subsurface conduits are the primary pathways that contaminant releases follow. Identifying

and intercepting these conduits with wells is an extremely formidable task. Identifying

contaminant transport pathways requires detailed site characterization beyond what is

currently performed at most RCRA facilities. In addition, the wide fluctuations in the water

table that are characteristic of aquifers dominated by conduit flow make identification and

satisfactory monitoring of the uppermost aquifer particularly difficult.

It may be possible for some facilities that are sited above conduit flow aquifers to

have ground water monitoring systems that meet the performance standards of 40 CFR

 264.97. The Regional Administrator may require the facility owner or operator to monitor

seeps, springs, and caves that are hydraulically connected to the uppermost aquifer and that

are within the facility boundary to supplement the monitoring well network. These

supplemental monitoring sites can be used in conjunction with point of compliance wells to

detect releases from the facility ( 264.97(a)(3)). However, the Agency expects that these

cases will be rare, and that most facilities sited in karst settings will be unable both to meet

the performance standards of  264.97 and to receive an operating permit. Therefore, prior to

locating a waste management facility in an area where any conduit flow exists, an owner or

operator should consider the inherent difficulties in meeting the ground water monitoring

requirements of Subpart F. The owner/operator should select a different location if it appears

as though a release to a conduit flow aquifer could not be detected or controlled during a high

precipitation event. The following sections of requirements and guidance are for owners and

operators of facilities located above aquifers dominated by conduit flow that meet the

performance standards of  264.97. These sections provide additional information on

designing a supplemental monitoring well network for the seeps, springs, and conduits that

are hydraulically connected to the uppermost aquifer and that are located on the facility

property.

5.2.2

Using Springs as Monitoring Sites in Aquifers Dominated by Conduit

Flow

In certain circumstances, the Regional Administrator may request that a strategy of

monitoring seeps, springs, and cave streams be applied to supplement monitoring well

systems in all aquifers dominated by conduits that drain to springs and that discharge on land

or along the shores of streams, rivers, lakes, or seas. In terranes where conduit flow

predominates, springs and cave streams (if they have been shown by tracer studies to drain

from the facility being evaluated) are the easiest and most reliable sites at which to monitor

ground water quality (Field, 1988; Quinlan, 1989; Quinlan, 1990).

Most springs that should be sampled regularly during tracer tests and ground water

monitoring are not shown on USGS topographic quadrangle maps. Furthermore, the inclusion

of a spring on a topographic map is not necessarily an indicator of the significance of its

discharge, as many minor springs are included on maps because of their cultural associations.

In certain cases, the owner/operator will need to conduct detailed field work to locate all

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