FUL 744 Heartland Trail 53717-1934

Integrated P Q g^^ ^923 53708-8923 Euviromneiltal Madison, Wl Solutions Telephone: 608-831-4444

Fax: 608-831-3334

EPA Region 5 Records Ctr.

346862

GROUNDWATER MODELING REPORT and PLAN for

RECOVERY SYSTEM ENHANCEMENTS at the

LEMBERGER SUPERFUND SITES

ADDENDUM NO. 1

PREPARED BY RMT, INC.

MADISON, WISCONSIN

September 2000

Galei^l/Kenoyer, Ph.D., P.G. Consulting Hydrogeologist

P..,..'. M.f^^i Eric Gredell, P.E. Project Manager

/ifeS

l:\WPMSN\Pn\00-O3449\42\R0O0344942-O0I.DOC 9/11/00 ® 2000 RMT, Inc. F i n a l

All Rights Reserved

Table of Contents

1. Introduction 1

2. Modifications to the Malcolm Pirnie Version of the Lemberger Groundwater

Flow Model 2

3. Model Input Parameter Values 3

4. Boundary Conditions 4

5. Flow Model Calibration Documentation 5

6. Transient Flow Simulation Results 6

7. Sensitivity Tests 8

7.1 Flow Model 8 7.2 Transport Model 8

8. Particle Tracking/Capture Zone Analysis 10

9. Conclusions and Recommendations 12

10. References 13

List of Tables

Table 1 Model Parameter Values

Table 2 Calibration Summary - Computed vs. Measured Heads

Table 3 Transient Simulation Summary - Predicted vs. Measured Drawdown

List of Figures

Figure 1 Recharge Zones

Figure 2a Calibration Run Heads - Model Layer 1

Figure 2b Cahbration Run Heads - Model Layer 2

Figure 2c Calibration Run Heads - Model Layer 3

RMT, Inc. I Lemberger Superfund Sites i.\ivpMSN\piT\oo-o3449\42\Rooo344942-ooi.DOC 9/11/00 final September2000

Figure 3a Calibration Summary - Computed vs. Measured Heads

Figure 3b Calibration Residuals Histogram

Figure 4a Transient Drawdown vs. Time - WeU OW-IOIA

Figure 4b Transient Drawdown vs. Time - Well OW-IOIB

Figure 4c Transient Drawdown vs. Time - Well OW-103A

Figure 4d Transient Drawdown vs. Time - Well OW-103B

Figure 4e Transient Drawdown vs. Time - Wells OW-104A, OW-104D, OW-104E, and

OW-104G

Figure 4f Transient Drawdown vs. Time - Wells OW-IOID, OW-104F, and OW-104H

Figure 4g Transient Drawdown vs. Time - Wells OW-105A and OW-105B

Figure 5 Flow Model Sensitivity Test Results

Figure 6 Transport Model Sensitivity Test Results

Figure 7 Existing Groundwater Extraction System Capture Zone and TCE

Iso-Concentration Map

List of Attachments

Attachment 1 Model Input/ Output Electronic Files on CD

Attachment 2 Malcolm Pimie Modeling Report, Section 3.2

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Section 1 Introduction

This Addendum No. 1 of the June 1999 Groundwater Modeling Report and Plan for Recovery

System Enhancements at the Lemberger Superfund Sites (the Modeling Report) (RMT, 1999)

was prepared in response to a request in a letter from the United States Environmental

Protection Agency (USEPA), Region 5, dated 29 November 1999 for additional documentation

of the flow and transport model that was presented in the Modeling Report. Responses to the

written comments provided by the USEPA and the Wisconsin Department of Natural Resources

(WDNR) on the Modeling Report were presented in a letter from RMT (on behalf of the

Lemberger Site Remediation Group [SRG]) dated 6 April 2000, in which it was agreed that

additional documentation of the existing flow and transport model would be provided.

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Section 2 Modifications to the Malcolm Pirnie

Version of the Lemberger Groundwater Flow Model

The existing three-dimensional MODFLOW model constiucted for the site (Malcolm Pimie,

1998) was adopted for use in the contaminant tiansport modeling, as summarized in the

Modeling Report. Minor adjustments to the bedrock hydraulic conductivity array in the

Malcolm Pimie model were made to provide a more accurate representation of the head

distiibution west of the Lemberger Transport and Recycling (LTR) and Lemberger LandfiU (LL)

sites. The effect of these adjustments was to move the location of the computed 805-foot

elevation contour of computed heads to a position that more closely matches the contour of

measured heads, while leaving other areas in the model essentially unchanged. Figure A-1 in

Appendix A of the June 1999 Modeling Report presents the distiibution of hydrauUc

conductivity values across the model domain for the bedrock aquifer. Electionic data fUes that

contain all the model input files for the flow model and the tiansport model are presented on

the compact disk (CD) in Attachment 1.

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Section 3 Model Input Parameter Values

The model input parameter values, for both the flow and tiansport models, are presented in

Table 1.

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Section 4 Boundary Conditions

The boundary conditions of the model were not changed from those used in the Malcolm Pimie

version of the Lemberger model (Malcolm Pimie, 1998). The boundary conditions are

documented in the Malcolm Pimie report in Subsection 3.2, pages 3-3 and 3-4 (Attachment 2 of

this Addendum No. 1). The graphical representation of these boundary condition is contained

in the Visual Modflow data fUes in Attachment 1 of this Addendum.

The distiibution of recharge values across the site that were used in the model is presented on

Figure 1. A discussion of how the recharge values were assigned was included in the response-

to-comments letter issued by RMT on 6 April 2000.

RMT, Inc. 4 Lemberger Superfund Sites i.\i\PMSN\PiT\oo-o3449U2\Rooo344942-ooi.DOC 9/17/00 Final September 2000

Section 5 Flow Model Calibration Documentation

Contoured values of the cahbration run-computed hydraulic heads are presented on Figures 2a,

2b, and 2c. The computed heads in the calibrated flow model were compared with measured

head values for the period from April 1997 to December 1999, following the startup of the

groundwater extiaction and tieatment system in March 1997. This period was selected because

it provided a large number of measurements that spanned over 2.5 years over both wet and dry

seasons. Arithmetic mean head values for the multiple measurements were calculated for each

of 40 calibration points (monitoring wells), which were selected to cover the domain of the

model, to provide a representative set of calibration points.

Figure 3a is a graphical comparison of computed versus measured head values in the various

layers of the model and aquifer. Figure 3b presents a histogram of the calibration run residuals

of the computed versus measured head values.

A tabular surrm\ary of computed heads versus measured heads for the 40 cahbration points is

presented in Table 2. The root-mean-square (RMS) of the residuals between measured and

computed values is 1.2 feet. With a range of hydraulic heads across the model domain of over

20 feet, the residuals are sufficiently small, for a long period of measurements, to indicate that

the hydrogeologic conditions are represented accurately in the flow model. The output files for

the calibration rim (Lem 43) are presented in Attachment 1.

RMT, Inc. 5 Lemberger Superfund Sites I.\\vPMSN\PlT\oo-03449\42\Rooo344942-ooi.DOC 9/11/00 f inal September2000

Section 6 Transient Flow Simulation Results

Transient conditions caused by the onset of groundwater pumping were simulated using the

calibrated (low model, to test the abiUty of the flow model to simulate the tiansient response of

hydraulic heads to a stiess. Steady-state calibration of the model does not provide a unique

solution for the observed heads in the aquifer. Cahbration of the model to the tiansient stiess

on the aquifer caused by pumping helps to accurately simulate capture zones of existing

extiaction weUs and the future response of the aquifer to pumping.

A series of pumping tests that were conducted on the extiaction wells shortly after installation

were simulated. The pumping tests typically were run for approximately 24 hours, with

hydraulic head measurements conducted on nearby monitoring weUs. Previous evaluations

performed by Malcolm Pimie (1998) indicated that the model simulations of the tiansient

response of the aquifer to pumping of the extiaction wells resulted in computed heads that

were reasonably close to observed values. To confirm that the model was stUl able to reproduce

the pumping test results, following minor changes in the hydrauUc conductivity distribution

northwest of the LTR site, RMT conducted a tiansient simulation of the aquifer's response to

pumping. Because the flow model revisions made by RMT were relatively minor and mainly

involved an area distant from the extiaction wells, the effects of the revisions were not expected

to be significant for the tiansient simulation.

The tiansient simulation model results are presented in Table 3. Attachment 1 contains the data

files for the tiansient simulation, Lem 43b tmst. Figures 4a through 4g present the graphical

plots of computed drawdowns versus time in monitoring wells located near the extiaction

wells. The short-term response of an aquifer to pumping is oftentimes highly variable, and is

significantly affected by small-scale heterogeneities in the aquifer, since the distance between

pumping wells and monitoring wells is small. In some cases, weUs that were more distant

showed larger drawdown than closer wells, due to aquifer heterogeneities. Nonetheless, as

seen in Table 3, the model was able to provide a reasonable approximation of the aquifer's

response to pumping.

The RMS of the residuals between measured values and computed values is 0.13 foot.

Discrepancies between the model results and the measured values are caused by aquifer

heterogeneities, storage coefficient values, and variabiUty in the pumping rates during the tests.

Transient simulation results are extiemely sensitive to storage coefficients used; however,

extensive adjustment of storage coefficients was not considered justified, since the storage

RMT, Inc. 6 Lemberger Superfund Sites i:\ivpMSN\PiT\oo.03449\42\Rooo344942-ooi.Doc 9/11/00 final September2000

coefficient values have no effect on steady-state conditions that occur following the initial

startup period. In surrunary, the results of the tiansient simulation confirm the abiUty of the

model to simulate tiansient conditions satisfactorily, providing a further indication that the

model is calibrated accurately to site conditions.

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Section 7 Sensitivity Tests

7.1 Flow Model

Parameters selected for sensitivity testing for the flow model included hydraulic conductivity of

model Layer 2 (the Lower Granular Unit), the hydrauUc conductivity of model Layer 3 (the

bedrock), and precipitation recharge to the aquifer. Values of the hydraulic conductivity and

recharge that were used in the caUbrated flow model were both increased and decreased, by

factors of 2 and 4, to test for the effect of the change on hydraulic heads predicted by the model.

Using the same set of calibration points that were used in assessing the cahbration, the effect of

the sensitivity testing was evaluated by comparing the RMS of the difference between measured

and model-predicted head values, for each model run used in the sensitivity testing.

The results of the sensitivity tests for the flow model parameters are presented on Figure 5. The

(low model is highly sensitive to increasing the value of recharge. Doubling the rate of recharge

increased the predicted heads, and the resulting RMS error increased from 1.2 to 5 feet. The

model results were much less sensitive to increasing the hydrauUc conductivity of the bedrock

(model Layer 3) or the Lower Granular Unit (model Layer 2).

The model was quite sensitive to decreasing the hydraulic conductivity of the bedrock, such

that decreasing the hydrauUc conductivity to half the calibrated values resulted in an increase in

the RMS of from 1.2 to 2.6 feet. The model was less sensitive to decreases in recharge values,

and to decreases in the hydraulic conductivity of model Layer 2, the Lower Granular Unit. The

model is less sensitive to decreases in recharge values than to increases tn recharge, because as

recharge is lowered, the boundary nodes (constant head, general head, and river) serve to

supply water to the model and keep the heads in the aquifer from dropping too low, under the

relatively permeable conditions in this aquifer system.

7.2 Transport Model

Important variables that were tested for sensitivity in the tiansport model included source

concentiation, biodegradation rate, and dispersivity. Source concentiation values used in the

calibrated tiansport model were increased to two times and four times the original (calibrated)

values, for aU zones and for aU stiess periods. The decay rate half-life values were increased to

two and three times those of the caUbrated model. The longitudinal and tiansverse dispersivity

values were increased to two and four times those of the calibrated model. The resulting total

RA/IT, Inc. 8 Lemberger Superfund Sites i:\ivpMSN\PiT\oo-03449\42\Rooo344942-ooi.DOC 9/11/00 final September 2000

mass of contaminant in the aquifer (both sorbed and dissolved) was computed by the model

and used to evaluate the effect of the parameter value changes on the model results.

The results of the sensitivity testing for the tiansport model are shown on Figure 6. The most

sensitive parameter was source concentiation in the constant-concentiation source nodes, with a

nearly 1:1 correspondence between the source concentiation and the calculated total

contaminant mass in the aquifer. Doubling the source concentiation resulted in a doubling of

the mass of contaminant in the aquifer. Only slightly less sensitive was the rate of

biodegradation; doubUng the haU-Ufe of degradation increased the total mass in the aquifer by

approximately 1.8 times. In contiast, the total mass of contaminant in the aquifer was only

slightly sensitive to the dispersivity values.

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Section 8 Particle Tracking/Capture Zone Analysis

Particle tiacking was conducted to evaluate the tiavel paths of groundwater that is extiacted by

the existing extiaction weUs. The horizontal extent of the approximate groundwater extiaction

zone was then compared with the extent of contaminants above the groundwater cleanup goals

defined in the Record of Decision (ROD) for the site. Attachment 1 contains the input and

output files for the particle tiacking run, Lem 43 tik2. Figure 7 shows the approximate

estimated extent of groundwater that currently exceeds the cleanup goals, as well as the particle

path lines of groundwater that is removed by the existing extiaction well system, at current

pumping rates. As can be seen from Figure 7, the approximate extent of capture of the existing

extiaction weU system in some areas is less than the extent of groundwater contaminants that

exceed the cleanup goals for the site. The particle tiacking analysis substantiates the conclusion

presented in the Modeling Report that the existing groundwater extiaction system, as it

currently operates, does not capture the full extent of the affected groundwater at the site.

However, some caution should be used in interpreting these results. The particle tiacking

modeling routine has several notable deficiencies that make it less reliable than a groundwater

flow/contaminant tiansport model as an indicator of the effectiveness of a groundwater

extiaction system. First, the particle tiacking analysis does not account for dispersion of

contaminants as groundwater flows through heterogeneities that exist in any aquifer system.

Secondly, the particle tiacking routine does not tiack concentiation changes that occur along the

flow paths of the groundwater. InabUity to account for reactions in the groundwater makes the

particle tiacking/capture zone analysis results overly conservative, i.e., the particle tiacking

tends to underestimate the ability of the existing extiaction well system to reduce the extent of

the groundwater contaminant plume over time.

In contiast to the particle tiacking model results, the groundwater flow/contaminant tiansport

model has been calibrated to both flow and concentiations, and is a more accurate predictor of

the future effectiveness of the groundwater extiaction system. The predicted 0.5 M-g/L contour

of TCE concentiations in the aquifer 15 years after the startup of the two proposed additional

extiaction weUs is also shown on Figure 7. This predicted location of the 0.5 |ig/L contour, and

the contiaction of the size of the plume from its current extent to the predicted extent 15 years

after startup of the enhanced groundwater extiaction system, would be caused by the combmed

effects of groundwater extiaction and biodegradation of contaminants in the aquifer. As

discussed in the Modelmg Report, the model predictions of the future extent of the plume are

relatively conservative, because they assume that the highest concentiations at the source

RMT, Inc. 10 Lemberger Superfund Sites i:\wpMSN\PiT\oo-03449\42\ROoo344942-ooi.DOC 9/11/00 f inal September2000

would remain constant over time. It is likely that the source area concentiations will actuaUy

decrease over time as the benefits of the landfill source contiol measures gradually show their

effects.

RMT, Inc. 11 Lemberger Superfund Sites i:\ivPMSN\piT\oo-03449\42\Rooo344942-oohDOC 9/11/00 final September 2000

Section 9 Conclusions and Recommendations

The model results and documentation that are presented in this addendum lead to the

following conclusions:

• The flow model is able to represent tiansient conditions (the short-term response of the aquifer to initiation of pumping) reasonably well.

• The cahbration of the model to steady-state pumping of the aquifer indicates that the flow model represents groundwater conditions in the aquifer reasonably well.

• The flow model results are most sensitive to increasing values of recharge and decreasing hydraulic conductivity in the bedrock.

• The tiansport model is most sensitive to the value of source concentiation, and to a lesser degree, biodegradation rate.

• Particle tiacking analysis indicates that the capture zone for the groimdwater extiaction well system is, in some areas, less than the extent of the groundwater contaminants that exceed cleanup goals for the site.

• The tiansport model is able to more accurately predict the future effectiveness of the groundwater extiaction system than the capture zone modeL because the tiansport model incorporates the effects of dispersion and biodegradation, and it is caUbrated to actual concentiations of contaminants in the aquifer, in addition to hydraulic heads.

• The tiansport model results indicate that the proposed addition of two new extiaction weUs to the existing extiaction well system will result tn steadily decreasing concentrations in the aquifer over time, and a substantiaUy reduced contaminant plume within 15 years.

The results and conclusions presented here, and in the Modeling Report, lead to the foUowing

recommendations:

• InstaU two additional groundwater extiaction wells (EW-6 and EW-7) into the bedrock aquifer near the "source" areas, where concentiations are highest, at the locations described tn the Modeling Report.

• Constiuct the two new extiaction wells, associated piping, and electiical supply and contiols, and modify the tieatment system to the specifications indicated in the Modeling Report.

• Modify the existing extiaction well system operations by turning off EW-51 (which extiacts groundwater mainly from the adjacent river), and decreasing the pumping rate of EW-2D from 50 gpm to 25 gpm, as recommended in the Modeling Report (RMT, 1999).

RMT, Inc. 1 2 Lemberger Superfiind Sites /.\IVPMSN\P;T\OO-03449\42\ROOO344942-OOI.DOC 9/11/00 final September 2000

Section 10 References

Malcolm Pimie. 1998. Lemberger Superfund Sites, remedial action modeling report, Lemberger LandfiU RD/RA, Operable Unit 1. October 1998.

RMT, Inc. 1999. Groundwater modeling report and plan for recovery system enhancements at the Lemberger Superfund Sites. June 1999.

'^MT, Inc. 13 Lemberger Superfund Sites i:\\,vPM5N\PiT\oo.o3449)42\ROD0344942-ooi.Doc 9/11/00 f ina l September2000

03 r-m CO

Table 1 Model Parameter Values

Horizontal hydraulic conductivity

Recharge

Kx/Ky

Kx/K.

Specific storage (Ss)

Specific yield (SY)

Longitudinal dispersivity

Transverse horizontal dispersivity

Transverse vertical dispersivity

Effective porosity

Chemical decay rate (haU-life)

Source concentiation:

Retardation coefficient

Layer 1 Layer 2

Layer 3

4 tn/yr to 14

= 1.0

= 0.1

= 0.0002

= 0.2

= 50 ft

= 0.5 ft

= 0.01 ft

Layer 1 Layer 2

Layer 3

in/yr

2 to 10 yrs., infinite

0.28 ft/d 4.5 to 450 ft/d

0.5 to 229 ft/d

0.4 0.25

0.1

= 19to200)ig/LTCE (see Table B-1 in Appendix B of Modeling Report)

= 0

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Lemberger Superfiind Sites Final September 2000

Calibration Summary Table 2 Computed vs. Measured Heads

MONITORING WELL

RM-11 RM-ID OW-104F RM-203D OW-104H OW-103B RM-210I OW-103A RM-IOD RM-210D RM-204D RM-103D RM-5I RM-5D RM-208D RM-4D RM-3D RM-208I OW-102A OW-102B OW-102D OW-102C RM-211D RM-202I RM-202D OM-105A OM-105B OW-IOIA RM-201I RM-205D RM-205I RM-IOID RM-IOII RM-201D RM-8D RM-7XD RM-306D RM-308D RM-303D RM-305D

MEASURED HEAD (ft)

790.7 790.7 791.2 791.0 792.1 793.6 794.6 793.5 795.0 795.2 797.7 799.3 799.4 800.5 800.8 800.6 801.3 801.5 801.8 801.8 801.9 802.0 801.8 802.9 802.9 804.3 804.3 804.6 804.6 804.7 804.7 804.8 804.9 804.5 805.8 806.3 807.6 807.9 808.6 808.2

COMPUTED HEAD (ft)

792.7 791.5 793.3 792.2 793.3 793.6 794.7 794.0 795.8 794.7 798.7 801.0 801.2 801.3 802.4 801.4 802.4 802.4 802.7 802.8 801.4 802.7 801.5 801.6 800.4 804.7 804.9 806.9 804.7 805.6 806.8 805.8 806.8 805.1 806.9 807.0 808.6 809.0 809.2 810.2

Mean Residual = 0.8 ft Mean Absolute Residual = 1.0 ft Root-Mean-Square = 1.2 ft

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Lemberger Superfund Sites final September 2000

Table 3 Transient Simulation Simimary - Predicted vs. Measured Drawdown

EXTRACnON WELL

EW-ID

EW-3D

EW-4I

EW-4D

EW-51

MONirORING WELL

OW-IOIA

OW-IOIB

OW-103A

OW-103B

OW-104A

OW-104D

OW-104E

OW-104G

OW-104D

OW-104F

OW-104H

OW-105A

OW-105B

TIME (days)

1

1

1

1

0.8

0.8

0.8

0.8

1

1

1

0.2

0.2

MEASURED DRAWDOWN

(ft)

0.32

0.54

0.27

0.28

0.12

0.12

0.12

0.12

0.26

0.3

0.23

0.25

0.34

PREDICTED DRAWDOWN

(ft)

0.1

0.1

0.26

0.26

0.05

0.05

0.07

0.05

0.11

0.22

0.17

0.31

0.21

RESIDUAL (ft)

0.22

0.44

0.01

0.02

0.07

0.07

0.05

0.07

0.15

0.08

0.06

-0.06

0.13

Mean Residual = 0.10 ft

Root-Mean-Square = 0.10 ft

Results are from model runs Lem 43 tmst and Lem 43b tmst.

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Lemberger Superfiind Sites final September 2000

O

c m 03

4 in./yr.

3000 6 0 0 0 9 0 0 0 I

1 2 0 0 0 I

1 5 0 0 0 I

1 8 0 0 0 2 3 2 6 0

R M T , I n c . P r o j e c t : L e m b e r g e r D e s c r i p t i o n : I e m 4 r 3 M o d e l l e r : M B G 1 5 J i a n OO

R e c h a r g e Z o n e s

V i s u a l M O D F L O W v .S .B .2 , (C) 1 9 9 5 — 1 9 9 9 W a t e r l o o H y d r o g e o l o g i c , I n c . N C : 9 0 N R : I I D NL: 3 C x a r r e n t L a y e r : 3

Figure 1 Recharge Zones

3000 9000 12000 150D0 IBOOO

RMT, Inc. P r o j e c t : L e m b e r g e r D e s c r i p t i o n : l e m 4 3 M o d e l l e r : MBG 2 5 M a y OO

C a l i b r a t i o n H e a d s

V i s u a l MODFLOW v.S.B.a. (C) 1 9 9 5 -W a t e r l o o H y d r o g e o l o g i c , I n c . NC: 9 0 NR: l l O NL: 3 C u . r r e n . t L a y e r : 1

1 9 9 9

Figure 2a Calibration Run Heads Model Layer 1

3000 12000

RMT, I n c . P r o j e c t : L e m . b e r g e r D e s c r i p t i o n : l e m 4 7 3 M o d e l l e r : MBG 2 5 M a y OO

C a l i b r a t i o n H e a d s

V i s u a l MODFLOW v.3 .8 .3 , (C) 1995—1999 W a t e r l o o H y d r o g e o l o g i c , I n c . NC: 9 0 NR: l l O NL: 3 C u r r e n t L a y e r : 2

Figure 2b Calibration Run Heads Model Layer 2

i

J ]

]

]

1 ]

J

]

1

3000 6000 12000 20461

RMT, Inc. P r o j e c t : L e n n b e r g e r D e s c r i p t i o n : l e m 4 3 M o d e l l e r : MBG 2 5 M a y OO

C a l i b r a t i o n H e a d s

V i s u a l MODFLOW v.2.8.2, (C) 1995—1999 W a t e r l o o H y d r o g e o l o g i c , I n c . NC: 9 0 N i t l l O NL: 3 C u r r e n t L a y e r : 3

Figure 2c Calibration Run Heads Model Layer 3

CilcuMtd vs. Otetrvtd HMMIS : SlMMly «lilft ® Extrapolated {Head] • Interpolated [Head] 95% confldence Interval

790.3 800.3 Obs. Heads (ft)

810.3

Num.Points: 40 Mean Error: 0.7875711 (ft)

Mean Absolute: 1.040532 (ft) Standard Error of the Estimate : 0.1485722 (ft)

Root mean squared : 1.217022 (ft) Normalized RMS : 6.799006 ( % )

Figure 3a Calibration Summary Computed vs Observed Heads

E (0 k .

o> o *• (0 X tf) CO 3 •o "(5 o o : c _o (Q k .

13

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/gm y T

y ^ y"^

in ~fsi

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in

in

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1 i 1 1 . 1 1 1 1 1 1

01 9 0

. 1^ i n

c t; o P c h-E 9 ' = i[

>..» § " Q ra Si ra -* g- g S g s « u. Z 5 B •

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Figure 3b Calibration Residuals Histogram

Figure 4a Transient Drawdown vs Time (OW-IOIA)

Drawdown vs. Time

Figure 4b Transient Drawdown vs Time (OW-IOIB)

Drawdown vs. Time

;:'6w-103WOW-1 raiwiDrawdownS

Time (dy) 0.83

Figure 4c Transient Drawdown vs Time (OW-103A)

Drawdown vs. Time

OW-103B/Polnt #1 /Drawdown

ro

d

Eo

1 E o

to CO

o d_

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Figure 4d Transient Drawdown vs Time {OW-103B)

Drawdown vs. Time

OW-104A/Point #1 /Drawdown

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Figure 4e Transient Drawdown vs Time (OW-104A,D,E,G)

Drawdown vs. Time

OW-104D/Point #1/Drawdown

OW-104H/Point #1 /Drawdown

OW-104F/OW-104F/Drawdown

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Figure 4f Transient Drawdown vs Time (OW-104D,F,H)

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Figure 4g Transient Drawdown vs Time (OW-105A,B)

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Electronic Files on CD

RMT, Inc. Lemberger Superfiind Sites i:\wPM5N\PiT\oo-03449\42\Rooo344942-ooi.DOC 09/11/00 final September 2000

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Attachment 2 Malcolm Pirnie Modeling Report,

Section 3.2

RMT, Inc. I:\IVPMSN\PIT\00-03449\42\R000344942-001.DOC 09/1 I/DO

Lemberger Superfiind Sites Final September 2000

bedrock aquifer between March and July, 1997. This map shows the groundwater divide

occurring south and east of the LTR site.

Groundwater movement within the model domain is dictated by the properties of the

three hydrogeologic units including hydraulic conductivity, the top and bottom elevations

of each unit, vertical hydraulic conductivity of each unit and spatial relation to recharge areas

and discharge boundaries.

3.2 Model Set Up

MODFLOW was used to simulate the groundwater system. MODFLOW considers

aquifer thickness, hydraulic conductivity, vertical conductance, boundary conditions and

aquifer stresses to predict hydraulic heads, and simulate the velocity and direction of

groundwater movement in three dimensions. The model area was descritized into three

layers representing the three geologic units, with 90 north-south columns and 110 east-west

rows, encompassing an area approximately 4.2 miles east-west and 3.8 miles north-south.

The columns and rows were of variable width to allow greater resolution in the areas of the

extraction wells to facilitate transient simulation of the pumping tests. Figure 3-2 shows the

model grid.

Figures 3-3 through 3-5 show the bottom elevations and areal distribution of Layers

1,2, and 3 (representing the CU, LGU and bedrock respectively). Because dry stratum exist

between the UGU and the LGU where the UGU is saturated, the UGU was not modeled.

Layer tops and bottoms were based on well and boring logs from the study area and were

generalized outside of the study area. Figures 3-6 and 3-7 show the top elevations of Layers

2 and 3. Layer 1 was simulated as an unconfined layer, so top elevations were not assigned

to it. Both Layers 2 and 3 were simulated as convertible layers, meaning that they can

simulate both flow under confined and unconfined conditions.

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Figures 3-8, 3-9, and 3-10 show the hydraulic conductivities used for each layer.

Layer 1 had a uniform hydraulic conductivity of 0.028 feet per day which is consistent with

its fine grained nature. Layer 2 had two distinct hydraulic conductivities, 283 feet per day

in the study area based on pumping tests in EW-4I and EW-51, and 5 feet per day in the

eastern half of the model outside of the existing data (based on well logs indicating a

presence of thick till east of the bedrock ridge). Layer 3 had hydraulic conductivities that

ranged from 0.5 feet per day to 283 feet per day based on pumping test results and packer test

results away from the pumping wells. It should be noted that the hydranlir: conductiviii*"-

used in this model (based on pumping test results) are significantly different than those used

in the previous models which were based on slug tests and packer tests. Table 3-1 shows

some of the discrepancies between the previously used values and the value: used in the

revised model.

Vertical hydraulic conductances were calculated based on a I to 10 relationship to

horizontal conductance. MODFLOW uses a vertical conductance value VCONT which is

calculated considering half the thickness of the overlying layer and half the thickness of the

underlying layer and the vertical conductance values of both layers. VCONT was assigned

in the model through the use of a grid calculator considering one tenth the hydraulic

conductivities and half the thickness of each layer.

Data concerning the boundary conditions, especially flow to and under the Branch

River was not available for this modeling effort. The effects of stream bed conductance

values on the model were assumed to be limited and the river was simulated using constant

head cells. Because the flow to the river is a "soft" boundary which may be overcome by

sufficient pumping, flow beneath the river was simulated using general heads boundaries.

General heads boimdaries act similarly to constant head cells, but contain a conductance

value which limits the amount of water which they can contribute to the model (constant

head cells can contribute an unlimited amount of water to the model). Constant head cells

and general head cells were also used to simulate boundaries where the surface water bodies

other than the Branch River exist (east, west, and north flowing streams). However, river

cells were used to simulate the upper reaches of the streams in the south central and south

P:\2049027\report\reportf.wpd 3-3

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eastern boundary of the model. It was found that constant heads at these locations

contributed more water than was explainable by the conceptual model. River cells were used

rather than general head boundaries so that the groundwater flow to and from these

boundaries could be easily segregated from other boundary conditions. Iterative analyses

of the river bottom conductance were conducted until the heads in these areas matched with

the conceptualized flow (these areas are outside of the existing data). No-flow boundaries

were used at the remaining model boundaries where no surface water bodies exist and

groundwatei- flow was not expected across the boundary. Figures 3-11,3-12 and 3-13 show

the locations of constant head, general head, and river cells.

Recharge applied to the model was estimated based on historical precipitation and

estimates of surface water run off and evapo-transpiration. The average precipitation in

Manitowoc Coimty is approximately 28 inches per year. Assuming a large amount of that

precipitation becomes either overland flow or is removed from the model domain, it is

reasonable to assume about that 15 percent becomes recharge. Therefore a recharge value

for the majority of the model was assigned 0.0009 feet per day (4 inches per year). Because

it is assumed that recharge is increased along the bedrock spine due to the lack of the low

hydraulic conductivity CU unit, this area was given a recharge rate of 0.003 feet per day

(approximately 14 inches per year). This recharge value was derived during calibration to

steady state heads and was necessary to achieve the observed groundwater divide. These

values of recharge are in agreement with published values for central Wisconsin (McGuiness,

USGS Water Supply Paper 1800, Plate 1 and Williams and others, USGS Water Supply

Paper 846, Plates 1 and 2).

3.3 Steady State Calibration

Once the model was set up, steady state simulations were conducted to produce

steady state heads for comparison to the mean heads from water levels measured between

March and July 1997 under the current pumping conditions. Figures 3-14, 3-15, and 3-16

show the model predicted heads in layers 1, 2, and 3. Typically, steady state heads are not

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