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Title: Nitrate Biogeochemistry and Reactive Transport in California Groundwater: LDRD Final Report

Abstract

Nitrate is the number one drinking water contaminant in the United States. It is pervasive in surface and groundwater systems,and its principal anthropogenic sources have increased dramatically in the last 50 years. In California alone, one third of the public drinking-water wells has been lost since 1988 and nitrate contamination is the most common reason for abandonment. Effective nitrate management in groundwater is complicated by uncertainties related to multiple point and non-point sources, hydrogeologic complexity, geochemical reactivity, and quantification of denitrification processes. In this paper, we review an integrated experimental and simulation-based framework being developed to study the fate of nitrate in a 25 km-long groundwater subbasin south of San Jose, California, a historically agricultural area now undergoing rapid urbanization with increasing demands for groundwater. The modeling approach is driven by a need to integrate new and archival data that support the hypothesis that nitrate fate and transport at the basin scale is intricately related to hydrostratigraphic complexity, variability of flow paths and groundwater residence times, microbial activity, and multiple geochemical reaction mechanisms. This study synthesizes these disparate and multi-scale data into a three-dimensional and highly resolved reactive transport modeling framework.

Authors:
; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
878204
Report Number(s):
UCRL-TR-219675
TRN: US0602300
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
07 ISOTOPES AND RADIATION SOURCES; 58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; 60 APPLIED LIFE SCIENCES; BIOGEOCHEMISTRY; CALIFORNIA; CONTAMINATION; DENITRIFICATION; DRINKING WATER; HYPOTHESIS; MANAGEMENT; NITRATES; REACTION KINETICS; SIMULATION; TRANSPORT; GROUND WATER

Citation Formats

Esser, B K, Beller, H, Carle, S, Cey, B, Hudson, G B, Leif, R, LeTain, T, Moody-Bartel, C, Moore, K, McNab, W, Moran, J, and Tompson, A. Nitrate Biogeochemistry and Reactive Transport in California Groundwater: LDRD Final Report. United States: N. p., 2006. Web. doi:10.2172/878204.
Esser, B K, Beller, H, Carle, S, Cey, B, Hudson, G B, Leif, R, LeTain, T, Moody-Bartel, C, Moore, K, McNab, W, Moran, J, & Tompson, A. Nitrate Biogeochemistry and Reactive Transport in California Groundwater: LDRD Final Report. United States. doi:10.2172/878204.
Esser, B K, Beller, H, Carle, S, Cey, B, Hudson, G B, Leif, R, LeTain, T, Moody-Bartel, C, Moore, K, McNab, W, Moran, J, and Tompson, A. Fri . "Nitrate Biogeochemistry and Reactive Transport in California Groundwater: LDRD Final Report". United States. doi:10.2172/878204. https://www.osti.gov/servlets/purl/878204.
@article{osti_878204,
title = {Nitrate Biogeochemistry and Reactive Transport in California Groundwater: LDRD Final Report},
author = {Esser, B K and Beller, H and Carle, S and Cey, B and Hudson, G B and Leif, R and LeTain, T and Moody-Bartel, C and Moore, K and McNab, W and Moran, J and Tompson, A},
abstractNote = {Nitrate is the number one drinking water contaminant in the United States. It is pervasive in surface and groundwater systems,and its principal anthropogenic sources have increased dramatically in the last 50 years. In California alone, one third of the public drinking-water wells has been lost since 1988 and nitrate contamination is the most common reason for abandonment. Effective nitrate management in groundwater is complicated by uncertainties related to multiple point and non-point sources, hydrogeologic complexity, geochemical reactivity, and quantification of denitrification processes. In this paper, we review an integrated experimental and simulation-based framework being developed to study the fate of nitrate in a 25 km-long groundwater subbasin south of San Jose, California, a historically agricultural area now undergoing rapid urbanization with increasing demands for groundwater. The modeling approach is driven by a need to integrate new and archival data that support the hypothesis that nitrate fate and transport at the basin scale is intricately related to hydrostratigraphic complexity, variability of flow paths and groundwater residence times, microbial activity, and multiple geochemical reaction mechanisms. This study synthesizes these disparate and multi-scale data into a three-dimensional and highly resolved reactive transport modeling framework.},
doi = {10.2172/878204},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Feb 24 00:00:00 EST 2006},
month = {Fri Feb 24 00:00:00 EST 2006}
}

Technical Report:

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  • Nitrate is the number one drinking water contaminant in the United States. It is pervasive in surface and groundwater systems, and its principal anthropogenic sources have increased dramatically in the last 50 years. In California alone, one third of the public drinking-water wells has been lost since 1988 and nitrate contamination is the most common reason for abandonment. Effective nitrate management in groundwater is complicated by uncertainties related to multiple point and non-point sources, hydrogeologic complexity, geochemical reactivity, and quantification of dentrification processes. In this paper, we review an integrated experimental and simulation-based framework being developed to study the fatemore » of nitrate in a 25 km-long groundwater subbasin south of San Jose, California, a historically agricultural area now undergoing rapid urbanization with increasing demands for groundwater. The modeling approach is driven by a need to integrate new and archival data that support the hypothesis that nitrate fate and transport at the basin scale is intricately related to hydrostratigraphic complexity, variability of flow paths and groundwater residence times, microbial activity, and multiple geochemical reaction mechanisms. This study synthesizes these disparate and multi-scale data into a three-dimensional and highly resolved reactive transport modeling framework.« less
  • A critical component of the State Water Resource Control Board's Groundwater Ambient Monitoring and Assessment (GAMA) Program is to assess the major threats to groundwater resources that supply drinking water to Californians (Belitz et al., 2004). Nitrate is the most pervasive and intractable contaminant in California groundwater and is the focus of special studies under the GAMA program. This report presents results of a study of nitrate contamination in the aquifer beneath the cities of Morgan Hill and Gilroy, CA, in the Llagas Subbasin of Santa Clara County, where high nitrate levels affect several hundred private domestic wells. The mainmore » objectives of the study are: (1) to identify the main source(s) of nitrate that issue a flux to the shallow regional aquifer (2) to determine whether denitrification plays a role in the fate of nitrate in the subbasin and (3) to assess the impact that a nitrate management plan implemented by the local water agency has had on the flux of nitrate to the regional aquifer. Analyses of 56 well water samples for major anions and cations, nitrogen and oxygen isotopes of nitrate, dissolved excess nitrogen, tritium and groundwater age, and trace organic compounds, show that synthetic fertilizer is the most likely source of nitrate in highly contaminated wells, and that denitrification is not a significant process in the fate of nitrate in the subbasin except in the area of recycled water application. In addition to identifying contaminant sources, these methods offer a deeper understanding of how the severity and extent of contamination are affected by hydrogeology and groundwater management practices. In the Llagas subbasin, the nitrate problem is amplified in the shallow aquifer because it is highly vulnerable with high vertical recharge rates and rapid lateral transport, but the deeper aquifers are relatively more protected by laterally extensive aquitards. Artificial recharge delivers low-nitrate water and provides a means of long-term remediation. Examination of nitrate concentration in relation to groundwater age indicates that the nitrate management plan has not yet resulted in a decrease in the flux of nitrate to the shallow aquifer in the areas tested.« less
  • A critical component of the State Water Resource Control Board's Groundwater Ambient Monitoring and Assessment (GAMA) Program is to assess the major threats to groundwater resources that supply drinking water to Californians (Belitz et al., 2004). Nitrate concentrations approaching and greater than the maximum contaminant level (MCL) are impairing the viability of many groundwater basins as drinking water sources Source attribution and nitrate fate and transport are therefore the focus of special studies under the GAMA program. This report presents results of a study of nitrate contamination in the aquifer beneath the City of Livermore, where high nitrate levels affectmore » both public supply and private domestic wells. Nitrate isotope data are effective in determining contaminant sources, especially when combined with other isotopic tracers such as stable isotopes of water and tritium-helium ages to give insight into the routes and timing of nitrate inputs to the flow system. This combination of techniques is demonstrated in Livermore, where it is determined that low nitrate reclaimed wastewater predominates in the northwest, while two flowpaths with distinct nitrate sources originate in the southeast. Along the eastern flowpath, {delta}{sup 15}N values greater than 10{per_thousand} indicate that animal waste is the primary source. Diminishing concentrations over time suggest that contamination results from historical land use practices. The other flowpath begins in an area where rapid recharge, primarily of low nitrate imported water (identified by stable isotopes of water and a tritium-helium residence time of less than 1 year), mobilizes a significant local nitrate source, bringing groundwater concentrations above the MCL of 45 mg NO{sub 3} L{sup -1}. In this area, artificial recharge of imported water via local arroyos induces flux of the contaminant to the regional aquifer. The low {delta}{sup 15}N value (3.1{per_thousand}) in this location implicates synthetic fertilizer. Geochemical modeling supports the hypothesis of separate sources, one including organic carbon, as from animal waste, and one not. In addition to these anthropogenic sources, natural nitrate background levels between 15 and 20 mg NO{sub 3} L{sup -1} are found in deep wells with residence times greater than 50 years.« less
  • The primary purposes of this project were to (1) improve and validate the LLNL/IMPACT atmospheric chemistry and aerosol transport model, (2) experimentally analyze size- and time-resolved aerosol measurements taken during spring 2001 in Northern California, and (3) understand the origin of dust impacting Northern California. Under this project, we (1) more than doubled the resolution of the LLNL-IMPACT global atmospheric chemistry and aerosol model (to 1 x 1 degree), (2) added an interactive dust emission algorithm to the IMPACT model in order to simulate observed events, (3) added detailed microphysics to the IMPACT model to calculate the size-distribution of aerosolsmore » in terms of mass, (4) analyzed the aerosol mass and elemental composition of the size- and time-resolved aerosol measurements made by our UC Davis collaborators, and (5) determined that the majority of the observed soil dust is from intercontinental transport across the Pacific. A detailed report on this project is in the attached document ''Impact of Long-Range Dust Transport on Northern California in Spring 2002'' (UCRL-TR-209597), except for the addition of aerosol microphysics, which is covered in the attached document ''Implementation of the Missing Aerosol Physics into LLNL IMPACT'' (UCRL-TR-209568). In addition to the technical results, this project has (1) produced a journal article presenting our results that will be submitted shortly, (2) enabled collaborations with UC Davis and the California Air Resources Board, (3) generated a direct DOE request and large computer allocation to simulate the radiative impact of sulfate aerosols at high-resolution over the last 50 years, and (4) contributed to successful LLNL responses to requests for proposals from (a) the DOE Atmospheric Science Program ($780k), (b) the DOE Atmospheric Radiation Measurement Program ($720k), and (c) the NASA Global Modeling and Analysis Program ($525k). The journal article will be based on the report listed above (''Impact of Long-Range Dust Transport on Northern California in Spring 2002''), and will be submitted to the Journal of Geophysical Research in the near future.« less
  • Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role ofmore » flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3-) and the long-term stability of immobilized uranium mineral phases after bioremediation processes are complete, and (4) the ability for metabolic uncoupling compounds to maintain microbial growth while limiting biomass production. The results of the laboratory experiments will be used to develop mathematical descriptive models for the coupled transport and reduction processes.« less