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Map

Interactive map showing the percentile of the most recently measured groundwater levels relative to long-term monthly statistics. Hovering over and clicking on each data point will provide additional information and data for the site. [<, less than; >, greater than; ≥, greater than or equal to; Not ranked, site has less than 10 years of data for the most recent month]

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Table of Data

About this application

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Well Types:

Continuous: Sites that currently have equipment to measure and record groundwater levels. Measurement frequency is typically hourly, but can be more frequent at select sites. For these sites, the mean daily value for a given day is used in the statistics presented on this web page. Many of these sites began as sites with periodic water-level data collection.

Periodic: Sites that are measured using a calibrated water-level tape by personnel in the field. Measurement frequency for sites range from monthly to annually.

RealTime: Sites that are Continuous and have transmitting capability so data are more likely to be current within the last day.

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Statistics

The most recent groundwater levels for sites with continuous data typically display the most recent daily-mean value from the prior day. The most recent water levels for sites with discrete (monthly) maybe recent, or may be several months in the past. Wells with most recent data older than 120 days are considered “Old Data” and are displayed with a white dot.

Water-level measurements are presented within a statistical framework. The percentile provides this statistical framework. A percentile is a value on a scale of 100 that indicates the percentage of a distribution that is equal to or below that value. For example, on the map of groundwater levels, the water level at the 90th percentile is equal to or greater than 90 percent of the monthly median groundwater levels in a given month over the period of analysis at the well. In general:

  • a percentile greater than 90 is considered much above normal,
  • a percentile greater than 75 and less than 90 is considered above normal,
  • a percentile between 25 and 75 is considered normal,
  • a percentile between 10 and 25 is considered below normal, and
  • a percentile less than 10 is considered much below normal.
  • Wells with most recent data older than 120 days are considered “Old Data”

The R HASP package is used to calculate the statistics and create the graphs on the individual site pages. Many of the sites displayed in this application that now have continuous water-level data were originally sites with monthly discrete data. The data from the discrete and continuous periods (daily maximum water levels) are combined into one record. The percentiles are determined for each site for each month by combining all values for a given month for the period of analysis. This allows for the use of long-term monthly data in the calculation of monthly statistics. Percentiles are determined only using approved USGS data. Recent data shown on the graphs may be provisional and subject to review. Monthly percentiles may change as new data are reviewed and approved.

How to Use This Application

On the included map, hovering your mouse cursor over a point will show the station name, and clicking on a point will show a pop-up window with site information, the most recent percentile, and the most recent water-level value. Within a pop-up window, clicking on the blue highlighted text called “See site graph and statistics” will lead to a site-specific web page which displays a graph of the water levels at the site over the last year, relative to water-level percentiles. A one-line table shows the percentiles for the month with the most recent water-level value.

References

Cunningham, W.L., Geiger, L.H., Karavitis, G.A., 2007, U.S. Geological Survey Climate Response Network: Factsheet 2007-3003, 4 p. online at https://pubs.usgs.gov/fs/2007/3003/pdf/2007-3003-hires.pdf accessed June 30, 2022.

Hydrologic AnalySis Package, 2022, in development, online at https://code.usgs.gov/water/stats/hasp, accessed June 30, 2022.

Disclaimers

These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Last updated: March 17, 2026
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