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FIRST AMENDMENT
to
SECOND AMENDED AND RESTATED
UNDERWRITING AND CONTINUING INDEMNITY AGREEMENT

    THIS FIRST AMENDMENT TO SECOND AMENDED AND RESTATED UNDERWRITING AND
CONTINUING INDEMNITY AGREEMENT dated as of June 13, 2000 (the "Amendment") is
entered into by and among (i) GREAT LAKES DREDGE & DOCK CORPORATION, a Delaware
corporation ("HOLDINGS"), and the SUBSIDIARIES of HOLDINGS from time to time
signatories hereto (collectively with HOLDINGS, the "INDEMNITORS"), and (ii)
RELIANCE INSURANCE COMPANY, a Pennsylvania corporation, UNITED PACIFIC INSURANCE
COMPANY, a Pennsylvania corporation, RELIANCE NATIONAL INSURANCE COMPANY, a
Delaware corporation, and RELIANCE SURETY COMPANY, a Delaware corporation
(collectively, the foregoing parties are referred to herein as "RELIANCE").

W I T N E S S E T H:

    WHEREAS, the INDEMNITORS and RELIANCE are parties to a certain Second
Amended and Restated Underwriting and Continuing Indemnity Agreement dated as of
August 19, 1998 (the "Agreement");

    WHEREAS, the INDEMNITORS have requested RELIANCE to amend a financial
covenant set forth in the Agreement; and

    WHEREAS, subject to the terms and conditions set forth herein RELIANCE is
willing to so amend the Agreement.

    NOW, THEREFORE, in consideration of the premises, and intending to be
legally bound hereby, the INDEMNITORS and RELIANCE hereby agree as follows:

    SECTION 1.  AMENDMENTS TO AGREEMENT.

    Subject to satisfaction of the conditions set forth in Section 2 of this
Amendment and in reliance on the INDEMNITORS' warranties set forth in Section 3
below, Section 6.20 of the Agreement shall be hereby amended by deleting the
reference therein to "1.4 to 1" and in its place substituting "1.2 to 1".

    SECTION 2.  CONDITIONS PRECEDENT.

    This Amendment shall be effective upon receipt by RELIANCE of the documents
listed below, each, unless otherwise noted, dated the date hereof, duly
executed, in form and substitute satisfactory to RELIANCE and in quantities
designed by RELIANCE:

(a)This Amendment executed by all parties hereto.

(b)The INDEMNITORS shall have delivered such other documents as RELIANCE may
reasonably request.

    SECTION 3.  WARRANTIES.

    To induce RELIANCE to enter into this Amendment, the INDEMNITORS warrant to
RELIANCE as of the date hereof and after giving effect to this Amendment that:

(a)The representations and warranties contained in Article V of the Agreement,
in Section 4 of each SECURITY AGREEMENT (A/R), in Section 4 of each SECURITY
AGREEMENT (EQUIPMENT), in Section 4 of the PLEDGE AGREEMENT and in Article 1 of
each of the VESSEL MORTGAGES are correct in all material respects on and as of
the date hereof as though made on and as of such date except to the extent
stated to relate to an earlier date, in which case such representation and
warranty shall be correct as of such earlier date; and

(b)No EVENT OF DEFAULT has occurred and is continuing.

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    SECTION 4.  GENERAL.

(a)Terms used but not otherwise defined herein are used herein as defined in the
Agreement.

(b)As hereby modified, the Agreement shall remain in full force and effect and
is hereby ratified, approved and confirmed in all respects.

(c)This Amendment shall be binding upon and shall inure to the benefit of the
INDEMNITORS and RELIANCE and respective successors and assigns of the RELIANCE.

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

IN WITNESS WHEREOF, this Agreement is executed by the parties on the day and
date first set forth above.

GREAT LAKES DREDGE & DOCK CORPORATION  
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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GREAT LAKES DREDGE & DOCK COMPANY
 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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LYDON DREDGING & CONSTRUCTION COMPANY, LTD.

 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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NATCO DREDGING LIMITED PARTNERSHIP
 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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2

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NORTH AMERICAN TRAILING COMPANY
 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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FIFTY-THREE DREDGING COMPANY
 
By:
/s/ LESLIE A. BRAUN   

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Leslie A. Braun

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Its: President

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DAWSON DREDGING COMPANY
 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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GREAT LAKES CARIBBEAN DREDGING, INC.
 
By:
/s/ DEBORAH A. WENSEL   

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Deborah A. Wensel

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Its: Vice President and CFO

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RELIANCE INSURANCE COMPANY
UNITED PACIFIC INSURANCE COMPANY
RELIANCE NATIONAL INSURANCE COMPANY
RELIANCE SURETY COMPANY
 
By:
/s/ NICOLAS SEMINARA   

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Nicholas Seminara

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Its: Vice President

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3

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FIRST AMENDMENT to SECOND AMENDED AND RESTATED UNDERWRITING AND CONTINUING
INDEMNITY AGREEMENT
W I T N E S S E T H: