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Z�.liaul#709-50 Rcm,,hal Fl,"SillilityT`em Repo,,t 131.ars I:c�'irinr�irntal Ee}�3�aar-�-23,_0f 4.4.1 Biofeasibility Laboratory Results Soil samples were analyzed for two types of bacteria: heterotrophic microbes (those that utilize only organic carbon substrates and generally comprise the great majority of bacteria) and hydrocarbon degrading heterotrophs (the bacteria that are most useful for the bioremediation of organic r' contaminants). Depending on various environmental conditions, bacterial density can vary from less than 10 colony forming units per gram(CFU/g) to 109 CFU/g. As a general rule petroleum hydrocarbon , degrading bacteria should comprise at least 10 percent of the total heterotrophic bacteria in soil � considered for bioremediation. Hydrocarbon utilizing bacteria were not detected in the soil samples collected at depths of 30 and 50 feet bgs. Additionally, the heterotrophic plate count was non detect in Ir the sample collected at 50 feet bgs and quite low in the sample collected at 30 feet bgs (200 CFU/g). } Soil samples were also analyzed for pH, iron, and nutrients. A soil pH near neutrality (6.0 to 8.5) is desired for optimal microbial growth under typical soil conditions. The pH values for the samples p^� collected at 30 and 50 feet bgs were 8.37 and 8.20, respectively. These values, although slightly high, E � are still within the range that would promote a maximum rate of growth for microbes. However, the high concentration of extractable iron (23,000 mg/kg at 30 feet bgs and 19,000 mg/kg at 50 feet bgs) may s suggest that dissolution of heavy metals from the soil particles under acidic conditions could inhibit bacterial growth. t The major nutritional factors that are essential compounds of importance for microbial nutrition in bioremediation are Nitrogen(as ammonia) and Phosphorus (as orthophosphate). Soil laboratory analysis indicated no detectable concentrations of either ammonia nitrogen or orthophosphate. Groundwater laboratory analysis indicated only slight concentrations of orthophosphate (0.30 mg/1) present in the groundwater grab sample collected from monitoring well MW-1C. If bioremediation were to occur, supplemental nutrients would have to be added to support bacterialln'owth. Generally, bacterial degradation can be inhibited when petroleum hydrocarbon concentrations exceed approximately 50,000 mg/kg because of toxicity of the contaminant to bacterial flora. Soil Iaboratory analysis indicated that concentrations of volatile fuel hydrocarbons (gasoline) ranged from 13 mg/kg (at 18