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Corrective Action Plan Page 21 ' Temporal fluctuations in the concentration of contaminants in the recovered water can also be induced by seasonal variations in the groundwater table elevation and by changes in drawdown in the recovery wells which influences the volume and distribution of contaminated soil that comes into contact with the water being drawn toward the wells However, as the recovery system continues to operate and contaminated water is purged ' from the most severely affected areas in the near field of the well, the overall trend is for the magnitudes of the temporal peaks in contaminant concentrations to decline To provide a basis for design of the groundwater treatment system, the results of analyses of samples recovered from monitoring wells NAV 3, NAV, 4 and ULT 9 in the period January 1993 to February 1994 were reviewed (see Table 3 for data base) These monitoring wells are located in the most contaminated region of the site and are closest to the proposed recovery wells (see Figure 6 for locations) To estimate the mean concentrations of contaminants in the influent to the treatment system in the period following startup, the arithmetic mean of the concentrations of total petroleum hydrocarbons (quantified as gasoline), toluene, benzene, total xylenes and ethyl benzene detected in all samples recover from each of the cited monitoring wells during the review period was computed These values have been designated as the Mean Maximum Concentrations and apply to the condition when all three of the recovery wells are being pumped at the same rate To estimate the highest concentration of a given contaminant that nught be present in the influent stream to the treatment system under any foreseeable condition, the situation of pumping from a single recovery well drawing water containing contaminant concentrations equal to the highest ever recorded in any groundwater sample that has been recovered from the site was considered Under this extreme condition, there would be no dilution of locally high concentrations of contaminants by mixing with water pumped from other wells where the concentration of the subject contaminant might be lower This study yielded extreme, upper-bound values for contaminant concentration in the influent stream to the groundwater treatment system These hypothetical parameters have been designated ' as Peak Temporal Concentrations The results of the calculations described above are presented in the table below Analyte Mean Maximum Peak Temporal Concentration Concentration mg/Liter (ppm) mg/Liter (ppm) TPH (as gasoline) 53 25 ' Benzene 01 02 Toluene 02 14 Total Xylenes 1 3 73