Limiting Potential Failures - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 112

SIDEBAR 6.2 FORENSIC HYDROLOGY
Systematic changes in water chemistry are often used to detect
plumes of contaminants around leaking landfills, underground storage
tanks, and mine waste. Similarly, changes in the chemical character of
water samples from ambient levels may indicate leakage from
impoundments into the surrounding groundwater system. Hydrochemical
facies are defined as areas of aquifers where the chemistry of the
groundwater is predictable within defined limits. A hydrochemical facies
model for the Appalachian coal field (Pennsylvania Department of
Environmental Protection, 1999; Wunsch, 1993) can be used to detect
groundwater contamination from coal waste. The water fraction of coal
slurry will chemically reflect the concentrated waste material in coal and
will also be the most mobile fraction to leak into the underlying or adjacent
bedrock, coal seams, and fractures. For example, site-specific data show
that coal waste effluent can be enriched in iron, aluminum, magnesium,
and sulfate (D.Taulbee, University of Kentucky, personal communication,
2001). Moreover, organic chemicals used in the beneficiation of coal
waste may also be used as a groundwater tracer to identify leakage from
impoundments. A more comprehensive suite of analyses could be used to
monitor and detect leakage from an impoundment by employing
geochemical modeling, which can uniquely identify and characterize water
samples. Thus, monitoring the chemical composition of water adjacent to
impoundments could be used to detect whether water is leaking from the
coal slurry and, with the other site-specific information, to determine
sensible mitigative programs.
Several water quality parameters normally associated with mining
impacts can be easily determined in-situ. For example, specific electrical
conductance, which is a measurement of capacity of a fluid to transmit an
electrical current, is directly proportional to increased solids or salt content
in the water. Water from waste impoundments or mine waste usually
contains increased dissolved salts, such that significant changes in
electric current can be a predictive tool for leakage. The pH of mine waste-
impacted water is often notably acidic, thus changes in pH can be
indicative of contaminated ground or surface water leakage.
Digital water quality monitoring equipment (i.e., data loggers) can
simultaneously record changes in several parameters that indicate water
impacted by mining or mining wastes. These tools can also be used to
obtain real-time water-quality data that can be accessed remotely over the
Internet or by radio or satellite transmission, and can be used to monitor
for leakage that may presage an impending failure. These instruments are
relatively inexpensive (approximately U.S. $5,000) and can be used for
predictive monitoring of hydrologic and chemical parameters that would
warn of impoundment failure.
In conjunction with chemical data, water levels could be monitored to
establish the hydrostatic head conditions around the impoundment. Digital
data collectors or data loggers can be used to monitor remotely
anomalous changes in hydraulic head in the adjacent strata or mine
workings. This too may indicate changing head conditions between the
slurry impoundment and surrounding aquifers or mines. Digital data
loggers to monitor these changes can be equipped with alarms that give
real-time warnings that head levels have surpassed a pre-determined
threshold. The instruments are proven in the field, relatively inexpensive,
and widely available.