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4.8 Water Resources Playas 15 to 20 Miles Northeast of INTEC, Where the Water Infiltrates

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4.8 Water Resources Playas 15 to 20 Miles Northeast of INTEC, Where the Water Infiltrates Affected Environment 4.8 Water Resources playas 15 to 20 miles northeast of INTEC, where the water infiltrates. This section describes hydrologic conditions The water in Birch Creek and the Little Lost regionally, at INEEL, and at INTEC. It includes River is diverted in summer months for irriga- groundwater and surface water characteristics, tion prior to reaching INEEL. During periods of such as drainage patterns, flood plains, physical unusually high precipitation or rapid snow melt, characteristics and water quality. water from Birch Creek and the Little Lost River may enter INEEL from the northwest and infil- trate the ground, recharging the underlying 4.8.1 SURFACE WATER aquifer. Surface water at INEEL consists of intermittent streams and spreading areas, and manmade per- 4.8.1.2 Local Drainage colation and evaporation ponds. The following sections describe the regional and local drainage INTEC is located on an alluvial plain approxi- characteristics, local runoff, flood plains, and mately 200 feet from the Big Lost River channel surface water quality. near the channel intersection with Lincoln Boulevard on INEEL. INTEC is surrounded by a stormwater drainage ditch system (DOE 1998). 4.8.1.1 Regional Drainage Stormwater runoff from most areas of INTEC flows through the ditches to an abandoned gravel INEEL is located in the Mud Lake-Lost River pit on the northeast side of INTEC. From the Basin (also known as the Pioneer Basin). Figure gravel pit, the runoff infiltrates and provides 4-8 shows major surface water features of this potential recharge to the Snake River Plain basin. This closed drainage basin includes three aquifer. The system is designed to handle a 25- main streams—the Big and Little Lost Rivers year, 24-hour storm event. DOE built a sec- and Birch Creek. These three streams drain the ondary system around the facility to hold water mountain areas to the north and west of INEEL, if the first system overflows. Because the land is although most flow is diverted for irrigation in relatively flat (slopes of generally less than 1 the summer months before it reaches the site percent) and annual precipitation is low, boundaries. Flow that reaches INEEL infiltrates stormwater runoff volumes are small and are the ground surface along the length of the stream generally spread over large areas where they beds, in the spreading areas at the southern end may evaporate or infiltrate the ground surface. of INEEL, and, if the stream flow is sufficient, in Annual precipitation at INEEL averaged 8.7 the ponding areas (playas or sinks) in the north- inches from 1951 through 1994. Annual net ern portion of INEEL. During dry years, there is evaporation from large water surfaces in the little or no surface water flow on the INEEL. Eastern Snake River Plain is 33 inches per year Because the Mud Lake-Lost River Basin is a (Rodriguez et al. 1997). closed drainage basin, water does not flow off INEEL but rather infiltrates the ground surface Man-made surface water features at INTEC con- to recharge the aquifer or is consumed by evap- sist of two percolation ponds used for disposal of otranspiration. The Big Lost River flows south- water from the service waste system, and sewage east from Mackay Dam, past Arco and onto the treatment lagoons and infiltration trenches for Snake River Plain. On INEEL, near the south- treated wastewater. Service water consists of western boundary, a diversion dam prevents raw water, demineralized water, treated water, flooding of downstream areas during periods of and steam condensate (Rodriguez et al. 1997). heavy runoff by diverting water to a series of The sewage treatment plant receives an average natural depressions or spreading areas (DOE sanitary sewage flow of 42,000 gallons per day. 1995). During periods of high flow or low irri- The percolation ponds receive approximately 1.5 gation demand, the Big Lost River continues to 2.5 million gallons of service wastewater per northeastward past the diversion dam, passes day and are each approximately 4.5 acres in size within 200 feet of INTEC, and ends in a series of (Rodriguez et al. 1997). DOE/EIS-0287 4-40 Idaho HLW & FD EIS N B i r c h W E Cre ree k L e S m h 22 i R a n ge 28 Playa 4 L Mud i TAN tt tl Lake le e Lo os Playa 2 st R iv er Playa 1 r Playa 3 Howe L o s t R iv e r R an g e INEEL NRF Arco ANL-W TRA INTEC 20 INEEL Diversion PBF/WERF Dam CFA ARA EBR-I A Spreading RWMC Areas B C D Atomic City LEGEND 26 Big Lost River System Primary Channels Big Lost River System Tributary Channels Playas Wetland & Spreading Areas FIGURE 4- . 02468 10 MILES Surface water features of the Mud Lake- Lost River Basin. SOURCE: DOE (1998). 4-41 DOE/EIS-0287 Affected Environment 4.8.1.3 Flood Plains Lincoln Boulevard near INTEC. The probable maximum flood would quickly overtop and Flood studies at the INEEL include the examina- wash out the diversion dam so there would tion of the flooding potential at INEEL facilities essentially be no effect on flows downstream of due to the failure of Mackay Dam, 45 miles the dam. The Lincoln Boulevard culverts are upstream of the INEEL from a probable maxi- capable of passing about 1,500 cubic feet per mum flood (Koslow and Van Haaften 1986). second (Berenbrock and Kjelstrom 1998). Due The U.S. Geological Survey has published a to the relatively flat topography in the vicinity of preliminary map of the 100-year flood plain for INTEC, debris plugging at the culverts would the Big Lost River on the INEEL (Berenbrock have little effect on the probable maximum flood and Kjelstrom 1998). As a result of this screen- elevation at INTEC. ing analysis, which indicated that INTEC may be subject to flooding from a 100-year flood, Estimates of the 100- and 500-year flows for DOE commissioned additional studies (Ostenaa the Big Lost River were most recently published et al. 1999) consistent with the requirements by the U.S. Geological Survey (Berenbrock and contained in DOE standards for a comprehen- Kjelstrom 1996) and the U.S. Bureau of sive flood hazard assessment (DOE 1996). Reclamation (Ostenaa et al. 1999). The U.S. There is no record of any historical flooding at Geological Survey 100-year flow estimate is the INTEC from the Big Lost River, although 7,260 cubic feet per second at the Arco gauging evidence of flooding in geologic time exists. station 12 miles upstream of the INEEL Diversion Dam. This estimate is based on 60 Flooding from a failure of Mackay Dam on the years of stream gauge data and conservative Big Lost River was evaluated for the potential assumptions. These assumptions attempt to impact on INEEL facilities (Koslow and Van address the effect of Big Lost River regulation Haaften 1986). The maximum flood evaluated and irrigation, which complicate the use of tra- was assumed to be caused by a probable maxi- ditional approaches to flood frequency analy- mum flood resulting in the overtopping and rapid sis. The U.S. Geological Survey published a failure of Mackay Dam. This flood would result preliminary one-dimensional map of the Big in a peak surface water elevation at INTEC of Lost River flood plain (Berenbrock and 4,917 feet, with a peak flow of 66,830 cubic feet Kjelstrom 1998) based on the 7,260 cubic feet per second in the Big Lost River measured near per second 100 year flow estimate (see Figure INTEC. The average elevation at INTEC is 4-9). In this study, it was assumed that the 4,917 feet (ESRF 1997). At this peak water sur- INEEL Diversion Dam did not exist and that face elevation, portions of INTEC would be 1,040 cubic feet per second would be captured flooded, especially at the north end. Because the by the diversion channel and flow to the ground surface at INEEL and INTEC is rela- spreading areas southwest of the Diversion tively flat, floodwaters outside the banks of the Dam. The model then routed the remaining Big Lost River would spread over a large area 6,220 cubic feet per second down the Big Lost and pond in the lower lying areas. The peak River channel on the INEEL. water velocity in the INTEC vicinity was esti- mated at 2.7 feet per second. Although flood A U.S. Army Corps of Engineers analysis of velocities are relatively slow and water depths existing data (Bhamidipaty 1997) and an are shallow, some facilities could be impacted. INEEL geotechnical analysis (LMITCO 1998) In particular, in the event of a design basis flood both concluded that the INEEL Diversion Dam with sufficient magnitude and duration, a poten- could withstand flows up to 6,000 cubic feet per tial effect could be the failure of bin set 1. This second. Culverts running through the diver- event is discussed in Section 5.2.7.3. sion dam could convey a maximum of an addi- tional 900 cubic feet per second but their Debris bulking was not considered in the flow condition and capacity as a function of water volumes for the probable maximum flood. Other elevation is unknown (Bhamidipaty 1997). than natural topography, the primary choke Although the net capacity of the INEEL points for probable maximum flood flows are the Diversion Dam may exceed U.S. Geological diversion dam on the INEEL and the culverts on Survey 100-year flow estimates, it is not certi- DOE/EIS-0287 4-42 Idaho HLW & FD EIS N W E S 22 28 Lit tl ee Lo st Mackay Ri ver 22 Mud Lake Howe er iv R t t s s INEEL gLo i Arco B TRA 20 INTEC 20 l d a r an C a v Atomic City e l u o w TRA B flo k n l a o p e c r ea ad n y i - L 0 10 rr Mo e n vv nt Railro r e oe Rii 26 Bo m u t n le s r va o e rd L v iig o B G .
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