<PAGE>
                                                                    Exhibit 4.10

        THIS INSTRUMENT GRANTS A SECURITY INTEREST BY A PUBLIC UTILITY
          THIS INSTRUMENT CONTAINS AFTER-ACQUIRED PROPERTY PROVISIONS

  __________________________________________________________________________



                      OLD DOMINION ELECTRIC COOPERATIVE,
                                    GRANTOR
                                      TO
                                 CRESTAR BANK,
                                    TRUSTEE

                           ________________________

                         NINTH SUPPLEMENTAL INDENTURE
                         Dated as of November 1, 1999


                            ______________________


          Supplemental to the Indenture of Mortgage and Deed of Trust
                            dated as of May 1, 1992


    ______________________________________________________________________


                 A Mortgage of Both Real and Personal Property






          THIS INSTRUMENT IS EXEMPT FROM RECORDATION TAX PURSUANT TO
       VIRGINIA CODE SECTION 58.1-803.D. RECORDATION TAX HAS BEEN PAID
         IN THE OFFICE OF THE CLERK OF THE CIRCUIT COURT FOR HALIFAX
             COUNTY, VIRGINIA ON A SECOND SUPPLEMENTAL INDENTURE
                      RECORDED IN DEED BOOK ___, PAGE ___
<PAGE>

                         NINTH SUPPLEMENTAL INDENTURE

                           _________________________


     THIS NINTH SUPPLEMENTAL INDENTURE, dated as of November 1, 1999 (the "Ninth
Supplemental Indenture"), between Old Dominion Electric Cooperative, a Virginia
power supply cooperative (the "Company"), whose mailing address and address of
its chief executive office is Innsbrook Corporate Center, 4201 Dominion
Boulevard, Glen Allen, Virginia 23060, and Crestar Bank, a Virginia banking
corporation, as trustee (the "Trustee"), having its principal corporate trust
office at 919 East Main Street, Corporate Trust Department, Richmond, Virginia
23219.

     WHEREAS, the Company has heretofore executed and delivered an Indenture of
Mortgage and Deed of Trust, dated as of May 1, 1992 (herein sometimes called the
"Original Indenture"), to secure, as provided therein, its bonds (in the
Original Indenture and herein called the "Bonds"), to be designated generally as
its "First Mortgage Bonds", and to be issued in one or more series as provided
in the Original Indenture; and

     WHEREAS, the Original Indenture was recorded among the land records in the
counties of Halifax, Louisa, Spotsylvania and Orange, Virginia, and a UCC Form 1
concerning the Original Indenture was recorded among the financing statement
records at the Virginia State Corporation Commission and the Counties of
Henrico, Halifax, Louisa, Spotsylvania and Orange; and

     WHEREAS, the Company has heretofore executed and delivered a First
Supplemental Indenture, dated as of August 1, 1992 (hereinafter the "First
Supplemental Indenture"), its Second Supplemental Indenture dated as of December
1, 1992 (hereinafter called the "Second Supplemental Indenture"), its Third
Supplemental Indenture, dated as of May 1, 1993 (hereinafter called the "Third
Supplemental Indenture"), its Fourth Supplemental Indenture, dated as of
December 15, 1994 (hereinafter called the "Fourth Supplemental Indenture"), its
Fifth Supplemental Indenture, dated as of February 29, 1996 (hereinafter called
the "Fifth Supplemental Indenture"), its Sixth Supplemental Indenture, dated as
of November 28, 1997, (hereinafter called the "Sixth Supplemental Indenture"),
its Seventh Supplemental Indenture, dated as of November 1, 1998 (hereinafter
called the "Seventh Supplemental Indenture") and its Eighth Supplemental
Indenture, dated as of November 30, 1998 (hereinafter called the "Eighth
Supplemental Indenture") supplementing the Original Indenture, each of which,
with the exception of the Fourth Supplemental Indenture, provided for the
creation of a new series of Bonds which subjected, or intended to subject, to
the lien of the Original Indenture certain property described therein and was
recorded among the land records for the counties of Halifax, Louisa,
Spotsylvania and Orange, Virginia and among the financing statement records at
the Virginia State Corporation Commission and the Counties of Henrico, Halifax,
Louisa,

                                       2
<PAGE>

Spotsylvania and Orange, Virginia, which recording offices will include the
recording offices in which this Ninth Supplemental Indenture will be recorded;
and

        WHEREAS, pursuant to the Original Indenture, the First Supplemental
Indenture, the Second Supplemental Indenture, the Third Supplemental Indenture,
the Fifth Supplemental Indenture, the Sixth Supplemental Indenture, the Seventh
Supplemental Indenture and the Eighth Supplemental Indenture there have been
executed, authenticated, delivered and issued and there are now outstanding
First Mortgage Bonds of the series and in the principal amount as follows:


                           Principal    Principal
                            Amount       Amount
       Series               Issued     Outstanding
-----------------------  ------------  ------------

7.27% First Mortgage     $ 50,000,000  $          0
Bonds, 1992 Series A,
Due December 1, 1997

7.97% First Mortgage      l50,000,000   113,600,000
Bonds, 1992 Series A,
Due December 1, 2002

8.76% First Mortgage      350,000,000   271,200,000
Bonds, 1992 Series A,
Due December 1, 2022

First Mortgage Bonds,       1,203,638             0
1992 Series B, Due
September 15, 1992

First Mortgage Bonds,       1,203,637             0
1992 Series B, Due
December 15, 1992

First Mortgage Bonds,       1,203,637             0
1992 Series B, Due
March 15, 1993

First Mortgage Bonds,       1,203,638             0
1992 Series B, Due
June 15, 1993

First Mortgage Bonds,       l,203,638             0





                                       3
<PAGE>

1992 Series B, Due
September 15, 1993

First Mortgage Bonds,       1,203,637             0
1992 Series B, Due
December 15, 1993

First Mortgage Bonds,         392,375             0
1992 Series B, Due
March 15, 1994

First Mortgage Bonds          392,376             0
1992 Series B, Due
June 15, 1994

First Mortgage Bonds          392,376             0
1992 Series B, Due
September 15, 1994

First Mortgage Bonds,         392,376             0
1992 Series B, Due
December 15, 1994

First Mortgage Bonds          392,375             0
1992 Series B, Due
March 15, 1995

First Mortgage Bonds,         392,376             0
1992 Series B, Due
June 15, 1995

First Mortgage Bonds          392,376             0
1992 Series B, Due
September 15, 1995

First Mortgage Bonds,         392,376             0
1992 Series B, Due
December 15, 1995

First Mortgage Bonds,         392,375             0
1992 Series B, Due
March 15, 1996

                                       4
<PAGE>

First Mortgage Bonds,      392,376          0
1992 Series B, Due
June 15, 1996

First Mortgage Bonds,      392,376          0
1992 Series B, Due
September 15, 1996

4.90% First Mortgage     1,025,000          0
Bonds, 1992 Series C,
Due December 1, 1997

First Mortgage Bonds,      392,376          0
1992 Series B, Due
December 15,1996

5.20% First Mortgage     1,075,000          0
Bonds, 1992 Series C,
Due December 1, 1998

5.40% First Mortgage     1,130,000  1,130,000
Bonds, 1992 Series C,
Due December 1, 1999

5.50% First Mortgage     1,190,000  1,190,000
Bonds, 1992 Series C,
Due December 1, 2000

5.70% First Mortgage     1,255,000  1,255,000
Bonds, 1992 Series C,
Due December 1, 2001

5.90% First Mortgage     1,330,000  1,330,000
Bonds, 1992 Series C,
Due December 1, 2002

6.00% First Mortgage     1,405,000  1,405,000
Bonds, 1992 Series C,
Due December 1, 2003

6.10% First Mortgage     1,495,000  1,495,000
Bonds, 1992 Series C,
Due December 1, 2004

                                       5
<PAGE>

6.35% First Mortgage       5,060,000    5,060,000
Bonds, 1992 Series C,
Due December 1, 2007

6.50% First Mortgage      10,845,000   10,845,000
Bonds, 1992 Series C,
Due December 1, 2012

6.00% First Mortgage      34,400,000    34,400,00
Bonds, 1992 Series C,
Due December 1, 2022

7.48% First Mortgage     130,000,000  129,000,000
Bonds, 1993 Series A,
Due December 1, 2013

7.78% First Mortgage     120,000,000  120,000,000
Bonds, 1993 Series A,
Due December 1, 2023

First Mortgage Bonds      25,565,962            0
1996 Series A, Due
February 28, 1997

First Mortgage Bonds         581,032            0
1996 Series B, Due
January 5, 1998

First Mortgage Bonds      10,649,541   10,649,541
1996 Series B, Due
April 15, 2018

First Mortgage Bonds      32,650,788   32,650,788
1996 Series B, Due
June 15, 2018

First Mortgage Bonds      32,650,788   32,650,788
1996 Series B, Due
September 15, 2018

First Mortgage Bonds      32,650,788   32,650,788
1996 Series B, Due
December 15, 2018

                                       6
<PAGE>

4.90% First Mortgage          1,025,000  1,025,000
Bonds, 1997 Series A,
Due December 1, 2001

4.25% First Mortgage Bonds    1,075,000  1,075,000
1998 Series A, Due
December 1, 2002

4.25%First Mortgage Bonds     5,000,000  5,000,000
1998 Series B, Due
December 1, 2002

  WHEREAS, in connection with the construction of a two-unit, coal-fired
electric generating facility (the "Project") in Halifax County, Virginia (in
which the Company has an undivided 50% interest), the Company installed certain
solid waste disposal and sewerage facilities (the "Facilities").  Pursuant to a
loan agreement dated as of December 1, 1992 (the "Loan Agreement"), between the
Company and the Industrial Development Authority of Halifax County, Virginia
(the "Authority"), the Authority assisted the Company with the financing of the
Facilities by issuing its Exempt Facility Revenue Bonds (Old Dominion Electric
Cooperative Project), Series 1992, in an aggregate principal amount of
$60,210,000.00 (the "Series 1992 Tax-Exempt Bonds").  The Company's obligation
to repay the loan from the Authority is evidenced by a new series of Bonds
designated First Mortgage Bonds, 1992 Series C (the "1992 Series C Bonds"); and

  WHEREAS, pursuant to a Third Supplemental Loan Agreement dated as of November
17, 1999 (the "Third Supplemental Loan Agreement"), between the Authority and
the Company, the Authority has agreed to issue a new series of refunding revenue
bonds in an aggregate principal amount of $1,130,000 (the "Series 1999 Tax-
Exempt Bonds") to refund the December 1, 1999, maturity of the Series 1992 Tax-
Exempt Bonds.  The Company's obligation to repay the loan from the Authority in
connection with the Series 1999 Tax-Exempt Bonds shall be evidenced by a new
series of Bonds to be designated First Mortgage Bonds, 1999 Series A (the "1999
Series A Bonds"), which will replace and refund the December 1, 1999, maturity
of the 1992 Series C Bonds.

  WHEREAS, the Board of Directors of the Company has established the 1999
Series A Bonds and the Board of Directors of the Company has authorized an issue
of One Million One Hundred Thirty Thousand and no/100 Dollars ($1,130,000)
principal amount thereof, and the Company has complied or will comply with all
provisions required to issue Additional Bonds provided for in the Original
Indenture; and

  WHEREAS, the Company desires to execute and deliver this Ninth Supplemental
Indenture, in accordance with the provisions of the Original Indenture, for the
purposes, among others, of (i) providing for the creation of a new series of
Bonds, designating the series to be created and specifying the form and
provisions of the Bonds of such series (the

                                       7
<PAGE>

Original Indenture, as heretofore and hereby supplemented and modified, being
herein sometimes called the "Indenture"), and (ii) modifying the terms,
provisions, restrictions or conditions of the Original Indenture; and

     WHEREAS, Section 13.01 of the Original Indenture provides that, without the
consent of the Holders of any of the Bonds at the time Outstanding, the Company,
when authorized by a Board Resolution and the Trustee, may enter into
supplemental indentures for the purposes and subject to the conditions set forth
in said Section 13.01; and

     WHEREAS, the Company proposes to modify the Original Indenture as provided
in Section 13.01; and

     WHEREAS, all acts and proceedings required by law and by the Articles of
Incorporation and Bylaws of the Company necessary to secure the payment of the
principal of (and premium, if any) and interest on the 1999 Series A Bonds, to
make the 1999 Series A Bonds to be issued hereunder, when executed by the
Company, authenticated and delivered by the Trustee and duly issued, the valid,
binding and legal obligations of the Company, and to constitute the Indenture a
valid and binding mortgage for the security of all of the Bonds, in accordance
with its and their terms, have been done and taken; and the execution and
delivery of this Ninth Supplemental Indenture has been in all respects duly
authorized;

     NOW, THEREFORE, THIS NINTH SUPPLEMENTAL INDENTURE WITNESSETH, that, to
secure the payment of the principal of (and premium, if any) and interest on the
Outstanding Secured Bonds, to confirm the lien of the Original Indenture upon
the Trust Estate mentioned therein including all property purchased, constructed
or otherwise acquired by the Company since the date of execution of the Original
Indenture, to secure performance of the covenants therein and herein contained,
to declare the terms and conditions on which the Outstanding Secured Bonds are
secured, and in consideration of the premises thereof and hereof and to modify
the Original Indenture, the Company by these presents does grant, bargain, sell,
alienate, remiss, release, convey, assign, transfer, mortgage, hypothecate,
pledge, set over and confirm to the Trustee, in trust, all property, rights,
privileges and franchises (other than Excepted Property) of the Company of the
character described in the Granting Clauses of the Original Indenture, including
all such property, rights, privileges and franchises acquired since the date of
execution of the Original Indenture, including, without limitation, all of those
fee and leasehold interests in real property, if any, which may hereafter be
constructed or acquired by it, but subject to all exceptions, reservations and
matters of the character therein referred to, and expressly excepting and
excluding from the lien and operation of the Indenture all properties of the
character specifically excepted by Subdivisions A through K of "Excepted
Property" in the Original Indenture to the extent contemplated thereby, and all
property heretofore released or otherwise disposed of pursuant to the provisions
of the Original Indenture.

     PROVIDED, HOWEVER, that (i) if, upon the occurrence of an Event of Default,
the Trustee, or any separate trustee or co-trustee appointed under Section 10.14
of the

                                       8
<PAGE>

Original Indenture or any receiver appointed pursuant to statutory provision or
order of court, shall have entered into possession of all or substantially all
of the Trust Estate, all the Excepted Property described or referred to in
Subdivisions A through G, inclusive, of "Excepted Property" in the Original
Indenture then owned or thereafter acquired by the Company shall immediately,
and, in the case of any Excepted Property described or referred to in
Subdivisions H through J inclusive, of "Excepted Property" in the Original
Indenture, upon demand of the Trustee or such other trustee or receiver, become
subject to the lien of the Original Indenture to the extent permitted by law,
and the Trustee or such other trustee or receiver may, to the extent permitted
by law, at the same time likewise take possession thereof, and (ii) whenever all
Events of Default shall have been cured and the possession of all or
substantially all of the Trust Estate shall have been restored to the Company,
such Excepted Property shall again be excepted and excluded from the lien of the
Original Indenture to the extent and otherwise as hereinabove set forth and as
set forth in the Original Indenture.

     The Company may, however, pursuant to Granting Clause Third of the Original
Indenture, subject any Excepted Property to the lien of the Original Indenture,
whereupon the same shall cease to be Excepted Property.

     TO HAVE AND TO HOLD all said property, rights, privileges and franchises of
every kind and description, real, personal or mixed, hereby and hereafter (by
Supplemental Indenture or otherwise) granted, bargained, sold, alienated,
remised, released, conveyed, assigned, transferred, mortgaged, hypothecated,
pledged, set over or confirmed as aforesaid, or intended, agreed or covenanted
so to be, together with all the appurtenances thereto appertaining unto the
Trustee and its successors and assigns forever.

     SUBJECT, HOWEVER, to (i) Permitted Encumbrances (as defined in Section
1.01 of the Original Indenture), (ii) to the extent permitted by Section 14.06
of the Original Indenture, as to property acquired since the date of execution
of the Original Indenture, (a) any duly recorded or perfected prior mortgage or
other lien that may exist thereon at the date of the acquisition thereof by the
Company, and (b) purchase money mortgages created by the Company at the time of
acquisition thereof, and (iii) defects of title to and encumbrances on property
described in Article IV of the First Supplemental Indenture.

     BUT IN TRUST, NEVERTHELESS, with power of sale, for the equal and
proportionate benefit and security of the Holders from time to time of all the
Outstanding Secured Bonds without any priority of any such Bond over any other
such Bond and for the enforcement of the payment of such Bonds in accordance
with their terms.

     UPON CONDITION that, until the happening of an Event of Default (as defined
in Section 1.01 of the Original Indenture) and subject to the provisions of
Article Six of the Original Indenture, the Company shall be permitted to possess
and use the Trust Estate, except cash, securities and other personal property
deposited, or required to be deposited, with the Trustee and to explore for,
mine, extract and dispose of coal, ore, gas, oil and

                                       9
<PAGE>

other minerals, to harvest standing timber and to receive and use the rents,
issues, profits, revenues and other income, products and proceeds of the Trust
Estate.

     AND IT IS HEREBY COVENANTED AND DECLARED that all the Bonds are to be
authenticated and delivered and the Trust Estate is to be held and applied by
the Trustee, subject to the further covenants, conditions and trusts set forth
in the Original Indenture, and the Company does hereby covenant and agree to and
with the Trustee, for the equal and proportionate benefit of all Holders of the
Bonds as follows:


                                   ARTICLE 1

      BONDS OF THE 1998 SERIES A AND CERTAIN PROVISIONS RELATING THERETO


     Section 1.01

     (A) Terms of the 1999 Series A Bonds.  There be hereby established a series
of Bonds, known as and entitled "First Mortgage Bonds, 1999 Series A"
(hereinafter referred to as the "1999 Series A Bonds") and the form thereof
shall be substantially as set forth in Section 1.01 (D).  The aggregate
principal amount of 1999 Series A Bonds which may be authenticated and delivered
and outstanding at any one time is limited to One Million One Hundred Thirty
Thousand and no/100 Dollars ($1,130,000).  The Trustee is hereby appointed as
Authenticating Agent for the 1999 Series A Bonds.

     The 1999 Series A Bonds shall be issuable in fully registered form without
coupons and in denominations of $5,000 and integral multiples thereof.  Each
1999 Series A Bond shall be dated the date of its issuance and delivery.  The
1999 Series A Bonds shall bear interest from their date payable on June 1, 2000,
and on each of June 1 and December 1 of each year thereafter at the rate of
5.25% per annum and shall mature, subject to prior redemption, on December 1,
2002.

     The 1999 Series A Bonds shall be issued to and registered in the name of
the Authority and subsequently will be assigned by the Authority to the Bank of
New York, as trustee (the "Tax-Exempt Bond Trustee") pursuant to that certain
Indenture of Trust, dated as of December 1, 1992, between the Authority and the
Tax-Exempt Bond Trustee (as supplemental and amended by that certain Third
Supplemental Tax-Exempt Indenture of Trust, dated as of November 17, 1999, the
"Tax-Exempt Indenture") and will secure the obligations of the Company under the
Loan Agreement, as supplemented and amended by the Third Supplemental Loan
Agreement").

     The 1999 Series A Bonds shall be lettered "A".  The principal and interest
on the 1999 Series A Bonds shall be payable in lawful money of the United States
of America to the registered owner of the 1999 Series A Bonds or its assignee in
accordance with the

                                       10
<PAGE>

provisions of the Third Supplemental Loan Agreement by wire transfer or other
method acceptable to such registered owner or its assignee in funds which will
be immediately available on the applicable principal and/or Interest Payment
Date or Redemption Date. Interest on the 1999 Series A Bonds shall be payable
without presentation of the 1999 Series A Bonds for payment. Payment of the
principal or Redemption Price of any 1999 Series A Bond shall be made by the
Company to the Tax-Exempt Bond Trustee upon presentation and surrender of such
Bond to the Trustee.

     The Regular Record Date referred to in Section 3.09 of the Original
Indenture for the payment of interest on the 1999 Series A Bonds shall be the
fifteenth day (whether or not a business day) of the calendar month next
preceding such Interest Payment Date.

    (B) Extraordinary Optional Redemption of 1999 Series A Bonds.

        (i)  The 1999 Series A Bonds are subject to extraordinary optional
redemption by the Company in whole at any time at a Redemption Price equal to
100% of the principal amount of such 1999 Series A Bonds, together with accrued
interest to the Redemption Date, upon the happening of any of the following
events:

             (a) Damage or destruction of the Facilities by fire or other
casualty to such extent that, or loss of title to or use of substantially all of
the Facilities as a result of the exercise of the power of eminent domain or
failure of title which, in the opinion of both the Company (expressed in a
certificate of an Officer of the Company) and an Engineer, both filed with the
Trustee and the Tax-Exempt Bond Trustee and, that (1) the Facilities cannot be
reasonably repaired, rebuilt or restored within a period of 12 months to their
condition immediately preceding such damage or destruction, or (2) the Company
is prevented from carrying on its normal operations at the Facilities for a
period of 12 months; or

             (b) A change in the Constitution of Virginia or of the United
States of America or a legislative or administrative action (whether local,
state or Federal) or a final decree, judgment or order of any court or
administrative body (whether local, state or Federal) contested by the Company
in good faith which causes (1) the Second Supplemental Loan Agreement or the
1999 Series A Bonds to become void or unenforceable or their performance in
accordance with the intent and purpose of the parties as expressed therein to be
impossible or (2) unreasonable burdens or excessive liabilities to be imposed on
the Authority or the Company.

       (ii)  The 1999 Series A Bonds are subject to extraordinary optional
redemption by the Company in part on any Interest Payment Date at a Redemption
Price equal to 100% of the principal amount of the 1999 Series A Bonds to be
redeemed, together with accrued interest to the Redemption Date in the event of
(i) damage or destruction to any part of the Facilities by fire or other
casualty or (ii) loss of title to any part of the Facilities as a result of the
exercise of eminent domain or failure of title, but only upon receipt by the
Trustee and the Tax-Exempt Bond Trustee of the following:

                                       11
<PAGE>

                 (a)  A certificate of an Officer of the Company stating that
there has been either (x) damage or destruction of the Facilities by fire or
other casualty or (y) loss of title to any part of the Facilities as a result of
the exercise of eminent domain or failure of title and that it is not in the
best interest of the Company to rebuild such portion of the Facilities; and

                 (b)  An Opinion of Counsel stating that the use of the
condemnation award or insurance proceeds resulting from such casualty or loss of
title, for purposes other than (x) rebuilding, restoring or repairing the
Facilities, or (y) redeeming the Series 1999 Tax-Exempt Bonds would cause the
interest paid or payable on the Series 1999 Tax-Exempt Bonds (other than
interest paid to any "substantial user" of the Facilities or "related person" as
those terms are defined in Section 147(a) of the Internal Revenue Code of 1986,
as amended (the "Code")) to be includable in the gross income of a holder of
Series 1999 Tax-Exempt Bonds for Federal income tax purposes under the Code (or
for Virginia state income tax purposes).

          (iii)  To exercise its option to redeem the 1999 Series A Bonds, in
whole under subsection (B)(i), above, or in part under subsection (B)(ii),
above, the Company shall comply with the provisions of Article Seven of the
Original Indenture, if applicable, and shall within 120 days after the event
permitting its exercise, file the required documentation with the Trustee and
the Tax-Exempt Bond Trustee and specify a date not more than 60 days thereafter
for making such payments.

     (C)  Mandatory Redemption of the 1999 Series A Bonds.  The 1999
Series A Bonds are subject to mandatory redemption in whole as promptly as
possible, but no later than 180 days after the occurrence of any Determination
of Taxability, at a Redemption Price equal to 100% of the principal amount of
the 1999 Series A Bonds to be redeemed plus interest accrued to the Redemption
Date.  For purposes of this paragraph, "Determination of Taxability" shall mean
(i) any enactment or amendment of any applicable statute or regulation, or (ii)
a final decree or judgment of any federal court, a final determination by the
United States Internal Revenue Service or a final judgment or determination by
any court or agency of the Commonwealth of Virginia, with the effect that
interest paid or payable on the Series 1999 Tax-Exempt Bonds (other than
interest paid to any "substantial user" of the Facilities or "related person" as
those terms are defined in Section 147(a) of the Code) is or was includable in
the gross income of a Series 1998 Tax-Exempt Bondholder for Federal income tax
purposes under the Code (or for Virginia state income tax purposes).  A
Determination of Taxability does not include any tax upon interest payable on
exempt facility bonds under Section 142 of the Code and other statutes and
regulations in effect on the date of issuance of the Series 1999 Tax-Exempt
Bonds and does not include any change in tax rates.  A Determination of
Taxability will be deemed to have occurred on the date on which the Tax-Exempt
Bond Trustee is first notified in writing of any such enactment, amendment,
judgment, decree or determination.

                                       12
<PAGE>

     (D) Form of 1999 Series A Bonds.  The 1999 Series A Bonds and the Trustee's
authentication certificate to be executed on the Bonds of said series shall be
substantially in the following form, with such appropriate insertions,
omissions, substitutions and other variations as are required or permitted by
the Original Indenture, and may have such letters, numbers or other marks of
identification and such legends or endorsements placed thereon as may be
required to comply with the rules of any securities exchange or as may,
consistently herewith, be determined by the Officers executing such Bonds, as
evidenced by their execution of such Bonds:


                          FORM OF 1999 SERIES A BONDS

          THIS FIRST MORTGAGE BOND, 1999 SERIES A, HAS NOT BEEN AND
         WILL NOT BE REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
         AMENDED, AND MAY NOT BE SOLD, OFFERED FOR SALE OR OTHERWISE
        TRANSFERRED WITHOUT REGISTRATION UNDER SUCH ACT OR IN RELIANCE
        UPON AN APPLICABLE EXEMPTION FROM REGISTRATION UNDER SUCH ACT.

                       Old Dominion Electric Cooperative
                      First Mortgage Bond 1999 Series A,
                             Due December 1, 2002

      No.                                                     $
                                                               _________________

       Old Dominion Electric Cooperative, a Virginia power supply cooperative
(herein called the "Company", which term includes any successor corporation
under the Indenture hereinafter referred to), for value received, hereby
promises to pay to _____________, or registered assigns, the principal sum of
______________ Dollars on December 1, 2002, and to pay interest (computed on the
basis of a 360-day year of twelve 30-day months) thereon from the date of this
Bond or from the most recent Interest Payment Date to which interest has been
paid or duly provided for, semi-annually on June 1 and December 1 in each year,
commencing June 1, 2000, at the rate of  _______% per annum, until the principal
hereof is paid or made available for payment.  The interest so payable, and
punctually paid or duly provided for, on any Interest Payment Date will, as
provided in the Indenture (as defined herein), be paid to the Person in whose
name this Bond is registered on the date of business on the Regular Record Date
for such interest, which shall be the fifteenth day (whether or not a business
day), of the calendar month next proceeding such Interest Payment Date.  Any
such interest not so punctually paid or duly provided for will forthwith cease
to be payable to the Holder on such Regular Record Date and may either be paid
to the Person in whose name this Bond is registered at the close of business on
a Special Record Date for the payment of such defaulted interest to be fixed by
the Trustee, notice whereof shall be given to Holders of Bonds of this series
not less than 10 days prior to such Special Record Date, or may be paid at any
time in any other lawful manner not inconsistent with the provisions of the
Indenture and acceptable to the Holder hereof.

                                       13
<PAGE>

     If any principal of or premium, if any, or interest on this Bond is not
paid when due (whether at maturity, upon acceleration or call for redemption or
otherwise), then the overdue installments of principal and, to the extent
permitted by law, interest shall bear interest until paid at the interest rate
borne by this Bond.

     The principal of and premium, if any, and interest on this Bond shall be
payable in lawful money of the United States of America to the registered owner
hereof in accordance with the provisions of the Loan Agreement (as defined
herein) by wire transfer or other method acceptable to such registered owner in
funds which will be immediately available on the applicable principal and/or
interest payment date or redemption date.  Interest on this Bond shall be
payable without presentation hereof.  Payment of the principal and premium, if
any, on this Bond shall be made by the Company to the holder hereof upon
presentation and surrender of such Bond to Crestar Bank, Richmond, Virginia, as
trustee ("Trustee") under the Indenture.

     This Bond is one of a duly authorized issue of Bonds of the Company
designated as its "First Mortgage Bonds" (herein called the "Bonds") issued and
to be issued in one or more series (which may have varying terms) under, and all
equally and ratably secured by, an Indenture of Mortgage and Deed of Trust,
dated as of May 1, 1992 (herein called the "Indenture"), between the Company and
the Trustee to which Indenture and all indentures supplemental thereto reference
is hereby made for a statement of the description of the properties thereby
mortgaged, pledged and assigned, the nature and extent of the security and the
respective rights, limitations of rights, duties and immunities thereunder of
the Company, the Trustee and the Holders of the Bonds and of the terms upon
which the Bonds are, and are to be, authenticated and delivered.  This Bond is
issued pursuant to the Ninth Supplemental Indenture, dated as of November 1,
1999 ("Ninth Supplemental Indenture"), between the Company and the Trustee.  The
Bonds are being issued to refund the December 1, 1999, maturity of the Company's
First Mortgage Bonds, 1992 Series C ("1992 Series C Bonds).  The 1992 Series C
Bonds were issued by the Company to repay a loan from the Industrial Development
Authority of Halifax County, Virginia ("Authority") made to the Company from the
proceeds of the Authority's $60,210,000 Exempt Facility Revenue Bonds (Old
Dominion Electric Cooperative Project) Series 1992 ("1992 Tax-Exempt Bonds") for
the purpose of acquiring, constructing and equipping certain solid waste and
sewage disposal facilities ("Facilities") for the Company pursuant to the Loan
Agreement, dated as of December 1, 1992 ("Loan Agreement"), between the Company
and the Authority.  The 1992 Tax-Exempt Bonds were issued pursuant to an
Indenture of Trust, dated as of December 1, 1992 (as amended and supplemented
"Tax-Exempt Indenture"), between the Authority and the Bank of New York, as
trustee ("Tax-Exempt Bond Trustee").  Pursuant to a Third Supplemental Loan
Agreement, dated as of November 17, 1999 ("Third Supplemental Loan Agreement"),
between the Authority and the Company and the Tax-Exempt Indenture, the
Authority has issued its Exempt Facility Refunding Revenue Bonds (Old Dominion
Electric Cooperative Project), Series 1999 ("1999 Tax-Exempt Bonds") in the
aggregate principal amount of $1,130,000, under that certain Third Supplemental
Tax-Exempt Indenture, dated as of November 17, 1999

                                       14
<PAGE>

("Third Supplemental Tax-Exempt Indenture"), between the Authority and the Tax-
Exempt Trustee.

     If at any time the amount held by the Tax-Exempt Bond Trustee in the Bond
Fund, as defined in the Tax-Exempt Indenture, should be sufficient to pay at the
times required the principal of, and premium, if any, and interest on the 1999
Tax-Exempt Bonds then remaining unpaid and to pay all fees and expenses of the
Tax-Exempt Bond Trustee accrued and to accrue through final payment of the 1999
Tax-Exempt Bonds, the Company shall not be obligated to make any further
payments hereunder, except to the extent losses may be incurred in connection
with investment of moneys in the Bond Fund.

     The Authority, by the execution of the Third Supplemental Tax-Exempt
Indenture and the assignment form at the foot of this Bond ("Assignment"), is
assigning this Bond and the payments thereon to the Tax-Exempt Trustee, acting
pursuant to the Third Supplemental Tax-Exempt Indenture, as security for the
1999 Tax-Exempt Bonds.  Payments of principal of, and premium, if any, and
interest on this Bond shall be made directly to the Tax-Exempt Bond Trustee for
the account of the Authority pursuant to such assignment and applied only to the
principal of, and premium, if any, and interest on the 1999 Tax-Exempt Bonds.
All obligations of the Company hereunder shall terminate when all sums due and
to become due pursuant to the Third Supplemental Tax-Exempt Indenture, this
Bond, the Third Supplemental Loan Agreement and the 1999 Tax-Exempt Bonds have
been paid or provided for in full.

     The Bond is subject to extraordinary optional redemption by the Company
in whole at any time at a Redemption Price equal to 100% of the principal amount
of such Bonds, together with accrued interest to the Redemption Date, upon the
happening of any of the following events:

          (a)  Damage or destruction of the Facilities by fire or other
casualty to such extent that, or loss of title to or use of substantially all of
the Facilities as a result of the exercise of the power of eminent domain or
failure of title which, in the opinion of both the Company (expressed in a
certificate of an Officer of the Company) and an Engineer, both filed with the
Trustee and the Tax-Exempt Bond Trustee, (1) the Facilities cannot be reasonably
repaired, rebuilt or restored within a period of 12 months to their condition
immediately preceding such damage or destruction, or (2) the Company is
prevented from carrying on its normal operations at the Facilities for a period
of 12 months; or

          (b)  A change in the Constitution of Virginia or of the United States
of America or a legislative or administrative action (whether local, state or
Federal) or a final decree, judgment or order of any court or administrative
body (whether local, state or Federal) contested by the Company in good faith
which causes (1) the Second Supplemental Loan Agreement or the 1999 Tax-Exempt
Bonds to become void or unenforceable or their performance in accordance with
the intent and purpose of the parties

                                       15
<PAGE>

as expressed therein to be impossible or (2) unreasonable burdens or excessive
liabilities to be imposed on the Authority or the Company.

     The Bond is subject to extraordinary optional redemption by the Company
in part on any Interest Payment Date at a Redemption Price equal to 100% of the
principal amount of the Bonds to be redeemed, together with accrued interest to
the Redemption Date in the event of (i) damage or destruction to any part of the
Facilities by fire or other casualty or (ii) loss of title to any part of the
Facilities as a result of the exercise of eminent domain or failure of title,
but only upon receipt by the Trustee and the Tax-Exempt Bond Trustee of the
following:

     (A) A certificate of an Officer of the Company stating that there has
been either (x) damage or destruction of the Facilities by fire or other
casualty or (y) loss of title to any part of the Facilities as a result of the
exercise of eminent domain or failure of title and that it is not in the best
interests of the Company to rebuild such portion of the Facilities; and

     (B) An opinion of counsel stating that the use of the condemnation award
or insurance proceeds resulting from such casualty or loss of title, for
purposes other than (x) rebuilding, restoring or repairing the Facilities, or
(y) redeeming the 1999 Tax-Exempt Bonds would cause the interest paid or payable
on the 1999 Tax-Exempt Bonds (other than interest paid to any "substantial user"
of the Facilities or "related person" as those terms are defined in Section
147(a) of the Internal Revenue Code of 1986, as amended, (the "Code")) to be
includable in the gross income of a holder of the 1999 Tax-Exempt Bonds for
federal income tax purposes under the Code (or for Virginia state income tax
purposes).

     To exercise such right of extraordinary redemption in whole or in part,
the Company shall comply with the provisions of Article Seven of the Indenture,
if applicable, and shall within 120 days after the event permitting its
exercise, file the required documentation with the Trustee and the Tax-Exempt
Bond Trustee and specify a date not more than 60 days thereafter for making such
payments.

     The Bonds are subject to mandatory redemption in whole as promptly as
possible, but not later than 180 days after the occurrence of any Determination
of Taxability (as defined in the Tax-Exempt Indenture) at a Redemption Price
equal to 100% of the principal amount of the Bonds to be redeemed plus interest
accrued to the Redemption Date.

     If the Bond is called for redemption, the Company has covenanted to cause
notice of the call for redemption to be given to each Holder of the Bond to be
redeemed at such Holder's address as the same shall last appear upon the Bond
Register, by first class mail at least 35 and no more than 60 days prior to the
Redemption Date.

                                       16
<PAGE>

     If an Event of Default with respect to the Bond shall occur and be
continuing, the principal of the Bond may be declared due and payable in the
manner and with the effect provided in the Indenture.

     The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of Bonds under the Indenture at any time
by the Company with the consent of the Holders of a majority in aggregate
principal amount of Bonds of all series at the time outstanding affected by such
modification.  The Indenture also contains provisions permitting the Holders of
a majority in principal amount of Bonds at the time outstanding, on behalf of
the Holders of all Bonds to waive compliance by the Company with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences.  Any such consent or waiver by the Holder of this Bond shall
be conclusive and binding upon such Holder and upon all future Holders of this
Bond and of any Bond issued upon the registration of transfer hereof or in
exchange hereof or in lieu hereof, whether or not notation of such consent or
waiver is made upon this Bond.

     No reference herein to the Indenture and no provision of this Bond or of
the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of, and premium, if any, and
interest on this Bond at the times, places and rates, and in the coin or
currency herein prescribed.

     As provided in the Indenture and subject to certain limitations therein set
forth, the transfer of this Bond is registrable in the Bond Register, upon
surrender of this Bond for registration of transfer at the office or agency
maintained by the Bond Registrar in Richmond, Virginia, duly endorsed by, or
accompanied by a written instrument of transfer in form satisfactory to the
Company and the Bond Registrar duly executed by the holder hereof or his
attorney duly authorized in writing, and thereupon one or more new Bonds of this
series or authorized denominations and for the same aggregate principal amount,
will be issued to the designated transferee or transferees.

     The Bonds of this series are issuable only in registered form without
coupons in denominations of $5,000 and any integral multiple thereof.  As
provided in the Indenture and subject to certain limitations therein set forth,
Bonds of this series are exchangeable for a like aggregate principal amount of
Bonds of this series of a different authorized denomination, but of the same
maturity, as requested by the Holder surrendering the same.

     No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

     Prior to due presentment of this Bond for registration of transfer and
subject to the Assignment, the Company, the Trustee and any agent of the Company
or the Trustee may treat the person in whose name this Bond is registered as the
owner hereof for all purposes,

                                       17
<PAGE>

whether or not this Bond be overdue, and neither the Company, the Trustee nor
any such agent shall be affected by notice to the contrary.

       Unless the context suggest otherwise, all capitalized terms used herein
and not otherwise defined shall have the same meaning assigned to them in the
Indenture.

                                       18
<PAGE>

       IN WITNESS THEREOF, the Company has caused this Bond to be duly executed.

       Dated:   ______________________

                                              OLD DOMINION ELECTRIC
                                                COOPERATIVE

                                              By: SPECIMAN
                                                  --------
                                                  Authorized Officer

                                       19
<PAGE>

                         CERTIFICATE OF AUTHENTICATION

       This is one of the Bonds of the series designated therein referred to in
the within-mentioned Indenture.

                                    CRESTAR BANK, a Virginia
                                      corporation, as Trustee

                              By:   SPECIMAN
                                    --------
                                    Authorized Signatory

                                       20
<PAGE>

                                  ASSIGNMENT


       The Industrial Development Authority of Halifax County, Virginia (the
"Authority"), hereby irrevocably assigns without recourse the foregoing Bond to
the Bank of New York, New York, New York (the "Tax-Exempt Bond Trustee"), as
trustee, acting pursuant to a Third Supplemental Indenture of Trust dated as of
November 17, 1999 (the "Third Supplemental Tax-Exempt Indenture"), between the
Authority and the Tax-Exempt Bond Trustee and hereby directs the Company, as the
issuer of this Bond, to make all payments of principal of, premium and interest
thereon directly to the Tax-Exempt Bond Trustee at its principal office in New
York, New York, or at such other place as the Tax-Exempt Bond Trustee may direct
in writing.  Such assignment is made as security for the payment of the
Authority's $1,130,000 Exempt Facility Refunding Revenue Bonds (Old Dominion
Electric Cooperative Project), Series 1999, issued pursuant to the Tax-Exempt
Indenture.


                          INDUSTRIAL DEVELOPMENT AUTHORITY OF
                          HALIFAX COUNTY, VIRGINIA


                          By:   SPECIMAN
                                --------
                                Chairman

                                       21
<PAGE>

                                  ARTICLE II

           PRINCIPAL AMOUNT PRESENTLY OUTSTANDING TO BE OUTSTANDING

     Section 2.01  Principal Amount Presently To Be Outstanding.  The total
aggregate principal amount of Bonds of the Company issued and outstanding and
presently to be issued and outstanding under the provisions of and secured by
the Indenture will be Eight Hundred Eight Million, Seven Hundred Forty-One
Thousand, Nine Hundred-Five Dollars ($808,741,905), namely Three Hundred Eighty-
Four Million, Eight Hundred Thousand Dollars ($384,800,000) principal amount of
First Mortgage Bonds, 1992 Series A, Fifty-eight Million, One Hundred Ten
Thousand Dollars ($58,110,000) principal amount of First Mortgage Bonds, 1992
Series C, Two Hundred Forty-Nine Million Dollars ($249,000,000) principal amount
of First Mortgage Bonds, 1993 Series A, One Hundred Nine Million, One Hundred
Eighty-Two Thousand, Nine Hundred Thirty-Seven Dollars ($108,601,905) principal
amount of First Mortgage Bonds, 1996 Series B, One Million Twenty-Five Thousand
Dollars ($1,025,000) principal amount of 1997 Series A Bonds, One Million
Seventy-Five Thousand Dollars ($1,075,000) principal amount of 1998 Series A
Bonds, Five Million Dollars ($5,000,000) principal amount of 1998 Series B Bonds
and now issued, outstanding and One Million One Hundred Thirty Thousand Dollars
($1,130,000) principal amount of 1999 Series A Bonds to be issued pursuant to
this Seventh Supplemental Indenture upon compliance by the Company with the
provisions of Section 5.01 and 5.02 and/or 5.03 and/or 5.04 of the Original
Indenture.

                                  ARTICLE III

                                 MISCELLANEOUS

     Section 3.01. This Ninth Supplemental Indenture is executed and shall be
construed as an indenture supplemental to the Original Indenture, and shall form
a part thereof, and the Original Indenture, as heretofore supplemented and as
hereby supplemented and modified, is hereby confirmed.  Except to the extent
inconsistent with the express terms hereof, all of the provisions, terms,
covenants and conditions of the Original Indenture shall be applicable to the
1999 Series A Bonds to the same extent as if specifically set forth herein.  All
capitalized terms used in this Ninth Supplemental Indenture shall be taken to
have the same meanings as in the Original Indenture, except in cases where the
context clearly indicates otherwise.

     Section 3.02. All recitals in this Ninth Supplemental Indenture are made by
the Company only and not by the Trustee; and all of the provisions contained in
the Original Indenture, in respect of the rights, privileges, immunities, powers
and duties of the Trustee shall be applicable in respect hereof as fully and
with like effect as if set forth herein in full.

     Section 3.03. Whenever in this Ninth Supplemental Indenture any of the
parties hereto is named or referred to, this shall, subject to the provisions of
Articles Ten and

                                       22
<PAGE>

Twelve of the Original Indenture, be deemed to include the successors and
assigns of such party, and all the covenants and agreements in this Ninth
Supplemental Indenture contained by or an behalf of the Company, or by or on
behalf of the Trustee shall, subject as aforesaid, bind and inure to the
respective benefits of the respective successors and assigns of such parties,
whether so expressed or not.

     Section 3.04. Nothing in this Ninth Supplemental Indenture, expressed or
implied, is intended, or shall be construed, to confer upon, or to give to, any
person, firm or corporation, other than the parties hereto and the Holders of
the Outstanding Bonds, any right, remedy or claim under or by reason of this
Ninth Supplemental Indenture or any covenant, condition, stipulation, promise or
agreement hereof, and all the covenants, conditions, stipulations, promises and
agreements in this Seventh Supplemental Indenture contained by or on behalf of
the Company shall be for the sole and exclusive benefit of the parties hereto,
and of the Holders of Outstanding Bonds.

     Section 3.05. This Ninth Supplemental Indenture may be executed in several
counterparts, each of such counterparts shall for all purposes be deemed to be
an original, and all such counterparts, or as many of them as the Company and
the Trustee shall preserve undestroyed, shall together constitute but one and
the same instrument.

     Section 3.06. Although this Ninth Supplemental Indenture is dated for
convenience and for the purpose of reference as of November 1, 1999, the actual
date or dates of execution by the Company and by the Trustee are as indicated by
their respective acknowledgments hereto annexed.

     Section 3.07. To the extent permitted by applicable law, this Ninth
Supplemental Indenture shall be deemed to be a Security Agreement and Financing
Statement whereby the Company grants to the Trustee a security interest in all
of the Trust Estate that is personal property or fixtures under the Uniform
Commercial Code, as adopted or hereafter adopted in one or more of the states in
which any part of the properties of the Company are situated.  The mailing
address of the Company, as debtor, is Innsbrook Corporate Center, 4201 Dominion
Boulevard, Glen Allen, Virginia 23060, and the mailing address of the Trustee,
as secured party, is Crestar Bank, Attention:  Corporate Trust Administration,
919 East Main Street, Richmond, Virginia 23219.

                   [SIGNATURES APPEAR ON THE FOLLOWING PAGE]

                                       23
<PAGE>

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



Company:                           OLD DOMINION ELECTRIC COOPERATIVE
Innsbrook Corporate Center
4201 Dominion Boulevard
Glen Allen, Virginia 23060
                                   By:    ______________________________
                                          Name:   Daniel M. Walker
                                          Title:  Vice President of
                                                  Accounting and Finance



Trustee:                           CRESTAR BANK
919 East Main Street
Corporate Trust Department
Richmond, Virginia 23219
                                   By:   ____________________________
                                         Name:   J. Lee Judy
                                         Title:  Senior Vice President



                                       24
<PAGE>

                                ACKNOWLEDGMENT



COMMONWEALTH OF VIRGINIA          )
                                  )
CITY/COUNTY OF__________________  )


  The foregoing instrument was acknowledged before me this _____ day of
November, 1999, by Daniel M. Walker, the Vice President of Old Dominion Electric
Cooperative, a Virginia power supply cooperative.



                                  ____________________________________
                                  Notary Public

My Commission expires:  _____________________


                                ACKNOWLEDGMENT



COMMONWEALTH OF VIRGINIA          )
                                  )
CITY/COUNTY OF__________________  )


  The foregoing instrument was acknowledged before me this _____ day of
November, 1999, by J. Lee Judy, the Vice President of Crestar Bank, a Virginia
banking corporation, on behalf of the Bank.



                                  ____________________________________
                                  Notary Public


My Commission expires:  _____________________


                                       25