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Corrective Action Plan Page 19 pumped well is equal to the gradient of the undisturbed groundwater flow away from the s well before pumping from the well begins, then, at the northern (i a down gradient) perimeter of the effective zone of influence of the pumped well, the gradient of the water table should be - 0 003 f1/ft In other words, the effective radius of influence of one of the proposed recovery well can be defined by the most distant down-gradient point at which ipumping from the well for a specified period (two weeks in this case considered here) produces a net change of 0 006 ft/ft in the groundwater gradient Entering this value for ds/dr into Eq 2 and solving for r yields a minimum radius of influence of 553 ft for the zone of influence of any one of the proposed groundwater recovery wells after it has been pumped at a steady rate of 10 gpm for two weeks (14 days) Although the derivation of the above estimate of the radius of influence of one of the proposed groundwater recovery wells required several simplifying assumptions, it is conservative and demonstrates that the proposed recovery well array will have a large area of influence that will be more than sufficient to produce hydraulic containment of the contaminated groundwater Furthermore, when all three recovery wells are pumped, the combined effect will produce greater drawdown at a given point and produce a larger area of influence than that produced by pumping from a single well as was assumed when making the estimate Soil Flushing and Cyclical Groundwater Pumping As discussed above, the proposed rates of pumping from the recovery wells will produce an extensive drawdown cone in the water table Within this zone of influence, hydraulic gradients will be steeply inclined toward the wells The resulting high groundwater flux ' will rapidly draw dissolved contaminants to the wells from both the near and far fields As it moves through the subsurface, this water flow will also flush hydrocarbons from the ' affected soils During the period immediately following the start of pumping there will be vigorous soil flushing action in the near field of the recovery wells where the hydraulic gradients and groundwater flux will be very high However, continuous steady pumping will draw down the water table in the near field of the wells so that it will be locally below the depth where ' the soil is most severely affected by contaminants The estimated drawn-down elevation of the groundwater table after steady pumping from the recovery well for a period of two weeks is shown on Figures 7 and 8 Under these conditions, the rate of remediation of the ' near-field soils will be inhibited Experience has shown that remediation of soil and groundwater is accelerated when the ' rate at which groundwater is recovered from an affected area is changed periodically compared to the rate of remediation achieved by steady pumping Each time that the pumping rate is changed, the groundwater level rises or falls and flushes contaminated soil ' in the zone around the water table This action is particularly beneficial in the near field of the wells where, during each drawdown cycle, water moves forcefully through the most severely affected soil and high flushing rates are achieved Periodic rises and falls of the