Remedial Investigation/recommended action-1995

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� � Sailors World, Inc. Summit Project No. 922030 � October 5, 1995 Page 8 � explosive readings were not detected during the survey. Reportedly, the club house building located on the site does not have a basement. Results of the vapor survey are summarized in � Table 5. - � 4.0 DISCUSSION AND CONCLUSIONS Soil and groundwater conditions at the site vary and fill (sand and clay) appears to be the soil � rype�present from approximately 3 to 8 feet below the ground surface. As discussed above in Section 3.2, soil moisture observations recorded for samples collected at this depth varied considerably based on the probe location and soil type encountered. It appears that the majority N of petroleum impacted soil was removed during excavation activities. Based on GME Consultants, Inc. boring logs, well logs, and data collected using the Geoprobe�, fine-grained soil (clay and silt) is present near the ground surface and predominates to a depth of at least 77 feet. � Because of the extensive clay/silt soil conditions and observations of what appears to be unsaturated soil at depth, vertical migration of dissolved petroleum hydrocarbons would be relatively slow. Movement of groundwater in the horizontal direction appears to be generally � southeast, toward Lake Minnetonka (Figure 3). � Analytical chemistry results for groundwater samples collected from Geoprobe� test probe locations indicated that the concentrations of dissolved petroleum hydrocarbons did not increase during the period of June 1994 to June 1995 and were generally less than the applicable HRLs. Of the fifteen probe locations, only four contained concentrations of benzene above HRLs, with � one of these four being located off site and adjacent to a former gasoline station. Benzene concentrations above HRLs were detected at P-3 (829 ppb), P-4 (224 ppb), P-12 (15 ppb), and P- � � 14 (205 ppb). However, concentrations of benzene detected in groundwater samples collected during this assessment have not exceeded 100 times the HRL and concentrations of toluene, ethylbenzene, xylenes, MTBE, 1,3,5-TMB, and 1,2,4-TMB were not detected above HRLs at the � fifteen probe locations. Also, sheens on the water table or free product have not been observed at the site. � It appears that surface water has not been significantly impacted by the petroleum hydrocarbons •detected on the site. Although groundwater movement appears to be toward Lake Minnetonka, concentrations of petroleum hydrocarbons were not detected in a surface water sample that was Mcollected approximately 20 feet from shore. Based on information collected and reviewed during this project, groundwater �with relatively low concentrations of dissolved-phase hydrocarbons � may seep into Lake Minnetonka. As a conservative estimate, concentrations of dissolved petroleum hydrocazbons in the groundwater as observed at probe location P-14 (benzene, 205 ppb) may be entenng the Lake through groundwater and surface water interaction. However, � considering the relatively low concentrations of dissolved petroleum hydrocarbons, the soil rypes underlying the area, and several processes including photodegradation, volatilization, evaporation, and dilution, future potential impacts to Lake Minnetanka from the reported � �