Monitoring Well Standards, Introduction
Groundwater monitoring wells are principally used for observing groundwater levels and flow conditions, obtaining samples for determining groundwater quality, and for evaluating hydraulic properties of water-bearing strata. Monitoring wells are sometimes referred to as "observation wells."
The quality of water intercepted by a monitoring well can range from drinking water to highly polluted water. In contrast, production or "water wells" are usually designed to obtain water from productive zones containing good- quality water.
The screen or perforated section of a monitoring well usually extends only a short length to obtain water from, or to monitor conditions within, an individual water-bearing unit or zone. Water wells are often designed to obtain water from multiple water-bearing strata. Although there are usually differences between the design and function of monitoring wells and the water wells, water wells sometimes are used as monitoring wells, and vice versa.
Monitoring wells, along with other types of wells, can provide a pathway for the movement of poor-quality water, pollutants, and contaminants. Because monitoring wells are often purposely located in areas affected by pollutants and contaminants, they pose an especially significant threat to groundwater quality if they are not properly constructed, altered, maintained, and destroyed.
The California Legislature amended the California Water Code in 1986 specifically to include requirements for monitoring well standards. Monitoring wells were previously assumed by the Department to be covered by the collective term "well" in the law.
History of Monitoring Wells
Monitoring wells were first used mainly for water level measurement. These wells were often referred to as piezometers in reference to the "piezometric surface" of groundwater. In recent years, the term "piezometric surface" is often replaced by "potentiometric surface." However, the term "piezometer" is still sometimes used for monitoring wells installed only for water level measurement.
Many water level monitoring wells constructed in the past were relatively large in diameter in comparison to today's monitoring wells. Wells up to 10- inches in diameter were often constructed to accommodate various means of water level measurement, including floats for mechanically-operated, continuous water level recorders. Many inactive water wells that could accommodate mechanical water level recording equipment were used as monitoring wells.
Modern electronic water level measuring and recording devices now allow for small-diameter water-level monitoring wells. Some continuous water-level measurement devices can be used in wells less than 2-inches in inside diameter.
The use of monitoring wells for groundwater sampling for chemical analysis has increased significantly in the past two decades. The following factors have all served to increase the frequency and scope of groundwater quality investigations and the number of monitoring wells constructed:
- Advances in analytical and environmental chemistry;
- Increased knowledge of the adverse effects of chemicals on humans;
- Public awareness of groundwater pollution;
- The advent of federal groundwater quality protection legislation in the 1970s, and,
- Statutes relating to groundwater enacted by the California Legislature.
Since the 1970s an entire industry has developed around groundwater quality monitoring and monitoring well construction. Numerous private firms are involved in providing technical services for the design and implementation of groundwater quality investigations. Many firm are involved in the manufacture, distribution, and marketing of materials and equipment used in constructing and operating monitoring wells.
Most monitoring wells constructed today are used to assess:
- The nature and distribution of pollutants and contaminants in groundwater;
- The nature and distribution of naturally occurring chemical constituents;
- Subsurface hydrologic conditions; and,
- Hydraulic properties of strata as they relate to pollutant and contaminant movement.
Some monitoring wells are designed to be multipurpose. Monitoring wells can sometimes be used as "extraction" or "injection" wells for mitigation of pollution or contamination.
Although a significant number of monitoring wells constructed today are for detection and assessment of groundwater quality impairment, many monitoring wells are constructed for evaluating groundwater supply conditions by allowing groundwater level measurement and/or aquifer testing. Still others are constructed for observing water levels associated with excavations and irrigated agriculture.
During 1989, approximately 20 percent of all well drilling in California was for monitoring wells, based on well driller's reports received by the Department of Water Resources. Monitoring wells have been constructed in nearly all California counties. The largest concentrations of water quality monitoring wells occur in metropolitan areas of the State. Large numbers of monitoring wells are installed for detection and assessment of leaks from underground storage tanks.
Types of Monitoring Wells
For the purpose of these standards, the term "monitoring well" is limited to wells designed to monitor subsurface water in the saturated zone, existing at or above atmospheric pressure (groundwater); rather than water, water vapor, and/or gases contained in the unsaturated or vadose zone. Monitoring devices used for the unsaturated zone differ significantly from those used for the saturated (groundwater) zone.
As shown in Figure 2 (B74-90) three basic types of monitoring wells or "installations" are:
- Individual monitoring wells;
- Nested monitoring wells; and,
- Clustered monitoring wells.
Individual monitoring wells consist of a single casing "string" within a borehole, as illustrated in Figure 2 (B74-90) and Figure 3 (B74-90). Individual monitoring wells are installed in unique locations apart from one another. They are the most common type of monitoring well constructed in California.
Nested monitoring wells consist of two or more casing strings within the same borehole. Normally the screened interval of each casing string is designed to obtain water from different aquifers or water-bearing zones. The purpose of a nested monitoring well is much the same as clustered monitoring wells.
Clustered monitoring wells consist of individual monitoring wells situated close together, but not in the same borehole. The wells within a cluster are normally constructed to obtain water from different aquifers or water-bearing zones. Clustered wells are most often used for monitoring groundwater conditions at various depths in roughly the same area.
A nested monitoring well can be difficult to construct because of multiple casings within the same borehole. Care is required during construction to ensure water-bearing zones for each casing string are hydraulically isolated from one another and the annular seals are effective. Some regulatory agencies may prohibit the use of nested monitoring wells for certain contamination or pollution investigations. Normally this can be due to uncertainties about whether water-bearing strata can be isolated and whether the annular seals in a nested well are always effective.
Individual casing strings for the various types of monitoring wells discussed above, are sometimes designed to obtain water from more than one aquifer or water-bearing unit. These casing strings usually have multiple intervals of openings or screen. Such well casing strings, often referred to as "multi-level monitoring wells," can sometimes serve as a preferential pathway for the movement of poor quality water, pollutants, and contaminants from one unit to another. Some regulatory agencies prohibit the use of multi-level monitoring wells for certain pollution or contamination investigations out of concern for water quality protection and data quality requirements.
Figure 2 (B74-90). Avenues of Entrance for Pollutants to Wells
Figure 3 (B74-90). Cross Section of a Typical Monitoring Well
Authority and Responsibilities of Other Agencies
As discussed above, Congress enacted major legislation dealing with groundwater quality protection during the 1970s. Regulatory programs initiated by federal legislation, such as the Resources Conservation and Recovery Act (RCRA) and its amendments, are administered by the U.S. Environmental Protection Agency. Some administration and enforcement activities related to federal legislation have been delegated to California State agencies.
The California Legislature enacted legislation expanding efforts for groundwater quality protection in California beyond federal requirements. The Legislature assigned several State agencies various responsibilities for investigation, mitigation, and control of groundwater pollution and contamination.
The lead enforcement agency for most groundwater quality protection issues in California is the State Water Resources Control Board (State Board) and the nine California Regional Quality Control Boards (Regional Boards). The State Board oversees the activities of the nine Regional Boards.
The Department of Health Services or, under some circumstances, the U.S. Environmental Protection Agency, is the lead enforcement agency for groundwater quality issues related to hazardous wastes.
The EPA, the Department of Health Services, and the State Board have adopted regulations or standards establishing monitoring requirements for "waste facilities". These regulations or standards include requirements for design and performance of monitoring wells that are often more stringent than standards in this bulletin.
Other State government organizations concerned or directly involved with groundwater quality assessment or protection in California include:
- Department of Conservation, Division of Oil and Gas,
- Department of Food and Agriculture,
- Integrated Waste Management Board, and,
- Department of Water Resources.
California cities, counties, and local water agencies are also involved with groundwater quality assessment and protection.
The Division of Oil and Gas has authority and responsibility for geothermal wells and other special wells constructed in the State's Geothermal Resources Areas (pursuant to Chapter 4, Division 3, California Public Resources Code). Shallow wells drilled for geothermal observation are subject to regulations and standards established by DOG.
After July 17, 1991, the California Environmental Protection Agency will oversee the activities of the State Water Resources Control Board and the Integrated Waste Management Board. Some of the environmental protection activities of the Department of Health Services and the Department of Food and Agriculture will also come under the California Environmental Protection Agency.Scope, Organization, and Limitations of Standards
Certain standards that apply to water wells also apply to monitoring wells. Therefore, the Monitoring Well Standards refer frequently to the Water Well Standards. Standards that apply only to monitoring wells, or that require emphasis, are discussed in detail in the Monitoring Well Standards. The Monitoring Well Standards are arranged in a format similar to the Water Well Standards.
These standards are not intended as a complete manual for monitoring well construction, alteration, maintenance, and destruction. These standards serve only as minimum statewide guidelines towards ensuring that monitoring wells do not constitute a significant pathway for the movement of poor quality water, pollutants, or contaminants. These standards provide no assurance that a monitoring well will perform a desired function. In most cases groundwater monitoring practices and monitoring well performance, or functional requirements, fall under the purview of the various agencies mentioned earlier. Ultimate responsibility for the design and performance of a monitoring well rests with the well owner and/or the owner's contractor, and/or technical representative(s).
Quick Links
- Bulletin 74-81 Introduction
- Bulletin 74-90 Introduction
- Part I. General, Water Well Standards
- Part II. Water Well Construction
- Part III. Destruction of Water Wells
- Monitoring Well Standards, Introduction
- Part I. Monitoring Well Standards, General
- Part II. Monitoring Well Construction
- Part III. Destruction of Monitoring Wells
- Cathodic Protection Well Standards
- Part I. General, Cathodic Protection Well Standards
- Part II. Cathodic Protection Well Construction
- Part III. Destruction of Cathodic Protection Wells
- Appendices