Orchestrating façades and fenestration has become a much elevated art in contemporary California. Highly articulating the way a building faces onto the street is an expertise of Oakland‐based ...architect Thom Faulders. Blaine Brownell, architect, educator and researcher in emergent materials, examines Faulders Studio's recent oeuvre and its audacious and attractive material expression.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Long-term performance is a key consideration for the granular iron permeable reactive barrier (PRB) technology because the economic benefit relies on sustainable operation for substantial periods of ...time. However, predictions on the long-term performance have been limited mainly because of the lack of reliable modeling tools. This study evaluated the predictive capability of a recently-developed reactive transport model at two field-scale PRBs, both having relatively high concentrations of dissolved carbonate in the native groundwater. The first site, with 8
years of available monitoring data, was a funnel-and-gate installation, with a low groundwater velocity through the gate (about 0.12
m d
−
1
). The loss in iron reactivity caused by secondary mineral precipitation was small, maintaining relatively high removal rates for chlorinated organics. The simulated concentrations for most constituents in the groundwater were within the range of the monitoring data. The second site, with monitoring data available for 5
years, was a continuous wall PRB, designed for a groundwater velocity of 0.9
m d
−
1
. A comparison of measured and simulated aqueous concentrations suggested that the average groundwater velocity through the PRB could be lower than the design value by a factor of two or more. The distribution and amounts of carbonate minerals measured in core samples supported the decreased groundwater velocity used in the simulation. The generally good agreement between the simulated and measured aqueous and solid-phase data suggest that the model could be an effective tool for predicting long-term performance of granular iron PRBs, particularly in groundwater with high concentrations of carbonate.
► This study evaluated capability of a reactive transport model at field-scale PRBs. ► Simulations were compared against monitoring data from two field-scale PRBs. ► The model could be a tool for predicting long-term performance of iron PRBs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Driverless cars promise to be a seductive, inevitable technology that will transform our cities in a multitude of ways. But, asks author and journalist Tim Maughan, are we really prepared for what ...lies ahead, or have we already fallen asleep at the wheel?
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In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling ...interval of 0·375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C min−1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C min−1 and the average percentage time spent above 2°C min−1 was ∼70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C min−1. Simultaneous measurements of two thermocouples 5·5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ∼10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.
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Recirculating well pairs are a proven means of implementing bioremediation and may also be useful for applying other in situ ground water remediation technologies. A bromide tracer test was performed ...to characterize the hydraulic performance of a recirculating well pair installed at Moffett Field, California. In particular, we estimate two important properties of the recirculating well pair: (1) the fraction of captured water that is recycled between the wells, and (2) the travel-time distribution of ground water in the induced zone of recirculation. We also develop theoretical estimates of these two properties and demonstrate they depend upon a dimensionless pumping rate, denoted xi. The bromide breakthrough curve predicted from theory agrees well with that determined experimentally at Moffett Field. The minimum travel time between the wells is denoted t(min). In theory, t(min) depends inversely on Q, the pumping rate in the recirculating wells, and is proportional to a2, the square of the distance between the wells. Both the experimental and theoretical travel-time distributions indicate that at least half the recirculating water travels between the wells along fast flowpaths (travel time < 2*t(min)). Therefore, when designing recirculating well pairs, engineers should ensure that t(min) will be sufficiently high to allow biologically mediated reactions (or other in situ remediation processes) sufficient time to proceed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The technical feasibility of in situ reductive dechlorination of cis‐dichloroethene (cDCE) and vinyl chloride (VC) was demonstrated at a sulfidogenic ground water site. Preceding laboratory studies ...had indicated that dechlorination at the site was limited by the supply of electron donors, that dechlorinating activity was sparsely and heterogeneously distributed, and that dechlorination was strongly enhanced by mixing sediments from multiple locations at the site. Based on these observations, the remediation strategy consisted of amending the ground water with sodium propionate solution using a pair of recirculation wells as a mixing device. This strategy was able to overcome the sparse initial distribution of biological activity by creating a treatment zone. Dechlorination and sulfate reduction commenced within 10 and 4 d, respectively, after propionate amendment began. Dechlorination efficiency increased during the 2 months of continuous operation. By the end of the 2 months, treatment converted ∼1000 μg/L cDCE nearly stoichiometrically into ethene, with only low concentrations of VC remaining. More than 90% of chlorinated ethenes were removed as the ground water traveled from one well to the other (travel time of ∼1 to 2 weeks). Near‐complete removal of ∼250 mg/L sulfate accompanied the rapid dechlorination, but no methanogenesis was observed. Aquifer clogging in the vicinity of the propionate injection wells became evident after ∼40 d of propionate amendment and was attributed to the growth of sulfate‐reducing bacteria and/or the formation of insoluble metal sulfides. Clogging was mitigated by pulsed amendment of the propionate solution.
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Trichloroethylene (TCE) was efficiently biodegraded in situ by aerobic cometabolism at the Moffett Federal Airfield test site, in the presence of phenol or toluene (Hopkins et al. Appl. Environ. ...Microbiol. 1993, 59, 2277; Hopkins et al. Environ. Sci. Technol. 1993, 27, 2542; Hopkins, G. D.; McCarty, P. L. Environ. Sci. Technol. 1995, 29, 1628). Using uncontaminated soil from this site as an inoculum, a semicontinuous slurry microcosm method was developed that reproduced in situ TCE degradation rates. The slurry method was then applied to evaluate the in situ TCE biodegradation potential at Edwards Air Force Base where full-scale application was contemplated. With 0.66 mg/L TCE and either 9.7 mg/L toluene or 13.4 mg/L phenol in the exchange fluid, steady state TCE removals varied between 87 and 99%, depending upon sample depth. Toluene and phenol growth yields based upon oxygen to substrate ratios were 0.77 and 0.59 g/g during the start-up phase and 0.52 and 0.36 g/g during steady state TCE removal, respectively. The TCE degradation rate constant ratio, k c/K c, was similar for the two substrates. Steady state TCE removals varied little in a given microcosm over 1 year of operation. In the Moffett and Edwards microcosms as well as at Moffett Federal Airfield (Fries et al. Appl. Environ. Technol. 1997, 63, 1523), toluene o-monooxygenase was the dominant TCE-oxidizing enzyme present.
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In sulfidogenic aquifers dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) by dehalogenating bacteria (DHB) is often incomplete, causing accumulation of cis-dichloroethylene ...(cDCE) and vinyl chloride (VC). Research described in this dissertation addresses this problem through coordinated laboratory and field experiments. Laboratory studies demonstrated dechlorination of approximately 100 μM PCE to ethylene in the presence of more than 1.5 mM sulfate over a period of more than three years. Hydrogen concentrations were 1.6 ± 0.2 nM during dechlorination of cDCE and VC and increased during sulfate reduction to 2.5 ± 0.3 nM in the absence of dechlorination. These data show that DHB can outcompete sulfate-reducing bacteria at low hydrogen levels. When hydrogen was added in excess, removal of 2 mM sulfate and dechlorination of 130 μM PCE to ethylene occurred simultaneously and were completed in less than 15 days. These results indicated that dechlorination by DHB can be enhanced by depleting sulfate. A protocol was developed by which sulfate was removed biologically with an excess of electron donor. This protocol was evaluated at the pilot scale at a sulfidogenic site (Moffett Federal Airfield, Mountain View, CA) where the groundwater was contaminated with approximately 1000 μM cDCE and 100 μM VC, and contained approximately 200 mg/L sulfate. Microcosm studies indicated that dechlorinating activity was sparse and unevenly distributed across the site. However, dechlorination rates were strongly enhanced when sediment samples from multiple wells and depths were combined in one composite microcosm. This observation suggested that uneven distribution of nutrients and requisite bacteria is a factor limiting contaminant removal. Data obtained in the pilot-scale field test was consistent with this hypothesis. In this test, the groundwater was amended with approximately 150 mg/L propionate and distributed into the subsurface using a recirculating well pair. Sulfate reduction and dechlorination commenced within four days after propionate amendment. Complete sulfate removal and near-complete transformation of cDCE to ethylene without methane formation was observed after two months of operation. Reaction rates increased with time, indicating growth of dechlorinating communities. Increasing water levels in one of the treatment wells suggests aquifer clogging by sulfate-reducing bacteria and insoluble metal sulfides.
