Introduction

The U.S. Geological Survey (USGS) has been working with Albany Utilities, Dougherty County, Georgia (Ga.) (fig. 1), to monitor groundwater quality and availability since 1977. Heavy pumping since the 1960s and 1970s from the Claiborne, Clayton, and Cretaceous aquifer system, which underlie the Upper Floridan aquifer, has resulted in substantial water-level declines in the Albany area (fig. 2; Hicks and others, 1981). To meet increasing demands, Albany Utilities developed a large well field that was put online during October 2003 (fig. 3). The well field is made up of eight supply wells that primarily withdraw water from the Upper Floridan aquifer. The Upper Floridan aquifer is a highly productive and porous limestone aquifer and is the uppermost reliable groundwater source in the area. Because of the karstic landscape and the local recharge to the aquifer, groundwater levels and quality may be affected by local and regional land use. During 1997, the Dougherty County Health Department collected water samples from the Upper Floridan aquifer from a well in the southwestern Albany area, Georgia, that supplied drinking water to a private school. These samples contained concentrations of nitrate greater than 10 milligrams per liter (mg/L), which is the primary maximum contaminant level for public drinking-water supplies (40 CFR, part 141, subpart B). The contaminated samples prompted the Dougherty County Health Department to sample over 700 wells in the area and identify a zone of nitrate contamination in the vicinity of the public-supply well field southwest of Albany, Ga. (Wenner and Reyher, 1999). Water from 12 percent of the wells sampled had nitrate concentrations above the 10-mg/L primary maximum contaminant level (40 CFR, part 141, subpart B; Wenner and Reyher, 1999). Each of the contaminated wells are open to the Upper Floridan aquifer, which supplies water for the public-supply well field and most domestic and irrigation wells in the southwest Albany area.

The USGS maintains a project website, “Groundwater Monitoring - Albany-Dougherty County Area, Georgia,” that contains a summary of the project, maps, and related publications (USGS, 2020a). The website also has a list of continuous monitoring wells with links to the USGS Water Data for the Nation database, allowing the user to access the data from that site.

Groundwater Levels

Water-level data were obtained from selected wells open to the Upper Floridan aquifer on an annual basis. During January 2021, water levels were collected from 35 wells and ranged from about 138 feet (ft) above the National Geodetic Vertical Datum of 1929 (NGVD 29) in the southern part of the study area to about 197 ft above NGVD 29 in the northern part of the study area (fig. 3). During December 2021, water levels were collected from 32 wells and ranged from about 136 to 196 ft above NGVD 29. During November 2022, water levels were collected from 39 wells and ranged from about 145 to 192 ft above NGVD 29. The hydraulic gradient of the Upper Floridan aquifer generally slopes southward and toward the Flint River at a rate of about 3–20 feet per mile but is generally around 7 feet per mile in the Albany area. The Flint River is a major discharge area for the aquifer; however, when the river is high, the gradient may reverse in the southern part of the study area (Peck and others, 2013).

Water levels are continuously monitored by the USGS in the study area in the Upper Floridan, Clayton, and Claiborne aquifers and Cretaceous aquifer system and are routinely measured in the surficial aquifers. The water-level data are available on the USGS NWIS database via the Albany project website (USGS, 2024; https://www.usgs.gov/centers/sawsc/science/groundwater-monitoring-albany-dougherty-county-area-georgia). Below is a summary of groundwater levels within these five aquifers during April 2020 through January 2023 relative to period-of-record median water levels. An example of a hydrograph from each aquifer (not including the surficial aquifer), along with the period-of-record median water levels for the well, is presented in figure 4. Water levels in each aquifer respond to drought conditions because of variations in recharge and (or) irrigation pumping. Figure 5 shows the areal percentages of Dougherty County, Ga. in U.S. Drought Monitor categories during March 1, 2020, through February 28, 2023 (National Drought Mitigation Center, 2024). The graph shows that Dougherty County experienced only short periods of abnormally dry (D0) conditions during March 2020 through October 2021. One hundred percent of the county experienced longer periods of abnormally dry (D0) conditions and moderate drought (D1) conditions from November 2021 through January 2023 (fig. 4). Hydrographs of wells 12L020 and 12L021 show water-level response to nearby pumping (fig. 5C–D). More information on current groundwater levels in Georgia is available on the USGS “Groundwater Conditions of Georgia” website at https://ga.water.usgs.gov/infodata/gwconditions/. The following water-level observations were made for the time period between April 2020 through January 2023:

Groundwater Quality

Samples have been collected according to standard USGS methods (USGS, variously dated) annually—typically after the growing season in the fall or early winter—since 1998 from as many as 19 wells in the Upper Floridan aquifer and the Flint River for water-quality analyses. The samples have primarily been analyzed for nitrate plus nitrite as N concentrations because of historically high concentrations of nitrate originally documented in well 12L061. Well 12L061 was abandoned during 2012, and sampling resumed at a new well (12L405) on the same property during 2014. Three wells in the northern part of the study area were sampled for pesticide concentrations, but none were detected (fig. 6). Nitrate plus nitrite as N concentrations from well 12L405 ranged from 7.6 mg/L during 2014 to 8.6 mg/L during 2016, which may indicate that the higher levels of 11–13.4 mg/L from well 12L061 could, in part, have been due to compromised well construction (fig. 7). Nitrate plus nitrite as N concentrations were below 1 mg/L from 2003 to 2012 at Flint River site 02352560 (figs. 6 and 7). Water-quality samples were collected and analyzed for major ions, including nitrate plus nitrite as N, at eight wells in January 2021, seven wells in December 2021, and eight wells in November 2022. Nitrate plus nitrite as N concentrations ranged from 2.3 mg/L in well 12L344 (Upper Floridan aquifer) to 10.5 mg/L in well 12L376 (surficial aquifer) during January 2021, 3.9 mg/L in well 12K180 (Upper Floridan aquifer) to 9.9 mg/L in well 12L277 (Upper Floridan aquifer) during December 2021, and 3.9 mg/L in well 12K180 (Upper Floridan aquifer) to 10.0 mg/L in well 12L376 (surficial aquifer) during November 2022 (figs. 6 and 7; table 1). During the last 3 years, nitrate plus nitrite as N concentrations in most of the wells, except for well 12K175, have remained about the same or decreased slightly (fig. 7). Concentrations in well 12K175 increased from 6.8 mg/L in January 2021 to 7.3 mg/L in November 2022 (table 1).

Nitrate plus nitrite as N trend lines were fit using simple linear regression for the period of 1998 through 2022. Statistical significance was determined for the trend lines using the p-value of the regression fit, with a criterion of less than 0.05 indicating significance (StatsDirect Ltd, 2000). Of the nine wells sampled for nitrate plus nitrite as N during 2021 and 2022, six were determined to have significant nitrate plus nitrite as N trends—five wells have significant increasing trends, and one well has a significant decreasing trend. Four of the wells with significant nitrate plus nitrite as N trends were chosen to represent trends in the study area and are shown in figure 8. Well 12L277, downgradient from the previously described area of elevated nitrate plus nitrite as N concentrations and upgradient from the well field (fig. 6), has an increasing nitrate plus nitrite as N trend of 0.16 milligram per liter per year. The nitrate plus nitrite as N concentrations in well 12L277 range from 6.3 mg/L during 2002 to 12.9 mg/L during 2014 (fig. 8) but have dropped to just below the U.S. Environmental Protection Agency maximum contaminant level of 10 mg/L (40 CFR, part 141, subpart B) for nitrate in drinking water in December 2021 (9.9 mg/L) and November 2022 (9.8 mg/L). Water-quality results from well 12L344 indicate that concentrations of nitrate plus nitrite as N were 6.0 mg/L in 1998 but have been at or below 3.0 mg/L since 2001 (fig. 8). This well is adjacent to an area of past organic fertilizer application (Wenner and Reyher, 1999; Warner and Lawrence, 2005). The trend analysis was run for well 12L344 a second time without the data points from 1998 and 1999 and showed no significant trend. The decrease from 1999 may indicate that the nitrate plus nitrite as N has reached a steady-state condition in this area. Nitrate plus nitrite as N concentrations in well 12L348 increased at a rate of 0.13 milligram per liter per year since 1998; however, levels have decreased from 9.6 mg/L during January 2020 to 8.6 mg/L in November 2022. Well 12L373 has an overall increasing nitrate plus nitrite as N trend from 1998 through 2022; however, recent sample results indicate a decreasing trend from 2016 through 2022 (fig. 8).

Two Albany Utility production wells, 12L047 and 12L399, were sampled for PFAS as part of a larger study conducted by the USGS (fig. 6; Smalling and others, 2023). Well 12L047 had one count of PFAS detected, perfluorobutanesulfonic acid at 3.8 nanograms per liter (ng/L), which is an estimate because it is below the reporting limit. Newly proposed maximum contaminant levels for perfluorooctane sulfonic acid (PFOS; 4 ng/L) and perfluorooctanoic acid (PFOA; 4 ng/L) were released in March 2023 by the U.S. Environmental Protection Agency as part of the National Primary Drinking-water Standards Rule (U.S. Environmental Protection Agency, 2023). Water-quality data for the Flint River and wells sampled as part of this investigation may be obtained from the USGS NWIS database at https://nwis.waterdata.usgs.gov/usa/nwis/qw (USGS, 2024).

Summary

The U.S. Geological Survey has been working cooperatively with Albany Utilities to monitor groundwater quality and availability since 1977. Groundwater in the Upper Floridan aquifer generally flows southward and toward the Flint River. During April 2020 through January 2023, water levels in the Upper Floridan and Claiborne aquifers were generally above median levels, based on the period of record data. Water levels in the Clayton and Cretaceous aquifers were near or below median levels.

Groundwater samples were collected from eight wells during January 2021, seven wells during December 2021, and eight wells during November 2022. Nitrate plus nitrite as nitrogen concentrations ranged from 9.7 to 10.5 milligrams per liter (mg/L) in the surficial aquifer and from 2.3 to 9.9 mg/L in the Upper Floridan aquifer. Upper Floridan aquifer well 12L277 has had nitrate plus nitrite as nitrogen concentrations between 9.8 and 12.9 mg/L since 2014. No pesticides were detected in the samples.