SITE INFORMATION AND CORRESPONDENCE

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04/23/2003 15:41 209$9251 WRIGHT ENVIRONMEN- PAGE 05 11--.� SWOO Task 4-WX Evaluation Report and Ground Water Pumping Test Workplan. Wright will prep= a report and workplan that describes the following: (1) The concepti ial site model and evaluation of MMs performed in Tasks 1 and 2; and, (2) ,A,workplan for perf.5rmi% and evaluating the ground water pumping test_ The work plait will describe test objectives such as establishing the aquifer parameters !needed for evaluating ground water extraction fewibility. We will desmbe the design of the test to be used, e.g. a 24€hour pumping test, nua ber of observation wells, location of observation wells, well construction details, test and sampling protocol, proposed data analysis method, and treatment/disposition of produced ground water. Wright will submit a draft copy of the report to PHS EHD for review prior to submission of a finalized copy to PHS EBD. Tasks 2, 3 and 4 noted above respectively will be used to develop remediation plans far site cleanup. Preliminary discussions between Ramage and PHS EHD indicate that options wer W open for site cleanup that could include groundwater pumping or ozone injection. At this tir.:w, the remediation approach has not been finalized until the additional plume definition is complete=d. Technical Approach(Task 1.) Four monitoring wells will be placed under approved PHS EHD permits at the locations shown on Figure 1. These wells will be placed in either public right-of-ways or private land where access agreements can be arranged. The technical approach is to perform the additional site asses.gment, install monitoring wells, and collect data to assist its developing interim and long-term cleanup plans for the site_ CPT logs and sampling showed that contaminants were present at the 60-foot, 115--foot depths, but not at the 130-foot depth. 4n the basis of the CPT data, aquifer zones below 50-feet .ippew located at about 60 Beet and 115 and 130 feet. Contaminants were present in the 60 foot a,id 115 foot depth but not at the 130-foot depth. Thin silt and clay strata may act as aquitards been the 50-foot and 60-65 foot depths, however the GPT logs show some vertical leakage'might occur on the basis of individual stratum tbckness. The deeper aquifer zone at 115 feet is separated by a sequence of silt and clay strata. These wells will require placing discrete screened intervals in the aqu er zone of interes,. We propose to screen five-foot screen lengths in the wells at the 58-63-foot depth and at the 111-119- foot depth based upon our review of the cross sections prepared by Ramage Environmen-ai and from the CPT log data. The drilling and well installation process will need to limit the paential for cross contamination and possible cornmunication in boreholes drilled for the wells. Page 3 Of 3