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PROPERTY CHANGES IN AQUEOUS SOLUTIONS DUE TO SURFACTANT TREATMENT OF PCE: IMPLICATIONS TO GEOPHYSICAL MEASUREMENTS
Citation:
WERKEMA, D. D. PROPERTY CHANGES IN AQUEOUS SOLUTIONS DUE TO SURFACTANT TREATMENT OF PCE: IMPLICATIONS TO GEOPHYSICAL MEASUREMENTS. Presented at American Geophysical Union Fall 2007 Meeting, San Francisco, CA, December 10 - 14, 2007.
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.
Description:
Select physicochemical properties of aqueous solutions composed of surfactants, dye, and
perchloroethylene (PCE) were evaluated through a response surface quadratic design
model of experiment. Nine surfactants, which are conventionally used in the
remediation of PCE, were evaluated with varying concentrations of PCE and indicator
dyes in aqueous solutions. 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 factor, and surfactant type (coded C) as a 10-level categorical
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 measured responses except pH. The Box-Cox plot
for transforms recommended a power transform for the conductivity response with
lambda (ë) = 0.50, and for the DO response, ë=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 terms B and C. Both DO and
density also showed a linear model with coded terms A, B, and C for DO; and terms A
and C for density. 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
physicochemical properties change due to surfactant remediation efforts, so will the
properties of the subsurface pore water 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.