Exelon filed with the Commission a Notification of Intent (NOI) to relicense the existing Conowingo Project. The Conowingo Project consists of a dam and appurtenant facilities located on the Susquehanna River near Darlington, MD.
The Conowingo Project is located on the Susquehanna River (at river mile 10) in Pennsylvania and Maryland, and has a total drainage area of 27,510 square miles.
Conowingo Dam is located in Maryland connecting Cecil and Harford counties, as is the lowermost six miles of the Project reservoir, Conowingo Pond. The remaining eight miles of Conowingo Pond are located in Pennsylvania, within York and Lancaster counties. Cecil and Harford counties have 99,695 and 239,993 residents, respectively, and population densities of 239 and 545 people per square mile, respectively. York and Lancaster counties have 421,049 and 498,465 residents, respectively, and population densities of 465 and 525 people per square mile, respectively. The nearest metropolitan area within the Susquehanna River watershed is Lancaster, Pennsylvania, approximately 32 miles to the northeast, with a population of about 54,672 people. Baltimore, Maryland with a population of approximately 637,455 lies 45 miles to southwest of the Conowingo Project (U.S. Census Bureau 2008).
The Conowingo Project is the most downstream of the five hydroelectric projects located on the Lower Susquehanna River. The upstream projects (York Haven, Safe Harbor, Holtwood, and Muddy Run) are located at river miles 56, 32, 24, and 22, respectively. Tidewater reaches up the Susquehanna River within four miles downstream of the Conowingo Dam, and the river is navigable by large vessels to Port Deposit, Maryland, located four miles downstream of the dam.
The reservoir, known as Conowingo Pond and formed by Conowingo Dam, extends approximately 14 miles upstream from Conowingo Dam to the lower end of the Holtwood Project tailrace. The Conowingo Pond is generally maintained at an elevation of 109.2 feet (National Geodetic Vertical Datum of 1929 [NGVD 1929]), with a surface area of 9,000 acres and a design storage capacity of 310,000 acre-feet, of which 71,000 acre-feet are usable storage.
The Conowingo Pond serves many diverse uses including hydropower generation, water supply, industrial cooling water, recreational activities and various environmental resources. Relative to hydropower generation, the Conowingo Pond serves as the lower reservoir for the 800-MW Muddy Run Pumped Storage Project (Muddy Run Project), located 12 miles upstream of the Conowingo Dam. It also serves as the source of cooling water for the 2,186 MW Peach Bottom Atomic Power Station (PBAPS), located approximately seven miles upstream of the Conowingo Dam. The Muddy Run Project has a maximum pumping capacity of 28,000 cfs, while PBAPS has a maximum withdrawal capacity of 2,230 MGD (3,450 cfs).
Conowingo Pond is used as a public water supply source, with the City of Baltimore and Chester Water Authority (CWA) having permitted withdrawals of 250 MGD (387 cfs) and 30 MGD (46 cfs), respectively.
The Conowingo Dam is a concrete gravity dam with a maximum height of approximately 94 feet and a total length of 4,648 feet. The dam consists of four distinct sections from east to west: a 1,190-foot long non-overflow gravity section with an elevation of 115.7 feet; an ogee shaped spillway, the major portion of which is 2,250 feet long with a crest elevation of 86.7 feet, and the minor portion of which is 135 feet long with a crest elevation of 98.7 feet; an intake-powerhouse section which is 950 feet long; and a 100-foot-long abutment section. The tailrace and spillway sections of the dam are separated by a dividing wall extending 300 feet downstream of the powerhouse. The dam and powerhouse also support U.S. Highway Route 1.
During original construction, the entire dam was erected upon a solid rock formation of granite and diorite. In 1978, to increase the capacity and upgrade the structure to meet stability requirements, the dam was anchored into the bedrock foundation rock by a post-tensioned anchorage system consisting of stranded wire tendons installed in holes drilled 105 feet through the structure and continuing another 60 feet into the foundation rock. A total of 537 tendons were installed across the non-overflow, spillway and powerhouse intake monoliths.
Flow over the ogee spillway sections is controlled by 50 stony-type crest gates with crest elevations of 86.7 feet and two regulating gates with crest elevations of 98.7 feet. Each of the crest gates are 22.5 feet high by 38 feet wide and have a discharge capacity of 16,000 cfs at a reservoir elevation of 109.2 feet. The two regulating gates are 10 feet high by 38 feet wide and have a discharge capacity of 4,000 cfs per gate at a reservoir elevation of 109.2 feet. Tailwater, which varies with discharge, is at an approximate elevation of 20.5 feet with all units operating with no spillway discharge (i.e. 86,000 cfs).
One 90-ton and two 60-ton gantry cranes are used to perform gate operations. All three gantry cranes can be powered from the 440-volt bus on the headworks. The two 60-ton gantry cranes each contain diesels for emergency backup power. The cranes are mounted on tracks that traverse the powerhouse intake structure and spillway sections of the dam.
Intakes and Powerhouse
The first seven turbine/generating units (1-7) are completely enclosed within the powerhouse, while the last four units (8-11) are an outdoor type of construction thereby eliminating a superstructure in this area. For Units 1-7, a 27-foot-diameter butterfly valve is installed at the entrance to the scroll case. These valves are operated by oil pressure cylinders which are operated from a central oil pressure system, but are rarely used. Unwatering is performed by placement of headgates and stoplogs.
The main power station superstructure enclosing Units 1-7 includes the generator room and the electrical bay. The electrical bay is located between the generator room and the powerhouse headworks and consists of the 13.8-kilovolt (kV) bus and switching equipment. Compartments for step-up transformers are located on the roof of the electrical bay, together with the station service control room and the main control room, from which windows afford a direct view of the generator room.
Units 8-11 are of an outdoor type of construction. Generator circuit breakers and electrical equipment are located in a two-story structure between the generator area and the headworks. The main step-up transformers are located on the roof of this structure.
The intakes for each unit are individually protected by seven trash racks; five are entirely steel (clear spacing of 5.375 inches) and two are steel framed with wood racks (clear spacing of 4.75 inches). The top two racks are constructed of wood due to frazzle ice accumulations on the steel sections. The racks were previously cleaned by a stationary crane. However, a multi-purpose gantry crane was installed in 2007 and is now used as a trash rake.
The current hydraulic equipment for Units 1, 3, 4, 6, and 7 consist of Francis-type single runner hydraulic turbines, operating at 81.8 revolutions per minute (RPM) and designed to develop 64,500 horsepower (hp) each at a point of best efficiency, under a normal head of 89 feet. Units 2 and 5 consist of 54,000 hp Francis-type turbines with single runners, operating at 81.8 rpm at a point of best efficiency under a normal head of 89 feet.
The electric generating equipment for Units 1 and 3 are Asea Brown Boveri, Inc. (ABB) 50,000 kilovolt-amperes (kVA) and 53,000 kVA, respectively, at 0.9 power factor, 60 hertz (Hz), 13,800 volt, three-phase vertical shaft water wheel type generators. Units 2, 4, 6 and 7 are Voith Siemens 53,000 kVA at 0.9 power factor, 60 Hz, 13,800 volt, three-phase vertical shaft water wheel type generator. Unit 5 is an ABB 40,000 kVA at 0.9 power factor, 60 Hz, 13,800 volt, three-phase vertical shaft water wheel type generator. Each generator is equipped with a static excitation system supplied with power from the main generator terminal. Switching and control equipment is provided to connect each pair of generators through individual 13.8 kV circuit breakers to a 13.8/220 kV transformer.
The hydraulic equipment for Units 8-11 consists of a Voith-Siemens mixed flow turbines. Each of these turbines operates at 120 rpm and is designed to develop not less than 85,000 hp each under a normal head of 86 feet.
The electric generating equipment for Unit 8 is a Voith Siemens 75,000 kVA at 0.9 power factor, 60 Hz, 13,800 volt, three-phase vertical shaft water wheel type generator. Units 9, 10, and 11 were originally supplied by Westinghouse Electric Corporation. These units were rewound by National Electric Coil Company with ratings of 61,800 kVA at 0.9 power factor, 60 Hz, 13,800 volt, three-phase vertical shaft water wheel type generators. Each generator is equipped with a static excitation system supplied with power from the main generator terminal. Switching and control equipment is provided to connect each pair of the four generators through individual 13.8 kV circuit breakers to a 13.8/220 kV transformer.
Additionally, two house turbines manufactured by S. Morgan-Smith, Inc. have been installed with a full gate capacity of 1,900 hp each when operating under a normal net head of 89 feet. The generators for these units are of Westinghouse manufacture and are rated at 1,600 kVA at 0.9 power factor each. These units provide station service and “black-start” capability.
Fish Passage Facilities
The Project currently operates two fish lifts. The west lift, adjacent to the right abutment, is currently operated under an agreement with the United States Fish and Wildlife Service (USFWS) for American shad egg production and other research purposes.
The newer east lift, which uses regulating gate bays for attraction flow, is used primarily to pass American shad and other migratory fishes during the April – June migration season.