<PAGE>   1
                                                                   EXHIBIT 10.21


                               ADDITIONAL GUARANTY

       THIS GUARANTY dated as of October 31, 2000 is executed in favor of BANK
OF AMERICA, N.A., as Agent, and the Lender Parties referred to below.

                                   WITNESSETH:

       WHEREAS, EARTHCARE COMPANY (the "Company") has entered into an Amended
and Restated Credit Agreement dated as of February 15, 2000 (as amended or
otherwise modified from time to time, the "Credit Agreement"; terms used but not
defined herein are used as defined in the Credit Agreement) with various
financial institutions and BANK OF AMERICA, N.A., as agent (in its capacity as
agent, together with any successor in such capacity, the "Agent"), pursuant to
which such financial institutions have agreed to make loans to, and issue or
participate in letters of credit for the account of, the Company;

       WHEREAS, the Agent, the Required Banks and the Company have entered into
a Second Amendment to the Credit Agreement dated as of the date hereof (the
"Second Amendment");

       WHEREAS, the undersigned is a significant investor in the Company, and
has previously executed a Guaranty dated as of February 15, 2000 (the "Existing
Guaranty") in favor of the Agent to guaranty the Liabilities (as defined below);
and

       WHEREAS, in consideration of the amendments, waivers and consents set
forth in the Second Amendment, the undersigned, subject to the terms hereof, is
willing to further guaranty the Liabilities as hereinafter set forth;

       NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the undersigned hereby
unconditionally and irrevocably, as primary obligor and not merely as surety,
guarantees the full and prompt payment when due, whether by acceleration or
otherwise, and at all times thereafter, of all obligations of the Company to
each of the Agent and each Lender Party (as defined below) under or in
connection with the Credit Agreement, the Notes, any other Loan Document, any
Hedging Contract entered into with any Lender Party and any other instrument or
document executed in connection with any of the foregoing, in each case
howsoever created, arising or evidenced, whether direct or indirect, absolute or
contingent, now or hereafter existing, or due or to become due (all such
obligations being herein collectively called the "Liabilities"); provided,
however, that the liability of the undersigned hereunder shall be limited to the
Maximum Principal Liability Amount (as defined below) plus interest accruing on
such amount (or such lesser amount of the Liabilities as is outstanding) after
demand by the Agent hereunder (including interest at the rate specified in any
applicable agreement accruing after any bankruptcy or insolvency proceeding with
respect to the Company regardless of whether such interest is an allowed claim
in such proceeding) plus all costs and expenses paid or incurred by the Agent or
any Lender Party in enforcing this Guaranty against the undersigned). As used
herein, (i) "Lender Party" means each



<PAGE>   2
Bank under and as defined in the Credit Agreement and any Affiliate of such a
Bank which is a party to a Hedging Contract with the Company; and (ii) Maximum
Principal Liability Amount means $20,000,000; provided that if the Company has
not completed a sale of the EarthLiquids Subsidiaries on or before December 31,
2000, the Maximum Principal Liability Amount shall be automatically increased to
an amount equal to the remainder of $40,000,000 minus the amount of all Asset
Sale Commitment Reductions made during the period from September 30, 2000
through December 31, 2000; and provided, further, that if the Maximum Principal
Liability Amount is increased on December 31, 2000, then the Maximum Principal
Liability Amount shall be decreased (but not below $20,000,000) by the amount of
all Asset Sale Commitment Reductions made after December 31, 2000. For purposes
of the foregoing, "Asset Sale Commitment Reduction" means any reduction in the
Commitments made pursuant to Section 6.1.3(b) of the Credit Agreement at a time
when no Event of Default or Unmatured Event of Default exists or will result
from such reduction or the sale of assets giving rise thereto.

       The undersigned acknowledges that the obligations of the undersigned
under this Guaranty are in addition to the obligations of the undersigned under
the Existing Guaranty and that the Agent and the Lender Parties may make demand
under this Guaranty, and enforce their rights and remedies under this Guaranty,
and enforce their rights and remedies under this Guaranty, before, after or
concurrently with making demand and/or enforcing rights and remedies under the
Existing Guaranty.

        The undersigned agrees that, in the event of the dissolution or
insolvency of the Company, or the insolvency, death or legal incapacity of the
undersigned, or the inability or failure of the Company or the undersigned to
pay debts as they become due, or an assignment by the Company or the undersigned
for the benefit of creditors, or the occurrence of any other Event of Default
under Section 12.1.4 of the Credit Agreement, and if such event shall occur at a
time when any of the Liabilities may not then be due and payable, the
undersigned will pay to the Agent for the account of the Lender Parties
forthwith the full amount which would be payable hereunder by the undersigned if
all Liabilities were then due and payable.

        This Guaranty shall in all respects be a continuing, irrevocable,
absolute and unconditional guaranty, and (except as expressly provided below)
shall remain in full force and effect (notwithstanding, without limitation, that
at any time or from time to time no Liabilities are outstanding) until all
Commitments have terminated and all Liabilities have been paid in full.

        The undersigned agrees that if at any time all or any part of any
payment theretofore applied by the Agent or any Lender Party to any of the
Liabilities is or must be rescinded or returned by the Agent or such Lender
Party for any reason whatsoever (including the insolvency, bankruptcy or
reorganization of the Company or the undersigned), such Liabilities shall, for
the purposes of this Guaranty, to the extent that such payment is or must be
rescinded or returned, be deemed to have continued in existence, notwithstanding
such application by the Agent or such Lender Party, and this Guaranty shall
continue to be effective or be reinstated, as the case may be, as to such
Liabilities, all as though such application by the Agent or such Lender Party
had not been made.


<PAGE>   3

       The Agent or any Lender Party may, from time to time, at its sole
discretion and without notice to the undersigned, take any or all of the
following actions: (a) retain or obtain a security interest in any property to
secure any of the Liabilities or any obligation hereunder, (b) retain or obtain
the primary or secondary obligation of any obligor or obligors, in addition to
the undersigned, with respect to any of the Liabilities, (c) extend or renew any
of the Liabilities for one or more periods (whether or not longer than the
original period), alter or exchange any of the Liabilities, or release or
compromise any obligation of the undersigned hereunder or any obligation of any
nature of any other obligor with respect to any of the Liabilities, (d) release
its security interest in, or surrender, release or permit any substitution or
exchange for, all or any part of any property securing any of the Liabilities or
any obligation hereunder, or extend or renew for one or more periods (whether or
not longer than the original period) or release, compromise, alter or exchange
any obligations of any nature of any obligor with respect to any such property,
and (e) resort to the undersigned for payment of any of the Liabilities when
due, whether or not the Agent or such Lender Party shall have resorted to any
property securing any of the Liabilities or any obligation hereunder or shall
have proceeded against any other obligor primarily or secondarily obligated with
respect to any of the Liabilities.

       The undersigned agrees to deliver to the Agent cash collateral, or other
collateral reasonably satisfactory to the Agent, in an amount (with the value of
any non-cash collateral being determined by the Agent in its discretion) not
less than $5,000,000 on or before October 31, 2000 and an additional $10,000,000
on or before November 30, 2000. Such collateral shall be held by the Agent as
security for the obligations of the undersigned hereunder pursuant to
documentation reasonably satisfactory to the Agent. Upon any demand by the Agent
hereunder, the Agent may immediately apply such collateral (or the proceeds
thereof in the case of non-cash collateral) to the payment of the Liabilities.
The undersigned acknowledges that the obligation to provide collateral set forth
in this paragraph is in addition to any obligation of the undersigned to provide
collateral pursuant to the Existing Guaranty.

       The undersigned hereby expressly waives: (a) notice of the acceptance by
the Agent or any Lender Party of this Guaranty, (b) notice of the existence or
creation or non-payment of all or any of the Liabilities, (c) presentment,
demand, notice of dishonor, protest, and all other notices whatsoever, and (d)
all diligence in collection or protection of or realization upon any Liabilities
or any security for or guaranty of any Liabilities.

       Notwithstanding any payment made by or for the account of the undersigned
pursuant to this Guaranty, the undersigned shall not be subrogated to any right
of the Agent or any Lender Party until such time as the Agent and the Lender
Parties shall have received final payment in cash of the full amount of all
Liabilities.

       The undersigned further agrees to pay all expenses (including the
reasonable attorneys' fees and charges) paid or incurred by the Agent or any
Lender Party in endeavoring to collect the Liabilities of the undersigned, or
any part thereof, and in enforcing this Guaranty against the undersigned.


<PAGE>   4

       The creation or existence from time to time of additional Liabilities to
the Agent or the Lender Parties or any of them is hereby authorized, without
notice to the undersigned, and shall in no way affect or impair the rights of
the Agent or the Lender Parties or the obligations of the undersigned under this
Guaranty.

       The Agent and any Lender Party may from time to time without notice to
the undersigned, assign or transfer any or all of the Liabilities or any
interest therein; and, notwithstanding any such assignment or transfer or any
subsequent assignment or transfer thereof, such Liabilities shall be and remain
Liabilities for the purposes of this Guaranty, and each and every immediate and
successive assignee or transferee of any of the Liabilities or of any interest
therein shall, to the extent of the interest of such assignee or transferee in
the Liabilities, be entitled to the benefits of this Guaranty to the same extent
as if such assignee or transferee were an original Lender Party.

       No delay on the part of the Agent or any Lender Party in the exercise of
any right or remedy shall operate as a waiver thereof, and no single or partial
exercise by the Agent or any Lender Party of any right or remedy shall preclude
other or further exercise thereof or the exercise of any other right or remedy;
nor shall any modification or waiver of any provision of this Guaranty be
binding upon the Agent or the Lender Parties, except as expressly set forth in a
writing duly signed and delivered on behalf of the Agent. No action of the Agent
or any Lender Party permitted hereunder shall in any way affect or impair the
rights of the Agent or any Lender Party or the obligations of the undersigned
under this Guaranty. For purposes of this Guaranty, Liabilities shall include
all obligations of the Company to the Agent or any Lender Party arising under or
in connection with the Credit Agreement, any Note, any other Loan Document, any
Swap Contract or any other document or instrument executed in connection with
any of the foregoing, notwithstanding any right or power of the Company or
anyone else to assert any claim or defense as to the invalidity or
unenforceability of any such obligation, and no such claim or defense shall
affect or impair the obligations of any of the undersigned hereunder.

       Pursuant to the Credit Agreement, (a) this Guaranty has been delivered to
the Agent and (b) the Agent has been authorized to enforce this Guaranty on
behalf of itself and the Lender Parties. All payments by the undersigned
pursuant to this Guaranty shall be made to the Agent for the benefit of the
Lender Parties.

       This Guaranty shall be binding upon the undersigned and the heirs and
legal representatives of the undersigned. All references herein to the Company
shall be deemed to include any successor or successors, whether immediate or
remote, to such corporation.

       This Guaranty shall be governed by and construed in accordance with the
laws of the State of Illinois applicable to contracts made and to be fully
performed in such State. Wherever possible, each provision of this Guaranty
shall be interpreted in such manner as to be effective and valid under
applicable law, but if any provision of this Guaranty shall be prohibited by or
invalid under such law, such provision shall be ineffective to the extent of
such prohibition or



<PAGE>   5

invalidity, without invalidating the remainder of such provision or the
remaining provisions of this Guaranty.

       This Guaranty may be executed in any number of counterparts and by the
different parties hereto on separate counterparts, and each such counterpart
shall be deemed to be an original but all such counterparts shall together
constitute one and the same Guaranty.

       This Guaranty may be secured by one or more security agreements, pledge
agreements or other similar documents.

       ANY LITIGATION BASED HEREON, OR ARISING OUT OF, UNDER OR IN CONNECTION
WITH THIS GUARANTY OR ANY OTHER LOAN DOCUMENT, SHALL BE BROUGHT AND MAINTAINED
EXCLUSIVELY IN THE COURTS OF THE STATE OF ILLINOIS OR IN THE UNITED STATES
DISTRICT COURT FOR THE NORTHERN DISTRICT OF ILLINOIS; PROVIDED, THAT ANY SUIT
SEEKING ENFORCEMENT AGAINST ANY COLLATERAL OR OTHER PROPERTY MAY BE BROUGHT, AT
THE AGENT'S OPTION, IN THE COURTS OF ANY JURISDICTION WHERE SUCH COLLATERAL OR
OTHER PROPERTY MAY BE FOUND. THE UNDERSIGNED HEREBY EXPRESSLY AND IRREVOCABLY
SUBMITS TO THE JURISDICTION OF THE COURTS OF THE STATE OF ILLINOIS AND OF THE
UNITED STATES DISTRICT COURT FOR THE NORTHERN DISTRICT OF ILLINOIS FOR THE
PURPOSE OF ANY SUCH LITIGATION AS SET FORTH ABOVE. THE UNDERSIGNED FURTHER
IRREVOCABLY CONSENTS TO THE SERVICE OF PROCESS BY REGISTERED MAIL, POSTAGE
PREPAID, TO THE ADDRESS SET FORTH OPPOSITE HIS SIGNATURE HERETO (OR SUCH OTHER
ADDRESS AS THE UNDERSIGNED SHALL HAVE SPECIFIED IN WRITING TO THE AGENT AS HIS
ADDRESS FOR NOTICES HEREUNDER) OR BY PERSONAL SERVICE WITHIN OR WITHOUT THE
STATE OF ILLINOIS. THE UNDERSIGNED HEREBY EXPRESSLY AND IRREVOCABLY WAIVES, TO
THE FULLEST EXTENT PERMITTED BY LAW, ANY OBJECTION WHICH HE MAY NOW OR HEREAFTER
HAVE TO THE LAYING OF VENUE OF ANY SUCH LITIGATION BROUGHT IN ANY SUCH COURT
REFERRED TO ABOVE AND ANY CLAIM THAT ANY SUCH LITIGATION HAS BEEN BROUGHT IN AN
INCONVENIENT FORUM.

       THE UNDERSIGNED, AND (BY ACCEPTING THE BENEFITS HEREOF) EACH OF THE AGENT
AND EACH LENDER PARTY, HEREBY WAIVES ANY RIGHT TO A TRIAL BY JURY IN ANY ACTION
OR PROCEEDING TO ENFORCE OR DEFEND ANY RIGHTS UNDER THIS GUARANTY, ANY OTHER
LOAN DOCUMENT AND ANY AMENDMENT, INSTRUMENT, DOCUMENT OR AGREEMENT DELIVERED OR
WHICH MAY IN THE FUTURE BE DELIVERED IN CONNECTION HEREWITH OR THEREWITH OR
ARISING FROM ANY BANKING RELATIONSHIP EXISTING IN CONNECTION WITH ANY OF THE
FOREGOING, AND AGREES THAT ANY SUCH ACTION OR PROCEEDING SHALL BE TRIED BEFORE A
COURT AND NOT BEFORE A JURY.



<PAGE>   6

       IN WITNESS WHEREOF, this Guaranty has been duly executed and delivered as
of the day and year first above written.


                                            ------------------------------------
Address:                                    Donald F. Moorehead, Jr.

c/o EarthCare Company
14901 Quorum Drive
Suite 200
Dallas, TX  75240