ML20087N460

Well Monitoring Program Annual Rept,1983

ML20087N460
Person / Time
Site:	Byron
Issue date:	12/31/1983
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20087N448	List: ML20087N447 ML20087N460
References
NUDOCS 8404030480
Download: ML20087N460 (8)

Text

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BYRON OBSERVATION WELL MONITORING PROGRAM ANNUAL REPORT FOR 1983 BYRON STATION

• COMMONWEALTH-EDISON COMPANY

. I. PURPOSE The purpose of this report is to present the groundwater and precipitation data collected as part.of the well monitoring program and to provide an interpretation of the groundwater conditions present in Area of Concern 11 along the Essential Service Water. (ESW) make-up pipeline. The purpose of the -

monitoring program 'is to provide for the collection of data necessary to close the requirements for a License Condition of

.the.U.S. Nuclear Regulatory Commission's Safety Evaluation-Report.

II. SCOPE The monitoring program. consists of the collection of field data from four observation wells and precipitation from the Byron Station' meteorological tower.

During the FSAR review by the NRC staff, Commonwealth Edison Company .(CECO)' agreed - to establish a groundwater monitoring program at the request of'the NRC.- Four observation wells were installed between ESW pipeline-Stations 45+20N and 53+00N (see Figure 1 for ' approximate locations) .

III. . ' OBSERVATION WELL CONSTRUCTION

.The four observation wells can be divided'into two categories.

Wells OW-1 and OW-2'were-installed to detect and measure the

presence of perched groundwater occurring in the soils above the bedrock surface. . Wells OW-3 and OW-4 were installed to measure the groundwatet level occurring:in the upper portion of the-dolomite bedrock.-

. Construction details for the wells are shown in Figure-2 and 3.

Exact locations, . elevation of the ' top of .the well casing, ele-

'vation of the.well tip,,and depth to the well tip are presented tin' Table'1..

LIV. DATA COLLECTION AND RESULTS -

The;four^ observation wells were installed between March 17, 1982, fand March' 25,'1982.- Monitoring of:the water levels in the four

. wells . began' on April ~12, ' 1982, and-has continued on a wec'kly basis ' for the. last. 20 months.

T- 84040304801840326 '3 Page 1 of 8

PDR ADOCK 05000454

• L R. PDR  :

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O The four observation wells were dry during all of 1982 and 1983.

The precipitation data for 1982 indicates that the total rain-fall at the Byron site was 29.81 inches or 5.31 inches less than the 1931-1960 mean yearly rainfall. The first 6 months of 1982 were 5.85 inches less than the mean for the first 6 months. The second half of 1982 was 0.54 inches greater than the second half of year mean for this area. The precipitation data for 1983 indicates that the total rainfall to date at the Byron site was 27.4;2 inches or 6.83 inches less than the prorated 1931-1960 mean yearly rainfall.

V. INTERPRETATION AND CONCLUSIONS The data collected during both 1982 and 1983 indicates the groundwater level in Area of Concern 11 is less than 809 feet

• MSL. As the two soil observation wells have been dry, there is no indication of the presence of perched groundwater oc-curring above the bedrock surface in Area of Concern 11. It is the applicant's position that the piezometric surface map (see FSAR Figure 2.4-24) shows an abnormally high groundwater level due to an extremely high level of precipitation.

Precipitation data for the Byron site is presented in Table 3.

This table presents the 1931-1960 mean precipitation and 1973, 1974, 1981, 1982 and 1983 precipitation levels. The piezometric surface map was based on July 1, 1974, well readings. The data presented in Table 3 indicate that all of 1973 and the first six months of 1974 were periods of exceptionally high precipita-tion. In addition to the period of exceptionally high precipita-tion, it is also possible that a certain amount of induced recharge was taking place from the grouting program being per-

, formed for the foundation of the main plant. #

Continuous grout.ng was taking place from May through November 1974. Large amounts of water was used in this operation with an unlined settling pond being located near the highest point of recharge shown on the July 1, 1974, piezometric surface map. This set of condi-tions caused an abnormally high groundwater level. An examination of water level data from 1974 indicates that the 1974 levels were an average of 14.3 feet, 11.3 feet, and 30.6 feet higher than the 1972, 1973 and 1975 levels, respectively. An examination of the piezometric surface map for the Galena-Platteville aquifer indicates that on July 1, 1974, the groundwater level in Area of Concern 11 was between 825 and 835 feet MSL. The bedrock sur-face in Area of Concern 11 is above elevation 832.8 feet MSL.

Therefore, it is highly unlikely that the grounduater level will ever be high enough to saturate the soil above the bedrock surface.

The NRC Safety Evaluation Report (NUREG-0876, February 1982) required that the monitoring program consider the maximum rate of groundwater rise in the site vicinity so that the level at which notification given to the NRC would allow enough time. to develop and implement contingency plans before groundvater elevation 850 feet MSL is exceeded in Area of Concern 11. The data base that has been developed from onsite groundwater measurements indicates that there is no zone of perched ground-water in the soil in Area of Concern 11 and that it is highly unlikely the grounduater level would ever reach elevation 850 Page 2 of 8

<. , feet MSL. Therefore, based upon lack of measured groundwater response the license condition should be closed and deleted from the NRC Safety Evaluation Report.

Table 1 BYRON OBSERVATION WELL DATA El. of Top of Depth to Bottom of Well Location PVC Casing Well From Top of PVC El. Well Tip (MSL) Casing (Ft) (MSL)

OW-1 49+20N-32+91.75E 870.65 31.58 839.07 OW-2B 48+26N 32+91.25E 870.67 22.74 847.93 OW-3 49+25N 32+92.5E 870.42 61.15 809.27 OW-4 47+35N 32+91.25E 870.03 60.93 809.10 Table 2 SCHEDULE FOR DATA COLLECTION Activity Year 1 and 2 After 2 Years (If necessary)

Spring Summer Fall Winter Observation Well Readings . Weekly Weekly Bi-weekly Montly Montly (OW-1, 2, 3 ,. & 4 i

Collection of '

Daily Precipita- Monthly

' tion Records Note: If the groundwater elevation rises above elevation 840 feet (MSL), regardless of season, monitoring of the wells shall be on a daily basis until such time that the water level falls below 840 feet .(MSL) .

At such time, the normal monitoring frequency may be resumed.

Page 3 of 8

. s.

• Table 3 INCHES OF PRECIPITATION AT THE BYRON STATION 1931-1960 Month Mean 1973 1974 1981 1982 1983 1.98 Jan 1.67 3.55 0.22 1.58 0.32 Feb. 1.44 1.56 1.65 2.40 0.20 1.56 March 2.46 4.53 2.03 0.65 3.63 1.81 April 3.05 9.92 3.41 5.21 1.271 3.62 May 3.83 6.98 6.98 1.84 2.68 4.62 '

June 4.30 5.16 6.30 5.88 1.85 3.00 6-mth subtotal 17.06 29.82 23.92 16.20 11.21 14.93 Change from m e a n -.

+12.76 +6.86 -0.86 -5.85 -2.13 July 4.14 5.81 1.48 1.14 5.43 2.11 Aug. 4.14 1.89 2.21 9.18 1.24 2.33 Sep. 3.51 8.52 0.35 3.51 0.76 3.31 Oct. 2.70 5.15 2.41 2.47 4.07 1.35 Nov. 2.37 1.97 2.31 1.63 3.81 3.39 Dec. 1.70 3.32 1.63 0.77 3.29 6-mth subtotal 18.06 26.66 10.39 18.70 18.60 Yearly Total 35.12 56.48 34.31 34.90 29.81 Change from nean +21.36 -0.81 -0.22 -5.31 Notes: '

1.

Precipitation data for April through December 1982 are from an on site recorder at the Byron Station. Data prior to April 1982 are from the Rockford. Airport.

Page 4 of 8

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