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HomeMy WebLinkAboutMiscellaneous PLANNER 1/3/2002 .. " "Drlineating the DrinI--;~,\ Water Protectian Area far S~rface W"'p;r Intakes ,~ ~ '~l;l{.1 ... 303(d) List ... Drinking Water ... Fact Sheets ... Groundwater ... Links ... Laans/Grants ... Nanpaint ... Natices ,.. On-Site ,.. Permits ... Rules ... Standards ... TMDLs ... UIC Q W >~ -- l' WNJ ()~ W a: . . ~ OJ Page I af3 . DEQ will be canducting the delineatians far the surface water intakes in Oregan using a Geagraphic Infarmatian System (GIS), The delineatian .of the saurcearea .or the "drinking water pratectian area" is a fundamental aspect .of the assessment .of a public water system, Far surface water systems, the drinking water pratectian area delineatian process begins by identifying the watershed The watershed area is alsa called the catchment basin .of a receiving water bady, The .outer baundary .of this watershed is the drainage divide farmed by the surraunding ridges and hills, The surface water delineation includes the entire watershed area upstream .of the public water system intake structure, This watershed area provides "saurce" water ta the surface water intake, A map of the drinking water protection area provides the community with the knawledge .of thegeogYapnic area providing the water ta the intake.JThis is the ~ .,', - ---,-- , ----.----.- area where cantaminatian"p6ses tne greatest threat ta the drinking water supply, Infarmatian abaut the drinking water pratectian area allaws the cammunity ta develap management strategies that will have the mast impact an pratecting the saurce .of the drinking water, ' After delineating the entire watershecJ.,_DE.9jclentifies,the'::sensitive~as" within the watershed,(!he objective in det~rmining.the,sensitive"area~lQi) rsurface-water sources "is'to"proaiiCe'Jjiljaple"informatian'ta -thecammunilfarfd) Ipublic'watersystem'that'is:usetu!'in"develaping-aha prioritizi'lg,RLotection/ 'strategies, The"listofthe sensitive areas tooe iaentitied within drinking water watersheds was defined by the DEQ advisary cammittee as the pracedures were develaped (see the "Saurce Water Assessment Plan"), The sensitive areas within a drinking water watershed includes both'Setoacks (land adjacent to stream) andothernatural-factors that'increase'the"risk-of'coiltaminatian"'af the) surface'wate2,The resulfisaniaelltificatian-afa-suDsetofthe entire wate,rshed.' "The sensitiiieiiieas arethos€'-where potentiarcantamination 'sources .or land' , use actiitities;"'i(pjesfiiit-:lialiea greater potentiartoimpacrttfe'wifteTsupply.j -- - . -"' ....-..--. "'- -'-~- -. --..-' ~-'. In establishing sensitive areas in a watershed, there are several limiting factars ta take inta accaunt. In using a Geagraphic Infarmatian System (GIS) ta delineate the sensitive areas within the watershed, DEQ locates existing GIS layers and other natural resaurce agency data sets, Nat all areas .of the state have been mapped far the natural resaurce parameters .of interest .or at the level '.of detail ideal far this type .of analysis, The availability of data atappropriate scales is alsa a patentiallimitatian, The sensitive area mapping may be limited simply by the lack .of readily available data, and canducting additianal research is nat passible within the time frame allawea ta da this assessment. DEQ staff has saught ta .obtain the best available infarmatian far each water system as the saurce water assessment was perfarmed, There are faur individual characteristics that determine the sensitivity .of areas http://www.deq.state.ar.us/wq/dwp/DWPAreaDelineatiansSW.htm 1/3/02 " Delineating the DrinY:"~ Water Protectian Area far Surface W-'~r Intakes within the drinking water watersheds'in the Saurce Water Assessment Plan procedures for Oregan water systems, A brief descriptian .of the sensitive area characteristics and the saurces .of the GIS data are included belaw, :- Sans itive. Area,Setbacks ~ --- - The first sensitive area is a setback using a~c:ansiste-hf1000~(abaut 300 meters)distance from-thewater"bcidy; The fOOO'sensitive' area setbacks are intenae(ftoiaentityth-ase areas-Where there are higher risks .of cantaminatian by spills or ather releases, simply due ta their praximity ta the water bady, The sensitive area setbacks are identified as a minimum .of 1000' fram centerline .of the intake stream and all perennial tributaries within the delineated drinking water watershed, The distance .of 1000' was based an EPA natianal guidance far the distance ta canduct the patential cantaminatian saurce inventaries adjacent ta streams, : Hig~!oirEros!.o!'-PotenHa.1 . / The sail erasian patential is determined by cambining the effects of slape and the sail eradibility factar ("K-facta~')'. Slapes within a watershed are evaluated using the 1 :24,000 SSURGO (Sail Survey Geagraphic Database) data sets fram the Natural Resources Canservatian Service, The slape far a map unit is a weighted average .of the average slape, The sail erodibility factar is alsa available in the SSURGO database and quantifies the susceptibility .of sail particles ta detachment and mavement by water including the effects .of rainfall, runaff, and infiltratian, The K- factar used is a weighted average .of .only the value far the surface layer .of the map unit. In the watershed. .only sails with "high" erodibility ratings were mapped as sensitive areas, Sails that classify as "high" include sail with slapes greater than 30% and K-factars greater than 0,25, This rating system is based an the Revised Universal Soil Loss Equation fram the USDA Agricultural Research Service as defined in the Washingtan's Standard Methadalagy far Canducting Watershed Analysis (Washingtan Farest Practices Baard, 1993), 'High-Permeatiility Soils' - _..~.__._--- Sails identified in the U.S, Geological Survey gealagic map .of Oregan GIS layer (1 :500,000 scale) as Recent Alluvial Depasits (Qal) are mapped as sensitive areas due ta the high patential far ground~ater _ recharge adjacent ta the stream, Alluvial depasits are:tYl1.igllly_very high, permeability-soils.JThese areas may be very vulnerable'ta rapid 'infiltratian-afCOritaminants ta groundwater and subsequent discharge to a stream or lakelreservair, (High Runoff Potential) - --. ~--~.~ The patential far high runaff rates was evaluated using the 1 :24,000 SSURGO (Sail Survey Geagraphic Database) data sets fram the Natural Resaurces Conservation Service, ClassD'soifS,;which are defined as ;sails"witti very slaw infiTtratian rates we'Felliapped as sensitive areas '---- .- ~~---- _ __.._--.....r within the baundaries .of the drinking water pratectian area, Map units are \ assigned ta hydralagic graups based an their majarity campanent. A Class D sail is typified as clayey, has a high water table, .or an imperviaus layer .occurs at a shallaw depth, Sails with these characteristics wauld have the patential far rapid runaff and subsequent transpart of sediments and passible cantaminants to the surface water body supplying the public water system, http://www.deq.state.ar.us/wq/dwp/DWPAreaDelineatiansSW.htm Page 2 af3 1/3/02 ,D€lineating the DrinV'; Water Protectian Area f<?r Surface W-+~r Intakes Page 3 af3 Additional Sensitive Areas There may be ather natural characteristics within a watershed that tan be mapped as sensitive, Madifying the list .of sensitive areas in this assessment can be dane by the publicwater system or the cammunity by identifying resaurces and procedures that are apprapriate far the individual system, Far example, the lacalcammunity may chaase ta add "transient snaw zanes", high rainfall areas, and landslide/debris-fiaw hazards ta the sensitive areas within their watershed, Due ta time canstraints, these additianal areas will nat be mapped by DEQ as part .of this source water assessment, but can be added by the lacal cammunity befare develaping a pratectian plan, Transient snaw zanes are typically defined as areas abave 1500 feet in the Oregan Caast Range. or abave 2000 feei in the Cascades. In same watersheds, these areas may be subject 10 rapid snawmelt .or rain-an- snaw events which increase the Iikelihaad .of transpart .of sediments ta the surface water badies in the watershed, Areas .of high rainfall .or irrigatian rates may increase the Iikelihaad .of transpart .of sediments and passible contaminants ta the surface water bady, These areas can be identified using average annual precipitation data fram Oregan Climate Service (years 1961 thraugh 1990) and irrigation/water rights data from Oregan Water Resaurces Department's water rights database, Mapping the high risk landslide and debris-fiaw areas can alsa be useful for evaluating sediment risks fram natural hazards within a drinking water watershed, The Department .of Farestry has recently campleted GIS- based landslide and debris flaw maps far western Oregan (Website add ress: http://www.ad!state.ar.us/gis/debris.html) , The final watershed map far each public water system intake includes a GIS camposite .of all sensitive areas identified by DEQ within the watershed, This campasite .or .overlay will enable the cammunities and respansible agencies ta facus future protectian effarts in these sensitive areas, ' DEQ Online is the official web site for the Oregon Departmentaf Environmental Quality. If you have,questionsor comments about the web site contact DEQ'S'oIebmaster. http://www.deq.state.ar.us/wq/dwp/DWPAreaDelineatiansSW.htm 1/3/02