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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549



                                 SCHEDULE 13G/A

                    Under the Securities Exchange Act of 1934

                               (Amendment No. 1)*


                               Clean Harbors, Inc.
--------------------------------------------------------------------------------
                                (Name of Issuer)


                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    184496107
                  --------------------------------------------
                                 (CUSIP Number)


                                 August 18, 2003
--------------------------------------------------------------------------------
             (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)

         [X]      Rule 13d-1(c)

         [ ]      Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the ACT
but shall be subject to all other provisions of the Act (however, see the
Notes).


Potential persons who are to respond to the collection of information contained
in this form are not required to respond unless the form displays a currently
valid OMB control number.

                               Page 1 of 10 pages


CUSIP No.      184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.      Glenn J. Krevlin
         I.R.S. Identification Nos. of above persons (entities only).
--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only
--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization           United States
--------------------------------------------------------------------------------
Number of                  5.      Sole Voting Power             542,500
Shares                     -----------------------------------------------------
Beneficially               6.      Shared Voting Power           0
owned by                   -----------------------------------------------------
Each                       7.      Sole Dispositive Power        542,500
Reporting                 -----------------------------------------------------
Person With                8.      Shared Dispositive Power      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person  542,500


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                                [ ]

11.      Percent of Class Represented by Amount in Row (9)         4.04%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)
--------------------------------------------------------------------------------
IN, HC




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

                               Page 2 of 10 pages


CUSIP No.            184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.      Krevlin Advisors, LLC
         I.R.S. Identification Nos. of above persons (entities only).
         13-4153005

--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only

--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization          Delaware

--------------------------------------------------------------------------------
Number of                  5.   Sole Voting Power:             542,500
Shares                    -----------------------------------------------------
Beneficially               6.   Shared Voting Power:           0
Owned by                  -----------------------------------------------------
Each                       7.   Sole Dispositive Power:        542,500
Reporting                 -----------------------------------------------------
Person With:               8.   Shared Dispositive Power:      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person   542,500


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                             [ ]

11.      Percent of Class Represented by Amount in Row (9)    4.04%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)

--------------------------------------------------------------------------------
OO



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

                               Page 3 of 10 pages


CUSIP No.            184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.      GJK Capital Management, LLC
         I.R.S. Identification Nos. of above persons (entities only).
         13-4146739

--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only

--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization          Delaware

--------------------------------------------------------------------------------
Number of                  5.   Sole Voting Power:             385,069
Shares                    -----------------------------------------------------
Beneficially               6.   Shared Voting Power:           0
Owned by                  -----------------------------------------------------
Each                       7.   Sole Dispositive Power:        385,069
Reporting                 -----------------------------------------------------
Person With:               8.   Shared Dispositive Power:      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person   385,069


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                             [ ]

11.      Percent of Class Represented by Amount in Row (9)    2.9%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)

--------------------------------------------------------------------------------
OO



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

                               Page 4 of 10 pages


CUSIP No.            184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.      Glenhill Capital LP
         I.R.S. Identification Nos. of above persons (entities only).
         13-4149785

--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only

--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization          Delaware

--------------------------------------------------------------------------------
Number of                  5.   Sole Voting Power:             385,069
Shares                    -----------------------------------------------------
Beneficially               6.   Shared Voting Power:           0
Owned by                  -----------------------------------------------------
Each                       7.   Sole Dispositive Power:        385,069
Reporting                 -----------------------------------------------------
Person With:               8.   Shared Dispositive Power:      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person   385,069


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                             [ ]

11.      Percent of Class Represented by Amount in Row (9)    2.9%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)

--------------------------------------------------------------------------------
OO



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

                               Page 5 of 10 pages


CUSIP No.            184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.      Glenhill Overseas Management, LLC
         I.R.S. Identification Nos. of above persons (entities only).
         02-0625266

--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only

--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization          Delaware

--------------------------------------------------------------------------------
Number of                  5.   Sole Voting Power:             157,431
Shares                    -----------------------------------------------------
Beneficially               6.   Shared Voting Power:           0
Owned by                  -----------------------------------------------------
Each                       7.   Sole Dispositive Power:        157,431
Reporting                 -----------------------------------------------------
Person With:               8.   Shared Dispositive Power:      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person   157,431


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                             [ ]

11.      Percent of Class Represented by Amount in Row (9)    1.2%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)

--------------------------------------------------------------------------------
OO



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

                               Page 6 of 10 pages


CUSIP No.            184496107

--------------------------------------------------------------------------------
1.       Names of Reporting Persons.    Glenhill Capital Overseas Partners Ltd.
         I.R.S. Identification Nos. of above persons (entities only).

--------------------------------------------------------------------------------
2.       Check the Appropriate Box if a Member of a Group (See Instructions)

         (a) [ ]

         (b) [X]
--------------------------------------------------------------------------------
3.       SEC Use Only

--------------------------------------------------------------------------------
4.       Citizenship or Place of Organization          Cayman Islands

--------------------------------------------------------------------------------
Number of                  5.   Sole Voting Power:             157,431
Shares                    -----------------------------------------------------
Beneficially               6.   Shared Voting Power:           0
Owned by                  -----------------------------------------------------
Each                       7.   Sole Dispositive Power:        157,431
Reporting                 -----------------------------------------------------
Person With:               8.   Shared Dispositive Power:      0
--------------------------------------------------------------------------------
9.       Aggregate Amount Beneficially Owned by Each Reporting Person   157,431


10.      Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)                                             [ ]

11.      Percent of Class Represented by Amount in Row (9)    1.2%

--------------------------------------------------------------------------------
12.      Type of Reporting Person (See Instructions)

--------------------------------------------------------------------------------
CO



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

                               Page 7 of 10 pages


Item 1.

(a)   The name of the issuer is Clean Harbors, Inc. (the "Issuer").

(b)   The principal executive office of the Issuer is located at 1501 Washington
      Street, Braintree, MA 02184.

Item 2.

(a)   The names of the persons filing this statement (the "Statement") are Glenn
      J. Krevlin, Krevlin Advisors, LLC, a Delaware limited liability Company
      ("Krevlin Advisors"), GJK Capital Management, LLC, a Delaware limited
      liability company ("GJK"), Glenhill Overseas Management, LLC, a Deleaware
      limited liability company ("Glenhill Overseas"), Glenhill Capital LP, a
      Delaware limited partnership ("Glenhill Capital"), and Glenhill Capital
      Overseas Partners Ltd., a Cayman Islands exempted company ("Overseas
      Partners") (collectively, the "Filers").

(b)   The Principal Business Office of the Filers is 650 Madison Avenue, 26th
      Floor, New York, New York 10022.

(c)   For citizenship information see item 4 of the cover sheet of each Filer.

(d)   This Statement relates to the Common Stock, $.01 par value, of the Issuer.

(e)   The CUSIP Number of the common stock of the Issuer is 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) [ ]  Group, in accordance with "240.13d-1(b)(1)(ii)(J);

Item 4. Ownership.

See Items 5-9 and 11 on the cover page for each filer.

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

Instruction. For computations regarding securities which represent a right to
acquire an underlying security see "240.13d-3(d)(1).

                               Page 8 of 10 pages


Item 5.  Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof
the reporting person has ceased to be the beneficial owner of more than five
percent of the class of securities, check the following [X].

Instruction: Dissolution of a group requires a response to this item.

Item 6.  Ownership of More than Five 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 five 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.

Item 7.  Identification and Classification of the Subsidiary Which Acquired the
         Security Being Reported on By the Parent Holding Company.

If a parent holding company or control person has filed this schedule, pursuant
to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit
stating the identity and the Item 3 classification of the relevant subsidiary.
If a parent holding company or control person has filed this schedule pursuant
to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification
of the relevant subsidiary.

Glenn J. Krevlin is the managing member and control person of Krevlin Advisors
and Glenhill Overseas. Krevlin Advisors is the managing member of GJK and GJK is
the general partner and control person of Glenhill Capital. Glenhill Overseas is
the investment manager of Overseas Partners. Glenhill Capital and Overseas
Partners are both private investment vehicles formed for the purpose of
investing and trading in a wide variety of securities and financial instruments.

                                                            [ ] EXHIBIT ATTACHED

Item 8.  Identification and Classification of Members of the Group

If a group has filed this schedule pursuant to Rule 13d-1(b)(1)(ii)(J), so
indicate under Item 3(j) and attach an exhibit stating the identity and Item 3
classification of each member of the group. If a group has filed this schedule
pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the
identity of each member of the group.

Item 9.  Notice of Dissolution of Group

Notice of dissolution of a group may be furnished as an exhibit stating the date
of the dissolution and that all further filings with respect to transactions in
the security reported on will be filed, if required, by members of the group, in
their individual capacity. See Item 5.

                                                            [ ] EXHIBIT ATTACHED

Item 10.   Certification

(a)      The following certification shall be included if the statement filed
         pursuant to "240.13d-1(b):

         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.

         The following certification shall be included if the statement filed
         pursuant to "240.13d-1(c):

(b)      By signing below I certify that, to the best of my knowledge and
         belief, the securities referred to above 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.

                               Page 9 of 10 pages


                                    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.


Dated:    August 27, 2003
                                      /s/ GLENN J. KREVLIN
                                      ------------------------------------------
                                      Glenn J. Krevlin


                                      KREVLIN ADVISORS, LLC

                                      By /s/ GLENN J. KREVLIN
                                         ---------------------------------------
                                         Glenn J. Krevlin,  Managing Member


                                      GJK CAPITAL MANAGEMENT, LLC

                                      By: Krevlin Advisors, LLC, Managing Member

                                      By /s/ GLENN J. KREVLIN
                                         ---------------------------------------
                                         Glenn J. Krevlin,  Managing Member


                                      GLENHILL CAPITAL LP

                                      By: GJK Capital Management, LLC,
                                          General Partner

                                      By: Krevlin Advisors, LLC, Managing Member

                                      By /s/ GLENN J. KREVLIN
                                         ---------------------------------------
                                         Glenn J. Krevlin,  Managing Member


                                      GLENHILL OVERSEAS MANAGEMENT, LLC

                                      By /s/ GLENN J. KREVLIN
                                         ---------------------------------------
                                         Glenn J. Krevlin,  Managing Member


                                      GLENHILL CAPITAL OVERSEAS PARTNERS LTD

                                      By /s/ GLENN J. KREVLIN
                                         ---------------------------------------
                                         Glenn J. Krevlin,  Director


The original statement shall be signed by each person on whose behalf the
statement is filed or his authorized representative. If the statement is signed
on behalf of a person by his authorized representative other than an executive
officer or general partner of the filing person, evidence of the
representative's authority to sign on behalf of such person shall be filed with
the statement, provided, however, that a power of attorney for this purpose
which is already on file with the Commission may be incorporated by reference.
The name and any title of each person who signs the statement shall be typed or
printed beneath his signature.

Note: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See "240.13d-7 for other parties
for whom copies are to be sent.

Attention: Intentional misstatements or omissions of fact constitute Federal
criminal violations (See 18 U.S.C. 1001)

                               Page 10 of 10 pages