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Exhibit 10.2

TETRA TECH, INC.

FOURTH AMENDMENT TO
NOTE PURCHASE AGREEMENT

$110,000,000
Senior Secured Notes

$92,000,000
7.28% Senior Secured Notes,
Series A, due May 30, 2011

$18,000,000
7.08% Senior Secured Notes,
Series B, due May 30, 2008

Dated as of May 12, 2005

To the Holders of the Senior Notes of
Tetra Tech, Inc. Named in the Attached Schedule I (the "Noteholders")

Ladies and Gentlemen:

        Reference is made to the Note Purchase Agreements, each dated as of
May 15, 2001, as amended by the First Amendment to Note Purchase Agreement dated
as of September 30, 2001, the Second Amendment to Note Purchase Agreement dated
as of April 22, 2003 and the Third Amendment to Note Purchase Agreement dated as
of December 14, 2004 (collectively, as in effect immediately prior to the
effectiveness hereof, the "Existing Note Agreement", and as amended hereby, the
"Note Agreement"), by and between Tetra Tech, Inc., a Delaware corporation (the
"Company"), and each of the Noteholders pursuant to which the Company issued
$92,000,000 aggregate principal amount of its 7.28% Senior Secured Notes,
Series A, due May 30, 2011 (collectively, as in effect immediately prior to the
effectiveness hereof, the "Existing Series A Notes", and as amended hereby, the
"Series A Notes") and $18,000,000 aggregate principal amount of its 7.08% Senior
Secured Notes, Series B, due May 30, 2008 (collectively, as in effect
immediately prior to the effectiveness hereof, the "Existing Series B Notes",
and as amended hereby, the "Series B Notes" and, together with the Series A
Notes, the "Notes"). Capitalized terms used and not otherwise defined herein
shall have the meanings ascribed to them in the Existing Note Agreement.

        The Company has requested that the Noteholders agree to amend certain
provisions of the Note Agreement, and the Noteholders have agreed to such
amendments on the terms and subject to the conditions set forth herein.

        In consideration of the premises and for good and valuable
consideration, the receipt and sufficiency of which are acknowledged, the
Company and the Noteholders agree as follows:

1.     AMENDMENT OF NOTE AGREEMENT

        Subject to the satisfaction of the conditions set forth in Section 4 of
this Fourth Amendment, the Noteholders and the Company hereby agree as follows:

        1.1.    Amendment of Section 1.    Section 1 of the Existing Note
Agreement is hereby amended by deleting the parenthetical expression
"(individually, a "Subsidiary Guarantor" and collectively, the "Subsidiary
Guarantors") in the seventh line thereof.

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        1.2.    Amendment of Section 7.1(a).    (a) Section 7.1(a) of the
Existing Note Agreement is hereby amended and restated to read in its entirety
as follows:

        "(a)    Interim Statements.    

        (i)    Quarterly Statements—Promptly when available, and in any event
not later than the earlier of (A) 45 days after the end of each Fiscal Quarter
(other than the last Fiscal Quarter of each Fiscal Year) and (B) one Business
Day after the date required to be filed with the SEC, duplicate copies of,

        (1)   a consolidated balance sheet of the Company and its Subsidiaries
as at the end of such quarter,

        (2)   consolidated statements of income of the Company and its
Subsidiaries for such quarter and (in the case of the second and third quarters)
for the portion of the Fiscal Year ending with such quarter, and

        (3)   consolidated statements of cash flows of the Company and its
Subsidiaries for such quarter or (in the case of the second and third quarters)
for the portion of the Fiscal Year ending with such quarter,

setting forth in each case in comparative form the figures for the corresponding
periods in the previous Fiscal Year, all in reasonable detail, prepared in
accordance with GAAP applicable to quarterly financial statements generally, and
certified by a Senior Financial Officer as fairly presenting, in all material
respects, the financial position of the companies being reported on and their
results of operations and cash flows, subject to changes resulting from year-end
adjustments, provided that delivery within the time period specified above of
copies of the Company's Quarterly Report on Form 10-Q prepared in compliance
with the requirements therefor and filed with the SEC shall be deemed to satisfy
the requirements of this Section 7.1(a)(i);

        (ii)   Monthly Statements—Promptly when available, and in any event not
later than 30 days after the end of each fiscal month in each Fiscal Year of the
Company (other than the last month of any Fiscal Quarter) ending after July 3,
2005 and prior to the Covenant Compliance Date, duplicate copies of,

        (A)  consolidated balance sheet of the Company and its Subsidiaries as
at the end of such fiscal month,

        (B)  consolidated statements of income of the Company and its
Subsidiaries for such fiscal month and for the portion of the Fiscal Year ending
with such fiscal month, and

        (C)  consolidated statements of cash flows of the Company and its
Subsidiaries for such fiscal month and for the portion of the Fiscal Year ending
with such fiscal month,

setting forth in each case in comparative form the figures for the corresponding
periods in the previous Fiscal Year, all in reasonable detail, prepared in
accordance with GAAP; and

        (iii)  Additional Current Asset Information—Contemporaneously with the
furnishing of the financial statements required pursuant to subsection
(a)(i) above,

        (A)  a summary of the accounts receivable of the Company and its
Subsidiaries (including a list of the 10 customers with the largest receivable
balances); and

        (B)  a list of bonded jobs of the Company and its Subsidiaries with a
value in excess of $1,000,000 (and specifying any related billed and unbilled
receivables with respect to such jobs), in each case as of the end of the
applicable Fiscal Quarter; and

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        (C)  an updated organizational chart listing all Subsidiaries and the
jurisdictions of their organization; and"

        (b)   Each reference in the Existing Note Agreement to "Section 7.1(a)"
is hereby amended to be a reference to "Section 7.1(a)(i)".

        1.3.    Amendment of Section 7.1(b).    Section 7.1(b) (Annual Financial
Statements) of the Existing Note Agreement is hereby amended by deleting the
phrase "within 105 days after the end of each Fiscal Year of the Company" and
replacing it with "promptly when available, and in any event not later than the
earlier of (A) 105 days after the end of each Fiscal Year and (B) one Business
Day after the date required to be filed with the SEC".

        1.4.    Amendment of Section 7.1(c).    Section 7.1(c) of the Existing
Note Agreement is hereby amended and restated to read in its entirety as
follows:

        "(c) [Intentionally Omitted]."

        1.5.    Amendment of Section 8.6.    The definition of "Remaining
Scheduled Payments" set forth in Section 8.6 of the Existing Note Agreement is
hereby amended and restated in its entirety to read as follows:

        "Remaining Scheduled Payments" means, with respect to the Called
Principal of any Note, all payments of such Called Principal and interest
thereon (calculated at the non-default rate of interest in effect with respect
to such Note immediately prior to the effectiveness of the Fourth Amendment)
that would be due after the Settlement Date with respect to such Called
Principal if no payment of such Called Principal were made prior to its
scheduled due date, provided that if such Settlement Date is not a date on which
interest payments are due to be made under the terms of the Notes, then the
amount of the next succeeding scheduled interest payment will be reduced by the
amount of interest accrued to such Settlement Date and required to be paid on
such Settlement Date pursuant to Section 8.2 or 12.1."

        1.6.    Amendment of Section 10.1.    Section 10.1 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "10.1    Adjusted Leverage Ratio; Priority Debt.

        The Company will not permit at any time:

        (a)   the Adjusted Leverage Ratio, as of the last day of any Computation
Period, to be greater than (a) 2.75 to 1 for any Computation Period ending
before April 2, 2006; (b) 2.50 to 1 for the Computation Period ending on
April 2, 2006; and (c) 2.25 to 1 for any Computation Period ending on or after
July 2, 2006.

        (b)   Priority Debt to exceed 15% of Adjusted Consolidated Net Worth."

        1.7.    Amendment of Section 10.2.    Section 10.2 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "10.2    Fixed Charge Coverage Ratio; Minimum Adjusted EBITDA.

        (a)   The Company will not permit the ratio of (i) the result of
(A) Adjusted EBITDA minus (B) Capital Expenditures, in each case for any
Computation Period described in the table below, to (ii) the sum of (A) Interest
Expense plus (B) all income taxes (including any franchise tax and any other tax
based upon gross or net income or receipts) paid by the Company and its
Subsidiaries plus (C) all required payments of principal of Indebtedness of the
Company and its Subsidiaries, in each case during such Computation Period (and

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determined on a consolidated basis), to be less than the ratio set forth
opposite such Computation Period in such table:

Computation Period

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  Ratio

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the Computation Period ending on April 2, 2006   1.05 to 1 any Computation
Period ending on or after July 2, 2006 through and including June 29, 2008  
1.10 to 1 the Computation Period ending September 28, 2008   1.15 to 1 any
Computation Period ending on or after December 28, 2008   1.25 to 1

For the avoidance of doubt, the ratio described in this Section 10.2(a) shall
not be measured prior to the Computation Period ending on April 2, 2006.

        (b)   The Company will not permit Adjusted EBITDA for any period set
forth in the table below to be less than the amount set forth opposite such
period:

Period

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  Amount

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the Fiscal Quarter ending July 3, 2005   $ 13,000,000 the period of two
consecutive Fiscal Quarters ending October 2, 2005   $ 28,000,000 the period of
three consecutive Fiscal Quarters ending January 1, 2006   $ 45,000,000 the
Computation Period ending April 2, 2006   $ 64,000,000 any Computation Period
ending on or after July 2, 2006   $ 70,000,000

        1.8.    Amendment of Section 10.3.    Section 10.3 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "10.3    Minimum Net Worth.

        The Company will not permit Net Worth at any time to be less than the
sum of (a) $245,000,000, plus (b) 50% of the sum of Consolidated Net Income for
each Fiscal Quarter, beginning with the Fiscal Quarter ending July 3, 2005 and
ending with the most recently-ended Fiscal Quarter for which the Company has
delivered financial statements (provided that if Consolidated Net Income is less
than zero for any Fiscal Quarter, for purposes of this Section 10.3,
Consolidated Net Income will be deemed to be zero for such Fiscal Quarter) plus
(c) 100% of the Net Cash Proceeds of any equity issued by the Company or any
Subsidiary (on a consolidated basis) after April 3, 2005."

        1.9.    Amendment of Section 10.4.    Section 10.4 (Liens) of the
Existing Note Agreement is hereby amended by deleting the parenthetical
expression in the second line thereof "(unless, concurrently with the
incurrence, assumption or creation of such Lien, the Company makes, or causes to
be made, effective provision whereby the Notes are equally and ratably secured
by a Lien on the same property or assets, including the execution of an
intercreditor agreement, in form and substance satisfactory to holders of the
Notes, between such holders and the holders of other Debt secured by a Lien in
such property)".

        1.10.    Amendment of Section 10.5.    Section 10.5 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "10.5    Asset Dispositions.

        The Company will not, and will not permit any Subsidiary to, sell,
transfer, convey, lease or otherwise dispose of, or grant options, warrants or
other rights with respect to, any of its assets, or sell, assign, pledge or
otherwise transfer any receivables, contract rights, general intangibles,
chattel paper or instruments, with or without recourse, except for
(a) dispositions of inventory or obsolete assets in the ordinary course of
business consistent with past practices and (b) other dispositions of

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assets, provided that (i) no disposition described in this clause (b) shall be
made if a Default or Event of Default exists or would result therefrom; and
(ii) after giving effect to any disposition pursuant to this clause (b), the
aggregate fair market value of all assets disposed of pursuant to this
clause (b) shall not exceed (x) at any time from and after July 21, 2004, 2.5%
of Consolidated Total Assets as of the end of the most recent Fiscal Year, and
(y) $10,000,000 in any Fiscal Year."

        1.11.    Amendment of Section 10.6.    Section 10.6 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "10.6    Mergers and Consolidations; Acquisitions.

        The Company will not, and will not permit any Subsidiary to, be a party
to any merger or consolidation, or purchase or otherwise acquire all or
substantially all of the assets or any stock of any class of, or any partnership
or joint venture interest in, any other Person (or of any division or business
unit of any Person), except (a) any such merger or consolidation of or by any
wholly-owned Subsidiary into the Company or any other Wholly-Owned Subsidiary,
(b) any such purchase or other acquisition by the Company or any Wholly-Owned
Subsidiary of the assets or stock of any Wholly-Owned Subsidiary, and
(c) acquisitions of all of the assets or stock of Persons which are in the same
or a similar line of business as the Company and its Subsidiaries; provided that
any acquisition described in this clause (c) must satisfy all of the following
conditions: (i) each Person so acquired shall comply with all of the terms of
this Agreement and the other Financing Documents that are applicable to such
Person; (ii) either the required majority of the board of directors (or other
equivalent governing body) of the Person so acquired incumbent at the time such
acquisition is proposed has acquiesced to the acquisition, or the acquisition is
otherwise deemed in the reasonable judgment of the Required Holders to be a
"friendly" acquisition; (iii) no Default or Event of Default shall have occurred
and be continuing at the time of, or would result from the making of, such
acquisition; (iv) the aggregate consideration (including assumed debt and stock
of the Company) for any one such acquisition or series of such related
acquisitions shall not exceed (A) during the period beginning April 3, 2005 and
continuing through April 2, 2006, $5,000,000; and (B) thereafter, $50,000,000;
(v) if such acquisition is made after April 2, 2006, then the Company's Adjusted
Leverage Ratio shall have been less than 1.75 to 1 as of the last day of the
most recently ended Fiscal Quarter for which financial statements are available
pursuant to Section 7.1(a); and (vi) substantially contemporaneously with any
such acquisition of stock, the Company shall grant, or cause the applicable
Person(s) to grant, to the Collateral Agent, for the benefit of the holders of
Notes, a first priority perfected security interest in all of the stock so
acquired."

        1.12.    Amendment of Section 10.7.    Section 10.7 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "Section 10.7    Disposition of Stock of Subsidiaries.

        (a)   The Company will not permit any Subsidiary to issue its capital
stock, or any warrants, rights or options to purchase, or securities convertible
into or exchangeable for, such capital stock, to any Person other than the
Company or another Wholly Owned Subsidiary, except (i) for directors' qualifying
shares, (ii) to satisfy local ownership requirements, (iii) in satisfaction of
valid preemptive or contractual rights of minority stockholders in connection
with the simultaneous issuance to the Company or a Subsidiary whereby the
Company and its Subsidiaries maintain the same proportionate ownership interest
and (iv) the issuance of stock convertible into stock of the Company by Tetra
Tech Canada Ltd. in connection with an acquisition.

        (b)   The Company will not, and will not permit any Subsidiary to, sell,
transfer or otherwise dispose of any shares of capital stock of a Subsidiary,
except (i) for directors'

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qualifying shares, (ii) to satisfy local ownership requirements, (iii) the sale
of all shares of capital stock of a Subsidiary which is permitted under
Section 10.5 and (iii) stock convertible into stock of the Company by Tetra Tech
Canada Ltd. in connection with an acquisition.

        (c)   If a Subsidiary at any time ceases to be such as a result of a
sale or issuance of its capital stock, any Liens on property of the Company or
any other Subsidiary securing Indebtedness owed to such Subsidiary, which is not
contemporaneously repaid, together with such Indebtedness, shall be deemed to
have been incurred by the Company or such other Subsidiary, as the case may be,
at the time such Subsidiary ceases to be a Subsidiary."

        1.13.    Amendment of Section 10.8.    Section 10.8 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follows:

        "Section 10.8    Excluded Subsidiaries.

        The Company shall not permit the Excluded Subsidiaries, collectively, to
(a) own at any time more than 2.5% of Consolidated Total Assets, (b) have more
than 2.5% of the consolidated revenues of the Company and its Subsidiaries in
any Fiscal Quarter or (c) be liable for more than 2.5% of the consolidated
liabilities of the Company and its Subsidiaries. For purposes of this
Section 10.8, all intercompany assets, revenues and liabilities that would be
properly eliminated in consolidation shall be deemed to be zero."

        1.14.    Additional Covenants to be Added to Section 10.    The
following new Sections are hereby added to the Existing Note Agreement
immediately following Section 10.10 thereof to read in their entireties as
follows:

        "Section 10.11    Limitations on Indebtedness.

        The Company will not, and will not permit any Subsidiary to, create,
incur, assume or suffer to exist any Indebtedness, except:

        (a)   obligations arising under the Financing Documents;

        (b)   Indebtedness in respect of Capital Leases;

        (c)   unsecured Indebtedness of Subsidiaries to the Company or to any
other Subsidiary;

        (d)   Hedging Agreements entered into by the Company or any Subsidiary
with the Collateral Agent or any Bank or any Affiliate thereof; provided that
all such Hedging Agreements are entered into to protect against bona fide
business risks and not for speculation;

        (e)   Guaranties in respect of any obligation of the Company or any
Subsidiary permitted under this Agreement;

        (f)    Indebtedness in respect of taxes, assessments or governmental
charges to the extent that payment thereof shall not at the time be required to
be made in accordance with Section 9.4;

        (g)   Indebtedness outstanding on the date hereof or hereafter incurred
in connection with Liens permitted by Section 10.4, and extensions, renewals and
refinancings of any Indebtedness described in this clause (g) so long as the
principal amount thereof is not increased;

        (h)   Subordinated Indebtedness;

        (i)    Indebtedness under the Credit Agreement;

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        (j)    Indebtedness constituting a portion of the deferred purchase
price for any acquisition permitted by Section 10.6(c); and

        (k)   other Indebtedness not exceeding in the aggregate $10,000,000."

        "Section 10.12    Restricted Payments.

        The Company will not, and will not permit any Subsidiary to, (a) declare
or pay any dividends on any of its capital stock (other than stock dividends),
(b) purchase or redeem any such stock or any warrants, units, options or other
rights in respect of such stock, (c) make any other distribution to
shareholders, (d) prepay, purchase, redeem or defease any Subordinated
Indebtedness, (e) make any payment on or in respect of any Subordinated
Indebtedness (other than scheduled payments of interest made in the form of
additional Subordinated Indebtedness or common stock), or (f) set aside funds
for any of the foregoing; provided that (i) any Subsidiary may declare and pay
dividends to the Company or to any other Wholly-Owned Subsidiary and (ii) so
long as no Default or Event of Default exists or would result therefrom and,
after giving effect thereto (and any incurrence of Indebtedness in connection
therewith), the Adjusted Leverage Ratio will be less than 1.75 to 1, the Company
may, at any time after April 2, 2006, repurchase shares of its capital stock for
immediate retirement in an aggregate amount, for all such repurchases made on or
after July 21, 2004, not to exceed 10.0% of Net Worth (measured as of the end of
the Fiscal Quarter immediately preceding any such purchase)."

        "Section 10.13    Loans and Advances.

        The Company will not, and will not permit any Subsidiary to, make any
loan or advance; except for (i) loans or advances by the Company to any
Subsidiary or by any Subsidiary to the Company, (ii) loans and advances to
officers and employees of the Company and its Subsidiaries for travel,
entertainment, relocation and similar ordinary business purposes in an aggregate
amount not exceeding $500,000 at any time outstanding and (iii) other loans and
advances in an aggregate amount not exceeding $5,000,000 at any time
outstanding."

        "Section 10.14    Minimum Revolver Availability.

        The Company will not, at any time, permit the Commitment Amount (as
defined in the Credit Agreement) to be less than $125,000,000. The terms of the
Commitment (as defined in the Credit Agreement) shall be as set forth in the
Credit Agreement on the Fourth Amendment Effective Date, or shall be on such
other terms as are reasonably satisfactory to the Required Holders."

        "Section 10.15    Most Favored Lender Status.

        If at any time the Company or any Subsidiary is a party to or shall
enter into any agreement, instrument or other document (excluding the Credit
Agreement, as in effect on the Fourth Amendment Effective Date) relating to
Indebtedness of the Company or such Subsidiary (each such agreement, instrument
or other document herein referred to as a "More Favorable Lending Agreement"),
which agreement, instrument or other document includes covenants (whether
affirmative or negative, and whether maintenance or incurrence) or defaults or
events of default (excluding any customary covenant or default relating to
collateral contained in any agreement, instrument or document secured by Liens
permitted by Section 10.4(e) or (h)) that are more restrictive than those
contained in this Agreement or are not provided for in this Agreement (each such
covenant or default or event of default herein referred to as "More Favorable
Provision"), then the Company shall promptly, and in any event within 5 Business
Days of entering into or becoming party to any such More Favorable Lending
Agreement (or within 5 Business Days of obtaining knowledge of any More
Favorable Lending Agreement), so advise and notify each holder of a Note in
writing. Such writing shall include a verbatim statement of such More Favorable
Provision. Thereupon, unless waived in writing by the Required Holders within 5
Business Days of

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such holders' receipt of such notice, such More Favorable Provision shall be
deemed incorporated by reference in this Agreement as if set forth fully herein,
mutatis mutandis, effective as of the date when such More Favorable Provision
became effective under such More Favorable Lending Agreement (each such More
Favorable Provision as incorporated herein is herein referred to as an
"Incorporated Provision") and no such Incorporated Provision may thereafter be
waived, amended or modified under this Agreement without the prior written
consent of the Required Holders. Thereafter, upon the request of the Required
Holders, the Company and the Required Holders shall enter into an additional
agreement or an amendment to this Agreement (as the Required Holders may
request), evidencing the incorporation of such Incorporated Provision
substantially as provided for in such More Favorable Lending Agreement;
provided, that no such additional agreement or amendment shall in any way be
required to make each Incorporated Provision effective. Each Incorporated
Provision shall (i) remain unchanged herein notwithstanding any subsequent
waiver, amendment or other modification of the More Favorable Lending Agreement
giving rise to such Incorporated Provision (except to the extent that an
amendment or other modification results in such provision being more restrictive
than such Incorporated Provision, in which case such Incorporated Provision
shall be amended or modified to become equally restrictive), and (ii) be deemed
deleted from this Agreement at such time as the applicable More Favorable
Lending Agreement shall be fully terminated and no amounts shall be outstanding
thereunder so long as at the time such More Favorable Lending Agreement shall
have been so terminated no Default or Event of Default exists hereunder."

        "Section 10.16    Further Assurances.

        The Company shall take, and cause each Subsidiary to take, such actions
as are necessary, or as the Required Holders or the Collateral Agent may
reasonably request, from time to time (including the execution and delivery of
guaranties, security agreements, pledge agreements, control agreements,
financing statements and other documents, the filing or recording of any of the
foregoing, the delivery of stock certificates and other collateral with respect
to which perfection is obtained by possession, the execution and delivery of
appropriate stock powers or other transfer instruments and the delivery of
appropriate legal opinions with respect to any of the foregoing) to ensure that
(i) the obligations of the Company hereunder and under the other Financing
Documents are (x) secured by all account receivables of the Company, all equity
interests in Subsidiaries owned by the Company and all of the Company's cash,
deposit accounts, investment property and financial assets and all proceeds of
the foregoing and (y) unconditionally guaranteed by all Subsidiaries (including,
promptly upon the acquisition or creation thereof, any Subsidiary acquired or
created after the date hereof) by execution of a counterpart of the Subsidiary
Guaranty; and (ii) the obligations of each Subsidiary under the Subsidiary
Guaranty are secured by all account receivables of such Subsidiary, all equity
interests in other Subsidiaries owned by such Subsidiary and all of such
Subsidiary's cash, deposit accounts, investment property and financial assets
and all proceeds of the foregoing; provided that unless the Required Holders
otherwise request in writing, (a) no Foreign Corporation (as defined below) or
Excluded Subsidiary shall be required to execute the Subsidiary Guaranty, pledge
any equity interest or grant a security interest in any property; and
(b) neither the Company nor any Subsidiary shall be required to pledge more than
65% of the stock of any Foreign Corporation. For purposes of the foregoing,
(A) a "Foreign Corporation" is any corporate Subsidiary which is incorporated in
a jurisdiction other than, and does substantially all of its business outside
of, the United States, and (B) the terms "investment property" and "financial
assets" shall have the respective meanings given to them in the Uniform
Commercial Code of any applicable jurisdiction."

        "Section 10.17    Quarterly Conference Call.

        Within 45 days following the end of each Fiscal Quarter, beginning with
the Fiscal Quarter ending July 3, 2005 and continuing through the Fiscal Quarter
ending April 2, 2006, the Company, in consultation with the holders of Notes and
the Banks, shall arrange a conference call with the holders of Notes and the
Banks during which Senior Financial Officers of the Company shall review the
consolidated financial and operating results of the Company for such Fiscal
Quarter and such other information regarding the financial condition,
operations, business, assets or prospects of the Company and its Subsidiaries as
any holder of Notes may reasonably request."

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        "Section 10.18    Unconditional Purchase Obligations.

        The Company will not, and will not permit any Subsidiary to, enter into
or be a party to any contract for the purchase of materials, supplies or other
property or services, if such contract requires that payment be made by it
regardless of whether or not delivery is ever made of such materials, supplies
or other property or services; provided that the Company or any Subsidiary may
enter into any such contract so long as (i) the aggregate amount of all payments
to be made under such contract does not exceed $2,000,000 and (ii) the aggregate
amount of all payments to be made under all such contracts in any Fiscal Year by
the Company and its Subsidiaries does not exceed $5,000,000."

        "Section 10.19    Inconsistent Agreements.

        The Company will not, and will not permit any Subsidiary to, enter into
any material agreement containing any provision which (a) would be violated or
breached by the performance by the Company or any Subsidiary of any of its
obligations hereunder or under any other Financing Document, (b) would prohibit
the Company or any Restricted Subsidiary from granting to the Collateral Agent,
for the benefit of the holders of Notes and certain other parties, a Lien on any
of its assets (other than (i) the Credit Agreement and (ii) customary negative
pledge provisions arising in connection with Liens permitted by Section 10.4(e)
and (h) that apply only to the specific property subject to any such Lien and
the proceeds thereof) or (c) would prevent any Subsidiary from paying cash
dividends, or making other cash distributions, to its parent."

        1.15.    Amendments of Section 11—Events of Default.    

        (a)   Section 11(c) is hereby amended and restated in its entirety to
read as follows:

        "(c) the Company defaults in the performance of or compliance with, any
term contained in Section 7.1(e), Section 9.5, any of Sections 10.1 through
10.19, inclusive; or".

        (b)   Section 11(l) is hereby amended by deleting the period at the end
of such section and replacing it with "; or".

        (c)   new Sections 11(m), 11(n) and 11(o) are hereby added to Section 11
immediately following Section 11(l) to read in their entireties as follows:

        "(m) default in the payment when due, or in the performance or
observance of, any material obligation of, or material condition agreed to by,
the Company or any Subsidiary Guarantor with respect to any purchase or lease of
goods or services exceeding $5,000,000 (except only to the extent that the
existence of any such default is being contested by the Company or such
Subsidiary in good faith and by appropriate proceedings and appropriate reserves
have been made in respect of such default); or"

        "(n) any Change in Control shall occur; or"

        "(o) the Company shall fail to comply with or to perform any covenant
incorporated herein pursuant to Section 10.15 and such failure shall continue
beyond any applicable grace period specified in the applicable More Favorable
Lending Agreement; or any event shall occur or condition shall exist that
(subject to the giving of any notice and/or the lapse of any applicable grace
period specified in the applicable More Favorable Lending Agreement) constitutes
an event of default under any provision of any More Favorable Lending Agreement
incorporated herein pursuant to Section 10.15.".

9

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        1.16.    Amendment of Section 22.1.    Section 22.1 of the Existing Note
Agreement is hereby amended and restated to read in its entirety as follow:

        "22.1.    Release of Subsidiary Guarantors and Subsidiary Stock.

        You and each subsequent holder of a Note agree to, and to direct the
Collateral Agent to, release any Subsidiary Guarantor from the Subsidiary
Guaranty or the capital stock of any Subsidiary Guarantor from the Pledge
Agreement (i) if such Subsidiary Guarantor ceases to be a Subsidiary as a result
of a sale, lease, transfer or other disposal of assets (including by way of
merger) permitted by Section 10.5, 10.6 or 10.7 or (ii) at such time as the
Banks direct the Collateral Agent to release such Subsidiary from the Subsidiary
Guaranty or release such capital stock from the Pledge Agreement; provided,
however, that you and each subsequent holder will not be required to release a
Subsidiary Guarantor from the Subsidiary Guaranty or the capital stock of a
Restricted Subsidiary from the Pledge Agreement under the circumstances
contemplated by clause (ii), if (A) a Default or Event of Default has occurred
and is continuing, (B) such Subsidiary Guarantor is to become a borrower under
the Credit Agreement or (C) such release is part of a plan of financing that
contemplates such Subsidiary Guarantor guaranteeing, or the capital stock of
such Subsidiary Guarantor securing, any other Indebtedness of the Company. Your
obligation to release a Subsidiary Guarantor from the Subsidiary Guaranty or the
capital stock of a Subsidiary Guarantor from the Pledge Agreement is conditioned
upon your prior receipt of a certificate from a Senior Financial Officer of the
Company stating that none of the circumstances described in clauses (A), (B) and
(C) above are true."

        1.17.    Schedule B—Additions and Modifications.    The following
definitions in Schedule B to the Note Agreement are amended to read in their
entirety, or are added to such Schedule B, in each case in appropriate
alphabetical order, as follows:

        "Applicable Interest Rate" means, a per annum interest rate equal to

        (a)   prior to the Fourth Amendment Effective Date and from and after
the Covenant Compliance Date, with respect to the Series A Notes, 7.28%, and
with respect to the Series B Notes, 7.08%, and

        (b)   from and after the Fourth Amendment Effective Date to and
including the Covenant Compliance Date, with respect to the Series A Notes,
8.28%, and with respect to the Series B Notes, 8.08%.

        "Adjusted EBITDA" means, for any period, the sum of Adjusted
Consolidated Net Income for such period, plus, to the extent deducted in
determining such Adjusted Consolidated Net Income, (x) federal, state, local and
foreign income, value added and similar taxes, (y) Interest Expense and
(z) depreciation and amortization expense; provided that Adjusted EBITDA shall
be calculated on a pro forma basis (in accordance with Article 11 of
Regulation S-X of the SEC) giving effect to (a) any acquisition made by the
Company or any Subsidiary during such period so long as, and to the extent that,
(i) the Company delivers to each holder of Notes a summary in reasonable detail
of the assumptions underlying, and the calculations made, in computing Adjusted
EBITDA on a pro forma basis and (ii) the Required Holders do not object to such
assumptions and/or calculations within 10 Business Days after receipt thereof;
and (b) any divestiture of a Subsidiary, division or other operating unit made
during such period. If the Company or any Subsidiary makes any acquisition of a
Person or assets which would result in a negative adjustment to Adjusted EBITDA
for any period, the Company shall, upon request of the Required Holders, deliver
the information required pursuant to clause (a)(i) of the preceding sentence so
that the calculation of Adjusted EBITDA will give effect to such acquisition.
Notwithstanding any other provision of this Agreement, (A) Adjusted EBITDA for
the Computation Period ending July 3, 2005 shall be equal to Adjusted EBITDA for
the Fiscal Quarter ending on such date multiplied by four; (B) Adjusted

10

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EBITDA for the Computation Period ending October 2, 2005 shall be equal to
Adjusted EBITDA for period of two consecutive Fiscal Quarters ending on such
date multiplied by two; and (C) Adjusted EBITDA for the Computation Period
ending January 1, 2006 shall be equal to Adjusted EBITDA for the period of three
consecutive quarters ending on such date multiplied by 11/3.

        "Change in Control" means that (a) any Person or group (within the
meaning of Rule 13d-5 of the SEC under the Securities Exchange Act of 1934 as
amended) shall become the beneficial owner (as defined in Rule 13d-3 of the SEC
under the Securities Exchange Act of 1934 as amended) of 20% or more of the
Voting Stock of the Company or (b) a majority of the members of the board of
directors of the Company shall cease to be Continuing Members.

        "Continuing Member" means a member of the board of directors of the
Company who either (a) was a member of the Company's board of directors on the
date hereof and has been such continuously thereafter or (b) became a member of
such board of directors after the date hereof and whose election or nomination
for election was approved by a vote of the majority of the Continuing Members
then members of the Company's board of directors.

        "Covenant Compliance Criteria" means the completion by the Company and
its Subsidiaries of three consecutive Fiscal Quarters (the first of which can
not be any earlier than July 3, 2005) in respect of which, as of the end of each
such Fiscal Quarter, both:

        (a)   the Adjusted Leverage Ratio set forth in Section 10.1(a) for the
Computation Periods ending at such times is less than or equal to 2.25 to 1; and

        (b)   the Fixed Charge Coverage Ratio set forth in Section 10.2 for the
Computation Periods ending at such times is equal to or greater than 1.25 to 1.

        "Covenant Compliance Date" means the date after the Covenant Compliance
Criteria have been met on which the holders of Notes receive the certificate of
a Senior Financial Officer described in Section 7.2 demonstrating compliance
with the Covenant Compliance Criteria as of the Fiscal Quarter then most
recently ended.

        "Excluded Subsidiary" means any Subsidiary designated as such on
Schedule II to the Fourth Amendment and any other Subsidiary designated in
writing by the Company to the holders of Notes.

        "Financing Documents" means this Agreement, the Notes, the Subsidiary
Guaranty, the Pledge Agreement, the Security Agreement and each other agreement,
document or instrument pursuant to which the Company or any Subsidiary Guarantor
grants collateral to the Collateral Agent for the benefit of the holders of
Notes and certain other parties."

        "Fourth Amendment" means that certain Fourth Amendment to Note Purchase
Agreement, dated as of May 12, 2005, among the Company and the holders of Notes
party thereto.

        "Fourth Amendment Effective Date" means May 12, 2005.

        "Incorporated Provision" is defined in Section 10.15.

        "More Favorable Lending Agreement" is defined in Section 10.15.

        "More Favorable Provision" is defined in Section 10.15.

        "Net Cash Proceeds" means, with respect to any issuance of equity
securities by the Company or any Subsidiary, the aggregate cash proceeds
received by the Company or such Subsidiary pursuant to such issuance, net of the
direct costs relating to such issuance (including sales and underwriter's
discounts and commissions and legal, accounting and investment banking fees).

11

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        "Net Worth" means, at any time, the consolidated stockholders' equity of
the Company and its Subsidiaries determined at such time in accordance with
GAAP.

        "Priority Debt" means, as of any date, the sum (without duplication) of
(a) outstanding Indebtedness of Subsidiaries that are not Subsidiary Guarantors
(other than Indebtedness owed to the Company or another Subsidiary) and
(b) Indebtedness of the Company and its Subsidiaries secured by Liens not
otherwise permitted by Sections 10.4(a) through (i).

        "SEC" means the Securities and Exchange Commission of the United States
of America.

        "Security Agreement" means the Second Amended and Restated Security
Agreement, dated as of May 12, 2005, among the Company, certain Subsidiaries and
the Collateral Agent, as amended, restated, supplemented or otherwise modified
from time to time."

        "Subsidiary Guarantor" means any Subsidiary that has entered into the
Subsidiary Guaranty (or shall have been required under the terms of
Section 10.16 to have entered into the Subsidiary Guaranty), whether in
connection with the Closing or thereafter pursuant to the Company's obligations
under Section 10.16 or otherwise.

        "Subordinated Indebtedness" means Indebtedness of the Company having
maturities and other terms, and which is subordinated to the obligations of the
Company and its Subsidiaries hereunder and under the other Financing Documents
in a manner, approved in writing by the Required Holders.

        "Wholly Owned Subsidiary" mean, at any time, any Subsidiary 100% of all
of the equity interests and voting interests (except directors' qualifying
shares) of which are owned by any one or more of the Company and the Company's
other Wholly Owned Subsidiaries at such time.

        1.18.    Schedule B—Deleted Definitions.    

        (a)   Deletions. The following definitions in Schedule B to the Existing
Note Agreement are hereby deleted:

        Disposition

        Excluded Sale and Leaseback Transactions

        Restricted Subsidiary

        Significant Subsidiary

        Unrestricted Subsidiary

        (b)   Treatment of Certain Deleted Definitions in Note Purchase
Agreement.

        (i)    "Restricted Subsidiary" and "Restricted Subsidiaries". Each
reference in the Existing Note Purchase Agreement to "Restricted Subsidiary" and
"Restricted Subsidiaries", other than any such reference in Section 11 thereof,
is hereby amended to be, and shall hereafter be deemed to be, a reference to
"Subsidiary" and "Subsidiaries" (including, any such reference contained within
the defined terms "Wholly-Owned Restricted Subsidiary" and "Wholly-Owned
Restricted Subsidiaries"), as applicable. Any such reference in Section 11 of
the Existing Note Agreement is hereby amended to be, and shall hereafter be
deemed to be, a reference to "Subsidiary Guarantor" or "Subsidiary Guarantors",
as applicable.

        (ii)   "Significant Subsidiary". Each reference in the Existing Note
Purchase Agreement to "Significant Subsidiary" and "Significant Subsidiaries" in
the Existing Note Agreement, is hereby amended to be, and shall hereafter be
deemed to be, a reference to "Subsidiary Guarantor" and "Subsidiary Guarantors",
as applicable.

12

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2.     AMENDMENT OF NOTES

        Subject to the satisfaction of the conditions set forth in Section 4 of
this Fourth Amendment, the Noteholders and the Company hereby agree as follows:

        2.1.    The Series A Notes.    The Existing Series A Notes shall be
deemed to be, automatically and without any further action, amended and restated
in their entirety as set forth on Exhibit 1A; except that the date, registration
number and principal amount set forth in each Existing Series A Note shall
remain the same.

        2.2.    The Series B Notes.    The Existing Series B Notes shall be
deemed to be, automatically and without any further action, amended and restated
in their entirety as set forth on Exhibit 1B; except that the date, registration
number and principal amount set forth in each Existing Series B Note shall
remain the same.

3.     REAFFIRMATION; REPRESENTATIONS AND WARRANTIES

        3.1.    Reaffirmation of Note Agreement.    The Company reaffirms its
agreement to comply with each of the covenants, agreements and other provisions
of the Note Agreement and the Notes, including the amendment of such provisions
effected by this Fourth Amendment.

        3.2.    Note Agreement.    The Company represents and warrants that the
representations and warranties contained in the Note Agreement are true and
correct as of the date hereof, except (a) to the extent that any of such
representations and warranties specifically relate to an earlier date, (b) for
such changes, facts, transactions and occurrences that have arisen since
September 30, 2001 in the ordinary course of business, (c) for such other
matters as have been previously disclosed in writing by the Company (including
in its financial statements and notes thereto) to the Noteholders and (d) for
other changes that could not reasonably be expected to have a Material Adverse
Effect.

        3.3.    No Default or Event of Default.    After giving effect to the
amendments contemplated hereby, there will exist no Default or Event of Default.

        3.4.    Authorization and Enforceability.    The execution, delivery and
performance by the Company of this Fourth Amendment and the Amended Security
Agreement (and the performance by its Subsidiaries of their obligations under
the Subsidiary Guaranty, the Pledge Agreement and the Amended Security
Agreement, in each case after giving effect to this Fourth Amendment) have been
duly authorized by all necessary corporate action and, except as provided
herein, do not require any registration with, consent or approval of, notice to
or action by, any Person (including any Governmental Authority) in order to be
effective and enforceable. The Note Agreement, the Notes, the Fourth Amendment,
the Pledge Agreement, the Security Agreement and the Subsidiary Guaranties each
constitute the legal, valid and binding obligations of the Company and each
Subsidiary party thereto, enforceable in accordance with their respective terms,
except as such enforceability may be limited by (i) applicable bankruptcy,
insolvency, fraudulent conveyance, reorganization, moratorium or other similar
laws affecting the enforcement of creditors' rights generally and (ii) general
principles of equity (regardless of whether such enforceability is considered in
a proceeding in equity or at law).

4.     EFFECTIVE DATE

        This Fourth Amendment shall become effective as of the date set forth
above upon the satisfaction of the following conditions:

        4.1.    Consent of Noteholders to Fourth Amendment.    Execution by the
Noteholders of at least a majority of the aggregate principal amount of the
Notes outstanding and receipt by the Noteholders of a counterpart of this Fourth
Amendment duly executed by the Company.

13

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        4.2.    Amendment to Security Agreement.    The Company, its
Subsidiaries and the Collateral Agent shall have entered into a Second Amended
and Restated Security Agreement, in the form attached hereto as Exhibit 2 (the
"Amended Security Agreement"), and the Noteholders shall have received a duly
executed copy thereof.

        4.3.    Opinion of Counsel.    The Company shall have delivered to the
Noteholders an executed opinion of counsel addressed to them in the form
attached hereto as Exhibit 3.

        4.4.    Amendment Fee.    Each Noteholder shall have received payment of
an amendment fee equal to 0.35% of the principal amount of the outstanding Notes
held by such Noteholder.

        4.5.    Expenses.    The Company shall have paid all fees and expenses
of special counsel to the Noteholders contemplated by Section 5.8 (to the extent
then billed).

        4.6.    Credit Agreement.    The Required Banks (as defined in the
Credit Agreement) and the Company shall have entered into a Second Amendment to
the Credit Agreement in form and substance satisfactory to the Noteholders, and
the Noteholders shall have received an executed copy of such amendment.

5.     MISCELLANEOUS

        5.1.    Ratification.    Except as amended hereby, the Note Agreement,
including the representations and warranties contained therein, shall remain in
full force and effect and is ratified, approved and confirmed in all respects as
of the date hereof.

        5.2.    Effect of Agreement.    Except as expressly provided herein,
(a) no terms or provisions of the Note Agreement or any other agreement are
waived, modified or changed by this Fourth Amendment, and (b) the terms of this
Fourth Amendment shall not operate as a waiver or amendment by the Noteholders
of, or otherwise prejudice the Noteholders' rights, remedies or powers under,
the Note Agreement or under any applicable law, and all of such rights, remedies
and powers are hereby expressly reserved.

        5.3.    Temporary Waiver.    The Required Holders hereby waive through
June 15, 2005 any non-compliance with Section 10.16 of the Note Agreement
resulting from non-perfection of the Collateral Agent's security interest in
cash, deposit accounts, investment property and financial assets so long as the
Company is diligently taking such actions as are necessary, or as the Collateral
Agent or the Required Holders may reasonably request, to perfect such security
interests.

        5.4.    Reference to the Note Agreement.    Upon the final effectiveness
of this Fourth Amendment, each reference in the Note Agreement and in other
documents describing or referencing the Note Agreement to the "Agreement," "Note
Agreement," "hereunder," "hereof," "herein," or words of like import referring
to the Note Agreement, shall mean and be a reference to the Note Agreement, as
amended hereby.

        5.5.    Binding Effect.    This Fourth Amendment shall be binding upon
and inure to the benefit of the respective successors and assigns of the parties
hereto.

        5.6.    Governing Law.    This Fourth Amendment shall be governed by and
construed in accordance with Illinois law.

        5.7.    Counterparts.    This Fourth Amendment may be executed in any
number of counterparts, each executed counterpart constituting an original, but
altogether only one instrument.

        5.8.    Expenses.    Without limiting the provisions of Section 15.1 of
the Note Agreement, the Company agrees to pay the reasonable costs and expenses
of the holders of Notes (including reasonable attorneys' fees and charges) in
connection with the preparation, execution and delivery of this Fourth Amendment
and the documents contemplated hereby.

[remainder of page intentionally blank; next page is signature page]

14

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        IN WITNESS WHEREOF, the Company and the Noteholders have caused this
Fourth Amendment to be executed and delivered by their respective officer or
officers thereunto duly authorized.

TETRA TECH, INC.  
By:
/s/  DAVID W. KING      

--------------------------------------------------------------------------------

Name: David W. King
Title: Chief Financial Officer and Treasurer
 

S-1

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NOTEHOLDERS:  
The foregoing is agreed to as of the date thereof.
 
MASSMUTUAL ASIA LIMITED
 
By:
Babson Capital Management LLC as Investment Adviser
 
By:
/s/  ELISABETH A. PERENICK      

--------------------------------------------------------------------------------

Name: Elisabeth A. Perenick
Title: Managing Director
 
MASSACHUSETTS MUTUAL LIFE INSURANCE COMPANY
 
By:
Babson Capital Management LLC as Investment Adviser
 
By:
/s/  ELISABETH A. PERENICK      

--------------------------------------------------------------------------------

Name: Elisabeth A. Perenick
Title: Managing Director
 

S-2

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C.M. LIFE INSURANCE COMPANY
 
By:
Babson Capital Management LLC as Investment Sub-Adviser
 
By:
/s/  ELISABETH A. PERENICK      

--------------------------------------------------------------------------------

Name: Elisabeth A. Perenick
Title: Managing Director
 

S-3

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PRUDENTIAL RETIREMENT CEDED BUSINESS TRUST
 
By:
Prudential Investment Management, Inc., as Investment Manager
 
By:
/s/  JOSEPH ALOUF      

--------------------------------------------------------------------------------

Name: Joseph Alouf
Title: Vice President
 
UNITED OF OMAHA INSURANCE COMPANY
 
By:
/s/  EDWIN H. GARRISON, JR.      

--------------------------------------------------------------------------------

Name: Edwin H. Garrison, Jr.
Title: First Vice President
 
MUTUAL OF OMAHA LIFE INSURANCE COMPANY
 
By:
/s/  EDWIN H. GARRISON, JR.      

--------------------------------------------------------------------------------

Name: Edwin H. Garrison, Jr.
Title: First Vice President
 

S-4

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HARTFORD LIFE INSURANCE COMPANY
 
By:
Hartford Investment Services, Inc., its Agent and Attorney-in-Fact
 
By:
/s/  EVA KONOPKA      

--------------------------------------------------------------------------------

Name: Eva Konopka
Title: Senior Vice President
 
NATIONWIDE LIFE INSURANCE COMPANY
 
By:
/s/  MARK W. POEPPELMAN      

--------------------------------------------------------------------------------

Name: Mark W. Poeppelman
Title: Authorized Signatory
 
NATIONWIDE LIFE AND ANNUITY INSURANCE COMPANY
 
By:
/s/  MARK W. POEPPELMAN      

--------------------------------------------------------------------------------

Name: Mark W. Poeppelman
Title: Authorized Signatory
 

S-5

--------------------------------------------------------------------------------

NATIONWIDE LIFE INSURANCE COMPANY OF AMERICA (formerly Provident Mutual Life
Insurance Company)
 
By:
/s/  MARK W. POEPPELMAN      

--------------------------------------------------------------------------------

Name: Mark W. Poeppelman
Title: Authorized Signatory
 
SECURITY FINANCIAL LIFE INSURANCE CO.
 
By:
/s/  KEVIN W. HAMMOND      

--------------------------------------------------------------------------------

Name: Kevin W. Hammond
Title: Senior Director—Investments
 
THE CANADA LIFE ASSURANCE COMPANY, as beneficial owner
 
By:
/s/  EVE HAMPTON      

--------------------------------------------------------------------------------

Name: Eve Hampton
Title: Vice President, Investments, U.S. Operations
 
By:
/s/  TAD ANDERSON      

--------------------------------------------------------------------------------

Name: Tad Anderson
Title: Manager, Investments, U.S. Operations
 

S-6

--------------------------------------------------------------------------------

CANADA LIFE INSURANCE COMPANY OF NEW YORK, as beneficial owner
 
By:
/s/  EVE HAMPTON      

--------------------------------------------------------------------------------

Name: Eve Hampton
Title: Vice President, Investments, CLAC
 
By:
/s/  TAD ANDERSON      

--------------------------------------------------------------------------------

Name: Tad Anderson
Title: Manager, Investments, CLAC
 
THRIVENT FINANCIAL FOR LUTHERANS (successor by merger to Lutheran Brotherhood)
 
By:
/s/  GLEN J. VANIC      

--------------------------------------------------------------------------------

Name: Glen J. Vanic
Title: Portfolio Manager
 
MODERN WOODMEN OF AMERICA
 
By:
/s/  MICHAEL E. DAU CFA      

--------------------------------------------------------------------------------

Name: Michael E. Dau CFA
Title: Manager, Fixed Income Division
 

S-7

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CONFIRMATION

        Each of the undersigned acknowledges receipt of the foregoing Fourth
Amendment and confirms the continuing validity and enforceability against such
undersigned of each of the Note Agreement, the Notes, the Subsidiary Guaranty,
the Pledge Agreement and the Security Agreement, in each case to the extent such
undersigned is a party thereto.

TETRA TECH, INC.
 
By:
/s/  DAVID W. KING      

--------------------------------------------------------------------------------

Name: David W. King
Title: Chief Financial Officer and Treasurer
 

S-8

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ADVANCED MANAGEMENT TECHNOLOGY, INC.
ARDAMAN & ASSOCIATES, INC.
COSENTINI ASSOCIATES, INC.
ENGINEERING MANAGEMENT CONCEPTS, INC.
EVERGREEN UTILITY CONTRACTORS, INC.
EXPERT WIRELESS SOLUTIONS, INC.
FHC, INC.
HARTMAN & ASSOCIATES, INC.
KCM, INC.
MFG, INC.
RIZZO ASSOCIATES, INC.
SCIENCES INTERNATIONAL, INC.
TETRA TECH CANADA LTD.
TETRA TECH CONSTRUCTION SERVICES, INC.
TETRA TECH CONSULTING & REMEDIATION, INC.
TETRA TECH EM INC.
TETRA TECH NUS, INC.
TETRA TECH RMC, INC.
THE THOMAS GROUP OF COMPANIES, INC.
VERTEX ENGINEERING SERVICES, INC.
WHALEN & COMPANY, INC.
WESTERN UTILITY CONTRACTORS, INC.

By:
/s/  DAVID W. KING      

--------------------------------------------------------------------------------

Name: David W. King
Title: Treasurer
 
GEOTRANS, INC.
SCM CONSULTANTS, INC.
TETRA TECH EC, INC.
 
By:
/s/  DAVID W. KING      

--------------------------------------------------------------------------------

Name: David W. King
Title: Assistant Treasurer
 

S-9

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SCHEDULE I

Series A Noteholders

--------------------------------------------------------------------------------

  Outstanding
Principal
Amount

--------------------------------------------------------------------------------

Massachusetts Mutual Life Insurance Company   $ 21,500,000 C.M. Life Insurance
Company     3,000,000 MassMutual Asia Limited     500,000 Connecticut General
Life Insurance Company     17,000,000 Life Insurance Company of North America  
  3,000,000 United of Omaha Insurance Company     12,000,000 Mutual of Omaha
Insurance Company     3,000,000 Hartford Life Insurance Company     15,000,000
Nationwide Life Insurance Company     7,000,000 Nationwide Life and Annuity
Insurance Company     3,000,000 Nationwide Life Insurance Company of America
(formerly Provident Mutual Life Insurance Company)     5,000,000 Security
Financial Life Insurance Co.     2,000,000

Series B Noteholders

--------------------------------------------------------------------------------

  Outstanding
Principal
Amount

--------------------------------------------------------------------------------

The Canada Life Assurance Company   $ 6,960,000 Canada Life Insurance Company of
New York     240,000 Thrivent Financial for Lutherans (successor by merger to
Lutheran Brotherhood)     4,800,000 Modern Woodmen of America     2,400,000

--------------------------------------------------------------------------------

SCHEDULE II

Excluded Subsidiaries

America's Schoolhouse Consulting Services, Inc.
Chen Northern, Inc.
Contract Operations—2, Inc.
Foster Wheeler Environmental Corporation
Kansas City Testing Laboratory, Inc.
KCM International, Inc.
LAL Corporation
Nebraska Testing Corporation
River Corridor Closure, LLC
SCM Architecture and Planning PC
SCM Staff Placement Specialists, Inc.
SulTech
Tetra Tech Caribe, Inc.
Tetra Tech Consulting & Remediation, Inc.
Tetra Tech Executive Services, Inc.
Tetra Tech International (BVI) Ltd.
Tetra Tech Leasing, LLC
Tetra Tech Technical Services, Inc.
Tetra Tech Wired Communications of California, Inc.
Thomas Aquatics, LLC
Thomas Communications & Technologies, LLC
Thomas Environmental Services, LLC
Thomas Management Services, LLC
Western Utility Cable, Inc.
Whalen do Brasil, Ltda.
Whalen Service Corps Inc.
Whalen/Sentrex LLC

--------------------------------------------------------------------------------

Exhibit 1A

FORM OF SERIES A NOTE

TETRA TECH, INC.

ADJUSTABLE RATE SENIOR SECURED NOTE,
SERIES A, DUE MAY 30, 2011

No. R-[            ]   [Date] $[            ]   PPN: 88162G A* 4

        FOR VALUE RECEIVED, the undersigned, TETRA TECH, INC. (herein called the
"Company"), a corporation organized and existing under the laws of the State of
Delaware, promises to pay to [            ], or registered assigns, the
principal sum of $[            ] on May 30, 2011, with interest (computed on the
basis of a 360-day year of twelve 30-day months) (a) on the unpaid balance
thereof at the Applicable Interest Rate per annum from the date hereof, payable
semiannually, on May 30 and November 30 in each year, commencing with the May 30
or November 30 next succeeding the date hereof (except that no interest payment
shall be made on May 30, 2001), until the principal hereof shall have become due
and payable, and (b) to the extent permitted by law on any overdue payment
(including any overdue prepayment) of principal, any overdue payment of interest
and any overdue payment of any Make-Whole Amount (as defined in the Note
Purchase Agreement referred to below), payable semiannually as aforesaid (or, at
the option of the registered holder hereof, on demand), at a rate per annum from
time to time equal to the greater of (i) 2% over the Applicable Interest Rate or
(ii) 2% over the rate of interest publicly announced by Bank of America, N.A.
from time to time in Chicago, Illinois as its "base" or "prime" rate.

        Payments of principal of, interest on and any Make-Whole Amount with
respect to this Note are to be made in lawful money of the United States of
America at the principal office of Bank of America, N.A. in Chicago, Illinois or
at such other place as the Company shall have designated by written notice to
the holder of this Note as provided in the Note Purchase Agreement referred to
below.

        This Note is one of a series of Senior Secured Notes (herein called the
"Notes") issued pursuant to the Note Purchase Agreements dated as of May 15,
2001 (as from time to time amended, collectively, the "Note Purchase
Agreement"), between the Company and the respective Purchasers named therein and
is entitled to the benefits thereof. Each holder of this Note will be deemed, by
its acceptance hereof, (i) to have agreed to the confidentiality provisions set
forth in Section 20 of the Note Purchase Agreement and (ii) to have made the
representation set forth in Section 6.2 of the Note Purchase Agreement.

        This Note is a registered Note and, as provided in the Note Purchase
Agreement, upon surrender of this Note for registration of transfer, duly
endorsed, or accompanied by a written instrument of transfer duly executed, by
the registered holder hereof or such holder's attorney duly authorized in
writing, a new Note for a like principal amount will be issued to, and
registered in the name of, the transferee. Prior to due presentment for
registration of transfer, the Company may treat the person in whose name this
Note is registered as the owner hereof for the purpose of receiving payment and
for all other purposes, and the Company will not be affected by any notice to
the contrary.

        The Company will make required prepayments of principal on the dates and
in the amounts specified in the Note Purchase Agreement. This Note also is
subject to optional prepayment, in whole or from time to time in part at the
times and on the terms specified in the Note Purchase Agreement but not
otherwise.

        If an Event of Default, as defined in the Note Purchase Agreement,
occurs and is continuing, the principal of this Note may be declared or
otherwise become due and payable in the manner, at the

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price (including any applicable Make-Whole Amount) and with the effect provided
in the Note Purchase Agreement.

        Payment of the principal of, and interest and Make-Whole Amount, if any,
on this Note, and all other amounts due under the Note Purchase Agreement, is
guaranteed pursuant to the terms of a Guaranty dated as of May 15, 2001 of
certain Subsidiaries of the Company.

        This Note shall be construed and enforced in accordance with, and the
rights of the parties shall be governed by, the law of the State of Illinois
excluding choice-of-law principles of the law of such State that would require
the application of the laws of a jurisdiction other than such State.

 
TETRA TECH, INC.

 
By:
     

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  Name:      

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  Title:      

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2

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Exhibit 1B

FORM OF SERIES B NOTE

TETRA TECH, INC.

ADJUSTABLE RATE SENIOR SECURED NOTE,
SERIES B, DUE MAY 30, 2008

No. R-[            ]   [Date] $[            ]   PPN: 88162G A@ 2

        FOR VALUE RECEIVED, the undersigned, TETRA TECH, INC. (herein called the
"Company"), a corporation organized and existing under the laws of the State of
Delaware, promises to pay to [            ], or registered assigns, the
principal sum of $[            ] on May 30, 2008, with interest (computed on the
basis of a 360-day year of twelve 30-day months) (a) on the unpaid balance
thereof at the Applicable Interest Rate per annum from the date hereof, payable
semiannually, on May 30 and November 30 in each year, commencing with the May 30
or November 30 next succeeding the date hereof (except that no interest payment
shall be made on May 30, 2001), until the principal hereof shall have become due
and payable, and (b) to the extent permitted by law on any overdue payment
(including any overdue prepayment) of principal, any overdue payment of interest
and any overdue payment of any Make-Whole Amount (as defined in the Note
Purchase Agreement referred to below), payable semiannually as aforesaid (or, at
the option of the registered holder hereof, on demand), at a rate per annum from
time to time equal to the greater of (i) 2% over the Applicable Interest Rate or
(ii) 2% over the rate of interest publicly announced by Bank of America, N.A.
from time to time in Chicago, Illinois as its "base" or "prime" rate.

        Payments of principal of, interest on and any Make-Whole Amount with
respect to this Note are to be made in lawful money of the United States of
America at the principal office of Bank of America, N.A. in Chicago, Illinois or
at such other place as the Company shall have designated by written notice to
the holder of this Note as provided in the Note Purchase Agreement referred to
below.

        This Note is one of a series of Senior Secured Notes (herein called the
"Notes") issued pursuant to the Note Purchase Agreements dated as of May 15,
2001 (as from time to time amended, collectively, the "Note Purchase
Agreement"), between the Company and the respective Purchasers named therein and
is entitled to the benefits thereof. Each holder of this Note will be deemed, by
its acceptance hereof, (i) to have agreed to the confidentiality provisions set
forth in Section 20 of the Note Purchase Agreement and (ii) to have made the
representation set forth in Section 6.2 of the Note Purchase Agreement.

        This Note is a registered Note and, as provided in the Note Purchase
Agreement, upon surrender of this Note for registration of transfer, duly
endorsed, or accompanied by a written instrument of transfer duly executed, by
the registered holder hereof or such holder's attorney duly authorized in
writing, a new Note for a like principal amount will be issued to, and
registered in the name of, the transferee. Prior to due presentment for
registration of transfer, the Company may treat the person in whose name this
Note is registered as the owner hereof for the purpose of receiving payment and
for all other purposes, and the Company will not be affected by any notice to
the contrary.

        The Company will make required prepayments of principal on the dates and
in the amounts specified in the Note Purchase Agreement. This Note also is
subject to optional prepayment, in whole or from time to time in part at the
times and on the terms specified in the Note Purchase Agreement but not
otherwise.

        If an Event of Default, as defined in the Note Purchase Agreement,
occurs and is continuing, the principal of this Note may be declared or
otherwise become due and payable in the manner, at the

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price (including any applicable Make-Whole Amount) and with the effect provided
in the Note Purchase Agreement.

        Payment of the principal of, and interest and Make-Whole Amount, if any,
on this Note, and all other amounts due under the Note Purchase Agreement, is
guaranteed pursuant to the terms of a Guaranty dated as of May 15, 2001 of
certain Subsidiaries of the Company.

        This Note shall be construed and enforced in accordance with, and the
rights of the parties shall be governed by, the law of the State of Illinois
excluding choice-of-law principles of the law of such State that would require
the application of the laws of a jurisdiction other than such State.

 
TETRA TECH, INC.

 
By:
     

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  Name:      

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  Title:      

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2

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Exhibit 2

SECOND AMENDED AND RESTATED SECURITY AGREEMENT

        THIS SECOND AMENDED AND RESTATED SECURITY AGREEMENT (this "Agreement")
dated as of May 12, 2005 is among TETRA TECH, INC. (the "Company"), each
subsidiary of the Company listed on the signature pages hereof, such other
subsidiaries of the Company as from time to time become parties hereto (together
with the Company, collectively the "Debtors" and individually each a "Debtor")
and BANK OF AMERICA, N.A. ("Bank of America"), in its capacity as Collateral
Agent (as defined below) for the Benefited Parties (as defined in the
Intercreditor Agreement referred to below).

W I T N E S S E T H:

        WHEREAS, the Company, various financial institutions (together with
their respective successors and assigns, the "Banks") and Bank of America, as
agent for the Banks (in such capacity, the "Credit Agent"), have entered into an
Amended and Restated Credit Agreement dated as of July 21, 2004 (the "Credit
Agreement");

        WHEREAS, the Company has entered into a Note Purchase Agreement dated as
of May 15, 2001 (the "Note Agreement"), pursuant to which certain note
purchasers (the "Noteholders") purchased $92,000,000 of the Company's 7.28%
Senior Secured Notes, Series A, due May 30, 2011, and $18,000,000 of the
Company's 7.08% Senior Secured Notes, Series B, due May 30, 2008 (together, the
"Senior Notes");

        WHEREAS, pursuant to an Amended and Restated Guaranty dated as of
May 15, 2001 (the "Guaranty"), certain subsidiaries of the Company have
guaranteed all obligations of the Company under the Credit Agreement, all
obligations of the Company under the Note Agreement and certain other
obligations of the Company;

        WHEREAS, the Credit Agent, the Noteholders and Bank of America, as
collateral agent, have entered into an Intercreditor Agreement dated as of
May 15, 2001 (the "Intercreditor Agreement"; capitalized terms used but not
defined herein shall have the respective meanings assigned thereto in the
Intercreditor Agreement), pursuant to which (i) such parties have agreed that
all Benefited Obligations shall be guaranteed and secured on a pari passu basis
and (ii) Bank of America shall act as collateral agent for the holders of the
Benefited Obligations (in such capacity, together with any successor in such
capacity, the "Collateral Agent");

        WHEREAS, the obligations of the Company in respect of the Benefited
Obligations and the obligations of each other Debtor under the Guaranty are to
be secured pursuant to this Agreement;

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

        1.    Definitions and Interpretation.    For purposes of this Agreement,
(a) in addition to terms defined in the preamble and recitals above, the terms
Account, Account Debtor, Certificated Security, Chattel Paper, Commodity
Account, Commodity Contract, Deposit Account, Financial Asset, General
Intangibles, Instruments, Investment Property, Securities Account, Security,
Security Entitlement and Uncertificated Security have the respective meanings
assigned to such terms in the UCC (as defined below), (b) the rules of
interpretation set forth in clauses (a), (c)(i) and (d) of Section 1.2 of the
Credit Agreement shall apply as if set forth in full herein, mutatis mutandis,
and (c) the following terms have the following meanings, respectively:

        Collateral—see Section 2.

        Default means the occurrence of any of the following events: (a) any
Event of Default; (b) any event which, if it continues uncured will, with lapse
of time or notice or both, constitute an Event of Default under Section 12.1.4
of the Credit Agreement, Section 11(g) or 11(h) of the Note

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Agreement or any substantially similar provision of any other Financing
Agreement; or (c) any warranty of any Debtor herein is untrue or misleading in
any material respect and, as a result thereof, the Collateral Agent's security
interest for the benefit of the Benefited Parties in any material portion of the
Collateral is not perfected or the Collateral Agent's rights and remedies with
respect to any material portion of the Collateral are materially impaired or
otherwise materially adversely affected.

        Liabilities means, (a) as to the Company, all Credit Obligations, all
Senior Note Obligations and all other Benefited Obligations; and (b) with
respect to each other Debtor, all obligations of such Debtor under the Guaranty.

        Permitted Lien means any Lien that is expressly permitted pursuant to
Section 10.8 of the Credit Agreement (but excluding any Lien on any Account or
on the stock of any Subsidiary of any Debtor).

        UCC means the Uniform Commercial Code as in effect from time to time in
the State of Illinois.

        2.    Grant of Security Interest.    As security for the payment of all
Liabilities, each Debtor hereby assigns to the Collateral Agent for the benefit
of the Benefited Parties, and grants to the Collateral Agent for the benefit of
the Benefited Parties a continuing security interest in, the following, whether
now or hereafter existing or acquired (the "Collateral"): all of such Debtor's
Accounts, Commodity Accounts, Commodity Contracts, Deposit Accounts, Financial
Assets, Investment Property, money (of any jurisdiction), Securities (whether
Certificated or Uncertificated Securities), Securities Accounts and Security
Entitlements; all of such Debtor's General Intangibles arising out of or related
to any of the foregoing; all of such Debtor's Chattel Paper and Instruments
evidencing any obligation arising out of or relating to any of the foregoing;
all interest of such Debtor in any goods the sale or lease of which shall have
given rise to, and in all guaranties and property securing payment or
performance under, any Account or other property described above; all of such
Debtor's books and records relating to any of the foregoing; and all proceeds
(including all insurance proceeds) of any of the foregoing.

        3.    Warranties.    Each Debtor warrants that: (i) no financing
statement (other than any which may have been filed on behalf of the Collateral
Agent or in connection with Permitted Liens) covering any of the Collateral is
on file in any public office; (ii) such Debtor is and will be the lawful owner
of all Collateral, free of all liens and claims whatsoever, other than the
security interest hereunder and Permitted Liens, with full power and authority
to execute and deliver this Agreement, to perform such Debtor's obligations
hereunder and to subject the Collateral to the security interest hereunder;
(iii) such Debtor's true legal name as registered in the jurisdiction in which
such Debtor is organized or incorporated, jurisdiction of organization or
incorporation, organizational identification number as designated by the
jurisdiction of its organization or incorporation, chief executive office and
principal place of business are as set forth on Schedule I hereto (and such
Debtor has not maintained its chief executive office or principal place of
business at any other location at any time after January 1, 2001 (or, in the
case of any Person which becomes a Debtor after the date hereof, 135 days prior
to the date such Person executes and delivers a counterpart hereof));
(iv) except as described in Schedule II, such Debtor is not now known and has
not, during the five years preceding the date of execution and delivery hereof
by such Debtor, been known by any trade name; and (v) except as disclosed on
Schedule III hereto, during the five years preceding the date of execution and
delivery hereof by such Debtor, such Debtor has not been known by any legal name
different from the one set forth on the signature page of this Agreement, nor
has such Debtor been the subject of any merger or other corporate
reorganization.

        4.    Collections, etc.    Until such time during the existence of a
Default as the Collateral Agent shall notify such Debtor of the revocation of
such power and authority, each Debtor (a) will, at its own expense, endeavor to
collect, as and when due, all amounts due under any of the Collateral, including

2

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the taking of such action with respect to such collection as the Collateral
Agent may reasonably request or, in the absence of such request, as such Debtor
may deem advisable, and (b) may grant, in the ordinary course of business, to
any party obligated on any of the Collateral, any rebate, refund or allowance to
which such party may be lawfully entitled, and may accept, in connection
therewith, the return of goods, the sale or lease of which shall have given rise
to such Collateral. The Collateral Agent, however, may, at any time that a
Default exists, whether before or after any revocation of such power and
authority or the maturity of any of the Liabilities, notify any parties
obligated on any of the Collateral to make payment to the Collateral Agent of
any amounts due or to become due thereunder and enforce collection of any of the
Collateral by suit or otherwise and surrender, release or exchange all or any
part thereof, or compromise or extend or renew for any period (whether or not
longer than the original period) any indebtedness thereunder or evidenced
thereby. Promptly following any request of the Collateral Agent during the
existence of a Default, each Debtor will, at its own expense, notify any parties
obligated on any of the Collateral to make payment to the Collateral Agent of
any amounts due or to become due thereunder.

        Upon request by the Collateral Agent during the existence of a Default,
each Debtor will establish a deposit account with the Collateral Agent (an
"Assignee Deposit Account") and will forthwith, upon receipt, transmit and
deliver to the Collateral Agent, in the form received, all cash, checks, drafts
and other instruments or writings for the payment of money (properly endorsed,
where required, so that such items may be collected by the Collateral Agent)
which may be received by such Debtor at any time in full or partial payment or
otherwise as proceeds of any of the Collateral for deposit in the Assignee
Deposit Account as security for payment of the Liabilities. Except as the
Collateral Agent may otherwise consent in writing, any such items which may be
so received by any Debtor will not be commingled with any other of its funds or
property, but will be held separate and apart from its own funds or property and
upon express trust for the Collateral Agent until delivery is made to the
Collateral Agent.

        No Debtor shall have any right to withdraw any funds deposited in the
applicable Assignee Deposit Account. The Collateral Agent may, from time to
time, in its discretion, and shall upon request of the applicable Debtor made
not more than once in any week, apply all or any of the then balance,
representing collected funds, in the Assignee Deposit Account, toward payment of
the Liabilities, whether or not then due, in such order of application as is set
forth in the Intercreditor Agreement, and the Collateral Agent may, from time to
time, in its discretion (subject to the terms of the Intercreditor Agreement),
release all or any of such balance to the applicable Debtor.

        The Collateral Agent is authorized to endorse, in the name of the
applicable Debtor, any item, howsoever received by the Collateral Agent,
representing any payment on or other proceeds of any of the Collateral.

        Each Debtor hereby appoints the Collateral Agent as the attorney-in-fact
for such Debtor for the purpose of carrying out the provisions of this Agreement
and taking any action and executing or completing any instrument which the
Collateral Agent may deem reasonably necessary or advisable to accomplish the
terms hereof, which appointment as attorney-in-fact is irrevocable and coupled
with an interest; provided that the Collateral Agent shall not exercise its
rights as such attorney-in-fact unless a Default exists.

        5.    Certificates, Schedules and Reports.    Each Debtor will from time
to time, as the Collateral Agent may request, deliver to the Collateral Agent a
schedule identifying each Account of such Debtor (not previously so identified)
subject to the security interest hereunder, and such additional schedules and
such certificates and reports respecting all or any of the Collateral at the
time subject to the security interest hereunder, and the items or amounts
received by such Debtor in full or partial payment of any of the Collateral, all
to such extent as the Collateral Agent may reasonably request. Any such
schedule, certificate or report shall be executed by a duly authorized officer
of such Debtor

3

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and shall be in such form and detail as the Collateral Agent may specify. Any
such schedule identifying any Account subject to the security interest hereunder
shall be accompanied (if the Collateral Agent so requests) by a true and correct
copy of the invoice evidencing such Account and by evidence of shipment or
performance.

        6.    Agreements of the Debtors.    Each Debtor (a) will, upon request
of the Collateral Agent, execute such financing statements and other documents
(and pay the cost of filing or recording the same in all public offices deemed
appropriate by the Collateral Agent) and do such other acts and things
(including the delivery to the Collateral Agent of all Certificated Securities
and Instruments (other than checks and similar items that are deposited in the
ordinary course of business)), all as the Collateral Agent may from time to time
reasonably request, to establish and maintain a valid security interest in the
Collateral (free of all other liens, claims and rights of third parties
whatsoever, other than Permitted Liens) to secure the payment of the Liabilities
(and each Debtor hereby authorizes the Collateral Agent to file any financing
statement without its signature, to the extent permitted by applicable law,
and/or to file a copy of this Agreement as a financing statement in any
jurisdiction; (b) after the occurrence and during the continuance of any
Default, will execute and file such assignment of claims forms under or pursuant
to the federal assignment of claims statute, 31 U.S.C. § 3726, as may be
necessary or desirable, or as the Collateral Agent may from time to time
request, in order to perfect and preserve the security interests and other
rights granted or purported to be granted to the Collateral Agent hereby (free
of all other liens, claims and rights of third parties whatsoever), (c) will
keep, at its address shown on Schedule I hereto, its records concerning the
Collateral, which records will be of such character as will enable the
Collateral Agent or its designees to determine at any time the status of the
Collateral, and no Debtor will, unless the Collateral Agent shall otherwise
consent in writing, duplicate any such records at any other address; (d) will
furnish the Collateral Agent such information concerning such Debtor, the
Collateral and the Account Debtors as the Collateral Agent may from time to time
reasonably request; (e) will permit the Collateral Agent and its designees, from
time to time, to inspect, audit and make copies of and extracts from all records
and all other papers in the possession of such Debtor pertaining to the
Collateral and the Account Debtors, and will, upon request of the Collateral
Agent during the existence of a Default, deliver to the Collateral Agent all of
such records and papers; (f) will, upon request of the Collateral Agent, stamp
on its records concerning the Collateral, and add on all Chattel Paper
constituting a portion of the Collateral, a notation, in form satisfactory to
the Collateral Agent, of the security interest of the Collateral Agent
hereunder; (g) will not change its jurisdiction of organization or incorporation
or its name, identity or corporate structure such that any financing statement
filed to perfect the Collateral Agent's interest under this Agreement would
become seriously misleading, unless such Debtor shall have given the Collateral
Agent not less than 10 days' prior notice of such change (provided that this
Section 6(g) shall not be deemed to authorize any change or transaction
prohibited under the Credit Agreement); and (h) will not sell, lease, assign or
create or permit to exist any lien on or security interest in any Collateral
other than liens and security interests in favor of the Collateral Agent and
Permitted Liens.

        7.    Remedies.    Whenever a Default exists, the Collateral Agent may
from time to time exercise any rights and remedies available to it under the UCC
or any other applicable law or otherwise available to it. Without limiting the
foregoing, whenever a Default exists the Collateral Agent may, to the fullest
extent permitted by applicable law, without notice, advertisement, hearing or
process of law of any kind, (a) sell any or all of the Collateral, free of all
rights and claims of any Debtor therein and thereto, at any public or private
sale, and (b) bid for and purchase any or all of the Collateral at any such
sale. Each Debtor hereby expressly waives, to the fullest extent permitted by
applicable law, any and all notices, advertisements, hearings or process of law
in connection with the exercise by the Collateral Agent of any of its rights and
remedies upon a Default. If any notification of intended disposition of any of
the Collateral is required by law, such notification, if mailed, shall be deemed
reasonably and properly given if mailed at least ten days before disposition,
postage prepaid, addressed

4

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to the applicable Debtor either at its address shown on Schedule I hereto or at
any other address of such Debtor appearing on the records of the Collateral
Agent. Any proceeds of any of the Collateral may be applied by the Collateral
Agent to the payment of expenses in connection with the Collateral, including
reasonable attorneys' fees and legal expenses, and any balance of such proceeds
shall be applied by the Collateral Agent toward the payment of the Liabilities
in accordance with the Intercreditor Agreement.

        8.    General.    The Collateral Agent shall be deemed to have exercised
reasonable care in the custody and preservation of any of the Collateral in its
possession if it takes such action for that purpose as any applicable Debtor
requests in writing, but failure of the Collateral Agent to comply with any such
request shall not of itself be deemed a failure to exercise reasonable care, and
no failure of the Collateral Agent to preserve or protect any rights with
respect to such Collateral against prior parties, or to do any act with respect
to the preservation of such Collateral not so requested by any Debtor, shall be
deemed a failure to exercise reasonable care in the custody or preservation of
such Collateral.

        No delay on the part of the Collateral Agent in exercising any right,
power or remedy hereunder shall operate as a waiver thereof nor shall any single
or partial exercise of any such right, power or remedy preclude any other or
further exercise thereof or the exercise of any other right, power or remedy. No
amendment, modification or waiver of, or consent with respect to, any provision
of this Agreement shall in any event be effective unless the same shall be in
writing, and signed and delivered by the party to be bound thereby, and then
such amendment, modification, waiver or consent shall be effective only in the
specific instance and for the purpose for which given.

        Each Debtor agrees to pay all expenses (including reasonable attorney's
fees and legal expenses) paid or incurred by the Collateral Agent in endeavoring
to collect the Liabilities of such Debtor, or any part thereof, and in enforcing
this Agreement against such Debtor, and such obligations will themselves be
Liabilities.

        No delay on the part of the Collateral Agent in the exercise of any
right or remedy shall operate as a waiver thereof, and no single or partial
exercise by the Collateral Agent of any right or remedy shall preclude other or
further exercise thereof or the exercise of any other right or remedy.

        This Agreement shall remain in full force and effect until all
Liabilities have been paid in full and all commitments to create Liabilities
have terminated. If at any time all or any part of any payment theretofore
applied by the Collateral Agent or any other Benefited Party to any of the
Liabilities is or must be rescinded or returned by the Collateral Agent or such
other Benefited Party for any reason whatsoever (including the insolvency,
bankruptcy or reorganization of any Debtor), such Liabilities shall, for the
purposes of this Agreement, to the extent that such payment is or must be
rescinded or returned, be deemed to have continued in existence, notwithstanding
such application by the Collateral Agent or such other Benefited Party, and this
Agreement shall continue to be effective or be reinstated, as the case may be,
as to such Liabilities, all as though such application by the Collateral Agent
or such other Benefited Party had not been made.

        This Agreement has been delivered at Chicago, Illinois, and shall be
construed in accordance with and governed by the laws of the State of Illinois
applicable to contracts made and to be fully performed in its such state.
Whenever possible, each provision of this Agreement shall be interpreted in such
manner as to be effective and valid under applicable law, but if any provision
of this Agreement shall be prohibited by or invalid under applicable law, such
provision shall be ineffective to the extent of such prohibition or invalidity,
without invalidating the remainder of such provision or the remaining provisions
of this Agreement.

        The rights and privileges of the Collateral Agent hereunder shall inure
to the benefit of its successors and assigns.

5

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        This Agreement may be executed in any number of counterparts and by the
different parties hereto 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 Agreement. At any time after the date of this
Agreement, one or more additional persons or entities may become parties hereto
by executing and delivering a counterpart to the Collateral Agent of this
Agreement. Immediately upon such execution and delivery (and without any further
action), each such additional person or entity will become a party to, and will
be bound by all the terms of, this Agreement. Delivery of a counterpart hereof,
or a signature page hereto, by facsimile shall be effective as delivery or an
original signed counterpart.

        ANY LITIGATION BASED HEREON, OR ARISING OUT OF, UNDER OR IN CONNECTION
WITH THIS AGREEMENT OR ANY OTHER FINANCING AGREEMENT, SHALL BE BROUGHT AND
MAINTAINED EXCLUSIVELY IN THE COURTS OF THE STATE OF ILLINOIS OR IN THE UNITED
STATES DISTRICT COURT FOR THE NORTHERN DISTRICT OF ILLINOIS; PROVIDED THAT ANY
SUIT SEEKING ENFORCEMENT AGAINST ANY COLLATERAL OR OTHER PROPERTY MAY BE
BROUGHT, AT THE COLLATERAL AGENT'S OPTION, IN THE COURTS OF ANY JURISDICTION
WHERE SUCH COLLATERAL OR OTHER PROPERTY MAY BE FOUND OR IN ANY JURISDICTION IN
WHICH A BANKRUPTCY, INSOLVENCY OR OTHER SIMILAR LEGAL OR EQUITABLE PROCEEDING IS
PENDING AGAINST ANY ONE OR MORE OF THE DEBTORS. EACH DEBTOR HEREBY EXPRESSLY AND
IRREVOCABLY SUBMITS TO THE JURISDICTION OF THE COURTS OF THE STATE OF ILLINOIS
AND OF THE UNITED STATES DISTRICT COURT FOR THE NORTHERN DISTRICT OF ILLINOIS
FOR THE PURPOSE OF ANY SUCH LITIGATION AS SET FORTH ABOVE. EACH DEBTOR FURTHER
IRREVOCABLY CONSENTS TO THE SERVICE OF PROCESS BY REGISTERED MAIL, POSTAGE
PREPAID, TO THE ADDRESS SET FORTH ON SCHEDULE I HERETO (OR SUCH OTHER ADDRESS AS
IT SHALL HAVE SPECIFIED IN WRITING TO THE COLLATERAL AGENT AS ITS ADDRESS FOR
NOTICES HEREUNDER) OR BY PERSONAL SERVICE WITHIN OR WITHOUT THE STATE OF
ILLINOIS. EACH DEBTOR HEREBY EXPRESSLY AND IRREVOCABLY WAIVES, TO THE FULLEST
EXTENT PERMITTED BY LAW, ANY OBJECTION WHICH IT MAY NOW OR HEREAFTER HAVE TO THE
LAYING OF VENUE OF ANY SUCH LITIGATION BROUGHT IN ANY SUCH COURT REFERRED TO
ABOVE AND ANY CLAIM THAT ANY SUCH LITIGATION HAS BEEN BROUGHT IN AN INCONVENIENT
FORUM.

        THE DEBTORS, THE COLLATERAL AGENT AND (BY ACCEPTING THE BENEFITS HEREOF)
THE BENEFITED PARTIES HEREBY WAIVE ANY RIGHT TO A TRIAL BY JURY IN ANY ACTION OR
PROCEEDING TO ENFORCE OR DEFEND ANY RIGHTS UNDER THIS AGREEMENT, ANY FINANCING
AGREEMENT AND ANY AMENDMENT, INSTRUMENT, DOCUMENT OR AGREEMENT DELIVERED OR
WHICH MAY IN THE FUTURE BE DELIVERED IN CONNECTION HEREWITH OR THEREWITH OR
ARISING FROM ANY FINANCING RELATIONSHIP EXISTING IN CONNECTION WITH ANY OF THE
FOREGOING, AND AGREE THAT ANY SUCH ACTION OR PROCEEDING SHALL BE TRIED BEFORE A
COURT AND NOT BEFORE A JURY.

6

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        IN WITNESS WHEREOF, this Agreement has been duly executed as of the day
and year first above written.

    TETRA TECH, INC.
 
 
 
      By: /s/  DAVID W. KING      

--------------------------------------------------------------------------------

David W. King
Chief Financial Officer and Treasurer
 
 
 
      ADVANCED MANAGEMENT TECHNOLOGY, INC.
ARDAMAN & ASSOCIATES, INC.
COSENTINI ASSOCIATES, INC.
ENGINEERING MANAGEMENT CONCEPTS, INC.
EVERGREEN UTILITY CONTRACTORS, INC.
EXPERT WIRELESS SOLUTIONS, INC.
FHC, INC.
HARTMAN & ASSOCIATES, INC.
KCM, INC.
MFG, INC.
RIZZO ASSOCIATES, INC.
SCIENCES INTERNATIONAL, INC.
TETRA TECH CANADA LTD.
TETRA TECH CONSTRUCTION SERVICES, INC.
TETRA TECH CONSULTING & REMEDIATION, INC.
TETRA TECH EM INC.
TETRA TECH NUS, INC.
TETRA TECH RMC, INC.
THE THOMAS GROUP OF COMPANIES, INC.
VERTEX ENGINEERING SERVICES, INC.
WHALEN & COMPANY, INC.
WESTERN UTILITY CONTRACTORS, INC.
 
 
 
      By: /s/  DAVID W. KING      

--------------------------------------------------------------------------------

David W. King
Treasurer        

7

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GEOTRANS, INC.
SCM CONSULTANTS, INC.
TETRA TECH EC, INC.
 
 
 
      By: /s/  DAVID W. KING      

--------------------------------------------------------------------------------

David W. King
Assistant Treasurer        

8

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BANK OF AMERICA, N.A.,
as Collateral Agent
 
 
 
      By: /s/  PAUL FOLINO      

--------------------------------------------------------------------------------

    Name: Paul Folino     Title: Assistant Vice President        

9

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ADDITIONAL SIGNATURE PAGE to the Second Amended and Restated Security Agreement
dated as of May 12, 2005 (the "Security Agreement") among Tetra Tech, Inc., Bank
of America, N.A., as Collateral Agent, and various Subsidiaries of Tetra Tech,
Inc.
 
 
 
      The undersigned is executing a counterpart of the Security Agreement for
purposes of becoming a party hereto (and attached hereto are supplemental
schedules setting forth information with respect to the undersigned required to
make the representations and warranties with respect to the undersigned set
forth in the Security Agreement accurate as of the date hereof).
 
 
 
      [                              ]
 
 
 
      By:      

--------------------------------------------------------------------------------

    Name:       Title:  

10

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SCHEDULE I
TO SECURITY AGREEMENT

CORPORATE INFORMATION
[TO BE INSERTED]

Debtor's Federal employment identification number:

Debtor's jurisdiction of organization:

Debtor's true and correct name as registered in its jurisdiction of
organization:

Debtor's organizational identification number in its jurisdiction of
organization:

Debtor's chief executive office:

Debtor's principal place of business:

--------------------------------------------------------------------------------

SCHEDULE II
TO SECURITY AGREEMENT

Tradenames
[TO BE ATTACHED]

--------------------------------------------------------------------------------

SCHEDULE III
TO SECURITY AGREEMENT

Prior Legal Names

The following companies were merged into Tetra Tech, Inc. and were formerly
known as:

Simons, Li & Associates, Inc.
IWA Engineers
C.D.C. Engineering, Inc.
Flo Engineering, Inc.

Tetra Tech EM Inc. (f/k/a PRC Environmental Management Inc.)

HSI GeoTrans, Inc. (f/k/a Hydro-Search, Inc. and GeoTrans, Inc.)

Cosentini Associates, Inc. (f/k/a L.M.W. Associates, Inc.)

MFG, Inc. (f/k/a McCulley, Frick & Gilman, Inc.)

Wahlen & Company, Inc. (CommSite Development Corporation was merged into
Whalen & Company, Inc.)

Tetra Tech NUS, Inc. (f/k/a NUS Acquisition Corp. and Halliburton NUS
Corporation)

--------------------------------------------------------------------------------

Exhibit 3

May 12, 2005

To the Financial Institutions
listed On Schedule I hereto
(the "Noteholders")

Re:Tetra Tech, Inc. and certain of its Subsidiaries

Ladies and Gentlemen:

        I have acted as counsel to Tetra Tech, Inc., a Delaware corporation (the
"Company"), and the subsidiaries of the Company listed on Exhibit A attached
hereto (collectively the "Guarantors" and, together with the Company, each an
"Obligor" and collectively the "Obligors") in connection with the Fourth
Amendment to Note Purchase Agreement, dated as of May 12, 2005 (the "Fourth
Amendment") among the Company and the Noteholders, pursuant to which the
following documents were amended: (a) the Note Purchase Agreements, each dated
as of May 15, 2001, (collectively, as previously amended and after giving effect
to the Fourth Amendment, the "Note Agreement") between the Company and the
Noteholders; (b) $92,000,000 in aggregate principal amount of the Company's
7.28% Senior Secured Notes, Series A, due May 30, 2011 (collectively, after
giving effect to the Fourth Amendment, the "Series A Notes"); and
(c) $18,000,000 aggregate principal amount of the Company's 7.08% Senior Secured
Notes, Series B, due May 30, 2008 (collectively, after giving effect to the
Fourth Amendment, the "Series B Notes", and together with the Series A Notes,
the "Notes"). Capitalized terms used herein without definition have the same
meanings as in the Note Agreement.

        This opinion is delivered to you pursuant to Section 4 of the Fourth
Amendment. In connection with this opinion, I have examined and relied upon the
following documents:

(a)the Note Agreement;

(b)the Notes;

(c)the Fourth Amendment;

(d)the Confirmation dated May 12, 2005 issued by the Obligors and attached to
the Fourth Amendment; and

(e)the Second Amended and Restated Security Agreement dated as of the date
hereof among the Obligors and the Collateral Agent (the "Amended Security
Agreement").

The documents referred to in items (c), (d) and (e) above are called the
"Amendment Documents;" the Note Agreement, the Notes and the Amendment Documents
are called the "Note Documents."

        In addition, I have examined such other records, documents, certificates
and instruments as I have deemed necessary or appropriate as a basis for the
opinions expressed below. In my examination I have assumed the genuineness of
all signatures (other than signatures of the officers of the Obligors), the
legal capacity of natural persons, the authenticity of all documents submitted
to me as originals, the conformity to original documents of all documents
submitted to me as certified or photostatic copies, and the authenticity of the
originals of such copies. As to any facts material to this opinion that I did
not independently establish or verify, I have relied upon certificates of public
officials and statements and representations of officers and other
representatives of the Obligors.

        To the extent that the obligations of any Obligor may be dependent upon
such matters, I have assumed for purposes of this opinion that (a) each
Noteholder and the Collateral Agent (individually a "Note Party" and
collectively, the "Note Parties") is duly incorporated or formed, validly
existing and in good standing under the laws of its jurisdiction of
incorporation or formation, (b) each Note Party has the corporate or other
organizational power and authority to execute and deliver the Fourth Amendment
and, in the case of the Collateral Agent, the Amended Security Agreement,
(c) each Note Party has duly authorized, executed and delivered the Fourth
Amendment and, in the case of the Collateral Agent, the Amended Security
Agreement, (d) each Note Party has the requisite corporate or

--------------------------------------------------------------------------------

other organizational power and authority to perform its obligations under each
Note Document to which it is a party, and (e) each Note Document constitutes the
legal, valid and binding obligation of each Note Party that is a party thereto,
enforceable against such Note Party in accordance with its terms.

        I have investigated such questions of law for the purpose of rendering
this opinion as I have deemed necessary. I am an attorney admitted to practice
in the State of California. I express no opinion as to matters under or
involving the laws of any jurisdiction other than the laws of the State of
California, United States federal law and the State of Delaware General
Corporation Law, as such laws presently stand (the "Subject Laws"). I am not
opining on, and I assume no responsibility as to, the applicability to or effect
on any of the matters covered herein of the laws of any other jurisdiction. With
regard to the opinions set forth in paragraphs 1 and 2, I note that certain
Guarantors are incorporated in jurisdictions other than California and Delaware.
To the extent my opinions in paragraphs 1 and 2 are governed by laws other than
the laws of the State of California and the Delaware General Corporation Law, I
have assumed that the laws of the State of California govern these matters. I
express no opinion with respect to federal securities or state securities or
"blue sky" laws or state or federal antifraud, antitrust or environmental laws.
In addition, I am not expressing any opinion as to the effect of noncompliance
by any Note Party with any state or federal laws or regulations applicable to
the transactions contemplated by the Note Documents because of the nature of
their respective businesses. I also assume that each Note Party will act in good
faith and in a commercially reasonable manner.

        For purposes of California usury laws, I have assumed, with your
permission, that each of the Noteholders is an admitted incorporated insurer, a
licensed finance lender, or by reason of its own business and financial
experience, it has the capacity to protect its own interests in connection with
the Amendment Documents.

        Based upon and subject to the foregoing and the limitations,
qualifications and exceptions set forth below, I am of the opinion that:

        1.     The Company is a corporation duly organized, validly existing and
in good standing under the laws of the State of Delaware, and each Guarantor is
duly organized and validly existing in good standing under the laws of the
jurisdiction of its organization. Each Obligor is duly qualified to transact
business as a foreign corporation and is in good standing in each other
jurisdiction in which it owns or leases property of a nature, or transacts
business of a type, that would make such qualification necessary, except where
the failure so to qualify would not have a Material Adverse Effect. Each Obligor
has the corporate power and authority to own its property and to carry on its
business as now being conducted. Each Obligor has the corporate power and
authority (a) to execute and deliver each Amendment Document to which it is a
party and (b) to perform its obligations under each Note Document to which it is
a party and to carry out the transactions contemplated thereby.

        2.     The execution and delivery by each Obligor of each Amendment
Document to which it is a party, and the performance by each Obligor of its
obligations under each Note Document to which it is a party, have been duly
authorized and approved by all necessary corporate or other organizational
action. Neither the execution and delivery by any Obligor of the Amendment
Documents to which it is a party nor the consummation by any Obligor of the
transactions contemplated by the Note Documents will breach, be in conflict
with, or constitute a default under (a) any Obligor's Certificate of
Incorporation, Articles of Incorporation or Bylaws, as the case may be, (b) any
contractual restriction (other than with respect to financial ratios or tests or
any aspect of the financial condition or results of operation of any Obligor as
to which I express no opinion) contained in any agreement, indenture, instrument
or other document that is material to the Company and its Subsidiaries
considered as a whole, (c) any judgment, order, injunction or decree known to
me, or (d) to my knowledge, any

2

--------------------------------------------------------------------------------

federal, California or Delaware General Corporation Law statute, rule or
regulation (including usury laws).

        3.     No authorization, approval or other action by, and no notice to
or filing with, any federal, California or Delaware governmental authority or
regulatory body is required for the execution and delivery by any Obligor of any
Amendment Document or the performance by any Obligor of any Note Document,
except for routine filings that may be required after the date hereof to
maintain good standing (corporate or otherwise) or to perfect Liens under the
Amended Security Agreement.

        4.     (a)    Each Amendment Document has been duly executed and
delivered by each Obligor that is a party thereto, and each Note Document
constitutes the legal, valid and binding obligation of Obligor that is a party
thereto, enforceable against such Obligor in accordance with its terms.

        (b)   With respect to the enforceability of the choice of law to govern
each of the Note Documents, although there is no controlling precedent and the
matter is not free from doubt, a California court or a federal court sitting in
the State of California in a properly litigated action should respect the choice
of Illinois law as the governing law and should apply Illinois law.

        5.     To my knowledge, other than as disclosed in the Company's
financial statements, there are no outstanding judgments against any Obligor,
and there is no action, suit or proceeding pending or threatened against any
Obligor, which is reasonably likely to have a Material Adverse Effect.

        In rendering the opinions set forth above, I have assumed that the laws
of the State of California would apply despite the selection of Illinois law as
the governing law in the Note Documents. In making the foregoing assumption, I
do not intend to imply that a California court would not give effect to such
selection of Illinois law.

        The opinions expressed herein are subject to the following
qualifications and comments:

        A.    Each Note Document is subject to the effect of (i) bankruptcy,
insolvency, fraudulent conveyance, reorganization, moratorium or other similar
laws relating to or affecting the rights of creditors generally and (ii) the
application of general principles of equity (regardless of whether enforcement
is considered in proceedings at law or in equity).

        B.    I express no opinion as to the effect of the laws of any
jurisdiction (other than the Subject Laws) wherein any Note Party may be located
which limit rates of interest that may be charged or collected by such Note
Party.

        C.    Insofar as certain provisions of the Note Documents may provide
for indemnification, enforceability thereof may be limited by public policy
considerations.

        D.    The provisions of the Note Documents that permit any Note Party to
take action or make determinations, or to benefit from indemnities and similar
undertakings of any Obligor may be subject to a requirement that such actions be
taken or such determinations by made, and any action or inaction by any Note
Party that may give rise to a request for payment under such an undertaking be
taken or not taken, on a reasonable basis and in good faith.

        E.    I express no opinion as to (i) whether provisions of any Note
Document that relate to the subject matter jurisdiction of the federal or state
courts of Illinois to adjudicate any controversy related to such Note Document
or the transactions contemplated thereby, (ii) any waiver of inconvenient forum
set forth in any Note Document, or (iii) any waiver of jury trial found in any
Note Document.

        F.     My opinions in paragraphs 2 and 3 above as to compliance with
certain statutes, rules and regulations are based upon a review of those
statutes, rules and regulations which, in my experience, are normally applicable
to transactions of the type contemplated by the Note Documents and statutes,
rules and regulations applicable to corporations conducting businesses similar
to those conducted by the Obligors.

3

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        This opinion letter is rendered only to, and is solely for the benefit
of, the Noteholders (and their respective successors and assigns, including,
without limitation, any future holder of a Note) in connection with the
transactions related to the Note Documents and may not be relied upon by such
Persons for any other purpose, or by any other Person for any purpose, in each
case without my prior written consent.

      Very truly yours,                       /s/  JANIS B. SALIN      

--------------------------------------------------------------------------------

Janis B. Salin
Vice President and General Counsel         Attachments: Schedule I
Exhibit A    

4

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Schedule I

Opinion Addressees

Massachusetts Mutual Life Insurance Company
c/o Babson Capital Management LLC
1295 State Street
Springfield, MA 01111

C.M. Life Insurance Company
c/o Babson Capital Management LLC
1295 State Street
Springfield, MA 01111

MassMutual Asia Limited
c/o Babson Capital Management LLC
1295 State Streete
Springfield, MA 01111

Prudential Retirement Ceded Business Trust
c/o Prudential Capital Group
Four Embarcadero Center
Suite 2700, 27th Floor
San Francisco, CA 94111

United of Omaha Life Insurance Company
4—Investment Loan Administration
Mutual of Omaha Plaza
Omaha, NE 68175-1011

Mutual of Omaha Insurance Company
4—Investment Loan Administration
Mutual of Omaha Plaza
Omaha, NE 68175-1011

Hartford Life Insurance Company
c/o Hartford Investment Management Company
P.O. Box 1744
Hartford, CT 06144-1744

Nationwide Life Insurance Company
One Nationwide Plaza (1-33-07)
Columbus, Ohio 43215-2220

Nationwide Life and Annuity Insurance Company
One Nationwide Plaza (1-33-07)
Columbus, Ohio 43215-2220

Nationwide Life Insurance Company of America
One Nationwide Plaza (1-33-07)
Columbus, Ohio 43215-2220

Security Financial Life Insurance Co.
4000 Pine Lake Road
P.O. Box 82248
Lincoln, NE 68501-2248

--------------------------------------------------------------------------------

The Canada Life Assurance Company
330 University Ave. SP-11
Toronto, ON M5G 1R8

Canada Life Insurance Company of New York
330 University Ave. SP-11
Toronto, ON M5G 1R8

Thrivent Financial For Lutherans
625 Fourth Avenue South
Minneapolis, MN 55415

Modern Woodmen of America
1701 First Avenue
Rock Island, IL 61201

--------------------------------------------------------------------------------

Exhibit A

Subsidiaries

Subsidiary

--------------------------------------------------------------------------------

  State Of Domicile

--------------------------------------------------------------------------------

GeoTrans, Inc.   Virginia
Tetra Tech EM Inc.
 
Delaware
KCM, Inc.
 
Washington
SCM Consultants, Inc.
 
Washington
Whalen & Company, Inc.
 
Delaware
Tetra Tech NUS, Inc.
 
Delaware
MFG, Inc.
 
Delaware
Tetra Tech Canada Ltd.
 
Ontario
Tetra Tech Construction Services, Inc.
 
Colorado
Cosentini Associates, Inc.
 
New York
Evergreen Utility Contractors, Inc.
 
Washington
eXpert Wireless Solutions, Inc.
 
Delaware
FHC, Inc.
 
Oklahoma
Rizzo Associates, Inc.
 
Massachusetts
Tetra Tech RMC, Inc.
 
Delaware
Vertex Engineering Services, Inc.
 
Massachusetts
Western Utility Contractors, Inc.
 
Illinois
Sciences International, Inc.
 
Delaware
The Thomas Group of Companies, Inc.
 
Delaware
Hartman & Associates, Inc.
 
Florida
Ardaman & Associates, Inc.
 
Florida
Tetra Tech EC, Inc.
 
Delaware
Engineering Management Concepts, Inc.
 
California
Advanced Management Technology, Inc.
 
Virginia
Tetra Tech Consulting & Remediation, Inc.
 
Delaware

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QuickLinks

Exhibit 10.2

TETRA TECH, INC. FOURTH AMENDMENT TO NOTE PURCHASE AGREEMENT
CONFIRMATION
SCHEDULE I
SCHEDULE II Excluded Subsidiaries

Exhibit 1A

FORM OF SERIES A NOTE

Exhibit 1B

FORM OF SERIES B NOTE TETRA TECH, INC. ADJUSTABLE RATE SENIOR SECURED NOTE,
SERIES B, DUE MAY 30, 2008

Exhibit 2

SECOND AMENDED AND RESTATED SECURITY AGREEMENT
W I T N E S S E T H
SCHEDULE I TO SECURITY AGREEMENT
CORPORATE INFORMATION [TO BE INSERTED]
SCHEDULE II TO SECURITY AGREEMENT
Tradenames [TO BE ATTACHED]
SCHEDULE III TO SECURITY AGREEMENT
Prior Legal Names

Exhibit 3