Presenting Water Quality Information

Section II

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Presenting Water Quality Information:305(b) and the Index of Watershed Indicators

Paul

Goe

tz, C

ary,

NC

IntroductionWater quality data can be

interpreted by resource managers,researchers, conservation groups,and other interested parties in avariety of ways, depending on howthe data are collected, compiled,and presented. Because of thesedifferences in data gathering andpresentation, similar data gatheredby different agencies might not bedirectly comparable. This sectionfocuses on two ways water qualitydata are presented — through the305(b) process and in EPA’s Index of Watershed Indicators (IWI).Examples from South Carolina areused to illustrate the two methodsof data presentation.

There are important linksbetween the 305(b) process and theIWI. 305(b) data are an integral partof the indices used in the IWI. Both305(b) and the IWI report on thecondition and vulnerability of water-bodies. Condition indicatorsdescribe the current status and func-tions of a waterbody while vulnera-bility is influenced by environmentalfactors or activities that can placestress on the resource, thoughperhaps not to the point that itsvalues or functions are impaired.

What is the Index of WatershedIndicators?

The Index of Watershed Indi-cators (IWI) is a compilation of infor-mation on the condition of aquaticresources in the United States. Justas a physician might take your tem-perature and blood pressure, check

your pulse, and listen to your heart-beat and respiration to determinethe status of your health, the Indexlooks at a variety of indicators thatpoint to whether rivers, lakes,streams, wetlands, and coastal areasare “well” or “ailing” and whetheractivities on the surrounding landsare placing these waters at risk.

The Index is in large part basedon the June 1996 EnvironmentalIndicators of Water Quality in theUnited States, developed by EPA inpartnership with States, Tribes,private organizations, and otherFederal agencies. The IndicatorsReport presents 18 national indica-tors of the health of our waterresources. The Index evaluates asimilar set of indicators, categorizedas “condition” and “vulnerability”indicators, for each of 2,111 water-sheds in 48 States. (Alaska, Hawaii,and the Territories will be added infuture versions of the Index.)

Why Watersheds?A watershed is defined in

nature by topography. It is the landarea that drains to a body of water,such as a lake, an estuary, or a river.The watershed’s drainage affects thewater flow or water level and, inmany cases, the overall condition ofdownstream bodies of water. Thus,a lake, river, or estuary is a reflectionof its watershed. EPA's Office ofWater, along with many localgroups and State agencies, hasbeen emphasizing the importanceof organizing water quality improve-ment efforts on a watershed basis.Downstream conditions are affectedby all contributing input fromupstream tributaries and adjacentland use activities.

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What Is the Size ofThese Watersheds?

The U.S. Geological Survey(USGS) has developed and mappeda geographic Hydrologic UnitClassification (HUC) System ofwatersheds at four different scales.The lower 48 States, for example,are comprised of 18 basins knownas regions. Subregions, identifiedwith a 4-digit number, nest withinthe regions, and 6-digit accountingunits are smaller yet. Within thoseaccounting units are 8-digit cata-loging units, which define water-sheds that are generally greaterthan 700 square miles in drainagearea. For the Index, watersheds aredepicted at the 8-digit scale — thesmallest unit in the nationally con-sistent HUC System. South Carolina,for example, has 31 catalogingunits, which vary in size from about500 to 1,800 square miles.

What Are theIndicators?

Phase I of the IWI project uses15 indicators or data layers. Theywere selected because they areappropriate to the IWI objectives,they have relatively uniform avail-ability across the Nation, and theycan be depicted at the 8-digit HUCscale. Seven of the indicators arerelated to the condition of theaquatic resources, and eight arerelated to vulnerability. Phase II willinclude Alaska, Hawaii, and PuertoRico and will add more data layerssuch as ground water.

Condition Indicators1. Assessed Rivers Meeting All

Designated Uses Establishedby State or Tribal WaterQuality Standards (§305(b)):Information reported by Statesand Tribes on the percentage ofwaters within the watershed thatmeet all uses established forthose waters as reported in 1994or 1996 reports to Congressrequired under Clean Water ActSection 305(b).

2. Fish and Wildlife ConsumptionAdvisories: Advisories recom-mended by States to restrictconsumption of locally harvestedfish or game due to the pres-ence of contaminants. (datafrom EPA’s National Listing ofFish and Wildlife ConsumptionAdvisories)

3. Indicators of Source WaterQuality for Drinking WaterSystems: Three data sets com-bined to give insight on theextent to which waters fromrivers, lakes, or reservoirs requiretreatment before use as drinkingwater based on (1) attainmentof the “water supply” desig-nated use under Section 305(b)based on river and lake water-bodies, (2) community watersupply systems with treatment inplace beyond conventional treat-ment or systems that were inviolation of source-related stan-dards in 1995 (Safe DrinkingWater Information System[SDWIS]), and (3) presence of

contaminants in source water atlevels that exceed one-half themaximum contaminant level(MCL). (The MCL is the level towhich a contaminant must beremoved from drinking water tomeet Safe Drinking Water Actsafety requirements.) (data fromEPA’s STORET database)

4. Contaminated Sediments: Thelevel of potential risk to humanhealth and the environmentderived from sediment chemicalanalysis, sediment toxicity data,and fish tissue residue data. (datafrom EPA’s National SedimentInventory)

5. Ambient Water Quality Data —Four Toxic Pollutants: Ambientwater quality data showingpercent exceedances of nationalcriteria levels, over a 6-yearperiod (1990-1996), of copper,hexavalent chromium, nickel,and zinc. (data from STORET)

Condition IndicatorsCondition indicators describe thecurrent status and functions of awaterbody. In the 305(b) process,States and Tribes evaluate condi-tions in a waterbody and reporton whether it supports, partiallysupports, or does not supportbeneficial uses. The Index reportson a number of condition indica-tors, including fish consumptionadvisories, contaminated sedi-ment, and wetlands loss.

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6. Ambient Water Quality Data —Four Conventional Pollutants:Ambient water quality datashowing percent exceedances of national reference levels, overa 6-year period (1990-1996), of ammonia, dissolved oxygen,phosphorus, and pH. (data fromSTORET)

7. Wetlands Loss Index: Percent-age of wetlands loss over ahistoric period (1870-1980) and more recently (1986-1996).(data from U. S. Fish and WildlifeService’s National WetlandInventory and Natural ResourcesConservation Service’s NationalResource Inventory, respectively)

12. Index of Agricultural RunoffPotential: A composite indexcomposed of (1) a nitrogenrunoff potential index, (2) mod-eled sediment delivery to riversand streams, and (3) a pesticiderunoff index. (data from NaturalResources Conservation Service)

13. Population Change: Popula-tion growth rate as a surrogateof many stress-producing activi-ties from urbanization. (datafrom Census Bureau)

14. Hydrologic Modification —Dams: An index that showsrelative reservoir impoundmentvolume in the watershed. Theprocess of impounding streamschanges their characteristics,and the reservoirs and lakesformed in the process can bemore susceptible to pollutionstress. (data from Corps ofEngineers)

15. Estuarine Pollution Suscepti-bility Index: An index thatmeasures an estuary's suscepti-bility to pollution based on itsphysical characteristics and itspropensity to concentratepollutants. (data from NationalOceanic and AtmosphericAdministration)

Vulnerability Indicators8. Aquatic/Wetlands Species at

Risk: Watersheds with highoccurrences of species at risk.(data from The Nature Conser-vancy and State Heritage data-bases)

9. Pollutant Loads DischargedAbove Permitted DischargeLimits — Toxic Pollutants:Discharges over a 1-year periodfor toxic pollutants, combinedand expressed as a percentageabove or below the total dis-charges allowed under theNational Pollutant DischargeElimination System (NPDES)permitted amount. (data fromEPA's Permit ComplianceSystem)

10. Pollutant Loads DischargedAbove Permitted DischargeLimits — ConventionalPollutants: Discharges over a1-year period for conventionalpollutants combined andexpressed as a percentageabove or below the totaldischarges allowed under theNPDES permitted amount.(data from EPA's PermitCompliance System)

11. Urban Runoff Potential: Anestimate of the potential forurban runoff impacts based onthe percentage of impervioussurface in the watershed, e.g.,roads, paved parking, and roofs.(data from USGS and CensusBureau)

Vulnerability IndicatorsVulnerability indicators describeenvironmental factors or activitiesthat can place stress on theresource, though perhaps not tothe point that its values or func-tions are impaired. In the 305(b)process, States and Tribes reporton waterbodies that currentlysupport a beneficial use, but arethreatened for that use do tocircumstances in the surroundingwatershed. The Index reports ona number of vulnerability indica-tors, including species at risk, pol-lutant loads, runoff potential, etc.

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Where Can YouView the IWI?

The Index of Watershed Indica-tors can be viewed on the Internetat http://www.epa.gov/surf/iwi andin a hard copy report available fromthe National Center for Environ-mental Publications and Information(NCEPI). The Index includes a mapof the United States with color-coded information on the overallcondition/vulnerability of eachwatershed, as well as national mapsdepicting each data layer for allwatersheds. The Internet version ofthe Index provides links to a broadrange of support material.

How Is the OverallWatershed ScoreDeveloped?

Each watershed is identified ashaving good quality, less serious ormore serious problems, and high orlow vulnerability. There is a separatecategory for watersheds with toolittle data for a valid characteriza-tion. Condition and vulnerabilityindicators are evaluated separatelyfor each watershed.

For the indicators, a minimumnumber of observations is necessaryto assign a “score.” If data for a par-ticular indicator are insufficient, thatis displayed on the map and indi-cated in the Profile. At least 4 of 7condition indicators and 6 of 8 vul-nerability indicators must be presentto calculate the overall index for anygiven watershed.

In aggregating the 15 indicatorsinto the overall Index, Indicator 1,Assessed Rivers Meeting All Desig-nated Uses, is weighted more heav-ily than other indicators because it isa comprehensive assessment andEPA believes considerable weightshould be given to the State andTribal 305(b) assessment process.

For instance, an individualWatershed Profile page (see examplefrom South Carolina) presents amap of each Cataloging Unit shownin relation to adjacent watershedsand the boundary of the State inwhich it is primarily located. Thisprofile also describes the physicalfeatures and demographics of thewatershed and display its OverallWatershed Score (one of sevencategories) and the scores for eachindividual indicator.

NOTE: Detailed information onsources of data, the method usedto characterize each data layer,and the method for combiningindividual indicators into theoverall Index is available throughthe Internet at www.epa.gov/surf.

What are Some of the Benefitsof the Index?

■ A focus on watershed resources: The Index provides easy-to-getinformation from many sources about local watersheds and theirneeds.

■ Knowledge is power: The Index enables managers and residents tounderstand, and therefore act responsibly about, their watershed.

■ Progress: Together, many organizations and people have beenworking to maintain and improve our water quality, and they have been successful in many areas, while maintaining population andeconomic growth.

■ Partners: Various Federal, State and nongovernmental organizationshave begun to combine their information to tell a coordinated story.Using this information, the combined forces of these organizationscan work together to better address our remaining problems andprotection needs.

■ Missing data: Indicators with too little data are clearly shown ingrey, indicating where information needs to be collected.

■ Monitoring: IWI uses information from many public and privatesources to provide a full picture of watershed health.

All other indicators are weightedequally. If Indicator 1 is not avail-able, the values of the other condi-tion indicators are increased by afactor of 3 to derive an Index score.

How Are 305(b) DataUsed in the IWI?

The IWI map of “assessed riversmeeting all designated uses estab-lished by state or tribal water qualitystandards” (Figure 1) presents a

national picture of the overall healthcondition of individual watersheds.Correctly read, the information pro-vided is interpreted as follows: “InX watershed, Y percent (as a range)of the assessed stream miles in thewatershed meet all designateduses.” Watersheds in which a highpercentage of waterbodies meetdesignated uses generally havebetter water quality than watershedsin which the percentage is low.Designated uses can be drinking

water supply, aquatic life support,fish and shellfish consumption, pri-mary and secondary contact recre-ation, and agriculture. Where awatershed shows a lower degree ofoverall designated use attainment, itis helpful to be able to break outdata summaries for specific uses.Different uses employ differentbenchmarks to define use attain-ment (e.g., bacteria counts forswimming use and dissolvedoxygen levels for aquatic life use).

80 - 100% Met50 - 79% Met20 - 49% Met< 20% MetInsufficient Data

Percent of Cataloging Unit WaterbodiesMeeting All Designated Uses:

Analysis of Alaska andHawaii reserved for Phase 2.

Sources: U.S. Environmental Protection Agency:National Water Quality Inventory

Index of Watershed Indicators

Figure 1. Assessed Rivers Meeting All Designated Uses Set in State/Tribal Water Quality Standards 1994/1996

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Data summaries on such pollutionstressors or the sources of the stres-sors may also be needed for manymanagement decisions. The poten-tials of such supplemental datapresentations are illustrated below.

Data Presentations —South CarolinaExample

While the 305(b) process andthe IWI depict similar water qualitydata, they differ both in scope andscale. As discussed, the Index dealswith a variety of indicators, a num-ber of which draw on data gatheredthrough means other than the305(b) process. IWI and 305(b) dataare also presented at different scales.305(b) data are typically gathered atthe waterbody level and then aggre-gated to the State level for reportingin the National Water Quality Inven-tory, while IWI presents data at theHUC level. The following exampleusing data from South Carolinademonstrates how data are reportedthrough IWI and the 305(b) processand compares and contrasts the twopresentations.

Figure 2 is a table of individualuse support in South Carolina taken

0

Total MilesSurveyed

Percent

26,314

91

0 4 5 0

0

63

016

Designated Use

Rivers and Streams (Total Miles = 35,461)

Lakes (Total Acres = 525,000)

Estuaries (T otal Square Miles = 945)

211,244 0

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The map in Figure 3 was gener-ated through a process called reachindexing, whereby waterbody-level305(b) use support data were linkedto a map of South Carolina’s hydro-graphy. Reach indexing is theprocess of linking water qualityinformation to the EPA Reach File, a hydrography dataset at the1:100,000 scale that will eventuallybecome part of a Federal standardNational Hydrography Dataset(NHD). The link between the mapand the water quality data is madeusing a geographic informationsystem (GIS). Reach indexing givesStates powerful mapping and spa-cial analysis capabilities for specificstreams within a watershed.

Figure 3, also taken from the1994 National Water Quality Inven-tory summary document, representsanother depiction of 305(b) data.This figure shows a map of SouthCarolina’s Edisto watershed. Eachstream in the watershed is color-coded to its corresponding usesupport status. This type of map isparticularly helpful to watershedresource managers who need toprioritize water quality monitoringand restoration projects in a water-shed. For example, red areas (whichdo not support all beneficial uses)might be targeted for improvementmeasures or additional research.

from the 1994 National WaterQuality Inventory summary docu-ment. These data were originallygathered at the waterbody level. In other words, State resourcemanagers assessed particular rivers,lakes, and estuaries in South Caro-lina, then compiled statistics at thestatewide level. For example, thedata show that 91% of rivers inSouth Carolina fully support aquaticlife use, as opposed to 75% ofestuarine waters. In this format, thedata are useful to individuals inter-ested in general water quality condi-tions across the State, such as a con-cerned citizen or legislator.

Figure 3. South Carolina’s Edisto Watershed

Fully SupportingPartially SupportingNot SupportingBasin Boundaries(USGS 6-Digit Hydrologic Unit)

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score, there are also scores for boththe condition and vulnerability ofthe Edisto watershed. As discussedabove, 305(b) assessment data forthe watershed are used to deter-mine the designated use attainmentscore. This indicator is weighedmore heavily than the others.

Through Surf Your Watershed,the IWI makes available 305(b) dataaggregated at the watershed scale.Figures 7 and 8 display aquatic lifeuse support in the Edisto watershedfor rivers and estuarine waters,

A resource manager might alsowant to view information just for asingle watershed in South Carolina.Through EPA’s World Wide Webpage, Surf Your Watershed, individ-uals can choose a particular water-shed in a State and obtain IWI infor-mation. Figure 5 shows the optionof obtaining IWI information for theEdisto watershed.

Figure 6 presents the IWI indica-tors for the Edisto watershed as theyare displayed in Surf Your Watershed.In addition to an overall watershed

IWI displays information at thesame watershed scale as the map ofthe Edisto watershed shown above.Figure 4 is an example of one wayin which the IWI presents informa-tion. The figure shows all the water-sheds in South Carolina color-codedby the IWI indicator of the percentof the watershed meeting all desig-nated uses. A map at this scalemight benefit a State resourcemanager who needs information onhow to allocate resources acrossSouth Carolina.

Sources: U.S. Environmental Protection Agency:National Water Quality Inventory

80 - 100% Met50 - 79% Met20 - 49% Met< 20% MetInsufficient Data

Percent of Cataloging UnitWaterbodies Meeting AllDesignated Uses:

Figure 4. Assessed Rivers Meeting All Designated Uses in South Carolina

Index of Watershed Indicators

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the area to have information on thecauses and sources of this impair-ment. The cause and source infor-mation for the Edisto watershedavailable through the IWI (Figures 9and 10) indicates that the mostprevalent causes of impairment inrivers are pathogens and turbidity,and the most prevalent sources ofpollution are agriculture, naturalsources, and municipal pointsources.

as a whole. This type of informationcan be helpful for a water qualitymanager interested in targetingresources across the State.

The IWI also makes available305(b) data on the causes andsources of impairment at the water-shed level. As Figure 3 demon-strates, there is a “hot spot” in theEdisto basin where a number ofstreams do not support all beneficialuses. It might be helpful forresource managers planning pro-grams to improve water quality in

respectively. The data show thatover 90% of the rivers and estuarinewaters in the watershed fully sup-port aquatic life use. It is interestingto compare these values to thestatewide numbers presented inFigure 2. While statewide, 91% ofSouth Carolina rivers fully supportedaquatic life use, only 75% of theState’s estuarine waters fully sup-ported this use. Thus, the data tellus that the Edisto watershed hasbetter than average estuarine waterquality than compared to the State

Figure 5. Surf Your Watershed World Wide Web Page for the Edisto Watershed

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Figure 6. Water Quality Information Presented Graphically on Surf Your Watershed

As displayed in Surf YourWatershed, IWI indicatorsof the condition of thewatershed are scored andassigned to one of threecategories — better waterquality, water quality withless serious problems, andwater quality with moreserious problems. Second,indicators of vulnerabilityare scored to create twocharacterizations of vul-nerability — high and low.These two sets of indica-tors are then combined tocreate the Overall Water-shed Score illustrated atthe right.

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Figure 7. Aquatic Life Use Support for Rivers in the Edisto Watershed

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Figure 8. Aquatic Life Use Support for Estuarine Waters in the Edisto Watershed

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ConclusionAs the South Carolina example

demonstrates, 305(b) and the IWIoffer many ways of viewing waterquality information. The scale atwhich data are aggregated, whetherit be at the National, regional, State,watershed, or waterbody level, pro-vides us with various “snapshots” ofwater quality conditions and vulner-ability. All of the presentations arevalid, but each is an attempt to pre-sent information in a different way,and each has strengths and weak-nesses. Determining which presenta-tion is best depends on the needs ofthe resource manager.

Figure 9. Major Causes of Impairment to Rivers in the EdistoWatershed

Figure 10. Major Sources of Impairment to Rivers in the Edisto Watershed

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