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Muddy Run Background

Exelon Generation Company, LLC (Exelon), is licensed by the Federal Energy Regulatory Commission (FERC, the Commission) to operate the 800-megawatt (MW) Muddy Run Pumped torage Project (Muddy Run Project) (FERC No. 2355). The current license for the Muddy Run Project was issued on September 21, 1964 and expires on August 31, 2014.

Exelon filed with the FERC a Notification of Intent (NOI) to relicense the existing Muddy Run Project on March 12, 2009. The Muddy Run Project Powerhouse and Upper Reservoir (Muddy Run Reservoir portion of the Project area) are located in Martic and Drumore Townships, Lancaster County, Pennsylvania, along the eastern shoreline of Conowingo Pond, approximately two miles ownstream of PPL’s Holtwood

Hydroelectric Project. The primary transmission line corridor portion of the Project area is located in Lancaster County and in Lower Chanceford and Peach Bottom Townships in York County. At this time, Exelon is not proposing to add capacity or make any physical modifications to the Muddy Run Project under the new license.

Project Location

The upper (or power) reservoir for the Muddy Run Project is located on the eastern shoreline of Conowingo Pond, which is the reservoir formed by the damming of the Susquehanna River by the Conowingo Dam near Darlington, Maryland. Conowingo Pond acts as the lower reservoir for the Muddy Run Project. The drainage area upstream of Conowingo Dam is 27,100 square miles. 

The Muddy Run Reservoir portion of the Project area is located entirely within Lancaster County, Pennsylvania. Based on the 2007 census estimates, Lancaster County has a population of 498,465 and a population density of 525 people per square mile. The nearest metropolitan area within the Susquehanna River watershed is Lancaster, Pennsylvania, approximately 21 miles to the northwest, with a population of about 54,672 people. Baltimore, Maryland, with a population of approximately 637,455, lies approximately 60 miles to south of the Project. The primary transmission line corridor is located in Lancaster and York County; York County has a population of 421,049 and a population density of 465 people per square mile (U.S. Census Bureau 2008).

Project Facilities

Muddy Run Reservoir

Muddy Run Reservoir (upper reservoir) is a 900-acre body of water impounding 60,000 acre-feet of water with an average depth of 60 feet. Of this, only the upper 50 feet (between elevations 520 feet and 470 feet National Geodetic Vertical Datum of 1929 [NGVD 1929]) of the reservoir (35,500 acre-feet) is available for power generation. The maximum elevation of the reservoir is 520 feet NGVD 1929, which is approximately 411 feet above normal elevation of the Conowingo Pond.

Conowingo Pond (lower reservoir) has a total surface area of approximately 9,000 acres and a design storage of 310,000 acre-feet. The pond elevation is generally maintained at 109.2 feet NGVD 1929.

Main Dam

Muddy Run Reservoir was created by building a rock-filled dam with a central impervious core across the Muddy Run ravine, approximately 2,500 feet from the Muddy Run Powerhouse. The Muddy Run Main Dam Embankment (Main Dam) (National Inventory of Dams (NID) PA00266) is 4,800 feet long, has a maximum height of 260 feet, and has upstream and downstream slopes of 2.5H:1V and 2.2H:1V, respectively. The crest of the dam is at elevation 533 feet, is 30 feet wide and is traversed by a 20-footwide two-laned roadway. The crest provides 13 feet of freeboard when the Muddy Run Reservoir water level is at elevation 520 feet.

East Dike

The east dike is approximately 800 feet long, has a crest width of 20 feet, has a maximum height of about 12 feet and has upstream and downstream slopes of 2.5H:1V and 2.2H:1V, respectively. The east dike is also a zoned earth and rock-fill embankment with an impervious core. The crest of the east dike was raised in 1990 from elevation 529 feet to its current level of 530.8 feet.

Recreation Pond Dike

The recreation pond dike, located in the drainage for the upper reservoir about two miles upstream of the main dam, is a zoned earth and rock fill embankment that forms a 100-acre constant level recreation reservoir. The recreation reservoir provides fishing and boating opportunities for area recreationsists. The dam is approximately 750 feet long, has a maximum height of about 90 feet and a crest width of 34 feet. The dike crest is at elevation 530 feet. The dam includes a four-foot-diameter concrete outlet pipe located in an excavated rock trench under the dam. The portion of the trench located under the impervious core of the dam has been backfilled with concrete after installation of the pipe. The outlet is controlled from the upstream end by a flap gate.

Canal Embankment

The canal embankment, or the Muddy Run Intake Channel Dam, forms the upper part of the intake channel which leads from the upper reservoir to the intake structure. The lower part of the channel is excavated in rock. The embankment has a maximum height of about 35 feet, side slopes of 1.5H: 1V and a minimum crest width of 25 feet. The upstream face of the embankment and the rock cut channel are lined with a nine-inch-thick reinforced concrete slab extending about 1,000 feet upstream on both sides of the canal from the cylinder gates. The upstream portion of the canal is an unlined soil and rock cut. River Road Bridge crosses this section of the canal.

Main Spillway

The spillway for the power reservoir is located on the west side of the intake canal. It is a non-gated concrete ogee-type structure 200 feet long, 20 feet high, has a crest elevation of 521 feet and discharges into a vegetated natural ravine.

The spillway is constructed between sections of the canal wall dikes and is flanked by concrete training walls. Discharges over the spillway would follow the natural ravine which joins Muddy Run Creek just above its confluence with the Susquehanna River. The purpose of the spillway is to protect the embankments from overtopping in the event of a probable maximum precipitation event that could not be passed though the generating units. The rated capacity of the spillway is 15,000 cfs.

Recreation Pond Spillway

The recreation pond spillway consists of a nearly level rock cut channel approximately 140 feet wide with an invert at elevation 520 feet. The spillway is traversed by a steel and concrete bridge which is used by pedestrian traffic and by recreation area Maintenance vehicles.

Intake Structure

 The intakes which admit water for power generation consist of four cylinder gates with trash racks (clear spacing of 5.375 inches). Each intake supplies two units and includes a cylindrical tower which leads to a 430-foot-deep vertical shaft. The vertical shafts and horizontal power tunnels are concrete lined with a diameter of 24.5 feet. The concrete lined power tunnels bifurcate approximately 500 feet upstream of the powerhouse. Beginning approximately 400 feet upstream of the powerhouse, the tunnels transition to 14-foot-diameter steel penstocks that continue downstream to connect to one of eight pump turbine units in the powerhouse. There are no inlet valves at the downstream end of the penstocks.

Powerhouse

The powerhouse has dimensions of approximately 600 feet long by 133 feet wide, and is constructed entirely of concrete. A gantry crane travels the length of the powerhouse and service bay.

The powerhouse turbines (Francis type) each have a hydraulic capacity of 4,000 cfs, for a total discharge capacity from the powerhouse of 32,000 cfs. The pumping capacity of the pump turbines is 3,500 cfs each for a total powerhouse pumping capability of 28,000 cfs. The draft tubes discharge directly to the Susquehanna River adjacent to the powerhouse. The units are equipped with trash racks (clear spacing of 5.75 inches) between the draft tube outlet and the river.

The electrical generating equipment consists of eight motor-generator units, each rated at 13.8 kilovolts (kV), 3 phase, 60 cycle, 100 MW at 0.9 power factor at a temperature rise of 140°F (60°C) as a generator. Switching and control equipment are connected to the eight motor-generators in pairs to the four 13.8-220 kV transformers. A 13.8 kV circuit breaker is provided on each motor-generator.

Automatic generation control equipment, capable of starting, running and stopping the units and their auxiliaries, is provided to permit remote operation of the plant in generation mode from the corporate office in Kennett Square, Pennsylvania or remote operation of critical operating functions in either the generation or pumping mode from the control room at the Conowingo Hydroelectric Project.

Transmission Lines

The primary transmission lines consist of two 220 kV three-phase, three-wire circuits. The lines, owned by Exelon, but leased to PECO Energy Company, an affiliate of Exelon, are identified as Line 220-06 and 220-07. Both lines begin at a 220-kV switching station located on the roof of the Muddy Run Powerhouse and run approximately 4.25 miles to the Peach Bottom Atomic Power Station (PBAPS) North Substation located in York County. Each line has a 230kV nominal phase-to-phase voltage and has a normal and emergency rating of 598,000 kVA. Both lines exist in a common 300 foot wide right-of-way, with some variations at the Susquehanna River crossing.

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