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HomeMy WebLinkAboutMiscellaneous PLANNER 1/3/2002 (2) "..r-~D'elineating the Drinlr"-a Water Protectian Area far Graundwc' 'r Systems ..-. ~ . . ,~ ~ W3!} ~ ... 303(d) List .. Drinking Water .. Fact Sheets ,.. Graundwater .. Links ... Laans/Grants .. Nanpaint ,.. Natices ,.. On-Site ,.. Permits ,.. Rules ... Standards ... TMDLs ,.. UIC 0 W :~ > -- :(j W \ ",N) 0 1\ , - W . . 0: ~ CO Page I af5 Delineating the Drinking Water Protection Area for IGroui1awjlte_rJ~yst~ms 1_ ,_ _ _ ". _ _"_ (includes Springs andrConjunctive_D_elllJ.ei!.t!ons) Delineating the drinking water protectian area (DWPA) far a graundwater system is perfarmed by identifying the surface area that directly .overlies that portion' of the aquifer that supplies the well, wellfieJd .or springs used far drinking water purpases by a public water system, Far aquifers that are being used by a public water system far aquifer starage and recavery (ASR), the delineatian will identify the surface area that .overlies the injectian "bubble" praduced during the starage phase, The geametry .of the bubble will be determined through a cambinatian' .of madeling and manitar well water level and water quality analysis, The determinatian is a natural autcame of Oregan's existing ASR permitting pracess, Oregan's "Wellhead Pratectian Guidance Manual" .outlines in detail the minimum requirements far state-certificatian .of a drinking water protectian area (DWPA), These requirements are in Administrative Rule (OAR 333-061-057) and are clasely linked with a patential manitaring reductian far public water systems as well as land use regulatians in the state, The methads far delineating public water systems using wells are based primarily an papulatian and are summarized in the text belaw, Springs are delineated using hydrogealagic methads as they are cansidered ta be groundwater saurces, Wells The size and shape .of the d~lineated areas are determined by substituting specific parameters inta a mathematical expressian the salution .of which gives information abaut the area in questian, The impartant parameters that are camman ta all methads are the factars that cantrol the geametry .of the delineated area, including pump rate. time-af-travel, and, where apprapriate, aquifer characteristics and the distribution .of hydraulic head, Adjusted Pump Rate. The pump rate (ie" gallans/minute) used in the madels is based an the average manthly rate determined aver the three manths .of highest use, As an example. can sider a cammunity whase water usage far the three highest manths is 1,200,000 gallons, 2,500,000 gallans and 770,000 gallans, representing July, August and September, respectively, The average manthly use then. is 1,490.000 gallans, which equals -48,586 gallans/day, which in turn equals -34 gpm, If actual data is nat available, the pump rate is estimated based an camparable cammunities, pump capacity .or papulatian served, Time-at-Travel. Although the capture zane far a given well extends ta an upgradient boundary, this distance may be measured in tens .of miles and be impractical with respect ta management strategies, Cansequently, the http://www.deq.state.or.us/wq/dwp/DWPAreaDelineationsGW.htm 1/3/02 Delineating the DrinV"',? Water Pratectian Area far Groundw"'~T Systems . . . .1 upgradient extent .of the capture zane is terminated at a specific time-af-travel (TOT) far groundwater through the aquifer, For systems with papulatians >500, the TOT used is 10 years, Far systems serving < 500 the TOT is 15 years because the methad .of delineatian is much less precise, Within each delineated area, subzanes are delineated at 2- and 5-year TOTs, The sharter time-af-travel delineatians are canstructed ta provide the cammunity with a better understanding af,the relatian between an indentified patential cantaminant saurce and the well. Patential saurces cauld be appraached from differing management strategies as a functian .of their TOT distance from the well. The area within the 2-year time-af-travel represents the "hat zane" far the area: potential contaminant sources within this area will prabably need extra attentian because .of their praximity ta the well. The 2-year TOT alsa pravides the .outer limit fram which micrabial saurces are likely ta impact the well. The gaal .of the subzanes is ta provide the cammunity with better data fram which ta build pratection strategies, Systems Serving <500 Population: Far systems of this size, the calculated fixed radius (CFR) methad is utilized, In this methad, the valume .of water needed aver the next 15 years is estimated, Using this value, the valume .of the aquifer, visualized as a vertical cylinder, is calculated using a porasity cansistent with well lag infarmatian and a length equal ta that .of the water-bearing zane, .or perforated interval, whichever is smaller. The drinking water protectian area, then is a circle directly above the cylinder, with the same radius as the cylinder, Similar calculatians are perfarmed using time values .of 2- and 5-years, The final delineation, therefare, cansists .of three concentric circles centered an the productian well having radii that refiect 2-,5- and 15-years .of water usage, A TOT .of 15 years is required far CFR delineatians because .of the very general nature .of this methad, Na infarmatian regarding groundwater fiaw .or aquifer permeability is cansidered Small systems with multipie wells, the CFRs of which averiap, are madeled in a mare saphisticated methad Cthe 500-3299 methad), ~ (~y_sJems_Serving.>500-Populiit~Farall systems serving >500 papulatian, -the develapment .of a canceptual madel .of the graundwater system is required, r The canceptual madel is a three-dimensianal pi~ture .of the hydragealagy .of the area, I.e" the aquifers. aquitards, areas .of recharge and discharge, and head distributian, The canceptual madel pravides far a mare representative determinatian .of the DWPA and is accomplished by the process .of hydrogealagic mapping, the process .of using available data ta .obtain infarmatian regarding the geametry and characteristics .of the relevant hydrogealagic units, The canceptual madel is a regianal picture .of the hydrogealagy, using regianal studies, well reparts, cross sectians and fence diagrams, estimates .of recharge and discharge. hydragealagic characteristics and hydraulic head distributian, Far systems in this class serving <3300, the abave parameters can be estimated fram regianal studies, specific capacity tests, or from infarmatian an available well reparts, Far systems serving 3300 ta 50,000, the hydrogealagic characteristics .of the aquifer will be derived wherever passiblefram canstant rate aquifer tests and the distributian .of hydraulic head will be determined by field measurement. The canceptuai madel is the basis far estimating the parameters used in the analytical madels that create the delineatians, Parameters include pump rate, parosity, degree .of canfinement .of the aquifer, hydraulic canductivity, aquifer thickness, gradient directian and magnitude, recharge if appropriate, and any aquifer baundaries, " - -------- ~ Sys!el!)_sServing,>.50,000,P-opulation,.:r;he analytical models discussed abave assume that the aquifer is hamageneaus and unifarm in its praperties, In http://www.deq.state.ar.us/wq/dwp/DWPAreaDelineatiansGW.htm Page 2 .of 5 1/3/02 Delineating the DrinV~,? Water Protectian Area far Groundwr' 'r Systems Page 3 .of 5 actuality. this is rarely the case; aquifers may change permeability, thickness, etc, alang their extent. Far systems serving larger papulatians, a mare saphisticated madel appraach, capable .of accammadating heterogeneaus aquifers, is required, Far these systems, a numerical appraach is cansidered apprapriate, In the numerical approach, the area is divided inta cells (palygans), each .of which can vary in their characteristics, Models can be twa- .or three- dimensianal. A further benefit .of the numerical madel approach is that they are capable .of being calibrated and validated sa that there is even greater canfidence in the madel results, NOTE: Far systems serving more than 50,000, OHD will work with the staff from the public water system in developing and/or refining existing models that predict the Drinking Water Protection Area, Most of these larger public water systems have already perfarmed some level of aquifer analysis and modeling, Model Sensitivity Analysis. In many cases, a range .of hydraulic characteristics is passible far a given aquifer .or hydragealagic setting, The sensitivity analysis pravides far the evaluatian .of haw sensitive the madel results are ta the variatian in any given parameter. This pracess allaws the madeler ta determine which parameters are mastimpartant in cantrblling the geametry .of the delineatian and therefare which shauld be determined ta the greatest degree .of accuracy, In thase cases where data refinement is nat possible, the delineatian will be campleted by .overlaying the individual delineatians representing the range(s) .of parameter(s) .of cancern, e,g,. transmissivity .or porasity, Porous Media Assumption. As indicated in the accampanying flaw chart, an evaluatian .of the paraus media assumptian relative ta the aquifer must be made, In a granular .or paraus medium, groundwater will mave directly dawngradient, assuming na significant preferential flow paths exist. Mast analytical models assume such a canditian, In fractured rock, hawever, graundwater will flaw preferentially alang fractures, which frequently are nat oriented perpendicular ta hydraulic head cantaurs, In areas where graundwater flaw is cantrolled by discrete fractures, the delineation will be .oriented similarly with the length being cantralled by estimated time-af-travel .or hydragealagic baundaries, Variations in Hydraulic Gradient. In many hydragealagic settings, the gradient may change significantly in directian and magnitude an a seasanal basis. awing ta changes in pumping levels and recharge, If the magnitude .of that variatian is knawn, delineatians are perfarmed under wet and dry canditians and .overlaid ta praduce the final delineatian, If the magnitude is nat knawn, the gradient directian is rotated through an angle .of 25 or 45 degrees, depending an whether the gradient is based on field measurements or regional data, respectively, The rotatian is accamplished fram bath sides .of the .observed gradient with independent delineatians perfarmed at the extreme pasitians and .overlaid on the .original delineatian, ' Multiple Water-Bearing Zones. If multiple water-bearing zanes occur within the hydrogealagic aquifer unit that are persistently separated by lawer-permeability units, the cambined thicknesses .of thase units is used as the aquifer thickness, If the permeability .of these multiple zanes vary significantly, the pump rate is partitianed between them based an their hydraulic canductivities and thicknesses and individual DWPAs are calculated far each and .overlaid ta praduce the final delineatian, ' If the water system is cantemplating adding new wells ta their inventories and nave patential sites selected, preliminary delineatians will be performed at thase sites using regianal aquifer data and estimated pump rates provided by the water system, This data may prave useful in selecting the ultimate site .of the new well. http://www.deq.state.ar.us/wq/dwp/DWPAreaDelineatiansGW.htm 1/3/02 Delineating the DrinJr'~16 Water Protectian Area for Groundwc' 'r Systems Springs The delineatian of spring saurces is accamplished salely through hydrogeologic mapping, This field pracess determines the gealagic structure that controls the lacatian .of the spring, its geametry and haw it is .oriented in the subsurface, This infarmatian allaws the hydragealagist ta determine the land surface that .overlies this structure and therefare accamplish the delineatian .of the spring's recharge area, The baundaries .of the spring's recharge area (the DWPA) is .often cantralled by gealagic features, In areas where the hydragealagic baundary is nat evident .or is same distance fram the spring. the size .of the DWPA will be canstrainedusing estimates .of the vela city .of graundwater in the subsurface, This will allaw the determinatian .of time-related zanes within the DWPA, .or determine the area .of spring recharge by dividing the spring discharge rate at law flaw (ft3/year) by an estimate .of the recharge rate ta the aquifer (ftiyear), The delineated areas will be placed in a GIS caverage that will be available an a statewide basis through the state's GIS Service Center's website, Individual water systems will receive a tapagraphic map with a preliminary map of the delineatian shawn as a functian .of the time-af-travel as saan as it has'been campleted, The purpase .of this is ta facilitate the cammunity's .or water system's invalvement in DEQ's inventary process, Final maps will be provided in a SWAP repart that will cantain the delineation, aquifer sensitivity analysis, patential cantaminant saurce inventary and susceptibility analysis, f1:onjuncti~e D!!]neationsl Graundwater and surface water are related campanents of the hydrolagic system that cantrols the distribution .of water an the surface and in the subsurface, Within this system, generally speaking, surface water receives "base flaw" fram graundwater and groundwater is .often in hydraulic cannectian with surface water. At a specific site, however, this may .or may nat be the case, Far example, alang a given stretch of stream flaw, the stream may be discharging ta graundwater, I.e" a lasing stream. rather than a gaining stream, Likewise, in a given drinking water pratectian area, the aquifer may nat'be deriving water from a surface water saurce, The Surface Water Treatment Rule .of the Safe Drinking Water Act directs states ta determine thase public water systems whase groundwater saurces are under the "Direct Influence .of Surface Wate~' because .of the patential risk .of Giardia in their drinking water. The Health Divisian develaped a pratacal ta evaluate this by first recagnizing graundwater systems that were in hydraulic connectian and then asking them ta canduct micraarganism analysis to evaluate the risk .of Giardia. Hydraulic cannectian can .occur either naturally, along lasing stretches .of streams .or at high-river stage, .or can be induced through high pumping rates, Through evaluatian afca-variatians .of temperature, canductivity, pH, etc" OHD has recagnized 57 (as .of 12/98) community water systems that were hydraulically cannected ta surface water. Same .of these systems had wells as deep as 200 feet and are as far fram a surface water saurce as 400 feet. Same cammunity water systems and mast nancammunity water systems are still in the pracess .of evaluatian, OHD will use the protacal established under the Surface Water Treatment Rule to identify graundwater systems drawing from surface water saurces far purpases .of the SWAP, It is envisianed that far thase public water systems that have groundwater saurces that are in hydraulic cannectian with a surface water saurce, the delineatian .of the groundwater saurce will .occur as described abave, Delineatian .of the surface water cantributian ta the graundwater system will be accamplished an a case-by:case basis, depending an the extent .of the connectian, distance from the surface water saurce, etc, In all cases. hawever, a http://www.deq.state.ar.us/wq/dwpIDWPAreaDelineatiansGW.htm Page 4 af5 1/3/02 . Delineating the DrinV'<:; Water Protectian Area far Groundw~'-" Systems partian .of the watershed area will be identified as a saurce .of drinking water far the cammunity in graundwater systems with hydraulic cannectians ta surface water. . ' DEQ and OHD will use data fram existing hydragealagic studies ta identify those surface-water saurces that receive significant cantributian fram graundwater, In same basins, there will be existing hydragealagic studies that will identify hydraulic head distributian fram which it can be inferred whether .or nat groundwater is discharging ta the stream .or other surface water bady .of concern, In ather cases, we will rely an data assaciated with the surficial soils and graundwater fiaw regime that discharge ta the surface as evidenced by streams exhibiting significant gains with little cantributians fram surface water runaff, DEQ Online is the official web site for the Oregon Department of Environmental Quality. If you have questions or comments about the web site contact DEQ's.vebmaster. http://www.deq.state.ar.us/wq/dwpIDWPAreaDelineatiansGW.htm Page 5 .of 5 1/3/02