New Jersey Geologic Survey
DGS07-1: Aquifer Recharge Potential for New Jersey Overview

This information is provided to compliment the FGDC-compliant metadata prepared for and provided with each data set and is not intended to replace that metadata.

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Table of Contents

Abstract

Overview

Processing

Aquifer Rankings (table)

County Aquifer Rankings (table)

Composite Aquifer-Recharge Potential Ranks

Limitations

Provisos

References

Abstract:

Aquifer recharge potential was mapped by superimposing ground-water recharge maps over aquifer maps. A rankings system was developed to display the potential for aquifer recharge. Ground-water recharge areas were mapped and ground-water recharge  was calculated and ranked as described in "A method for evaluating ground-water-recharge areas in New Jersey" (E.G. Charles and others, 1993). Aquifer designations and delineations  from "Aquifers of New Jersey" (G. C. Herman and others, 1998), were used to produce a coverage of aquifer ranks.

Aquifers were ranked based on the median yield of selected non-domestic well yields. Yield was used as it was indicative of the capacity of the aquifer to supply water, which defines an aquifer. The prevalence of yield data made it possible to develop a ranking system over a regional area. The median yield was chosen as the ranking criterion as it more precisely indicated the central point of the data as opposed to the average. Large outlier values often found in the yield data can greatly influence the average. The median is the value at which half of the data values are above and half are below.

Overview:

All geographic data were prepared using ESRI Arc/Info™or ArcView™ geographic information system software. Downloadable data were prepared using WinZip™ compression software and Adobe Illustrator™software (see Proviso below). Data CDs, available by request only, were prepared using the ISO-9660 CD file system standard and can be read by any computer and operating system with ISO-9660 compatibility.

Watershed management area is indicated by the two numbers after the initial "w" of the filename which corresponds to the number of the watershed management area. County is indicated by the first three letters of the file name corresponding to the first 3 letters of the County. Each shapefile was converted or exported from a corresponding Arc/Info coverage of the same name. The "shapefiles" are composed of three constituent files: SHP file containing the geographic elements (lines, points or polygons), the SHX file containing the geographic coordinate information and the DBF file containing the data attached to each geographic element.

Processing:

Aquifer coverages were created by clipping the Aquifers of New Jersey (G. C. Herman and others, 1998) coverage using the boundary of the area of interest (county or WMA).

Aquifer rank coverages were created by applying aquifer ranks for each aquifer based upon county/WMA well-yield data or statewide rankings to those aquifers which had no county/WMA well-yield data, then dissolving the coverage against that rank.

To create a system to rank these aquifers the NJGS analyzed statewide aquifer and well data that included well yield, hydraulic conductivity, specific capacity, transmissivity, and storativity. Well-yield data from a high-yield subset of non-domestic wells were used because they provided the most comprehensive data and were the most representative of the potential water-yielding ability of the aquifer (Sloto and others, 1990). Well-yield data were obtained from NJGS project databases and from the USGS Ground Water Site Index (GWSI) database (Vowinkel and others,1982). Statistical analysis showed that the median (a value, in an ordered set of values, below and above which there is an equal number of values) of the well yield could be used to adequately assess the aquifer. The ranges of yields for the rankings are selected based upon natural breaks in the data. These ranges were further refined after discussions with NJGS hydrogeologic staff. The five statewide rankings are as follows:

Once these ranges were established, statewide rankings were determined for each aquifer using median yield. If well-yield data were not available for an aquifer, it was ranked based upon its lithologic characteristics compared to the ranked aquifers, and the combined professional judgment of the NJGS geologic and hydrogeologic staff.

The county aquifer rank was created by retrieving well-yield data for each aquifer in that county. Medians were calculated for well-yield for data containing three or more values. The statewide ranking scale was then applied to the results. Aquifers which did not have county well data were assigned their corresponding statewide rank.The following table contains county well yield data, in gpm, used to rank county aquifers, the aquifer's cooresponding county and statewide rank, and the aquifers which were assigned only their statewide rank:

CompositeAquifer Recharge Potential Ranks:

Aquifer-recharge potential coverages(*aqrp) were created through the combination of ground-water recharge coverage and the aquifer rank coverage in the area of interest (county/WMA). Aquifer recharge or recharge to water-bearing geologic units is defined by this study as the groundwater which reaches the water table in the uppermost geologic unit with a thickness of 50 feet or greater. After the combination of the two coverages, a composite ranking of 25 possible aquifer-recharge potentials was produced by combining the 5 possible ground-water recharge ranks with the 5 possible aquifer ranks.This composite, aquifer-recharge potential rank highlights the multiple relationships between the ground-water-recharge area ranks (indicative of the infiltration rate) and the underlying water-table aquifer ranks (indicative of the aquifer's capacity to absorb, transmit and supply water). The following table shows the composite rankings:

As can be seen, ground-water-recharge rates vary independently across the underlying aquifers. High-ranked ground-water-recharge areas can be found on low-ranked aquifers. This indicates infiltration or recharge at higher rates than the aquifer can absorb. This excess recharge provides water to wetlands and for stream baseflow. When high-rank, ground-water-recharge areas are located over high-ranked aquifers, this indicates an area where recharge rates are matched more closely to the aquifer's ability to absorb this water and are indicative of important aquifer-recharge areas.

This coverage incorporates additional assumptions besides those outlined in the ground-water-recharge methodology as presented by Charles and others (1993). These assumptions are: (1) Any lateral flow of ground water along boundaries of differing hydraulic conductivity has not been incorporated in this map. (2) The influence of topography on recharge is considered to have been addressed in the ground-water-recharge methodology as presented in Charles and others (1993). (3) Each constituent coverage may not have exactly matched in there geographic extent. This may have led to polygon slivers at the edges for which no recharge was calculated. In the interest of timely delivery, these polygons may not have been removed.

Limitations:

This data is subject to all limitations inherent in the NJGS ground-water recharge methodology as outlined in Part IV in GSR-32 and any other limitations noted above. Geographic data is reliable to 1:24,000 scale. Please refer to NJDEP GIS web site for further information on constituent coverages and metadata. (http://www.state.nj.us/dep/gis)

Provisos:

The data is supplied as is with no implied support or warranty by the NJGS. The end-user is responsible for any alterations to the original data. 

The mention of third party software products does not constitute an endorsement of these products by the NJGS. The NJGS does not support these products nor is the NJGS liable for any problems or damages arising from their download, use and/or misuse.

References

• Charles, E.G., Behroozi, C., Schooley, J, Hoffman, J.L.,1993, New Jersey Geological Survey Geological Survey Report GSR 32, A method for evaluating ground-water-recharge areas in NewJersey: N.J. Dept. of Envir. Prot. and Energy, Div. of Sci. and Res., N.J. Geol. Survey, Trenton, N.J. 95 p.

• Herman, G.C., Canace, R.J., Stanford, S.D., Pristas, R.S., Sugarman, P.J., French, M.A., Hoffman, J.L., Serfes, M.S., Mennel, W.J., 1998, NJGS Open-file Map OFM 24 and Digital Geodata Series DGS98-5, Aquifers of New Jersey: N.J. Dept. of Envir. Prot. and Energy, Div. of Sci. and Res., N.J. Geol. Survey, Trenton, N.J.

• Sloto, R. A., Cecil, L. D., Senior, L. A., 1991, U. S.Geol. Survey Water Resouces Invest. Rep. 90-4076 Hydrogeology andground-water flow in the carbonate rocks of the Little Lehigh Creek Basin, Lehigh County, Pennsylvannia: U. S. Geol. Survey, pg. 15.

• Vowinkel, E.F., Daniels, R., Brown, P.H., Ryan, J.J., 1982, Ground-water site index [GWSI], User's Guide: U.S. Geol. Survey, Water Resour. Div., N.J. Dist., Trenton, N.J., 28 p.