INSTRUMENT OF AMENDMENT TO THE
MDU RESOURCES GROUP, INC.
401(k) RETIREMENT PLAN

The MDU Resources Group, Inc. 401(k) Retirement Plan (as amended and restated
June 1, 2009) (the “Plan”), is hereby further amended, effective May 1, 2010,
unless otherwise indicated, as follows:

1.  
By replacing the table in Section D-1-2 Eligibility to Share in the Profit
Sharing Feature of Supplement D-1,  Provisions Relating to the Profit Sharing
Feature for Certain Participating Affiliates, with the following table:

Participating Affiliate
Current Effective Date
(Original Effective Date)
Anchorage Sand & Gravel Company, Inc. (excluding President)
January 1, 1999
Baldwin Contracting Company, Inc.
January 1, 1999
Bell Electrical Contractors, Inc.
January 1, 2002
Bitter Creek Pipelines, LLC1
January 1, 2010
(January 1, 2001)
Concrete, Inc.
January 1, 2001
Connolly-Pacific Co.
January 1, 2007
DSS Company2
January 1, 2004
(July 8, 1999)
E.S.I., Inc.
January 1, 2008
(January 1, 2003)
Fairbanks Materials, Inc.
May 1, 2008
Frebco, Inc.
January 1, 2008
(July 1, 2000)
Granite City Ready Mix, Inc.
June 1, 2002
Great Plains Natural Gas Co.
January 1, 2008
Hawaiian Cement (non-union employees hired after December 31, 2005)
January 1, 2009
Jebro Incorporated
November 1, 2005
Kent’s Oil Service
January 1, 2007
Knife River Corporation – Northwest (the Central Oregon Division, f/k/a HTS)
January 1, 2010
(January 1, 1999)
Knife River Corporation – Northwest (the Southern Idaho Division)
January 1, 2010
(January 1, 2006)

 
1

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

 

 
Participating Affiliate
Current Effective Date
(Original Effective Date)
Knife River Corporation – Northwest (the Spokane Division)
January 1, 2010
(January 1, 2006)
Knife River Corporation - South   (f/k/a Young Contractors, Inc.)
January 1, 2008
(January 1, 2007)
LTM, Incorporated
January 1, 2003
 
Montana-Dakota Utilities Co. (including union employees)
January 1, 2008
Wagner Industrial Electric, Inc.
January 1, 2008
 
Wagner Smith Equipment Co.
January 1, 2008
(July 1, 2000)
WBI Holdings, Inc.1
January 1, 2009
 
WHC, Ltd.
September 1, 2001
 
Williston Basin Interstate Pipeline Company1
January 1, 2009
 

1 Requirement to be an Active Employee on the last day of the Plan Year does not
apply.  Eligible employees participating in a management incentive compensation
plan or an executive incentive compensation plan are not eligible for a Profit
Sharing Contribution.  Employees of the Total Corrosion Solutions division of
Bitter Creek Pipelines, LLC are excluded from this feature.
2 In the event a Participating Affiliate adopts a Profit Sharing Feature,
effective as of the date of participation in the Plan, the amount of any such
contribution allocated to a Supplement D-1 Participant shall be based upon
Compensation, excluding bonuses, received while in the employ of the
Participating Affiliate after the date of acquisition by the Company or any
Affiliate.

Explanation: This amendment removes KRC Aggregate, Inc. as a Participating
Affiliate of Supplement D-1 of the Plan as of May 1, 2010, the date KRC
Aggregate, Inc. merged into Concrete, Inc.  In accordance with the provisions of
this Supplement D-1, hours of service completed with KRC Aggregate, Inc. are
recognized for purposes of this amendment.

2.  
By amending the following entry to Schedule A to the Plan:

For employees hired prior to May 1, 2010, WHC, Ltd. (WHC) shall make a matching
contribution equal to one hundred percent (100%) of each WHC employee’s
participating savings contribution, up to the maximum savings contribution of
five (5%) of compensation for each pay period. For employees hired on or after
May 1, 2010, WHC, Ltd. (WHC) shall make a matching contribution equal to fifty
percent (50%) of each WHC employee’s participating savings contribution, up to
the maximum savings contribution of six (6%) of compensation for each pay
period.

Explanation: This change updates Schedule A to change the matching contribution
for eligible employees of WHC hired on or after May 1, 2010,  as a result of
standardizing retirement benefits for the Pacific Region of Knife River
Corporation.

 
2

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

 

3.  
By adding the following new entries to Schedule B:

Knife River Corporation – North Central (dba Knife River – North Dakota
Division) shall make supplemental contributions on behalf of its Davis-Bacon
Employees in such amounts as may be necessary to satisfy the Prevailing Wage
Law’s required fringe cost to the extent that the sum of the employer Matching
and Profit Sharing Contributions, if any, for a period are insufficient to
satisfy the Prevailing Wage Law’s required fringe cost pursuant to Supplement G.
 
Effective as of May 1, 2010.
 
 ***************************************
 
Ames Sand & Gravel, Inc. shall make supplemental contributions on behalf of its
Davis-Bacon Employees in such amounts as may be necessary to satisfy the
Prevailing Wage Law’s required fringe cost to the extent that the sum of the
employer Matching and Profit Sharing Contributions, if any, for a period are
insufficient to satisfy the Prevailing Wage Law’s required fringe cost pursuant
to Supplement G.
 
Effective as of May 1, 2010.
 
***************************************

Explanation: This amendment provides the manner in which the above Participating
Affiliates are implementing the provisions of the Davis-Bacon feature,
Supplement G.

IN WITNESS WHEREOF, MDU Resources Group, Inc., as Sponsoring Employer of the
Plan, has caused this amendment to be duly executed by a member of the MDU
Resources Group, Inc. Employee Benefits Committee (“EBC”) on this 28th day of
May, 2010.

 
MDU RESOURCES GROUP, INC.
 
   EMPLOYEE BENEFITS COMMITTEE
             
By:
/s/ Doran N. Schwartz                           
   
Doran N. Schwartz, Chairman

 
3

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