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Energy and Environment Directorate

Research Capabilities

Subsurface Monitoring and Compliance

The objective of a subsurface monitoring program is to select and implement a suite of monitoring technologies that are both technically robust and cost-effective and provide an effective means of evaluating the behavior of the subsurface and subsurface processes (i.e., verify that the site is behaving as predicted and within any regulatory constraints) and to detect any unforeseen events (i.e., verify that a site is not endangering underground sources of drinking water). Both direct and indirect (e.g. geophysical) measurements may be used collaboratively with numerical models to help verify that the subsurface is operating as predicted. Monitoring wells provide direct access to the subsurface and are fundamental to compliance monitoring at permitted facilities.

General Groundwater Monitoring Requirements

Groundwater monitoring systems must be capable of yielding samples from the uppermost aquifer that represent both background groundwater water quality (usually from an upgradient well) and the extent of groundwater contamination at a compliance (e.g. waste management unit) boundary from downgradient wells. Each time groundwater is sampled, the owner and operator must determine the rate and direction of groundwater flow and measure the water elevation in each well. The number, spacing, and depths of monitoring wells depend on site-specific characteristics such as aquifer thickness and groundwater flow rate and direction. Unless approved by the appropriate Director of an approved state, a qualified groundwater scientist must certify these system specifications. In addition, all monitoring well boreholes and other measurement, sampling, and analytical devices must be operated to meet design specifications for the duration of the groundwater-monitoring program. The U.S. Environmental Protection Agency recognizes that local conditions can make installation of a monitoring well system around each permitted facility difficult. In approved states, multiple regulated units may share a common groundwater monitoring system, provided that sharing the multiple unit system is as protective of human health and the environment as installing a separate monitoring system for each unit.

Measuring Groundwater Monitoring Compliance

Consistent sampling and analytical procedures are essential to obtain reliable monitoring results that accurately measure hazardous constituents and other parameters established in either detection monitoring or assessment monitoring programs. Each groundwater-monitoring program must be developed to ensure that monitoring results provide an accurate representation of groundwater quality at both background and downgradient wells. For example, sampling and analysis programs must include procedures and techniques for sample collection, sample preservation and shipment, analytical procedures, chain of custody control, and quality assurance and quality control (QA/QC) procedures. In evaluating groundwater quality monitoring data, the owner and operator must use one of the approved statistical methods. The selected method, which will be used to identify statistically significant evidence of groundwater contamination at a monitoring well, must be appropriate for the type and distribution of chemical constituents detected, or suspected to be present, in the groundwater. The frequency and number of groundwater samples necessary to establish groundwater quality vary with the project objectives, monitoring design, and type of statistical methods selected for data analysis.

PNNL Monitoring Network Design

PNNL scientists have extensive experience in designing subsurface-monitoring systems that meet local conditions as well as state and/or federal requirements. Sometimes those two objectives are in conflict; technology and scientific methods do not progress at the same pace as legislation. Where enforcement flexibility is possible, staff of the Geosciences Group can offer scientifically defensible network design recommendations that may not be directly addressed in the strict language of state and federal statutes. Provided that regulatory authorities are willing to explore new and innovative approaches to subsurface monitoring, our staff can apply the latest scientific techniques to measure facility compliance.

Energy and Environment

Core Research Areas