Bruce N. Bjornstad

Pore‐size constraints on the activity and survival of subsurface bacteria in a late cretaceous shale‐sandstone sequence, northwestern New Mexico

To investigate the distribution of microbial biomass and activities to gain insights into the physical controls on microbial activity and potential long‐term survival in the subsurface, 24 shale and sandstone cores were collected from a site in northwestern New Mexico. Bacterial biomass in the core samples ranged from below detection to 31.9 pmol total phospholipid fatty acid (PLFA) g‐1 of rock with no apparent relationship between lithology and PLFA abundance. No metabolic activities, as determined by anaerobic mineralization of [14C]acetate and [14C]glucose and 35SO4 2‐ reduction, were detected in core samples with pore throats <0.2 fan in diameter, smaller than the size of known bacteria. However, enrichments revealed the presence of sulfate‐re‐ducing bacteria, and 35SO4 2‐ reduction was detected upon extended (14 days) incubation in some small‐pore‐throat samples. In contrast, relatively rapid rates of metabolic activity were more common in core samples containing a significant fraction of pore throat...

Microbiology of vadose zone paleosols in South-Central Washington State

Three unsaturated subsurface paleosols influenced by moisture recharge, including a highly developed calcic paleosol, were studied to investigate the microbiology of paleosols. Two near-surface paleosols, one impacted by moisture recharge and the other beyond the influence of recharge, were also sampled to directly assess the effect of moisture recharge on the activity and composition of the microbial community associated with paleosols. The highly developed paleosol had a higher population of culturable heterotrophs, a greater glucose mineralization potential, a higher microbial diversity based on colony morphology, and a more than 20-fold higher concentration of ATP than the two weakly developed paleosols. The recharged near-surface paleosol, as compared to the near-surface paleosol unaffected by recharge, had a lower population of culturable heterotrophs, smaller mineralization rate constant, and lower richness based on colony morphology. The recharged paleosols contained predominantly gram-negative isolates, whereas the paleosol unaffected by recharge contained predominantly gram-positive isolates. Storage at 4°C of subsurface and near-surface paleosol samples containing high water potential increased the population of culturable aerobic heterotrophs, decreased diversity in colony morphology, and increased first-order rate constants and decreased lag times for glucose mineralization. These results indicate that aerobic heterotrophs are present in deep vadose zone paleosols and that there is potential for stimulation of their in situ growth and activity.

Microbial Abundance and Activities in Relation to Water Potential in the Vadose Zones of Arid and Semiarid Sites

Numbers and activities of microorganisms were measured in the vadose zones of three arid and semiarid areas of the western United States, and the influence of water availability was determined. These low-moisture environments have vadose zones that are commonly hundreds of meters thick. The specific sampling locations chosen were on or near U.S. Department of Energy facilities: the Nevada Test Site (NTS), the Idaho National Engineering Laboratory (INEL), and the Hanford Site (HS) in southcentral Washington State. Most of the sampling locations were uncontaminated, but geologically representative of nearby locations with storage and/or leakage of waste compounds in the vadose zone. Lithologies of samples included volcanic tuff, basalt, glaciofluvial and fluvial sediments, and paleosols (buried soils). Samples were collected aseptically, either by drilling bore-holes (INEL and HS), or by excavation within tunnels (NTS) and outcrop faces (paleosols near the HS). Total numbers of microorganisms were counted using direct microscopy, and numbers of culturable microorganisms were determined using plate-count methods. Desiccation-tolerant microorganisms were quantified by plate counts performed after 24 h desiccation of the samples. Mineralization of 14C-labeled glucose and acetate was quantified in samples at their ambient moisture contents, in dried samples, and in moistened samples, to test the hypothesis that water limits microbial activities in vadose zones. Total numbers of microorganisms ranged from log 4.5 to 7.1 cells g-1 dry wt. Culturable counts ranged from log <2 to 6.7 CFU g-1 dry wt, with the highest densities occurring in paleosol (buried soil) samples. Culturable cells appeared to be desiccation-tolerant in nearly all samples that had detectable viable heterotrophs. Water limited mineralization in some, but not all samples, suggesting that an inorganic nutrient or other factor may limit microbial activities in some vadose zone environments.

Vertical stratification of subsurface microbial community composition across geological formations at the Hanford Site

Microbial diversity in subsurface sediments at the Hanford Site 300 Area near Richland, Washington state (USA) was investigated by analysing 21 samples recovered from depths of 9-52 m. Approximately 8000 near full-length 16S rRNA gene sequences were analysed across geological strata that include a natural redox transition zone. These strata included the oxic coarse-grained Hanford formation, fine-grained oxic and anoxic Ringold Formation sediments, and the weathered basalt group. We detected 1233 and 120 unique bacterial and archaeal OTUs (operational taxonomic units at the 97% identity level) respectively. Microbial community structure and richness varied substantially across the different geological strata. Bacterial OTU richness (Chao1 estimator) was highest (> 700) in the upper Hanford formation, and declined to about 120 at the bottom of the Hanford formation. Just above the Ringold oxic-anoxic interface, richness was about 325 and declined to less than 50 in the deeper reduced zones. The deeper Ringold strata were characterized by a preponderance (c. 90%) of Proteobacteria. The bacterial community in the oxic sediments contained not only members of nine well-recognized phyla but also an unusually high proportion of three candidate divisions (GAL15, NC10 and SPAM). Additionally, 13 novel phylogenetic orders were identified within the Deltaproteobacteria, a clade rich in microbes that carry out redox transformations of metals that are important contaminants on the Hanford Site.

Long History of Pre‐Wisconsin, Ice Age Cataclysmic Floods: Evidence from Southeastern Washington State

Cataclysmic Ice Age floods in the Pacific Northwest began as early as 1.5–2.5 Ma, on the basis of an evaluation of surface exposures and recent borehole studies within southeastern Washington. Field evidence suggests at least two episodes of pre‐Wisconsin (i.e., >130 ka) glacial‐outburst flooding. A Middle Pleistocene flood is identified by normal magnetic polarity, calcrete‐capped deposits that yield maximum Th/U age dates from 200 to >400 ka. The deposits with reversed polarity are correlated to Early Pleistocene (>780 ka) floods. While exposures of pre‐Wisconsin deposits are limited because of erosion and/or burial, the record of earlier Pleistocene flooding is preserved within giant flood bars. These bars show incremental growth, representing a composite from cataclysmic floods deposited intermittently through the Pleistocene. In one giant flood bar, up to 100 m thick, deposits interpreted as Matuyama age indicate that the bar had grown to half its present height by 780 ka. Furthermore, Matuyama‐age, reversed‐polarity flood deposits may be underlain by up to another 15 m of normally magnetized deposits at the base of the flood sequence. This normal‐polarity interval appears to be associated with Early Pleistocene cataclysmic floods, perhaps of Olduvai age (>1.77 Ma). Many of the features associated with cataclysmic floods, such as coulees, giant bars, and streamlined loess hills, may have been established during the Early Pleistocene and were only slightly modified by up to hundreds of subsequent flood episodes.

Microbiological characteristics of pristine and contaminated deep vadose sediments from an arid region

The unsaturated (vadose) zone in arid and semiarid regions can be >100 m thick and may receive little or no moisture recharge from the surface. The microbiological properties of the vadose zone are of interest because of the potential for microorganisms to impact the fate and transport of contaminants in these environments. At numerous sites in the western United States, large volumes of wastewater or process water have been disposed of directly to the surface or shallow subsurface and have subsequently migrated through the vadose zone to the groundwater. The purpose of this study was to determine and compare the microbial properties of pristine and impacted vadose zone sediments. Vadose zone sediments from depths ranging from 24 to 90 m were obtained from 3 boreholes drilled on the Hanford site in south‐central Washington State. One borehole was located in a pristine area and the other two were located in areas where wastewater had been disposed of directly to the surface and near subsurface. An open‐flo...

Limited Field Investigation Report for Uranium Contamination in the 300 Area, 300-FF-5 Operable Unit, Hanford Site, Washington

Four new CERCLA groundwater monitoring wells were installed in the 300-FF-5 Operable Unit in FY 2006 to fulfill commitments for well installations proposed in the Hanford Federal Facility Agreement and Consent Order Milestone M-24-57. Wells were installed to collect data to determine the distribution of process uranium and other contaminants of potential concern in groundwater. These data will also support uranium contaminant transport simulations and the wells will supplement the water quality monitoring network for the 300-FF-5 OU. This report supplies the information obtained during drilling, characterization, and installation of the new groundwater monitoring wells. This document also provides a compilation of hydrogeologic, geochemical, and well construction information obtained during drilling, well development, and sample collection/analysis activities.

Transport of Multiple Tracers in Variably Saturated Humid Region Structured Soils and Semi-arid Region Laminated Sediments

The processes governing physical nonequilibrium (PNE)—coupled preferential flow and matrix diffusion—are diverse between humid and semi-arid regions, and are directly related to climate and rock/sediment type, and indirectly related to subsequent soil profile development. The fate and transport of contaminants in these variably saturated undisturbed media is largely a function of the influence of PNE processes. Large cores of laminated silts and sands were collected from the US Department of Energy Pacific Northwest National Laboratory (PNNL) in semi-arid south central Washington. Additional cores of weathered, fractured interbedded limestone and shale saprolite were collected from the Oak Ridge National Laboratory (ORNL) in humid eastern Tennessee. PNNL cores were collected parallel (FBP) and perpendicular (FXB) to bedding, and the ORNL core was 30° to bedding. Saturated and unsaturated transport experiments were performed using multiple nonreactive tracers that had different diffusion coefficients (Br−, PFBA, and PIPES), in order to identify the influence of PNE on the fate and transport of solutes. In the ORNL structured saprolite, solute transport was governed by coupled preferential flow and matrix diffusion, as evidenced by tracer separation and highly asymmetric breakthrough curves (BTC). BTCs became more symmetric as preferential flowpaths became inactive during drainage. Tracer separation persisted during unsaturated flow suggesting the continued importance of nonequilibrium mass transfer between flowpaths and the immobile water that was held in the soil matrix. No evidence of PNE was observed under near-saturated conditions in the semi-arid region (PNNL) laminated silts and sands. Unsaturated flow in cores with discontinuous layering resulted in preferential flow and the development of perched, immobile water as evidenced by early breakthrough and separation of tracers. Conversely, transport parallel to laterally continuous beds did not result in preferential flow, the development of perched water, or tracer separation regardless of water content. These observations suggested that desaturation had two effects: (1) grain size variations between individual beds resulted in different antecedent water contents, and (2) the exchange of water and solutes between individual sedimentary beds was subsequently inhibited. Under unsaturated conditions, these effects may promote either stable lateral flow, or unstable vertical finger flow coupled with the development of perched, immobile water.

Characterization of Vadose Zone Sediment: Uncontaminated RCRA Borehole Core Samples and Composite Samples

This report was revised in September 2008 to remove acid-extractable sodium data from Tables 4.14, 4.16, 5.20, 5.22, 5.43, and 5.45. The sodium data was removed due to potential contamination introduced during the acid extraction process. The rest of the text remains unchanged from the original report issued in February 2002. The overall goal of the of the Tank Farm Vadose Zone Project, led by CH2M HILL Hanford Group, Inc., is to define risks from past and future single-shell tank farm activities. To meet this goal, CH2M HILL Hanford Group, Inc. asked scientists from Pacific Northwest National Laboratory to perform detailed analyses on vadose zone sediment from within the S-SX Waste Management Area. This report is one in a series of four reports to present the results of these analyses. Specifically, this report contains all the geologic, geochemical, and selected physical characterization data collected on vadose zone sediment recovered from Resource Conservation and Recovery Act (RCRA) borehole bore samples and composite samples.

Biogeochemistry of anaerobic lacustrine and paleosol sediments within an aerobic unconfined aquifer

The geochemistry and the distribution and abundance of anaerobic bacteria were determined for sediments sampled in a deep borehole in south‐central Washington. The sampled sediments consisted of a 12‐m‐thick lacustrine sequence underlain by 8 m of paleosol grading into 5 m of silty sands, within an aerobic unconfined aquifer otherwise composed of transmissive sands and gravels. Concentrations of porewater sul‐fate varied systematically with depth, reaching a minimum of 3.9 mg L ‐1 in the central portion of the lacustrine sequence. Lacustrine sediments contained up to 1 wt% total organic carbon, whereas other sediments contained less than 0.2 wt% organic carbon. Fermentative bacteria were present throughout the sampled sequence, and were assumed to be responsible for primary degradation of organic carbon. Dissimilatory iron‐reducing bacteria (DIRB) were at maximum abundance where bioavailable Fe(III) and organic carbon were present at favorable combined concentrations. Sul‐fate‐reducing bacteria were cultu...