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II <br />II <br />II <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br />City of Gree(uy <br />24 January 2002 <br />Page 3 <br />1. Evacuate water in the gravel pit ponds using portable high capacity discharge pumps and <br />discharge the water into at the 35" Avenue Stonmvater Ditch along 35" Avenue and b) <br />the remaining ditch segment ahrng the east edge of the gravel pit. Desvatering ditches and <br />sumps may be constructed to assist in the water removal. <br />2. Install two precipitation gauges. <br />3. install tour pairs of monitoring wells on the north, east, south and west sides of the gravel <br />pit. For each well pair, one well will be located on the inside of [he completed slurry <br />wall and the other well will be located on the outside of the slurry wall. Each well will be <br />installed to bedrock. A minimum of 10 fr of well screen will be installed at the bottom of <br />the well. <br />4. Instal! a shallow perimeter dewatering trench (i.e. 2 ft ro 4 f[) with a sump area to collect <br />drainage in each of the ponds, ensuring that water flows unrestricted to each sump. The <br />fins! sump location and the depth of the trench will be determined after surface water has <br />been completety evacuated. <br />5. Pump each sump until groundwater monitoring welts demonstrate that steady-state <br />conditions exist. <br />6. Once steady state conditions have been achieved, pump each sump for 90 days and retard <br />the total volume of water pumped from each sump ushtg totalizers installed at the <br />discharge points far each pump. Monitoring will be performed daily by trained personnel <br />from the City with oversight provided by Haley & Aldrich. <br />7. Determine effective precipitation inflow into the reservoir by performing daily <br />precipitation measurements at each rain gauge. Measurements shat! be performed as <br />needed by trained personnel with oversight provided by Haley & Aldrich. <br />$. Determine the seepage of groundwater by taking the rata! volume of water removed <br />during the 40-day period and subtracting out the calculated volume of water intlow due to <br />effective precipitation within the lined area. <br />9. Estimate the seepage of groundwater into the lined area for a completely dewatered <br />condition by calculating the seepage using the seepage data obtained in step 8. An <br />example calculation has been auached. <br />Assuming a perimeter length of 8,450 feet with an average vertical depth of 55 feet, and a <br />bottom urea of 74.4 acres, the rota( calculated inflow, based an a completely dewatered pit <br />and the total allowable intlow from groundwater seepage during the 90-day tes[ for each of <br />the standards were calculated (attached}, assuming the tined area is complerely dewatered. <br />tiate: epm indicates gallons per minu[e <br />