'651 Colby Drive, Waterloo, Ontario, Canada N2V 1C2A CONESTOGA-ROVERS Telephone:. (519) 884-0510 Fax- (519) 884-0525& ASSOCIATES www.CRAworld.com

KWMADANflI I

To: Tim Gosnell and Al Haeger4 Exelon REF. No.: 016841-37

FROM: Phil Harvey/Hongze Gao/Nicholas Fitzpatrick ev/30 DATE: March 6, 2007

RE: Evaluation on Impacts of Private Well Pumping andPonded Surface Water on Groundwater FlowExelon Generation Company, LLCBraidwood Station, Braceville, Illinois

This memorandum provides the assessment results of a capture zone analysis for three private water wellslocated along Smiley Road. This memorandum also presents an evaluation of the impact of historicallyponded water (containing tritium) near the private homes. These analyses are being performed todetermine whether private wells could have intercepted tritiated water resulting from a spill in the Fall of2000 from vacuum breaker 2 (0CW136).

The three wvter wells are located on Smiley Road, just southwest comer of the Exelon Pond; they areowned by lames, Keca, and Phelpsiiespectively and shown on Figure 1. Although only two of theseresidences existed in 2000 (current Phelps and James homes), all three are considered for conservatism.Two areas of historically ponded water containing tritium were evaluated. The first is a ditch along SmileyRoad (Figure 2) and the second is the low grassy area east of the residential properties (Figure 3). Floodingof these areas is documented by photographs that Exelon took as they responded to the event.

1.0 METHODS

CRA employed the existing three-dimensional (3D) groundwater flow model that was developed by CRA(August 2006) and further calibrated under a transient pumping condition (CRA, December 2006). Themodel was used to evaluate both the private well capture zones and the potential impacts of the tritiatedponded water.

The capture zone analysis associated with the three private wells was carried out through groundwaterparticle tracking, and an analytical capture zone width calculation. The particle tracking programMODPATH (Pollock, 1994) was applied to conduct the particle tracking. MODPATH uses the groundwaterflow field simulated by the MODFLOW-2000, as used in the existing 3D groundwater flow model, tocalculate particle pathways through the simulated groundwater flow field based on advective processes.

The graphical user interface (GUI) Groundwater Vistas (Rumbaugh, 2005) was employed to provide pre-and post-processing for the numerical flow model.

RISISTERIC COSPAXI FOR

ISO 9001(hGtINER,/\

CRA MEMORANDUM Page 2

2.0 CAPTURE ZONE CALCULATIONS FOR THE PRIVATE WATER WELLS

A typical single family home water usage is estimated to be 45 to 90 gallons per day (GPD) per person(Metcalf and Eddy, 1991). In order to use a conservatively high estimate of water usage it was assumed thateach resident used 100 GPD and that each house had four residents totaling 400 GPD per house. Theanalysis made no allowance for lawn sprinkling or other outdoor watering since the spill occurred inOctober and November. The groundwater flow model (MODFLOW) was run under a state-state condition.

A line of particles was released from an area upgradient of the three private wells, and forward particletracking was simulated under the steady-state pumping condition. The pathlines originated from theupgradient area and the simulated groundwater elevation contours are presented on Figure 1.

An analytical capture zone calculation was also performed using the Todd Equation (1976). Based on Todd,the capture zone width at the infinite location upgradient of the pumping well under a steady statecondition is expressed as:

Lr = 2YL = Q/(2Kbi)

where,

LY is the upstream inflow zone (limits of groundwater entering the pumping well), or capture zone

width at the infinite upstream distance (L);

Q is the discharge rate (L3/T);

K is the hydraulic conductivity of the aquifer (L/T);

b is the aquifer thickness (L);

i is the groundwater hydraulic gradient.

The capture zone width at the line of the extraction well is Ly/2, or YL.

The parameters for this capture zone calculation are presented in Table 1. As a result, the capture zonewidth of each individual private well is only 2.0 ft. The hand calculation result suggests that the simulationresults from the 3D model are reasonable.

It can be concluded, based on the 3D numerical and the analytical solution, that the pumping of these threeprivate wells does not have any discernible impact on the local groundwater flow due to the insignificantpumping of groundwater. The groundwater flow pathlines and the capture zone calculation resultsdemonstrate that the capture zone of each individual well is very small with the three wells barelycapturing any cross-gradient water. Also, their capture zones do not reach any part of the current observedtritium plume (Figure 1) associated with the Vacuum Breakers 2 and 3, under the simulated condition,since the limit of the plume is over 350 feet east of the nearest private water well.

CRA MEMORANDUM Page 3

3.0 EVALUATION OF HISTORICALLY PONDED AREAS OF SURFACE WATER

Two scenarios were simulated of the historically ponded water containing tritium. As a worst case, it isassumed that the ponded surface water can fully saturate the soil above the water table. The systemconfigurations and the simulated results are presented in the following sections.

3.1 Scenario I Configuration and 3D Numerical Model Results - Ditch along Smiley Road

Scenario 1 (ditch along Smiley Road) has a 2-ft wide and about 1000-ft long infiltration gallery to simulatethe ponded surface water observed in the ditch along the south side of Smiley Road as a result of the waterleak from VB-2 in the Fall of 2000 (Figure 2). The ponded water is assumed to occur for 30 consecutive dayswith a stable water level of 598 ft AMSL (which is about 1 ft above the ground surface).

The Smiley Road ditch was simulated as river cells in the model. The river stage was set to be 598 ft AMSLand the riverbed bottom was set to be 596 ft AMSL. The river conductance was calculated by the modelusing a hydraulic conductivity of 77.8 ft/day for river bedding material.

To obtain the results, eight model observation points were used aligned perpendicular to the infiltrationtrench as shown on Figure 2 with distances of 50 ft, 100 ft, 150 ft, 200 ft, 250 ft, 300 ft, 400 ft, and 500 ft awayfrom the Smiley Road ditch through the property of Phelps.

The transient model simulated groundwater elevations and groundwater elevation increases (with respectto the initial groundwater elevation at the corresponding locations) due to the impact of the ponded waterin the ditch are presented on Figures 4 and 5, respectively.

Figures 4 and 5 demonstrate that the ponded water in the ditch would likely cause a groundwater elevationincrease, and that the system would not reach a steady-state condition even at the end of the 30-day period.The figures also show that the closer one is to the ditch, the more groundwater levels will increase.

Groundwater Movement Toward Private Water Wells

Particles were released along the ditch to evaluate how far the particles south of the ditch would travel inthe 30-day period. As shown on Figure 6, the pathlines are very short indicating tritium in the pondedditch would only be limited to the immediate vicinity after the 30-day groundwater mounding period.Specifically, the model predicts a travel distance of only 15-20 feet away from the ponded ditch in 30 days(Figure 6).

3.2 Scenario 2 Configuration and 3D Numerical Model Results- Ponded Surface Water South of Smiley Road and East of Private Water Wells

Scenario 2 (ponded water east of private water wells) simulated the ponded surface water of about 480 ft by480 ft in size located to the east of the residential properties and south of Smiley Road which resulted fromthe VB-2 leak (Figure 3) that occurred in 2000. The ponded water is assumed to remain for 30 days with astable water level of 599 ft AMSL (which is about 1 ft above the ground surface). Similarly, the riverpackage with a river stage of 599 ft AMSL and a riverbed bottom of 597 ft AMSL was used to simulate thesurface water infiltration.

CRA MEMORANDUM Page 4

Similar to Scenario 1, eight model observation points were used aligned perpendicular to the infiltrationpond as shown on Figure 3 with distances of 50 ft, 100 ft, 150 ft, 200 ft, 250 ft, 300 ft, 400 ft ,and 500 ft awayfrom the infiltration pond through the three private properties.

The transient model simulated groundwater elevations and groundwater elevation increases due to theimpact of the ponded water are presented on Figures 7 and 8, respectively.

Figures 7 and 8 demonstrate that the ponded water would likely cause a groundwater elevation increase,and that the system would not reach a steady-state condition at the end of the 30-day period. The figuresalso show that the closer one is to the ponded water, the more groundwater levels will increase.

Groundwater Movement Toward Private Water Wells

Particles were released along the western edge of the ponded area to evaluate how far the particles in theponded area would travel in the 30-day period toward the residential area. As shown on Figure 9, thepathlines are very short indicating tritium in the ponded area would only be limited to the immediatevicinity after the 30-day groundwater mounding period. Specifically, the model predicts a travel distanceof only 20-25 feet away from the ponded area in 30 days (Figure 9).

3.3 Conclusion With Regard To Surface Water Ponding

Based on the above 3D transient groundwater flow model simulations for the two scenarios and theassociated particle tracking results, it can be concluded that while the 30-day period of surface waterponding would likely cause groundwater elevation increases in the vicinity of ponded areas, tritium in theponded areas could not travel far away from the ponded areas and therefore could not have impacted thelocal private wells. Since all standing water was removed upon discovery, the driving force for continuedmigration toward the private wells was removed immediately after the analyzed 30-day period. Normalground water movement would have then been adequate to sweep any tritium laced water north and awayfrom the residences.

REFERENCES

CRA, August 2006. Groundwater Flow and Tritium Transport Modeling, Braidwood Generation Station,Braceville, Illinois, Report prepared by Conestoga-Rovers & Associates, for Exelon GenerationCompany, LLC.

CRA, September 2006. Hydrogeologic Investigation Report, Fleetwide Assessment, Braidwood GenerationStation, Braceville, Illinois, Report prepared by Conestoga-Rovers & Associates, for Exelon GenerationCompany, LLC.

CRA, December 2006. Transient Groundwater Flow Model Calibration and Transport Model,Scenario Update, Memorandum (#25) prepared by Conestoga-Rovers & Associates, for ExelonGeneration Company, LLC.

Metcalf & Eddy, Inc., 1991. Wastewater Engineering, Treatment, Disposal, and Reuse, Third Edition",McGraw-Hill, Inc., New York.

CRA MEMORANDUM Page 5

Pollock, D. W., 1994. User's Guide for MODPATH/MODPATH-PLOT, Version 3: A Particle TrackingPost-Processing Package for MODFLOW, the U.S. Geological Survey Finite-Difference Ground-WaterFlow Model, United States Geological Survey Open-File Report 94-464, Reston, Virginia.

Rumbaugh, J. 0., 2005. Guide to Using Groundwater Vistas, Version 4.19, Environmental Simulations Inc.,Herndon, Virginia.

Todd, D. K., 1976. Groundwater Hydrology, Second Edition, John Wiley & Sons, pp. 122-123.

Page 1 of 1

TABLE 1

PRIVATE WELL CAPTURE ZONE HAND CALCULATION

Pumping Rate1 Hydraulic Conductivity 2 Aquifer Thickness 3 Hydraulic Gradient 4 Capture Zone WidthGPD ft/day ft ft

400 77.8 25 0.007 2.0

Notes:

1. Assumed household water usage in gallons per day.2. 3D groundwater flow model calibrated value (CRA, August 2006).3. Average saturated aquifer thickness.

4. CRA, Fleetwide Report (September 2006).

CRA 016841Memo30-T1.xis

EXELON POND

[FATLAN

LEGEND

..PLANT PROPETY LINE................ ... ....... BLOWDOWN LINE

- EXTENT OF TRITIUM- 593,5- GROUNDWATER CONTOUR

PATHLINES@) PRIVATE WELL LOCATION

figure 1

SIMULATED GROUNDWATER CONTOURS AND PATHLINESASSESSMENT OF PRIVATE WELL PUMPING

EXELON GENERATION - BRAIDWOOD STATIONBraceWvIle, Illinois

/ I".

0 100 200ft

N*,~ \\

N

\ 'KLJj

EXELON POND

FATLANREEVES

NK E

1 .1 <~ /3250ft

... ...

1 SMIEYRAD>

/m/z

............

I WATER LEVEL IN DITCH: 598 f1 AMSL

///l

/I

//

//

/0 4oE -/

/,//

.50011 //

//

/

I/

/

.50 . .

LEGENDPLANT PROPETY LINE

BLOWDOWN LINEEXTENT OF TRITIUMPONDED DITCHOBSERVATION LOCATION

figure 2

SCENARIO 1: PONDED DITCH LOCATION AND MODEL OBSERVATION POINTSASSESSMENT OF PONDED WATER IMPACT TO PRIVATE WELLS

EXELON GENERATION - BRAIDWOOD STATIONBraceville, Illinois

16841-37IMEM0030O)N-WA002 MAR EE12007

C-!

0 100 200ft

REEVES

N

N

N

LAJ I

EXELON POND

iK I

// I

-, I

SM11LEYROAO

mz

FATLAN

.. ..... ...... ...

......

-4v- ' ft 3Of 2000 f t 5 Oq5t0

' "PHELPS

/

/- - - - - - - - - -

//

NN.

/

/

A

!i

.7) 0 05/2007

LEGEND

PLANT PROPETY LINEBLOWDOWN LINEEXTENT OF TRITIUMOBSERVATION LOCATIONPONDED AREA

figure 3

SCENARIO 2: PONDED AREA LOCATION AND MODEL OBSERVATION POINTSASSESSMENT OF PONDED WATER IMPACT TO PRIVATE WELLS

EXELON GENERATION - BRAIDWOOD STATIONBraceville, Illinois

16841 -37(MEMOO3O)GN-WAOO3 MAR 06/2007

M 11

C)

rtW

Z

co)

C)

C)

C>

C>

DJ

C)

U)0

U')

C)

L

OO

C

> D

D

LLýi Fý

T

00000 9

FO

w<

1 14'l

c ,

II U

I I

C.

IW

wa Z

!tE

W

0II

LI'~

0

E1

1

I Hi1

CI

Hi W

z (5

(

ClZ

Ii I

9f U

) 0

1 E

0

U

*C

t) ~

C

) C

) e

~ C

'i '-

' 0

(~)

see~,u~iON

P~a

IOW

P~

fOJO

ele

nw

0

597.5

597-

596.5 I- -

59-..• • : ..... _ ' . .....

c 596--__

j -- -- -.- -

- - -- - Obs- 50 ft Ht3 594.5- / •,/ ,

EZ--g- Obs-100 ft

7 . - t -, ,@ Obs-150 ft

:$ 593.5 X,___________ -4- Obs-400 ft____.! -•"-"Obs-250 ft

2 -4--.---0-- Obs-300 ft593.5 Os40f

0 Obs-500 ft

593 . I

0 5 10 15 20 25 30

Time (Days)

figure 5SCENARIO 1: SIMULATED GROUNDWATER ELEVATION VS. TIME

3D NUMERICAL TRANSIENT SIMULATION RESULT00• EXELON GENERATION - BRAIDWOOD STATION

Braceviyle, Illinois016841-37(MEMO30) GN-WA-HYD (N:\HEG\16841\3DMODEL\FLOW\FlowForWCFP\Output-Plots\16841-37(Memo3O)-Fig5.xis) FEB 2007

EXELON POND

0 40 BOfO

-r -

'NN'

ttPw.1~®~Nn

'N H,I ii =

SMILEYROAD ........... . . . . . ......... ~ z. :i**'1iNi- 0 f . M. ................. • i ...............................VV MM''I LN\{\~ ~ ~ TT0T\00 W

PWA-2

PW-3 (

... . .... .. .. i I'

PHELPS . /

T'l{ • ? 'r T ( r 1 • i • , .....

K

///

//

/

//

/

LEGEND..PLANT PROPETY LINE

.................... ........ BLOWDOWN LINE

EXTENT OF TRITIUMPONDED DITCH

FW-N PRIVATE WELL LOCATIONPATHLINES

figure 6

SCENARIO 1: PATHLINES FROM PONDED DITCHASSESSMENT OF PONDED WATER IMPACT TO PRIVATE WELLS

EXELON GENERATION - BRAIDWOOD STATIONBracevilla, Illinois

46841.37(MEMO030)GN-WA004 MAR 0612007

16B41-37(MEMOO3E)GN-WA004 MAR 06/2007

6

F

zS4-

__ _ _ _ _ I '___ _ _ _ _ _ _ _ _ _ _ _

__ __ _ _____.. ... __.............___ I .............. - ,--- ° ........ ft

-- ,_,_ - -- , -.-- Obs--00 ft= •," /I •• ] Obs-150 ft

--9- - Obs-300 ft---- Obs-400 ft

t Ob-0 ft0, ,I I Obs-500, ft

0 5 10 15 20 25 30

Time (Days)

figure 7SCENARIO 2: SIMULATED GROUNDWATER LEVEL INCREASE VS. TIME

3D NUMERICAL TRANSIENT SIMULATION RESULTEXELON GENERATION - BRAIDWOOD STATION

Braceville, Illinois(

016841-37(MEMO30) GN-WA-HYD (N:\HEG\16841\3DMODEL\FLOW\FlowForWCFP\Output-Plots\16841-37(Memo3O)-Fig7.xls) FEB 2007

597 -_- __...__. ..._____--C:... __ _ _ _ _ _ _ ___ ___ ___ _ _,_ __ __ __ -___ _-

.0

M- P 7•7 .. .. -- ---- s f

- - -•.. .... .0 0 ......~595.

5'-- Obs- 50 ft

594- Obs-3 00 ftE ______________ __________ Obs-200 ft

593 Obs-250 ft______________ ____ __ _ ___ ___________ -- Obs-300 ft _ _ _ _ _ _ _

-+-- Obs-400 ft0-- Obs-500 ft

592 1-

0 5 10 15 20 25 30Time (Days)

figure 8SCENARIO 2: SIMULATED GROUNDWATER ELEVATION VS. TIME

3D NUMERICAL TRANSIENT SIMULATION RESULTEXELON GENERATION - BRAIDWOOD STATION

Braceville, Illinois016841-37(MEMO30) GN-WA-HYD (N:\HEG\16841\3DMODEL\FLOW\FlowForWCFP\Output-Plots\16841-37(Memo3O)-Fig8.xls) FEB 2007

\ \\\EXELON POND

............ \0 40 80ft

• " ..• . ... • ' i !

- N a . .....

... ....... ....

Pw-H!

PW-2

KECA

I_ SIL.........

PHELPS .

/I

LEGEND..PLANT PROPETY LINE

.............. ... BLOWDOWN LINE- EXTENT OF TRITIUM

PONDED AREArwv1 OF PRIVATE WELL LOCATION

•->•.-•PATHILINES

figure 9SCENARIO 2: PATHLINES FROM PONDED AREA

ASSESSMENT OF PONDED WATER IMPACT TO PRIVATE WELLSEXELON GENERATION - BRAIDWOOD STATION

Bracevil/e, Illinois

16841.37(MEM003O)GN-WA005 MAR 0612007