RELATIONSHIP OF NITRATE CONCENTRATIONS TO DISTANCE OF WELL SCREEN OPENINGS BELOW CASING WATER LEVELS1

ABSTRACT: Data from 54 well in central and eastern Kansas developed in unconsolidated deposits of Quaternary age indicate that nitrate concentrations are inversely related to the depth of the well screen opening below the water level in the well casing because this relationship was found to exist in an area of Nebraska and in a large area of Kansas, the relationship is generally valid over a wide geo- graphical area. In addition, the data indicate that the incidence of nitrate concentrations exceeding 45 milligrams per liter and nitrate concentrations, in general, are significantly lower in water from wells with screens deeper than 25 feet below the water table in unconfined aquifers or where screens are placed in deep confined aquifers. No concentrations of nitrate greater than 45 milligrams per liter were in obseved wells where screens were deeper than 60 feet below the casing water level. These findings suggest that general placement of well screens as far below the water table as possible in unconfined unconsolidated aquifers in Kansas. and possibly other areas of the Midwest, may be an effective measure in preventing undesirable nitrate concentrations in ground water supplies. particularly in areas where nitrate is a problem.     

Potentially recoverable resources: How recoverable?

There are a number of factors which are likely to limit the proportion of potentially recoverable resources that will actually be recovered. The most important of these concern the way minerals are distributed within the crust and trends in energy costs associated with mineral production. This article offers a pessimistic view of the prospects for mineral supplies early in the 21st century. The resource situation is even less hopeful when the possibility of extending the material living standards of the developed countries to everyone likely to be living on earth late next century is considered.     

Investment and future mineral production

The author reviews recent estimates of world resources and reserves and notes that reserves tend to grow with mineral consumption. Legal and economic constraints to the extraction of minerals are at least as important as physical availability. The author also points out that there is far more investment in minerals (government induced investment, companies diversifying into mining, etc) than some commentators suggest. However, the large mining projects of the 1960s belong to the past, and supplies of minerals may well become tight if there is a concerted economic boom.     

A new baseline model for estimating willingness to pay from discrete choice models

We show a substantive problem exists with the widely-used ratio of coefficients approach to calculating willingness to pay (WTP) from discrete choice models. The correctly calculated standard error for WTP using this approach is shown to be undefined. This occurs because the cost parameter's standard error implies some possibility the true parameter value is arbitrarily close to zero. We propose a simple yet elegant way to overcome this problem by reparameterizing the (negative) cost variable's coefficient using an exponential transformation to enforce the theoretically correct positive coefficient. With it the confidence interval for WTP is now finite and well behaved.     

The nature and significance of public exposure to arsenic: a review of its relevance to South West England

In South West England, more than two hundred years of intensive exploitation of metalliferous ore deposits, combined with the natural processes of pedogenesis from mineral-rich parent rocks, has resulted in the creation of a aignificant area of arsenic-contaminated wastes and soils. The scale of arsenic dispersion by natural and anthropogenic processes is such that 722 km² of land contains concentrations of arsenic in excess of 110 g g^–1, more than twice the maximum that might be expected in a normal soil.The general rationale for the clean-up of derelict and contaminated mining sites often includes aesthetic factors and the desirability of preventing the dispersion of contaminants beyond the site boundaries. Only in extreme cases is public health directly invoked as justification for remediation. In South West England, if arsenic constitutes a genuine threat to the public, an increased rate of site remediation would be justified. The primary purpose of this review is to establish whether or not widespread arsenic contamination (principally of soils) has any measurable effects on public health in South West England, and how this might affect current contaminated site remediation policy. The review is based on data from previous research in the region, and other relevant international studies of mining and smelting communities, and other populations exposed to elevated arsenic concentrations. The literature reviewed also includes the determination of the extent and sources of contamination, and pathways between source and man.While the contamination of potable waters in some countries has led to measurable health effects, this scenario has not yet been identified in South West England, and there is little reason to believe that significantly contaminated potable water supplies would escape detection for extended periods of time under the current monitoring regime.In relative terms (based on both globaland local data), one of the most significant links between contaminated soils and humans appears to be contaminated food stuffs. In absolute terms, such exposure is low due to the natural constraints on arsenic uptake by herbage, cereal crops and vegetables, and the food chain does not appear to have been significantly compromised in South West England. Chronic health effects are unlikely as excessive arsenic concentrations in locally grown food crops remain rare.With the problems of confounding medical and social factors, it is not surprising that studies in South West England have failed to identify chronic exposure to arsenic at very low concentrations as a significant health risk. Those studies that indicate otherwise do not stand up to close scrutiny. It appears that the number of additional deaths arising from the widespread arsenic contamination in South West England is small. The relative benefits of a costly statistical study to actually determine the number of additional deaths might be considered minimal, but one major area could benefit from further studies: the sensitivity of certain population sub-groups to environmental arsenic exposure. Of particular interest are children, for whom significant exposure to arsenic via soil ingestion may be occurring.Based on available information, there appears to be no justification for a large programme of site remediation. Resources should, however, be expended on enlightening the general public, and private and governmental organisations as regards the gap between the perceived and actual significance of arsenic contamination in South West England.To whom correspondence should be addressed.     

珠江三角洲地区大气中有机氯农药的被动采样观测

利用PUF被动采样装置,对珠江三角洲地区大气中有机氯农药(OCPs)进行监测.结果显示,广东省大气中有机氯农药主要是滴滴涕(DDTs)、六六六(HCH)及氯丹(Chlordane),其中DDTs约占总OCPs的54.5%;香港大气中农药残留主要是氯丹和DDTs,氯丹约占总含量的51.3%.珠三角地区大气中有机氯农药空间分布差异明显(580-5500pg·m-3),香港平均浓度远远低于广东省.另外,广东省仍有工业DDT在使用,造成广东省大气中有"新"的工业DDT输入;而三氯杀螨醇是香港大气中DDT高含量的重要来源;广东省和香港HCH主要源于林丹使用的残留,香港的Eastern及Tsuen Wan源于工业六六六使用的残留;珠江三角洲所有采样点的HCB含量较低,大气中HCB少量残留可能是HCB作为药物中间体的化学合成及HCB在大气中长距离传输的结果.     

安徽霍邱李老庄铁矿-菱镁矿床地质特征及成因类型

霍邱铁矿田位于华北地台南缘,处于北淮阳山字型构造脊柱部位。李老庄铁矿—菱镁矿床置于霍邱铁矿田中部。该矿床主要产于上太古界霍邱群变质岩系中,矿体赋存于富镁碳酸盐中,矿石类型可以分为菱镁矿磁铁矿石和蛇纹石磁铁矿石,各占25%。成矿物质来源于这些变质岩系的多层、分散的含铁建造矿源层中。依据矿床地质特征,结合矿石同位素地质和测年结果,李老庄铁矿—菱镁矿铁矿床是晚太古代海相火山—沉积变质型矿床。     

黄河断流对三角洲附近海域生态环境影响的研究

本文根据多年调查监测数据研究成果，以及经济和社会统计资料，论述了黄河断流的历史与现状，定性定量地评价了黄河断流对三角洲附近海域生态环境的影响，并提出了缓解和预警对策。     

长江三角洲晚第四纪陆-海交互地层的光释光年代学

长江三角洲地层的年代学研究对探讨晚第四纪以来我国东部沿海地区陆海交互作用历史以及海岸地貌的形成与演化具有重要价值。本研究选择长江三角洲YZ07和EGQD14两支钻孔开展系统光释光（optically stimulated luminescence,OSL）测年研究,总结前期已发表的50个年代数据并收集整理该区域相关钻孔的年代地层资料,探讨在可靠的年代框架约束下晚第四纪长江三角洲沉积地层演变特征,取得了以下几点认识：（1）在长江三角洲地区,常规OSL测年以较细石英颗粒OSL测年效果较为理想;对粗颗粒石英,若存在长石包裹体对石英OSL信号的影响,建议用脉冲释光测年（POSL）技术加以解决。（2）以YZ07孔为例,¹⁴C测年和OSL测年结果对比表明在三角洲海岸地区,¹⁴C测年方法建立的年代地层框架需要谨慎对待,建议在此区域开展年代地层学研究时可以尝试将两种测年方法结合使用,以确保年代地层框架的准确和可靠。（3）针对争议较大的氧同位素3阶段（MIS3）沉积环境问题,EGQD14孔给出了新的年代学证据,认为MIS3阶段（约30?—?50 ka）长江三角洲可能是陆地河流相沉积环境为主导,这也得到了区域相邻的几支钻孔沉积记录的佐证。（4）两支钻孔从年代学角度证实了前人关于末次盛冰期（Last Glacial Maximum,LGM）以来长江三角洲发育下切河谷的沉积学判识和地层学论断。此外,多钻孔的年代地层学特征也验证了全新世时段海平面变化控制下的长江三角洲及海岸演变的时空动态。     

土壤中多氯联苯的综合污染指数评价方法研究

借鉴综合污染指数的概念,引入加拿大环境理事会制订的土壤中多氯联苯(PCBs)标准指标.建立了PCBs污染的毒害性分污染指数(TPI)、持久性分污染指数(PPI)和生物累积性分污染指数(BPI)加权计算的综合污染指数(IPI)评价方法以及各污染指数的相关表达式,确定了土壤环境中PCBs的毒害性转换系数(Ti)、持久性转换系数(Pi)和生物累积性转换系数(Bi).利用建立的土壤中PCBs的综合污染指数评价方法定量评价了现代黄河三角洲地区土壤中的PCBs污染现状,22个采样点的PCBs污染的IPI值在1.1-531.7之间,整个现代黄河三角洲地区的PCBs污染现状属轻度污染.该评价体系综合地考虑了PCB8同系物间的环境行为差异,较现有的PCBs总量评价方法更科学合理,在持久有机污染物(POPs)的污染评价方面具有推广价值.