Clean Harbors Inc. ownership disclosure: D1 Capital Partners L.P. and Daniel Sundheim report beneficial ownership of 1,338,281 shares of Common Stock, representing 2.5% of the class. The percentage is calculated using 52,910,946 shares outstanding as of February 11, 2026 from the 2025 Form 10-K.
The statement identifies shared voting and dispositive power over the 1,338,281 shares and notes the Investment Vehicle holds the economic interests. Signatures are dated May 15, 2026.
Positive
None.
Negative
None.
Insights
D1 Capital reports a 2.5% stake via shared control over 1,338,281 shares.
The filing shows shared voting power and shared dispositive power of 1,338,281 shares, calculated against an outstanding base of February 11, 2026. This is a passive ownership disclosure under Schedule 13G/A rather than an active acquisition statement.
Future filings may report changes in position; the disclosed structure indicates the investment vehicle, not necessarily the individual, holds economic rights.
Ownership is reported as shared authority through an investment manager structure.
The report attributes beneficial ownership to the Investment Vehicle and notes Mr. Sundheim indirectly controls the manager. The statement includes the Investment Vehicle's right to receive dividends and sale proceeds for the reported shares.
Signatures from both the General Counsel and Mr. Sundheim are present and dated May 15, 2026.
Key Figures
Beneficially owned shares:1,338,281 sharesPercent of class:2.5%Shares outstanding:52,910,946 shares+1 more
4 metrics
Beneficially owned shares1,338,281 sharesReported beneficial ownership for D1 Capital/Daniel Sundheim
Percent of class2.5%Calculated using shares outstanding as of Feb 11, 2026
Shares outstanding52,910,946 sharesShares outstanding as of Feb 11, 2026 per 2025 Form 10-K
CUSIP184496107Clean Harbors Inc. Common Stock identifier
"This statement is filed by D1 Capital Partners L.P."
A Schedule 13G/A is an amended public filing with the U.S. securities regulator that updates a previous Schedule 13G, disclosing when an individual or group holds a substantial (typically over 5%) stake in a company and is claiming a passive, non‑controlling intent. Investors monitor these updates because rising or falling holdings can signal changing confidence, potential future moves, or shifts in voting power — like watching a public ledger where large shareholders quietly adjust their positions.
Shared Dispositive Powerregulatory
"Shared Dispositive Power 1,338,281.00"
Beneficially ownedfinancial
"Amount beneficially owned: The information required by Item 4(a)"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 1)
Clean Harbors Inc.
(Name of Issuer)
Common Stock, par value $0.01 per share
(Title of Class of Securities)
184496107
(CUSIP Number)
03/31/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
184496107
1
Names of Reporting Persons
D1 Capital Partners L.P.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
1,338,281.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
1,338,281.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
1,338,281.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
2.5 %
12
Type of Reporting Person (See Instructions)
IA, PN
SCHEDULE 13G
CUSIP Number(s):
184496107
1
Names of Reporting Persons
Daniel Sundheim
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
1,338,281.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
1,338,281.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
1,338,281.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
2.5 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Clean Harbors Inc.
(b)
Address of issuer's principal executive offices:
42 Longwater Drive, PO Box 9149, Norwell, MA 02061-9149.
Item 2.
(a)
Name of person filing:
This statement is filed by D1 Capital Partners L.P. (the "Investment Manager") and Daniel Sundheim (the "Mr. Sundheim"). The foregoing persons are hereinafter sometimes referred to as the "Reporting Persons."
The Investment Manager is a registered investment adviser and serves as the investment manager of private investment vehicles and accounts, including D1 Capital Partners Master LP (the "Investment Vehicle"), and may be deemed to beneficially own the shares of common stock, par value $0.01 per share (the "Common Stock") of Clean Harbors Inc. (the "Company") held by the Investment Vehicle and/or its subsidiary. Mr. Sundheim indirectly controls the Investment Manager and may be deemed to beneficially own the shares of Common Stock issuable held by the Investment Vehicle and/or its subsidiary.
The filing of this statement should not be construed as an admission that any Reporting Person is, for the purposes of Section 13 of the Securities Exchange Act of 1934, as amended, the beneficial owner of the securities reported herein.
(b)
Address or principal business office or, if none, residence:
D1 Capital Partners L.P.
9 West 57th Street, 36th Floor
New York, New York 10019
Daniel Sundheim
c/o D1 Capital Partners L.P.
9 West 57th Street, 36th Floor
New York, New York 10019
(c)
Citizenship:
Investment Manager - Delaware
Mr. Sundheim - United States of America
(d)
Title of class of securities:
Common Stock, par value $0.01 per share
(e)
CUSIP No.:
184496107
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
The percentage set forth in this Schedule 13G is calculated based upon an aggregate of 52,910,946 shares of Common Stock reported to be outstanding as of February 11, 2026, as reported in the Company's Annual Report on Form 10-K for the year ended December 31, 2025, filed with the Securities and Exchange Commission on February 18, 2026.
(b)
Percent of class:
2.5%
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(ii) Shared power to vote or to direct the vote:
The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(iii) Sole power to dispose or to direct the disposition of:
The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
(iv) Shared power to dispose or to direct the disposition of:
The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference.
Item 5.
Ownership of 5 Percent or Less of a Class.
Ownership of 5 percent or less of a class
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required.
See item 2(a). The Investment Vehicle (and/or its subsidiary) has the right to receive and the power to direct the receipt of dividends from, and the proceeds from the sale of, the shares of Common Stock reported herein.
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
D1 Capital Partners L.P.
Signature:
/s/ Amanda Hector
Name/Title:
Amanda Hector, General Counsel and Chief Compliance Officer
What stake does D1 Capital Partners report in CLH?
D1 Capital Partners reports beneficial ownership of 1,338,281 shares, equal to 2.5% of Clean Harbors' common stock based on 52,910,946 shares outstanding as of February 11, 2026 reported in the 2025 Form 10-K.
Who holds voting and dispositive power for the reported CLH shares?
The filing reports shared voting power and shared dispositive power over 1,338,281 shares. Authority is attributed to the Investment Manager and indirectly to Daniel Sundheim as controller of that manager.
Does the filing indicate D1 Capital will sell or buy CLH shares?
No transaction action is stated. This Schedule 13G/A is a passive ownership disclosure listing beneficial ownership, voting and dispositive arrangements; it does not report an open-market purchase or sale in this excerpt.
What outstanding share base was used to calculate the 2.5% ownership?
The percentage is calculated using an aggregate of 52,910,946 shares outstanding as of February 11, 2026, as reported in Clean Harbors' Form 10-K for the year ended December 31, 2025.
Who certified the Schedule 13G/A for CLH and when?
The filing is signed by Amanda Hector, General Counsel and Chief Compliance Officer, and by Daniel Sundheim individually, with signatures dated May 15, 2026.
