SECOND AMENDMENT

     THIS SECOND AMENDMENT (this "Second Amendment") dated as of June 20, 
1997 is to the Credit Agreement (the "Credit Agreement") dated as of 
September 15, 1995 between TETRA TECH, INC. (the "Company") and BANK OF 
AMERICA ILLINOIS (the "Bank").  Unless otherwise defined herein, terms 
defined in the Credit Agreement are used herein as defined therein.

     WHEREAS, the parties hereto have entered into the Credit Agreement which 
provides for the Bank to make Loans to, and to issue Letters of Credit for 
the account of, the Company from time to time; and

     WHEREAS, the parties hereto desire to amend the Credit Agreement as set 
forth below;

     NOW, THEREFORE, in consideration of the premises and for other good and 
valuable consideration (the receipt and sufficiency of which are hereby 
acknowledged), the parties hereto agree as follows:

    SECTION 1  AMENDMENTS.  Effective on (and subject to the occurrence of) 
the Second Amendment Effective Date (as defined below), the Credit Agreement 
shall be amended as follows:

    SECTION 1.1 MARGIN. The definition of "Margin" in Section 1 of the Credit 
Agreement is amended in its entirety to read as follows:

         MARGIN means (i) if the Total Debt to EBITDA Ratio is greater than
    2.00 to 1, 1.25% per annum in the case of Eurodollar Loans and Financial
    Standby Letters of Credit and 0.625% per annum in the case of Non-Financial
    Standby Letters of Credit, (ii) if the Total Debt to EBITDA Ratio is equal
    to or less than 2.00 to 1 but greater than or equal to 1.00 to 1, 1.00% per
    annum in the case of Eurodollar Loans and Financial Standby Letters of
    Credit and 0.50% per annum in the case of Non-Financial Standby Letters of
    Credit, and (iii) if the Total Debt to EBITDA Ratio is less than 1.00 to 1,
    0.75% per annum in the case of Eurodollar Loans and Financial Standby
    Letters of Credit and 0.375% per annum in the case of Non-Financial Standby
    Letters of Credit.  The Margin shall be deemed to be determined pursuant to
    CLAUSE (III) above until the first date following the effective date of the
    Second Amendment dated as of June 20, 1997 to this Agreement by which a
    compliance certificate is required to be delivered by the Company pursuant
    to SECTION 10.1.4.  If any compliance certificate required to be delivered
    by



    the Company pursuant to SECTION 10.1.4 shall give rise to any adjustment
    in the Margin pursuant to the foregoing sentence, such adjustment shall be
    effective for all Loans (including any then-outstanding Loans) on the date
    which is 45 days (90 days in the case of any certificate delivered in
    connection with the annual audit report of the Company) after the date as
    of which such certificate is prepared; PROVIDED that if any such
    certificate (together with the related financial statements) is not
    delivered on or before the date due pursuant to SECTION 10.1.4, then the
    Margin shall be 1.25% per annum in the case of Eurodollar Loans and
    Financial Standby Letters of Credit and 0.625% per annum in the case of
    Non-Financial Standby Letters of Credit from such due date until such
    certificate is delivered. 

    SECTION 1.2 REVOLVING TERMINATION DATE.  The definition of "Revolving 
Termination Date" in Section 1 of the Credit Agreement is amended by deleting 
the date "September 15, 1998" therein and substituting therefor the date "May 
30, 2000".

    SECTION 1.3  SECTION 2.1.  Section 2.1 of the Credit Agreement is amended 
in its entirety to read as follows:

         2.1  COMMITMENT OF THE BANK.  On and subject to the terms and
    conditions of this Agreement, the Bank agrees (a) to make loans to the
    Company on a revolving basis ("LOANS") from time to time before the
    Revolving Termination Date in such amounts as the Company may from time to
    time request and (b) to issue standby letters of credit containing such
    terms and conditions as shall be permitted pursuant to this Agreement and
    satisfactory to the Bank (collectively the "LETTERS OF CREDIT" and each
    individually a "LETTER OF CREDIT") for the account of the Company from time
    to time before the Revolving Termination Date in such amounts as the
    Company may from time to time request; PROVIDED, that (x) the sum of (i)
    the aggregate outstanding principal amount of all Loans PLUS (ii) the
    aggregate Stated Amount of all Letters of Credit shall not at any time
    exceed $25,000,000 (less any reductions to the Commitment made pursuant to
    SECTION 6.1) and (y) the aggregate Stated Amount of all Letters of Credit
    shall not at any one time exceed $10,000,000.

    SECTION 1.4  SECTION 2.5.  Section 2.5 of the Credit Agreement is amended 
by deleting the language "shall not be greater than one year and" in line 8 
thereof.

    SECTION 1.5  SECTION 5.1.  Section 5.1 of the Credit Agreement is amended 
by deleting the percentage "0.375%" therein and substituting therefor the 
percentage "0.25%".


                                    -2-


    SECTION 1.6  SECTION 5.2.  Section 5.2 of the Credit Agreement is amended 
in its entirety to read as follows:

         5.2 LETTER OF CREDIT FEES.  The Company agrees to pay the Bank a
    letter of credit fee for each Letter of Credit in an amount equal to (x)
    the Margin multiplied by (y) the Stated Amount of such Letter of Credit,
    payable in arrears on the last day of each calendar quarter and on the
    Revolving Termination Date for the period from and including the date of
    the issuance of such Letter of Credit to and including such date or the
    date upon which such Letter of Credit expired or was terminated.  Such
    letter of credit fee shall be computed for the actual number of days
    elapsed on the basis of a year consisting of 365 or, if applicable, 366
    days.  In addition, the Company agrees to pay all other fees of the Bank
    (at the standard rates of the Bank in effect from time to time) with
    respect to each Letter of Credit (including, without limitation, all fees
    associated with any transfer of a Letter of Credit), such fees to be
    payable on demand upon invoice by the Bank therefor.

    SECTION 1.7  SECTION 6.1.1.  Section 6.1.1 of the Credit Agreement is 
amended in its entirety to read as follows:

              6.1.1  SCHEDULED REDUCTIONS OF COMMITMENT.  The amount of the
    Commitment shall be permanently reduced on each of the following dates to
    the amounts set forth opposite such dates:

      Commitment                    Maximum 
    Reduction Date                  Commitment
    --------------                  ----------

    May 30, 1998                  $ 20,000,000
    May 30, 1999                    15,000,000.

    SECTION 1.8  SECTION 6.1.2.  Section 6.1.2 of the Credit Agreement is 
amended by deleting the amount "$1,000,000" therein and substituting therefor 
the amount "$5,000,000". 

    SECTION 1.9  SECTION 10.1.3.  Section 10.1.3 of the Credit Agreement is 
amended in its entirety to read as follows:

         10.1.3 [INTENTIONALLY OMITTED].

    SECTION 1.10  SECTION 10.6.1.  Section 10.6.1 of the Credit Agreement is 
amended in its entirety to read as follows:

         10.6.1    MINIMUM TANGIBLE NET WORTH.  Not at any time permit Tangible
    Net Worth to be less than the sum of (i) $38,000,000 PLUS (ii) 50% of
    Consolidated Net Income for each Fiscal Quarter ending after June 30, 1997
    PLUS (iii)


                                    -3-


    100% of all proceeds (net of any underwriting discounts and
    brokers' commissions) of any offering or distribution of the Company's
    common stock or of any other equity investment in the Company. 

    SECTION 1.11  SECTION 10.6.5.  Section 10.6.5 of the Credit Agreement is 
amended in its entirety to read as follows:

         10.6.6    FIXED CHARGE COVERAGE.  Not permit the ratio, for any
    Computation Period, of (i) EBITDA PLUS operating lease expense (whether or
    not paid) of the Company and its Subsidiaries for such Computation Period
    to (ii) interest expense of the Company and its Subsidiaries PLUS all
    payments on Capital Leases and operating leases (without double-counting
    with interest expense) by the Company and its Subsidiaries PLUS all
    Restricted Payments PLUS all taxes paid by the Company and its Subsidiaries
    PLUS Capital Expenditures of the Company and its Subsidiaries, in each case
    during such Computation Period, to be less than 1.25 to 1 for any
    Computation Period.

    SECTION 1.12  SECTION 10.6.6.  Section 10.6.6 of the Credit Agreement is 
amended in its entirety to read as follows:

         10.6.6 [INTENTIONALLY OMITTED].

    SECTION 1.13  SECTION 13.  Section 13 of the Credit Agreement is amended 
by adding a new Section 13.11 following Section 13.10  of the Credit 
Agreement which will read as follows:

         SECTION 13.11  CONSENT TO JURISDICTION.  THE COMPANY IRREVOCABLY
    AGREES THAT ALL ACTIONS OR PROCEEDINGS IN ANY WAY, MANNER OR RESPECT
    ARISING OUT OF OR FROM OR RELATED TO THIS AGREEMENT OR ANY LOAN DOCUMENT
    SHALL BE LITIGATED IN COURTS HAVING SITUS WITHIN THE CITY OF CHICAGO, STATE
    OF ILLINOIS.  THE COMPANY HEREBY CONSENTS AND SUBMITS TO THE JURISDICTION
    OF ANY LOCAL, STATE OR FEDERAL COURT LOCATED WITHIN SAID CITY AND STATE AND
    WAIVES PERSONAL SERVICE OF ANY AND ALL PROCESS UPON THE COMPANY, AND AGREES
    THAT ALL SUCH SERVICE OF PROCESS MAY BE MADE BY REGISTERED MAIL DIRECTED TO
    THE COMPANY AT THE ADDRESS STATED ON THE SIGNATURE PAGE HEREOF AND SERVICE
    SO MADE SHALL BE DEEMED TO BE COMPLETED UPON ACTUAL RECEIPT THEREOF.

    SECTION 1.14   EXHIBIT A.   Exhibit A to the Credit Agreement is hereby
amended in its entirety to read in the form of EXHIBIT A hereto.

    SECTION 2  CONSENT.  The Bank hereby consents to the acquisition by the 
Company of Whalen & Company, Inc. ("W&C") and


                                     -4-


Whalen Service Corps., Inc. ("Whalen Service") through a merger of W&C and 
Whalen Service with and into the Company pursuant to the Reorganization 
Agreement dated as of ________, 1997 (the "Reorganization Agreement") among 
the Company, W&C, Whalen Service and the stockholders named in the 
Reorganization Agreement the "Acquisition").

    SECTION 3  LETTERS OF CREDIT. Notwithstanding any provision of the Credit 
Agreement to the contrary, the Company and the Bank (i) agree that the Bank 
may issue Letters of Credit ("Non-Dollar LCs") in currencies other than 
Dollars, (ii) confirm that all Non-Dollar LCs previously issued under the 
Credit Agreement are deemed properly issued thereunder and (iii) further 
agree as follows with respect to such Non-Dollar LCs:

    3.1  The Company agrees that its reimbursement obligation under Section 2.6
         of the Credit Agreement in respect of any Non-Dollar LC (a) shall be
         payable in the currency in which such Non-Dollar LC was issued and (b)
         shall bear interest at a rate per annum equal to the sum of Overnight
         Rate PLUS the Margin for Eurodollar Loans PLUS 2% for each day from
         and including the disbursement date of such Non-Dollar LC to but
         excluding the date such obligation is paid in full (it being
         understood that any payment received after 12:00 noon, Chicago time,
         on any day shall be deemed received on the following Business Day).
    
    3.2  For purposes of determining whether there is availability for the
         Company to request, continue or convert any Loan, or request, extend
         or increase the face amount of any Letter of Credit, under the Credit
         Agreement, the Dollar Equivalent Amount of each Non-Dollar LC shall be
         calculated on the date such Loan is to be made, continued or converted
         or such Letter of Credit is to be issued, extended or increased.

    3.3  For purposes of determining the amount of the unused portion of the
         Commitment and letter of credit fees, the Dollar Equivalent Amount of
         any Non-Dollar LC shall be determined on each of (i) the date of an
         issuance, extension or change in the face amount of such Non-Dollar
         LC, (ii) the date of any payment by the Bank in respect of a drawing
         under such Non-Dollar LC, (iii) the last day of each calendar month
         and (iv) each day on which the Commitment is reduced.

    3.4  If, on the last day of any calendar month or any day on which the
         Commitment is reduced, the sum of the principal amount of all Loans
         plus the Stated Amount of all Letters of Credit (valuing the Stated
         Amount of any


                                     -5-


         Non-Dollar LC at the Dollar Equivalent Amount thereof as
         of such day) would exceed the Commitment, then the Company will
         immediately eliminate such excess by prepaying Loans and/or causing
         one or more Letters of Credit to be reduced or terminated.

    3.5  If, for the purposes of obtaining judgment in any court, it is
         necessary to convert a sum due in respect of any Non-Dollar LC in one
         currency into another currency, the rate of exchange used shall be
         that at which in accordance with normal banking procedures the Bank
         could purchase the first currency with such other currency on the
         Business Day preceding that on which final judgment is given.  The
         obligation of the Company in respect of any such sum due from it to
         the Bank hereunder shall, notwithstanding any judgment in a currency
         (the "Judgment Currency") other than that in which such sum is
         denominated in accordance with the applicable provisions of the
         applicable Non-Dollar LC and this letter amendment (the "Agreement
         Currency"), be discharged only to the extent that on the Business Day
         following receipt by the Bank of any sum adjudged to be so due in the
         Judgment Currency, the Bank may in accordance with normal banking
         procedures purchase the Agreement Currency with the Judgment Currency. 
         If the amount of the Agreement Currency so purchased is less than the
         sum originally due to the Bank in the Agreement Currency, the Company
         agrees, as a separate obligation and notwithstanding any such
         judgment, to indemnify the Bank against such loss.  If the amount of
         the Agreement Currency so purchased is greater than the sum originally
         due to the Bank in such currency, the Bank agrees to return the amount
         of any excess to the Company (or to any other Person who may be
         entitled thereto under applicable law).

    3.6  For purposes of the foregoing provisions of this SECTION 3, the
         following terms have the following meanings:

              DOLLAR EQUIVALENT AMOUNT means, at any time for any currency, the
         equivalent amount in Dollars as determined by the Bank at such time on
         the basis of the Spot Rate for the purchase of Dollars with such
         currency. 

              OVERNIGHT RATE means, for any day, the rate of interest per annum
         at which overnight deposits in the applicable currency, in an amount
         approximately equal to the amount with respect to which such rate is
         being determined, would be offered for such day by the London


                                     -6-


         Branch of Bank of America National Trust and Savings Association
         ("BofA") to major banks in the London or other applicable offshore
         interbank market.  The Overnight Rate for any day which is not a
         Business Day (or on which dealings are not carried on in the
         applicable offshore interbank market) shall be the Overnight Rate 
         for the preceding Business Day.

              SPOT RATE means, for any currency, the rate quoted by BofA (as
         defined in the preceding definition) for the purchase by BofA of such
         currency with another currency through its FX Trading Office at
         approximately 8:00 a.m., San Francisco time, on the date two Business
         Days prior to the date as of which the applicable foreign exchange
         computation is to be made.

    SECTION 4  COLLATERAL DOCUMENTS.  The Company and the Bank hereby agree 
that, concurrently with the transfer of any assets to the New Obligor (as 
defined below), the Company will deliver the following documents to the Bank 
(it being understood that the failure to deliver any such documents shall 
constitute an Event of Default under the Credit Agreement:

    (a) RESOLUTIONS OF NEW OBLIGOR.  Certified copies of resolutions of the 
Board of Directors of the New Obligor authorizing the execution and delivery 
of the Security Agreement,  the Security Agreement Amendment and the Guaranty 
and the performance of its obligations under each of the Amended Security 
Agreement and the Guaranty.

    (b) INCUMBENCY AND SIGNATURE CERTIFICATES OF NEW OBLIGOR.  A certificate 
of the Secretary or the Assistant Secretary of the New Obligor certifying the 
names and true signatures of the officers of the New Obligor authorized to 
execute, deliver and perform, as applicable, the Guaranty, the Security 
Agreement and all other documents to be executed in connection therewith.

    (c) GUARANTY.  A counterpart of the Guaranty duly executed by the New 
Obligor.

    (d) SECURITY AGREEMENT.  A counterpart of the Security Agreement duly 
executed by the New Obligor, together with such UCC financing statements as 
the Bank may request in order to perfect the security interest of the Bank in 
the collateral granted under the Security Agreement.

    (e) SECURITY AGREEMENT AMENDMENT.  A counterpart of the Security 
Agreement Amendment duly executed by the Company and its Subsidiaries 
(including the New Obligor).


                                    -7-


    (f) PLEDGE AGREEMENT AMENDMENT.  A counterpart of the Pledge Agreement 
Amendment duly executed by the Company, together with the share certificates 
of the New Obligor and stock powers executed in blank with respect thereto.

    (g) OPINION.  The opinion of Riordan & McKinzie, counsel to the Company 
and its Subsidiaries, in form and substance satisfactory to the Bank.

    SECTION 5  REPRESENTATIONS AND WARRANTIES.   The Company represents and 
warrants to the Bank that each warranty set forth in Section 9 of the Credit 
Agreement is true and correct as if made on the date hereof, (b) the 
execution and delivery by the Company of this Second Amendment, the New Note 
(as defined below) and the letter agreement (the "Pledge Agreement 
Amendment") dated as of June 20, 1997 amending the Pledge Agreement, the 
execution and delivery by Whalen & Company, Inc. (the "New Obligor") of the 
Security Agreement and the Guaranty, the execution and delivery by the 
Company and its Subsidiaries (including the New Obligor) of the letter 
agreement (the "Security Agreement Amendment") dated as of June 20, 1997 
amending the Security Agreement, the performance by the Company of its 
obligations under the Credit Agreement as amended hereby (as so amended, the 
"Amended Credit Agreement"), the New Note and the Pledge Agreement as amended 
by the Pledge Agreement Amendment (as so amended, the "Amended Pledge 
Agreement"), the performance by the New Obligor of its obligations under the 
Guaranty and the Security Agreement and the performance by the Company and 
its Subsidiaries (including the New Obligor) of their respective obligations 
under the Security Agreement as amended by the Security Agreement Amendment 
(as so amended, the "Amended Security Agreement") (i) are (or with respect to 
those documents to be executed and delivered as of June 20, 1997, upon the 
execution and delivery thereof will be) within the corporate powers of the 
Company and each Subsidiary (including the New Obligor), (ii) have been (or 
with respect to those documents to be executed and delivered as of June 20, 
1997, upon the execution and delivery thereof will be) duly authorized by all 
necessary corporate action, (iii) have received (or with respect to those 
documents to be executed and delivered as of June 20, 1997, upon the execution 
and delivery will have received) all necessary governmental approval and (iv) 
do not and will not contravene or conflict with any provision of law or of 
the charter or by-laws of the Company or any Subsidiary (including the New 
Obligor) or of any indenture, loan agreement or other material contract, 
order or decree which is binding upon the Company or any Subsidiary 
(including the New Obligor), (c) this Second Amendment, the Amended Credit 
Agreement, the New Note, the Pledge Agreement Amendment, the Amended Pledge 
Agreement, the Security Agreement Amendment, the Amended Security Agreement 
and the Guaranty is (or with respect to those documents to be executed and 
delivered as of June 20, 1997, upon the execution and


                                     -8-


delivery thereof will be) the legal, valid and binding obligation of the 
Company or such Subsidiary (including the New Obligor) which is party 
thereto, as applicable, enforceable against the Company or such Subsidiary 
(including the New Obligor) in accordance with its terms, except as 
enforceability may be limited by bankruptcy, insolvency or other similar laws 
of general application affecting the enforcement of creditor's rights or by 
general principles of equity limiting the availability of equitable remedies, 
(d) the Acquisition will comply in all material respects with all applicable 
legal requirements, and all necessary governmental, regulatory, shareholder 
and other consents and approvals required for the consummation of the 
Acquisition will be, prior to the consummation thereof, duly obtained and in 
full force and effect, (e) the execution and delivery of the Reorganization 
Agreement, and the consummation of the transactions contemplated thereby will 
not violate any requirement of law, and (f)  all of the representations and 
warranties of the Company and, to the best of the Company's knowledge, W&C 
and Whalen Service contained in the Reorganization Agreement are true and 
correct in all material respects as of the date such representations and 
warranties were made and as of the date of the consummation of any 
transaction under the Reorganization Agreement.

     SECTION 6  EFFECTIVENESS.  The amendments set forth in SECTION 1, and 
the consent set forth in SECTION 2, shall become effective, as of the day and 
year first above written, on such date (the "Second Amendment Effective 
Date") that the Bank shall have received (i) an amendment fee of $25,500, 
(ii) counterparts of this Second Amendment executed by the parties hereto and 
(iii) each of the following documents in form and substance satisfactory to 
the Bank:

    (a) RESOLUTIONS OF COMPANY.  Certified copies of resolutions of the Board 
of Directors of the Company authorizing the execution and delivery of this 
Second Amendment, the New Note, the Pledge Agreement Amendment, and the 
Security Agreement Amendment and the performance of its obligations under 
each of the Amended Credit Agreement, the New Note, the Amended Pledge 
Agreement and the Amended Security Agreement.

    (b) INCUMBENCY AND SIGNATURE CERTIFICATE OF COMPANY.  A certificate of 
the Secretary or the Assistant Secretary of the Company certifying the names 
and true signatures of the officers of the Company authorized to execute, 
deliver and perform, as applicable, this Second Amendment and all other 
documents to be executed in connection therewith.

    (c) NEW NOTE.  The promissory note of the Company (herein called the "New 
Note"), substantially in the form of Exhibit A to


                                     -9-


to the Credit Agreement, payable to the order of the Bank in the aggregate 
principal amount of $25,000,000.

    (d) ACQUISITION.  Evidence, satisfactory to the Bank, that the 
Acquisition has occurred or will occur concurrently with the effectiveness of 
this Second Amendment.

    (e) OPINION.  The opinion of Riordan & McKinzie, counsel to the Company 
and its Subsidiaries, in the form of ATTACHMENT I.

     SECTION 7  MISCELLANEOUS.
                -------------

     SECTION 7.1  CONTINUING EFFECTIVENESS, ETC.  As herein amended, the 
Credit Agreement shall remain in full force and effect and is hereby ratified 
and confirmed in all respects.

     SECTION 7.2  COUNTERPARTS.  This Second Amendment may be executed in any 
number of counterparts and by the different parties on separate counterparts, 
and each such counterpart shall be deemed to be an original but all such 
counterparts shall together constitute one and the same Second Amendment.

     SECTION 7.3  GOVERNING LAW.  This Second Amendment shall be a contract 
made under and governed by the internal laws of the State of Illinois.

     SECTION 7.4  SUCCESSORS AND ASSIGNS.  This Second Amendment shall be 
binding upon the Company and the Bank and their respective successors and 
assigns, and shall inure to the benefit of the Company and the Bank and the 
successors and assigns of the Bank.




                                    -10-


    Delivered at Chicago, Illinois, as of the day and year first above 
written.

                             TETRA TECH, INC.


    
                             By_________________________________
                               Title____________________________


                             BANK OF AMERICA ILLINOIS

    

                             By_________________________________
                               Title____________________________
 


Each of the undersigned hereby acknowledges and agrees to the foregoing 
Second Amendment and the Amended Credit Agreement and hereby confirms the 
continuing effectiveness of the Guaranty and the Security Agreement with 
respect to the Amended Credit Agreement.

                        

                             HSI GEOTRANS, INC.

                             By:___________________________
                             Title:________________________


                             SIMONS, LI & ASSOCIATES, INC. 

                             By:___________________________
                             Title:________________________

    

                             TETRA TECH EM, INC.

                             By:___________________________
                             Title:________________________



                                      EXHIBIT A

                                       FORM OF
                                         NOTE


$25,000,000   June 20, 1997
Chicago, Illinois

    The undersigned, for value received, promises to pay to the order of BANK 
OF AMERICA ILLINOIS, an Illinois banking corporation having its principal 
office at 231 South LaSalle Street, Chicago, Illinois (the "Bank") at the 
principal office of the Bank in Chicago, Illinois, TWENTY-FIVE MILLION 
DOLLARS or, if less, the aggregate unpaid amount of all Loans made by the 
undersigned pursuant to the Credit Agreement referred to below (as shown on 
the schedule attached hereto (and any continuation thereof) or in the records 
of the Bank), such principal amount to be payable in installments as set 
forth in the Credit Agreement.

    The undersigned further promises to pay interest on the unpaid principal 
amount of each Loan from the date of such Loan until such Loan is paid in 
full, payable at the rate(s) and at the time(s) set forth in the Credit 
Agreement. Payments of both principal and interest are to be made in lawful 
money of the United States of America.

    This Note evidences indebtedness incurred under, and is subject to the
terms and provisions of, the Credit Agreement, dated as of September 15, 1995
(herein, as amended or otherwise modified from time to time, called the "Credit
Agreement"; terms not otherwise defined herein are used herein as defined in the
Credit Agreement), between the undersigned and the Bank, to which Credit
Agreement reference is hereby made for a statement of the terms and provisions
under which this Note may or must be paid prior to its due date or its due date
accelerated.  

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




    This Note is made under and governed by the internal laws of the State of 
Illinois.

                                  TETRA TECH, INC.

                                  By:__________________________

                                     Title:____________________
















                                      -2-


Schedule Attached to Note dated June 20, 1997 of TETRA TECH, INC. payable to 
the order of BANK OF AMERICA ILLINOIS.

Date and           Date and
Amount of          Amount of
Loan or of         Repayment or of     Interest
Conversion from    Conversion into     Period/                  Unpaid
another type of    another type of     Maturity    Principal    Notation
Loan               Loan                Date         Balance     Made by

                         1.  FLOATING RATE LOANS
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________

                           2.  EURODOLLAR LOANS
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________


                                     -3-