ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01834.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe recently completed National Pesticide Survey conducted by the United States Environmental Protection Agency (EPA) has identified the presence of various pesticides in ground water. The detection of pesticides in the nation's ground water has raised concerns for public health which has led resource managers in federal and state agencies to recognize that risk assessment is vital for water quality protection. This paper presents a methodology for risk‐based evaluation of ground‐water contamination by agricultural pesticides. The methodology utilizes the Risk of Unsaturated/Saturated Transport and Transformation of Chemical Concentrations (RUSTIC) model to provide simulations that yield the probable risks associated with a given pesticide. Risk is expressed in terms of the probability of predicted pesticide mass exceeding its recommended health standards. Three widely used agricultural herbicides, simazine, atrazine, and alachlor, were evaluated using long‐term (1960–1986) meteorological data for Ames, Iowa. Results indicate that for a well 8 m deep located 200 m horizontally from a pesticide application area in an alluvial sand and gravel setting, the probability of exceeding the maximum contaminant level (MCL) for simazine is about 35%, whereas it is nearly zero for both atrazine and alachlor. Prudent use of simazine in very susceptible areas is reco

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01835.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractExtensive agricultural activity often increases the salt load of the unsaturated zone. The focus of the study was a field investigation of the effects of saline‐water irrigation and gypsum addition in a semiarid region with loessial soils, where intensive evaporation conditions prevail. Using drilling (∼20 m) to obtain sedimentary deposit samples, it was shown that most of the salts added by agricultural activity accumulate in the unsaturated profile. Seventy to ninety percent of SO4−2, Na+, and Cl−added are retained in the upper 2–4 meters of the profile after 6 to 12 years of cultivation, regardless of the soil type. The most common accumulating ions are Na+and SO4−2that minimize gypsum amendment thereby increasing with time the danger of an irreversible loss of the loessial soil as prod

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01836.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA simple analytical expression is presented which predicts how solute concentrations evolve with time in a pumped well. The basic expression is for uniform recharge and uniform concentration of a conservative solute (e.g. nitrate) in the recharge. It shows that pumped concentrations are independent of pumping rates. The expression can be developed to allow for more complex patterns of recharge and solute loading, and an example is given with three zones of recharge and concentrations, induced river recharge, and a cross‐boundary inflow. Predictions are made for Edgmond Bridge, a new pumping station which lies in a drift‐filled valley in the Triassic sandstone aquifer of Shropshire, UK. The model predicts that concentrations of nitrate will stay below the drinking water limit for 78 years, although this would be substantially reduced if the aquifer were significantly layered or if nitrate loads from agriculture increased. Predictions were reevaluated after two years and found to be consistent with observed patterns once actual, rather than expected, conditions were incorporated in the mo

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01837.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractNitrate derived from commercial NH4NO3fertilizer, δ15N =+1.5 %0, applied to fertility plots was extracted from two cores to depths of 46 and 52 ft. In both cores the δ15N of the extracted nitrate‐nitrogen (NO3‐N) showed that it became heavier with depth. Although this isotope fractionation did not cause δ15N values to overlap with those characteristic of animal waste sources (>+ 10%0), δ15N values were as high as +8%0at the bottom of one profile. The gradual increase in δ15N with depth in the bottom 20 to 30 ft of the cores is consistent with denitrification at these depths. Clay content was much more variable with depth and was significantly associated with NO3‐N concentrations (r =+0.9) in the core with 30% clay. Correlation of NO3‐N concentrations to clay content was not significant in the other core with 50% clay. In both cores smectite and illite were the dominant clays; chlorite, and aluminum and iron oxyhydroxides were not detected by XRD. Anion exchange capacity measurements confirmed that it was not responsible for the observed variability in NO3‐N concentrations or δ15N values.Potassium chloride (KC1) extracts yielded significantly higher NO3‐N concentrations (p<0.005) and lighter δ15N values (p40%) provide more realistic estimates of ground‐water lo

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01838.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe annual regime of shallow ground‐water levels across Poland is analyzed according to the dominance of continental and oceanic air masses. Mean monthly ground‐water levels are transformed into relative values and, in order to show the spatial patterns of the annual regime throughout Poland, the contours of such values are derived for each month of the year.The shallow ground‐water regime in Poland can be correlated with the degree of the climatic continentality. The main difference between the mildly oceanic northwestern part of Poland and the continental eastern part is the pattern of the winter regime which responds differentially to snowmelt. In the northwestern part of Poland, ground‐water levels during late fall and winter are higher than those in the continental eastern part of the country. From April to September, there is no distinct difference between the ground‐water levels in those two parts

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01839.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAn analytical method is developed whereby longitudinal and transversal dispersivities can be determined for a two‐dimensional plume generated by slug tracer injection in a uniform ground‐water flow field. One solution procedure requires concentration versus time data from two sampling wells through which the plume passes. A second solution procedure uses a least‐squares method to obtain optimal parameter estimations when only one sampling well is available. Both methods are particularly useful since they do not require a priori knowledge of either the direction or magnitude of the pore velocity. Detailed example calculations illustrate the solution procedures and show that these methods are succe

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01840.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractEvaluation of ground‐water exchange between ponds or large‐radius conduits and surrounding aquifers is a common problem in contaminant migration studies. Analytic solutions are useful tools for this evaluation, particularly when the system is incompletely characterized. Solutions are derived below for application to ponds, lakes, and natural or artificial conduits with a known discharge/recharge flux. General features of migration in this setting are determined by the ratio of pond flux (source/sink) to regional flux crossing the pond boundary. When this ratio is large (pond dominates) the effect of the pond is indistinguishable from a well. At intermediate values, movement from the pond against the regional flow is inhibited, and discharge plumes are shifted downgradient relative to those for a well. At small ratios only a narrow plume will emerge from the downgradient side of a discharging pond, considerably narrower but longer than predicted for a well of the same stren

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01841.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA technique based on numerical ground‐water flow modeling and unconstrained nonlinear optimization has been developed to provide guidance for protecting municipal ground‐water supplies from contamination through capture zone management. The technique involves conventional finite‐difference ground‐water flow modeling and numerical flowpath/travel time calculation coupled with nonlinear mathematical programming. The objective of the technique is to specify pumping rates for wells in a wellfield such that the configuration of capture zones in relation to existing potential sources of contamination minimizes the risk of contamination while maintaining the required total water output from the wellfield. An important feature of the technique is its ability to incorporate realistic boundary conditions, complicated aquifer configurations, and spatially varying aquifer properties to whatever degree site‐specific data are available. Also, the technique is implemented on a personal computer. This approach to ground‐water supply protection enhances conventional wellhead protection area delineation because a greater level of protection can be achieved if potential contaminant sources are not even included in capture zones, rather than attempting to reduce the threat of those sources. The effectiveness of the technique was verified through application to a hypothetical ground‐water system. Practical aspects were demonstrated with an application in Pékin, Illinois. These efforts demonstrate the utility of an innovative modeling technique in ground‐water qu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01842.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo water quality concerns with aquifer storage and recovery (ASR) operations are (1) the fate of organochlorine compounds, such as trihalomethanes (THMs), in the treated recharge source, and (2) the formation of organochlorine compounds from precursor materials following the chlorination of recovered water. The fate of chloroorganic compounds in chlorinated Colorado River water was studied during a 1989 recharge/recovery operation conducted by the Las Vegas Valley Water District (LVVWD). Water samples were obtained from two dual‐purpose wells during the pumping cycle for THMs and other indicators of organochlorine precursors. The percentage recovery of THMs was approximately the same as the percentage recovery of Colorado River water. This suggests that the removal of organochlorine compounds (e.g., by sorption) did not appreciably occur in the aquifer materials at the two well sites. Recovery of source water was incomplete. Accordingly, dissolved organic carbon (DOC), representing precursor material, remained in the aquifer at the end of the pumping cycle. The Las Vegas experience suggests that prolonged recharge and storage of Colorado River water in similar hydrogeologic basins (e.g., the Tucson basin) could result in problems with THM compliance at the well head. This will be a problem if THM standards are reduced during the interval that water is store

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1993.tb01843.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY