Manual on Subsurface Investigations (2019)

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117 C H A P T E R 7 Hydrogeologic Characterization Introduction Hydrogeology plays a significant role in the geotechnical analysis, design, and performance of the subsurface features of the transportation infrastructure. Thus, a hydrogeologic characterization to gain an understanding of the distribution, thickness, composition, and continuity of the lithologic units and anthropogenic features (e.g., wells, pumps, vaults, pipelines, trenches) that may influence groundwater flow is critical to most subsurface investigation programs. Results of hydrogeologic characterizations are specifically used to address issues such as slope failures, landslides, piping erosion, subsidence, subgrade pumping, heave in excavations, and uplift of structures due to buoyancy (FHWA 2007). A comprehensive hydrogeologic characterization should include information on (i) geology and hydrogeology, (ii) aquifer characteristics, (iii) aquitard characteristics, and (iv) the direction and gradient of groundwater flow (CalEPA 2012, Ohio EPA 2018). Additionally, information on the nature and extent of groundwater contamination may be needed if the project site is a brownfield. Guidelines for evaluating the nature and extent of groundwater contamination are beyond the scope of this manual; see CalEPA (2012) and Ohio EPA (2018) for more information. Geology and Hydrogeology Knowledge of the site geology and stratigraphy is essential to define the hydrogeologic framework and identify pathways for groundwater flow. It is necessary to define water-bearing zones that allow groundwater movement (i.e., aquifers) and zones that may restrict movement of groundwater (i.e., aquitards), as well as any geologic features that may affect groundwater movement, such as faults, folds, fractures, buried channel deposits, or solution features. These zones are generally identified by observing and testing the material from boreholes. Correlation between boreholes is necessary to evaluate whether a layer is laterally continuous across the site. Geophysical methods can also be used to direct or augment the characterization of stratigraphy. The subsurface can be divided into unsaturated (vadose) and saturated (phreatic) zones. Groundwater in the saturated zone can occur in confined or unconfined aquifers. A confined aquifer is bound by relatively impermeable layers (i.e., aquitards). Water levels in wells or piezometers in a confined aquifer rise above the bottom of an upper confining layer (i.e., an artesian condition) and define a potentiometric or piezometric surface. An aquifer that has a water table as its upper boundary is unconfined. A water table is a surface where hydrostatic pressure equals atmospheric pressure. In general, most water-bearing aquifers are not entirely confined or unconfined, and are called semiconfined or leaky. A special case of an unconfined zone is a perched water table, which may develop when a relatively impervious layer of limited horizontal extent is located between the water table and the ground surface. Groundwater accumulates above this impervious layer. Perched zones may drain into an underlying zone or may be permanent. Water held immediately above the water table by capillary forces is the capillary fringe, the height of which depends on the diameter of the interstices. The thickness of the capillary fringe may vary from a fraction of an inch in gravel to several feet in fine-grained soils.

118 Aquifer Characteristics Aquifers are water-bearing soil or rock zones that transmit water easily. The following are the key characteristics of an aquifer that should be evaluated as part of a hydrogeologic characterization: • Hydraulic conductivity • Porosity • Permeability • Transmissivity • Storage coefficient (confined aquifers) or specific yield (unconfined aquifers) 7.3.1 Hydraulic Conductivity Hydraulic conductivity is a coefficient of proportionality between the hydraulic gradient and the velocity of fluid flow through a permeable medium. The hydraulic conductivity of geologic materials varies over many orders of magnitude from approximately 102 to 10-11 centimeters per second (cm/s). Generally, fine- grained materials are characterized by lower values. Spatial variations in hydraulic conductivity largely control groundwater flow through subsurface materials. Many geologic materials exhibit anisotropy with respect to hydraulic conductivity. Anisotropy typically is the result of small-scale stratification such as bedding of sedimentary deposits or fractures. In bedded deposits, the hydraulic conductivity may be several orders of magnitude higher in the direction parallel to bedding. There are several field and laboratory techniques for determining the hydraulic conductivity of geologic materials. In general, field tests are favored over laboratory tests because results better represent in situ conditions. 7.3.2 Porosity Porosity is a measure of the amount of void space in a material. It is expressed quantitatively as the ratio of the volume of voids to the total volume of the porous material. Since groundwater moves and is stored within pores and fractures (i.e., voids), porosity is important in describing flow. Primary porosity refers to the original interstices created when a material, such as rock or soil, was formed. It is the dominant porosity in unconsolidated materials, such as soil, and in loosely cemented or weakly indurated sedimentary rocks. Secondary porosity refers to interstices created after a material was formed such as fractures (joints and faults), openings along bedding planes, solution cavities, cleavage, and schistosity. Secondary porosity is the dominant form in consolidated materials (e.g., well cemented and strongly indurated sedimentary rocks) and is the only effective porosity in most igneous and metamorphic rocks. Porosity may be calculated via weight-volume relationships from measurements on undisturbed samples, or it may also be measured via borehole geophysical methods such as gamma-gamma density and neutron porosity (see Chapter 4). 7.3.3 Permeability Permeability also describes the ease with which a porous medium can transmit a liquid under a hydraulic or potential gradient. It differs from hydraulic conductivity in that it is a property of the porous media only and is independent of the nature of the fluid, so it is often called intrinsic permeability. It is related to hydraulic conductivity by: = where = intrinsic permeability

119 = hydraulic conductivity = dynamic viscosity of the fluid = acceleration of gravity Intrinsic permeability has units of area. In general, hydraulic conductivity is measured in a site investigation. However, intrinsic permeability is sometimes used as an input into models. 7.3.4 Transmissivity Transmissivity is the amount of water that can be transmitted horizontally by the saturated thickness of an aquifer. For confined aquifers, transmissivity is equal to the product of the hydraulic conductivity and the saturated thickness of the aquifer: = where T = transmissivity b = saturated thickness of the aquifer Transmissivity is expressed in units of area divided by time (e.g., m2/day, ft2/day). For unconfined aquifers, the saturated thickness is the height of the water table above the top of an underlying confining unit. Field methods for calculating hydraulic conductivity often involve measuring the transmissivity and dividing by the saturated thickness. 7.3.5 Storage coefficient and Specific Yield Storage coefficient (or storativity) is a dimensionless number that represents the water that a formation releases or absorbs from storage per unit surface area per unit change in head. The storage coefficient of a confined aquifer is caused by the compressibility of the water and mineral framework and is the product of the specific storage and the thickness. Storage coefficient for confined aquifers is generally on the order of 0.005 or less. Storage coefficient of an unconfined aquifer is essentially the same except that the decline is in the water table. With unconfined aquifers, water is drained out of pore space, and air is substituted as the water table drops. The water that is drained by gravity is often referred to as specific yield. The specific yield of most alluvial saturated zones ranges from 10 to 25 percent. Aquitard Characteristics Aquitards are confining layers that limit the vertical movement of water. They are generally comprised of silt and clay with low hydraulic conductivity (i.e., less than approximately 10-6 cm/s) and can impede the vertical flow of water. Some aquitards have poor integrity due to secondary permeability in the form of fractures, rootlets, or other features. Because of the existence of natural and man-made features that provide preferential pathways for groundwater movement, no aquitard is completely impermeable. Moreover, hydraulic conductivity may vary considerably within an aquitard. Therefore, characterizing aquitards is a critical element of site investigations. For example, the depth, thickness, and extent of aquitards must be determined prior to locating monitoring and extraction wells or selecting screened intervals for piezometers. Perched zones, in which groundwater mounds over an aquitard that is limited in lateral extent, should also be identified. Field investigative methods for delineating aquitards can include indirect methods (e.g., CPTs, geophysical surveys) and direct methods (e.g., inspecting samples). Hydraulic conductivity can be measured in the laboratory from undisturbed soil samples as discussed in Chapter 8.

120 Direction and Gradient of Groundwater Flow Potentiometric information (from piezometers or monitoring wells with short well screens) and measurements of the hydraulic conductivity of aquifers are used to estimate the direction and gradient of groundwater flow. These data are used in conjunction with an understanding of the site geology and stratigraphy. Because groundwater flows in the direction of decreasing hydraulic head, horizontal and vertical components of flow direction and gradient can be determined by acquisition and interpretation of water level data obtained from monitoring wells and piezometers. Potentiometric surface maps are typically constructed to show horizontal groundwater flow directions. Water-level elevation is plotted on a base map and linear interpolation of the data points is made to construct lines (contours) of equal elevation. The data used should be from well intakes located in the same hydrostratigraphic zone and at the same elevation. The water-table is a particular potentiometric surface for an unconfined aquifer. Water table maps should be based on elevations from wells screened across the water table. The flow direction for each zone may be determined by drawing flow lines perpendicular to the contours. A reliable interpretation of groundwater flow must consider geologic data and interactions with surface water. Horizontal hydraulic gradient is the change in total head with change in distance in the direction of flow. The gradient generally is analogous to the slope of the potentiometric or water-table surface. Gradients can range from greater than 1 (near a point of discharge) to less than 0.0001, a value associated with extensive area of flat terrain and high hydraulic conductivity. The horizontal gradient can be calculated by dividing the difference in head between two contour lines on a potentiometric map by the orthogonal distance between them. In addition to considering the horizontal component of flow, an investigation or monitoring program should directly assess the vertical component and the interconnection between saturated zones. The vertical component within a formation can be determined by comparing heads in well or piezometer clusters screened in that zone. Hydraulic connection between saturated zones can be determined by pumping a lower zone and monitoring changes in water levels measured in zones above the pumped zone. Vertical gradients between zones can be determined if hydraulic connection exists. A site could exhibit different horizontal and vertical gradients depending on where measurements are taken. Gradients are influenced by the characteristics of the groundwater zone (e.g., hydraulic conductivity, thickness), boundary conditions (e.g., rivers), precipitation, and anthropogenic influences. Groundwater Measurements This section focuses on methods used to obtain information about groundwater conditions, including potentiometric and water-table surfaces, pressure heads, groundwater flow, and hydraulic conductivity. As noted above, knowledge of the site geology and stratigraphy is essential for a comprehensive hydrogeological characterization. Methods for evaluating the site geology and stratigraphy are described in Chapters 4 through 6. 7.6.1 Methods for Groundwater Levels and Pressures The common methods commonly used to establish groundwater levels and measure pressure heads include the following: • Existing information sources • Geotechnical borings • Monitoring wells • Piezometers • Geophysical testing

121 7.6.1.1 Existing Information Sources Existing information pertaining to hydrogeology is available from a variety of sources including (i) the United States Geological survey (USGS) Office of Groundwater and Water Science Centers located in each state; the USDA Natural Resources Conservations Services; hydrogeologic databases or publications from state or local government agencies (e.g., natural resources, geological survey); logs and reports from public, private, and industrial monitoring wells; and geologic and groundwater reports by local consultants. This information can be gathered and reviewed quickly as part of the preliminary hydrogeologic characterization to help plan the scope of site-specific investigations. 7.6.1.2 Geotechnical Borings Borings conducted during geotechnical field investigations may be used to establish groundwater elevations. After the required boring termination depths have been achieved, groundwater level readings are usually taken immediately after drilling or coring and again at least 12 hours (preferably 24 hours) after drilling or coring. Geotechnical borings in sandy soils often cave in. When caving occurs, the depth of caving should be noted because it may coincide with the water table elevation. In borings where drilling mud is used, a filter cake often forms and obscures the groundwater level. In these situations, bailing the geotechnical boring is required prior to measuring the groundwater level. 7.6.1.3 Monitoring Wells Monitoring (or observation) wells are used to evaluate aquifer characteristics and determine groundwater flow direction and gradient. They are well suited to long-term studies of groundwater conditions and sites where groundwater samples must be obtained periodically. Wells may be installed solely for groundwater measurements, or, more commonly, geotechnical borings can be converted to wells. Monitoring wells may be either single-level or multilevel designs. Single-level wells are screened in only one zone, whereas multilevel wells are screened in several discrete zones and are configured to eliminate hydraulic connection between screened zones. Figures 7-1 and 7-2 illustrate both types of wells. Single-level wells are the predominant type used for hydrogeologic characterization. Screened intervals are generally 10 ft (3 m) or less; however, site conditions may warrant longer screens. For example, longer screened intervals may be needed for wells screened across a fluctuating water table. Multiple zones may be monitored by drilling successively deeper boreholes close together and installing a single-screened well in each hole. This type of installation is known as a monitoring well cluster (Figure 7-2). Nested wells, which contain multiple wells in a single borehole, are generally not recommended because of difficulties involved with installing reliable seals between zones. Installing well clusters rather than nested wells is the preferable method of monitoring multiple groundwater zones. Multilevel wells provide an alternative to cluster wells when monitoring a series of intervals in a single water-bearing zone is required. Multilevel wells should not be installed across aquitards or confining layers. Detailed information on designing, installing, and developing monitoring wells is available in ASTM D5092, Sprecher (2008), CalEPA (2012), CalEPA (2014), and Ohio EPA (2018).

122 Source: CalEPA (2014) Figure 7-1. Single-level monitoring well Source: CalEPA (2014) Figure 7-2. Multilevel monitoring wells

123 To enable consistent and accurate water level elevation measurements, each monitoring well should have a surveyed elevation reference point that is consistently used when measuring water levels and total well depth. If monitoring wells have been installed and surveyed over time during successive phases of investigations at a site, it is recommended that a single elevation survey be conducted for the entire network to ensure that the reference point elevations are accurate. Water levels should be referenced to mean sea level or a fixed marker to a precision of 0.01 ft (0.3 cm). Less precision (i.e., 0.1 ft [3 cm]) may be acceptable, depending on the slope of the potentiometric surface or water table and the distance between measuring points. Greater precision is necessary where the slope is gradual, or wells or piezometers are close together. In newly installed wells, water levels should be allowed to stabilize for at least 24 hours after well development prior to making measurements. Additional time (e.g., one week) may be necessary for low-yielding wells. Several methods are available to measure the water level elevation in monitoring wells (and geotechnical boreholes). The simplest method is to use a steel measuring tape with a weight attached to the end. The volume of the weight should be small to minimize the amount of water displaced, particularly in small- diameter wells. The lower 2 ft (0.6 m) of the tape is rubbed with carpenter's chalk. Measurements are made by lowering the weighted tape until the chalked section slightly passes the water surface. The depth to the water level is calculated by subtracting the depth of penetration indicated by waterline in the chalked section from the reading at the elevation reference point for the well. This method is accurate, but can be cumbersome especially when multiple readings are required because the tape must be removed from the borehole to reapply the chalk each time a reading is taken. An alternative is to listen for an audible splash when the weight breaks the surface of the water in the well, but this method is less accurate. An electric water-level indicator uses a weighted probe attached to the lower end of an electric cable. Depth readings are marked on the electric cable at fixed intervals. Water level measurements are made by lowering the weighted probe until it reaches the water surface in the well. When the probe contacts the water surface, an electrical circuit in the probe is closed and the device sends a signal to a readout unit. The depth to the water level is obtained via the marked readings on the cable at the elevation reference point for the well. This method is accurate; however, errors may occur if oil has accumulated on the water surface in the well. Finally, an electrical pressure transducer can be placed at the bottom of a monitoring well. The transducer measure changes in pressure caused by changes in water levels within the well. The pressure can be used to calculate the height of the column of water above the transducer and thus the water level elevation in the well. This type of measurement is accurate, easily automated, and enables a large amount of data can be collected efficiently. ASTM D6000 provides guidance on the tabular and graphical presentation of water-level information obtained from monitoring wells. Figure 7-3 shows an example of a potentiometric surface map developed using data from monitoring wells.

124 Source: Geosyntec Consultants, Inc. Figure 7-3. Example potentiometric surface map 7.6.1.4 Piezometers Piezometers are used to measure groundwater levels and pressure heads in saturated soil, rock, or other porous material. Piezometers differ from monitoring wells in that they are used to measure the groundwater level or pressure head at only a specific point (i.e., depth). Two types of piezometers commonly used: (i) open standpipe (or Casagrande-type) piezometers and (ii) electronic piezometers. Open standpipe piezometers are constructed in a manner similar to monitoring wells, but typically have shorter screened intervals to isolate a specific depth. Electronic piezometers (e.g., vibrating-wire, pneumatic, strain-gage) use pressure transducers that commonly are grouted into place with a bentonite-cement grout or directly pushed into place in soft soils at the desired depth. Both single-level and multilevel configurations are possible. The transducer responds to pressure variations as water levels rise and fall and sends an electrical signal to a readout unit. Piezometric data from transducers may also be transmitted via wireless telemetry to a remote location, eliminating the need to send personnel into the field for manual readings. ASTM D7764 describes procedures for acceptance testing vibrating-wire piezometers prior to installation to ensure they are working properly. 7.6.1.5 Geophysical Testing As described in Chapter 4, there are several surface geophysical methods that may be used to determine the water table elevation, including seismic refraction and reflection, electrical resistivity, and GPR. Geophysical methods are useful (i) in the preliminary phases of a hydrogeologic characterization to cover a large area in a time- and cost-effective manner to gain an understanding of the overall groundwater conditions before selecting locations for monitoring wells and piezometers, and (ii) as a means to interpolate between widely spaced, existing monitoring well and piezometer locations. Geophysical investigations

125 should always be complemented by direct observation of groundwater conditions by means of monitoring wells and piezometers. 7.6.2 Methods for Aquifer Characteristics Aquifer tests provide a means of determining the properties of water-bearing zones in the subsurface, including hydraulic conductivity, permeability, transmissivity, storage coefficient, and specific yield. Aquifer properties are commonly used in engineering models to analyze groundwater flow (i.e., seepage analyses). ASTM D4043 contains detailed guidance on selecting a type of aquifer test based on the specific hydrogeological conditions (e.g., confined, unconfined, leaky aquifer) at a site, along with references to specific ASTM guides and standards for each type of test. Two common types of aquifer tests—pumping and slug tests—are briefly described below. More information is provided in Ohio EPA (2018). Packer tests and piezo-dissipation tests using the CPTu are also included below. It may be beneficial to use laboratory measurements of hydraulic conductivity to augment results of field testing as laboratory tests may provide valuable information about the vertical component of hydraulic conductivity of aquifer (and aquitard) materials. However, because of the limited sample size, laboratory tests commonly miss secondary permeability features such as fractures and joints, and can greatly underestimate hydraulic conductivity. Therefore, field methods provide the best estimate of hydraulic conductivity in most cases. Laboratory tests for measuring hydraulic conductivity are discussed in Chapter 8. 7.6.2.1 Pumping Tests Pumping tests involve withdrawing water at a constant discharge rate from a control (or extraction) well and monitoring the drawdown in one or more observation wells at varying radial distances from the control well. The following factors need to be considered in designing a pumping test: • Design of the control and observation wells to ensure they are screened at the appropriate depths • Observation well locations relative to the control well • Pumping rate • Duration of the test • Measurement of the discharge rate at the control well • Measurement of the water level in the observation wells • Methods of data analysis The discharge rate should be measured frequently (e.g., 5-minute intervals) at the beginning of the test, and adjusted if necessary to achieve the desired constant rate. Once the discharge rate stabilizes, the frequency of measurement can be decreased (e.g., 2-hour intervals). Measurement of the water levels in the observations wells are typically conducted according to the schedule in Table 7-1. The duration of the test depends on the method used to interpret the results. Once the withdrawal phase of the pumping test is complete, the recovery of water levels in the observation wells should also be monitored using the same frequency of measurements shown in Table 7-1. Additional details on how to conduct a pumping test are described in ASTM D4050. Table 7-1. Typical water level measurement intervals for observation wells Elapsed Time Measurement Frequency 3 minutes 30 seconds 3 to 15 minutes 1 minute 15 to 60 minutes 5 minutes

126 Elapsed Time Measurement Frequency 1 to 2 hours 10 minutes 2 to 3 hours 20 minutes 3 to 15 hours 1 hour 15 to 60 hours 5 hours Source: ASTM D4050 Numerous methods are available to analyze data from pumping tests to calculate hydraulic conductivity, permeability, transmissivity, storage coefficient, and specific yield. The appropriate method depends on whether (i) the control well and observation wells fully or partially penetrate the aquifer; (ii) the aquifer is confined, leaky, or unconfined; and (iii) steady-state or unsteady-state (or nonequilibrium) flow conditions exist as shown in Table 7-2. A detailed presentation of these methods is beyond the scope of this manual, but Kruseman and de Ridder (1994) provide a comprehensive description and discussion of these methods and others that can be used to interpret pumping tests. In addition, ASTM D4043 provides detailed guidance on selecting appropriate interpretation method for pumping tests for a variety of situations as well as references to additional ASTM guides and standards for each method. Figure 7-4 shows the observed drawdown in four observation wells during a pumping test in a fully penetrating well in a confined aquifer. The calculated hydraulic conductivity is 0.30 cm/s, and the storage coefficient is 1.2 × 10-3. Table 7-2. Methods for interpreting pumping tests Well Configuration Aquifer Type Steady-State Flow Unsteady-State Flow Fully penetrating Confined Theis’s method Theis’s method Jacob’s method Leaky DeGlee’s method Hantush-Jacob’s method Walton’s method Hantush’s inflection-point method Hantush’s curve-fitting method Neuman-Witherspoon’s method Unconfined Theis-Dupuit’s method Neuman’s curve-fitting method Partially penetrating Confined Huisman’s correction method I and II Hantush’s modifications of the Theis and Jacob methods Leaky Huisman’s correction method I and II Week’s modifications of the Walton and Hantush curve-fitting methods Unconfined - Streltsova’s curve-fitting method Neuman’s curve-fitting method Source: Kruseman and de Ridder (1994)

127 Source: Geosyntec Consultants, Inc. Figure 7-4. Example results from pumping test in a confined aquifer 7.6.2.2 Slug Tests Slug (or instantaneous head) tests are the most common in situ tests conducted to estimate hydraulic conductivity of subsurface materials. Slug tests are conducted by introducing a sudden increase or decrease in hydraulic head in a control well and subsequently measuring the response of the water level in the same well. Slug tests require at most a few hours to conduct and are useful for making preliminary estimates of transmissivity and hydraulic conductivity before conducting a pumping test. Slug tests are best suited for formations that exhibit low hydraulic conductivity; the slug test is generally not suitable for fractured rocks. One disadvantage of a slug test compared to pumping tests is that the slug test involves a more localized area in the immediate vicinity of the control well, and thus the results may be influenced by the gravel pack, poor well development, or skin effects along the borehole wall. The sudden change in hydraulic head may be induced by (i) injecting or withdrawing a known amount of water into the control well, (ii) placing or removing a mechanical plug (i.e., slug) below the water level causing a change in the water level, or (iii) increasing or decreasing the air pressure in a closed control well. The response of the water level in the control well to the sudden change in head should be measured frequently during the initial portion of the test. For materials with high hydraulic conductivity, the water level will recover quickly, and it may be necessary to use an electrical pressure transducer to enable frequent measurements. Once the water level has recovered to approximately 60 to 80 percent of its pretest level, water level measurements can be made less often. Additional details on how to conduct a pumping test are described in ASTM D4044. There are several methods for calculating the transmissivity and hydraulic conductivity from the results of the slug test (Kruseman and de Ridder 1994). The methods developed by Cooper et al. (1967), Papadopulos et al. (1973), Kipp (1985), and van der Kamp (1976) are intended for use with a fully penetrating well in a confined aquifer. ASTM D4104, D5785, and D5881 describe these methods in detail. Bouwer and Rice (1976) and Bouwer (1989) developed a method for fully or partially penetrating wells in an unconfined aquifer, which is described in ASTM D5912. Figure 7-5 shows an example of the results from a slug test conducted in an unconfined aquifer. The hydraulic conductivity calculated from the slope of the line fit to the linear portion of the data is 1.5 × 10-2 cm/s. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.01 0.1 1 10 100 1000 Dr aw do w n (fe et ) Elapsed Time (minutes) MW-A (31 ft) MW-B (55 ft) MW-C (82 ft) MW-D (134 ft)

128 Source: Geosyntec Consultants, Inc. Figure 7-5. Example results from slug test in an unconfined aquifer 7.6.2.3 Piezo-dissipation Testing CPTu tests can be used to estimate the hydraulic conductivity of soils by measuring the dissipation with time of excess pore pressures induced by penetration. Chapters 5 and 9 provide detailed information on conducting and interpreting piezo-dissipation testing via the CPTu, respectively. 7.6.2.4 Packer Tests Packer tests are suitable for measuring the transmissivity and storage coefficient of rock formations with low hydraulic conductivity. The test is conducted by first lowering a device into the borehole and hydraulically inflating rubber packers above and below the depth range to be tested in order to seal off this range. Either (i) a constant pressure is applied to the water between the upper and lower packers and the resulting flow rate into the surrounding rock formation is measured (ASTM D4630) or (ii) a transient pressure pulse is applied to the water between the packers and the decay of the pulse with time is measured (ASTM D4631). The advantages of packer tests are that they are useful for testing rock masses with a wide range of hydraulic conductivities and can be conducted much more rapidly than pumping or slug tests in rock masses with low hydraulic conductivities. For the constant pressure test, the transmissivity and storage coefficient can be calculated by fitting the flow rate vs. time data using the method developed by Jacob and Lohman (1952). Similarly, for the pressure pulse test, the transmissivity and storage coefficient can be calculated by fitting the time-dependent decay of the pressure using the method developed by Bredehoeft and Papadopulos (1980). ASTM D4630 and D4631 provide additional details on these methods of interpretation.

129 Chapter 7 References Bouwer, H., 1989. “The Bouwer-Rice Slug Test—An Update.” Ground Water, Vol 27, No. 3, pp. 304–309. Bouwer, H., and R.C. Rice. 1976. “A Slug Test for Determining Hydraulic Conductivity of Unconfined Aquifers with Completely or Partially Penetrating Wells.” Water Resources Research, Vol 12, No. 3, pp. 423–423. Bredehoeft, J.D., and S.S. Papadopulos. 1980. “A Method for Determining the Hydraulic Properties of Tight Formations.” Water Resources Research, Vol 16, pp. 233–238. CalEPA. 2012. Guidelines for Planning and Implementing Groundwater Characterization of Contaminated Sites. California Environmental Protection Agency, Department of Toxic Substances Control, June. CalEPA. 2014. Well Design and Construction for Monitoring Groundwater at Contaminated Sites. California Environmental Protection Agency, Department of Toxic Substances Control, June. Cooper, H.H., Jr., J.D. Bredehoeft, and I.S. Papadopulos. 1967. “Response of a Finite-Diameter Well to an Instantaneous Charge of Water.” Water Resources Research, Vol 3, No. 1, pp. 263–269. FHWA. 2007. Geotechnical Technical Guidance Manual. Federal Highway Administration, Washington, DC, pp. 4–59. Jacob, C.E., and S.W. Lohman. 1952. “Non-Steady Flow to a Well of Constant Drawdown in an Extensive Aquifer.” Transactions American Geophysical Union, Vol 33, 1952, pp. 559–569. Kipp, K. L., Jr. 1985. “Type Curve Analysis of Inertial Effects in the Response of a Well to a Slug Test.” Water Resources Research, Vol 21, No. 9, 1985, pp. 1397–1408. Kruseman, G.P., and N.A. de Ridder. 1994. Analysis and Evaluation of Pumping Test Data. Second edition, Publication 47, International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands. Ohio EPA. 2018. Technical Guidance Manual for Hydrogeologic Investigations and Ground Water Monitoring. Ohio Environmental Protection Agency, Columbus, OH. Papadopulos, I.S., J.D. Bredehoeft, and H.H. Cooper, Jr. 1973. “On the Analysis of Slug Test Data.” Water Resources Research, Vol 9, No. 4, pp. 1087–1089. Sprecher, S.W. 2008. Installing Monitoring Wells in Soils (Version 1.0). National Soil Survey Center, Natural Resources Conservation Service, USDA, Lincoln, Nebraska. van der Kamp, G., 1976. “Determining Aquifer Transmissivity by Means of Well Response Tests: The Underdamped Case.” Water Resources Research, Vol 12, No. 1, pp. 71–77.