Ryan C. Rowland

Deep Aquifer Remediation Tools: Theory, Design, and Performance Modeling

Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.

Sulfate-Reducing Bacteria in the Zero Valent Iron Permeable Reactive Barrier at Fry Canyon, Utah

Publisher Summary This chapter presents a study in which a zero valent iron (ZVI) permeable reactive barrier (PRB) was installed in a shallow, colluvial aquifer contaminated with uranium in Fry Canyon, Utah, in September 1997. Aerobic and anaerobic iron corrosion reactions in the ZVI PRB have created a highly reducing, oxygen-depleted, and hydrogen gas-enriched geochemical environment in the PRB that is favorable for sulfate-reducing bacteria (SRB). Stable sulfur isotope, microbiologic, and geochemical evidence indicates that SRB are active in the ZVI PRB. The stable sulfur isotope and SO42– data from wells in the ZVI PRB and a downgradient well show that sulfur is removed by DSR through a Rayliegh-type distillation process. The enrichment factor computed from the Rayleigh plot is close to the values measured in other field investigations of DSR in groundwater systems. The thermodynamic speciation calculations and stable sulfur isotope data indicate that sulfide precipitation is the only sink for sulfur in the PRB. The distribution of SO42- concentrations indicates that most of the sulfide precipitation is occurring in the first 0.15 m of the PRB.

Development and Performance of an Iron Oxide/Phosphate Reactive Barrier for the Remediation of Uranium-Contaminated Groundwater

Publisher Summary This chapter reports on the laboratory and field testing of engineered solid mixtures for use with deep aquifer remediation tool (DART) technology for the removal of groundwater metal contamination resulting from mining and ore processing. In laboratory testing mixtures of pelletized bone charcoal (bone char apatite) and hematite pellets coated with amorphous iron oxide are studied in various ratios in both batch and column experiments, to evaluate the effectiveness of the mixture in removing uranium from groundwater. The variables include phosphate levels in solution and on the iron oxide surface, pellet ratios, and aging of the solids. Laboratory batch experiments indicate phosphorus adsorption by the iron oxide pellets, but there is no apparent increase in uranium removal in mixtures compared to bone char pellets alone. In contrast, column experiments show greater uranium removal by the mixture of materials, possibly as a result of longer aging times and/or higher adsorbed phosphorus concentrations. No evidence of autonite formation is also found. Field tests using DART deployment technology also compares various pellet ratios and includes shallow DART deployment in an unpumped well array in Fry Canyon, Utah, the site of an abandoned uranium upgrader operation, and deep DART emplacement 146 m below land surface during active mining at the Christensen Ranch in situ uranium mine in northeastern Wyoming. An additional field test at Fry Canyon also includes DART testing with zerovalent iron. This study demonstrates that DARTs can effectively remove contaminants. Both laboratory column and the Fry Canyon field results suggest that a mixture of materials can be more effective at contaminant removal than a single reactive barrier material, although efficiencies of removal in the field tests could not be determined accurately due to a lack of knowledge of the input fluxes of U(VI) to the DARTs.

Assessment of potential migration of radionuclides and trace elements from the White Mesa uranium mill to the Ute Mountain Ute Reservation and surrounding areas, southeastern Utah

In 2007, the Ute Mountain Ute Tribe requested that the U.S. Environmental Protection Agency and U.S. Geological Survey conduct an independent evaluation of potential offsite migration of radionuclides and selected trace elements associated with the ore storage and milling process at an active uranium mill site near White Mesa, Utah. Specific objectives of this study were (1) to determine recharge sources and residence times of groundwater surrounding the mill site, (2) to determine the current concentrations of uranium and associated trace elements in groundwater surrounding the mill site, (3) to differentiate natural and anthropogenic contaminant sources to groundwater resources surrounding the mill site, (4) to assess the solubility and potential for offsite transport of uranium-bearing minerals in groundwater surrounding the mill site, and (5) to use stream sediment and plant material samples from areas surrounding the mill site to identify potential areas of offsite contamination and likely contaminant sources. The results of age-dating methods and an evaluation of groundwater recharge temperatures using dissolved-gas samples indicate that groundwater sampled in wells in the surficial aquifer in the vicinity of the mill is recharged locally by precipitation. Tritium/helium age dating methods found a “modern day” apparent age in water samples collected from springs in the study area surrounding the mill. This apparent age indicates localized recharge sources that potentially include artificial recharge of seepage from constructed wildlife refuge ponds near the mill. The stable oxygen isotope-ratio, delta oxygen-18, or δ(18O/16O), known as δ18O, and hydrogen isotope-ratio, delta deuterium, or δ(2H/1H), known as δD, data indicate that water discharging from Entrance Spring is isotopically enriched by evaporation and has a similar isotopic fingerprint as water from Recapture Reservoir, which is used as facilities water on the mill site. Water from Recapture Reservoir also is used to irrigate fields surrounding the town of Blanding and infiltration of this irrigated water also could contribute to the enriched isotopic fingerprint observed for Entrance Spring. Similarities in the delta sulfur-34sulfate values in water samples from the wildlife ponds and tailings cells indicate a potential contaminant linkage between the tailings cells and the refuge ponds that could be related to wind carried (eolian) transport of aerosols from the tailings cells. To date (2010), neither the delta sulfur-34sulfate nor the delta oxygen-18sulfate values measured in the wells and springs surrounding the uranium mill site have an isotopic signature characteristic of water from the tailings cells. Except for Entrance Spring and Mill Spring, all groundwater samples collected at down-gradient sample sites during this study had dissolved-uranium concentrations in the range expected for naturally-occurring uranium. The uraniumisotope data indicate that the mill is not a source of uranium in the groundwater in the unconfined-aquifer at any site monitored during the study, with the possible exception of Entrance Spring. The uranium-234 to uranium-238 activity ratios measured in water samples collected at Entrance Spring, and the decrease in this ratio associated with an increase in the concentration of dissolved uranium indicate potential mixing of uranium ore with groundwater at the spring through eolian transport of small particles from ore-storage pads and uncovered ore trucks, with subsequent deposition in the Entrance Spring drainage, followed by dissolution in the unconfined groundwater. The isotopic values of uranium found in other water samples collected during the study do not appear to be related to uranium ore deposits. Water samples collected from Entrance Spring contained the highest median uranium concentrations relative to water samples collected from the other wells and springs monitored during the study. Water samples collected from Entrance Spring also contained elevated concentrations of selenium and vanadium. Sediment samples collected from three ephemeral drainages east of the uranium mill site (including Entrance Spring) contained uranium concentrations exceeding background values downwind of the predominant wind directions at the site. Sediment samples collected from ephemeral drainages on the south and west boundaries of the uranium mill site generally did not exceed background-uranium concentrations. Elevated concentrations of uranium and vanadium, indicating offsite transport, were found in plant tissue samples collected north-northeast, east, and south of the mill site, downwind of 2 Assessment of potential migration of radionuclides and trace elements from the White Mesa uranium mill the predominant wind directions at the site. The uranium and vanadium concentrations in plant tissue samples collected west of the uranium mill site were low. On the basis of the study results, consideration should be given to future monitoring programs in areas surrounding the uranium mill site to address current and future environmental concerns. These potential monitoring programs should consider (1) quarterly monitoring of majorand trace-element concentrations in selected springs and wells; (2) annual monitoring of Entrance Spring for uranium isotopes, delta sulfur34sulfate, delta oxygen-18, and delta deuterium; (3) annual monitoring of background water quality at selected spring and monitoring well sites; (4) periodic sampling and chemical analyses of sagebrush in areas east of the uranium mill site coupled with off-site fugitive dust monitoring; (5) installation of a new monitoring well upgradient from the East and West wells; (6) the addition of non-routine chemical constituents to ongoing monitoring programs within the uranium mill site that could provide additional insight(s) into potential contaminant sources and processes; and (7) archiving future monitoring data into a maintained database that is easily accessible to all project stakeholders.

Deep Aquifer Remediation Tools

Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.

Chapter 5 – Deep Aquifer Remediation Tools: Theory, Design, and Performance Modeling

Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.Publisher Summary This chapter focuses on deep aquifer remediation tools (DARTs), which have been developed for the emplacement of permeable reactive barriers (PRB) through arrays of non-pumping wells and which offer a number of advantages compared to classic trench installation methods, including easy replacement of spent reactive material and deeper installation depths. A DART is composed of a rigid polyvinyl chloride shell with high-capacity flow channels that contains the permeable reactive material and flexible wings to direct the flow of groundwater into the reactive material. The three factors which has to be considered while evaluating the feasibility of using DARTs for PRB emplacement include the hydrology of the system, the construction engineering of the DART itself, and the residence time required for contaminant removal reactions. The computer simulation indicates that the reactive material used in a DART should be engineered to have an X value 50 to 200 times greater than the K value of the aquifer material. This difference in K cancapture groundwater from an upgradient width of aquifer equal to about 1.8 to 1.9 times of the diameter of the nonpumping well. Important design features for DARTs include the maximization of the open surface area of the DART housing, maximization of the volume of groundwater that can flow through the reactive materials, allowance for easy production of DARTs with various diameters and lengths, easy emplacement of a DART, easy access to the reactive material, and minimization of the cost of production.