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Data from Decadal Change in Groundwater Quality Web Site, 1988-2016

Metadata Updated: October 28, 2023

Evaluating Decadal Changes in Groundwater Quality: Groundwater quality data were collected from 5,000 wells between 1988-2001 by the National Water-Quality Assessment Project. Samples are collected in groups of 20-30 wells with similar characteristics called networks. About 1,500 of these wells in 67 networks were sampled about 10 years later between 2002-2012 (second sampling event) to evaluate decadal changes in groundwater quality. Between 2012 and 2016 (third sampling event), a subset of these networks has been sampled again, allowing additional results to be displayed on the web page: Decadal changes in groundwater quality. This is the third iteration of data added to the website, so this data release is referred to herein as Version 3.0. With the additional data, it is possible to evaluate changes in water quality between the 2nd and 3rd sampling event for 19 additional networks (35 total), changes in water quality between the 1st and 3rd sampling event for 15 additional networks (27 total), and changes across all 3 sampling events for 13 additional networks (27 total). A total of 78 networks have been sampled at least twice. Samples were obtained from monitoring wells, domestic-supply wells, and some public-supply wells before any treatment on the system. Groundwater samples used to evaluate decadal change were collected from networks of wells with similar characteristics. Some networks, consisting of domestic or public supply wells, were used to assess changes in the quality of groundwater used for drinking water supply. Other networks, consisting of monitoring wells, assessed changes in the quality of shallow groundwater underlying key land use types such as agricultural or urban lands. Networks were chosen based on geographic distribution across the Nation and to represent the most important water-supply aquifers and specific land-use types. Online Mapper Showing Decadal Changes in Groundwater Quality: Decadal changes in concentrations of nutrients, metals, and pesticides and other organic contaminants in groundwater were evaluated in 78 networks across the Nation by comparing changes between selected sampling events. Decadal changes in median concentrations for a network are classified as large, small, or no change in comparison to a benchmark concentration. For example, a large change in chloride concentrations indicates that the median of all differences in concentrations in a network is greater than 5 percent of the chloride benchmark per decade. For chloride, which has a Secondary Maximum Contaminant level of 250 milligrams per liter, this would mean the change in concentration exceeded 12.5 milligrams per liter (mg/L), or 5 percent of the benchmark.
Decadal Groundwater Quality Networks: 230 networks were sampled from 1988 to 2001 to assess the status of the Nation's groundwater quality. Each dot on the above map represents the center point of a network of about 20 to 30 wells. Networks sampled in the first round only are shown in green. 67 networks were resampled from 2002 to 2012 to assess decadal changes in groundwater quality and are shown in blue. Networks sampled from 2012 to 2014 and at least one previous round are shown in orange.

Access & Use Information

Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Created Date June 1, 2023
Metadata Updated Date October 28, 2023

Metadata Source

Harvested from DOI EDI

Additional Metadata

Resource Type Dataset
Metadata Created Date June 1, 2023
Metadata Updated Date October 28, 2023
Publisher U.S. Geological Survey
Identifier USGS:5ced390be4b02eb068de91f5
Data Last Modified 20200826
Category geospatial
Public Access Level public
Bureau Code 010:12
Metadata Context
Metadata Catalog ID
Schema Version
Catalog Describedby
Harvest Object Id e20066fc-e748-4e62-b70b-7318dd274b8e
Harvest Source Id 52bfcc16-6e15-478f-809a-b1bc76f1aeda
Harvest Source Title DOI EDI
Metadata Type geospatial
Old Spatial -128.696099187,20.664375973,-64.589455608,51.047319151
Publisher Hierarchy White House > U.S. Department of the Interior > U.S. Geological Survey
Source Datajson Identifier True
Source Hash 9136b8f369156ba74865f26b4df030aed29e6db1e4984310f101c2c08c1dce76
Source Schema Version 1.1
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