A METHOD TO DETERMINE PUMPING RATE AND TIME FROM FIELD TEST DATA FOR EFFECTIVE GROUNDWATER REMEDIATION BY PUMP-AND-TREAT METHOD

Abstract

When planning a groundwater remediation by the pump-and-treat method, the location and number of pumping wells should be determined by taking pumping time and pumping rate into account. A relationship between the critical operating efficiency and the design of the pump-and-treat remediation was derived through analysis of data from eight radial convergent tracer tests. A relation between the capture zone and the radius of influence (ROIs) was deduced in this study. The pumping time for critical removal of dissolved contaminants through repetitive pumping and resting was evaluated at test sites for varying Péclet number. Results suggested that critical removal increased, and the critical pumping time needed for critical removal to occur was found to increase with the Péclet number. A relationship between the critical removal and the critical pumping time based on the Péclet number was derived. Although the maximum reasonable cumulative removal of dissolved contaminants can be determined during actual operations at a site, a preliminary estimation is possible using the derived relationship between the Péclet number and critical removal if the Péclet number for the site is known during the design and planning stage. Critical removal can vary with site, but it is desirable to set a target removal rate of <50% regardless of how high the Péclet number is. Based on the determined pumping rate and the Péclet number of the site, the required pumping time can be estimated through the critical pumping time curves derived in this study. This study also analyzed the capture zone of a pumping well and its relationship with the radius of influence (ROIs), which is defined as the distance from a well where the drawdown s occurs. The Cooper-Jacob equation (1946) and the Theis equation (1935) were used to develop a method for determining the pumping rate required to encompass the ROIs required for groundwater remediation. Results show that the pumping rate is directly proportional to ROIs and that the drawdown criteria s, which determines the ROIs is inversely proportional to the Ti value (transmissivity × hydraulic gradient). By applying the ROIs according to pumping rates (ROIs-Q relation curve) at Site 1, 2 and 3, the pumping rates related to the required ROIs can be derived. By investigating the Ti value and the drawdown by pumping are investigated at particular sites while planning pump-and-treat remediation, the results can be used to evaluate the necessary drawdown criterion through the relationship between the drawdown criterion s and Ti (s-Ti relation curve), as shown in this study, and then the ROIs can be determined according to the pumping rate. The method proposed in this study can be applied before actual operating at the design stage. The critical pumping time and pumping rate should be adjusted according to results obtained in the field during operation.