ML19347A860

Preliminary Review,Soil Parameters Used in USGS Rept 78-138,Effects of Seepage from Fly-Ash Settling Ponds & Const Dewatering on Groundwater Levels in Cowles Unit,In Dunes Natl Lakeshore,In.

ML19347A860
Person / Time
Site:	Bailly
Issue date:	05/31/1980
From:	NORTHERN INDIANA PUBLIC SERVICE CO.
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ML19347A859	List: ML19347A858 ML19347A860
References
MW79-720, NUDOCS 8009300421
Download: ML19347A860 (34)

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I Preliminary Review II I Soil Parameters Used in USGS Report 78-138

' Effects of Seepage From Fly-Ash Settling Ponds & Construction Dewatering on Ground-Water Levels in the Cowles Unit, Indiana I Dunes National Lakeshore, Indiana' I

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l TABLE OF CONTENTS l 1

4 ll PAGE il LIST OF FIGURES 11

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1.0 INTRODUCTION

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il 2.0 GENERAL SITE CONDITIONS 3 l

e 3.0 CONFINING LAYER (UNIT 2) 7 l

4.0 PERMEABILITIES AND PUMPING TESTS 12 I i

j 5.0 GROUNDWATER LEVELS 17 l i

6.0 INFLUENCE OF NIPSCO'S PRESSURE RELIEF [

SYSTEM ON GROUNDWATER LEVELS AT COWLES BOG 18 '

7.0 CONCLUSION

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LIST OF REFERENCES I

FIGURES

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LIST OF FIGURES FIGURE NO. DRAWING NO. TITLE 1 MW79-720E4 Elevation of the Surface of Unit 2, Bailly Generating Station Nuclear 1.

2* MW79-720E5 Thickness of Unit 2, Bailly Generating Station Nuclear 1. )

3* MW79-720E6 Generalized Soil Profile A-A, Bailly Generating Station Nuclear 1.

4* MW79-720E7 Generalized Soil Profile B-B Bailly Generating Station Nuclear 1.

I 5* MW79-720E8 Generalized Soil Profile C-C Bailly Generating Station Nuclear 1.

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6 MW79-720Al Elevation of the Surface of Unit 2 and Saturated Thickness of Unit 1 in Area of BSCO

, East Office.

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• Overlay attached I n3 w r o n o m a

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1.0 INTRODUCTION

Northern Indiana Public Service Company (NIPSCO) retained D'Appolonia Consulting Engineers, Inc. (D'Appolonia) to review the soil parameters used in USGS Report 78-138 by Meyer and Tucci (1979) (Reference 1) prepared for the National Park Service (NPS).

D'Appolonia has been involved as a geotechnical consultant in the Indiana dunes area since 1959 at the site of Midwest Steel Company, since 1963 at the site of Bethlehem Steel Corporation (BSCO) and since 1966 at the site of the Port cf Indiana. A part of D'Appolonia's respouaibility was large scale subsurface investigations and dewatering using deepwell and wellpoint systems.

Reference 1 summarizes a two year study of soil and groundwater conditions within a study area located north of U.S. 12, between the Port of Indiana I and Mineral Springs Road in Porter County, Indiana.

shown in Figure 1.

The study area is A portion of the Indiana Dunes National Lakeshore (IDNL) is adjacent to NIPSCO's Bailly Generating Station where a nuclear powered unit ic under construction. The' principal objective of the USGS study was to determine the effects of construction dewatering on the groundwater levels within 1DNL. A digital model of the groundwater regime was constructed by USGS for this purpose. The finite-difference model (Trescott 1975) was used to simulate and predict changes of groundwater flow in three dimensions throughout the study area.

At a meeting on January 31, 1980 NPS informed NIPSCO that USGS, using the model, had predicted groundwater changes from NIPSCO's pressure I relief system up to 0.5 feet at Cowles Bog.- That prediction is grossly inconsistent with observed data in the area, and accordingly, D'Appolonia undertook a study of the input data used by USGS.

This report is a preliminary review of the soil parameters used in Reference 1 and is limited to permeabilities and layering in Unit 1 WkY Obs0NNA

2 I (unconfined aquifer), Unit 2 (confining layer) and Unit 3 (confined aquifer).

This review is based upon a large body of data, including pump tests and observations during construction over a period extending from 1959 to the present.

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3 2.0 GENERAL SITE CONDITIONS I The study area consists principally of land owned by BSCO, NIPSCO and NPS. Throughout the BSCO site (Burns Harbor Plant) over 800 borings were drilled, five of which were drilled within IDNL. These five borings are shown in the overlay of Figure 2. These were drilled when BSCO was the owner of the land in the area of the borings. Within the study area over 400 observation wells and over 70 dewatering wells were installed.

Over 120 soil borings were drilled on the NIPSCO property (Beilly Gener-ating Station). In addition to these, numerous borings were drilled l along NIPSCO's transmission tower lines. Some of these bsrings were shallow and augered. I Although USGS installed over 30 observation wells within IDNL, adjacent I to Bailly N-1, soil sampling was conducted in only one of these. The remaining were either driven or installed by jetting.

In Reference 1 the soils are divided into four units. The following descriptions of these units are extracted from Reference 1.

I Unit 1, unconfined aquifer, consists primarily of fine sand with lateral hydraulic conductivity of 167 ft/ day.

The saturated thickness ranges from 0 to 35 feet. l l

Unit 2, confining layer, consists chiefly of clay with a thickness ranging from 0 to 80 feet.

l Unit 3, confined aquifer, consists chiefly of fine to medium sand with lateral hydraulic conductivity equal to that of Unit 1. The thickness of the unit ranges from 0 to 80 feet.

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I 4 I Unit 4, primarily silt and clay with a thickness i

ranging from 60 to 140 feet. The characteristics of Unit 4 are not considered in this review.

I Reference 1 describes the study area as approximately 80% industrialized land and 20% national lakeshore. Surficial physical features include the interdunal ponds (Pond Nos. 1, 2, 3 and 7), the fly-ash settling )

ponds (Pond Nos. 10, 11, 12 and 13) and the Great Marsh which contains )

I an area known as Cowles Bog, designated as a National Landmark. Reference 1 states that there are some questions as to the exact location of the bog.

Figure 1 is a plan of the study area showing the location of Bailly j Generating Station Nuclear 1 (Bailly N-1), the Burns Harbor Plant (BSCO),

the ponds and Cowles Bog.

Relying upon numerous borings, pumping tests and knowledge gained through experience in the area, soil conditions and layering can be well defined at the BSCO and NIPSCO sites. This is not true for the IDNL portion of of the study area since logs of only five borings and one water supply well (W1) are available for analysis. However, they are sufficient to underline the contradictions in the data between Reference 1 and these logs.

I D'Appolonia's review of the available data indicates that the water-bearing soils within the study area should not be modeled as two aquifers (unconfined and confined) separated by a pra.:tically impervious layer.

I Generally there is one aquifer partly unconfined and partly confined because the confining layer is discontinuous and thus absent in many locations. The sands of Unit 3 are directly connected through many large openings in the confining layer (Unit 2) to the sands of Unit 1 and to Lake Michigan as a line source. A detailed description of the confining layer is presented in the next section. The sands of Units 1 and 3 are basically fine sands (sometimes fine to medium) with the same permeabilities.

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During our review several discrepancies were discovered between the actual conditions and the conditions presented in Reference 1 relating to BSCO dewatering wells. The following are discrepancies which would have significant effects on the model construction, calibration and estimated permeabilities and consequently the reliability of predicted water levels.

1. USGS states that five wells are in operation, three of which are screened only in Unit 3.

The actual condition is that all dewatering wells at that time were installed to the full depth of Unit 3 and were fully gravel packed through Units 1, 2 and 3 creating the f'ollowing conditions during operation.

I a. Where the confining layer is absent the well operates in a partial gravity aquifer, not in a confined aquifer as the wells were apparently modeled in Reference 1.

b. Where the confining layer is present, the aquifers must be analyzed as gravity above and'artesian-gravity below the confining layer.

I c. During operation all dewatering wells are withdrawing water from "both" aquifers.

I Because the wells are fully gravel packed, they cannot be considered to be operating in only one aquifer.

2. It is reported that the water levels during pumping are maintained within a few feet of the top of the I HDMPOLOMA

I 6 I well screen (some screens are 40 feet long). Actually, water 1cvels were kept at the lowest possible level to achieve maximum drawdowns and in most cases were held within 3 to 5 feet of the bottom of the well.

All these differences reduce the reliability of model predictions and item (2) alone introduces serious error.

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E 3.0 CONFINING LAYER (UNIT 2)

Reference 1 reports Unit 2 as a contineous relatively impervious layer sloping to the north-northwest. USGS shows Unit 2 to be absent only at the south end of the study area and at a very small area southeast of Bailly N-1. The elevation of the surface of Unit 2 and areas where it is absent, as presented in Reference 1, are shown on Figure 1 which is an enlargement of Figure 8 from Reference 1. Figure 2 is an enlargement of Figure 7 from 9eference 1 showing the thickness of Unit 2 and the two areas where Unit 2 is absent. The overlay on Figure 2 was constructed I by D'Appolonia using all the available data useful in defining Units 2 and 3. Based on our rnview of the data, Unit 2 is neither continuous nor uniformly sloping as presented in Reference 1.

Unit 2 consists of two layers, organic silt and silty cley, separated in plan and elevation. The organic silt, where present, acts as a partial confining layer throughout the southern portions of the NIPSCO and BSCO sites. At the north end of both sites, the layers of silty clay are present and stretch " finger-like" from the north (where they are part of the silty clay matrix) towara the south, disappearing into fine sand.

The southern limit of these silty clay layers (" fingers") is shown in the overlay of Figure 2 as glacial-lacustrine clay. The typica: shape and orientation of the silty clay and organic silt layers are shown in Figures 1 and 4. The fine sand layers between the " fingers" locally may act as confined aquifers under pumping conditions or during some seasonal changes. Groundwater levels in the sand layers are the same under static water conditions. It is also evident that the approximate north I

limit of Unit 3 as shown on the overlay of Figure 2 is much different from the one presented in Reference 1.

The layers of organic silt (upper confining layer) are found at higher elevations than the clay layers (lower confining layer) located along the lake shore. These are not the same layers and can be distinguished on the basis of composition. Although the composition of the lower I

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• I confining layer varies slightly between borings, it can be characterized as silty clay or claycy silt (occasionally silt). In contrast, the upper confining layer is an organic silt or calcareous clayey silt containing numerous shell fragments and some organic material. Differ-er.ces in depositional environments account for the compositional differences.

The lower confining layer was deposited first under glacial-lacustrine conditions whereas the upper confining layer was deposited later in a marsh-like environment, possibly similar to the interdunal conditions that existed before industrial development of the BSCO and NIPSCO sites.

The sequence of deposition and different composition of the upper and lower confining layers is additional information to confirm that Unit 2 is composed of two layers separated in plan and elevation.

Based on our knowledge of the Port of Indiana, Midwest Steel and BSCO sites we can conclude that the layering and discontinuity of Unit 2 is.

valid for the areas weat of the NIPSCO site and from the information

, available is indicated to be valid for the areas to the east through the IDNL area along the lake shoreline.

I Reference 1 (p. 14) states: "The foundations of the buildings (BSCO) extend to an average depth of 20 feet below the (ground) surface, causing Unit 1 to be thinner below the buildings. Some of the founda-tions extend below the top of Unit 2 and interrupt the continuity of Unit 1."

In fact, the majority of the building foundations at the BSCO plant are six to seven feet below ground surface placing them above the static I groundwater table. Same of the footings for buildings and equipment are 20 or more feet deep. Unit 2 (organic silt) has been removed beneath practically all deep foutings to avoid excessive settlement und to I improve the draining of perched water above Unit 2 during dewatering.

In many areas, during construction dewatering, Unit 2 (organic silt) was removed or perforated with a system of sand drains to induce vertical drainage. The areas in which Unit 2 was removed or perforated are shown on the overlay of Figure 2.

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The data clearly shows that the organic silt (upper confining layer) is not continuous. It is either absent or perforated over a significant portion of the study area.

I A review of the bo';ings along the NIPSCO transmission tower line revealed some discrepancies between the actual ccaditions of the confining layer and conditions assumed in Reference 1. As shown on the overlay of Figure 2, the Unit 2 layer appears to be absent In some areas east of the fly-ash settling ponds and in the vicinity of the Dune Acres Substation and U.S.

12. The top of the confining layer south of the t.ubstation occurs at approximately elevation 581 in the tower borings. Figure 8 in Reference 1 shows the top of the confining layer in this area at approximately elevation 623. Ground surface elevations in this area are approximately 613. Accordingly, Reference 1 assumes the top of the confining layer to be about 10 feet above the real ground surface. Obviously the assumption is invalid.

To better illustrate the actual conditions within the study area as opposed to those reported in Referenca 1, three generalized soil profiles have been constructed, the locations of which are shown in Figures 1 and 2.

1. Generalized Soil Profile A-A is located along the west boundary of the study area. Using data from 12 borings in which detailed samples were secured, the profile is constructed and presented as " actual conditions" in Figure 3. The overlay of Figure 3 shows the condition reported in Reference 1. A comparison I yields the following:

. Unit 2 virtually does not exist as a confining layer.

. Unit 3 is fully connected to the sand above Unit 2 and to Lake Michigan as a line source.

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. Unit 3 has a much different thickness, shape and extension than presented in Reference 1.

. The organic silt layer is about 20 feet higher than the clay layers and it is not connected to the clay layers toward the north.

2. Generalized Soil Profile B-B is located along the north-south property line between NIPSCO and BSCO. Nineteen borings were used to construct this profile which is shown in Figure 4. The overlay shows the data reported in Reference 1. A comparison of these profiles yields the following:

. Unit 2 does not exist as a continuous layer.

. Unit 2 is absent throughout a large portion of the profile.

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. Unit 3 is directly connected through large openings to the sand above Unit 2 and to Lake Michigan.

. The organic silt layers are about 20 feet higher than the clay layer.

. The organic silt layers are reasonably horizontal and not uniformly sloping as presented in Reference 1.

3. Generalized Soil Profile C-C is located along the east boundary of the study area (Mineral Springs Road).

Only two borings and a water supply well log of the l Town of Dune Acres are available along this profile. l This information was insufficient to construct the profile along a distance of over 5,000 feet. Infor-mation from the logs is shown in Figure 5 with the l

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11 overlay showing the assumed subsurface conditions reported in Reference 1. From Figure 5 and the overlay it can be seen that:

. The thickness of Unit 2 is substantially different from that reported.

. The elevation of the top of Unit 2 is different from that reported at the south end (Boring 709).

. Unit 3 is altogether different from that reported.

Profiles A-A and B-B are typical in the north-south direction throughout the BSCO and NIPSCO sites.

I A review of Borings 706, 709, 712 and 715 (see overlay, Figure 2) shows that the top of Unit 2 is essentially flat in the area around Cowles Bog, and does not slope as reported in Reference 1. This data indicates that discrepancies between actual and assumed c9nditions exist in the area of IDNL but, lacking additional data, a better definition of the differences is not possible.

Based on our review of the data relative to the confining layer, we believe there ara sufficient differences between actual and assumed subsurface lithology that the model cannot be relied upon to produce satisfactory pred*.ctions of groundwater variations at Cowles Bog due to pumping at Bailly N-1.

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[ 4.0 PERMEABILITIES AND PUMPING TESTS

[ For convenience we have extracted pertinent quotes from Reference 1 relative to permeabilities (hydraulic conductivity).

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Lateral hydraulic-conductivity values for unit I were calculated from specific-capacity d.ata for four large-( diameter industrial wells in the study area. The specific-capacities were first converted to transmis-sivities for the individual screened interval of each

[ well by the nonsteady technique for unconfined aquifers (Theis, 1963). The value of the screened-interval transmissivity thus obtained was divided by the screen length of the well to obtain the hydraulic conductivity.

[ Meyer and others (1975, P.17-21) have explained this technique and the assumptions inherent in it. Ilydraulic-conductivity values for each of the wells in unit 1 sere

( averaged to obtain an average lateral hydraulic conducti-vity of 167 ft/ day for unit 1. This value is at the upper end of the range of lateral hydraulic-conductivity values

[ reported for this unit in Porter and LaPorte Counties by Rosenshein and Hunn (1968).

A determination of hydraulic conductivity by the procedure

[ used for unit 1 was attempted for unit 3, by using specific-capacity data for large industrial wells constructed in unit 1 and the nonsteady techniques for confined aquifers

{ by Brown (1963). Analysis of the data was complicated because breaching of the confining layer by the gravel '

pack around each well permitted vertical movement of water from unit 1 to unit 3 during pumping. This condition would tend to cause the hydraulic-conductivity values for unit 3 to be too large. Correction of the data for this violation of one of the necessary conditions for using

[ the preceding techniques was not possible. Because the two units are similar lithologically, generally consisting of fine to medium sand, and because, as reported by Rosen-( shein and Hunn (1968), the lateral hydraulic conductivities of the two units are similar, a value of lateral hydraulic conductivity equal to that of unit I was assumed for unit 3.

Following is a quote from page 18 of USGS Report 75-312 by Meyer and others (Reference 4) relative to the technique used to calculate permeability.

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The specific capacities of the wells in each group were converted to transmissivity values for the individual screened intervals using the non-steady technique for unconfined aquifers givea by Theis (1963). This method makes use of the relation:

T' = Q/s (K - 264 log SS + 264 log t) where Q is the well discharge, in gallons per minute; j s is the drawdown in the well after pumping for time t in days; S is the aquifer specific yield, dimensionless; and T' is a value related to transmissivity by means of a graph given by Theis (1963, p. 334). K is a constant for a given well of radius, r, which, for an unconfined aquifer, is given by the relationship:

K = 264 log (3.74r2x 10 6)

The value of T' was converted to transmissivity, T, for the screened interval using a graph presented by Theis. The value of screened-interval transmissivity thus obtained was divided by the screen length of the well to obtain the hydraulic conductivity.

The industrial wells referenced were not in any case isolated in only Unit 1. Accordingly, the technique described for determining permeability is not applicable. That is perhaps the reason that Reference 1 obtains permeability data inconsistent with that obtained by other methods. The principal features that are not accounted for in the USGS analysis are summarized below.

. All dewatering wells at that time were installed through Unit 1 and Unit 2 (if present) into Unit 3.

. All wells are gravel yacked to the depth of the well.

. It is not possible to develop a reasonable estimate of the portion of the well discharge coming fcom Unit 1 for a well gravel packed through the depth of three units and pumping water at the same time from Unit 1 and Unit 3.

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. It is not possible to develop a reasonable estimate of the portion of drawdown in a well caused by pumping from Unit I when the well is pumping water from Units 1 and 3 at the same time.

. Specific-capacities reported on well logs are excessive because they are based on short-duration i tests.

It should be noted that the calculated average permeability of 167 ft/ day (589 x 10 ~4 cm/sec) was used in the USGS model for Units 1 and 3.

This value was used as the average knowing that it is the extreme upper value of the range reported by others for the same sands. Although BSCO made the dewatering information available during the study for the more than 70 dewatering wells we found no reference to permeability at the BSCO site in Reference 1.

I The permeability of sands can be estimated using the empirical relation of Dj o and K by llazen (Reference 2, pp. 32 & 33):

K = C(Di o)2 (1) where K = the coefficient of permeability, cm/sec.

C = 100 D i o = particle diameter at 10% finer by weight, expressed in cm.

Ilundreds of grain size distribution curves had been developed for sands at the BSCO site and it was found that the majority of sands have a D o i varying between 0.1 mm to 0.2 mm. Using Equation 1, the permeability is estimated to be in the range of 100 x 10 ~4 cm/sec to 400 x 10~4 cm/sec. l Equation 1 was verified by numerous pumping tests and laboratory tests l for sands in the Mississippi and Arkanses River Valleys. However, the I mwronom

15 most reliable procedure for determining the in situ permeabilty of a water-bearing formation is a field pumping test (Reference 2).

In 1963 a field pumping test was conducted at the BSCO site prior to any deep well dewatering activity. The average in situ permeability of the

, sands was calculated to be 250 x 104 cm/sec or 71 ft/ day.

The average permeability obtained using Equation 1 is in agreement with the permeability obtained by the field pumping test.

The permeability of 250 x 10 4 cm/sec (71 ft/ day) has been used success-fully since 1963 for the design of dewatering systems at the LSCO site and has resulted in remarkable agreement between predicted values and subsequent observed drawdown.

In 1979 a field pumping test was conducted in Unit 3 at the site of Bailly N-1 (Reference 5). Using 80 feet as the thickness of Unit 3 and an average transmissivity of 12,000 GFD/ft, it was found that the resulting permeability is 70 x 10~4 cm/sec.

Estimating the permeability of Unit 3 from grain size distribution data within the excavation for Bailly N-1 we found that it is in the range of 68 x 104 cm/see to 180 x 104 cm/sec.

I Permeabilities at the NIPSCO site are slightly lower than those at the BSCO site. This is attributed to some silty fine sand layers encountered in the borings located within the excavation for Bailly N-1.

I Comparing the permeability used in the model by USGS and the permeabilities

• by the pumping tests and empirical methods it is evident that

.-..aeability used in the model for Unit 1 and Unit 3 is two to eight times higher than the permeability obtained empirically and by the pumping tests.

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E 16 We agree with the USGS conclusion that the sands of Units 1 and 3 are similar and that the permeabilities could be assumed to be the same.

Ilowever, we cannot agree that the average permeability of the sands is l 167 f t/ day (589 x 10 4 cm/sec) in the face of more reliable data to the contrary. i I

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17 5.O GROUNDWATER LEVELS D'Appolonia's review was not directed toward groundwater levels but a review of the reported data reveals that some 1cvels near the boundary of the study area are so different from actual conditions that they alone seriously limit the value of model predictions at extreme distances from the excavation. The enclosed Figure 6 is compiled from data in Figures 6 and 8 of Reference 1 and shows the elevation of the surface of Unit 2 and the saturated thickness of Unit 1 for October 26, 1976 in the area of the BSCO East Office. Groundwater levels can be obtained by adding the saturated thickness of Unit 1 to the elevation of the surface of Unit 2. Using the enclosed Figure 6, it can be calculated for October 26, 1976 that the groundwater levels were at elevation 620!

north of the BSCO East Office building and elevation 6301 at the South Shore Railroad crossing at the entrance road to NIPSCO and BSCO. Ground surface elevation in these areas is approximately 614 indicating that the groundwater levels were 6 to 16 feet above the existing ground surface. That condition obviously does not exist.

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18 6.0 INFLUENCE OF NIPSCO'S

, PRESSURE RELIEF SYSTEM ON GROUNDWATER LEVELS AT COWLES BOG NPS informed NIPSCO at a meeting on January 31, 1980 that USGS, using the model, had predicted groundwater changes from NIPSCO's pressure relief system up to 0.5 feet at Cowles Bog. In our view, the differences

(' between the assumptions used in the model and the actual subsurface conditions preclude making predictions of groundwater level changes ar

{ Cowles Bog.

The point at which predicted changes are calculated is over 8,000 feet from the location of the pressure relief system. This indicates that the radius of influence, which is the limit of lateral extension of a cone of depression, would be in excess of 8,000 feet. To conclude that groundwater level changes (drawdown) will result from pumping a we11 point

( system through a fine sand media at a distance of over 8,000 feet is unrealistic and contrary to the empirical data presented in engineering

{ literature, pumping tests and observed data at the BSCO and NIPSCO sites.

The pressure relief system is designed to operate by vacuum as a well-point system capable of changing the groundwater level 20 feet in Unit 3 in the area of the Bailly N-1 reactor building.

( The radius of influence (R) for both artesian and gravity flows can be estimated from the.following equation (Reference 2, p. 150):

R = C(H-h y )% (2) where R = Radius of influence (feet)

H-h = Drawdown in the well (feet)

K = Permeability expressed in 10' cm/sec units C = Dimensionless constant C=3 for artesian and gravity wells C = 1.5 to 2.0 for a single line of we11 points

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19 Examining Equation 2 we can see that the radius of influence depends on the water level change at the point of withdrawal and the permeability.

It is independent of the pumping rate.

Equation 2 was verified using pumping tests on wells in the Mississippi River Valley by the U.S. Army Corps of Engineers. It was also verified for a line of wellpoints by the Moretrench Corporation (Reference 3. p. 307).

This equation was successfully used at the BSCO site and on many other dewetering projects.

For verification of Equation 2 at Bailly N-1 we used the data from a NIPSCO pumping test conducted in 1979 (Section 4.0 of this report).

Using a permeability of 70 x 10~4 cm/sec and a drawdown of 26 feet at the test well, the resulting value of the radius of influence is 653 feet. This value is compatible with the radius of influence of 600 feet observed at the end of the test.

I Using Equation 2 and in the extreme case C = 3 and the permeability from the pumping tests, the radius of influence can be calculated for a groundwater change of 20 feet in Unit 3 at Bailly N-1 generated by the pressure relief system.

. The radius of influence is approximately 500 feet for the permeability obtained by the pumping test at the NIPSCO site.

I . Using the permeability obtained by the pumping test at the BSCO site, the radius of influence is approxi-a mately 950 feet.

Even if the USGS model permeability of 589 x 10 4 cm/sec is used (which has been shown to be excessively high and inconsistent with other dt.ta.

Section 4.0 of this report) with 20 feet of drawdown at Bailly N-1, a radius of influence of 1450 feet results. To produce a six inch drawdown i

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at a distance of.8,000 feet, the radius of influence would be over six times t' e extreme case of 1450 feet, a condition that is not supported by independent analysis and observed data. )

Based on the above, it is evident that Cowles Bog is beyond the influence of the pressure relief system. Accordingly, the groundwater level at Cowles Bog will not be altered as a result of construction dewatering at )

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7.0 CONCLUSION

The prelh::inary review of soil parameters used in Reference 1 and soil and pumping test. data available within the study area have produced information which was used for comparison of actual data to data used in Reference 1. This information was used throughout this report in the form of statements and conclusions. In addition, part of the informa-tion is presented graphically on six figures with four overlays. A review of this data leads to the conclusions we have outlined below.

1. There is a large body of data relative to soil parameters within the study area.

2. We have found major discrepancies between the actual data and the data used by USGS.

a. The permeability used for Units 1 and 3 is incorrect.

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b. Unit 2 is not continuous; it contains many openings.

c. There are differences in the surface elevations of Unit 2.

d. Unit 3 is connected to the sands above Unit 2 through many large openings.

e. Units 3, ? and 3 are different in shape and in thickness than indicated in the model.

f. There are major differences in the elevations of groundwater between those assumed and those existing.

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g. There are not two distinct aquifers (unconfined and confined) throughout the study area. In many areas they are connected and act as one.

3. The radius of influence for the pressure relief system is estimated to be less than 950 feet.

'iherefore the system would not have any effect on Cowles Bog located over 8,000 feet from the Bailly N-1 site.

4. The cone of depression from the pressure relief system would not reach the bog area even if we assume that Unit 2 is continuous throughout the study area with an opening (" window") only under the bog.

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For these reasons we conclude that the model, as it is presently constructed, cannot reliably predict groundwater movements in Cowles Bog.

Respectfully submitted, Richard F. Brissette N

Stevo Dobrijevic RFB:SD: jar Project MW79-720 May, 1980 I DAPPOILONIIA

LIST OF REFERENCES

1. Meyer, William and Patrick Tucci, January, 19}9, 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,78-138.

2. Departments of the Army, the Navy, and the Air Force, April, 1971, Dewatering and Groundwater Control for Deep Excavations, TM 5-818-5, NAVFAC P-418, AFM 88-5, Chap. 6.

3. Leonards, G. A., ed. 1962, Foundation Engineering, McGraw-Hill, New York.

4. Meyer, William, J. P. Reussow and D. D. Gillies, 1975, Availability of Ground Water in Marion County, Indiana, U.S. Geological Survey I 5.

Open-File Report 75-312, p. 87.

Sargent & Lundy, Chicago, Illinois, Dames & Moore, Park Ridge, Illinois, Ground / Water Technology, Inc., Denville, New Jersey, August 27, 1979, Supplementary Information, Hydrogeologic Evaluation of Construction Dewatering, Bailly Generating Station, Nuclear 1, Northern Indiana I Public Service Company.

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REFERENCE:

USGS REPORT 78-138 HDAR"HNDNADA'M 991893 NERCULENE. ASS StelTH CO . PGH P A LTl5 30. 9 0 79