Digital Bedrock Aquifer Characteristics by Physiographic Section of Pennsylvania

In 2001, the Bureau of Topographic and Geologic Survey (the Bureau) released the Digital Bedrock Geology of Pennsylvania. This dataset was based on Map 1, Geologic Map of Pennsylvania, by T. M. Berg and others. 

In 2004, the Bureau released Water Resource Report 69 (W69), Hydrogeologic and Well-Construction Characteristics of the Rocks of Pennsylvania by Gary M. Fleeger, Thomas A. McElroy, and Michael E. Moore. This report is mainly a Microsoft Access database, which can be purchased from the Bureau. These aquifer characteristics data are from selected water wells that could be field verified.

The digital aquifer characteristics dataset provides selected water-well construction and groundwater statistics for bedrock geologic units by the 23 physiographic sections of Pennsylvania, as shown on the Bureau’s Map 13. The dataset represents a derivative product of the two datasets mentioned above. Namely, it is a merger of the digital bedrock geology dataset and selected water well and groundwater data from W69. The derivative data are available for downloading below in “geodatabase” and shapefile formats. Files containing metadata (information about the datasets and how they were prepared) are included within the files.

The datasets were partitioned based on an unpublished dataset of the physiographic sections of the state. In the compilation process, the digital bedrock geology layer was clipped to the boundaries of each physiographic section. Because the physiographic boundaries were based on topography only, they tend to separate small portions of geologic formations that occur predominantly in certain physiographic sections. In W69, a few physiographic section boundaries had been modified to coincide with the boundaries of some geologic units. Therefore, some geologic units clipped by physiographic section are “missing” from the W69 summaries for a particular physiographic section. In the current dataset, the source of the data (that is, the physiographic section) from W69 is indicated to clarify this. Most often, slivers of polygons in one section are assigned data from an adjacent physiographic section where that unit predominantly occurs. Geologic formations that are small in areal extent and have no information were included but were not assigned any aquifer characteristics.

The groundwater data are water-well statistics for most geologic units in the state and include the following parameters:

•well depth (feet below ground surface)
•casing length (feet including any extension above the ground surface)
•static water level (feet below ground surface)
•well yield (gallons per minute)
•specific capacity (gallons per minute per foot of drawdown)
•water-bearing zones (in 50-foot depth intervals)
 
For the first five parameters, statistical summaries include number of water-well records, minimum and maximum values, and 10th, 25th, 50th (median), 75th, and 90th percentiles of values. Tallies of water-bearing zones and their densities by depth intervals are added as well.

See the metadata for more information. In addition, users will benefit from reading background information on the datasets contained in W69 and the state’s digital bedrock geology.

W69 was based on approximately 50,000 water wells. The areal distribution of the wells is an important factor in determining the amount of confidence to place in the information. The density of water wells per geologic unit along with the water wells locations are provided so that the user can judge data representativeness. In some areas, wells occur at a concentration of less than one per 100 mi2 so limited confidence in data representativeness should be given. In other areas with more information, geologic units legitimately exhibit a natural amount of variance in their data values; here the statistical data should be considered more reliable.

We welcome feedback from users regarding these datasets. Please contact Stuart Reese with your comments, recommendations, and suggestions.



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