Exhibit 4.1


FOURTH
SUPPLEMENTAL INDENTURE


THIS FOURTH
SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”) dated as of
December 26, 2006 by and among Great Lakes Dredge & Dock Corporation, a
Delaware corporation (the “Issuer”), NASDI Holdings Corporation, a Delaware
corporation, Great Lakes Dredge & Dock Company, a New Jersey corporation,
Great Lakes Caribbean Dredging, Inc., a Delaware corporation, Dawson Marine
Services Company, a Delaware corporation, North American Site Developers, Inc.,
a Massachusetts corporation, Fifty-Three Dredging Corporation, a New Jersey
corporation, JDC Soil Management & Development Inc., a Massachusetts
corporation and Great Lakes Dredge & Dock Company, LLC, a Delaware limited
liability company (collectively, the “Guarantors”), Great Lakes
Dredge & Dock Holdings Corp., a Delaware corporation (“Holdings”)
and BNY Midwest Trust Company, an Illinois trust company, as trustee under the
indenture referred to below (the “Trustee”).


RECITALS


WHEREAS, the
Issuer and the Guarantors have previously executed and delivered to the Trustee
an indenture, dated as of December 22, 2003, as supplemented and amended from
time to time (the “Indenture”), providing for the issuance of an
aggregate principal amount of up to $175,000,000 of 73⁄4% Senior Subordinated
Notes due 2013 (the “Notes”);


WHEREAS, pursuant
to that certain Merger Agreement dated as of the date hereof by and among the
Issuer and Holdings, the Issuer shall merge with and into Holdings and Holdings
shall be the surviving corporation;


WHEREAS, Holdings,
as the surviving corporation, is required under Section 5.01 of the Indenture
to execute and deliver to the Trustee a supplemental indenture pursuant to
which Holdings shall assume all of the obligations of the Issuer under the
Indenture, the Registration Rights Agreement and the Notes; and


WHEREAS, pursuant
to Section 9.01 of the Indenture, the Issuer, the Guarantors, Holdings and the
Trustee are authorized to execute and deliver this Supplemental Indenture.


NOW THEREFORE, in
consideration of the foregoing and mutual covenants herein contained and
intending to be legally bound, the parties hereto mutually covenant and agree
for the equal and ratable benefit of the holders of the Notes as follows:


1.             DEFINED TERMS. As used in this
Supplemental Indenture, terms defined in the Indenture or in the preamble or
recital hereto are used herein as therein defined, except that the term “holders”
in this Supplemental Indenture shall refer to the term “Holders” as defined in
the Indenture and the Trustee acting on behalf of and for the benefit of such
Holders. The words “herein,” “hereof” and hereby and other words of similar
import used in this Supplemental Indenture refer to this Supplemental Indenture
as a whole and not to any particular section hereof.


2.             ASSIGNMENT AND ASSUMPTION.









 



(a)           As of the date hereof, the Issuer
hereby transfers and assigns to Holdings, and Holdings hereby assumes and
undertakes from the Issuer, all rights, powers, commitments, obligations and
liabilities of the Issuer under the Indenture, the Registration Rights
Agreement and the Notes (collectively, the “Assigned Instruments”) and
agrees to be bound by all other applicable provisions of the Assigned
Instruments.


(b)           With effect on and after the date
hereof, the Issuer shall be released from its obligations and covenants under
the Assigned Instruments.


3.             NOTICES. All notices or other
communications to Holdings shall be given as provided for the Company in 13.02
of the Indenture.


4.             RATIFICATION OF INDENTURE;
SUPPLEMENTAL INDENTURES PART OF INDENTURE. Except as expressly amended hereby,
the Indenture is in all respects ratified and confirmed and all the terms,
conditions and provisions thereof shall remain in full force and effect. This
Supplemental Indenture shall form a part of the Indenture for all purposes, and
every holder of Notes heretofore or hereafter authenticated and delivered shall
be bound hereby.


5.             GOVERNING LAW. THIS SUPPLEMENTAL
INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF
THE STATE OF NEW YORK.


6.             TRUSTEE MAKES NO REPRESENTATION.
The Trustee makes no representation as to the validity or sufficiency of this
Supplemental Indenture. The recitals and statements herein are deemed to be
those of the Issuer and the Guarantors and not of the Trustee.


7.             COUNTERPARTS. The parties may sign
any number of copies of this Supplemental Indenture. Each signed copy shall be
an original, but all of them together represent the same agreement.


8.             EFFECT OF HEADINGS. The Section
headings herein are for convenience only and shall not affect the construction
thereof.


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IN WITNESS
WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly
executed as of the date first above written.


	
  

  	
  ISSUER:

  
	
   

  	
  GREAT LAKES DREDGE & DOCK CORPORATION

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  GUARANTORS:

  
	
   

  	
  GREAT LAKES DREDGE & DOCK COMPANY, LLC

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  GREAT LAKES DREDGE & DOCK COMPANY

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  



 



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  GREAT LAKES CARIBBEAN DREDGING, INC.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  DAWSON MARINE SERVICES COMPANY

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  NORTH AMERICAN SITE DEVELOPERS, INC.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  



 



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  FIFTY-THREE DREDGING CORPORATION

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Paul Dinquel

  
	
   

  	
  Name:

  	
  Paul Dinquel

  
	
   

  	
  Title:

  	
  VP

  
	
   

  	
   

  
	
   

  	
  JDC SOIL MANAGEMENT & DEVELOPMENT INC.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  NASDI HOLDINGS CORPORATION

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  
	
   

  	
   

  
	
   

  	
  HOLDINGS:

  
	
   

  	
  GREAT LAKES DREDGE & DOCK HOLDINGS CORP.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /s/ Deborah A. Wensel

  
	
   

  	
  Name:

  	
  Deborah A. Wensel

  
	
   

  	
  Title:

  	
  Sr. VP & CFO

  



 



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  TRUSTEE:

  
	
   

  	
  BNY MIDWEST TRUST COMPANY, As Trustee

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  M. Callahan

  
	
   

  	
  Name: 

  	
  M. Callahan

  
	
   

  	
  Title:

  	
  Vice President

  



 



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