The Impact of Electron Donor Zeta Potential and Hydrophile / Lipophile Balance on Subsurface Distribution
Ben Mork, Regenesis, San Clemente , CA

Natural Transport Processes and Amendment Distribution in the Subsurface  
Matt Petersen, GE Global Research, Schenectady, NY
Mark Harkness, GE Global Research,Schenectady, NY  
Bernie Kueper, Queen’s University, Kingston , ON , CAN
Ashley Wemp, Queen’s University, Kingston , ON , CAN
Jim Graham, Waterloo Numberical Modeling Corp, Kitchener , ON , CAN

Reductive Dechlorination of VOCs by In-Situ Bioaugmentation: Four Case Studies of Success
Carl Elder, Geosyntec Consultants, Acton, MA
Douglas Larson, Geosyntec Consultants, Acton, MA
Brian Hitchens, Geosyntec Consultants, San Diego, CA
Sam Williams, Geosyntec Consultants, San Diego, CA

Effective Distribution and Longevity of Hydrogen Donors for Enhanced Reductive Dechlorination
Maureen Dooley, Regenesis, Wakefield, MA
Drew Baird, Regenesis, Greenville, SC

The Impact of Electron Donor Zeta Potential and Hydrophilic / Lipophilic Balance on Subsurface Distribution
Ben Mork, Ph.D.,  Regenesis, Inc., 1011 Calle Sombra, San Clemente, CA 92670, Tel: 949-366-8000, Fax: 949-366-8090, Email: bmork@regenesis.com

Adequate distribution of electron donor substrates is a critical performance determinant in the successful field-scale in-situ reductive dechlorination of contaminants in aquifers. Transport in the subsurface is governed by hydrogeologic characteristics of the aquifer under treatment and, equally importantly, by the characteristics of the electron donor substrate itself.

Over the last decade, electron donor technology has evolved away from simple sugar substrates that rapidly ferment and require continuous application, and complex electron donor substrates have emerged allowing for a range of hydrogen release rates from a single application. Many of these substrates / proprietary products contain slower releasing components of very low solubility. The distribution of these substrates will be dependent on not only their aqueous solubility but also on the oil/water partitioning of the substrates which is governed by the specific hydrophilic/lipophilic balance index (HLB) of the compound considered.

Distribution of these substrates is additionally affected by chemical properties of the aquifer. These include aspects of the water chemistry such as ionic speciation/concentration, and aspects of aquifer matrix geochemistry such as the fraction of organic carbon (Foc) and zeta potential between the soil particle surface and these substrates.

The HLB of the electron donor substrate governs its ability to form emulsions when preparing the material for subsurface application, as well as governing the requirement for chemical emulsifiers to aid in the stabilization of the product. Additionally, and perhaps most importantly, the HLB indicates the propensity for the substrate to spontaneously form micelles (sub-micron size colloids) that advance the forward movement of the substrate through the contaminated aquifer.

This paper reviews the impact of substrate HLB and the inherent zeta potential on subsurface adhesion to aquifer matrices, microemulsion formation, and microemulsion/micelle movement in the subsurface for a range of substrates of differing characteristics. Data are presented from laboratory studies involving aquifer simulation columns (6 m in length) which demonstrate the positive impact of achieving spontaneous micelle formation on the advancement of electron donors in aquifer materials. Data are then presented from full-scale field applications of a mid-range HLB electron donor designed to achieve extended aquifer distribution through optimized micellar transport, with examples taken from both granular aquifer and deep fractured rock settings.  

The practical relevance to the remedial design engineer of HLB and sub-surface distribution with regard to field performance and overall project cost / performance is then critically discussed.

Natural Transport Processes and Amendment Distribution in the Subsurface

Matthew Petersen, GE Global Research, 1 Research Circle, Niskayuna , NY , 12309 , US , Tel: 518 387 7054, Fax: 518 387 6972, Email: petersen@research.ge.com
Mark Harkness, GE Global Research, 1 Research Circle, Niskayuna , NY , 12309 , US , Tel: 518 387 5949, Fax: 518 387 7611, Email: harkness@crd.ge.com
Bernie Kueper, Queen’s University, Kingston , ON , CAN, Tel: 613 533 6834, Fax: 613 533 2128, Email: kueper@civil.queensu.ca
Ashley Wemp, Queen’s University, Kingston , ON , CAN, Tel: 613 533 6834, Fax: 613 533 2128, Email: 3aw25@queensu.ca
Jim Graham, Waterloo Numberical Modeling Corp, Kitchener , ON , CAN, Tel: 519 576 4858, Fax: 519 653 7149, Email: jim@wnmcorp.com

Adequate spatial distribution of amendments (e.g., oxidants, reductants, electron donors) in the subsurface is critical to successful remediation.  Use of injection well spacings that are too wide, fluid volumes that are too small, or injection heads that are too low, can result in an insufficient volume of material delivered to the subsurface.  Often, an underlying assumption in these situations is that diffusion and dispersion will act to distribute materials in the subsurface.  In many situations, these mechanisms are insufficient to promote long-range transport of materials away from the injection point.  The result is inadequate amendment distribution and poor remediation performance on a wide scale.

The most certain way to achieve the desired distribution of materials is to add sufficient injection fluid to physically displace materials around the injection point.  While this process may be impacted by soil heterogeneity, this effect can be estimated and radii of influence (ROI) based upon displaced fluid volumes calculated.  Required injection volumes can be quite large because these volumes are dependent on the square of the ROI, so that the resulting injection times can be quite long.  This reality can make injection using a direct push rig less attractive because of long times required in the field.   However, several field strategies are available to reduce overall injection times.

The paper to be presented will address each of these points by combining analytical and numerical solutions of transport phenomena, simple design and cost models, and observations from laboratory and field data to better understand the transport and distribution of materials in porous media.

Reductive Dechlorination of VOCs by In-Situ Bioaugmentation: Four Case Studies of Success
Carl Elder, Geosyntec Consultants, 289 Great Rd, Suite 105 , Acton , MA 01720 , Tel: 978-263-9588, Fax: 978-263-9594, Email: celder@geosyntec.com
Douglas Larson, Geosyntec Consultants, 289 Great Rd, Suite 105 , Acton , MA 01720 , Tel: 978-263-9588, Fax: 978-263-9594, Email: dlarson@geosyntec.com
Brian Hitchens, Geosyntec Consultants, 10875 Rancho Bernardo Rd, Suite 200, San Diego, CA  92127; Tel: 858-674-6559, Fax: 858-674-6586, Email: bhitchens@geosyntec.com
Sam Williams, Geosyntec Consultants, 10875 Rancho Bernardo Rd, Suite 200, San Diego, CA  92127; Tel: 858-674-6559, Fax: 858-674-6586, Email: swilliams@geosyntec.com

This paper presents four case studies where in-situ bioaugmentation was used to remediate chlorinated VOCs in groundwater.  The applications vary in the medium treated, electron donor used and/or method of delivery for the amendments.  These case studies demonstrate the versatility of bioremediation approaches.  The advantages and disadvantages of each approach are provided as well as recommendations for which approaches are better suited for various types of sites (i.e., soil/rock type, area treated, available infrastructure, etc.).

The first case study demonstrates the use of a soluble donor delivered into a fine-grained sand aquifer using a groundwater recirculation system to treat a large source area.  This approach achieved approximately 90% reduction in chlorinated solvent mass throughout the source within four years. Currently, the system is shutdown and data are being collected to justify site closure.

The second case study demonstrates (1) source treatment in low-permeability clay and bedrock using emulsified oil, and (2) installation of a biobarrier in bedrock to cut-off the dissolved plume.  Both systems are performing superbly and the majority of the VOCs have been degraded within a few years.  This site demonstrates how bioremediation approaches can be combined and used at sites which are challenging for other remediation approaches.

The third site is a one-acre plume in a low-permeability aquifer below an active manufacturing facility. Manufacturing operations in and around the treatment area limited remediation options and intrusive work.  Bioremediation using existing wells and temporary infrastructure was selected for the site, and within a year, significant reductions in VOC concentrations have been observed with many wells in and down gradient of the treatment area.

The fourth case study demonstrates the use of passive in-situ methods to remediate a half-acre plume in a low permeability aquifer containing VOC concentrations indicative of potential DNAPL.  Over 250 temporary direct push injection points were used to deliver over 400,000 gallons of emulsified oil solution and 120 liters of microbial culture in less than 4 weeks.  VOC concentrations were reduced to below the MCL across the majority of the study area within approximately 9 months.  The distribution of electron donor after one year varies across the study area based on distance from the injection points, density of injection points, and proximity to the perimeter of the treated area.  

Bioremediation is a versatile remedial approach that can produce quick, effective and relatively inexpensive remediation of chlorinated VOCs.  However, it must be implemented in a way that is compatible with constraints imposed by site geology and geochemistry, constituent concentration and composition, size of the treatment area, regulatory requirements, site use, available infrastructure, and project timeline and budget.  This presentation demonstrates the effective use of bioremediation at sites with varying conditions and provides recommendation on bioremediation approaches.  

Effective Distribution and Longevity of Hydrogen Donors for Enhanced Reductive Dechlorination
Drew Baird, Regenesis, 115-B Broadus Ave , Greenville , SC 29601 , Tel: 864-240-9181, Fax: 864-240-9182, Email: dbaird@regenesis.com
Maureen Dooley, Regenesis, 19 Belmont Road , Wakefield , MA 01880 , Tel: 781-245-1320, Fax: 781-245-1329, Email: mdooley@regenesis.com

This paper will present data from three field sites demonstrating the effective distribution and longevity of an advanced, controlled release electron donor technology. The three chlorinated solvent sites, located in New York , Ireland , and Portugal , illustrate treatment in challenging geologic and geochemical environments. The New York site geology is a predominantly medium- to coarse-grained till with sulfate concentrations exceeding 250 mg/L. Pilot-scale donor injections were performed in 2006 in two areas of the site. Rigorous sampling and analysis over a 19-month period document distribution through the treatment zones, a shift into optimal geochemical conditions, a 95% reduction in parent TCE, and ethene production.  Anaerobic geochemical conditions have persisted for at least 19 months post-injection. The biggest challenge at the site in Ireland is the fractured bedrock environment. The data highlight the distribution of the controlled release donor and the resultant shift in geochemical conditions and biodegradation rates; over 6 month period, TCE degradation rates increased by more than 16 times. The site in Portugal presented the dual challenge of high seepage velocity (up to 900 feet per year) and high solvent concentrations (up to 52 mg/L). Rapid, effective distribution of the donor is illustrated by a 90% reduction in parent PCE within 2 months after the injection event. Despite the high-flow environment, the donor longevity was shown to be at least 18 months.

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