WORK PLANS - Laserfiche WebLink

Home Browse Search

• Ms. Lori Duncan April 12, 2002 Page 6 Project 880-039.1A One of the major disadvantages of pump -and -treat is that the degree of contaminant removal is highly dependent on the chemical nature of the contaminant and the subsurface geology. Sites where the contaminants are in a mobile, dissolved state and minimal sorption has occurred are ideal for pump -and -treat remediation. The success of the remediation also depends on whether the subsurface hydrogeology is relatively homogeneous or uniform. These conditions are rarely met, and the effectiveness of the pump -and -treat method is questionable when the conditions are not ideal. The difficulties encountered with contaminant chemistry and subsurface geology heterogeneity often increases the cost and time required to achieve remediation goals consistent with regulatory requirements. In addition, pumping groundwater from multiple zones can increase the potential for cross contamination and accelerate vertical migration of contaminants. To establish if groundwater extraction and treatment would be a feasible alternative at this site a step -draw down extraction test is proposed. The step -draw down test will be performed in well MW -4R -S. The test will consist of pumping the well at four successively higher discharge rates of 90 minutes duration for each rate. The proposed discharge rates will be approximately 2, 5, 8, and 10 gallons per minute (gpm). Extracted water will be stored onsite prior to disposal. During these tests, depth to water will be measured in the pumped well at the following elapsed times after the beginning of each step at a minimum: 1, 2, 4, 10, 20, 50, and 90 minutes. At the end of each step, depth to water will also be measured in wells MW -1 R, VW -2 and VW -3. Static water level measurements will be obtained in the test well and the nearest monitoring well within ten minutes before start of pumping. Discharge measurements will be made each time a water level measurement is made in the pumped well. After testing, the pump will be turned off and the aquifer allowed to recover for at least two hours. The data analysis will focus on the relationship between discharge and drawdown, and these results will be presented as a graph to be used by IT in the evaluation of groundwater extraction and treatment feasibility. IT CORPORATION SAC:\\\SACRFP 1 \COMMON\sacDP\2002\PRJ\PJ8\880\8800391 A.2ac.doc (01040000)