Well Field Practice: aquifer characterization through conducting and interpreting of aquifer pump tests.

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In January of 2003, CSUF drilled and completed a deep multiport-monitoring well on the north side of campus. This was done in order to gain a better understanding of the local subsurface geology and groundwater conditions in and around CSUF. Samples were collected from the drill hole (boring) every 5-feet. The total depth of the well is 870 feet below ground surface (grade). Borehole geophysical data (E-log) information was collected from the boring prior to the installation of the well pipe. As you describe the soil samples, compare and contrast your findings to those of the geophysical signature (gamma-ray log) found in the accompanying "E-log" for the boring.

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Fundamentals of subsurface flow and transport, emphasizing the role of groundwater in the hydrologic cycle, the relation of groundwater flow to geologic structure, and the management of contaminated groundwater. Topics include: Darcy equation, flow nets, mass conservation, the aquifer flow equation, heterogeneity and anisotropy, storage properties, regional circulation, unsaturated flow, recharge, stream-aquifer interaction, well hydraulics, flow through fractured rock, numerical models, groundwater quality, contaminant transport processes, dispersion, decay, and adsorption. Includes laboratory and computer demonstrations.

This course covers fundamentals of subsurface flow and transport, emphasizing the role of groundwater in the hydrologic cycle, the relation of groundwater flow to geologic structure, and the management of contaminated groundwater. The class includes laboratory and computer demonstrations.

Students first study the movement of water in aquifers through a lecture on Darcy's flow experiment. Then they practice applying the concepts of hydraulic conductivity and head differentials to 1 dimensional column examples. Next they use flow simulators to view flow through a cross section of an aquifer model. This activity is the final piece in the development of the idea of head driven flow. Students are given data about the thickness and head values of an aquifer member. They plot the aquifer thickness and potentiometric surface then determine the flow direction and estimate the groundwater flow velocity.

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This activity is a single, semester-long project that involves a hydrogeologic assessment of a property in Central Texas. The project is presented in the lab portion of a hydrogeology class, and it is broken into several separate steps. Each step is treated as a separate assignment, however, the data and results associated with each assignment are applied towards the overall goal of the project. Students are required to maintain a file and a master Excel workbook containing all information, data, and results from each of the steps. All this information is then used to develop an analytical model that simulated drawdowns in the aquifer. This model is used to answer the primary question associated with the project. The results are then documented in a technical report.

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A toddler wading pool or similar tank is filled with common sand (available from home improvement stores in bags) to a depth of 15-20 cm. The sand is saturated with a slow inflow and outflow to a floor drain. A 2-inch PVC slotted screen section is buried in the sand near the center of the tank with a capped end at the bottom. Small (1 cm diameter or similar) slotted or perforated PVC or copper tubing are placed as piezometers in the sand at short distances (e.g., 10-20 cm) from the pumping "well." A fountain pump capable of discharging up to 100-150 ml/min is placed within the "well" with adequate discharge tubing to conduct the water to a drain. A stopcock is placed in the tubing to control flow. Alternatively, if the tank of sand is on a very sturdy table, a simple siphon with tubing can be used as a pump. Drawdown is determined by the difference between a pre-pumping level measurement from the top of the "piezometers" and subsequent measurements made in the same "piezometer" at times after pumping starts. Water levels may be measured using chalked wooden rods. Alternatively, a small cork with a slender wooded food skewer marked in millimeter increments can be placed in each piezometers and the students can watch the change in level of the markings relative to the top of the "piezometer." Flow is repeatedly measured using a graduated cylinder. At the start of the test, students or teams of students are assigned to either take water level measurements at a specific piezometer or to measure and control the flow rate. The data are collected on a logarithmically increasing time interval for about an hour. The flow and drawdown data are analyzed by various means (Theis curve, Jacob straight-line method, Bolton curves, etc.) either manually or using AQTESOLV or similar software. Though the drawdowns are small, the data have provided quite reasonable estimates of hydraulic conductivity for the sand.

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This activity provides an approach to teach field methods that is programmed to avoid common pitfalls in teaching field methods to students. The two common problems that are avoided is familiarity with equipment and improved group function.

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To prepare to view the TCE animation, students could view the 'A Civil Action' movie and the instructor could read to them excerpts from the trial testimony and images from Woburn, wells G and H, geologic materials, geologic cross sections, the trial participants, and the federal courtroom in Boston (available as a attachment to this activity and at a website listed below). The discussion in Bair (2001) about scientists in the courtroom, the specific (excerpted) testimony presented by the three expert witnesses in the 'A Civil Action' trial, a chart summarizing the differences in their testimony, and the views of a federal judge on the goal of science versus the goal of a civil trial may also be worthwhile reading by the class prior to the assignment.

The instructor could also show students the large plates included in the USGS report by Myette and others (1987) that display potentiometric data and contours before and after the famous aquifer test performed in December 1985 and January 1986, just before the trial, and discuss the ramifications of having only two sets of water-level measurements to characterize all the changes in the flow system between 1964 and 1979, when wells G and H periodically operated. This makes students consider the substantial differences in making predictions based on a steady-state conceptualization of the flow system or a transient conceptualization.

The instructor could also show the animation of induced infiltration from the Aberjona River to wells G and H that also was created by Martin van Oort (M.S., 2005) and based on the research of Maura Metheny (M.S., 1998; Ph.D., 2004) at Ohio State University. Viewing both animations enables students to see that the water produced by wells G and H is a highly transient mixture derived from many different source areas within the valley.

The article by Bair and Metheny (2002) concerning the remediation activities at the Wells G & H Superfund Site could be used to show how groundwater contamination is cleaned up, why different remediation schemes needed to be used in different hydrogeologic settings, and why cleanup to U.S. EPA standards can take decades.

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This unit shows how GPS records of surface elevation can be used to monitor groundwater changes. Students calculate secular trends in the GPS time series and then use the original and detrended records to identify sites that are dominated by the elastic response to regional groundwater changes versus those dominated by local subsidence. They then compare the magnitude and timescales of fluctuations in Earth's surface elevation that result from sediment compaction, regional groundwater extraction, and natural climatic variability. This unit provides students with hands-on experience of the challenges and advantages of using geodetic data to study the terrestrial water cycle. The case study area is in California and the GPS records include the period of the profound 2012 -- 2016 drought.

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Note: Although the term GPS (Global Positioning System) is more commonly used in everyday language, it officially refers only to the USA's constellation of satellites. GNSS (Global Navigation Satellite System) is a universal term that refers to all satellite navigation systems including those from the USA (GPS), Russia (GLONASS), European Union (Galileo), China (BeiDou), and others. In this module, we use the term GPS even though, technically, some of the data may be coming from satellites in other systems.

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Online-ready: The exercise is electronic and could be done individually or in small online groups. Lecture is best done synchronously due to the technical nature. Discussion would be better that way too.

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This module looks at the feasibility of using deeper wells as a source of low As water. The data sets are described in detail by van Geen et al. (van Geen et al., 2003; van Geen et al., 2002).

Students are being introduced to background information about the Arsenic problem in Bangladesh in lecture format. This includes health aspects and the history of the issue. They also have been using the sand tank groundwater model distributed by the University of Wisconsin Stevens Point (https://www.uwsp.edu/cnr-ap/watershed/Pages/GroundwaterModelWorkshop.aspx) to develop an intuitive understanding of groundwater flow and transport and are familiar with basic hydrogeological concepts. They inject a dye into the shallow aquifer of the model and study how pumping effects the migration of the Arsenic plume (Fig 1).

Students get an Excel spreadsheet that contains the longitude, latitude, and depth of 6000 wells and a satellite image that shows the area of investigation. They use Arc GIS software to plot data on the satellite image (Fig. 2), or alternatively plot the data as a function of longitude and latitude as a bubble plot in Excel. They find that the distribution of As in many regions is very heterogeneous. They then select sub-regions and look at the depth distribution and find that often there is a gap in the depth population of wells which turns out to be due to a clay layer varying in thickness that separates the shallow aquifer from the deep aquifer. The depth distribution (Fig. 3) of As also shows a characteristic pattern with most of the elevated As concentrated in the top 30 meters.
Students then discuss remediation options, in particular the possibility of switching to neighboring wells and using deeper groundwater as an alternative source of drinking water. They find that in many regions there are safe wells within a few hundred m of the high As well. However, it is not clear how long these wells will remain low in dissolved As and there are social barriers as well to use the neighbors well. They then determine a depth below which As concentrations are low in their region and elevate the risk of using deeper groundwater for drinking water and irrigation. They find that personal use is resulting in only ~1cm year-1 of water use, while irrigation (~1 m year-1) would considerably lower the water table and potentially could contaminate the deeper aquifer as well. The conclusion is that if deeper groundwater is utilized its use should be limited to personal use.

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This exercise is part of a sequence of exercises to help students understand single and multiple aquifer tests. In class, students will receive data from pumping tests at University of Minnesota's hydrogeology field site. Instead of using commercial software, students will create interactive modeling tools to facilitate curve matching and to collaborate on understanding aquifer tests at different scales using different methods. The approaches used in this exercise can be extended to develop models to compare single and multiple aquifer tests using different approaches.

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This exercise uses an analytical method (Grubb, 1993) and Excel to calculate the capture zone shape for a TCE remediation well in Wooster, Ohio. The case study description given in an extensive PowerPoint presentation. The capture-zone equations are programmed by the student into an Excel worksheet and used to delineate the contributing area of a contaminant recovery well. Students can then experiment with by varying the pumping rate, hydraulic conductivity, and hydraulic gradient to better understand the sensitivity of these parameters on capture-zone shape.

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