Pilot-Scale Demonstration of Surfactant-Enhanced PCE Solubilization at the Bachman Road Site. 2. System Operation and Evaluation

Abstract

A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted during the summer of 2000 at the Bachman Road site in Oscoda, MI. Part two of this two-part paper describes results from partitioning and nonpartitioning tracer tests, SEAR operations, and post-treatment monitoring. For this field test, 68 400 L of an aqueous solution of 6% (wt) Tween 80 were injected to recover tetrachloroethene-nonaqueous phase liquid (PCE-DNAPL) from a shallow, unconfined aquifer. Results of a nonreactive tracer test, conducted prior to introducing the surfactant solution, demonstrate target zone sweep and hydraulic control, confirming design-phase model predictions. Partitioning tracer test results suggest PCE-DNAPL saturations of up to 0.74% within the pilot-scale treatment zone, consistent with soil core data collected during site characterization. Analyses of effluent samples taken from the extraction well during SEAR operations indicate that a total of 19 L of PCE and 95% of the injected surfactant were recovered. Post-treatment monitoring indicated that PCE concentrations at many locations within the treated zone were reduced by as much as 2 orders of magnitude from pre-SEAR levels and had not rebounded 450 days after SEAR operations ceased. Pilot-scale costs ($365 900) compare favorably with design-phase cost estimates, with approximately 10% of total costs attributable to the intense sampling density and frequency. Results of this pilot-scale test indicate that careful design and implementation of SEAR can result in effective DNAPL mass removal and a substantial reduction in aqueous concentrations within the treated source zone under favorable geologic conditions

Metric Identification and Protocol Development for Characterizing DNAPL Source Zone Architecture and Associated Plume Response

“…Brooks et al, 2002;Hartog et al, 2010;Jalbert et al, 2003;Jin et al, 1997;Moreno-Barbero et al, 2007;Ramsburg et al, 2005;Willson et al, 2000). Trichloroethene (TCE) (ACS grade) was employed as a representative DNAPL, and 2-propanol (IPA) (HPLC grade), which is miscible with water, was used as a solvent in preparing samples for analysis.…”

“…PCE-NAPL infiltration and entrapment was simulated with UTCHEM 9.0 using 16 realizations of a baseline permeability field representative of a relatively homogeneous glacial outwash deposit. Permeability field realizations were developed using Sequential Gaussian Simulation geostatistical methods (Lemke et al 2004) conditioned to the Bachman, Michigan site (Abriola et al 2005). Three spill scenarios were examined in each permeability realization (Table M.1.4), namely: a release consistent with a slow, persistent leak (400 day release); a release corresponding to a catastrophic release (4 day release); and a spill configuration with a 400-day release at two separate locations in the domain (see .…”

“…Care must be taken when designing and interpreting the results from tests employing partitioning tracers as analysis may prove difficult due to the convoluted effects of poor characterization of i C p K (over estimation of S n ) and the hydraulic accessibility of the NAPL (under estimation of S n ). Few studies report the concentrations at which partition coefficients were measured, and those that do report the data employed to evaluate i C p K often evaluate the partition coefficient at concentrations that are much lower than those introduced to the subsurface (Jawitz et al, 1998;Brooks et al, 2002;Meinardus et al, 2002;Jalbert et al, 2003;Ramsburg et al, 2005;MorenoBarbero et al, 2007;Hartog et al, 2010). The injection concentrations employed in these field tests may be within the linear partitioning range, but without thorough characterization of the tracer/NAPL interactions, the range over which the linear assumption is valid remains unknown.…”

Development of Assessment Tools for Evaluation of the Benefits of DNAPL Source Zone Treatment

“…Numerical simulations were performed in nonuniform permeability fields conditioned to samples collected at the Bachman Road (MI) field site Ramsburg et al 2005). Several geostatistical simulation methodologies were employed to examine the influence of modeling methodology on simulation results and to generate a set of numerical realizations that encompass the variety of source zone architectures that may be expected in the field .…”

“…This experiment was intended to combine knowledge gained from the 1-D biotic column experiments and the 2-D abiotic aquifer cell experiments to evaluate metabolic reductive dechlorination in a heterogeneous, multidimensional setting. Additionally, this experiment was conducted to assess the feasibility of combining treatment remedies, surfactant enhanced aquifer remediation (SEAR) with bioaugmentation, for the treatment of a PCE-DNAPL source zone based on evidence from the Bachman Road site study Ramsburg et al 2005). The aquifer cell design was based on the aquifer cell employed in the abiotic 2-D aquifer cell experiments, with slightly smaller overall dimensions (63.5 cm in length x 38 cm in height x 1.4 cm in thickness) and modifications to allow for continuous anaerobic operation.…”