Modeling of Contaminant Movement Near Pumping Wells: Saturated-Unsaturated Flow with Particle Tracking

A transient axisymmetric saturated-unsaturated numerical flow model was coupled with a particle tracking model to investigate the movement of contaminants when a shallow unconfined aquifer is pumped at a constant rate. The particle tracking model keeps track of locations and masses of solutes in the aquifer, and the time of capture by the well. At the end of each time-step the flow model solves the Richard's equation for the hydraulic head distribution from which elemental velocities are calculated. Solutes are then displaced for a period equivalent to the time-step using both the magnitude and direction of the elemental velocities. Numerical experiments were performed to investigate effluent concentrations in wells with screens of different length and in different positions relative to zones of stratified contamination. At early times of pumping the effluent concentrations were similar to the concentrations adjacent to the well screen, but at late times, the concentrations approached the vertically averaged concentration in the aquifer. Time to attain the vertically averaged concentration was determined by the well geometry, initial location of the contaminant plume in relation to the well screen, and hydraulic properties of the aquifer. The results are consistent with the hydraulics of flow to a pumping well and of particular importance, they demonstrate that short-term pump tests could give erroneous design concentrations for pump-and-treat systems. The model provides a means of quantifying arrival times and mixing ratios. It could therefore provide a useful means of designing production wells in aquifers with stratified contamination and more efficient recovery systems for aquifer remediation.     

Configuring Detection Wells Near Landfills

A graphical method was devised for designing contaminant detection monitoring networks in aquifers. The approach eliminates bias in detection efficiency among well pairs, thereby improving the overall efficiency of a ground water monitoring network. In the equidistant configurations derived by the graphical approach, all wells are located the same distance from a landfill, but the distance is measured parallel to ground water flow, Measured perpendicular to ground water flow, there is also an equal spacing between wells in an equidistant network. A simulation model was used to compare an equidistant network to a peripheral monitoring configuration, in which wells were spaced evenly along the downgradient boundaries of a landfill. The equidistant network yielded a 12.4% higher detection efficiency and also facilitated earlier release detection. In practice, the graphical approach that yields equidistant configurations can be used to identify candidate monitoring networks to detect potential releases from landfills.     

An Analysis of Nitrate-Nitrogen in Ground Water Beneath Unsewered Subdivisions

Water samples from private water supply wells in five unsewered subdivisions were tested for nitrate-nitrogen to determine the possible impact of septic systems on ground water quality. Three subdivisions are located in Eau Claire County and two in LaCrosse County, Wisconsin.
The nitrate-nitrogen concentrations in the wells were analyzed in relation to ground water flow direction, the location of septic systems within the subdivision, and the hydrogeologic and physical characteristics of the subdivisions. A comparison of three nitrogen mass balance models helped to identify the possible sources of nitrate-nitrogen in the wells.
The results indicate that nitrogen from septic systems and lawn fertilizer cause nitrate-nitrogen to increase in the ground water beneath the downgradient side of the subdivisions. In three of the five subdivisions the highest nitrate-nitrogen value exceeds the drinking water standard of 10 mg/L.     

Benchmark Analysis of Solute Transport with Multiaquifer Wells

A benchmark analysis is developed for assessing the reliability of the representation of multiaquifer wells in numerical solute transport simulators. The analysis considers the installation of a well that penetrates two aquifers that are otherwise isolated. The interconnection of the two aquifers by the multiaquifer well leads to the capture of a plume in an upper aquifer and the development of a plume in a lower aquifer. The benchmark analysis couples an exact Laplace transform solution for radially convergent transport with a generalization of an exact Laplace transform solution for radially divergent transport. The benchmark analysis is used to test the multiaquifer well simulation capability incorporated recently in MT3DMS. The results of the analysis provide insights into important issues of model accuracy and efficiency. The results of the analysis also highlight the potential implications of installing wells with relatively long screens at sites with contaminated groundwater.     

天津两井水位同震效应分析

从不同的方位对天津地区两口地震观测专用井记录到的国外7级、国内6级以上的地震进行分析。两口井所处的地理位置、地质结构、井深及其含水层岩性不同,对同一地震的表现形式也不尽相同。通过对比分析,得到井水位对地震的响应特点及几点认识：观测井孔一般对远场大震记录比较灵敏,而对近震及地方震反映不灵敏;井孔水位仪记录的水位波幅与震级、震中距有关;井孔同震效应的能力和井孔对固体潮的反映能力不一致。     

泉水和井水温度长期观测资料的初步统计

依据中国地震台网中心前兆数据库中的水温数据,绘制了中国大陆用于地震监测预报的泉水温度分布图以及井下50—149m和150—250m的水温分布图,统计了人工和数字化观测水温中长期趋势性上升或下降的测点,分析了数字化观测水温长期趋势性变化的原因。结果表明,泉主要分布在川滇、青藏高原东北缘、中天山、郯庐断裂带及邻区、北京西北和福建沿海等地,这些泉与断裂构造具有较好的空间相关性;其中水温大于25℃的温泉多分布在中强地震多发区;井水温度的空间分布具有北方地区水温低于南方地区、小区域内的温差不显著等特征,其主要受控于气候因素;井下150—250m与50—149m水温相比,符合随深度增加水温升高的地热规律;人工观测水温中10%为客观的长期趋势性变化;数字化观测水温中24%为长期趋势性变化,其中一部分是水温的客观反映,另一部分是水温仪零飘的反映。     

华安汰内水氡井近震映震能力分析

通过对华安汰内观测井1987年以来的氡值资料及近震映震能力的分析,发现震前明显突跳异常的近震震中近北西向展布在福安—南靖断裂两侧,结合区域地质构造背景,探讨了这种现象发生的原因。