Water Quality Assessment Methods

Water quality assessment is a critical process for maintaining and improving the health of our aquatic ecosystems. States and other jurisdictions play a vital role in this process, setting standards and conducting assessments to ensure that water bodies meet designated uses.

How States Assess Water Quality

Water quality assessment begins with water quality standards. States and other jurisdictions adopt water quality standards for their waters. EPA must then approve these standards before they become effective under the Clean Water Act.

Water quality standards have three elements:

• the designated uses assigned to waters (e.g., swimming, the protection and propagation of aquatic life, drinking)
• the criteria or thresholds that protect fish and humans from exposure to levels of pollution that may cause adverse effects
• the anti-degradation policy intended to prevent waters from deteriorating from their current condition.

After setting standards, states assess their waters to determine the degree to which these standards are being met. To do so, states may take biological, chemical, and physical measures of their waters; sample fish tissue and sediments; and evaluate land use data, predictive models, and surveys.

For more information on state water quality standards, visit the National Water Quality Standards site.

Integrated Report

An Integrated Report is a biennial state submittal that includes the state’s findings on the status of all its assessed waters (as required under section 305(b) of the Clean Water Act), a listing of its impaired waters and the causes of impairment, and the status of actions being taken to restore impaired waters (as required under section 303(d)).

EPA first issued guidance to the states in 2001 encouraging them to integrate their water quality assessment information into one report. Before the issuance of this guidance, these were separate state 305(b) and 303(d) reports, and in many cases the findings and assessment data in them did not agree. EPA has issued additional guidance on Integrated Reporting in subsequent years.

The purpose of this guidance was to streamline and reduce the reporting burden to the states and improve the information needed to make water quality management decisions. For information on the guidance issued by EPA, see Implementing Clean Water Act Section 303(d): Impaired Waters and Total Maximum Daily Loads (TMDLs).

States are as a whole moving toward improved integration of their 305(b) and 303(d) reports. However, EPA guidance on integration is relatively new, and states are not required to integrate their reports. Because 303(d) lists require public comment and EPA approval, this process may delay the development of the 305(b) report, so states may prefer to prepare separate 303(d) and 305(b) reports.

Since states are not REQUIRED to integrate their 305(b) and 303(d) reports, there may always be some states that do not prepare integrated reports. However, most states are working toward integration.

Categories of Use Support

Waters rated by the states as "good" fully support all of their designated uses.

Waters rated by the states as "threatened" currently support all of their designated uses, but one or more of those uses may become impaired in the future (i.e., water quality may be exhibiting a deteriorating trend) if pollution control actions are not taken.

Waters rated as "impaired" by the states cannot support one or more of their designated uses.

Causes and Sources of Impairment

Where possible, states, tribes and other jurisdictions identify the pollutants or stressors causing water quality impairment. These causes of impairment keep waters from meeting the criteria adopted by the states to protect designated uses. Causes of impairment include chemical contaminants (such as PCBs, metals, and oxygen-depleting substances), physical conditions (such as elevated temperature, excessive siltation, or alterations of habitat), and biological contaminants (such as bacteria and noxious aquatic weeds).

Where possible, states, tribes and other jurisdictions identify where pollutants or stressors (causes of impairment) are coming from. These sources of impairment are the activities, facilities, or conditions that generate the pollutants that keep waters from meeting the criteria adopted by the states to protect designated uses. Sources of impairment include, for example, municipal sewage treatment plants, factories, storm sewers, modification of hydrology, agricultural runoff, and runoff from city streets.

Water Quality Assessment Techniques

Monitoring Data Used for Water Quality Assessments

State water quality assessments are normally based upon five broad types of monitoring data: biological integrity, chemical, physical, habitat, and toxicity. Each type of data yields an assessment that must then be integrated with other data types for an overall assessment. Depending on the designated use, one data type may be more informative than others for making the assessment.

• Biological integrity data are objective measurements of aquatic biological communities (usually aquatic insects, fish, or algae) used to evaluate the condition of an aquatic ecosystem. Biological data are best used when deciding whether waters support aquatic life uses.
• Chemical data include measurements of key chemical constituents in water, sediments, and fish tissue. Examples of these measurements include metals, oils, pesticides, and nutrients such as nitrogen and phosphorus. Monitoring for specific chemicals helps states identify the causes for impairment and helps trace the source of the impairment.
• Physical data include characteristics of water such as temperature, flow, dissolved oxygen, and pH. Physical attributes are useful screening indicators of potential problems, often because they can have an impact on the effects of chemicals.
• Habitat assessments include descriptions of sites and surrounding land uses; condition of streamside vegetation; and measurement of features such as stream width, depth, flow and substrate. They are used to supplement and interpret other kinds of data.
• Toxicity testing is used to determine whether an aquatic life use is being attained. Toxicity data are generated by exposing selected organisms such as fathead minnows or daphnia ("water fleas") to known dilutions of water taken from the sampling location. These tests can help determine whether poor water quality results from toxins or degraded habitat.

Hundreds of organizations around the country conduct some type of water quality monitoring. They also include state, interstate, tribal and local water quality agencies; research organizations such as universities; industries and sewage and water treatment plants; and citizen volunteer programs. Geological Survey, National Park Service and Forest Service also conduct water quality monitoring. They may collect water quality data for their own purposes or to share with government decision makers. States evaluate and use much of these data when preparing their water quality reports.

EPA’s national STORET Data Warehouse is a repository of much of this water quality information. It serves as an archive to protect our investment in water quality monitoring, and provides the interested public and water resource managers access to the wide range of data collected by these many sources.

Determining Trends in Water Quality

It is not appropriate to use the information in this database to make statements about national trends in water quality. The methods states use to monitor and assess their waters and report their findings vary from state to state and even over time. Many states target their limited monitoring resources to waters of interest, and therefore assess only a small percentage of their waters. These may not reflect conditions in state waters as a whole. States often monitor a different set of waters from cycle to cycle. Even weather conditions - such as prolonged drought - can have an impact on whether waters meet their standards from one year to the next.

The science of monitoring and assessment itself changes. We know, for example, that a number of states have increased the amount of fish tissue sampling they conduct and as a result are finding more problems and issuing more protective fish consumption advisories. Improved monitoring, in short, can affect the information in this database by increasing the identification of water quality problems. States may also, over time, change how they issue or report fish consumption advisories.

National water quality trends are best determined using scientifically-based studies designed to sample water quality conditions at randomly-selected sites that are statistically representative of the Nation's many distinct ecological regions. EPA and the states have embarked on such probability-based studies of coastal waters, lakes and reservoirs, rivers and streams, and wetlands. For more information, see the National Aquatic Resource Surveys site.

Statewide Statistical Surveys

Statewide statistical surveys are water quality assessments designed to yield unbiased estimates of the condition of a whole resource (such as all lakes or streams in a state) based on monitoring a representative sample of those waters. They can be used to track trends in water condition at the state scale or sub-state scale. Statistical surveys use standardized methods to quantify, with documented confidence, the extent of water quality problems and the extent of key stressors.

Statistical surveys complement more traditional targeted monitoring and assessment programs that generally target only waters of concern or interest.

EPA’s 2010 Integrated Reporting guidance includes a reporting template to help states report the results of their statewide statistical surveys using ATTAINS.

Statistical Surveys vs. Targeted Monitoring

States use two main approaches to assess water quality: statistical surveys and targeted monitoring. Much like opinion polls or indicators of economic health, statewide statistical surveys sample a representative yet randomly selected set of waters of a certain type (e.g., streams and rivers, lakes) and draw unbiased estimates of the condition of all waters of that same type in the state.

Site-specific targeted monitoring, on the other hand, is aimed only at those waters judged to be of concern or interest. Targeted monitoring is used to provide needed information to support management decisions at watershed and local scales (e.g., whether a water meets its water quality standards) for only those individual waters monitored and should not be extrapolated to the larger universe of all of a state’s rivers and streams, lakes, etc.

There are many differences between statewide statistical surveys and site-specific targeted monitoring, even though it is possible that their findings may appear similar. These differences affect how they are best used to inform water quality management.

The two approaches differ in scope and design. They are assessing two different populations: statistical surveys generate an unbiased estimate of the whole resource (such as all streams), while targeted monitoring addresses only the subset of waters determined by the state to be of concern or particular interest. The two approaches may also differ in method. Statistical surveys use a set of consistent sampling and analytical methods to ensure that results can be aggregated and compared over time. A state’s targeted monitoring program may rely on sampling methods that vary by waterbody or watershed, management need, or over time.

State statistical surveys provide a standardized measure for tracking changes over time and evaluating, at a broad scale, progress in investments to protect and restore water quality. Targeted monitoring provides information on the nature of water quality problems for the subset of those waters that were assessed, allows the state to identify individual waters that are not meeting water quality standards, and helps states set priorities for those waters.

Total Maximum Daily Load (TMDL)

A Total Maximum Daily Load, or TMDL, is a calculation of the maximum amount of a pollutant that can be present in a segment and still allow attainment of water quality standards, and an allocation of that amount to the pollutant’s sources. The TMDL calculation is TMDL = WLA + LA + MOS, where, WLA is the sum of wasteload allocations (point sources), LA is the sum of load allocations (nonpoint sources and background), and MOS is the margin of safety.

The MOS accounts for any lack of knowledge concerning the relationship between load and wasteload allocations and water quality. The TMDL analysis must take into account critical conditions such as high and low flows and seasonal variations in water quality. The waste load allocation in a TMDL is implemented through NPDES permits, but there is no federal regulatory requirement to implement the allocation to nonpoint sources.

Additional Water Quality Measurements

A wide variety of parameters are measured across environmental, utility, and laboratory settings. Common water quality measurements include temperature, dissolved oxygen, pH, ORP, conductivity, and turbidity, though many additional parameters can enhance your platform. Water quantity, such as level, is also frequently assessed.

Parameter	Description
Nitrogen Levels	Measures nitrogen levels as ammonia or ammonium.
Cyanobacteria	Also known as blue-green algae.
Dissolved Organic Matter (DOM)	Measures dissolved organic matter (DOM) in water that can impact light absorption and aquatic life health.
Chloride	A component of salt in minerals and oceans.
Chlorophyll	Enables plants and other chlorophyll-containing organisms to perform photosynthesis.
Colorimetry	Methods used to determine water chemical concentrations by measuring light absorption and color.
Heavy Metals	Present in the environment as a result of both natural and industrial processes.
Sugars	Includes measurements like glucose, lactose, and sucrose.
ORP (Oxidation-Reduction Potential)	Determine the oxidizing or reducing potential of a water sample.
pH	Describes how acidic or basic a solution is, depending on a solution’s ion content.
Temperature	A critical factor affecting water chemistry and biological activities.
Water Level	Measures the volume of water in bodies like rivers and lakes.

Our long-term river and stream monitoring team collects long-term data to track trends in stream health and contribute to watershed studies and water quality improvement plans. Our water quality scientists also maintain a network of continuous monitoring stations, in partnership with our streamflow scientists, to collect 24-hour data for dissolved oxygen, temperature, pH, and conductivity in many rivers and streams statewide.

Our surface water, groundwater, and aquatic ecosystems are priceless resources, used by people across the Nation for drinking, irrigation, industry, and recreation.

Since then, NAWQA has produced scientific data and knowledge that is used by national, regional, state, and local agencies to develop science-based policies and management strategies to improve and protect water resources used for drinking water, recreation, irrigation, energy development, and ecosystem needs.

SPARROW (SPAtially Referenced Regression On Watershed attributes) models estimate the amount of a contaminant transported from inland watersheds to larger water bodies by linking monitoring data with information on watershed characteristics and contaminant sources.

Scientists are characterizing groundwater quality in principal aquifers, the primary source of the Nation's groundwater used for drinking. Concentrations of inorganic constituents, such as arsenic and nitrate, and organic constituents, such as pesticides and volatile organic compounds, are compared to benchmarks established for the protection of human health. Groundwater hydrologists are developing statistical models that predict where a contaminant is likely to occur in groundwater and at what concentration. These models extrapolate groundwater quality in areas and at depths where groundwater has not yet been sampled.

Surface water and groundwater are intimately connected and are constantly interacting. The Integrated Watershed Studies team is quantifying how water and chemicals move between the landscape, streams and rivers, and groundwater.