Exhibit 10.21

EXECUTION COPY

FIRST AMENDMENT TO CREDIT AGREEMENT

Dated as of January 13, 2016

This FIRST AMENDMENT TO CREDIT AGREEMENT (this “Amendment”) is by and among NPL
CONSTRUCTION CO., a Nevada corporation and CENTURI CONSTRUCTION GROUP, INC.
(formerly known as Isleworth Holding Co.), a Nevada corporation, as US
Borrowers, LYNXUS CONSTRUCTION GROUP INC. (formerly known as 2431251 Ontario
Inc.), a corporation organized under the laws of the Province of Ontario,
Canada, as Canadian Borrower, the Lenders party hereto, and WELLS FARGO BANK,
NATIONAL ASSOCIATION, a national banking association, as administrative agent
for the Lenders (in such capacity, the “Administrative Agent”).

PRELIMINARY STATEMENTS

WHEREAS, the Borrowers, the lenders party thereto (the “Lenders”) and the
Administrative Agent entered into that certain Credit Agreement dated as of
October 1, 2014 (as amended hereby and as further amended, restated, amended and
restated, supplemented or otherwise modified from time to time, the “Credit
Agreement”); and

WHEREAS, the Borrowers have requested that the Administrative Agent and the
Lenders agree to amend the Credit Agreement as specifically set forth herein
and, subject to the terms of this Amendment, the Administrative Agent and the
Lenders party hereto have agreed to grant such request.

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the parties hereto hereby agree as follows:

Section 1.    Capitalized Terms.    All capitalized terms not otherwise defined
in this Amendment (including without limitation in the introductory paragraph
and the Preliminary Statements hereto) shall have the meanings as specified in
the Credit Agreement.

Section 2.    Amendment to Credit Agreement.    Subject to and in accordance
with the terms and conditions set forth herein, the Administrative Agent and the
Lenders party hereto hereby agree to amend the Credit Agreement as follows:

(a)    The cover page to the Credit Agreement is hereby amended by:
(i) replacing “ISLEWORTH HOLDING CO.” with “CENTURI CONSTRUCTION GROUP, INC.
(formerly known as Isleworth Holding Co.)” and (ii) replacing “2431251 ONTARIO
INC.” with “LYNXUS CONSTRUCTION GROUP INC. (formerly known as 2431251 Ontario
Inc.)”.

(b)    The preamble to the Credit Agreement is hereby amended by: (i) replacing
“ISLEWORTH HOLDING CO.” with “CENTURI CONSTRUCTION GROUP, INC. (formerly known
as Isleworth Holding Co.)” and (ii) replacing “2431251 ONTARIO INC.” with
“LYNXUS CONSTRUCTION GROUP INC. (formerly known as 2431251 Ontario Inc.)”.

(c)    The listing of Schedules in the Credit Agreement is hereby amended to
delete the following:

“Schedule 12.22 – Holding Company Reorganization Description”

(d)    The definition of “Adjusted Consolidated Net Income” in Section 1.1 of
the Credit Agreement is hereby amended and restated in its entirety as follows:

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“Adjusted Consolidated Net Income” means Consolidated Net Income for the
applicable period, but excluding in calculating Consolidated Net Income (solely
to the extent Consolidated Net Income for such period is greater than $0),
(a) impairment charges with respect to intangible assets and non-cash charges
related to deferred taxes in an aggregate amount of up to $10,000,000 accrued
for the applicable period of calculation and (b) amortization of goodwill in an
aggregate amount of up to $20,000,000 accrued for the applicable period of
calculation.

(e)    The definition of “Base Rate” in Section 1.1 of the Credit Agreement is
hereby amended by replacing each reference therein to “LIBOR” with “the LIBOR
Rate”.

(f)    The definition of “Canadian Borrower” in Section 1.1 of the Credit
Agreement is hereby amended by replacing “2431251 Ontario Inc.” with “Lynxus
Construction Group Inc. (formerly known as 2431251 Ontario Inc.)”.

(g)    The definition of “Carson Water” in Section 1.1 of the Credit Agreement
is hereby amended by inserting the following phrase at the end of such
definition:

“, and, after the Holding Company Reorganization, a direct Subsidiary of the
Holding Company”

(h)    Section 1.1 of the Credit Agreement is hereby amended by adding the
following additional defined term in appropriate alphabetical order:

“Centuri” means Centuri Construction Group, Inc. (formerly known as Isleworth
Holding Co.), a Nevada corporation.

(i)    The definition of “Change in Control” in Section 1.1 of the Credit
Agreement is hereby amended and restated in its entirety as follows:

“Change in Control” means an event or series of events by which:

(a)    prior to the Holding Company Reorganization, (i) Southwest Gas shall fail
to own, directly or indirectly, and control at least ninety-six percent (96%) on
a fully diluted basis of the economic and voting Equity Interests of Centuri,
and (ii) Centuri shall fail to own, directly or indirectly, and control (A) one
hundred percent (100%) on a fully diluted basis of the economic and voting
Equity Interests of NPL, and (B) one hundred percent (100%) on a fully diluted
basis of the economic and voting Equity Interests of the Canadian Borrower; and

(b)    after the Holding Company Reorganization, (i) Centuri shall fail to own,
directly or indirectly, and control (A) one hundred percent (100%) on a fully
diluted basis of the economic and voting Equity Interests of NPL, and (B) one
hundred percent (100%) on a fully diluted basis of the economic and voting
Equity Interests of the Canadian Borrower or (ii) the Holding Company shall fail
to own, directly or indirectly, and control one hundred percent (100%) on a
fully diluted basis of the economic and voting Equity Interests of each of the
Borrowers.

 

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(j)    The definition of “Consolidated Companies” in Section 1.1 of the Credit
Agreement is hereby amended and restated in its entirety as follows:

“Consolidated Companies” means Centuri and its Subsidiaries.

(k)    The definition of “Consolidated EBITDA” in Section 1.1 of the Credit
Agreement is hereby amended by replacing clause (iii) with the following new
clause (iii):

“(iii) amortization (including, for the avoidance of doubt, impairment charges,
and amortization of goodwill and intangible assets acquired or arising from a
business acquisition, regardless of whether presented as a separate line item or
included in other book entries), depreciation and other non-cash charges (except
to the extent that such non-cash charges are reserved for cash charges to be
taken in the future), including any non-cash equity based compensation expense,”

(l)    Section 1.1 of the Credit Agreement is hereby amended by adding the
following additional defined term in appropriate alphabetical order:

“First Amendment Effective Date” means January 13, 2016.

(m)    The definition of “Holding Company” in Section 1.1 of the Credit
Agreement is hereby amended and restated in its entirety as follows:

“Holding Company” means a California corporation the common Equity Interests of
which are owned 100% by the existing shareholders of Southwest Gas immediately
prior to the consummation of the Holding Company Reorganization.

(n)    The definition of “Holding Company Reorganization” in Section 1.1 of the
Credit Agreement is hereby amended and restated in its entirety as follows:

“Holding Company Reorganization” means the organizational reorganization of the
Consolidated Companies following the First Amendment Effective Date and on
substantially the terms described in the Form 8-K filed by Southwest Gas on
October 13, 2015 in which, along with other organizational changes, Southwest
Gas will be replaced by the Holding Company as the ultimate parent company,
Southwest Gas will become an indirect Subsidiary of the Holding Company, Carson
Water will become a direct Subsidiary of the Holding Company, and Centuri shall
continue to own all of the Equity Interests of the Subsidiaries of Centuri
(including NPL and the Canadian Borrower) immediately prior to the consummation
of the Holding Company Reorganization, all subject to compliance with
Section 12.22.

(o)    The definition of “LIBOR Rate” in Section 1.1 of the Credit Agreement is
hereby amended by inserting the following sentence at the end of such
definition:

“Notwithstanding the foregoing, if the LIBOR Rate shall be less than zero, such
rate shall be deemed to be zero for purposes of this Agreement.”

(p)    The last sentence of the definition of “Subsidiary” in Section 1.1 of the
Credit Agreement is hereby amended and restated in its entirety as follows:

 

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“Unless otherwise qualified, references to “Subsidiary” or “Subsidiaries” herein
shall refer to those of Centuri.”

(q)    The definition of “US Borrowers” in Section 1.1 of the Credit Agreement
is hereby amended by replacing “Isleworth Holding Co., a Nevada corporation” in
clause (b) with “Centuri”.

(r)    The definition of “US Credit Parties” is hereby amended by deleting “and,
after the Holding Company Reorganization, the Holding Company”.

(s)    Section 1.3 of the Credit Agreement is hereby amended by deleting clause
(d) in its entirety.

(t)    Section 7.20 of the Credit Agreement is hereby amended by inserting the
following sentences at the end of such Section:

“Each Credit Party, its Subsidiaries and their respective officers and employees
and to the knowledge of each Credit Party, its directors and agents, are in
compliance with Anti-Corruption Laws and applicable Sanctions in all material
respects. No Loan or Letter of Credit, use of the proceeds of any Loan or Letter
of Credit or other transactions contemplated hereby will violate Anti-Corruption
Laws or applicable Sanctions. Each Credit Party and its Subsidiaries are in
compliance in all material respects with all Anti-Corruption Laws and the
PATRIOT Act.”

(u)    Section 8.15 of the Credit Agreement is hereby amended by inserting the
following sentence at the end of such Section:

“The Borrower will not request any Extension of Credit, and the Borrower shall
not use, and shall ensure that its Subsidiaries and its or their respective
directors, officers, employees and agents shall not use, the proceeds of any
Extension of Credit (i) in furtherance of an offer, payment, promise to pay, or
authorization of the payment or giving of money, or anything else of value, to
any Person in violation of any Anti-Corruption Laws or (ii) in any manner that
would result in the violation of any Sanctions applicable to any party hereto.”

(v)    Clause (d) of Section 9.1 of the Credit Agreement is hereby amended and
restated in its entirety as follows:

“(d)    Indebtedness incurred in connection with Capital Leases and purchase
money Indebtedness and incurred in the ordinary course of business of the
Consolidated Companies in an aggregate amount not to exceed $65,000,000 at any
time outstanding; provided that (i) such Indebtedness is incurred concurrently
with or within twenty-four (24) months after the applicable acquisition,
construction, repair, replacement or improvement and (ii) no more than
$45,000,000 of such Indebtedness may be incurred during any twelve (12) month
period;”

(w)    Clause (h) of Section 9.2 of the Credit Agreement is hereby amended by
replacing, in clause (i) thereof, “substantially simultaneously with” with
“concurrently with or within twenty-four (24) months of”.

 

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(x)    Section 9.3 of the Credit Agreement is hereby amended by: (i) adding
“and” after the semicolon in clause (vi), (ii) replacing “; and” at the end of
clause (vii) with a period and (iii) deleting clause (viii) in its entirety.

(y)    Clause (i) of Section 9.4 of the Credit Agreement is hereby amended by
replacing “a” with “the”.

(z)    Clause (viii) of Section 9.7 of the Credit Agreement is hereby amended
and restated in its entirety as follows:

“(viii) customary overhead allocations and intercompany charges applied by
Centuri on a consistent basis to its Subsidiaries generally.”

(aa)    Clause (b) of Section 9.8 of the Credit Agreement is hereby amended by
deleting “except to effectuate a Holding Company Reorganization,”.

(bb)    Clause (i) of Section 10.1 of the Credit Agreement is hereby amended by
inserting “ (or, after the Holding Company Reorganization, the Holding Company
or any Subsidiary thereof)” after “Southwest Gas”.

(cc)    Clause (j) of Section 10.1 of the Credit Agreement is hereby amended by
inserting “ (or, after the Holding Company Reorganization, the Holding Company
or any Subsidiary thereof)” after both references to “Southwest Gas”.

(dd)    Section 12.1 of the Credit Agreement is hereby amended by: (i) replacing
“NPL Construction Co.” in 12.1(a) with “Centuri Construction Group, Inc.”,
(ii) replacing “rpingle@GoNPL.com” in 12.1(a) with “rpringle@NextCenturi.com”,
and (iii) replacing “NPL” in 12.1(c) with “Centuri”.

(ee)    Section 12.22 of the Credit Agreement is hereby amended by:
(i) replacing each reference to “NPL” with “Centuri”, (ii) inserting “and” after
the semicolon in clause (a)(i), (iii) inserting “(or such shorter period as
agreed to by the Administrative Agent in its sole discretion)” after “thirty
(30) days” in clause (a)(ii), (iv) replacing the semicolon at the end of clause
(a)(ii) with a period, (v) deleting clauses (a)(iii) and (a)(iv) in their
entirety and (vi) deleting clause (d) in its entirety.

Section 3.     Conditions of Effectiveness.    The effectiveness of the
amendments in Section 2 shall be subject to the satisfaction of each of the
following conditions precedent:

(a)    the Administrative Agent shall have received counterparts of this
Amendment executed by each Borrower, each other Credit Party, the Administrative
Agent and the Required Lenders;

(b)    the representations and warranties of the Credit Parties contained in
Section 4 shall be true and correct; and

(c)    all reasonable out-of-pocket costs and expenses incurred by the
Administrative Agent as of the date hereof in connection with the preparation,
negotiation, execution and delivery of this Amendment and the other instruments
and documents to be delivered hereunder (including, without limitation, the
reasonable fees, charges and disbursements of legal counsel for the
Administrative Agent in connection with the preparation, negotiation, execution
and delivery of this Amendment) shall have been paid by the Borrowers.

 

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Section 4.    Representations and Warranties of the Credit Parties.    Each
Credit Party represents and warrants as follows:

(a)    Each Credit Party has the right, power, and authority and has taken all
necessary corporate or other action to authorize the execution, delivery and
performance of this Amendment. This Amendment constitutes a legal, valid and
binding obligation of such Credit Party, enforceable against each Credit Party
that is party hereto in accordance with its terms, subject to applicable
bankruptcy, insolvency, reorganization, moratorium or other laws affecting
creditors’ rights generally and subject to general principles of equity,
regardless of whether considered in a proceeding in equity or at law.

(b)    The execution, delivery and performance by each Credit Party of this
Amendment and the transactions contemplated hereby do not and will not, by the
passage of time, the giving of notice or otherwise, (i) require any Governmental
Approval or violate any Applicable Law relating to any Credit Party or any
Subsidiary thereof where the failure to obtain such Governmental Approval or
such violation could reasonably be expected to have a Material Adverse Effect,
(ii) conflict with, result in a breach of or constitute a default under the
articles of incorporation, bylaws or other organizational documents of any
Credit Party or any Subsidiary thereof, (iii) conflict with, result in a breach
of or constitute a default under any indenture, agreement or other instrument to
which such Person is a party or by which any of its properties may be bound or
any Governmental Approval relating to such Person, which could, individually or
in the aggregate, reasonably be expected to have a Material Adverse Effect,
(iv) result in or require the creation or imposition of any Lien upon or with
respect to any property now owned or hereafter acquired by such Person other
than Permitted Liens or (v) require any consent or authorization of, filing
with, or other act in respect of, an arbitrator or Governmental Authority and no
consent of any other Person is required in connection with the execution,
delivery, performance, validity or enforceability of this Amendment other than
consents, authorizations, filings or other acts or consents for which the
failure to obtain or make could not, individually or in the aggregate,
reasonably be expected to have a Material Adverse Effect.

(c)    After giving effect to this Amendment, the representations and warranties
contained in each of the Loan Documents are true and correct in all material
respects, except for any representation and warranty that is qualified by
materiality or reference to Material Adverse Effect, which such representation
and warranty are true and correct in all respects, on and as of the date hereof
as though made on and as of such date (other than any such representations or
warranties that, by their terms, refer to a specific date, in which case as of
such specific date).

(d)    No Default or Event of Default shall exist after giving effect to this
Amendment.

Section 5.    Reference to and Effect on the Loan Documents.    On and after the
effectiveness of this Amendment, each reference in the Credit Agreement to “this
Agreement”, “hereunder”, “hereof” or words of like import referring to the
Credit Agreement, and each reference in each of the other Loan Documents to “the
Credit Agreement”, “thereunder”, “thereof” or words of like import referring to
the Credit Agreement, shall mean and be a reference to the Credit Agreement, as
amended by this Amendment and this Amendment shall constitute a Loan Document.

(a)    The Credit Agreement and each of the other Loan Documents, as
specifically amended by this Amendment, are and shall continue to be in full
force and effect and are hereby in all respects ratified and confirmed.

(b)    The execution, delivery and effectiveness of this Amendment shall not,
except as expressly provided herein, operate as a waiver of any right, power or
remedy of any Lender or the

 

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Administrative Agent under any of the Loan Documents, nor constitute a waiver of
any other provision of any of the Loan Documents.

Section 6.    Reaffirmations.    Each Credit Party (a) consents to this
Amendment and agrees that the transactions contemplated by this Amendment shall
not limit or diminish the obligations of such Person, or release such Person
from any obligations, under any of the Loan Documents to which it is a party,
(b) confirms and reaffirms its obligations under each of the Loan Documents to
which it is a party and (c) agrees that each of the Loan Documents to which it
is a party remain in full force and effect and are hereby ratified and
confirmed.

Section 7.    Execution in Counterparts.    This Amendment may be executed in
counterparts (and by different parties hereto in different counterparts), each
of which shall constitute an original, but all of which when taken together
shall constitute a single contract. Delivery of an executed counterpart of a
signature page of this Amendment by facsimile or in electronic (i.e., “pdf” or
“tif”) format shall be effective as delivery of a manually executed counterpart
of this Amendment.

Section 8.    Governing Law.    This Amendment and any claim, controversy,
dispute or cause of action (whether in contract or tort or otherwise) based
upon, arising out of or relating to this Amendment and the transactions
contemplated hereby and thereby shall be governed by, and construed in
accordance with, the law of the State of New York.

Section 9.    Entire Agreement.    This Amendment and the other Loan Documents,
and any separate letter agreements with respect to fees payable to the
Administrative Agent, the Issuing Bank, the Swingline Lender and/or the Lead
Arrangers, constitute the entire agreement among the parties relating to the
subject matter hereof and supersede any and all previous agreements and
understandings, oral or written, relating to the subject matter hereof.

[Signature Pages Follow]

 

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed
by their respective officers thereunto duly authorized, as of the date first
above written.

 

BORROWERS: NPL CONSTRUCTION CO., as US Borrower By:   /s/ RICARDO B. PRINGLE
Name:  Ricardo B. Pringle Title:    Secretary CENTURI CONSTRUCTION GROUP, INC.,
as US Borrower By:   /s/ KEVIN NEILL Name:  Kevin Neill Title:    Senior Vice
President/Chief Financial Officer and Treasurer LYNXUS CONSTRUCTION GROUP INC.,
as Canadian Borrower By:   /s/ DEREK A. VAN PATTER Name:  Derek A. Van Patter
Title:    Secretary GUARANTORS: SOUTHWEST ADMINISTRATORS, INC., as a US
Subsidiary Guarantor By:   /s/ RICARDO B. PRINGLE Name:  Ricardo B. Pringle
Title:    Secretary VISTUS CONSTRUCTION GROUP, INC., as a US Subsidiary
Guarantor By:   /s/ RICARDO B. PRINGLE Name:  Ricardo B. Pringle
Title:    Secretary

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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BRIGADIER PIPELINES INC., as a US Subsidiary Guarantor By:   /s/ RICARDO B.
PRINGLE Name:  Ricardo B. Pringle Title:    Secretary LINK-LINE CONTRACTORS
LTD., as a Canadian Subsidiary Guarantor By:   /s/ DEREK A. VAN PATTER
Name:  Derek A. Van Patter
Title:    Vice President/Finance and Corporate Secretary 2018429 ONTARIO LTD.,
as a Canadian Subsidiary Guarantor By:   /s/ DEREK A. VAN PATTER Name:  Derek A.
Van Patter Title:    Secretary and Treasurer W.S. NICHOLLS CONSTRUCTION INC., as
a Canadian Subsidiary Guarantor By:   /s/ DEREK A. VAN PATTER Name:  Derek A.
Van Patter Title:    Secretary and Treasurer W.S. NICHOLLS INDUSTRIES INC., as a
Canadian Subsidiary Guarantor By:   /s/ DEREK A. VAN PATTER Name:  Derek A. Van
Patter Title:    Secretary and Treasurer

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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ADMINISTRATIVE AGENT AND LENDERS: WELLS FARGO BANK, NATIONAL ASSOCIATION, as
Administrative Agent, Swingline Lender, Issuing Lender and Lender By:   /s/
BRENDA K. ROBINSON Name:  Brenda K. Robinson Title:    Senior Vice President

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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BANK OF AMERICA, N.A., as Lender By:   /s/ KENNETH TEBELMAN Name:  Kenneth
Tebelman Title:    Vice President

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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CANADIAN IMPERIAL BANK OF COMMERCE, as Swingline Lender, Issuing Lender and
Lender By:   /s/ SCOTT MCCAHILL Name:  Scott McCahill Title:    Authorized
Signatory By:   /s/ JAMES LOGAN Name:  James Logan Title:    Authorized
Signatory

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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UMB BANK, N.A., as Lender By:   /s/ KYLE MCMILLIAN Name:  Kyle McMillian
Title:    Vice President

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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U.S. BANK NATIONAL ASSOCIATION, as Lender By:   /s/ HOLLAND H. WILLIAMS
Name:  Holland H. Williams Title:    Vice President

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page

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NATIONAL BANK OF ARIZONA, as Lender By:   /s/ SABINA ANTHONY Name:  Sabina
Anthony Title:    Vice President

 

NPL Construction Co.

First Amendment to Credit Agreement

Signature Page