Final report for DOE Grant No. DE-FG02-07ER64404 - Field Investigations of Microbially Facilitated Calcite Precipitation for Immobilization of Strontium-90 and Other Trace Metals in the Subsurface

Abstract

This final report is organized into 2 sections. The first section (page 2) describes the multiinstitutional 13 month Rifle Colorado Field Campaign with an emphasis on the contributions to the campaign by the University of Idaho. The second section (page 16) of the report describes the overall accomplishments including a list of publications for the entire project. Sr, is co-precipitation in calcite. We have previously found that that nutrient addition can stimulate microbial ureolytic activity that this activity accelerates calcite precipitation and co-precipitation of Sr, and that higher calcite precipitation rates can result in increased Sr partitioning. We have conducted integrated field, laboratory, and computational research to evaluate the relationships between ureolysis and calcite precipitation rates and trace metal partitioning under environmentally relevant conditions, and investigated the coupling between flow/flux manipulations and precipitate distribution.A field experimental campaign conducted at the Integrated Field Research Challenge (IFRC) site located at Rifle, CO was based on a continuous recirculation design; water extracted from a down-gradient well was amended with urea and molasses (a carbon and electron donor) and re-injected into an up-gradient well. The goal of the recirculation design and simultaneous injection of urea and molasses was to uniformly accelerate the hydrolysis of urea and calcite precipitation over the entire inter-wellbore zone. The urea-molasses recirculation phase lasted, with brief interruptions for geophysical surveys, for 12 days followed by long-term monitoring which continued for 13 months. Following the recirculation phase we found persistent increases in urease activity (as determined from 14 C labeled laboratory urea hydrolysis rates) in the upper portion of the inter-wellbore zone. We also observed an initial increase (approximately 2 weeks) in urea concentration associated with injection activities followed by decreasing urea concentration and associated increases in ammonium and dissolved inorganic carbon (DIC) following the termination of injection. Based on the loss of urea and the appearance of ammonium, a first order rate constant for urea hydrolysis of 0.18 day -1 rate with an associate R f for ammonium of 11 were estimated. This rate constant is approximately 6 times higher than estimated for previous field experiments conducted in eastern Idaho. Additionally, DIC carbon isotope ratios were measured for the groundwater. Injected urea had a δ

Final report for DOE Grant No. DE-SC0006609 - Persistence of Microbially Facilitated Calcite Precipitation as an in situ Treatment for Strontium-90

“…The number of ureC gene copies also shows a decreasing trend (with scatter) with depth although with much less variation than for the urease activity (note the log scale for activity and the linear scale for gene copies). Although we observed a positive correlation between ureC gene counts and activity for initial measurements and during increases in biomass associated with the urea recirculation period Smith et al 2012b), the long-term results obtained from the BS-11-2 core do not follow this pattern. DNA extraction from the long-term sediment samples was more difficult than from the samples collected prior to and during recirculation, and variation in extraction efficiency may have contributed some systematic biases to the core results.…”

“…Figure 4 shows the variation with depth of (a) estimated urease activity and (b) ureC gene abundance. The urease activity in the sediments from the upper meter of the aquifer was 30 times higher than the activity in sediments from the lower portion of the aquifer; the latter values are near background levels for the site (Smith et al 2012a). The number of ureC gene copies also shows a decreasing trend (with scatter) with depth although with much less variation than for the urease activity (note the log scale for activity and the linear scale for gene copies).…”

“…Although the injected fluids and associated stimulation of urease activity may move beyond the interwellbore zone, significant urea hydrolysis was only observed in the inter-well bore zone. Furthermore, based on the observations of changes in carbon isotope ratios in the groundwater (Smith et al 2012a) and the solids, the enhanced precipitation of calcite and/or other carbonates at very low level can be inferred to only have occurred in the interwellbore zone. This final report is organized into 2 sections.…”

“…UreC genes (10 9 copies kg -1 ) b a the Rifle sediments (Smith et al 2012a). Such a change in calcite content, assuming homogeneous distribution over the inter-wellbore zone, would be extremely difficult to observe directly given that the preexisting calcite content of the site ranges from ~0.6 to 2.8%.…”

Field-scale bio-cementation tests to improve sands

“…Although MICP experimentation has been largely confined to the laboratory, field-scale applications have been demonstrated with success in the Netherlands (van Paassen, 2011), and are currently being implemented at a US Department of Energy site in Rifle, Colorado (Smith et al, 2012). The future of MICP as a practical ground improvement method is dependent on these field-scale applications, which provide essential information about the biogeochemical process at the metre scale.…”