Case Study For Delineating A Contributing Area To A Well In A Fractured Siliciclastic Bedrock Aquifer Near Lansdale Pennsylvania PDF Download

Approximately one third of the U.S. population uses public supply wells (PSWs) as their drinking water source and recently a greater focus has been placed on assessing the risk of contaminants entering PSWs. Among the many contaminants of concern are chemical and microbiological indicators of wastewater contamination. This research project used a variety of field methods to better understand the primary mechanisms that control the transport of human enteric viruses and other wastewater contaminants in bedrock multi-aquifer systems and to develop effective methods for assessing the vulnerability of PSWs in such settings. At a field site in Madison, WI, borehole investigations suggest that fractures in siliclastic bedrock are important transport pathways from the surface to the deep aquifer. Some fractured intervals have transmissivity values several orders of magnitude higher than non-fractured intervals. In a siliciclastic aquifer near a public supply well, fractures may have an important role in the transport of sewer-derived wastewater contaminants. Reverse water-level fluctuations (RWFs), a phenomenon in which water levels rise briefly in response to pumping, were detected in monitoring wells. Data from pressure transducers located at varying depths and distances from a PSW suggest that the RWFs propagate rapidly through fractures to influence wells hundreds of meters from the pumping well. The rate and cycling frequency of pumping is an important factor in the magnitude of RWFs. The pattern of RWF propagation can be used to better define fracture connectivity in an aquifer system. Time sequenced sampling for geochemical wastewater indicators and human enteric viruses is a useful tool for characterizing transport within an aquifer system. There is an apparent connection between recharge events and increased flow in sanitary sewers and, based on limited data, these increased wastewater flows appear linked with virus detection in groundwater at short times after these events. In order to accurately assess the vulnerability of PSWs to near surface contaminants it is important to characterize fracture flow and the impact of PSW pumping. The use of RWFs to determine fracture connectivity is an important method to accomplish this goal.