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Corrective Action Pian Page 17 of contaminated groundwater while maintaiiung the total flow rate to the treatment system within its rated capacity To check that the proposed groundwater pumping rate will be sufficient to recover contaminated water from throughout the area affected by contamination without excessively drawing down the water table, the following estimates of water table drawdown and radius of influence of the groundwater recovery wells have been made Drawdown. To prevent the submersible pumps running in air and overheating, the water level in a recovery well must not be drawn down to such a level that there is less than 2 ft of water above the top of the pump Refemng to Figure 9, and allowing for the 3 ft sand trap at the bottom of the casing and a pump with a body length of 2 ft, this limitation restricts pumping from an individual well to a rate that will produce a maximum drawdown of 11 ft (i a under maximum drawdown the water level in the well casing would be 18 ft below the ground surface) During groundwater pumping tests conducted at the site in January 1994 (Ref 11), pumping from a well of similar depth and screened over a similar interval to the proposed recovery wells lowered the water level in the well casing by 4 45 ft within one minute after start of pumping at a steady rate of 9 5 gpm The logarithmic slope of the time- drawdown plot, As, was 0 58 Applying the proportionality rules for the relationships between pumping rate and drawdown and As (Ref 3), for a 10 gpm pumping rate the drawdown after 1 nun would be 4 68 ft and the adjusted value of As would be 0 61 Applying the figures given above to the case of pumping from a single well yields an ' estimated drawdown of 8 16 ft at the proposed normative pumping rate of 10 gpm after steady pumping for one year This is well within the 11 ft lirrutation that has been set to protect the pumps and allows a margin of safety for the drawdown that will actually occur when all three wells are pumped simultaneously Maximum Singlc-well Pumping Rate- Using the same methods of estimation, if a single well was pumped at a steady rate of 15 gpm the water level in the casing would be drawn down 11 ft (i a to 18 ft beneath the ground surface - the limn established to protect the pumps) after approximately two weeks (14 days) Based on this estimate, the maximum sustained rate of groundwater extraction under conditions when water is pumped from any one of the three proposed recovery wells has been set at 15 gpm If desired, single-well, pumping rates greater than 15 gpm could actually be sustained for periods up to several days without drawing down the water level in the casing to a depth greater than 18 ft beneath the ground surface Also, even if that limit were reached, the pumps would not actually be damaged because, as described later, their action will be controlled by signals from level sensors installed in the well so that they will be energized and de-energized as water levels rise and fall above and below preset limits However, in general, such a mode of operation will be avoided because it would cause excessive on-off cycling of the groundwater extraction and treatment system