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EXHIBIT 10.6    
    

TETRA TECH, INC.  

 
 

THIRD 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 December 14, 2004 

To
the Holders of the Senior Notes

    of Tetra Tech, Inc. Named in

    the Attached Schedule I 

Ladies
and Gentlemen: 

        Reference
is made to the Note Purchase Agreement dated as of May 15, 2001, as amended by the First Amendment to Note Purchase Agreement dated as of September 30, 2001 and
the Second Amendment to Note Purchase Agreement dated as of April 22, 2003 (the "Note Agreement"), between Tetra Tech, Inc., a Delaware corporation (the "Company"), and you 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 (the "Series A Notes") and $18,000,000 aggregate
principal amount of its 7.08% Senior Secured Notes, Series B, due May 30, 2008 (the "Series B Notes" and, together with the Series A Notes, the "Notes"). You are referred
to herein individually as a "Holder" and collectively as the "Holders". Capitalized terms used and not otherwise defined herein shall have the meanings ascribed to them in the Note Agreement, as
amended hereby. 

        The
Company has advised you that it will not be in compliance with Section 10.1(a) (Ratio of Consolidated Indebtedness to EBITDA) or Section 10.2 (Fixed Charge Coverage) of
the 

 

Note
Agreement for the fiscal quarter ending October 3, 2004 or in the foreseeable future. The Company has requested an amendment of those terms and you have agreed to such amendment on the
terms and 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 Holders agree as follows: 

1.     AMENDMENT OF NOTE AGREEMENT  

        1.1.    Amendment of Section 10.1. Section 10.1 of the Note Agreement is amended 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: (i) 3.25 to 1 for any Computation Period ending before
July 3, 2005; 3.00 to 1 for the Computation Period ending on July 3, 2005; or 2.25 to 1 for any Computation Period ending on or after October 2, 2005; or 

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

        1.2.    Amendment
of Section 10.2. Section 10.2 of the Note Agreement is amended to read in its entirety as follows: 

        "10.2    Fixed Charge Coverage Ratio; Minimum Adjusted EBITDA.

        (a)    The
Company will not permit the ratio, for any Computation Period ending on or after October 2, 2005, of (i) Adjusted EBITDA less Capital Expenditures to
(ii) Interest Expense plus all income taxes (including any franchise or other tax based upon gross or net income or receipts) paid by the Company and its Subsidiaries plus all required payments
of principal of Indebtedness of the Company and its Subsidiaries, in each case during such Computation Period (and determined on a consolidated basis), to be less than 1.25 to 1. 

        (b)    The
Company, will not permit Adjusted EBITDA to be less than the amount set forth below for any Computation Period ending on the relevant date set forth below: 

	Minimum Adjusted EBITDA
 
	 	Computation Period Ending

	$67,000,000	 	October 3, 2004
	$56,000,000	 	January 2, 2005
	$52,500,000	 	April 3, 2005
	 	 	 

2

 

	

$60,000,000	
 	

July 3, 2005
	$90,000,000	 	October 2, 2005

        1.3.    Amendment
of Section 10.8. Section 10.8 of the Note Agreement is amended by deleting the word "and" at the end of
Section 10.8(c), deleting the period at the end of Section 10.8(d) and inserting in substitution therefor "; and" and adding a new Section 10.8(e), to read in its entirety as
follows: 

        (e)    in
no event may a Subsdiary be designated Unrestricted unless it is an Excluded Subsidiary, as such term is defined in the Credit Agreement. 

        1.4.    Section 22.
Section 22 of the Note Agreement (including Sections 22.1 and 22.2) is amended to read in its entirety as
follows: 

        "22. RESERVED."

        1.5.    Schedule B.
The following definitions in Schedule B to the Note Agreement are amended to read in their entirety or are added,
in appropriate alphabetical order, as follows: 

        "Adjusted Consolidated Net Income" means, for any period, the net income or loss of the Company and its Restricted Subsidiaries for such
period, excluding (a) extraordinary nonrecurring gains or losses and (b) non-cash impairment of property, plant and equipment and of intangible assets. 

        "Adjusted EBITDA" means, for any Computation 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 Securities and Exchange Commission) giving effect to (a) any acquisition made by the Company or any Restricted Subsidiary during such Computation 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 Restricted Subsidiary,
division or other operating unit made during such Computation Period. If the Company or any Restricted 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. 

3

 

        "Adjusted Leverage Ratio" means, as of any date, the ratio of (a) Funded Debt on such date to (b) Adjusted EBITDA for the
Computation Period most recently ended on or prior to such date. 

        "Capital Expenditures" means all expenditures which, in accordance with GAAP, would be required to be capitalized and shown on the
consolidated balance sheet of the Company, but excluding expenditures made in connection with the replacement, substitution or restoration of assets to the extent financed (i) from insurance
proceeds (or other similar recoveries) paid on account of the loss of or damage to the assets being replaced or restored or (ii) with awards of compensation arising from the taking by eminent
domain or condemnation of the assets being replaced. 

        "Computation Period" means any period of four consecutive Fiscal Quarters ending on the last day of a Fiscal Quarter. 

        "Consolidated Net Income" means, with respect to the Company and its Restricted Subsidiaries for any period, the consolidated net income
(or loss) of the Company and its Restricted Subsidiaries for such period. 

        "Fiscal Quarter" means a fiscal quarter of a Fiscal Year. 

        "Fiscal Year" means any period of 12 consecutive calendar months ending on Sunday which is closest to the last day of September.
References to a Fiscal Year with a number corresponding to any calendar year (e.g. "Fiscal Year 2004") refer to the Fiscal Year ending on the Sunday which is closest to the last day of September
occurring during such calendar year. For example, Fiscal Year 2004 shall refer to the Fiscal Year ending October 3, 2004. Fiscal Year 2005 shall refer to the Fiscal Year ending
October 2, 2005, and Fiscal Year 2006 shall refer to the Fiscal Year ending October 1, 2006. 

        "Funded Debt" means all Indebtedness of the Company and its Restricted Subsidiaries, excluding (i) contingent obligations in
respect of Guaranties (except, in each case, to the extent constituting Guaranties in respect of Indebtedness of a Person other than the Company or any Restricted Subsidiary), (ii) Hedging
Obligations and (iii) Indebtedness of the Company to Restricted Subsidiaries and Indebtedness of Restricted Subsidiaries to the Company or to other Restricted Subsidiaries. 

        "Hedging Agreement" means any interest rate swap, interest rate cap, interest rate collar or similar agreement protecting against
fluctuations in interest rates, any currency swap, forward currency exchange agreement or similar agreement protecting against fluctuations in currency exchange rates, any commodity swap or similar
agreement protecting against fluctuations in commodity prices, any option to enter into any of the foregoing, and any combination of any of the foregoing. 

        "Hedging Obligations" means, with respect to any Person, obligations of such Person under Hedging Agreements. 

4

 

        "Indebtedness" with respect to any Person means, at any time, without duplication, (a) all indebtedness of such Person for borrowed
money, whether or not evidenced by bonds, debentures, notes or similar instruments, (b) all obligations of such Person as lessee under Capital Leases which have been recorded as liabilities on
a balance sheet of such Person, (c) all obligations of such Person to pay the deferred purchase price of property or services (other than trade accounts payable in the ordinary course of
business), including "earn-outs" and similar obligations, (d) all indebtedness secured by a Lien on the property of such Person, whether or not such indebtedness shall have been
assumed by such Person (it being understood that if such Person has not assumed or otherwise become personally liable for any such indebtedness, the amount of the Indebtedness of such Person in
connection therewith shall be limited to the lesser of the face amount of such indebtedness or the fair market value of all property of such Person securing such indebtedness), (e) all
obligations, contingent or otherwise, with respect to the face amount of all letters of credit (whether or not drawn) and banker's acceptances issued for the account of such Person, (f) net
Hedging Obligations of such Person and (g) all Guaranties of such Person. The amount of Indebetedness arising in connection with any "earn-out" or similar obligation shall be equal
to the maximum reasonably expected liability with respect thereto as of the date of determination. 

        "Interest Expense" means, for any Computation Period, the consolidated interest expense of the Company and its Restricted Subsidiaries for
such Computation Period (including all imputed interest on Capital Leases). 

The
definition of EBITDA in Schedule B is deleted. 

2.     REAFFIRMATION; REPRESENTATIONS AND WARRANTIES  

        2.1.    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 Third Amendment. 

        2.2.    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 Holders and (d) for other changes that could not reasonably be expected to have a Material Adverse Effect. 

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

        2.4.    Authorization.
The execution, delivery and performance by the Company of this Third Amendment have been duly authorized by all necessary
corporate action and, except as 

5

 

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 and this Third Amendment each constitute the legal, valid and binding obligations of the Company, 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). 

3.     EFFECTIVE DATE  

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

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

        3.2.    Amendment
Fee. Each Holder shall have received payment of an amendment fee equal to 0.275% of the principal amount of the outstanding Notes
held by such Holder. 

        3.3.    Expenses.
The Company shall have paid all fees and expenses of special counsel to the Holders. 

        3.4.    Credit
Agreement. The Banks and the Company shall have amended Sections 10.6.2 (Fixed Charge Coverage Ratio) and 10.6.3 (Adjusted Leverage
Ratio) of the Credit Agreement in a manner substantially identical to the amendments of Sections 10.1(a) and 10.2 of the Note Purchase Agreement contained in this Third Amendment and each Holder shall
have received a copy of such amendment to the Credit Agreement in the form executed.. 

4.     MISCELLANEOUS  

        4.1.    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. 

        4.2.    Reference
to and Effect on the Note Agreement. Upon the final effectiveness of this Third 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. 

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

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

6

 

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

7

  

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

	 	 	TETRA TECH, INC.
	

 	
 	

By:	

/s/  DAVID W. KING      
 David W. King

Chief Financial Officer and Treasurer

S-1

 

HOLDERS:

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	 
	

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-2

 

	

CONNECTICUT GENERAL LIFE INSURANCE COMPANY	

 
	

By:	

CIGNA Investments, Inc. (authorized agent)	

 
	

By:	

	

 
	Name:	    	 
	Title:	 	 
	

LIFE INSURANCE COMPANY OF NORTH AMERICA	

 
	

By:	

CIGNA Investments, Inc. (authorized agent)	

 
	

By:	

	

 
	Name:	    	 
	Title:	 	 

S-3

 

	

UNITED OF OMAHA LIFE INSURANCE COMPANY	

 
	

By:	

/s/  EDWIN H. GARRISON, JR.      
	

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

UNITED OF OMAHA LIFE INSURANCE COMPANY	

 
	

By:	

/s/  EDWIN H. GARRISON, JR.      
	

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

MUTUAL OF OMAHA INSURANCE COMPANY	

 
	

By:	

/s/  EDWIN H. GARRISON, JR.      
	

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

HARTFORD LIFE INSURANCE COMPANY	

 
	By:	Hartford Investment Services, Inc., its Agent and Attorney-in-Fact	 
	

By:	

/s/  RONALD MENDEL      
	

 
	Name:	Ronald Mendel	 
	Title:	Managing Director	 
	 	 	 

S-4

 

	

NATIONWIDE LIFE INSURANCE COMPANY	

 
	

By:	

/s/  MARK W. POEPPELMAN      
	

 
	Name:	Mark W. Poeppelman	 
	Title:	Vice President	 
	

NATIONWIDE LIFE AND ANNUITY INSURANCE COMPANY	

 
	

By:	

/s/  MARK W. POEPPELMAN      
	

 
	Name:	Mark W. Poeppelman	 
	Title:	Vice President	 
	 	 	 

S-5

 

	

NATIONWIDE LIFE INSURANCE

COMPANY OF AMERICA (formerly

PROVIDENT MUTUAL LIFE

INSURANCE COMPANY)	

 
	

By:	

/s/  MARK W. POEPPELMAN      
	

 
	Name:	Mark W. Poeppelman	 
	Title:	Vice President	 
	

SECURITY FINANCIAL LIFE INSURANCE CO.	

 
	

By:	

/s/  KEVIN W. HAMMOND      
	

 
	Name:	Kevin W. Hammond	 
	Title:	Vice President

Chief Investment Officer	 
	

THE CANADA LIFE ASSURANCE COMPANY as beneficial owner	

 
	

By:	

/s/  TAD ANDERSON      
	

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

By:	

/s/  JAMES G. LOWERY      
	

 
	Name:	James G. Lowery	 
	Title:	Ass't. V.P., Investments, U.S. Operations	 
	

CANADA LIFE INSURANCE COMPANY OF NEW YORK as beneficial owner	

 
	

By:	

/s/  TAD ANDERSON      
	

 
	Name:	Tad Anderson	 
	Title:	Manager, Investments, CLAC	 
	

By:	

/s/  JAMES G. LOWERY      
	

 
	Name:	James G. Lowery	 
	Title:	Ass't. V.P., Investments, CLAC	 
	 	 	 

S-6

 

	

THRIVENT FINANCIAL FOR LUTHERANS,

    Successor by merger to Lutheran

    Brotherhood

	

 
	

By:	

	

 
	Name:	 	 
	Title:	 	 

S-7

 

	

MODERN WOODMEN OF AMERICA	

 
	

By:	

/s/  MICHAEL E. DAU      
	

 
	Name:	Michael E. Dau	 
	Title:	 	 

S-8

 
 
 

CONFIRMATION    
    

        Each of the undersigned acknowledges receipt of the foregoing First 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 to which such undersigned is a party. 

	 	 	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 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
	

 	
 	

GEOTRANS, INC.

SCM CONSULTANTS, INC.

TETRA TECH FW, INC.
	

 	
 	

By:	

/s/  DAVID W. KING      
 David W. King

Assistant Treasurer

S-9

  

 
 

SCHEDULE I    
    

	Series A Holders
 
	 	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 Life 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
	Provident Mutual Life Insurance Company	 	 	5,000,000
	Security Financial Life Insurance Co.	 	 	2,000,000

       

	Series B Holders
 
	 	Outstanding

Principal

Amount

	The Canada Life Assurance Company	 	$	6,960,000
	Canada Life Insurance Company of New York	 	 	240,000
	Lutheran Brotherhood	 	 	4,800,000
	Modern Woodmen of America	 	 	2,400,000

I-1

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EXHIBIT 10.6

THIRD AMENDMENT TO NOTE PURCHASE AGREEMENT

CONFIRMATION

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EXHIBIT 10.20    
    

 
 

INDEMNITY AGREEMENT    
    

        THIS INDEMNITY AGREEMENT (this "Agreement") dated as
of                        , 2004, is made by and between Tetra Tech, Inc., a Delaware corporation (the
"Company"), and                        (the "Indemnitee"). 

R
E C I T A L S: 

        A.    The
Company recognizes that competent and experienced persons are increasingly reluctant to serve as directors and officers of corporations unless they are protected by
comprehensive liability insurance or indemnification, or both, due to increased exposure to litigation costs and risks resulting from their service to such corporations, and due to the fact that the
exposure frequently bears no reasonable relationship to the compensation of such directors or officers. 

        B.    The
statutes and judicial decisions regarding the duties of directors and officers are often difficult to apply, ambiguous or conflicting, and therefore fail to provide
such directors with adequate, reliable knowledge of legal risks to which they are exposed or information regarding the proper course of action to take. 

        C.    The
Company and the Indemnitee recognize that plaintiffs often seek damages in such large amounts and the costs of litigation may be so substantial (whether or not the
case is meritorious), that the defense and/or settlement of such litigation is often beyond the personal resources of directors and officers. 

        D.    The
Company believes that it is unfair for its directors and officers to assume the risk of substantial judgments and other expenses which may occur in cases in which the
director and/or officer, as the case may be, received no personal profit and in cases where such person acted in good faith. 

        E.    Section 145
of the General Corporation Law of Delaware ("Section 145"), under which the Company is organized, empowers the Company to indemnify its
directors and officers by agreement and to indemnify persons who serve, at the request of the Company, as the directors and officers of other corporations or enterprises, and expressly provides that
the indemnification provided by Section 145 is not exclusive. 

        F.    The
Board of Directors of the Company has determined that contractual indemnification as set forth herein is not only reasonable and prudent but necessary to promote the
best interests of the Company and its stockholders. 

        G.    The
Company desires and has requested the Indemnitee to serve or continue to serve as a director and/or officer of the Company. 

        H.    The
Indemnitee only is willing to serve, or to continue to serve, as a director and/or officer of the Company if the Indemnitee is furnished the indemnity provided for
herein by the Company. 

 
A
G R E E M E N T: 

        NOW
THEREFORE, in consideration of the mutual covenants and agreements set forth below, the parties hereto, intending to be legally bound, hereby agree as follows: 

        1.    Definitions.

        (a)    Agent.
For purposes of this Agreement, "agent" of the Company means any person who: (i) is or was a director and/or officer of the
Company or a subsidiary of the Company; or (ii) is or was serving at the
request of, for the convenience of, or to represent the interest of the Company or a subsidiary of the Company as a director, officer or trustee of, or in any other capacity with, another foreign or
domestic corporation, partnership, joint venture or employee benefit plan. 

        (b)    Expenses.
For purposes of this Agreement, "expenses" includes all direct and indirect costs of any type or nature whatsoever (including,
without limitation, all attorneys' fees and related disbursements, other out-of-pocket costs and reasonable compensation for time spent by the Indemnitee for which he is not
otherwise compensated by the Company or any third party, provided that the rate of compensation and estimated time involved is approved in advance by the Board of Directors of the Company), actually
and reasonably incurred by the Indemnitee in connection with either the investigation, defense or appeal of a proceeding or establishing or enforcing a right to indemnification under this Agreement,
Section 145 or otherwise, and amounts paid in settlement by or on behalf of the Indemnitee, but shall not include any judgments, fines or penalties actually levied against the Indemnitee. 

        (c)    Proceedings.
For the purposes of this Agreement, "proceeding" means any threatened, pending, or completed action, suit, arbitration, hearing
or other proceeding, whether civil, criminal, administrative, investigative or any other type whatsoever. 

        (d)    Subsidiary.
For purposes of this Agreement, "subsidiary" means any corporation of which more than 50% of the outstanding voting securities
are owned directly or indirectly by the Company, by the Company and one or more other subsidiaries, or by one or more other subsidiaries. 

        2.    Agreement
to Serve. The Indemnitee agrees to serve and/or continue to serve as an agent of the Company or a subsidiary of the Company, at the
will of such corporation (or under separate agreement, if such agreement exists), in the capacity the Indemnitee currently serves as an agent of such corporation, so long as the Indemnitee is duly
appointed or elected and qualified in accordance with the applicable provisions of the Bylaws of such corporation or of any subsidiary thereof, or until such time as the Indemnitee tenders his
resignation in writing; provided, however, that nothing contained in this Agreement is intended to create any right to continued employment of the Indemnitee in any
capacity or to give the Company the right to require the Indemnitee to resign from the Board of Directors of the Company. This Agreement shall continue in force after the Indemnitee has ceased to
serve as a director or officer of the Company. 

2

 

        3.    Indemnification.

        (a)    Indemnification
in Third Party Proceedings. Subject to Section 10 below, the Company shall indemnify the Indemnitee if the Indemnitee
is a party to or threatened to be made a party to or otherwise involved in any proceeding (other than a proceeding by or in the name of the Company to procure a judgment in its favor) by reason of the
fact that the Indemnitee is or was an agent of the Company, or by reason of any act or inaction by him in any such capacity, against any and all expenses and liabilities of any type whatsoever
(including, but not limited to, judgments, fines and penalties), actually and reasonably incurred by him in connection with the investigation, defense, settlement or appeal of such proceeding, but
only if the Indemnitee acted in good faith and in a manner he reasonably believed to be in, or not opposed to, the best interests of the Company, and, with respect to any criminal action or
proceeding, had no reasonable cause to believe Indemnitee's conduct was unlawful, pursuant to the presumption set forth in subsection (c) below, as applicable. The
termination of any proceeding by judgment, order of court, settlement, conviction or on plea of nolo contendere, or its equivalent, shall not, of itself, create a
presumption that the Indemnitee did not act in good faith in a manner which he reasonably believed to be in, or not opposed to, the best interests of the Company, and with respect to any criminal
proceedings, that such person had reasonable cause to believe that his conduct was unlawful. 

        (b)    Indemnification
in Derivative Actions. Subject to Section 10 below, the Company shall indemnify the
Indemnitee if the Indemnitee is a party to or threatened to be made a party to or otherwise involved in any proceeding by or in the name of the Company to procure a judgment in its favor by reason of
the fact that the Indemnitee is or was an agent of the Company, or by reason of any act or inaction by him in any such capacity, against all expenses actually and reasonably incurred by the Indemnitee
in connection with the investigation, defense, settlement, or appeal of such proceedings, but only if the Indemnitee acted in good faith and in a manner he reasonably believed to be in, or not opposed
to, the best interests of the Company, pursuant to the presumption set forth in subsection (c) below; provided, however, that no indemnification under this
Section 3 shall be made in respect of any claim, issue or matter as to which the Indemnitee shall have been finally adjudged to be liable to the Company by a court
of competent jurisdiction due to willful misconduct of a culpable nature in the performance of the Indemnitee's duty to the Company, unless and only to the extent that any court in which such
proceeding was brought shall determine upon application that, despite the adjudication of liability but in view of all the circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses as such court shall deem proper. 

        (c)    Conclusive
Presumption Regarding Indemnitee Conduct. With respect to Sections 3(a) and
3(b) above, the Indemnitee shall be conclusively presumed to have acted in good faith and in a manner Indemnitee reasonably believed to be in, or not opposed to, the best
interests of the Company, and, with respect to any criminal action or proceeding, to have had no reasonable cause to believe Indemnitee's conduct was unlawful, unless a determination is made that the
Indemnitee has not acted in accordance with the standards set forth above (i) by the Board of Directors by a majority vote of a quorum thereof consisting of directors who were not parties to
the proceeding due to which a claim is made under this Agreement, (ii) by the stockholders of the Company by a majority vote of stockholders who were not parties to such a proceeding, or
(iii) in a written opinion of independent legal counsel, selection of whom has been approved by the 

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Indemnitee
in writing or, if not so approved, then approved by a panel of arbitrators, one of whom is selected by the Company, another of whom is selected by the Indemnitee and the last of whom is
selected by the first two arbitrators so selected. 

        4.    Indemnification
of Expenses of Successful Party. Notwithstanding any other provisions of this Agreement, to the extent that the Indemnitee
has been successful on the merits or otherwise in defense of any proceeding or in defense of any claim, issue or matter therein, including the dismissal of any action without prejudice, the Company
shall indemnify the Indemnitee against all expenses actually incurred in connection with the investigation, defense or appeal of such proceeding. 

        5.    Partial
Indemnification. If the Indemnitee is entitled under any provision of this Agreement to indemnification by the Company for some or a
portion of any expenses or liabilities of any type whatsoever (including, but not limited to, judgments, fines or penalties) actually incurred by him in the investigation, defense, settlement or
appeal of a proceeding but is not entitled, however, to indemnification for the total amount thereof, the Company shall nevertheless indemnify the Indemnitee for the portion thereof to which the
Indemnitee is entitled. 

        6.    Advancement
of Expenses. Subject to Section 10(b) below, the Company shall advance all expenses incurred
by the Indemnitee in connection with the investigation, defense, settlement or appeal of any proceeding to which the Indemnitee is a party or is threatened to be made a party by reason of the fact
that the Indemnitee is or was an agent of the Company. The Indemnitee hereby undertakes to repay such amounts advanced only if, and to the extent that, it shall ultimately be determined that the
Indemnitee is not entitled to be indemnified by the Company as authorized by this Agreement. The advances to be made hereunder shall be paid by the Company to or on behalf of the Indemnitee within
30 days following delivery of a written request therefor by the Indemnitee to the Company. 

        7.    Notice
and Other Indemnification Procedures. 

        (a)    Notification
of Proceeding. Promptly after receipt by the Indemnitee of notice of the commencement of or the threat of commencement of any
proceeding, the Indemnitee shall, if the Indemnitee believes that indemnification with respect thereto may be sought from the Company under this Agreement, notify the Company of the commencement or
threat of commencement thereof. 

        (b)    Request
for Indemnification. Any indemnification requested by the Indemnitee under Section 3 hereof
shall be made no later than 10 days after receipt of the written request of the Indemnitee, unless a good faith determination is made by the Company's Board of Directors within said
10-day period in accordance with one of the methods set forth in Section 3(c) above that the Indemnitee is not or (subject to final judgment or other
final adjudication as provided in Section 10(a) below) ultimately will not be entitled to indemnification hereunder. 

        (c)    Application
for Enforcement. Notwithstanding a determination under Section 7(b) above that the
Indemnitee is not entitled to indemnification with respect to any specific proceeding, the Indemnitee shall have the right to apply to any court of competent jurisdiction for the 

4

 

purpose
of enforcing the Indemnitee's right to indemnification pursuant to this Agreement. In such an enforcement hearing or proceeding, the burden of proving by clear and convincing evidence that
indemnification or advances are not appropriate shall be on the Company. Neither the failure of the Company (including its Board of Directors, stockholders, independent legal counsel or the panel of
arbitrators) to have made a determination prior to the commencement of such action that the Indemnitee is entitled to indemnification hereunder, nor an actual determination by the Company (including
its Board of Directors or independent legal counsel or the panel of arbitrators) that the Indemnitee is not entitled to indemnification hereunder, shall be a defense to the action or create any
presumption that the Indemnitee is not entitled to indemnification hereunder. 

        (d)    Indemnification
of Certain Expenses. The Company shall indemnify the Indemnitee against all expenses incurred in connection with any hearing
or proceeding under this Section 7 unless the Company prevails by clear and convincing evidence in such hearing or proceeding. 

        8.    Assumption
of Defense. In the event the Company shall be obligated to pay the expenses of any proceeding against the Indemnitee, the Company,
if appropriate, shall be entitled to assume the defense of such proceeding, with counsel reasonably acceptable to the Indemnitee, upon the delivery to the Indemnitee of written notice of its election
to do so. After delivery of such notice, approval of such counsel by the Indemnitee and the retention of such counsel by the Company, the Company shall not be liable to the Indemnitee under this
Agreement for any fees of counsel subsequently incurred by the Indemnitee with respect to the same proceeding, provided that (a) the Indemnitee shall have the right to employ his counsel in
such proceeding at the Indemnitee's expense; and (b) if (i) the employment of counsel by the Indemnitee has been previously authorized in writing by the Company, (ii) the
Indemnitee's counsel delivers a written notice to the Company stating that such counsel has reasonably concluded that there may be a conflict of interest between the Company and the Indemnitee in the
conduct of any such defense or (iii) the Company shall not, in fact, have employed counsel to assume the defense of such proceeding within a reasonable time, not exceeding 60 days or, if
shorter, such period as shall not prejudice the defense of the Indemnitee, then in any such event the fees and expenses of the Indemnitee's counsel shall be at the expense of the Company. 

        9.    Insurance.
The Company shall maintain directors' and officers' liability insurance ("D&O Insurance") with respect to which the Indemnitee is
named as an insured. Notwithstanding any other provision of this Agreement, the Company shall not be obligated to indemnify the Indemnitee for expenses, judgments, fines or penalties which have been
paid directly to the Indemnitee by D&O Insurance. If commercially available, the D&O Insurance shall provide for coverage in the minimum amount of
$20,000,000. The Company shall not take any action intended to change the terms of the D&O Insurance or the rights of the insureds granted thereunder without providing notice to, and obtaining the
approval of, the Board of Directors. At the time the Company receives from the Indemnitee any notice of the commencement of a proceeding, the Company shall give prompt notice of the commencement of
such proceeding to the insurers in accordance with the procedures set forth in the policy. The Company shall thereafter take all necessary or desirable action to cause such insurers to pay, on behalf
of the Indemnitee, all amounts payable as a result of such proceeding in accordance with the terms of such policy. 

5

 

        10.    Exceptions.

        (a)    Certain
Matters. Any provision herein to the contrary notwithstanding, the Company shall not be obligated pursuant to the terms of this
Agreement to indemnify the Indemnitee on account of any proceeding (i) with respect to remuneration paid to the Indemnitee if it is determined by final judgment or other final adjudication, in
either case not subject to further appeal, that such remuneration was in violation of law; (ii) which final judgment is rendered against the Indemnitee for an accounting of profits made from
the purchase or sale by the Indemnitee of securities of the Company pursuant to the provisions of Section 16(b) of the Securities Exchange Act of 1934, as amended; or (iii) which (but
only to the extent that it) is determined by final judgment or other final adjudication, in either case not subject to further appeal, that the Indemnitee's conduct was in bad faith, knowingly
fraudulent or deliberately dishonest. For purposes of the foregoing sentence, a final judgment or other adjudication may be reached in either the underlying proceeding or action in connection with
which indemnification is sought or a separate proceeding or action to establish rights and liabilities under this Agreement. 

        (b)    Claims
Initiated by the Indemnitee. Any provision herein to the contrary notwithstanding, the Company shall not be obligated pursuant to the
terms of this Agreement to indemnify or advance expenses to the Indemnitee with respect to proceedings or claims initiated or brought voluntarily by the Indemnitee and not by way of defense, except
with respect to proceedings brought to establish or enforce a right to indemnification under this Agreement or any other statute or law or otherwise as required under Section 145, but such
indemnification or advancement of expenses may be provided by the Company in specific cases if the Board of Directors of the Company finds it to be appropriate. 

        (c)    Action
for Indemnification. Any provision herein to the contrary notwithstanding, the Company shall be obligated pursuant to the terms of
this Agreement to indemnify the Indemnitee for any expenses incurred by the Indemnitee with respect to any proceeding instituted by the Indemnitee to enforce or interpret this Agreement unless the
Company prevails in such proceeding by clear and convincing evidence. 

        (d)    Unauthorized
Settlements. Any provision herein to the contrary notwithstanding, the Company shall not be obligated pursuant to the terms of
this Agreement to indemnify the Indemnitee under this Agreement for any amounts paid in settlement of a proceeding effected without the Company's written consent. Neither the Company nor the
Indemnitee shall unreasonably withhold consent to any proposed settlement; provided, however, that the Company may in any event decline to consent to (or to otherwise
admit or agree to any liability for indemnification hereunder in respect of) any proposed settlement if the Company determines in good faith (pursuant to
Section 7(b) above) that the Indemnitee is not or ultimately will not be entitled to indemnification hereunder. 

        (e)    Securities
Act Liabilities. Any provision herein to the contrary notwithstanding, the Company shall not be obligated pursuant to the terms
of this Agreement to indemnify the Indemnitee or otherwise act in violation of any undertaking appearing in and required by the rules and regulations promulgated under the Securities Act of 1933, as
amended (the "Act") in any registration statement filed with the Securities and Exchange Commission under the Act. 

6

 

The
Indemnitee acknowledges that paragraph (h) of Item 512 of Regulation S-K currently generally requires the Company to undertake in connection with any registration
statement filed under the Act to submit the issue of the enforceability of the Indemnitee's rights under this Agreement in connection with any liability under the Act on public policy grounds to a
court of appropriate jurisdiction and to be governed by any final adjudication of such issue. The Indemnitee specifically agrees that any such undertaking shall supersede the provisions of this
Agreement and to be bound by any such undertaking. 

        11.    Nonexclusivity.
The provisions for indemnification and advancement of expenses set forth in this Agreement shall not be deemed exclusive of
any other rights which the Indemnitee may have under any provision of law, the Company's Certificate of Incorporation or Bylaws, in any court in which a proceeding is brought, the vote of the
Company's stockholders or disinterested directors, other agreements or otherwise, both as to action in the Indemnitee's official capacity and to action in another capacity while occupying his position
as an agent of the Company, and the Indemnitee's rights hereunder shall continue after the Indemnitee has ceased acting as an agent of the Company and shall inure to the benefit of the heirs,
executors and administrators of the Indemnitee. Any provision herein to the contrary notwithstanding, the Company may provide, in specific cases, the Indemnitee with full or partial indemnification if
the Board of Directors of the Company determines that such indemnification is appropriate. 

        12.    Subrogation.
In the event of payment under this Agreement, the Company shall be subrogated to the extent of such payment to all of the
rights of recovery of the Indemnitee, who, at the request and expense of the Company, shall execute all papers required and shall do everything that may be reasonably necessary to secure such rights,
including the execution of such documents as may be necessary to enable the Company effectively to bring suit to enforce such rights. 

        13.    Interpretation
of Agreement. It is understood that the parties hereto intend this Agreement to be interpreted and enforced so as to provide
indemnification to the Indemnitee to the fullest extent now or hereafter permitted by law. 

        14.    Severability.
If any provision or provisions of this Agreement shall be held to be invalid, illegal or unenforceable for any reason
whatsoever, (a) the validity, legality and enforceability of the remaining provisions of the Agreement (including without limitation, all portions of any paragraphs of this Agreement containing
any such provision held to be invalid, illegal or unenforceable, that are not themselves invalid, illegal or unenforceable) shall not in any way be affected or impaired thereby; and (b) to the
fullest extent possible, the provisions of this Agreement (including, without limitation, all portions of any paragraph of this Agreement containing any such provision held to be invalid, illegal or
unenforceable, that are not themselves invalid, illegal or unenforceable) shall be construed so as to give effect to the intent manifested by the provision held invalid, illegal or unenforceable and
to give effect to Section 13 hereof. 

        15.    Modification
and Waiver. No supplement, modification or amendment of this Agreement shall be binding unless executed in writing by the
parties hereto. No waiver of any of the provisions of this Agreement shall be deemed or shall constitute a waiver of any other provision hereof (whether or not similar) nor shall such waiver
constitute a continuing waiver. 

7

 

The
indemnification rights afforded to the Indemnitee hereby are contract rights and may not be diminished, eliminated or otherwise affected by amendments to the Certificate of Incorporation or Bylaws
of the Company or by other agreements. 

        16.    Successors
and Assigns. The terms of this Agreement shall bind, and shall inure to the benefit of, the successors and assigns of the parties
hereto, including, without limitation, the surviving corporation in any merger transaction or other business combination or reorganization to which the Company is a party. 

        17.    Duration
of Agreement. This Agreement shall continue until and terminate upon the later of: (i) ten years after the date that
Indemnitee shall have ceased to serve as a director or officer of the Company; or (ii) the final termination of any proceeding then pending in respect of which the Indemnitee is grated rights
of indemnification or advance of expenses hereunder and of any proceeding commenced by the Indemnitee pursuant to Section 7 hereof relating thereto. 

        18.    Counterparts.
This Agreement may be executed in one or more counterparts, each of which shall for all purposes be deemed to be an original
but all of which together shall constitute one and the same Agreement. Only one such counterpart signed by the party against whom enforceability is sought needs to be produced to evidence the
existence of this Agreement. 

        19.    Enforcement.

        (a)    Reliance.
The Company expressly confirms and agrees that it has entered into this Agreement and assumed the obligations imposed on it hereby
in order to induce the Indemnitee to serve or continue to serve as a director and/or officer of the Company or its subsidiaries, and to serve upon any committee of the Board of Directors of the
Company or its subsidiaries as requested by such Board, and the Company acknowledges that the Indemnitee is relying upon this Agreement in serving as a director and/or officer of the Company or its
subsidiaries and a member of any such committee. 

        (b)    Entire
Agreement. This Agreement constitutes the entire agreement between the parties hereto with respect to the subject matter hereof and
supersedes all prior agreements and understandings, oral, written and implied, between the parties hereto with respect to the subject matter hereof. 

        20.    Contribution.
To the fullest extent permissible under applicable law, if the indemnification provided for in this Agreement is unavailable
to the Indemnitee for any reason whatsoever, the Company, in lieu of indemnifying the Indemnitee, shall contribute to the amount incurred by the Indemnitee, whether for judgments, fines, penalties,
excise taxes, amounts paid or to be paid in settlement and/or for expenses, in connection with any claim relating to an indemnifiable event under this Agreement, in such proportion as is deemed fair
and reasonable in light of all of the circumstances of such proceeding in order to reflect (i) the relative benefits received by the Company and the Indemnitee as a result of the event(s)
and/or transaction(s) giving rise to such proceeding; and (ii) the relative fault of the Company (and its directors, officers, employees and agents) and the Indemnitee in connection with such
event(s) and/or transaction(s). 

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        21.    Notice.
Except as otherwise provided herein, any notice or demand which, by the provisions hereof, is required or which may be given to or
served upon the parties hereto shall be in writing and, if by telegram, telecopy or telex, shall be deemed to have been validly served, given or delivered when sent, if by personal delivery, shall be
deemed to have been validly served, given or delivered upon actual delivery and, if mailed, shall be deemed to have been validly served, given or delivered three business days after deposit in the
United States mails, as registered or certified mail, with proper postage prepaid and addressed to the party or parties to be notified at the addresses set forth on the signature page of this
Agreement (or such other address(es) as a party may designate for itself by like notice). 

        22.    Governing
Law. This Agreement shall be governed exclusively by and construed according to the laws of the State of Delaware, as applied to
contracts between Delaware residents entered into and to be performed entirely within Delaware. 

        IN
WITNESS WHEREOF, the parties hereto have entered into this Agreement effective as of the date first above written. 

	 	 	THE COMPANY:
	

 	
 	

TETRA TECH, INC.

a Delaware corporation
	

 	
 	

By:	

	 	 	Name:	Li-San Hwang
	 	 	Title:	Chairman and Chief Executive Officer
	    	 	 	 
	 	 	Address:	3475 East Foothill Boulevard

Pasadena, California 91107
	

 	
 	

THE INDEMNITEE:
	

 	
 	

 Signature of the Indemnitee
	

 	
 	

 Print or Type Name of the Indemnitee
	

 	
 	

Address:	

 

9

QuickLinks

EXHIBIT 10.20

INDEMNITY AGREEMENT

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