EPA Office of Water, Washington, DC. TMDL Program Results Analysis Fact Sheet # EPA841-F-09-006, December 2009
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Fact Sheet:
The Impaired Waters with TMDLs National Geospatial Dataset
Background: the Clean Water Act, impaired waters and TMDLs
The goal of the Clean Water Act (CWA) is "to restore and maintain the chemical, physical, and biological integrity of the
Nation's waters". Under section 303(d) of the CWA, states, territories, and authorized tribes, collectively referred to in the
Act and here as "states," are required to develop lists of impaired waters. A state's 303(d) impaired waters list is
comprised of all waters where required pollution controls are not sufficient to attain or maintain applicable water quality
standards. The law requires that states establish a prioritized schedule for waters on the lists and develop Total
Maximum Daily Loads (TMDLs). A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can
receive and still meet water quality standards, and an allocation of the load reduction needed from various sources of the
pollutant. Most TMDLs are technical documents that summarize the analysis and lay the groundwork for beginning to
plan restoration. Over 40,000 TMDLs have been developed, and the number is continually increasing.
EPA consolidates states' 303(d) listing and TMDL development information into the Assessment and TMDLs Tracking and
Implementation System (ATTAINS), providing publicly available information on over 40,000 tracked waters and access to
impaired waters data at local and national scales. Impaired waters data in tabular format appear online at
www.epa.gov/waters/ir and as geographic information systems (CIS) datasets (see Figure 1) available for download at
http://epamap32.epa.qov/radims/.
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Figure 1: Mapped data on impaired waters (a) and impaired waters with one or more TMDLs (b) are available online from EPA.
Geospatial data on impaired waters and TMDLs
National geospatial datasets on impaired waters are produced and periodically updated by EPA using state-re ported data.
The CIS versions of state 303(d) lists are provided to EPA by states after the lists are approved and finalized. EPA
compiles the state datasets, reconciles differences in format, and indexes the data to the National Hydrography Dataset
Plus (NHDP/us) to provide a nationally consistent reference. The indexed datasets are housed in EPA's Reach Address
Database (RAD), including the 2002 Impaired Waters Baseline National Geospatial Dataset containing impaired
waters as of the 2002 baseline reporting year, and the 303(d) Listed Impaired Waters National Geospatial Dataset that
includes more recent state CIS data (from variable dates) available as of mid-2008. The RAD also provides dynamic
access to individual state or watershed-level data downloads as these become available. Figure 1 a is an example of CIS
data based on impaired waters reported as of the 2002 baseline year used in EPA Strategic Plan tracking.
Based on widespread interest in CIS data on impaired waters, EPA has developed The Impaired Waters with TMDLs
National Geospatial Dataset that identifies all impaired waters for which at least one TMDL has been developed. Figure
1 b is an example from this dataset, showing the waters with TMDLs for the same set of impaired waters shown in Figure
1a. This dataset is available through the RAD for public download and is updated periodically as resources permit.
Starting with the shapefiles of impaired waters, this new dataset was developed by relating all mapped, impaired waters to
all information on existing TMDLs. To appear in this dataset, impaired waters must have been mapped and at least one
of their impairment causes must have been addressed by a TMDL. Users should note, however, that the dataset cannot
encompass all waters with all TMDLs, because numerous TMDLs are completed before their state CIS data are finalized
and new TMDLs are continually being developed. Nevertheless, the dataset provides a valuable spatial record of the
availability of thousands of TMDLs that can be used in the CIS environment. These spatial data can be related to tabular
information, such as pollutant types or water body names, extracted from ATTAINS.
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EPA Office of Water, Washington, DC. TMDL Program Results Analysis Fact Sheet # EPA841-F-09-006, December 2009
A step further- linking TMDL maps to TMDL documents
The following example shows how a user can access impaired waters information, mapped waters with TMDLs, and
TMDL documents for the same location, all through EPA data systems. Grand River, Michigan appears as an impaired
water in Figure 1 (see also Figure 2). Online data from ATTAINS reveal that this water body's LIST ID is MI082816H and
its causes of impairment include pathogens, organic enrichment and sediment. Two TMDL documents have been
completed and their TMDL IDs are 9498 and 9499; 9499 alone is used in the example below.
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Figure 2: Grand River, Michigan example of a water body mapped as impaired (purple) as well as having a TMDL (orange).
Having found the TMDL ID 9499, the user goes online to the EPA's Expert Query
tool (Figure 3) at www.epa.qov//waters/tmdl/expert query to obtain the TMDL
document. Note that Expert Query can also be used to search for other
information about the Grand River by selecting one of the views about 303(d)
information and using the LIST ID number instead of the TMDL ID number.
The user follows the directions online, and selects the columns TMDL ID and
ASSOCIATED TMDL DOCUMENTS, at a minimum (Figure 4), which then
returns a hot link for TMDL ID 9499.
Figure 3: An online search for TMDL 9499
Selection Criteria for Expert Query
STEP 3; Enter Search Criteria and Organize the Output
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