HomeMy WebLinkAboutMiscellaneous PLANNER 1/3/2002
.. " "Drlineating the DrinI--;~,\ Water Protectian Area far S~rface W"'p;r Intakes
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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
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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
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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'
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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)
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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
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1/3/02
,D€lineating the DrinV'; Water Protectian Area f<?r Surface W-+~r Intakes
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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