摘要:

ABSTRACT:In the United States, millions of dollars are currently spent to monitor water quality for a whole suite of organic compounds. However, results of several surveys conducted in the past decade indicate that only a few pesticides occur in a small proportion of wells. Screening methods based on historical evidence of contamination patterns and knowledge of the locales will have significant potential to reduce these costs and effectively identify contamination problems. In this paper, the economics of utilizing two screening methods, sequential analysis and sample compositing, in the design of monitoring strategies is captured In the form of mathematical models and illustrated for a state‐level monitoring program. When the two methods are adopted, the total analytical cost to conclusively identify contaminated wells in a network of 4,000 wells is shown to range from $12,500 to $1,575,000 depending on the extent of contamination. In contrast, the total analytical cost of a conventional program where all the wells in the network are sampled and tested for a standard suite of pesticides at a cost of $250/sample is one million dollars. Given such wide range in costs, it is prudent to incorporate the screening concepts presented in this paper in the development of cost‐effective monitoring progr

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03312.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:A UNIX‐based windows application was developed to integrate a phosphorus transport model with the Geographic Resources Analysis Support System (GRASS). The system prioritizes potential phosphorus loading from fields or cells in a watershed and can evaluate the effects of alternate management practices on phosphorus yield. The model simulates phosphorus loading by using a daily mass balance on a unit‐area basis and incorporates the effects from rainfall, topography, soil properties, fertilizer and animal waste application, and management. Model predictions include dissolved and sediment‐bound phosphorus yield, runoff volume, and sediment yield. Within the integrated GRASS‐modeling system, the user can obtain model input data, execute the model using various options, rank model input and out. put data, and display them as GRASS‐based maps or data tables. All functions are menu driven, developed using C language and X‐window tools to run on a SUN workstation platform. The system provides a powerful and efficient tool for prioritizing phosphorus loading from nonpo

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03313.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:The arid Southwest of the United States is confronted with increasing water demands and a limited resource. Past efforts to meet water demand have been directed toward development of scarce water resources. While development programs have been successful in stretching available supply, few feasible development options remain. Furthermore, heavy water utilization has affected water quality within drainage basins. It seems likely that water management will play a much more significant role in water resource allocation in the future. This paper will examine water development activity in the Southwest to date. Attention will be given to several of the problems that have arisen. The paper will then examine water management options. Particular attention will be given to water management options being implemented in the State of Arizona.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03314.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT. Characterizing ecological indicators such as water quality is necessary to effectively manage human‐dominated systems such as the New Jersey Pinelands. Pinelands surface waters are naturally acidic and low in nutrients and other dissolved substances. Water quality for 14 Pinelands stream sites monitored by the U.S. Geological Survey was characterized in relation to land use. A gradient of increasing pH, specific conductance, and concentration of dissolved calcium, dissolved magnesium, total nitrite + nitrate‐nitrogen, total ammonia‐nitrogen, and total phosphorus was associated with a watershed disturbance gradient of increasing land use intensity and waste water flow. These two parallel gradients emphasized the significant effect that watershed disturbance can have on natural water chemistry in the Pinelands. The results of this study can be applied to planning and regulatory programs in the Pine

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03315.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:High‐capacity wells are used as a convenient and economical means of sampling groundwater quality. Although the inherent limitations of using these wells are generally recognized, little has been done to investigate how these wells actually sample groundwater. A semi‐analytical particle tracking model is used to illustrate the influence of variable vertical contaminant distributions and aquifer heterogeneity on the composition of water samples from these wells during short pumping periods. The hypothetical pumping well used in the simulations is located in an unconfined, alluvial aquifer with a shallow water table and concentration gradients of nitrate‐nitrogen contamination. This is a typical setting for many irrigated areas in the United States. The main conclusions are: (1) high‐capacity wells underestimate the average amount of contamination within an aquifer; (2) shapes of concentration‐time curves for high‐capacity wells appear to be governed by the distribution of the contaminant and travel times to the well; (3) variables such as well construction, pumping rate, and hydrogeologic properties contribute to the magnitude of the concentration‐time curves at individual high‐capacity wells; and (4) a sampling strategy using concentration‐time curves based on the behavioral characteristics of the well rather than individual samples will provide a much better framework for interpreting spatial contamin

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03316.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:A model for estimating the probability of exceeding groundwater quality standards at environmental receptors based on a simple contaminant transport model is described. The model is intended for locations where knowledge about site‐specific hydrogeologic conditions is limited. An efficient implementation methodology using numerical Monte Carlo simulation is presented. The uncertainty in the contaminant transport system due to uncertainty in the hydraulic conductivity is directly calculated in the Monte Carlo simulations. Numerous variations of the deterministic parameters of the model provide an indication of the change in exceedance probability with change in parameter value. The results of these variations for a generic example are presented in a concise graphical form which provides insight into the topology of the exceedance probability surface. This surface can be used to assess the impact of the various parameters on exceedance probabilit

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03317.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:In the past, much effort has been put into the development of sophisticated mathematical models to describe settlement and consolidation of water deposited sediments. Such models often aim at completeness and accuracy in modeling the physical processes involved. However, as a result of the generality of the descriptions, the models often fail to compute local circumstances satisfactorily. In specific cases, the empirical approach may prove to be highly competitive and reliable. In large water bodies in the central part of the The Netherlands, the alluvial “IJsselmeer‐deposit” is a common type of fresh water sediment. Its deposition and settlement started in 1932, when anthropogenic activities changed the physical and chemical conditions of the lakes drastically. Five representative cores of this sediment were taken in deep zones of the lakes. Periodic water depth surveys over the last sixty years at these locations provided information on the net sedimentation rate and the total thickness of this Ijsselmeer‐deposit at known time intervals. In order to calculate a time‐equivalent of the depth scale, correction factors for soil consolidation are introduced. A decrease in the total thickness of individual sediment layers is proportional to the decrease of its volume, which is derived fromin situcharacteristics. Correction factors are based on a simplification of various stages of compression (i.e., O percent, 30 percent, and 45 percent). A factor n, which represents changes of water content of the sediment as a dependence of clay content, is derived for each layer, allowing an inverse calculation procedure to determine the initial, uncompressed thickness of each layer. Hence, a fairly reliable time scale in depth can be reconstructed. Furthermore, the radionuclide activity was measured in some cores and the degree of organic and inorganic pollution was determined in numerous layers of all cores. Cs‐isotopic tracers (137Cs,134Cs) give a good reconstruction of the last six decades of physical changes of the sediment and the degree of pollution, assuming post depositional redistribution and transformation of pollutants to be negligible. The results showed close coherence to calculated

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03318.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:Flow rates, pH, iron concentration, and manganese concentration were measured during several storm events at two constructed wetlands receiving mine water. During a substantial rain event, flow rates at both the wetland outlets surpassed flow rates at the wetland inlets, reflecting incident rainfall and differences in wetland area at the two sites. A significant positive correlation existed between local rainfall and outflow rates at the larger wetland, but not between rainfall and inflow rates. During storm events, outlet pH, relative to inlet pH, was slightly elevated at the larger wetland, and depressed at the smaller wetland. However, over the course of one year, rainfall was uncorrelated to outlet pH in the larger wetland. A substantial rain event at the smaller wetland resulted in a temporary elevation in outlet iron concentrations, with treatment efficiency reduced to near zero. However, in the larger wetland, outlet iron concentrations were not significantly affected by storm events. Although rainfall and outlet iron concentration were not significant correlates at the larger wetland, flow rate was positively correlated to outlet iron concentration. A normal manganese treatment efficiency of 50 percent at the smaller wetland was reduced to zero during a heavy rain.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03319.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:A large storm in December 1990 allowed the evaluation of flood predictions from a hydrologic model (TOPMODEL) that had been previously calibrated on the West Fork of Walker Branch Watershed, a gauged 37.5 ha catchment near Oak Ridge, Tennessee. The model predicts both hydrograph dynamics and the spatial distribution of overland flow using an index based on topography. Maximum extent of overland flow during the storm was determined from patterns of leaf litter removal from valley bottoms. Both the flood hydrograph and the extent of overland flow were accurately predicted using model parameters obtained from a three‐month period of normal flow conditions during 198

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03320.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

ABSTRACT:There is considerable potential for use of channel dimension data in planning‐level models for resource and impact assessment. The channel dimension data is used to route flows and sediment through the basin. The cost of obtaining actual surveyed data for large watersheds is typically prohibitive. Predictive equations have been developed based on 674 stations from watersheds across the United States which encompass a wide variety of channel types and sizes. These equations were tested against an independent data set and found to be adequate for use in planning‐level models. Future research is advocated which would include data from regions and stream types not included in this st

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1994.tb03321.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY