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t <br /> 21 pH and Soil Moisture <br /> The optimal pH for effective bioremediation is in the range of six to eight A pH outside of tins <br /> range may negatively affect microbial metabolism and contaminant biodegradation Results of the <br /> laboratory pH measurements are reported in Table l The pH of soil samples ranged from 7 4 to <br /> 83 Sample SB-1-3B which exhibited the slightly higher pH (8 3), is not high enough to prevent <br /> t bacterial activity <br /> The moisture content values for the soil samples were 14 2, 18 0, and 5 50 percent (weight to <br /> weight) The samples were characterized as sandy silt, silt and sand respectively Moisture <br /> control is critical to successful bioremediation <br /> 2.2 Background Nutrient Concentrations <br /> Nutrients essential for bioremediation are nitrogen, as ammonium, and phosphorous, as ortho- <br /> phosphate The existing nutrient concentrations in all samples are defined initially to determine <br /> the need for nutrient additions Results of the analyses for these inorganic nutrients are shown in <br /> Table 1 The ammonium concentration in the soil samples was below the detection limit This <br /> suggests that the lack of ammonium in the soil samples may limit the rate and effectiveness of <br /> remediation Phosphate concentrations in the soil samples were also low, ranging from 64 7 <br /> mg/kg to 109 mg/kg Nutrient additions are recommended to avoid nutrient limited microbial <br /> activity and biodegradation <br /> 2.3 Microbial Enumerations <br /> In situ treatment requires the presence of hydrocarbon-degrading bacteria To determine if <br /> 1 appropriate bacteria are present, bacteria are quantified according to two categories The first <br /> category includes heterotrophic bacteria, defined as those bacteria capable of growing on dilute, <br /> it <br /> solidified nutrient medium Heterotrophs represent a very general class of bacteria that are <br /> typically abundant in soil and groundwater Quantification of this category provides a measure of <br /> the overall size and vigor of the bacterial population <br /> The second category includes hydrocarbon-degrading bacteria These bacteria are quantified after <br /> growing in an environment where the petroleum hydrocarbons are the only available carbon (or <br /> food) source In this study the petroleum hydrocarbon used as the carbon source was diesel fuel <br /> vanD=,Ber&/14 2 <br />