Monitored natural attenuation (MNA) has been widely used as a remedial strategy, acknowledged by the EPA as the most appropriate technology for cost effective remediation under certain site conditions. Despite the widespread use of MNA, empirical methods are lacking to evaluate the sustainability of MNA at a site. The objective of this thesis is to investigate the natural attenuation capacity (NAC) as a quantitative metric for evaluating the sustainability of MNA for contaminants in groundwater systems. Five DoD sites were selected for this study, where the common thread between the sites is the existence of a mature chlorinated ethene groundwater plume and the use of MNA as the long-term remediation strategy. Constituent specific NAC values were quantified and statistically examined to determine past performance of MNA at the sites. A conceptual decision model was developed to be a framework of the statistical tools demonstrated in this thesis. Analyzing MNA sustainability at a site can be separated into two components; past performance of natural attenuation and evaluation of current MNA parameters. The former is the focus of this thesis where NAC is the screening metric and the temporal trend in the rate of natural attenuation being evaluated. Within the conceptual decision model, the use of NAC as a screening tool in combination with a specific analysis of MNA parameters allows engineers, regulators, and decision makers to clearly determine whether MNA at a site is sustainable and whether site specific remediation goals will be met. / Master of Science

<p>Chlorinated solvents are common contaminants in soil and water. Under anaerobic conditions microbes are capable of transforming chlorinated solvents into ethylene which would result in a remediation of the contaminated area. In order to use natural attenuation as a remediation method evidence of continuous degradation is required. Furthermore, the degradation must occur at a sufficient rate and continuous monitoring of the site is needed until the demanded levels are achieved. A field study was performed on the basis of data from a dry-cleaning facility contaminated mainly by perchloroethylene. The purpose of the study was to define the existing situation regarding distribution and transformation of contaminant in order to evaluate the possibilities of using natural attenuation as a method of remediation. Degradation of perchloroethylene proceeds through successive removal of chlorine, with the formation of trichloroethylene, dichloroethylene, vinyl chloride and ethylene. There exists evidence of degradation as far as vinyl chloride on the site but whether transformation continues to ethylene is not established. The computer model Biochlor was used to simulate distribution and degradation of the contaminants. The site possesses a complex hydrogeology and the existing data are not sufficient to distinguish the effect of degradation from other factors such as spreading of contaminant between different layers of soil. Since degradation failed to be quantified, natural attenuation can not be recommended as a safe remediation method at the considered site without further investigations.</p> / <p>Klorerade lösningsmedel är vanligt förekommande föroreningar i mark och vatten. Under anaeroba förhållanden kan mikrober omvandla klorerade kolväten till eten vilket leder till rening av det förorenade området. För att kunna använda denna naturliga nedbrytning som saneringsmetod krävs bevis för att nedbrytning fortskrider i tillräcklig utsträckning för att rena området och därefter krävs kontinuerlig provtagning till dess målen för saneringen har uppnåtts. En fallstudie utfördes utifrån data från en kemtvättsfastighet förorenad av i första hand perkloreten. Syftet var att kartlägga föroreningssituationen med avseende på spridning och nedbrytning av de klorerade föreningarna för att undersöka om naturlig nedbrytning var en möjlig framtida saneringsmetod. Nedbrytning av perkloreten sker stegvis genom att klor avspjälkas, under bildande av produkterna trikloreten, dikloreten, vinylklorid och etengas. Nedbrytning av förorening har konstaterats ske på fastigheten fram till vinylklorid men huruvida nedbrytning avstannat där eller fullföljts till etengas är ej klarlagt. Datormodellen Biochlor användes för att simulera spridning och nedbrytning av utsläppet. Fältplatsen har en komplex hydrogeologi och befintliga fältdata var inte tillräckliga för att särskilja nedbrytningens effekt från faktorer såsom spridning av förorening mellan olika jordlager. Eftersom nedbrytningen inte kunde kvantifieras kan naturlig nedbrytning inte rekommenderas som säker saneringsmetod på denna fältplats utan kompletterande analyser.</p>

Natural attenuation of trichloroethene (TCE) and technetium (99Tc) was studied for five consecutive seasons (from January 2002 to January 2003) in Little Bayou Creek. The stream receives ground water discharge from an aquifer contaminated by past waste disposal activities at the Paducah Gaseous Diffusion Plant (PGDP), a uranium enrichment facility near Paducah, Kentucky. Results from stream gaging, contaminant monitoring, tracer tests (with bromide, nitrate, rhodamine WT and propane) and simulation modeling indicate the TCE is naturally attenuated by volatilization and dilution, with volatilization rates related to the ambient temperature and surface discharge rate. The only apparent mechanism of 99Tc attenuation is dilution. Travel times of non-gaseous tracers were found to be similar and have highest values in October and lowest in June. It was also estimated from modeling that the transport of the solutes in the stream was mostly one-dimensional with insignificant secondary storage.

Regulatory acceptance of monitored natural attenuation (MNA) requires demonstration that natural processes, such as sorption and biodegradation, attenuate specific contaminants of concern on a time scale that is comparable to other remediation options while concurrently preventing contaminant migration to site-specific points of contact. Two of the tools used to demonstrate the efficacy of MNA, microcosm experiments and numerical fate and transport modeling, were examined in this study. In the first phase of this work, laboratory microcosm studies were initiated as part of an overall MNA site assessment to determine whether a native microbial consortia collected with a soil sample from a petroleum-hydrocarbon contaminated site was capable of biodegrading specific polynuclear aromatic hydrocarbon (PAH) compounds. Results indicated that selected PAH compounds were biodegraded under simulated natural conditions using oxygen and sulfate as electron acceptors. In the second phase of this study, a numerical experiment was conducted using the three-dimensional, multiple substrate, multiple electron acceptor fate and transport model SEAM3D (Waddill and Widdowson, 1997) to evaluate the impact of including iron(III)-reducing conditions during numerical simulations of natural attenuation. Results for this phase of the study indicated that the mass of hydrocarbon simulated as biodegraded by the iron(III)-reducing population was significantly larger than hydrocarbon biodegradation under aerobic conditions. The final component of research used the SEAM3D model to interpret field observations recorded during a natural attenuation experiment where the fate and transport of selected hydrocarbon contaminants (BTEX and naphthalene) was tracked through an extremely heterogeneous, but well-instrumented test aquifer. Results from the calibrated model for the NATS experiment indicated that the majority of the contaminant remained in the non-aqueous phase during the first year of the experiment, and that aerobic biodegradation was the dominant natural attenuation process. Model results were particularly sensitive to the rate of contaminant release and the starting mass of electron acceptor. / Ph. D.

The potential for biodegradation of contaminants in soil was assessed using an array of molecular methods, including terminal restriction fragment length polymorphism (TRFLP), quantitative polymerase chain reaction (qPCR), and traditional culturing techniques combined with sequencing of the 16S or ITS regions of the cultured bacteria and fungi. Soil was collected from the Santa Susana Field Laboratory (SSFL), which was the site of numerous liquid-propulsion rocket engine tests as well as nuclear energy research and development, which led to contamination of the soil with a wide variety of constituents. The contaminants of interest (COIs) at this site include polychlorinated biphenyls (PCBs), dioxins, polycyclic aromatic hydrocarbons (PAHs) and non-PAH petroleum hydrocarbons (PHCs). Various metals, most notably mercury and silver, are also present on the site. The purpose of this study was to determine if biodegradation is contributing to natural attenuation of contaminants in the soil, what organisms are likely causing biodegradation, and what rate(s) can be expected in the future. A literature review was conducted to investigate the chemical properties of theses COIs, their toxicity, and abiotic and biotic degradation. This research concluded that these COIs can be biodegraded if the right bacteria and/or fungi are present and active in the soil in sufficient numbers under the right conditions. Many known biodegraders of the COIs were identified in the literature review along with the most common pathways of biodegradation and degradation rates observed in field and laboratory studies. Soil was collected from 30 sample locations, with 3 sets of 10 samples containing high concentrations of one COI but low concentration of the others. PHCs and PAHs were found to be largely co-located, so 10 samples were selected for both of them. The remaining 20 samples were split evenly between PCBs and dioxins. DNA was extracted directly from all 30 soil samples and amplified using PCR for TRFLP analyses. Two soil samples were sent to Microbial Insights® for qPCR analysis. This analysis included 18 gene targets for the degradation of PHCs and PAHs, as well as the target gene for Dehalococcoides (an anaerobic dechlorinating bacteria). For each culturing a model chemical was selected to represent each COI and added to Bushnell-Haas agar plates containing no added carbon source other than the model compounds. The model chemicals were No. 2 diesel fuel for PHCs, naphthalene for PAHs, PCB #1 (monochloro) for PCBs, and dibenzofuran for dioxin. These plates were used to screen for biodegrading bacteria and fungi for each COI. Once cultured, 16S and ITS sequencing were used to identify these potential COI degraders and determine what TRFLP peak they would produce. The identity of isolated organisms was compared to information from the literature to assess the likelihood of COI biodegradation at SSFL. From the culturing experiments, 45 organisms were isolated, sequenced, and identified. The 45 included 14 unique bacteria and seven unique fungi. Of these, 10 different bacterial species and 5 different fungal species have been reported as COI biodegraders or belong to genera that contain reported COI biodegraders. TRFLP analysis revealed that the soil type has more effect on the microbial population than the presence of any of the COIs. There were no specific peaks that were significantly correlated to any specific COI. The peak distributions were fairly even, indicating a large amount of biodiversity in the microbial populations of the soil samples. The qPCR analysis revealed that SSFL soils contain significant populations of microbes that can degrade PHCs aerobically. Anaerobic PHC, anaerobic PAH, and aerobic PAH targets were not detected. A small amount of Dehalococcoides was detected in one of the samples. Collectively this study suggests that microbes present in SSFL soils are capable of biodegrading PHCs, and the genes for such biodegradation are actively being expressed. With the exception of a small population of Dehalococcoides, bacteria associated with the biodegradation of PAHs, PCBs, and/or dioxins were not detected. However, several strains of fungi were identified which have been reported to mediate cometabolic biodegradation of these compounds. Since these fungi do not require anaerobic conditions, they are more likely to contribute to natural attenuation than bacterial reductive dechlorination. Laboratory microcosm experiments are suggested for estimating rates of biodegradation at SSFL under natural attenuation conditions. Bioaugmentation and/or biostimulation methods should also be investigated in addition of natural attenuation. These microcosm experiments are currently underway in a companion study at Cal Poly by graduate student Mackenzie Billings.

Permeable reactive barrier (PRB) technology is increasingly considered for in situ treatment of contaminated groundwater; however, current design formulas for PRBs are limited and do not properly account for all major physical and attenuation processes driving remediation. This study focused on developing a simple methodology to design PRBs that is easy to implement while improving accuracy and being more conservative than the available design methodologies. An empirical design equation and a simple analytical design equation were obtained to calculate the thickness of a PRB capable of degrading a contaminant from a source contaminant concentration to a maximum contaminant level at a Point of compliance . Both equations integrate the fundamental components that drive the natural attenuation process of the aquifer and the reactive capacity of the PRB.The empirical design equation was derived from a dataset of random hypothetical cases that used the solutions of the PRB conceptual model (Solution I). The analytical design equation was derived from particular solutions of the model (Solution II) which the study showed fit the complex solutions of the model well. Using the hypothetical cases, the analytical equation has shown that it gives an estimated thickness of the PRB just 15 % lower or higher than the real thickness of the PRB 95 percent of the time. To calculate the design thickness of a PRB, Natural attenuation capacity of the aquifer can be estimated from the observed contaminant concentration changes along aquifer flowpaths prior to the installation of a PRB. Bench-scale or pilot testing can provide good estimates of the required residence times ( Gavaskar et al. 2000) , which will provide the reactive capacity of the PRB needed for the calculation. The results of this study suggest also that the installation location downgradient from the source of contaminant is flexible. If a PRB is installed in two different locations, it will achieve the same remediation goals. This important finding gives engineers and scientists the choice to adjust the location of their PRBs so that the overall project can be the most feasible and cost effective. / Master of Science

Groundwater parameter analysis, microcosm experiments, and microcosms modeling were undertaken to assess the potential of Monitored Natural Attenuation as a remediation strategy at Site 12 at the Naval Amphibious Base (NAB) Little Creek. Site 12 was contaminated with PCE waste disposed by a former dry cleaning facility. In the groundwater analysis, contaminant characteristics and redox indicators were evaluated to assess the reductive dechlorination potential of Site 12. The results of the groundwater analysis indicated that Site 12 exhibited sulfate-reducing and methanogenic conditions which provide the required environment for reductive dechlorination. However, Site 12 only demonstrated partial reductive dechlorination to cis-1,2-DCE and possible anaerobic oxidation of cis-1,2-DCE and VC to CO₂. Microcosms were designed to further evaluate the extent of microbial degradation of the chlorinated ethenes at Site 12 and to provide concentration versus time data for the estimation of chlorinated ethenes' biodegradation rates. The extent of degradation in the microcosms was consistent with the groundwater data. However, ethene production was not observed and the quantity of TCE measured for two of the microcosms differed substantially when compared to the groundwater data. The microcosm model used SEAM3D to simulate the results of the microcosm experiments (concentration versus time data) to estimate the biodegradation rates of PCE and its daughter products. The SEAM3D reductive dechlorination package, based on Monod kinetics, predicted for the MLS12-Shallow microcosm maximum specific utilization rates for PCE, TCE, cis-1,2-DCE and VC at 0.4, 0.42, 0.05, and 0.25 day⁻¹, respectively and half saturation coefficients for PCE, TCE, cis-1,2-DCE and VC at 0.41, 0.01, 0.07, and 0.02 mg/L, respectively. The results of this study suggest that while the groundwater environment provides the necessary conditions for reductive dechlorination, Site 12 is not an efficient system for reductive dechlorination. This lack of efficiency may stem from sparse microbial populations capable of reducing cis-1,2-DCE or the system may contain levels of PCE which inhibit the further reduction of cis-1,2-DCE. Based on the observed inhibitory relationship between PCE and cis-1,2-DCE and VC production, source removal would reduce the PCE levels and encourage further reductive dechlorination at Site 12. Therefore, the recommended first step for a monitered natural attenuation-based remediation strategy at Site 12 should be source removal. / Master of Science

Accidental spills of hydrocarbons from underground storage tanks or pipelines are a common cause of subsurface contamination. Anthropogenic hydrocarbon contamination of soil is a global issue throughout the industrialised world. In England and Wales alone, 12% of all serious contamination incidents in 2007 were hydrocarbon related. Biodegradation could be in situ process leading to a decrease of benzene concentrations in groundwater. Recently, monitored natural attenuation has become an effective alternative to the more active remediation methods for the in situ treatment of contaminated subsurface environments. The main objective of this study was to examine the possibility of adopting monitored natural attenuation as a remediation technique for the contaminated groundwater aquifer. In this natural attenuation study, the following tasks were conducted bioremediation investigation, biological first-order decay rates, Mann-Kendall Test model and BIOSCREEN model for the contaminated groundwater aquifer. In this study, a full-scale natural bioremediation investigation was conducted at a petroleum hydrocarbon spill site. In this study, The calculated biodegradation capacity (8.261 mg/L) at this site is much higher than the detected concentrations of petroleum-hydrocarbons (3-4 mg/L) within the most contaminated area inside the plume. Thus, natural biodegradation should be able to remove the contaminants effectively. The calculated biological first-order decay rates for benzene were between 1.7¡Ñ10-3-9.0¡Ñ10-4 day-1 respectively. Mann-Kendall test was applied to analyze the trend of contaminant variations. Results show that the S-value of monitor wells SW-1W, SW-4W, SW-42W, SW-23W, SW-30W, SW-67W and SW-70W were -2.23607, -1.16276, -1.52053, -1.34164, -1.26323, 0 and -1.34164, respectively. The negative S values reveal that the all contaminants tended to decrease. This indicates that the hydrocarbon plume at this site is not expanding, and has been contained effectively by the natural attenuation mechanisms. BIOSCREEN model from the groundwater analyses indicate, a first-order decay model reached the downgradient monitor well located 220 m from the spill location. that approximately 89% of the contaminate removal was due to biodegradation processes. The study of petroleum-hydrocarbons bacterial consortium were include Aquincola tertiaricarbonis L10¡BBosea sp. GR060219¡BBrachymonas petroleovorans strain CHX¡BHydrogenophaga sp. p3(2011)¡BHydrogenophaga sp.¡BMethylibium sp. YIM 61602¡BMycobacterium sp.¡BRhodoferax sp. IMCC1723¡BRhodoferax sp.¡BUncultured Rhodocyclaceae bacterium clone Elev_16S_975¡BUncultured Rhodocyclaceae bacterium clone eub62B1¤ÎUncultured Beggiatoa sp. clone GE7GXPU01BJTWR. Thus, the in situ bioremediation technology has the potential to be developed into an environmentally, economically and naturally acceptable remediation technology. Evidences for the occurrence of natural attenuation include the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial species; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Results indicate that natural attenuation can effectively contain the plume, and biodegradation processes played an important role on contaminant removal.

Contamination of groundwater by petroleum-hydrocarbons is a serious environmental problem. Monitored natural attenuation (MNA) is a passive remedial approach to degrade and dissipate contaminants in groundwater. In this study, a full-scale natural bioremediation investigation was conducted at a gasoline spill site. Results show that the concentrations of major contaminants [benzene, toluene, ethylbenzene, and xylenes (BTEX)] dropped to below detection limit before they reached the downgradient monitor well. This indicates that natural biodegradation process was the major cause of the contaminant reduction. In this study, 1,2,4-trimethylbenzene (1,2,4-TMB) was used as tracer to calculate the biological decay rates of BTEX. The calculated biological first-order decay rates for ethylbenzene, m+p-xylene, toluene, benzene, and o-xylene were 1.5¡Ñ10-3, 1.2¡Ñ10-3, 7.0¡Ñ10-4, 6.7¡Ñ10-4, and 1.2¡Ñ10-4, respectively. Mann-Kendall test was applied to analyze the trend of contaminant variations. Results show that the S-value of four monitor wells (CT-4, CT-41, CT-42, and CT-7) were -0.52, -1.57, -0.52, and -1.22, respectively. The negative S values reveal that the all contaminants tended to decrease. This indicates that the hydrocarbon plume at this site is not expanding, and has been contained effectively by the natural attenuation mechanisms. Evidences for the occurrence of natural attenuation include the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial species; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Results also show that the biodegradation capacity (46.02 mg/L) for BTEX and 1,2,4-TMB was much higher than the detected contaminants within the plume. Results indicate that natural attenuation can effectively contain the plume, and biodegradation processes played an important role on contaminant removal.

Site characterization methods for measuring the occurrence, magnitude, and rate of microbial mediated transformation processes were evaluated to assess the implementation of monitored natural attenuation (MNA) at chlorinated ethenes contaminated sites. A model site in Arizona, the Park-Euclid WQARF site in Tucson, was selected for the study. Field, geochemical, and compound specific carbon isotope fractionation (CSI) data confirm intrinsic biodegradation is occurring in the perched aquifer. Use of the BIOCHLOR model and a screening protocol support the potential for reductive dehalogenation found in the perched aquifer. Biotransformation of tetrachloroethene to cis-1,2-dichloroethene (cis-DCE) was achieved in microcosm studies. Transformation of cis-DCE to vinyl chloride and to ethene is, at the moment, the laboratory rate limiting step. PCR analysis established that the aquifer contains Dehalococcoides sp. and other dechlorinating microorganisms, though genes that encode for enzymes capable of achieving complete dehalogenation of the chlorinated contaminants were confirmed only in one monitoring well. The regional aquifer shows little evidence of intrinsic biodegradation. This study corroborates that CSI analysis can be used as an additional line of evidence to evaluate and verify MNA. Microbial analysis provides relevant information about the capabilities of native microbial communities to carry out reductive dehalogenation and thus, to naturally attenuate chlorinated compounds at a contaminated site. The combination of microcosm studies, CSI analysis, and bacterial DNA identification is becoming a convincing line of evidence for the assessment of MNA application to chloroethenes contaminated sites.