,
     lease or transfer of any of the assets of Borrower, Guarantor or any other
     guarantor of Borrower's Obligations to any other Person;

          (i)  any change in the ownership of the capital stock of Borrower or
     any other guarantor of Borrower's Obligations or any change in the
     relationship between Borrower, Guarantor or any other guarantor of
     Borrower's Obligations, or any termination of any such relationship;

          (j)  to the extent permitted by law, any release or discharge by
     operation of law of Borrower, Guarantor or any other guarantor of
     Borrower's Obligations from any obligation or agreement contained in any of
     the Loan Instruments; or

                                   -3-
<PAGE>
 
          (k)  to the extent permitted by law, any other occurrence,
     circumstance, happening or event, whether similar or dissimilar to the
     foregoing and whether foreseen or unforeseen, which otherwise might
     constitute a legal or equitable defense or discharge of the liabilities of
     a guarantor or surety or which otherwise might limit recourse against
     Borrower or Guarantor.

     4.   Waivers.  Guarantor unconditionally waives (i) notice of any of the
          -------                                                            
matters referred to in Section 2 above, (ii) all notices which may be required
                       ---------                                              
by statute, rule of law or otherwise, now or hereafter in effect, to preserve
intact any rights against Guarantor, including, without limitation, any demand,
presentment and protest, proof of notice of non-payment under any of the Loan
Instruments and notice of any Incipient Default or any Event of Default or any
failure on the part of Borrower, Guarantor or any other guarantor of Borrower's
Obligations to perform or comply with any covenant, agreement, term or condition
of any of the Loan Instruments, (iii) any right to the enforcement, assertion or
exercise against Borrower, Guarantor or any other guarantor of Borrower's
Obligations of any right or remedy conferred under any of the Loan Instruments,
(iv) any requirement of diligence on the part of any Person, (v) any requirement
to exhaust any remedies or to mitigate the damages resulting from any default
under any of the Loan Instruments, (vi) any notice of any sale, transfer or
other disposition of any right, title or interest of Lender under any of the
Loan Instruments, and (vii) the benefit of all principles or provisions of law,
statutory or otherwise, which are or might be in conflict with the terms of this
Guaranty, including without limitation any right to exhaustion of any security
for the Note prior to any action hereunder or any requirement that Lender
relinquish any lien or security interest in any collateral prior to commencing
an action hereunder or after obtaining a judgment hereunder until payment and
performance of all of the obligations and liabilities under the Note and Loan
Instruments have been satisfied in full, and the provisions of Arizona Revised
Statutes, Sections 12-1566, 12-1641 et seq., 33-814, 44-142 and 16 Arizona
                                    ------                                
Revised Statutes, Rules of Civil Procedure, Rule 17(f), and Guarantor agrees
that its obligations shall not be affected by any circumstances, whether or not
referred to herein, which might otherwise constitute a legal or equitable
discharge of a guarantor or surety.

     5.   Reinstatement.  The obligations of Guarantor pursuant to this Guaranty
          -------------                                                         
shall continue to be effective or automatically be reinstated, as the case may
be, if at any time payment of any of Borrower's Obligations or Guarantor's
Obligations is rescinded or otherwise must be restored or returned by Lender
upon the insolvency, bankruptcy, dissolution, liquidation or reorganization of
Guarantor, Borrower or any other guarantor of Borrower's Obligations or
otherwise, all as though such payment had not been made.

     6.   Successors and Assigns. This Guaranty shall inure to the benefit of
          ----------------------                                             
Lender, its successors and assigns.  This Guaranty shall be binding on Guarantor
and her successors and assigns, heirs and personal representatives, and shall
continue in full force and effect until all of Borrower's Obligations and
Guarantor's Obligations are paid and performed in full.

     7.   No Waiver of Rights.  No delay or failure on the part of Lender to
          -------------------                                               
exercise any right, power or privilege under this Guaranty or any of the other
Loan Instruments shall operate as a waiver thereof, and no single or partial
exercise of any right, power or privilege shall preclude any other or 

                                   -4-
<PAGE>
 
further exercise thereof or the exercise of any other power or right, or be
deemed to establish a custom or course of dealing or performance between the
parties hereto. The rights and remedies provided herein are cumulative and not
exclusive of any rights or remedies provided by law. No notice to or demand on
Guarantor in any case shall entitle Guarantor to any other or further notice or
demand in the same, similar or other circumstance.

     8.   Modification.  The terms of this Guaranty may be waived, discharged,
          ------------                                                        
or terminated only by an instrument in writing signed by the party against which
enforcement of the change, waiver, discharge or termination is sought.  No
amendment, modification, waiver or other change of any of the terms of this
Guaranty shall be effective without the prior written consent of Lender.

     9.   Costs and Expenses.  Guarantor agrees to pay on demand all costs and
          ------------------                                                  
expenses incurred by or on behalf of Lender (including, without limitation,
expenses and attorneys' fees) in enforcing Borrower's Obligations or Guarantor's
Obligations.

     10.  Joinder.  Guarantor agrees that any action to enforce this Guaranty
          -------                                                            
may be brought against Guarantor without any reimbursement or joinder of
Borrower or any other guarantor of Borrower's Obligations in such action.

     11.  Severability.  If any provision of this Guaranty is deemed to be
          ------------                                                    
invalid by reason of the operation of any law, or by reason of the
interpretation placed thereon by any court or other Governmental Body, this
Guaranty shall be construed as not containing such provision and the invalidity
of such provision shall not affect the validity of any other provision hereof,
and any and all other provisions hereof which otherwise are lawful and valid
shall remain in full force and effect.

     12.  JURISDICTION.  GUARANTOR HEREBY AGREES THAT ALL ACTIONS OR PROCEEDINGS
          ------------                                                          
INITIATED BY GUARANTOR AND ARISING DIRECTLY OR INDIRECTLY OUT OF THIS GUARANTY
OR ANY OR ALL OF THE OTHER LOAN INSTRUMENTS TO WHICH GUARANTOR IS A PARTY SHALL
BE LITIGATED IN THE SUPERIOR COURT OF ARIZONA, MARICOPA COUNTY DIVISION, OR THE
UNITED STATES DISTRICT COURT FOR THE DISTRICT OF ARIZONA, OR, IF LENDER
INITIATES SUCH ACTION, IN ADDITION TO THE FOREGOING COURTS, ANY COURT IN WHICH
LENDER SHALL INITIATE OR REMOVE SUCH ACTION, TO THE EXTENT SUCH COURT OTHERWISE
HAS JURISDICTION.  GUARANTOR HEREBY EXPRESSLY SUBMITS AND CONSENTS IN ADVANCE TO
SUCH JURISDICTION IN ANY ACTION OR PROCEEDING COMMENCED IN OR REMOVED BY LENDER
TO ANY OF SUCH COURTS, AND HEREBY AGREES THAT PERSONAL SERVICE OF THE SUMMONS
AND COMPLAINT, OR OTHER PROCESS OR PAPERS ISSUED THEREIN, MAY BE MADE IN THE
MANNER PROVIDED BELOW, AND AGREES THAT SERVICE OF SUCH SUMMONS AND COMPLAINT OR
OTHER PROCESS OR PAPERS MAY BE MADE BY REGISTERED OR CERTIFIED MAIL ADDRESSED IN
THE MANNER SET FORTH IN SECTION 17 BELOW.  GUARANTOR WAIVES ANY CLAIM THAT
                        ----------                                        
PHOENIX, ARIZONA OR THE DISTRICT OF ARIZONA IS AN INCONVENIENT FORUM OR AN
IMPROPER FORUM BASED ON LACK OF VENUE.  SHOULD GUARANTOR, AFTER BEING SO SERVED,
FAIL TO APPEAR OR ANSWER TO ANY SUMMONS, COMPLAINT, PROCESS OR PAPERS SO SERVED
WITHIN THE PERIOD OF TIME PRESCRIBED BY LAW 

                                   -5-
<PAGE>
 
AFTER THE MAILING THEREOF, GUARANTOR SHALL BE DEEMED IN DEFAULT AND AN ORDER
AND/OR JUDGMENT MAY BE ENTERED BY LENDER AGAINST GUARANTOR AS DEMANDED OR PRAYED
FOR IN SUCH SUMMONS, COMPLAINT, PROCESS OR PAPERS. THE EXCLUSIVE CHOICE OF FORUM
FOR GUARANTOR SET FORTH IN THIS SECTION 12 SHALL NOT BE DEEMED TO PRECLUDE THE 
                                ----------            
ENFORCEMENT BY LENDER OF ANY JUDGMENT OBTAINED IN ANY OTHER FORUM OR THE TAKING
BY LENDER OF ANY ACTION TO ENFORCE THE SAME IN ANY OTHER APPROPRIATE
JURISDICTION.

                          ______________________
                           GUARANTOR'S INITIALS

     13.  APPLICABLE LAW.  THIS GUARANTY SHALL BE GOVERNED AS TO VALIDITY,
          --------------                                                  
INTERPRETATION, EFFECT AND IN ALL OTHER RESPECTS BY LAWS AND DECISIONS OF THE
STATE OF ARIZONA.  FOR PURPOSES OF THIS SECTION 13, THIS GUARANTY SHALL BE
                                        -----------                       
DEEMED TO BE PERFORMED AND MADE IN THE STATE OF ARIZONA.

     14.  WAIVER OF RIGHT TO JURY TRIAL.  GUARANTOR ACKNOWLEDGES AND AGREES THAT
          -----------------------------                                         
ANY CONTROVERSY WHICH MAY ARISE UNDER THIS GUARANTY WOULD BE BASED UPON
DIFFICULT AND COMPLEX ISSUES AND THEREFORE, GUARANTOR AGREES THAT ANY COURT
PROCEEDING ARISING OUT OF ANY SUCH CONTROVERSY WILL BE TRIED IN A COURT OF
COMPETENT JURISDICTION BY A JUDGE SITTING WITHOUT A JURY.

                          ______________________
                           GUARANTOR'S INITIALS

     15.  WAIVER OF RIGHTS AGAINST BORROWER.  NOTWITHSTANDING ANYTHING TO THE
          ---------------------------------                                  
CONTRARY WHICH MAY BE CONTAINED HEREIN, GUARANTOR HEREBY UNCONDITIONALLY AND
IRREVOCABLY AGREES THAT SHE (I) WILL NOT AT ANY TIME ASSERT AGAINST BORROWER ANY
RIGHT OR CLAIM, AT LAW OR IN EQUITY, TO INDEMNIFICATION, REIMBURSEMENT,
CONTRIBUTION, RESTITUTION OR PAYMENT FOR OR WITH RESPECT TO ANY AND ALL AMOUNTS
GUARANTOR MAY PAY OR BE OBLIGATED TO PAY TO LENDER, INCLUDING, WITHOUT
LIMITATION, BORROWER'S OBLIGATIONS, GUARANTOR'S OBLIGATIONS AND ANY AND ALL
OTHER OBLIGATIONS WHICH GUARANTOR MAY PERFORM, SATISFY OR DISCHARGE, UNDER OR
WITH RESPECT TO THIS GUARANTY, AND (II) WAIVES AND RELEASES ALL SUCH RIGHTS AND
CLAIMS, AT LAW OR IN EQUITY, TO INDEMNIFICATION, REIMBURSEMENT, CONTRIBUTION,
RESTITUTION OR PAYMENT WHICH GUARANTOR MAY HAVE NOW OR AT ANY TIME AGAINST
BORROWER. GUARANTOR FURTHER UNCONDITIONALLY AND IRREVOCABLY AGREES THAT SHE
SHALL HAVE NO RIGHT OF SUBROGATION, AND WAIVES ANY RIGHT TO ENFORCE ANY REMEDY
WHICH LENDER NOW HAS OR HEREAFTER MAY HAVE AGAINST BORROWER AND WAIVES ANY
DEFENSE BASED UPON AN ELECTION OF REMEDIES BY LENDER, WHICH DESTROYS OR

                                   -6-
<PAGE>
 
OTHERWISE IMPAIRS ANY SUBROGATION RIGHTS OF GUARANTOR AND/OR THE RIGHT OF
GUARANTOR TO PROCEED AGAINST BORROWER FOR REIMBURSEMENT.

     16.  TIME OF THE ESSENCE.  TIME FOR THE PERFORMANCE OF GUARANTOR'S
          -------------------                                          
OBLIGATIONS UNDER THIS GUARANTY IS OF THE ESSENCE.

     17.  Notices. All notices and writing to Guarantor under this Guaranty
          -------                                                          
shall be in writing and shall be (i) delivered in person or (ii) mailed, postage
prepaid, either by registered or certified mail, return receipt requested, or by
overnight express carrier, addressed in each case as follows:

     Guarantor:               Kathleen A. Elnaggar
                              GDC Engineering Inc.
                              822 Neosho Avenue
                              Baton Rouge, Louisiana 70802
                              Telecopy No: (504) 383-2789

     With a Copy To:          John Glover
                              Taylor, Porter, Brooks & Phillips, L.L.P.
                              Premier Bank Building, 8th Floor

                              451 Florida Street
                              Baton Rouge, Louisiana 70802
                              Telecopy No: (504) 346-8049

or to any other address as Guarantor shall designate in a written notice to
Lender.  All notices sent pursuant to the terms of this Section 18 shall be
                                                        ----------         
deemed received (i) if personally delivered, then on the date of delivery, (ii)
if sent by overnight, express carrier, on the next Business Day immediately
following the day sent, or (iii) if sent by registered or certified mail, on the
earlier of the fifth Business Day following the day sent or when actually
received.

     18.  Financial Statements.  As soon as available and in any event within
          --------------------                                               
120 days after the end of each calendar year, Guarantor shall provide to Lender
a personal financial statement as of December 31 of the immediately prior
calendar year, in a form and with a certification satisfactory to Lender, and a
true, correct and complete copy of Guarantor's Federal tax return, as filed, for
the immediately prior calendar year.

                                   -7-
<PAGE>
 
     IN WITNESS WHEREOF, Guarantor has caused this Guaranty to be executed as of
the date first above written.


                                        ______________________________________
                                        TRUST FOR THE BENEFIT OF TAREK ELNAGGAR,
                                        SHARIF JOSEPH ELNAGGAR AND JEANNE-MARIE
                                        ELNAGGAR, CREATED BY THE LAST WILL AND
                                        TESTAMENT OF HAMEED AHMED ELNAGGAR DATED
                                        MARCH 20, 1988, APPEARING THROUGH AND
                                        REPRESENTED BY ITS DULY QUALIFIED
                                        TRUSTEE, KATHLEEN J. ELNAGGAR



                                        ______________________________________
                                        KATHLEEN JORDAN ELNAGGAR, individually
                                        and as Usufructuary under the Last Will
                                        and Testament of Hameed Ahmed Elnaggar
                                        dated March 20, 1988

                                   -8-
<PAGE>
 
                                 CONSENT

     The undersigned, the beneficiaries of the testamentary trust for the
benefit of Tarek Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie Elnaggar
created by the Last Will and Testament of Hameed Ahmed Elnaggar dated March 20,
1988, which Will was probated in The Succession of Hameed Ahmed Elnaggar,
Probate No. 56829, Nineteenth Judicial District, Parish of East Baton Rouge,
State of Louisiana, hereby consent to the execution, delivery and performance of
this Guaranty by the Trustee on behalf of the Trust and agree that the assets of
the Trust shall be liable for the obligations of the Trust, as Guarantor under
this Guaranty.

     Dated:  December __, 1994.


                                             _________________________________
                                             Sharif Joseph Elnaggar


                                             _________________________________
                                             Tarek Elnaggar


                                             _________________________________
                                             Jeanne-Marie Elnaggar

                                   -9-
<PAGE>
 


                      FIFTH AMENDMENT TO LOAN INSTRUMENTS


     THIS FIFTH AMENDMENT TO LOAN INSTRUMENTS (the "Fifth Amendment") is dated
as of this ____ day of March, 1995 by and among GDC ENGINEERING, INC., a
Louisiana corporation ("Borrower"), KATHLEEN J. ELNAGGAR in her capacity as
trustee (the "Trustee") of the testamentary trust for the benefit of Tarek
Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie Elnaggar (the "Trust") created
by the Last Will and Testament of Hameed Ahmed Elnaggar dated March 20, 1988
(the "Will"), which Will was probated in THE SUCCESSION OF HAMEED AHMED
ELNAGGAR, PROBATE NO. 56829, NINETEENTH JUDICIAL DISTRICT, PARISH OF EAST BATON
ROUGE, STATE OF LOUISIANA (the "Succession"), KATHLEEN JORDAN ELNAGGAR, one and
the same as Kathleen J. Elnaggar, individually and in her capacity as
usufructuary under the Will, a person of the full age of majority and a resident
of Baton Rouge Parish, Louisiana ("K. Elnaggar") (each of Borrower, the Trustee,
the Succession and K. Elnaggar are sometimes hereinafter referred to
individually as an "Obligor" and collectively as the "Obligors"), and FINOVA
CAPITAL CORPORATION, a Delaware Corporation, formerly known as Greyhound
Financial Corporation ("Lender").

     WHEREAS, there is in effect a Loan Agreement dated December 30, 1992
between Borrower and Lender, as amended by Amendment to Loan Instruments dated
June 30, 1993 among Obligors and Lender, Second Amendment to Loan Instruments
dated October 26, 1993 among Obligors and Lender, Third Amendment to Loan
Instruments dated April 1, 1994 among Obligors and Lender and Fourth Amendment
to Loan Instruments dated December 30, 1994 among Obligors and Lender
(collectively, together with this Fifth Amendment, the "Loan Agreement"),
pursuant to which Lender committed to loan to Borrower an amount not to exceed
the principal sum of $4,900,000 to refinance existing debt of Borrower and
$4,000,000 to fund certain capital expenditures (the "Loan");

     WHEREAS, Obligors have requested that Lender modify the financial covenant
with respect to Accounts Receivable Turnover;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein, and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Obligors and Lender,
intending to be legally bound, agree as follows:



     1.   Definitions.   Except as otherwise defined herein, all capitalized
          -----------                                                       
terms used herein shall have the meanings ascribed thereto in the Loan
Agreement.

     2.   Recitals.  The Recitals set forth above are true and accurate and are
          --------                                                             
incorporated herein by this reference.

     3.   Amounts Outstanding.  Obligors hereby acknowledge and agree that (a)
          -------------------                                                 
as of February 2, 1995, the principal amount of the Loan outstanding is
$3,445,843.55 and the accrued and unpaid interest is $1,165.40, and (b) as of
the date of execution hereof by Obligors, 
<PAGE>
 
there are no defenses, claims or offsets to payment of such principal amount and
the other indebtedness evidenced by the Note.

     4.   Accounts Receivable Turnover.  Section 7.20 of the Loan Agreement is
          ----------------------------                                        
hereby deleted in its entirety and the following inserted therefor:

               7.20  Accounts Receivable Turnover.  Commencing 
                     ----------------------------              
          Quarter Period with the Four ending November 30, 1994,
          permit the Accounts Receivable Turnover for the Four
          Quarter Periods ending February 28, May 31 and August
          31 to be greater than 45 days, or permit the Accounts
          Receivable Turnover for the Four Quarter Period ending
          November 30 to be greater than 60 days.

     5.   Annual Statements.  Section 6.3.3 of the Loan Agreement is hereby
          -----------------                                                
amended to add the following:

          Notwithstanding anything to the contrary contained
          herein, the Basic Financial Statements and the
          statements of Operating Cash Flow and Excess Cash Flow
          for Borrower's fiscal year end November 30, 1994 only,
          shall be delivered to Lender as soon as available, but
          in no event later than 120 days after the close of
          Borrower's fiscal year.

     6.   Notices.  Section 11.1 of the Loan Agreement with respect to the
          -------                                                         
notices to Lender is hereby deleted in its entirety and the following inserted
therefor:

                    FINOVA Capital Corporation
                    1850 North Central Avenue
                    P.O. Box 2209
                    Phoenix, Arizona 85002-2209
                    Attention: Vice President, Operations Management
                    Telecopy No.: (602) 207-6833

          Copy to:  FINOVA Capital Corporation
                    1850 North Central Avenue
                    P.O. Box 2209
                    Phoenix, Arizona 85002-2209
                    Attention:  Vice President, Law
                    Telecopy No.: (602) 207-5036

                    and

                                      -2-
<PAGE>
 
                    FINOVA Capital Corporation
                    10 South LaSalle Street
                    Suite 2121
                    Chicago, Illinois 60603
                    Attention:  Adolph G. Letke
                    Telecopy No.: (312) 855-1779

                    and

                    Fennemore Craig
                    Two North Central Avenue
                    Suite 2200
                    Phoenix, Arizona 85004-2390
                    Attention:  Jay S. Kramer
                    Telecopy No.: (602) 257-8527

     7.   Release.  Each Obligor and her or its officers, directors,
          -------                                                   
shareholders, employees, predecessors, personal representatives, executors,
executrixes, heirs, successors and assigns, each hereby fully release, remise
and forever discharge Lender and all past and present officers, directors,
agents, employees, servants, partners, shareholders, attorneys and managers of
Lender, and all of their respective heirs, personal representatives,
predecessors, successors and assigns, for, from and against any and all claims,
demands, causes of action, controversies, offsets, obligations, losses, damages,
and liabilities of every kind and character whatsoever, including without
limitation any action, omission, misrepresentation or other basis of liability
founded either in tort or contract and the duties arising thereunder that said
Obligor, or any of her or its respective predecessors, successors and assigns,
or any one or more of them, has had in the past, or now has, whether known or
unknown, whether currently existing or hereafter asserted, relating in any
manner to, or arising from or in connection with, the indebtedness evidenced by
the Note, any negotiations, loan administration, exercise of rights and
remedies, payment, offset with respect to, or other matter relating to such
indebtedness, any Collateral securing payment and performance of such
indebtedness, or any matter preliminary to the execution and delivery by
Obligors and Lender of this Fifth Amendment, or any statement, action, omission
or conduct of Lender or any of its officers, directors, agents, employees,
servants, partners, shareholders, attorneys and managers relating in any manner
to such indebtedness, Collateral or this Fifth Amendment; provided, however,
that the foregoing release and discharge shall not apply to the obligations of
Lender expressly set forth in this Fifth Amendment or first arising after the
date of this Fifth Amendment.

     8.   Modifications.  No amendment, modification, change, waiver, release or
          -------------                                                         
discharge hereof or hereunder shall be effective unless evidenced by an
instrument in writing signed by the party against whom enforcement is sought.

     9.   Severability.  If any provision hereof is invalid or unenforceable,
          ------------                                                       
the other provisions hereof shall remain in full force and effect and shall be
liberally construed in favor of Lender in order to effectuate the other
provisions hereof.

                                      -3-
<PAGE>
 
     10.  Binding Nature.  The provisions of this Fifth Amendment shall be
          --------------                                                  
binding upon, and inure to the benefit of, the respective successors and assigns
(including without limitation, any receiver, debtor in possession or trustee in
bankruptcy) of Lender and any of Obligors.

     11.  APPLICABLE LAW.  THE OBLIGATIONS OF OBLIGORS HEREUNDER, UNDER THE LOAN
          --------------                                                        
AGREEMENT, AS MODIFIED HEREBY, AND UNDER THE OTHER LOAN INSTRUMENTS, ARE TO BE
PERFORMED IN, AND THIS FIFTH AMENDMENT IS, AND THE LOAN AGREEMENT AND OTHER LOAN
INSTRUMENTS HAVE BEEN, EXECUTED, DELIVERED AND ACCEPTED IN, AND THIS FIFTH
AMENDMENT, THE LOAN AGREEMENT, AS MODIFIED HEREBY, AND THE OTHER LOAN
INSTRUMENTS SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE INTERNAL
LAWS AND DECISIONS OF, THE STATE OF ARIZONA (WITHOUT REGARD FOR ITS CONFLICTS OF
LAW PRINCIPLES), AND BY EXECUTION HEREOF OBLIGORS AND LENDER EACH AGREE THAT
SUCH LAWS AND DECISIONS OF THE STATE OF ARIZONA SHALL GOVERN THIS FIFTH
AMENDMENT, THE LOAN AGREEMENT, AS MODIFIED HEREBY, AND THE OTHER LOAN
INSTRUMENTS, NOTWITHSTANDING THE FACT THAT THERE MAY BE OTHER JURISDICTIONS
WHICH MAY BEAR A REASONABLE RELATIONSHIP TO THE TRANSACTIONS CONTEMPLATED
HEREBY; PROVIDED, HOWEVER, THAT WITH RESPECT TO PROCEDURAL AND SUBSTANTIVE
MATTERS RELATING ONLY TO THE CREATION, PERFECTION AND ENFORCEMENT BY LENDER OF
ITS RIGHTS AND REMEDIES AGAINST ANY REAL OR PERSONAL PROPERTY COLLATERAL LOCATED
IN ANY STATE OTHER THAN ARIZONA, SUCH MATTERS SHALL BE GOVERNED BY THE LAWS OF
THE STATE IN WHICH SUCH PROPERTY IS LOCATED.

     12.  JURISDICTION AND VENUE.  OBLIGORS HEREBY AGREE THAT ALL ACTIONS OR
          ----------------------                                            
PROCEEDINGS INITIATED BY OBLIGORS, OR ANY OF THEM, AND ARISING DIRECTLY OR
INDIRECTLY OUT OF THE LOAN INSTRUMENTS SHALL BE LITIGATED IN THE SUPERIOR COURT
OF ARIZONA, MARICOPA COUNTY DIVISION, OR THE UNITED STATES DISTRICT COURT FOR
THE DISTRICT OF ARIZONA OR, IF LENDER INITIATES SUCH ACTION, IN ADDITION TO THE
FOREGOING COURTS, ANY COURT IN WHICH LENDER SHALL INITIATE SUCH ACTION, TO THE
EXTENT SUCH COURT HAS JURISDICTION. OBLIGORS HEREBY EXPRESSLY SUBMIT AND CONSENT
IN ADVANCE TO SUCH JURISDICTION IN ANY ACTION OR PROCEEDING COMMENCED BY LENDER
IN ANY OF SUCH COURTS, AND HEREBY WAIVE PERSONAL SERVICE OF THE SUMMONS AND
COMPLAINT, OR OTHER PROCESS OF PAPERS ISSUED THEREIN, AND AGREE THAT SERVICE OF
SUCH SUMMONS AND COMPLAINT OR OTHER PROCESS OR PAPERS MAY BE MADE BY REGISTERED
OR CERTIFIED MAIL ADDRESSED TO OBLIGORS, OR ANY OF THEM, AT THE ADDRESS TO WHICH
NOTICES ARE TO BE SENT PURSUANT TO THE LOAN AGREEMENT. OBLIGORS EACH WAIVE ANY
CLAIM THAT PHOENIX, ARIZONA OR THE DISTRICT OF ARIZONA IS AN INCONVENIENT FORUM
OR AN IMPROPER FORUM BASED ON LACK OF VENUE. SHOULD OBLIGORS, OR ANY OF THEM,
AFTER BEING SO 

                                      -4-
<PAGE>
 
SERVED, FAIL TO APPEAR OR ANSWER TO ANY SUMMONS, COMPLAINT, PROCESS OR PAPERS SO
SERVED WITHIN THE NUMBER OF DAYS PRESCRIBED BY LAW AFTER THE MAILING THEREOF,
SUCH BORROWER(S) SHALL BE DEEMED IN DEFAULT AND AN ORDER AND/OR JUDGMENT MAY BE
ENTERED BY LENDER AGAINST SUCH BORROWER(S) AS DEMANDED OR PRAYED FOR IN SUCH
SUMMONS, COMPLAINT, PROCESS OR PAPERS. THE EXCLUSIVE CHOICE OF FORUM FOR
OBLIGORS SET FORTH IN THIS SECTION SHALL NOT BE DEEMED TO PRECLUDE THE
ENFORCEMENT, BY LENDER, OF ANY JUDGMENT OBTAINED IN ANY OTHER FORUM OR THE
TAKING, BY LENDER, OF ANY ACTION TO ENFORCE THE SAME IN ANY OTHER APPROPRIATE
JURISDICTION, AND OBLIGORS HEREBY WAIVE THE RIGHT TO COLLATERALLY ATTACK ANY
SUCH JUDGMENT OR ACTION.

     13.  WAIVER OF RIGHT TO JURY TRIAL.  LENDER AND OBLIGORS ACKNOWLEDGE AND
          -----------------------------                                      
AGREE THAT ANY CONTROVERSY WHICH MAY ARISE UNDER ANY OF THE LOAN INSTRUMENTS OR
WITH RESPECT TO THE TRANSACTIONS CONTEMPLATED THEREBY WOULD BE BASED UPON
DIFFICULT AND COMPLEX ISSUES AND, THEREFORE, THE PARTIES AGREE THAT ANY LAWSUIT
ARISING OUT OF ANY SUCH CONTROVERSY SHALL BE TRIED IN A COURT OF COMPETENT
JURISDICTION BY A JUDGE SITTING WITHOUT A JURY.

     14.  Amendment.  This Fifth Amendment and the other Loan Instruments
          ---------                                                      
executed prior or pursuant hereto constitute the entire agreement between the
parties hereto with respect to the transactions contemplated hereby or thereby
and supersede any prior agreements, whether written or oral, relating to the
subject matter hereof. Except as specifically amended herein, the Loan Agreement
shall remain in full force and effect. In the event of any conflict between the
terms and provisions of this Fifth Amendment and the terms and provisions of the
Loan Agreement, the terms and provisions of this Fifth Amendment shall govern
and prevail. Nothing contained in this Fifth Amendment is intended to or shall
be construed as relieving any person or entity, whether a party to this Fifth
Amendment, or not, of any of such person's or entity's obligations to Lender.

     15.  Effectiveness. This Fifth Amendment shall not become effective unless
          -------------                                                        
and until Borrower shall have paid to the Persons entitled thereto the following
fees and expenses:

               (1)  Lender's attorneys' fees and costs incurred in connection
with this Fifth Amendment.

               (2)  an administration fee of $500 to Lender in connection with
the documentation of this Fifth Amendment.

                                      -5-
<PAGE>
 
     IN WITNESS WHEREOF, this Fifth Amendment is executed as of the date first
above written.

                                   LENDER:

                                   FINOVA CAPITAL CORPORATION, a 
                                   Delaware corporation


                                   By:_________________________________________
                                   Name:_______________________________________
                                   Title:______________________________________

 
                                   OBLIGORS:

                                   GDC ENGINEERING, INC., a Louisiana 
                                   corporation



                                   By:_________________________________________
                                   Name:_______________________________________
                                   Title:______________________________________




                                   TRUST FOR THE BENEFIT OF TAREK ELNAGGAR,
                                   SHARIF JOSEPH ELNAGGAR AND JEANNE-MARIE
                                   ELNAGGAR, CREATED BY THE LAST WILL AND
                                   TESTAMENT OF HAMEED AHMED ELNAGGAR DATED
                                   MARCH 20, 1988, APPEARING THROUGH AND
                                   REPRESENTED BY ITS DULY QUALIFIED TRUSTEE,
                                   KATHLEEN J. ELNAGGAR


                         
                                   ___________________________________________
                                   KATHLEEN JORDAN ELNAGGAR,
                                   individually and as Usufructuary under the
                                   Last Will and Testament of Hameed Ahmed
                                   Elnaggar dated March 20, 1988

                                      -6-
<PAGE>
 
                                                                   Exhibit 4(b)

                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

     THIS SIXTH AMENDMENT TO LOAN INSTRUMENTS (the "Sixth Amendment") is
dated as of this 15th day of March, 1996 by and among GDC ENVIRO-SOLUTIONS,
INC., a Louisiana corporation, f/k/a GDC Engineering Inc. ("Borrower"), KATHLEEN
J. ELNAGGAR in her capacity as trustee of the testamentary trust for the benefit
of Tarek Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie Elnaggar (the
"Trust") created by the Last Will and Testament of Hameed Ahmed Elnaggar dated
March 20, 1988, and individually (collectively, "Kathleen J. Elnaggar"), GDC
HOLDINGS CORPORATION, a Louisiana corporation ("Holdings"), and FINOVA CAPITAL
CORPORATION, a Delaware Corporation, f/k/a Greyhound Financial Corporation
("Lender").

     WHEREAS, there is in effect a Loan Agreement dated December 30, 1992
between Borrower and Lender, as amended by Amendment to Loan Instruments dated
June 30, 1993 among Borrower, Kathleen J. Elnaggar and Lender, Second Amendment
to Loan Instruments dated October 26, 1993 among Borrower, Kathleen J. Elnaggar
and Lender, Third Amendment to Loan Instruments dated April 1, 1994 among
Borrower, Kathleen J. Elnaggar and Lender, Fourth Amendment to Loan Instruments
dated December 30, 1994 among Borrower, Kathleen J. Elnaggar and Lender and
Fifth Amendment to Loan Instruments dated March 10, 1995 among Borrower,
Kathleen J. Elnaggar and Lender (collectively, together with this Sixth
Amendment, the "Loan Agreement"), pursuant to which Lender committed to loan to
Borrower an amount not to exceed the principal sum of $4,900,000 to refinance
existing debt of Borrower and $4,000,000 to fund certain capital expenditures
(the "Loan");

     WHEREAS, Kathleen J. Elnaggar gifted 527,969 shares of her Borrower
Capital Stock to Tarek Elnaggar and Tarek Elnaggar pledged to Lender all of the
Borrower Capital Stock now owned or hereafter acquired by Tarek Elnaggar to
secure the payment and performance of the obligations of Borrower to Lender;

     WHEREAS, Borrower sold 394,160 shares of the issued Borrower Capital
Stock to Harry C. Conger and Harry C. Conger pledged to Lender all of the
Borrower Capital Stock now owned or hereafter acquired by Harry C. Conger to
secure the payment and performance of the obligations of Borrower to Lender;

     WHEREAS, Borrower issued to James H. Hutchinson two (2) 1995 Class A
Warrants (Nos. 1 and 2) for the purchase of 50,000 shares each of the Borrower
Capital Stock and Borrower issued to B. Jim Porter four (4) 1995 Class A
Warrants (Nos. 3, 4, 5 and 6) for the purchase of 50,000 shares each of the
Borrower Capital Stock (collectively, the "Warrants");

     WHEREAS, Kathleen J. Elnaggar, Tarek Elnaggar, Harry C. Conger, B. Jim
Porter, and James H. Hutchinson (collectively, the "Individual Pledgors")
executed and delivered to Lender that certain Security Agreement and Shareholder
Pledge Agreement dated August 21, 1995 (the "Individual Pledge Agreement") and
delivered to Lender all of the issued and outstanding Borrower Capital Stock;
<PAGE>
 
     WHEREAS, Lender timely and properly delivered the notice of exercise of the
payment of Excess Cash Flow pursuant to Section 2.9.2 of the Loan Agreement, for
the period ending November 30, 1994;

     WHEREAS, the Individual Pledgors, Borrower and Holdings desire to (a)
exchange all of the Borrower Capital Stock for all of the capital stock of
Holdings pursuant to Section 351 of the Internal Revenue Code of 1986, as
amended (the "GDC/Holdings Stock Exchange"), (b) exchange the Warrants for
warrants for the capital stock of Holdings, (c) cause Holdings to guarantee to
Lender the payment and performance of the obligations of Borrower on a limited
recourse basis (the "Holdings Guaranty") and pledge all of the Borrower Capital
Stock to secure the payment and performance of the obligations of Borrower and
Holdings (the "Holdings Pledge Agreement"), and (d) engage in certain other
transactions as more fully described herein;

     WHEREAS, the GDC/Holdings Stock Exchange and such other transactions
require the consent of Lender and waiver by Lender of certain of the provisions
of the Loan Agreement and Loan Instruments;

     WHEREAS, in consideration of the agreements of Lender contained herein,
Borrower will pay Lender a Profit Participation Fee of $500,000 and a
Restructure Fee of $300,000, which is based upon calculation of the Profit
Participation Fee as a Call as of August 31, 1995; and

     WHEREAS, Borrower desires that Lender provide a new equipment facility in
an amount not to exceed $850,000 for acquisition of equipment in connection with
the IT Contract and any other Advance Contracts approved by Lender;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein, and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Borrower, Kathleen J.
Elnaggar and Lender, intending to be legally bound, agree as follows:

     1.   Definitions.   Except as otherwise defined herein, all capitalized
          -----------                                           
terms used herein and in the Recitals above shall have the meanings ascribed
thereto in the Loan Agreement.

     2.   Recitals.  The Recitals set forth above are true and accurate and are
          --------                                                         
incorporated herein by this reference.

     3.   Amounts Outstanding.  Borrower, Holdings and Kathleen J. Elnaggar
          -------------------                                              
hereby acknowledge and agree that (a) as of, and including, February 29, 1996,
the principal amount of the Loan outstanding is $2,766,327.63 and the accrued
and unpaid interest is $25,087.06, and (b) as of the date of execution hereof by
Borrower, Holdings and Kathleen J. Elnaggar, there are no defenses, claims or
offsets to payment of such principal amount and the other indebtedness evidenced
by the Note.

     4.   Representations, Warranties, Acknowledgments and Agreements.  As
          -----------------------------------------------------------     
material inducements to Lender to enter into this Sixth Amendment, and
acknowledging Lender's reliance 

                                      -2-
<PAGE>
 
upon the truth and accuracy thereof, Borrower with respect to subsections (a)
through (e), Holdings with respect to subsections (f) through (j), Kathleen J.
Elnaggar, as trustee with respect to subsections (k) through (n), and Kathleen
J. Elnaggar, individually, with respect to subsections (o) through (q),
represent, warrant and covenant that:

          (a)  Borrower is a corporation, duly organized, validly existing and
in good standing under the laws of the State of Louisiana.

          (b)  This Sixth Amendment has been duly authorized by all necessary
corporate action and has been duly executed and delivered by an authorized
officer of Borrower, and the Sixth Amendment constitutes a legal, valid and
binding agreement enforceable against Borrower in accordance with its terms;

          (c)  As of the date hereof, Borrower is not the subject of a pending
bankruptcy proceeding and Borrower is not aware of any threatened bankruptcy
proceeding against Borrower nor is Borrower presently contemplating filing such
a proceeding;

          (d)  Except as disclosed in EXHIBIT 5.8.A hereof, there are no
lawsuits pending or threatened against Borrower, or instituted by Borrower in
which the party defendant has counterclaimed against Borrower;

          (e)  The execution and delivery of this Sixth Amendment and any other
instruments executed and delivered to Lender concurrently herewith, and the full
and complete performance of the provisions hereof will not result in any breach
of, or constitute a default under, or result in the creation of any lien, charge
or encumbrance upon any property or assets of Borrower under any indenture,
mortgage, deed of trust, bank loan or credit agreement or other instrument to
which Borrower is a party or by which Borrower is bound;

          (f)  Holdings is a corporation, duly organized, validly existing and
in good standing under the laws of the State of Louisiana.

          (g)  This Sixth Amendment, the Holdings Guaranty and the Holdings
Pledge Agreement have been duly authorized by all necessary corporate action and
have been duly executed and delivered by an authorized officer of Holdings, and
the Sixth Amendment, the Holdings Guaranty and the Holding Pledge Agreement
constitute legal, valid and binding agreements enforceable against Holdings in
accordance with their terms;

          (h)  As of the date hereof, Holdings is not the subject of a pending
bankruptcy proceeding and Holdings is not aware of any threatened bankruptcy
proceeding against Holdings nor is Holdings presently contemplating filing such
a proceeding;

          (i)  There are no lawsuits pending or threatened against Holdings, or
instituted by Holdings in which the party defendant has counterclaimed against
Holdings;

          (j)  The execution and delivery of this Sixth Amendment and any other
instruments executed and delivered to Lender concurrently herewith, and the full
and complete 

                                      -3-
<PAGE>
 
performance of the provisions hereof will not result in any breach of, or
constitute a default under, or result in the creation of any lien, except as
created under the Holdings Pledge Agreement, charge or encumbrance upon any
property or assets of Holdings under any indenture, mortgage, deed of trust,
bank loan or credit agreement or other instrument to which Holdings is a party
or by which Holdings is bound;


          (k)  This Sixth Amendment has been duly authorized by all necessary
action and has been duly executed and delivered by the authorized trustee of the
Trust, and the Sixth Amendment constitutes a legal, valid and binding agreement
enforceable against the Trust in accordance with its terms;

          (l)  As of the date hereof, the trustee is not the subject of a 
pending bankruptcy proceeding and the trustee is not aware of any threatened
bankruptcy proceeding against the Trust nor is the trustee presently
contemplating filing such a proceeding;

          (m)  There are no lawsuits pending or threatened against the Trust, 
or instituted by the Trust in which the party defendant has counterclaimed
against the Trust;

          (n)  The execution and delivery of this Sixth Amendment and any
other instruments executed and delivered to Lender concurrently herewith, and
the full and complete performance of the provisions hereof will not result in
any breach of, or constitute a default under, or result in the creation of any
lien, charge or encumbrance upon any property or assets of the Trust under any
indenture, mortgage, deed of trust, bank loan or credit agreement or other
instrument to which the Trust is a party or by which the Trust is bound;

          (o)  As of the date hereof, Kathleen J. Elnaggar is not the subject of
a pending bankruptcy proceeding and Kathleen J. Elnaggar is not aware of any
threatened bankruptcy proceeding against her nor is Kathleen J. Elnaggar
presently contemplating filing such a proceeding;

          (p)  There are no lawsuits pending or threatened against Kathleen J.
Elnaggar, or instituted by Kathleen J. Elnaggar in which the party defendant has
counterclaimed against Kathleen J. Elnaggar;

          (q)  The execution and delivery of this Sixth Amendment and any other
instruments executed and delivered to Lender concurrently herewith, and the full
and complete performance of the provisions hereof will not result in any breach
of, or constitute a default under, or result in the creation of any lien, charge
or encumbrance upon any property or assets of Kathleen J. Elnaggar under any
indenture, mortgage, deed of trust, bank loan or credit agreement or other
instrument to which Kathleen J. Elnaggar is a party or by which Kathleen J.
Elnaggar is bound;

     5.   No Misrepresentation.  Borrower, Holdings and Kathleen J. Elnaggar
          ---------------------                                    
severally on its or her own behalf, and not jointly, represent, warrant and
covenant as follows: that no representation or warranty made by Borrower,
Holdings or Kathleen J. Elnaggar and contained herein or in the other Loan
Instruments, and no certificate, information or report furnished or to

                                      -4-
<PAGE>
 
be furnished by Borrower, Holdings or Kathleen J. Elnaggar in connection with
any of the Loan Instruments or any of the transactions contemplated hereby or
thereby, contains or will contain a misstatement of material fact, or omits or
will omit to state a material fact required to be stated in order to make the
statements contained herein or therein not misleading in the light of the
circumstances under which such statements were made; and there is no fact known
or reasonably foreseen by Borrower, Holdings or Kathleen J. Elnaggar that will
materially adversely affect Borrower, Holdings or Kathleen J. Elnaggar or its or
their respective financial conditions, operations, Property, business,
prospects, profits or the ability of Borrower, Holdings or Kathleen J. Elnaggar
to consummate the transactions and perform its or their obligations pursuant to
the Loan Instruments that has not expressly been disclosed to Lender in writing.
Kathleen J. Elnaggar shall not be liable for any misrepresentations made by any
other Person after the release of the K. Elnaggar Guaranty.

     6.   Reaffirmation of Security Interest.  Except for the Security Interests
          ----------------------------------                          
arising from the Individual Pledge Agreement, which was terminated immediately
prior to the execution of this Agreement, Borrower and Kathleen J. Elnaggar
hereby confirm and agree that Lender's Security Interests, and Lender's lien
priority, in all of the Collateral previously pledged, assigned, transferred or
granted to Lender shall continue to secure the payment and performance of
Borrower's obligations following the execution, delivery and effectiveness of
this Sixth Amendment and the documents, instruments and agreements contemplated
hereby and thereby.

     7.   Waiver of Certain Defaults; No Waiver of Other Defaults.  Except as
          -------------------------------------------------------         
expressly provided herein, this Sixth Amendment is not a waiver of any present
or future default of Borrower or a release or relinquishment of any Lien,
Security Interest, rights or remedies securing payment and performance of
Borrower's obligations or the enforcement thereof, except as specifically
provided herein. Such Liens, Security Interests, rights and remedies are hereby
ratified, confirmed, preserved, renewed and extended by Borrower and Kathleen J.
Elnaggar in all respects, except as expressly provided herein. Notwithstanding
this Section 7, Lender hereby waives all of the events of default listed on
SCHEDULE 7 hereto (collectively, the "Permitted Defaults," and individually, a
"Permitted Default"); provided, however, this waiver shall not constitute a
waiver of any other default not known to Lender or reasonably contemplated by
Lender in connection with the transactions contemplated by this Sixth Amendment.

     8.   Release.  Borrower, Holdings and Kathleen J. Elnaggar and its and 
          -------                                                          
their officers, directors, shareholders, employees, predecessors, personal
representatives, executors, executrixes, trustees, heirs, successors and
assigns, each hereby fully release, remise and forever discharge Lender and all
past and present officers, directors, agents, employees, servants, partners,
shareholders, attorneys and managers of Lender, and all of their respective
heirs, personal representatives, predecessors, successors and assigns, for, from
and against any and all claims, demands, causes of action, controversies,
offsets, obligations, losses, damages, and liabilities of every kind and
character whatsoever, including, without limitation, any action, omission,
misrepresentation or other basis of liability founded either in tort or contract
and the duties arising thereunder that Borrower, Holdings or Kathleen J.
Elnaggar, or any of its or their respective predecessors, successors and
assigns, or any one or more of them, has had in the past, or now has, whether
known or unknown, whether currently existing or hereafter asserted, relating in
any manner to, or arising from or in connection with, the indebtedness evidenced
by the Note, any negotiations, loan administration, exercise of rights and
remedies, payment, offset 

                                      -5-
<PAGE>
 
with respect to, or other matter relating to such indebtedness, any Collateral
securing payment and performance of such indebtedness, or any matter preliminary
to the execution and delivery by Borrower, Holdings and Kathleen J. Elnaggar and
Lender of this Sixth Amendment, or any statement, action, omission or conduct of
Lender or any of its officers, directors, agents, employees, servants, partners,
shareholders, attorneys and managers relating in any manner to such
indebtedness, Collateral or this Sixth Amendment; provided, however, that the
foregoing release and discharge shall not apply to the obligations of Lender
expressly set forth in this Sixth Amendment or first arising after the date of
this Sixth Amendment.

     9.   Effectiveness. This Sixth Amendment shall not become effective unless
          -------------                                                 
and until Lender shall have received the following documents and instruments,
all in form and substance satisfactory to Lender and duly executed by the
Persons required to do so, and Borrower shall have paid to the Persons entitled
thereto the following fees and expenses:

          (a)  This Sixth Amendment.

          (b)  A Limited Recourse Continuing Guaranty from Holdings in the form
attached hereto as Exhibit "A" and incorporated herein by this reference (the
                   -----------                                               
"Holdings Guaranty").

          (c)  A Security Agreement and Shareholder Pledge Agreement from
Holdings in the form attached hereto as Exhibit "B" and incorporated herein by
                                        -----------                           
this reference (the "Holdings Pledge Agreement").

          (d)  The original stock certificates evidencing all of the issued and
outstanding capital stock of Borrower, together with assignments separate from
certificate or stock powers, executed in blank by Holdings.

          (e)  First Amendment to Continuing Guaranty between K. Elnaggar and
Lender.

          (f)  Any Uniform Commercial Code financing statements or filings or
notices required under applicable law to (i) reflect Borrower's name change and
(ii) properly perfect Lender's Security Interests arising from the Holdings
Pledge Agreement.

          (g)  Uniform Commercial Code financing statements or filings or 
notices required under applicable law to perfect Lender's security interest in
inventory located in Mississippi and South Carolina.

          (h)  Evidence of Key Man Life Insurance in the amount of $1,000,000
insuring the life of Elnaggar and $500,000 insuring the life of Reed, and
Assignments of such Key Man Life Insurance to Lender, in form and substance
satisfactory to Lender, executed by Borrower and the insurance company(s).

          (i)  Evidence of all property and liability insurance required in
connection with the Loan Instruments.

                                      -6-
<PAGE>
 
          (j)  A certificate from Borrower's environmental consultant that (s)he
has searched the public databases and DK Industries, Inc. has not been named as
a "Potentially Responsible Party" with respect to any federal Superfund site.

          (k)  Financial statements of Kathleen J. Elnaggar, individually and as
trustee of the Trust prepared as of May 31, 1995, together with a certificate
from Kathleen J. Elnaggar certifying that the financial statements fairly
present her financial position as of such date and that there have been no
material adverse changes in her financial statements or net worth since May 31,
1995.

          (l)  An officers' certificate and incumbency certificate from 
Borrower, together with corporate resolutions of Borrower authorizing the
transactions contemplated by this Sixth Amendment.

          (m)  An officers' certificate and incumbency certificate from 
Holdings, together with corporate resolutions of Holdings authorizing the
GDC/Holdings Stock Exchange and the execution and delivery of this Sixth
Amendment, the Holdings Guaranty and the Holdings Pledge Agreement.

          (n)  Attorneys' opinion letters from counsel to Borrower, Kathleen
J. Elnaggar and Holdings.

          (o)  Evidence satisfactory to Lender that after giving effect to any
transaction costs and other expenses in connection with this Sixth Amendment,
including, without limitation, any brokerage fees or other commissions, and all
borrowings which are outstanding thereunder, the amount which is available for
borrowing under the Working Capital Loan equals or exceeds $150,000.

          (p)  Consents to the Sixth Amendment from the Working Capital Lender
or Working Capital Lender Substitution, if applicable, and LSC, Louisiana Seed
Capital Fund Limited Partnership and Louisiana Economic Development Corporation.

          (q)  $100,000, in immediately available funds, as partial payment of
the Restructure Fee, which shall be deemed to be fully earned and non-refundable
upon execution of this Sixth Amendment.

          (r)  Accrued and unpaid interest on the Loan to, but not including,
March 1, 1996.

          (s)  Lender's attorneys' fees and costs incurred in connection with
this Sixth Amendment in immediately available funds, including, without
limitation, UCC searches and key employee background searches.

          (t)  A fully executed copy of the IT Contract in form and substance
satisfactory to Lender.

                                      -7-
<PAGE>
 
          (u)  Such other documents and instruments as Lender shall reasonably
request.

     10.  Release of Individual Pledge Agreement.  Immediately prior to the
          --------------------------------------                    
execution of this Sixth Amendment, the Individual Pledge Agreement was
terminated, notwithstanding anything to the contrary in Section 8 of the
Individual Pledge Agreement, but subject to Section 11.3 of the Loan Agreement,
and Lender delivered to Borrower the original stock certificates evidencing the
Borrower Capital Stock issued in favor of the Individual Pledgors and any
original assignments or stock powers executed by the Individual Pledgors in
Lender's possession.

     11.  Loan Agreement Definitions.  (a) The definitions of "Accountants",
          --------------------------                         
"Advance Contracts", "Borrower's Obligations", "Contract Equipment", "Initial
Advance", "Interest Rate", "Key Man Life Insurance", "Obligors", "Operating Cash
Flow", "Principals", "Remaining Portion", "Shareholders", "Shareholder Pledge
Agreement" and "Subordinated Debt" in Section 1.1 of the Loan Agreement are
hereby deleted in their entirety and the following inserted therefor:

               Accountants: Any so-called "Big 6" public accounting
               -----------
          firm,Hein & Associates or any other independent certified
          public accounting firm selected by Borrower and satisfactory
          to Lender.

               Advance Contracts: The IT Contract and any other
               -----------------  
          contracts requiring acquisition of Contract Equipment and
          approved by Lender.

               Borrower's Obligations: (i) any and all Indebtedness
               ---------------------- 
          due or to become due, now existing or hereafter arising, of
          Borrower to Lender pursuant to the terms of this Loan
          Agreement or any other Loan Instrument, including, without
          limitation, the Profit Participation Fee, the Restructure
          Fee, the Maintenance Fee for the current calendar year and
          all prior calendar years during the term of the Loan, and
          the Termination Fee, and (ii) the performance of the
          covenants of Borrower contained in the Loan Instruments.

               Contract Equipment: Any equipment required in
               ------------------
          connection with the IT Contract and any other Advance
          Contracts.

               Initial Advance: $4,900,000 of the proceeds of the Loan
               ---------------
          disbursed on or about December 30, 1992, with a current
          outstanding principal balance of $2,766,327.63 as of March
          15, 1996.

               Interest Rate: a per annum rate of interest equal to
               ------------- 
          the Base Rate, plus 250 basis points.

                                      -8-
<PAGE>
 
               Key Man Life Insurance: each of the policies of key man
               ----------------------                                        
          life insurance issued in favor of Borrower and insuring the
          lives of Elnaggar and Reed, or Harry C. Conger, each of
          which policies of insurance shall be (i) in an amount of (A)
          $1,000,000 with respect to Elnaggar, and (B) $500,000 with
          respect to Reed, or (C) $2,000,000 with respect to Harry C.
          Conger, (ii) issued by an insurer and otherwise in form and
          content satisfactory to Lender and (iii) assigned to Lender
          pursuant to the applicable Assignment of Key Man Life
          Insurance.

               Obligors: Borrower and, subject to Section 3.3,
               --------                           -----------
          Kathleen J. Elnaggar in her capacity as trustee (the
          "Trustee") of the testamentary trust for the benefit of
          Tarek Elnaggar, Sharif Joseph Elnaggar and Jeanne-Marie
          Elnaggar (the "Trust"), and individually.

               Operating Cash Flow: for any period, the net income of
               -------------------
          Borrower for such period:

               (i)  plus the sum of the following, to the extent
          deducted in determining net income for such period:

                    (A) interest paid or accrued on
               Indebtedness, including, without limitation,
               interest on Capitalized Leases that is imputed in
               accordance with GAAP;

                    (B) Depreciation and amortization of assets;

                    (C) extraordinary losses from sales or
               dispositions of Property outside of the normal
               course of Borrower's Business; and
                    
                    (D) any special charges, extraordinary
               charges or non-recurring charges;

               (ii) minus the sum of the following, to the extent
                    -----
          included in determining net income for such period:

                    (A) all payments made by Borrower during such
               period with respect to Capital Expenditures, other
               than Subsequent Advance Expenditures;

                              -9- 
<PAGE>
 
                   (B) extraordinary gains from sales or
               dispositions of Property outside of the normal
               course of Borrower's Business and all
               extraordinary non-cash gains; and

                   (C) dividends or distributions declared or
               paid or deemed paid pursuant to Section 7.5
               hereof; and
               
                    (D) for purposes of Excess Cash Flow payments
               pursuant to Section 2.9.2 hereof only, fifty
               percent (50%) of all cancellation/termination fees
               received by Borrower from Occidental Chemical
               Corporation or its successors or assigns ("Oxy
               Chem") in connection with that certain agreement
               dated September 21 and 28, 1994 between Borrower
               and Oxy Chem, a copy of which is attached hereto
               as EXHIBIT 2.9.2 and incorporated herein by this
               reference.

               Principals: collectively, Kathleen J. Elnaggar, Tarek
               ---------- 
          Elnaggar and Harry C. Conger.


               Remaining Portion: An amount not to exceed $850,000.
               -----------------                                    

               Shareholder:  Holdings.
               -----------             

               Shareholder Pledge Agreement: A Security Agreement and
               ----------------------------
          Shareholder Pledge Agreement executed by Holdings in favor
          of Lender in form acceptable to Lender, pursuant to which
          Lender is granted a Lien on all of the Borrower Capital
          Stock.

               Subordinated Debt: collectively, the LSC Indebtedness,
               -----------------
          the Shareholder Indebtedness and the New Subordinated
          Indebtedness.

and (b) Section 1.1 of the Loan Agreement is are hereby amended to add the
following definitions:

               Base Price: the invoice cost of any Contract Equipment
               ----------
          (after adjustment for applicable discounts or allowances),
          less tax, destination charges, freight, delivery charges,
          set-up costs, testing costs, accessories or add-ons and any
          other additional charges above the base price of the
          Contract Equipment.

                                -10-
<PAGE>
 
               Holdings: GDC Holdings Corporation, a Louisiana
               --------
          corporation, and its permitted successors and assigns.

               IT Contract: That certain Subcontract Agreement dated
               -----------
          March 1 and 11, 1996 between Borrower and IT Corporation
          with respect to the American Creosote contract.
          
               Net Income: For any period, the net income (or loss) of
               ----------
          Borrower for such period.

               New Subordinated Indebtedness: Any Indebtedness for
               -----------------------------
          Borrowed Money incurred after the date of the Sixth
          Amendment owing by Borrower to any Person, except for
          refinancing of existing Indebtedness for Borrowed Money.

               Orderly Liquidation Value: The estimated gross cash
               ------------------------- 
          dollar amount derived from the sale of the assets, given
          limited time to find a purchaser or purchasers, and
          considering a completed sale of all assets. No guarantees or
          warranties are made as to condition, and purchasers are
          responsible for removal of the purchased assets at their own
          risk and expense. Orderly Liquidation Value allows only
          limited time for market exposure, and also considers the
          physical condition, quantity, difficulty of removal, as well
          as the overall marketability of the asset group. No
          consideration is given to additional value that might be
          obtained because of product line, equipment in place, going
          operation or other elements of value that could or might be
          produced at liquidation, but could not be reasonably
          assumed.
          
               Public Company: DK Industries, Inc. or another company
               --------------
          satisfactory to Lender with a class of equity securities
          registered under Section 12(b) or 12(g) of the 1934 Act, and
          subject to the periodic reporting requirements set forth in
          Section 13 of the 1934 Act.

               Restructure Fee: $300,000.
               ---------------              

               Specially Manufactured Equipment: Contract Equipment
               --------------------------------
          (a) with a Base Price equal to or in excess of $40,000 and
          (b)(i) which will not be delivered to Borrower within 28
          days after the first Subsequent Advance for such Contract
          Equipment or (ii) requires multiple Subsequent Advances for
          such Contract Equipment.

               1934 Act: The Securities Exchange Act of 1934, as
               --------
          amended.
                                                           
                                -11-
<PAGE>
 
     12.  Time Periods.   Section 1.2 of the Loan Agreement is hereby
          ------------                                               
deleted in its entirety and the following inserted therefor:



                    1.2 TIME PERIODS. In this Loan Agreement and the
               other Loan Instruments, in the computation of periods
               of time from a specified date to a later specified
               date, (i) the word "from" means "from and including,"
               (ii) the words "to" and "until" each mean "to, but
               excluding" and (iii) the words "through," "end of" and
               "expiration" each mean "through and including." Unless
               otherwise specified, all references in this Loan
               Agreement and the other Loan Instruments to a (i)
               "month" shall be deemed to refer to a calendar month,
               (ii) "quarter" shall be deemed to refer to the period
               from (A) the first day of such Person's fiscal year
               through the end of the third month of such Person's
               fiscal year, (B) the first day of the fourth month of
               such Person's fiscal year through the last day of the
               sixth month of such Person's fiscal year, (C) the first
               day of the seventh month of such Person's fiscal year
               through the last day of the ninth month of such
               Person's fiscal year, or (D) the first day of the tenth
               month of such Person's fiscal year through the last day
               of such Person's fiscal year, and (iii) "year" shall be
               deemed to refer to a period from the first day of such
               Person's fiscal year through the last day of such
               Person's fiscal year.

          13.  Loan. Section 2.1 of the Loan Agreement is hereby
               ----
deleted in its entirety and the following inserted therefor:

               2.1 LOAN. The Loan shall consist of a term loan in an
                   ----
               amount not to exceed $3,616,327.63.

          14.  Remaining Portion - Subsequent Advances.  (a)  Section 
               ---------------------------------------               
2.2.2(a) of the Loan Agreement is hereby deleted in its entirety and the
following inserted therefor:

                    (A) PURPOSES. The proceeds of the Remaining
                        --------
               Portion shall be utilized to acquire Contract Equipment
               in connection with the IT Contract and any Advance
               Contract approved by Lender.

(b) Section 2.2(b)(i), (ii), (iii) and (iv) of the Loan Agreement are hereby
deleted in their entirety and the following inserted therefor:

                         (I) NO DEFAULT. No Event of Default or
                             ----------
               Incipient Default shall exist or be created as a result
               of the making of any such Subsequent Advance.

                                -12-
<PAGE>
 
                    (II) REQUEST FOR ADVANCE; INFORMATION. Not less
                         --------------------------------
               than 7 days prior to each anticipated Subsequent
               Advance, Borrower shall deliver to Lender a written
               request for a Subsequent Advance, which shall be
               accompanied by such documents as Lender may request and
               evidence satisfactory to Lender that (A) the aggregate
               amount of all Subsequent Advances (including the then
               requested Subsequent Advance) do not exceed, in the
               aggregate, $850,000, (B) Borrower has paid, or will
               contemporaneously with the first Subsequent Advance for
               each item of Contract Equipment will pay, the
               difference between the contract price for the Contract
               Equipment and the Base Price, (C) the amount of the
               requested Subsequent Advance to acquire the Contract
               Equipment (together with any prior Subsequent Advances
               used to acquire such Contract Equipment) does not
               exceed, in the aggregate, 80% of the Base Price of such
               Contract Equipment, (D) title to all Contract Equipment
               (except the Specially Manufactured Equipment) purchased
               previously with Subsequent Advances is owned by
               Borrower, the purchase price for all Contract Equipment
               (except the Specially Manufactured Equipment) purchased
               previously with Subsequent Advances has been fully
               paid, and all Contract Equipment (except the Specially
               Manufactured Equipment) purchased previously with
               Subsequent Advances is in the possession of Borrower,
               (E) with respect to Specially Manufactured Equipment,
               (1) the Specially Manufactured Equipment is
               identifiable collateral, (2) title to the Specially
               Manufactured Equipment has been transferred to
               Borrower, subject only to the vendor's purchase money
               security interest for the remainder of the contract
               price, (3) the vendor's secured lender(s) and the
               landlord(s) of the premises where the Specially
               Manufactured Equipment is manufactured, assembled or
               stored have waived any lien rights with respect to the
               Specially Manufactured Equipment, and (4) the vendor
               has agreed to deliver the Specially Manufactured
               Equipment to a location designated by Lender upon
               receipt of a notice of default and payment of the
               remainder of the contract price for the Specially
               Manufactured Equipment, and (F) none of the Contract
               Equipment is goods covered by a certificate of title or
               goods which are not covered by a certificate of title
               but are mobile and are of a type normally used in more
               than one jurisdiction, such as motor vehicles,
               trailers, rolling stock, airplanes, shipping
               containers, road building and construction machinery
               and commercial harvesting machinery and the like.
               Notwithstanding anything to the contrary in clause (D)
                                                           ----------
               above, Borrower may, at any time, have requested and/or
               received Subsequent Advances of up to $150,000 for
               Contract Equipment (including Specially Manufactured
               Equipment designated by Borrower in writing) which is
               not yet titled to, and/or not yet in the

                                -13-
<PAGE>
 
               possession of, the Borrower and, provided further,
               Contract Equipment titled to, and in the possession of,
               the Borrower, but not yet paid for in full shall be
               considered perfected if the only condition to
               perfection is payment of the Base Price (which, at
               Lender's discretion, may be paid directly to the
               vendor).

                    (III) AVAILABILITY; FREQUENCY. No Subsequent
                          -----------------------
               Advance shall be made after December 31, 1996. Each
               such Subsequent Advance shall be in an amount not less
               than $100,000.

                    (IV) SATISFACTION OF LENDER. Before any Subsequent
                         ----------------------
               Advance is made there shall be delivered to Lender, and
               Lender must be satisfied with (A) an analysis which
               demonstrates that of each of the Advance Contracts can
               be performed profitably by Borrower, (B) the
               performance record, including payment history, safety
               and delivery of services, of all parties to the Advance
               Contracts and (C) the anticipated warranty terms
               provided by each manufacturer of any portion of the
               Contract Equipment. Lender waives satisfaction of
               Clause (B) with respect to the IT Contract.
               ----------  
and (c) Sections 2.2(c) and 2.2(d) of the Loan Agreement are hereby deleted in
their entirety.

          15.  Payment of Principal and Interest.  Section 2.5 of the Loan
               ---------------------------------                          
Agreement is hereby deleted in its entirety and the following inserted therefor:

                    2.5 PAYMENTS OF PRINCIPAL AND INTEREST. The
                        ----------------------------------
               principal and interest of the Loan shall be repaid in
               one (1) interest only installment on March 1, 1996 and
               59 successive monthly installments of principal and
               interest, commencing on the first business day of April
               1996. The first 58 of such installments shall be in an
               amount equal to (a) interest in arrears calculated at
               the Interest Rate or the Default Interest Rate, as
               applicable, and (b) a principal component in an amount
               equal to the sum of the following: (i) the principal
               portion of a seven-year level mortgage amortization
               schedule, calculated upon the Interest Rate which is in
               effect on February 1, 1996 and the principal balance of
               the Loan which is outstanding on February 2, 1996
               (after application of invoice due February 1, 1996)
               plus (ii) with respect to each Subsequent Advance, the
               principal portion of a seven-year level mortgage
               amortization schedule, calculated upon the Interest
               Rate which is in effect on the applicable Subsequent
               Advance Date and the amount of such Subsequent Advance.
               All remaining principal, including the principal amount
               of all Subsequent Advances, and any accrued interest
               and other sums which are due and owing

                                -14-
<PAGE>
 
          pursuant to the Loan Instruments, shall be paid in full on the first
          business day of February 2001.

     16.  Subsequent Advance Fee.   Section 2.8.1(b) of the Loan
          ----------------------                                
Agreement is hereby deleted in its entirety.

     17.  Maintenance Fee. Section 2.8.2 of the Loan Agreement is hereby deleted
          ---------------                                            
in its entirety and the following inserted therefor:

               2.8.2     MAINTENANCE FEE. On or before December 31,
                         ---------------    
          1993, December 31, 1994 and December 31, 1995, Borrower
          shall pay to Lender an annual maintenance fee of $35,000. On
          or before December 31, 1996 and on or before December 31 of
          each year (or partial year) thereafter during which the Loan
          is outstanding (or upon payment or prepayment of the Loan in
          full), Borrower shall pay to Lender an annual maintenance
          fee (the "Maintenance Fee") equal to $100,000. Such
          Maintenance Fee shall be deemed to be earned on January 1 of
          each calendar year, whether or not the Loan is paid in full
          prior to December 31 of such calendar year and is not
          subject to proration in the event of payment or prepayment
          of the Loan in full, whether by payment of the Loan at
          maturity, by optional prepayment or by acceleration after an
          Event of default. Lender acknowledges receipt of the
          Maintenance Fee for calendar years 1993, 1994 and 1995.
          Notwithstanding the foregoing, if the Loan is timely paid at
          maturity, the Maintenance Fee for the last year of the
          scheduled term of the Loan shall be prorated based upon the
          actual number of days the Loan is outstanding in such year
          and a 360 day year.

     18.  Profit Participation Fee.    Section 2.8.3 of the Loan Agreement is
          ------------------------                                
hereby deleted in its entirety and the following inserted therefor:

               2.8.3 PROFIT PARTICIPATION FEE. As an additional
                     ------------------------                           
          inducement to Lender to make the Loan, Borrower agrees to
          pay to Lender a profit participation fee (the "Profit
          Participation Fee") of $500,000, which shall be deemed to be
          fully earned upon the effectiveness of the Sixth Amendment
          to Loan Instruments dated March 15, 1996 (the "Sixth
          Amendment") and which shall be payable upon the earlier of
          full prepayment of the Loan, whether by optional prepayment
          or acceleration after an Event of default, or the following
          dates:

                                      -15-
<PAGE>
 
<TABLE>
<CAPTION>
          Date                           Amount
         ============================================================
         <S>                             <C>
 
          September 30, 1996             $100,000
         ------------------------------------------------------------
          October 31, 1996               $100,000
         ------------------------------------------------------------
          November 30, 1996              $100,000
         ------------------------------------------------------------ 
          December 15, 1996              $200,000
         ============================================================
</TABLE>
  
               Borrower or Holdings shall provide Lender with a copy
          of any private placement memorandum for the Private
          Placement, documents evidencing or describing the Public
          Company Merger given to shareholders or prospective
          investors or any final prospectus in connection with any
          equity offering by Public Company as soon as available. Upon
          the written request of Lender, Borrower and Holdings shall
          use reasonable good faith efforts to permit Lender to
          convert all or any portion of the Profit Participation Fee
          for stock, options and/or warrants in Holdings or the Public
          Company, as the case may be, for the same price and on the
          same terms and conditions as such stock, options and/or
          warrants are being offered to other prospective investors or
          stockholders at the time of the Private Placement and/or
          equity offering, as the case may be, provided that the
          aggregate amount of stock, options and/or warrants purchased
          by Lender shall be less than ten percent (10%) of the issued
          and outstanding stock of Holdings or Public Company (but
          excluding any stock issued for unexercised options or
          warrants), and, provided further, that the minimum
          conversion amount for any offering shall be $100,000 and any
          conversion amount in excess thereof shall be in increments
          of $25,000. The cost of the stock, options and/or warrants
          acquired by Lender in such conversion(s) shall be applied
          against the Profit Participation Fee in the inverse order of
          payment of the Profit Participation Fee.

     19.  Fees. Section 2.8 of the Loan Agreement is hereby amended to add the
          ----                                                 
following: 

               2.8.4 RESTRUCTURE FEE. As an additional inducement to
                     ---------------
          Lender to enter into the Sixth Amendment and in
          consideration of the modifications and agreements of Lender
          contained therein, Borrower agrees to pay to Lender the
          Restructure Fee, which shall be deemed to be fully earned
          upon the effectiveness of the Sixth Amendment and which
          shall be payable upon the earlier of full prepayment of the
          Loan, whether by optional prepayment or acceleration after
          an Event of default, or the following dates:

                                      -16-
<PAGE>
 
<TABLE> 
<CAPTION> 
         ============================================================
           Date                              Amount
         ------------------------------------------------------------
         <S>                                 <C>  
          Upon the effectiveness of the      $100,000
          Sixth Amendment
         ------------------------------------------------------------
          May 31, 1996                       $100,000
         ------------------------------------------------------------
          July 31, 1996                      $100,000
         ============================================================
</TABLE>

               2.8.5 APPLICATION OF CASH TO PROFIT PARTICIPATION FEE
                     -----------------------------------------------
          AND RESTRUCTURE FEE. Except as otherwise provided in the
          -------------------
          last sentence of this Section 2.8.5, in the event that
          Public Company, Borrower or Holdings receives any cash from
          any source, including, without limitation, sale of stock,
          debentures, options or warrants, sale of assets, and loans,
          within seven (7) days thereafter, Borrower shall pay to
          Lender an amount equal to twenty percent (20%) multiplied by
          the amount of cash received by Public Company, Borrower
          and/or Holdings to be applied toward the scheduled payments
          of the Profit Participation Fee and the Restructure Fee in
          the inverse order of maturity, but in no event more than the
          then remaining balance of the Profit Participation Fee and
          Restructure Fee. Notwithstanding anything to the contrary
          contained above, cash from operations, Permitted Payments,
          conversion of existing debt to equity and refinancings of
          existing debt to the extent of such existing debt are
          specifically excluded from the Borrower's payment obligation
          above.

               2.8.6 TERMINATION FEE. In consideration of the making
                     ---------------
          of the Loan by Lender to Borrower, Borrower agrees that upon
          any partial or full prepayment of the Loan, whether by
          optional prepayment or acceleration after an Event of
          Default, in addition to the principal prepayment, all
          accrued and unpaid interest on such prepayment, and upon a
          full prepayment, the Maintenance Fee for the current
          calendar year and all prior calendar years during the term
          of the Loan, the Restructure Fee and the Profit
          Participation Fee, Borrower shall pay to Lender a
          termination fee (the "Termination Fee") equal to three
          percent (3%) of the principal amount prepaid if such
          prepayment occurs on or prior to January 1, 1998, and two
          percent (2%) of the principal amount prepaid if such
          prepayment occurs after January 1, 1998.

     20.  Excess Cash Flow Payments. Section 2.9.2(a) of the Loan Agreement is
          -------------------------                                  
hereby deleted in its entirety and the following inserted therefor:

               (a) EXCESS CASH FLOW PAYMENTS. Until the Loan is paid
                   -------------------------              
          in full, for the years ending November 30, 1993 and

                                      -17-
<PAGE>
 
          November 30, 1994, Borrower shall pay to Lender 50% of the
          Excess Cash Flow for such years, and until the Loan is paid
          in full, for each year commencing with the year ending
          September 30, 1995, Borrower shall pay to Lender 25% of the
          Excess Cash Flow for such year, provided in each case Lender
          has delivered a notice to Borrower prior to the expiration
          of 30 days after the later to occur of the date (i) upon
          which Borrower is required to deliver to Lender the Basic
          Financial Statements for such year pursuant to subsection
          6.3.3 or (ii) of actual receipt of the Basic Financial
          Statements for such year pursuant to subsection 6.3.3. Any
          such payment received pursuant to the provisions of this
          subparagraph (a) shall be applied to Borrower's Obligations
          as described in subparagraph (c) of this subsection 2.9.2.
          Lender acknowledges receipt of the Excess Cash Flow payment
          for the year ending November 30, 1993. Borrower acknowledges
          timely and proper delivery and receipt of the notice
          demanding payment of the Excess Cash Flow for the year
          ending November 30, 1994. Lender and Borrower agree that the
          amount of the Excess Cash Flow for the year ending November
          30, 1994 is $119,735. Lender and Borrower agree that the
          Excess Cash Flow payment for the year ending November 30,
          1994 and, if exercised, the Excess Cash Flow payment for the
          year ending September 30, 1995, shall not be due and payable
          until March 31, 1997. Borrower's obligation to pay the
          Excess Cash Flow payments required in this Section 2.9.2
          shall terminate and be of no further force or effect (i) for
          the years ending November 30, 1994, September 30, 1995
          (based upon the 10-month Basic Financial Statements for the
          period ending September 30, 1995) and September 30, 1996,
          if, on or prior to March 31, 1997, and (ii) for all years
          ending on September 30, 1997 or later, if on or before
          September 30 of such year, (a) Borrower delivers to Lender a
          current appraisal of the Collateral prepared by an Appraiser
          satisfactory to Lender and otherwise in form and substance
          satisfactory to Lender with an Orderly Liquidation Value of
          the Collateral equal to or exceeding eighty percent (80%) of
          the then outstanding principal balance of the Loan plus any
          Subsequent Advances which Lender is committed to advance,
          but has not yet disbursed (the "OLV Appraisal") and (b) at
          the time of delivery of the appraisal, no monetary Event of
          Default has occurred and is continuing. Any such appraisal
          shall be deemed "current" for up to six (6) months after the
          effective date of the appraisal. Excess cash flow payments
          required to be paid by Lender shall not be subject to the
          Termination Fee in Section 2.8.6 above and not be included
          in calculating the debt service payments to Lender in
          connection with subsequent Excess Cash Flow payment
          calculations.

                                      -18-
<PAGE>
 
     21.  Involuntary Prepayment. Section 2.9.3 of the Loan Agreement is hereby
          ----------------------                             
deleted in its entirety and the following inserted therefor:

               2.9.3 INVOLUNTARY PREPAYMENT. Notwithstanding anything
                     ----------------------                      
          to the contrary contained herein, it is the intent of the
          parties to this Agreement, that the Profit Participation
          Fee, the Restructure Fee, the Maintenance Fee for the
          current calendar year and all prior calendar years during
          the term of the Loan, and the Termination Fee, shall be
          payable upon any involuntary prepayment of the Loan,
          including, without limitation, any involuntary prepayment
          due to an acceleration of the Loan by Lender upon the
          occurrence of an Event of Default, except for Excess Cash
          Flow payments required by Lender.

     22.  Note and Security. Article III of the Loan Agreement is hereby amended
          -----------------                                        
to add the following:

               3.3 K. ELNAGGAR GUARANTEE. Borrower's Obligations shall
                   --------------------- 
          be secured by the K. Elnaggar Guarantee. The K. Elnaggar
          Guarantee shall be terminated and of no further force or
          effect upon the occurrence or non-occurrence of all of the
          following: (a) Lender's receipt of aggregate payments of
          $500,000 of the Profit Participation Fee and/or the
          Restructure Fee in good funds, (b) all scheduled principal
          and interest payments to the date of Lender's receipt of the
          last payment required under clause (a) above have been made,
                                      ---------- 
          (c)(i) there is no then currently effective written notice
          of an Event of Default, or then currently effective written
          notice of an Incipient Default, on the date of Lender's
          receipt of the last payment required under clause (a) above,
                                                     ---------- 
          or (ii) if there is a then currently effective written
          notice of an Event of Default, or a then currently effective
          written notice of an Incipient Default, on the date of
          Lender's receipt of the last payment required under clause
                                                              ------ 
          (a) above, if Lender does not accelerate the Indebtedness
          ---
          within 30 days thereafter, and (d) the Shareholder
          Indebtedness has, or will concurrently be, converted into
          equity of Borrower, Holdings or Public Company. Upon the
          written request of Borrower or K. Elnaggar, Lender shall
          confirm in writing whether or not the K. Elnaggar Guarantee
          has been terminated.

               3.4 PUBLIC COMPANY GUARANTY. In the event that the
                   -----------------------         
          Public Company Merger (as defined herein) is consummated,
          Public Company shall execute and deliver to Lender the
          Public Company Guaranty (as defined herein). If, prior to
          the execution and delivery of the Public Company Guaranty or
          at any time thereafter, Borrower delivers to Lender the OLV
          Appraisal and at the time of delivery of the OLV Appraisal,
          no monetary Event of

                                      -19-
<PAGE>
 
          Default has occurred and is continuing, the obligation of
          Public Company to provide the Public Company Guaranty shall
          terminate or, if the Public Company Guaranty has been
          delivered to Lender, the Public Company Guaranty shall be
          terminated and of no further force or effect.

     23.  Restrictions. Section 5.3.2 of the Loan Agreement is hereby deleted in
          ------------                                          
its entirety and the following inserted therefor:

               5.3.2 RESTRICTIONS. (i) Except for the Holdings Pledge
                     -------------         
          Agreement and normal and customary restrictions on "change
          of control" in credit facilities, Borrower is not a party
          to, and has no knowledge of, any agreement restricting the
          transfer of any shares of Borrower Capital Stock, and (ii)
          except as described in EXHIBIT 5.3.1, has no outstanding
          stock or securities convertible into or exchangeable or
          exercisable for any shares of Borrower Capital Stock or
          other equity interests in Borrower, or any rights to
          subscribe for or to purchase, or any options for the
          purchase of, or any agreements providing for the issuance
          (contingent or otherwise) of, or any calls, commitments or
          claims of any character relating to, any of the shares of
          the Borrower Capital Stock or any securities convertible
          into or exchangeable or exercisable for any shares of the
          Borrower Capital Stock or other equity interests of
          Borrower. Borrower is not required to file, and Borrower has
          not filed, pursuant to Section 12 of the Act, a registration
          statement relating to any class of debt or equity
          securities.

     24.  Facility Sites. Section 5.5.3 of the Loan Agreement is hereby deleted
          --------------                                             
in its entirety and the following inserted therefor:

               5.5.3 FACILITY SITES. There is set forth in EXHIBIT 
                     --------------
          5.5.3 the locations of all inventory, equipment, goods and
          principal places of business presently used in the operation
          of Borrower's Business which provide revenues to Borrower in
          excess of $25,000. None of such locations shall be changed
          without the prior written consent of Lender and no portion
          of the Collateral having value in excess of $25,000 shall be
          removed to any state other than the states of Texas,
          Louisiana, New York, Mississippi and South Carolina unless,
          within 30 days after the removal thereof, Borrower delivers
          to Lender written notice of such removal, which notice shall
          (i) describe the Collateral which has been so removed and
          (ii) set forth the address to which such Collateral shall be
          removed.

     25.  Monthly Statements. Section 6.3.1 of the Loan Agreement is hereby
          ------------------                                         
deleted in its entirety and the following inserted therefor:

                                      -20-
<PAGE>
 
               6.3.1 MONTHLY STATEMENTS. As soon as available and in
                     ------------------
          any event within 30 days after the end of each month a (i)
          copy of Borrower's (A) balance sheet as of the end of such
          month and (B) statements of operations, Operating Cash Flow,
          and Excess Cash Flow for such month and for the period from
          the beginning of the current year through the end of such
          month setting forth in each case in comparative form the
          corresponding figures for the corresponding period in the
          preceding year, and (ii) report on the aggregate revenues
          and gross margins achieved by Borrower on each contract
          pursuant to which Borrower is to provide services consisting
          primarily of either environmental engineering or waste
          remediation, all in reasonable detail, containing such
          information as Lender may require, and certified as complete
          and correct (subject to normal year-end adjustments) by the
          President or Chief Financial Officer.

     26.  Holdings Financial Statements. Section 6.3 of the Loan Agreement is
          -----------------------------                              
hereby amended to add the following:

               6.3.13 HOLDINGS FINANCIAL STATEMENTS. 
                      -----------------------------
               (a)  As soon as available and in any event within 45
          days after the end of each quarter, a copy of the
          consolidated and consolidating (a) balance sheet of Holdings
          as of the end of such quarter and (b) statements of income
          and operations, cash flow and shareholders' equity
          (collectively, the "Holdings Financial Statements"), setting
          forth in each case in comparative form the corresponding
          figures for the preceding quarter, if any, all in reasonable
          detail. Each of the Holdings Financial Statements shall be
          (x) prepared by Holdings and (y) accompanied by a
          certificate from the President or Chief Financial Officer of
          Holdings certifying that such Holdings Financial Statements
          were prepared in accordance with GAAP, fairly present the
          financial position of Holdings as of the dates indicated
          therein and the results of operations of Holdings for the
          periods indicated therein, and there is no Event of Default
          or Incipient Default that has occurred and is continuing as
          of the date of such certification, or if an Event of Default
          or Incipient Default has occurred and is continuing,
          specifying such Event of Default or Incipient Default and
          the proposed action to remedy same.

               (b)  As soon as available and in any event within 120
          days after the close of each year, a copy of the Holdings
          Financial Statements, setting forth in each case in
          comparative form the corresponding figures for the preceding
          year, if any, all in reasonable detail. Each of the annual
          Holdings Financial

                                      -21-
<PAGE>
 
          Statements shall be (x) prepared by Holdings, (y)
          accompanied by a certificate from the President or Chief
          Financial Officer of Holdings certifying that such Holdings
          Financial Statements were prepared in accordance with GAAP,
          fairly present the financial position of Holdings as of the
          dates indicated therein and the results of operations of
          Holdings for the periods indicated therein, and there is no
          Event of Default or Incipient Default that has occurred and
          is continuing as of the date of such certification, or if an
          Event of Default or Incipient Default has occurred and is
          continuing, specifying such Event of Default or Incipient
          Default and the proposed action to remedy same.

               6.3.14 PUBLIC COMPANY FINANCIAL STATEMENTS.
                      ----------------------------------- 

               (a)  In the event that the Public Company Merger (as
          defined herein) is consummated and for so long as the Public
          Company Guaranty (as defined herein) is in effect, within 5
          days after filing with the Securities Exchange Commission,
          but in no event later than 30 days after the due date for
          filing with the Securities Exchange Commission, as such due
          date may be extended, cause Public Company to provide to
          Lender copies of all 10-Q, 10-K and 8-K Reports filed or
          required to be filed with the Securities Exchange
          Commission. The annual financial statements of Public
          Company (the "Public Company Financial Statements") shall be
          accompanied by an opinion of the Accountants, which shall be
          (I) unqualified as to going concern and scope of the audit
          and (II) state that (1) the examination by the Accountants
          in connection with the annual Public Company Financial
          Statements has been made in accordance with generally
          accepted auditing standards and, accordingly, included such
          tests of the accounting records and such other procedures as
          were considered necessary under the circumstances, (2) such
          Public Company Financial Statements fairly present the
          financial position and results of operation of Public
          Company and (3) such Public Company Financial Statements
          have been prepared in accordance with GAAP and that such
          GAAP in accordance with which such Public Company Financial
          Statements were prepared are consistent with those applied
          in prior periods.

     27.  Insurance. Section 6.6 of the Loan Agreement is hereby amended to add
          ---------                                                  
the following:

          As soon as practicable, but in no event later than thirty
          (30) days after the effectiveness of the Sixth Amendment,
          Borrower shall deliver to Lender evidence of Key Man Life
          Insurance for Harry C. Conger in the amount of $2,000,000
          naming Borrower as

                                      -22-
<PAGE>
 
          beneficiary, together with the applicable Assignment of Key
          Man Life Insurance. Upon acceptance by Lender of the Key Man
          Life Insurance for Harry C. Conger, together with the
          applicable Assignment of Key Man Life Insurance, Borrower
          may terminate the Key Man Life Insurance for Elnaggar and/or
          Reed.

     28.  Borrowings. Section 7.1 of the Loan Agreement is hereby deleted in its
          ----------                                                 
entirety and the following inserted therefor:

               7.1  BORROWING. Create, incur, assume or suffer to
                    ---------
          exist any liability for Indebtedness for Borrowed Money
          except (i) Borrower's Obligations, (ii) the Working Capital
          Debt, (iii) the Subordinated Debt and (iv) the Ally
          Obligations; provided, however, the portion of the
          Subordinated Debt constituting New Subordinated Indebtedness
          shall not exceed $750,000 at any time, and prior to Borrower
          incurring New Subordinated Indebtedness, the lender of the
          New Subordinated Indebtedness shall execute and deliver to
          Lender a subordination agreement in a form acceptable to
          Lender, which subordination agreement shall only permit
          scheduled principal and/or interest payments to the lender
          on the last day of any month provided that no monetary Event
          of Default has occurred and is continuing and, after giving
          effect to such principal and/or interest payment, Borrower
          would be in compliance with all financial covenants in this
          Loan Agreement. The Shareholder Indebtedness shall be
          converted to equity in Borrower, Holdings or the Public
          Company as a condition precedent to Lender's release of the
          K. Elnaggar Guaranty.

     29.  Merger and Acquisition. Section 7.3 of the Loan Agreement is hereby
          ----------------------                              
deleted in its entirety and the following inserted therefor:

               7.3  Merger and Acquisition. Consolidate with or merge
                    ----------------------
     with or into any Person or acquire directly or indirectly all of
     the capital stock, equity interests or Property of any Person,
     except for the merger of 3E Corporation of Louisiana with and
     into Borrower with Borrower being the surviving corporation or
     the acquisition of all or substantially all of the assets of 3E
     Corporation of Louisiana by Borrower subject to an asset purchase
     agreement satisfactory to Lender.

     30.  Dividends and Purchase of Stock. Section 7.5 of the Loan Agreement is
          -------------------------------                            
hereby deleted in its entirety and the following inserted therefor:

 
               7.5    Dividends and Purchase of Stock. Declare or pay
                      -------------------------------
      any dividends with respect to the Borrower Capital Stock or
      apply any of its Property to the purchase, redemption or other
      retirement

                                      -23-
<PAGE>
 
          of, or set apart any sum for the payment of, or make any
          distribution by reduction of capital or otherwise in respect
          of, any of the shares of the Borrower Capital Stock;
          provided, however, Borrower may pay dividends or make
          distributions in respect of the shares of the Borrower
          Capital Stock or otherwise transfer cash or other assets or
          property to Holdings during Borrower's fiscal year 1996 only
          (collectively, "Permitted Payments"), regardless of the form
          of such Permitted Payments, if ALL of the following
          conditions are satisfied: (a) the aggregate amount of such
          Permitted Payments shall not exceed $200,000, (d) Permitted
          Payments may not be made more frequently than once per month
          and shall be made effective as of the last day of such
          month, (e) Permitted Payments shall not exceed in any one
          month $50,000, (f) no Event of Default shall have occurred
          and be continuing pursuant to Section 8.1.1 hereof with
          respect to scheduled principal and interest payments, the
          Profit Participation Fee or the Restructure Fee only.
            
     31.  Investments, Loans, etc. Section 7.7 of the Loan Agreement is hereby
          -----------------------
amended to add the following:

               7.7.4  PERMITTED PAYMENTS TO HOLDINGS. Permitted
                      ------------------------------
          Payments satisfying all of the terms and conditions in
          Section 7.5.

               32.  Fundamental Business Changes. Section 7.8 of the Loan
                    ----------------------------
Agreement is hereby deleted in its entirety and the following inserted therefor:


               7.8  FUNDAMENTAL BUSINESS CHANGES. (a) Engage in any
                    ----------------------------
          business other than Borrower's Business or change Borrower's
          fiscal year, except, upon written notice to Lender, (i)
          Borrower may change its fiscal year-end from November 30 to
          September 30, (ii) subject to subsection 7.8(b) below,
          Borrower may acquire the property commonly known as 822
          Neosho Avenue, Baton Rouge, Louisiana (the "Headquarters
          Property") "subject to" or assume the obligations and
          liabilities of the mortgagor(s) under a first lien to a
          Person who is not an Affiliate in an amount not to exceed
          $436,500 encumbering the Headquarters Property and under the
          second mortgage in favor of Kathleen J. Elnaggar encumbering
          the Headquarters Property (the "Second Mortgage"), and (iii)
          Borrower may engage in the development and utilization of
          bioremediation techniques for treating organic and inorganic
          wastes, provided that within 60 days after the consummation
          of the Public Company Merger, Borrower shall assign, and
          Public Company, or a subsidiary of Public Company other than
          Borrower, shall assume, all right, title, interest,
          obligations and liabilities of Borrower, and NBL
          Technologies, Inc. ("NBL") and Jan Berkowitz shall release
          Borrower from such obligations and

                                      -24-
<PAGE>
 
          liabilities, under that certain Facilities, Technology and
          Production Lease dated July 1, 1995 between NBL and
          Borrower, and the Employment Agreement dated July 1, 1995
          between Borrower and Jan Berkowitz

               (b)  As conditions precedent to Borrower's acquisition
          of the Headquarters Property, Borrower shall, or shall cause
          Kathleen J. Elnaggar to, deliver to Lender the following:

                    (i)   A Standstill Agreement executed by
               Kathleen J. Elnaggar with respect to the
               Second Mortgage, in form and substance
               satisfactory to Lender.

                    (ii)  A mortgage in favor of Lender
               encumbering the Headquarters Property
               executed and acknowledged by Borrower, in
               form and substance satisfactory to Lender,
               together with evidence in the form of title
               insurance or an attorneys' abstract and
               opinion as to the validity and priority of
               the mortgage, subject only to monetary liens
               for current taxes and governmental
               assessments, a first lien to a Person who is
               not an Affiliate in an amount not to exceed
               $436,500 and the Second Mortgage in an amount
               not to exceed $450,000.

                    (iii) A copy of the promissory note
               secured by the Second Mortgage and the Second
               Mortgage, certified as a true, complete and
               correct copy of the original documents by
               Kathleen J. Elnaggar and Borrower.

                    (iii) A copy of the promissory note
               secured by the first lien mortgage and the
               first lien mortgage, certified as a true,
               complete and correct copy of the original
               documents by Kathleen J. Elnaggar and
               Borrower.

                    (iv)  A current (no earlier than six
               months prior to the conveyance date) phase 1
               environmental site assessment prepared by
               Borrower's environmental consultant in
               accordance with the Standard Practice for
               Environmental Site Assessments: Phase 1
               Environmental Site Assessment Process
               (Designation: E 1527 - 93), as

                                      -25-
<PAGE>
 
               approved by the American Society for Testing
               and Materials on March 15, 1993, with respect
               to the Headquarters Property, concluding that
               the assessment has revealed no evidence of
               recognized environmental conditions in
               connection with the Headquarters Property or
               otherwise satisfactory to Lender.

     33.  Capital Expenditures. Section 7.14 of the Loan Agreement is hereby
          --------------------                                        
deleted in its entirety and the following inserted therefor:

               7.14 CAPITAL EXPENDITURES. Make or incur obligations
                    --------------------
          for Capital Expenditures during any year, including, without
          limitation, expenditures with respect to Permitted Senior
          Indebtedness, of the aggregate amount thereof, individually
          or in the aggregate, would exceed $350,000 in any such year
          (including the portion of the cost of any Contract Equipment
          not paid from Subsequent Advance Expenditures), except that
          during the period from the Closing Date through December 31,
          1996, the limitation set forth in this Section 7.15 shall be
          in addition to any Subsequent Advance Expenditures.
          Notwithstanding anything to the contrary contained herein,
          during the period from the effectiveness of the Sixth
          Amendment until the one year anniversary of the
          effectiveness of the Sixth Amendment, Borrower may make or
          incur obligations for Capital Expenditures (which are fully
          paid within such one year period) in an amount equal to the
          amount of Subordinated Debt actually incurred after the
          effectiveness of the Sixth Amendment (excluding Subordinated
          Debt incurred to refinance existing Subordinated Debt and
          any portion of the New Subordinated Debt paid to Lender
          pursuant to Section 2.8.5), provided that the holder of such
                      -------------    
          Subordinated Debt executes and delivers a subordination
          agreement in form and substance satisfactory to Lender and
          which includes a subordination of any purchase money
          security interest in the Collateral. The Shareholder
          Indebtedness may not be refinanced.

     34.  Transactions with Affiliates. Section 7.15 of the Loan Agreement is
          ----------------------------                           
hereby deleted in its entirety and the following inserted therefor:

          7.15 TRANSACTIONS WITH AFFILIATES. Unless Lender has a
               ----------------------------
          currently effective Public Company Guaranty, sell, lease,
          assign, transfer or otherwise dispose of any Property to any
          Affiliate of Borrower, any Principal or any Shareholder,
          lease Property, render or receive services or purchase
          assets from any such Affiliate, Principal or Shareholder or
          otherwise enter into any contractual relationship with any
          Affiliate of Borrower, any Principal or any Shareholder,

                                      -26-
<PAGE>
 
          except Borrower may consummate the transactions specifically
          contemplated by this Agreement and the Sixth Amendment and
          otherwise lease Property, render or receive services or
          purchase assets from any such Affiliate, Principal or
          Shareholder provided each such transaction is on terms and
          conditions no less favorable to Borrower than those terms
          and conditions which would have been obtained in an arm's
          length transaction consummated with a Person who is not an
          Affiliate, Principal or Shareholder. Any payments or other
          remuneration in any form made by Borrower to or for the
          benefit of Holdings during Borrower's fiscal year 1996 and
          on or after the date of the Sixth Amendment shall be a
          Permitted Payment and shall be subject to the terms and
          conditions in Section 7.5. Notwithstanding anything to the
          contrary contained herein, Borrower may only pay to Kathleen
          J. Elnaggar the first two (2) installment payments, in the
          aggregate amount not to exceed $50,000, under the promissory
          note or other evidence of indebtedness of Borrower to
          Kathleen J. Elnaggar secured by the Headquarters Property.
          Nothing in this Section is intended to modify the existing
          obligations of Borrower under the lease of the Headquarters
          Property.

     35.  Minimum Operating Cash Flow. Section 7.18 of the Loan Agreement is
          ---------------------------                            
hereby deleted in its entirety and the following inserted therefor:

               7.18 MINIMUM OPERATING CASH FLOW. Permit Operating Cash
                    ---------------------------
          Flow for the Four Quarter Period ending on the last day of
          each fiscal quarter of Borrower beginning with the fiscal
          quarter ending June 30, 1996 to be less than the product of
          (A) the Senior Debt Service for the applicable Four Quarter
          Period multiplied by (B) 1.1 for the Four Quarter Period
          ending June 30, 1996; 1.25 for the Four Quarter Period
          ending September 30, 1996; and 1.4 for the Four Quarter
          Period ending December 31, 1996 and for each Four Quarter
          Period thereafter.

     36.  Accounts Receivable Turnover. Section 7.20 of the Loan Agreement is
          ----------------------------                           
hereby deleted in its entirety and the following inserted therefor:

               7.20 ACCOUNTS RECEIVABLE TURNOVER. Permit the Accounts
                    ----------------------------
          Receivable Turnover (excluding Accounts Receivable arising
          from the IT Contract) for the Four Quarter Periods ending on
          the last day of each of the first 3 fiscal quarters of
          Borrower's fiscal year to be greater than 45 days, permit
          the Accounts Receivable Turnover for the Accounts Receivable
          arising from the IT Contract only for the Four Quarter
          Periods ending on the last day of each of the first 3 fiscal
          quarters of Borrower's fiscal year to be greater than 60
          days, or permit the Accounts Receivable

                                      -27-
<PAGE>
 
          Turnover for the Four Quarter Period ending on the last day
          of Borrower's fiscal year to be greater than 60 days
          (including Accounts Receivable arising from the IT
          Contract).

     37.  Total Debt Service.  Section 7.22 of the Loan Agreement is hereby 
          ------------------                                        
deleted in its entirety and the following inserted therefor:

               7.22  TOTAL DEBT SERVICE. Permit Operating Cash Flow for the Four
                     ------------------    
          Quarter Period ending on the last day of each fiscal quarter
          of Borrower beginning with the fiscal quarter ending June
          30, 1996 to be less than the product of (A) Total Debt
          Service the for applicable Four Quarter Period, multiplied
          by (B) 1.0 for the Four Quarter Period ending June 30, 1996;
          1.1 for the Four Quarter Period ending September 30, 1996;
          and 1.15 for the Four Quarter Period ending December 31,
          1996 and for each Four Quarter Period thereafter.

     38.  Availability - Working Capital Loan. Section 7.23 of the Loan 
          -----------------------------------                         
Agreement is hereby deleted in its entirety and the following inserted therefor:

               7.23  WORKING CAPITAL LOAN. At any time, permit total
                     --------------------
          Working Capital Debt to exceed 90% of Eligible Accounts
          Receivable, without regard to the maximum amount of Working
          Capital Debt.

     39.  Limitations on Business Activities of Holdings.  Section 7 of the Loan
          ----------------------------------------------            
Agreement is hereby amended to add the following:

               7.24  LIMITATIONS ON BUSINESS ACTIVITIES OF HOLDINGS.  
                     ----------------------------------------------
               Permit Holdings to undertake, and Holdings shall not
          undertake, any business operations except those business
          operations necessary and normally associated with a holding
          company, and Holdings shall not consolidate with or merge
          with or into any Person, or acquire directly or indirectly
          all or substantially all of the capital stock, equity
          interests or Property of another Person, except Holdings may
          (a) consummate a private placement for a minimum of $500,000
          pursuant to a private placement memorandum (the "Private
          Placement"), (b) consummate the transactions described in
          that certain letter of intent dated September 7, 1995
          between Holdings and DK Industries, Inc., as amended by
          First Amendment to Letter of Intent dated October 5, 1995
          and proposed amendment described in letter dated October 7,
          1995 from Robert Wiegand to Jeffrey A. Bartholomew (the
          "Public Company Merger"), provided that DK Industries, Inc.
          or its successor executes and delivers to Lender a
          Continuing Guaranty substantially in the form attached
          hereto as EXHIBIT
                                     -28-
<PAGE>
 
          7.24 and incorporated herein by this reference (the "Public
          Company Guaranty"), (c) consummate the transactions
          described in that certain Option Agreement for Purchase of
          Stock dated September 25, 1995 between Jan Berkowitz and
          Holdings, (d) consummate the transactions described in that
          certain GDC/3E Acquisition Agreement dated August 21, 1995
          between 3E Corporation of Louisiana and Holdings, (e)
          consummate the transactions described in that certain
          Agreement to Purchase and Sell dated October 16, 1995
          between Kathleen J. Elnaggar and Holdings, (f) consummate
          the transactions described in that certain GDC Holdings
          Corporation Debt Acquisition Agreement dated October 8, 1995
          among Kathleen J. Elnaggar, Borrower and Holdings, provided
          that Holdings immediately thereafter contributes the
          Subordinated Indebtedness to Borrower for cancellation, (g)
          obtain funds to make and make loans constituting New
          Subordinated Indebtedness to Borrower upon the terms and
          conditions contained in this Loan Agreement, and (h)
          guarantee obligations of Borrower (collectively, the
          "Permitted Holdings Transactions"). The Permitted Holdings
          Transactions are permitted by Lender on the express
          condition that such Permitted Holdings Transactions are
          consummated substantially in accordance with the terms,
          conditions and provisions described in the referenced
          agreements. Any material modification, amendment or waiver
          of the terms, conditions or provisions of any such agreement
          shall require the prior written consent of Lender.

     40.  Bankruptcy, etc..    Section 8.1.5 of the Loan Agreement is hereby 
          ----------------                                           
delated in its entirety and the following inserted therefor:

          8.1.5  BANKRUPTCY, ETC.
                 ----------------

                 (a)  If Borrower or Holdings shall (i) file, or
          consent by answer or otherwise, to the filing against
          Borrower or Holdings of a petition for relief or
          reorganization or arrangement or any other petition in
          bankruptcy or insolvency under the laws of any jurisdiction,
          (ii) make an assignment for the benefit of creditors, (iii)
          consent to the appointment of a custodian, receiver, trustee
          or other officer with similar powers for Borrower or
          Holdings, or for any substantial part of the Property owned
          by Borrower or Holdings, or (iv) be adjudicated insolvent.

                 (b)  If any Governmental Body of competent
          jurisdiction shall enter an order appointing, without
          consent of Borrower or Holdings, a custodian, receiver,
          trustee or other officer with similar powers with respect to
          Borrower or Holdings, or with respect to any substantial
          part of the Property belonging to

                                     -29-
<PAGE>
 
          Borrower or Holdings, or if an order for relief shall be
          entered in any case or proceeding for liquidation or
          reorganization or otherwise to take advantage of any
          bankruptcy or insolvency law of any jurisdiction, or
          ordering the dissolution, winding-up or liquidation of
          Borrower or Holdings, or if any petition for any such relief
          shall be filed against Borrower or Holdings and such
          petition shall not be dismissed or stayed within 30 days.

     41.  Notices.   Section 11.1 of the Loan Agreement with respect to the 
          -------                                                     
notices to Borrower is hereby deleted in its entirety and the following inserted
therefor:

                     GDC Enviro-Solutions, Inc.
                     822 Neosho Avenue
                     Baton Rouge, Louisiana 70802
                     Attn: Mr. Harry C. Conger, CEO
                     Attn: Mr. Donald L. Murphy, Secretary
                     Telecopy No: (504) 383-2789

With a Copy To:      Martha S. Nachman, Esq.
                     Bearman, Talesnick & Clowdus, P.C.
                     1200 Seventeenth Street, Suite 2600
                     Denver, CO 80202-5826
                     Telecopy No: (303) 572-6511

     42.  Exhibits.  EXHIBITS 1.1(D), 1.1(E), 5.3.1, 5.5.3, 5.8.A AND 7.6 to the
          --------                                                  
Loan Agreement are hereby deleted in their entirety and replaced by EXHIBITS
1.1(D), 1.1(E) 5.3.1, 5.5.3, 5.8.A AND 7.6 attached hereto, which are
incorporated in the Loan Agreement by this reference.

     43.  Modifications.  No amendment, modification, change, waiver, release or
          -------------                                              
discharge hereof or hereunder shall be effective unless evidenced by an
instrument in writing signed by the party against whom enforcement is sought.

     44.  Severability.  If any provision hereof is invalid or unenforceable, 
          ------------                                        
the other provisions hereof shall remain in full force and effect and shall be
liberally construed in favor of Lender in order to effectuate the other
provisions hereof.

     45.  Counterparts.  This Sixth Amendment may be executed in one or more
          ------------                                              
counterparts, each of which shall be deemed an original instrument and all of
which combined shall constitute one and the same instrument.

     46.  Binding Nature.  The provisions of this Sixth Amendment shall be
          --------------                                         
binding upon, and inure to the benefit of, the respective successors and assigns
(including without limitation, any receiver, debtor in possession or trustee in
bankruptcy) of Lender, Borrower and Kathleen J. Elnaggar.

                                     -30-
<PAGE>
 
     47.  Fraudulent Conveyance and Preference.  In the event there is a final,
          ------------------------------------                        
non-appealable action in any bankruptcy or insolvency proceeding ordering
recovery, or compelling the return, of all or a portion of the Restructure Fee
or the Profit Participation Fee, whether by fraudulent transfer, preference
action or otherwise, the deferral and contingent waiver or the waiver of the
Excess Cash Flow payments and the modification of the Profit Participation Fee
provision in Section 2.8.3 of the Loan Agreement, shall, immediately and without
notice or the taking of any other action, be null and void, and without effect,
and to the extent necessary, all rights of Lender shall be restored and
reinstated and may be immediately enforced and pursued as if the revisions to
Sections 2.8.3 and 2.9.2(a) of the Agreement had not been made. Notwithstanding
the foregoing, upon compliance with the provisions of Section 3.3 hereof, the
release of the K. Elnaggar Guarantee shall be final and not subject to
restoration or reinstatement.

     48.  APPLICABLE LAW.  THE OBLIGATIONS OF BORROWER AND KATHLEEN J. ELNAGGAR
          --------------                                              
HEREUNDER, UNDER THE LOAN AGREEMENT, AS MODIFIED HEREBY, AND UNDER THE OTHER
LOAN INSTRUMENTS, ARE TO BE PERFORMED IN, AND THIS SIXTH AMENDMENT IS, AND THE
LOAN AGREEMENT AND OTHER LOAN INSTRUMENTS HAVE BEEN, EXECUTED, DELIVERED AND
ACCEPTED IN, AND THIS SIXTH AMENDMENT, THE LOAN AGREEMENT, AS MODIFIED HEREBY,
AND THE OTHER LOAN INSTRUMENTS SHALL BE CONSTRUED IN ACCORDANCE WITH AND
GOVERNED BY THE INTERNAL LAWS AND DECISIONS OF, THE STATE OF ARIZONA (WITHOUT
REGARD FOR ITS CONFLICTS OF LAW PRINCIPLES), AND BY EXECUTION HEREOF BORROWER
AND KATHLEEN J. ELNAGGAR AND LENDER EACH AGREE THAT SUCH LAWS AND DECISIONS OF
THE STATE OF ARIZONA SHALL GOVERN THIS SIXTH AMENDMENT, THE LOAN AGREEMENT, AS
MODIFIED HEREBY, AND THE OTHER LOAN INSTRUMENTS, NOTWITHSTANDING THE FACT THAT
THERE MAY BE OTHER JURISDICTIONS WHICH MAY BEAR A REASONABLE RELATIONSHIP TO THE
TRANSACTIONS CONTEMPLATED HEREBY; PROVIDED, HOWEVER, THAT WITH RESPECT TO
PROCEDURAL AND SUBSTANTIVE MATTERS RELATING ONLY TO THE CREATION, PERFECTION AND
ENFORCEMENT BY LENDER OF ITS RIGHTS AND REMEDIES AGAINST ANY REAL OR PERSONAL
PROPERTY COLLATERAL LOCATED IN ANY STATE OTHER THAN ARIZONA, SUCH MATTERS SHALL
BE GOVERNED BY THE LAWS OF THE STATE IN WHICH SUCH PROPERTY IS LOCATED.

     _____________     _______________   ___________    ____________
     initial           initial           initial        initial


     49.  JURISDICTION AND VENUE.  BORROWER AND KATHLEEN J. ELNAGGAR HEREBY
          ----------------------                                    
AGREE THAT ALL ACTIONS OR PROCEEDINGS INITIATED BY BORROWER OR KATHLEEN J.
ELNAGGAR, OR ANY OF THEM, AND ARISING DIRECTLY OR INDIRECTLY OUT OF THE LOAN
INSTRUMENTS SHALL BE LITIGATED IN THE SUPERIOR COURT OF ARIZONA, MARICOPA COUNTY
DIVISION, OR THE UNITED STATES DISTRICT COURT FOR THE DISTRICT OF

                                     -31-
<PAGE>
 
ARIZONA OR, IF LENDER INITIATES SUCH ACTION, IN ADDITION TO THE FOREGOING
COURTS, ANY COURT IN WHICH LENDER SHALL INITIATE SUCH ACTION, TO THE EXTENT SUCH
COURT HAS JURISDICTION. BORROWER AND KATHLEEN J. ELNAGGAR HEREBY EXPRESSLY
SUBMIT AND CONSENT IN ADVANCE TO SUCH JURISDICTION IN ANY ACTION OR PROCEEDING
COMMENCED BY LENDER IN ANY OF SUCH COURTS, AND HEREBY WAIVE PERSONAL SERVICE OF
THE SUMMONS AND COMPLAINT, OR OTHER PROCESS OF PAPERS ISSUED THEREIN, AND AGREE
THAT SERVICE OF SUCH SUMMONS AND COMPLAINT OR OTHER PROCESS OR PAPERS MAY BE
MADE BY REGISTERED OR CERTIFIED MAIL ADDRESSED TO BORROWER OR KATHLEEN J.
ELNAGGAR AT THE ADDRESS TO WHICH NOTICES ARE TO BE SENT TO BORROWER PURSUANT TO
THE LOAN AGREEMENT. BORROWER AND KATHLEEN J. ELNAGGAR EACH WAIVE ANY CLAIM THAT
PHOENIX, ARIZONA OR THE DISTRICT OF ARIZONA IS AN INCONVENIENT FORUM OR AN
IMPROPER FORUM BASED ON LACK OF VENUE. SHOULD BORROWER OR KATHLEEN J. ELNAGGAR,
OR ANY OF THEM, AFTER BEING SO SERVED, FAIL TO APPEAR OR ANSWER TO ANY SUMMONS,
COMPLAINT, PROCESS OR PAPERS SO SERVED WITHIN THE NUMBER OF DAYS PRESCRIBED BY
LAW AFTER THE MAILING THEREOF, SUCH BORROWER(S) SHALL BE DEEMED IN DEFAULT AND
AN ORDER AND/OR JUDGMENT MAY BE ENTERED BY LENDER AGAINST SUCH BORROWER(S) AS
DEMANDED OR PRAYED FOR IN SUCH SUMMONS, COMPLAINT, PROCESS OR PAPERS. THE
EXCLUSIVE CHOICE OF FORUM FOR BORROWER AND KATHLEEN J. ELNAGGAR SET FORTH IN
THIS SECTION SHALL NOT BE DEEMED TO PRECLUDE THE ENFORCEMENT, BY LENDER, OF ANY
JUDGMENT OBTAINED IN ANY OTHER FORUM OR THE TAKING, BY LENDER, OF ANY ACTION TO
ENFORCE THE SAME IN ANY OTHER APPROPRIATE JURISDICTION, AND BORROWER AND
KATHLEEN J. ELNAGGAR HEREBY WAIVE THE RIGHT TO COLLATERALLY ATTACK ANY SUCH
JUDGMENT OR ACTION.

     ___________   ___________    ____________   ______________
     initial       initial        initial        initial

     50.  WAIVER OF RIGHT TO JURY TRIAL.  LENDER, BORROWER AND KATHLEEN J.
          -----------------------------                       
ELNAGGAR ACKNOWLEDGE AND AGREE THAT ANY CONTROVERSY WHICH MAY ARISE UNDER ANY OF
THE LOAN INSTRUMENTS OR WITH RESPECT TO THE TRANSACTIONS CONTEMPLATED THEREBY
WOULD BE BASED UPON DIFFICULT AND COMPLEX ISSUES AND, THEREFORE, THE PARTIES
AGREE THAT ANY LAWSUIT ARISING OUT OF ANY SUCH CONTROVERSY SHALL BE TRIED IN A
COURT OF COMPETENT JURISDICTION BY A JUDGE SITTING WITHOUT A JURY.

     _____________     ______________    ___________  ______________
     initial           initial           initial      initial

                                     -32-
<PAGE>
 
     51.  Amendment.  This Sixth Amendment and the other Loan Instruments
          ---------                                          
executed prior or pursuant hereto constitute the entire agreement between the
parties hereto with respect to the transactions contemplated hereby or thereby
and supersede any prior agreements, whether written or oral, relating to the
subject matter hereof. Except as specifically amended herein, the Loan Agreement
shall remain in full force and effect. In the event of any conflict between the
terms and provisions of this Sixth Amendment and the terms and provisions of the
Loan Agreement, the terms and provisions of this Sixth Amendment shall govern
and prevail. Nothing contained in this Sixth Amendment is intended to or shall
be construed as relieving any person or entity, whether a party to this Sixth
Amendment, or not, of any of such person's or entity's obligations to Lender.

     52.  All Loan Instruments.  Each of the other Loan Instruments is amended 
          --------------------                                        
so that any reference therein to a definition or agreement amended hereby shall
be deemed to be a reference to such definition or agreement, as applicable, as
amended hereby.


                          [THE REMAINDER OF THIS PAGE
                         IS LEFT INTENTIONALLY BLANK]

                                     -33-
<PAGE>
 
     IN WITNESS WHEREOF, this Sixth Amendment is executed as of the date first
above written.
                                    LENDER:

                                    FINOVA CAPITAL CORPORATION, a 
                                    Delaware corporation

                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________
 
                                    BORROWER:

                                    GDC ENVIRO-SOLUTIONS, INC., a 
                                    Louisiana corporation

                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________

 
                                    ____________________________________________
                                    KATHLEEN J. ELNAGGAR, AS TRUSTEE FOR THE
                                    BENEFIT OF TAREK ELNAGGAR, SHARIF JOSEPH
                                    ELNAGGAR AND JEANNE-MARIE ELNAGGAR, CREATED
                                    BY THE LAST WILL AND TESTAMENT OF HAMEED
                                    AHMED ELNAGGAR DATED MARCH 20, 1988

                                    ____________________________________________
                                    KATHLEEN JORDAN ELNAGGAR, 
                                    individually

                                    HOLDINGS:

                                    GDC HOLDINGS CORPORATION, a 
                                    Louisiana corporation

                                    By:_________________________________________
                                    Name:_______________________________________
                                    Title:______________________________________

                                     -34-
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                EXHIBIT 1.1(D)

               GDC ENVIRO-SOLUTIONS, INC. - LIST OF SHAREHOLDERS

                GDC Holdings Corporation       3,814,160 shares
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                EXHIBIT 1.1(E)

                    DESCRIPTION OF SHAREHOLDER INDEBTEDNESS


BEFORE GDC/HOLDINGS STOCK EXCHANGE:

<TABLE>
<CAPTION>
Principal Amount*        Date                       Holder
----------------         ----                       ------
<C>                  <S>                   <C>
$    700             April 23, 1991        Kathleen Elnaggar, as Trustee   
 676,825             June 19, 1991         Kathleen Elnaggar, as Trustee   
  72,000             August 14, 1991       Kathleen Elnaggar, as Trustee   
  21,000             November 14, 1991     Kathleen Elnaggar, as Trustee   
 137,212             December 18, 1992     Kathleen Elnaggar, Individually 
   8,000             September 16, 1991    Kathleen Elnaggar, As Trustee    

--------
$915,737
</TABLE>

*plus accrued interest


AFTER GDC/HOLDINGS STOCK EXCHANGE:

                                     NONE
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                EXHIBIT  5.3.1

                   DESCRIPTION OF CAPITALIZATION OF BORROWER

        Authorized Shares - 5,000,000 shares no par value common stock

BEFORE GDC/HOLDINGS STOCK EXCHANGE:

     No. of Shares Issued      Holder
     --------------------      ------

          2,111,874            K. Elnaggar
            780,157            Elnaggar Trust
            527,969            Tarek Elnaggar
            394,160            Harry C. Conger
        -----------                      

     Total  3,814,160

     No. of Warrants Issued
     ----------------------

            200,000            B. Jim Porter
            100,000            James M. Hutchinson
        -----------                          

     Total  300,000

NOTE: IN CONNECTION WITH THE GDC/HOLDINGS STOCK EXCHANGE, THE SHAREHOLDER
INDEBTEDNESS WILL BE CONVERTED TO 932,512 WARRANTS FOR THE BORROWER CAPITAL
STOCK AND 574,488 SHARES OF THE BORROWER CAPITAL STOCK, WHICH WILL THEN BE
CONVERTED TO WARRANTS AND/OR STOCK OF HOLDINGS.

AFTER GDC/HOLDINGS STOCK EXCHANGE:

     No. of Shares Issued           Holder
     --------------------           ------

          3,814,160                 GDC Holdings Corporation

     No. of Warrants Issued
     ----------------------

            None                        N/A
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                EXHIBIT  5.5.3

        BORROWER'S CHIEF EXECUTIVE OFFICE AND OTHER PLACES OF BUSINESS
                             (EXCLUDING JOB SITES)

CHIEF EXECUTIVE OFFICE:

GDC Enviro-Solutions, Inc.
822 Neosho Avenue
Baton Rouge, Louisiana  70802

OTHER OFFICE:

Sales Office (Ronald Reed)
4418 Autumn Lane
Lewiston, New York  10492

STATES IN WHICH QUALIFIED TO DO BUSINESS:

Louisiana (state of incorporation)
Mississippi
New York
Texas
South Carolina
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                EXHIBIT  5.8.A

                       PENDING OR THREATENED LITIGATION

     The following are all the actions, suits, arbitration proceedings or claims
pending or threatened against GDC:

     1.R. Troy Boone, et al v. GDC Engineering, Inc., et al, Docket No. 93-967-
          B-MS, United States District Court, Middle District of Louisiana,
          alleging personal injury of an employee of BCI Environmental
          Construction, Inc.

     2.EEOC claim filed against GDC Engineering, Inc. by Ricky LaGrange alleging
          racial discrimination.

     3.Ollie Lynn Turbeville, et al v. Rubicon, Inc., GDC Engineering, Inc., et
          al. Docket No. 54,657, 23rd Judicial District Court, Parish of
          Ascension, State of Louisiana, alleging damages, including punitive
          damages for personal injury to an employee of GDC Engineering Inc.

     4.George Arab, et al v. Thermal Process Systems, Inc., Docket No. 54,450,
          23rd Judicial District Court, Parish of Ascension, State of Louisiana,
          alleging damages for personal injury to an employee of GDC
          Engineering, Inc.

     5.EEOC Claim filed against GDC by Johnny Manual alleging age and gender
          discrimination.

     6.Ronald O. Clesi v. Pala Interstate, Inc., ABC Insurance Co., Shell Oil,
          and GDC Engineering Inc. Docket No. 44,340-C, 29th Judicial District
          Court, Parish of St. Charles, State of Louisiana, alleging damages,
          including punitive damages, for personal injury while employed by GDC
          Engineering, Inc.
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                 EXHIBIT  7.6

                     DESCRIPTION OF PERMITTED COMPENSATION

<TABLE>
<CAPTION>
                         DATE OF
                         EMPLOYMENT
OFFICERS                 AGREEMENT                     ANNUAL SALARY
--------                 ---------                     -------------
<S>                      <C>                           <C>
Kathleen J. Elnaggar     September 1, 1995                 $150,000
 
Tarek Elnaggar           September 14, 1994                $100,580
 
Harry C. Conger          December 16, 1994                 $130,000
                         Amended July 15, 1995
                         and August 21, 1995
 
Donald L. Murphy, Jr.    September 14, 1995                $ 85,580
 
Ron Reed                 March 4, 1993                 $ 104,418 increased
                                                       by COLA annually
</TABLE>


(1)  Does not include value of other benefits which are described in the
     Employment Agreements, copies of which have been provided to Lender.
<PAGE>
 
                      SIXTH AMENDMENT TO LOAN INSTRUMENTS

                     GDC ENVIRO-SOLUTIONS, INC., BORROWER
                      FINOVA CAPITAL CORPORATION, LENDER

                                  SCHEDULE 7

                               COVENANT WAIVERS

1.   Change of name to GDC Enviro-Solutions, Inc and Amendment to Bylaws to
     create office of Chief Executive Officer (Section 7.11).

2.   Execution and performance of Employment Agreements listed in Exhibit 7.6 of
     Sixth Amendment (Sections 7.6 and 7.15).

3.   Execution and performance of Agreement listed in Sections 32 and 39 of
     Sixth Amendment (Sections 7.7, 7.8, 7.12 and 7.15).

4.   Amendment or termination of any Shareholders' Agreements and Issuance of
     shares to Kathleen J. Elnaggar and Harry C. Conger, transfer of shares to
     Tarek Elnaggar, issuance of Warrants (but not shares) to Kathleen J.
     Elnaggar, B. Jim Porter and James M. Hutchinson, and execution of
     Subscription Agreement for GDC/Holdings Stock Exchange and any changes of
     control relating thereto or from the Private Placement or the Public
     Company Merger (Sections 7.13 and 7.16 and Pledge Agreement).

5.   Execution of Spectrum Consulting Agreement and amendments (Sections 7.4,
     7.8 and 7.12). The Spectrum Consulting Agreement was subsequently
     terminated.

6.   Execution of the Facilities, Technology and Production Lease dated July 1,
     1995 between NBL and Borrower, and the Employment Agreement dated July 1,
     1995 between Borrower and Jan Berkowitz, and the performance of the
     obligations of Borrower thereunder (Sections 7.4, 7.7, 7.8, and 7.12).

7.   Execution of Letter of Intent with DK Industries, Inc. (Section 7.3).

8.   Voting of shares by Existing GDC Shareholders after any Incipient Default
     or Event Of Default has occurred (Pledge Agreement).

9.   Failure to provide Notices of Defaults and Adverse Events (Section 6.3.8(b)
     and (c)).

10.  Non-monetary defaults under agreements with Working Capital Lender (Section
     6.16).

11.  Delay in payment of Excess Cash Flow for year ended November 30, 1994
     pending amendment of Loan Agreement (Section 6.13).
<PAGE>
 
12.  Late submission of Financial Statements and other information (Section
     6.3).

13.  Non-monetary defaults under agreements with LSC and Ally (Section 6.5).

14.  Late Certifications regarding environmental matters (Section 6.9).

15.  Temporary advance to officer of Borrower (subsequently repaid) (Section
     7.7.3)

16.  Failure to comply with financial standards and have required minimum
     availability (Sections 7.18, 7.19, 7.20, 7.21, 7.22 and 7.23).

17.  Extension of Lease for additional 5 years if acquisition does not occur
     (Sections 7.15 and 7.16).

18.  Failure to deliver financial statements of Kathleen J. Elnaggar (Guaranty
     and Loan Amendment).

19.  Liens existing on February 16, 1996 (Section 7.2).

20.  Possible failure to comply with Excess Cash Flow limitation with respect to
     monthly payments to Louisiana Seed Capital Fund Limited Partnership and
     Louisiana Economic Development Corporation (LSC Intercreditor Agreement,
     Section 3.2(a)).

21.  Breach of any representation or warranty relating to any matter listed
     above or otherwise expressly waived in the Sixth Amendment (Section 8.1.3).

NOTE: Unless otherwise noted, references in parentheses are to Section numbers
of existing Loan Agreement with FINOVA Capital Corporation.

                                      -2-