Maryland Department of Natural Resources

National Ground-Water Monitoring Network

The National Ground-Water Monitoring Network (NGWMN) was sponsored by the Federal Advisory Committee on Water Information's (ACWI) Subcommittee on Ground Water (SOGW) and was established in 2009 with a pilot network. The goal of the NGWMN is to provide information needed for planning, management, and development of groundwater supplies to meet current and future water needs and ecosystem requirements. This is being accomplished by aggregating suitable groundwater data from local, State, and Federal organizations. A consensus-based framework document was developed to provide guidance to ensure that the data are comparable and can be included in a nationally consistent network. The framework design focuses on providing information needed to assess the quantity of groundwater reserves as constrained by quality. The scale of the network focuses on Principal and Major Aquifers of the United States.

Lowering a pvc slug into a monitoring well

The Maryland Geological Survey has received funding through NGWMN grants since July 2018. MGS shares the concerns of other agencies and organizations which monitor our nation’s groundwater – that the collected data should be reliable, consistent, and comparable as recommended by the Subcommittee on Ground Water of the Advisory Committee on Water Information. Many of the wells we use to collect water-level data are valuable long-term data sources (21 wells are over 50 years old), but for this reason they are also vulnerable to deterioration or blockage related to their old age and lack of pumping.

A primary goal of MGS's NGWMN grant activities has been to assess the condition of our well network of 112 NGWMN wells, and consequently the integrity of the water-level data that we collect from these wells. We do this by performing two primary tasks: slug testing and well camera surveys.

Slug Tests

Slug testing is a quick and effective way to assess hydraulic connectivity between a well and the aquifer in which it is screened. During the test, a PVC slug - able to displace water in the casing by at least 1 foot - is lowered beneath the static water level, causing the water level to rise and then return to pre-test static levels in the well. Following recovery, the slug is removed and the water level response is recorded until water levels once again return to pre-test static level. Throughout the test, a pressure transducer with data logger records water-level data.

Most of the monitoring wells targeted for slug testing have prior hydraulic data in the form of either constant-rate aquifer tests or specific capacity pump tests. Using slug-test data, we intend to identify wells that show slow response (low hydraulic conductivity) or anomalous response considering prior hydraulic testing. These wells will be flagged for further investigation (well camera surveys) or redevelopment to clean out the screen openings and reestablish hydraulic connection to the aquifer sediments. Data from the slug tests will serve as an important baseline for future slug testing.

Degrees of encrustation in PVC monitoring wells

Well Camera Surveys

MGS utilizes a portable well camera system that is able to examine wells and record video from depths up to 1,200 feet. This video is examined to identify well casing and screen integrity, scaling, sediment accumulation, bacteria, and physical obstructions. Debris in wells that prevent the camera from reaching total depth is removed from the well (to the extent possible). Wells that exhibit significant scaling, sedimentation, and blockage of screen openings are targeted for additional investigation or rehabilitation (debris removal, pumping, or redevelopment). Wells with more serious problems such as holes in the casing are repaired or abandoned. Finally, well construction details (casing and screen diameter, materials, and intervals) are noted from the camera surveys and compared to the reported data. Any inconsistencies in well construction data are corrected in the USGS National Water Information System (NWIS) database.

Well-depth measurement (well sounding) is performed in addition to the camera surveys. Sounding is performed using a tag line with 1,500 ft cable. Well integrity could be compromised, and additional investigation may be warranted, if the sounded depth differs significantly from the reported depth of a well.

NGWMN grant activities by Fiscal Year

FY2018 (July 1, 2018 – June 30, 2019)

During this grant period, MGS

  • compiled and collected information to fill gaps in metadata for 112 NGWMN well sites including lithologic information and well-construction data
  • performed GPS surveys at 67 wells to collect more accurate altitude and coordinate data for wells
  • repaired 23 wells with known problems, including removal of deteriorated shelters and installation of locking caps
  • conducted borehole camera surveys in 29 wells to visually inspect wells and well depth measurements to identify sediment accumulation or obstructions
  • performed slug tests in 45 wells to identify clogged screens and to establish a baseline for future comparison.

FY2019 (July 1, 2019 – June 30, 2020)

During this grant period, tasks are focused on well integrity assessment. We are currently

  • conducting borehole camera surveys in 42 wells to visually inspect wells and well depth measurements to identify sediment accumulation or obstructions
  • performing slug tests in 28 wells to identify clogged screens and to establish a baseline for future comparison

FY2020 (September 30, 2020 – September 29, 2021)

MGS has been awarded another grant to verify the integrity of water-level data collected in our network wells, with a particular focus on our fractured-rock wells. We plan to

  • perform GPS/total station leveling surveys to update altitude and coordinate information for 4 wells
  • conduct borehole camera surveys in 19 wells to visually inspect wells and well depth measurements to identify sediment accumulation or obstructions
  • perform slug tests in 12 wells to identify clogged fractures or screens and to establish a baseline for future comparison

Additional Information

Acknowledgements and Disclaimer

This material is based upon work supported by the U.S. Geological Survey under Cooperative Agreements No. G18AC00080 and G19AC00183. The views and conclusions contained on this webpage are those of MGS and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey.