ML19209B580
| ML19209B580 | |
| Person / Time | |
|---|---|
| Site: | Bailly |
| Issue date: | 10/01/1979 |
| From: | INTERIOR, DEPT. OF, NATIONAL PARK SERVICE |
| To: | |
| Shared Package | |
| ML19209B572 | List: |
| References | |
| NUDOCS 7910100184 | |
| Download: ML19209B580 (11) | |
Text
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P00R ORGNAL USGS/NPS Plan for Determining C.swatering of the Indiana Dunes National Lakeshore adjacent to NIPSCO Bailly Generating Station I. Description of observation-well network Since 1973, numerous monitoring wells have been installed in the vicinity of the NIPSCO Bailly site. NIPSCO has installed approximately 40 observation wells; 22 of these wells are s..reened in the unconfined aquifer (unit 1). The U.S.G.S. has installed approximately 35 wells, 28 in unit
- 1. Although water-levels in wells screened in the confined aquifer (unit
- 3) are being monitored by both the U.S.G.S. and NIPSCO, dewatering of unit 3 is unlikely because NIPSCO's dewatering ef forts are directed only toward unit 1. Water-level declines will be observed in unit 3 as a result of the dewatering of unit 1. However, according to the results of U.S. Geological Survey Water Resources Investigations78-138, the water-level declines in unit 3 will not be sufficient to dewater any portion of that aquifer.
T he re f o re , only the observation wells screened in unit I are analyzed in monection with this plan. Attachment I shows the location of U.S.G.S. and N!PSCO observation wells in unit 1.
II. Definition of unJesired dewatering at NPS/NIPSCO boundary It has been shown that ground-water levels near the NIPSCO Bailly site are artificially high because of a ground-water mound produced by seepage f rom fly-ash settling ponds (l'.S. Geological Survey, Water Resources Investigations78-138). Because the NPS cannot tolerate unnatu ral movement of ground water across its boundary, it has sought and obtained an agreement with NIPSCO to seal the fly-ash ponds by about October 1, 1981.
Once the fly-ash ponds are Jealed, the ground-water mound will dissipate and the ground-water system will return to its natural state in about 2 years. The National Park Service has taken the position that NIPSCO need not take action to mitigate water-level declines within the Lakeshore
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caused by construction dewatering that merely lower the artificial ground-water mound. In other words, only dewatering that is greater in magnitude than the estimated height of the ground-water mound need be mitigated. Thus, the g rou nd-w a t e r levels that NPS wants to have restored and then preserved are those that would have been present naturally prior to introduction of fly-ash pond seepage. Because pre-seepage water levels were never documented, they can only be estimated. The oest approximation of these water levels was obtained through the model analysis of Meyer and Tucc i (U.S.G.S. , W.R. I.78-138). In this analysis, the model was calibrated by simulating water levels measured in unit 1 on Oc tober 26, 1976, which was prior to any pumping f rom the excavation at the N!PSCO Bailly site. Simulated water levels for tait I are shown in figure 25 of JRI repott 78-138. Af ter model calibration, the te rminat io of fly-ash pond seepage was simulated, resulting in the water-level d+elines shown in figure 27 of that report. Attachment 2 shows the model-simulated water levels in unit I for October 26, 1976 with the effect of fly-ash pond seepage removed. According to model simulation, these water levels are those that would have been present in unit 1 ou October 26, 1976 had seepage f rom the fly-ash ponds neve r occu rred.
For the purpose of determining the magnitude of dewatering impact on the notural water ;evels in unit I due to N1PSCO's evacuation, these model-simulated water levels wiL2*be used as reference water levels. On the basis of the accuracy of the model calibration, the et ciaated accuracy of the reference water levels probably is within two feet.
III. The Control Well Because water level, fluctuate seasonally due to changes in recharge to and discharge f rom the ground-water system, refere e water levels must be adjusted. U.S.C.S. well 25, located on North Mineral Springs Road two miles east of the NIPSCO construction site, was selected as the control well to make the seasonal adjustments to reference water levels. This well was selected because it met the following criteria:
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- 1. It is screened in the upper unconfined aquifer (unit 1).
- 2. Water-level data is available since January 1976, one year and two months prior to the first pumping from the NIPSCO excavation (March 1977).
- 3. The hydrograph of well 25 (attachment 3) shows no obvious effects of artificial stress and apparently depicts only natural seasonal water-level changes.
4 Model results indicate that well 25 has not been significantly affected by fly-ash pond seepage and would probably not be affected by construction dewatering at the NIPSCO site. These two c riteria are necessary oecause it is possible that water-level declines due to both const ruction dewatering and termination of fly-ash pond seepage may occur simultaneously.
- 5. Water-level fluctuations in U.S.C.S. well 25 (see attachment 3) have been similar to those observed in NIPSCO wells. For example, the
.nange in water level in U.S.C.S. well 25 f rom May to October 1976 was
-3.3 feet. For the same period, water-level changes in NIPSCO wells 16, 17, and 18 were -3.1, -3.8, and -3.1 feet, respectively. From October 1978 to May 1, 1979, the water-level change in U.S.C.S. well 25 was +1.3 feet. For the same period, water-level changes in NIPSCO wells 16, 18, and 54 were +1.7, +1.1, and +1.5 feet, respectively.
Although similar water-level fluctu tions have been observed in U.S.C.S. well 24, its average seasonal fluctuation (2.9 feet) is greater than the average for U.S.C.S. well 25 (2.1 f eet). This is probably because well 24 is farther f rom the discharge area of the unconfined aquif er (Lake Michigan) than well 25.
- 6. U.S.C.S. well 25 is easily accessible for frequent measurement and servicing in all kinds of weather, unlike the U.S.G.S. wells in the sand dunes between NIPSCO and Mineral Springs Road.
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IV. Data Collection All NIPSCO wells shown on attachment 1 are equipped with recc rders except wells 62, 65, 67, 72, 73, and 74. NIPSCO services its re:ording observation wells and measures water levels in the nonrecording wells weekly. All water level data, as well as pumpage data, are sent to the U.S.C.S. and received about two weeks following collection. U.S.G.S. wells G-1, G-2, G-6, 23 25, and 26 are equipped with recorders that are serviced every two weeks (beginning July 2, 1979). Processing time for recorder data is about two weeks. All other U.S.C.S. wells re measured by U.S.G.S. personnel on a quarterly basis, or more frequently if needed. NIPSCO also measures water levels in U.S.G.S. wells 21 through 23, D-1 through D-3, and C-1 through G-6 monthly. These water-level data are also sent to the U.S.G.S. In addition, U.S.G.S. personnel assist with the servicing and measurement of all NIPSCO wells on a quarterly basis. V. Data Analysis Procedure
- 1. Using the model grid (figure 24 of WRI 78-138) and the model-simulated water levels shown in attachment 2, a reference ,2ter level can be determined for each U.S.G.S. and NIPSCO well shown on att.'chment 1.
Examples of reference water levels are tabulated in column (2) of attachment 4.
- 2. For any observation well, the adjustment of water level made to the referen e water level for a particular day will be equal to the mean water level in U.S.C.S. well 25 on the day in question minus the observed water level in U.S.G.S. well 25 on October 26, 1976, that is 601.9 feet above 1929 NGVD. The adjustment can be either positive or negative, depending on whether the wa:er level in U.S.G.E. well 25 on the day in question is higher or Icwer than it was on October 26,
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1976. Exa= oles of adjusted reference water levels are tabulated in column (3) of attachment 4 for all U.S.G.S. wells on March 13, 1979, and for all NIPSCO wells c- un rch 28, 1979. The adjustment for these two days is different because the water level in U.S.C.S. well 25 rose 0.08 foot f rom March 13 to March 28.
- 3. TLe final step in determining the magnitude of undesired dewatering is the comparisan of measured wester levels and adjusted reference water levels for observation wells. Column (4) of attachment 4 lists water levels measured in U.S.C.S. and NIPSCO wells on the dates indicated.
Column (5) shows the dif ferences between measured water levels and adjusted reference water levels for all wells. These values represent the deviations f rom the w~ater levels desired by NPS for wells within the Lakeshore. As long as these values remain positive, no dewatering below the desired water le' el is occurring. When undesired dewa.czing occurs, these values will become negative. These deviations from adjusted reference water levels can be calculated at any time for which water-level data is available. However, because of present and anticipated data collection schedules, there would be a two- to four-week delay f rom the time water levels were recorded in the field to the time when calculations would be made. VI. Accuracy of Plan for Determining Devotering of the Indiana Dunes National Lakeshore Water-level changes in wells r enetrating unit 1 can be measured accurately to within 0.01 foot. However, separation of water-level changes into individual components is not feasibla because too many phenomena, such as variation in natural recharge to and discharge f rom the aquifer, changes in the level of Lake Michigan, termination of fly-ash pond seepage, industrial pumping, and construction dewatering, simultaneously influence
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water levels in unit 1. Therefore, only the gross changes in water level can be measured directly. Because this procedure for separating the ef fects of dewatering f rom other effects relics heavily on model-simulated water-levels, the overall accuracy of the determination of dewatering is subject to the accuracy of the model, which is about + 2 feet. VII. Modifications to U.S.C.S. Observation-Well Network
- 1. To facilitate detection of water-level declines within and near National Lakeshore property due to construction dewatering, a new well (26) has been installed and equipped with a digital water-level reco rd e r. The well has been placed just inside the National Lakeshore boundary opposite NIPSCO well 54 (see attachment 1) where, according to aodel simulations, maximum dewatering of the Lakeshore is expected.
- 2. U.S.C.S. wells 19 and 20 have been removed f rom the monitoring network. Analysis of water-level data indicates that water levels measured in these wells are not representative of either unit 1 or unit
- 3. Inclusion of water levels f rom these wells in a map of the water table for unit 1 produces an anomalous featuce (figure 13, WRI 78-133) which could not be duplicated in the model analysis (figure 25, WRI 78-133). Apparently these wells were driven through unit 1 and into a sand lense in unit 2. Thus, these wells have little value in the monitoring network and should be discontinued.
- 3. U.S.G.S. well 25 was equipped with a digital water-level recorder on June 27, 1979.
4 Beginning July 2, 1979, U.S.G.S. recording observation wells will be serviced every two weeks and water-level records will be processed on a current basis.
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Attachment 4 Reference and Adjusted Reference Natcr Levels for I;SGS and ' TPSCO Monitoring Wells in I! nit 1, Pfa rch 1979*
- Deviation from Adj us t ed Adjusted Reference Refeu.4.3 Re fe rence Ffeasured Water f.evel (5)
Well No. (1) Water f.evel (2) Nater 1.cVel (3) Nater level (4) [(4) Pfinus (3)]_ (JSGS Wells - 3/13/79 - Water level in llSCS 25 = 603.33 Adjustment = 603. 33 - 601.90 = + 1.4 3 21 595.7 597.1 608.83 +11.7 22 595.7 597.1 608.55 +11.5 23 595.8 597.2 608.04 +10.8 24 (outside modeled area) 607.57 -- 25 (control well) 603.33 -- 104 609.0 610.4 611.88 + 1.5 106 (outside modeled area) 604.26 -- 108 (outside nodeled area) 662.78 -- 109 607.6 609.0 613.16 + 4.2 D-1 594.0 595.4 606.28 +10.9 D-2 595.8 ' 597.2 602.36 + 5.2 D-3 598.5 599.9 609.17 + 9.3 D-4 596.4 597.8 600.96 + 3.2 D-5 601.7 603.1 606.97 + 3.8 D-6 599.4 600.8 602.80 + 2.0 D7 604.4 605.8 607.60 + 1.8 DS 609.0 610.4 612.32 + 1.9 c-1 596.4 597.S 615,26 +17.5 c-2 597.7 599.1 612.12 +13.0 c-3 597.7 599.1 613.00 +13.9 c.4 598.5 599.9 -- -- C-5 598.5 599.9 613.53 +13.6 C-6 602.3 603.7 610.93 + 7.2 c.7 604.6 606.0 608.46 + 2.5 C-8 604.6 606.0 607.99 + 2.0 C-9 605.3 607.2 -- -- C-10 605.S 607.2 608.79 + 1.6 New IJSGS Well 26 594.4 595.8 -- --
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. . r Deviation fro.n Adjusted Adjusted Reference Reference Reference P!casured Water I.cyc1 (5) Wel1 No. (1) Nater f.evel (2) Water Level (3) Water I.cyc1 (4) [(4) Plinus (3)] NIPSCO Wells - 3/28/79 Adju:,tnent = 603.41 - 601.90 = +1.51 14 593.8 595.3 601.37 + 6.1 15 539.0 590.5 591.14 + 0.6 16 596.3 597.8 605.03 + 7.2 17 593.8 595.3 600.30 + 5.0 18 595.8 597.3 603.75 + 6.5 19 593.7 595.2 599.98 + 4.8 20 593.2 594,7 597.50 + 2.8 SIC 591.6 593.1 593.57 + 0.5 52C 593.0 594.5 598.85 + 4.4 53C- 592.8 594.3 596.70 + 2.4 54C 594.4 595.9 605.49 + 9.6 55C 592.0 593.5 597.78 + 4.3 50C 596.3 ~ 597.8 603.15 + 5.4 57C 593.1 . 594.6 598.47 + 3.9 58 594.6 , 596,1 607.28 +11.2 59C 595.8 597.3 613.17 +15.9 62 591.8 596.3 610.64 +14.3 65 593.9 595.4 605.71 +10.3 07 593.7 595.2 601.08 + 5.9 72 SS7.9 589.4 589.50 + 0.1 73 587.2 588.7 589.87 + 1.2 74 587.7 589.2 593.02 + 3.8 I'atun is National Geodetic Vertical Datum of 1929 (NGVD)
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