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------------- Site Chamacrization and Sc -, mediation Plan: 7500 ff e,st Eleventh Street, Traci Page 12 no analytes of concern affect the soil and groundwater. However, to define adequately the lateral extent of the plume, these points should be within a reasonable distance beyond the fringe of the plume. To effect this optimal lE location of exploration points, probing locations selected early in the investigation will be located at points that are judged to be beyond the limit of the plume. Additional exploration points will then be selected at points closer to the periphery of the plume until its geometry is adequately defined. Beck the investigation in these areas will be primarily concerned with the detection 3 of analytes in groundwater, a groundwater sample will be re_covered using a hydro-punch at essentially all of those points of exploration. Other exploration points in the interior of the plume, such as in the vicinity of the tank and dispenser pits on the 7500 West Eleventh Street property, will then be investigated to provide information on the vertical extent of the zone of subsurface affected by hydrocarbons and the concentrations of the analytes of concern in soil and groundwater at those locations. Where practicable, it is intended to drive soil probes with continuous transparent core liners through the full depth of the zone of hydrocarbon- affected soil at essentially all exploration points This will permit the probe or hydro-punch holes to be logged by a geotechnical engineer and used to develop _ a model of the hydrostratigraphy of the site. This information will*Provide a basis for development of a more complete understanding of the three- dimensional characteristics of the hydrocarbon plume and will aid the optimal selection of groundwater-monitoring well sites. (Note- it is recognized that it may not be practicable to drive probes or hydro-punches through the full depth of affected soil, particularly in the most heavily-affected areas around the tank and dispenser pits. However, as will be discussed later, groundwater-quality monitoring wells will be installed in these and other areas using open-stem auger drilling techniques capable of penetrating to any required depth that can be anticipated-) "4 The geotechnical engineer responsible for the field work will use visual and olfactory indicators of the presence of hydrocarbons in the soil cores as an initial screening for the presence and distribution of analytes of concern in the soil at each explored location The engineer will also use those indicators to select samples of the cores for laboratory analysis. (N.B. To avoid unnecessary analytical costs, analyses will not be performed on some cores from some exploration points in cases where analyses of samples from other exploration !_>f points would provide the information necessary to meet the objectives of the investigative work.) To prepare core samples for analysis, the cores will be retained in their plastic core tubes and their ends will be closed with plastic caps secured by adhesiveless tape. The core samples will then be labeled for identification and placed in a cooler on chemical ice for transportation within 24 hours to a sic