Jo Ann M. Gronberg 20111130 2 raster digital data Reston, Virginia U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?arsenic_map National Water-Quality Assessment Program Trace Elements National Synthesis Project 2011 http://water.usgs.gov/nawqa/trace/data/index.html This map shows arsenic values, in micrograms per liter, for groundwater samples from about 31,000 wells and springs in 49 states compiled by the United States Geological Survey (USGS), and is an updated version of figure 1 from Ryker (2001). Cited Reference: Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36. This arsenic point map was created as an update to figure 1 from Ryker (2001) because the legend from figure 1 was found to be ambiguous; value ranges, in micrograms per liter, for each color overlapped at the end points (dark green: 1-3, light green: 3-5, yellow: 5-10, orange: 10-50, red: at least 50). Reproduction of the map revealed that the actual legend should be dark green: less than 3, light green: 3 to less than 5, yellow: 5 to less than 10, orange: 10 to less than 50, red: at least 50. The legend and map were updated to more clearly identify points exceeding the U.S. Environmental Protection Agency arsenic Maximum Contaminant Level of 10 micrograms per liter (dark green: less than or equal to 3, light green: greater than 3 to less than or equal to 5, yellow: greater than 5 to less than or equal to 10, orange: greater than 10 to less than or equal to 50, red: greater than 50). These samples were collected for studies on potable groundwater resources by the USGS, the Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department of Natural Resources, and the six New England states, New Hampshire, Vermont, Maine, Massachusetts, Rhode Island, and Connecticut. Estimation of the arsenic concentration in groundwater in any specific area must consider the following limitations and sources of variability: 1) The data include a variety of well types, including private wells, public supply wells, and monitoring wells not used for water supply. 2) These groundwater samples do not represent drinking water served by public water supply systems because these utilities may treat or mix groundwater with high concentrations from individual wells to meet drinking water standards before delivering it to consumers. 3) The appearance of the arsenic distribution is influenced by the order in which wells are plotted. In this map, wells with higher concentrations are drawn on top of those with more moderate concentrations. This over-plotting may exaggerate the frequency of high values in areas where wells are close together. 4) Arsenic concentration may vary with depth within the same aquifer, or between aquifers that are stacked vertically - for example, a shallow sand and gravel aquifer can overly a deeper bedrock aquifer. The map does not show the vertical distribution of arsenic. 5) Many of the wells were sampled more than once, but evaluation of the data indicates that there is no relation between arsenic concentration and time for most of the wells; the most recent data point was usually selected to represent a given well (Focazio and others, 2000). With these qualifications in mind, the data provide an estimate of arsenic occurrence in the groundwater resource in general. For additional detail on the studies behind the map, along with more detailed maps for portions of the U.S., visit the USGS at http://water.usgs.gov/nawqa/trace/arsenic/index.html. Cited and Related References: Focazio, M.J., Welch, A.H., Watkins, S.A., Helsel, D.R., and Horn, M.A., 2000, A retrospective analysis on the occurrence of arsenic in ground-water resources of the United States and limitations in drinking-water-supply characterizations: U.S. Geological Survey Water-Resources Investigations Report 99-4279, 21 p. Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36. Welch, A.H., Watkins, S.A., Helsel, D.R., and Focazio, M.J., 2000, Arsenic in ground-water resources of the United States: U.S. Geological Survey Fact Sheet 063-00, 4 p. 19730101 000000 20000330 000000 date range of data Complete None planned -158.631946 -66.991122 68.143334 25.39050 None Arsenic inlandWaters groundwater None United States Data from Wisconsin, Minnesota, Texas, New Hampshire, Vermont, Maine, Massachusetts, Rhode Island, and Connecticut should be obtained directly from the state agency. See Supplemental Information. U.S. Geological Survey, National Water-Quality Assessment Program Neil M. Dubrovsky Chief, Trace Elements National Synthesis Project mailing and physical

CSUS Placer Hall, 6000 J Street

California Water Science Center

Sacramento California 95819 US 916-278-3078 916-278-3071 nmdubrov@usgs.gov http://water.usgs.gov/GIS/browse/arsenic_map.gif Map of arsenic in groundwater of the United States gif USGS arsenic data was collected by Focazio and others (2000) and Welch and others (2000), and updated by Ryker (2001). Ryker (2001) also included data retrieved from several state agencies: the Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department of Natural Resources, the New Hampshire Department of Environmental Services, the Vermont Department of Environmental Conservation, the Maine Bureau of Health, Geological Survey, and Department of Conservation, the Massachusetts Department of Environmental Quality, the Rhode Island Department of Health, and the Connecticut Department of Health. USGS arsenic data can be accessed at http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html. State data should be obtained directly from the state agency. Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcGIS 10.0.3.3600 Focazio, M.J., Welch, A.H., Watkins, S.A., Helsel, D.R., and Horn, M.A., U.S. Geological Survey 20000101 U.S. Geological Survey Water-Resources Investigations Report 99-4279 Report and data available at http://pubs.usgs.gov/wri/wri994279/. Dubrovsky, N.M., U.S. Geological Survey 20111130 Project web page available at http://water.usgs.gov/nawqa/trace/arsenic/index.html. Welch, A.H., Watkins, S.A., Helsel, D.R., and Focazio, M.J., U.S. Geological Survey 20000501 U.S. Geological Survey Fact Sheet 063-00 Report available at http://pubs.usgs.gov/fs/2000/fs063-00/. Point features present. Represents 1973-2000 data retrieved from USGS and state agencies. There are areas where data are sparse. For example, Texas, Wisconsin, Idaho, California, New Jersey, Minnesota, and Washington are represented by over 1000 wells; Rhode Island, Kentucky, Mississippi, and New York are represented by fewer than 100 wells. Ryker, S.J. 20011101 map Geotimes Newsmagazine of the Earth Sciences vol. 46, no. 11 Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater-- A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46 no. 11, p. 34-36. On line at: http://www.agiweb.org/geotimes/nov01/feature_Asmap.html. onLine 19730101 000000 20000330 date range of data Ryker (2001) map Ryker, S.J., U.S. Geological Survey 20011101 2, updated from Focazio and others (2000) spreadsheet On line at: http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html. onLine 19730101 000000 20000330 date range of data USGS arsenic data USGS arsenic data USGS arsenic data from Focazio and others (2000) and Welch and others (2000) were updated by Ryker (2001). Data were also supplemented by data retrieved from several state agencies: the Minnesota Pollution Control Agency, the Texas Water Development Board, the Wisconsin Department of Natural Resources, the New Hampshire Department of Environmental Services, the Vermont Department of Environmental Conservation, the Maine Bureau of Health, Geological Survey, and Department of Conservation, the Massachusetts Department of Environmental Quality, the Rhode Island Department of Health, and the Connecticut Department of Health. USGS arsenic data can be accessed at http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html. State data should be obtained directly from the state agency. 20010101 000000 U.S. Geological Survey Sarah J. Ryker mailing

12201 Sunrise Valley Drive, Mail Stop 516

Reston Virginia 20192 703-648-5210 702-648-5792 sjryker@usgs.gov 1) Figure 1 from Ryker (2001) is a map showing arsenic concentration, in micrograms per liter, from groundwater wells in the United States, representing different concentration ranges by different colors. This map was found to be ambiguous, because value ranges for each color overlapped at the end points (3, 5, 10, 50). It was necessary to determine the actual legend used and to see if it identified values exceeding the U.S. Environmental Protection Agency (USEPA) arsenic Maximum Contaminant Level (MCL) of 10 micrograms per liter. At present it was unclear if 10 was represented by yellow or orange. 2) Point feature "ident", which spatially represented the arsenic data from 31032 wells, was retrieved from trace element archive for Ryker (2001). See earlier process step for data sources. Determined that "ident" was a derivative of the point feature "wells31032", which was used in the fig1_pts.aml creating the original figure 1 from Ryker (2001). 3) A map was produced using commands from fig1_pts.aml, which corresponded to the following legend: dark green: <3, light green: >=3 to <5, yellow: >=5 to <10, orange: >=10 to <50, red: at least 50. 3) Verified that figure 1 from Ryker (2001) matched this map (from step 3) by overall visual inspection and spot checking points at the end values, 3, 5, 10, and 50. 4) To more clearly identify points that exceed the USEPA arsenic MCL, a map was produced using the following legend: dark green: <=3, light green: >3 to <=5, yellow: >5 to <=10, orange: >10 to <=50, red: >50. 5) arsenic_map.mxd was reviewed by Naomi Nakagaki and Donna Knifong to insure that the legend accurately described the colored data points. Nakagaki ran statistics in INFO to verify that the number of values in each category matched the "count" produced in ArcMap. 6) Metadata was reviewed by Naomi Nakagaki, Donna Knifong and Neil Dubrovsky. 20111121 000000 U.S. Geological Survey Jo Ann M. Gronberg Hydrologist mailing

345 Middlefield Road, Mail Stop 470

Menlo Park California 94025 650-329-4423 650-329-4463 jmgronbe@usgs.gov Raster Pixel 513 656 Albers Conical Equal Area 29.5 45.5 -96 23 0.00000 0.00000 coordinate pair 0.000100 0.000100 Meters Albers Conical Equal Area 55 65 -154 50 0.00000 0.00000 coordinate pair 0.000100 0.000100 Meters North American Datum of 1983 GRS1980 6378206.4 294.98 arsenic_map.png Map of arsenic concentrations in groundwater of the US in PNG file format USGS Arsenic in groundwater Concentration of arsenic from groundwater samples USGS 0 15000 micrograms per liter The map of arsenic in groundwater of the United States is presented in PNG file format. Arsenic values are shown in micrograms per liter. The map is updated from Ryker (2001) to identify wells exceeding the USEPA arsenic MCL of 10 micrograms per liter. Ryker, S.J., 2001, Mapping arsenic in groundwater--A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v. 46, no. 11, p. 34-36. U.S. Geological Survey Ask USGS - Water Webserver Team mailing

445 National Center

Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://water.usgs.gov/user_feedback_form.html Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of these data, software, or related materials. The use of firm, trade, or brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. The names mentioned in this document may be trademarks or registered trademarks of their respective trademark owners. png digital map Winzip 168 KB http://water.usgs.gov/GIS/dsdl/arsenic_map.zip http://water.usgs.gov/nawqa/trace/data/index.html None. This dataset is provided by USGS as a public service. 20041122 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing address

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Reston VA 20192 USA 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+arsenic_map FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998