Document:

Exhibit 10.16

              ARCH SUPPLEMENTARY AND DEFERRAL BENEFIT PENSION PLAN
                           Effective February 8, 1999
               As Amended by a First Amendment Dated July 29, 1999

                               ARTICLE I. THE PLAN

      1.1   ESTABLISHMENT OF PLAN. Arch Chemicals, Inc. (the "Company" or
"Arch") hereby establishes a Supplementary and Deferral Benefit Pension Plan for
the benefit of certain salaried employees of Arch and other Employing Companies
who may be eligible to participate in the Plan. The Plan is known as the "Arch
Supplementary and Deferral Benefit Pension Plan" and is effective February 8,
1999 or, if later, the effective date of the spin-off of Arch from Olin
Corporation (the "Effective Date"). For purposes of this Plan, an "Employing
Company" means any company which has adopted this Plan and is included within
the definition of an Employing Company under the terms of the Arch Chemicals
Employees' Pension Plan and any other qualified defined benefit plans maintained
by Arch (collectively, the "Qualified Plans").

      1.2   PURPOSE OF PLAN. The purpose of this Plan is to provide benefits to
certain current and former salaried employees of Arch and other Employing
Companies whose benefits under the Qualified Plans ("Qualified Plan Benefits")
are limited (i) by Section 415 of the Internal Revenue Code of 1986, as amended
(the "Code"), (ii) by the limitations on compensation that can be taken into
account in calculating qualified plan benefits under Section 401(a)(17) of the
Code, and (iii) by the inability to include in compensation for Qualified Plan
Benefits any salary and awards of management incentive compensation that have
been deferred by Eligible Employees into non-qualified plans or arrangements.
These limitations are collectively referred to herein as "Benefit Limitations".
This Plan is intended to provide such employees and their Beneficiaries with
benefits ("Supplemental Pension Benefits") equal to the difference between what
their Qualified Plan Benefits would be absent the Benefit Limitations, and what
their Qualified Plan Benefits would be with the imposition of the Benefit
Limitations.

      1.3   NATURE OF PLAN. This Plan is divisible into two components: that
portion which qualify for the exemption from the Employee Retirement Income
Security Act ("ERISA") as an "excess benefit plan", and that portion which
provides for benefits in excess of applicable compensation limits, and is
intended to be a supplemental executive retirement plan for management and
highly compensated employees.

                             ARTICLE II. ELIGIBILITY

      2.1   Any salaried Arch Employee who is eligible to receive a Qualified
Plan Benefit from the Company or an Employing Company, the amount of which is
reduced by reason of the application of a Benefit Limitation (as previously
defined) shall be a Participant in this Plan and be eligible to receive a
Supplemental Pension Benefit as provided in this Plan. For purposes of
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this Plan, an "Arch Employee" includes (i) any employee who is defined as an
Arch Employee within the meaning of the Employee Benefits Allocation Agreement
dated as of February 8, 1999 by and between Arch and Olin Corporation ("Olin"),
as well as (ii) any salaried employee hired by Arch after the Effective Date of
this Plan. For purposes of this Plan, the term "Distribution Date" shall mean
February 8, 1999.

      2.2   ASSUMPTION OF PRIOR OLIN PLAN LIABILITIES FOR ARCH EMPLOYEES;
TRANSFERS OF RESERVES. In conjunction with establishing this Plan, Arch hereby
assumes the liabilities of Olin for the provision of benefits to participants
who, immediately prior to the Distribution Date (as previously defined) were
participants in either or both of the Olin Supplementary Pension Plan or the
Olin Deferral Benefit Pension Plan as in effect on the Distribution Date
(collectively, the "Olin Supplementary and Deferral Benefit Plan") and who, as
of the Effective Date, transfer to, and become employed by Arch or its
affiliated companies. In consideration of such assumption of liability, Olin has
transferred, as of the Effective Date, to Arch (or to a rabbi trust established
by Arch) the reserves (including any assets held in a rabbi trust or similar
vehicle) reflecting the value of the accrued liabilities being transferred,
determined in accordance with Olin's established policies and accounting
methods, uniformly applied for calculating liabilities under its non-qualified
plans.

                      ARTICLE III. CALCULATION OF BENEFITS.

      3.1   AMOUNT OF BENEFIT. The Supplemental Pension Benefit payable to a
Participant retiring on or after his Normal Retirement Date shall be calculated
in the form of a single life annuity, commencing at the Participant's Normal
Retirement Date (as defined in the Qualified Plans) or, if later, his actual
retirement date and shall be a monthly amount equal to the difference between
(a) and (b) below:

      (a)   the monthly amount of the Qualified Plan Benefit to which the
      Participant would have been entitled had such benefit been calculated (i)
      including non-qualified deferred payments of regular salary and deferred
      awards under any applicable management incentive plan, and (ii) without
      regard to the Benefit Limitations imposed by Sections 415 and 401(a)(17)
      of the Code; and

      (b)   the monthly amount of the Qualified Plan Benefit actually payable to
      the Participant.

The amounts described in (a) shall be calculated as of the date that the
Participant terminates service with the Company and all other Employing
Companies, in the form of a single life annuity payable over the lifetime of the
Participant commencing at his Normal Retirement Date (or, if later, his actual
retirement date).

For purposes of determining the amount and entitlement to the benefits described
in (a) and (b) above, a Participant shall be credited with the service,
compensation, and accrued benefit that the Participant was credited with under
the Olin Supplementary and Deferral Benefit Plan, and Olin qualified defined
benefit pension plan(s) as of the Distribution Date, provided however that such
crediting shall not occur under this Plan until such employee has released Olin
and its affiliates,

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and the Olin Supplementary and Deferral Benefit Plan, from any liability, or
claim for benefits, with respect to the Employee's participation in said plans.

      3.2   TRANSFERS BETWEEN ARCH AND OLIN. It is contemplated that Plan
Participants may transfer their employment after the Distribution Date and on or
before February 8, 2000 from Arch to Olin and VICE VERSA and commence, or
resume, participation in the Supplementary and Deferral Benefit Pension Plan(s)
of the new employer.

      (a)   TRANSFER TO OLIN FROM ARCH. In the event that a Plan Participant
      transfers employment to Olin after the Distribution Date and on or before
      February 8, 2000, benefit accrual under this Plan shall cease and Arch
      shall remain liable for payment of any benefits accrued under this Plan to
      the date of transfer. No reserves shall be transferred with respect to any
      such Participant. No separation from service shall be deemed to occur
      under this Plan permitting a distribution under this Plan and benefits
      hereunder shall not commence until the Participant has terminated his
      employment with Olin (and its affiliates) and has otherwise qualified for
      benefits hereunder. When commenced, benefits payable hereunder shall be
      based upon the Participant's service with Arch (and, if applicable, any
      past service with, and compensation from, Olin and its affiliates
      recognized as of the Distribution Date), provided, however that Arch shall
      continue to recognize a Participant's service with Olin and its affiliates
      subsequent to his transfer to Olin solely for purposes of determining the
      Participant's vesting and attainment of retirement dates under this Plan.

      (b)   TRANSFER FROM OLIN TO ARCH. In the event that an Olin employee
      transfers employment to Arch from Olin after the Distribution Date and on
      or before February 8, 2000, benefit accrual under the Olin Supplementary
      and Deferral Benefit Plan shall cease and Olin shall remain liable for
      payment of any benefits accrued under those Plans to the employee's date
      of transfer to Arch. No reserves shall be transferred from Olin or the
      Olin Supplementary and Deferral Benefit Plan with respect to such Olin
      employee. Benefits shall not commence under the Olin Supplementary and
      Deferral Benefit Plan until the former Olin employee terminates service
      with Arch and its affiliates and has otherwise qualified for benefits
      under the Olin Supplementary and Deferral Benefit Plan. Following such
      transfer, Olin shall continue to credit such employee's service with Arch
      and its affiliates subsequent to his transfer to Arch solely for purposes
      of determining his vesting and attainment of retirement dates under the
      Olin Supplementary and Deferral Benefit Plan. In computing the benefits,
      and determining attainment of retirement ages under this Plan, Arch shall
      recognize the compensation received, and service rendered by such
      Participant while employed by Olin and its affiliates up to the
      Participant's date of transfer to Arch. When benefits commence under this
      Plan, they shall be offset by the benefit that would be payable to the
      Participant from the Olin Supplementary and Deferral Benefit Plan, as of
      the date benefits commence hereunder, regardless of when, or whether, such
      benefit under the Olin Supplementary and Deferral Benefit Plan actually
      commences.

                         ARTICLE IV. PAYMENT OF BENEFITS

      4.1.  BENEFITS COMMENCING ON OR AFTER REACHING EARLY RETIREMENT DATE.

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      (a)   A Participant may retire from active service with Arch and all
Employing Companies and commence benefits under this Plan at any time after
reaching his fifty-fifth (55th) birthday (his "Early Retirement Date"),
provided, however, that no election as to the commencement date of benefits
under this Plan, including any election under Section 4.4, shall be given effect
if not made at least twelve (12) full months prior to the Participant's actual
retirement. In the case of a Participant who transfers directly to Olin on or
prior to February 8, 2000, "actual retirement" shall be construed to mean
retirement or termination of service from Olin and its affiliates. Service with
Olin and its affiliates shall be credited in enabling the Participant to attain
his early retirement age under this Plan. A Participant may commence benefits
under this Plan regardless of the date on which he actually commences benefits
under the Arch Chemicals Employees' Pension Plan or other Qualified Plan.

      (b)   For purposes of determining whether a Participant has reached his
fifty-fifth (55th) birthday and, thus, is eligible to commence benefits under
this Section 4.1(a) instead of on a deferred vested basis, any Participant who
has completed at least seven (7) Years of Creditable Service (as defined in the
Arch Chemicals Employees' Pension Plan) and who is at least age fifty-two (52),
but less than age fifty-five (55) on the date his service is terminated (without
taking into account any severance period) other than (i) for cause or (ii) as a
result of a voluntary termination, shall be treated as continuing as an eligible
Employee until the date on which the Participant reaches age fifty-five (55). A
Participant in this Plan shall be credited with his prior service with Olin and
its affiliates, as well as his service with Arch, in enabling the Participant to
attain his early retirement age under this Plan. In the case of Participants who
transfer directly to Olin on or before February 8, 2000, service with Olin and
its affiliates shall be credited in determining whether the Participant has
reached age 55 under this paragraph (b). Such service shall be imputed for the
sole purposes of determining whether the Participant qualifies for subsidized
early retirement benefits, and shall not be treated as "Benefit Service" for the
purpose of calculating the amount of the benefit under this Plan. A Participant
may not commence benefits hereunder until he actually reaches age fifty-five
(55).

      (c)   With respect to a Participant retiring from active service on or
after reaching his Early Retirement Date, the Plan Administrator will calculate
the Participant's retirement benefit then payable from all Arch non-qualified
and Qualified Plans using, in the case of the Qualified Plan Benefit, the
Benefit Limitations then in effect, and using the early retirement reductions
specified in the Qualified Plan based upon the benefit commencement date elected
by the Participant for commencement of his qualified and non-qualified plan
benefits. In the case of a Participant who elects to defer commencement of his
Qualified Plan benefits, the Arch non-qualified pension plans, including this
Plan, shall provide for the payment of the Participant's estimated Qualified
Plan benefit until such time as the Participant actually commences his qualified
plan benefit, at which time the amount of the Participant's non-qualified plan
benefit, including the benefits payable from this Plan, shall be reduced dollar
for dollar, but not below $0, by the amount of the Qualified Plan benefit
ultimately payable to the Participant, based upon the Benefit Limitations in
effect when the Participant actually commences receipt of such Qualified Plan
benefit.

      4.2   DEFERRED VESTED EMPLOYEES. Any Participant who terminates active
service with Arch and all Employing Companies prior to having reached age
fifty-five (55), may commence

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benefits under this Plan at any time after having reached age fifty-five (55);
provided, however, that his benefit hereunder shall subject to the actuarial
reductions that would be applicable under the Arch Chemicals Employees' Pension
Plan and further provided that, in the case of Participants who transfer
directly to Olin on or prior to February 8, 2000, service with Olin and its
affiliates shall be counted in enabling such Participants to retire on or after
age fifty-five (55) and actually retiring from Olin and its affiliates, in
accordance with Section 4.1 above. In the event that an Arch Employee is
re-employed by Olin on or prior to February 8, 2000, and again participates in
the Olin Supplementary and Deferral Benefit Plan, no separation from service
shall be deemed to occur permitting a distribution of benefits under this, or
any other, provision of this Plan.

      4.3   PAYMENT OF REGULAR MONTHLY BENEFITS ALONG WITH QUALIFIED PLAN
BENEFITS.

      (a)   In the event that the Participant (i) does not elect to establish an
employee-grantor trust in accordance with Section 4.4(a), (ii) does not elect to
receive Accelerated Benefits in accordance with Section 4.4(a), and (iii) elects
to commence his benefits under this Plan at the same time that he commences his
Qualified Plan Benefit, then the Supplemental Pension Benefit payable hereunder
shall be paid commencing at the same time and in the same form as that in which
the Qualified Plan Benefit is payable to the Participant. If the Participant
elects an actuarially equivalent form of benefit payment with respect to his
Qualified Plan Benefit, that same form of payment shall apply to payment of his
Supplemental Pension Benefit. Any election to receive regular monthly benefits
under this Section 4.3 must be made at least one full year prior to the
Participant's Accelerated Benefit Commencement Date.

      (b)   An election by the Participant with respect to the timing and form
of this Supplemental Pension Benefit shall be effective only if consented to by
the Plan Administrator. If not so approved, then the timing and form of the
Supplemental Pension Benefit shall be selected by the Plan Administrator in its
sole discretion.

      (c)   A Supplemental Pension Benefit that is payable in any form other
than a single life annuity, or which commences at any time prior to the
Participant's Normal Retirement Date shall be calculated using the same
conversion factors and actuarial adjustments as those specified in the Qualified
Plan as of the date that such benefit is being determined.

      4.4   CHOICE OF EMPLOYEE-GRANTOR TRUST OR PAYMENT OF ACCELERATED BENEFITS.

      (a)   As of October 31 of the calendar year following the year in which a
Participant meets the Minimum Benefit Accumulation threshold provided for in
Section 4.5, the Actuarial Present Value (determined as hereinafter provided) of
the after-tax amount of a Participant's Supplemental Pension Benefit shall be
deposited in an employee-grantor trust established by the Participant unless, at
least one full year prior to the funding of such employee-grantor trust, the
Participant shall instead have elected to receive "Accelerated Benefits" as
hereinafter provided.

      (i)   If a Participant elects to receive Accelerated Benefits, then the
      Actuarial Present Value of such Benefits shall be paid, at the election of
      the Compensation Committee (or its designee), either in a single sum or in
      up to three (3) annual installments (such single

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      sum or annual installments being referred to in this Plan as "Accelerated
      Benefits").

      (ii)  The Participant's Accelerated Benefits shall commence on his
      Accelerated Benefit Commencement Date, which shall be twelve full months
      following a Participant's actual retirement date at age fifty-five (55) or
      later (the "Participant's "Accelerated Benefit Commencement Date"). For
      purposes of determining whether a Participant has reached his fifty-fifth
      (55th) birthday and, thus, is eligible to commence benefits under Section
      4.1(a) instead of on a deferred vested basis under Section 4.2, Section
      4.1(b) shall apply. In the case of a Participant who transfers directly to
      Olin (or its affiliates) on or before February 8, 2000, "actual
      retirement" shall be construed to mean retirement or termination of
      service from Olin and its affiliates. Service with Olin and its affiliates
      shall be credited in enabling the Participant to attain his early
      retirement age (but not in determining his Years of Benefit Service) under
      this Plan.

      (b)   In the event that an actively employed Participant elects not to
establish an employee-grantor trust, but instead to receive Accelerated
Benefits, regular monthly benefits shall commence to be paid upon such
Participant's actual retirement in accordance with Section 4.1 until such
Participant reaches his Accelerated Benefit Commencement Date, at which time
Accelerated Benefits shall be paid in the form and manner determined by the
Compensation Committee (or its designee), either in a single sum, in up to three
(3) annual installments, or in a combination of annuity payments and either a
single sum or annual installments, provided, however that, with respect to
Participants who transfer to Olin on or before February 8, 2000, no benefits
shall be paid under this Plan until they terminate service with Olin and its
affiliates.

      (c)   In lieu of funding an employee-grantor trust or receiving
Accelerated Benefits, the Participant may elect, at least one full year prior to
such Accelerated Benefit Commencement Date, to receive benefit payments in an
annuity for life in accordance with Section 4.1 of this Plan.

      4.5   ASSUMPTIONS USED FOR DETERMINING AMOUNT TO BE CONTRIBUTED TO
      EMPLOYEE-GRANTOR TRUST; THRESHOLD FOR ACCELERATED BENEFITS.

      (a)   ACTUARIAL ASSUMPTIONS FOR EMPLOYEE-GRANTOR TRUST. In determining the
Actuarial Present Value of the Participant's Plan benefit to be used for
purposes of funding an employee-grantor trust, the benefit shall be determined

            (i)   as of the close of the Plan Year (i.e., December 31) prior to
            the year in which the employee grantor trust is being funded;

            (ii)  using the Code Section 415 limits and 401(a)(17) limits then
            currently in effect as of the date on which the actuarial present
            value is being determined or, alternatively, in the discretion of
            the Plan Administrator, using projected limits, determined based
            upon reasonable assumptions concerning cost-of-living indices;

            (iii) using an annuity purchase rate based upon a discount rate
            equal to the rate for a zero coupon Treasury strip (determined
            approximately at the time of the deposit

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            to the employee-grantor trust) with a maturity that approximates the
            Participant's life expectancy determined as of the date the payment
            to the trust is scheduled to be made; and

            (iv)  assuming that the benefit commences under this Plan

                  (a)   on the Participant's 65th birthday, if the Participant
                  terminates service (or is treated as terminating service)
                  prior to age 55;

                  (b)   on the Participant's 62nd birthday, if the Participant
                  terminates service on or after reaching age 55 and before
                  reaching age 62; and

                  (c)   on the Participant's 65th birthday, if the Participant
                  terminates service on or after reaching age 62.

      (b)   ACTUARIAL ASSUMPTIONS FOR DETERMINING ACCELERATED BENEFITS. In
      determining the Actuarial Present Value of the Participant's Accelerated
      Benefit, the benefit shall be determined

            (i)   as of the close of the Participant's retirement or termination
            of service; and

            (ii)  using an annuity purchase rate based upon a discount rate
            equal to the rate for a zero coupon Treasury strip (determined
            approximately at the time that Accelerated Benefits are scheduled to
            commence) with a maturity that approximates the Participant's life
            expectancy determined as of the date the payment is scheduled to be
            made.

      (c)   MINIMUM BENEFIT ACCUMULATION THRESHOLD. No Accelerated Benefits
      shall commence to be paid, and no Participant shall be given the
      opportunity to fund an employee-grantor trust, until the Participant has
      accumulated benefits under this Plan, and the Arch Senior Executive
      Pension Plan which, in the aggregate, have an actuarial present value of
      at least One Hundred Thousand Dollars ($100,000.00).

      4.6   DEATH BENEFITS.

      (a)   The Beneficiary of a Participant who dies AFTER commencing regular
      monthly benefits under Section 4.1 of this Plan shall receive a death
      benefit under this Plan only if the form selected by, or in force with
      respect to, the Participant under the Qualified Plan provides for a death
      benefit. For purposes of this Plan, a Participant's Beneficiary shall be
      the Beneficiary designated to receive death benefits under the Qualified
      Plan.

      (b)   The Beneficiary of a Participant who dies after having elected to
      receive Accelerated Benefits, but who as of the date of his death has not
      received the entire value of his Accelerated Benefits, shall receive the
      remainder of any Accelerated Benefits not yet paid in the form of payment
      in effect with respect to the Participant.

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         (c) If a Participant dies prior to commencement of his Qualified Plan
Benefits under circumstances in which a pre-retirement survivor annuity is
payable under the Qualified Plan, then a supplemental surviving Spouse benefit
shall be payable under this Plan in a monthly amount that shall be equal to the
difference between

            (i)   the monthly amount of the Qualified pre-retirement survivor
            benefit to which the surviving Spouse would have been entitled under
            the Qualified Plan had such benefit been calculated (i) including
            non-qualified deferred payments of regular salary and deferred
            awards under the management incentive plan, and (ii) without regard
            to the Benefit Limitations imposed by Sections 415 and 401(a)(17) of
            the Code; and

            (ii)  the monthly amount of the Qualified pre-retirement survivor
            benefit that is actually payable to the surviving Spouse.

      (d)   For purposes of this Plan, the term "Spouse" shall mean the person
to whom a Participant is validly married at the date of his death, as evidenced
by a marriage certificate issued in accordance with state law; provided however,
that (i) if a Participant's Spouse at his or her death was not the Participant's
Spouse at least 12 months prior to the Participant's death, no Surviving
Spouse's retirement allowance shall be paid, and (ii) common law marriages shall
not be recognized hereunder.

      4.7   BENEFIT UPON A CHANGE OF CONTROL.

      (a)   LUMP SUM PAYMENT UPON A CHANGE OF CONTROL.

      The spin-off of Arch from Olin shall not be deemed to be a change of
control entitling any Participant herein to benefits under this Plan or the Olin
Supplementary and Deferral Benefit Plan. Notwithstanding any other provision of
the Plan, upon a Change in Control as defined in 4.7(c), each Participant
covered by the Plan shall automatically be paid a lump sum amount in cash by the
Company sufficient to purchase an annuity which, together with the monthly
payment, if any, under a Rabbi or other trust arrangement established by the
Company to make payments hereunder in the event of a Change in Control and/or
pursuant to any other annuity purchased by the Company for the Participant to
make payments hereunder, shall provide the Participant with the same monthly
after-tax benefit as he would have received under the Plan based on the benefits
accrued to the Participant hereunder as of the date of the Change in Control.
Payment under this Section shall not in and of itself terminate the Plan, but
such payment shall be taken into account in calculating benefits under the Plan
which may otherwise become due the Participant thereafter.

      (b)   NO DIVESTMENT UPON A CHANGE OF CONTROL. If a Participant is removed
from participation in the Plan after a Change of Control has occurred, in no
event shall his years of Benefit Service accrued prior to such removal, and the
benefit accrued prior thereto, be adversely affected.

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      (c)   CHANGE OF CONTROL DEFINED.

      For purposes of the Plan, a "Change in Control" of the Company shall have
      occurred in the event that

            (i)   the Company ceases to be, directly or indirectly, owned of
            record by at least 1,000 stockholders;

            (ii)  a person, partnership, joint venture, corporation or other
            entity, or two or more of any of the foregoing acting as "person"
            within the meaning of Section 13(d)(3) of the Securities Exchange
            Act of 1934, as amended (the "Act"), other than the Company, a
            majority-owned subsidiary of the Company or an employee benefit plan
            of the Company or such subsidiary (or such plan's related trust),
            become(s) the "beneficial owner" (as defined in Rule 13d-3 of the
            Act) of 20% or more of the then outstanding voting stock of the
            Company; or

            (iii) during any period of two consecutive years, individuals who at
            the beginning of such period constitute the Company's Board of
            Directors (together with any new Director whose election by the
            Company's Board or whose nomination for election by the Company's
            stockholders, was approved by a vote of at least two-thirds of the
            Directors of the Company then still in office who either were
            Directors at the beginning of such period or whose election or
            nomination for election was previously so approved) cease for any
            reason to constitute a majority of the Directors then in office; or

            (iv)  all or substantially all of the business of the Company is
            disposed of pursuant to a merger, consolidation or other transaction
            in which the Company is not the surviving corporation or the Company
            combines with another company and is the surviving corporation
            (unless the shareholders of the Company immediately following such
            merger, consolidation, combination, or other transaction
            beneficially own, directly or indirectly, more than 50% of the
            aggregate voting stock or other ownership interests of (x) the
            entities, if any, that succeed to the business of the Company or (y)
            the combined company);.or

            (v)   the shareholders of the Company approve a sale of all or
            substantially all of the assets of the Company or a liquidation or
            dissolution of the Company.

      (d)   ARBITRATION. Any dispute or controversy arising under or in
connection with the Plan subsequent to a Change in Control shall be settled
exclusively by arbitration in Connecticut, in accordance with the rules of the
American Arbitration Association then in effect. Judgment may be entered on the
arbitrator's award in any court having jurisdiction.

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                               ARTICLE V. FUNDING

      5.1   UNFUNDED PLAN. This Plan shall be unfunded. All payments under this
Plan shall be made from the general assets of the Employing Company of the
Participant. No provision shall at any time be made with respect to segregating
any assets of Arch or another Employing Company for payment of benefits
hereunder. No Participant, surviving Spouse or any other Beneficiary shall have
any interest in any particular assets of an Employing Company by reason of the
right to receive a benefit under this Plan and shall have the rights only of a
general unsecured creditor of Employing Company with respect to any rights under
the Plan.

      5.2   LIABILITY FOR PAYMENT. Each Employing Company shall pay the benefits
provided under this Plan with respect to Participants who are employed, or were
formerly employed by it during their participation in the Plan. In the case of a
Participant who was employed by more than one Employing Company, the Committee
shall allocate the cost of such benefits among such Employing Companies in such
manner as it deems equitable. The obligations of the Employing Company shall not
be funded in any manner.

      5.3   ANTI-ALIENATION. No Participant or Beneficiary shall have the right
to assign, transfer, encumber or otherwise subject to any lien any payment or
any other interest under this Plan, nor shall such payment or interest be
subject to attachment, execution or levy of any kind.

                         ARTICLE VI. PLAN ADMINISTRATION

      6.1   PLAN ADMINISTRATOR. The Company hereby appoints the Pension
Administration and Review Committee as the Plan Administrator (the "Plan
Administrator" or "Committee"). Any person, including, but not limited to, the
directors, shareholders, officers and employees of the Company, shall be
eligible to serve on the Committee. Any person so appointed shall signify his
acceptance by undertaking the duties assigned. Any member of the Committee may
resign by delivering written resignation to the Company. The Company may also
remove any member of the Committee by delivery of a written notice of removal,
which shall take effect upon delivery or on a date specified. Upon resignation
or removal of a Committee member, the Company shall promptly designate in
writing such other person or persons as a successor.

      6.2   ALLOCATION AND DELEGATION. The Committee members may allocate the
responsibilities among themselves, and shall notify the Company in writing of
such action and the responsibilities allocated to each member.

      6.3   POWERS, DUTIES AND RESPONSIBILITIES. Except for those powers
expressly reserved to the Selection Committee, the Plan Administrator shall have
all power to administer the Plan for the exclusive benefit of the Participants
and their Beneficiaries, in accordance with the terms of the Plan. The Plan
Administrator shall have the absolute discretion and power to determine all
questions arising in connection with the administration, interpretation and
application of the Plan. Any such determination by the Plan Administrator shall
be conclusive and binding upon all persons. The Plan Administrator may correct
any defect or reconcile any inconsistency in such manner and to such extent as
shall be deemed necessary or advisable to carry out the

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purposes of the Plan; provided, however, that such interpretation or
construction shall be done in a non-discriminatory manner and shall be
consistent with the intent of the Plan.

      The Plan Administrator shall:

            (a)   compute the amount and kind of benefits to which any
      Participant shall be entitled hereunder;

            (b)   maintain all necessary records for the administration of the
      Plan;

            (c)   interpret the provisions of the Plan and make and publish such
      rules for regulation of the Plan as are consistent with the terms hereof;

            (d)   assist any Participant regarding his rights, benefits or
      elections available under the Plan; and

            (e)   communicate to Participants and their Beneficiaries concerning
      the provisions of the Plan.

      6.4   RECORDS AND REPORTS. The Plan Administrator shall keep a record of
all actions taken and shall keep such other books of account, records and other
information that may be necessary for proper administration of the Plan. The
Plan Administrator shall file and distribute all reports that may be required by
the Internal Revenue Service, Department of Labor or others, as required by law.

      6.5   APPOINTMENT OF ADVISORS. The Plan Administrator may appoint
accountants, actuaries, counsel, advisors and other persons that it deems
necessary or desirable in connection with the administration of the Plan.

      6.6   MAJORITY ACTIONS. The Committee shall act by a majority of their
numbers, but may authorize one or more of them to sign all papers on their
behalf.

      6.7   INDEMNIFICATION OF MEMBERS. The Company shall indemnify and hold
harmless any member of the Committee and of the Compensation Committee from any
liability incurred in his or her capacity as such for acts which he or she
undertakes in good faith as a member of such Committee.

      6.8   CONSTRUCTION OF PLAN TERMS. Except as otherwise expressly provided
in this Plan, all terms and conditions of the Qualified Plan shall be applicable
to a Supplemental and Deferral Pension Benefit payable hereunder.

                     ARTICLE VII. TERMINATION AND AMENDMENT

      7.1   AMENDMENT OR TERMINATION. The Company may amend or terminate the
Plan at any time, in whole or in part, by action of its Board of Directors, the
Compensation Committee

                                       11
<PAGE>

of the Board, or any other duly authorized committee or officer. Any Employing
Company may withdraw from participation in the Plan at any time. No amendment or
termination of the Plan or withdrawal therefrom by an Employing Company shall
adversely affect the vested benefits payable hereunder to any Participant for
service rendered prior to the effective date of such amendment, termination or
withdrawal.

                           ARTICLE VIII. MISCELLANEOUS

      8.1   GENDER AND NUMBER. Whenever any words are used herein in the
masculine, feminine or neuter gender, they shall be construed as though they
were also used in another gender in all cases where such would apply, and
whenever any words are used herein in the singular or plural form, they shall be
construed as though they were also used in another form in all cases where they
would so apply.

      8.2   ACTION BY THE COMPANY. Whenever the Company under the terms of this
Plan is permitted or required to do or perform any act or thing, it shall be
done and performed by an officer or committee duly authorized by the Board of
Directors of the Company.

      8.3   HEADINGS. The headings and subheadings of this Plan have been
inserted for convenience of reference only and shall not be used in the
construction of any of the provisions hereof.

      8.4   UNIFORMITY AND NON DISCRIMINATION. All provisions of this Plan shall
be interpreted and applied in a uniform nondiscriminatory manner.

      8.5   GOVERNING LAW. To the extent that state law has not been preempted
by the provisions of ERISA or any other laws of the United States heretofore or
hereafter enacted, this Plan shall be construed under the laws of the State of
Connecticut.

      8.6   EMPLOYMENT RIGHTS. Nothing in this Plan shall confer any right upon
any Employee to be retained in the service of the Company or any of its
affiliates.

      8.7   INCOMPETENCY. In the event that the Plan Administrator determines
that a Participant is unable to care for his affairs because of illness or
accident or any other reason, any amounts payable under this Plan may, unless
claim shall have been made therefor by a duly appointed guardian, conservator,
committee or other legal representative, be paid by the Plan Administrator to
the spouse, child, parent or other blood relative or to any other person deemed
by the Plan Administrator to have incurred expenses for such Participant, and
such payment so made shall be a complete discharge of the liabilities of the
Plan therefor.

      IN WITNESS WHEREOF, Arch Chemicals, Inc. has caused this Plan to be
executed by its duly authorized officer as of February 8, 1999.

                                       12
<PAGE>

Dated:                                 ARCH CHEMICALS, INC.

                                       By: /s/ Mark A. Killian
                                           -------------------------------------
                                           Its Vice President of Human ResourcesARCH SENIOR EXECUTIVE PENSION PLAN
                        Effective as of February 8, 1999
               As Amended by a First Amendment Dated July 29, 1999

                               ARTICLE I. THE PLAN

      1.1   ESTABLISHMENT OF PLAN. Arch Chemicals, Inc. (the "Company" or
"Arch") hereby establishes a non-qualified deferred compensation plan known as
the Arch Senior Executive Pension Plan for the benefit of certain salaried
employees of Arch and other Employing Companies who may be eligible to
participate. The Plan is effective February 8, 1999 or, if later, the effective
date of the spin-off of Arch from Olin Corporation (the "Effective Date"). For
purposes of this Plan, an "Employing Company" means any company which has
adopted this Plan and is included within the definition of an Employing Company
under the terms of the Arch Chemicals Employees' Pension Plan and any other
qualified defined benefit plans maintained by Arch (collectively, the "Qualified
Plans").

      1.2   PURPOSE. The purpose of this Plan is to attract and retain a
management group capable of assuring Arch's future success by providing them
with supplemental retirement income under this Plan. This Plan is intended to be
an unfunded, nonqualified deferred compensation plan for select management
employees.

                             ARTICLE II. ELIGIBILITY

      2.1   PARTICIPATION. Any Arch Employee whose job is rated at 2,000 Hay
Points (or the equivalent) or more, and who is selected by the Board of
Directors of the Company or the Compensation Committee of the Board (referred to
in this Plan as the "Selection Committee" or "Compensation Committee"), shall
participate in the Plan (a "Participant"). As provided hereinafter, the
Selection Committee shall also have the power to remove any Participant from the
Plan, whether or not he or she has begun to receive benefits hereunder.

For purposes of this Plan, an "Arch Employee" includes (i) any employee who is
defined as an Arch Employee within the meaning of the Employee Benefits
Allocation Agreement dated as of February 8, 1999 by and between Arch and Olin
Corporation ("Olin"), as well as (ii) any salaried employee hired by Arch after
the Effective Date of this Plan.

The term "Distribution Date" shall mean February 8, 1999.

                                      -1-
<PAGE>

      2.2   ASSUMPTION OF PRIOR OLIN PLAN LIABILITIES FOR ARCH EMPLOYEES;
TRANSFERS OF RESERVES. In conjunction with establishing this Plan, Arch hereby
assumes the liabilities of Olin for the provision of benefits to participants
who, immediately prior to the Distribution Date (as previously defined) were
participants in the Olin Senior Executive Pension Plan as in effect on the
Distribution Date (the "Olin Senior Plan") and who, as of the Effective Date
transfer to, and become employed by, Arch or its affiliated companies. In
consideration of such assumption of liability, Olin has transferred, as of the
Effective Date, to Arch (or to a rabbi trust established by Arch) the reserves
(including any assets held in a rabbi trust or similar vehicle) reflecting the
value of the accrued liabilities being transferred, determined in accordance
with Olin's established policies and accounting methods, uniformly applied for
calculating liabilities under its non-qualified plans.

                              ARTICLE III. BENEFITS

      3.1   BENEFIT FORMULA. As of the Distribution Date, each Eligible Employee
who, immediately prior to the Distribution Date, was a participant in the Olin
Senior Plan, shall be credited in this Plan with an accrued benefit equal to
that credited to such individual under the Olin Senior Plan as of the
Distribution Date (based upon the Eligible Employee's Average Compensation and
service with Olin), provided however that such crediting shall not occur under
this Plan until such employee has released Olin and its affiliates, and the Olin
Senior Plan, from any liability, or claim for benefits, with respect to the
Employee's participation in said plan.

Upon retirement, as hereinafter provided, a Participant shall be entitled to
receive an annual "Retirement Allowance" equal to THE LESSER OF (a) and (b)
below:

      (a)   three percent (3%) of the Participant's Average Compensation,
      multiplied by the sum of his Years of Benefit Service credited while the
      employee was a Participant in this Plan and, prior to this Plan, the Olin
      Senior Plan, plus one and one-half percent (1 1/2%) of the Participant's
      Average Compensation multiplied by his aggregate Years of Benefit Service
      credited under all qualified defined benefit plans of Arch which includes
      Years of Benefit Service credited under the Olin Employees Pension Plan
      while the employee was not a Participant in either this Plan or the prior
      Olin Senior Plan, provided that the resulting percentage of Average
      Compensation shall be reduced by one-third of one percent (1/3%) for each
      month by which the Participant's benefits under this Plan begin prior to
      his sixty-second (62nd) birthday;

      reduced by the sum of

            (i)   the Participant's annual retirement allowance payable from all
            Arch Qualified Plans and any other nonqualified defined benefit
            pension plans of the Company and all Employing Companies, including,
            without limitation, the Arch Chemicals Employees' Pension Plan), and
            the

                                      -2-
<PAGE>

            equivalent actuarial value of any other arrangement with the Company
            or an Employing Company which the Plan Administrator, in its sole
            discretion, determines to be a pension supplement (collectively
            referred to hereinafter as the "Other Arch Plans"); plus

            (ii)  fifty percent (50%) of the Participant's Primary Social
            Security Benefit.

      (b)   fifty percent (50%) of the Participant's Average Compensation,
      reduced by the sum of

            (i)   the amount of annual retirement benefits from the Arch
            Chemicals Employees' Pension Plan and all Other Arch Plans (as
            previously defined) and all qualified and non-qualified deferred
            compensation plans of the Participant's previous and subsequent
            employers; and

            (ii)  fifty percent (50%) of the Participant's Primary Social
            Security Benefit.

      (c)   For purposes of determining a Participant's "Average Compensation",
      "Years of Benefit Service", "Retirement Allowance" and "Primary Social
      Security Benefit" under this Plan, such terms shall have the same meaning
      as that contained in the Arch Chemicals Employees' Pension Plan and shall
      include credit for the compensation received, and service rendered by such
      Participant while employed by Arch and its affiliates, as well as by Olin
      and its affiliates up through the Distribution Date (or through February
      8, 2000 in the case of Participants transferring from Olin pursuant to
      Section 3.5). In calculating a Participant's Average Compensation under
      this Plan, (i) "Average Compensation" under this Plan shall also include
      deferred amounts of regular salary and deferrals under management
      incentive plans (other than the Performance Unit Plan, the EVA Bonus Bank
      or similar bonus bank arrangements, and other long-term incentive and
      long-term bonus plans of Olin and Arch); (ii) executive severance which is
      payable to certain Participants under employment agreements shall be
      treated as if paid over the number of months of salary used to calculate
      the amount of such severance, even if such severance is received in a lump
      sum; (iii) Average Compensation shall be calculated without regard to the
      dollar limitations imposed by Section 401(a)(17) of the Internal Revenue
      Code; and (iv) "Years of Benefit Service" shall include service imputed as
      a result of treating any executive severance paid as having been received
      over the number of months used to calculate such severance.

      (d)   The annual retirement allowances payable under the Arch Chemicals
      Employees' Pension Plan, Other Arch Plans and from pension plans of the
      Participant's previous employers, which are to be used to reduce the
      benefit payable under (a) or (b) above, shall be determined assuming (i)
      that the Participant selected a 50% joint and survivor annuity under such
      plans, (ii) began

                                      -3-
<PAGE>

      receiving benefits thereunder at their actual commencement date (rather
      than the commencement date for benefits under this Plan), and (iii) using
      the actuarial equivalent factors specified in the plans which are the
      subject of the offset or, if such factors are not reasonably available,
      such factors as may, from time to time, be elected by the Plan
      Administrator.

3.2   EARLY RETIREMENT.

      (a)   Except as otherwise provided in Section 4.2(a), a Participant may
      retire from active service with Arch and all Employing Companies and
      commence benefits under this Plan at any time after reaching his
      fifty-fifth (55th) birthday, provided, however, that Accelerated Benefits
      (as provided in Section 4.2(b) of the Plan) may not commence until at
      least twelve (12) full months following the Participant's actual
      retirement. In the case of a Participant who transfers directly to Olin on
      or before February 8, 2000, (i) "actual retirement" shall be construed to
      mean retirement or termination of service from Olin and its affiliates,
      and (ii) service with Olin (and its affiliates) shall be credited in
      enabling the Participant to attain his early retirement age (but not in
      determining Years of Benefit Service) under this Plan.

      (b)   For purposes of (i) determining whether a Participant has reached
      his fifty-fifth (55th) birthday and, thus, is eligible to commence
      benefits under this Section 3.2 instead of on a deferred vested basis, and
      (ii) calculating the annual retirement allowance from the Arch Chemicals
      Employees' Pension Plan which is to be used as an offset, any Participant
      who has completed at least seven (7) Years of Creditable Service (as
      defined in the Arch Chemicals Employees' Pension Plan) and who is at least
      age fifty-two (52), but less than age fifty-five (55) on the date his
      service is terminated (without taking into account any severance period)
      other than (i) for cause or (ii) as a result of a voluntary termination,
      shall be treated as continuing as an eligible Employee until the date on
      which the Participant reaches age fifty-five (55). A Participant in this
      Plan shall be credited with his prior service with Olin and its
      affiliates, as well as Arch and its affiliates, in enabling the
      Participant to attain his early retirement age under this Plan. In the
      case of a Participant who transfers directly to Olin on or before February
      8, 2000, service with Olin shall be credited in determining whether the
      Participant has reached age 55 under this paragraph (b). Such service
      shall be imputed for the sole purposes of determining whether the
      Participant qualifies for subsidized early retirement benefits, and shall
      not be treated as "Benefit Service" for the purpose of calculating the
      amount of the Participant's Retirement Allowance. A Participant may not
      commence benefits hereunder until he actually reaches age fifty-five (55).

      3.3   DEFERRED VESTED EMPLOYEES. Any Participant who terminates active
service with Arch and all Employing Companies prior to having reached age
fifty-five (55) may commence benefits under this Plan only after having reached
age sixty-five (65); provided however that, in the case of a Participant who
transfers directly to Olin on

                                      -4-
<PAGE>

or prior to February 8, 2000, service with Olin and its affiliates shall be
counted in enabling such Participant to retire on or after attaining age
fifty-five (55) (and actually retiring from Olin), in accordance with Section
3.2 above. In the case of a deferred vested Participant, benefits paid from this
Plan will assume that the Participant did not commence benefits under the Arch
Chemicals Employees' Pension Plan until he or she reached age sixty-five (65),
even though the Participant may actually commence benefits under the Arch
Chemicals Employees' Pension Plan prior to that date. In the event that an Arch
Employee is re-employed by Olin prior to February 8, 2000, and again
participates in the Olin Senior Plan, no separation from service shall be deemed
to occur permitting a distribution of benefits under this, or any other,
provision of this Plan.

      3.4   CALCULATION OF BENEFIT IF PARTICIPANT IS DISABLED. In the event that
a Participant becomes Totally Disabled as that term is defined in the Arch
Chemicals Employees' Pension Plan, the Participant shall continue to receive the
same service credit under this Plan as would be applicable to Totally Disabled
nonbargaining employees covered by the Arch Chemicals Employees' Pension Plan.
The disabled Participant's benefit under this Plan shall be calculated in
accordance with 3.1(a) and (b), and shall be payable as of the date that the
Participant is no longer Totally Disabled (if such date occurs after age
fifty-five (55)) or at age sixty-five (65), if the Employee is still then
Disabled. If a Participant is no longer Disabled prior to reaching age
fifty-five (55), then his entitlement to benefits shall be determined under
Section 3.3, if he terminates service prior to reaching age 55, or under the
other applicable provisions of this Plan, if he returns to active service. No
Participant shall qualify for Disability Benefits hereunder once he or she is no
longer actively employed by Arch, Inc. or its affiliates.

      3.5   TRANSFERS BETWEEN ARCH AND OLIN. It is contemplated that Plan
Participants may transfer their employment after the Distribution Date and on or
before February 8, 2000 from Arch to Olin and VICE VERSA and commence, or
resume, participation in the Senior Executive Pension Plan of the new employer.

      (a)   TRANSFER TO OLIN FROM ARCH. In the event that a Plan Participant
      transfers employment to Olin after the Distribution Date and on or prior
      to February 8, 2000, benefit accrual under this Plan shall cease and Arch
      shall remain liable for payment of any benefits accrued under this Plan to
      the date of transfer. No reserves shall be transferred with respect to any
      such Participant. As provided in Section 3.3, no separation from service
      shall be deemed to occur under this Plan permitting a distribution under
      this Plan and benefits hereunder shall not commence until the Participant
      has terminated his employment with Olin and has otherwise qualified for
      benefits hereunder. When commenced, benefits payable hereunder shall be
      based upon the Participant's service with Arch (and, if applicable, any
      past service with, and compensation from, Olin and its affiliates
      recognized as of the Distribution Date), provided, however that Arch shall
      continue to recognize a Participant's service with Olin and its affiliates
      subsequent to his transfer to Olin solely for purposes of determining the
      Participant's vesting and attainment of retirement dates under this Plan.

                                      -5-
<PAGE>

      (b)   TRANSFER FROM OLIN TO ARCH. In the event that an Olin employee
      transfers employment to Arch from Olin after the Distribution Date and on
      or prior to February 8, 2000, benefit accrual under the Olin Senior Plan
      shall cease and Olin shall remain liable for payment of any benefits
      accrued under the Olin Senior Plan to the employee's date of transfer to
      Arch. No reserves shall be transferred from Olin or the Olin Senior Plan
      with respect to such Olin Employee. Benefits shall not commence under the
      Olin Senior Plan until the former Olin employee terminates service with
      Arch and its affiliates and has otherwise qualified for benefits under the
      Olin Senior Plan. Following such transfer, Olin shall continue to credit
      such employee's service with Arch and its affiliates subsequent to his
      transfer to Arch solely for purposes of determining his vesting and
      attainment of retirement dates under the Olin Senior Plan. In computing
      the benefits, and determining attainment of retirement ages under this
      Plan, Arch shall recognize the compensation received, and service rendered
      by such Participant while employed by Olin and its affiliates up to the
      Participant's date of transfer to Arch. When benefits commence under this
      Plan, they shall be offset by the benefit that would be payable to the
      Participant from the Olin Senior Plan, as of the date benefits commence
      hereunder, regardless of when, or whether, such benefit under the Olin
      Senior Plan actually commences.

                         ARTICLE IV. PAYMENT OF BENEFITS

      4.1   PAYMENT OF BENEFITS; IN GENERAL.

      In the event that the Participant (i) does not elect to establish an
employee-grantor trust in accordance with Section 4.2(a), (ii) does not elect to
receive Accelerated Benefits in accordance with Section 4.2(a), and (iii) elects
to commence his benefits under this Plan at the same time that he commences his
Qualified Plan Benefit, then the Retirement Allowance payable hereunder shall be
paid commencing at the same time and in the same form as that in which the
Qualified Plan Benefit is payable to the Participant. If the Participant elects
an actuarially equivalent form of benefit payment with respect to his Qualified
Plan Benefits, that same form of payment shall apply to payment of his
Retirement Allowance hereunder. Any election to receive regular monthly benefits
under this Section 4.3 must be made at least one full year prior to the
Participant's Accelerated Benefit Commencement Date.

4.2   PAYMENT PROVISIONS FOR ACTIVE EMPLOYEES.

      (a)   As of October 31 of the calendar year following the year in which an
      actively employed Participant meets the Minimum Benefit Accumulation
      threshold provided for in Section 4.4(c), the Actuarial Present Value
      (determined as hereinafter provided) of the after-tax amount of an
      actively employed Participant's Retirement Allowance shall be deposited in
      an employee-grantor trust established by the Participant unless, at least
      one full year prior to the funding of such employee-grantor trust, the
      Participant shall instead have elected to receive "Accelerated Benefits"
      as hereinafter provided. If a Participant elects to receive

                                      -6-
<PAGE>

      Accelerated Benefits, then the Actuarial Present Value of such Benefits
      shall be paid, at the election of the Chairman of the Board of Directors
      of the Company, either in a single sum or in up to three (3) annual
      installments (such single sum or annual installments being referred to in
      this Plan as "Accelerated Benefits"). The Participant's Accelerated
      Benefits shall commence on his Accelerated Benefit Commencement Date,
      which shall be twelve full months following his actual retirement date at
      age fifty-five (55) or later (the "Participant's Accelerated Benefit
      Commencement Date"). In the case of a Participant who transfers directly
      to Olin on or before February 8, 2000, "actual retirement" shall be
      construed to mean retirement or termination of service from the transferee
      employer. Service with Olin (and its affiliates) shall be credited in
      enabling the Participant to attain his early retirement age (but not in
      determining his Years of Benefit Service) under this Plan.

      (b)   In the event that an actively employed Participant elects not to
      establish an employee-grantor trust, but instead to receive Accelerated
      Benefits, regular monthly benefits shall commence to be paid upon such
      Participant's actual retirement in accordance with Section 4.3 until such
      Participant reaches his Accelerated Benefit Commencement Date, at which
      time Accelerated Benefits shall be paid in the form and manner determined
      by the Compensation Committee (or its designee), either in a single sum,
      in up to three (3) annual installments, or in a combination of annuity
      payments and either a single sum or annual installments

      (c)   Alternatively, the actively employed Participant may elect, at least
      one full year prior to such Accelerated Benefit Commencement Date, to
      receive his entire benefit in the form of an annuity in accordance with
      Section 4.3 of this Plan.

4.3   PAYMENT OF REGULAR MONTHLY BENEFITS.

      (a)   Participants retiring from active service from Arch and all
      Employing Companies may elect to receive regular monthly benefits in lieu
      of receiving Accelerated Benefits or establishing an employee-grantor
      trust. Such monthly benefits shall be calculated and payable (without
      reduction for the death benefit protection) in the form of a joint and 50%
      survivor annuity with the Participant's Spouse as the joint annuitant.

      (b)   Any Participant who terminates service with Arch and all Employing
      Companies before reaching age 55 may not commence benefits under this Plan
      prior to reaching age 65 unless he is eligible for "lay-off credit"
      pursuant to Section 3.2(b) and, thus, is deemed to qualify for early
      retirement benefits. Any benefits payable under this Plan with respect to
      a Participant who terminates service prior to reaching age 55, and who is
      not eligible for any imputed service under the lay-off provisions of
      Section 3.2(b), will be calculated assuming that the Participant did not
      commence benefits under the Arch Chemicals Employees'

                                      -7-
<PAGE>

      Pension Plan until reaching age 65, even though his actual commencement
      date under the Arch Chemicals Employees' Pension Plan may have been
      earlier.

4.4   ASSUMPTIONS USED FOR DETERMINING AMOUNT TO BE CONTRIBUTED TO
EMPLOYEE-GRANTOR TRUST; THRESHOLD FOR ACCELERATED BENEFITS.

      (a)   ACTUARIAL ASSUMPTIONS FOR EMPLOYEE-GRANTOR TRUST. In determining the
      Actuarial Present Value of the Participant's Plan benefit to be used for
      purposes funding an employee-grantor trust, the benefit shall be
      determined:

            (i)   as of the close of the Plan Year (i.e., December 31) prior to
            the year in which the employee grantor trust is being funded;

            (ii)  using an annuity purchase rate based upon a discount rate
            equal to the rate for a zero coupon Treasury strip (determined
            approximately at the time of the deposit to the employee-grantor
            trust) with a maturity that approximates the Participant's life
            expectancy determined as of the date the payment to the trust is
            scheduled to be made; and

            (iii) assuming that the benefit commences under this Plan

                  (a)   on the Participant's 65th birthday, if the Participant
                  terminates service (or is treated as terminating service)
                  prior to age 55;

                  (b)   on the Participant's 62nd birthday, if the Participant
                  terminates service on or after reaching age 55 and before
                  reaching age 62; and

                  (c)   on the Participant's 65th birthday, if the Participant
                  terminates service on or after reaching age 62.

      (b)   ACTUARIAL ASSUMPTIONS FOR DETERMINING ACCELERATED BENEFITS. In
      determining the Actuarial Present Value of the Participant's Accelerated
      Benefit, the benefit shall be determined:

            (i)   as of the close of the Participant's retirement or termination
            of service;

            (ii)  using an annuity purchase rate based upon a discount rate
            equal to the rate for a zero coupon Treasury strip (determined
            approximately at the time the Accelerated Benefit is scheduled to
            commence) with a maturity that approximates the Participant's life
            expectancy determined as of the date the payment is scheduled to be
            made; and

            (iii) assuming that the benefit commences under this Plan

                  (a)   on the Participant's 65th birthday, if the Participant
                  terminates service (or is treated as terminating service)
                  prior to age 55;

                                      -8-
<PAGE>

                  (b)   on the Participant's 62nd birthday, if the Participant
                  terminates service on or after reaching age 55 and before
                  reaching age 62; and

                  (c)   on the Participant's 65th birthday, if the Participant
                  terminates service on or after reaching age 62.

      (c)   MINIMUM BENEFIT ACCUMULATION THRESHOLD. No Accelerated Benefits
      shall commence to be paid, and no Participant shall be given the
      opportunity to fund an employee-grantor trust, until the Participant has
      accumulated benefits under this Plan, the Arch Supplementary and Deferral
      Benefit Pension Plan which, in the aggregate, have an actuarial present
      value of at least One Hundred Thousand Dollars ($100,000.00).

4.5   SURVIVING SPOUSE BENEFIT.

      (a)   The Surviving Spouse of a Participant who dies AFTER commencing
      regular monthly benefits shall receive a survivor benefit for his or her
      lifetime equal to 50% of the monthly payments that were being paid to the
      Participant under the Plan as of his death.

      (b)   The Surviving Spouse of a Participant who dies after having elected
      to receive Accelerated Benefits, but who as of the date of his death has
      not received the entire value of his Accelerated Benefits, shall receive
      the remainder of any Accelerated Benefits not yet paid in the form of
      payment in effect with respect to the Participant.

      (c)   The Surviving Spouse of any Participant who dies PRIOR to benefit
      commencement shall be entitled to receive a benefit equal to 50% of the
      benefit that the Participant would have been entitled to had he survived
      to the earliest date on which he could commence benefits hereunder,
      retired and commenced monthly regular benefits under the Plan, and then
      died the next day.

      (d)   Notwithstanding (a) -(c) above, if the Surviving Spouse is more than
      four years younger than the Participant, the Surviving Spouse's benefit
      under this Plan shall be reduced so that the present value of the spouse's
      lifetime benefit, as determined by the Company, is the same as it would
      have been if he or she were only four years younger than the Participant.

      (e)   For purposes of this Plan, the term "Spouse" shall mean the person
      to whom a Participant is validly married at the date of his death, as
      evidenced by a marriage certificate issued in accordance with state law;
      provided however, that (i) if a Participant's Spouse at his or her death
      was not the Participant's Spouse at least 12 months prior to the
      Participant's death, no Surviving Spouse's retirement allowance shall be
      paid, and (ii) common law marriages shall not be recognized hereunder.

                                      -9-
<PAGE>

4.6   BENEFIT UPON A CHANGE OF CONTROL.

      (a)   LUMP SUM PAYMENT UPON A CHANGE OF CONTROL.

      The spin-off of Arch from Olin shall not be deemed to be a change of
      control entitling any Participant herein to benefits under this Plan or
      the prior Olin Senior Plan. Notwithstanding any other provision of the
      Plan, upon a Change in Control, each Participant covered by the Plan shall
      automatically be paid a lump sum amount in cash by the Company sufficient
      to purchase an annuity which, together with the monthly payment, if any,
      under a Rabbi or other trust arrangement established by the Company to
      make payments hereunder in the event of a Change in Control and/or
      pursuant to any other annuity purchased by the Company for the Participant
      to make payments hereunder, shall provide the Participant with the same
      monthly after-tax benefit as he would have received under the Plan based
      on the benefits accrued to the Participant hereunder as of the date of the
      Change in Control. Payment under this Section shall not in and of itself
      terminate the Plan, but such payment shall be taken into account in
      calculating benefits under the Plan which may otherwise become due the
      Participant thereafter.

      (b)   NO DIVESTMENT UPON A CHANGE OF CONTROL. If a Participant is removed
      from participation in the Plan after a Change of Control has occurred, in
      no event shall his years of Benefit Service accrued prior to such removal,
      and the benefit accrued prior thereto, be adversely affected.

      (c)   CHANGE OF CONTROL DEFINED.

      For purposes of the Plan, a "Change in Control" of the Company shall have
      occurred in the event that

            (i)   the Company ceases to be, directly or indirectly, owned of
            record by at least 1,000 stockholders;

            (ii)  a person, partnership, joint venture, corporation or other
            entity, or two or more of any of the foregoing acting as "person"
            within the meaning of Section 13(d)(3) of the Securities Exchange
            Act of 1934, as amended (the "Act"), other than the Company, a
            majority-owned subsidiary of the Company or an employee benefit plan
            of the Company or such subsidiary (or such plan's related trust),
            become(s) the "beneficial owner" (as defined in Rule 13d-3 of the
            Act) of 20% or more of the then outstanding voting stock of the
            Company; or

            (iii) during any period of two consecutive years, individuals who at
            the beginning of such period constitute the Company's Board of
            Directors (together with any new Director whose election by the
            Company's Board or whose nomination for election by the Company's
            stockholders, was approved by a vote of at least two-thirds of the
            Directors of the Company then still in office who either were
            Directors at the beginning of such period or whose election or
            nomination for

                                      -10-
<PAGE>

            election was previously so approved) cease for any reason to
            constitute a majority of the Directors then in office; or

            (iv)  all or substantially all of the business of the Company is
            disposed of pursuant to a merger, consolidation or other transaction
            in which the Company is not the surviving corporation or the Company
            combines with another company and is the surviving corporation
            (unless the shareholders of the Company immediately following such
            merger, consolidation, combination, or other transaction
            beneficially own, directly or indirectly, more than 50% of the
            aggregate voting stock or other ownership interests of (x) the
            entities, if any, that succeed to the business of the Company or (y)
            the combined company); or

            (v)   the shareholders of the Company approve a sale of all or
            substantially all of the assets of the Company or a liquidation or
            dissolution of the Company.

      (d)   ARBITRATION. Any dispute or controversy arising under or in
      connection with the Plan subsequent to a Change in Control shall be
      settled exclusively by arbitration in Connecticut, in accordance with the
      rules of the American Arbitration Association then in effect. Judgment may
      be entered on the arbitrator's award in any court having jurisdiction.

            4.7   REMOVAL FROM THE PLAN; NON-PAYMENT OF BENEFITS.

      (a)   Any Participant may be removed from the Plan by the Compensation
      Committee at any time "for cause", as determined by the Compensation
      Committee in its sole discretion, whether or not the Participant has begun
      to receive payments under the Plan, and whether or not the Participant's
      employment has been terminated. "Cause" shall include, without limitation,
      rendering services in any capacity to a competitor of the Company or
      Employing Company without the consent of the Compensation Committee.
      Neither the Participant nor his or her Spouse shall be entitled to receive
      any payments from the Plan from and after the date of the removal of the
      Participant nor have any cause of action as a result of such removal. The
      Participant or Spouse shall not be required to return any payments made
      prior to removal of the Participant from the Plan.

      (b)   The Compensation Committee may notify a Participant that he or she
      is being suspended from the Plan as a result of job performance which the
      Compensation Committee in its sole discretion deems unsatisfactory. From
      and after the date of such notification and notwithstanding the
      Participant's actual Hay Points, he or she will not be deemed to have
      2,000 or more Hay Points for purposes of calculating the Participant's
      Retirement Allowance. Any prior Years of Benefit Service shall not be
      affected by such suspension.

                                      -11-
<PAGE>

                               ARTICLE V. FUNDING

      5.1   UNFUNDED PLAN. This Plan shall be unfunded. All payments under this
Plan shall be made from the general assets of Arch and other Employing
Companies.

      5.2   LIABILITY FOR PAYMENT. Arch and each other Employing Company shall
pay the benefits provided under this Plan with respect to Participants who are
employed, or were formerly employed by it during their participation in the
Plan. In the case of a Participant who was employed by more than one Employing
Company, the Committee shall allocate the cost of such benefits among such
Employing Companies in such manner as it deems equitable. The obligations of the
Employing Company shall not be funded in any manner. The rights of any person to
receive benefits under this Plan are limited to those of a general creditor of
the Employing Company liable for payment hereunder.

      5.3   ANTI-ALIENATION. No Participant or beneficiary shall have the right
to assign, transfer, encumber or otherwise subject to any lien any payment or
any other interest under this Plan, nor shall such payment or interest be
subject to attachment, execution or levy of any kind.

                         ARTICLE VI. PLAN ADMINISTRATION

      6.1   PLAN ADMINISTRATOR. The Company hereby appoints the Pension
Administration and Review Committee as the Plan Administrator (the "Plan
Administrator" or "Committee"). Any person, including, but not limited to, the
directors, shareholders, officers and employees of the Company, shall be
eligible to serve on the Committee. Any person so appointed shall signify his
acceptance by undertaking the duties assigned. Any member of the Committee may
resign by delivering written resignation to the Company. The Company may also
remove any member of the Committee by delivery of a written notice of removal,
which shall take effect upon delivery or on a date specified. Upon resignation
or removal of a Committee member, the Company shall promptly designate in
writing such other person or persons as a successor.

      6.2   ALLOCATION AND DELEGATION. The Committee members may allocate the
responsibilities among themselves, and shall notify the Company in writing of
such action and the responsibilities allocated to each member.

      6.3   POWERS, DUTIES AND RESPONSIBILITIES. The Plan Administrator shall
have all power to administer the Plan for the exclusive benefit of the
Participants and their Beneficiaries, in accordance with the terms of the Plan.
The Plan Administrator shall have the absolute discretion and power to determine
all questions arising in connection with the administration, interpretation and
application of the Plan. Any such determination by the Plan Administrator shall
be conclusive and binding upon all persons. The Plan Administrator may correct
any defect or reconcile any inconsistency

                                      -12-
<PAGE>

in such manner and to such extent as shall be deemed necessary or advisable to
carry out the purposes of the Plan; provided, however, that such interpretation
or construction shall be done in a non-discriminatory manner and shall be
consistent with the intent of the Plan.

The Plan Administrator shall:

      (a)   compute the amount and kind of benefits to which any Participant
shall be entitled hereunder;

      (b)   maintain all necessary records for the administration of the Plan;

      (c)   interpret the provisions of the Plan and make and publish such rules
for regulation of the Plan as are consistent with the terms hereof;

      (d)   assist any Participant regarding his rights, benefits or elections
available under the Plan; and

      (e)   communicate to Participants and their Beneficiaries concerning the
provisions of the Plan.

      6.4   RECORDS AND REPORTS. The Plan Administrator shall keep a record of
all actions taken and shall keep such other books of account, records and other
information that may be necessary for proper administration of the Plan. The
Plan Administrator shall file and distribute all reports that may be required by
the Internal Revenue Service, Department of Labor or others, as required by law.

      6.5   APPOINTMENT OF ADVISORS. The Plan Administrator may appoint
accountants, actuaries, counsel, advisors and other persons that it deems
necessary or desirable in connection with the administration of the Plan.

      6.6   MAJORITY ACTIONS. The Committee shall act by a majority of their
numbers, but may authorize one or more of them to sign all papers on their
behalf.

      6.7   INDEMNIFICATION OF MEMBERS. The Company shall indemnify and hold
harmless any member of the Committee and of the Compensation Committee from any
liability incurred in his or her capacity as such for acts which he or she
undertakes in good faith as a member of such Committee.

                     ARTICLE VII. TERMINATION AND AMENDMENT

      7.1   AMENDMENT OR TERMINATION. The Company may amend or terminate the
Plan at any time, in whole or in part, by action of its Board of Directors, the
Compensation Committee of the Board or any other duly authorized committee or
officer. Any Employing Company may withdraw from participation in the Plan at
any time. No amendment or termination of the Plan or withdrawal therefrom by an

                                      -13-
<PAGE>

Employing Company shall adversely affect the vested benefits payable hereunder
to any Participant for service rendered prior to the effective date of such
amendment, termination or withdrawal.

                           ARTICLE VIII. MISCELLANEOUS

      8.1   GENDER AND NUMBER. Whenever any words are used herein in the
masculine, feminine or neuter gender, they shall be construed as though they
were also used in another gender in all cases where such would apply, and
whenever any words are used herein in the singular or plural form, they shall be
construed as though they were also used in another form in all cases where they
would so apply.

      8.2   ACTION BY THE COMPANY. Whenever the Company under the terms of this
Plan is permitted or required to do or perform any act or thing, it shall be
done and performed by an officer or committee duly authorized by the Board of
Directors of the Company.

      8.3   HEADINGS. The headings and subheadings of this Plan have been
inserted for convenience of reference only and shall not be used in the
construction of any of the provisions hereof.

      8.4   UNIFORMITY AND NON DISCRIMINATION. All provisions of this Plan shall
be interpreted and applied in a uniform nondiscriminatory manner.

      8.5   GOVERNING LAW. To the extent that state law has not been preempted
by the provisions of ERISA or any other laws of the United States heretofore or
hereafter enacted, this Plan shall be construed under the laws of the State of
Connecticut.

      8.6   EMPLOYMENT RIGHTS. Nothing in this Plan shall confer any right upon
any Employee to be retained in the service of the Company or any of its
affiliates.

      8.7   INCOMPETENCY. In the event that the Plan Administrator determines
that a Participant is unable to care for his affairs because of illness or
accident or any other reason, any amounts payable under this Plan may, unless
claim shall have been made therefor by a duly appointed guardian, conservator,
committee or other legal representative, be paid by the Plan Administrator to
the spouse, child, parent or other blood relative or to any other person deemed
by the Plan Administrator to have incurred expenses for such Participant, and
such payment so made shall be a complete discharge of the liabilities of the
Plan therefor.

                                      -14-
<PAGE>

      IN WITNESS WHEREOF, Arch Chemicals, Inc. has caused this Plan to be
executed by its duly authorized officer as of February 8, 1999.

                                    ARCH CHEMICALS, INC.

                                    By: /s/ MARK A. KILLIAN
                                        -------------------------------------
                                        Its Vice President of Human Resources

                                      -15-

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