ML20062K218

Ack Receipt of & Attached Documents Re Proposed Plan for Lakeshore Const & Dewatering Activities.W/O Encl Evaluations

ML20062K218
Person / Time
Site:	Bailly
Issue date:	12/14/1979
From:	Ballard R Office of Nuclear Reactor Regulation
To:	Whitehouse J INTERIOR, DEPT. OF, NATIONAL PARK SERVICE
Shared Package
ML19221A733	List: CY-79-344, Forwards 780330 Rept, Hydrogeological Evaluation of Const Dewatering. W/O Encl ML20062K198 ML20062K207 ML20062K210 ML20062K218
References
SECY-79-344, NUDOCS 8012020750
Download: ML20062K218 (1)

Text

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2iving ycar lettar of Octct2r 1,199, and

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21s descriting your prcT,osed plan for the i i.a es ..

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report i'i ic;.2rt cf th Ir Tlin %r * '.

's ~ 2u ; o , th? utility suinitt?d . f de:;htirir.; so ts to T.'

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.. i . ,ria .nj uiti ation of pot:ntial effects cThisf this us sub:aitted 1::a unt. by le 1.E:a Li':si.2re.5:ef f; y.a; r:.:antly re.~,uested and :ere sent atoco?y o l afs;r2

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.'u past sn aral y.:3rs our s taf fs have i warted infoc. al yh;..ever .'.1 t

t ';;h an.en:ies can rcat th2ir rcsicosit,ilit ?s;ld not have to de;;ad cn infor.

v..e .;f ;o:k action to assure th3t ycu ::ou list for

[-3.; ;ni:i; ion, viz, we placed you on the official distribticr. in t.hich y ;

.. rills s.hich ;e1.'e genu2icc..e 2 rate and send cut ycu any cca:ents related r:y have to pro'sle rela tive 's to such re . e a n i t O.: r s t . *r m .

>  :. rial at any ti. e.

- . f the N1P3C0 roccrt is . W1ic:d . lan in in. .

.',cci.+< cf car evaluetion thus far o clesare 1. 1: 2 have also ta!.cn the liL2rty of revi21.f r g 3 ;r pin Enc

.;il cr.J N e co cents are givcn l t h2 f rgt = ph>;27

':e lout f;r..ard to ccntir.ved cooperation with yeu .n 4

Sincerely, i

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' .j r.,rld L C'2'%:i

! F,onald L. ? 311::rd , C!.i 2f Enviren er.'a1 Trc, Sets E' w ;h 1 i Division of Site saf:.ty ard ci.vir.r. +it'l "ml tic .

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.- 1... *:n of Ccestructica Co..ctaring" uith Attechrcr.t A "Su--.ary Eepert

.ig ti:n cr.d Tcsting fcr Grour.d.zater Prc-ssure Relief Durir.; Cctstructi:n") , ,

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.1 : . P 2 inicr. a'icr. ;r scr.ted, ue cor.cluda that the pro;;; ed phn c: ti.i-

1. :s c . ' c a:lc c;; ronch to the ds atering ; rch1G ; has little p ,ta .d21 i '. .- rc:.r:2 cfinite effects to grounductor; and that the existing r: nite.rir.;

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C : . .f':ct offsite fer.tures (except as rected icitw).

' e Ar c sti. t.irg car revist: tc ir.clude the Tcrtiens of the repcet C:aling

.i'.a ;r :-*.'.res fcr prevantir; cad niti;ating the offcets of toils s! culd thcy-

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s rtr*. cf the ; cri: ':, tcr.n ir.clud:d as a 70rtion of the oficrt ca.r:rdy ' eing und:rtchen in corn:-ction with the pile driving r,re : sal under ravi:v. T::ts, this portien of our revien is not yet corplete. .

T a ci'ect of the ash pond :021in-} cn grounductar icvels and ronitoring has i :n c : si/ared by toth of our staffs. 1:ouevar, while the ash pond secpage i: .. ? is r.ot a dir2ct Unit 1 problem, we should at least be cuare of the .

!f n ; ra.;r .1 yea intend t o irplc :ent. Therefore, we rc.luest that ~ue be

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ci'cd a cei.rtesy copy of any re,rorts and plc.ns for scaling the pc-ds which

' :.ld v.:ri111y irprove cur understandir.g of the a;procch, proced;r2s,

i. .. :sd . , cnd ro.1it: ring to be cred, and any .cotcotial. ir;ccis on the

it:rir.. r.cd c.iti.ction 'r:c.ran.

Sincerely, .

.l i Bor.ald L. Bellard, Chief

\ Environ cntti Frojects Crarch 1 .,

Civistor. ci Site Safet3 cf.d Envi r::r. i.qtal .:.r.t i rs t s f . .

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.ei.:randa. The following comen;s cite the sp:-cific nem ,rar.dn by da*.e ,

to ..hich the cc;nents apply.

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' PS that i;ITS 3 advise the, 30 f ajs in 1:can:e of changes in datatiring _

p r;ing ri. s. Tuse p -ing rates are d:: ated by vagaries ci ccnttr;ction and ,.etsar. It is generally nst feasib.e to schedule ccnstruction de-

.3.ering so far in advance. 14:..sver, f;IPSC3 should be required to' inform

, 7.75 of ch jes in pumping rates as soon as the changes are .3'e or anticip'ated.

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! ": - ' , in:d S pte Ler 4,1979, with attachnent: The description of the c.5erati;r. :. ell network and the US3S preposed nonitoring program is ,

1..:i v .n .h r :..::ti:,ns that :;iPSCO dewatering efforts will be directed cr..j tr..ards the ;r.it 1 aquifer (for clarification " unit 1" in the referen:e 1:: . ..: : ref2rs to the shailcw acuifer). F.ecent prcrosals by ';I?SCO, r::i i: ally t~ se ccntained in their Au ust 27. 1979 reruest a*e it clear ds. .% ':..nirirg of the deeper aquifer will be necessary.

f- . p ase: The '.'MS proposed nenitcring system is based principally on

. e .011, i s' ::.ned U5351: ell 25. The cecpesal asserts that a nath?d has

. En 1.:.:r.;fied to reflect seas:nal chan;e in the overall rionitcrir.g control .

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:n .his assertion. The U.S. Geological Survey, using the elevation c f 1:2ii 25 n one day in history, modeled the overall shape and sicpe of the

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s;.ite.. (i.e. , the referen:e i.ater surf ace). In o.;r cpinion not only-tre el;vation but the shape of this t: ster surface nay vary seastnally. H:vever,

( 1:.e ..nitoring program assa.Tes that the internal gradients, fitw- directions, e tc. , r...ain the sa.e and cnly the elevation of the surface char.ges hith the scairn. This has not t.:-en docnanted ar.d we would suggest that further re-

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nt nay be n2eded in considering

• scascr.a1 variaticns in grounh.ater _

clacatians.

.2r.2ral c: . ant: Altraugh the program aprears cxtensive and well-thought -

r;;, tLee a; pears also to be s:..e redur.dency. He suggest that the program b: revi ..ed t.ith this in i..ind to assure that duplication is minimized.

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g Nortaheen Indiana Public Secvice Compang w Nuclear Staff RR 3, Box 501 Chesterton, IN 46304 December 27, 1979 ,

BAILLY GENERATING STATION N-1 -,

Mr. Ronald Ballard, Chief g Environmental Projects Branch No. 1 Of fice of Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission i Washington, D.C. 20545 ,

RE: NORTHERN INDIA!JA PUBLIC SERVICE COMPANY-BAILLY GENERATING STATION NUCLEAR 1 DOCKET NO. 50-367 .

Dea r Mr. Ballard:

Enclosed herewith are twenty-five (25) copies of a report titled " Groundwater Monitoring Program Following Sealing of bettling Basins at Bailly Generating Station", dated December 18, 1979. This report is submitted as a result of our commitment (see our letter to you dated August 27, 1979) to provide a groundwater monitoring program sixty days in advance of commence-ment of construction to seal the ash settling basins. That ,

construction is currently planned to begin in March 1980.

In the past, programs to determine the effects of construction dewatering on the groundwater table and the criteria for the mitiga-tion of those effects have assumed seepage of considerable quantities of water f rom the existing ash ponds into the groundwater table on a continuous basis. However, in response to an expressed desire by the National Park Service to allow the groundwater levels within the National Lakeshore to return to their natural levels, Northern Indiana Public Service Company (NIPSCO) undertook te seal the ponds.

The enclosed report describes the groundwater levels that can be anticipated af ter the groundwater mound created by the seepage is completely dissipated. This e6Ilmate is based in large part on the three-dimensional mathematical model of groundwater levels which was developed by the United States Geological Survey (USGS) for the t National Park Service. Much of the data required for the development and " tuning" of this model was developed by NIPSCO and the USGS in a cooperative effort.

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Mr. Ronald Ballard, Chief December 27, 1979 Page Two a

As requested in your letter of November 21, 1979, we are also enclosing a preliminary drawing which gives tentative details con-cerning the method to be used for sealing the settling basins. As a courtesy and to assist your understanding, we shall furnish additional information when developed. If you have any specific l

questions, please let me know.

Sincerely,

&^ , - - ~ _

R. J. Bohn Manager, Nuclear Staff KJP/mlk Enclosures 4

CC: National Park Service (w/ enclosure) i File: Docket File File: Indiana Dunes National Lakeshore

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CARGENT O LUNDY ENGINEER 5 CHICAGO GROUND WATER MONITORING PROGRAM FOLLOWING SEALING OF SETTLING BASINS AT BAILLY GENERATING STATION l

NORTIIE Rf! INDIANA PUBLIC SERVICE COMPANY BAILLY GENERATING STATION, NUCLEAR 1 December 27, 1979 Prepared by:

Sargent & Lundy Chicago, Illinois l

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SARGENT & LUNDY E N GlN E E R S CMsCAGO TABLE OF CONTENTS I. INTRODUCTION...................................... 1 II.

SUMMARY

........................................... 2 III. METHOD OF SEALING THE SETTLING BASINS............. 6 IV. EXISTING HYDROGEOLOGIC CONDITIONS................. 7 V. FUTURE HYDROGEOLOGIC CONDITIONS . . . . . . . . . . . . . . . . . . 10

. VI. CONSEQUENCES OF SEALING THE SETTLING BASINS...... 12 VII. EVALUATION OF EFFECTS OF CONSTRUCTION DEWATERING. 15 VIII. MODIFICATION OF THE MITIGATION CRITERION......... 21 IX. MONITORING....................................... 23 X. CONCLUSIONS...................................... 25 3

XI. REFERENCES....................................... 28 TABLE 1.......................................... 29 TABLE 2.......................................... 30 EXHIBITS..........................................iv 1

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SARGENT O LUNDY cNathccao CMIC AGO ,

LIST OF TABLES Table 1 Reference Ground Water Levels for the Unconfined Aquifer Table 2 USGS Observation Wells Monitored By NIPSCo l

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SARGENT & LUNDY ENGINEERS CHICAGO LIST OF EXHIBITS Exhibit 1 Existing Ground Water Monitoring Network Exhibit 2 Preliminary Settling Liner Basin Plan and Detail Exhibit 3 Potentiometric Surface Map for the_ Unconfined Aquifer on November 7, 1979 Exhibit 4 Potentiometric Surface Map for the Confined Aquifer on November 7, 1979 Exhibit 5 Seasonal Fluctuations in NIPSCo Wells 16, 18, 19, and USGS Well 25 Exhibit 6 Changes in the Monitoring Network 1

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SARGENT & LUNDY ENoshEEns C HIC AGO I. INTRODUCTION A dewatering system is required for the construction of Bailly Generating' Station, Nuclear 1 (Bailly N-1) because tne foundations are below the ground water level. A network of observation wells was installed to monitor ground water l levels in the vicinity of the site during construction

! dewatering. The existing monitoring network is described in l r Reference 1. Drawdown limits for ground water levels in the unconfined aquifer at the site boundary caused by construction dewatering have been established with the Nuclear Regulatory Commission (NRC). Specific drawdown limits for implementing ground water recharge using a trickling filter recharge system are given in Reference 2. The recharge system is described in References 1 and 2.

Tne design of the present monitoring and recharge system was l based in part on the assumption that seepage from the settling basins, located southeast of the Bailly N-1 excavation (Exhibit 1), would continue during the interval of construction cewatering for Bailly N-1. However, under the terms of an-agreement between Northern Indiana Public Service Company

! (NIPSCo) and the U.S. Department of the Interior, NIPSCo is l

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undertaking a program to seal the settling basins to eliminate seepage into the adjacent Indiana Dunes National Lakeshore (National Lakeshore) . Sealing of the settling basins is l

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SARGENT Q LUNDY E N G: NEERs CMICAGO scheduled to begin in March 1980. After the settling basins-are sealed, ground water _ levels will decline across the Bailly site and a portion of the adjoining National Lakeshore.

The present method of evaluating drawdown in the National ,

Lakeshore resulting from construction dewatering for Bailly N-1 cannot differentiate between declines in ground water levels resulting from construction dewatering and those caused by sealing the settling basins.

Tne purpose of this report is to present a method for evaluating the effects of Bailly N-1 construction dewatering on the unconfined aquifer in the adjoining National Lakeshore once the settling basins are sealed. This report also describes the method of sealing the settling basins, the existing and future site hydrogeologic conditions, and modifications to the mon;toring program. The impact of sealing the settling Lasins on the mitigation criterion is also discussed. -

II. S UMERY NIPSce has implemented a program of ground water monitoring wnich includes, if necessary, recharge to protect ground water levels in the adjacent National Lakeshore from excessive drawdown caused by construction dewatering for Bailly N-1.

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SARGENT & LUNDY ENGINEERS CHICAGO The existing monitoring program and trickling filter recharge ,

system are described along with the present mitigation criterion in References 1 and 2.  ;

Upon sealing the settling basins, ground water levels across the Bailly site and a portion of the adjoining National Lakeshore will decline to their natural state as desired by  ;

the National Park Service (NPS). These declines will be  ;

independent of construction dewatering activities. Ground  ;

water level declines resulting from Bailly N-1 construction dewatering may also occur during dissipation of the ground watcr mound following sealing of the settling basins. As a result, the method presently used to evaluate drawdown ,

attricutable to construction dewatering, as described in Reference 1, will no longer be valid because it cannot differentiate between drawdown caused by construction dewatering and simultaneous declines resulting from sealing of the .

settling basins. Thus, an alternate method of evaluating the effects of construction dewatering has been developed whien incorporates the ground water level declines that will ,

result from sealing the settling basins.

The U.S. Geological Survey (USGS) has constructed a three-dimensional digital model to simulate the ground water flow system in the vicinity of Bailly N-1 (Reference 4). Using th E model, the USGS has generated reference ground' Water J

1evels which represent the ground water levels that would 3

o SARGENT & LUNDY ENGINEERS CMsCAGO have occurred across the Bailly site and adjacent National Lakeshore on October 26, 1976, had there never been any seepage from the settling basins (Reference 5). (Construction dewatering for Bailly N-1 had not begun on that date.)

] The US35 reference levels are listed in Table 1. It is ^

these ground water levels that the NPS wants rectored and preserved in the adjacent National Lakeshore (Reference 5) . c NIPSCo will use the USGS reference levels to evaluate the necessity for mitigation during dissipation of the ground +

water mound created by seepage from the settling basins.

The mitigation criterion previously established in Reference 2 has been modified to comply with the NPS position stated in Beference 5 that ground water levels in the National Lakeshore be maintained at their natural levels. The criterion shoula alsc reflect the 32 -foot accuracy of the reference levels (Ref erence 5) . Therefore, NIPSCo will adopt a draw-down limit of two feet at the eastern property line as the basis for implementing mitigation. Except for the months r during which the ground is frozen, specific drawdown limits at observation wells 54C, 16, and 67 will be 2.0, 2.5, and 3.0 feet below the seasonally adjusted reference levels, ,

respectively. When the ground is frozen, the respective l

drawdown limits will be 3.0, 3.5, and 4.0 feet below the 1

seasonally adjusted reference levels. These modified draw-down limits will be applied after sealing of the settling J

A 4 CARGENT & LUNDY ,.

ENGINEERS cwicaoo basins begins. Mitigation will be accomplished using the

, trickling filter recharge system described in Reference 1 and 2. Mitigation will not be required if declines in ground water levels cannot be attributed to construction r

r dewatering for Bailly N-1. This includes such instances as

1) smaller ground water level declines at NIPSCo's eastern j property line than are measured farther east in the adjacent [

National Lakeshore or 2) ground water levels that have declined uniformly across the adjacent National Lakeshore. j If the ground water mound has substantially dissipated before Bailly N-1 construction resumes, the USGS reference [

levels r.ay be verified using ground water levels measured in I

the observation wells. New baseline ground water levels f w 11 then be established from these measurements as the bi: sis f or implementing mitigation. In this event, NIPSCo f i

will return to the mitigation criterion previously established in Reference 2.

i-NIPSCo will install two new observation wells in the unconfined aquifer north of Settling Basin 10, as shown on Exhibit 6.

These new observation wells will be used in conjunction with the existing USGS and NIPSCo observation wells to verify the ,

USGS reference levels following dissipation of the ground water mound. NIPSCo will also begin weekly monitoring of the USGS observation wells identified in Table 2 approxi-mately one month before sealing of the settling basins 5

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• SARGENTQ LUNDY E N G I N E E D D-CmCAGO

- begins. Weekly monitoring shall continue until construction dewatering for Bailly N-1 is terminated.

III. METHOD OF SEALING THE SETTLING BASINS The settling basins will be sealed by installing a double .

liner in the existing settling basins and bottom ash area.

The double liner will consist of a compacted clay liner overlain by a membrane liner. The configuration of the i

sealed settling basins and typical liner construction ,'

detail are shown on Exhibit 2. One set of settling basins anc a portion of the bottom ash area will remain in service at all times during installation of the liners to permit the continued operation of Bailly Generating Station, Units 7 and 8 (Bailly 7&8). Water that is not recycled for plant use !resently leaves the syster by seepage from the unlined settling basins. However, this seepage will no longer exist whc1 construction begins in the second set of settling  ;

basins. Excess water which is not recycled will then be discharged to Lake Michigan following treatment to meet existing chemical discharge limitations, i

Construction of the liners will require excavation to El.

+30.* Tne water level in the unlined settling basins varies Plant grade is El. +40. Elevations refer to NIPSCo datum, where '

El. 0.00 equals mean Lake Michigan Level, El. 576.80 feet (IGLD, 1955).

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CARGENT & LUNDY

. cuotNEERS C HIC ASD from El. +36 to +41. As shown by USGS observation wells G-1, G-3, and G-5, ground water levels around the settling basins are also high, usually above El. +35 (Exhibit 3).

Thus, dewatering will be required around the settling basins to allow construction of the liners. Water removed by the dewatering system will be discharged to the operating set of settling basins.

A water budget analysis will be performed on each primary.

and secondary settling basin once every two years to evaluate the effectiven.ess of the liners in preventing leakage. For the analysis, precipitation, evaporation and changes in water levels will be monitored for one week while inflow is halted to the basin being tested.

IV. EXISTING HYDROGEOLOGIC CONDITIONS As described in References 1 and 3, two aquifers are present in the Bailly N-1 excavation area, one unconfined and one confined. Available boring and observation well data indicate that both aquifers are also present in the vicinity of the settling basins and adjacent National Lakeshore. However, the stratigraphy beneath the settling basins and adjacent National Lakeshore differs from that in the excavation area,.

as described in this section.

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SARGENT G LUNDY ENGINEEDS CHICAGO The unconfined aquifer beneath the settling basins and adjacent National Lakeshore consists of fine to medium-sand with some graval and occasional thin layers of organic material. In contrast to the stiff silty clay confining layer present beneath the Bailly N-1 excavation, the unconfined and confined aquifers in the vicinity of the settling basins are separated by a soft, calcareous clayey silt containing numerous shell fragments and some organic material. The thickness of the confining layer ranges from less than five

feet to 16 feet in the four borings that penetrated this layer. The top of the confining layer varies in elevation from approximately +4 at the west end of the settling basins to approximately +9 at the east end. The top elevation and thickness of the confining layer in the National Lakeshore area are not known because no USGS borings reached the necessary depth. Based upon two' borings drilled to rock on i

NIPSco property (NIPSCo 59 and USGS 102), the confined aquifer consists of fine to coarse sand and extends to approximately El. -72 to -75. Interbedded clay and silt layers in the confined aquifer are not as prevalent in the vicinity of the settling basins as beneath the Bailly N-1 excavation.

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Ground water levels in the unconfined and confined aquifers i l

are measured in the observation wells shown on Exhibit 1. l l

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SARGENT & LUNDY E N GlN E E R S CMICAGO l

l Ground water levels at the Dailly site respond to changes in: 1) natural recharge to and discharge from the aquifers caused by variations in precipitation, evapotranspiration, and fluctuations in the level of Lake Michigan; 2) the rate of pumping by nearby industries; 3) the amount of water discharged to the unlined settling basins during operation of bailly 768; and 4) the rate of construction dewatering for Bailly N-1. Potentiometric surface maps for the unconfined

([ and confined aquifers, prepared using water levels measured on November 7, 1979, are included as Exhibirs 3 and.4.

Comparison of these maps with Exhibits 1 and 2 of Reference

incicates that ground water levels in both aquifers have declined since July 5, 1979. Since there has been minimal change in the rate of construction dewatering from July to November 1979, the observed decline must be caused by some combination of the first three factors. Seasonal declines ,

nave been observed in ground water levels measured across the ba111y site every year since monitoring began in 1975 (Exhibit 5).

l l Long-term seepage from the unlined settling basins has created a large ground water mound in the unconfined aquifer.

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In response to thin seepage, ground water levels in the adjoining National Lakeshore have risen such that the present water tabic is above the ground surface in some topographically-l l

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l SARGENT & LUNDY ENGINEERS CMILA(.O low areas. This has resulted in the development of' permanent-interdunal ponds. Formerly, only the deeper portions of the

{ interdunal ponds retained any water, and then only during the wetter times of the year.

f V. FUTURE HYDROGEOLOGIC CONDITIONS As described in Section IV, seepage from the unlined settling 7 ~

basins has created s large ground water mound in the unconfined aquifer. The National Park Service, who administers the l

adjacent Indiana Dunes National Lakeshore, considered the-elevated ground water levels to be unnatural and therefore undesirable, and requested that NIPSCo terminate seepage from the settling basins.

..n un.:ned octtling basins serve as an artificial, constant source of recharge to which the ground water flow system has ad 3 usted. sealing of the settling basins will cut off this source of recharge. Consequently, ground water levels will cecl'.ne to the level that can be maintained by recharge from c infiltrating precipitation.

Using a three-dimensional digital model, Meyer and Tucci of the USGS quantified the amount of water-level decline that may be expected once the settling basins are sealed (Reference 10

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I SARGENT & LUNDY l '

CNGtNCERS I

CHIC AGO 4). The model predicts declines of about 15 feet in the unconfined aquifer under the settling basins and as much.as

' 10 feet along NIPSCo's eastern property line with the National Lakeshore. Water levels in all the interdunal ponds will i

fall several feet below the bottom of the ponds, except that some warer would remain in the deepest holes in Interdunal Pond 7 (Reference 4). At the Bailly N-1 excavation, the model predicts a decline of about five feet in the unconfined

- aquifer. These predicted declines are independent of any

(

decline resulting from construction dewatering for Bailly N-1.

The USGS model also predicts a two- to seven-foot decline in potentiometric levels in the confined aquifer following sealing of the settling basins (Reference 4). The distance from the settling basins and the vertical hydraulic con-ductivity of the confining layer control the magnitude of the decline. The greatest declines will be in those areas where the vertical hydraulic conductivity of the confining I layer is the highest. Based upon the model results, the greatest declines in the confined aquifer will occur at the west end of Interdunal Pond 1, where boring data indicate the confining layer is abnent and the vertical hydraulic conductivity should be the highest.

Meyer and Tucci (Reference 4) also determined from model 1 1

I 11 l

l

SARGENT Q L'JNDY ENGINEERS CMic AGo experiments-the time necessary for dissipation of the ground water mound created by seepage from the settling basins. Water levels will decline rapidly following sealing of the settling basins, but the rate of decline will decrease witn time. Most of the ground water mound will have dissipated within two years after the basins are sealed (Reference 4).

flowever , as indicated in Section III, dewatering around the.

settling basins is required for installation of the liners, Thc effect of this dewatering will be to accelerate the rate f

cf dissipation of the ground water mounc.

Tne USGF model also predicts declines of less than three feet in the unconfined aquifer and less than five feet in the confined aquifer at NIPSCo's eastern property line resulting from construction dewatering for Bailly N-1 (k forence 4). Thus, the water level decline in the unconfined aquticr at the property line attributable to construction dewatering for Bailly N-1 will amount to less than one-third of ne decline expected to result from sealing the settling basins. Water level declines in the confined aquifer caused by construction dewatering will be about the same as declines predicted for sealing the settling basins.

VJ. CONSEQUENCES OF SEALING THE SETTLING BASINS According to the present construction schedule, installation 12

'-~ -

SARGENT & LUNDY ENoNetas C MIC AGO of the liners in the second set of settling basins will begin'by mid-summer 1980. Seepage from the settling basins will be terminated at that. time. However, ground. water levels across the Bailly site and adjoining National Lakeshore will begin to decline as'soon as dewatering begins around the settling basins.

Ground water levels in the unconfined aquifer are presently nigher'than potentiometric levels in the confined aquifer across most of the area. This indicates that' ground water 2s cocing from the unconfined to the confined aquifer.

liowever, projected declines across the Bailly site and a portion of the adjacent National Lakeshore following sealing-of the settling basins are greater in the unconfined aquifer-inar in the confined aquifer and the direction of seepage l

bc reversed in some areas after the mound has dissipated.

l Tnis phenomenon is most evident at the west end of Interdunal Ponu 1 (Attachment 2 of Reference 5) where the closed contour at Li. 596 (NGVD)* represents a mound in the unconfined i

aquifer caused by seepage from the underlying confined aquifer.

• National Geodetic Vertical Datum (1929); El. 596.00 NGVD corresponds to El. +17.33 NIPSCo datum.

13 i .

SARGENT Q LUNDY chosNccas CMIC AGO Sealing of the settling basins will also lower the ground water levels in the vicinity of Bailly N-1 excavation, thereby reducing the dewatering rate. Previous reports have established that much of the water pumped from the excavation is derived from the confined aquifer (References 1 and 3).

How much the dewatering rate will be reduced following sealing of the settling basins will largely depend on the vertical hydraulic conductivity of the confining layer.

Tne uncertain nature of the confining layer in that area l precludes ar. accurate estimate of the reduction in the required dewatering rate.

Despite the reduction in ground water levels across the Bailly site fol. lowing dissipation of the ground water mound, the dewatering rate must be increased from the present level for construction of the Bailly N-1 foundation as described

. ht f o rences 1, J, and 3. The increased rate of construction dewatering will cause ground water levels to decline temporarily near the excavation whereas dissipation of the ground water mound will result in a permanent decline in ground water levels. Given the present construction schedule for sealing the settling basins, it is possible that both declines would occur simultaneously. Application of the mitigation criterion to water levels measured in the observation wells under these circumstances would require a means of separating the i 14

. - = -

, , SARGENT & LUNDY ENGINEERS

' CMIC AGO decline resulting from construction dewatering from that caused by all of the other factors listed'in Section IV, including sealing the settling basins.

r The present method of evaluating drawdown in the unconfined f

i aquifer resulting from construction dewatering for Bailly N-1 relies upon an assumed constant shape of pre-dewatering water table contours. Although this method takes.into account seasonal fluctuations in ground water levels, it cannot be used to differentiate declines caused by sealing the settling basins from those caused by construction dewatering should these declines occur. simultaneously. Therefore, a method for evaluating the effects of construction dewatering during and after dissipation of the mound has been developed and is described in Section VII.

VII. EVisLUATION OF THE EFFECTS OF CONSTRUCTIO:: DEWATERING Prom the time ground water monitoring at the Bhilly N-1 site began in 1974, it was obvious that ground water levels-in the unconfined aquifer were influenced by seepage from  ;

the unlined settling basins. There is no record of pre-

' seepage ground water levels. However, using the digital model developed by Meyer and Tucci (Reference .5) , the USGS has produced a map showing the ground water levels that l would have occurred in the unconfined aquifer on October 26, 1976, had there never been any seepage from the settling 15 ,

SARGENT Q LUNDY ENGINEERS CmCaGo basins (Attachment 2 in Ref erence 5) . Because construction cewatering for Bailly N-1 did not begin until March 1977, the ground water levels shown on this map represent the response of the unconfined aquifer only to nearby industrial pumping and seasonal variations in recharge and discharge.

l l The USGS estimates the accuracy of these ground water levels, hereafter called reference levels, to be about +2 feet _

(Reference 5).

NIPSC0 will use the USGS reference levels, which are presented

12. Table 1, to evaluate the necessity for mitigation during and after dissipation of the ground water mound. However, the reference levels cre not static and adjustments must be made to reflect natural seasonal fluctuations in the unconfined aquifer before the reference levels can be compared to actual ground water levels measured in the observation ,

wells. Since all of the NIPSCo observation wells are located l within the large ground water mound created by seepage from the settling basins, these observation wells cannot be used to determine the seasonal fluctuation during dissipation of l

the mound. The response of the observation well used to makc seasonal ad]ustments to the reference levels should not be affacted by either sealing of the settling basins or construction dewatering for Bailly N-1. In addition,-the ground water level should have been measured in that observation 16

l SARGENT & LUf4DY ENGlNEERS CMICAGO l

l well on October 26, 1976, the same date for'which the USGS reference levels were identified. Only two observation wells in the unconfined aquifer appear'to satisfy these criteria: USGS observation wells 24 and 25 (Exhibit 1).

Five-year hydrographs for NIPSCo observation wells 16, 18, 19, and USGS well 25 are plotted on Exhibit 5. The hydro-graph for USGS observation well 24 (not plotted) is similar

(

to that for USGS well 25. While the hydrographs show ground water levels fluctuate seasonally at each observation well, the average seasonal range in ground water levels is 3.9 feet in the NIPSCo observation wells and 2.1 feet in USGS well 25. In addition, the seasonal high and low ground water levels are observed in the USGS wells about three months before they occur in the NIPSCo observation wells.

D2: :_ren ts in hydrogeologic setting probably account for

( tnese differences in seasonal fluctuations: the NIPSCo observation wells are located in an area of relatively high und varying topography (dunes) whereas USGS wells 24 and 25 are ]ocated in a large, low marsh characterized by standing water throughout much of the year.

Despite the observed differences in seasonal fluctuations, NIPSCo will use USGS well 25 as the base well for seasonal adjustments to the reference levels. Seasonal adjustments will be made in the following manner:

17

SARGENT O LUNDY -

cuciscens CHIC AGO

1) Determine the difference between the observed water.

level in USGS well 25 on any day in question and the base level of +23.23 measured on October 26, 1976. The difference will be positive if the observed level is higher than the base level, negative if it ,is lower.

l 2) Adjust the reference levels at each observation well by adding the difference between the base and observed water levels-determined above for USGS well 25 to the levels given in Table 1.

3) Compare the measured ground water levels in the obser-vation wells to the adjusted reference levels to determine whether ground water levels have declined below the natural levels the NPS wants to preserve in the adjacent National Lakeshore.

If USGS well 25 is out of service for any reason, NIPSCo will use data from USGS well 24 to make seasonal adjustments' to tne reference levels. The procedure for making seasonal adjustments will be the same as described above for USGS w;11 25 except that the base level for well 24 is +27.77.

The above procedure assumes that seasonal fluctuations in ground water levels at the NIPSCo site during and after 18

- _- - _----_---_-J

+ . _

i j

SARGENT & LUNDY ENGtNEERS i CMIC AGO .

dissipation of the ground water mound will be identical to those observed offsite in USGS well 25. This assumption cannot be verified since ground water-levels were not measured prior to the existence of the settling basins. As shown on 1

Exhibit 5, the seasonal behavior of USGS well 25 since 1975 t

is comparable to that in the NIPSCo observation wells.

i i

As stated earlier in this section, the accuracy of the USGS model-simulated reference levels is about +2 feet. Furthermore, assumed values of average annual recharge, hydraulic con--

ductivity and storage coefficient for the aquifers, and tnickness of each aquifer and the confining layer are in-corporated in the model. Limited information is available regarding tne nature of the confining layer or the confined aquifer in the National Lakeshore near the settling basins (Section IV). Thus, even in those areas not affected by construction dewatering for Bailly N-1, ground water levels measured following dissipation of tha ground water mound may t

nc: match the seasonally adjusted reference levels at all locations.

If the ground water mound completely dissipates before construction of Bailly N-1 resumes, the USGS reference levels can be verified using ground water levels measured in 1

the NIPSCo and USGS ob.-ervation wells. Assuming the rate of 19

t i

i SARGENTO LUNDY ENGINEERS CwiCAGO construction. dewatering does not change significantly during dissipation of the ground water mound, potentiometric.

surface maps prepared for the unconfined aquifer following dissipation of the mound will be modified to remove the crawdown caused by the present low rate of construction dewatering. The drawdown can be subtracted out using standard relationships between discharge rate, dravdown, and distance ,

to obtain a new potentiome*.ric surface map and, thus, new g baseline reference levels based upon actual measurements of around water levels in the observation wells.

4 In the event that new baseline ground water levels can be established for the unconfined aquifer before construction 4

of Bailly N-1 resumes, NIPSCo will use these baseline levels to evaluate the effect on the adjacent National Lakeshore of an-2 subsequent construction dewatering. The baseline levels 1

i must also be adjusted seasonally in the same manner as the USGS reference levels. Hydrographs of the ground water ,

levels measured in NIPSCo and USGS observation wells.will be plotted to identify which observation wells reflect only seasonal fluctuations. One of the observation wells so  ;

identified will be used to make seasonal adjustments to the i

new baseline levels. t f

4

)

i, 20

SARGENTO LUNDY ENGINEERS cmCAGo VIII. MODIFICATION OF THE MITIGATION CRITERION The ground water levels the NPS wants restored and preserved in the National Lakeshore adjacent to the Bailly site are the natural levels that would occur had there never been any seepage from the settling basins. To this end, the NPS has taken the position that NIPSCo need not mitigate the water level decline due to construction dewatering as long as

,- ground water levels in the National Lakeshore remain above the USGS reference levels (Ref erence 5) . Thus, the mitigation criterion previously established in Reference 2 should be modified to reflect the expressed desire of the NPS to restore ground water levels in the National Lakeshore to natural conditions.

Accordingly, NIPSCO will use the reference levele identified I ri tne USGS/NPS monitoring plan (Reference 5) to evaluate the necessity for mitigation during dissipation of the ground water mound. Specific drawdown limits will be applied at the same three NIPSCO observation wells identified in Reference 2: 54C, 16, and 67. However, because the USGS estimates the accuracy of the reference levels to be about 12 feet (Ref erence 5) , NIPSCo will establish a limit of two feet of drawdown at the eastern property line attributable to construction dewatering as the basis for implementing mitigation measures. Thus, the specific drawdown limits for 21

SARGENT & LUNDY ENGINEERS Cm:CAGo initiation of ground water recharge during the months the ground is not frozen will be 2.0 feet below the seasonally adjusted reference level at well 54C, 2.5 feet at well 16, and 3.0 feet at well 67. For the months during which the ground is frozen, NIPSCO will use a drawdown criterion of 3.0 feet. The drawdown limits then become 3.0 feet, 3.5 feet, and 4.0 feet at observation wells 54C, 16, and 67, respectively. This minimal increase in allowable _ drawdown during the winter months will have a negligible effect because vegetation is dormant during these months.

4 If construction of Bailly N-1 resumes before the ground water mound has completely dissipated, the USGS reference levels will be used throughout the interval of Bailly N construction cewatering to evaluate whether any undesired t.ewatering of the adjacent National Lakeshore has occurred.

.1nce drawdown caused by construction dewatering will decrease as the distance from the Bailly N-1 excavr. tion increases, the effect on ground water levels in the adjacent National Lakeshore will be greatest at NIPSCo's eastern property i line. Evidence of any dewatering effects will also appear first at the property line. It ground water levels decline less than two feet below the reference levels at the property. i line but more than two feet below the reference levels farther east, the decline in the National Lakeshore cannot L

be attributed to construction dewatering. Similarly, uniform-22

O 1 4s + 4 Jtt SARGENT & LUNDY E N GIN E E R S CMsC AGO declines in ground water levels below the reference levels across the National Lakeshore cannot be caused by Bailly N-1 construction dewatering. Mitigation is not required  ;

under these circumstances. NIPSCo will initiate ground i water recharge if the ground water levels measured in obser-vation wells 54C, 16, and 67 fall below the modified drawdown limits given above. .

c If the ground water mound has substantially dissipated before construction resumes, the new baseline levels identified from actual measurements of ground water levels in the observat2on wells will be used to evaluate the drawdown at the property line attributable to construction dewatering (Section VII). In this case, NIPSCo will return to the mitigation criterion established in Reference 2 which permits one foot of drawdown at the property line (two feet during tne winter months).

3: . MON I TORI NG ,

i A

The existing network of observation wells installed and monitored by NIPSCo is shown on Exhibit 1. Installation 4

details for these observation wells are given in Reference t

1. The charts on observation wells having continuous recording equipment are changed once a week. Water levels in the interdunal ponds, settling basins, and observation wells without recorders are measured the same day the recorder

• 23

SARGENT O LUNDY ENGfNEERS CM4C AGO charts are changed. NIPSCo also measures the water levels once a month in the USGS observation wells listed in Table 2.

In June 1979 the USGS installed observation well 26 in the National Lakeshore 10 feet east of NIPSCo's eastern property line. The observation well is 19 feet deep and measures the water level in the unconfined aquifer. NIPSCo began monitoring USGS well 26 on a monthly basis in November 1979. At the same time, NIPSco dropped USGS observation wells 19 and 20 from the list of USGS wells to be measured monthly because the meacured water levels were not representative of either the unconfined or confined aquifer (Reference 5).

In addition to these changes in the monitoring network, NIPSco will install two observation wells in the unconfined aqu:fer north of Settling Basin 10 at the locations shown on Exnibit 6. The observation wells will consist of standard we11 points installed in the same manner as USGS well 26 to approximately El. +10. The new observation wells will be used i t. conjunction with the existing USGS wells to periodically prepare water t-N1e profiles as the dissipation of the ground water mound progresses and to verify the reference levels predicted by the USGS model after the mound has dissipated.

24

GARGENT O LUNDY ENGsNetms C MIC AGO I

l l

During the dissipation of the ground water mound, the USGS plans to collect the data tapes from their observation wells having continuous recorders, including control well 25, every two weeks. NIPSCo receives the USGS water level summary approximately two weeks after it is collected.

Thus, up to four weeks may elapse before it is known whether dewatering below the reference levels has occurred or is likely to occur in the National Lakeshore.

To eliminate some of this delay, NIPSCo will monitor USGS observation wells 24 an'd 25, and those listed in Table 2 on the same schedule as NIPSCo's wells during and after the sealing of the settling basins. Determination of the water level in USGS wells 24 and 25 will permit the immediate seasonal adjustment of water levels measured in the other USGS and N1PSCo observation wells. NIPSCo will begin weekly monitoring of the USGS observation wells approximately one monthbefoIesealingofthesettlingbasinsbegins. Weekly monitoring of the NIPSCo and USGS observation wells will continue until construction dewatering for Bailly N-1 is terminated.

X. CONCLUSIONS This report describes the anticipated decline in ground water levels in a portion of the Indiana Dunes National 25

. - - . . _ - - _ _ _ .l

CARGENT & LUNDY ENo NEERO CMIC&GO Lakeshore following sealing of the settling basins and the modifications in the method of evaluating the effects of construction dewatering for Bailly N-1 necessitated by this decline. The modifications to the evaluation method, including .

specific changes to the mitigation criterion, monitoring network, and monitoring frequency are summarized below:

1. During dissipation of the ground water mound, NIPSCo  ;

will use the USGS reference levels given in Table 1 as the basis for determining whether any dewatering of the adjacent National Lakeshore has occurred as a consequence of construction dewatering for Bailly N-1. If construction-of Bailly N-1 resumes after the ground water mound has dissipated, new baseline levels will be established from potentiometric levels measured in the observation wells.

.. The mitigation criterion during the period the ground water mound is dissipating shall be changed to reflect I the +2-foot accuracy of the reference levels. Specifi-cally, ground water recharge will be initiated through-out most of the year when drawdown attributable to construction dewatering for Bailly N-1 exceeds 2.0 feet at NIPSCo's eastern property line. As applied to individual observation wells, the drawdown limits will be 2.0, 2.5, and 3.0 feet below the seasonally adjusted E

26

SARGENTQ LUNDY ENGINEERS CM sC AGO reference levels at NIPSCo wells 54C, 16, and 67, respectively. During the winter months, the respective drawdown limits will be increased to 3.0, 3.5 and 4.0 feet belcw the seasonally adjusted reference levels.

4

3. The drawdown criteria for mitigation will remain as i

established in Reference 2 if the ground water mound  ;

dissipates before construction resumes on Bailly N-1.

4. NIPSCo will install two new observation wells in the unconfined aquifer north of Settling Basin 10 to monitor the dissipation of the ground water mound and to verify f

the reference levels after dissipation is complete.

5. NIPSco will begin monitoring the USGS observation wells

• i listed in Table 2 weekly approximately one month  ;

be: ore sealing of the settling basins begins. Weekly monitoring of the USGS and NIPSCo observation wells shall be continued until construction dewatering for Bailly N-1 is terminated.

4 E

t i

t

)

27

SARGENT Q LUNDY E N GlN E E R s CM sC AGO XI. REFE RENCES

1. Sargent & Lundy, "Hydrogeologic Evaluation of Construction Dewatering, Bailly Generating Station, Nuclear 1",

March 30, 1978,

2. Sargent & Lundy, " Response to NRC Questions, Bailly Generating Station, Nuclear 1", July 20, 1978.

3. Sargent & Lundy, " Supplementary Information, Hydrogeologic Evaluation of Construction Dewatering, Bailly Generating Station, Nuclear 1", August 27, 1979.

4. William Meyer and Patrick Tucci, " Effects of Seepage' from Fly-Ash Settling Ponds and Construction Dewatering

- on Ground-Water Levels in the Cowles Unit, Indiana Dunes National Lakeshore, Indiana": U.S. Geological Survey Water-Resources Investigations ~8-138, 1979.

5. National Park Service, letter to Nuclear Regulatory Commission, October 1, 1979: "USGS/NPS Plan for Determining Dewatering of the Indiana Dunes National Lakeshore Adjacent to NIPSCo Bailly Generating Station."

28 i

5 l

t SARGENT & LUNDY ENGfNEERS C onC&Go TABLE 1 REFERENCE GROUND WATER LEVELS FOR THE UNCONFINED AQUIFER  :

t USGS Well Reference NIPSCo Well Reference Number Level (ft) Number Level (ft) 1 21 +17.0 14 +15.1 22 +17.0 15 +10.3 23 +17.1 16 +17.6

^

24 +27.8 17 +15.1 25 +23.2 18 +17.1 ,

26 +15.7 19 +15.0 104 +30.3 20 +14.5  ;

D-1 +15.3 51C +12.9 >

D-2 +17.1 52C +14.3-D-3 +19.8 53C +14.1 D-4 +17.7 54C +15.7

• D-5 +23.0 SSC +13.3 D-6 +20.7 56C +17.6 D-7 +25.7 57C +14.4 D-8 +30.3 58 +15.9 '

G-1 +17.7 59C +17.1 G-2 +19.0 62 +1f.l.

G-3 +19.0 65 +15.2 G-4 67

! +19.8 +15.0 G-5 +19.8 72 +9.2 -

G-6 +23.6 73 +8.5 G-7 +25.9 74 +9.0 G-8 +25.9 G-9 +27.1 $

G-10 +27.1 NOTES:

1. Ground water levels are referenced to NIPSCo datum. To I convert these levels to NGVD (1929), add 578.67 feet.

2. The levels listed here are the USGS reference water levels identified in Reference 5 for October 26, 1976.

3. The reference ground water levels were generated from ,

the USGS digital model described in Reference 5 and represent the ground water levels that would have been measured had seepage from the settling basins never occurred. The USGS considers these levels to be accurate to +2 feet (Reference 5) .

, 4. Reference levels given for USGS observation wells 24 and t 25 are actual ground water levels measured on October 26, 1976.

5. Construction dewatering for Bailly N-1 did not begin until March 1977.

i

CARGENTO LUNDY E N GIN E E R D CMICAGO TABLE 2 USGS OBSERVATION WELLS MONITORED BY NIPSCO t

19 D-3 20 G-1 1

1 21 G-2 22 G-3

- 23 G-4 26 G-5 D-1 G-6 D-2 4

NOTES:

1. USGS observation wells listed above are-monitored monthly by NIPSCo.

2. USGS wells 19 and 20 were dropped from the list of wells monitored by NIPSCo in November 1979.

3. NIPSCo added USGS well 26 to this list in November 1979.

4. NIPSCo will begin weekly monitoring of USGS wells 24 and 25, and all other USGS wells listed above approximately cne month before sealing of the settling basins begins.

5. Monitoring of USGS observation' wells shall continue until construction dewatering for Bailly N-1 is terminated.

t 30 i

s = *. ,

1. % UNITED STATES

!yl g' % NUCLEAR REGULATORY COMMISSION wash NotoN.o.c.2csss

{f.t*g%

1,N.

..... f 7

De$ecl'c. 50-367 FEB 0 : ED

/

MEMORANDUM FOR: Ronald I.. Ballard, Chief Environmental Projects Branch No. 1, DSE FROM:

L. G. Hulman, Chief Hydrology-Meteorology Branch, DSE BAILLY !!UCLEAR POWER PLANT CONSTRUCTION DEWATERItG,

SUBJECT:

MONITORING AND MITIGATION PROGRAM

(* The following coments and recommendation on the subject are a result of reviewing the Permittee's December 27, 1979 letter and of attending the meeting with the t!ational Park Service, USGS, and NIPSCO in Indianapolis on January 31, 1980.

1 The Permittee has proposed significant changes to tne construction de-watering monitoring and mitigation program which was developed toThe minimize the impact of construction dewatering at the National LakeShore.

proposal vill not, in our opinion, ameliorate the effects established by the USGS, acting as consultr.t to the National Park Service, for two reasons:

a. The limiting action levels of drawdown at the Permittee's property line will not meet the National Park Service goal; and

b. The proposed mitigation program cannot supply sufficient water to the affected aquifer to accomplish its intended purpose.

k.

National Park Service has stated they want to minimize or eliminate any-impacts of construction dewatering. In my view, this statement is con-2 tradictory to NRC's conrnon practice of allowing non-damaging impacts; the Furthermore, practice upon which the Construction Permit EIS was issued.

no adverse impacts of construction dewatering have been identified.

3. The National Park Service's conclusion that there will be construction dewatering impacts almost a mile from the reactor site is predicated on USGS numerical modeling studies. The bases for the USGS conclusions are not in the public domain, but the USGS has agreed to allow access to both the data and analyses in their local office, subject to change upon USGS I headquarters review. They will not allow copies thereof to be reviewed elsewhere. I h3 ob '

So b22.2d@S

l

.. t . .. ,

f

' --- . , g Ronald L. Ballard ,

4 The primary bases for the conclusion of dewatering effects approximately a mile from the plant is the absence of an aquifer confining layer in the vicinity of the location in question. The USGS, and to my knowledge no one else, has data to support such a conclusion. The USGS and National Park Service plan to attempt to verify the assumption in the future (possibly by FY 81).

I recommend that the Permittee's proposed changes to the monitoring and mitigation program be disapproved. Furthermore, I recomend that I&E monitor construction dewatering activities to assure that the Permittee adequately meets his CP requirements, and has not violated reporting require-ments. Finally, as a matter of clarification, I was informed by the

{' Permittee's representative at the January 31 meeting that anomalies in the November 1979 data supplied to us in support of the Construction Permit were caused by testing of the mitigation program and by a landslide in the ,

southwest corner of the excavation.

' ! , M4r%

, r..

L. . ulman, Chief Hydrology-fieteorology Branch Division of Site Safety and .

Environmental Analysis cc: H. R. Denton ,

R. C. DeYoung H. D. Thornburg, I&E

(' W. E. Kreger -

W. Regan L. Rubenstein P. Crane, OGC R. P. Geckler  !

S. oldberg, OELD M. . Lynch j

. H. Hendrickson, Indiana Dunes National Lakeshore

. Bivins i

i l

l i

,. . . . _ - ,