CHALLENGES OF A KARST DYE-TRACING INVESTIGATION IN AN URBAN BROWNFIELDS AREA

Urban karst areas do not always lend themselves well to traditional karst investigation methods such as dye-tracing. Often the impetus for an urban karst investigation is the detection of chemicals at a specific location, such as a spring, leading landowners or regulators to ask for the source area of that spring. If historic dye traces have not been done or recorded and disseminated in an accessible database, new studies may be hampered by limited access to typical karst features such as sinkholes and springs (many of which may have been covered over with engineering projects). Dye tracing may also be impacted by urban stormwater management – which may direct excess water into tracing routes and thus interfere with common tools used to size appropriate dye-injection amounts. Other tools more recently added to the karst toolbox, such as shallow geophysics, may also be hampered by urban infrastructure (e.g., electrical interference from utility lines). Lastly, common urban issues such as trespassers, homeless individuals, or simply inquisitive young people may also impede the progress of investigation.

A recent investigation to determine the source of water to a hydrocarbon-contaminated spring uncovered during Brownfields remediation activities at an urban karst site encountered many of these issues. A combination of Dye-Tracing and shallow geophysics methods were used to determine possible subsurface flowpaths feeding the spring. Urban issues posed challenges for the project – including high-discharge stormflows related to urban pavement runoff, limited dye input locations due to urban cover and past landscape alteration, and even interference with geophysical methods due to urban infrastructure. The issues encountered and efforts to address those issues and arrive at a successful end result of the karst investigation are presented.