Delineation of recharge areas for selected wells in the St. Peter-Prairie du Chien-Jordan aquifer, Rochester, Minnesota

Water Supply Paper 2397
Prepared in cooperation with the U.S. Environmental Protection Agency
By:  and 

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Abstract

Accurate delineation of recharge areas for wells is an important requisite to protecting ground-water quality. Zones of transport and zones of contribution are two types of recharge areas that can be delineated. Analytical-calculation, numerical-modeling, and hydrogeologic-mapping methods were used to delineate recharge areas for two high-capacity wells (greater than about 200 gallons per minute discharge) completed in a karstic aquifer in the city of Rochester, in southeastern Minnesota. One well is less than 1,000 feet from a river in an area where the aquifer is unconfined, whereas the other well is more than 2,000 feet from a stream in an area where a bedrock confining unit is present.

Ground-water travel times from points along the top of the aquifer to a pumped well are identified by use of a constructed map showing lines of equal advective travel time. A zone of transport, therefore, is defined by the area bounded by lines of equal travel time. Zones of transport are delineated by analytical models (calculations) and by numerical models that account for hydrologic factors. Analytical models that were used include fixed-radius (Theis drawdown, Theis time-of-travel, and volumetric equation) and variable shape. Numerical modeling was done with the U.S. Geological Survey three-dimensional ground-water-flow model MODFLOW and particle-tracking code MODPATH. The zone-of-transport areas for each of the two wells calculated by the various analytical models were very similar. The Theis-drawdown method yielded results that compared least favorably with results from the other analytical methods. The zone-of-transport areas computed by use of the numerical model were generally larger than areas computed by use of analytical models.

Hydrogeologic mapping and numerical modeling were used to delineate zones of contribution to wells, defined as all parts of a ground-water-flow system that could supply water to a well. The zones of contribution delineated by use of numerical modeling have similar orientation (parallel to regional flow directions) but significantly different areas than the zones of contribution delineated by use of hydrogeologic mapping. Differences in computed areas of recharge are attributed to the capability of the numerical model to more accurately represent (1) the three-dimensional flow system, (2) hydrologic boundaries such as streams, (3) variable recharge, and (4) the influence of nearby pumped wells, compared to the analytical models.

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Publication type Report
Publication Subtype USGS Numbered Series
Title Delineation of recharge areas for selected wells in the St. Peter-Prairie du Chien-Jordan aquifer, Rochester, Minnesota
Series title Water Supply Paper
Series number 2397
DOI 10.3133/wsp2397
Year Published 1993
Language English
Publisher U.S. Geological Survey
Publisher location Washington, D.C.
Contributing office(s) Minnesota Water Science Center
Description v, 39 p.
Country United States
State Minnesota
City Rochester
Other Geospatial St. Peter-Prairie du Chien-Jordan aquifer
Online Only (Y/N) N
Additional Online Files (Y/N) N
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