State Water Resources Research Institute Program

Project ID: 2011CT233B
Title: A Dye Displacement Method to Characterize Water Contributing Fractures in Wells in Crystalline Bedrock
Project Type: Research
Start Date: 3/01/2012
End Date: 2/29/2013
Congressional District: 2
Focus Categories: Water Quality, Groundwater, Toxic Substances
Keywords: fractured rock, groundwater, contamination, fracture location, water contributing fractures
Principal Investigator: robbins, gary a (University of Connecticut)
Federal Funds: $ 23,017
Non-Federal Matching Funds: $ 46,034
Abstract: In Connecticut, wells installed in fractured crystalline bedrock are an important water source. When bedrock wells are found to be contaminated, it is rare for the source of contamination to be identified owing to the costs and uncertain outcome of investigations. More often the water supply is left contaminated and wells are abandoned, if alternative water supplies are available, or wells are fitted with expensive filter systems. Contaminant concentrations in bedrock wells are generally determined using a spigot on the water system which provides a weighted average contaminant concentration, depending on such factors as the number of water contributing fractures that intersect the well and their contaminant concentrations. As an average, contaminant concentration data obtained from a well may be misleading in deciphering the source and extent of contamination. Understanding the source and extent of contamination in wells in fractured crystalline bedrock requires information on the depth of water contributing fractures, their recharge rates, which fractures are contaminated and the contaminant concentrations. Currently, to gain this information requires the application of a sequence of conventional investigatory tools, including downhole geophysics to locate fractures, downhole heat pulse flow meter tests to determine which fractures are water contributing, packer tests to isolate fractures, and pumping tests to determine hydraulic properties and obtain water quality samples. In combination the use of these methods is very costly, time consuming and logistically intense in application. As such, detailed investigations into bedrock contamination are rarely performed. We are proposing to test a dye displacement method that can greatly simplify and reduce the costs for investigating contaminated wells in crystalline bedrock. In concept the method entails the following steps: (1) mixing non-toxic dyes (Rhodamine WT and Fluorescein) in a well, (2) rapidly removing a small portion of dyed water from the well, (3) monitoring the water level recovery, (4) profiling the well for the dyes to determine the location of fresh water zones. In this manner, the location of fresh water zones mark the location of water contributing fractures, the length of the fresh water zones can be used to determine fracture transmissivity and sampling fresh water zones can be used to determine the concentration of contamination from fractures. To help develop and validate procedures, we are proposing to conduct laboratory testing on a well model, followed by field testing of wells that have been previously characterized using conventional techniques on the University of Connecticut Campus.

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