Groundwater Solutions: Innovating to Address Emerging Issues for Groundwater Resources: Alphabetical Content Listing
John Wilson, Ph.D
John Wilson, Ph.D
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.
Min-Ying Chu, Ph.D., PE
Mark Klemmer, PE
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
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.
Marc W. Killingstad
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.
Nick Welty, PG
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.
Jeremy Birnstingl, Ph.D.
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.
Seth Kellogg, PG
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
Remediation of Large Groundwater Plumes through Optimized Extraction System and Monitored Natural Attenuation
Noman Ahsanuzzaman, Ph.D., PE
Superfund Optimization Strategy: Extracting Lessons Learned on Managing Large Plumes from 640 Optimization Recommendations
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.
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.
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.
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.
Jeffrey R. Hale, PG
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.
Patrick Curry, PG
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
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
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.
Kristen Thoreson, Ph.D
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.
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
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.
Xin Song, Ph.D.
Technical Resources to Respond to Environmental Releases of Poly- and Perfluoralkyl Substances (PFAS)
This presentation will provide an overview of the PFAS Team work (which will be well underway) and explain how others can participate.
Caitlin Bell, PE
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.
James Woolford, Ph.D.
Angel Gebeau, PE
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
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
Regulatory Closure of a Large Groundwater Plume and Redevelopment at a Legacy Aerospace Site – NASA Downey CA
Fred Payne, Ph.D.
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.
John Horst, PE
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
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.
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.
Rick Cramer, PG
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
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
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
Rich Royer, Ph.D.
Thomas Mohr, PG
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
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
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.
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.
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.