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301.
Shen Qiushi Zhang Lu Kimirei Ismael Aaron Wang Zhaode Gao Qun Chen Shuang Yu Cheng 《中国海洋湖沼学报》2019,37(1):134-145
The vertical distributions of trace metals and physicochemical parameters in water columns in Kigoma Bay and Kungwe Bay in eastern Lake Tanganyika, Tanzania, were studied. The Al, Ba, Ca, Co,K, Mg, Mn, Mo, Na, Sn, Sr, and V concentrations were low and varied very little with depth. The toxic heavy metal(As, Cr, Cu, Ni, Pb, and Zn) concentrations were relatively high in the surface water, and the Cu, Ni, Pb, and Zn concentrations decreased with depth. Principal component and cluster analyses indicated that the metals in the lake had three main sources. Al, Ba, Ca, Co, Cu, Cr, Mn, Sr, Sn, and V were found to be geogenic; As, Cr, Cu, Mo, Ni, Pb, Sn and Zn anthropogenic; and As, Ca, Co, Mg, and Na biogenic.Human health risk assessments were performed, and it was found that trace metals in the water at most of the sampling sites would cause no potential adverse ef fects or non-carcinogenic health risks through dermal contact or ingestion. However, trace metals in surface water in Kungwe Bay could have certain adverse ef fects on human health through the ingestion pathway(the total hazard quotient for ingestion(ΣHQi ng)was 1.75(a value 1 was de?ned as possibly indicating adverse ef fects). The Pb HQi ng for surface water in Kungwe Bay was 1.50 and contributed 80% of the ΣHQ_(ing_, implying that Pb pollution is a water quality and safety problem that needs to be carefully monitored and the potential sources identi?ed. 相似文献
302.
Concurrent Treatment of 1,4‐Dioxane and Chlorinated Aliphatics in a Groundwater Recirculation System Via Aerobic Cometabolism
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Min‐Ying Jacob Chu Peter J. Bennett Mark E. Dolan Michael R. Hyman Aaron D. Peacock Adria Bodour Richard Hunter Anderson Douglas M. Mackay Mark N. Goltz 《Ground Water Monitoring & Remediation》2018,38(3):53-64
This research demonstrates that groundwater contaminated by a relatively dilute but persistent concentration of 1,4‐dioxane (1,4‐D), approximately 60 μg/L, and chlorinated aliphatic co‐contaminants (1.4 to 10 μg/L) can be efficiently and reliably treated by in situ aerobic cometabolic biodegradation (ACB). A field trial lasting 265 days was conducted at Operable Unit D at the former McClellan Air Force Base and involved establishing an in situ ACB reactor through amending recirculated groundwater with propane and oxygen. The stimulated indigenous microbial population was able to consistently degrade 1,4‐D to below 3 μg/L while the co‐contaminants trichloroethene (TCE) and 1,2‐dichloroethane (1,2‐DCA) were decreased to below 1 μg/L and 0.18 μg/L, respectively. A stable treatment efficiency of more than 95% removal for 1,4‐D and 1,2‐DCA and of more than 90% removal for TCE was achieved. High treatment efficiencies for 1,4‐D and all co‐contaminants were sustained even without propane and oxygen addition for a 2‐week period. 相似文献
303.
Michael Truex Chris Johnson Tamzen Macbeth Dave Becker Kira Lynch Dominic Giaudrone Aaron Frantz Hope Lee 《Ground Water Monitoring & Remediation》2017,37(3):28-44
Pump‐and‐treat (P&T) is a widely applied remedy for groundwater remediation at many types of sites for multiple types of contaminants. Decisions regarding major changes in the remediation approach are an important element of environmental remediation management for a site using P&T. While existing guidance documents provide information on design, operation, and optimization for P&T systems, these documents do not provide specific technical guidance to support remedy decisions regarding when to transition to a new remedy or to initiate closure of the P&T remedy. A structured approach for P&T performance assessment was developed and is described herein, using analysis of three example P&T systems. These examples highlight key aspects of the performance assessment decision logic and represent assessment outcomes associated with optimizing the P&T system, transitioning from P&T to natural attenuation, and supplementing P&T with another technology to hasten transition to natural attenuation. 相似文献
304.
Despoina K. Skoulidou Aaron J. Rosengren Kleomenis Tsiganis George Voyatzis 《Celestial Mechanics and Dynamical Astronomy》2018,130(11):77
In this paper, we study the long-term dynamical evolution of highly elliptical orbits in the medium-Earth orbit region around the Earth. The real population consists primarily of Geosynchronous Transfer Orbits (GTOs), launched at specific inclinations, Molniya-type satellites and related debris. We performed a suite of long-term numerical integrations (up to 200 years) within a realistic dynamical model, aimed primarily at recording the dynamical lifetime of such orbits (defined as the time needed for atmospheric reentry) and understanding its dependence on initial conditions and other parameters, such as the area-to-mass ratio (A / m). Our results are presented in the form of 2-D lifetime maps, for different values of inclination, A / m, and drag coefficient. We find that the majority of small debris (\(>70\%\), depending on the inclination) can naturally reenter within 25–90 years, but these numbers are significantly less optimistic for large debris (e.g., upper stages), with the notable exception of those launched from high latitude (Baikonur). We estimate the reentry probability and mean dynamical lifetime for different classes of GTOs and we find that both quantities depend primarily and strongly on initial perigee altitude. Atmospheric drag and higher A / m values extend the reentry zones, especially at low inclinations. For high inclinations, this dependence is weakened, as the primary mechanisms leading to reentry are overlapping lunisolar resonances. This study forms part of the EC-funded (H2020) “ReDSHIFT” project. 相似文献
305.
Radium mass-balance in Jamaica Bay, NY: Evidence for a substantial flux of submarine groundwater 总被引:3,自引:3,他引:3
Aaron J. Beck John P. Rapaglia J. Kirk Cochran Henry J. Bokuniewicz 《Marine Chemistry》2007,106(3-4):419-441
A mass balance for the naturally-occurring radium isotopes (224Ra, 223Ra, 228Ra, and 226Ra) in Jamaica Bay, NY, was conducted by directly estimating the individual Ra contributions of wastewater discharge, diffusion from fine-grained subtidal sediments, water percolation through marshes, desorption from resuspended particles, and water exchange at the inlet. The mass balance revealed a major unknown source term accounting for 19–71% of the total Ra input, which could only be resolved by invoking a source from submarine groundwater. Shallow (< 2 m depth) groundwater from permeable sediments in Jamaica Bay was brackish and enriched in Ra relative to surface bay waters by over two orders of magnitude. To balance Ra fluxes, a submarine groundwater input of 0.8 × 109–9.0 × 109 L d− 1 was required. This flux was similar for all four isotopes, with individual estimates varying by less than a factor of 2. Our calculated groundwater flux was 6- to 70-fold higher than the fresh groundwater discharge to the bay estimated by hydrological methods, but closely matched direct flow rates measured with seepage meters. This suggests that a substantial portion of the discharge consisted of recirculated seawater. The magnitude of submarine groundwater discharge varied seasonally, in the order: summer > autumn > spring. Chemical analyses suggest that the recirculated seawater component of submarine groundwater delivers as much dissolved nitrogen to the bay as the fresh groundwater flux. 相似文献