Evaluating the Effectiveness of Ground Water Extraction Systems

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Abstract
The most common process for remediating contaminated ground water is extraction and treatment. Data from 19 on‐going and completed ground water extraction systems were collected and analyzed (U.S. EPA 1989b) to evaluate the effectiveness of this process in achieving cleanup concentration goals for ground water. This analysis indicated several trends including (1) containment of ground water plumes was usually achieved; (2) contaminant concentrations dropped significantly initially followed by a leveling out; (3) after the period of initial rapid decline, the continued decreases in concentration were usually slower than anticipated; and (4) certain data important to optimizing system design and operation had often not been collected during the site characterization phase.Factors limiting the achievement of cleanup concentration goals fell into four basic categories: (1) hydrogeological factors, such as subsurface heterogeneity, low‐permeability units, and presence of fractures; (2) contaminant‐related factors, such as high sorption to soil and presence of non‐aqueous phases (dissolution from a separate non‐aqueous phase or partitioning of contaminants from the residual non‐aqueous phase); (3) continued migration from source areas and the size of the plume itself; and (4) system design factors, such as pumping rates, screened intervals, and extraction well locations.The findings of this study indicate that ground water extraction is an effective method for preventing additional migration of contaminant plumes and achieving risk reduction. However, the findings indicate that in many situations, it may not be practicable to rely solely on ground water extraction and treatment to achieve health‐based cleanup concentrations throughout the contaminated zone and fulfill the primary goal of returning ground water to beneficial use.This study suggests several recommendations (U.S. EPA 1989a) for improving ground water response actions including (1) actions to contain contaminant plumes should be initiated early; (2) data on vertical variation of hydraulic conductivity, distribution of the contaminant mass, and partitioning of contaminants to soil or a stationary phase in the saturated zone should generally be collected as part of the site characterization process; (3) remedial actions should be implemented in stages to better utilize information on aquifer response as the system is being designed and implemented; (4) remedial actions should be monitored and modified during operation to optimize system efficiency; and (5) methods to enhance extraction effectiveness and efficiency should be considered.

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