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Mr. Harlan K.nol' R.E.H.S. <br />November 29, 2005 <br />Page 2 <br />1.0 Lateral and Vertical Extent of the Soil Contamination <br />The current lateral and vertical extent of the soil contamination will be evaluated by collecting <br />soil samples for analysis from around the former tank location and from between the former tank <br />location and the enclosure to the Thornton Municipal Well. Soil samples will be collected using <br />a GeoprobeTm drive sampler commencing from a depth of four feet and continuing to the depth <br />of first encountered groundwater. The approximate positions of twelve anticipated GeoprobeTm <br />soil sample locations are shown on Figure 3. <br />2.0 Lateral and Vertical Extent of the Groundwater Contamination <br />The lateral and vertical extent of the groundwater contamination will be evaluated through <br />collection and analysis of grab groundwater samples from the twelve GeoprobeTm holes and <br />through the installation of deeper monitoring wells adjacent to three of the existing shallow <br />monitoring wells. <br />Existing monitoring wells are screened from approximately 10 to 30 feet below ground surface <br />and the proposed deeper monitoring wells will be screened from approximately 30 to 40 feet <br />below ground surface, depending on the stratigraphic section encountered. The three proposed <br />deeper monitoring wells will be paired with existing monitoring wells MW -1, MW -2, and MW - <br />4. These new wells will be included in the quarterly groundwater monitoring program. <br />The three proposed deeper monitoring wells and the existing shallower monitoring wells will be <br />surveyed for potentiometric surface evaluation and so that the information can be uploaded to the <br />Geotracker GeoX, GeoY, and GeoZ database. <br />3.0 Assessing Performing Groundwater Extraction from Monitoring Wells MW3 and MW4 <br />As a preliminary step for an evaluation for performing groundwater extraction from monitoring <br />wells MW -3 and MW -4 the potentiometric surface response to the pumping regime of Thornton <br />Municipal Supply Well No. 2 will be assessed through measuring the water levels in monitoring <br />wells MW -1, MW -2, and MW -4 every 20 minutes for a five day period. The potentiometric <br />surface response monitoring will be conducted prior to the installation of the proposed deeper <br />monitoring wells. These data will be presented as hydrographs and as a graph depicting <br />variations in gradient direction. <br />MW -3 is near the center of the triangle formed by monitoring wells MW -1, MW -2, and MW -4 <br />and is adjacent to the former excavation boundary. The monitoring wells were installed in 1990 <br />and the former excavation occurred in 1996. The presence of monitoring well MW -3 may have <br />defined the northwestern extent of that excavation and may have limited soil removal in that <br />i I2OGEOL A GROUNDWATER CONSULTANCY <br />