About site selection criteria

The agency that is reporting the data. Agency codes are fixed values assigned by the National Water Information System (NWIS). A list of agency codes is available.

Each site in the USGS data base has a unique 2- to 15-digit identification number. Site numbers are assigned based on this logic. You can search using an exact match or match using a partial site number. To use an exact match you must include all of the digits including any leading zeros (0) that make up the complete site number. A site will not be found if the site number has a leading zero and it is not included in the string tested using an exact match.

Note: The speed of the search using site numbers (and site names) is very fast using exact matches. The next fastest is matching from the beginning. Searches that match any part of the number (or name) are much slower.

This is the official name of the site in the database. For well information this can be a district-assigned local number. Do NOT include "river", "lake", "creek" or other hydrological term. Search for "trinity" not "trinity river", or a complete or partial local number. All name searches are NOT case sensitive.

Note: Site name searches are the slowest way to find sites, and take 5 to 10 times longer than searches using the site number. The fastest site name search is matching from the beginning. Searches that match any part of the name are much slower.

A list of multiple site numbers separated by carriage returns (generated by pressing the ENTER key on your keyboard) are used to display many sites simultaneously. Each site in the USGS data base has a unique 2 to 15-digit identification number. You can search using an exact match or match using a partial number. To use an exact match you must include all of the digits including any leading zeros (0) that make up the complete site number. A site will not be found if the site number has a leading zero and it is not included in the string tested using an exact match.

A previously saved file of USGS site identification numbers, in the format:

USGS 11447650
USGS 394523084582301

The file may be prefixed by the agency code.

A previously saved file of USGS site identification numbers.

The name of the state or territory in which the site is located.

The name of the county or county equivalent (parish, borough, etc.) in which the site is located. A list of codes is available.

The contiguous United States is broken into 18 different major watersheds. Alaska, Hawaii, and Puerto Rico each have a separate watershed. Additional information is available.

Hydrologic units are geographic areas representing part or all of a surface drainage basin or distinct hydrologic feature and are delineated on the State Hydrologic Unit Maps. Each hydrologic unit is identified by a unique number (HUC), and a name. Additional information is available.

Note: Not all groundwater sites have been associated with a Hydrologic Unit. Such sites will not be retrieved using this search criteria.

When looking at a map, consider a rectangle that encloses the area of interest to you. The maximum latitude and longitude define the upper-left corner, and the minimum latitude and longitude define the lower-right corner of that box. To find the approximate latitude and longitude try the USGS MapFinder. For the best results define the smallest practical latitude-longitude box that includes the area of interest; retrievals from unnecessarily large latitude-longitude boxes (1x1 degree, for example) may yield many undesired sites.

Examples
Degrees- Minutes- Seconds	Decimal Degrees
100 59 01	100.91
45 09 34	45.11

The topographic setting of the site. This is not equivalent to the type of data collected at the site.
A list of the codes are available.

The code indicating the type of site to which these data apply. The codes and their meanings are available.

Altitude of the site referenced to the specified Vertical Datum.

The area enclosed by a topographic divide from which direct surface runoff from precipitation normally drains by gravity into the stream above that point.

All USGS data falls into one or more of these categories

Any Data Type	Matches data for any available options
Current Conditions and Recent Daily Data	Real-time Data is any data down to the 15 minute interval that has been transmitted in the last 120 days. Recent Daily-Value Data is the average daily value for a site and it is usually for the past year and a half of recorded values.
Surface Water	Water flow and levels in streams, lakes and springs.
Water Quality	Chemical and physical data for streams, lakes, springs, and wells.
Groundwater	Water levels in wells.

The depth of the finished well, in feet below land surface datum.

Note: Not all groundwater sites have information on Well Depth. Such sites will not be retrieved using this search criteria.

The total depth to which the hole was initially drilled, in feet below land surface datum.

Note: Not all groundwater sites have information on Hole Depth. Such sites will not be retrieved using this search criteria.

Date the well was completed.

National aquifers are the principal aquifers or aquifer systems in the United States, defined as regionally extensive aquifers or aquifer systems that have the potential to be used as a source of potable water.

Most of the national aquifers were published on the map sheet Principal Aquifers, part of the National Atlas of the United States of America. A few additional national aquifers were added from descriptions in the Groundwater Atlas of the United States. The aquifer names are regional names, and may not reflect local names used to refer to an aquifer. National aquifers are identified in the USGS water resources database using the codes available here.

Note: Not all groundwater sites can be associated with a National Aquifer. Such sites will not be retrieved using this search criteria.

A list of National aquifer codes and names is available.

Local aquifers in the USGS water resources data base are identified by a geohydrologic unit code (a three-digit number related to the age of the formation, followed by a 4 or 5 character abbreviation for the geologic unit or aquifer name).

Note: Not all groundwater sites have been associated with a Local Aquifer. Such sites will not be retrieved using this search criteria.

Name of the aquifer. Also known as the geohydrologic unit.

Note: Not all groundwater sites have been associated with a Local Aquifer. Such sites will not be retrieved using this search criteria.

Local aquifer codes and names are fixed values assigned by the National Water Information System (NWIS).

Groundwater occurs in aquifers under two different conditions. Where water only partly fills an aquifer, the upper surface is free to rise and decline. These aquifers are referred to as unconfined (or water-table) aquifers. Where water completely fills an aquifer that is overlain by a confining bed, the aquifer is referred to as a confined (or artesian) aquifer. When a confined aquifer is penetrated by a well, the water level in the well will rise above the top of the aquifer (but not necessarily above land surface).

Number of records found meeting a given criteria.

Period of record for the data selected. You can enter either or both of the first date or end date to restrict search. The search is done against the first and last date of record for the given type of data, not against the actual data values. Thus, if a site has one sample collected on 1910-01-01 and all following samples collected between 1980-01-01 and 1990-01-01, and the search "first date" is 1950-01-01, this site will pass the test since the period of record for the site would be from 1910-01-01 to 1990-01-01. (NOTE: checking data values explicitly, and not using a summary of the data is time consuming and is not supported currently. )

Dates can be entered in any of the following formats:
FORMAT	EXAMPLE
YYYY-MM-DD	2000-05-12
YYYY-M-D	2000-5-12
M/D/YYYY	5/12/2000
M D YYYY	5 12 2000
YYYYMMDD	20000512
YYYY.M.D	2000.5.12

Medium type refers to the specific environmental medium that was sampled and analyzed. Medium type differs from site type because one site type, such as surface water, could have data for several media, such as water, bottom sediment, fish tissue, and others. For a listing of the medium types look in the [Codes Help Section]

Parameters are grouped into major categories of water-quality data. Each parameter belongs to one group only. Parameter codes associated with each group.

5-digit number used in the US Geological Survey computerized data system, National Water Information System (NWIS), to uniquely identify a specific constituent. List of parameter code names, and help finding a code.

A previously saved file of parameter codes, in the following format:

01130	Minor and Trace Inorganics	Lithium, water, filtered, micrograms per liter
01131	Minor and Trace Inorganics	Lithium, suspended sediment, recoverable, micrograms per liter
01132	Minor and Trace Inorganics	Lithium, water, unfiltered, recoverable, micrograms per liter

List of parameter code names, and help finding a code.

CAS Registry Number is a Registered Trademark of the American Chemical Society. CAS recommends the verification of the CASRNs through CAS Client ServicesSM.

http://www.epa.gov/srs/

Water Quality method codes are associated with one or many parameter codes. The method codes and associated parameters used in NWIS are available

The Update time option provides the ability to select sites that have been updated within the last x minutes (or other interval). The available intervals are dependent on the data being queried - Real-time inventory data intervals are minutes, while Site inventory and Streamflow measurements intervals are minutes, days, weeks, months, or years. It should be kept in mind that while most real-time sites record data onsite every 15 minutes, they only transmit those data to the web database every 1 to 4 hours.