An Analytical Method to Determine Ground Water Supply Well Network Designs

An analytical method is provided where the ground water practitioner can quickly determine the size (number of wells) and spacing of a well network capable of meeting a known ground water demand. In order to apply the method, two new parameters are derived that relate theoretical drawdown to the maximum drawdown that is achievable without mining the aquifer. The size of a well network is shown to be proportional to the ground water demand and inversely proportional to the transmissivity and available head. The spacing between wells in a supply well network is shown to be most sensitive to a derived parameter r _{HA/ 3}, which is related to the available head and the propagation of drawdown away from a theoretical well if the total ground water demand was applied to that well. The method can be used to quickly determine the required spacing between wells in well networks of various sizes that are completed in confined aquifers with no leakance.     

Application of an Analytical Solution as a Screening Tool for Sea Water Intrusion

Sea water intrusion into aquifers is problematic in many coastal areas. The physics and chemistry of this issue are complex, and sea water intrusion remains challenging to quantify. Simple assessment tools like analytical models offer advantages of rapid application, but their applicability to field situations is unclear. This study examines the reliability of a popular sharp‐interface analytical approach for estimating the extent of sea water in a homogeneous coastal aquifer subjected to pumping and regional flow effects and under steady‐state conditions. The analytical model is tested against observations from Canada, the United States, and Australia to assess its utility as an initial approximation of sea water extent for the purposes of rapid groundwater management decision making. The occurrence of sea water intrusion resulting in increased salinity at pumping wells was correctly predicted in approximately 60% of cases. Application of a correction to account for dispersion did not markedly improve the results. Failure of the analytical model to provide correct predictions can be attributed to mismatches between its simplifying assumptions and more complex field settings. The best results occurred where the toe of the salt water wedge is expected to be the closest to the coast under predevelopment conditions. Predictions were the poorest for aquifers where the salt water wedge was expected to extend further inland under predevelopment conditions and was therefore more dispersive prior to pumping. Sharp‐interface solutions remain useful tools to screen for the vulnerability of coastal aquifers to sea water intrusion, although the significant sources of uncertainty identified in this study require careful consideration to avoid misinterpreting sharp‐interface results.     

Economics of Sample Compositing as a Screening Tool in Ground Water Quality Monitoring

Recent advances in high throughput/automated compositing with robotics/field-screening methods offer seldom-tapped opportunities for achieving cost-reduction in ground water quality monitoring programs. An economic framework is presented in this paper for the evaluation of sample compositing as a screening tool in ground water quality monitoring. When the likelihood of occurrence of a contaminant in a well is very small, the use of sample compositing instead of routine exhaustive sampling will lead to reduction in analytical efforts. Such reduction will be maximum when there are no contaminated wells in the network. An N-fold reduction will result when none of the wells in a network of N wells are contaminated. When 25 percent or more wells in a network are contaminated, the use of sample compositing will require, at the most, an additional 50 percent analytical effort compared to exhaustive sampling. A quantitative measure of the cost-effectiveness of sample compositing as a screening tool is shown to be dependent on two factors: a ratio (f1) of laboratory analytical cost to that of well installation and field sampling costs and a ratio (f2) of the expected number of contaminated wells to that of the total number of wells in the network. Several useful mathematical results of primary interest are derived and illustrated with case examples in the paper. Selected areas for further research are also outlined.     

A Computerized Ground Water Monitoring System

This article describes a computer automated, hydrologic analysis system designed to allow the collection of high quality, long-term pumping test data. The instrument solves two of the major problems encountered in the field during aquifer tests: insufficient data, particularly during the early part of a test when drawdown is rapid; and high labor costs associated with long-term monitoring.
To illustrate the system's application, results are presented from the test of a highly transmissive aquifer. The aquifer's drawdown response was rapid; thus the time-drawdown curve was essentially flat after the first two minutes of the test, and correspondingly rapid data acquisition was essential for a unique solution of the aquifer's three-dimensional hydraulic conductivities.     

A New System for Ground Water Monitoring

This paper describes a new system for ground water monitoring, "the BAT System," which includes the following functions: (a) sampling of ground water in most types of soils, (b) measurement of pore water pressure, and (c) in situ measurement of hydraulic conductivity. The system can also be used for tracer tests. The system utilizes a permanently installed filter tip attached to a steel or PVC pipe. Installation is normally performed by pushing the tip down to the desired depth. The filter tip can also be buried beneath a landfill. The primary feature of the new system is that the filter tip contains a self-sealing quick coupling unit, which makes it possible to temporarily connect the filter tip to adapters for various functions, e.g. water sampling and for measurement of pore pressure and hydraulic conductivity. The new technique makes sampling of both pressurized water and gas possible. Samples are obtained directly in hermetically sealed, pre-sterilized sample cylinders. Sampling of ground water and measurement of pore pressure can be repeated over a long period of time with undiminished accuracy. This technique is also well-adapted for taking water samples from different strata in a soil profile, in both the saturated and unsaturated zones. Actual installations range from 0.5 to 60m depth.     

The Hydropunch™: An In Situ Sampling Tool for Collecting Ground Water from Unconsolidated Sediments

The Hydropunch™ is a stainless steel and Teflon® sampling tool that is capable of collecting a representative ground water sample without requiring the installation of a ground water monitoring well. To collect a sample, the Hydropunch (Patent #4669554) is connected to a small-diameter drive pipe and either driven or pushed hydraulically to the desired sampling depth. As the tool is advanced, it remains in the closed position, which prevents soil or water from entering the Hydropunch. Once the desired sampling depth is obtained, the tool is opened to the aquifer by pulling up the drive pipe approximately 1.5 feet (0.46m). In the open position, ground water can flow freely into the sample chamber of the tool. When the sample chamber is full, the Hydropunch is pulled to the surface. As the tool is retracted, check valves close and trap the ground water in the sample chamber. At the surface the sample is transferred from the Hydropunch to an appropriate sample container. The tool is a fast, inexpensive alternative for collecting ground water samples from a discrete interval. It is excellent for vertical profiling or defining the areal extent of a contaminant plume.     

Developing A National Drinking Water Regulation for Disinfection of Ground Water

The Safe Drinking Water Act directs EPA to promulgate requirements for disinfection of ground water-based drinking water systems. The Ground- water Disinfection Rule regulatory workgroup, made up of representatives from EPA, the states, and other interested parties, is actively considering the issues for the wide range of elements necessary to ensure a regulation that will protect public health and can be feasibly implemented. This regulation is likely to require disinfection of ground water sources and systems found to be contaminated or vulnerable to contamination.     

A Laboratory Evaluation of Ground Water Sampling Mechanisms

The reliability of ground water monitoring information can be assured by careful selection of sample handling and analytical procedures. Sampling mechanism selection has been studied far less than analytical methodologies (Scalf et al. 1981, Nacht 1983). This study has as its primary goal the identification of reliable sampling mechanisms for purgeable organic compounds and gas-sensitive chemical parameters in ground water. Carefully controlled sampling experiments were run to investigate the error contributed to chemical results due to sampling mechanism alone. Fourteen commercial sampling devices in five mechanistic categories were evaluated for their performance in sample collection for solution parameters, dissolved gases and purgeable organic compounds. Systematic errors related to sampling mechanism can reduce the accuracy of monitoring data by factors of two to three times that involved in analytical procedures.