Case Study of a Long-Term Aquifer Test in Support of Municipal Well Field Expansion in the Maryland Piedmont

A long-term aquifer test was conducted on two new municipal supply wells in partial fulfillment of Water Appropriation and Use Permit requirements issued by the Maryland Department of Environment.  The municipal well permits required a 60-day operational test to assess the impact of municipal water withdrawals on nearby private supply wells.  During the test, the municipal wells, all open borehole wells in fractured siltstone bedrock, were pumped at their maximum permitted rates for a total withdrawal of about 380 GPM. 

Continuous water-level monitoring of nearby private residential and agricultural wells was conducted before, during, and after the pumping test, in addition to precipitation monitoring.  While none of the private wells suffered immediate loss of use during the test, water-level data from pre-test and test conditions were used to predict 90-day draw downs in the private wells.  These results were compared to the upper water-yielding fractures and/or well construction details to identify potentially-impacted private wells. 

Water levels in most wells responded rapidly and significantly to precipitation events.  For this reason, initiation of the test during a period of dry weather and ongoing precipitation monitoring was critical.  Anomalous conditions were encountered in several wells, including continuous disturbance in transducer readings attributed to pump vibration, semi-diurnal water-level fluctuations, and rapid water-level recovery in response to precipitation events.