<PAGE>
 
                                                                     Exhibit 4.5


     =====================================================================


                          THE PROVIDENCE GAS COMPANY

                                      To

                     STATE STREET BANK AND TRUST COMPANY,

                               as  Successor to

                     RHODE ISLAND HOSPITAL TRUST COMPANY,

                                    Trustee



                           _________________________

                       NINETEENTH SUPPLEMENTAL INDENTURE

                           ________________________

                           Dated as of April 1, 1998


     =====================================================================
<PAGE>
 
                               TABLE OF CONTENTS

<TABLE> 
<CAPTION> 
SECTION                              HEADING                               PAGE
<S>                                                                        <C> 
Parties....................................................................  1

FORM SERIES S BOND.........................................................  2

ARTICLE FIRST.    SERIES S BONDS. .........................................  7

         Section 1.01 .....................................................  7
         Section 1.02 .....................................................  8
         Section 1.03 .....................................................  8
         Section 1.04...................................................... 10
         Section 1.05...................................................... 11
         Section 1.06...................................................... 13

ARTICLE SECOND.   ISSUANCE OF $15,000,000 OF SERIES S BONDS AND
                  CLOSING OF SUCH SERIES AT THAT AMOUNT.................... 14

         Section 1.01...................................................... 14
         Section 2.02...................................................... 14

ARTICLE THIRD.    ADDITIONAL PROVISIONS.................................... 14

         Section 3.01...................................................... 14
         Section 3.02...................................................... 14
         Section 3.03...................................................... 14
         Section 3.04...................................................... 14
         Section 3.05...................................................... 15
         Section 3.06...................................................... 15
         Section 3.07...................................................... 15
         Section 3.08...................................................... 15
         Section 3.09...................................................... 16
         Section 3.10...................................................... 16
         Section 3.11...................................................... 17
         Section 3.12...................................................... 17
         Section 3.13...................................................... 17
         Section 3.14...................................................... 17
         Section 3.15...................................................... 17
         Section 3.16...................................................... 17

Signatures................................................................. 19
</TABLE> 

ATTACHMENTS TO NINETEENTH SUPPLEMENTAL INDENTURE:

SCHEDULE I   - Schedule of Property and Interests Therein
SCHEDULE II  - Schedule of Released Property
<PAGE>
 
  THIS NINETEENTH SUPPLEMENTAL INDENTURE, dated as of April 1, 1998, between THE
PROVIDENCE GAS COMPANY, a corporation created by Special Act of the General
Assembly of the State of Rhode Island ( herein after sometimes called the
"Company"), party of the first part, and STATE STREET BANK AND TRUST COMPANY, a
Massachusetts trust company (successor to Rhode Island Hospital Trust National
Bank, which succeeded Rhode Island Hospital Trust Company), as trustee under the
Company's First Mortgage herein below mentioned (hereinafter sometimes called
the "Trustee"), party of the second part:

  WHEREAS the Company by an Indenture, dated as of January 1, 1922, as
supplemented by a First Supplemental Indenture, dated as of February 6, 1933, a
Second Supplemental Indenture, dated as of June 1, 1944, a Third Supplemental
Indenture, dated as of April 1, 1948, a Fourth Supplemental Indenture, dated as
of January 1, 1958, a Fifth Supplemental Indenture, dated as of July 1, 1960, a
Sixth Supplemental Indenture, dated as of September 1, 1963, a Seventh
Supplemental Indenture, dated as of November 1, 1971, an Eighth Supplemental
Indenture, dated as of July 1, 1972, a Ninth Supplemental Indenture, dated as of
October 1, 1975, a Tenth Supplemental Indenture, dated as of April 1, 1976, an
Eleventh Supplemental Indenture, dated as of September 1, 1978, a Twelfth
Supplemental Indenture, dated as of September 1, 1983, a Thirteenth Supplemental
Indenture, dated as of May 1, 1986, a Fourteenth Supplemental Indenture, dated
as of August 1, 1988, a Fifteenth Supplemental Indenture, dated as of June 1,
1990, a Sixteenth Supplemental Indenture, dated as of September 1, 1992, a
Seventeenth Supplemental Indenture, dated as of November 1, 1993, and an
Eighteenth Supplemental Indenture, dated as of December 1, 1995 (said
instruments being herein after sometimes called, respectively, the "Original
Indenture", the "First Supplemental Indenture",  the "Second Supplemental
Indenture", the "Third Supplemental Indenture", the "Fourth Supplemental
Indenture", the "Fifth Supplemental Indenture", the "Sixth Supplemental
Indenture", the "Seventh Supplemental Indenture", the "Eighth Supplemental
Indenture", the "Ninth Supplemental Indenture", the "Tenth Supplemental
Indenture", the "Eleventh Supplemental Indenture", the "Twelfth Supplemental
Indenture", the "Thirteenth Supplemental Indenture", the "Fourteenth
Supplemental Indenture", the "Fifteenth Supplemental Indenture", the "Sixteenth
Supplemental Indenture", the "Seventeenth Supplemental Indenture", and the
"Eighteenth Supplemental indenture", and the Original Indenture as supplemented
by whatsoever supplements , including, if apt, this Nineteenth Supplemental
Indenture, as have been or shall have been executed and delivered at the
pertinent time, being herein after sometimes called, collectively, the
"Indenture"), mortgaged its property and franchises, including after-acquired
property and franchises, to the Trustee to secure its First Mortgage Bonds
issued and to be issued thereunder accordance with the provisions of said
Indenture, and there are now outstanding thereunder $10,000,000 principal amount
of First Mortgage Bonds, Series M, 10.25% due July 31, 2008, being all of an
original issue of $10,000,000 principal amount of bonds of said Series M,
$10,000,000 principal amount of First Mortgage Bonds, Series N, 9.63% due May
30, 2020, being all of an original issue of $10,000,000 principal amount of
bonds of said Series N, $12,5000,000 principal amount of First Mortgage Bonds,
Series O, 8.46% due September 30, 2022, being all of an original issue of
$12,500,000 principal amount of bonds of said Series O, $12,500,000 principal
amount of First Mortgage Bonds, Series P, 8.09%
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture


due September 30, 2022, being all of an original issue of $12,500,000 principal
amount of bonds of said Series P, $9,600,000 principal amount of First Mortgage
Bonds, Series Q, 5.62% due November 30, 2003, being a portion of an original
issue of $16,000,000 principal amount of  bonds of said Series Q and $15,000,000
principal amount of  First Mortgage Bonds, Series R, 7.50% due December 15,
2025, being all of an original issue of $15,000,000 principal amount of bonds of
said Series R; and

  WHEREAS the Company has determined, by due corporate action, to provide for
the immediate issuance, execution, authentication and delivery of $15,000,000 in
aggregate principal amount of its fully registered First Mortgage Bonds in the
principal amount of $15,000,000 to be known as the Company's First Mortgage
Bonds, Series S, 6.82% (herein after sometimes called "bonds of Series S" or
"Series S bonds") due April 1, 2018; and

  WHEREAS each of the bonds to be issued hereunder and the certificate of the
Trustee to be endorsed on the bonds of such series are to be substantially in
the following forms, respectively, to wit:

[FORM OF SERIES S BOND]

No. R-                                                                $ ________

                                                                PPN_____________

THE PROVIDENCE GAS COMPANY

FIRST MORTGAGE BOND, SERIES S, 6.82%

Due April 1, 2018

  THE PROVIDENCE GAS COMPANY, a corporation created by Special Act of the
General Assembly of the State of Rhode Island (herein after called the
"Company"), for value received, hereby promises to pay
____________________________or registered assigns, on the first day of April,
2018, the principal sum of _____________________________Dollars
($_____________), and to pay interest thereon (unless this bond shall have been
called for previous redemption and payment duly provided therefor) at the rate
of six and eighty-two hundredths per cent (6.82%) per annum, payable semi-
annually on the first day of April and October in each year, commencing the
first day of October, 1998, until said principal sum shall have become due.  The
Company promises to pay, on demand, interest on any overdue principal (including
any overdue prepayment of principal) and premium, if any, and (to the extent
permitted by applicable law) on any overdue installment of interest, at the rate
of seven and eighty-two hundredths per cent (7.82%) per annum.  Interest shall
be computed on the basis of a 360-day year of twelve 30-day months, except that
this means of computation shall not operate to deprive the holder of this bond
of interest for any day or days when applied to a period of less than six
calendar months.  The principal of, interest on and

                                      -2-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture


premium, if any, on this bond shall, subject to the provisions of Section 3.07
of the Nineteenth Supplemental Indenture hereinafter described, be payable at
the office of State Street Bank and Trust Company, in Boston, Massachusetts (or
at the office of its successor trustee in the trust to which reference is herein
after made), in such coin or currency of the United States of America as shall
be legal tender for the payment of public and private debts at the time of
payment.

    This bond is one of a duly authorized issue of First Mortgage Bonds of the
Company, unlimited as to aggregate principal amount except as set forth in the
Indenture hereinafter mentioned, issuable in series and is one of a series known
as First Mortgage Bonds, Series S, 6.82%, all bonds of all series being issued
and to be issued under and pursuant to and all equally secured (except as and
sinking or other analogous fund, established in accordance with the provisions
of the Indenture hereinafter mentioned, may afford additional security for the
bonds of any particular series) by an Indenture, dated as of January 1, 1922, as
supplemented by a First Supplemental Indenture, dated as of February 6, 1933, a
Second Supplemental Indenture, dated as of June 1, 1944, a Third Supplemental
Indenture, dated as of April 1, 1948, a Fourth Supplemental Indenture, dated as
of January 1, 1958, a Fifth Supplemental Indenture, dated as of  July 1, 1960, a
Sixth Supplemental Indenture, dated as of September 1, 1963, a Seventh
Supplemental Indenture, dated as of November 1, 1971, an Eighth Supplemental
Indenture, dated as of  July 1, 1972, a Ninth Supplemental Indenture, dated as
of October 1, 1975, a Tenth Supplemental Indenture, dated as of April 1, 1976,
an Eleventh Supplemental Indenture, dated as of September 1, 1978, a Twelfth
Supplemental Indenture, dated as of September 1, 1983, a Thirteenth Supplemental
Indenture, dated as of May 1, 1986, a Fourteenth Supplemental Indenture, dated
as of August 1, 1988, a Fifteenth Supplemental Indenture, dated as of June 1,
1990, a Sixteenth Supplemental Indenture, dated as of September 1, 1992, a
Seventeenth Supplemental Indenture, dated as of November 1, 1993, an Eighteenth
Supplemental Indenture, dated as of December 1, 1995 and a Nineteenth
Supplemental Indenture, dated as of April 1, 1998 (said twenty instruments being
hereinafter called, collectively, the "Indenture"), all duly executed and
delivered by the Company to State Street Bank and Trust Company, in Boston
Massachusetts, as successor to Rhode Island Hospital Trust National Bank, which
succeeded Rhode Island Hospital Trust Company (hereinafter called the
"Trustee"), as trustee, to which Indenture and to all indentures supplemental
thereto reference is hereby made for a description of the property transferred,
assigned and mortgaged thereunder, the nature and extent of the security, the
terms and conditions upon which the bonds are secured and additional bonds may
be issued and secured, and the rights of the holders or registered owners of
said bonds, of the Trustee and of the Company in respect of such security.
Subsequent series of said bonds may vary as to date, date of maturity, rate of
interest and in other ways as in the Indenture provided or permitted.

    Notwithstanding any provisions of the Indenture (including, without
limitation, Section 41 thereof) the bonds of Series S shall be subject to
redemption only in the manner and to the extent provided in Section 1.03 and
Section 1.05 of the Nineteenth Supplemental Indenture.

                                      -3-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture
 

   This bond is transferable by the registered owner hereof, in person or by
duly authorized attorney, on books to be kept for that purpose in the office of
the Company, in Providence, Rhode Island, upon surrender thereof at said office
for cancellation and upon presentation of a written instrument of transfer duly
executed, and thereupon the Company shall issue in the name of the transferee or
transferees, and the Trustee shall authenticate and deliver, a new bond or
bonds, of like form and in an authorized denomination or in authorized
denominations of the same series, for the same aggregate principal amount.
Bonds of this series, upon surrender thereof at said office, may be exchanged
for the same aggregate principal amount of bonds of this series of another
authorized denomination or other authorized denominations, all upon payment of
the charges, if any, and subject to the terms and conditions specified in the
Indenture.

   In case of default by the Company, as set forth in the Indenture, the
principal of all the bonds of each and every series issued and outstanding
thereunder may be declared or may become due and payable in the manner and with
the effect provided in the Indenture.

          No recourse shall be had for the payment of any part of either the
principal or interest of this bond, or for any claim based hereon, or otherwise
in any manner in respect hereof or in respect of the Indenture, to or against
any stockholder, officer or director, past, present or future, of the Company,
by virtue of any statute or provision or rule of law, or by the enforcement of
any assessment or penalty, all such liability being expressly waived and
released by the acceptance of this bond.

          This bond shall not become obligatory for any purpose until
authenticated by the execution by the Trustee of the certificate endorsed
hereon.

          IN WITNESS WHEREOF, THE PROVIDENCE GAS COMPANY has caused its
corporate seal to be hereto affixed and this bond to be signed by its President
or Vice President and its Treasurer or Assistant Treasurer, the ________day of
________________________________.


                                  THE PROVIDENCE GAS COMPANY

                              By______________________________________
                                          President

[CORPORATE SEAL]

                              and
                              by____________________________________
                                          Treasurer



                                      -4-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture



[FORM OF TRUSTEE'S CERTIFICATE]

          This is one of the bonds of Series S of the issue described in the
Indenture within mentioned.

                              STATE STREET BANK AND TRUST COMPANY,
                                 as Successor to Rhode Island Hospital Trust
                                 Company, Trustee

 
                              By________________________________________
                                         Authorized Signature

          WHEREAS the Company also desires to confirm the lien of the Indenture
upon property (intended to be thereby mortgaged) acquired by the Company since
the execution of the Eighteenth Supplemental Indenture;

          NOW, THEREFORE, THIS NINETEENTH SUPPLEMENTAL INDENTURE WITNESSETH:
That The Providence Gas Company, pursuant to and in execution of the powers,
authorities and obligations conferred, imposed and reserved in the Original
Indenture, as heretofore supplemented by the First, Second, Third, Fourth,
Fifth, Sixth, Seventh, Eighth, Ninth, Tenth, Eleventh, Twelfth, Thirteenth,
Fourteenth, Fifteenth, Sixteenth, Seventeenth and Eighteenth Supplemental
Indentures, and every other power, authority and obligation thereto appertaining
or enabling, in consideration of the premises and of the authentication,
purchase and acceptance of the Series S bonds, of $10 duly paid to the Company
by the Trustee and of other good and valuable considerations, receipt whereof is
hereby acknowledged, and for the purpose of confirming the Original Indenture
and said First, Second, Third, Fourth, Fifth, Sixth, Seventh, Eighth, Ninth,
Tenth, Eleventh, Twelfth, Thirteenth, Fourteenth, Fifteenth, Sixteenth,
Seventeenth and Eighteenth Supplemental Indentures, as hereby supplemented, and
in order to secure, equally and ratably, the payment of the principal of and the
interest on all of the bonds at any time outstanding under the Indenture
according to their tenor, purport and effect and in order to secure the faithful
performance and observance of all of the covenants and conditions set forth
herein and in the Original Indenture, as heretofore supplemented by the First,
Second, Third, Fourth, Fifth, Sixth, Seventh, Eighth, Ninth, Tenth, Eleventh,
Twelfth, Thirteenth, Fourteenth, Fifteenth, Sixteenth, Seventeenth and
Eighteenth Supplemental Indentures, by these presents hereby confirms (except
for property hereinafter expressly reserved and excluded from the lien of the
Indenture) the mortgage, conveyance, pledge, assignment and transfer of the
properties, franchises, rights and privileges set forth and described in the
Original Indenture and said Second, Third, Fourth, Fifth, Sixth, Seventh,
Eighth, Ninth, Tenth, Eleventh, Twelfth, Thirteenth, Fourteenth, Fifteenth,
Sixteenth, Seventeenth and Eighteenth Supplemental Indentures, and does hereby
grant, bargain, sell, release, convey, mortgage, confirm, assign, transfer,
pledge and set over unto the Trustee, and its successors in the trust, and its
and their assigns, upon the trusts established by the Indenture, all and
singular:

                                      -5-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture
 

          A.  The "Schedule of Property and Interests Therein" hereto attached 
as Schedule I and made a part hereof.

          B.  The Company's gasworks, plant and machinery, purifiers,
generators, service and other pipes, holders, mains, meters, shops, tools,
implements, fixtures, appurtenances, and (except for property hereinafter
expressly reserved and excluded from the lien of the Indenture) all other real
and tangible personal property now owned or which shall hereafter be acquired by
the Company, or its successor or successors, and used or useful in connection
with its business of making, distributing, purchasing and selling gas, and with
any other business authorized or permitted by the Company's charter, and all of
the Company's leasehold interests in any of such property now or hereafter
leased by the Company as a leasee and all corporate and other franchises of the
Company, and all permits, ordinances, easements, privileges, immunities and
licenses, all rights to lay, construct, maintain and operate systems for the
distribution and transmission of gas and other agencies for the supply to itself
or others of light, heat and power, and all rights of way, grants and consents
which the Company now owns or which it may hereafter acquire, being intended to
include, among other things covered by the Indenture, the entire existing and
future light, heat and power business of the Company and all of its existing and
all of its future rights, franchises, permits, ordinances and licenses to
transact and conduct the same, and each and every part thereof (except as
hereinafter noted) as provided in the Original Indenture and said Second, Third,
Fourth, Fifth, Sixth, Seventh, Eighth, Ninth, Tenth, Eleventh, Twelfth,
Thirteenth, Fourteenth, Fifteenth, Sixteenth, Seventeenth and Eighteenth
Supplemental Indentures, which are hereby made a part hereof, to the same extent
as if set forth herein at length, excepting, however, and there is expressly
reserved and excluded from the lien of the Indenture:

               (1) Such of said properties or interests therein heretofore
conveyed to the Trustee as may have been released by the Trustee or sold or
otherwise disposed of as permitted by the provisions of the Indenture; and

               (2) All right, title and interest of the Company now owned or
hereafter acquired in and to

                    (a)  all cash, bonds, shares of stock, obligations and other
securities not deposited with the Trustee under the provisions of the
Indenture;

                    (b)  all accounts and bills receivable (other than for the
recovery of real property or establishing a lien or charge thereon or right
therein) and choses in action not specifically assigned to the Trustee and
pledged with the Trustee hereunder;

                    (c)  all goods, wares, merchandise, products and by-products
held for sale in the ordinary course of business;

                    (d)  all materials and supplies held for consumption in
operation;

                                      -6-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture
 
                    (e) all conversion burners, water heaters, stoves and
refrigerators rented to customers or held for rental;

                    (f)  all motor vehicles; and

               (3) The last day of each of the demised terms created by any
lease of property now leased to the Company and the last day of any demised term
under each and every lease hereafter made or acquired by the Company and, under
each and every renewal of any lease the last day of each and every such demised
term being hereby expressly reserved to and by the Company; until and unless a
default shall be made in one or more obligations of the Company under the
Indenture and such default shall have continued beyond the period of grace, if
any, applicable in respect thereof, and the Trustee or any receiver or other
official shall take control of the mortgaged properties, in which event the
Indenture shall (to the extent permitted by law) become and be a lien upon all
of the classes of property set forth in 2 above (subject to any liens or
encumbrances then existing thereon), and the Trustee, receiver or other official
shall (to the extent permitted by law) be entitled to possess, use and dispose
of the same in carrying on the operation of the Company's enterprise and to
include the same in any sale under power of sale conferred by the Indenture or
by law.

          TO HAVE AND TO HOLD all of said property, real, personal and mixed,
now owned or hereafter acquired, mortgaged and conveyed by the Company as
aforesaid, or intended so to be, unto the Trustee, and its successors in said
trust, and to them and to their assigns forever.

          IN TRUST, NEVERTHELESS, for the purposes, with the powers and subject
to the agreements, covenants and conditions set forth and expressed in the
Original Indenture, as supplemented and modified by the First Supplemental
Indenture,  the Second Supplemental Indenture, the Third Supplemental Indenture,
the Fourth Supplemental Indenture, the Fifth Supplemental Indenture, the Sixth
Supplemental Indenture, the Seventh Supplemental Indenture, the Eighth
Supplemental Indenture, the Ninth Supplemental Indenture, the Tenth Supplemental
Indenture, the Eleventh Supplemental Indenture, the Twelfth Supplemental
Indenture, the Thirteenth Supplemental Indenture, the Fourteenth Supplemental
Indenture, the Fifteenth Supplemental Indenture, the Sixteenth Supplemental
Indenture, the Seventeenth Supplemental Indenture, Eighteenth Supplemental
indenture and this instrument, it being agreed as follows, to with:

                                 ARTICLE FIRST
                                SERIES S BONDS

  Section 1.01.  There shall be and is hereby created a new series of bonds
entitled "First Mortgage Bonds, Series S, 6.82%" (herein sometimes called the
"Series S bonds" or "bonds of Series S"), limited in aggregate principal amount,
except as noted in Section 2.02 hereof, to Fifteen Million Dollars
($15,000,000), and to be issued as prescribed in Section 2.01 hereof.  Series S
bonds shall be fully registered bonds of the denomination of One Thousand
Dollars ($1,000) and multiples thereof.  All Series S bonds shall mature April
1, 2018 and shall bear interest at the rate and payable at the times specified
in the form of Series S bond set forth herein.  The principal of, interest on
any premium, if any, on bonds of Series S

                                      -7-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

shall, subject to the provisions of Section 3.07, be payable at the office of
the Trustee in such coin or currency of the United States of America as shall
be legal tender for the payment of public and private debts.

          Bonds of Series S shall be numbered "R-1" and consecutively upwards.

   Section 1.02.  Bonds of Series S shall be exchangeable for a like aggregate
principal amount of bonds of such series of another authorized denomination or
other authorized denominations.

  Section 1.03.  Notwithstanding any provisions of the Indenture (including,
without limitation, section 41 thereof) the bonds of Series S shall be subject
to redemption only in the manner and to the extent provided in this Section 1.03
and in Section 1.05.

          (a)  Optional Redemption of Series S Bonds with Premium.  The Company
   shall have the option, at any time and from time to time, of redeeming the
   outstanding Series S bonds, either in whole or in part (but if in part then
   in units of $100,000) upon not less than 30 days nor more than 60 days prior
   written notice to each registered owner, by payment of the principal amount
   of the Series S bonds to be redeemed, and accrued interest thereon to, but
   not including, the date of redemption together with the Yield-Maintenance
   Premium, if any.

       As used in this Section 1.03:

          "Yield-Maintenance Premium" shall mean, with respect to any series S
     bond, a premium equal to the excess, if any, of the Discounted Value of the
     Called Principal of such Series S bond over the amount of such Called
     Principal; provided that the Yield-Maintenance Premium shall in no event be
     less than zero.

          "Called Principal" shall mean, with respect to any Series S bond, the
     principal of such Series S bond that is to be redeemed pursuant to the
     provisions of this Section 1.03.

          "Discounted Value" shall mean, with respect to the Called Principal of
     any Series S bond, the amount calculated by discounting all Remaining
     Scheduled Payments with respect to such Called Principal from their
     respective scheduled due dates to the date on which such Called Principal
     is to be redeemed, in accordance with accepted financial practice and at a
     discount factor (applied on a semiannual basis) equal to the sum of (i) the
     Reinvestment Yield with respect to such Called Principal, plus (ii) 0.25%.

          "Reinvestment Yield" shall mean the yield reported as of 10:00 a.m.
     Boston, Massachusetts time on the fifth Business Day prior to the date of
     redemption of the Series S bonds on the display designated "USD" of the
     Bloomberg Financial Markets Services Screen (or, if not available, any
     other nationally recognized trading screen reporting on-line intraday
     trading in United States government securities) for actively traded U.S.
     Treasury securities

                                      -8-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

     having a maturity corresponding to the maturity of the Called Principal or
     if such yield shall not be reported as of such time or shall not be usable,
     then the arithmetic mean of the yields for the two columns under the
     heading "Week Ending" published in the Statistical Release under the
     caption "Treasury Constant Maturities" for the maturity of the Called
     Principal (rounded to the nearest month).  If no maturity exactly
     corresponds to the maturity of the Called Principal, yields for the next
     longer and the next shorter published maturities shall be calculated
     pursuant to the foregoing sentence and the Reinvestment Yield shall be
     interpolated from such yields on a straight-line basis (rounding in each of
     the relevant periods to the nearest month).  For the purposes of
     calculating the Reinvestment Yield, the most recent Statistical Release
     published prior to the date of determination of the Yield-Maintenance
     Premium shall be used.
 
          "Statistical Release" shall mean the then most recently published
     statistical release designated "H.15(519)" or any successor publication
     which is published weekly by the Federal Reserve System and which
     establishes yields on actively traded U.S. Government Securities adjusted
     to constant maturities or, if such statistical release is not published at
     the time of any determination hereunder, then such other reasonably
     comparable index which shall be designated by the holders of 66-2/3% in
     aggregate principal amount of the outstanding Series S bonds.

          "Remaining Scheduled Payments" shall mean, with respect to the Called
Principal of any Series S bond, all payments of such Called Principal and
interest thereon that would be due after the date scheduled for redemption
thereof if no redemption of such Called Principal were made prior to its
scheduled due date.

          "Business Day", as used in the definition of Reinvestment Yield, shall
     mean any day excluding Saturday, Sunday and any day which shall be , in New
     York, New York, a legal holiday or a day on which banking institutions are
     authorized by law to close.

     (b)   Optional Redemption of Series S Bonds Out of Condemnation Proceeds.
In the event that any property subject to the lien of the Indenture is (x) taken
by any governmental or other lawful authority pursuant to a Qualified
Condemnation, or (y) sold by the Company in anticipation of a Qualified
Condemnation for a price which, in the good faith judgment of the Board of
Directors of the Company (as evidenced by a resolution thereof) is deemed to be
equal to or greater than the fair market value of the property so sold, then the
Company shall have the option (to be exercised within 60 days after such taking
or sale), of applying a pro rata portion of the net cash proceeds resulting from
such taking or sale to the redemption of outstanding Series S bonds by payment
of the principal amount of the Series S bonds to be redeemed and accrued
interest thereon to the date of redemption plus, in the cash of any event
described in clause (y) above, an amount equal to the Yield-Maintenance

                                      -9-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture


Premium, if any.  The pro rata portion shall be determined by reference to all
bonds of all series then outstanding under the Indenture.

          As used in this Section 1.03(b) "Qualified Condemnation" shall mean
any taking by condemnation or eminent domain which (i) results in an award to
the Company which, in the good faith judgment of the Board of Directors of the
Company (as evidenced by a resolution thereof) is deemed to be equal to or
greater than the fair market value of the property so taken, and (ii) is deemed
by said Board of Directors (as evidenced by a resolution thereof) to be
authorized and proper or which has been contested by the Company in good faith
and by appropriate proceedings.
 
          (c)   Miscellaneous.  Except as herein otherwise set forth, the
provisions of Article Fourth of the Original Indenture, with respect to the
procedures for call and redemption, prior to maturity, of Series A and Series B
bonds, shall apply to the call and redemption, prior to maturity, of all bonds
of Series S so to be called and redeemed.  All Series S bonds redeemed pursuant
to the provisions hereof shall be canceled by the Trustee and shall be delivered
to or upon the order of the Company, and shall not be reissued.

          Whenever any series S bonds are to be redeemed, the Trustee shall
allocate to each registered owner a proportion of the Series S bonds to be
redeemed, equal, as nearly as practicable, to the proportion that the principal
amount of the bonds of such series then outstanding hereunder, registered in the
name of such owner, bears to the principal amount of all bonds of such series
then outstanding under the Indenture.

          Redemption notices for Series S bonds shall be given to each
registered owner by registered mail and not by publication.  The redemption
notice given to each registered owner shall comply with the provisions of
Article Fourth of the Original Indenture and shall also specify (i) the
principal amount of such owner's Series S bonds to be redeemed, (ii) the accrued
interest payable in connection with such redemption, and (iii) the Company's
estimate of the Yield-Maintenance Premium, if any, payable in connection with
such redemption.  The Company's final computation of the amount of any Yield-
Maintenance Premium payable in connection with any such redemption shall
furnished to the registered owners of the series S bonds to be prepaid as soon
as practicable after determination thereof and, in all events, not less than
three days prior to the date of such redemption.  The Trustee shall have no
responsibility for determining independently the amount of any Yield-Maintenance
Premium payable in connection with any redemption hereunder.

   Section 1.04.   The Company covenants and agrees that, so long as any Series
S bonds are outstanding hereunder, it will pay no dividends and make no
distribution either in cash or property (other than dividends payable in its
common stock), on any class of its capital stock and will purchase or redeem
none of its stock of any class if the sum of all dividends and all
distributions, purchases and redemptions on or of its stock of any class paid or
made by it (including any then proposed to be paid or made) after September 30,
1997 and any losses incurred after that date, charged or properly chargeable
against earned surplus, would exceed the amount of its net income earned after
that date plus Twelve Million Dollars


                                     -10-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

($12,000,000), provided, however, that there shall be excluded in making the
calculation aforementioned so much of the aggregate of expenditures, including
the reasonable value of property or securities, made by the Company for the
redemption or purchase of its capital stock as does not exceed the aggregate of
all amounts, including the reasonable value of property or securities, received
by it through the disposal, since September 30, 1997, of additional capital
stock.  Notwithstanding the foregoing sentence, the Company may make regular
dividend payments on, and mandatory sinking fund redemptions of , all shares of
its 8.7% Redeemable Cumulative Preferred Stock or any class of its preferred
stock which may hereafter be issued, to persons other than person controlled by,
controlling or under common control with the company, provided that such
payments and redemptions made after September 30, 1997 shall be included in any
computation under this Section 1.04.  The term  "control," as used in this
paragraph, shall mean ownership of 10% or more of the voting securities of the
Company or such other person.  The term "net income," as used in this paragraph,
shall mean the net income available for dividends, determined in accordance with
generally accepted accounting principles, after allowance for all taxes and
other income deductions.  The term "common stock" , as used in this paragraph,
shall mean stock of the Company of the class which is now outstanding.

          Section 1.05.  In the event that a Restructuring Put Event (as defined
below) shall occur or the Company shall have knowledge of any proposed
Restructuring Transaction which will result in a Restructuring Put Event, the
Company will give written notice (the "Restructuring Put Notice") of such fact
to the Trustee and all holders of the bonds of Series S.  The Restructuring Put
Notice shall be delivered promptly upon receipt of such knowledge by the Company
and in any event no later than five days after such Restructuring Put Event.
The Restructuring Put Notice shall (I) describe the facts and circumstances of
such Restructuring Put Event (including the effective date of such Restricting
Put Event) in reasonable detail, (ii) make reference to this Section 1.05 and
the right of the holders of the bonds of Series S to require the Company to
redeem their bonds of Series S on the terms and conditions provided for herein,
(iii) state that each holder must make a declaration of its intent to have the
Series S bonds held by it redeemed, and (iv) specify the date by which the
holder must respond to such restructuring Put Notice pursuant to this Section
1.05 in order to make such declaration.

          Upon the receipt of such Restructuring Put Notice or, if no
Restructuring Put Notice is given, upon receipt of actual knowledge of a
Restructuring Put Event, the holder of any bonds of Series S shall have the
privilege, upon written notice (the "Declaration Notice") to the Trustee and the
Company, of declaring all Series S bonds held by such holder serving such
Declaration Notice to become due and payable and thereupon such Series S bonds
shall become due and payable on such date (the "Restructuring Put Payment Date")
as the Company shall specify in a written notice of redemption delivered to the
Trustee and such holder, which notice shall be delivered by the Company to the
Trustee and such holder not later than 10 days after the Company's receipt of
the Declaration Notice.  The Company covenants and agrees to redeem in full on
the Restructuring Put Payment Date all bonds of Series S held by such holder
serving such Declaration Notice to the Company.  The Restructuring Put Payment
Date shall be not later than 20 days after the date that the Company has
received the Declaration Notice.  In the event that a Restructuring Put Notice

                                     -11-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

has in fact been given as herein above required, such Declaration Notice shall
be served prior to 60 days after receipt of such Restructuring Put Notice, and
in the event that a Restructuring Put Notice has not been given as herein above
required, such Declaration Notice shall be served prior to 30 days after the
holder serving such Declaration Notice shall have actual knowledge of such
Restructuring Put Event.  In the event that a Restructuring Put Notice is given
and the Company does not receive a Declaration Notice within the time period set
forth above, the Series S bonds held by such holder shall become due and payable
as a result of such Restructuring Put Event on a Restructuring Put Payment Date
within 20 days following such time period as shall be specified by a written
notice of redemption delivered by the Company to the Trustee and such holder not
later than 10 days following such time period and the Company covenants and
agrees to redeem in full on such Restructuring Put Payment Date all bonds of
Series S held by such holder; provided that the bonds of Series S of such holder
shall not be subject to such redemption if the Company receives within such time
period written notice from such holder in which it elects not to exercise the
right to have such bonds redeemed.

          As used herein, the following terms shall have the meanings set forth
below:

          A "Restructuring Transaction" shall mean any of the following:  (i)
the consolidation of the Company into or merger of the Company with any other
Person, (ii) any transaction as a result of which Providence Energy Corporation
shall own less than 51% of the Voting Stock of the Company, (iii) the sale by
the Company of all or substantially all of its assets to another Person or (iv)
the acquisition by the Company for all or substantially all of the assets of
another Person.

          A "Restructuring Put Event" shall occur if (i) a Restructuring
Transaction has taken place or shall take place and (ii) either (A) the
Company's long-term secured senior debt rating by a Designated Rating Agency
prior to the Restructuring Transaction shall be an Acceptable Rating and after
giving effect to the Restructuring Transaction and as a result thereof, the
rating of the long-term secured senior debt of the Restructuring Surviving
Entity by a Designated Rating Agency shall be less than an Acceptable Rating or
(B) the Company's long-term secured senior debt rating by a Designated Rating
Agency prior to the Restructuring Transaction (the "Company secured Senior Debt
Rating") shall be less than an Acceptable Rating and after giving effect to the
Restructuring Transaction and as a result thereof, the rating of the long-term
secured senior debt of the Restructuring Surviving Entity by a Designated Rating
Agency shall be lower than the Company Secured Senior Debt Rating.

          The "Restructuring Surviving Entity" shall mean after giving effect to
a Restructuring Transaction, the Company, provided that (i) if the Restructuring
Transaction is a merger or consolidation in which the Company is merged with or
consolidated into another entity, the surviving entity shall be Restructuring
Surviving Entity or (ii) if the Restructuring Transaction is a conveyance by the
Company of all or substantially all of its assets, the entity acquiring such
assets shall be the Restructuring Surviving Entity.

                                     -12-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

     "Acceptable Rating" shall mean in the case of S&P a rating of BBB (or the
then current equivalent thereof) or better and in the case of Moody's a rating
of Baa2 (or the then current equivalent thereof) or better or in the case of any
other Designated Rating Agency, a rating equivalent to an Acceptable Rating
assigned by S&P or Moody's or in the event no such equivalent rating is so
assigned, then the highest rating assigned by such other Designated Rating
Agency most closely approximately such rating by S&P or Moody's.

     "Designated Rating Agency" shall mean S&P or Moody's; provided, that in the
event both S&P and Moody's are not rating the long-term secured senior debt of
Company or the Restructuring Surviving Entity at a time when such a rating is
required to determine whether a Restructuring Put Event has occurred, then
another rating agency of recognized national standing and satisfactory to the
holders of 66-2/3% in principal amount of the Series S bonds then outstanding.

     "Moody's" shall mean Moody's Investors Service, Inc.

     "Person" shall mean an individual, a partnership, limited liability
company, corporation or trust.

     "S&P" shall mean Standard & Poor's Corporation.

     "Voting Stock" shall mean securities of any class or classes, the holders
of which are ordinarily, in the absence of contingencies, entitled to elect a
majority of the corporate directors (or others performing similar functions).

     All redemptions of Series S bonds pursuant to this Section 1.05 shall be
made by the payment of the aggregate principal amount remaining unpaid on such
Series S bonds and accrued inters thereon to the date of such redemption. Any
redemption of less than all of the outstanding Series S bonds made pursuant to
this Section 1.05 shall be applied to the payment in full of the Series S bonds
held by the holders providing a Declaration Notice and by the holders referred
to in the last sentence of the second paragraph of this Section 1.05.

     Section 1.06.  The Company covenants and agrees that monies received by the
Trustee described in the first sentence of Section 41 of the Indenture will not
be applied to the purchase of any bonds issued and outstanding under the
Indenture unless the Company purchases bonds of each outstanding series with
such monies in an amount equal to the percentage thereof which the principal
amount of the bonds of such series is of the principal amount of the bonds of
all series then outstanding. In the event the Company purchases any bonds
pursuant to the preceding sentence, such bonds shall immediately thereafter be
canceled and no bonds of the same series shall be issued in substitution
therefor.

                                      -13-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

                                ARTICLE SECOND
                 ISSUANCE OF $15,000,000 OF SERIES S BONDS AND
                     CLOSING OF SUCH SERIES AT THAT AMOUNT

     Section 2.01.  Upon the execution and delivery hereof, the Company will
execute and deliver to the Trustee and the Trustee will authenticate and deliver
to the Company Fifteen Million Dollars ($15,000,000) in aggregate principal
amount of Series S bonds.

     Section 2.02.  The issue of Series S bonds hereunder is hereby limited to
the Fifteen Million Dollars ($15,000,000) in aggregate principal amount of bonds
of such series to be initially issued as provided in Section 2.01 hereof and to
Series S bonds issued in exchange or substitution for outstanding Series S bonds
under the provisions of the Indenture, permitting the exchange of bonds for
other bonds (under the provisions of Section 1.02 hereof), or permitting the
issuance of bonds in lieu of lost, stolen, destroyed or mutilated bonds, or
permitting the exchange of definitive bonds for temporary bonds.

                                 ARTICLE THIRD
                             ADDITIONAL PROVISIONS

     Section 3.01.  The Company covenants and agrees that it has good right and
lawful authority to mortgage the properties described in the granting clauses
hereof and after-acquired property as provided herein and that it is lawfully
seized and possessed of the same (except with respect to after-acquired
property).

     Section 3.02.  The Company covenants and agrees that since the date of the
Eighteenth Supplemental Indenture no real estate or interest therein has been
taken by exercise of the right of eminent domain or released from the Indenture
or subjected to any easement which has not been terminated of record except as
listed on the "Schedule of Released Property" attached hereto as Schedule II.

     Section 3.03.  The Company covenants and agrees that (a) it will not
incorporate into its gas distribution system for operation as lessee or
otherwise any personal property or fixtures owned by another person or entity
except such property of a type expressly reserved and excluded from the lien of
the Indenture; and (b) without limiting the generality of the foregoing, it will
not enter into, as lessee, any leases of personal property, fixtures or improved
real property if the cost of all such items so leased less accumulated
depreciation taken from time to time in accordance with generally accepted
accounting principles would be in excess of 15% of the principal amount of bonds
then outstanding under the Indenture.

     Section 3.04.  The Company covenants and agrees that it will promptly
comply with all laws, ordinances or governmental rules and regulations to which
it is subject, including without limitation, the Occupational Safety and Health
Act of 1970, the Employee Retirement Income Security Act of 1974 and all laws,
ordinances, governmental rules and regulations relating to environmental
protection in all applicable jurisdictions, the violation of which would
materially and adversely affect the properties, business, prospects, profits or
condition of the Company or would result in any lien or charge upon any property
of the

                                      -14-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

Company which would materially and adversely affect the conduct of the Company's
operations.

     Section 3.05.  The Company covenants and agrees that it will not permit any
employee benefit plan maintained by it to be terminated in a manner which would
result in the imposition of a lien on any property of the Company pursuant to
Section 4068 of the Employee Retirement Income security Act of 1974, as amended.

     Section 3.06.  No bonds owned or held by, for the account of or for the
benefit of the Company or any other obligor on the bonds (other than bonds
pledged to secure an obligation) shall be deemed entitled to share in any
payment or distribution provided in Article Sixth of the Indenture, provided
that the Trustee shall be protected in making any such payment or distribution
unless it shall have actual knowledge that the bonds in respect of which such
payment or distribution is made are so owned or held.

     Section 3.07.  Payments of any amounts with respect to the series S bonds
shall be made at such place and in such manner as shall be provided in  6.4 of
the Bond Purchase Agreement dated as of April 1, 1998 (the "Bond Purchase
Agreement"), between the Company and the original purchaser of said Series S
bonds, or at such other places and in such other manners as may, from time to
time, be agreed upon in writing among the Company, the Trustee and the holder of
the Series S bond in question.

     Section 3.08.  Anything contained elsewhere in the Indenture
notwithstanding, and without limiting the effect of Section 3.15 of this
Nineteenth Supplemental Indenture, so long as any of the Series S bonds shall
remain outstanding, the Trustee shall be entitled to exercise any of the
remedies provided in the Indenture (including, without limitation, the remedies
provided in Sections 33, 46, 47, 48 and 49 of Indenture):
 
          (a)  if the Company shall default in the payment of any interest
     payable on any Series S bonds and such default shall have continued for a
     period of ten days, or the Company shall default in the payment of
     principal on any Series S bonds at final maturity or at any date fixed for
     the optional redemption thereof pursuant to the provisions of Section 1.03
     of this Nineteenth Supplemental Indenture or at any date fixed for
     redemption thereof pursuant to the provisions of Section 1.05 of this
     Nineteenth Supplemental Indenture;

          (b)  if the Company or any subsidiary of the Company shall fail to
     make when due or payable (including applicable grace periods, if any) any
     payment required to be made by it in respect of any indebtedness (other
     than the Series S bonds), the outstanding aggregate principal amount of
     which indebtedness is at the time of such failure in excess of three
     million dollars ($3,000,000);

          (c)  if the Company shall fail in the observance or performance of any
     other convenant, condition or agreement not enumerated in this Section
     herein above, contained in the Indenture (including this Nineteenth
     Supplemental Indenture) or in the Bond Purchase Agreement, and such failure
     shall continue for a period of sixty (60) days after such failure shall
     first become known to the President or the Financial

                                      -15-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

     Vice President of the Company, or to any person charged with the
     responsibilities normally associated with either of such offices;

          (d)  if any representation or warranty made by the Company herein, or
     made by the Company in the Bond Purchase Agreement, or made by the Company
     in any statement or certificate furnished by the Company in connection with
     the consummation of the issuance and delivery of the Series S bonds or
     furnished by the Company pursuant hereto or pursuant to the Bond Purchase
     Agreement, is untrue in any material respect as of the date of the issuance
     or making thereof;

          (e)  if final judgment or judgments for the payment of money
     aggregating in excess of $100,000 is or are outstanding against the Company
     or against any property or assets of the Company and any one of such
     judgments has remained unpaid, unvacated, unbonded or unstayed by appeal or
     otherwise for a period of 30 days from the date of its entry;

          (f)  in the event of the entry of a decree or order by a court having
     jurisdiction in the premises adjudging the Company a bankrupt or insolvent,
     or approving as properly filed a petition seeking reorganization,
     arrangement, adjustment or composition of, or in respect of, the Company
     under applicable Federal bankruptcy law or any other applicable Federal or
     State law, or appointing a receiver, liquidator, assignee, trustee,
     sequestrator (or other similar official) or the Company or of any
     substantial part of its property, or ordering the winding up or liquidation
     of its affairs, and the continuance of any such decree or order unstayed an
     in effect for a period of 60 consecutive days; or

          (g)  in the event of the institution by the Company of proceedings to
     be adjudicated a bankrupt or insolvent, or the consent by it to the
     institution of bankruptcy or insolvency proceedings against it, or the
     filing by it of a petition or answer or consent seeking reorganization or
     relief under applicable Federal bankruptcy law or any other similar
     applicable Federal or State law, or the consent by it to the filing of any
     such petition or the appointment of a receiver, liquidator, assignee,
     trustee, sequestrator (or other similar official) of the Company or of any
     substantial part of its property, or the making by it of an assignment for
     the benefit of creditors, or the admission by it in writing of its
     inability to pay its debts generally as they become due, or the taking of
     corporate action by the Company in furtherance of any such action.

     Section 3.09.  This Nineteenth Supplemental Indenture shall become void
when the Original Indenture shall be void.

     Section 3.10.  Dates of supplemental indentures and of bonds are intended
as and for dates for the identification of such bonds and such instruments,
respectively, and are not intended to indicate that any such instrument or any
bond was and no such instrument or bond has been or is to be executed on a
Sunday or a legal holiday, the respective dates when supplemental indentures
were executed being the dates or respective dates of the acknowledgments of the
parties thereto.

                                      -16-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

     Section 3.11.  Whenever reference is made in this Nineteenth Supplemental
Indenture to a Section or an Article of the Original Indenture and such Section
or Article has been amended by this instrument or any of the indentures
supplemental to the Original Indenture enumerated herein above, or two or more
of them, then such reference shall be to such Section or Article as so amended,
whether or not herein expressly so stated.

     Section 3.12.  The Company, at its own cost and expense, will forthwith,
upon the execution and delivery by the parties hereto of this Nineteenth
Supplemental Indenture, cause the same to be recorded pursuant to law in all
offices for the recording of mortgages of real or personal property in which
such recordation is necessary in order to perfect and protect the lien hereof,
and, in any event, in all such offices in which it has caused or may cause the
Original Indenture to be recorded.

     Section 3.13.  Anything in the Series S bonds or in the Indenture to the
contrary notwithstanding, upon receipt by the Company or the Trustee of evidence
reasonably satisfactory to the Company or the Trustee of the ownership of and
loss, theft, destruction or mutilation of any Series S bond and (a) in the case
of loss, theft or destruction, of indemnity or security reasonably satisfactory
to it (provided, however, that if the holder of such Series S bond is an
institution having a minimum net worth of $10,000,000 or more, its own affidavit
and undertaking of indemnity shall be deemed to be satisfactory evidence,
indemnity, and security) or (b) in the case of mutilation, upon surrender and
cancellation thereof, the Company at its expense will execute, and thereupon the
Trustee will authenticate and deliver in lieu thereof, a new bond, executed and
authenticated in the same manner as the bond being replaced, in an aggregate
principal amount equal to the unpaid portion of the principal amount of the bond
being replaced.

     Section 3.14.  This Nineteenth Supplemental Indenture may be executed in
any number of counterparts, each of which shall be deemed an original; and such
counterparts shall constitute but one and the same instrument, which shall for
all purposes be sufficiently evidenced by any such original counterpart.

     Section 3.15.  For any default by the Company in the covenants,
stipulations, promises and agreements herein contained or contained in the bonds
of Series S, the Trustee and the bondholders shall have the same rights and
remedies, subject to the same limitations, as are provided in the Original
Indenture.

     Section 3.16.  The Company hereby agrees to unconditionally indemnify,
defend and hold, and covenants not to sue, the Trustee and each holder of the
bonds of Series S from time to time, their respective directors, officers,
employees and agents harmless for or against any loss, liability, damage,
expense or claim (including, but not limited to, reasonable fees of attorneys,
experts and professionals and reasonable environmental consulting fees and
sampling and analysis costs which are incurred in investigating such claims,
defending such claims and prosecuting the Company under the indemnity provided
by this Section 3.16, whether arising under the federal Comprehensive
Environmental Response, Compensation and Liability Act, 42 U.S.C. Sections 9601
et seq., the federal Resource Conservation and Recovery Act, 42 U.S.C. Sections
6901 et seq., or any similar state law or regulation providing for liability for
responding to a release of hazardous substances (the

                                      -17-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

"Environmental Laws") (excepting only those attributable solely and completely
to the willful misconduct of any holder or holders of the bonds of Series S))
which may be incurred by or asserted against any holder of the bonds of Series S
directly or indirectly arising or resulting from, or relating to, any of the
following:  (1) the presence of any Hazardous Substances (hereinafter defined)
on any property previously, presently or hereafter owned, possessed, occupied,
operated or utilized by the Company; (2) the presence of any Hazardous
Substances on any real property, not previously, presently hereafter owned,
possessed, occupied or operated by the Company, which Hazardous Substances were
used, generated, manufactured, produced, stored, transported, disposed,
released, discharged, abandoned or handled by the Company; and (3) the violation
by the Company of any Environmental Law.  This indemnity shall continue in full
force and effect after repayment of the bonds of Series S, and its duration
shall be forever.

     "Hazardous Substance" shall mean any hazardous or toxic material, substance
or waste, pollutant or contaminant which is regulated under any statute, law,
ordinance, rule or regulation of any local, state, regional or federal authority
having jurisdiction over the property of the Company or its use, including but
not limited to any material, substance or waste which is: (a) defined as a
hazardous substance under Section 311 of the Federal Water Pollution Control Act
(33 U.S.C. 1317) as amended; (b) regulated as a hazardous waste under Section
1004 or Section 3001 of the Federal Solid Waste Disposal Act, as amended by the
Resource Conservation and Recovery Action (42 U.S.C. 6901 et seq.), as amended,
(c) defined as hazardous substance under Section 101 of the Comprehensive
Environmental Response, Compensation and Liability Act (42 U.S.C. 960 et seq.),
as amended or (d) defined or regulated as a hazardous substance or hazardous
waste under any rules or regulations promulgated under any of the foregoing
statutes.

                                      -18-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture

     IN WITNESS WHEREOF, The Providence Gas Company has caused its corporate
seal to be hereto affixed and these presents to be executed, acknowledged and
delivered in its name and on its behalf by its Senior Vice President and the
Assistant Treasurer, and said State Street Bank and Trust Company, as successor
as Trustee to Rhode Island Hospital Trust National Bank, which succeeded Rhode
Island Hospital Trust Company, has caused its corporate seal to be hereto
affixed and these presents to be executed and delivered by one of its officers,
all hereunto duly authorized, as of the day and year first above written.

                                            THE PROVIDENCE GAS COMPANY

(CORPORATE SEAL)                              By    /s/ James DeMetro
                                                 -------------------------
                                                        James DeMetro           
                                                 Its Senior Vice President      
                                                                                
                                                                                
                                              By     /s/ Peter J. Gill          
                                                  -----------------------       
                                                        Peter J. Gill
                                                  Its Assistant Treasurer

Signed, sealed and delivered
in the presence of:

/s/ Witness
------------------------
as to The Providence Gas
    Company

                                            STATE STREET BANK AND TRUST COMPANY,
                                             Trustee

 
[CORPORATE SEAL]
                                              By     /s/ Gary Dougherty        
                                                --------------------------
                                                     Authorized Officer

Signed, sealed and delivered
in the present of:

/s/ Witness
---------------------------
as to State Street Bank and
    Trust Company

                                      -19-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture


STATE OF RHODE ISLAND   )
                       ):SS.:
COUNTY OF PROVIDENCE    )

     In Providence, this 6th day of April A.D. 1998, personally appeared before
me James DeMetro, to me known and known by me to be a Senior Vice President of
THE PROVIDENCE GAS COMPANY, one of the parties that executed the foregoing
instrument, and acknowledged said instrument to be his free act and deed in his
capacity, and the free act and deed of said corporation; and on oath stated that
hew ad duly authorized to execute said instrument and that the seal affixed
thereto is the corporate seal of said corporation.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal, the day and year first above written.


                                                  /s/ Eleanore F. Gaines    
                                                  ----------------------
                                                       Notary Public

My Commission Expires: 7/14/2001
                                                    [Notarial Seal]

STATE OF RHODE ISLAND  )
                      ):SS.:
COUNTY OF PROVIDENCE  )

     In Providence, this 6th day of April A.D. 1998, personally appeared before
me Peter J. Gill, to me known and known by me to be an Assistant Treasurer of
THE PROVIDENCE GAS COMPANY, one of the parties that executed the foregoing
instrument, and acknowledged said instrument to be his free act and deed in his
said capacity; and the free act and deed of said corporation; and on oath stated
that he was duly authorized to execute said instrument and that the seal affixed
thereto is the corporate seal of said corporation.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal, the day and year first above written.

                                                      /s/ Anne W. Connor
                                                ------------------------------
                                                         Notary Public

My Commission Expires: 12/23/2001

                                                  [Notarial Seal]

                                      -20-
<PAGE>
 
The Providence Gas Company                     Nineteenth Supplemental Indenture



STATE OF RHODE ISLAND  )
                      ):SS.:
COUNTY OF PROVIDENCE   )

     In Providence, this 6th day of April A. D. 1998, personally appeared before
me Gary Doughery, to me known and known by me to be an Assistant Vice President
of STATE STREET BANK AND TRUST, one of the parties that executed the foregoing
instrument, and acknowledged said instrument to be his free act and deed in his
said capacity, and the free act and deed of said corporation; and on oath stated
that he was duly authorized to execute said instrument and that the seal affixed
thereto is the corporate seal of said corporation.

     IN WITNESS WHEREOF, I have hereunto set my hand and affixed my official
seal, the day and year first above written.


                                                   /s/ Jacqueline G. Maynard
                                                  ---------------------------
                                                         Notary Public

                                                  [Notarial Seal]

My Commission Expires: 6/25/2001

                                      -21-
<PAGE>
 
                   SCHEDULE OF PROPERTY AND INTEREST THEREIN

     The following described tracts or parcels of land with all buildings and
improvements thereon and therein, situated in the County of Providence, in said
State of Rhode Island:

FIRST PARCEL:

     Situated on the northerly side of Goff Street, in the City of Providence,
bounded and described as follows:

Beginning, for the southeasterly corner of the tract hereby conveyed, at a stone
bound in the northerly line of Goff Street at the southwesterly corner of land
now or formerly of George K. Webster; thence northerly bounding easterly on said
Webster land, 77.53 feet, more or less, to land now or formerly of Sands, Taylor
& Wood; thence westerly, bounding northerly on said Sands, Taylor & Wood land,
approximately 88 feet, to the southwesterly corner of said Sands, Taylor & Wood
land; thence northerly, bounding easterly on said Sands, Taylor & Wood land, 116
feet, more or less to Blackstone Street; thence westerly bounding northerly on
said Blackstone Street, 351.05 feet, more or less to land now or formerly of
John E. Devron; thence southerly, bounding westerly in part on said Devron land,
and in part on lands now or formerly of Mary H. Baldwin, Edward Brophy and wife
and Joseph Haselden and wife, about 220.66 feet, more or less, to a stone bound;
thence westerly at a right angel to said last described line; bounding northerly
on said Haselden land, 24.38 feet to a stone bound; thence southerly, at an
interior angle of 101 degrees 21', bounding westerly on land now or formerly of
Benjamin Dubinsky, 45.29 feet, to a stone bound; thence southerly at an interior
angle of 152 degrees 42' bounding westerly on land now or formerly of the Apco
Manufacturing Company, 39.20 feet to a stone bound and said Goff Street; thence
easterly along the northerly line of said Goff Street, 498.23 feet, more or
less, to a stone bound and the place of beginning.  Being the same premises
conveyed to Providence Gas Company by deed of Oxford Land Company dated October
28, 1903, filed in Book 460, Page 197 in Providence Land Records and by deed of
Walter E., Thomas C. and Louis A. Gladding dated March 8, 1904, recorded in said
Providence Land Records in Deed Book 464, Page 113.

     Excepting from the above premises the property conveyed to Providence
Energy Company by Quiteclaim Deed of Providence Gas Company dated September 29,
1989, recorded in Deed Book 2116, Page 118, and property conveyed to Astro
Plating Works Corp. by Quitclaim Deed dated July 18, 1983, filed in Providence
Land Records in Deed Book 1246, Page 615.






                                   SCHEDULE I
                     (to Nineteenth Supplemental Indenture)

<PAGE>
 
                         SCHEDULE OF RELEASED PROPERTY



                                     None





                                  SCHEDULE II
                    (to Nineteenth Supplemental Indenture)