Groundwater Inventory, Monitoring, and Assessment Technical Guide - DRAFT

Groundwater Inventory, Monitoring, and Assessment Technical Guide

Contents

4.0Monitoring Groundwater and Groundwater Systems

4.1Groundwater Monitoring Design

4.1.1Groundwater Monitoring Program Objectives

4.1.2Types of Groundwater Monitoring Programs

4.1.3Process for Designing a Groundwater Monitoring Network

4.1.4Considerations in Monitoring Network Design

4.2Groundwater Level Monitoring

4.2.1Selection of Observation Wells, Springs, and Other Sites

4.2.2Frequency of Water-Level Measurements

4.2.3Quality Assurance for Water-Level Measurement

4.2.4Long-term Water-Level Monitoring Data

4.3Groundwater Quality Monitoring

4.3.1Selection of Groundwater Quality Monitoring Sites and Parameters

4.3.2Frequency of Groundwater Quality Sampling

4.3.3Techniques and Protocols for Groundwater Quality Sampling

4.3.4Sources of Sampling Error

4.3.5Quality Assurance and Quality Control Plans

4.4Evaluation and Reporting

4.4.1Water Quality Data Reporting

4.4.2Water-Level Data Reporting

References

Appendix 4-A – Quality Assurance and Quality Control Guidelines for Field Data Collection

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4.0Monitoring Groundwater and Groundwater Systems

Groundwater monitoring encompasses a wide variety of activities, including routine measurements of water level in a network of observation or pumping wells, dye tracer studies, collection of groundwater samples for characterization of the extent and movement of contaminants, and installation and maintenance of stream gauges and meteorological stations. The nature and scope of monitoring programs vary widely depending on the objectives of and resources available. This section describes how to define monitoring objectives that are consistent with investigative objectives, as well as how to select environmental indicators that are consistent with monitoring objectives. This section also presents general guidelines for designing monitoring programs. Specific guidance is providedfor collection of two of the most common types of parameters in groundwater monitoring: groundwater levels and groundwater quality.

The information in this section and associated documents is not intended to provide complete instructions on how to perform the described activities. Although Forest Service personnel may be able to perform some of them, most activities will require contractors with the appropriate skills and equipment. This information is primarily intended to provide Forest Service personnel with a basic understanding of the common activities and options associated with these types of projects, and a base of knowledge to facilitate communication and project management.

4.1Groundwater Monitoring Design

When designing and implementing monitoring programs, it is vital to consider the differences in the spatial and temporal characteristics of ground and surface waters. Groundwater has a three-dimensional distribution within a geologic framework, defined by aquifer and geologic characteristicsand limited accessibility (that is, groundwater must be sampled through a well, spring, or cave). Therefore, the design and implementation of a groundwater monitoring program must be based on a conceptual model grounded in a thorough understanding of the unique hydrogeologic characteristics of the groundwater-flow systemunder investigation and the locations of particular land uses and contaminant sources likely to affect groundwater quality.

4.1.1Groundwater Monitoring Program Objectives

The first step in any monitoring program is defining the objectives of the monitoring. The general objectives for groundwater monitoring programs are:

  • Assess background groundwater quantity and quality conditions;
  • Comply with statutory and regulatory mandates;
  • Determine changes (or lack thereof) in groundwater conditions over time to define existing and emerging trends, guide monitoring and management priorities, and to evaluate effectiveness of land and watermanagement practices and programs; and
  • Improve understanding of the natural and human-induced factors affecting groundwater (e.g., land use activities or facilities).

The monitoring program objectives should be specified in writing so that both the specialists and decision makers have clear understanding of the purpose and goals of the monitoring.

Effective project management of inventory and monitoring programs can ensure appropriate quality assurance and quality controls are incorporated into all program phases. Data quality benefits not only from development of an inventory or monitoring plan, but also from use of techniques and practices described in Appendix 4-A.

4.1.2Types of Groundwater Monitoring Programs

Several types of groundwater monitoring are conducted by Federal, State, local, and private organizations to accomplish one or more of the objectives stated above. The general types include: background monitoring (national or statewide monitoring), baseline monitoring (in advance of project or activity initiation), and monitoring for compliance of permitted facilities.

Gathering background or baseline waterquality data often involves sampling an area for the first time. A wide variety of chemical, physical, and biological contaminants may affect groundwater resources (Fetter1999). As a result, background groundwatermonitoring programs are designed to establish characteristics and to investigate long-term trends in resource conditions. The parameters measured in baseline monitoring programs provide data on pre-activitygroundwater conditions. Some common baseline parameters in groundwater are water levels, temperature, and concentrations of elements, species or chemical substances present which are derived naturally fromgeological, biological or atmospheric sources or from human activities. For these monitoring efforts, parameters are identified on the basis of a thorough understanding of the resource to be evaluated and the potential water quality changes or sources of contamination involved.

Compliance monitoring is conducted in response to specific regulatory requirements or permit conditions for facilities regulated under various programs. These can include the Resource Conservation and Recovery Act (RCRA), the Safe Drinking Water Act, or monitoring in support of remedial activitiessuch as the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Compliance monitoring is also conducted for mining and special use permits.

4.1.3Process for Designing a Groundwater Monitoring Network

A general process for designing a groundwater monitoring network once objectives of the monitoring program areclearly specifiedis outlined below (modified from Florida Department Environmental Protection 2008, table 1). This approach was designed for monitoring water quality to identify contaminants and should be adjusted to reflect the monitoring objectives in specific applications.

1)Describe the physical and hydrogeologic characteristics of the area, including:

  1. Direction and rate of groundwater flow, including impermeable barriers to flow.
  2. Hydraulic characteristics (hydraulic conductivity, storage properties) of aquifer(s).
  3. Areal extent and thickness of aquifer(s).
  4. Vertical hydraulic conductivity, thickness, and extent of any confining beds.
  5. Topography, soil, and vegetation information, and surface water drainage systems surrounding the site.
  6. Areas of potential recharge (includingseptic return, wastewater recharge basins, and effluent streams).
  7. Areas of potential discharge (including springs, wetlands, and pumping wells).
  8. Precipitation and evaporation rates.
  9. River, stream, and spring flow rates.
  10. Ambient groundwater quality.

2)Depending on project objectives, identify the characteristics of the area relevant to groundwater quality or contamination.

  1. Known water quality for all aquifers, other groundwater-bearing media, and associated surface water.
  2. The locations of known or suspected releases of contamination that could impact groundwater and the associated types of contamination.
  3. The locations of known or suspected activities with a potential to release contamination to groundwater and the associated types of contamination.
  4. The locations and extents of known or suspected groundwater contaminant plumes and the associated types of contamination.
  5. The locations and extents of other known or suspected groundwater quality concerns and the associated types of constituents.
  6. The locations and nature of all potential groundwater receptors (including, water supply wells, springs, and groundwater-dependent ecosystems).
  7. Potential flow paths and their associated characteristics that could affect water quality or the migration of contaminants (including, hydraulic conductivity, natural attenuation factors, and the presence of chemicals or constituents that could reduce or increase contaminant migration or impacts).

3)Establish project data quality objectives and associated levels of data quality. Depending on project objectives (e.g., meeting regulatory requirements), there may be required procedures for quality assurance and quality control. Otherwise consult applicable guidance materials (for example, the U.S. Environmental Protection Agency [EPA] website on quality management at U.S. EPA 2012).

4)Establish criteria for selecting existing monitoring wells and other monitoring sites(Lapham et al. 1997, pp. 6-11 discuss selection of existing wells, selection criteria for the wells, and limitations and advantages of using existing wells for groundwater monitoring).

  1. Obtain design specifications and construction data for the existing monitoring wells, confirm they can be used to meet project objectives, and establish elevations of measuring points at the selected wells and other monitoring sites.
  2. Identify the existing monitoring points meeting the criteria to be used.

5)Identify the locations of the proposed monitoring sites necessary to fill in the gaps in the existing monitoring sites.

  1. Determine the construction and development requirements of any new wells (see Forest Service GroundwaterTechnical Note on Well Construction and Development) or other monitoring sites;

6)Indicate those designated as background or potentially contaminated sites.

7)Establishand document natural background (where available) or background quality of the groundwater in the vicinity of the monitoring network.

8)Develop measurement and sampling frequency for monitoring sites.

9)Establish a schedule periodically to review the monitoring data (to check for anomalies, data collection or equipment problems and network effectiveness), and establish data analysis protocols for review of monitoring data.

10)Develop a decommissioning plan for sites[1] in the monitoring network for such a time when the network is no longer required (note that some states may have limits on how long wells may remain in place if they are no longer being used as well as requirements for their abandonment; check for any State requirements or guidance first).

11)Develop a field safety plan for conducting the monitoring activities.

4.1.4Considerations in Monitoring Network Design

Observation networks are designed for a specific purpose. A network may be used to monitor long-term effects of climatic changes on groundwater systems, to monitor the effects of a new well field adjacent to a unit on groundwater levels within the administrativeboundaries, or to monitor contaminant movement from a landfill or other pollution source. Each of these networks has different design considerations.

This section includes a general discussion of factors that should be considered in the design of monitoring networks, including well placement, the use of new and existing wells, and cost as a limitation on monitoring. Forest ServiceGroundwater Technical Notes address related field procedures, including:

  • Groundwater Level Measurement,
  • Well Construction and Development,
  • Groundwater Monitoring Well Installation for Shallow Water Tables and Wetlands
  • Groundwater Sampling

Proper design of a monitoring network is critical to meeting monitoring objectivessuccessfully. Groundwater monitoring undertaken by the Forest Service typically is oriented towards addressing site-specific or project-specific issues such as mine operations, CERCLA activities, snow making, water rights, drinking-water system operation, or particular Forest Service research projects, including prescribed fire and thinning(ACWI 2009, p. 25). Other Federal agencies, such as the U.S. Department of Interior, U.S. Geological Survey (USGS) and the National Park Service, EPA, and individual State agencies also maintain groundwater monitoring networks, but each network is designed to meet agencies’ specific objectives. Although this section focuses on the use of monitoring wells, both springs and surface water bodies (if present) should also be monitored to provide a more complete picture of the hydrologic system.

A well-designed groundwater monitoring network will fulfill the monitoring objectives and be cost effective. The type, depth, construction details, and locations of wells and the types and locations of other monitoring points that comprise the network (see Forest Service Groundwater Technical Note onMonitoring Well Construction and Development) are highly dependent on the objectives of the network. For example, is the network intended to monitor groundwater levels only or to also monitor waterquality? Is the network intended to monitor natural or undisturbed groundwater conditions or to monitor the effects of development (e.g., pumping, mining) or contaminant movement? If the network is intended to monitor the effects of development or land management activities, baseline hydrologic conditions shouldbe established by the network prior to development. If the network is intended to monitor movement of existing or potential contaminants, information on thetype(s) of contaminantsand the frequency of monitoring will be needed. In addition, it will be necessary to identify whether the contaminants of interest might exist at background levels in the groundwater system. A network intended to monitor salt-water intrusion into an aquifer will be much simpler than one intended to monitor low levels of hazardous chemicals.

Equally critical to the success of the monitoring network is an understanding of the hydrogeologic conditions of the area to be monitored. This understanding is fostered through the development of a conceptual model of the area. Knowledge of groundwater flow paths allow monitoring wells to be located in the correct areas to detect contaminants, as well as to monitor background conditions (i.e., uncontaminated conditions or pre-existing occurrences). Design of a network to monitor a relatively uniform, alluvial aquifer can be very different from a network to monitor groundwater in a fractured-rock or karst aquifer. The American Society for Testing Materials (ASTM 1996) and U.S. EPA (Quinlan 1989) developed guidelines for monitoring and sampling groundwater in karst and fractured-rock aquifers.

Selection of the optimum number of wells to include in the monitoring network is often a hit-and-miss process. It may be impractical and expensive to include all existing wells in the network, although this is commonly done. Wells may exist in areas or produce from depths or ranges of depths that will not monitor or detect movement of the contaminant of interest so these wells may not need to be monitored. Use of statistical methods to select wells to monitor, or to locate new wells, may improve the cost effectiveness of the network as illustrated in figure 4-1. This pair of maps illustrate that a small number of strategically-placed wells can provide a much greater “return on investment” than a large number of wells. Visual Sample Plan (VSP) developed by the Pacific Northwest National Laboratory ( and Spatial Analysis and Decision Assistance (SADA) developed by the University of Tennessee-Knoxville ( are two well developed and widely accepted software tools that support the development of a defensible sampling plan based on statistical sampling theory and the statistical analysis of sample results. They can be downloaded and used for free.

Figure 41—(A) Water-level elevation in the Equus Beds aquifer, in central Kansas, based on a network of 244 observation wells. (B) Water-level elevation in the Equus Beds aquifer, based on data from a network of 47 wells selected by using 16-square-mile hexagons. The two contour maps are very similar, differing by less than 5 percent. (Taylor and Alley 2001, figs. C-1, C-2).

Analysis of groundwater models may also help to identify gaps in the monitoring network and indicate areas where additional monitoring wells need to be located. If wells need to be drilled to fill in gaps in the monitoring network, they should be located and constructed in such a way as to ensure that objectives of the monitoring network are met. In addition to wells, springs and surface water bodies within the area should also be monitored, even if they are on adjoining private land.

For identifying and delineating contaminant plumes it has become common practice to use an approach that permits rapid collection and field-based analysis of samples so that new sample locations can be identified and sampled during the same field effort. Ideally, the extent of contamination will be identified in just one round of fieldwork. The Triad approach was originally developed by the U.S. EPA to specifically facilitate these types of “dynamic field investigations.” It is now supported by multiple Federal and State agencies through the Triad Resource Center (2012).

The most common approach is to use direct-push technology, such as a Geoprobe®, to establishholes and install temporary wells for collection of soil and grab groundwater samples. For small investigations, sample location selection is guided by visual or olfactory indications of contamination in soil samples as well as field measurements or screening by using easily operated equipment. For large investigations, more advanced field-based analytical techniques, including mobile field laboratories, can cost effectively allow selection of new sample points and delineation of contamination in the field. Permanent monitoring wells are then installed and sampled for laboratory analyses to confirm the results of the initial investigation. If the contaminants of concern are sufficiently volatile, it may be more cost effective to perform a soil gas survey first to tentatively identify the extent of contamination and then place and sample monitoring wells to confirm it.

Surface geophysical methods might allow preliminary identification or delineation of important geological or hydrogeological characteristics or contaminant extent(see Forest Service Groundwater Technical Note on Geophysical Methods). This may help minimize the number of monitoring wells required while optimizing their placement.

Monitoring Program Design

Monitoring program design addresses the geographic area covered by the program, the number and type of wells and other monitoring sites needed to characterize conditions accurately, the frequency of measurement or sampling, and the parameters to be monitored, including the specific water quality constituents to be analyzed (if any). In determining the program design, a critical issue affecting program costs is the decision whether to use existing wells or to install new monitoring wells. Existing wells may be found in the area to be monitored in the form of community water supply or residential drinking water wells, irrigation wells, or wells used for compliance monitoring or other ambient monitoring activities. Existing wells may be adequate to support the monitoring program if they are completed within the aquifer of concern, screened at an appropriate sampling depth, constructed properly, and in sufficiently acceptable condition so as not to interfere with the sampled analytes.