1. Correlating Hydraulic Conductivity Values to Geologic
Well Log Descriptions of Licking County, Ohio
AquiferType
Gravel
Sand-&-Gravel
Clay-&-Gravel
Clay
Claywash
Sand
Clay,Sand&Gravel
Limestone
Bedrock
Sandstone
Shale-&-Sandstone
Shale
Siltstone
David H. Scott, William A. Avalon and Jonathan Levy
Department of Geology and Environmental Earth Science, Miami University
Well Construction & Design
Hydraulic Conductivities Map
Aquifer Type MapIntroduction Results
Conclusion
Bibliography
Data & Results
Figure 1: Sample Driller Report & Well Diagram
Well design is determined by geological site selection. A typical design consists of a casing to
position the well and screen to capture water and prevent sediment from entering the well.
Figure 3: Geology-Aquifer Type Map
Two major aquifer types found in Licking County are sandstone and sand-&-gravel. Individual well sites are indicated
and kriging tools were used to represent generalized geologies.
Figure 4: Hydraulic Conductivity Map
Estimate hydraulic conductivities in ft/d throughout Licking County based on aquifer draw-down pumping tests.
Highly permeable zones correspond to the occurrence of sand-&-gravel (Figure 3).
Table 1: Summary Table
Hydraulic conductivity data from driller reports in Licking Co., Ohio, organized
by aquifer type and order from largest-to-smallest geometric mean values.
Table 2: Aquifer Type Significance Table
Aquifer types with bars indicating no significant difference between their
geometric means at a p-value = 0.05.
Figure 5: Major Aquifer Types in Ohio
The major aquifer types within Licking Co. published by the Ohio EPA closely resemble the
distribution of sandstone and sand & gravel aquifers predicted in Figure 3.
Figure 2. Hydraulic Conductivity Histograms for Sand-&-Gravel and Sandstone.
Histograms indicate the data are log-normally distributed and demonstrate the higher
average K values associated with the sand-&-gravel.
When considering the use and management of groundwater
systems, the most important properties of geologic materials are
the porosity and the hydraulic conductivity. Hydraulic
conductivity is a measure of the ease with which fluids can pass
through a geologic medium. It is the most important parameter
to estimate when predicting aquifer yields, sustainable pumping
rates or rates of contaminant transport. Estimations of hydraulic
conductivity are also difficult because for any given type of
geologic medium, there can be variations through four or five
orders of magnitude.
In many states, including Ohio, when a borehole is drilled for a
water-well installation, the driller is required to file a well driller’s
report (shown in Figure 1 with an example well log and well
diagram). In Ohio, these reports are filed with the Ohio
Department of Natural Resources (ODNR), and the reports
include an aquifer pumping test that gives the well owner an
idea of the pumping capacity of the well. This pumping test also
allows estimation of the hydraulic conductivity of the geologic
formation surrounding the well. The ODNR has an electronic
data base of all the filed drilling reports and these reports allow
estimations of hydraulic conductivity at hundreds of thousands
of well sites across Ohio. The well logs also give a description of
the geologic formation where the pump is set.
The purpose of our research was to estimate the hydraulic
conductivity at as many well sites as possible within Licking
County, Ohio and relate those estimations to the geologic
setting. Our objective was to provide a quantitative description
of the mean and range of hydraulic conductivities for each major
aquifer type. Such descriptions could then be used in future
work to estimate hydraulic conductivities based on the
underlying geology.
Records provided by the ODNR, to the Department of Geology
and Environmental Earth Science at Miami University, include
over ten-thousand recorded pumping tests performed in Licking
Co. These pumping test reports include, the well radius (rw), the
pumping rate (Q), the length of the test (t), and the drawdown in
the well (Sm). To calculate hydraulic conductivity, we first
calculate the transmissivity of the formation according to:
Equation 1
where S is the storage coefficient estimated to be 0.0005 for all
formations. Note that T falls on both sides of Eq. 1. We
therefore had to apply an iterative solution technique to
converge on the proper T values. Hydraulic conductivity (K) is
the transmissivity per unit length that the well is exposed to the
aquifer (L):
Equation 2
The length used in Eq. 2 corresponded to the screen length for
wells in unconsolidated formations or the open interval of wells
set in rock.
Initial calculations of K revealed many obvious errors in the
information transcribed to the ODNR database, necessitating our
review and correction of thousands of records.
Well logs typically contain a recorded geologic aquifer type
description, usually corresponding to the deepest formation
encountered. Drillers’ descriptions comprised about 160
different aquifer types. We consolidated these into 13 major
aquifer types to allow better county-wide characterizations and
comparisons.
Methods
Each major aquifer type comprised a wide range of K values
(Table 1). K distributions for each aquifer type were log-normal
(as exemplified for sandstone and sand-&-gravel, Figure 2). All
statistics were therefore performed on the log-transformed
values. Geometric means were used to characterize the central
values and the 95% confidence intervals for the means reflect
the log-normal distributions. T-tests were performed to indicate
significant differences between aquifer types. Table 2 shows
each aquifer type with bars drawn under the types whose means
are not significantly different at the p = 0.05 confidence level.
As expected, the formations with the highest K values were
gravel followed by sand-&-gravel; sand and combinations of clay,
sand-&-gravel had lower average K values. Rock formations had
yet lower values with limestones and sandstones having higher
average K values than shales and siltstones. Formations that
were described as clay or clay wash, however, had unexpectedly
high K values. The discrepancies might be due to the low
numbers of wells tested and the fact that other formations may
fall within the well-screen intervals, and these were not
represented in the aquifer-type descriptions.
Spatial distributions of the aquifer type (Figure 3) and K values
(Figure 4) were compiled for all of Licking County using ArcMap®.
For Figure 3, we focused on only the two aquifer types reported
as the most prevalent according the Ohio EPA (Figure 5). The
occurrence of sand-&-gravel and the resulting higher K values are
clearly correlated with the major river valleys.
Correlating hydraulic conductivity values to geologic well log
descriptions can provide valuable regional aquifer characteristics
that support sustainable use and development of aquifer
systems. The ODNR has access to an abundance of well-log
information for the entire state. It is possible to conduct similar
studies anywhere with access to driller reports. However, we
found many errors in the drilling-report information transcribed
to the electronic database. The database needs to be carefully
checked for all future analyses.
Bradbury, K. R. and E. R. Rothschild. "A Computerized Technique for Estimating the Hydraulic Conductivity of Aquifer from Specific
Capacity Data." Ground Water, v.23, no.2 (1985): 240-246.
Cobb, Michael. "Worksheet for Estimating Transmissivity and Hydraulic Conductivity from Specific Capacity Test Data." Madison: UW-
Madison Department of Geology and Geophysics, 16 December 2001.
Fetter, C.W. Applied Hydrology, Fourth Edition. Upper Saddle River: Pentice Hall, 2001. Text Book.
Ohio Department of Natural Resources (ODNR). "Well drillers information from Licking County, Ohio." Columbus, 3 February 2015.
Ohio Environmental Protection Agency. "Major Aquifers and Ground Water Quality in Ohio." February 2014. OhioEPA. PDF. April 2015.
Summary Table
Correlating Hydraulic Conductivity Values to Geologic Well Log Descriptions of Licking County, Ohio
Gravel
Sand-&-
Gravel
Clay-&-Gravel Clay Clay wash Sand
Clay, Sand &
Gravel
Limestone Bedrock Sandstone
Shale-&-
Sandstone
Shale Siltstone
Wells Tested 781 2006 153 9 9 768 434 78 430 1703 1866 1496 55
Minimum (ft/d) 1.17E-02 2.62E-02 6.81E-03 8.47E-02 1.45E+00 1.58E-03 2.20E-03 5.87E-03 9.37E-03 1.04E-03 1.04E-03 1.17E-03 2.69E-03
Maximum (ft/d) 4690 4095 2157 440 479 5614 1728 2014 532 1772 1772 1049 488
Median (ft/d) 70.1 66.8 35.9 33.8 12.8 13.5 19.1 6.55 4.72 4.85 4.77 3.70 1.94
Geometric mean (ft/d) 58.0 56.9 34.8 22.0 18.9 14.2 13.8 7.51 4.51 4.44 4.29 3.23 1.98
95% Confidence Interval
of the Mean (ft/d) 51.5-65.5 52.9-61.1 24.8-48.8 2.45-197 4.22-85.1 12.3-16.4 11.2-17.2 4.06-13.9 3.78-5.38 3.97-4.98 3.84-4.78 2.88-3.62 1.11-3.53
Std.Dev. (ft/d) 389 302 340 184 170 327 165 324 44.2 132 127 70.8 66.0