6.

Abandoned domestic, agricultural, or industrial well.

7.

Well randomly drilled for dye injection.

To save the trouble and expense of a wasted dye test, percolation or slug tests should

be conducted at the injection point to determine if the injection point is open to the aquifer

and to see how rapidly it drains. The tracer injection point should be on, or as near as is

practicably possible to, the facility property. The use of injection sites that are not near the

facility property will most certainly be questioned by the regulatory authority because of the

possibility that the monitoring locations identified by the tracer test are not hydraulically

connected to the facility.

The detection limit for fluorescent dyes is lower than nonfluorescent dyes, therefore, in

general, less fluorescent dye is required for tracer tests (Quinlan, 1987). Although fluorescent

dyes exhibit many of the properties of an ideal tracer, a number of factors interfere with

concentration measurement. These factors include suspended sediment load, temperature, pH,

CaCO concentration, salinity, etc. (Quinlan, 1987). At the sampling point, preferably a

3

spring, grab samples can be taken or small pockets of nylon can be filled with activated

charcoal and suspended in the water. The dye adsorbs very strongly on to the charcoal and is

later desorbed in a lab and analyzed. To detect dyes, a filter fluorometer can be used in the

field or a spectrofluorometer can be used in the lab. For additional discussions of

ground water tracing, the reader is referred to Davis et al. (1985), and the EPA documents

Application of Dye Tracing Techniques for Determining Solute Transport Characteristics of

Ground Water in Karst Terranes (1988), and Ground Water Monitoring in Karst Terranes

(1989). In addition, Quinlan (1990) discusses the special problems of ground water

monitoring in karst terranes.

Figure 12 is a map that shows how the results of a dye tracing study can be displayed

graphically. The most important information to depict is the location of: all points where

dye was introduced (sinkholes, sinking streams, wells, etc.); all springs and wells in the area;

and those springs and wells where dye was recovered. The routes travelled by the dye are

usually shown as straight or curvilinear lines that connect the tracer injection points and the

springs. In most cases, straight lines should be used to schematically depict the routes

travelled by the dye, unless extensive data have been collected to justify the depiction of the

ground water flow paths as curvilinear lines. Line drawings of known cave systems with

hydraulically connected streams that occur between the surface introduction points and the

springs or wells where dye was recovered also are useful for such a map.

5.2.5

Sampling Frequency in Aquifers Dominated by Conduit Flow

Under 40 CFR Part 264 Subpart F, ground water monitoring frequency is specified by

the Regional Administrator in the facility's permit and either must at a minimum include four

samples collected semi annually during detection and compliance monitoring periods pursuant

November 1992

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