ML101970386

Ground Water Investigation: an Improved Flow Net to Evaluate Pathways for a Potential Ground Water Release

ML101970386
Person / Time
Site:	Prairie Island
Issue date:	12/31/2009
From:	Donkers C Xcel Energy
To:	Office of Information Services
References
FOIA/PA-2010-0209
Download: ML101970386 (14)

Text

-.9 PRAIRIE ISLAND NUCLEAR GENEkTING PLANT (P INGP). GROU,3ND WATER, INVESTIG-ATIONý:

AN IMPROVED FLOW NET TO EVALUATE PATHWAYS FOR A POTENTIAL GROUND WATER RELEASEt

/,

Prepared by:

tChuck Donke4Xce' Energy, December 2009

i PRAIRIE ISLAND NUCCLEAR GENERATING PLANT (GGP) GROUND WATER INVESTIGATI*iON:

AN IMPROVED FLOW NET TO EVALUATE PATHWAYS FOR,A POTENTIAL GROUND WATER RELEASE, BACKGROUNDz

,A,flow net 'is*one method to determine the groundwater path way between twoqpoints.

An ithrove&*.fiwnetwas sýUght to identify potential receptors in the everit'that a hypothetical ground water release were to occur at-the Prairie'island'Nuclear Generating'Plant (PINGP)., Aflow net is a static

'snap siioofia dynfamoit 9st'em. It is'constructed pti grii&Ot Ibations collected frm Wste wells: for a.specific date. To improve upoh the currenit flow riet, perspeitiv6e wbs fieedId'How:

rep~resentative is the "sna sht ohe entirey kecentstudies (ULiSG1997) suggested large rain events could causeshortiterm deviaitionsfrom the existiig~fowt Inliigiht ofthisibnformation, Xcel Energy developed a stdy to identipft he magnitude and quantifythe duration of such changeS:inflowdirectibn.

PROJEC-& OSIGN The tprei.seofthiso ivestigation was to identify short term cha0nges in"flow direction duetoJthe influence of floodingorlarge rain events. Seven (7) wells were edqluilped.with water le6el tiransducers and d*at !oggers. Hourly ground water elevations were collected 'inthese seven weIls from:Mar.ch30, 2009 thre Dece6mber:16, 2009. Using methodology develbped by"Pinder(Velocity ClcdulationFrom RandomjtyLocated Heads, Pihder et aL 1981), hourly flow directionsn werIe calulated "for pre-de6finhed 9areas.

To *improv~e the PINGs flow net,two methods were~employed. Surfer, a commerially available jinterp.latiof p .rogrIamwasus Ied to produce a m -r cIccurate pred*ctioh of ground water flowvpaths but Aitdoes not lend itself-to processing large amounts of time varialle da1ta. Theieth6dIlogýy.de.veloped by Pinder lends itself to processing large volUmesof data, and huius dentifying shott*m .upsets; howeverP it is less accurate than other ijiethods. The~two methods comopkinen-t each other byOutting the more

,accurate "snap shot" in to perspective for-the fullyear.

R;EsULTS.

'Figuree1 depicts the PINGP site, and identifiesýwhich Wells werejequipp-ed with datalIoggers, Figure 2 presents the hydrographs for the hourly data,from seven wells plusississippi River and'VAermillion Riv6erCeevationis. -Figures3 thru 6 depict ground water elevation contours for the site when aliwelIs

,were sampled and the approximate no-flow bounidary. The no-f66w bouindaryis:the approximate

i northen and western lim~it of flow originating fr'm thePlNQP. Figqre 7 illustrates the indild .alflow

_elements(areas)'that were used to calculate the hourly flow directibns. Figdie 8ilustrates flow vs. time for each area. Figure 9 is a delineation of groundwaier whichfis down gradient fIDom odirectin Athe PINGP using a compilation of'all data generated in this, investigation0.

Hy~dro_gph Aspects5

As~shlown*on Figure 2, the study period extended from March 30, 2009 thru December 16, 2009. Stage Adata-from bthe Mississippi and Vermillion RiVerS-Were avadiable startilng~on Februalry 6,2009.. As,

intend'edthis period included several significant events including the spring flood, and several large, ra.ihn evenrts in Jiui'Vand August. The-following. observations were ma~de:ý o' Typical.(non-food) flowisfrom MississippiRiver (highest head) to the groundwater under the Prairie Island Plant tO theyVermillionh(ilowest head). This con diltion occur o6verabout 90% of the study period.

TThe i*y*crographs indicate g*round water 'e!vationsdo respond':to spring' flooding. There is a short lag time between flooding and the rise in ground water elevations. 'Ground water elevations are also slower to recede.

w, Groundiwater'elevations were higheerthan th6 Mississippi Riverand the Vermillion River for about f6Ourweek's duringthe. spring flood periob. Thlis suggests that a brief reversal of flow (firdr groundwater'towafrd the rivers bccurs overaboOt 1:,,o%6f the study priod., 'Grbundwater flow:duringtthis period would likely be: radially.outward, from groundwater to surface water.

SSeveral large'raineVents0(1" to-2"/da) occurredin* August. Ground water elevations rose several inches.:in response to this. pretpitation. However.all wells responded in a similar fashion, suggesting no moundingof ground'water.

ýGround water Elevation contour Maps Ground water elevations were interpolated using Surfer for four sampling events. Mississippi River and Viermillion*River elevations were included in the surfer applications; the inclusion of these data. resulted in the depiction, of a strong southwesterly flowdirection.. Because water flows frfmornreas. of higher head to areassoflower head elevationthis southwesterly flow direction appears to be areasonable charactetizatin of actua flow conditiocns throughout.henmajority ofthe study period. This

.characterization is also supported by the hydr6gfaph data and the apparent higher:head in the ississippi River relative to the Vermillion River duringsthemajority of the study period. The following observations were made:

o GroundWater flow paths (flow dire~ction.his*pierpiiduilar to eleVation contou*s) generallytrend

,southwest~as described above 0 Radial flowis exhibited near P-bfdue tolocalized moxnIirg ofIthe water table., The mounding influence may be due the presence of severalwate r features suchlas thecooling tower canalsi a

,sur.fbce.draihage-ditch and septic drainrfidlds. The observedm6uiridihib*i dimniishis withiiva

~ho*distan~ce ~from rthe wejl,zreiurningtjothle predminant.souihweeser!y.w direction.

• Gýoiud Watgr.gradients are. depicted in Figtir&s 3--6. The legth* of*thector irrw tails are proportionalto the:gradiqot; thp longerthe tail, the steeper the gradient. Assuming similar geology, this generallyindictates ffaster'travel velocities.

Hourly Flow Directions Fowdirections were, calulated'hourly; for foura reas FigUrege7 Illustrate the are*s*represented by

'theses hourly. directidt'ns Figure 8d .istratesfl'6wdirectimns 0 *Ihefllo ig obserattionswere made!ý the predominantiflow direction, spatiallyand in-termsof duration.is~sotithwest (2,25 deg from T

rbth4). The greatest deviation from this predominhant trend occuprreýdwfithin 4-.8weeks after the Duriing the months of April andqMay, Area

• nd Area 4 reportetd westerly flows. however gfound wat*,gradients were.sigriificantiy less during these`,tirmes anditheduration of timeVwas, short. Therefore the.actual distance traveled, in awesterly direction, issmalldue to lower gradients and the short duration of the deviation.

The four static flow nets depicted ihn figures 3-6 correspond to stable flowiconditions, observed:

T forihemajotity of the year. Theseflow netsiareirep.esentative;for tse throughout-the year Wkith~ thei possible exception of 4-6 We~eksjafter the sPriflood.

ýCONCCUSIONS*.

• No~eIdence of ground water mod ppd.gWas bbserved whith orreiate~d to. a.rge rain events.

• Mounding was.observed near O.40. .Radial ground water flowwas'noted. The numerous infiltration sources, (septic drain fi6lds, drainage ditc', aand c-liigtower canals)ýare believed to contribute to the mounding effect..

• The inclusion of river elevations wi~th- wte elevations im~pre theinterpolated-grgund din water contours.-and hence the flowhnet!

S'Thespring flood demonstrated tte largest influence uponEgrudwater flowdirections. Flood influences extend 4-6 weeks after the*flo*d recedes.

• With the e~xceptipn of the 4-6 weeks~a*.er spri.ng fooodjground water flowssouthwest t.'Wards the.VrmJllion River.

o "e.liow n~ets presented in this report (~iiur's 3-6) represent,f lwpath's for approximately 10 idfhtihs dout of the yeat.

o iven theishortduration and limitediarealextent of the flow reversals. a hypothetical release froM the Prairie Island Plant could move only a relatively'ýshbrt distarcite feromthe plant~during a spring flood event before it would be'redirected to the predominant:flow direction (to the so uthwest).

• The data collected duringithis investigapion suggestthat there is no direct ground water Vpathway connec.ting the IjNGP and neighbo~s t~o the north and westi ofthe plant..

SCalculatih*ig hourly fWirte-ti~n~s1'entified the montbs ,of,AprilV4nd May as h'avin"the gteatest potential fbrwesterlyflow. Although.the significance of these%.westerty'flows, istconsidered mlitire~mm d t costiruct additional flow nets, .Using,!,aliIws, during thiS period of flux.

Figur~e L.

+ PINGP Grouncl \Vrter Monitoaring System.

~

V~,U ~by

__ Pipe Efev..

,59228 2355090: 93ý02-MW- "3592201 5858668 88.83

-71 M". t.591842' 2357597. 82M3 MW. ' 593885 23557,14 .M95.S4 MW-8 59944; 235654; 697,47

.pZ*.4 P-10, 5 23497, 69316

. R255297 898.19 J& J 594449 *,O42' 69,72 P- 592998 2353997 899;19.

P-S 594002 2354501 69551 P6 595250 2354802, 893 P-7 594449 2355235 697.97 J96790,. 2354934 882.9Z

ýPZ-21 59%743 25259, 889.05 PZ-4 5942n2 2352598 688.5 P . *591502 2358299 %95.93 PZ-74 L594469 2356158. 97.85.

PZ :595471 2353662, 96.652

~,Wetequii~edj %with'a' d t~ ogger

/0> k t7; -007

Figure 2. PINGP 2009 Hydog-raphs 680.,00 14 678&00 12, U- 676.00 - PZ-2 i0: - P-iTO w

toC PZ-4

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' 674.'00

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a) C LL 0' (0 co An.

Figure ý3,f Ground' V/oter- Ele vat Icnrs bflG

Fow Vectors For 7/11/2006,,

ý6( L... tý.-

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, 593944 2355654- 69Z7

.P 59338 SlO ;2355497k 69315 P-11 594949 2355297 5:98.19 P4 59444. 2354002: 697,72 P.,3 5929 2353997, 69819 P-5 594002 .:235450f 695.51 P.- 595250 2354802 6W3-P7 . 594449. 2355235 697.97 PZA1 595790 2354934: 6829.

PZ-2 596743 2352589".. 6 5 PZ.4 594252 235598. 696.

5*9PZ02 2356299 695.93 PZ-7 594469, 2356150I 697.5 PZ,8 595471 . :2353662 696.52 Np-ftow boounldary; The~

_________ pproxirýAte norther-r

ýmd. southern limits. of

,Ftow Or'iginc6tirg ;A

?1NGP F~or a specific dAky.

AWeL. gqufped, withý .(rdcita 'logg~er g

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FigOr'el 4 Grourd Water'- E~.evc~tiohns O R~ow, Vectors iLorw 7/9/2008 SMIL.Yd~ by Top of Riser

'VI ori 'Eait Pipe ELev MW-4 :592236A 1355M90 ý83.O2.

MW.5 59220 23586566: W68.83

.7 MW46 591842 123575971 W82.33 MW-7 -593885' .2365714. 695.54 MW.8.' 593944.., 2356854 697A7

1o. 593538- .-23-59 693.16 P-lI 594949,: 2355297ý 69819a P-2 !59444T 2354002 697,72*

P43 :592998 2353997 698.t9 P-5 594002 2354501 89551 P46 595250 12354802. 699;3,1 697.97

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'596743 2352569: 6W905 P2.4ý 594262 2352598 .696.53 P75; 5915602, 2358299 '695.93'

ýPZ-7 594489 2356,158. ý697.85 P2-a .595471 2353862 ,696.52 No-f ow boundlary;. The ckpproxilmcae n~orthern and -sout'herri Limits OF P.I..P .o.speciric drqye.

4 wie~tt eqipd wtbo da~tq, iogger' C

Fig u r E 5:

Grourd Water ELevqt.!ons o*ncl Flo~w Veact*ors For 7/8/2009 V1( - S.-yr{

6- i V~e Noilh Siit pipefREer 592236 :2355090 695.02

~MW-S 592201 2356566 666,83

~MW "6591642 2357597 682.33 MW.7 59368 ý-2355714' 695.54 MY", 593944 2355654 697.47 P-10 5S93538 2355497 693.16 P4 I "594949 2355297 P;2 594449 1354002, 697-72 P 592998 2353997 698:19 P-S5 594002 23501 695.5 P.ý6ý 595250 '255402 699.3 P.ý7g. 594449, 235235 697-97 K.PZ.1 596790 2354934 682.91 PZ-2 596743 235259 669.05 PZ-4 594262 2352596 696,53 PZ5 ,,591V50 2356299 695.93 PZ_71594469, 235615 69'785 PZ.8-. .- 595471-, 2353W2 69652

_______No-r~ov boundary, The aproximate northern and southern Uinits of

,flow. originating at PIGP' for . ;sPecifjc 4 de equipe.4 ait oatLog

'6 G

Figu:re GCround Wote- Elevaotions andc FLWw Vettors Por, 12:/16/-`200'9

-ti Nd.i-b 21, 20l07, wd. NOMi EWs PipeElev MV"4 592236 2355090. 693.02 MW.5- 59220 2356566 W6.683

ýMW.6 591642 2357597 682.33 MW-7 593M'5 :23557,14 69.54

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PZ-2, 596743ý 2352589 6M89:05

PZ-4 594262ý 2352596: 696.53 PZ-5' 591502 2356299ý 695.93 PZi7, '594469, -2356158 6971.85 V:W 5195471 - 2353682z ,696.52 NO-4loiv~bounciryý THO' ro~xfima e nor'therrý c~nd jsouthern Limit~s of

';~*ow &iginating i at day;fr~ p'cf Welt equiped with a data Logger A

I

Figure 7.T-PINGRi Ground Wvoter Monitoring, Systemn

+ Areias Haurly Flow, Oire*Ction is.

CseeF1~ure8 for resu,[to)*

lm%*ý L S-fiýLli qo 21. 207 Top ofRizer MIE Namh Et PieEe hM44 sg2236 2355090 89302 MW-S 592201 2358568, 86.83 fW.6 591642 2357597 882-33 M 593685  : 695.54

ýMW-S- 593944.: 2356654 6974

- f, N10", 593538 :2355497 83.18 P'14 594949 1355297 69.19 N. 594449, 2354002, 697.72 P3 6592998: ý23597 698.19 P4. '594002 235501 895.51 P-6 595250 23402 89.

P-7,. 59,49. F 2M235 697.0-A 596790 -23549034 ,q62:r PZ-1 ,

PZ-Z. $ 9W43-,1-2352589 .689.0,5.

PZ.4.594262S..23525S& '696.53 PZ-6' S91502ý 2356299 -895.91 PZ-7< 594469: 2358158 697;85 Z595471 .235366 6M52 4~ Wett eqviped withý ia d to 'logger

'C

4 Figure 8. P1NGP, Flow Direction vs Time

,(See Figure 7 For Area Locati"ns)

'270 225 0

z

-Area 1 E 180 0 -Area 2 135 -Area 3

-Area 4

ý90 45 0

(000N 1,*- CO~ -MO MO C4CC -~

Composite oF PI'iNGP No-Ftow BoundIary Clondili "Ois',&

Arawhich is down

• gradient of~ the, PIN4GP 4