Sec Form 4 Filing - ENERGY CAPITAL PARTNERS II, LLC @ Summit Midstream Partners, LP - 2020-05-28

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person ENERGY CAPITAL PARTNERS II, LLC 2. Issuer Name and Ticker or Trading Symbol Summit Midstream Partners, LP [ SMLP] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 40 BEECHWOOD ROAD 3. Date of Earliest Transaction (MM/DD/YY) 05/28/2020 (Street) SUMMIT, NJ07901 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Units (Limited Partner Interests) 05/28/2020 D 5,915,827 D 0 I By SMLP Holdings, LLC ( 2 ) ( 3 ) Common Units (Limited Partner Interests) 05/28/2020 D 45,318,866 D 0 I By Summit Midstream Partners, LLC ( 2 ) ( 3 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ENERGY CAPITAL PARTNERS II, LLC 40 BEECHWOOD ROAD SUMMIT, NJ07901 X ENERGY CAPITAL PARTNERS II, LP 40 BEECHWOOD ROAD SUMMIT, NJ07901 X ENERGY CAPITAL PARTNERS II-A, LP 40 BEECHWOOD ROAD SUMMIT, NJ07901 X ENERGY CAPITAL PARTNERS II-B IP, LP 40 BEECHWOOD ROAD SUMMIT, NJ07901 X ENERGY CAPITAL PARTNERS II-C (SUMMIT IP), LP 40 BEECHWOOD ROAD SUMMIT, NJ07901 X Energy Capital Partners II (Summit Co-Invest), LP 40 BEECHWOOD ROAD SUMMIT, NJ07901 X Signatures Energy Capital Partners II, LLC, By: /s/ Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date Energy Capital Partners II, LP, By: Energy Capital Partners GP II, LP Its: General Partner By: Energy Capital Partners II, LLC Its: General Partner By: /s/ Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date Energy Capital Partners II-A, LP, By: Energy Capital Partners GP II, LP Its: General Partner By: Energy Capital Partners II, LLC Its: General Partner By: Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date Energy Capital Partners II-B IP, LP, By: Energy Capital Partners GP II, LP Its: General Partner By: Energy Capital Partners II, LLC Its: General Partner By: /s/ Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date Energy Capital Partners II-C (Summit IP), LP, By: Energy Capital Partners GP II, LP Its: General Partner By: Energy Capital Partners II, LLC Its: General Partner By: /s/ Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date Energy Capital Partners II (Summit Co-Invest), LP, By: Energy Capital Partners GP II Co- Investment (Summit), LLC Its: General Partner By: Energy Capital Partners II, LLC Its: Managing Member By: /s/ Christopher M. Leininger, Partner and General Counsel 10/22/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On May 28, 2020, pursuant to a purchase agreement, dated as of May 3, 2020, the Issuer purchased (i) all the outstanding limited liability company interests of Summit Midstream Partners, LLC ("Summit Investments"), which is the sole member of Summit Midstream Partners Holdings, LLC ("SMP Holdings"), which in turn owns 45,318,866 common units representing limited partner interests in the Issuer (the "Common Units"), and (ii) 5,915,827 Common Units held by SMLP Holdings, LLC ("SMLP") for a total purchase price of $35 million in cash and warrants to purchase up to 10 million Common Units. As a result of these transactions, Summit Investments became a wholly owned subsidiary of the Issuer. ( 2 )Summit Investments is the sole member of SMP Holdings. Energy Capital Partners II, LLC ("ECP") indirectly controls Energy Capital Partners II, LP ("ECP II"), Energy Capital Partners II-A, LP ("ECP II-A"), Energy Capital Partners II-B IP, LP ("ECP II-B"), Energy Capital Partners II-C (Summit IP), LP ("ECP II-C"), and Energy Capital Partners II (Summit Co-Invest), LP ("ECP Summit Co-Invest" and together with ECP II, ECP II-A, ECP II-B and ECP II-C, the "ECP Funds"). ( 3 )Prior to the transactions reported herein, the ECP Funds owned a majority of the membership interests in Summit Investments and therefore may have been deemed to indirectly beneficially own the Common Units held of record by SMP Holdings. The ECP Funds, other than ECP Summit Co-Invest, hold all of the membership interests in SMLP. Accordingly, each of them, other than ECP Summit Co-Invest, may have been deemed to share beneficially ownership of the Common Units held by SMLP.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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