ML20170A392
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Page 1 of 17 DSAR-2.7 Site and Environs Hydrology Rev 1 Safety Classification: Usage Level:
Safety Information Change No.: EC 69788 Reason for Change: This section is being updated to align with Permanently Defueled Technical Specifications.
Preparer: J. Dolton Fort Calhoun Station
DSAR-2.7 Information Use Page 2 of 17 Hydrology Rev. 1 Table of Contents 2.7 HYDROLOGY ............................................................................................................... 5 2.7.1 Surface Drainage ............................................................................................ 5 2.7.1.1 General .............................................................................................. 5 2.7.1.2 River Stage and Flow ......................................................................... 6 2.7.1.3 River Temperature ........................................................................... 10 2.7.1.4 River Water Analyses ....................................................................... 11 2.7.2 Ground Water ................................................................................................ 13 2.7.2.1 General ............................................................................................ 13 2.7.2.2 Site Water Table and Transmissibility .............................................. 14 2.7.2.3 Well Water Analyses ........................................................................ 16
DSAR-2.7 Information Use Page 3 of 17 Hydrology Rev. 1 List of Tables Table 2.7 Missouri River Dams .......................................................................................... 5 Table 2.7 Average Missouri River Water Temperatures (f) at the Metropolitan Utilities District of Omaha Intake (27 Year Average) ...................................................... 10 Table 2.7 Analysis of Missouri River Water at the Metropolitan Utilities District of Omaha Intake 1973 Through 1981 .................................................... 12
DSAR-2.7 Information Use Page 4 of 17 Hydrology Rev. 1 List of Figures The following figures are controlled drawings and can be viewed and printed from the listed aperture cards.
Figure No. Title Aperture Card 2.7-1 Upper Missouri River Basin ............................................................... 36047 2.7-2 Stage Duration Curve ........................................................................ 36048 2.7-3 Flow Duration Curve .......................................................................... 36049 2.7-4 Missouri River Rating Curve .............................................................. 36050
DSAR-2.7 Information Use Page 5 of 17 Hydrology Rev. 1 2.7 Hydrology 2.7.1 Surface Drainage 2.7.1.1 General The plant site is bounded on the northeast and southeast by a portion of Blair Bend of the Missouri River. The Corps maintains river structures to prevent further meandering of the channel within the alluvial flood plain; the structures take the form of pile dikes and bank revetments.
There are six dams upstream of the plant site (see Figure 2.7-1) that control the river flow. These structures are listed in Table 2.7-1 in the order from the nearest to the site (Gavins Point) to the most distant (Fort Peck). There are no dams, locks, or similar structures on the Missouri downstream of the plant site.
Table 2.7 Missouri River Dams Initial Year Name Location of Service Gavins Point South Dakota - Nebraska 1956 Fort Randall South Dakota 1953 Big Bend South Dakota 1964 Oahe South Dakota 1962 Garrison North Dakota 1956 Fort Peck Montana 1940 The Corps of Engineers has stated (Reference 12) that sedimentation will not affect the flood control capability of the reservoir system for 200 years or more.
DSAR-2.7 Information Use Page 6 of 17 Hydrology Rev. 1 2.7.1.2 River Stage and Flow High Water Level The flow frequency information contained below and in Figure 2.7-1 and Figure 2.7-3 represents the best flow frequency information that was available during plant design. Multiple flow frequency studies have subsequently been completed by the United States Army Corps of Engineers and others which predict different flood elevations for the various return periods; however, the original flow frequency information is being maintained because of its historical significance.
Figures 2.7-2 and 2.7-3 show the Missouri River stage and flow duration curves at the plant site. Reference 12 states that: "The water level that will be equaled or exceeded 1% of the time is 998 feet - this is a stage-duration value, not a flood peak. The 1% probability flood peak stage is 1001.3 feet. This is a momentary peak that has a 1% chance of occurrence in any year.
The 0.1 percent probability flood peak stage is not determinable by statistical analysis with sufficient precision for planning use.
However, the design flood peak stage of 1,004.2 feet is the proper order of magnitude for a 0.1 percent probability flood (Reference 12). As a matter of fact, extrapolation of the probability curve would yield a value slightly less than 1,004.2 feet for the 0.1 percent probability flood. Therefore, 1,004.2 feet is conservative and is proper for use."
Although extensive studies of the effects of possible flood conditions have not been made by the Corps of Engineers in the vicinity of the Fort Calhoun site along the Missouri River valley, those available do allow conservative estimates of flood levels to be made under specific postulated conditions as summarized in Reference 1. Stage discharge relations for the Missouri River at the Fort Calhoun site from the Corps of Engineers are shown in Figure 2.7-4. The basis for the stage discharge curve includes an actual measurement in the vicinity during flood conditions in 1952 when the discharge was approximately 400,000 CFS. At higher flows the curve has been extrapolated conservatively based on Missouri River valley cross sections in the area that indicate little comparative increase in cross-sectional width greater than about twelve miles above the 1952 flood level of about 1,008.6 feet MSL. Because the plant is permanently defueled, the plant will remain shut down when the flood water level exceeds the permanently installed protection provisions, minimizing the likelihood of an accident.
DSAR-2.7 Information Use Page 7 of 17 Hydrology Rev. 1 The Corps of Engineers has made a preliminary estimate of the maximum probable flood resulting from the runoff from a maximum probable rain storm over the area below the Gavins Point dam. This flood yields a peak discharge of 550,000 CFS at the plant site. The discharge includes an assumed out-flow of 50,000 CFS from the Gavins Point reservoir also caused by the maximum probable rain storm. The flood peak stage at the site is estimated to be approximately 1009.3 feet Mean Sea Level (MSL)
(Reference 21).
The flood resulting from failure of either the Oahe dam or the Fort Randall dam has been estimated by the Corps of Engineers. The hydrological events resulting in the failure of one of these dams concurrent with the events giving rise to a maximum probable flood described above yields a peak discharge of approximately 1,200,000 CFS at the plant site and a flood elevation of about 1,013 to 1,014 feet MSL (Reference 21).
It is estimated that the large flows would take about two days to travel from Gavins Point to the Fort Calhoun site. Thus, many hours, and possibly a day's warning would be available before the effects would be felt at the site. Moreover, a watch is maintained by the U.S. Weather Bureau to warn of rising levels in the tributary streams below Gavins Point. Arrangements were made with the U.S. Weather Bureau to warn the plant operating staff of any expected rises in Missouri River level. Rainfall sufficient to cause an appreciable flood would have to be heavy and occur over an extensive area.
Flood Protection Flooding protection for Class 1 structures other than containment is provided using a three tiered approach. The basis for the three separated flood elevations are discussed below along with protections required for each elevation:
Along with the protections discussed below, sandbagging in key areas is used to supplement flood protection strategies.
1,007 Feet Passive protection is provided to a flood elevation of 1,007 feet.
Below 1,007 feet, portions of these structures containing safety related equipment are constructed of sealed concrete.
DSAR-2.7 Information Use Page 8 of 17 Hydrology Rev. 1 The basis for providing passive protection to 1,007 feet is as stated in Reference 20:
It was recommended that based on Corps of Engineers' letter dated February 7, 1967 (Reference 12), and the flood data presented by them that the finished grade site elevation could safely be set at 1,004 feet since the 0.1% [Note, Reference 20 lists this value as 0.01%, which has subsequently been found to be a typographical error] probability flood is in this range.
However, although the Corps of Engineers have stated that the 1952 flood should not be repeated because of better flood controls on the Missouri River, it is prudent to set the plant sill elevation at 1,007 feet as this was the high water mark according to local eye-witnesses at the Fort Calhoun site during this 1952 flood.
1,009.3 Feet The Corps of Engineers "preliminary estimate" of probable maximum flood that might occur as a result of runoff from a probable maximum rainstorm over the area below Gavins Point coupled with an assumed outflow of 50,000 CFS from Gavins Point reservoir is 1,009.3 feet (Reference 21).
Flooding protection against the 1,009.3 foot flood in the auxiliary building is provided by removable flood barriers which extend to 1014 feet. When required, these flood barriers are installed in openings leading to safety related equipment on the 1,007 foot floor elevation.
Flooding protection against the 1,009.3 foot flood in the intake structure is provided by removable flood barriers which extend to at least 1014 feet and intake cell level control maintained by the raw water pumps. When required, these flood barriers are installed in all exterior openings on the operating level of the intake structure. In addition, a flood barrier is installed at the outlet of the screen wash discharge trough at the south end of the traveling screens. The intake cell level will be maintained below 1,007.5 feet by closing the exterior sluice gates and throttling the intake cell flood water inlet valves and/or varying the raw water pump output to remove the inlet flow. Flood water isolation valves are available to isolate a failed open flood water inlet valve if required (References 42 and 44).
The flood water inlet and isolation valves, attached piping, and immediate components remain functional for a flood following a seismic event (References 43 and 44).
DSAR-2.7 Information Use Page 9 of 17 Hydrology Rev. 1 1,014 Feet The Corps of Engineers estimate of the flood level that might result from the failure of Oahe or Fort Randall dams coincident with the probable maximum flood that produces the 1,009.3 foot flood is 1,014 feet.
Flooding protection against the 1,014 foot flood in the auxiliary building is provided by removable flood barriers and sandbagging.
When required, these flood barriers are installed in openings leading to safety related equipment on the 1,007 foot and 1,011 foot floor elevations. Sandbagging is required at the 1,013 foot elevation of the equipment hatch room (Room 66).
Flooding protection in the intake structure against the 1,014 foot flood is accomplished in the same manner as it is for the 1,009.3 foot flood.
Section 3.1.5 of the Safety Evaluation of Reference 23 states:
"The plant can accommodate flood levels up to 1007 feet MSL without special provisions and up to a still water level of 1009.3 feet MSL by lowering steel flood gates mounted above all accesses in safety related structures. The plant could be protected from water levels greater than this (due to wave runup and splash) by construction of temporary earth levees and/or sandbag barriers."
Thus, above 1,007 feet, Class 1 structures are designed for hydrostatic loads only (See Section 5.11). The intake structure is a Class 1 structure up to 1,007.5 feet (see Section 9.8.6).
Access to the intake veranda is lost when the east doors to the intake structure are blocked by installing the flood barriers which must be installed prior to a river level of 1004 feet. [DJA1]
For information pertaining to protection of raw water pumps and their drives against floods, see Section 9.8.6.
The elevation of raw water pump suction bells is 973 feet 9 inches MSL and the required normal submergence above the bottom of the suction bell is 3 foot 0 inches, or an elevation of 976 feet 9 inches MSL. Actual low water levels at Blair, Nebraska (approximately four miles upstream from the plant site) due to icing conditions have been recorded as low as 987.4 feet MSL.
These conditions are transient in nature and would not jeopardize suction of the raw water pumps.
DSAR-2.7 Information Use Page 10 of 17 Hydrology Rev. 1 With respect to low river flow at the site, the release from Gavins Point is 12,000 CFS as a normal minimum depending largely on availability of water. Flows during the non-navigation season will range from 12,000 CFS to 18,000 CFS. In years when an extended period of drought has depleted storage reserves, release flows may periodically run as low as 6,000 cfs, this according to the Corps of Engineers' published annual operating plan. An ice jam formation can temporarily reduce low flows to even lower values but such partial stream blockages rarely occur and several methods have been developed to quickly nullify their effects.
At low river levels, debris and/or ice on the traveling screens and/or trash racks can cause significant head loss potentially reducing intake cell levels below the normal raw water pump minimum submergence level (MSL) of 976 feet 9 inches.
A head loss from the traveling screens of less than 1 inch between the river and intake cell(s) can occur when the river level is at 9769 (Reference 40). Analysis demonstrates that the raw water pumps can provide the required flow for all conditions with a cell level at 9768 (Reference 41).
Based on the above, adequate cooling water will be available to meet plant requirements.
2.7.1.3 River Temperature Table 2.7-2 shows the average monthly and yearly Missouri River water temperatures taken at the Metropolitan Utilities District of Omaha intake over a 27 year period. The intake is 19.6 river miles downstream of the plant site.
Table 2.7 Average Missouri River Water Temperatures (°f) at the Metropolitan Utilities District of Omaha Intake (27 Year Average)
Monthly Average January 32 February 33 March 37 April 49 May 61 June 71 July 78 August 77 September 68 October 56
DSAR-2.7 Information Use Page 11 of 17 Hydrology Rev. 1 November 43 December 34 Yearly Average 53 2.7.1.4 River Water Analyses Table 2.7-3 shows a summary of river water analyses of samples taken at the Metropolitan Utilities District of Omaha intake from 1973 through 1981.
DSAR-2.7 Information Use Page 12 of 17 Hydrology Rev. 1 Table 2.7 Analysis of Missouri River Water at the Metropolitan Utilities District of Omaha Intake 1973 Through 1981 Constituent Average Values (mg/l unless noted)
Calcium 61.2 Magnesium 23.8 Sodium 65.7 Sulphate 200.6 Chloride 12.7 Nitrate 2.6 Phosphate 0.1 Silica 8.9 Iron 0.0 Manganese <0.05 Potassium 5.1 Arsenic <0.01 Selenium <0.004*
Silver <0.002 Beryllium <0.01 Copper <0.02 Chromium <0.02 Lead <0.01 Zinc <0.03 Strontium <0.5*
Aluminum 0.04 Vanadium <0.003*
Total Dissolved Solids 524 Free Carbon Dioxide 0.0 Total Hardness 248.0 pH (no units) 8.16 Conductivity @ 25C, mho 685 Color Units, Platinum-Cobalt Scale 7.9 Carbonate 0.0 Bicarbonate 199
DSAR-2.7 Information Use Page 13 of 17 Hydrology Rev. 1 Table 2.7-3 (continued)
Constituent Average Values (mg/l unless noted)
Fluoride 0.59 Bromide 0.38*
Organic 2, 4, 5 - TP <0.003*
Total Alkalinity 163 Dissolved Oxygen 9.8 Non-Carbonate Hardness 85 Surfactants (LAS) <0.03 Suspended Solids 223 BOD 1.3 COD 19 Ammonia Nitrogen 0.09*
Fecal Coliform (per 100 ml.) 2257*
Gross Beta (picocuries/L) 3.67**
- Values not available for all nine years. Average, in these instances, are based on the number of years for which data was recorded.
2.7.2 Ground Water 2.7.2.1 General Ground water is from two sources. The first is the Missouri River Valley, where ample ground water is obtained from the Pleistocene Valley fill and alluvial sand and gravels. The water table ranges from 2 to 17 feet below the surface, and coincides with the elevation of the river in the bottom land adjacent to the river. The second source of ground water are the terraces and loess hill upland regions. In these areas, the majority of wells are drilled or dug and provide water mainly from the glacial sands and gravels.
The movement of ground water under the uplands is toward and into the Missouri River trench. The occurrence of springs along the base of the bluff confirms the movement of ground water from the hills to the river.
The development and use of ground water adjacent to the Missouri River and downstream of the plant will be monitored as a result of normal coordination with state and local authorities. The need for an evaluation of potential effects on these wells will be determined periodically.
DSAR-2.7 Information Use Page 14 of 17 Hydrology Rev. 1 2.7.2.2 Site Water Table and Transmissibility Water levels taken in a series of borings drilled during July and August, 1966, reveal that the ground water levels at the site varied from elevations 993.7 to 992.4 feet, while the river levels recorded during this same period ranged from elevations 993.2 to 992.4 feet. Ground water levels vary with changes in the river level. The rate of ground water flow in the alluvial soils varies with the permeability. However, rate of flow is very low, because of the low gradients, and again, is toward the river. The coefficient of permeability varied from about one-half to three feet per day in the upper sandy silt and silty sand. In the lower fine-to-coarse sand and gravel, coefficients of permeability as high as 20 feet per day were measured.
Pumping tests were conducted to evaluate the gross permeability and transmissibility characteristics of the alluvial deposits. At a pumping rate of about 700 gallons per minute, the maximum drawdown in the well was 21 feet. The ultimate radius of influence of the test well was between 1,300 and 1,800 feet. The gross permeability of the deep water bearing sands and gravels amounts to 1,100 gallons per day per square foot. The soils are in direct hydrologic connection with the Missouri River.
The hydrologic characteristics of the site and surrounding area and the pattern of the ground water are such that accidental discharge of radioactive fluids into the ground would have no adverse effects on existing or potential ground water users. Such fluids would percolate slowly in the direction of the Missouri River.
Thus, hydrological conditions are favorable for the location and operation of a nuclear facility.
DSAR-2.7 Information Use Page 15 of 17 Hydrology Rev. 1 Thirteen groundwater monitoring wells (both shallow and deep) were installed at FCS from August 15 through August 27, 2007.
Hydro geological information was collected and evaluated by Terracon Consultants Incorporated. A second review and evaluation was performed by Radiation Safety and Control Services incorporated. Soils observed during the advancement of the well borings consisted primarily of unconsolidated lean clay, silt, and sand. These materials appear to be representative of Missouri River alluvium, although some relatively shallow soils may represent construction fill. The unconsolidated sediments that underlie the plant site can be grouped into two units: an upper fine grained sandy clay with silt approximately 20 to 50 feet thick, and an underlying fine to coarse sand with some gravel. This lower unit extends to the relatively flat-lying carbonate bedrock surface at a depth of approximately 70 to 75 feet below grade.
Both unconsolidated units are water bearing, but the deeper unit has higher hydraulic conductivity. The depth to ground water ranges about 15 to 20 feet below ground surface. The resulting hydraulic gradient within the unconsolidated sediments is relatively flat. This low hydraulic gradient, combined with moderate hydraulic conductivity of the fine grained alluvial material, results in relatively slow ground water velocity beneath the site. Water table and potentiometric surface contour maps constructed based upon water levels measured in the new wells indicate groundwater flow directions different from the directions presumed prior to construction of the wells. Two conditions at FCS produce groundwater flow gradients opposite to those originally presumed. The first condition affecting groundwater flow is the pumping of the ground water supply well located at the northwest corner of the old warehouse. Testing during construction of the well determined that it is capable of producing approximately 500 gpm, and a continuous average flow of approximately 200 gpm. Pumping of this well induces drawdown of groundwater levels in its vicinity and in the area between the well and approximately the turbine building, a reversal of the seasonally normal flow gradient toward the Missouri River.
DSAR-2.7 Information Use Page 16 of 17 Hydrology Rev. 1 The second condition impacting groundwater flows is bank recharge. The Missouri River is in hydraulic connection with the groundwater in the alluvial aquifer. During periods of relatively high river stage, which occur generally from April through September when precipitation is greatest, river water recharges the nearby alluvial aquifer and induces groundwater flow gradients outward from the river channel. These gradients reverse seasonally, during periods of lower river stage. Groundwater flows at the landfill site were calculated at velocities of less than 0.8 ft day, toward or away from the river, based on river stage.
In summation, the setting of the plant appears to be within a dynamic groundwater environment influenced by pumping of the ground water supply well, river level, and seasonal amounts of precipitation. Consequently, the site groundwater monitoring program must account for potential variations in flow directions present within the industrial area.
2.7.2.3 Well Water Analyses Samples were taken from the test well on the plant site at eight-hour intervals during August, 1966. The chemical analyses of these samples are summarized in Table 2.7-4. Throughout the sampling period, the well-water temperature was 54°F; no large seasonal temperature variations can be expected. Other samples were taken at bore holes and subsequently analyzed. However, the analyses reported in Table 2.7-4 are typical and adequately describe the ground water.
DSAR-2.7 Information Use Page 17 of 17 Hydrology Rev. 1 Table 2.7 Test Well Water Analysis Sample No. 1 Sample No. 2 Sample No. 3 Sample No. 4 Sample No. 5 Sample No. 6 Sample No. 8 As As As As As As As As As As As As As As Analysis CaCO3 Ion CaCO3 Ion CaCO3 Ion CaCO3 Ion CaCO3 Ion CaCO3 Ion CaCO3 Ion Fe, ppm 26.0 14.5 28.4 15.9 27.6 15.4 27.6 15.4 28.1 15.7 28.1 15.7 28.1 15.7 Mn, ppm 1.2 0.6 4.9 2.7 5.1 2.8 4.0 2.2 5.1 2.8 5.6 3.1 4.7 2.6 Na, ppm 118.0 54.3 106.9 49.2 104.5 48.1 104.2 47.9 96.0 44.2 96.0 44.2 91.5 42.1 K, ppm 4.5 3.5 4.4 3.4 4.4 3.4 4.4 3.4 4.1 3.2 5.1 4.0 4.4 3.4 Ca, ppm 420.0 168.0 408.0 163.2 398.8 159.5 399.6 159.8 401.0 160.4 394.0 157.6 406.0 162.4 Mg, ppm 220.0 52.8 212.0 50.9 214.4 51.5 237.8 57.1 203.0 48.7 274.0 65.7 248.0 59.5 Total Cations,ppm 789.7 293.7 764.6 285.3 754.8 280.7 777.6 285.8 737.3 275.0 802.8 290.3 782.7 285.7 SO4, ppm 151.5 145.4 174.7 167.7 159.6 153.2 181.3 174.0 160.7 154.3 164.2 157.6 147.8 141.9 C1, ppm 183.9 130.6 14.1 10.0 8.5 6.0 11.3 8.0 8.5 6.0 5.6 4.0 8.5 6.0 HCO3, ppm 454.0 553.9 575.4 702.0 586.4 715.4 584.8 713.5 568.0 693.0 632.9 772.1 626.2 764.0 NO3 ppm 0.3 0.4 0.4 0.5 0.3 0.4 0.2 0.3 0.1 0.1 0.1 0.1 0.2 0.3 Total Anions, ppm 789.7 830.3 764.6 880.2 754.8 875.0 777.6 895.8 737.3 853.4 802.8 933.8 782.7 912.2 SiO2 ppm 22.6 23.4 23.0 20.6 27.3 23.0 23.0 Total Dissolved Solids, 1,146.0 1,188.9 1,178.7 1,202.2 1,155.7 1,247.1 1,220.9 ppm Total Hardness, ppm, 640.0 620.0 613.2 637.4 604.0 668.0 654.0 CaCO3 Alkalinity, ppm CaCO3 454.0 575.4 586.4 584.8 568.0 632.9 626.2 pH 7.0 7.0 7.4 7.4 7.3 7.4 7.5 Conductivity, mmh 1,400 1,250 1,240 1,240 1,250 1,250 1,200 NOTES 1. Samples taken at 8-hour intervals, August 26 to 29, 1966.
- 2. Sample No. 7 was invalid.