Water-quality and streamflow data

collected by the USGS as part of its national programs such as NAWQA (National Water-Quality Assessment), NASQAN (National Stream Quality

Accounting Network), and NSIP (National Streamflow Information Program), and

data from local studies reside in the National Water Information System (NWIS)

database of the USGS. This database is

now accessible through the Internet as

NWISWeb (see web sites listed on p. 4).

A broad range of data types at a variety of

scales covering various time periods are

available to water managers at NWISWeb. These data can be used to identify

impaired waters, determine pollutants and

pollutant loads, and prioritize water bodies for TMDL development.

As an example, Tennessee’s waterquality regulatory agencies listed over-enrichment of nutrients as the cause of impairment of 37 stream segments and 2

lakes within the lower Tennessee River

Basin. Each water body listed is required

to have a TMDL developed as part of the

process to reduce nutrient concentrations.

As part of a NAWQA assessment in this

basin, nutrient inputs from nonpoint and

point sources were determined for the lower Tennessee and 11 tributary basins (fig.

2). These data are used now by resource

managers and policy makers for nutrient

management (Woodside and Hoos, 2001).

The nationwide streamflow-gaging

network operated by the USGS in cooperation with State agencies and other cooperators provides data that can be used to

support TMDL studies. As an example,

streamflow data from the cooperative

USGS-New Jersey Department of Environmental Protection (NJDEP) streamgaging network were used to select an appropriate water-quality model to assess

nonpoint-source pollution on the Passaic

River and the tributary Whippanny River.

In addition, water-quality data collected

in these rivers as part of a joint NJDEP –

USGS cooperative network were used by

NJDEP to identify specific pollutants that

were close to exceeding or had exceeded

TMDL values. This enabled NJDEP to

focus their sample analysis on specific

pollutants, thereby saving thousands of

dollars in analytical costs.

Monitoring and Assessment

The USGS routinely measures

streamflow nationwide. In rivers, lakes,

and estuaries nationwide, USGS also

measures concentrations of constituents

such as suspended sediment, nutrients,

bacteria, trace metals, toxic organic

compounds, and dissolved oxygen.

These data are valuable for calculation

of the current load of each constituent of

concern when developing a TMDL (table 1) and to establish a baseline for

trends. Because the load is the product

of the flow and constituent concentration, accurate measurements of both are

essential. These data can be used to determine the natural variability of flow

and constituent concentration within the

stream and critical periods during which

concentrations of pollutants may vary

based on seasonal or daily variations in

flow, water chemistry, point-source discharge, or other variables.

Flow-weighted water-quality sampling is a standard USGS sampling procedure and, under most flow conditions,

results in a more accurate representation

of the actual constituent concentration in

the stream than a grab sample. Because

pollutant concentrations can vary with

stream depth, channel morphology, and

Figure 2. Estimated total nitrogen and the proportions of inputs from wastewater,

atmospheric deposition, and agricultural inputs in the lower Tennessee River

Basin and tributary basins.

Table 1. The USGS can assist States, Territories, and authorized Tribes with the

tasks that are part of the TMDL process

4

2

3

1

STREAM YIELDS OF

NITROGEN, IN TONS PER

SQUARE MILE PER YEAR

Tennessee

Mississippi Alabama

Duck River

(Williamsport Bridge)

Duck River

(Normandy Dam) Clarks River

Duck River

(Hurricane Mills)

Shoal Creek

Buffalo River

Elk River (Prospect)

Elk River

(Tims Ford Dam)

Town Creek

Sequatchie River

Flint Creek

LOCATION OF

SAMPLING SITE

NITROGEN SOURCE

EXPLANATION

NONPOINT SOURCE

POINT SOURCE

Kentucky

Georgia

Steps to restore water quality

through TMDL assessments

Identify impaired waters and determine pollutants

Prioritize water bodies for TMDL development

Determine current loads of pollutants in streams

Calculate maximum load that a water body can carry and

remain unimpaired (TMDL)

Determine the necessary load reductions to meet the TMDL

Identify sources of pollutants and relative contributions from

point-and nonpoint sources

Evaluate the effectiveness of alternative plans to achieve the

TMDL and restore water-body designated uses

Monitor the water body during and after implementation of

the plan to determine if TMDL levels are met and maintained

USGS Contributions to TMDL Assessments

Evaluation

of existing

data

Development

of new

approaches

and tools

Monitoring

and

assessment

Information

sharing and

technology

transfer
other factors (fig. 3), a flow-weighted sample is collected by sampling along vertical

profiles at several locations across the width

of the stream channel. The result is a waterquality sample that integrates the full range

of concentrations of a given constituent

across a stream channel. This type of sample accurately reflects the load carried by

the natural system.

Working in a variety of hydrologic settings across the country, the USGS has developed expertise needed to design networks, determine sampling frequency and

sampling methods, and to interpret data.

Understanding the hydrologic system and

how chemical constituents are transported

under varying flow conditions is important

in evaluating how accurately a calculated

load represents the actual load of a constituent. Interpretations provided by the USGS

assist water-resource managers in developing TMDLs.

A TMDL implementation may include

changes in land management, construction

practices, permit limits, or planting buffers.

After TMDL implementation, continued

monitoring to calculate loads and trends is

necessary to assess the effects that the

TMDL has on the water body. Changes

measured must be evaluated to determine

whether they result from the TDML implementation or natural variation in the stream.

Interpretation of follow-up monitoring can

determine if the TMDL-defined loading

goals are achieved and if they are meeting

the goal of fishable and swimmable waters.

USGS programs at the watershed,

state, regional, and national levels can provide data for assessment and monitoring of

water bodies as part of the TMDL process.

For example, the USGS in cooperation

with the Kansas Department of Health and

Environment has developed a water-quality

network that provides real-time load estimates for use in determining TMDLs.

Continuously recorded data and data from

periodic water-quality sampling are used to

develop surrogate relations between physical properties of water that can be measured continually and transmitted as nearly

real-time data, and chemical constituents of

concern that cannot be measured continuously. Relations have been developed to

estimate fecal coliform bacteria from continuous turbidity measurements on the Little Arkansas River (fig. 4) to estimate loads

and help define the accuracy of the data

used for calculating TMDLs. These nearly

real-time data may also be useful for considering human whole-body contact and

recreation criteria, for adjusting water-treatment strategies, and for preventing adverse

effects on aquatic life.

Development of New Approaches and

Tools

The USGS can develop watershedspecific tools to assist resource managers

in identification of the primary sources of

pollutants and their relative contributions

and in evaluation of the effectiveness of

alternative TMDL plans. Laboratory procedures pioneered by USGS researchers

can detect low-level concentrations of pollutants and identify emerging contaminants. New equipment for environmental

monitoring is developed and tested by the

USGS. These new procedures and tools

may play an important role in establishing

future TMDLs. In addition, sampling protocols are updated by the USGS to incorporate the latest advances in field-sampling methods, resulting in consistent data

collection across the country and over

time. Sampling protocols are provided

and frequently updated in publications

such as the National Field Manual for the

Collection of Water-Quality Data (U.S.

Geological Survey, 1997–present).

Figure 4. Comparison of measured loads of fecal coliform bacteria with estimated

loads determined from turbidity at two sites on the Little Arkansas River, Kansas.

Figure 3. Sediment concentration variations below the confluence of the

Mississippi and St. Croix Rivers during the spring snowmelt of 1994.

Jan. 1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

Feb. Mar. Apr. May Jun.

1999

Fecal coliform bacteria load, in billion colonies per day

Jul. Aug. Sept.

A. Little Arkansas River at Highway 50 near Halstead

B. Little Arkansas River at Highway 50 near Sedgwick

Oct. Nov. Dec.

Estimated

load

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

Measured

load