GIS README FILE
2006 303d/305b Assessment Shape Files
Waters included on the Nevada 2006 303(d) Impared Waters List are shown as Category 5 waters (See category description below). Please remember that if one beneficial use is impaired for a water body, all uses for that waterbody are shown as category 5 even if other uses are fully supported.
Assessment methodologies are discussed in Nevada's 2006 303(d) Impaired Waters List.
When investigating the Beneficial Use/Assessment/Cause combinations for a waterbody, it is recommended that you start with the GIS identify tool. Once a waterbody is selected, the identify sidebar will show the waterbody and each reference will show the different Beneficial Use, Attainment, and Cause combinations.
When projecting waters by Causes, Beneficial Uses or Attainment understand that if a water has more than one value in a field, only the top layer will be illustrated. For example, if a water is listed for multiple causes (impairments), such as arsenic, boron, and mercury; when all values are added to the cause field, only the arsenic (the top layer) will be visible, boron and mercury will be covered by the arsenic layer.
A shape file showing waters with a TMDL is also provided. As stated above, use the identify tool to locate the TMDL and it's ID number. To see a detailed report of the TMDL and/or to download the reports (if available) please go to the the EPA Total Maximum Daily Loads website and drill down to the specific TMDL (it may be easier to use a search engine and search for "Detailed TMDL ID: ####). Additional TMDL information is also available on the NDEP Total Maximum Daily Loads website.
DATABASE FIELDS IN SHAPE FILES
ASSESSMENT DATA BASE ATTAINMENT CATEGORIES
Category 1: Fully Supporting.
Attaining all designated beneficial uses. Assessment units with sufficient data to determine that all designated beneficial uses are supported.
Category 2: Some Uses Attaining.
Available information indicates that some, but not all of the designated beneficial uses are supported, but at least one designated beneficial use has insufficient information for a use assessment.
Category 3: Insufficient Information.
Insufficient or no data and information is available to determine if any designated beneficial use is attained. Assessment units have insufficient data to assess any designated beneficial use as "fully supporting" or "impaired."
Category 4: Impaired or Threatened for One or More Designated Uses, but a TMDL Is Not Necessary.
Assessment units with at least one beneficial use assessed as "impaired" or "threatened" but development of a Total Maximum Daily Load (TMDL) analysis is not needed (at this time), for the following reasons:
4a - A TMDL has already been completed, is being implemented, and appears to be sufficient; or
4b - Other pollution control requirements are reasonably expected to result in the attainment of the water quality standard; or
4c - The impairment is caused by pollution but not a pollutant.
Category 5: Not Supporting.
One or more uses are impaired or threatened for one or more designated beneficial uses by a pollutant, and a TMDL needs to be developed or revised.