POWER OF ATTORNEY

Know all by these presents, that the undersigned hereby constitutes
and appoints each of Rick L Wittenbraker, John Tsai, Courtney Tippy and
Linda J. Smith as the undersigned's true and lawful attorneys-in-fact,
with full power of substitution, to:

(1) execute for and on behalf of the undersigned, in the undersigned's
capacity as a reporting person of Waste Management, Inc. (the
"Company") pursuant to Section 16 of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), and the rules and regulations
thereunder, Forms 3, 4 and 5 in accordance with Section 16(a) of the
Exchange Act and any Form 144, Form 8-K or other form required to be
filed relating to the transaction covered by such report (collectively,
the "Required Forms");

(2) do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete and execute
any such Required Forms and timely file such Required Forms with the
United States Securities and Exchange Commission, any stock exchange,
or other authority or body; and

(3) take any other action of any type whatsoever in connection with
the foregoing which, in the opinion of any of such attorneys-in-fact
or their substitutes, may be of benefit to, in the best interest of,
or legally required by, the undersigned, it being understood that the
documents executed by any of such attorneys-in-fact or their
substitutes on behalf of the undersigned pursuant to this Power of
Attorney shall be in such form and shall contain such terms and
conditions as any of such attorneys-in-fact or their substitutes may
approve in the discretion of any such person.

The undersigned hereby grants to each such attorney-in-fact or their
substitutes full power and authority to do and perform any and every
act and thing whatsoever requisite, necessary, or proper to be done
in the exercise of any of the rights and powers herein granted, as
fully to all intents and purposes as the undersigned might or could
do if personally present, with full power of substitution or
revocation, hereby ratifying and confirming all that any of such
attorneys-in-fact, or the substitute or substitutes of any of such
attorneys-in-fact, shall lawfully do or cause to be done by virtue
of this Power of Attorney and the rights and powers herein granted.
The undersigned acknowledges that the foregoing attorneys-in-fact
or their substitutes, in serving in such capacity at the request
of the undersigned, are not assuming, nor is the Company assuming,
any of the undersigned's responsibilities to comply with Section 16
of the Exchange Act or any other law, rule or regulation.

This Power of Attorney shall remain in full force and effect until
the undersigned is no longer required to file Required Forms with
respect to the undersigned's holdings of and transactions in
securities issued by the Company, unless earlier revoked by the
undersigned in a signed writing delivered to the foregoing
attorneys-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of this 18th day of January, 2011.


Signature:	/s/Grace Cowan
Name:		Grace Cowan