EMPLOYMENT AGREEMENT

          THIS  AGREEMENT  by  and  between   Safety-Kleen   Corp.,  a  Delaware
corporation (the "Company"), and Grover C. Wrenn (the "Executive"),  dated as of
the    day of August, 2000.
   ---

                               W I T N E S S E T H

          WHEREAS,  the  Company  wishes to provide  for the  employment  by the
Company of the Executive,  and the Executive wishes to serve the Company, in the
capacities and on the terms and conditions set forth in this Agreement;

          NOW, THEREFORE, it is hereby agreed as follows:

          1. TERM.  The term of this Agreement (the "Term") shall commence as of
March  6,  2000  (the  "Commencement  Date")  and  shall  end  upon  the  second
anniversary of the Commencement Date.

          2. POSITION AND DUTIES. (a) During the Term, the Executive shall serve
as the President and Chief Operating Officer of the Company with such duties and
responsibilities as are customarily  assigned to such positions,  and such other
duties and responsibilities not inconsistent  therewith as may from time to time
be assigned to him by the Chief  Executive  Officer of the Company or the Board.
During the Term,  the Company  shall cause the  Executive  to be included in the
slate of persons  nominated to serve as directors on the Board and shall use its
best efforts to have the Executive  elected and  reelected to the Board.  If the
Executive  is not  elected  or  reelected  as a member of the Board it shall not
constitute Good Reason under Paragraph 4(c) hereunder.

          (1) During the Term,  and  excluding  any periods of vacation and sick
leave to which  the  Executive  is  entitled,  and  except  as may be  otherwise
authorized by the Board,  the Executive  shall devote  substantially  all of his
attention  and time during  business  hours to the  business  and affairs of the
Company and shall carry out such  responsibilities  faithfully and  efficiently.
The Executive may serve on corporate,  industry,  civic or charitable boards and
committees,  so long as the Executive  secures the prior written  consent of the
Board to engage in such activities,


 <PAGE>

which consent will not be unreasonably  withheld,  and Exhibit A attached hereto
contains a list of such current activities which are all hereby approved.

          (2) Other than for periods  spent  traveling  in  connection  with the
performance of the Executive's duties hereunder, the Executive shall be based in
Columbia,  South  Carolina.  During the Term,  the  Company  shall  provide  the
Executive  with an  executive  apartment  in the  Columbia  area (which shall be
reasonably acceptable to Executive) and shall pay the customary temporary living
expenses  (including all  transportation  costs) associated with the Executive's
stay in the Columbia  area.  The aggregate  cost to the Company shall not exceed
$3,500 per month for living  expenses  plus  $25,000  per year for  taxation  on
transportation.   The  Executive  shall  provide  the  Company  with  acceptable
documentation substantiating such living expenses and tax costs.

          3. COMPENSATION. (a) BASE SALARY. During the Term, the Executive shall
receive an annual base salary  ("Annual  Base  Salary") of $650,000.  The Annual
Base Salary shall be payable in accordance  with the Company's  regular  payroll
practice for its senior executives, as in effect from time to time.

          (1) PLAN OF REORGANIZATION/SALE BONUS. If the Executive is employed by
the Company on the date a plan of reorganization  for the Company is consummated
in connection  with any Chapter 11  bankruptcy  or similar  proceeding or on the
date of the consummation of the sale of  substantially  all of the assets of the
Company (the "Sale")  then,  within  fifteen (15) days of such  consummation  or
sale, the Company shall pay to the Executive a bonus of $1,250,000 (the "Plan of
Reorganization/Sale  Bonus"),  in  recognition  of the  Executive's  efforts  in
facilitating such reorganization or sale.

          (2)  DISCRETIONARY  BONUS.  The Executive shall be eligible to receive
such  bonuses  as may be  determined  from  time  to  time  by the  Compensation
Committee of the Board,  which shall consist  solely of  independent  directors,
pursuant to criteria to be established by such Compensation  Committee,  payable
from any bonus pool established under Company's employee incentive  compensation
program.  The Agent for the  Pre-Petition  Secured  Lenders  and  counsel to the
Official  Committee of Unsecured  Creditors  shall be apprised of any such bonus
award  prior to its  payment  and  shall be given a  reasonable  opportunity  to
comment thereon.

          (3) OTHER  BENEFITS.  During  the  Term:  (1) the  Executive  shall be
entitled to participate in all applicable fringe benefit and perquisite programs
and savings and  retirement  plans  (other than any  non-qualified  supplemental
retirement or


                                        2

<PAGE>

"top-hat"  plans),  practices,  policies and programs of the Company to the same
extent that such benefits were  provided to the Chief  Operating  Officer of the
Company  immediately prior to March 6, 2000 or are otherwise  generally provided
to other  senior  executives  of the  Company and (2) the  Executive  and/or the
Executive's  eligible  dependents,  as the case may be,  shall be  eligible  for
participation  in, and shall receive all benefits under, all applicable  welfare
benefit plans,  practices,  policies and programs provided by the Company to the
same  extent,  and  subject  to the same  terms,  conditions,  as  other  senior
executives  of the Company  unless  otherwise  provided  for in this  Agreement;
provided,  however,  the Company  shall  waive any and all  waiting  periods and
pre-existing  condition exclusions under its plans and programs  contemplated by
this  Section  3(d) with  respect  to the  participation  offered  and  coverage
provided to the Executive and his eligible dependents, as the case may be.

          (4)  INDEMNIFICATION.  The Company  agrees to  indemnify  and hold the
Executive  harmless,  to the fullest extent permitted under applicable law, for,
from and against any and all losses,  claims,  damages,  liabilities  or actions
(including  security holder actions,  in respect  thereof) related to or arising
out of the  Executive's  employment with or service to the Company or any of its
affiliates,  including Executive's role as a member of the Board,  subsequent to
March 6, 2000,  except for actions  finally  determined  by a court of competent
jurisdiction  to have  been  taken  in bad  faith or to have  constituted  gross
negligence or willful misconduct. At all times during the Term, the Company will
maintain director and officer liability insurance coverage and policies covering
the Executive which are no less favorable than those currently maintained by the
Company and  applicable  to the  Executive.  Following  any  termination  of the
Executive's  employment or service with the Company, the Company shall cause any
director and officer liability  insurance  policies  applicable to the Executive
prior to such  termination  to remain in  effect  on a  claims-made  basis for a
period of three  years  following  termination  of, if  longer,  any  applicable
statute of  limitations.  Nothing in this Agreement is intended to infringe such
rights  the  Executive  may  have  under  the  Company's  bylaws,   articles  of
incorporation or otherwise.

          (5)  LEGAL  FEES.  As soon as  reasonably  practicable  after the date
hereof, the Company shall reimburse the Executive for all legal fees incurred by
him in  connection  with the  negotiation,  preparation  and  execution  of this
Agreement;  provided,  however,  that such reimbursement shall not exceed $5,000
(including  amounts paid to counsel for David E. Thomas, Jr. with respect to his
Agreement).

          4. TERMINATION OF EMPLOYMENT. (a) DEATH OR DISABILITY. The Executive's
employment shall terminate  automatically  upon the


                                        3

<PAGE>

Executive's  death during the Term.  The Company  shall be entitled to terminate
the  Executive's  employment  because of the Executive's  Disability  during the
Employment  Period.  "Disability"  means that (i) the Executive has been unable,
for six (6) consecutive  months,  to perform the  Executive's  duties under this
Agreement,  as a result of  physical  or mental  illness or  injury,  and (ii) a
physician  selected  by the  Company  or its  insurers,  and  acceptable  to the
Executive or the  Executive's  legal  representative,  has  determined  that the
Executive is so disabled.  A termination  of the  Executive's  employment by the
Company for Disability shall be communicated to the Executive by written notice,
and shall be  effective  on the 30th day  after  receipt  of such  notice by the
Executive (the "Disability  Confirmation Date"), unless the Executive returns to
full-time   performance  of  the   Executive's   duties  before  the  Disability
Confirmation Date.

          (1)  TERMINATION  BY THE  COMPANY.  The Company  may, by  delivering a
written   termination  notice  to  the  Executive,   terminate  the  Executive's
employment at any time during the Term for Cause or without Cause. "Cause" means
(i) the willful and continued failure by the Executive  substantially to perform
his duties with the  Company  (other than any such  failure  resulting  from the
Executive's death or his incapacity due to physical or mental illness or injury)
after a written demand for substantial performance is delivered to the Executive
by the Board, which demand specifically identifies the manner in which the Board
believes that the Executive has not  substantially  performed his duties and the
Executive  has failed to correct  such  failure to  substantially  perform  such
duties within thirty (30) days after such written  demand is delivered;  or (ii)
the willful  engaging  by the  Executive  in conduct  that is  demonstrably  and
materially  injurious to the Company,  monetarily  or  otherwise,  and no act or
failure to act on the Executive's part shall be deemed "willful" unless done, or
omitted to be done, by the  Executive  not in good faith and without  reasonable
belief that such action or omission was in the best interests of the Company.

          (2)  TERMINATION  BY  EXECUTIVE.  The  Executive  may, by delivering a
written termination notice to the Company,  terminate his employment at any time
during the Term with Good Reason or without Good Reason. "Good Reason" means (i)
the Company has failed to cure any  material  breach or default by it under this
Agreement  within thirty (30) days after  receiving  written notice thereof from
the  Executive  or (ii) the Company is not able to comply in a material  respect
with applicable environmental laws and regulations,  after receiving an opinion,
upon  the  request  of  the  Company,  of  Arnold  &  Porter,  Esqs.  that  such
non-compliance  is material and there exists a significant risk that he could be
exposed to personal liability in connection therewith.


                                        4

<PAGE>

          (3) TERMINATION  FOLLOWING PAYMENT OF THE PLAN OF  REORGANIZATION/SALE
BONUS.  The  Company  may, by  delivering  a written  termination  notice to the
Executive, terminate the Executive's employment during the sixty (60) day period
following the payment of the Plan of Reorganization/Sale  Bonus. For purposes of
this Agreement,  if the Sale is not pursuant to the Plan of Reorganization,  the
Executive  shall be deemed to have been  terminated  within  the sixty  (60) day
period  following such Sale and shall have no entitlement to severance  benefits
or compensation  under this Agreement.  Any such termination shall be treated as
though it were with Cause.

          (4) DATE OF TERMINATION;  RESIGNATION. The "Date of Termination" means
the date of the Executive's death, the Disability Confirmation Date, the date on
which the termination of the Executive's  employment by the Company for Cause or
without Cause or following the payment of the Plan of Reorganization/Sale  Bonus
or by the Executive with Good Reason or without Good Reason is effective, as the
case  may  be,  or the  expiration  of the  Term.  Effective  as of the  Date of
Termination,  the  Executive  shall  resign  from the  Board  and from all other
offices and positions with the Company and its affiliates.

          5.  OBLIGATIONS  OF THE COMPANY UPON  TERMINATION.  (a) OTHER THAN FOR
CAUSE, DEATH OR DISABILITY OR UPON EXPIRATION OF THIS AGREEMENT.  If, during the
Term,  the Company  terminates the  Executive's  employment for any reason other
than (i) Cause, (ii) death (iii)  Disability,  or (iv) during the sixty (60) day
period following payment of the Plan of  Reorganization  Bonus or (v) subsequent
to the  payment of a Sale Bonus,  or at the  expiration  of the Term,  or if the
Executive  terminates his  employment for Good Reason,  the Company shall pay to
the  Executive,   not  later  than  thirty  (30)  days  following  the  Date  of
Termination,  (A) an amount equal to the  Executive's  then current  Annual Base
Salary (without giving effect to reductions  thereto) and (B) any unpaid amounts
of the Executive's  Annual Base Salary and other amounts earned through the Date
of Termination. In addition, if such termination is other than the expiration of
the Term,  during the second year following the  Executive's  termination  under
this section 5(a), in a time and manner  consistent  with the Company's  payroll
cycle the Executive  shall also receive  monthly  payments  equal to 1/12 of the
Executive's  Annual Base Salary  (which amount shall be reduced by the amount of
any salary earned by Executive during such month). The Company shall also pay or
provide to the Executive,  on or following  such a  termination,  any earned and
unpaid bonuses,  previously  deferred  compensation  and benefits payable to the
Executive under the terms of the Company's qualified pension plans, according to
the terms of


                                        5

<PAGE>

such  plans as in  effect  immediately  prior to the  Date of  Termination  (the
"Accrued  Benefits").  For a period not to exceed eighteen (18) months following
the Date of  Termination or the  expiration of the Term of this  Agreement,  and
only until the Executive  obtains full replacement  coverage,  the Company shall
reimburse  the  Executive  for the cost of any  premiums  paid by the  Executive
pursuant  to his (or  any of his  eligible  dependent's)  election  to have  the
Company provide "continuation  coverage" (within the meaning of Section 4980B of
the Internal  Revenue Code of 1986, as amended (the "Code")) under the Company's
(or, if applicable, an affiliate's) group health plan.

          (1) DEATH AND DISABILITY.  If the Executive's employment is terminated
by reason of the  Executive's  death or Disability  during the Term, the Company
shall pay to the  Executive  or, in the case of the  Executive's  death,  to the
Executive's  designated  beneficiaries (or, if there is no such beneficiary,  to
the Executive's  estate or legal  representative),  in a lump sum in cash within
thirty  (30)  days  after  the  Date of  Termination,  the sum of the  following
amounts: (1) any portion of the Executive's Annual Base Salary and other amounts
earned  through  the Date of  Termination  that has not yet been  paid  plus (2)
either  the  amount  of life  insurance  proceeds  or the  amount  of  long-term
disability  insurance  proceeds to which the Executive is entitled under current
Company  policy.  On or following  the Date of  Termination,  the Company  shall
provide the Executive with the Accrued  Benefits.  For a period not to exceed 18
months  following  the Date of  Termination,  the Company  shall  reimburse  the
Executive for the cost of any premiums paid by the Executive pursuant to his (or
any  of  his  eligible   dependent's)  election  to  have  the  Company  provide
"continuation  coverage" (within the meaning of Section 4980B of the Code) under
the Company's (or, if applicable, an affiliate's) group health plan.

          (2) BY THE COMPANY FOR CAUSE; BY THE EXECUTIVE;  FOLLOWING  PAYMENT OF
THE PLAN OF  REORGANIZATION/SALE  BONUS.  If  during  the  Term the  Executive's
employment is  terminated  by the Company for Cause or following  payment of the
Plan of  Reorganization/Sale  Bonus  pursuant to Section 4(d) hereof,  or if the
Executive's employment is terminated by the Executive without Good Reason during
the  Term,  the  Company  shall  pay to the  Executive  in a  lump  sum in  cash
immediately  prior to the Date of  Termination,  any portion of the  Executive's
Annual Base Salary and other amounts earned through the Date of Termination that
has not been paid.  On or following the Date of  Termination,  the Company shall
provide the Executive with the Accrued  Benefits.  For a period not to exceed 18
months following the Date of Termination,  but only until Executive obtains full
replacement coverage,  the Company shall reimburse the Executive for the cost of
any premiums paid by the Executive pursuant to his (or any


                                        6

<PAGE>

of his eligible  dependent's) election to have the Company provide "continuation
coverage"  (within the meaning of Section 4980B of the Code) under the Company's
(or, if applicable,  an affiliate's) group health plan, provided,  however, that
no such reimbursement shall be made in the event of a termination for Cause.

          6. NON-EXCLUSIVITY OF RIGHTS.  Nothing in this Agreement shall prevent
or limit  the  Executive's  continuing  or  future  participation  in any  plan,
program,  policy or practice  provided by the Company or any of its subsidiaries
or affiliated  companies for which the Executive may be selected by the Board to
participate in, nor shall anything in this Agreement  limit or otherwise  affect
such rights as the Executive may enter into under any contract or agreement with
the Company or any of its subsidiaries or affiliated companies (which contracts,
if any, shall be subject to Board  approval).  Vested benefits and other amounts
that the  Executive is otherwise  entitled to receive under any such other plan,
policy,  practice or program of, or any contract of agreement  with, the Company
or any of its  subsidiaries  or  affiliated  companies  on or after  the Date of
Termination  shall be  payable in  accordance  with the terms of each such plan,
policy, practice,  program, contract or agreement, as the case may be, except as
explicitly modified by this Agreement.

          7. FULL  SETTLEMENT.  The  Company's  obligation  to make the payments
provided for in, and otherwise to perform its obligations  under, this Agreement
shall not be affected by any set-off, counterclaim, recoupment, defense or other
claim,  right or action  that the  Company may have  against  the  Executive  or
others. In no event shall the Executive be obligated to seek other employment or
take any  other  action  by way of  mitigation  of the  amounts  payable  to the
Executive  under any of the  provisions of this  Agreement as such amounts shall
not be reduced,  regardless of whether the Executive  obtains other  employment,
except  that the second year of  severance  payments  contemplated  in section 5
shall be reduced by the amount of any salary earned by Executive in such month.

          8. CONFIDENTIAL INFORMATION. The Executive shall keep confidential all
trade secret or  confidential  information,  knowledge  or data  relating to the
Company or any of its subsidiaries or affiliated  companies and their respective
businesses that the Executive  obtains during the Executive's  employment by the
Company  or any of its  subsidiaries  or  affiliated  companies  and that is not
public  knowledge  (other than as a result of the Executive's  violation of this
Section 8)  ("Confidential  Information").  The Executive shall not communicate,
divulge or disseminate  Confidential Information at any time during or after the
Executive's  employment with the Company,  except with the prior written consent
of the Company or as otherwise required by law or legal process.


                                        7

<PAGE>

          9. DISPUTE RESOLUTION;  ATTORNEYS' FEES. All disputes arising under or
related to the  employment of the Executive or the  provisions of this agreement
shall be settled by the  United  States  Bankruptcy  Court for the  District  of
Delaware  while the  Company's  Chapter  11 case is  pending  and  otherwise  by
arbitration  under the rules of the  American  Arbitration  Association  then in
effect, such arbitration to be held in Columbia, South Carolina, as the sole and
exclusive  remedy of either party and judgement on any arbitration  award may be
entered in any court of competent jurisdiction.  The Company agrees to reimburse
legal  fees  incurred  by the  Executive  in any such  dispute to the extent the
Executive prevails in the dispute.

          10.  SUCCESSORS.  (a) This Agreement is personal to the Executive and,
without the prior written consent of the Company, shall not be assignable by the
Executive  otherwise than by will or the laws of descent and distribution.  This
Agreement  shall inure to the benefit of and be enforceable  by the  Executive's
legal representatives.

          (1) This  Agreement  shall inure to the benefit of and be binding upon
the Company.

          11.  MISCELLANEOUS.  (a) This  Agreement  shall be  governed  by,  and
construed in accordance  with, the laws of the State of South Carolina,  without
reference to principles of conflict of laws.  The captions of this Agreement are
not part of the  provisions  hereof  and  shall  have no force or  effect.  This
Agreement may not be amended or modified except by a written agreement  executed
by the parties hereto or their respective successors and legal representatives.

          (1) All notices and other communications under this Agreement shall be
in  writing  and  shall be  given  by hand  delivery  to the  other  party or by
registered  or  certified  mail,  return  receipt  requested,  postage  prepaid,
addressed as follows:

                              If to the Executive:

                              Grover C. Wrenn
                              1301 Gervais Street
                              19th Floor
                              Columbia, South Carolina 29201


                                        8

<PAGE>

                              With a copy to:

                              David S. Kurtz, Esq.
                              Skadden, Arps, Slate, Meagher & Flom (Illinois)
                              333 West Wacker Drive
                              Chicago, Illinois 60606

                               If to the Company:

                              Safety-Kleen Corp.
                              1301 Gervais Street
                              Columbia, South Carolina  29201
                              Attention:  Henry H. Taylor

                              With a copy to:

                              David S. Kurtz, Esq.
                              Skadden, Arps, Slate, Meagher & Flom (Illinois)
                              333 West Wacker Drive
                              Chicago, Illinois 60606

or to such other  address as either  party  furnishes to the other in writing in
accordance  with this  paragraph (b) of Section 11.  Notices and  communications
shall be effective when actually received by the addressee.

          (2)  The  invalidity  or  unenforceability  of any  provision  of this
Agreement shall not affect the validity or enforceability of any other provision
of this  Agreement.  If any provision of this Agreement shall be held invalid or
unenforceable  in part, the remaining  portion of such provision,  together with
all other  provisions of this Agreement,  shall remain valid and enforceable and
continue in full force and effect to the fullest extent consistent with law.

          (3) Notwithstanding any other provision of this Agreement, the Company
may withhold from amounts payable under this Agreement all federal, state, local
and  foreign  taxes that are  required  to be  withheld  by  applicable  laws or
regulations.

          (4) The  Executive's  or the  Company's  failure to insist upon strict
compliance with any provisions of, or to assert, any right under, this Agreement
shall


                                        9

<PAGE>

not be  deemed  to be a  waiver  of such  provision  or  right  or of any  other
provision of or right under this Agreement.

          (5) The rights and benefits of the Executive  under this Agreement may
not be anticipated,  assigned, alienated or subject to attachment,  garnishment,
levy,  execution or other legal or equitable  process except as required by law.
Any attempt by the Executive to anticipate,  alienate,  assign,  sell, transfer,
pledge,  encumber or charge the same shall be void. Payments hereunder shall not
be considered assets of the Executive in the event of insolvency or bankruptcy.

          (6) This  Agreement may be executed in several  counterparts,  each of
which shall be deemed an original,  and said  counterparts  shall constitute but
one and the same instrument.


                                       10

<PAGE>

                  IN  WITNESS  WHEREOF,  the  Executive  has  hereunto  set  the
Executive's  hand and,  pursuant to the  authorization of its Board, the Company
has caused this  Agreement  to be executed in its name on its behalf,  all as of
the day and year first above written.


                                      --------------------------------
                                      Grover C. Wrenn

                                      SAFETY-KLEEN CORP.


                                       By:
                                          ----------------------------
                                          John W. Rollins, Jr.


                                       11

<PAGE>

                                    EXHIBIT A

Strategic Diagnostics, Inc.
Director

Eckerd College
Trustee

                                       A-1