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National Water-Quality Assessment (NAWQA) Program

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Nutrients National Synthesis Project

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Data on nutrients in the streams, rivers, and ground water of the United States

Explanation of Ground Water Data

    The National Water-Quality Assessment (NAWQA) Program analyzes water quality at the national scale using consistent well type, sampling depth, targeted land use, and laboratory analytical methods. NAWQA study units generally conduct three types of ground-water studies: (1) "land-use studies," which sample shallow ground water (just below the water table) beneath a targeted land use (such as agricultural or urban land); (2) "major aquifer surveys," which sample deeper ground water irrespective of overlying land use and commonly used for drinking; and (3) "flowpath studies" that investigate ground water-surface water interactions by sampling ground water along an individual flow path that terminates in a stream. The data provided here are from land-use and major-aquifer studies, which are designed to facilitate statistical comparison of regional water-quality conditions. This data set, identical to the one being used in the USGS Periodic National Summary, is a carefully prepared subset of the NAWQA national-synthesis database. The data subset is designed to minimize sampling bias from different sampling strategies. The data subset represents "land-use studies" and "subunit surveys" of major aquifers in study units. The following sites are excluded from this data set:

    Concentrations are in milligrams per liter (mg/L) or micrograms per liter (g/L). A negative value indicates that the concentration in the sample is below the value which follows, the laboratory method reporting limit, with the absolute value of this number giving the method reporting limit, and a "." in a field indicates there are no data available. The codes and their meanings for the Depth-to-Water Measurement are:

    Definitions of fields in the data set are provided in the following list. "P" codes are the five-digit numbers used to identify water-quality constituents and properties in the USGS National Water Information System (NWIS) and the U.S. Environmental Protection Agency Data Storage and Retrieval System (STORET). Most "P" codes are preceded by a remark field which contains important information about that measurement. A "<" indicates that the concentration in the sample is below the value which follows, the laboratory method reporting limit, a concentration preceded by "E" indicates an estimated value, and a concentration preceded by ">" indicates a value "greater than" the maximum calibration value for the method.

    The Ground Water Site Description table gives precise information (latitude and longitude in NAD83) about the geographic location of each site.


SUCODE USGS sampling network identifier
TYPE Type of ground-water network
STAID USGS site identifier
WELLD Well depth, feet
OPEND Depth to top of open interval, feet
DATE Date of water-quality sampling and water-level measurement
WATERD Depth to water, feet
R72019 Remark concerning depth-to-water measurement
LABNO USGS sample identifier
P00010 Water temperature, degrees Celsius (C.)
P00095 Specific conductance, microsiemens (s)/cm @ 25 degrees C.
P90095 Specific conductance, microsiemens/cm
P00300 Oxygen, dissolved, mg/L
P00400 pH, whole water, field, standard units
P00403 pH, whole water, laboratory, standard units
P00419 Alkalinity, whole water, incremental titration, field, mg/L as CaCO3
P00447 Carbonate, whole water, incremental titration, field, mg/L as CO3
P00450 Bicarbonate, whole water, incremental titration, field, mg/L as HCO3
P00452 Carbonate, dissolved, incremental titration, field, mg/L as CO3
P00453 Bicarbonate, dissolved, incremental titration, field, mg/L as HCO3
P90410 Alkalinity, mg/L as CACO3
P00608 Ammonia, dissolved, mg/L as N
P00613 Nitrite, dissolved, mg/L as N
P00623 Ammonia and organic nitrogen, dissolved, mg/L as N
P00631 Nitrite and nitrate, dissolved, mg/L as N
P00666 Phosphorus, dissolved., mg/L as P
P00671 Orthophosphate, dissolved., mg/L as P
P00681 Carbon, organic, dissolved., mg/L as C
P00915 Calcium, dissolved, mg/L as Ca
P00925 Magnesium, dissolved, mg/L as Mg
P00930 Sodium, dissolved, mg/L as Na
P00935 Potassium, dissolved, mg/L as K
P00940 Chloride, dissolved, mg/L as Cl
P00945 Sulfate, dissolved, mg/L as SO4
P00950 Fluoride, dissolved, mg/L as F
P71870 Bromide, dissolved, mg/L as Br
P00955 Silica, dissolved, mg/L as SiO2
P01046 Iron, dissolved, g/L as Fe
P01056 Manganese, dissolved, g/L as Mn
P70300 Residue, dissolved, at 180 degrees C., mg/L


STATION USGS station identifier
LATITUDE Latitude; degrees, minutes, seconds; NAD83
LONGITUDE Longitude; degrees, minutes, seconds; NAD83
LATDD Latitude; decimal degrees; NAD83
LONDD Longitude; decimal degrees; NAD83

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Page Last Modified: Tuesday, 20-Oct-2009 16:04:47 EDT