Exhibit 10.7
                                LETTER OF INTENT

This  Letter of Intent is made and  entered  into  February  18,  1997 among ADA
Environmental  Solutions  LLC, a Colorado  limited  liability  company  ("ADA"),
ADA-ES, Inc., a Colorado corporation, the parent company of ADA and the owner of
all the membership interests in ADA ("Parent"),  the shareholders of Parent (the
"Parent  Shareholders")  named on the signature page hereof and Earth  Sciences,
Inc., a Colorado  corporation  ("ESI').  ADA, the Parent  Company and the Parent
Shareholders are collectively referred to herein as the "ADA Parties."

WHEREAS,  the ADA Parties are seeking funding to accomplish the business plan as
set  forth  in the  document  entitled  "Business  Plan  for  ADA  Environmental
Solutions - Flue Gas Conditioning  Technology for Cost Effective  Enhancement of
ESPs and Baghouses," dated March 1996 (the "Business  Plan"),  which among other
matters  discusses  the  use of  phosphoric  acid  for  treatment  of  flue  gas
particulates;

WHEREAS, ESI's wholly-owned subsidiary intends to produce phosphoric acid at its
facility in Calgary; and

WHEREAS,  ESI desires to acquire a 51 % interest in ADA and an option to acquire
a 100% equity  interest in the Parent Company and provide the funding  necessary
to accomplish the Business Plan, all in accordance with the terms and conditions
set forth in this Letter of Intent;

NOW,  THEREFORE,  the ADA  Parties  and  ESI,  in  consideration  of the  mutual
covenants  set forth  herein  and other  good and  valuable  consideration,  the
receipt of which is hereby acknowledged by each of the parties,  hereby agree as
follows:

1. Acquisition of Membership Interest in ADA.
---------------------------------------------

Simultaneously with the execution and delivery of this letter of intent, ESI has
paid  ADA  cash  in the  amount  of  $400,000  and  has  been  issued  by ADA in
consideration thereof a membership interest representing a four and eight tenths
percent (4.8%) interest in ADA. The operating  agreement of ADA has been amended
simultaneously  herewith  to reflect  the  ownership  by ESI of such  percentage
interest.

      In the event the  transactions  specified  in  Paragraph 2 hereof have not
been  consummated  on or before  April 30,  1997,  ESI shall  have the option of
requiring  ADA  to  repurchase  such  4.8%  by  making  equal  monthly  payments
commencing  not later than April  30,1998  over a two (2) year  period  totaling
$400,000  plus  interest  at a  compound  rate of 8% per annum from the date the
funds  are  received  by ADA  until  payment  is  made to ESI In the  event  the
transactions  specified  in Paragraph 2 hereof have not been  consummated  on or
before  April 30, 1997 and ESI shall not, by May 15, 1997  exercise its right to
cause ADA to repurchase the foregoing membership  interest,  then ADA shall have
the right to purchase  such  membership  interest  over a one year period on the
same terms, such right to be exercised on or before June 15, 1997.


2.   Acquisition   of  Additional   Interest  in  ADA  and  Option  From  Parent
Shareholders.
--------------------------------------------------------------------------------

(a) The Parties will use their good faith  efforts to  consummate  the following
transactions on or before April 30, 1997 (the "Closing Date"):

(i) ESI, or a wholly-owned  subsidiary of ESI, will acquire an additional  46.2%
equity  interest  from ADA in exchange for  $500,000 in cash and a  non-interest
bearing  note in the amount of  $1,600,000  (the  "Note"),  payable as  follows:
$600,000 on or before June 30, 1997;  $500,000 on or before January 1, 1998; and
$500,000 on or before April 30, 1998.

(ii) The Parent Shareholders will grant ESI an irrevocable option (the "Option")
to acquire all of their shares in Parent  during a six month  period  commencing

<PAGE>


May 1, 1998 and ending October 31, 1998 in exchange (the  "Exchange") for shares
of common  stock,  $.01 par value per share (the  "Common  Stock")  of ESI.  The
number of shares of Common  Stock to be issued (the  "Shares")  in the  Exchange
shall be 1,715,600. The Shares will be
restricted  from  trading  pursuant  to rules  of the  Securities  and  Exchange
Commission;  however,  ESI will prepare and file (at its expense) a registration
statement  with  the  SEC  with  respect  to the  offering  and  sale  or  other
disposition of the Shares within 3 months of the exercise of the Option.

(b) The following  shall be conditions  precedent to the  obligations of the ADA
Parties and ESI to consummate the  transactions  specified in Paragraph 2(a) and
to ESI's right to exercise the Option:

(i) ESI shall provide assurances to the ADA Parties, acting reasonably, that the
additional  funding  needed to pay the Note, is or will be available to ESI. ESI
acknowledges  that on April 30, 1997  $400,000 and on June 30, 1997  $330,000 of
the  proceeds  will be used to  repay  certain  indebtedness  owed by ADA to ADA
Technologies,  Inc. incurred for operating  expenses of ADA. ESI agrees to cause
ADA to make such payment.

(ii) ESI shall satisfy itself, acting reasonably,  that the nature and prospects
of ADA  are,  in  material  respects,  as set  forth  in the  Business  Plan and
financial  statements that have been provided to ESI, and that there has been no
material adverse change in the business from what is set forth therein.

(iii) ADA shall satisfy itself, acting reasonably, that the nature and prospects
of ESI are, in all  material  respects,  as set forth in ESI's 1995 Form 10-KSB,
1996  Quarterly  Form  10-QSB,  and  other  materials  that  have been or may be
provided  to ADA,  and that  there has been no  material  adverse  change in the
business from what is set forth therein.

(iv)  ADA  and  ESI  will  negotiate  satisfactory  employee  contracts  for the
continued  employment of certain individuals and satisfaction of certain accrued
incentives by issuance of 36,305 of Common Stock of ESI.

(v) ESI shall use its best efforts to make  available  one seat on the ESI Board
of Directors to the ADA Parties so long as, in the  aggregate,  they own no less
than one million  shares of Common  Stock and agrees to  nominate an  individual
designated by the ADA Parties for such seat. Management shareholders of ESI will
enter into appropriate voting agreements, agreeing to vote their shares in favor
of one individual designated by the ADA Parties for such seat.

(vi) ADA and ESI will use their best efforts to effect the Exchange of Shares on
a tax free basis.

(vii) The parties shall negotiate and execute definitive documentation regarding
the  transactions  set forth in Paragraph  2(a).  Such  agreement  shall contain
customary  terms and conditions  normally  contained in an agreement for a stock
exchange and shall  provide,  among other things,  the terms and  conditions set
forth in subparagraphs (i), (iv), (v) and (vi) above and following:

(aa) Standard  representations  and warranties  regarding ESI's,  Parent's,  and
ADA's  financial  conditions,  operations,  assets and  liabilities  and capital
stock;

(bb) Covenants by the parties that the transactions shall comply with applicable
law;

(cc) In the event  that ESI does not  exercise  the  Option,  ADA shall have the
option to repurchase  all of the  membership  interest in ADA owned by ESI for a
purchase  price equal to $900,000 plus any amount paid by ESI on the Note,  such
price to be payable over a three year period in equal monthly  installments with
interest at a compound rate of 8% per annum. Upon exercise of such option by ADA
the Note shall be canceled.

(dd) In the event that ESI shall default on any payments on the Note, the Option
shall automatically terminate and ADA shall have the option to repurchase all of
the  membership  interest  in ADA  owned by ESI for a  purchase  price  equal to
$900,000 plus any amounts paid by ESI on the Note, such price to be payable over
a three year period in equal  monthly  installments  with interest at a compound
rate of 8% per  annum.  Upon  exercise  of such  option by ADA the Note shall be
canceled.

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<PAGE>


(ee) Satisfactory  registration  rights provisions  applicable to the Shares and
the resale thereof by the Parent Shareholders.

(ff) ESI will maintain covenants to continue listing of Common Stock on NASDAQ.

3. Cooperation.
---------------

     The parties to this Letter of Intent  recognize  that open  disclosure  and
cooperation  are essential to consummate the several  transactions  contemplated
hereby,  and each party hereby commits to use its best efforts to accomplish the
goals agreed upon herein.  Any cost incurred by any party during the period from
the date of signing  this Letter of Intent  until the Closing  Date shall be for
that party's own account. Prior to the expiration of the Option, the ADA Parties
shall not permit any issue or transfer of any equity  interest in ADA or Parent,
except as contemplated herein.

4. Press Release.
   -------------

     The parties agree to issue,  as soon as practical,  a joint press  release,
substantially  in the form of the attached Exhibit A, to announce the agreements
made herein.

5.  This Letter of Intent shall be binding on all parties hereto.
--  -------------------------------------------------------------


     IN WITNESS WHEREOF,  the parties hereto have executed this Letter of Intent
as of the day and year hereinabove first written.

 Earth Sciences, Inc.


By:_/s/ Mark H. McKinnies
    ---------------------------------
    Mark H. McKinnies, its President


ADA Environmental Solutions, LLC

By:_/s/ Michael D. Durham                 By:  /s/ Judith A. Armstrong
   ----------------------------------          --------------------------------
Michael D. Durham, its Manager                 Judith A. Armstrong
                                           President, ADA Technologies, Inc.

ADA-ES, Inc.

By:_/s/ Judith A. Armstrong               By:  /s/ Kenneth E.Baldrey
   -----------------------------------         --------------------------------
Judith A. Armstrong,                         Kenneth E. Baldrey, 2% Shareholder
President, ADA Technologies, Inc.
 80% Shareholder


By:_/s/C. Jean Bustard                     By:  /s/Cameron E. Martin
   ------------------------------------        --------------------------------
     C. Jean Bustard, 6% Shareholder         Cameron E. Martin,  1% Shareholder


By:__/s/ John F. Wurster
   -------------------------------------
     John F. Wurster, 11% Shareholder

                                                                    
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