Determination Of Groundwater Recharge To The Triassic Brunswick Formation Of Southeastern Pennsylvania

Abstract

The Triassic Brunswick Formation is an important aquifer in south­eastern Pennsylvania and northern and central New Jersey, an area where rapid development is producing increased groundwater use. In order to prevent groundwater mining, it is necessary to have knowledge of the rate of groundwater recharge. Based on streamflow data during periods of baseflow recession, Moody and Associates, Inc. (1975) estimated the average annual recharge rate for the Brunswick Formation to be between 300,000 and 400,000 gallons/day/square mile. In this study the groundwater recharge rate for the Brunswick Forma­tion was calculated by the baseflow recession and hydrologic budget methods using streamflow and climatic data from three small water­sheds. The baseflow recession method yielded annual groundwater recharge rates which ranged from 441,000 gallons/day/square mile to 663,000 gallons/day/square mile. Annual groundwater recharge rates calculated using the hydrologic budget method ranged from 321,000 gallons/day/square mile to 424,000 gallons/day/square mile. Based on the results of both methods, the average annual recharge rate is 447,000 gallons/day/square mile. Although the baseflow recession method yielded reasonable annual recharge rates, it does not produce accurate results for shorter time periods. Monthly groundwater recharge rates calculated using the hydrologic budget are much more representative of actual seasonal variations than those calculated using the baseflow recession method. The primary advantage of the baseflow recession method is that it is simpler to use and requires much less data. The results of this study illustrate that groundwater recharge is controlled by both the hydraulic characteristics of the aquifer and climatic conditions. During the winter months, when there is a precipitation excess, the hydraulic characteristics of the aquifer determine the maximum potential recharge rate. However, during the summer months when there is less precipitation and greater evapotranspiration, the maximum potential recharge rate is not attained.