January 16, 1990

BY HAND

Leslie McVickar Silresim Remedial Project ManagerUnited States Environmental

Protection Agency90 Canal Street Boston, Massachusetts 02150

Re: Silresim DNAPL Investigation

Dear Leslie:

In your letter of December 21, 1989, you provided a more detailed outline of the 'elements and objectives of an investigation and trgatability study for dense non-aqueousphase liquids (•DNAPL•) in the shallow and medium overburden at the Silresim Superfund Site. As set forth in your letter, EPA has requested the Silresim Site Trust to undertake this work in connection with our RI/FS for the Site.

In order to evaluate the EPA request, the Trust has conferred with GZA, our RI/FS consultant, and with Dr. John Cherry, a leading authority on the effects and cleanup of DNAPL contamination. As a result of these discussions and after consultation with the Silresim Site Ezecutive Committee, we wish to convey our willingness to undertake some of the activities outlined in your letter and our desire to defer certain other tasks at this time.

Our approach is based on our understanding that existingtechnologies for DNAPL removal other than pumping and treatingof groundwater are likely to be inappropriate and unproductive at the Silresim Site. In order to determine whether this is indeed correct, we wish to conduct a literature review to assess the efficacy of DNAPL removal meaaures at other sites. We also intend to measure certain characteristics and para tera of DRAPL contaminated groundwater samples alreadycoll ct d at the Silresim Site, such as density, viscosity, and surface tension, and to reasses otb r existing site data to d t rmin the efficacy of employing particular DNAPL removal

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Leslie McVickar Page 2 January 16, 1990

technologies at the Site. Within the next few weeks, Dr. Cherry and GZA representatives expect to discuss specificelements of this study effort with you and the EPA technical staff.

While this work is being carried out, w~ wish to defer Site investigation -in the shallow and medium overburden. Uponcompletion of our DNAPL removal· study, we will be better able to assess whether such a field study is warranted.

Beca~se we expect that pumping and treating of groundwaterwill be necessary regardless of the outcome of the DNAPL · removal study, we intend to install the three deep bedrock wells and the confirmatory borings referenced in paragraph B, page 1, of your December 21 letter. This will ensure that we have adequate knowledge of on-site groundwater migration at all levels, including the deep bedrock. We will of course consult with you and your staff regarding the exact location of these wells.

We hope that the foregoing discussion is responsive to all matters raised in your December 21 letter. With respect to the FS-2 deliverable mentioned on the first page of your letter, we await receipt of your comments and will respond to them as quickly as possible. Please contact me if you have any comments or further questions.

Sincerely yours,'-....../ .

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DP-0088/S