Groundwater Solutions: Innovating to Address Emerging Issues for Groundwater Resources: Alphabetical Content Listing

Contaminated Large Plumes

John Wilson, Ph.D

Abiotic Degradation of TCE by Naturally Occurring Magnetite can be Important in Large Plumes

John Wilson, Ph.D
Significant quantities of magnetite occur in many aquifers. In these aquifers, abiotic degradation of TCE by magnetite can be an important mechanism for natural attenuation. There is a direct correlation between the quantity of magnetite in aquifer sediments and their magnetic susceptibility. The magnetic susceptibility of aquifer sediment can be characterized with good sensitivity and at low cost using a downhole sonde in conventional monitoring wells at the site.

An empirical relationship has been established between the mass magnetic susceptibility of aquifer sediment and the rate constant for degradation of TCE and cis-DCE in the sediment. In a variety of aerobic unconsolidated sand aquifers, the magnetic susceptibility ranged from 2E-07 to 2E-06 m3 kg-1. Biological reductive dechlorination of TCE or cis-DCE would not be expected in these aquifers. However, the field-scale bulk rate constants for TCE or cis-DCE degradation varied from 0.1 per year to 0.7 per year with a median near 0.3 per year.

In large plumes, the rate constant for abiotic degradation of TCE by magnetite may be large enough that abiotic degradation is adequate to support monitored natural attenuation (MNA) as a remedy or part of a remedy at the site. If the concentration of TCE is 100 μg/L or less, and the degradation rate constant is 0.3 per year, the concentration can be brought to the MCL in 10 years of travel time along the flow path in the groundwater.

Aerobic Cometabolic Biodegradation to Treat Emerging Chemicals and Co-Contaminants in Dilute Plumes

Min-Ying Chu, Ph.D., PE
One of the major challenges in managing large dilute plumes is treating recalcitrant emerging contaminants such as 1,4-dioxane (14D), 1,2,3-trichloropropane, and N-Nitroso-dimethylamine. Conventional technologies (e.g., in situ anaerobic bioremediation or ex situ granular carbon adsorption) selected to treat primary contaminants (e.g., chlorinated solvent compounds) are often inadequate to treat emerging contaminants. Aerobic cometabolic biodegradation has been considered a promising remedial technology that can concurrently treat a wide spectrum of organic contaminants to very low concentrations. The feasibility of concurrent treatment of all contaminants via the aerobic cometabolic biodegradation process was demonstrated at the former McClellan Air Force Base site in California. The primary substrates, HD10 propane and oxygen, were added to recirculated groundwater to stimulate the aerobic cometabolic activity of the indigenous microbial population in situ. The treatment results show that 14D can be treated to concentrations below 1 ug/L and co-contaminants trichloroethene, 1,2-dichloroethane, and 1,1dichlorehene can be concurrently treated to their respective analytical method detection limits of 0.23, 0.18, and 0.2 ug/L, respectively. The degrading activity lasts for more than two weeks without the addition of primary substrates, indicating the stability and robustness of the treatment process. The treatment efficiencies are contaminant specific, ranging from 90 to 99%, comparable to the efficiencies observed in other similar field studies that used significantly higher primary substrate loading rates. In this presentation, the insights gained from this demonstration field test will be shared; various potential applications, including different suites of contaminants, various types of substrates, enhanced natural attenuation, and mass flux management will be presented. Finally, implementation of in situ aerobic cometabolic biodegradation under various large dilute plume scenarios will be described.

A New Framework for Accelerated Site Closure: Dynamic Remedy Implementation

Mark Klemmer, PE
A decade ago, a resurgence in the field of hydrogeology began as groundwater remediation practitioners and researchers re-examined solute transport processes from the perspective of groundwater remediation. This re-evaluation led to better framework of the solute transport phenomena, recognizing that plume development and transport are mostly influenced by advection and diffusion, rather than advection and dispersion. These observations changed how we investigate sites; now focusing on high-resolution characterization to locate zones where contaminant mass is moving and zones where mass is stored. Remediation strategies have also changed, particularly at large sites, where combined remedies, tailored to hydrogeology, sources, and scale are the norm. However, challenges still exist, in particular how we extrapolate local data to larger scales. Consider remediation systems, technology aside; asymptotic performance is usually observed within a few years following startup. System optimization is to be expected, but the question remains the same, what drives lulls in performance.

The presented case study illustrates the application and performance of Directed Groundwater Recirculation (DGR). The most important difference between DGR and conventional P&T is the reliance on the CSM to develop a hydraulic flushing framework, a dynamic operation plan, and the approach for continuous adaption based on actual remedial performance. The DGR system is operating at 65gpm to remediate the diffuse plume and overcome the challenges of advection and stagnation. The system began operation in December 2014 with 29-extraction-wells and 58-extraction-wells with contractually driven goals, to allow property transfer within 18 months, and regulatory goals thereafter. The DGR system removed most of mass within 8 months, meeting contractual obligations for property transfer everywhere. Regulatory criteria in the shallow portion of the aquifer have been met. Details will be presented to discuss lingering, low-concentration exceedances in deep portions of the aquifer, required further efforts to achieve stringent criteria for vinyl chloride (2µg/L).

A New Perspective on Flow, Transport, and Achievable Endpoints in Large Plume Restoration: Removing the Diffusion Road Block

Scott Potter, Ph.D., PE
Designers of remediation systems for cleaning up contaminated groundwater plumes are faced with the challenge of developing reliable estimates of the time to meet metrics. Common questions from responsible parties, regulators, and stakeholders include: 1) how long will it take to achieve performance goals? 2) how much less time would it take to clean up 70% or 80% of the plume foot print? 3) how much time to reduce the plume concentrations by 90% or 99%? or simply 4) when can we turn the remedy off? While engineers may struggle to answer these questions, diffusion has become the prumary technical basis for uncertainty. This presentation analyzes the movement of groundwater and contaminants by focusing on permeability contrasts to define primary, secondary, tertiary flow pathways. This approach, combined with high resolution plume delineation, allows us to distinguish between slow advection and diffusion, and identify more effective remedial approaches.

The division of flow through aquifers by order-of-magnitude contrasts in hydraulic conductivity defines the conceptual three-compartment model of flow and transport. The primary flow pathways defined by the most permeable facies within an aquifer are advective pathways that convey 90% of groundwater flow; 9.0% of groundwater flow occurs through secondary pathways where advection is slower and the effects of storage begin to emerge; while the tertiary pathways represent only 1% of flow and contaminants in true storage zones. Primary advection zones are the most conducive to remediation, reagent delivery, and treatment; the secondary pathways are slower advection zones where clean-up is possible but will take more time; while storage zones need to be assessed for restoration and the potential to recontaminate advective pathways. This concept is applied to data from multiple sites to provide new insights on projects that were less successful and to identify strategies for future approaches to be more robust.

A Systematic Approach for Designing and Operating DGR™ Systems to Advance Plume Restoration

Marc W. Killingstad
Dynamic Groundwater Recirculation or DGR™ is an innovative remedial strategy that significantly advances conventional pump and treat (P&T) designs of the past. Rather than simply hydraulically contain the groundwater plume, which is often the objective of a traditional P&T system, a DGR™ system creates dynamic groundwater flow conditions that serve to boost the natural flushing processes occurring within an impacted aquifer. Because the underlying concept of a DGR™ system is relatively simple— accelerate the influx of clean groundwater to promote aquifer flushing by driving contaminant mass out of the aquifer (both flow and storage zones) via enhanced advection and diffusion—DGR™ can be a highly effective remedial technology particularly when applied to sites with soluble contaminants, complex geology, and/or large diffuse plumes. To date, DGR™ systems have been successfully implemented at a number of contaminated sites (both large- and small-scale) located across the United States in diverse geologic settings helping to restore aquifers impacted by a range of contaminants.

As with any remedial technology, proper design and operation are critical to the success of a DGR™ system. Since DGR™ is a relatively new remedial technique, fundamental design and operating principles and practices have not yet been fully established. As such, a systematic approach for design and operation of an effective DGR™ system has been developed though our collective experience. Several examples are presented to illustrate the guiding principles of this approach and to highlight the computer-based tools that are applied.

Big Plume; Little Remediation – Smart Characterization in Action

Nick Welty, PG
The best remediation strategy begins with a new approach to site investigation. Traditional site investigation methods assume a uniformity of conditions in the subsurface, and the result is a conceptual site model based on a relatively small dataset collected from a monitoring well network. Because monitoring wells simply report contaminant concentrations, rather than mass flux, the monitoring well dataset fails to provide the information necessary to accurately evaluate potential risks and liabilities or understand likely clean-up timeframes.

We recommend the Smart Characterization approach, which creates a mass-flux based conceptual site model by integrating dynamic, real-time, high-density soil and groundwater sampling with hydrostratigraphic interpretations and 3D permeability mapping. By classifying the subsurface into transport, slow advection, and storage zones, we can tailor characterization approaches based on the mass transport behavior. We capture the high resolution flux data into a digitalconceptual site model, which is linked with a business decision framework we call Return On Investigation, or ROI. When applied correctly, Smart Characterization methods result in an ROI through reduced total cost of remediation, better definition of uncertainty and risk, and understanding achievable endpoints before remediation commences.

As a case study, we present a site with a one-mile long, 10 PPM TCE plume, which was rapidly characterized using real-time, high-resolution Smart Characterization methods. These characterization data were used to build a 3D digital CSM and ultimately obtain site closure pending in 2017. The most significant finding is that human health and the environment could be protected largely using administrative methods. It is certain that this conclusion would not have been reached with traditional characterization methods. Therefore, this project also demonstrates the ROI concept: the site characterization for the project cost far less than decades of useless active remediation which would not result in any further reduction of risk.

Converting Contaminated Aquifers into Purifying Filters: Colloidal Activated Carbon

Jeremy Birnstingl, Ph.D.
Legacy groundwater plumes of halogenated organic solvent contaminants are often large and diffuse. In situ treatment of these plumes is often considered infeasible due largely to the long term back-diffusion of contaminants from lower permeability matrices within heterogeneous aquifers systems.

Recent innovations in dispersion chemistry has resulted in the development of a highly sorbent, colloidal activated carbon which has been demonstrated to flow easily into aquifer matrices. Once distributed in the subsurface, the colloidal material will permanently deposit to form a coating on the aquifer matrix while leaving groundwater flow unrestricted. Dissolved contaminants rapidly sorb into the activated carbon and are stripped from groundwater fluxing through the treated zone or back-diffusing from lower permeability zones. Biodegradation of the contaminants concentrated upon the carbon layer is accelerated by the use of dispersion chemistry that serves as long term electron donor and the option of bioaugmenting with contaminant-degrading microbial consortia (e.g. DHC).

Data is presented from a dual-porosity tank study conducted at Colorado State University which supports the hypothesis that colloidal activated carbon, when applied in high flux zones, is highly effective at the long-term treatment of back-diffusion. Key data from this study includes the observation of limited daughter product formation in conjunction with Dehalococcoides populations that are two orders of magnitude higher in the presence of the colloidal activated carbon than without. Additional data is also included on the ability of the colloidal carbon to migrate throughout both the transmissive and the lower permeability soil layers.

Results of pilot-scale and full-scale commercial remediation projects are also presented which indicate that colloidal activated carbon may be an effective solution in treating back-diffusing legacy plumes. Technical hurdles to success are described and future development plans are discussed.

Groundwater and PFAS: State of Knowledge and Practice

Seth Kellogg, PG
Per- and polyfluoroalkyl substances (PFASs) are a unique class of emerging drinking water contaminants that have shown widespread occurrence in groundwater and surface water resources, and due to their toxicological characteristics are increasingly the focus of environmental protection agencies worldwide. Starting in October 2016, 37 scientists and engineers voluntarily collaborated through the National Ground Water Association to develop information for the broader groundwater community. Using a consensus-driven process that included a public comment period, their efforts resulted in Groundwater and PFAS: State of Knowledge and Practice, published earlier in 2017.

NGWA published this PFAS document to assist members and other groundwater professionals who may be tasked with investigating the transport pathways and extent of PFASs in groundwater and surface water, assessing potential risks to receptors, or designing and constructing engineering controls to manage subsurface PFAS contamination. The main purpose of this document is to summarize the current state of knowledge and practice regarding PFAS fate, transport, remediation, and treatment, recognizing that knowledge in this field is advancing. This document also aims to summarize current technologies, methods, and field procedures being used to characterize sites and test remediation and treatment technologies.

Groundwater/Lake Interactions Affect Large-Scale Migration and Attenuation of PFAS and VOC Plumes in the Cape Cod Aquifer, Massachusetts

Denis R. LeBlanc
Migration and natural attenuation of poly- and perfluoroalkyl substances (PFASs) and volatile organic compounds (VOCs) in the surficial Cape Cod glacial outwash aquifer are strongly affected by groundwater flow patterns near kettle lakes. The plumes originate from historical sources, including a former fire-training area (FTA), and are generally narrow and thin owing to limited macrodispersion in the groundwater system. The PFAS plume from the FTA, which has concentrations of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) above the recently established U.S. Environmental Protection Agency drinking water health advisory, is 20 m thick and less than 100 m wide near its source. The PFAS plume and several VOC plumes intersect two groundwater flow-through kettle lakes. Groundwater-flow models and the isotopic composition of lake water and groundwater (delta-18O and delta-2H) show that deep groundwater passes beneath the lakes, while shallow groundwater discharges into and mixes in the lakes and then recharges the aquifer at the downgradient sides of the lakes, creating zones of lake-water-derived groundwater (“lake shadows”) as much as 75 m thick and 2 km wide in the aquifer. Parts of several VOC plumes terminate at the lakes, where VOCs in the water are removed by volatilization and other processes, but other parts pass beneath the lakes and are present in deep groundwater more than 5 km from their sources. The PFAS plume at least partly discharges to a kettle lake about 1.1 km from the FTA. Unlike the VOCs, PFASs persist in the lake water and re-enter the aquifer downgradient from the lake, creating a broad, thick dilute zone of elevated PFAS concentrations downgradient from the lake. These observations demonstrate that contaminant fate and large-scale plume migration are affected by groundwater/lake interactions and the different behaviors of the contaminants along the flow path.

Remediation of Large Groundwater Plumes through Optimized Extraction System and Monitored Natural Attenuation

Noman Ahsanuzzaman, Ph.D., PE
A site-wide groundwater extraction and optimization process has been ongoing at a former large munition manufacturing process facility in the United States. The site contains five large RDX plumes with combined surface area of 4,500 acres. The other smaller comingled plumes are largely covered within the footprint of the RDX plumes. A formal dispute between the government agencies was resolved in 2008. An adaptive groundwater extraction system has been implemented to contain the plumes and mass reduction of RDX. The final Record of Decision (ROD) directs the relocation of extraction wells over time to maximize mass reduction of RDX. According to the ROD, the optimized groundwater extraction phase will continue for 15 years or more until a specific target concentration is reached. Once reached, the extraction system will be discontinued and monitoring natural attenuation (MNA) will be followed for another 45 years. Based on the preliminary remedial goal (PRG) for RDX of 2 µg/L and the site-specific half-life of 8 years, the ideal target concentration at the end of extraction phase is estimated to be 100 µg/L. The optimization process of the extraction phase is limited to the maximum treatment capacity of 2,400 gpm from the two on-site treatment plants. An extensive groundwater model has been utilized to optimize the relocation of the extraction wells annually. Additional challenge of the remedial action is to obtain the desired attenuation rate throughout the plumes at the end of the extraction phase. Following the completion of the remedial action in 60 years, the groundwater should restore to drinking water standard and allow unrestricted use. The total cost of the groundwater extraction system to date is approximately $70 million, including capital and O&M (operation and maintenance) costs.

Superfund Groundwater Remedy Performance

Linda Fiedler
The US Environmental Protection Agency (EPA) Superfund statutes, policy and guidance define Superfund’s groundwater cleanup mission by providing an expectation that groundwater will be returned to its beneficial use. In this presentation EPA will present the findings of an analysis of groundwater remedy performance at selected Superfund sites, ranging from less difficult cleanups involving small dilute groundwater plumes in simple hydrogeologic settings, to more difficult cleanups such as large plumes with high concentrations, complex hydrogeologic settings, and dense nonaqueous phase liquids. The study examines key aspects of the groundwater remedies, including progress towards achieving remedial action objectives (RAOs), cleanup approaches applied, contaminants addressed, hydrogeology, and the magnitude of cleanup. Results of this analysis show that, for the range of Superfund sites and plumes studied, there have been significant reductions in contaminant concentrations and plume size, and in some cases, the groundwater plumes have been remediated to stringent RAOs, including those based on federal and state drinking water standards.

Superfund Optimization Strategy: Extracting Lessons Learned on Managing Large Plumes from 640 Optimization Recommendations

Carlos Pachon
The USEPA Superfund Program has expanded its remedy optimization program, tripling the average number of optimization and technical support events to about 21 per year. By expanding the optimization program, EPA has realized benefits from optimization, such as increasing remedy effectiveness, improving technical performance, reducing costs, moving sites to completion, and lowering the environmental footprint of remediation activities. In 2015 EPA collected information on the status of the optimization recommendations made at 61 events conducted between 2011 and 2015. The in-depth analysis of the data yielded insightful information on how optimization practices are helping us tackle large contaminated plumes. Through a close analysis of the more than 600 individual recommendations made over these four years, we are also learning about which technical practices are helping us achieve the optimization goals.

Will It Work Here? Site Assessment to Determine Suitability for Passive Treatment of Nitrogen

Marcel Belaval
Nitrogen loading to embayments and the resulting eutrophication of estuaries are among the most pressing environmental challenges faced by communities on Cape Cod. Currently, local and regional governments are engaged in a planning process to address nutrient pollution in embayments, the largest controllable source of which is septic systems. In the hydrogeologic setting of Cape Cod, high densities of septic systems distributed across the landscape produce large areas of elevated inorganic nitrogen in the aquifer. While nutrient reduction via sewering is one option communities are implementing, communities are also exploring approaches that provide alternatives to conventional sewering. One such alternative approach is the use of permeable reactive barriers (PRBs) using carbon based media for remediation of nitrate in groundwater.

In 2015, the U.S. Environmental Protection Agency, with assistance from the U.S. Geological Survey and the Cape Cod Commission, developed an assessment protocol to identify hydrologic site conditions appropriate for use of PRBs under typical Cape groundwater and nitrogen source circumstances. The protocol was applied at five potential PRB sites in the towns of Falmouth, Barnstable, Orleans, Mashpee, and Dennis. Sites were selected following an earlier regional-scale evaluation of candidate sites that utilized available data such as expected nitrogen loading, modeled groundwater elevation and flow direction, and distance to receiving surface waters. At each of the sites, a series of monitoring wells was installed to measure hydraulic gradients, monitor water quality and characterize aquifer materials. The protocol developed for site assessments helps define the level of effort needed to determine the suitability of a site for PRB treatment. The results from using this protocol underscore the importance of collecting site-specific hydrologic data before concluding that PRB treatment is an appropriate alternative approach to remediate nitrogen, even in settings where elevated groundwater nitrogen may impact large areas of an aquifer.

Emerging Contaminants

Hunter Anderson, Ph.D.

Assessment of PFAS in Soil and Groundwater: Direct Comparison of New Analytical Technologies for Comprehensive Analysis of PFAS Including Precursors

Erika Houtz, Ph.D.
In addition to PFOS and PFOA there are numerous other “precursor” compounds in firefighting foams which present an ongoing source of PFOS and PFOA and other perfluorinated sulphonates and carboxylates. PFAS contaminated source zones are often associated with large plumes as in some firefighting foam formulations the majority of PFAS are anionic and are not retarded significantly in aquifers, however in some foams cationic or zwitterionic precursors are at significant concentrations or dominate the formulations. These cationic / zwitterionic will bind to soils via ion exchange mechanisms, producing a lesser mobile source mass, which can evolve more mobile anionic perfluoroalkyl acids (PFAAs) as “dead end” daughter products via biotransformation reactions.

Precursors are not accounted for by US. EPA method 537 (LC-MS/MS) but have been identified as a source of PFAA’s, so to characterize soil, sediment and waters impacted with PFAS, it is important to assess the precursor concentrations. This presentation will describe new analytical methods to quantify the total concentration of precursors and PFAA’s in water and soil samples.

Soil and groundwater from PFAS contaminated sites as well as soil spiked with characterized AFFF were analyzed by conventional, and new and detailed analytical methods. Results demonstrate that PFOA and PFOS only account for only a small portion of the PFAS present in some impacted soil and groundwater.

This next generation of new PFAS analytical techniques will generate more comprehensive analytical data supporting more robust conceptual site models and improve understanding of PFAS fate and transport. Accounting for precursors will be key for successful design of remedial systems.

Boron as an Emerging Contaminant at Coal Ash Sites and Large Plume Management Metrics

Stephanie Jones
Boron is an emerging contaminant at coal ash sites that readily leaches from coal combustion residuals (CCR) and is commonly detected at high concentrations in groundwater. EPA promulgated the Federal CCR Rule in 2015 which identifies boron as an Appendix III indicator constituent for detection monitoring. Unlike other regulated constituents present at high concentrations in CCR, boron does not attenuate onto aquifer solids via sorption or precipitation of new minerals and thus it often produces large plumes in groundwater downgradient of CCR units. A recent settlement between utilities, EPA, and NGOs indicates that boron should be added to the list of constituents in Appendix IV of the final CCR Rule. Under the proposed change, a statistical exceedance of background concentrations for boron will trigger cleanup to background with the edge of the unit as the point of compliance.

The Interstate Technology and Regulatory Council (ITRC) published guidance on mass flux and mass discharge concepts in 2010 that have since been embraced at several CERCLA sites as interim remedy performance standards for source control measures and as metrics for the transition to less aggressive remedial operations. These mass discharge metrics are now being applied at CCR sites as a management tool for large boron plumes. They provide a means to quantify the mass discharge reduction needed from source control at CCR units to achieve background or risk-based screening levels across large plume areas. In combination with fate and transport modeling, the mass discharge metrics can be useful in supporting evaluation of groundwater remedies including monitored natural attenuation (MNA), in situ treatment, and source control/monitoring. They can also be used to prioritize units for closure in multi-unit systems.

Distribution of PFOS in Groundwater from AFFF Storage, Handling, and Use

Jeffrey R. Hale, PG
Discharge of aqueous film forming foam (AFFF), containing perfluorooctane sulfonate (PFOS), differs from typical mechanisms of contaminant release (inadvertent leaks and spills). Mechanisms include, 1) low volume spills of foam concentrate during storage or transfer; 2) one-off, high-volume, broadcast application of foam solution for firefighting; 3) periodic, moderate to high volume, broadcast application of foam solution for apparatus testing or training. AFFF is applied by mixing foam concentrate and water to make foam solution that is aerated when sprayed, producing finished foam. Thousands of gallons of foam solution may be applied for a fire or training event. Foam solution drains from the finished foam as an aqueous film with low surface tension that floats on fuel, facilitating soil infiltration and potential interaction with subsurface LNAPL.

PFOS concentrations >1,000 µg/L in shallow groundwater were measured beneath fire training and AFFF bulk storage areas compared to concentrations <50 µg/L beneath satellite AFFF storage, fire, and apparatus testing locations. Concentrations <20 µg/L were measured in groundwater beneath distal areas of runoff infiltration. PFOS soil concentrations also correspond to surface use: 16 mg/kg (bulk storage), 5.59 mg/kg (fire training), 1.57 mg/kg (satellite storage), 0.258 mg/kg (runoff channel). Shallow soil and groundwater concentrations are correlated by location (R2 = 0.89), indicating PFOS in groundwater is largely a function of initial direct infiltration over broad areas versus prolonged migration in groundwater from a discrete source. Shallow soil concentrations represent a residual fingerprint of past infiltration to groundwater. More than a decade after AFFF was used at one facility, the migration distance of PFOS in groundwater remains much less than both the width of the soil fingerprint and the distal extent of groundwater impacts due to channelized runoff and infiltration.

Emerging Characterization for Emerging Contaminants: Saturated Soil Sampling and 1,4-Dioxane

Patrick Curry, PG
Detailed characterization of 1,4-dioxane source areas is critical to designing an effective remedy strategy, but most characterization approaches do not provide the resolution required to make informed decisions. When understanding mass distribution and the limitations imposed by hydrostratigraphy are critical, a Smart Characterization approach, such as high-frequency saturated soil sampling, is the best investigation method to support remedy design. Once complete, the high-density dataset can be coupled with soil-water partitioning analysis to estimate the dissolved phase mass present in both the transport zones and storage zones at unparalleled resolution. The difference between groundwater and saturated soil results from co-located samples is diagnostic of plume maturity and the potential presence of residual source mass.

Saturated soil sampling is particularly well suited for evaluating low-permeability source areas where contaminant mass resides in storage zones that cannot be easily characterized with groundwater sampling. The advent of rapid on-site analytical methods for 1,4-dioxane using solid phase micro extraction (SPME) allow for a cost-effective, adaptive approach to source characterization. We recommend completing soil borings on a dense, adaptive grid and using real-time analysis to minimize the number of borings required to meet the objectives of the investigation. Detailed soil logging and geotechnical data collected in parallel with contaminant data provides the hydrostratigraphic context for the analytical results.

These concepts are illustrated for a RACER Trust site located in Michigan where a perched source areas contribute to a deep 1,4-dioxane plume located in weathered bedrock. The Smart characterization approach led to a plume maturity diagnosis revealing the source contained a small percentage of mass relative to the plume, and the distribution of mass at the release point was concentrated in low permeability storage zones. The results demonstrated that remediation was better focused on treating the downgradient plume rather than focused on a depleted source mass.

Enhanced In Situ Co-Metabolic Biodegradation of 1,4-Dioxane in Weathered Bedrock via Propane Biosparging

Andrea Krevinghaus, PE
The application of in situ biodegradation is a technology commonly used to mitigate chlorinated volatile organic compounds. Similarly, research and field demonstrations have shown co-metabolic biodegradation of 1,4-dioxane is a viable mechanism for treating 1,4-dioxane in groundwater. In situ co-metabolic biodegradation using propane biosparging is a remedy in which propane, air, nutrients, and propane oxidizing microorganisms, are delivered to the subsurface to enhance in situ co-metabolic biodegradation of 1,4-dioxane. More traditional 1,4-dioxane remedies such as advanced oxidation processes are typically very costly and complex, a propane biosparge system has the potential to be a much more cost effective and streamlined remedy.

In September 2016 a propane biosparge pilot test was initiated at the RACER Trust site in Lansing, MI. Air and propane were injected into contaminated weathered bedrock at 3 cubic feet per minute and up to 35 percent of the lower explosive limit (LEL) for 11 to 12 hours per day into each of two sparge wells. The propane concentration was increased from 15 to 35 percent LEL during the test to evaluate any change in the rate of biodegradation. Bioaugmentation with a propanotrophic culture was conducted, alongside nutrient addition of diammonium phosphate.

After four months of operation, 1,4-dioxane concentrations decreased up to 98 percent at monitoring locations within the test area. Higher reductions were observed at locations that were better connected with the sparge well and had increased dissolved oxygen (greater than 3 milligrams per liter) and propane (greater than 100 micrograms per liter). It was also concluded that increasing the propane from 15 to 35 percent of the LEL did not increase the rate at which 1,4-dioxane was degraded. Providing distribution of the gas mixture within the weathered bedrock will therefore be the key to making biosparging a viable remedy for the site.

Insights from Detailed Subsurface Characterization of a Plume of Poly- and Perfluoroalkyl Substances on Cape Cod, MA

Andrea K. Weber
Poly- and perfluoroalkyl substances (PFASs) are persistent contaminants introduced to the environment through their use in firefighting, industry, and commercial products. Owing to growing evidence of potential adverse human health outcomes such as cancer, obesity, and thyroid disease from PFAS exposure, the U.S. Environmental Protection Agency recently issued drinking water health advisories for two PFASs—perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). Aqueous film-forming foams (AFFFs) used for firefighting are a significant source of PFASs in groundwater. At hundreds of locations throughout the United States, AFFFs were used regularly over several decades at fire training areas (FTAs). Leaching of contaminated soil beneath often unlined FTAs has resulted in PFAS plumes in aquifers that are sources of drinking water.

Groundwater sampling in 2014-15 near an FTA on Cape Cod, MA, where AFFFs were used from 1970 to 1985 revealed a plume of PFAS contamination that extends more than 1.2 km downgradient from the FTA and passes beneath wastewater infiltration beds (WWIBs) used for disposal of treated municipal wastewater from 1936 to 1995. PFASs in samples collected near the water table at the FTA and WWIBs indicate that both sites are continuing sources of PFASs to the aquifer despite several decades since their last use, although PFAS concentrations from the WWIBs are much lower than those from the FTA. The shallow groundwaters beneath the two sites have different PFAS compositions, a finding that may be useful for differentiating PFAS source types at other locations. Results from total oxidizable precursor assays conducted using groundwater from the plume showed the presence of mobile perfluoroalkyl acid precursors that can degrade into perfluoroalkyl acids such as PFOS and PFOA, indicating that the total mobile mass of PFASs can be greater than what is typically measured directly with current laboratory techniques.

In Situ Containment of PFOA/PFOS using Colloidal Activated Carbon

Kristen Thoreson, Ph.D
With the increasing awareness of widespread contamination associated with PFOA, PFOS, and other PFAS compounds, there is an established need for new and lower cost treatment options that can address the large, dilute plumes that these contaminants commonly form. This paper examines the use of a colloidal activated carbon that readily distributes within contaminated aquifers, providing a method for establishing an in situ containment barrier for retarding the migration of PFOA and PFOS.

  

Laboratory studies were conducted to measure the adsorption isotherms for PFOA and PFOS with a distributable form of colloidal activated carbon. The isotherm data was then used in an adapted version of the BioChlor model in order to estimate the expected adsorption longevity that a barrier of the colloidal carbon can provide for PFOA and PFOS considering the flux and the concentration. Additionally, a 16-foot sand column experiment was conducted to determine the ability of the colloidal activated carbon to flow and deposit in an aquifer.

The measured PFOA and PFOS isotherms were fit to the Freundlich equation and the isotherm parameters were determined. The isotherm measurements included a demonstration that a dose of the colloidal activated carbon could reduce 100 mg/L of PFOA and PFOS to below the 2016 revised EPA health advisory limits of 0.07 mg/L. Using the measured isotherm parameters within the BioChlor model, it was shown that a 50 mg/L plume of either PFOS or PFOA traveling with a velocity of 120 ft/yr could be contained and meet EPA limits with a single barrier of the colloidal activated carbon for up to 8 years. While this timeframe will also depend on other water components, for example TOC and additional contaminants present, the containment time can be increased with multiple barriers or a higher dose of the colloidal carbon.

 

 

Overview of Remediation Technologies for PFAS-Contaminated Groundwater

Jed Costanza
This presentation will provide an overview of current and promising remediation technologies to treat PFAS-contaminated groundwater. To date, only ex situ conventional technologies such as pumping PFAS-contaminated groundwater with aboveground treatment by granular activated carbon (GAC) have been selected for use. Other aboveground treatment technologies such as ion exchange adsorption, reverse osmosis, and nanofiltration have the potential to replace GAC or be used with GAC to remove a broader range of PFASs from groundwater. And proprietary adsorbents are being marketed as alternatives or compliments to GAC. More novel ex situ technologies such as sonochemical treatment show promising results in bench-scale research. Chemical oxidation and reduction are also promising with bench-scale work showing the potential to degrade some PFASs. Additional work is being conducted to develop these chemical-based degradation technologies for the in situ treatment of PFAS-contaminated sites. Unfortunately, aerobic bioremediation is not likely to be applicable for PFASs with studies reporting that perfluorinated compounds are resistant to microbial degradation. Microbiological degradation of PFASs under anaerobic conditions is an underdeveloped area of research that warrants additional study.

Real-time Multi-stream Cr(VI) Monitor Validates RCOF Treatment Process at California Water Utility

Tom Williams
Utilities employing drinking water remediation techniques to address hexavalent chromium [Cr(VI)] contamination must measure influent and effluent chromium levels to adequately control and optimize water treatment and removal processes. High frequency, reliable and accurate data is essential to process validation, yet laboratory analysis can take up to two weeks to return results. A new water quality instrument was developed to facilitate the real-time analysis of Cr(VI) using a novel sensitive voltammetric detector that allows selective determination for hexavalent and total chromium.

The first commercial application of the real-time Cr(VI) monitor was undertaken at a California Water Utility obtaining eighty-five percent of their water supply from a groundwater source where hexavalent chromium [Cr(VI)] is a naturally occurring mineral. As a result of Cr(VI) dissolving into the water supply, 8 of their 12 inland water wells contain elevated levels of Cr(VI) exceeding the regulatory limit. Whereas the regulatory MCL has been set at 10 ppb, these 8 wells average 13 ppb of Cr(VI).

A Reduction/Coagulation/Oxidation/Filtration (RCOF) process was pilot tested under a variety of simulated operational conditions. The Cr(VI) monitor was used to provide real-time and multi-stream analysis of influent and effluent chromium levels during the pilot. During pilot testing the Cr(VI) monitor helped capture a high frequency data stream which was combined with other process data to simulate the impact of operational changes on contaminant levels and help validate the RCOF treatment methodology. Examples of operational changes include varying chemical feed dosing levels, contact time, and backwash frequencies. The real-time input on chromium levels helped to keep the pilot project on time and aid in a cost-effective effective treatment design suitable for full-scale implementation.

The methodology, validation, performance and application of the real-time Cr(VI) monitor that aided in process design and validation will be presented.

Remediation of Poly- and Perfluoro Alkyl Substances: New Remediation Technologies for Emerging Challenges

Jeffrey McDonough
Background/Objectives. Poly- and perfluoro alkyl substances (PFAS) comprise a diverse class of contaminants which include PFOS (perfluorooctane sulfonate) and PFOA (perfluorooctanoic acid). PFAS are not amenable to bioremediation or conventional chemical oxidation and are difficult to remediate in situin soil and groundwater systems. Further complicating the remediation challenges are the presence of precursor PFAS that are often present at locations where class B firefighting foams has been released and are not analysed for by standard analytical laboratory methods (US EPA method 537). These precursors can act as a source of perfluorinated carboxylates and sulphonates, as some precursors are less mobile but they all will biotransform over time forming perfluorinated compounds as dead end daughter products.

Approach/Activities. Innovative and emerging remediation solutions for PFAS include a number of types of technologies to address highly concentrated source zones, mitigate mass flux of impacts to aquifers or address PFAS in abstracted water. Use of granular activated carbon (GAC) to treat PFAS will only effectively remove a proportion of these contaminants from groundwater, whilst offering a very low binding capacity for PFOS (as compared to hydrocarbons), so can be costly. Challenges of more comprehensive PFAS treatment in water are currently addressed using technologies such as reverse osmosis or nano-filtration. There are new precipitation technologies for water treatment such as PerFluorAd, novel ion exchange resins, sonolysis, generation of solvated electrons, thermal approaches and sorptive media which show promise and will be summarized.

Results/Lessons Learned. Recent results from laboratory trials with several technology will be presented.

Sorptive Removal of Perfluorooctane Sulfonate from Aqueous Solution by Layered Double Hydroxides

Xin Song, Ph.D.
Perfluorooctane sulfonate (PFOS) is one of the most often detected perfluorinated compounds in both aqueous systems and biota. Because of its common occurrence in water resources as well as its toxicity and bioaccumulation, PFOS has become a compound of global concern and been recognized as an emerging contaminant. In this study, we seek for efficient, cost-effective and sustainable materials, which can be utilized to treat PFOS contaminated groundwater. Layered double hydroxides (LDHs), a class of anionic clays with layered structures, were investigated to evaluate their efficiency to remove PFOS from aqueous systems, hence, their potential to be used as an injection reagent to remediate PFOS contaminated groundwater. Here, we studied the sorptive removal of PFOS from aqueous solution by the nitrate, carbonate and chloride forms of intercalated LDHs. Batch experiments showed that the sorption process was very fast with an equilibrium time of less than 1h and the nitrate form of LDH showed the greatest ability to sorb PFOS with a removal rate of 95.7% at 1 mg/L of initial concentration. The sorption equilibrium data was well fitted with the Langmuir model, indicating a monolayer sorption of PFOS by LDHs. The maximum PFOS uptake capacity of LDHs differed with three forms of LDHs, with the maximum uptake capacity reached 865 mg/g by the nitrate form of LDH. The solution chemistry factors including pH, ionic strength and coexisting ions influenced PFOS sorption by LDHs. The sorption mechanism included surface adsorption as well as intercalation.

Technical Resources to Respond to Environmental Releases of Poly- and Perfluoralkyl Substances (PFAS)

Patricia Reyes
The Interstate Technology and Regulatory Council (ITRC) has formed a PFAS Team of state, federal, academic, industry, and public representatives to address the need for a concise, yet comprehensive, source of PFAS information for environmental practitioners and decision-makers. The scientific community’s understanding of PFAS sources, site characterization, environmental fate and transport, analytical methods, and remediation is growing rapidly. However, there is no central clearinghouse available that presents this information in a manner that is easily accessible for those other than subject-matter experts. As a result, there is a gap in the broad technical understanding necessary for informed and expedited decisions by regulators and policy makers. The project will produce a series of six fact sheets, each synthesizing key information for one of the following core subjects: (1) History and Use of Environmental Sources, (2) Nomenclature Overview and Physicochemical Properties, (3) Fate and Transport, (4) Site Characterization Tools, Sampling Techniques, and Laboratory Analytical Methods, (5) Remediation Technologies and Methods, and (6) Regulatory Summary. Following these will be the release of a detailed technical-regulatory guidance document and an internet-based training course, which will provide links to pertinent scientific literature, stakeholder points of view, technical challenges and uncertainties, and the necessary breadth and depth not given by the fact sheets.

This presentation will provide an overview of the PFAS Team work (which will be well underway) and explain how others can participate.

Using Stable Isotope Probing to Confirm Biodegradation of 1,4-Dioxane During In-Situ Remediation

Caitlin Bell, PE
1,4-Dixoane is a common co-contaminant with chlorinated solvents and treatment of 1,4-dioxane via natural or enhanced biodegradation processes provides a viable remedial strategy. 1,4-Dioxane can be co-metabolically biodegraded in the presence of alkane gases and oxygen. At Vandenberg Air Force Base in California, historical use of chlorinated solvents resulted in 1,4-dioxane in groundwater. Previously, in-situ propane biosparging was implemented and resulted in 1,4-dioxane concentration reductions (as published by others). This work builds on the prior field demonstration to confirm biodegradation as the mechanism for 1,4-dioxane concentration decreases via stable isotope probing (SIP). SIP includes addition of a 13C-enriched compound into the test system to act as a carbon-atom tracer to track the biotransformation of 1,4-dioxane.

This second propane biosparge field demonstration was initiated in December 2015. Operation of the system included sparging a mixture of air and propane (20 percent of the LEL) at up to 5 standard cubic feet per minute into one sparge point, for 30 minutes every four hours. Bioaugmentation with a propanotrophic culture was conducted, alongside nutrient addition of diammonium phosphate. SIP included use of Bio-Trap®samplers “baited” with isotopically enriched 1,4-dioxane.

After two months of operation, 1,4-dioxane concentrations decreased approximately 45 to 83 percent at monitoring locations in the test area. The SIP results confirmed the biodegradation mechanism associated with 1,4-dioxane groundwater concentration decreases. The co-metabolic biotransformation of 13C-enriched 1,4-dioxane is expected to result in generation of carbon dioxide which was measured as 13C-enriched dissolved inorganic carbon. Additionally, evaluation of microbial biomass indicated incorporation of 13C into the cellular phospholipids. Because significant carbon uptake into microbial biomass is not commonly associated with co-metabolism, the 13C-enriched biomass values observed here may be attributed to uptake of the mineralization intermediates or the carbon dioxide end product, rather than the 1,4-dioxane directly.

Keynote

James Woolford, Ph.D.

Large Plumes: Combined Remedies

James Cummings

1,4Dioxane and PAH removal with Ozone Peroxide Advanced Oxidation Process

Angel Gebeau, PE
Minnesota Pollution Control Agency (MPCA) contracted with AECOM to design full-scale potable water treatment for volatile organic compound (VOCs), 1,4 Dioxane, and poly aromatic hydrocarbon (PAH) removal at two potable wells for a Minneapolis metro area water system. AECOM completed testing to confirm the treatment processes selected for the full-scale design. Pilot and bench scale testing included spiking 1,4 Dioxane and PAHs, oxidation with chlorine, filtration, air stripping, and advanced oxidation process (AOP). Two AOP treatment systems were originally reviewed: 1.ultraviolet light and hydrogen peroxide AOP and 2. ozone and hydrogen peroxide AOP. Final testing focused on ozone and hydrogen peroxide AOP. The proposed system was designed to remove iron, manganese, radium, volatile organic compounds (VOCs), PAHs, and 1,4 dioxane. Ammonia and nitrate were reviewed due to the presence of ammonia in the raw water.

Existing granular media filtration is utilized for iron and radium removal. Manganese removal is incomplete due to competition with ammonia for oxidant within the system.

VOC removal including cis-1,2-dichloroethene (DCE), Trans-1,2- DCE, Dichlorofluroomethane, Trichloroethene (TCE), and vinyl chloride was successful with the air stripping process.

The advanced oxidation process testing resulted in 99% reduction in 1,4 dioxane from 23 ppb to 0.13 ppb with ozone and hydrogen peroxide AOP, meeting the state treatment requirements. Various doses of ozone and hydrogen peroxide were used with varying results in the pilot testing process and will be discussed. PAH reduction was also reviewed with 94% reduction in the preliminary iron and manganese filtration process. Additional review is currently underway for PAH reduction in the AOP process and results will be available at the time of the conference.

This presentation summarizes testing objectives, layout, and results from initial bench scale testing, pilot testing at the well sites, and additional bench scale testing for chemical dose optimization.

Combining ZVI and Organic Substrates for Full-Scale Treatment of Dilute Trichloroethene Plume in an Aerobic Aquifer

Daniel P. Leigh, PG
Background/Objectives.A chlorinated ethene plume, consisting primarily of trichloroethene, at the Concord Naval Weapons Station (CNWS) extended approximately 700 feet down gradient from the source area and up to 100 feet below ground surface. The effected aquifer consists of unconsolidated silt, sands and clays and is unconfined and semiconfined. Groundwater in the treatment area is highly aerobic and had sulfate concentrations up to 250 mg/L. The dechlorinating bacteria, Dehalococcoides sp., was not detected in the aquifer. An Enhanced Anaerobic Bioremediation (EAB) pilot test demonstrated complete degradation the chlorinated ethene (CE) concentration from approximately 5,000 microgram per liter (μg/L) to less than 5 μg/L in approximately 500 days. Although EAB alone was effective, the Navy wanted to evaluate a more aggressive approach to achieve site cleanup. A Design Optimization Test (DOT) was conducted to evaluate enhancement of the biological approach by In Situ Chemical Reduction (ISCR). The ISCR approach was demonstrated to treat the CEs substantially quicker than the EAB alone by enhancing abiotic degradation of dichloroethene following biological reduction of trichloroethene.

Results/Lessons Learned. The injection process distributed substrates a minimum of 15 feet from the injection point. The ISCR process rapidly degraded TCE, dichloroethene (DCE) and vinyl chloride (VC) to below MCLs in the majority of the plume during the first injection event. Small areas of the plume in which substrate was not effectively distributed was treated with a second injection event. The reduced treatment time in the ISCR approach is attributed to β-elimination of DCE compared to the hydrogenolysis pathway in the EAB approach. This aggressive approach was demonstrated to effectively treat a laterally and vertically extensive CE plume in an aerobic aquifer.

Flexible Adaptive Decision Document and Attentive Implementation of Combined Remedies – ERH and ERD - at NPL Site, Grants, NM

Sairam Appaji
This presentation will discuss the development of a flexible, progressive Combined Remedy Record of Decision (ROD) for an NPL drycleaner site in Grants, NM. The presentation will discuss implementation of Electrical Resistance Heating (ERH) beneath an operating dry cleaner to address source zone PCE, and Enhanced Reductive Dechlorination (ERD) to address less contaminated zones and the downgradient dissolved phase plume. Results, Lessons Learned – e.g., protection of utilities in the ERH zone, and trend data in dissolved phase contamination will be presented.

Regulatory Closure of a Large Groundwater Plume and Redevelopment at a Legacy Aerospace Site – NASA Downey CA

Fred Payne, Ph.D.
Regulatory closure has now been achieved for the 4,000-foot-long chlorinated solvent plume underlying the former NASA Industrial Plant located in Downey, California. The site was treated with soil vapor extraction, then enhanced reductive dichlorination (biostimulation) was conducted between 2005-2012. Spot treatments using permanganate-based in-situ chemical oxidation in the lower vadose zone and bioaugmentation in the groundwater were also conducted. The site was in post-remediation monitoring between 2012-2016 and the LARWQCB issued a no-further-requirements-for-groundwater letter in March, 2017.

Cleanup of large plumes is often thought to be unachievable and, as a result, management strategies typically employ containment or deferral approaches that require long-term stewardship. The former NASA Industrial Plant is a counter-example to conventional expectations, at which a large plume cleanup was achieved concurrent with a $1B redevelopment effort that includes a hospital, medical office complexm and extensive retail space.

Several sources contributed to the groundwater cVOC plume, which was eventually mapped to be greater than 4,000-feet long, comprising tetrachloroethene (PCE) and trichloroethene (TCE), and their dechlorination products cis-DCE and vinyl chloride. Groundwater was encountered approximately 45-60 feet below surface in the interbedded, predominantly fined-grained sediments of the San Gabriel River alluvium.

Groundwater remediation efforts began in 2005 with the installation of 10 injection well transects (144 injection wells, total) perpendicular to groundwater flow, supporting an inject-and-drift carbohydrate amendment process. The transect strategy allowed concurrent remedial action and redevelopment, with only limited need for rerouting or replacement of remedial system infrastructure.

The site is now fully utilized in its redeveloped state. All redevelopment and site cleanup obligations have been fulfilled, notably including successful completion of the guaranteed, fixed-cost-to-closure contract for cleanup of the 4,000-foot-long chlorinated solvent groundwater plume.

The performance of the groundwater remedy at the former NASA Downey site challenges conventional thinking on the restoration of large, complex, groundwater plumes.

Large Plumes: Geology and Conceptual Site Models

Chris Evans

Big Data & Augmented Reality: The Future of Conceptual Site Models has Arrived

John Horst, PE
The next generation of the conceptual site model (CSM) is the big data, digital CSM, which continues the evolution in the industry from static to dynamic CSMs and 2D to 3D CSMs. The first generation of CSMs were sections in investigation reports- 2D static figures to illustrate key elements like geologic cross sections, groundwater flow maps, and contaminant contours. As high-resolution, Smart Characterization methods are becoming widely adopted, CSMs are more dynamic, requiring us to synthesize “big data” and develop 4D interpretations with more data than ever before. The CSM paradigm has shifted towards the digital CSM which better leverages new tools for data mining, interpretation, synthesis and visualization.

One advantage is streamlined reporting: an investigation report typically requires dozens of 2D cross sections and plume maps, but the digital CSM allows the development of intelligent reports which require far less effort, through the application of multilayered 3D and 4D interpretations. Rather than flipping back and forth between figures and tables in a report, stakeholders can dynamically change the field of view, zooming in on details and evaluating the data behind the interpretation. Software solutions like dynamic PDFs and cloud-based, geographical information system team sites enable open access to the interpretations and the underlying data.

We will also demonstrate the next frontier in digital CSMs- augmented reality. Augmented reality enables one to combine a live view of the physical world with computer generated information – the data behind the interpretation. Rather than viewing a 3D model on a computer screen, one is able to interact with the information in a holographic image – from inside the rendering – changing the field of view with the wave of a hand, or selecting data behind the interpretation by selecting a boring log or sample location with a voice command or hand gesture.

Stratigraphic Flux – Applying Sequence Stratigraphy and High-Resolution Site Characterization to Find Contaminant Flux

Joseph Quinnan, PE, PG
Background/Objectives. The advent of mass flux and high-resolution site characterization methods in recent years has led to more quantitative conceptual site models. Stratigraphic flux combines relative mass flux derived from high resolution site characterization with a sequence stratigraphy perspective on geologic interpretation to provide a framework for classifying and ranking transport potential: transport zones, slow advection zones, and storage zones. The goal of the approach is to develop a 3D stratigraphic flux model to enable stakeholders to understand the controlling influence of aquifer architecture on plume dynamics, thereby improving the reliability and cost-effectiveness of restoration strategies.

Approach/Activities. To demonstrate the utility of the method real-time, high-resolution site characterization methods were used to obtain co-located stratigraphy, permeability, and TCE concentration data in transects downgradient of a former chrome pit. Whole core saturated soil sampling and calculated equivalent groundwater concentrations were performed to map distributions TCE and daughter products, as well as total chrome. Comparative analyses were completed using HPT and vertical aquifer profile groundwater sampling at select locations to verify method results.

Results/Lesson Learned. The 3D stratigraphic flux model showed that significant TCE source mass continues to reside in the saturated clay-rich soils. Groundwater concentrations in the alluvium decreased several orders of magnitude with distance from the source and limited transport was focused in a relatively narrow band in the unconsolidated aquifer. The results from this project suggest that the stratigraphic flux approach is a useful tool for tracking contaminants at sites with complex geology, allowing for targeted remedial approaches.

Understanding Fate and Transport of PFAS to Develop Good Conceptual Site Models of AFFF Impacted Facilities

Ian Ross, Ph.D.
Background/Objectives. Poly- and Perfluoroalkyl substances (PFAS) are used in a wide range of industrial applications and commercial products due to their unique surface tension and levelling properties.. PFAS are also major components of firefighting foams known as Aqueous Film Forming Foam (AFFF). The PFAS group of compounds consists of both perfluorinated compounds, where all carbons are saturated with F atoms, and polyfluorinated compounds, where both fluorine saturated carbons and carbons with hydrogen bonds are present. The understanding of the fate and transport of these compounds in the environment is complex and challenging and will be discussed.

Results/Lessons Learned. The concepts of “biological funneling” and “dark matter” show that PFAS behave significantly differently to other contaminants and existing conceptual site models (CSM) need to be adapted to adequately understand the fate and transport of these contaminants. Examples of CSMs from AFFF impacted sites will be presented.

Using Geology to Follow the Groundwater, Follow the Flow to Successful Remediation

Rick Cramer, PG
Recently in our industry there has been a developing best practice that focuses on the geology to define the subsurface “plumbing”, which can make or break groundwater remediation programs. The subsurface provides the greatest uncertainty when addressing complex contaminated groundwater sites. “It’s dark down there” and the data from boring logs represent only a small fraction of the subsurface and do not present a complete picture. To increase our understanding of the subsurface, Environmental Sequence Stratigraphy (ESS) is an established methodology that focuses on 1) a critical understanding of the sedimentary depositional environment, 2) formatting of lithology data to emphasize vertical grain-size distribution, and 3) a stratigrapher’s knowledge of facies models and related grain-size pattern recognition. These components result in an interpretation and prediction of the geology between boring logs that significantly reduces the uncertainty and provides the framework for characterizing contaminant migration pathways and defining the conceptual site model (CSM). ESS is considered an emerging best practice for complex site CSMs by US EPA and US Air Force (AFCEC).

 

Examples will be presented that show the efficacy of ESS as a critical path to complex site investigation and remediation. The methodology has been successfully applied at numerous complex contaminated groundwater sites throughout the US, including over 25 US DOD facilities. The case studies will provide examples of best practices in applying geology to CSMs and provide “rules of thumb” to test the efficacy of your CSM, such as the following questions.

  • Is groundwater flow, and the contaminant plume, controlled by geologic features (e.g., buried sand channels)?
  • Does the CSM adequately define the geologic features?
  • What tools are available to define the geologic features that carry groundwater contamination?
  • How do buried sand channels and other geologic features affect source identification?
  • How do they affect remedial design?

Panel and Group Brainstorming: How Can Better Site Characterization Lead to More Effective Management of Large Plumes?

Tyler Gass, PG, PHg

Protecting Water Supply

Patricia Reyes

Advanced Oxidation Plant at the Tucson International Airport Area Groundwater Remediation Project

Jeff Biggs
Public health and safety has always been, and will continue to be, one of Tucson Water’s (TW) top priorities. The Tucson International Airport Area Groundwater Remediation Project (TARP) wells and water treatment plant are owned and operated by TW. These facilities have been cleaning up groundwater at one of Arizona’s largest Federal Superfund sites and providing TW’s customers with high-quality drinking water for over two decades.

TW has been operating the TARP remediation wellfields and water treatment plant to remove trichloroethene (TCE) and other volatile organic chemicals (VOCs) from groundwater as part of the Tucson International Airport Area Federal Superfund site remediation since 1994. The treated water is used as a source for Tucson’s potable water distribution system. In 2002, 1,4-dioxane was first detected in TARP groundwater. The process at the TARP water treatment plant was ineffective for 1,4-dioxane removal. TW closely monitored 1,4‑dioxane levels and began blending to reduce concentrations from TARP. Years before revised regulations were published, TW began studying long-term solutions and develop contingency plans for deploying advanced oxidation, the only proven municipal-scale treatment process for this contaminant.

With direction from Tucson’s Mayor and City Council, TW commissioned design and construction of a new Advanced Oxidation Process (AOP) treatment facility adjacent to TARP to treat groundwater from the remediation wells upstream of the existing plant.

Tucson’s AOP facility is the first application of UV AOP technology in Arizona for groundwater remediation producing municipal drinking water and the State’s first drinking water treatment facility targeting 1,4‑dioxane. The facility employs several innovative elements designed to ensure consistent water quality, provides fail-safe automated operation, and minimizes operating costs by optimizing energy and chemical use. It is also the first municipal drinking water UV AOP facility in the U.S. to utilize granular activated carbon (GAC) specifically for excess hydrogen peroxide quenching.

Contamination of Public Wells by Perfluorochemicals: How Three New Hampshire Utilities Approached the Problem.

Jeffrey Marts, PG
Perfluorochemicals (PFC’s) are emerging contaminants of concern that have adversely impacted hundreds of residential wells and numerous municipalities in New Hampshire who rely on groundwater resources. The varying release mechanisms of PFC’s (e.g. air emissions versus liquid spills) has had a major influence on the nature and extent of groundwater contamination requiring different approaches of mitigation/remediation to ensure the continuity of public water supply delivery.

Emery & Garrett Groundwater Investigations has been engaged in providing professional consulting services to three different municipalities in NH whose public groundwater sources have been adversely impaired by PFC contamination. Different release mechanisms of PFC’s and the associated response to protect public health were highly varied and unique for these three communities. One community’s groundwater sources were adversely impacted as a result of an air release from a local manufacturing facility. This led to the shutdown of two production wells capable of producing more than 1,000,000 gallons per day. Another NH community lost groundwater production wells as a result of PFC’s that leached into the local groundwater system from a release of firefighting foam. Lastly, a third community has had a well shut down as a result of an alleged release of PFC’s from a landfill at a metals recycling facility, though the source investigation is still ongoing.

These PFC impacts have substantially impaired the water supply available to these communities who only three years ago had never heard of, or been concerned about, these compounds. This paper will address how each of these communities has approached the problem and how they are attempting to mitigate/remediate the situation. The PFC contamination crisis has brought to light how important it is for communities to develop excess capacity in case of an emergency and develop groundwater monitoring programs to assess new contaminant threats associated with PFC’s.

Cost Recovery Options for Emerging Contaminants- Shifting Treatment Costs from Ratepayers to Polluters

Richard Head
Remediation efforts to provide high-quality drinking water come at a significant financial burden to water utilities and public entities. Whether addressing a regulated drinking water constituent or an emerging contaminant of concern it becomes increasingly challenging to deliver affordable water. While every case must be evaluated on its facts, legal precedence has been set for recovering the costs of cleaning up contaminated drinking water and shifting treatment costs from ratepayers to polluters. Under the theory of “products liability” manufacturers of chemicals responsible for contamination are held accountable for the associated treatment costs— including but not limited to replacement or treatment of affected well, capital costs, well connection and distribution system costs, operation and maintenance costs for the lifetime of affected wells, and protection against future uncertainty through the inclusion of contamination contingency clauses in settlement documents. By including a legal review of cost recovery options as part of their systematic approach to evaluate remediation efforts water utilities may be able to lessen their financial burden associated with providing high-quality drinking water. This presentation will detail the legal review process that can be undertaken by a utility interested in pursing cost recovery options for regulated or emerging contaminants. The factors to consider when evaluating manufacturer liability will be reviewed. General resource commitments and timelines for undertaking this process will also be particularized. To see the legal review process in context a case study from the State of New Hampshire will be deconstructed; twenty-two major oil companies were sued for adding MTBE to New Hampshire’s gasoline knowing that it would contaminate the State’s drinking water supplies resulting in over $372 million in settlements and jury verdict which helped fund the creation of an MTBE Remediation Bureau in the State’s Department of Environmental Services.

Emerging Contaminants: Situational Management Staying Ahead of the Issue

Rich Royer, Ph.D.
The management of public and private drinking water supplies impacted with emerging contaminants such as Poly- and Perfluorinated Alkyl Substances (PFAS) can present several unique challenges. With these contaminants being identified in an increasing number of water supplies, a system is needed to prioritize analysis of water resources that are utilized by the public either through municipal or private systems. When an issue is identified, clarity of communication becomes paramount. Any public communication strategy needs to acknowledge the breadth of information readily and rapidly available to most people today, and be prepared to deal with potential confusion or misunderstandings. Providing accurate, relevant information about emerging contaminants can be especially challenging as they often have fluid or varying levels of regulation and their potential risks are often poorly understood by the public. The response action to an impact needs to be well coordinated and consider both short- and long-term solutions. Many technical challenges can also arise when emerging contaminants need to be treated, either at existing treatment plants or in individual residences. Technically sound but expedient testing may be required to refine the treatment design depending on the nature of the contaminant of concern. A holistic approach to managing impacts that encompasses communication, organization, and technology is necessary to respond to drinking water supplies impacted by emerging contaminants such as PFAS.

Explaining 1,4-Dioxane Occurrence in America’s Public Water Supplies

Thomas Mohr, PG
1,4-Dioxane samples were collected and analyzed from 4,864 U.S. public water systems for the 3rd Unregulated Contaminant Monitoring Rule (UCMR3) to understand the nature of its occurrence and the basis for establishing drinking water standards. 1,4-Dioxane was detected in samples from 21% of 4864 PWSs, and exceeded EPA’s Health Advisory Level (0.35 mg/L) in 6.9% of PWSs. 1,4-Dioxane ranked second for frequency of detection among the 28 UCMR3 contaminants.

1,4-Dioxane is now familiar as a groundwater contaminant, but the detection frequency for 1,4-dioxane in surface water was only marginally lower than in groundwater (by a factor of 1.25). Groundwater concentrations were higher than those in surface water and contributed to a higher frequency of exceeding the reference concentration (by a factor of 1.8), indicating that surface water sources tend to be more dilute. Sampling from large PWS increased the likelihood of 1,4-dioxane detection 2.18 times relative to small systems.

What are the implications of these findings? This presentation reviews the nature of 1,4-dioxane detections and evaluates co-contaminant association patterns to confirm the likely sources of 1,4-dioxane in PWSs. The consequences of 1,4-dioxane detections are evaluated in the context of health risk and drinking water treatment costs. Some water supply systems may need to improve their treatment capabilities in response to 1,4-dioxane detections, which can be an expensive challenge, owing to 1,4-dioxane’s infinite solubility, lack of volatility, and low propensity to adsorb to granular activated carbon. The UCMR3 data suggest there remain many unresolved 1,4-dioxane release sites, for which there will be a growing market for consultant remediation services.

This presentation will profile 1,4-dioxane occurrence, explain why its historical use manifests today as a drinking water contaminant, and how water utilities nationwide are addressing the problem.

Fast-Tracked Design-Build of a GAC Treatment System for Removal of PFOA from a Municipal Drinking Water Supply

Bjorn Cuento
Perfluorooctanoic acid (PFOA) was detected in public drinking water above the USEPA drinking water Health Advisory at a high profile project site requiring a comprehensive strategy to restore community drinking water. In response, one 900 gpm and a second 700 gpm GAC treatment system were constructed within an accelerated timeframe for a community that was under a “do not drink “ ban on the local groundwater-sourced potable water supply.

The project involved well water evaluation, verification of water distribution model, treatment process design, permitting, construction, start-up, and operation and maintenance of the GAC systems, with the permitting, construction and start-up phases completed within a six-week project timeframe.

The project was completed in two parallel phases. In the first, regulatory approval was being sought for the interim design package focusing on the GAC treatment process and major mechanical components, while the final design package was being jointly completed in the parallel second phase. Successful execution required close coordination with the local mayor and public works department, multiple state and federal regulatory agencies, utility companies, contractors, and our private-industry client.

The project was completed two days ahead of the scheduled deadline was a finalist for the Delaware Chapter of the American Council of Engineering Companies (ACEC) Grand Conceptor Award. All stakeholders and the community continue to be satisfied with ongoing system operation and maintenance, and the supply of potable water.

Fate and Transport Modeling of PFOS in a Fractured Chalk Aquifer Towards a Large Scale Drinking Water Abstraction

Kelly S. Houston, PE
Background/Objectives. In December 2005 the largest explosion in Western Europe since World War Two occurred at the Buncefield Oil Storage Terminal in the UK. In controlling the resulting fires approximately 250,000 litres of firefighting foam containing PFOS were deployed, a proportion of which directly impacted the underlying chalk Principal Aquifer which lies within a protected drinking water abstraction zone. Investigations identified PFOS to be present in groundwater beneath the site resting at approximately 35m below ground level, source concentrations of PFOS ranged from between 20 to 50µg/l well above the 0.3 µg/l guidance values in the UK.

Many questions remain regarding the fate, transport, attenuation, and remediation of PFOS, which is classed as a persistent organic pollutant (POP). Recent advancements in the science of environmental toxicology of PFAS have drawn attention to these chemicals and the need for a better understanding of their behaviour in the environment.

Results/Lessons Learned. The project has resulted in significant insights being gained regarding transport of PFOS in fractured rock at the site, including characterization of background PFOS concentrations and attenuation mechanisms such as retardation and dual-porosity mass transfer characteristics. Giving the significant increase in recognition of the number of potential PFAS source zones globally and the significant number of drinking water supplies at risk these insights will be of interest to a wide audience.

Treating Emerging Contaminants in Drinking Water: LADWP’s Planning and Design

Nicole Blute, Ph.D., PE

The City of Los Angeles encompasses an area of 465 square miles with a population of nearly 4 million residents. Local groundwater provides approximately 11% of the City’s total water supply and the City has a goal of achieving 50% of the water sources supply from the San Fernando Basin by 2035.

Many Los Angeles Department of Water and Power (LADWP) groundwater production wells in the San Fernando Basin are impacted by contamination caused by various commercial and industrial activities. Without comprehensive containment and groundwater basin remediation, the City will significantly lose the ability to use this valuable local resource within the next decade. To improve groundwater clean-up and increase the supply of high quality renewable water resources for the City, LADWP is undertaking a program to evaluate and implement groundwater treatment throughout the SFB. This 10 year program of up to $600M will greatly improve local renewable water supplies for the City.

Design of treatment for the first wellfield is underway and illustrates the complexity of trying to implement treatment of the various contamination plumes given the extensive pumping activity within the basin. Challenges have included evaluation of contaminants of concern, treatment alternatives, and facility sizing given project uncertainties. Extensive modeling and bench-scale testing have been completed to reduce the potential uncertainties and improve the treatment design criteria. The results of the engineering evaluation has been the design of an innovative UV advanced oxidation treatment facility with granular activated carbon for peroxide quenching that will treat the primary contaminant of concern (i.e., 1,4-dioxane), as well as VOCs.

This paper will present the approach for beginning the expansion of LADWP’s groundwater treatment facilities and treatability testing results providing the foundation for the design.

Treatment of Perfluorinated Compounds to Protect Two Drinking Water Supplies

Kyle Hay
Even with the recent EPA reductions in Health Advisory levels (May 2016) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), the debate continues regarding acceptable exposure levels in drinking water supplies. Sources of PFASs include industrial and commercial product manufacturing and firefighting foams associated with air force bases and airports. These highly stable contaminants are persistent within our natural environment, encompass a family of dozens of compounds, and may have unique health effects.

Two different sites, one each in New Hampshire and Vermont, have experienced PFOS/PFOA contamination and have provided excellent opportunities for research of effective treatment with regard to drinking water. Treatment alternatives, risk reduction measures, public education efforts and medical monitoring efforts are consistently being evaluated. Pilot testing has been completed to analyze the effects of carbon treatment on the water systems, with a focus on maintaining adequate corrosion control and confirming the appropriateness of large-scale treatment designs. Demonstration testing of the same technology is ongoing to evaluate the effectiveness and develop a better understanding of carbon treatment over the long-term. This presentation discusses the implementation of both the Pilot testing and Demonstration project in the larger context of providing safe drinking water and maintaining an awareness of public demand and public health.

Reception

Refreshment Break

Refreshment Break

Registration

Registration

Welcome and Keynote

Maureen Sullivan

Wrap-Up/Adjournment