A. Roger Anzzolin, Environmental Engineer/Hydrogeologist,

U.S. Environmental Protection Agency

Office of Ground Water and Drinking Water

Mary Siedlecki, Research Geochemist

Research Triangle Institute

Ground water is a vital national resource. In many parts of the Nation, ground water serves as the only reliable source of drinking and farm and livestock irrigation water. Unfortunately, this vital resource is vulnerable to contamination and ground water contamination problems are being reported throughout the country.

To ascertain the extent to which our Nation’s ground water resources have been impacted by contamination problems, Section 106(e) of the Clean Water Act (CWA) requests that each State monitor ground water quality and report the findings to Congress in their biennial 305(b) State Water Quality Reports. Recognizing that an accurate representation of our Nation’s ambient ground water quality condition is a complex problem, the U.S. Environmental Protection Agency (EPA), in partnership with interested States, critiqued the existing guidelines and proposed changes to the guidelines that would enhance assessment of ground water quality within the 305(b) program. The new guidelines were introduced to States for the 1996 305(b) reporting cycle.

The most significant change in the 1996 guidelines was the request that States report ground water quality data for selected aquifers or hydrogeologic settings (e.g., watersheds) within the State. The focus on specific aquifers or hydrogeologic settings provides for a more quantitative assessment of ground water quality than was possible prior to 1996.

State response to the new ground water guidelines was excellent. Thirty-three States reported ground water quality data. In total, data were reported for 162 aquifers and other hydrogeologic settings. States used data from ambient monitoring networks, public water supply systems (PWS), private and unregulated wells, and special studies. Finished water quality data from PWS were the most frequently used source of data. Ambient monitoring networks and untreated water quality data from PWS and private and unregulated wells were the next most frequently used sources of data.

Ground water data reported by States in their 1996 305(b) State Water Quality Reports reflected the diversity of our Nation’s individual ground water management programs. This diversity presents a challenge in assessing ground water quality on a national basis. For preparation of the National Water Quality Inventory 1996 Report to Congress, ground water quality assessments were performed using comparable data groupings. Data most closely approximating actual ground water quality conditions (e.g, untreated ground water) were given special consideration in the assessments.

In 1972, Congress enacted the first comprehensive national clean water legislation in response to growing public health concern over serious and widespread water pollution. The CWA is the primary Federal law that protects the health of our Nation’s waters, including lakes, rivers, and coastal areas. Beginning in 1974, Section 106(e) of the CWA required States to carry out as part of their programs:

Monitoring data gathered by States under Section 106(e) of the CWA were submitted to the Administrator in biennial State Water Quality Reports as required under Section 305(b) of this same act. The first such report was submitted to the Administrator in 1974. This report consisted primarily of data derived from water quality databases in existence at the time (e.g., U.S. EPA STORET). Data evaluation was negligible and ground water quality data were absent from the report. Similar reports were produced for 1975 and 1976. Although a hiatus in report production occurred between 1976 and 1982, reports have been generated biennially since 1982.

Ground water was included in the biennial reports for the first time in 1982. It was introduced as one of "two additional water quality-related issues most commonly cited by States" as of concern. The half page of text devoted to these additional issues pointed out that ground water contamination was widely reported in over half the States.

Given that States were expressing concern over ground water related issues, a set of guidelines was developed to assist States in reporting ground water information. The first set of guidelines was developed for the 1986 biennial reporting cycle. In these guidelines, States were provided with minimum ground water reporting criteria, which focused on identifying the major sources of contamination impacting ground water resources. The 1986 biennial report was formatted into four sections: ground water use in the United States, major sources of ground water contamination and contaminants of concern, ongoing State programs for ground water protection, and current Federal initiatives designed to assist States in developing their ground water protection programs. All subsequent biennial reports contain these same sections.

For the 1988 biennial report, several States broadly described their ground water resources as being "excellent" to "good" in quality. Based on this information, it was concluded that the Nation’s ground water resources were "quite good." Similar conclusions were drawn in subsequent biennial reports.

Broad generalizations concerning the quality of State ground water resources failed to provide either a complete or an accurate representation of ambient ground water conditions (i.e., background or baseline water quality conditions). However, assessing the quality of our Nation’s ground water resources is no easy task. An accurate and representative assessment of ambient ground water conditions ideally requires a well-planned and well-executed monitoring plan. Such plans are expensive and may not be compatible with State administrative, technical, and programmatic initiatives. As a consequence, EPA, in partnership with interested States, critiqued the existing guidelines and proposed changes to the guidelines that would improve assessment of ground water quality within the 305(b) program.

The most significant change for 1996 was the request that States provide ground water information for selected aquifers or hydrogeologic settings (e.g., watersheds) within the State. The focus on specific aquifers and hydrogeologic settings provides for a more quantitative assessment of ground water quality than was possible in previous reporting cycles. The new guidelines were introduced to States as part of the 1996 305(b) reporting cycle.

To ensure consistency with previous 305(b) reporting cycles, the 1996 Guidelines incorporated all of the components requested during previous 305(b) reporting cycles. Specifically, the 1996 Guidelines continued to request an overview of ground water contamination sources and a description of State programs dedicated to ground water protection. In addition, the 1996 Guidelines contained two new table formats encouraging States to report data for selected aquifers or hydrogeologic settings within the State.

States reported on the type and number of contamination sites per aquifer or hydrogeologic setting having the potential to adversely impact ground water quality using Table 1. Specifically, States were asked to identify the type and number of contaminant source(s) present in the reporting area (e.g., NPL, LUST, RCRA, Superfund), the number of sites that are listed or have confirmed releases, and the number of sites with confirmed ground water contamination. The data reported in Table 1 provide a measure of aquifer vulnerability.

States reported ground water monitoring data for selected aquifers or hydrogeologic settings using Table 2. States compared quantitative ground water monitoring data to water quality standards. Depending upon the results of the comparison, the data were summarized into major categories, including "not detected at or above the method detection limit (MDL)," "exceeding the MDL but less than the maximum contaminant level (MCL) defined under the Safe Drinking Water Act," and "exceeding the MCL." This type of data provides a measure of the condition of the aquifer.

Because the concept of reporting quantitative data for specific aquifers within a State was new, EPA recommended that ground water quality be assessed incrementally. For 1996, States were encouraged to set a priority for reporting results for areas of greatest ground water demand and/or vulnerability. With each subsequent 305(b) reporting cycle, States were encouraged to continue the process through the assessment of progressing numbers of aquifers or hydrogeologic settings. In this way, an increasingly greater area of each State will be assessed.

Reporting ground water quality data on an aquifer-specific basis was new to the 305(b) program in 1996. Due to differences in State programs and priorities, it was anticipated that there would be wide variation in reporting style among the States. Still, State response to the new Guidelines was excellent and it was evident that States welcomed the changes made in the program.

Thirty-three States reported data summarizing ground water quality. In total, data were reported for 162 specific aquifers and other hydrogeologic settings. States that were unable to report ground water data for specific aquifers assessed ground water quality using a number of different hydrogeologic settings or "reporting units," including statewide summaries, counties, watersheds, basins, and special monitoring areas within a State that stood out due to potential vulnerability. Figure 1 presents an overview of the States that were able to provide ground water quality data for specific or "differentiated hydrogeologic units" within the State.

Ground Water Quality Data Sources

Data collection and organization vary among the States. Furthermore, a single data source for assessing ground water quality did not exist for purposes of the 1996 biennial report. EPA suggested several types of data that could be used for assessment purposes (e.g., ambient ground water monitoring data, untreated water collected from private or unregulated wells, untreated water collected from public water supply wells, and special studies).

States were encouraged to use available data that best reflected the quality of the resource. Depending upon data availability and the judgment of the ground water professionals, one or multiple sources of data were used in the assessments. The majority of the States opted to use multiple sources of data. As shown in Figure 2, States used data collected from ambient monitoring networks, public water supply systems, private and unregulated wells, facility monitoring wells, and special studies.

Finished water quality data from public water supply systems were the most frequently used source of data (Figure 3). Ambient monitoring networks and untreated water quality data from private and unregulated wells were the next most frequently used sources of data.

The primary basis for assessing ground water quality using Table 2 is the comparison of chemical concentrations measured in ground water to water quality standards. For 1996, EPA suggested that States consider using MCLs defined under the Safe Drinking Water Act (SDWA). In general, most States used the MCL concentrations for comparison purposes. Exceptions occurred when State-specific standards were available.

It was not possible for States to sample and analyze ground water for every known constituent. For ease of reporting, EPA suggested that the ground water quality data be summarized into parameter groups (e.g., VOCs, SVOCs, and nitrate). These three groups were recommended because they are generally indicative of contamination originating as a result of human activities. States were also encouraged to report data for any other constituents of interest.

Nationally, more States reported data for volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), nitrates, and metals than any other constituent or group of constituents. Parameter groups and individual constituents identified by States in their 1996 305(b) reports are summarized in Table 3. As shown, States reported data for a wide variety of constituents. Organic as well as inorganic and microbial constituents were included in the ground water assessments depending upon State interests and priorities. Although the greatest quantity of data was reported to nitrate and VOCs, it was clear that States were also concerned with SVOCs, pesticides, metals, and bacteria.

Ground water quality data reported by States in 1996 represented difference sources, often with different monitoring purposes. As a consequence, national comparisons were not appropriate. Rather, ground water quality comparisons were performed using comparable data groupings. Data most closely approximating actual ground water quality conditions (e.g., untreated ground water ) were given special consideration in the assessments.

The 1996 biennial report presented tabulations of data. Table 4 presents an example of ground water quality data reported for nitrate. As shown, 15 States reported nitrate data for ambient monitoring networks. Nitrate was measured at concentrations exceeding the MCL of 10 mg/L in 8 of the 15 States for a total of 26 units and 267 wells impacted by nitrate. Thus, approximately 50% of the reporting States indicated elevated levels of nitrate in ground water collected from ambient monitoring networks. This percentage was even higher for States reporting data for untreated water from PWS systems and from private/unregulated wells (i.e., nitrate levels exceeding the MCL were reported by five out of seven States for untreated water from PWS and by nine out of ten States for untreated water from private/unregulated wells).

The most significant change in the assessment of ground water quality within the 305(b) program was the focus on assessing ground water quality for specific aquifers and/or hydrogeologic settings. The positive response from States indicated that they welcomed the changes made in 1996 and were responding by developing and implementing plans to report more aquifer-specific information in the future. Still, ground water data reported in 1996 were too diverse and too sparse to be used to characterize ground water quality nationally for the 1996 305(b) reporting cycle. Despite this shortcoming, a framework for reporting ambient ground water quality data on a biennial basis has been developed under the 305(b) program, and it is expected that data diversity will decrease with each successive 305(b) cycle as the direction and focus of the program become clearer to both States and EPA. Thus, with additional 305(b) reporting cycles, the data set will achieve the necessary maturity to characterize our Nation’s ground water resources in a meaningful fashion.

With a framework for reporting ground water quality data on a national basis in place, the next step is to begin accumulating sufficient data to characterize the condition of our Nation’s ground water resources. States have begun reporting data for the 1998 305(b) cycle. Although States are increasing their individual coverages by assessing aquifers not previously assessed during the 1996 cycle, national coverage will still not be achieved in 1998. However, based on their State Water Quality Reports, it is evident that some States have achieved a level of sophistication to allow the assessment of ground water quality on a statewide basis.

Idaho is one State that currently uses a geographic information system (GIS) dataset and displays the data spatially. The State of Idaho supplied coverages in the form of hydrogeologic subareas, major aquifer flow systems, and statewide monitoring well locations. Nitrate concentrations measured in 1995 and 1996 in monitoring wells constituting the State monitoring network were also supplied by Idaho. The concentration measured in each of the wells is presented graphically in Figure 4. This same information is summarized in Figure 5 according to the number of wells in an aquifer having a certain percentage of nitrate concentrations exceeding background levels.

As shown in the attached set of figures, it is possible to provide ground water layers on a state-by-state basis given that the individual States can provide both the aquifer coverage and associated data. The 1998 Report to Congress will highlight and illustrate individual State efforts.

With individual States leading the way, it is clear the meaningful and representative assessment of ground water quality can be achieved within the 305(b) program in the near future.

Table 1. Ground Water Contamination Summary

Table 4. Nitrates

MCL = Maximum contaminant level.

PWS = Public water supply.