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' r <br /> Geological Technics Inc. • Page 4 <br /> Sinclair Trucking <br /> Report-Subsurface Investigation <br /> t Project No.320.2 <br /> r <br /> July 21,1999 <br /> ' 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> Conclusions <br /> ' Geological Technics Inc. concludes that: <br /> 1. Some residual contamination of BTEX and TPH-G are present in the soil and <br /> groundwater. <br /> ' 2. Only the 12-16 foot sand unit shows significantly elevated levels of BTEX and TPH-G. <br /> 3. Only MW-1 (source) and MW-4 (down gradient) exhibit concentrations of BTEX & <br /> TPH-G. Thus demonstrating that the groundwater gradient transports these contaminants <br /> ' to the NE, away from the nearest sensitive receptor (i.e., the domestic well in the subject <br /> 4. Tro ert <br /> he The BTEX and TPH-G appear not to pose a threat to public health of the <br /> environment. <br /> tRecommendations <br /> Geological Technics Inc. makes the following recommends: <br /> ' 1. Two more groundwater monitoring events should be performed, one this summer and one <br /> this fall. <br /> 2. Both of these monitoring events should include the following analysis: <br /> ■ BTEX by method 8020 <br /> ■ TPH-G by method 8415m <br /> ■ Selected natural attenuation parameters listed below to determine if biodegradation is <br /> actually attenuating this contamination. <br /> I. Total Alkalinity (T Alk) <br /> 2. Iron (Fe) <br /> 3. Nitrate (N0) <br /> 4. Sulfate (SO4) <br /> 5. Dissolved Oxygen (DO) <br /> 6. Oxidation-Reduction Potential (ORP) <br /> ' The following table gives general characteristics of background conditions compared to <br /> conditions inside the plume at two stages of evolution. <br /> ' Parameter Source of Me Background Plume Behavior Plume Behavior <br /> Parameter Core Margins <br /> ' <br /> Dissolved Oxygen' aAcceptor Positive a ue Deplete Mildly ep ete <br /> urate e Acceptor Site pets is Depe-E of ep ete <br /> Ferrous lronj Metabolic Byproduct Site petsis nric a of Enriched <br /> Suff ate a cceptor Site Specific 0 e_pFet-e-ff Mildly ep ete <br />' <br /> Methane" eta o isypro uct Very Low �ilig t Enriched <br /> Temperaturej MetaBolic ypro uct Site peri tcevate ig t Elevated <br /> p eta a isypro uct rte peci tc evateUnaffected— <br /> Alkalinity <br /> Metabolic ypro uct ite pect is EnricFe Unaffected— <br /> Redox Potential Metabolic ypro uct Positive a ue Depleted Slightly-Eo—Wer <br /> Conductivity Metabolic byproduct ate pets is Lowered Unaffecte-T— <br /> Hydrogen' a Acceptor Non Detect Elevnte "light evate <br /> 1 <br />