Senior Environmental Engineer
GSI Environmental Inc
Dr. David Adamson is a senior engineer at GSI Environmental Inc. in Houston, Texas. Dr. Adamson has more than 15 years of environmental project experience in academic research and environmental consulting, and he is a licensed Professional Engineer in Texas. He has worked as a post-doctoral research associate at Cornell University, and he has held lecturer, research scientist, and Adjunct Assistant Professor positions at Rice University in the Civil and Environmental Engineering Department. He has conducted and published research on a variety of areas related to subsurface contamination and biological remediation. Since joining GSI in 2004, Dr. Adamson’s professional experience includes site investigation, characterization, and remediation, with projects in the U.S., Europe, Latin America, and the Middle East, including the design, implementation, and management of full-scale remediation projects. He has extensive expertise in projects dealing with natural attenuation, source zone characterization, emerging contaminants, matrix diffusion, and the development and testing of innovative treatment technologies. He has served as a Principal Investigator or co-Principal Invesigtator on several DoD-sponsored research projects, including those focused on 1,4-dioxane, innovative long-term monitoring strategies, enhanced amendment delivery systems, and improved characterization and treatment methods for contaminants in low permeability matrices.
PLATFORM PRESENTER - Emerging Contaminants: Tick Tock
A Comprehensive Evaluation of UCMR3 Drinking Water Data and Implications for Site Cleanup Requirements
This study will present the results of a comprehensive evaluation of the data collected as part of the United States Environmental Protection Agency’s (USEPA) Third Unregulated Contaminant Monitoring Rule program (UCMR3). This program collects data on the occurrence of specific contaminants from the Candidate Contaminant Lists (i.e., ones that do not have health-based standards) within public drinking water systems. The first two rounds of UCMR monitoring collected hundreds of thousand of data points over two three-year periods and cost tens of millions of dollars, but regulatory actions based on these results have been slow. To-date, none of the contaminants monitored during UCMR1 and UCMR2 have established MCLs, in part because the low frequency of detection in drinking water supplies for the majority of contaminants.
The UCMR3 monitoring program was different than its predecessors in two key ways: (1) USEPA defined minimum reporting limits (typically <1 ug/L for each comtaminant based on analytical capabilities) that were expected to increase detection frequencies; (2) several contaminants with a higher suspected prevalence in drinking water systems were included in the monitoring list. UCMR3 monitoring was completed between January 2013 and December 2015 and included 28 individual contaminants plus multiple microbiological constituents. System size dictated participation in UCMR3 monitoring (i.e., only a select number of smaller systems were included) as well as the number of analytes for each system. As of June 2016, 4864 systems had reported results, with the number of concentration records totaling over 1 million.
Several statistical techniques are being used to evaluate this massive dataset, ranging from exploratory data analysis to linear discriminate analysis. Key differentiators during these analyses include detection frequency, exceedance frequency (based on health-based reference concentrations), contaminant class, geographic location, concentration, system size, water type (surface vs. groundwater vs. mixture), disinfectant type, co-occurrence, and temporal trends.
The evaluation addresses a number of key questions about the occurrence of these unregulated contaminants. Specifically, several contaminants (e.g., metals) proved to be widely prevalent but posed little apparent risk based on a comparison to health-based reference concentrations. In general, contaminants were present above these reference concentrations in samples from a limited number of systems (~1% or less), including PFOA and PFOS which were compared to USEPA’s recently-updated provisional health advisories. Exceptions included chlorate (38% systems with exceedences) and 1.4-dioxane (7% of systems with exceedences). 1,4-dioxane was the most highly influenced by the reference concentration used for determining exceedences; decreasing the cancer risk from 10-4 to 10-6 increased the number of water systems exceeding the reference concentration from 0 to 336. 1,4-dioxane, PFASs, and other organics were much more likely to be associated with groundwater sources and thus are particularly relevant in driving changes to subsurface remediation requirements. Contaminant co-occurrence patterns appear to be strongly influenced by the size of the system, the contaminant class, and the water type. Given the increased detection and exceedence rates being demonstrated in UCMR3, there is a potential that the regulatory determination process will be accelerated relative to the rate associated with previous rounds of monitoring.
Fe(III)-Mediated Photodecomposition of Per- and Poly-fluorinated Alkyl Substances for Remediation of Groundwater
Fe(III)-Mediated Photodecomposition of Per- and Poly-fluorinated Alkyl Substances for Remediation of Groundwater The overall goal of this study was to investigate and demonstrate the potential for photodecomposition of PFASs in the presence of ferric iron (Fe(III)) to serve as an innovative, sustainable, and cost-effective in-situ remediation technologies for PFAS-contaminated groundwater. This novel technology is based on a reaction mechanism that requires only sunlight and a source of ferric iron to proceed. Photodecomposition of PFASs occurs by one of several pathways that involve the formation of radical oxygen species and organic free radicals. As a result, a long-chain PFAS is cut down by one carbon atom at a time with the subsequent release of two fluoride ions and carbon dioxide. Based on bench-scale studies described below, a degradation half-life of approximately 5 days was observed under quiescent conditions for a representative PFAS (PFOA). This photodecomposition process has several significant advantages as a potential remediation technology for groundwater impacted by PFASs: (1) the reaction is reliable and easy to initiate; (2) the reaction proceeds under commonly observed groundwater conditions, with no need for high pressure, elevated temperatures, extreme pH or redox conditions that pose a safety concern or harm soil quality; and (3) the reaction inputs are either very inexpensive (Fe(III) is basically rust) or free (sunlight).
Bench-scale testing was used to confirm the potential efficacy of this technology. In these studies, PFOA (48.3 uM, 20 mg/L) was decomposed in the presence of Fe(III) (0.48 mM, 26.8 mg/L) under direct sunlight without any extra energy input. The PFOA concentration was reduced by 97.8% after 28 days and converted to shorter-chain intermediate PFCAs (C2-C7) and ultimately to F-. The F- concentration in the solution increased from 0 mg/L to 1.74 mg/L after 28 days, with a defluorination extent (F-released/F in PFOA) of 13.6%. The extent of PFOA decomposition and defluorination for this Fe(III)/sunlight approach was also compared to three alternative systems under sunlight illumination: Fe(III) alone, Fe(III) with persulfate and Fe(III) with H2O2 (Figure 3). Fe(III)-alone achieved the highest PFOA decomposition efficiency (97.8%) while Fe(III)+persulfate removed 88.9% (p<0.05), and Fe(III)+H2O2 system removed 74.8% (p<0.05). H2O2 and persulfate can react with water to form •OH and SO4-• radicals, respectively, which can degrade PFOA. However, addition of H2O2 or persulfate hindered PFOA removal. Apparently, these oxidants disrupted the formation of a Fe(III)-PFOA adduct, which is presumed to be critical for this degradation pathway.
The proof-of-concept results were used to develop potential in situ and ex situ treatment options for this technology. The most promising in situ approach is expected to be a passive subsurface reactor constructed using large-diameter caissons (i.e., unpumped wells) that serve to focus groundwater flow and provide contact between PFASs, Fe(III), and supplied light. The most likely ex situ treatment approach is expected to be high-concentration PFAS solutions from a groundwater extraction system. The technology is not particularly sensitive to the concentration of PFASs in the groundwater and thus may be suitable for niche applications where other technologies cannot achieve performance objectives.