fracture trace or lineament, or at the intersection of such linear features, will intercept a cave

stream.

Wells that were originally sited without consideration of conduit flow should be used

for monitoring only if tracing has first proven a connection from the waste management

facility to each of the monitoring wells under varying flow conditions. Domestic,

agricultural, and industrial wells are sited and installed for purposes other than ground water

monitoring. Even previously installed monitoring wells designed to detect contaminants, to

intercept contaminant plumes, or to function as upgradient monitoring wells should be

considered randomly located unless they were deliberately sited along fracture traces or

fracture trace intersections. Piezometer clusters are excellent in porous media, but will

provide relatively little information in most karst terranes. Piezometer clusters do have value

in defining the diffuse flow component of a karst aquifer, but this could lead to (1) incorrect

interpretation of subsurface flow characteristics, and (2) greatly added site characterization

expenses. Randomly located and non randomly located wells not intended for aquifer testing

or ground water tracing should be used as monitoring wells only if tracing shows a direct link

to the conduit system to be monitored. Such wells should not, however, be used as

monitoring wells for a facility above an aquifer dominated by conduit flow or diffuse flow,

unless tracer studies show that the well is downgradient from the facility to be monitored.

5.2.4

Tracing to Identify Monitoring Sites in Aquifers Dominated by Conduit

Flow

Ground water tracing is a well developed tool that enables catchment boundaries to be

delineated, ground water flow velocities to be estimated, areas of recharge and discharge to be

determined, and sources of pollution to be identified. Ground Water Tracers, by Davis et al.

(1985) is an EPA sponsored compendium that discusses many facets of ground water tracing.

Another good reference concerning ground water tracing is Quinlan (1990). It is important to

consult an individual who is experienced in ground water tracing, and to get approval from

the appropriate regulatory authorities before any tracer study is initiated.

A tracer should have a number of properties to be considered useful, including the

following:

Its potential chemical and physical behavior in ground water should be

understood;

It should travel with the same velocity as the water and not interact with solid

material;

It should be nontoxic for most uses;

It should be inexpensive;

November 1992

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