{"id":1828,"date":"2026-02-14T04:28:43","date_gmt":"2026-02-14T04:28:43","guid":{"rendered":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/chapter\/ch091-xhtml\/"},"modified":"2026-08-01T11:45:51","modified_gmt":"2026-08-01T11:45:51","slug":"box-2-estimating-storativity-and-specific-storage-ss","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/an-introduction-to-hydraulic-testing-in-hydrogeology\/chapter\/box-2-estimating-storativity-and-specific-storage-ss\/","title":{"raw":"Box 2 Estimating Storativity and Specific Storage (Ss)","rendered":"Box 2 Estimating Storativity and Specific Storage (Ss)"},"content":{"raw":"
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\r\n
\r\n
\r\n
\r\n\r\nSaturated geologic materials both transmit and store water. The storage capacity is defined by storativity. Excerpts from Woessner and Poeter (2020) that pertain to defining storativity and specific storage for unconfined and confined water bearing units are reproduced here for the reader\u2019s convenience. Tables of values are also provided in this Box.\r\n\r\n<\/div>\r\n
\r\n\r\nUnconfined Aquifer Storativity<\/strong>\r\n\r\n<\/div>\r\n
\r\n\r\nThe storativity for an unconfined aquifer is dominated by the gravity drainage term, specific yield ([latex]S_{y}[\/latex]). Specific yield reflects the volume of water that drains by gravity when the water table is lowered or fills with water when the water table is raised (Figure\u00a0Box\u00a02\u20111). The storativity ([latex]S[\/latex]) of an unconfined aquifer is composed of two components as shown in Equation\u00a0Box\u00a02\u20111.\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
<\/th>\r\n[latex]S_{unconfined} = S_{y} + S_{s}b_{average}[\/latex]<\/th>\r\n(Box\u00a02\u20111)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{unconfined}[\/latex]<\/th>\r\n=<\/th>\r\nstorativity of an unconfined aquifer (dimensionless)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
[latex]S_{y}[\/latex]<\/td>\r\n=<\/td>\r\nspecific yield (dimensionless)<\/td>\r\n<\/tr>\r\n
[latex]S_{s}[\/latex]<\/td>\r\n=<\/td>\r\nspecific storage (L\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
[latex]b_{average}[\/latex]<\/td>\r\n=<\/td>\r\naverage thickness before and after a water level change (L)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\n\"\"\r\n\r\n<\/div>\r\n
\r\n
\r\n\r\nFigure Box\u00a02\u20111 \u2011<\/strong> Schematic of components of storativity ([latex]S[\/latex]) of an unconfined aquifer. a) Illustration of the definition of the storage coefficient, which is the volume of water released or added to storage per unit change in head normal to the earth\u2019s surface per unit area. b) As the water table is lowered 1 meter, the volume of water released per cubic meter of unconfined aquifer is almost entirely accounted for by water that drains from pores as described by specific yield, [latex]S_{y}[\/latex]. The portion of the aquifer that underlies the drained portion also yields a small quantity of water (small blue arrows in black volume) in response to the reduced weight (water drained) of overlying water. The structure of the solids (black volume) compresses (reducing the volume of pore space) as indicated by the compressibility of the aquifer skeleton, [latex]\\alpha,\\ ([\/latex]jagged vertical line). In addition, there is a small expansion of the slightly compressible water, [latex]n\\beta[\/latex], (blue dot and white arrows). This property of the aquifer is called specific storage, [latex]S_{s}[\/latex]. The volume of water released from gravity drainage is orders of magnitude larger than the volume squeezed from the saturated portion of the aquifer, [latex]S_{s}b_{average}[\/latex]. As a result, [latex]S_{y}[\/latex] is used to represent unconfined aquifer storativity (Woessner & Poeter, 2020; gw-project.org<\/u><\/a>\u2197).\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\n\r\nThe specific yield is the volume of water that can drain by gravity from a saturated volume of material divided by the total volume of that material. The fractional volume of water that remains in the sample is called specific retention ([latex]S_{r}[\/latex]). It is assumed that, when water is added to storage and the water table rises, the pore spaces that fill already contain only the volume of water indicated by the value of specific retention.\r\n\r\n<\/div>\r\n
\r\n\r\nThe second term of Equation\u00a0Box\u00a02\u20111 is the product of the specific storage<\/u> ([latex]S_{s}[\/latex]) and the average of saturated thickness before and after drainage ([latex]b_{average}[\/latex]). The specific storage is defined as the volume of water that is released from (or added to) storage per unit volume of saturated material. When multiplied by the saturated thickness it accounts for a small amount of water that is released from a unit area of aquifer in response to the relief of stress on the material below the drained pores. It is usually orders of magnitude smaller than the specific yield and is ignored when characterizing storage properties of unconfined systems (Woessner & Poeter, 2020). Table\u00a03 in Woessner and Poeter (2020) is reproduced here to provide estimates of Sy<\/sub><\/em> for range of earth materials (Table\u00a0Box\u00a02\u20111).\r\n\r\n<\/div>\r\n
\r\n
\r\n
\r\n\r\nTable\u00a0Box\u00a02\u20111\u00a0\u2011\u00a0<\/strong>Summary of specific yield values of common earth materials compiled by Morris and Johnson (1967) with additional data from Rivera (2014), Freeze and Cherry (1979), and Domenico and Schwartz (1998) (from Woessner & Poeter, 2020). \u201cNA\u201d represents not available.\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Measurements of Specific Yield for Some Common Earth Materials (Percent)<\/strong><\/th>\r\n<\/tr>\r\n<\/thead>\r\n
Material<\/strong><\/td>\r\nNumber of Samples<\/strong><\/td>\r\nRange of Specific Yield Percent<\/strong><\/td>\r\n<\/tr>\r\n
Unconsolidated Sediments<\/strong><\/td>\r\n<\/tr>\r\n
Clay<\/td>\r\n27<\/td>\r\n1 \u2011 18<\/td>\r\n<\/tr>\r\n
Silt<\/td>\r\n299<\/td>\r\n1 \u2011 40<\/td>\r\n<\/tr>\r\n
Loess<\/td>\r\n5<\/td>\r\n14 \u2011 22<\/td>\r\n<\/tr>\r\n
Eolian sand<\/td>\r\n14<\/td>\r\n32 \u2011 47<\/td>\r\n<\/tr>\r\n
Sand (fine)<\/td>\r\n287<\/td>\r\n1 \u2011 46<\/td>\r\n<\/tr>\r\n
Sand (medium)<\/td>\r\n297<\/td>\r\n16 \u2011 46<\/td>\r\n<\/tr>\r\n
Sand (coarse)<\/td>\r\n143<\/td>\r\n18 \u2011 43<\/td>\r\n<\/tr>\r\n
Gravel (fine)<\/td>\r\n33<\/td>\r\n13 \u2011 40<\/td>\r\n<\/tr>\r\n
Gravel (medium)<\/td>\r\n13<\/td>\r\n17 \u2011 44<\/td>\r\n<\/tr>\r\n
Gravel (coarse)<\/td>\r\n9<\/td>\r\n13 \u2011 25<\/td>\r\n<\/tr>\r\n
Consolidated Sediments<\/strong><\/td>\r\n<\/tr>\r\n
Shale<\/td>\r\nNA<\/td>\r\n0.5 \u2011 5<\/td>\r\n<\/tr>\r\n
Siltstone<\/td>\r\n13<\/td>\r\n1 \u2011 33<\/td>\r\n<\/tr>\r\n
Sandstone (fine-grained)<\/td>\r\n47<\/td>\r\n2 \u2011 40<\/td>\r\n<\/tr>\r\n
Sandstone (medium-grained)<\/td>\r\n10<\/td>\r\n12 \u2011 41<\/td>\r\n<\/tr>\r\n
Limestone and dolomite<\/td>\r\n32<\/td>\r\n0 \u2011 36<\/td>\r\n<\/tr>\r\n
Karstic limestone<\/td>\r\nNA<\/td>\r\n2 \u2011 15<\/td>\r\n<\/tr>\r\n
Igneous and Metamorphic Rocks<\/strong><\/td>\r\n<\/tr>\r\n
Fresh granite and gneiss<\/td>\r\nNA<\/td>\r\n<0.1<\/td>\r\n<\/tr>\r\n
Weathered granite\/gneiss<\/td>\r\nNA<\/td>\r\n0.5 \u2011 5<\/td>\r\n<\/tr>\r\n
Fractured basalt<\/td>\r\nNA<\/td>\r\n2 \u2011 10<\/td>\r\n<\/tr>\r\n
Vesicular basalt<\/td>\r\nNA<\/td>\r\n5 \u2011 15<\/td>\r\n<\/tr>\r\n
Tuff<\/td>\r\n90<\/td>\r\n2 \u2011 47<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nConfined Storativity and Specific Storage<\/strong>\r\n\r\n<\/div>\r\n
\r\n\r\nConfined systems remain saturated as the potentiometric surface rises and falls. No gravity drainage occurs. Storativity of a confined system is composed of the water released by the compression and expansion of the unit framework and stored water (Figure Box\u00a02\u20112). The following material is reproduced from Woessner and Poeter (2020).\r\n\r\n<\/div>\r\n
\r\n\r\n\"\"\r\n\r\n<\/div>\r\n
\r\n
\r\n
\r\n\r\nFigure\u00a0Box\u00a02\u20112 \u2011<\/strong> Schematic of the parameters controlling storativity, [latex]S[\/latex], of a confined aquifer. The aquifer remains fully saturated as a unit change in the potentiometric surface occurs. Water is released from the entire saturated thickness, [latex]b[\/latex], of the aquifer by compression of the skeleton,\u00a0\ud835\udefc\u00a0(jagged line) and expansion of the pore water (blue arrows), [latex]n_{e}\\beta[\/latex] (Woessner & Poeter, 2020; gw-project.org<\/u><\/a>\u2197).\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n
\r\n\r\nWhen water is released from or added to storage the saturated geologic material either expands or contracts (changes in the effective stress (grain to grain) and\/or the water expands or contracts (changes in the pore water pressure). The storativity is defined as representing the volume of water released from or entered storage per unit change in head normal to the surface, per unit area. As the aquifer remains saturated no water gravity drains from the formation.\r\n\r\n<\/div>\r\n
\r\n\r\nThe confined storativity is defined as the specific storage multiplied by the unit\u2019s saturated thickness (Equation\u00a0Box\u00a02\u20112).\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
[latex]S_{confined} = S_{s}b = b\\rho g\\ \\left( \\alpha + n_{e}\\beta \\right)[\/latex]<\/th>\r\n(Box\u00a02\u20112)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{confined}[\/latex]<\/th>\r\n=<\/th>\r\nstorativity of an unconfined aquifer (dimensionless)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
[latex]S_{s}[\/latex]<\/td>\r\n=<\/td>\r\nspecific storage (L\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
[latex]b[\/latex]<\/td>\r\n=<\/td>\r\nunit saturated thickness (L)<\/td>\r\n<\/tr>\r\n
d<\/em><\/td>\r\n=<\/td>\r\ndensity of water (ML\u20113<\/sup>)<\/td>\r\n<\/tr>\r\n
g<\/em><\/td>\r\n=<\/td>\r\nacceleration due to gravity (LT\u20112<\/sup>)<\/td>\r\n<\/tr>\r\n
a<\/em><\/td>\r\n=<\/td>\r\ncompressibility of solid matrix (LT2<\/sup>M\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
ne<\/sub><\/em><\/td>\r\n=<\/td>\r\neffective porosity (dimensionless)<\/td>\r\n<\/tr>\r\n
[latex]\\beta[\/latex]<\/td>\r\n=<\/td>\r\ncompressibility of water (LT2<\/sup>M\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nThe specific storage, Ss<\/sub><\/em>, is defined as the volume of water released from or entered storage per unit change in head normal to the surface, per unit volume of material. The difference in the storativity and specific storage term is that storativity includes the storage properties of the entire thickness of the unit and the specific storage describes the properties of a unit volume of the material.\r\n\r\n<\/div>\r\n
\r\n\r\nComputing Specific Storage<\/strong>\r\n\r\n<\/div>\r\n
\r\n\r\nEquation\u00a0Box\u00a02\u20113 is used to compute specific storage when values of the compressibility of the materials making up confined system are measured or estimated from literature values.\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
<\/th>\r\n[latex]S_{s} = \\rho g\\ \\left( \\alpha + n_{e}\\beta \\right)[\/latex]<\/th>\r\n(Box\u00a02\u20113)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{s}[\/latex]<\/th>\r\n=<\/em><\/th>\r\nspecific storage (L\u20111<\/sup>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
[latex]\\alpha[\/latex]<\/td>\r\n=<\/em><\/td>\r\ncompressibility of the material solid structure (LT2<\/sup>M\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
[latex]n_{e}[\/latex]<\/td>\r\n=<\/em><\/td>\r\neffective porosity (dimensionless)<\/td>\r\n<\/tr>\r\n
\u03b2<\/em><\/td>\r\n=<\/em><\/td>\r\ncompressibility of water (LT2<\/sup>M\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
\u03c1<\/em><\/td>\r\n=<\/em><\/td>\r\ndensity of water (ML\u20113<\/sup>)<\/td>\r\n<\/tr>\r\n
g<\/em><\/td>\r\n=<\/em><\/td>\r\nacceleration due to gravity (LT\u20112<\/sup>)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nDomenico and Mifflin (1965) presented a table of vertical compressibility, \u03b1<\/em>, for geologic materials. This information can be used with Equation\u00a0Box\u00a02\u20113 to compute specific storage for various confined materials. Dunn (2023) reports that the specific storage values can also be computed assuming water is incompressible (\u03b2<\/em>=0).\r\n\r\n<\/div>\r\n
\r\n\r\nDomenico and Mifflin (1965) noted that the specific storage can be approximated by Equations Box\u00a02\u20114 through Box\u00a02\u20116. Parameters such as vertical compressibility, the bulk modulus of compression, and coefficient of consolidation are derived from laboratory tests or the literature. Box\u00a09 briefly describes laboratory triaxial and consolidation testing methods used to obtain these parameters.\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
<\/th>\r\nSs<\/sub>= (av<\/sub>\u03b3w<\/sub>)\/(1+e)<\/em><\/th>\r\n(Box\u00a02\u20114)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{s}[\/latex]<\/th>\r\n=<\/em><\/th>\r\nspecific storage (L\u20111<\/sup>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
[latex]\\alpha[\/latex]<\/td>\r\n=<\/em><\/td>\r\ncompressibility of the material solid structure (LT2<\/sup>M\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
\u03b3w<\/sub><\/em><\/td>\r\n=<\/em><\/td>\r\nspecific weight of water (ML\u20112<\/sup>T\u20112<\/sup>)<\/td>\r\n<\/tr>\r\n
e<\/em><\/td>\r\n=<\/em><\/td>\r\nvoid ratio (dimensionless)<\/td>\r\n<\/tr>\r\n
<\/td>\r\nSs<\/sub> =\u03b3w<\/sub>\/Ec<\/sub><\/em><\/td>\r\n(Box\u00a02\u20115)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{s}[\/latex]<\/th>\r\n=<\/em><\/th>\r\nspecific storage (L\u20111<\/sup>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
\u03b3w<\/sub><\/em><\/td>\r\n=<\/em><\/td>\r\nspecific weight of water (ML\u20112<\/sup>T\u20112<\/sup>)<\/td>\r\n<\/tr>\r\n
Ec<\/sub><\/em><\/td>\r\n=<\/em><\/td>\r\nbulk modulus of compression (ML\u20111<\/sup>T\u20112<\/sup>)<\/td>\r\n<\/tr>\r\n
<\/td>\r\nSs<\/sub> = Kv<\/sub>\/cv<\/sub><\/em><\/td>\r\n(Box\u00a02\u20116)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nwhere:\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n
[latex]S_{s}[\/latex]<\/th>\r\n=<\/em><\/th>\r\nspecific storage (L\u20111<\/sup>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
Kv<\/sub><\/em><\/td>\r\n=<\/em><\/td>\r\nvertical permeability (LT\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n
cv<\/sub><\/em><\/td>\r\n=<\/em><\/td>\r\ncoefficient of vertical consolidation (L2<\/sup>T\u20111<\/sup>)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nWe modified Table\u00a01 of Domenico and Mifflin (1965) to report values of specific storage in units of m\u20111<\/sup> (Table\u00a0Box\u00a02\u20112). Two values of specific storage are shown, one computed assuming water is incompressible and the last column accounting for the compressibility of water, \u03b3ne<\/sub>B<\/em>, given an assumed porosity value (Woessner & Poeter, 2020). Table\u00a0Box\u00a02\u20112 shows that including the compressibility of water in the calculation of Ss<\/sub><\/em> has minimal influence on specific storage values (i.e., differences occur in the 3rd significant figure and beyond). Dunn (2023) also provides a good discussion of specific storage (https:\/\/www.dunnhydrogeo.com\/home\/aquifer-storativity-t<\/u><\/a>\u2197).\r\n\r\n<\/div>\r\n
\r\n\r\nTable\u00a0Box\u00a02\u20112<\/strong> Material properties including, geologic unit skeletal compressibility (\u03b1), assumed values of effective porosity (ne<\/sub>), an assumed value for the specific weight of water \u03b3 as 9,810 kgm\u20112<\/sup>s\u20112<\/sup>, and calculated values of Ss<\/sub> with and without consideration of the compressibility of water (\u03b2 = 4.3x10\u201110<\/sup> ms2<\/sup>kg\u20111<\/sup>). Porosity values are based on material type and have little effect on the calculation of Ss<\/sub> due to the low compressibility of water (modified from Domenico & Mifflin (1965) and Dunn (2023) at the website: https:\/\/www.dunnhydrogeo.com\/home\/aquifer-storativity-t<\/u><\/a>\u2197).\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Material<\/th>\r\n\u03b1<\/em> range<\/th>\r\nSs<\/sub><\/em> = \u03b3\u03b1<\/em><\/th>\r\nAssumed ne<\/sub><\/em><\/th>\r\nSs<\/sub><\/em> = \u03b3<\/em>(\u03b1<\/em>+ne<\/sub>\u03b2<\/em>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
<\/td>\r\nms2<\/sup>kg\u20111<\/sup><\/td>\r\nm\u20111<\/sup><\/td>\r\ndimensionless<\/td>\r\nm\u20111<\/sup><\/td>\r\n<\/tr>\r\n
Plastic Clay<\/td>\r\n2.0x10\u20116<\/sup><\/td>\r\n1.96x10\u20112<\/sup><\/td>\r\n0.6<\/td>\r\n1.96x10\u20112<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n2.5x10\u20117<\/sup><\/td>\r\n2.45x10\u20113<\/sup><\/td>\r\n0.6<\/td>\r\n2.46x10\u20113<\/sup><\/td>\r\n<\/tr>\r\n
Stiff Clay<\/td>\r\n2.5x10\u20117<\/sup><\/td>\r\n2.45x10\u20113<\/sup><\/td>\r\n0.5<\/td>\r\n2.45x10\u20113<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n1.3x10\u20117<\/sup><\/td>\r\n1.28x10\u20113<\/sup><\/td>\r\n0.5<\/td>\r\n1.28x10\u20113<\/sup><\/td>\r\n<\/tr>\r\n
Medium Hard Clay<\/td>\r\n1.3x10\u20117<\/sup><\/td>\r\n1.28x10\u20113<\/sup><\/td>\r\n0.4<\/td>\r\n1.28x10\u20113<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n6.8x10\u20118<\/sup><\/td>\r\n6.67x10\u20114<\/sup><\/td>\r\n0.4<\/td>\r\n6.69x10\u20114<\/sup><\/td>\r\n<\/tr>\r\n
Loose Sand<\/td>\r\n1.0x10\u20117<\/sup><\/td>\r\n9.81x10\u20114<\/sup><\/td>\r\n0.35<\/td>\r\n9.82x10\u20114<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n5.1x10\u20118<\/sup><\/td>\r\n5.00x10\u20114<\/sup><\/td>\r\n0.35<\/td>\r\n5.02x10\u20114<\/sup><\/td>\r\n<\/tr>\r\n
Dense Sand<\/td>\r\n2.0x10\u20118<\/sup><\/td>\r\n1.96x10\u20114<\/sup><\/td>\r\n0.3<\/td>\r\n1.97x10\u20114<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n1.3x10\u20118<\/sup><\/td>\r\n1.28x10\u20114<\/sup><\/td>\r\n0.3<\/td>\r\n1.29x10\u20114<\/sup><\/td>\r\n<\/tr>\r\n
Dense Sandy Gravel<\/td>\r\n1.0x10\u20118<\/sup><\/td>\r\n9.81x10\u20115<\/sup><\/td>\r\n0.15<\/td>\r\n9.87x10\u20115<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n5.1x10\u20119<\/sup><\/td>\r\n5.00x10\u20115<\/sup><\/td>\r\n0.15<\/td>\r\n5.07x10\u20115<\/sup><\/td>\r\n<\/tr>\r\n
Rock fissured\/jointed<\/td>\r\n6.8x10\u20119<\/sup><\/td>\r\n6.67x10\u20115<\/sup><\/td>\r\n0.01<\/td>\r\n6.68x10\u20115<\/sup><\/td>\r\n<\/tr>\r\n
<\/td>\r\n3.3x10\u201110<\/sup><\/td>\r\n3.24x10\u20116<\/sup><\/td>\r\n0.01<\/td>\r\n3.28x10\u20116<\/sup><\/td>\r\n<\/tr>\r\n
Rock sound<\/td>\r\n3.3x10\u201110<\/sup><\/td>\r\n3.24x10\u20116<\/sup><\/td>\r\n0.0001<\/td>\r\n3.24x10\u20116<\/sup><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nAnother common method used to estimate S<\/em> for confined aquifers was proposed by Lohman (1972). He noted that storativity of confined aquifers typically range from 0.00001 to 0.001 (1x[latex]10^{- 5}[\/latex] to 1x[latex]10^{- 3}[\/latex]). He suggests the storativity for a confined aquifer can be approximated as 0.000003\/m times the aquifer thickness in meters. This approximation basically results in using 0.000003\/m as an estimate of the specific storage for all confined earth materials. Using his approach, estimated storativity values are in the 10\u20115<\/sup> to 10\u20114<\/sup> range when the thickness of rock based confined systems are 10\u2019s to 100\u2019s of meters. Lohman\u2019s (1972) approach provides a poor estimate of specific storage when aquifer or aquitard materials are something other than hard rock. Thus, specific storage estimates based on Table\u00a0Box\u00a02\u20112 should be used with aquifer thicknesses to estimate storativity values for confined systems when pumping test computed values are not available.\r\n\r\n<\/div>\r\n
\r\n\r\nReturn to where text first links to Box\u00a02<\/a>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
<\/div>\r\n<\/div>\r\n<\/div>","rendered":"
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Saturated geologic materials both transmit and store water. The storage capacity is defined by storativity. Excerpts from Woessner and Poeter (2020) that pertain to defining storativity and specific storage for unconfined and confined water bearing units are reproduced here for the reader\u2019s convenience. Tables of values are also provided in this Box.<\/p>\n<\/div>\n

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Unconfined Aquifer Storativity<\/strong><\/p>\n<\/div>\n

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The storativity for an unconfined aquifer is dominated by the gravity drainage term, specific yield ([latex]S_{y}[\/latex]). Specific yield reflects the volume of water that drains by gravity when the water table is lowered or fills with water when the water table is raised (Figure\u00a0Box\u00a02\u20111). The storativity ([latex]S[\/latex]) of an unconfined aquifer is composed of two components as shown in Equation\u00a0Box\u00a02\u20111.<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n
<\/th>\n[latex]S_{unconfined} = S_{y} + S_{s}b_{average}[\/latex]<\/th>\n(Box\u00a02\u20111)<\/th>\n<\/tr>\n<\/thead>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n
[latex]S_{unconfined}[\/latex]<\/th>\n=<\/th>\nstorativity of an unconfined aquifer (dimensionless)<\/th>\n<\/tr>\n<\/thead>\n
[latex]S_{y}[\/latex]<\/td>\n=<\/td>\nspecific yield (dimensionless)<\/td>\n<\/tr>\n
[latex]S_{s}[\/latex]<\/td>\n=<\/td>\nspecific storage (L\u20111<\/sup>)<\/td>\n<\/tr>\n
[latex]b_{average}[\/latex]<\/td>\n=<\/td>\naverage thickness before and after a water level change (L)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\"\"<\/p>\n<\/div>\n

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Figure Box\u00a02\u20111 \u2011<\/strong> Schematic of components of storativity ([latex]S[\/latex]) of an unconfined aquifer. a) Illustration of the definition of the storage coefficient, which is the volume of water released or added to storage per unit change in head normal to the earth\u2019s surface per unit area. b) As the water table is lowered 1 meter, the volume of water released per cubic meter of unconfined aquifer is almost entirely accounted for by water that drains from pores as described by specific yield, [latex]S_{y}[\/latex]. The portion of the aquifer that underlies the drained portion also yields a small quantity of water (small blue arrows in black volume) in response to the reduced weight (water drained) of overlying water. The structure of the solids (black volume) compresses (reducing the volume of pore space) as indicated by the compressibility of the aquifer skeleton, [latex]\\alpha,\\ ([\/latex]jagged vertical line). In addition, there is a small expansion of the slightly compressible water, [latex]n\\beta[\/latex], (blue dot and white arrows). This property of the aquifer is called specific storage, [latex]S_{s}[\/latex]. The volume of water released from gravity drainage is orders of magnitude larger than the volume squeezed from the saturated portion of the aquifer, [latex]S_{s}b_{average}[\/latex]. As a result, [latex]S_{y}[\/latex] is used to represent unconfined aquifer storativity (Woessner & Poeter, 2020; gw-project.org<\/u><\/a>\u2197).<\/p>\n<\/div>\n<\/div>\n

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The specific yield is the volume of water that can drain by gravity from a saturated volume of material divided by the total volume of that material. The fractional volume of water that remains in the sample is called specific retention ([latex]S_{r}[\/latex]). It is assumed that, when water is added to storage and the water table rises, the pore spaces that fill already contain only the volume of water indicated by the value of specific retention.<\/p>\n<\/div>\n

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The second term of Equation\u00a0Box\u00a02\u20111 is the product of the specific storage<\/u> ([latex]S_{s}[\/latex]) and the average of saturated thickness before and after drainage ([latex]b_{average}[\/latex]). The specific storage is defined as the volume of water that is released from (or added to) storage per unit volume of saturated material. When multiplied by the saturated thickness it accounts for a small amount of water that is released from a unit area of aquifer in response to the relief of stress on the material below the drained pores. It is usually orders of magnitude smaller than the specific yield and is ignored when characterizing storage properties of unconfined systems (Woessner & Poeter, 2020). Table\u00a03 in Woessner and Poeter (2020) is reproduced here to provide estimates of Sy<\/sub><\/em> for range of earth materials (Table\u00a0Box\u00a02\u20111).<\/p>\n<\/div>\n

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Table\u00a0Box\u00a02\u20111\u00a0\u2011\u00a0<\/strong>Summary of specific yield values of common earth materials compiled by Morris and Johnson (1967) with additional data from Rivera (2014), Freeze and Cherry (1979), and Domenico and Schwartz (1998) (from Woessner & Poeter, 2020). \u201cNA\u201d represents not available.<\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Measurements of Specific Yield for Some Common Earth Materials (Percent)<\/strong><\/th>\n<\/tr>\n<\/thead>\n
Material<\/strong><\/td>\nNumber of Samples<\/strong><\/td>\nRange of Specific Yield Percent<\/strong><\/td>\n<\/tr>\n
Unconsolidated Sediments<\/strong><\/td>\n<\/tr>\n
Clay<\/td>\n27<\/td>\n1 \u2011 18<\/td>\n<\/tr>\n
Silt<\/td>\n299<\/td>\n1 \u2011 40<\/td>\n<\/tr>\n
Loess<\/td>\n5<\/td>\n14 \u2011 22<\/td>\n<\/tr>\n
Eolian sand<\/td>\n14<\/td>\n32 \u2011 47<\/td>\n<\/tr>\n
Sand (fine)<\/td>\n287<\/td>\n1 \u2011 46<\/td>\n<\/tr>\n
Sand (medium)<\/td>\n297<\/td>\n16 \u2011 46<\/td>\n<\/tr>\n
Sand (coarse)<\/td>\n143<\/td>\n18 \u2011 43<\/td>\n<\/tr>\n
Gravel (fine)<\/td>\n33<\/td>\n13 \u2011 40<\/td>\n<\/tr>\n
Gravel (medium)<\/td>\n13<\/td>\n17 \u2011 44<\/td>\n<\/tr>\n
Gravel (coarse)<\/td>\n9<\/td>\n13 \u2011 25<\/td>\n<\/tr>\n
Consolidated Sediments<\/strong><\/td>\n<\/tr>\n
Shale<\/td>\nNA<\/td>\n0.5 \u2011 5<\/td>\n<\/tr>\n
Siltstone<\/td>\n13<\/td>\n1 \u2011 33<\/td>\n<\/tr>\n
Sandstone (fine-grained)<\/td>\n47<\/td>\n2 \u2011 40<\/td>\n<\/tr>\n
Sandstone (medium-grained)<\/td>\n10<\/td>\n12 \u2011 41<\/td>\n<\/tr>\n
Limestone and dolomite<\/td>\n32<\/td>\n0 \u2011 36<\/td>\n<\/tr>\n
Karstic limestone<\/td>\nNA<\/td>\n2 \u2011 15<\/td>\n<\/tr>\n
Igneous and Metamorphic Rocks<\/strong><\/td>\n<\/tr>\n
Fresh granite and gneiss<\/td>\nNA<\/td>\n<0.1<\/td>\n<\/tr>\n
Weathered granite\/gneiss<\/td>\nNA<\/td>\n0.5 \u2011 5<\/td>\n<\/tr>\n
Fractured basalt<\/td>\nNA<\/td>\n2 \u2011 10<\/td>\n<\/tr>\n
Vesicular basalt<\/td>\nNA<\/td>\n5 \u2011 15<\/td>\n<\/tr>\n
Tuff<\/td>\n90<\/td>\n2 \u2011 47<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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Confined Storativity and Specific Storage<\/strong><\/p>\n<\/div>\n

\n

Confined systems remain saturated as the potentiometric surface rises and falls. No gravity drainage occurs. Storativity of a confined system is composed of the water released by the compression and expansion of the unit framework and stored water (Figure Box\u00a02\u20112). The following material is reproduced from Woessner and Poeter (2020).<\/p>\n<\/div>\n

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Figure\u00a0Box\u00a02\u20112 \u2011<\/strong> Schematic of the parameters controlling storativity, [latex]S[\/latex], of a confined aquifer. The aquifer remains fully saturated as a unit change in the potentiometric surface occurs. Water is released from the entire saturated thickness, [latex]b[\/latex], of the aquifer by compression of the skeleton,\u00a0\ud835\udefc\u00a0(jagged line) and expansion of the pore water (blue arrows), [latex]n_{e}\\beta[\/latex] (Woessner & Poeter, 2020; gw-project.org<\/u><\/a>\u2197).<\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n

\n

When water is released from or added to storage the saturated geologic material either expands or contracts (changes in the effective stress (grain to grain) and\/or the water expands or contracts (changes in the pore water pressure). The storativity is defined as representing the volume of water released from or entered storage per unit change in head normal to the surface, per unit area. As the aquifer remains saturated no water gravity drains from the formation.<\/p>\n<\/div>\n

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The confined storativity is defined as the specific storage multiplied by the unit\u2019s saturated thickness (Equation\u00a0Box\u00a02\u20112).<\/p>\n<\/div>\n\n\n\n<\/colgroup>\n\n\n
[latex]S_{confined} = S_{s}b = b\\rho g\\ \\left( \\alpha + n_{e}\\beta \\right)[\/latex]<\/th>\n(Box\u00a02\u20112)<\/th>\n<\/tr>\n<\/thead>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n\n\n\n\n
[latex]S_{confined}[\/latex]<\/th>\n=<\/th>\nstorativity of an unconfined aquifer (dimensionless)<\/th>\n<\/tr>\n<\/thead>\n
[latex]S_{s}[\/latex]<\/td>\n=<\/td>\nspecific storage (L\u20111<\/sup>)<\/td>\n<\/tr>\n
[latex]b[\/latex]<\/td>\n=<\/td>\nunit saturated thickness (L)<\/td>\n<\/tr>\n
d<\/em><\/td>\n=<\/td>\ndensity of water (ML\u20113<\/sup>)<\/td>\n<\/tr>\n
g<\/em><\/td>\n=<\/td>\nacceleration due to gravity (LT\u20112<\/sup>)<\/td>\n<\/tr>\n
a<\/em><\/td>\n=<\/td>\ncompressibility of solid matrix (LT2<\/sup>M\u20111<\/sup>)<\/td>\n<\/tr>\n
ne<\/sub><\/em><\/td>\n=<\/td>\neffective porosity (dimensionless)<\/td>\n<\/tr>\n
[latex]\\beta[\/latex]<\/td>\n=<\/td>\ncompressibility of water (LT2<\/sup>M\u20111<\/sup>)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

The specific storage, Ss<\/sub><\/em>, is defined as the volume of water released from or entered storage per unit change in head normal to the surface, per unit volume of material. The difference in the storativity and specific storage term is that storativity includes the storage properties of the entire thickness of the unit and the specific storage describes the properties of a unit volume of the material.<\/p>\n<\/div>\n

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Computing Specific Storage<\/strong><\/p>\n<\/div>\n

\n

Equation\u00a0Box\u00a02\u20113 is used to compute specific storage when values of the compressibility of the materials making up confined system are measured or estimated from literature values.<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n
<\/th>\n[latex]S_{s} = \\rho g\\ \\left( \\alpha + n_{e}\\beta \\right)[\/latex]<\/th>\n(Box\u00a02\u20113)<\/th>\n<\/tr>\n<\/thead>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n\n\n
[latex]S_{s}[\/latex]<\/th>\n=<\/em><\/th>\nspecific storage (L\u20111<\/sup>)<\/th>\n<\/tr>\n<\/thead>\n
[latex]\\alpha[\/latex]<\/td>\n=<\/em><\/td>\ncompressibility of the material solid structure (LT2<\/sup>M\u20111<\/sup>)<\/td>\n<\/tr>\n
[latex]n_{e}[\/latex]<\/td>\n=<\/em><\/td>\neffective porosity (dimensionless)<\/td>\n<\/tr>\n
\u03b2<\/em><\/td>\n=<\/em><\/td>\ncompressibility of water (LT2<\/sup>M\u20111<\/sup>)<\/td>\n<\/tr>\n
\u03c1<\/em><\/td>\n=<\/em><\/td>\ndensity of water (ML\u20113<\/sup>)<\/td>\n<\/tr>\n
g<\/em><\/td>\n=<\/em><\/td>\nacceleration due to gravity (LT\u20112<\/sup>)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

Domenico and Mifflin (1965) presented a table of vertical compressibility, \u03b1<\/em>, for geologic materials. This information can be used with Equation\u00a0Box\u00a02\u20113 to compute specific storage for various confined materials. Dunn (2023) reports that the specific storage values can also be computed assuming water is incompressible (\u03b2<\/em>=0).<\/p>\n<\/div>\n

\n

Domenico and Mifflin (1965) noted that the specific storage can be approximated by Equations Box\u00a02\u20114 through Box\u00a02\u20116. Parameters such as vertical compressibility, the bulk modulus of compression, and coefficient of consolidation are derived from laboratory tests or the literature. Box\u00a09 briefly describes laboratory triaxial and consolidation testing methods used to obtain these parameters.<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n
<\/th>\nSs<\/sub>= (av<\/sub>\u03b3w<\/sub>)\/(1+e)<\/em><\/th>\n(Box\u00a02\u20114)<\/th>\n<\/tr>\n<\/thead>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n\n
[latex]S_{s}[\/latex]<\/th>\n=<\/em><\/th>\nspecific storage (L\u20111<\/sup>)<\/th>\n<\/tr>\n<\/thead>\n
[latex]\\alpha[\/latex]<\/td>\n=<\/em><\/td>\ncompressibility of the material solid structure (LT2<\/sup>M\u20111<\/sup>)<\/td>\n<\/tr>\n
\u03b3w<\/sub><\/em><\/td>\n=<\/em><\/td>\nspecific weight of water (ML\u20112<\/sup>T\u20112<\/sup>)<\/td>\n<\/tr>\n
e<\/em><\/td>\n=<\/em><\/td>\nvoid ratio (dimensionless)<\/td>\n<\/tr>\n
<\/td>\nSs<\/sub> =\u03b3w<\/sub>\/Ec<\/sub><\/em><\/td>\n(Box\u00a02\u20115)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n
[latex]S_{s}[\/latex]<\/th>\n=<\/em><\/th>\nspecific storage (L\u20111<\/sup>)<\/th>\n<\/tr>\n<\/thead>\n
\u03b3w<\/sub><\/em><\/td>\n=<\/em><\/td>\nspecific weight of water (ML\u20112<\/sup>T\u20112<\/sup>)<\/td>\n<\/tr>\n
Ec<\/sub><\/em><\/td>\n=<\/em><\/td>\nbulk modulus of compression (ML\u20111<\/sup>T\u20112<\/sup>)<\/td>\n<\/tr>\n
<\/td>\nSs<\/sub> = Kv<\/sub>\/cv<\/sub><\/em><\/td>\n(Box\u00a02\u20116)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

where:<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n
[latex]S_{s}[\/latex]<\/th>\n=<\/em><\/th>\nspecific storage (L\u20111<\/sup>)<\/th>\n<\/tr>\n<\/thead>\n
Kv<\/sub><\/em><\/td>\n=<\/em><\/td>\nvertical permeability (LT\u20111<\/sup>)<\/td>\n<\/tr>\n
cv<\/sub><\/em><\/td>\n=<\/em><\/td>\ncoefficient of vertical consolidation (L2<\/sup>T\u20111<\/sup>)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

We modified Table\u00a01 of Domenico and Mifflin (1965) to report values of specific storage in units of m\u20111<\/sup> (Table\u00a0Box\u00a02\u20112). Two values of specific storage are shown, one computed assuming water is incompressible and the last column accounting for the compressibility of water, \u03b3ne<\/sub>B<\/em>, given an assumed porosity value (Woessner & Poeter, 2020). Table\u00a0Box\u00a02\u20112 shows that including the compressibility of water in the calculation of Ss<\/sub><\/em> has minimal influence on specific storage values (i.e., differences occur in the 3rd significant figure and beyond). Dunn (2023) also provides a good discussion of specific storage (https:\/\/www.dunnhydrogeo.com\/home\/aquifer-storativity-t<\/u><\/a>\u2197).<\/p>\n<\/div>\n

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Table\u00a0Box\u00a02\u20112<\/strong> Material properties including, geologic unit skeletal compressibility (\u03b1), assumed values of effective porosity (ne<\/sub>), an assumed value for the specific weight of water \u03b3 as 9,810 kgm\u20112<\/sup>s\u20112<\/sup>, and calculated values of Ss<\/sub> with and without consideration of the compressibility of water (\u03b2 = 4.3×10\u201110<\/sup> ms2<\/sup>kg\u20111<\/sup>). Porosity values are based on material type and have little effect on the calculation of Ss<\/sub> due to the low compressibility of water (modified from Domenico & Mifflin (1965) and Dunn (2023) at the website: https:\/\/www.dunnhydrogeo.com\/home\/aquifer-storativity-t<\/u><\/a>\u2197).<\/p>\n<\/div>\n\n\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Material<\/th>\n\u03b1<\/em> range<\/th>\nSs<\/sub><\/em> = \u03b3\u03b1<\/em><\/th>\nAssumed ne<\/sub><\/em><\/th>\nSs<\/sub><\/em> = \u03b3<\/em>(\u03b1<\/em>+ne<\/sub>\u03b2<\/em>)<\/th>\n<\/tr>\n<\/thead>\n
<\/td>\nms2<\/sup>kg\u20111<\/sup><\/td>\nm\u20111<\/sup><\/td>\ndimensionless<\/td>\nm\u20111<\/sup><\/td>\n<\/tr>\n
Plastic Clay<\/td>\n2.0×10\u20116<\/sup><\/td>\n1.96×10\u20112<\/sup><\/td>\n0.6<\/td>\n1.96×10\u20112<\/sup><\/td>\n<\/tr>\n
<\/td>\n2.5×10\u20117<\/sup><\/td>\n2.45×10\u20113<\/sup><\/td>\n0.6<\/td>\n2.46×10\u20113<\/sup><\/td>\n<\/tr>\n
Stiff Clay<\/td>\n2.5×10\u20117<\/sup><\/td>\n2.45×10\u20113<\/sup><\/td>\n0.5<\/td>\n2.45×10\u20113<\/sup><\/td>\n<\/tr>\n
<\/td>\n1.3×10\u20117<\/sup><\/td>\n1.28×10\u20113<\/sup><\/td>\n0.5<\/td>\n1.28×10\u20113<\/sup><\/td>\n<\/tr>\n
Medium Hard Clay<\/td>\n1.3×10\u20117<\/sup><\/td>\n1.28×10\u20113<\/sup><\/td>\n0.4<\/td>\n1.28×10\u20113<\/sup><\/td>\n<\/tr>\n
<\/td>\n6.8×10\u20118<\/sup><\/td>\n6.67×10\u20114<\/sup><\/td>\n0.4<\/td>\n6.69×10\u20114<\/sup><\/td>\n<\/tr>\n
Loose Sand<\/td>\n1.0×10\u20117<\/sup><\/td>\n9.81×10\u20114<\/sup><\/td>\n0.35<\/td>\n9.82×10\u20114<\/sup><\/td>\n<\/tr>\n
<\/td>\n5.1×10\u20118<\/sup><\/td>\n5.00×10\u20114<\/sup><\/td>\n0.35<\/td>\n5.02×10\u20114<\/sup><\/td>\n<\/tr>\n
Dense Sand<\/td>\n2.0×10\u20118<\/sup><\/td>\n1.96×10\u20114<\/sup><\/td>\n0.3<\/td>\n1.97×10\u20114<\/sup><\/td>\n<\/tr>\n
<\/td>\n1.3×10\u20118<\/sup><\/td>\n1.28×10\u20114<\/sup><\/td>\n0.3<\/td>\n1.29×10\u20114<\/sup><\/td>\n<\/tr>\n
Dense Sandy Gravel<\/td>\n1.0×10\u20118<\/sup><\/td>\n9.81×10\u20115<\/sup><\/td>\n0.15<\/td>\n9.87×10\u20115<\/sup><\/td>\n<\/tr>\n
<\/td>\n5.1×10\u20119<\/sup><\/td>\n5.00×10\u20115<\/sup><\/td>\n0.15<\/td>\n5.07×10\u20115<\/sup><\/td>\n<\/tr>\n
Rock fissured\/jointed<\/td>\n6.8×10\u20119<\/sup><\/td>\n6.67×10\u20115<\/sup><\/td>\n0.01<\/td>\n6.68×10\u20115<\/sup><\/td>\n<\/tr>\n
<\/td>\n3.3×10\u201110<\/sup><\/td>\n3.24×10\u20116<\/sup><\/td>\n0.01<\/td>\n3.28×10\u20116<\/sup><\/td>\n<\/tr>\n
Rock sound<\/td>\n3.3×10\u201110<\/sup><\/td>\n3.24×10\u20116<\/sup><\/td>\n0.0001<\/td>\n3.24×10\u20116<\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

Another common method used to estimate S<\/em> for confined aquifers was proposed by Lohman (1972). He noted that storativity of confined aquifers typically range from 0.00001 to 0.001 (1x[latex]10^{- 5}[\/latex] to 1x[latex]10^{- 3}[\/latex]). He suggests the storativity for a confined aquifer can be approximated as 0.000003\/m times the aquifer thickness in meters. This approximation basically results in using 0.000003\/m as an estimate of the specific storage for all confined earth materials. Using his approach, estimated storativity values are in the 10\u20115<\/sup> to 10\u20114<\/sup> range when the thickness of rock based confined systems are 10\u2019s to 100\u2019s of meters. Lohman\u2019s (1972) approach provides a poor estimate of specific storage when aquifer or aquitard materials are something other than hard rock. Thus, specific storage estimates based on Table\u00a0Box\u00a02\u20112 should be used with aquifer thicknesses to estimate storativity values for confined systems when pumping test computed values are not available.<\/p>\n<\/div>\n

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Return to where text first links to Box\u00a02<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n

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