UK Kentucky Water Resources Research Institute

Waterworks Archive

Groundwater and Soil Analysis on a Statewide Scale in Kentucky

by Burl I. Naugle
Mid-America Remote Sensing Center (MARC) and
Department of Geosciences
Murray State University

In this study, water-well data from the Kentucky Division of Water, Kentucky Natural Resources and Environmental Protection Cabinet (KNREPC), database were related to the State General Soil Geographic Data Base (STATSGO) general soils map. Water well parameters included in the study were the depth of wells, depth to bedrock, and depth to static water level. In addition, soil parameters pertinent to modeling the flow of contaminants from underground storage tanks, average permeability, percent clay, and percent organic matter, were derived for the entire soil profile and for the top and bottom soil layer of each mapped Kentucky soil (Soil ID) and of the soils of 20 physiographic region/soil type groupings (RT,region/type). Statistical analyses were performed showing that all of the parameters were significantly different on the basis of soil ID and region/type. Additional statistical analyses were performed to determine if the differences among region/types were still significant when taking into account the differences among soil IDs within the region/types. A more-detailed version of this report was published in the KWRRI report "Identificaton of Appropriate Standards for Corrective Action for a Release from Petroleum Underground Storage Tanks."

Kentucky STATSGO general soils data were obtained from the KNREPC in the ARC/INFO Geographic Information System format. Both locational (map) information and attribute (soil parameters) information were utilized to derive tabular and mapped data. The general soils data had been generated under a USDA Soil Conservation Service (SCS) project in 1985. General soils (643 separate polygons) were mapped on 1:250,000 scale maps by KNREPC Division of Conservation and SCS employees. Soil and physical characteristics were compiled for 2137 different soil phases or sequences with 7342 phase/layer combinations making up 195 different general soils categories (Soil IDs). Entire profile means and top and bottom layer means of permeability, clay, and organic matter were generated for each soil ID and each region/type.

The 20 soil region/types included in this study are listed below along with some physiography and characteristics:

1. River alluvium: Alluvial soils formed on floodplains of large rivers;

2. Purchase loess: Windblown soils;

3. Purchase alluvium;

4. Western Pennyroyal: Formed from loess and Miss. age limestone;

5. Western Penny. alluvium;

6. Western Penny. loess;

7. Western Coalfield: Formed from Penn. age sandstone, siltstone, and shale;

8. Western Coalfield alluvium;

9. Western Coalfield loess;

10. Knobs: Formed from Lower Miss. and Devonian age siltstone and shale;

11. Knobs alluvium;

12. Eastern Pennyroyal: Formed from Miss. age limestone;

13. Eastern Pennyroyal alluvium;

14. Outer Bluegrass: Formed from Silurian and Outer Bluegrass loess;

17. Inner Bluegrass: Formed from Ordivician age limestone;

18. Inner Bluegrass alluvium; 19. Eastern Coalfield: Formed from Upper Miss. and Penn. age sandstone, siltstone, and shale; and

20. Eastern Coalfield alluvium.

These region/types are best seen in the large STATSGO maps included in the previous publication. Some of the alluvial soil IDs (5) on the map had to be split in order to accomodate the region/type classification. A small scale map of the STATSGO soils showing eight divisions is included here.

Kentucky water well data (13,004 records that overlaid the STATSGO map) were obtained from the Kentucky Division of Water. Well parameters included latitude, longitude, depth of well, surface elevation, depth to bedrock, depth to static water level, water yield, and water yield units. Well records with depth to bedrock or static water level equal to zero were excluded from further analysis leaving 10,860 water well data records. The depth data (well depth, depth to bedrock, and depth to static water level) were all skewed to the right. Logarithmic transformations were applied to the depth data to use standard statistical techniques which assume a Gaussian normal distribution. The resulting data were much more symmetric and appeared to reasonably approximate a normal distribution.

Only 164 of the 195 soil IDs contained valid well data. Of these, only 132 soil IDs contained more than 2 wells. Three of the region/types: Western Pennyroyal alluvium, Western Pennyroyal loess, and Outer Bluegrass loess, did not have enough wells to calculate a valid mean. The Western Pennyroyal alluvium and Western Pennyroyal loess are almost completely contained in the Land Between the Lakes (LBL). In addition, some of the wells (24) were located in STATSGO polygons representing water, probably the result of small scale soil mapping or misregistration.

Statistical analyses were undertaken to determine if the parameter means were significantly different on the basis of soil ID and/or region/type. All of the soil and well parameters (entire profile mean permeability, clay, and organic matter; top and bottom layer permeability, clay, and organic matter; logarithmic depth of wells, log. depth to bedrock, and log. depth to static water level) were significantly different (alpha level much less than .05) on the basis of both soil ID and region/type classification. This does not mean, of course, that the parameters are significantly each region/type, but it does mean that there are at least some groups or individual categories that have significantly different parameters from other groups or individuals. It appeared that the variation in some of the parameters due to soil ID within a region/type were larger than the differences in the means between region/types so an analysis was performed to test that hypothesis. All of the parameters tested were still significantly different (alpha < .05) on the basis of region/type except for well depth and depth to static water level. Thus the classification of well depth and depth to static water level into region/types is not a very satisfactory classification.

In many cases the separation of the soils from a physiographic region into different types of soils such as aluvium, loess, etc. results in meaningful parameter differences. However, there are sometimes larger differences in mean parameter values among soil IDs within region/types than between region/types. This is especially true for well depth and depth to static water level as discussed above.

Some of the soil layers in the STATSGO database consisted of bedrock, which did contain permeability values but did not contain organic matter data other than zero percent. This may result in some uncertainty in both the bottom layer permeability and organic matter values.

Some of the significant items from an underground storage tank perspective are:

1. The depth to bedrock is significantly larger in the Jackson Purchase (RT= 2 or 3) than in the rest of the state.

2. The average depth to bedrock in the Inner Bluegrass (RT= 17 or 18) is less than 10 feet, although these depths are not significantly different than those of much of the state.

3. Only three soil IDs that contained more than two water wells had an average depth to well water of less than 20 feet.

4. The Western Coalfield and Western Pennyroyal (RT= 4 or 7) have average depths to static water level of 128 and 93 feet (medians: 89.5 and 78 feet), respectively. The variations are so large that definitive statements cannot be made on a region/type basis. It can certainly be said, however, that most water being drawn from wells in Kentucky, especially in the Western Coalfield and the Western Pennyroyal, is coming from deep rather than surface aquifers.

5. The percent organic matter in the lowest soil layer is indeed very small. The average for the entire state is very near the 0.1 percent used in McGinley's (1993) analysis. Some of the assumptions used in the STATSGO soils database may be a little suspect, i.e. bedrock layers have no organic matter. This is somewhat compensated for, however, by the fact that the depth at which contamination would be present is below the depth of the soil profile (less than 6ft) considered in the STATSGO database.

6. All of the intrinsic permeabilities of the bottom layer of soils fall within the range of those used in McGinley's (1993) analysis.

Last modified: November 28, 1995

Copyright © 1995 University of Kentucky - Kentucky Water Resources Research Institute