The principal use of this standard is in the identification of effective groundwater monitoring constituents for a detection-monitoring program. The significance of the guide is to minimize the false positive rate for the facility by only monitoring those constituents that are intrinsic to the waste mass and eliminate those constituents that are present in background in concentrations that confound evaluation from downgradient wells.
Federal, state and local regulations require large generic lists of constituents to be monitored in an effort to detect a release from a WMU. However, identification and selection of parameters based on site-specific physical and chemical conditions are in many cases also acceptable to regulatory agencies and result in a more effective and environmentally protective groundwater monitoring system.
Naturally occurring soil and groundwater constituents within and near a WMU area should be determined prior to the development of a monitoring program. This is important in the selection of site-specific constituents lists and avoiding difficulties with a regulatory authority regarding sources of monitored constituents.
Site-specific lists of constituents relative to the WMU will provide for the regulator those constituents which will effectively measure the performance of a WMU rather than the use of a generic list that could include naturally occurring constituents as well as those not present in the WMU.
Site-specific constituent lists often result in fewer monitored constituents (that is, monitoring programs are optimized). This process is critical to the overall success of the monitoring program for the following reasons:
The reduction of the monitoring constituents to only those found or expected to be found or derived from site-specific source material will reduce the number of false-positive results since only those parameters that could indicate a release are monitored.
The use of constituents that contrast significantly to background groundwater eliminates those that could lead to erroneous results merely due to temporal and spatial variability of components found in the natural geochemistry of the upper-most water-bearing zone.
Where statistics are required, fewer statistical comparisons through well and constituent optimization enhances the statistical power (or effectiveness) of the monitoring program (Gibbons, 1994; USEPA, July 1992).
Eliminating the cost of unnecessary laboratory analyses produces a more efficient and cost-effective monitoring program and minimizes the effort required by both the local enforcement agency and the owner/operator to respond (either with correspondence or additional field/laboratory efforts) to erroneous detection decisions.
This type of approach is acceptable to regulatory agencies arid applicable under most groundwater monitoring programs under RCRA regulations. For example, in determining the alternate constituent list at Solid Waste Facilities, 40 CFR 258.54(a)(l) allows for deletion of 40 CFR 258 Appendix I constituents if it can be shown that the removed constituents are not reasonably expected to be in or derived from the waste contained in the unit. 40 CFR 258(a)(2) allows approved States to establish an alternate list of inorganic parameters in lieu of all or some of the heavy metals (constituents 1-14 in Appendix I to Part 258), if the alternative constituents provide a reliable indication of inorganic releases from the unit to groundwater.
The framework for this standard is generally based on the guidelines established under 40 CFR 258.54(a)(l) to optimize a groundwater-monitoring network in such a manner as to still provide an early warning system of a release from the WMU. This guidance document is, however, applicable for all WMU, not just those associated with solid waste disposal facilities. In determining the alternative constituents, consideration must be made f......
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