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 for: (1) the types, quantities, and concentrations of constituents in wastes managed at the waste management unit (or WMU); (2) the mobility, stability, and persistence of waste constituents in the unsaturated zone beneath the WMU; (3) the detectability of indicator parameters, waste constituents, and reaction products in groundwater; and (4) the concentration or contrast between monitoring constituents in leachate and in background groundwater.

An essential factor in this guide is the knowledge of the quality of the potential source material [for example, the types and concentrations of liquid or other leachable wastes (that is, leachate) within the WMU]. The characterization of the source material is critical in determining an optimum set of indicator parameters that provide an early warning system of a release from the unit. Details for the appropriate levels of effort required to characterize the waste stream or source(s) in the WMU are not included within this guidance document. Waste stream and/or source data collected by the owner/operator as well as liquid data from key collection points (that is, sumps or natural gravity drain collection points) are an integral part of any waste characterization process.

Another key factor to be used in this guide is knowledge of background quality of groundwater unaffected by the WMU and knowledge of local sources other than the WMU that may presently be impacting groundwater quality. The main objective then is to choose those constituents that are derived from the WMU (for example, are present in the leachate or residual liquids) at much higher concentrations than groundwater and/or that are only present in the waste or waste residuum (for example, leachate) and absent in groundwater. The analytes chosen must also be mobile, persistent, and easily quantifiable in the specific hydrogeologic and groundwater regime.

1.1 This standard provides a general method of selecting effective constituents for detection monitoring programs at RCRA Waste Disposal Facilities. The process described in this standard presents a methodology that takes into consideration physical and chemical characteristics of the source material(s), the surrounding hydrogeologic regime, and site-specific geochemistry to identify and select those parameters that provide most effective detection of a potential release from a waste management unit (WMU).

1.2 In the following sections, complete details of evaluation of effective monitoring constituents for a groundwater detection-monitoring program were based on site-specific waste characterization.

1.3 The statistical methodology described in the following sections should be used as guidance. Other methods may also be appropriate based on site-specific conditions or for monitoring situations or media that are not presented in this document.

1.4 This practice offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education, experience and professional judgements. Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged without consideration of a project's many unique aspects. The word standard in the title of this document only means that the document has been approved through the ASTM consensus process.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.