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                                                                    EXHIBIT 10.4

                             MEMORANDUM OF AGREEMENT

         THIS MEMORANDUM OF AGREEMENT ("MOA") is entered into this 15th day of
June, 2001 by and between EnviroClean International, Inc. (formerly known as
Advanced EnviroTech Systems, Inc.,) with offices at 12750 Merit Drive-Park
Central VII, Suite 770, Dallas, Texas 75251 (hereinafter "ENVI"), and
Intercontinental Manufacturing Company, a division of Datron, Inc., having an
address at 1200 N. Glenbrook Drive, Garland, Texas 75040 (hereinafter "IMCO").

         WHEREAS, ENVI owns certain intellectual property rights in and to a
solid waste treatment technology marketed under the trade name EnviroClean
Thermal Oxidation System ("TOS"); and

         WHEREAS, ENVI has entered into an arrangement with IMCO wherein ENVI
has granted IMCO the exclusive right to, among other things, market TOS to
certain foreign countries including, without limitation, the Kingdom of Saudi
Arabia; and

         WHEREAS, in consideration for granting such exclusive marketing rights,
ENVI is entitled to receive from IMCO a royalty fee for each TOS sold by IMCO;
and

         WHEREAS, in order to attempt to effect a sale of a quantity of TOS
units to the Kingdom of Saudi Arabia, IMCO deems it necessary to reduce the unit
sales price of TOS below those levels previously contemplated, which action will
also require a reduction to the royalty percentage rate applied to such
contemplated sales; and

         WHEREAS, ENVI is willing to accept a reduced royalty on such sales to
the Kingdom of Saudi Arabia in return for the potential marketing benefits that
could be expected to occur as a result of the market exposure such a sale to the
Kingdom of Saudi Arabia could create; and

         WHEREAS, ENVI owes IMCO for certain expenses incurred by IMCO on ENVI's
behalf and has previously agreed to reimburse IMCO for these amounts owed by, in
part, permitting IMCO to retain portions of any such royalties received from TOS
sales; and

         WHEREAS, ENVI and IMCO desire to amend the manner in which any such
royalty amounts are to be applied to reduce the amounts owed IMCO by ENVI.

         NOW THEREFORE, the parties hereto, in consideration of the foregoing
and of the mutual covenants, agreements and conditions herein contained, do
hereby agree as follows:

         1.    REVISED ROYALTY RATE. ENVI and IMCO hereby agree that, with
               respect to the sale of any TOS units made by IMCO to the
               Kingdom of Saudi Arabia (including, without limitation, any
               persons, firms or entities acting as contractors or agents of
               the Kingdom of Saudi Arabia) during the six (6) month period
               commencing as of the effective date of the MOA, royalties will
               accrue at the flat rate of $25,000 per TOS unit.

         2.    APPLICATION OF ROYALTY AMOUNTS. ENVI and IMCO hereby agree
               that, with respect to the sale of any TOS units made by IMCO
               to the Kingdom of Saudi Arabia (including, without limitation,
               any persons, firms or entities acting as contractors or agents
               of the Kingdom

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               of Saudi Arabia), any royalty amounts applicable to any such
               TOS sales will be applied cumulatively in the following manner;

                   o    First, to reduce that amount owed by ENVI to IMCO and
                        generally referred to as the "contingent accounts
                        payable", in the approximate amount of $400,000.

                   o    Second, applicable royalties up to an amount of $500,000
                        in excess of the "contingent accounts payable amount"
                        will be permanently waived by ENVI as a means to permit
                        IMCO to achieve a reduction in the selling price of
                        TOS units below those levels previously contemplated
                        by IMCO.

                   o    Third, any royalties received in excess of those
                        permanently waived or applied to the "contingent
                        accounts payable" amount (the "excess royalties"), shall
                        be paid to ENVI. In the event that the quantity of TOS
                        units ordered by the Kingdom of Saudi Arabia is
                        sufficient to result in any such "excess royalties",
                        IMCO will use its reasonable best efforts to collect and
                        remit such royalty amounts to ENVI on an accelerated
                        basis.

         3.    CONVERSION OF IMCO ACCOUNTS RECEIVABLE. At present, IMCO has
               on its books an accounts receivable due from ENVI in the
               approximate amount of $600,000. IMCO hereby agrees to accept
               and ENVI agrees to tender to IMCO common stock shares in a
               company named MedSolutions, Inc., a corporation formed or to
               be formed by ENVI, in full satisfaction of the amount of this
               accounts receivable. ENVI and IMCO agree that IMCO shall
               receive a number of shares in MedSolutions, Inc., equal to
               that number derived by dividing the total amount of the
               approximate $600,000 accounts receivable due IMCO by $1.25,
               the anticipated per share price of MedSolutions, Inc. at date
               of initial issuance.

         4.    COMPLETE AGREEMENT. This agreement sets forth the entire
               understanding of the parties with respect to this MOA and
               supersedes all prior agreements, covenants, arrangements,
               communications and representations with respect to this MOA
               and supersedes all prior agreements, covenants, arrangements,
               communications and representations with respect to the subject
               matter of this MOA.

         IN WITNESS WHEREOF, the parties hereto have caused this MOA to be
executed as of the day and year first written above.

INTERCONTINENTAL MANUFACTURING COMPANY       ENVIROCLEAN INTERNATIONAL, INC.

          By:   /s/ S.J. NUZZO               By:   /s/ MATTHEW H. FLEEGER
             -------------------------          -----------------------------
                   S. J. Nuzzo                        Matthew H. Fleeger<PAGE>

                                                                    EXHIBIT 4(a)

                             FIRST AMENDMENT TO THE
                        1997 EQUITY PARTICIPATION PLAN OF
                                DUANE READE INC.

            Duane Reade Inc. (the "Company"), a corporation organized under the
laws of the State of Delaware, by resolution of its Board of Directors (the
"Board") adopted the 1997 Equity Participation Plan of Duane Reade Inc. (the
"Plan"), effective as of June 18, 1997. Section 10.2 of the Plan allows the
Board to amend the Plan in certain respects at any time or from time to time.

            In order to amend the Plan in certain respects, this Amendment to
the Plan has been adopted by a resolution of the Board on December 15, 1998,
effective as set forth herein. This amendment to the Plan, together with the
Plan, constitutes the entire Plan as amended to date.

            1. AMENDMENT TO SECTION 1.14(I). Section 1.14(i) of the Plan is
amended, effective as of December 15, 1998, to read in its entirety as follows:

            "(i) the average closing price of a share of Common Stock on the
principal exchange on which shares of Common Stock are then trading, if any (or
as reported on any composite index which includes such principal exchange), over
the five trading days immediately preceding the date of determination, or"

            2. AMENDMENT TO SECTION 2.1(A). Section 2.1(a) of the Plan is
amended, effective as of December 15, 1998, to provide that the aggregate number
of shares of Common Stock which may be issued upon the exercise of stock options
or other awards under the Plan pursuant to Section 2.1(a) shall be increased
from 1,321,181 shares to 1,971,181 shares; PROVIDED, HOWEVER, that the foregoing
increase in the number of shares that may be issued upon exercise of stock
options or other awards under the Equity Plan shall not be effective without the
approval of a majority of the Company's stockholders given on or before December
15, 1999; PROVIDED, FURTHER, that if the Company's stockholders do not approve
the foregoing increase prior to December 15, 1999, any stock options or other
awards granted with respect to a number of shares in excess of 1,321,181 shall
be void ab initio.

            3. AMENDMENT TO SECTION 2.1(B). Section 2.1(b) of the Plan is
amended, effective as of December 15, 1998, to read in its entirety as follows:

            "(b) The maximum number of shares which may be subject to Options,
awards of Restricted Stock, Performance Awards, Dividend Equivalents, awards of
Deferred Stock, Stock Payments or Stock Appreciation Rights granted under the
Plan to any individual in any calendar year shall not exceed the Award Limit. To
the extent required by Section 162(m) of the Code, shares subject to Options
which are canceled shall continue to be counted against the Award Limit."

Dated: March 30, 1999               DUANE READE INC.

                                    By:    /s/ William J. Tennant
                                        --------------------------------
                                       William J. Tennant
                                       Senior Vice President, Chief
                                       Financial Officer and Secretary<PAGE>

                                                                   EXHIBIT 4(b)

                             SECOND AMENDMENT TO THE
                        1997 EQUITY PARTICIPATION PLAN OF
                                DUANE READE INC.

            Duane Reade Inc. (the "Company"), a corporation organized under the
laws of the State of Delaware, by resolution of its Board of Directors (the
"Board") adopted the 1997 Equity Participation Plan of Duane Reade Inc. (the
"Plan"), effective as of June 18, 1997. Section 10.2 of the Plan allows the
Board to amend the Plan in certain respects at any time or from time to time.

            In order to amend the Plan in certain respects, this Amendment to
the Plan has been adopted by a resolution of the Board on February 13, 2001,
effective as set forth herein. This amendment to the Plan, together with the
Plan, constitutes the entire Plan as amended to date.

            1. AMENDMENT TO SECTION 1.3. Section 2.1(a) of the Plan is amended,
effective as of the date of approval of a majority of the Company's
stockholders, to read in its entirety as follows:

            "(a) The shares of stock subject to Options, awards of Restricted
Stock, Performance Awards, Dividend Equivalents, awards of Deferred Stock, Stock
Payments or Stock Appreciation Rights shall be the Company's Common Stock, par
value $.01 per share. The aggregate number of such shares which may be issued
upon exercise of such Options, rights or awards under the Plan shall not exceed
2,971,181. The shares of Common Stock issuable upon exercise of such Options,
rights or awards may be either previously authorized but unissued shares or
treasury shares."

PROVIDED, HOWEVER, that the foregoing amendment shall not be effective without
the approval of a majority of the Company's stockholders given on or before
February 13, 2002; PROVIDED, FURTHER, that if the Company's stockholders do not
approve the foregoing amendment prior to February 13, 2002, any stock options or
other awards granted with respect to a number of shares in excess of 1,971,181
shall be void ab initio.

Dated: February 13, 2001               DUANE READE INC.

                                       By:     /s/ John K. Henry
                                            ----------------------------
                                            John K. Henry
                                            Senior Vice President, Chief
                                            Financial Officer and Secretary

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