Exhibit 10.11

SIXTH AMENDMENT TO SUPPLEMENTAL

RETIREMENT/DEATH BENEFITS AGREEMENT

This SIXTH AMENDMENT TO SUPPLEMENTAL RETIREMENT/DEATH BENEFITS AGREEMENT (this Amendment), effective as of December 31, 2008, is made
and entered into by and among POST, BUCKLEY, SCHUH & JERNIGAN, INC., a Florida corporation (PBS&J), THE PBS&J CORPORATION, a Florida corporation (collectively with PBS&J, the Corporation),
and JOHN B. ZUMWALT (the Employee).

Background

The Corporation and Employee are parties to a Supplemental Retirement/Death Benefits Agreement dated December 17, 1987, as amended (as further
amended from time to time, the Agreement). The parties desire to further amend the Agreement to reflect the current and revised understanding of the parties with respect to certain rights, obligations and benefits of the parties
under the Agreement, and to bring the terms of the Agreement into compliance with the requirements of Sections 409A of the Internal Revenue Code of 1986, as amended (the Code).

Operative Terms

The parties
hereto agree as follows:

1. Post-Employment Health Benefits. Section 1 of the First Amendment dated May 19, 1998 between
the Corporation and Employee (First Amendment) is hereby deleted in its entirety and replaced with Reserved.

2. Consulting Compensation. Section 4 of the First Amendment is amended as follows:

(a) The first sentence thereof is
amended by replacing the phrase the date of termination of the Employees active and daily employment with the Corporation with the following phrase: the date of the Employees separation from service from the
Corporation.

(b) The fourth sentence of thereof is amended and restated to read as follows: The Consulting Retainer shall be
paid whether or not Employee is requested by the Corporation to provide consulting or advisory services and shall be payable in equal installments in accordance with the Corporations regular payroll dates in effect on the date of separation
from service.

3. Post-Employment Expenses.

(a) Section 2 of the Second Amendment dated November 22, 1999 between the Corporation and Employee (Second Amendment), as amended by Section 1 of the Third Amendment dated
January 2, 2002 between the Corporation and Employee (Third Amendment), is amended and restated to read as follows:

The Corporation shall reimburse the Employee for all reasonable expenses described on Exhibit B to the Agreement incurred by Employee during the period commencing on the date of Employees separation from service from the
Corporation and ending on the date that is fifteen (15) years thereafter (Coverage Period).



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(b) Appendix 1 attached to this Sixth Amendment is attached to the Agreement as the new
Exhibit B thereto.

4. Payment Terms for Reimbursements and In-Kind Benefits. Notwithstanding anything to the contrary in the
Agreement, the following terms and conditions govern the reimbursement of expenses and provision of in-kind benefits under the Agreement (including under Sections 1 and 3 of this Sixth Amendment thereto):

(a) The expense reimbursement or in-kind benefit will be made or provided only during the applicable period of time specifically set forth in the
Agreement.

(b) All expense reimbursements will be made upon Employees request in accordance with the Corporations normal
policies (to the extent consistent with this Section 4) but, to the extent the expense reimbursements are not exempt from the requirements of Section 409A of the Code, reimbursement shall be made no later than the last day of the calendar
year immediately following the calendar year in which the expense was incurred.

(c) To the extent the expense reimbursements or in-kind
benefits are not exempt from the requirements of Section 409A of the Code, (1) the amount of expenses eligible for reimbursement, or in-kind benefits provided, during a taxable year will not affect the expenses eligible for reimbursement,
or in-kind benefits to be provided, in any other taxable year, and (2) the right to the reimbursement or the in-kind benefit will not be subject to liquidation or exchange for another benefit.

5. Separation from Service. To the extent necessary to comply with Section 409A of the Code, references to termination of
employment, separation from service or variations thereof in the Plan shall mean the Employees separation from service from the PBS&J Controlled Group within the meaning of Section 409A(a)(2)(A)(i) of the
Code and the rules of Treasury Regulations Section 1.409A-1(h); provided that less than 50% is adopted in lieu of the default 20% or less standard for determining a separation from service. The PBS&J
Controlled Group means the Corporation and every entity or other person which collectively with the Corporation constitutes a single service recipient (as that term is defined in Treasury Regulations Sections 1.409A-1(g)) as the result of
the application of the rules of Treasury Regulations Sections 1.409A-1(h)(3).

6. This Amendment records the final, complete, and exclusive
understanding among the parties regarding the amendment of the Agreement. In the event of a conflict or inconsistency between the provisions of this Amendment and the Agreement, the provisions of this Amendment shall control and govern. As amended
by this Amendment, the Agreement remains in full force and effect in accordance with its terms; provided that Employee acknowledges that (and his designated beneficiary, heirs, successors and assigns) the benefits described in Sections 1, 2
and 3 of the original Agreement dated December 17, 1987 (as amended) will be provided under the terms of the PBSJ Corporation Key Employee Capital Accumulation Plan effective as of September 30, 2008. Without limiting the generality of the
foregoing, the Employees obligations under Sections 4 and 5 of the original Agreement dated December 17, 1987, and the Corporations rights under Section 6 thereof, remain in full force and effect.



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7. This Amendment may be executed in multiple counterparts, each of which shall be deemed an original,
but all of which shall constitute one and the same instrument, notwithstanding that all of the parties are not signatories to the original or the same counterpart. A partys receipt of a facsimile signature page or portable document format
(PDF) copy of a signature page to this Amendment shall be treated as the partys receipt of an original signature page.

[Signature
Pages Follow]



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SIGNATURE PAGE TO SIXTH AMENDMENT TO

SUPPLEMENTAL RETIREMENT/DEATH BENEFITS AGREEMENT

The undersigned have executed
this Amendment to be effective as of the date first written above.



POST, BUCKLEY, SCHUH & JERNIGAN, INC., a Florida corporationBy:

/s/ Donald J. VranaName:

Donald J. VranaTitle:

CFOTHE PBS&J CORPORATION, a Florida corporationBy:

/s/ Donald J. VranaName:

Donald J. VranaTitle:

CFO/s/ John B. ZumwaltJOHN B. ZUMWALT




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Appendix 1

Exhibit B  Schedule of Reimbursable Expenses



|    |  |                                                                                                       
|--- |  | ------------------------------------------------------------------------------------------------------
|(a) |  | Cellular Telephone (one).                                                                             
|    | 
|(b) |  | State-of-the-Art Computer (new unit every third calendar year during the Coverage Period).            
|    | 
|(c) |  | Internet Access Charges.                                                                              
|    | 
|(d) |  | Professional/Financial Newspapers and Magazines.                                                      
|    | 
|(e) |  | Airline Club Membership (one).                                                                        
|    | 
|(f) |  | Inclusion as American Airlines Platinum Tier member (or equivalent at another airline).               
|    | 
|(g) |  | Budget Rental Car Optimum level (or equivalent at another company).                                   
|    | 
|(h) |  | Annual Tax Return Preparation.                                                                        
|    | 
|(i) |  | Annual Physical Exam.                                                                                 
|    | 
|(j) |  | Use of Breckenridge Condominium for two weeks per calendar year, including one week during ski season.
|    | 
|(k) |  | Automobile lease, including insurance, tag, maintenance and repairs.                                  
|    | 
|(l) |  | Air fare (business class, or first class where business class is not available).                      
|    | 
|(m) |  | Country Club Membership dues and fees (subject to maximum of $3,600 per calendar year).               

Subject to the requirements of Section 409A of the Code, the Corporation may amend, modify or terminate this
Exhibit B at any time.