INFLUENCE OF WELL WATER QUALITY VARIABILITY ON SAMPLING DECISIONS AND MONITORING1

ABSTRACT: Local governmental agencies responsible for decisions in ground water quality management need not only data on ground water quality but they also must understand the relationship of accuracies and risks associated with this data as related to the number of wells to sample. In this report we address this problem by using the philosophical doctrines of probabilism and relativism with simple statistical procedures. This requires a reasonable estimate of the population variance in a quality parameter for a given management-unit area, and requires that the decisionmaker formulate constraints with an acceptable standard error of the sample mean and be willing to accept some level of probability of being Wrong. This technique is illustrated using a 21-year data base of well water chemical data in a 653 km² ground water quality study area in the San Joaquin Valley of California.     

MATHEMATICAL GENERALIZATION OF STREAM TEMPERATURE IN CENTRAL NEW ENGLAND1

ABSTRACT: The empirical fit of an annual harmonic function to stream temperature measurements in central New England can be improved by considering a harmonic period of less than 365 days instead of 365 or 366 days. Generalized equations, developed using periodic temperature data from 27 streamflow stations, allow predictions of stream temperature at any site given (1) the mean basin altitude (E), in meters above mean sea level, and (2) station latitude (LAT), in degrees. Stream temperature t, in degrees Celsius, on day number d, in days starting with January 1, is estimated as: in which, M = 31.48 – 0.0025 (E) ? 0.4635 (LAT) with standard error of estimate of 0.62°C, and τ= 1228.88 – 21.01 (LAT) with standard error of estimate of 14.1 days.     

MODELING DRINKING WATER QUALITY VIOLATIONS WITH BAYESIAN NETWORKS1

ABSTRACT: Compliance violations at community water systems are rare but represent significant human health risks. These risks are mediated by the decision schema of human operators at water treatment facilities. However, causal uncertainty among physical and human factors involved in water quality problems complicates assessment of their probability and severity. This study uses a probabilistic Bayesian network modeling approach to explore the causes of compliance violations in a sample of water treatment systems in Pennsylvania. The model presented here is one of several created by treatment system operators during an expert elicitation process. The expert model alone predicts violations poorly, suggesting that experts make inaccurate quantitative estimates. However, Bayesian networks are capable of combining the subjective expertise of treatment system operators with the objective compliance histories of the facilities they manage, and the expert model accurately predicts violations when trained with historical compliance data. Analysis of the trained network reveals those components of the treatment process, including environmental and system characteristics as well as operator decisions, that play the greatest role in determining the likelihood of major violation types. Among operator decisions, coagulant dosing and filter backwash frequency are the most important determinants of violation likelihood.     

MASS LOAD ESTIMATION ERRORS UTILIZING GRAB SAMPLING STRATEGIES IN A KARST WATERSHED1

ABSTRACT: Developing a mass load estimation method appropriate for a given stream and constituent is difficult due to inconsistencies in hydrologic and constituent characteristics. The difficulty may be increased in flashy flow conditions such as karst. Many projects undertaken are constrained by budget and manpower and do not have the luxury of sophisticated sampling strategies. The objectives of this study were to: (1) examine two grab sampling strategies with varying sampling intervals and determine the error in mass load estimates, and (2) determine the error that can be expected when a grab sample is collected at a time of day when the diurnal variation is most divergent from the daily mean. Results show grab sampling with continuous flow to be a viable data collection method for estimating mass load in the study watershed. Comparing weekly, biweekly, and monthly grab sampling, monthly sampling produces the best results with this method. However, the time of day the sample is collected is important. Failure to account for diurnal variability when collecting a grab sample may produce unacceptable error in mass load estimates. The best time to collect a sample is when the diurnal cycle is nearest the daily mean.     

A method of comparing the performance of air classifiers

An experimental and theoretical comparison is made between a “zig-zag” air classifier and a straight-duct type. Equations are presented, based on a model already published, for the effective diffusivity of spherical particles in a turbulent air stream. The diffusivity reflects the tendency of particle species to diffuse the “wrong” way, that is to be lost. The lower the value of the effective diffusivity, the more efficient is the classifier. It is shown that the effective diffusivities are lower in the “zig-zag” classifier than in the straight-duct type especially for the “light” species. It is also shown that the effective diffusivities of “light” and “heavy” species are similar in value, indicating the mid-point as the optimum feed location. It is also shown that, at high values of the air/solids ratio, the effective diffusivities can be easily estimated by using mixtures of regular particles, or simply by feeding a single species of spherical particles. The effective diffusivities were found to be independent of the number of stages in the “zig-zag” classifier, and took values similar to freestream diffusion values.The method described represents a very simple test which could be applied to proposed designs of air classifier to enable a comparison of effectiveness to be made.     

RESERVOIR RELEASES TO USES WITH DIFFERENT RELIABILITY REQUIREMENTS1

ABSTRACT: Releases from a reservoir may be allocated to a number of uses, each of which may require a given volume of water at a different reliability. The paper provides a method that can be used to estimate the volume of water associated with a given reliability for each use of water when the proportion of releases allocated to each use is known. These results can be used to evaluate the meeting of specified objectives under a published release policy derived by stationary stochastic dynamic programming. The results can also be used to solve water allocation problems when the probability distribution of available water is known (or can be estimated) and water has multiple uses, each of which has different volume and reliability requirements.     

CONTINUOUS SIMULATION OF RECEIVING WATER QUALITY TRANSIENTS1

: This paper presents solutions to the one-dimensional, transient conservation of mass equations for the coupled biochemical oxygen demand-dissolved oxygen (BOD-DO) reactions, based on the principle of superposition, for continuously discharging plane sources. The solutions are applied within the framework of a continuous simulation model to allow the derivation of water quality frequency curves and frequency histograms of consecutive hourly dissolved oxygen violations, for any desired standard. Receiving water response is determined for waste inputs from urban wet weather, dry weather, and upstream sources. An application to Des Moines, Iowa, and Des Moines River indicated that urban storm water impacts on the stream can be masked in the cumulative frequency curve representation, but the benefits of storm water control are clearly shown in frequency histograms of the duration of consecutive stream standard violations.     

“比例原则”视野下我国环境执法按日连续处罚制度的完善

"按日连续处罚"制度已经在环境执法中显示了巨大的威慑力,但"按照原处罚数额按日连续处罚"的计罚模式不符合行政法中的"比例原则"。在违法行为"先轻后重"或者"先重后轻"的情形下,都可能造成"过罚不当"的问题。对于初始违法情节类似,但复查时违法情节大相径庭的不同违法者,会出现"不同情节相同处罚"的不公平情形。在现有制度框架下,对于"先重后轻"的违法行为,可以考虑在违法者的改正行为已经取得显著成效的情形下不予按日连续处罚,同时依据《环境行政处罚办法》的规定,将该已经显著减轻的违法排污行为视为新的违法行为进行处罚。对于"先轻后重"的违法行为,可以在进行按日连续处罚时,视具体违法情节动用限产停产、查封扣押或者行政拘留等处罚措施。理想状态下,应当摒弃"按照原处罚数额"按日计罚的规定,改为数据值式的按日计罚,即规定"……拒不改正的,处每日××万元以上××万元以下的罚款",以更好地实现"过罚相当"。为了避免持续性违法行为对环境造成更大的损害,按日计罚的最长期限不宜超过三十日。违法者超过三十日仍然不改正违法行为的,应当及时采取责令限产停产、查封扣押或责令关闭等措施。     

Impacts of changes in water quality on recreation behavior and benefits in Finland

The implementation of the European Union Water Framework Directive (WFD) requires nationally generalizable estimates of the benefits of protecting inland and coastal waters. As an alternative to benefit transfers and meta-analyses, we utilize national recreation inventory data combined with water quality data to model recreation participation and estimate the benefits of water quality improvements. Using hurdle models, we analyze the association of water clarity in individuals' home municipalities with the three most common water recreation activities – swimming, fishing and boating. The results show no effect on boating, but improved water clarity would increase the frequency of close-to-home swimming and fishing, as well as the number of fishers. Furthermore, to value the potential benefits of the WFD, we estimate the consumer surplus of a water recreation day using a travel cost approach. A water policy scenario with a 1-m improvement in water clarity for both inland and coastal waters indicates that the consumer surplus would increase 6% for swimmers and 15% for fishers. In contrast to previously estimated abatement costs to improve water quality, net benefits could turn out to be positive. Our study is a promising example of applying existing national recreation inventory data to estimate the benefits of water quality improvements for the purposes of the WFD.     

THE FLEXIBLE TOLERANCE METHOD FOR ESTIMATING HYDROLOGIC PARAMETERS IN THE ROOT ZONE1

In this study, a constrained minimization method, the flexible tolerance method, was used to solve the optimization problems for determining hydrologic parameters in the root zone: water uptake rate, spatial root distribution, infiltration rate, and evaporation. Synthetic soil moisture data were first generated using the Richards' equation and its associated initial and boundary conditions, and these data were then used for the inverse analyses. The results of inverse simulation indicate the following. If the soil moisture data contain no noise, the rate of estimated water uptake and spatial root distribution parameters are equal to the true values without using constraints. If there is noise in the observed data, constraints must be used to improve the quality of the estimate results. In the estimation of rainfall infiltration and surface evaporation, interpolation methods should be used to reduce the number of unknowns. A fewer number of variables can improve the quality of inversely estimated parameters. Simultaneous estimation of spatial root distribution and water uptake rate or estimation of evaporation and water uptake rate is possible. The method was used to estimate the water uptake rate, spatial root distribution, infiltration rate, and evaporation using long‐term soil moisture data collected from Nebraska's Sand Hills.     

A STAGE DISTRIBUTION APPROACH TO ESTIMATING ICE RELATED FLOODING PROBABILITIES1

ABSTRACT: A procedure is presented for estimating flooding probabilities resulting from either open water or ice condition events. The methodology involves individually fitting a distribution function to water stages from open water and ice events and determining the composite probability of exceedence of any stage value. The parameters of the two distribution functions are estimated using censored maximum likelihood. The approach is evaluated with a Monte Carlo sampling program and is applied to estimate flooding probabilities on the Yukon River.     

中美水质评价方法比较

国内外的研究都表明,从保护人类、野生动植物和自然生态环境健康角度出发,按照水体自然属性并结合人类对水体的使用和保护要求对水体进行功能划分,制定合理与水体使用功能相适应的水环境质量标准,并采取控制措施使水体水质达到该标准,是既合理、经济,又能有效保护水环境的方法.其关键是如何按照水质标准对水环境质量进行客观准确评价,这既是保护水环境的基础性工作,直接关系到水环境保护和排污控制措施的有效性,也是我国目前急需解决的重要课题.本文首先对美国水环境质量评价方法体系作了概要介绍,然后对我国水环境质量评价现状进行分析,通过对比美国和我国的水环境质量评价方法,对我国水环境质量评价提出了建议和研究方向.     

Calibration Catchment Selection for Flood Regionalization Modeling1

Wan Jaafar, Wan Zurina, and Dawei Han, 2012. Calibration Catchment Selection for Flood Regionalization Modeling. Journal of the American Water Resources Association (JAWRA) 48(4): 698‐706. DOI: 10.1111/j.1752‐1688.2012.00648.x Abstract: There are two unsolved problems in flood regionalization model development related to the quantity and quality of calibration catchments: (1) how many calibration catchments should be used? and (2) how to select the calibration catchments? This study explores these two questions through a case study on the median annual maximum flood (QMED) model in the United Kingdom. It has been found that the chance of developing a good QMED model decreases significantly when the number of calibration catchments drops below a critical number (e.g., 60 in the case study). However, no significant improvement is achieved if the number of calibration catchments is above it. This number could be used as a benchmark for choosing randomly selected calibration catchments. Across a broad range of calibration catchment numbers, there are good and poor calibrated models regardless of calibration catchment numbers. High quality models could be developed from a small number of calibration catchments and also poor models from a large number of calibration catchments. This indicates that the number of calibration catchments may not be the dominating factor for developing a high quality regionalization model. Instead, the information content could be more important. The study has demonstrated that the standard deviation values between the best and poorest groups are distinctive and could be used in choosing appropriate calibration catchments.     

PHYSICAL DETERMINANTS OF ECONOMIC VALUE OF RIPARIAN BUFFERS IN AN AGRICULTURAL WATERSHED1

ABSTRACT: Economic values of riparian buffers in a watershed are evaluated by the changes in the net economic return for farming with and without riparian buffers when achieving the same water quality objectives. The simulated water quality impacts of alternative farming systems using SWAT and experimental data for riparian buffers are used in a mathematical optimization model to estimate net economic return for farming subject to a water quality objective. Physical characteristics such as stream length, channel slope, average land slope, cropland percentage and several soil attributes are identified in the watershed using ARC/INFO GIS. A regression model is then used to evaluate the impacts of these physical characteristics on the estimated economic values of buffers. The study is conducted in Goodwater Creek watershed, Missouri. The results show the estimated economic value of buffers is significantly affected by some soil properties, stream length, and cropland percentage in watershed and can be used to improve the effectiveness of riparian buffers at watershed and regional levels.     

Estimating Sediment and Nutrient Loads in Four Western Lake Superior Streams

Total suspended solids (TSS) and total phosphorus (TP) have been shown to be strongly correlated with turbidity in watersheds. High‐frequency in situ turbidity can provide estimates of these potential pollutants over a wide range of hydrologic conditions. Concentrations and loads were estimated in four western Lake Superior trout streams from 2005 to 2010 using regression models relating continuous turbidity data to grab sample measures of TSS and TP during differing flow regimes. TSS loads estimated using the turbidity surrogate were compared with those made using FLUX software, a standard assessment technique based on discharge and grab sampling for TSS. More traditional rating curve methodology was not suitable because of the high variability in the particulates vs. discharge relationship. Stream‐specific turbidity and TSS data were strongly correlated (r² = 0.5 to 0.8; p < 0.05) and less so for TP (r² = 0.3 to 0.7; p < 0.05). Near‐continuous turbidity monitoring (every 15 min) provided a good method for estimating both TSS and TP concentration, providing information when manual sample collection was unlikely, and allowing for detailed analyses of short‐term responses of flashy Lake Superior tributaries to highly variable weather and hydrologic conditions while the FLUX model typically resulted in load estimates greater than those determined using the turbidity surrogate, with 17/23 stream years having greater FLUX estimates for TSS and 18/23 for TP.     

Assessing Uncertainty in Estimates of Nitrogen Loading to Estuaries for Research, Planning, and Risk Assessment

Parametric (propagation for normal error estimates) and nonparametric methods (bootstrap and enumeration of combinations) to assess the uncertainty in calculated rates of nitrogen loading were compared, based on the propagation of uncertainty observed in the variables used in the calculation. In addition, since such calculations are often based on literature surveys rather than random replicate measurements for the site in question, error propagation was also compared using the uncertainty of the sampled population (e.g., standard deviation) as well as the uncertainty of the mean (e.g., standard error of the mean). Calculations for the predicted nitrogen loading to a shallow estuary (Waquoit Bay, MA) were used as an example. The previously estimated mean loading from the watershed (5,400 ha) to Waquoit Bay (600 ha) was 23,000 kg N yr⁻¹. The mode of a nonparametric estimate of the probability distribution differed dramatically, equaling only 70% of this mean. Repeated observations were available for only 8 of the 16 variables used in our calculation. We estimated uncertainty in model predictions by treating these as sample replicates. Parametric and nonparametric estimates of the standard error of the mean loading rate were 12–14%. However, since the available data include site-to-site variability, as is often the case, standard error may be an inappropriate measure of confidence. The standard deviations were around 38% of the loading rate. Further, 95% confidence intervals differed between the nonparametric and parametric methods, with those of the nonparametric method arranged asymmetrically around the predicted loading rate. The disparity in magnitude and symmetry of calculated confidence limits argue for careful consideration of the nature of the uncertainty of variables used in chained calculations. This analysis also suggests that a nonparametric method of calculating loading rates using most frequently observed values for variables used in loading calculations may be more appropriate than using mean values. These findings reinforce the importance of including assessment of uncertainty when evaluating nutrient loading rates in research and planning. Risk assessment, which may need to consider relative probability of extreme events in worst-case scenarios, will be in serious error using normal estimates, or even the nonparametric bootstrap. A method such as our enumeration of combinations produces a more reliable distribution of risk.     

Risk-based economic decision analysis of remediation options at a PCE-contaminated site

Remediation methods for contaminated sites cover a wide range of technical solutions with different remedial efficiencies and costs. Additionally, they may vary in their secondary impacts on the environment i.e. the potential impacts generated due to emissions and resource use caused by the remediation activities. More attention is increasingly being given to these secondary environmental impacts when evaluating remediation options. This paper presents a methodology for an integrated economic decision analysis which combines assessments of remediation costs, health risk costs and potential environmental costs. The health risks costs are associated with the residual contamination left at the site and its migration to groundwater used for drinking water. A probabilistic exposure model using first- and second-order reliability methods (FORM/SORM) is used to estimate the contaminant concentrations at a downstream groundwater well. Potential environmental impacts on the local, regional and global scales due to the site remediation activities are evaluated using life cycle assessments (LCA). The potential impacts on health and environment are converted to monetary units using a simplified cost model.A case study based upon the developed methodology is presented in which the following remediation scenarios are analyzed and compared: (a) no action, (b) excavation and off-site treatment of soil, (c) soil vapor extraction and (d) thermally enhanced soil vapor extraction by electrical heating of the soil. Ultimately, the developed methodology facilitates societal cost estimations of remediation scenarios which can be used for internal ranking of the analyzed options. Despite the inherent uncertainties of placing a value on health and environmental impacts, the presented methodology is believed to be valuable in supporting decisions on remedial interventions.     

实验用水对总氮检测结果的影响

用RO纯水与超纯水分别作为实验用水,通过标准曲线及空白、标准样品、水样等总氮测定对比实验,发现两种实验用水的标准曲线及空白值、标准样品的检测均受控,但两种纯水对比实验显示相对于超纯水而言,RO纯水中有一定浓度的总氮,同时在水样检测中用RO纯水作实验用水测定值明显低于用超纯水作实验用水的测定值,其差值与RO纯水中总氮值相符。实验结果表明总氮检测中不能只以标准曲线、空白值和标准样品测定值作为受控标准,要考虑实验用水中硝酸根离子的影响。     

IMPACTS OF WATER QUALITY IMPROVEMENT ON SITE VISITATION: A PROBABILISTIC MODELING APPROACH1

ABSTRACT: The influence of perceptions of water quality on the likelihood of recreating at a particular recreation site is investigated using a logit model. The model is estimated for St. Albans Bay, Vermont. A hypothetical improvement in water quality was shown to greatly increase the probability of at least one visit to the bay during a season. This implies that many recreationists who do not use the bay at present will do so if water quality improves. A demand model for predicting site visitation must, therefore, include current nonusers in the sample. Failure to do so would result in misleading predictions about future demand for the bay.     

Estimating Suspended Solids from Turbidity in the Robeson Creek,NC Watershed

The purpose of this project was to assess the effect of estimating total suspended solids (TSS) concentrations from turbidity on TSS loads for streams in the Robeson Creek watershed. Discharge was monitored continuously and base‐flow grab and storm event composite samples were collected and analyzed for TSS and turbidity from five sites during five years of monitoring. For base‐flow samples, the TSS‐turbidity relationship for all five sites was poor indicating that TSS concentrations in base flow cannot be estimated from a TSS‐turbidity relationship. To test the effect of analyzing fewer samples, TSS from every third and the first 20 samples collected from each site was used to develop TSS‐turbidity relationships. In addition, the TSS‐turbidity relationship developed from the most downstream site was used to estimate TSS concentrations from turbidity measured at the other four sites. For four of the five sites, analyzing every third sample for TSS and using the TSS‐turbidity relationship to estimate the missing TSS concentrations would result in mean TSS loads that were not significantly different from the observed. Using the TSS‐turbidity relationship from the outlet to estimate TSS from turbidity measured at the other four sites resulted in significantly different mean TSS loads at three of the four sites. These results indicate that estimating TSS concentrations from turbidity using a TSS‐turbidity relationship developed from a subset of the overall dataset should be done with great caution.