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Exhibit 10.36.1

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Northest Utilities Service Company

000 Xxxxxx Xxxxxx, Xxxxxx, XX 00000

P. O. Xxx 000

Xxxxxxxx, XX 00000-0000

Tel: (000) 000-0000

Fax: (000) 000-0000

Xxxx Xxxxx

March 1, 2006

Xxxxxx Xxxxxx

Ameresco, Inc.

000 Xxxxx Xxxxxx

Xxxxx 000

Xxxxxxxxxxx, XX 00000

Re:

Stock Purchase Agreement, dated February 1, 2006, between Select Energy Services, Inc. and Ameresco, Inc. (SPA)

Dear Xxxxxx:

Section 10.01(d)(i) of the SPA provides the right for either party to the agreement to terminate if the Closing has not occurred by March 3, 2006 (30 days). Based upon the current direction of our refinancing efforts, we believe it makes sense for the right to terminate under this section to be extended for an additional 30 days. In other words, neither party would have the right to terminate under Section 10.01(d)(i) of the SPA until 60 days has lapsed from the date of the agreement. If you agree, please have. an appropriate representative from your organization execute the letter. If you have any questions, please don't: hesitate to contact me.

Sincerely yours,

/s/ Xxxx Xxxxx

Xxxx Xxxxx

Director of Accounting, NUEI

Agreed and accepted by:

/s/ Xxxxxx X. Xxxxxx

Name:  Xxxxxx X. Xxxxxx

Title:  VP/CFO

cc:

Xxx Xxxxxxx, FMI

Xxxxx Xxxxx, NU

Xxxx Xxxxxx, DBH