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Records of surface-water quality are usually obtained at or near stream-gaging stations because interpretation of records of surface-water quality nearly always requires corresponding discharge data. Records of surface-water quality in this report may involve a variety of types of data and measurement frequencies.
Classification of Records
Water-quality data for surface-water sites are grouped into one of three classifications. A continuing-record station is a site where data are collected on a regularly scheduled basis. Frequency may be once or more times daily, weekly, monthly, quarterly or semi-annually. A partial-record station is a site where limited water-quality data are collected systematically over a period of years. Frequency of sampling is usually less than quarterly. A miscellaneous station is a site other than a continuing or partial-record station, where random samples are collected to give better areal coverage to define water-quality conditions in the river basin.
A careful distinction needs to be made between "continuing records", as used in this report, and "continuous recordings," which refers to a continuous graph or a series of discrete values punched at short intervals on a paper tape. Some records of water quality, such as temperature and specific conductance, may be obtained through continuous recordings; however, because of costs, most data are obtained only monthly or less frequently. Locations of stations for which records on the quality of surface-water appear in this report are displayed by activating the appropriate theme coverage.
On-Site Measurements and Sample Collection
A primary concern of the water-quality data acquisition efforts of the U.S. Geological Survey is how well the data collected represent on-site water-quality conditions. Measurements of unstable variables such as water temperature, pH, and dissolved oxygen are made on site when samples are taken to assure that the reported readings accurately represent the water-quality at the time of sampling. Standard U.S. Geological Survey procedures for the collection, treatment, and, if necessary, shipment of samples prior to laboratory analysis are also followed to assure that the constituents for which these samples are analyzed have changed minimally from their on-site values. These representative sampling procedures are documented in publications on "Techniques of Water-Resources Investigations," Book 1, Chapter D2; Book 3, Chapter C2; and Book 5, Chapters A1, A3, and A4. These TWRI's are listed in the Publications on Techniques of Water-Resources Investigations section of this report. The procedures are consistent with ASTM standards and generally follow ISO standards. Supplemental information to that found in the listed references may be obtained from the U.S. Geological Survey, Georgia District Office.
One sample can adequately define the water quality at a given time if the mixture of solutes throughout the stream cross-section is homogeneous. However, the concentration of solutes at different locations in the cross section may vary widely with different rates of water discharge, depending on the source of material and the turbulence and mixing of the stream. Some streams must be sampled through several vertical sections to obtain a representative sample needed for an accurate mean concentration and for use in calculating load. All samples obtained for the National Stream-Quality Accounting Network (NASQAN) program are obtained from at least several verticals. Whether samples collected at other sites are obtained from the centroid of flow or from several verticals, depends on flow conditions and other factors that must be evaluated by the collector.
Water Temperature
Water temperatures are measured at the water-quality stations, and are also obtained at the time of discharge measurements for water-discharge stations. At stations where recording instruments are used, maximum and minimum temperatures for each day are published. Daily-mean temperatures for these stations and water temperatures measured at the time of water-discharge measurements are on file in the District Office.
Large streams have a small diurnal temperature change; shallow streams may have a daily range of several degrees and may follow closely the changes in air temperature. Some streams may be affected by waste-heat discharge.
Sediment
Suspended-sediment concentrations are determined from samples collected by using depth-integrating samplers. Samples are usually obtained at several verticals in the cross section, or a single sample may be obtained at a fixed point and a coefficient applied to determine the mean concentration in the cross section. Although data collected periodically may represent conditions only at the time of sampling, data are useful in establishing seasonal relations between quality and streamflow and in predicting long-term sediment-discharge characteristics of a stream. The methods used in the computation of sediment records are described in the TWRI Book 5, Chapter C1 and are consistent with ASTM standards and generally follow ISO standards.
In addition to the records of suspended-sediment discharge, records of the periodic measurements of the particle-size distribution of the suspended sediment and bed material are included for some stations.
Laboratory Measurements
Samples for indicator bacteria are analyzed locally. Samples for the National Stream-Quality Accounting Network, the Hydrologic Benchmark Network, and several long-term trend stations are analyzed in the U.S. Geological Survey laboratory in Arvada, Co. The Alabama District Sediment Laboratory or the Pennsylvania District Sediment Laboratory analyzes all sediment samples. Georgia Environmental Protection Division (EPD) network samples are analyzed by the Laboratory Services Section, Georgia Department of Natural Resources, Environmental Protection Division, and this is so stated in the "Remarks" section of the station description. Methods used to analyze sediment samples and to compute sediment records are described in the TWRI Book 5, Chapter C1. Methods used by the U.S. Geological Survey laboratories are given in the TWRI Book 1, Chapter D2; Book 3, Chapter C2; and Book 5, Chapters A1, A3, A4, and A5. These methods are consistent with ASTM standards and generally follow ISO standards.
Data Presentation
Water-quality records collected at a surface-water daily-record station are published immediately following that record, regardless of the sampling frequency. Station number and name are the same for both records. If no daily surface-water record is available, continuing water-quality record is published with its own station number and name in the regular downstream-order sequence, while data for partial-record stations and miscellaneous sites appear in separate tables following tables of discharge at partial-record stations and miscellaneous sites. Here each partial-record station and miscellaneous site is published with its own station number and name in the regular downstream-order sequence and without descriptive statements.
For continuing-record stations, information pertinent to the history of station operation is provided in descriptive headings preceding the tabular data. These descriptive headings give details regarding location, drainage area, period of record, type of data available, instrumentation, general remarks, cooperation, and extremes for constituents measured daily. Tables of chemical, physical, biological, and radiochemical data obtained at a frequency less than daily are presented first. In tables where both field and laboratory measurements of the same parameter are published (pH, specific conductance, and total alkalinity in this report), the laboratory determinations represent the quality of the sample at the time of analysis. Laboratory values for parameters measured in the field generally will be comparable to the field values for these parameters. Differences between the field and laboratory values represent a summation of (1) actual changes in the sample between the time of collection and the time of analysis, (2) errors in precision associated with instrument operation, and (3) errors in accuracy inherent in the instruments themselves. Tables of "daily values" of specific conductance, pH, water temperature, dissolved oxygen, and suspended sediment then follow in sequence.
If the location is identical to that of the discharge-gaging station, the LOCATION and the DRAINAGE AREA statements are not repeated in the descriptive headings. The following information, as appropriate, is provided with each continuing record station. Comments that follow clarify information presented under the various headings of the station description:
LOCATION.--See Data Presentation under "Records of Stage and Water Discharge;" same comments apply.
DRAINAGE AREA.--See Data Presentation under "Records of Stage and Water Discharge;" same comments apply.
PERIOD OF RECORD.--This indicates the periods for which there are published water-quality records for the station. The periods are shown separately for records of constituents measured daily or continuously and those measured less than daily. For those measured daily or continuously, periods of record are given for the constituents individually.
EXTREMES.--Maximums and minimums are given only for constituents measured daily or more frequently. None are given for constituents measured weekly or less frequently, because the true maximums or minimums may not have been sampled. Extremes, when given, are provided for both the period of record and for the current water year.
REVISIONS.--If errors in water-quality records are discovered after publication, appropriate updates are made to the Water-Quality File in the U.S. Geological Survey's computerized data system, NWIS, and subsequently by monthly transfer of update transactions to the U.S. Environmental Protection Agency's STORET system. Because the usual volume of updates makes it impractical to document individual changes in the State data-report series or elsewhere, potential users of U.S. Geological Survey water-quality data are encouraged to obtain all required data from the appropriate computer file to insure the most recent updates.
Remark Codes
The remark codes that may appear with the water-quality data in this report are as follows:
| Printed Output | Remark |
|---|---|
| E | Estimated value. |
| < | Actual value is known to be greater than the value shown. |
| >> | Actual value is known to be less than the value shown. |
| & | Biological organism estimated as dominant. |
| D | Biological organism count equal to or greater than 15 percent (dominant). |
| K | Results based on colony count outside the acceptance range (non-ideal colony count). |
| L | Biological organism count less than 0.5 percent (Organism may be observed rather than counted). |
| V | Analyte was detected in both the environmental sample and the associated blanks. |
Precipitation-quality data represent analyses of time-composite samples, most often for a collection period of one week. This is in contrast to most of the published surface-water-quality data which represent samples taken at specific times. The U.S. Geological Survey collects precipitation-quality data in Georgia collaborating with the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), a cooperative research program of Federal, State and private organizations.
On-Site Measurements and Sample Collection
Precipitation samples are collected with wet/dry collectors or bulk samplers. The wet/dry collector is the preferred precipitation sampler and consists of a bucket that is open only during periods of wet (rainfall, snow, etc.) precipitation. During dry periods the sample bucket is covered, thus excluding dry-fall precipitation from the sample. Bulk samplers are less desirable because they collect both wet- and dry-fall precipitation. However, they are useful as backups during times when the wet/dry samplers fail to properly function. Bulk samplers consist of a catchment area, such as a funnel, where the sample is collected and then fed through a delivery tube to the sample receptacle. The tubing is looped in order to minimize sample evaporation. If necessary, wet/dry samplers can also be used as makeshift bulk samplers by leaving them in the open position for the collection period.
Accurate measurements of precipitation quantity also are made at each station. One of two types of recording gages is normally used. National Trends Network (NTN) stations are equipped with weighing-bucket rain gages, which graphically record rainfall as well as count rainfall events. The other commonly used recording gage consists of a rainfall catchment pipe and a float-driven digital recorder that periodically records the water level in the pipe.
Time-composite wet- and bulk-precipitation samples are collected and brought back to the laboratory and weighed. Rainfall quantity is estimated from the sample weight. A temperature-density correction can be applied if desired but normally this correction results in a very small change in the estimated quantity of rainfall. An estimation of the sampler efficiency is made by computing the ratio of rainfall amount collected in the sample bucket to that measured by the recording rain gage. This collector efficiency ratio is an important indicator of possible collector malfunction. For example, a ratio substantially less than one indicates that the wet/dry collector was not opening properly and thus, excluding rainfall.
After weighing the sample, a small portion is removed for measurement of pH, specific conductance, and, in some instances, titratable acidity. The pH and specific conductance are both determined electrometrically according to methods described in the National Atmospheric Deposition Program "NADP Instruction Manual: Site Operation". The remainder of the sample is then used for laboratory chemical analyses. This portion of the sample is shipped to the laboratory raw and untreated. In the case of NTN operation, the original bucket is resealed and mailed to the Illinois State Water Survey Central Analytical Laboratory (CAL) for analysis. In all other instances, sample portions are preserved, treated, and analyzed according to specific project requirements.
Data presentation
Records of precipitation quality are published following the "Records of ground-water" section of this report. As with records of daily water discharge and surface-water quality, precipitation-quality records consist of two parts, a station header and a data table. The station header contains the descriptive information pertinent to the establishment, location, and operation of the site. Records are presented alphabetically by county and, within each county, by latitude, longitude, and sequence number. As with ground-water wells, the primary site identifier used for precipitation-quality stations in this report is the 15-digit composite of these three numbers. The following text presents a clarification of the subheadings that follow the station identification number and station name.
LOCATION.--See Data Presentation under "Records of Stage and Water Discharge"; same comments apply.
PERIOD OF RECORD.--This indicates the periods for which there are published precipitation-quality records for the station. Periods of record are presented separately for each type of sample collected at the site (in this report, either wet precipitation, bulk precipitation, or both).
INSTRUMENTATION.--In this section, an abbreviated-style listing of the data recording and sample-collection equipment permanently housed at the site is presented.
REMARKS.--This section is reserved for comments pertaining to unusual or extraordinary circumstances or to qualifying information that must be used to accurately interpret the data presented for the site. More general comments, which may pertain to several or all of the sites, are presented in the introductory part of the report.
Records of precipitation quality for site GA99 can be accessed through the World Wide Web (WWW) at:
http://nadp.sws.uiuc.edu/nadpdata
The U.S. Geological Survey (USGS) is the principal Federal water-data agency and, as such, collects and disseminates about 70 percent of the water data currently being used by numerous State, local, private, and other Federal agencies to develop and manage our water resources. The USGS provides near real-time stage and discharge data for many of the gaging stations equipped with the necessary telemetry and historic daily-mean and peak-flow discharge data for most current or discontinued gaging stations through the World Wide Web (WWW). Some water-quality and ground water data also are available through the WWW. These data may be accessed nation-wide at:
In addition, considerable information concerning the water resources in Georgia can be accessed through the WWW at:
Data can also be provided in various machine-readable formats by email or 3-1/2 inch floppy disk. Information about the availability of specific types of data or products, and user charges, can be obtained locally from the Georgia District Office at the following address: