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REPORT ON THE GEOELECTRICAL DETECTION OF SURFACTANT ENHANCED AQUIFER REMEDIATION OF PCE: PROPERTY CHANGES IN AQUEOUS SOLUTIONS DUE TO SURFACTANT TREATMENT OF PERCHLOROETHYLENE: IMPLICATIONS TO GEOPHYSICAL MEASUREMENTS
Citation:
WERKEMA, D. D. REPORT ON THE GEOELECTRICAL DETECTION OF SURFACTANT ENHANCED AQUIFER REMEDIATION OF PCE: PROPERTY CHANGES IN AQUEOUS SOLUTIONS DUE TO SURFACTANT TREATMENT OF PERCHLOROETHYLENE: IMPLICATIONS TO GEOPHYSICAL MEASUREMENTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-08/031, 2008.
Impact/Purpose:
Land Preservation and Restoration - by providing improved scientific knowledge and developing and applying more cost effective tools, models and methods to inform decisions on land restoration.The remediation of tetrachloroethene (commonly called perchloroethylene, or PCE) in the near subsurface is generally accomplished using various technologies including: oxidation, thermal heating, pump-and-treat, solvent/co-solvent flushing, surfactant-enhanced aquifer remediation (SEAR), and biologically mediated degradation. The selected remediation method(s) must be effective either individually, or in combination, in degrading the PCE to achieve acceptable health levels. The above remediation methods were evaluated to investigate the physical property changes which may occur during their use in the remediation of PCE. The evaluation was made with the intent to understand the implications of these changes to the geophysical response. Understanding and predicting the geophysical response due to the remediation of PCE has widespread implications to reduce clean up monitoring costs, measure the effectiveness of remediation methods, and increase the overall efficiency of ground water remediation efforts. Through non-invasive and minimally invasive surface geophysical methods, the remediation and clean up of a contaminated site can be mapped and monitored. Therefore, using this criterion, the remediation method should be effective at reducing the PCE concentration, yet be only mildly reactive with the subsurface so as not to mask or overwhelm any potential geophysical measurement method.
Description:
Select physicochemical properties of nine surfactants which are conventionally used in the remediation of perchloroethylene (PCE, a.k.a. tetrachloroethene) were evaluated with varying concentrations of PCE and indicator dyes in aqueous solutions using a response surface quadratic design model of experiment. Stat-Ease Design Expert v7 was used to generate the experimental design and perform the analysis. Two hundred forty experiments were performed using PCE as a numerical factor (coded A) from 0 to 200 parts per million (ppm), dye type (coded B) as a 3-level categorical nominal factor, and surfactant type (coded C) as a 10-level categorical nominal factor. Five responses were measured: temperature (oC), pH, conductivity (μS/cm), dissolved oxygen (DO, mg/L), and density (g/mL). Diagnostics proved a normally distributed predictable response for all of the measured responses except pH. The result from the Box-Cox plot for transforms recommended a power transform for the conductivity response with lambda (λ) = 0.50, and for the DO response with, λ = 2.2. The overall mean of the temperature response proved to be a better predictor than the linear model. The conductivity response is best fitted with a linear model using significant coded factors B and C. The DO model is also linear with coded factors A, B, and C significant. The model for the density response is a two factor interaction (2FI) model with significant coded factors C and AC. Some of the surfactant treatments of PCE significantly alter the conductivity, DO, and density of the aqueous solution. However, the magnitude of the density response is so small that it does not exceed the instrument tolerance. Results for the conductivity and DO responses provide predictive models for the surfactant treatment of PCE and may be useful in determining the potential for geophysically monitoring surfactant enhanced aquifer remediation (SEAR) of PCE. As the aqueous physical properties change due to surfactant remediation efforts, so will the properties of the subsurface pore water, all of which are influential factors in geophysical measurements. Geoelectrical methods are potentially the best suited to measure SEAR alterations in the subsurface because the conductivity of the pore fluid has the largest relative change. This research has provided predictive models for alterations in the physicochemical properties of the pore fluid to SEAR of PCE. Future investigations should address the contribution of the solid matrix in the subsurface and the solid-fluid interaction during SEAR of PCE contamination.