ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02066.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02067.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA new method is presented to determine the transmissivity and the storage coefficient from recovery data measured after a pumping period of an aquifer test. Previously available methods can determine the storage coefficient during the pumping period only or under restrictive conditions. This method requires observations from a minimum of two points (e.g., the pumping well and an observation well). For each time during recovery, the drawdowns observed in the two wells are first plotted with regard to the distance from the pumping well centrum, giving an intercept A and a slope B for each pair of data. The plot of A values with regard to time allows to calculate the transmissivity value, while the plot of B values versus time gives the storage coefficient value. The method is applied to two sets of field data, and the results obtained are close to those obtained using the classical methods (Theis or Jacob) applied to the drawdown data obtained during the pumping period. This method well determines transmissivity and storativity from recovery data obtained at short times after the completion of pumping, i.e., for times shorter than those which can be used by the Cooper‐Jacob approximatio

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02069.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThree sandy subsurface materials and a sandy surface soil (Orangeburg Series) from the Upper Coastal Plain, were used to assess the influence of mineralogy and surface chemistry on the determination of physical transport parameters using ionic tracers. The clay mineralogy of the surface soil consisted primarily of kaolinite, hydroxy‐interlayered vermiculite, and gibbsite, while the dominant clay mineralogy of the subsurface materials consisted of kaolinite, goethite, and mica (illite). Repacked columns of the four differing strata were leached with tritiated (∼ 200 pCi mL–1) Bromide solutions, either MgBr2or KBr, of varying ionic strengths (0.1–0.001 N). Pore‐water velocities estimated by bulk density and mass flux were consistent with those estimated from tritium breakthrough. In contrast, Br–breakthrough differed drastically within the four materials and was altered by experimental conditions (sample drying, carrier cation, etc.). The retardation for 0.001NKBr varied from 0.94 for the surface soil to 2.15 for the subsurface materials and increased with increasing Fe oxide content. For the subsurface samples, Br–was retarded to a greater degree in the presence of Mg2+compared to K+. In contrast, oven drying the sample reduced the degree of Br–retardation observed for the subsurface materials. These results indicate that retardation can vary dramatically within materials of similar texture, mineralogy, and origin. The apparent conservative behavior of an ionic species under a given set of conditions (mineralogy, pH, ionic strength, scale size, predominant counter ion) does not automatically ensure that transport will remain conservative as those conditions are altered by changes in experimental design or unforeseen circumstances encountered at

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02070.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractPentachlorophenol‐acclimated methanogenic consortia were incubated at temperatures of 5, 10, 21, and 31° C in physical models of an interceptor trench. Four identical 5.4 cm diameter brass columns packed with a uniform pea gravel were operated with a 2 day hydraulic retention time in a continuous upflow mode. The columns were fed 25 or 50 mg of acetate per liter, 0.32 or 4.0 μMpentachlorophenol, and a dilute vitamin and nutrient mixture. In the columns operated at 31 and 21° C, pentachlorophenol was reductively dechlorinated at theorthopositions to form 2,3,4,5‐tetrachlorophenol and 3,4,5‐trichlorophenol. 3,4,5‐Trichlorophenol was the sole degradation product observed in the effluent. The lag period prior to pentachlorophenol biotransformation increased with decreasing temperature. At 31° C, a lag of 72 hours was observed; at 21° C the lag was 120 hours; and at 10° C the lag was 744 hours. No biodegradation of pentachlorophenol was observed at 5° C within an 888 hour period. Conversion of pentachlorophenol to 3,4,5‐trichlorophenol was complete within the first 7.6 cm of the column at 31 and 21° C. Loss of 90% of the pentachlorophenol was observed over the 30 cm column at 10° C. An interceptor trench inoculated with a temperature‐ and pentachlorophenol‐acclimated methanogenic consortia has the potential to anaerobically biotransform pentachlorophenol at temper

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02071.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractDi‐n‐butyl phthalate (DBP) was found to be transformed by microorganisms under aerobic and anaerobic conditions at 10° C in microcosms simulating the Canadian Forces Base (CFB) Borden subsurface environment. Biotransformation of DBP was observed under aerobic, nitrate‐reducing, Fe(III)‐reducing, and sulfate‐reducing conditions. The biotransformation of DBP in the microcosms was significantly decreased as the redox potential was lowered, especially under sulfate‐reducing conditions. However, other factors such as nutrient depletion and buildup of toxic intermediates could have affected the biotransformation rates. The highest DBP biotransformation rate (0.57 μg DBP.g sediment−1.day−1) was observed under aerobic conditions whereas the lowest rate (0.05 μg DBP.g sediment−1.day−1) was under sulfate‐reducing conditions. Biotransformation of DBP at 10° C was significantly enhanced by the addition of 10 mM NaNO3suggesting that both the addition of nitrate and high redox conditions favor its biotransformation i

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02072.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractApproaches to investigate possible recharge during a pumping test period are demonstrated by analyzing the pumping test data from the Nottingham aquifer, UK. The pumping lasted more than 200 days and the data for different observed periods are used to obtain aquifer parameters. If recharge is ignored, estimated transmissivities and storativities change progressively with the observation time. This indicates that a gradually added new source may be involved. Then the observed data in both pumping and recovery periods at one of the pumping sites are matched by the data calculated from the Theis equation. The match is very good except near the end of the recovery period. It shows that the real drawdown recovered more quickly than predicted by the model, indicating that the aquifer obtained extra recharge from other sources. The match between the observation and the model is improved by including a fixed‐head boundary or leakage in the model. The recharge to the aquifer is estimated to be 19% and 34% of the pumpage at the end of pumping, depending on the method used. The real source of the additional recharge is not clear; it could be from the surface water in the unconfined area, the storage of the aquitard, the compaction of the aquitard, or a combination of the three. This requires further hydrogeological investigatio

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02073.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe Clarendon Basin of south‐central Jamaica has been recognized for its productive sugar cane industry since the late 1800s. Much of its success is attributed to rich alluvial soils, a year‐round tropical climate and copious supplies of good quality irrigation water from a karstic limestone aquifer of Tertiary age. This aquifer extends throughout the northern part of the basin, but ends abruptly at the South Coast Fault, an east west feature that forms the northern boundary of a deep graben filled with alluvial sediments. These alluvial sediments are the only source of water for the area south of the fault (the Vere Plain). However, the sediments also lap onto the limestone to the north of the fault (the Clarendon Plain) and provide a supplementary ground‐water source. By the early 1970s nearly 200 wells supplied irrigation water for over 20,000 hectares of land. As development increased, the salinity of the ground water increased. Consequently, many wells were closed down and several sugar plantations were abandoned. In the study presented here, major ion (Ca, Mg, Na, K, HCO3, Cl, SO4, and NO3), minor ion (F, Br, and I), and environmental isotope (δ18O,δD) hydrochemistry is used to resolve the hydrodynamics of ground‐water flow in the basin and identify the source and mode of emplacement of the saline water.Oxygen and hydrogen isotope data confirm that while the major well production areas are located in lowland coastal areas, recharge originates almost exclusively as rainfall in the cooler elevated parts of the basin above 750 m (asl). Subsurface conduit flow brings this water to the limestone well fields, and any excess water is able to cross the South Coast Fault to feed the alluvial aquifer of the Vere Plain. The thin alluvial aquifer of the Clarendon Plain also receives limestone water but this water does not enter entirely by subsurface means. Instead data suggest that while some of the water can be attributed to natural upward vertical leakage in the northwest of the Clarendon Plain, the remainder can be attributed to the seepage of irrigation water drawn, at least in part, from wells developed in the underlying limestone.Saline ground waters affect all the aquifers of the basin and several potential sources have been proposed. Major and minor ion data point to a sea‐water source, and a sea‐water wedge extending beneath the thick alluvial aquifer of the Vere Plain is an obvious candidate for the source of salinity observed in wells from this aquifer. Closer examination of the chemical data reveals, however, that wells in the limestone and alluvial aquifers to the north of the South Coast Fault do not derive their salinity from this source location, and instead draw sea water from the east and west along the relatively permeable South Coast Fault zone. This water can move to limestone wells directly; wells in the alluvium of the Clarendon Plain, however, receive most of the saline water indirectly via leakage of irrigation water pumped initially from the limestone. Sea water drawn along the fault may also be the primary source of salinity in the aquifer of the Vere Plain but this cannot be confirmed on the basis of hydrochemical e

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02074.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractDuring storm events, the shallow disposal facilities at Oak Ridge National Laboratory become inundated, and subsurface stormflow may intermittently extract radionuclides from the surrounding soils and the wastes themselves. It is estimated that 90% of the rain water infiltrating the soil horizons becomes subsurface stormflow, yet stormflow is a poorly understood process. The objectives of this research are to model stormflow: (1) to identify important parameters for waste site monitoring and data collections; (2) to evaluate remediation designs; and (3) to investigate the effect of local heterogeneities on stormflow paths. Numerical models of a proposed waste disposal site were developed, and a Latin‐hypercube simulation technique was used to study the uncertainty of model parameters. Sensitivity analyses of model parameters suggested that hydraulic conductivity was the most influential parameter. However, local heterogeneities may alter flow patterns and result in complex recharge and discharge processes. Hydraulic conductivity, therefore, may not be used as the only reference for subsurface flow monitoring and engineering designs. Neither of two engineering designs, capping and French drains, was found to be effective in hydrologically isolating downslope waste trenches. However, combinations of both designs may prove more effective than either one alon

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02075.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractLake Chad, a closed basin lake, is the only large surface‐water body in the African Sahel. Future water resource development in the Chad Basin requires an understanding of the hydrogeology of the basin. In this paper we examine the hydraulic relationship between the lake and the phreatic aquifer of the Chad Formation. Electrical resistivity data from 30 surveys were combined with over 60 open well measurements to construct a water‐table map of the southwestern quadrant of the lake. The map indicates that the Lake Chad water level is at a higher hydraulic level than the phreatic aquifer and that the ground‐water flow is southwest, away from the lake. The average measured seepage rate into the phreatic aquifer in the southwestern and southern parts of the lake was 7.1 × 10−3m/d (median = 1.3 × 10−3m/d) which is about 21% of the annual water input to the lake. This measured seepage flux (9.96 × 109m3/yr) can account for about 107% of the annual solute input to the lake. Solute transport model simulations indicate about 32% (15.3 × 109m3/yr) of the input water and 152% (2.87 × 1012g/yr) of the total solute input can be removed by ground‐water recharge (seepage) from the lake. These results provide an explanation to account for the freshness of Lake Chad's water despite its surficial closed basin geologic setting: solutes delivered to the lake via surface‐water inflow leave the lake via ground‐water recharge. These results also indicate recharge from the lake (∼ 1010m3/yr) represents an enormous amount of water available as a ground‐water resou

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1996.tb02076.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY