<PAGE>

                                                                    Exhibit 3(y)

                         CERTIFICATE OF INCORPORATION
                                      OF
                             ICF KAISER GCH, INC.


SECTION 1.01.    NAME.
-------------    -----

The name of the Corporation is ICF Kaiser GCH, Inc.

SECTION 2.01.    REGISTERED OFFICE AND AGENT.
-------------    ----------------------------

The registered office of the Corporation in the State of Delaware is located in
the County of New Castle, at 1013 Centre Road, Wilmington 19805. Its registered
agent at such address is Corporation Service Company.

SECTION 3.01.    PURPOSES.
-------------    ---------

The purpose of the Corporation is to engage in any lawful act or activity for
which corporations may be organized under the General Corporation Law of
Delaware.

SECTION 4.01.    AUTHORIZED SHARES.
-------------    ------------------

The total number of shares of capital stock which the Corporation shall have
authority to issue is one thousand (1,000) shares of Common Stock having a par
value of one dollar ($1.00) per share.

SECTION 5.01.    INCORPORATOR.
-------------    -------------

The name and mailing address of the incorporator is Paul Weeks, II, 9300 Lee
Highway, Fairfax, Virginia  22031-1207.

SECTION 5.02.    DURATION.
-------------    ---------

The Corporation is to have perpetual existence.

SECTION 6.01.    LIMITATION OF LIABILITY.
-------------    ------------------------

(a) No person shall be liable to the Corporation for any loss or damage suffered
by it on account of any action taken or omitted to be taken by him or her as a
director or officer of the Corporation, if such person (i) in good faith
exercised or used the same degree of diligence, care and skill as an ordinarily
prudent person would have exercised or used under similar circumstances, or (ii)
took, or omitted to take, such action in good faith reliance upon advice of
counsel for the Corporation, or upon books of account or reports made to the
Corporation by any of its officers or by an independent certified public
accountant, or by an appraiser selected with reasonable care by the Board of
Directors or by any committee designated by the Board of Directors, or in good
faith reliance upon other records of the Corporation.

(b) No director of the Corporation shall be liable to the Corporation or its
stockholders for monetary damages for breach of fiduciary duty as a director,
provided that the foregoing shall not eliminate or limit the liability of a
director (i) for any breach of the director's duty of loyalty to the Corporation
or its stockholders, (ii) for acts or omissions not in good faith or which
involve intentional misconduct or a knowing violation of law, (iii) under
Section 174 of the Delaware General Corporation Law, or (iv) for any transaction
from which the director derived an improper personal benefit.

SECTION 7.01.    RATIFICATION BY STOCKHOLDERS.
-------------    -----------------------------

Any contract, transaction or act of the Corporation, the Board of Directors, or
a committee of the Board of Directors which shall be approved or ratified by a
majority of a quorum of the stockholders entitled to vote at any meeting or,
without a meeting, by the written consent of the holders of a majority of the
stock entitled to vote shall be as valid and binding as though approved or
ratified by every stockholder of the Corporation; but any failure of the
stockholders to approve or ratify such contract, transaction or act, when and if
submitted, shall not be deemed in any way to invalidate the same or to deprive
the Corporation, its directors or officers, of their right to proceed with such
contract, transaction or act.


SECTION 8.01.    INDEMNIFICATION OF DIRECTORS AND OFFICERS FOR ACTIONS, SUITS,
-------------    -------------------------------------------------------------
                 OR PROCEEDINGS OTHER THAN BY OR IN THE RIGHT OF THE
                 ---------------------------------------------------
                 CORPORATION.
                 -----------
<PAGE>

                                                 CERTIFICATE OF INCORPORATION OF
                                                            ICF KAISER GCH, INC.
                                                                     Page 2 of 6

To the full extent permitted by law, the Corporation shall indemnify any person
who was or is a party or is threatened to be made a party to any threatened,
pending or completed action, suit or proceeding, whether civil, criminal,
administrative or investigative (other than an action by or in the right of the
Corporation), by reason of the fact that he or she is or was or has agreed to
become a director or officer of the Corporation or is or was serving or has
agreed to serve at the request of the Corporation as a director or officer of
another corporation, partnership, joint venture, trust or other enterprise
(including employee benefit plans), or by reason of any action alleged to have
been taken or omitted in such capacity, against costs, charges, expenses
(including attorneys' fees), judgments, fines and amounts paid in settlement
actually and reasonably incurred by him or her on his or her behalf in
connection with any threatened, pending or completed action, suit or proceeding
and any appeal therefrom, including but not limited to liability and expenses
incurred on account of profits realized by him or her in the purchase or sale of
securities of the Corporation, if and only if he or she acted in good faith and
                               --------------
in a manner he or she reasonably believed to be in or not opposed to the best
interests of the Corporation, and, with respect to any criminal action or
proceeding, had no reasonable cause to believe his or her conduct was unlawful;
the termination of any action, suit or proceeding by judgment, order,
settlement, conviction, or upon a plea of nolo contendere or its equivalent
                                          ---- ----------
shall not, of itself, create a presumption that the person did not act in good
faith and in a manner which he or she reasonably believed to be in or not
opposed to the best interests of the Corporation, and, with respect to any
criminal action or proceeding, had reasonable cause to believe that his or her
conduct was unlawful.


SECTION 8.02.    INDEMNIFICATION OF DIRECTORS AND OFFICERS FOR ACTIONS OR SUITS
-------------    --------------------------------------------------------------
                 BY OR IN THE RIGHT OF THE CORPORATION.
                 --------------------------------------

To the full extent permitted by law, the Corporation shall indemnify any person
who was or is a party or is threatened to be made a party to any threatened,
pending or completed action or suit by or in the right of the Corporation to
procure a judgment in its favor by reason of the fact that he or she is or was
or has agreed to become a director or officer of the Corporation or is or was
serving or has agreed to serve at the request of the Corporation as a director
or officer of another corporation, partnership, joint venture, trust or other
enterprise (including employee benefit plans), or by reason of any action
alleged to have been taken or omitted in such capacity, against costs, charges
and expenses (including attorneys' fees) actually and reasonably incurred by him
or her on his or her behalf in connection with the defense or settlement of any
threatened, pending or completed action or suit and any appeal therefrom, or the
defense or settlement of any claim, issue or matter, if and only if he or she
                                                     --------------
acted in good faith and in a manner he or she reasonably believed to be in or
not opposed to the best interests of the Corporation except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the Corporation
unless and only to the extent that the Court of Chancery of Delaware or the
court in which such action or suit was brought shall determine upon application
that, despite the adjudication of such liability but in view of all the
circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such costs, charges and expenses which the Court of Chancery or
such other court shall deem proper.

SECTION 8.03.    INDEMNIFICATION OF OTHERS FOR ACTIONS, SUITS, OR PROCEEDINGS
-------------    ------------------------------------------------------------
                 OTHER THAN BY OR IN THE RIGHT OF THE CORPORATION.
                 -------------------------------------------------

To the full extent permitted by law, the Corporation, in the sole discretion of
the Board of Directors of the Corporation, may indemnify any person who was or
is a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of the Corporation), by
reason of the fact that he or she is or was or has agreed to become an employee,
agent or contractor of the Corporation, or is or was serving or has agreed to
serve at the request of the Corporation as a director, officer, employee, agent
or contractor of another corporation, partnership, joint venture, trust or other
enterprise (including employee benefit plans), or by reason of any action
alleged to have been taken or omitted in such capacity, against costs, charges,
expenses (including attorneys' fees), judgments, fines and amounts paid in
settlement actually and reasonably incurred by him or her or on his or her
behalf in connection with any threatened, pending or completed action, suit or
proceeding and any appeal therefrom, including but not limited to liability and
expenses incurred on account of profits realized by him or her in the purchase
or sale of securities of the Corporation, if and only if he or she acted in good
                                          --------------
faith and in a manner he or she reasonably believed to be in or not opposed to
the best interests of the Corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful; the
termination of any action, suit or proceeding by judgment, order, settlement,
conviction, or upon a plea of nolo contendere or its equivalent shall not, of
                              ---- ----------
itself, create a presumption that the person did not act in good faith and in a
manner which he or she reasonably believed to be in or not opposed to the best
interests of the Corporation, and, with respect to any criminal action or
proceeding, had reasonable cause to believe that his conduct was unlawful.

SECTION 8.04.    INDEMNIFICATION OF OTHERS FOR ACTIONS OR SUITS BY OR IN THE
-------------    -----------------------------------------------------------
                 RIGHT OF THE CORPORATION.
                 -------------------------

To the full extent permitted by law, the Corporation, in the sole discretion of
the Board of Directors of the Corporation, may
<PAGE>

                                                 CERTIFICATE OF INCORPORATION OF
                                                            ICF KAISER GCH, INC.
                                                                     Page 3 of 6

indemnify any person who was or is a party or is threatened to be made a party
to any threatened, pending or completed action or suit by or in the right of the
Corporation to procure a judgment in its favor by reason of the fact that he or
she is or was or has agreed to become an employee, agent or contractor of the
Corporation, or is or was serving or has agreed to serve at the request of the
Corporation as a director, officer, employee, agent or contractor of another
corporation, partnership, joint venture, trust or other enterprise (including
employee benefit plans), or by reason of any action alleged to have been taken
or omitted in such capacity, against costs, charges and expenses (including
attorneys' fees) actually and reasonably incurred by him or her or on his or her
behalf in connection with the defense or settlement of any threatened, pending
or completed action or suit and any appeal therefrom, or the defense or
settlement of any claim, issue or matter, if and only if he or she acted in good
                                             -----------
faith and in a manner he or she reasonably believed to be in or not opposed to
the best interests of the Corporation except that no indemnification shall be
made in respect of any claim, issue or matter as to which such person shall have
been adjudged to be liable to the Corporation unless and only to the extent that
the Court of Chancery of Delaware or the court in which such action or suit was
brought shall determine upon application that, despite the adjudication of such
liability but in view of all the circumstances of the case, such person is
fairly and reasonably entitled to indemnity for such costs, charges and expenses
which the Court of Chancery or such other court shall deem proper.

SECTION 8.05.    INDEMNIFICATION FOR COSTS, CHARGES AND EXPENSES OF SUCCESSFUL
-------------    -------------------------------------------------------------
                 PARTY.
                 ------

Notwithstanding the other provisions of this Certificate, to the extent that a
director or officer of the Corporation or other person indemnified under
Sections 9.01 through 9.04, herein, has been successful on the merits or
otherwise, including, without limitation, the dismissal of an action without
prejudice, in defense of any action, suit or proceeding referred to above, or in
defense of any claim, issue or matter therein, he or she shall be indemnified
against all costs, charges and expenses (including attorneys' fees) actually and
reasonably incurred by him or her or on his or her behalf in connection
therewith.

SECTION 8.06.    DETERMINATION OF RIGHT TO INDEMNIFICATION.
-------------    ------------------------------------------

Unless otherwise ordered by a court, any indemnification under Sections 9.01
through 9.04, herein, shall be paid by the Corporation unless a determination is
made (i) by the Board of Directors by a majority vote of a quorum consisting of
directors who were not parties to such action, suit or proceeding, or (ii) if
such a quorum is not obtainable, or, even if obtainable a quorum of
disinterested directors so directs, by independent legal counsel in a written
opinion, or (iii) by the stockholders, that indemnification of an individual
entitled to indemnification under Sections 9.01 through 9.04, herein, is not
proper in the circumstances because he or she has not met the applicable
standard of conduct set forth in Sections 9.01 through 9.04, herein.

SECTION 8.07.    ADVANCE PAYMENT OF COSTS, CHARGES AND EXPENSES.
-------------    -----------------------------------------------

To the full extent permitted by law, the Corporation shall, upon request, pay
costs, charges and expenses (including attorneys' fees) incurred by a person
entitled to indemnification pursuant to Sections 9.01 and 9.02, herein, and, if
applicable, pursuant to Sections 9.03 and 9.04, herein, in defending a civil or
criminal action, suit or proceeding in advance of the final disposition of such
action, suit or proceeding; provided, however, that the payment of such costs,
                            --------  -------
charges and expenses incurred by a director or officer in his or her capacity as
a director or officer (and not in any other capacity in which service was or is
rendered by such person while a director or officer) in advance of the final
disposition of such action, suit or proceeding shall be made only upon receipt
of an undertaking by or on behalf of the director or officer to repay all
amounts so advanced in the event that it shall ultimately be determined that
such director or officer is not entitled to be indemnified by the Corporation as
authorized in this certificate; such costs, charges and expenses incurred by
other employees, agents and contractors may be so paid upon such terms and
conditions, if any, as the Board of Directors deems appropriate.

SECTION 8.08.    PROCEDURE FOR INDEMNIFICATION.
-------------    ------------------------------

Any indemnification or advance of costs, charges and expenses provided for in
Sections 9.01 through 9.07, herein, shall be made promptly, and in any event
within sixty days, upon the written request of the person entitled to
indemnification; the right to indemnification or advances as granted by this
Certificate shall be enforceable by a director or officer or other person
indemnified hereunder in any court of competent jurisdiction. If the Corporation
denies such request, in whole or in part, or if no disposition thereof is made
within sixty days, such person's costs, charges and expenses incurred in
connection with successfully establishing his right to indemnification, in whole
or in part, in any such action shall also be indemnified by the Corporation; it
shall be a defense to any such action (other than an action brought to enforce a
claim for the advance of costs, charges and expenses pursuant to Section 9.07,
herein, where the required undertaking, if any, has been received by the
Corporation) that the claimant has not met the standard of conduct set forth in
Sections 9.01 through 9.04, herein. Neither the failure of the Corporation
(including its Board of Directors, its independent legal counsel, and its
stockholders) to have made a determination prior to the commencement of such
<PAGE>

                                                 CERTIFICATE OF INCORPORATION OF
                                                            ICF KAISER GCH, INC.
                                                                     Page 4 of 6

action that indemnification of the claimant is proper in the circumstances
because he or she has met the applicable standard of conduct set forth in
Sections 9.01 through 9.04, herein, nor the fact that there has been an actual
determination by the Corporation (including its Board of Directors, its
independent legal counsel, and its stockholders) that the claimant has not met
such applicable standard of conduct, shall be a defense to the action or create
a presumption that the claimant has not met the applicable standard of conduct.

SECTION 8.09.    AUTHORIZATION OF CORPORATION OFFICERS.
-------------    --------------------------------------

The proper officers of the Corporation are, and each of them acting without the
other is, authorized to take any action, for and in the name of the Corporation,
which the officer deems necessary or appropriate (as conclusively presumed from
the taking of such action) to carry out and effect the foregoing Sections 9.01
through 9.08.

SECTION 8.10.    OTHER RIGHTS; CONTINUATION OF RIGHT TO INDEMNIFICATION.
-------------    -------------------------------------------------------

The indemnification and advancement of expenses provided by this Certificate
shall not be deemed exclusive of any other rights to which a person seeking
indemnification or advancement of expenses may be entitled under any law
(present or future, common or statutory), by-law, agreement, vote of
stockholders or disinterested directors or otherwise, both as to action in his
or her official capacity and as to action in another capacity while holding
office or while employed by or acting as an agent for the Corporation, and shall
continue as to a person who has ceased to serve in the capacity making him or
her eligible for indemnification, and shall inure to the benefit of the estate,
heirs, executors and administrators of such person; all rights to
indemnification under this Certificate shall be deemed to be a contract between
the Corporation and each director and officer of the Corporation and, as
applicable, any other person indemnified hereunder who serves or served in such
capacity at any time while this Certificate as well as the relevant provisions
of the Delaware General Corporation Law or any other applicable laws are or were
in effect; any repeal or modification hereof or of such provisions of such law
shall not in any way diminish any rights to indemnification of such director or
officer or other person entitled to indemnification or the obligations of the
Corporation arising hereunder.

SECTION 8.11.    SAVINGS CLAUSE.
-------------    ---------------

If this Certificate or any portion hereof shall be invalidated on any ground by
any court of competent jurisdiction, then the Corporation shall nevertheless
indemnify each director and officer, and may indemnify any other person entitled
to indemnification, as to costs, charges and expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement with respect to any
action, suit or proceeding, whether civil, criminal, administrative or
investigative, including an action by or in the right of the Corporation, to the
full extent permitted by any applicable portion of this Certificate that shall
not have been invalidated and to the full extent permitted by applicable law. To
the full extent permitted by law, the Corporation may enter into and perform
agreements with persons, including, without limitation, present and former
officers, directors and employees of the Corporation and of companies acquired
by or merged with the Corporation, obligating the Corporation, among other
things, to provide indemnification and advancement of costs, charges and
expenses to such persons in addition to any indemnification or advancement which
may be available to such person under Sections 9.01 through 9.10 of this
Certificate.

SECTION 8.12.    INSURANCE.
-------------    ----------

The Board of Directors may cause the Corporation to purchase and maintain
insurance on behalf of any person who is or was or has agreed to become a
director or officer of the Corporation, or is or was serving at the request of
the Corporation as a director or officer of another corporation, or as its
representative in a partnership, joint venture, trust or other enterprise
(including employee benefit plans), against any liability asserted against such
person and incurred in any such capacity or arising out of such status, whether
or not the Corporation would have the power to indemnify such person.

SECTION 8.13.    ADOPTION OF BY-LAWS.
-------------    --------------------

The Board of Directors may from time to time adopt By-laws with respect to
indemnification and may amend such By-laws to provide at all times the fullest
indemnification permitted by the General Corporation Law of the State of
Delaware.

SECTION 9.01.    SETTLEMENT OF DEBTS.
-------------    --------------------

Whenever a compromise or arrangement is proposed between this Corporation and
its creditors or any class of them and/or between this Corporation and its
stockholders or any class of them, any court of equitable jurisdiction within
the State of Delaware
<PAGE>

                                                 CERTIFICATE OF INCORPORATION OF
                                                            ICF KAISER GCH, INC.
                                                                     Page 5 of 6

may, on the application in a summary way of this Corporation or of any creditor
or stockholder thereof or on the application of any receiver or receivers
appointed for this Corporation under the provisions of Section 291 of Title 8 of
the Delaware Code or on the application of trustees in dissolution or of any
receiver or receivers appointed for this Corporation under the provisions of
Section 279 of Title 8 of the Delaware Code, order a meeting of the creditors or
class of creditors, and/or of the stockholders or class of stockholders of this
Corporation, as the case may be, to be summoned in such manner as the said court
directs. If a majority in number representing three fourths in value of the
creditors or class of creditors, and/or of the stockholders or class of
stockholders of this Corporation, as the case may be, agree to any compromise or
arrangement and to any reorganization of this Corporation as a consequence of
such compromise or arrangement, the said compromise or arrangement and the said
reorganization shall, if sanctioned by the court to which the said application
has been made, be binding on all the creditors or class of creditors, and/or on
all the stockholders or class of stockholders, of this Corporation, as the case
may be, and also on this Corporation.

SECTION 10.01.   ELECTIONS OF DIRECTORS.
--------------   -----------------------

Elections of directors need not be by written ballot unless the By-laws of the
Corporation shall so provide.

SECTION 11.01.   STOCKHOLDERS MEETINGS, RECORDS.
--------------   -------------------------------

Stockholders meetings may be held within or without the State of Delaware, as
the By-laws may provide. The books of the Corporation may be kept (subject to
any provision in the General Corporation Law of the State of Delaware) outside
of the State of Delaware at such place or places as may be designated from time
to time by the Board of Directors (or duly authorized committee of the Board of
Directors) or in the By-laws of the Corporation.

SECTION 12.01.   BY-LAWS.
--------------   --------

The Board of Directors (or a duly authorized committee of the Board of
Directors) of the Corporation shall have the power to make and, except as may be
expressly stated in the By-laws, to alter and repeal its By-laws.

SECTION 13.01.  AMENDMENT OF CERTIFICATE OF INCORPORATION.
--------------  ------------------------------------------

The Corporation reserves the right to amend, alter, change or repeal any
provision contained in this certificate, in the manner now or hereafter
prescribed by the General Corporation Law of Delaware, and all rights conferred
upon stockholders herein are granted subject to this reservation.


IN WITNESS WHEREOF the undersigned, being the incorporator hereinbefore named,
for the purpose of forming a corporation pursuant to the General Corporation Law
of the State of Delaware, do make this certificate hereby declaring and
certifying that this is my act and deed and the facts herein stated are true,
and accordingly have hereto set my signature this 11th day of October 1994.


                                                  Paul Weeks, II
<PAGE>

                           CERTIFICATE OF AMENDMENT
                      OF CERTIFICATE OF INCORPORATION OF
                             ICF KAISER GCH, INC.

     ICF Kaiser GCH, Inc., a corporation organized and existing under the
General Corporation Law of Delaware (the "Corporation"), hereby does certify:

     FIRST: That the Corporation has not received any payments for its stock.

     SECOND: That the Sole Director of the Corporation, by the written consent
filed with minutes of the Board, adopted a resolution proposing and declaring
advisable the following amendment of the Certificate of Incorporation of the
Corporation:

     RESOLVED, that the Certificate of Incorporation of the Corporation be
     amended by deleting Section 1.01 in its entirety and inserting in its place
     the following new language:

     Section 1.01.  Name.  The name of the Corporation is ICF Kaiser Remediation
     ------------   ----
     Company.


     THIRD: That the aforesaid amendment was duly adopted in accordance with the
applicable provisions of Section 241 of the General Corporation Law of the State
of Delaware.


     IN WITNESS WHEREOF, ICF Kaiser GCH, Inc. has caused this Certificate to be
signed by Charles A. Debelius, its President and attested by Cynthia L.
Hathaway, its Assistant Secretary, this 1st day of March 1995.


                                        ICF Kaiser GCH, Inc.
                                        (Now: ICF KAISER REMEDIATION COMPANY)


                                        By:  /s/Charles A. Debelius
                                             President
Attest:

                                        By:  /s/Cynthia L. Hathaway
                                             Assistant Secretary