Denver Federal Center Research Articles

Rebuttal to Correspondence on "Sediment Sources and Sealed-Pavement Area Drive Polycyclic Aromatic Hydrocarbon and Metal Occurrence in Urban Streams".

ADVERTISEMENT RETURN TO ARTICLES ASAPPREVCorrespondence/Rebut...Correspondence/RebuttalNEXTRebuttal to Correspondence on “Sediment Sources and Sealed-Pavement Area Drive Polycyclic Aromatic Hydrocarbon and Metal Occurrence in Urban Streams”Travis S. SchmidtTravis S. SchmidtU.S. Geological Survey, 3162 Bozeman Avenue, Helena, Montana 59601, United StatesMore by Travis S. Schmidthttps://orcid.org/0000-0003-1400-0637, Christopher C FullerChristopher C FullerU.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, United StatesMore by Christopher C Fuller, Sharon L. QiSharon L. QiU.S. Geological Survey, P.O. Box 25046, MS 415 Denver Federal Center, Lakewood, Colorado 80225, United StatesMore by Sharon L. Qi, and Allen C. Gellis*Allen C. GellisU.S. Geological Survey, 5522 Research Park Drive, Baltimore, Maryland 21228, United States*[email protected]More by Allen C. Gellishttps://orcid.org/0000-0002-3449-2889Cite this: Environ. Sci. Technol. 2023, XXXX, XXX, XXX-XXXPublication Date (Web):April 10, 2023Publication History Received28 March 2023Published online10 April 2023https://doi.org/10.1021/acs.est.3c02351Not subject to U.S. Copyright. Published 2023 by American Chemical SocietyRIGHTS & PERMISSIONSArticle Views-Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (722 KB) Get e-AlertsSUBJECTS:Chemical composition,Geological materials,Materials,Mathematical methods,Metals Get e-Alerts

Hydraulic conductivity can no longer be considered a fixed property when quantifying flow between groundwater and surface water

Hydrological ProcessesVolume 35, Issue 6 e14226 INVITED COMMENTARY Hydraulic conductivity can no longer be considered a fixed property when quantifying flow between groundwater and surface water Donald O. Rosenberry, Corresponding Author Donald O. Rosenberry rosenber@usgs.gov orcid.org/0000-0003-0681-5641 U.S. Geological Survey, Lakewood, Colorado, USA Correspondence Donald O. Rosenberry, U.S. Geological Survey, MS 413, Denver Federal Center, Lakewood, CO 80225, USA. Email: rosenber@usgs.govSearch for more papers by this authorPeter Engesgaard, Peter Engesgaard orcid.org/0000-0002-5925-8757 Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, DenmarkSearch for more papers by this authorChristine Hatch, Christine Hatch orcid.org/0000-0002-4996-1617 Department of Geosciences, University of Massachusetts Amherst, Amherst, Massachusetts, USASearch for more papers by this author Donald O. Rosenberry, Corresponding Author Donald O. Rosenberry rosenber@usgs.gov orcid.org/0000-0003-0681-5641 U.S. Geological Survey, Lakewood, Colorado, USA Correspondence Donald O. Rosenberry, U.S. Geological Survey, MS 413, Denver Federal Center, Lakewood, CO 80225, USA. Email: rosenber@usgs.govSearch for more papers by this authorPeter Engesgaard, Peter Engesgaard orcid.org/0000-0002-5925-8757 Department of Geosciences and Natural Resource Management, University of Copenhagen, Copenhagen, DenmarkSearch for more papers by this authorChristine Hatch, Christine Hatch orcid.org/0000-0002-4996-1617 Department of Geosciences, University of Massachusetts Amherst, Amherst, Massachusetts, USASearch for more papers by this author First published: 09 May 2021 https://doi.org/10.1002/hyp.14226Citations: 3Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume35, Issue6June 2021e14226 This article also appears in:HPToday: Invited Commentaries RelatedInformation

Benchmarking COMSOL Multiphysics Single-Subchannel Thermal-Hydraulic Analysis of a TRIGA Reactor with RELAP5 Results and Experimental Data

COMSOL Multiphysics has been used to conduct thermal-hydraulic analysis in multiple nuclear applications. The aim of this study is to benchmark the prediction accuracy of COMSOL Multiphysics in performing thermal-hydraulic analysis of TRIGA (Training, Research, Isotopes, General Atomics) reactors such as the Geological Survey TRIGA Reactor (GSTR) by comparing its predictions with RELAP5 (a widely used code in nuclear thermal-hydraulic analysis) results and experimental data. The GSTR type is Mark I with a full thermal power of 1 MW, and it resides at the Denver Federal Center (DFC) in Colorado. The numerical investigation of the present work is carried out by developing single-subchannel thermal-hydraulic models of the GSTR utilizing RELAP5 and COMSOL codes. The models estimate the temperatures (fuel, outer clad, and coolant) and water flow patterns in the core as well as fuel element powers at which void starts to form within the coolant subchannels. Then, these models’ predictions are quantitatively evaluated and compared with the measured data.

Improving Earthquake Rupture Forecasts Using California as a Guide

Research Article| October 03, 2018 Improving Earthquake Rupture Forecasts Using California as a Guide Edward H. Field; Edward H. Field aU.S. Geological Survey, Denver Federal Center, P.O. Box 25046, MS‐966, Denver, Colorado 80225‐0046 U.S.A., field@usgs.gov Search for other works by this author on: GSW Google Scholar Working Group on California Earthquake Probabilities Working Group on California Earthquake Probabilities Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2018) 89 (6): 2337–2346. https://doi.org/10.1785/0220180151 Article history first online: 03 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Edward H. Field, Working Group on California Earthquake Probabilities; Improving Earthquake Rupture Forecasts Using California as a Guide. Seismological Research Letters 2018;; 89 (6): 2337–2346. doi: https://doi.org/10.1785/0220180151 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT This article discusses ways in which earthquake rupture forecast models might be improved. Because changes are most easily described in the context of specific models, the third Uniform California Earthquake Rupture Forecast (UCERF3) and its presumed successor, UCERF4, is used as a basis for discussion. Virtually all of the issues and possible improvements discussed are nevertheless general and should therefore be applicable to other regions as well. Two common themes are a need for better epistemic uncertainty representation and the potential utility of physics‐based simulators. Given the large number of possible improvements, coupled with challenges in defining the potential value of each, which will vary among uses, community feedback is invaluable in terms of setting priorities. We should also strive to define more objective valuation metrics. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Candidate Products for Operational Earthquake Forecasting Illustrated Using the HayWired Planning Scenario, Including One Very Quick (and Not‐So‐Dirty) Hazard‐Map Option

Research Article| April 18, 2018 Candidate Products for Operational Earthquake Forecasting Illustrated Using the HayWired Planning Scenario, Including One Very Quick (and Not‐So‐Dirty) Hazard‐Map Option Edward H. Field; Edward H. Field aU.S. Geological Survey, Denver Federal Center, P.O. Box 25046, MS 966, Denver, Colorado 80225‐0046 U.S.A. Search for other works by this author on: GSW Google Scholar Kevin R. Milner Kevin R. Milner bUniversity of Southern California, Southern California Earthquake Center, 3651 Trousdale Parkway #169, Los Angeles, California 90089‐0742 U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information Edward H. Field aU.S. Geological Survey, Denver Federal Center, P.O. Box 25046, MS 966, Denver, Colorado 80225‐0046 U.S.A. Kevin R. Milner bUniversity of Southern California, Southern California Earthquake Center, 3651 Trousdale Parkway #169, Los Angeles, California 90089‐0742 U.S.A. Publisher: Seismological Society of America First Online: 18 Apr 2018 Online Issn: 1938-2057 Print Issn: 0895-0695 © Seismological Society of America Seismological Research Letters (2018) 89 (4): 1420–1434. https://doi.org/10.1785/0220170241 Article history First Online: 18 Apr 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Edward H. Field, Kevin R. Milner; Candidate Products for Operational Earthquake Forecasting Illustrated Using the HayWired Planning Scenario, Including One Very Quick (and Not‐So‐Dirty) Hazard‐Map Option. Seismological Research Letters 2018;; 89 (4): 1420–1434. doi: https://doi.org/10.1785/0220170241 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT In an effort to help address debates on the usefulness of operational earthquake forecasting (OEF), we illustrate a number of OEF products that could be automatically generated in near‐real time. To exemplify, we use an M 7.1 mainshock on the Hayward fault, which is very similar to the U.S. Geological Survey (USGS) HayWired earthquake planning scenario. Given that there is always some background level of hazard or risk, we emphasize that probability gains (the ratio of short‐term to long‐term‐average estimates) might be of particular interest to users. We also illustrate how such gains are highly sensitive to forecast duration and latency, with the latter representing how long it takes to generate the forecast and/or to take action. The influence of fault‐based information, which has traditionally been ignored in OEF, is also evaluated using the newly developed the third Uniform California Earthquake Rupture Forecast epidemic‐type aftershock sequence (UCERF3‐ETAS) model. We find that the inclusion of faults only makes a difference for hazard and risk metrics that are dominated by large‐event likelihoods. We also show how the ShakeMap of a mainshock represents a decent estimate of the ground motions that have a 6% chance of being exceeded due to aftershocks in the week that follows. The ultimate value of these types of OEF products can only be determined in the context of specific uses, and because these vary widely, institutions responsible for providing OEF products will depend heavily on user feedback, especially when making resource‐allocation decisions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Normal faulting and evolution of fluid discharge in a Jurassic seafloor ultramafic-hosted hydrothermal system

Research Article| April 16, 2018 Normal faulting and evolution of fluid discharge in a Jurassic seafloor ultramafic-hosted hydrothermal system Jeff Alt; Jeff Alt 1Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Laura Crispini; Laura Crispini 2Dipartimento di Scienze della Terra dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, Corso Europa 26, 16132 Genoa, Italy Search for other works by this author on: GSW Google Scholar Laura Gaggero; Laura Gaggero 2Dipartimento di Scienze della Terra dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, Corso Europa 26, 16132 Genoa, Italy Search for other works by this author on: GSW Google Scholar David Levine; David Levine 1Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Giorgia Lavagnino; Giorgia Lavagnino 2Dipartimento di Scienze della Terra dell’Ambiente e della Vita (DISTAV), Università degli Studi di Genova, Corso Europa 26, 16132 Genoa, Italy Search for other works by this author on: GSW Google Scholar Pat Shanks; Pat Shanks 3U.S. Geological Survey, 973 Denver Federal Center, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Cayce Gulbransen Cayce Gulbransen 3U.S. Geological Survey, 973 Denver Federal Center, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Geology (2018) 46 (6): 523–526. https://doi.org/10.1130/G40287.1 Article history received: 05 Oct 2017 rev-recd: 23 Mar 2018 accepted: 23 Mar 2018 first online: 16 Apr 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Jeff Alt, Laura Crispini, Laura Gaggero, David Levine, Giorgia Lavagnino, Pat Shanks, Cayce Gulbransen; Normal faulting and evolution of fluid discharge in a Jurassic seafloor ultramafic-hosted hydrothermal system. Geology 2018;; 46 (6): 523–526. doi: https://doi.org/10.1130/G40287.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract We document a normal fault that lies at a high angle to an oceanic detachment that exposed peridotite on the Jurassic seafloor. Faults such as this are inferred to be discharge zones for ultramafic-hosted hydrothermal systems, but have not yet been sampled from the modern seafloor. The fault comprises 0.5–2-m-thick zones of sheared talc + sulfide within serpentinite, and ends upward in carbonated serpentinite, massive sulfide, and pillow basalts. Talc alteration and enrichment in metals, light rare earth elements, and 34S of the fault rocks provide evidence of a conduit for discharge of high-temperature hydrothermal fluids related to fluid circulation and mineralization. At the seafloor, the fault rocks have been replaced by later Fe-dolomite + minor quartz, chlorite, and sulfides at temperatures of 90–120 °C during waning hydrothermal activity. This is the first view of the subsurface discharge zone of a seafloor ultramafic-hosted hydrothermal system, showing that normal faults provide pathways to focus fluid flow and reaction. An important new result is field and geochemical evidence that high-temperature hydrothermal systems with black smoker–type venting, sulfide mineralization, and talc alteration can evolve to lower-temperature Lost City–type venting and carbonate mineralization. You do not currently have access to this article.

Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon

Research Article| November 01, 2014 Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon Joseph P. Colgan; Joseph P. Colgan † 1U.S. Geological Survey, Denver Federal Center, Bldg. 25, PO Box 25046, Lakewood, Colorado 80225 †Corresponding author: e-mail, jcolgan@usgs.gov Search for other works by this author on: GSW Google Scholar Christopher D. Henry; Christopher D. Henry 2Nevada Bureau of Mines and Geology, Mail Stop 178, University of Nevada, Reno, Nevada 89557 Search for other works by this author on: GSW Google Scholar David A. John David A. John 3U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information Joseph P. Colgan † 1U.S. Geological Survey, Denver Federal Center, Bldg. 25, PO Box 25046, Lakewood, Colorado 80225 Christopher D. Henry 2Nevada Bureau of Mines and Geology, Mail Stop 178, University of Nevada, Reno, Nevada 89557 David A. John 3U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025 †Corresponding author: e-mail, jcolgan@usgs.gov Publisher: Society of Economic Geologists Received: 25 Jun 2013 Accepted: 08 Mar 2014 First Online: 09 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (7): 1843–1862. https://doi.org/10.2113/econgeo.109.7.1843 Article history Received: 25 Jun 2013 Accepted: 08 Mar 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Joseph P. Colgan, Christopher D. Henry, David A. John; Evidence for Large-Magnitude, Post-Eocene Extension in the Northern Shoshone Range, Nevada, and Its Implications for the Structural Setting of Carlin-Type Gold Deposits in the Lower Plate of the Roberts Mountains Allochthon. Economic Geology 2014;; 109 (7): 1843–1862. doi: https://doi.org/10.2113/econgeo.109.7.1843 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The northern Shoshone and Toiyabe Ranges in north-central Nevada expose numerous areas of mineralized Paleozoic rock, including major Carlin-type gold deposits at Pipeline and Cortez. Paleozoic rocks in these areas were previously interpreted to have undergone negligible postmineralization extension and tilting, but here we present new data that suggest major post-Eocene extension along west-dipping normal faults. Tertiary rocks in the northern Shoshone Range crop out in two W-NW–trending belts that locally overlie and intrude highly deformed Lower Paleozoic rocks of the Roberts Mountains allochthon. Tertiary exposures in the more extensive, northern belt were interpreted as subvertical breccia pipes (intrusions), but new field data indicate that these “pipes” consist of a 35.8 Ma densely welded dacitic ash flow tuff (informally named the tuff of Mount Lewis) interbedded with sandstones and coarse volcaniclastic deposits. Both tuff and sedimentary rocks strike N-S and dip 30° to 70° E; the steeply dipping compaction foliation in the tuffs was interpreted as subvertical flow foliation in breccia pipes. The southern belt along Mill Creek, previously mapped as undivided welded tuff, includes the tuff of Cove mine (34.4 Ma) and unit B of the Bates Mountain Tuff (30.6 Ma). These tuffs dip 30° to 50° east, suggesting that their west-dipping contacts with underlying Paleozoic rocks (previously mapped as depositional) are normal faults. Tertiary rocks in both belts were deposited on Paleozoic basement and none appear to be breccia pipes. We infer that their present east tilt is due to extension on west-dipping normal faults. Some of these faults may be the northern strands of middle Miocene (ca. 16 Ma) faults that cut and tilted the 34.0 Ma Caetano caldera ~40° east in the central Shoshone Range (<5 km south of Mill Creek), but further mapping is necessary to trace the faults through the highly deformed Paleozoic rocks that surround the isolated Tertiary outcrops. Significant post-Eocene extensional faulting in the northern Shoshone Range may have important implications for both the structure of the Roberts Mountains allochthon and the exposure of potentially mineralized rocks in its lower plate, both of which were likely east-tilted and repeated by west-dipping faults together with overlying Tertiary rocks. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Installation of a New Neutron Beam Facility at the U.S. Geological Survey TRIGA Reactor

The fleet of research and training reactors is aging, and no new research reactors are planned in the United States; thus, there is a need to expand the capabilities of existing reactors to meet users’ needs. To address these needs, the Colorado School of Mines added a neutron beamline facility to the U.S. Geological Survey TRIGA Reactor (GSTR), a 1-MW(thermal) Mark-I TRIGA reactor located at the Denver Federal Center in Lakewood, Colorado. The original GSTR design did not include any beam ports, and future research efforts will benefit from a neutron beam at the GSTR. Adding new beamline facilities to existing research reactors is both rare and challenging, and this paper describes the design and installation of a new neutron beamline facility at a Mark-I TRIGA reactor with no existing beamline facilities. The design and construction of a radiation beamstop for the new beamline is described in detail. A neutronics model of the neutron beam provides researchers with a useful tool for experiment design. The new neutron beam has a measured length-to-diameter ratio of 200 ± 10, a neutron flux of 2.2×106 ± 6.4×105 n/cm2-s, and an average cadmium ratio of 7.4 using copper, gold, manganese, and indium foils.

Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California

Research Article| November 01, 2011 Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California Jeffrey S. Pigati; Jeffrey S. Pigati † 1U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, Colorado 80225, USA †E-mail: jpigati@usgs.gov Search for other works by this author on: GSW Google Scholar David M. Miller; David M. Miller 2U.S. Geological Survey, 345 Middlefield Road, MS-973, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Jordon E. Bright; Jordon E. Bright § 3School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA §Current address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA. Search for other works by this author on: GSW Google Scholar Shannon A. Mahan; Shannon A. Mahan 4U.S. Geological Survey, Denver Federal Center, Box 25046, MS-974, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Jeffrey C. Nekola; Jeffrey C. Nekola 5Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar James B. Paces James B. Paces 6U.S. Geological Survey, Denver Federal Center, Box 25046, MS-963, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (11-12): 2224–2239. https://doi.org/10.1130/B30357.1 Article history received: 21 Jun 2010 rev-recd: 16 Dec 2010 accepted: 29 Jan 2011 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey S. Pigati, David M. Miller, Jordon E. Bright, Shannon A. Mahan, Jeffrey C. Nekola, James B. Paces; Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California. GSA Bulletin 2011;; 123 (11-12): 2224–2239. doi: https://doi.org/10.1130/B30357.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract During the late Pleistocene, emergent groundwater supported persistent and long-lived desert wetlands in many broad valleys and basins in the American Southwest. When active, these systems provided important food and water sources for local fauna, supported hydrophilic and phreatophytic vegetation, and acted as catchments for eolian and alluvial sediments. Desert wetlands are represented in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits. Groundwater discharge deposits contain information on the timing and magnitude of past changes in water-table levels and, thus, are a source of paleohydrologic and paleoclimatic information. Here, we present the results of an investigation of extensive groundwater discharge deposits in the central Mojave Desert at Valley Wells, California. We used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at Valley Wells, which we dated using radiocarbon, luminescence, and uranium-series techniques. We also analyzed the sediments and microfauna (ostracodes and gastropods) to reconstruct the specific environments in which they formed. Our results suggest that the earliest episode of high water-table conditions at Valley Wells began ca. 60 ka (thousands of calendar yr B.P.), and culminated in peak discharge between ca. 40 and 35 ka. During this time, cold (4–12 °C) emergent groundwater supported extensive wetlands that likely were composed of a wet, sedge-rush-tussock meadow mixed with mesic riparian forest. After ca. 35 ka, the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the Last Glacial Maximum (LGM). The water table dropped further after the LGM, and xeric conditions prevailed until modest wetlands returned briefly during the Younger Dryas cold event (13.0–11.6 ka). We did not observe any evidence of wet conditions during the Holocene at Valley Wells. The timing of these fluctuations is consistent with changes in other paleowetland systems in the Mojave Desert, the nearby Great Basin Desert, and in southeastern Arizona, near the border of the Sonoran and Chihuahuan Deserts. The similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late Pleistocene in desert wetlands scattered throughout the American Southwest were likely driven by synoptic-scale climate processes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Deep permeable fault–controlled helium transport and limited mantle flux in two extensional geothermal systems in the Great Basin, United States

This study assesses the relative importance of deeply circulating meteoric water and direct mantle fluid inputs on near-surface 3 He/ 4 He anomalies reported at the Coso and Beowawe geothermal fields of the western United States. The depth of meteoric fluid circulation is a critical factor that controls the temperature, extent of fluid-rock isotope exchange, and mixing with deeply sourced fluids containing mantle volatiles. The influence of mantle fluid flux on the reported helium anomalies appears to be negligible in both systems. This study illustrates the importance of deeply penetrating permeable fault zones (10 −12 to 10 −15 m 2 ) in focusing groundwater and mantle volatiles with high 3 He/ 4 He ratios to shallow crustal levels. These continental geothermal systems are driven by free convection.

Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA

Research Article| March 01, 2011 Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA Gabrielle Kurth; Gabrielle Kurth * 1Department of Earth and Environmental Science, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801, USA *Current address: O'Reilly, Talbot & Okun Associates, Inc., 293 Bridge Street, Springfield, Massachusetts 01375, USA. Search for other works by this author on: GSW Google Scholar Fred M. Phillips; Fred M. Phillips † 1Department of Earth and Environmental Science, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801, USA †E-mail: phillips@nmt.edu Search for other works by this author on: GSW Google Scholar Marith C. Reheis; Marith C. Reheis 2U.S. Geological Survey, MS 980, Box 25046, Denver Federal Center, Denver, Colorado 80225-0046, USA Search for other works by this author on: GSW Google Scholar Joanna L. Redwine; Joanna L. Redwine 3Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada 89512, USA Search for other works by this author on: GSW Google Scholar James B. Paces James B. Paces 2U.S. Geological Survey, MS 980, Box 25046, Denver Federal Center, Denver, Colorado 80225-0046, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (3-4): 744–768. https://doi.org/10.1130/B30010.1 Article history received: 14 Jan 2009 rev-recd: 04 Feb 2010 accepted: 09 Feb 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Gabrielle Kurth, Fred M. Phillips, Marith C. Reheis, Joanna L. Redwine, James B. Paces; Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA. GSA Bulletin 2011;; 123 (3-4): 744–768. doi: https://doi.org/10.1130/B30010.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Closed-basin pluvial lakes are sensitive recorders of effective moisture, and they provide a terrestrial signal of climate change that can be compared to marine and ice records of glacial-interglacial cycles. Although the most recent deep-lake cycle in the western Great Basin (at ca. 16 ka) has been studied intensively, comparatively little is known about the longer-term Quaternary lacustrine history of the region. Lacustrine features higher than those of the most recent highstand have been discovered in many locations throughout the western Great Basin. Qualitative geomorphic and soil studies of shoreline sequences above the latest Pleistocene level suggest that their ages increase as a function of increasing altitude.The results of cosmogenic nuclide dating using chlorine-36 depth profiles from three sites in Nevada (Walker Lake, Columbus Salt Marsh, and Newark Valley), combined with uranium-series and radiocarbon ages, corroborate the geomorphic and soil evidence. The 36Cl results are consistent with available 14C ages and together indicate that the most recent highstands of all three lakes occurred ca. 20–15 ka, late in marine isotope stage (MIS) 2, as shown by previous ages. The 36Cl ages indicate that older lakes in all three basins reached highstands between 100 and 50 ka, and most likely during MIS 4. Shorelines of this age are at about the same or higher altitudes as the younger, MIS 2 shorelines in those basins. The 36Cl results combined with uranium-series ages and one tephra correlation obtained on shorelines higher in altitude than those of MIS 4 and 2 lakes suggest that there were also major lake highstands in the western Great Basin at ca. 100–200 ka, likely corresponding with MIS 6, and during at least two older periods. From these results, we conclude that the preserved shorelines show an apparent decrease in maximum levels with time, suggesting long-term drying of the region since the early middle Pleistocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Analysis of Elevation Changes Detected from Multi-Temporal LiDAR Surveys in Forested Landslide Terrain in Western Oregon

Research Article| November 01, 2010 Analysis of Elevation Changes Detected from Multi-Temporal LiDAR Surveys in Forested Landslide Terrain in Western Oregon WILLIAM J BURNS; WILLIAM J BURNS 1Oregon Department of Geology and Mineral Industries, 800 NE Oregon Street, Portland, OR 97232 Search for other works by this author on: GSW Google Scholar JEFFREY A COE; JEFFREY A COE 2U.S. Geological Survey, Denver Federal Center, Mail Stop 966, Denver, CO 80225 Search for other works by this author on: GSW Google Scholar BASAK SENER KAYA; BASAK SENER KAYA 3Colorado School of Mines, Division of Engineering, Golden, CO 80401 Search for other works by this author on: GSW Google Scholar LINA MA LINA MA 4Oregon Department of Geology and Mineral Industries, 800 NE Oregon Street, Portland, OR 97232 Search for other works by this author on: GSW Google Scholar Author and Article Information WILLIAM J BURNS 1Oregon Department of Geology and Mineral Industries, 800 NE Oregon Street, Portland, OR 97232 JEFFREY A COE 2U.S. Geological Survey, Denver Federal Center, Mail Stop 966, Denver, CO 80225 BASAK SENER KAYA 3Colorado School of Mines, Division of Engineering, Golden, CO 80401 LINA MA 4Oregon Department of Geology and Mineral Industries, 800 NE Oregon Street, Portland, OR 97232 Publisher: Association of Environmental & Engineering Geologists First Online: 02 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 Copyright © 2010 EEGS Environmental & Engineering Geoscience (2010) 16 (4): 315–341. https://doi.org/10.2113/gseegeosci.16.4.315 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIAM J BURNS, JEFFREY A COE, BASAK SENER KAYA, LINA MA; Analysis of Elevation Changes Detected from Multi-Temporal LiDAR Surveys in Forested Landslide Terrain in Western Oregon. Environmental & Engineering Geoscience 2010;; 16 (4): 315–341. doi: https://doi.org/10.2113/gseegeosci.16.4.315 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract We examined elevation changes detected from two successive sets of Light Detection and Ranging (LiDAR) data in the northern Coast Range of Oregon. The first set of LiDAR data was acquired during leaf-on conditions and the second set during leaf-off conditions. We were able to successfully identify and map active landslides using a differential digital elevation model (DEM) created from the two LiDAR data sets, but this required the use of thresholds (0.50 and 0.75 m) to remove noise from the differential elevation data, visual pattern recognition of landslide-induced elevation changes, and supplemental QuickBird satellite imagery. After mapping, we field-verified 88 percent of the landslides that we had mapped with high confidence, but we could not detect active landslides with elevation changes of less than 0.50 m. Volumetric calculations showed that a total of about 18,100 m3 of material was missing from landslide areas, probably as a result of systematic negative elevation errors in the differential DEM and as a result of removal of material by erosion and transport. We also examined the accuracies of 285 leaf-off LiDAR elevations at four landslide sites using Global Positioning System and total station surveys. A comparison of LiDAR and survey data indicated an overall root mean square error of 0.50 m, a maximum error of 2.21 m, and a systematic error of 0.09 m. LiDAR ground-point densities were lowest in areas with young conifer forests and deciduous vegetation, which resulted in extensive interpolations of elevations in the leaf-on, bare-earth DEM. For optimal use of multi-temporal LiDAR data in forested areas, we recommend that all data sets be flown during leaf-off seasons. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Iron hydroxy carbonate formation in zerovalent iron permeable reactive barriers: Characterization and evaluation of phase stability

Predicting the long-term potential of permeable reactive barriers for treating contaminated groundwater relies on understanding the endpoints of biogeochemical reactions between influent groundwater and the reactive medium. Iron hydroxy carbonate (chukanovite) is frequently observed as a secondary mineral precipitate in granular iron PRBs. Mineralogical characterization was carried out using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray absorption spectroscopy on materials collected from three field-based PRBs in the US (East Helena, MT; Elizabeth City, NC; Denver Federal Center, CO). These PRBs were installed to treat a range of contaminants, including chlorinated organics, hexavalent chromium, and arsenic. Results obtained indicate that chukanovite is a prevalent secondary precipitate in the PRBs. Laboratory experiments on high-purity chukanovite separates were carried out to constrain the room-temperature solubility for this mineral. An estimated Gibbs energy of formation (Δ f G°) for chukanovite is − 1174.4 ± 6 kJ/mol. A mineral stability diagram is consistent with observations from the field. Water chemistry from the three reactive barriers falls inside the predicted stability field for chukanovite, at inorganic carbon concentrations intermediate to the stability fields of siderite and ferrous hydroxide. These new data will aid in developing better predictive models of mineral accumulation in zerovalent iron PRBs.

Visualizing fossilization using laser ablation–inductively coupled plasma–mass spectrometry maps of trace elements in Late Cretaceous bones

Research Article| June 01, 2009 Visualizing fossilization using laser ablation–inductively coupled plasma–mass spectrometry maps of trace elements in Late Cretaceous bones Alan E. Koenig; Alan E. Koenig 1U.S. Geological Survey, Box 25046, MS-973, Denver Federal Center, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Raymond R. Rogers; Raymond R. Rogers 2Geology Department, Macalester College, Saint Paul, Minnesota 55105, USA Search for other works by this author on: GSW Google Scholar Clive N. Trueman Clive N. Trueman 3School of Ocean and Earth Science, University of Southampton, SO13 4ZH Southampton, UK Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (6): 511–514. https://doi.org/10.1130/G25551A.1 Article history received: 06 Oct 2008 rev-recd: 05 Jan 2009 accepted: 18 Jan 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alan E. Koenig, Raymond R. Rogers, Clive N. Trueman; Visualizing fossilization using laser ablation–inductively coupled plasma–mass spectrometry maps of trace elements in Late Cretaceous bones. Geology 2009;; 37 (6): 511–514. doi: https://doi.org/10.1130/G25551A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Elemental maps generated by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) provide a previously unavailable high-resolution visualization of the complex physicochemical conditions operating within individual bones during the early stages of diagenesis and fossilization. A selection of LA-ICP-MS maps of bones collected from the Late Cretaceous of Montana (United States) and Madagascar graphically illustrate diverse paths to recrystallization, and reveal unique insights into geochemical aspects of taphonomic history. Some bones show distinct gradients in concentrations of rare earth elements and uranium, with highest concentrations at external bone margins. Others exhibit more intricate patterns of trace element uptake related to bone histology and its control on the flow paths of pore waters. Patterns of element uptake as revealed by LA-ICP-MS maps can be used to guide sampling strategies, and call into question previous studies that hinge upon localized bulk samples of fossilized bone tissue. LA-ICP-MS maps also allow for comparison of recrystallization rates among fossil bones, and afford a novel approach to identifying bones or regions of bones potentially suitable for extracting intact biogeochemical signals. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Memorial of Benjamin F. Leonard III, 1921-2008

Other| May 01, 2009 Memorial of Benjamin F. Leonard III, 1921–2008 Daniel E. Kile; Daniel E. Kile * 1U.S. Geological Survey, MS 413, Denver Federal Center, Denver, Colorado 80225, U.S.A. *E-mails: dekile@usgs.gov; kvevans@usgs.gov Search for other works by this author on: GSW Google Scholar Karl V. Evans Karl V. Evans * 2U.S. Geological Survey, MS 973, Denver Federal Center, Denver, Colorado 80225, U.S.A. *E-mails: dekile@usgs.gov; kvevans@usgs.gov Search for other works by this author on: GSW Google Scholar Author and Article Information Daniel E. Kile * 1U.S. Geological Survey, MS 413, Denver Federal Center, Denver, Colorado 80225, U.S.A. Karl V. Evans * 2U.S. Geological Survey, MS 973, Denver Federal Center, Denver, Colorado 80225, U.S.A. *E-mails: dekile@usgs.gov; kvevans@usgs.gov Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X © 2009 American Mineralogist American Mineralogist (2009) 94 (5-6): 859–861. https://doi.org/10.2138/am.2009.545 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Daniel E. Kile, Karl V. Evans; Memorial of Benjamin F. Leonard III, 1921–2008. American Mineralogist 2009;; 94 (5-6): 859–861. doi: https://doi.org/10.2138/am.2009.545 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Benjamin Franklin Leonard III, at age 87, passed away peacefully at his home in McCall, Idaho, on September 5, 2008. Ben had a long and distinguished career at the U.S. Geological Survey, where he established himself as an accomplished field geologist and an internationally recognized expert in ore microscopy. Born in Dobbs Ferry, New York, on May 12, 1921, Ben spent much of his early life in the eastern United States, graduating from Hamilton College in 1942 (B.S.), a salutatorian and member of Phi Beta Kappa, and then Princeton University in 1946 (M.A.) and 1951 (Ph.D.), where he was a... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Isotopic, geochemical, and temporal characterization of Proterozoic basement rocks in the Quitovac region, northwestern Sonora, Mexico: Implications for the reconstruction of the southwestern margin of Laurentia

A detailed geochemical characterization of 19 representative Proterozoic basement rocks in the Quitovac region in northwestern Sonora, Mexico, has identified two distinct Paleoproterozoic basement blocks that coincide spatially with the previously proposed Caborca and “North America” blocks. New U-Pb zircon geochronology revises their age ranges, the Caborca (1.78–1.69 Ga) and “North America” (1.71–1.66 Ga) blocks at Quitovac, and precludes a simple age differentiation between them. In addition, Grenvillian-age granitoids (ca. 1.1 Ga), spatially associated with the Caborca block have been identified at Quitovac. Nd isotopes and major- and trace- element geochemistry support the distinction of these Paleoproterozoic blocks. Granitoids of the “North America” block are characterized by depleted eNd values (3.4–3.9) and younger Nd model ages (1800–1740 Ma) and have lower K 2 O, Y, Rb, Ba, Th, REE, and Fe/Mg values than coeval rocks of the Caborca block. The Caborca block granitoids are likewise characterized by slightly less depleted eNd (0.6–2.6) and older Nd model ages (2070–1880 Ma). Despite the subtle differences, granitoids from both the Caborca and “North America” blocks exhibit island arc-like affinities. We propose that the Proterozoic basement rocks from the Quitovac region are an extension of the Proterozoic crustal provinces in the southwestern United States. Specifically, rocks of the Caborca block exhibit an affinity to rocks of either the Yavapai province or the Mojave– Yavapai transition zone, whereas rocks of the “North America” block have signatures similar to those of the Mazatzal province or possibly the Yavapai province of Arizona. The new isotopic ages and geochemical data do not support the existence of the Late Jurassic Mojave–Sonora megashear at Quitovac, as originally proposed. However, the Quitovac region accounts only for a small fraction of the Proterozoic basement in Sonora, so these findings do not eliminate the possibility of a megashear elsewhere in northern Sonora. Our new data create the possibility of alternative hypotheses for the distribution of Paleoproterozoic crustal provinces in southwestern North America that affect reconstructions of the original southwestern margin of Laurentia, and reduce uncertainties in the configuration, timing, and existence of the Proterozoic supercontinent, Rodinia.

Long-term performance of permeable reactive barriers using zero-valent iron: geochemical and microbiological effects.

Geochemical and microbiological factors that control long-term performance of subsurface permeable reactive barriers were evaluated at the Elizabeth City, North Carolina, and the Denver Federal Center, Colorado, sites. These ground water treatment systems use zero-valent iron filings (Peerless Metal Powders Inc.) to intercept and remediate chlorinated hydrocarbon compounds at the Denver Federal Center (funnel-and-gate system) and overlapping plumes of hexavalent chromium and chlorinated hydrocarbons at Elizabeth City (continuous wall system). Zero-valent iron at both sites is a long-term sink for carbon, sulfur, calcium, silicon, nitrogen, and magnesium. After about four years of operation, the average rates of inorganic carbon (IC) and sulfur (S) accumulation are 0.09 and 0.02 kg/m2/year, respectively, at Elizabeth City where upgradient waters contain <400 mg/L of total dissolved solids (TDS). At the Denver Federal Center site, upgradient ground water contains 1000 to 1200 mg/L TDS and rates of IC and S accumulation are as high as 2.16 and 0.80 kg/m2/year, respectively. At both sites, consistent patterns of spatially variable mineral precipitation and microbial activity are observed. Mineral precipitates and microbial biomass accumulate the fastest near the upgradient aquifer-Fe0 interface. Maximum net reductions in porosity due to the accumulation of sulfur and inorganic carbon precipitates range from 0.032 at Elizabeth City to 0.062 at the Denver Federal Center (gate 2) after about four years. Although pore space has been lost due the accumulation of authigenic components, neither site shows evidence of pervasive pore clogging after four years of operation.

Formation of ferrihydrite and associated iron corrosion products in permeable reactive barriers of zero-valent iron.

Ferrihydrite, which is known to form in the presence of oxygen and to be stabilized by the adsorption of Si, PO4 and SO4, is ubiquitous in the fine-grained fractions of permeable reactive barrier (PRB) samples from the U.S. Coast Guard Support Center (Elizabeth City, NC) and the Denver Federal Center (Lakewood, CO) studied by high-resolution transmission electron microscopy and selected area electron diffraction. The concurrent energy-dispersive X-ray data indicate a strong association between ferrihydrite and metals such as Si, Ca, and Cr. Magnetite, green rust 1, aragonite, calcite, mackinawite, greigite and lepidocrocite were also present, indicative of a geochemical environment that is temporally and spatially heterogeneous. Whereas magnetite, which is known to form due to anaerobic Fe0 corrosion, passivates the Fe0 surface, ferrihydrite precipitation occurs away from the immediate Fe0 surface, forming small (<0.1 microm) discrete clusters. Consequently, Fe0-PRBs may remain effective for a longer period of time in slightly oxidized groundwater systems where ferrihydrite formation occurs compared to oxygen-depleted systems where magnetite passivation occurs. The ubiquitous presence of ferrihydrite suggests that the use of Fe0-PRBs may be extended to applications that require contaminant adsorption rather than, or in addition to, redox-promoted contaminant degradation.

Discussion and reply: Variation in displacement along strike of the South Virgin−White Hills detachment fault: Perspective from the northern White Hills, northwestern ArizonaDiscussion

Research Article| April 01, 2001 Discussion and reply: Variation in displacement along strike of the South Virgin−White Hills detachment fault: Perspective from the northern White Hills, northwestern ArizonaDiscussion R. Ernest Anderson R. Ernest Anderson 1U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Author and Article Information R. Ernest Anderson 1U.S. Geological Survey, Denver Federal Center, Denver, Colorado 80225, USA Publisher: Geological Society of America Received: 02 Dec 1999 Revision Received: 01 Mar 2000 Accepted: 18 May 2000 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2001) 113 (4): 532–533. https://doi.org/10.1130/0016-7606(2001)113<0532:DARVID>2.0.CO;2 Article history Received: 02 Dec 1999 Revision Received: 01 Mar 2000 Accepted: 18 May 2000 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. Ernest Anderson; Discussion and reply: Variation in displacement along strike of the South Virgin−White Hills detachment fault: Perspective from the northern White Hills, northwestern ArizonaDiscussion. GSA Bulletin 2001;; 113 (4): 532–533. doi: https://doi.org/10.1130/0016-7606(2001)113<0532:DARVID>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Duebendorfer and Sharp (1998) interpreted three faults in the Gold Butte−White Hills area, Arizona, as forming a 55-km-long detachment fault, the South Virgin−White Hills detachment fault. They suggested that the fault might represent a breakaway for extensional allochthons located to the west. Their report deals mainly with the central segment of the South Virgin−White Hills detachment fault, i.e., the Salt Spring fault segment. This discussion addresses two apparent inconsistencies, one spatial and one temporal, in their portrayal of the faulting and tilting in the area of the Salt Spring segment. An alternative interpretation that does not include a detachment fault... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Hydraulic and Geochemical Performance of a Permeable Reactive Barrier Containing Zero‐Valent Iron, Denver Federal Center

AbstractThe hydraulic and geochemical performance of a 366 m long permeable reactive barrier (PRB) at the Denver Federal Center, Denver, Colorado, was evaluated. The funnel and gate system, which was installed in 1996 to intercept and remediate ground water contaminated with chlorinated aliphatic hydrocarbons (CAHs), contained four 12.2 m wide gates filled with zero‐valent iron. Ground water mounding on the upgradient side of the PRB resulted in a tenfold increase in the hydraulic gradient and ground water velocity through the gates compared to areas of the aquifer unaffected by the PRB. Water balance calculations for April 1997 indicate that about 75 % of the ground water moving toward the PRB from upgradient areas moved through the gates. The rest of the water either accumulated on the upgradient side of the PRB or bypassed the PRB. Chemical data from monitoring wells screened down‐gradient, beneath, and at the ends of the PRB indicate that contaminants had not bypassed the PRB, except in a few isolated areas. Greater than 99 % of the CAH mass entering the gates was retained by the iron. Fifty‐one percent of the CAH carbon entering one gate was accounted for in dissolved C1 and C2 hydrocarbons, primarily ethane and ethene, which indicates that CAHs may adsorb to the iron prior to being dehalogenated. Treated water exiting the gates displaced contaminated ground water at a distance of at least 3 m downgradient from the PRB by the end of 1997. Measurements of dissolved inorganic ions in one gate indicate that calcite and siderite precipitation in the gate could reduce gate porosity by about 0.35 % per year. Results from this study indicate that funnel and gate systems containing zero‐valent iron can effectively treat ground water contaminated with CAHs. However, the hydrologic impacts of the PRB on the flow system need to be fully understood to prevent contaminants from bypassing the PRB.