Geological Survey of Alabama
Link to: Geological Survey of Alabama Groundwater Program
NGWMN Contact:
Ann Arnold
(205) 247-3618
The Geological Survey of Alabama (GSA) has been actively monitoring groundwater conditions in the state since the early 1950s through a network of observation wells. The current network is a real-time network and updates are available daily via an online portal. Real-time data collection began in 2010, with the installation of the first equipment in some of the observation wells used for periodic monitoring. Since 2010, GSA has focused on expanding the network, which now includes 29 well sites to monitor daily water-level elevation changes across the state. Ten of the real-time wells are used to report groundwater level response to drought to various stakeholders throughout the state.
The GSA monitors wells from eight Principal aquifers in Alabama. These are the: Mississippian aquifers, Pennsylvanian aquifers, Valley and Ridge, Piedmont and Blue Ridge aquifers, Mississippi embayment aquifer system, Southeastern Coastal Plain aquifer system, Floridan aquifer system, and the Coastal Lowlands and Surficial aquifer system.
NGWMN Projects:
Initial project to become a NGWMN data provider.
2020: 11/16/2020 to 11/15/2022
Project is to provide persistent data services for two years to ensure that data continues to flow to the NGWMN Data Portal, that sites and site information are up to date. They will also do well maintenance work at five wells that need wellhead repair work.
2021 Round 1: 7/15/2021 to 7/14/2022
Project is to perform persistent data services work to classify and add surveillance wells to the NGWMN.
2021 Round 2: 11/1/2021 to 10/31/2022
Project is to perform well rehabilitation work on one well. They will be doing a downhole camera survey of the well followed by scrubbing and acid washing. They will complete the work by doing a step-drawdown test to determine aquifer properties for future comparison.
NGWMN Presentations:
None
Site Selection and Classification
Site Selection
The purpose of the NGWMN is to provide a national overview of long-term trends across regional aquifer systems. As such, wells are selected to differentiate between the effects of short-term and long-term hydrologic stressors across the aquifers. The GSA staff selected wells from our current water-level monitoring programs to meet the requirements of the NGWMN after reviewing the criteria for inclusion into the USGS catalog.
The 29 wells in Alabama's real-time network were established as trend-monitoring wells, and the daily data are currently being served to the NGWMN. Trend monitoring is designed to look at long-term and seasonal water-levels at frequent measuring intervals for a limited number of wells across the state. The GSA-GAP staff selected trend wells from the state's real-time network, which derives water-level elevation data from eight of the nine aquifer systems identified in Alabama.
Surveillance monitoring is designed to periodically "tie together" the trend monitoring well data, providing greater spatial coverage to fill in the gaps of the more frequent (but fewer sites) trend well measurements. The frequency of measurements made in Alabama's surveillance wells is semi-annual and provides an extensive snapshot of aquifer conditions. The 468 periodic program wells in Alabama were thoroughly reviewed for potential inclusion into the USGS NGWMN surveillance well network. Wells were selected in order of usefulness and suitability of the water-level measurements as data points for inclusion in the national network. After screening out those wells that were deemed ineligible for the national network based on criteria discussed in following paragraphs, the remaining monitoring well candidates were ranked using a decision matrix of weighted factors for future inclusion into the USGS NGWMN.
The selection of periodic wells to be further evaluated for potential inclusion into the NGWMN surveillance network was a three-step process. In the first step, ineligible wells were eliminated from further consideration. In general, these eliminated wells either had access problems or did not have detailed lithologic or well construction data on record. In the graphical breakdown presented in Figure 2, a total of 104 wells were not eligible for the NGWMN due to a lack of minimum data requirements. The GSA staff eliminated the public supply wells and periodic monitoring wells within a 1-mile radius of a public supply from further consideration as potential surveillance wells, due the possible drawdown effects of high capacity pumping. After removing the 121 wells within a conservative 1-mile radius of pumping influence as shown in figure 2, a total of 243 wells remained to be further evaluated for inclusion in the NGWMN.
The second step was a process of evaluation for the remaining 243 wells, whereby each of five factors were quantified and weighted, in relation to the network goals. During this evaluation process, 71 wells were identified that had less than 5 years of water-level data and were removed from consideration. The remaining 172 candidate wells in Alabama's current periodic water-level monitoring program were ranked according to the following factors: years of data, distance from public supply wells, proximity to other monitoring wells, distance from real-time wells, and proximity to a stream gage.
The first factor 'years of data' allowed for a simple weighting scheme at 10-year intervals. Wells with 50 or more years of water-level measurements were assigned a weight of 1, 40 to 49 years of data yielded a weight of 2, and so forth.
The second factor 'distance from public supply wells' was evaluated numerically according to the methods described above.
The third factor of 'proximity to other monitoring wells' was evaluated geospatially using the locations in ArcGIS. A circle of 5-mile radius was created around each well, and the number of additional wells intercepted by this imaginary buffer were counted. The higher the count the higher the numeric ranking assigned, thus lowering the priority.
The fourth factor 'distance from real time wells' was measured as described above, with the intention of preventing too much redundancy in the monitoring dataset.
The fifth factor 'proximity to stream gage' worked in the opposite way of the previous factors which incorporated distance measurements. The closer a stream gage the lower the rank (resulting in a higher priority on the list such as number 1 or 2). Monitoring wells in close proximity to streams are valuable because these water-level measurements can quantify surface water/groundwater hydrologic communication, thus providing input about lag time in flow rates.
The third and final step of the process was to rank the wells as potential candidates in the NGWMN surveillance subnetwork. Listed in the order of consideration, the following factors were weighted that improved the priority ranking for the well's inclusion into the USGS NGWMN as a surveillance site.
These rating factors and a consideration of spatial coverage and density will be used to select the final periodic wells to be included in the NGWMN Surveillance Network in Alabama.
Classification
Groundwater monitoring wells from both the trend and surveillance network were further evaluated for placement into the appropriate well classification subnetworks. These well classification subnetworks were defined as background, suspected changes, and documented changes in section 1.4.3 of "A National Framework for Ground-Water Monitoring in the United States" (SOGW, 2013). The delineation of these well classification subnetworks is based upon the anthropogenic effects on water levels due to land use and development on both groundwater recharge rates, and withdrawal due to pumping.
Background Subnetwork
As defined by the USGS NGWMN, the background subnetwork includes monitoring sites that show minimal anthropogenic effects as measured from water-level elevations. At this time, 22 of the 29 GSA trend network wells are classified as background in the NGWMN water level database (see figure 1 and table 1). The spatial distribution of the background wells includes eight of the nine principal aquifers located in Alabama.
Hydrographs produced for the period of record for all the trend wells were examined, comparing the initial water-level elevations with current measurements. These hydrographs are presented in the Assessment of groundwater resources in Alabama report (GSA, 2018). Initial water-level measurements for most of the trend wells date back to the 1950s or 1960s, providing an average period of record of 60+ years. Water levels in most of the unconfined wells displayed wide seasonal fluctuation, indicating the significant contribution of water due to precipitation, recharging the aquifer systems. A wide range of water-level variation (on the order of tens of feet) is observable in many of the unconfined aquifer hydrographs. However, there is no clear trend of water level decline in these hydrographs examined for the period of record. Without a stringent linear regression statistical analysis of all water-level measurements in tandem with nearby precipitation stations, changes in water levels may be associated with natural seasonal hydrologic stressors.
Suspected Changes Subnetwork
The suspected changes subnetwork includes monitoring sites that provide data from principal aquifer systems that have water level changes anticipated due to anthropogenic influence. This subnetwork may be in areas where land-use changes are anticipated based on population growth and property development. At this time, seven wells of the trend network of GSA wells are currently listed in the suspected changes subnetwork. classified as having known or anticipated anthropogenic effects. Six of the seven wells are located in the southern half of the state, below the Fall Line, and the seventh well, GSAL128672, is in Jefferson County. The principal aquifers with suspected changes in water levels due to anthropogenic influence include the Southeastern Coastal Plain and confining unit, Floridan, Coastal Lowland, and the Valley and Ridge formations. The GSA staff will continue to evaluate the water-level monitoring data to further distinguish long-term trends.
Documented Changes Subnetwork
The documented changes subnetwork includes monitoring wells that provide data from principal aquifer systems that have documented anthropogenic effects. At this time, the GSA staff have not placed any of Alabama's wells, neither trend nor surveillance, into the subnetwork of documented changes as defined by the USGS NGWMN. As more data becomes available and reviewed, this determination could change.
Data Collection Techniques
FIELD TECHNIQUES
Water-level data in the real-time network wells are measured continuously by pressure transducers and data loggers. The data is transmitted via the OTT intelligent top cap (ITC) technology to the GSA office computers via a 3G cellular network. Water levels are recorded every two hours by the pressure transducer, stored in the ITC datalogger and then transmitted via short messaging service (SMS) once a day to the GSA office. The GSA staff routinely review the water-level elevation data points for any possible errors due to slight variations in salinity and correct for local barometric pressure drops during extreme weather systems. Water-level elevations are averaged for the 24-hour period, and the daily mean value is served to the NGWMN portal, recorded as daily average trend monitoring data.
In the three Coastal lowlands aquifer system wells of the NGWMN, the GSA staff have addressed the potential influence of salinity variation due to sea water. As part of this project, GSA-GAP staff replaced the existing pressure transducer probes with a dual probe that can effectively measure both salinity and water depth.
Water levels in the periodic program wells are measured manually by GSA staff using a steel tape and chalk. A graphic overview of the sampling methodology is included on the GSA website, https://gsa.state.al.us/gsa/groundwater/periodic/methodology, and described in detail elsewhere (GSA, 2018).
References
Geological Survey of Alabama, 2018, Assessment of groundwater resources in Alabama, 2010-2016: Geological Survey of Alabama Bulletin 186, 426 p.
Data Management
Data Management Procedures
Real-time water-level data transmitted by SMS to the GSA office is received by OTT Hydras 3 software installed on a dedicated computer. On a daily basis, scripts written in the Hydra 3 software send both the two-hour raw data and daily average data to a dedicated hard drive for storage and to the GSA server where the water-level data can be accessed for uploading to the NGWMN and GSA websites and be available for research purposes.
Periodic water-level data is tabulated and stored in Excel spreadsheets on the computer data server and uploaded to the GSA-GAP's RBDMS database. The data is copied and stored on a separate data back-up storage device each evening. The updated data is served daily to the USGS portal.
Minimum data elements
Criteria entered for wells selected for upload to the NGWMN registry include:
- Agency name;* Unique site number and name;* Location information including state, county, latitude and longitude with the horizontal datum and method used and accuracy;* Altitude in specified units with the vertical reference datum and method used and accuracy;* Well depth in specified units;* The national aquifer designation and local aquifer name;* The type of groundwater site and aquifer type;* Whether the site is in a water level (WL) subnetwork and the WL system name from which the data is uploaded;* Whether the well meets the criteria for WL baseline (five years of data), well type, well characteristics, well purpose and well purpose notes;* Whether the well is part of the water quality (QW) subnetwork; and* The URL to the specified data on the data provider's website.
Other Agency Information
GSA Periodic Monitoring Program
Statewide Groundwater Assessment (2010-2016)