How big is Muddy Run?

Muddy Run has a reported capacity of 1,072 MW. Source: EIA Form 860.

What kind of plant is Muddy Run?

Muddy Run is a Hydroelectric Pumped Storage facility in Lancaster County, PA, participating in the PJM market.

Where is Muddy Run located?

Muddy Run is in Lancaster County, PA, inside the PJM balancing area.

Who operates Muddy Run?

Muddy Run is operated by Constellation Power, Inc according to the EIA generator inventory. Reporting membership does not by itself establish ultimate ownership.

When did Muddy Run start operating?

Muddy Run reports a commercial operation date of 1966. Current status: operating. Source: EIA Form 860.

How much electricity does Muddy Run generate?

Muddy Run reported 1,938.1 GWh over the twelve months to 2026-06. For a storage plant this is reported gross generation — a discharge proxy, not a cycle count or a conventional capacity factor.

How does Muddy Run compare to other plants?

By capacity, Muddy Run ranks #7 of 39 operating plants of the same technology nationally. It ranks #1 of 2 in PA.

Muddy Run — 1,072 MW hydro plant, Lancaster County, PA

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Muddy Run — 1,072 MW hydro plant, Lancaster County, PA · Ask the Grid

Overview

Power / energy: 1,072 MW / 10,720 MWh
Reported plant capacity and configuration.
Technology: Hydroelectric Pumped Storage
Primary generation technology.
Registry anchor: Plant 3164
Constellation Power, Inc · Lancaster County · PJM
Storage duration: 10 hours
Battery subsystem rating.
Operating status: Operating
Muddy Run is operating.
Commercial operation: 1966
Best-supported operating milestone.

Profile

Grid role: Pumped-storage generation for peak demand with off-peak pumping and storage arbitrage.
Context: Muddy Run was the largest pumped-storage hydroelectric power plant in the world when it began commercial operation. Its output supports regional peak-demand requirements, particularly during hot summer afternoons.
Physical build: Muddy Run is an operational pumped-storage hydroelectric facility comprising a dam across the Muddy Run ravine, an upper reservoir, a powerhouse, and eight reversible generating/pumping units. Water flows from the upper reservoir through the turbines to Conowingo Pond, and the units operate as pumps to refill the upper reservoir. The plant; its turbines and generators were later refurbished, with rehabilitation and modernization reported during 1992–1996 and 1998–2000. The owner reports 1,070 MW from eight units, while the EIA-based plant record reports 1,072 MW total nameplate capacity. Installed equipment identified in the sources includes eight Francis turbines rated at 138 MW each and eight electric generators.

Structured profile

Reported capacity: 1,072 MW
Hydroelectric Pumped Storage
Energy: 10,720 MWh
10-hour storage duration
Commercial operation: 1966
Operating status: operating
Muddy Run is operating.
Location: Lancaster County
PJM

Related assets

Similar plants ranked by technology, capacity, and distance.

Conowingo

Hydroelectric · 530.8 MW

Harford County

Same type12 mi away

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Safe Harbor

Hydroelectric · 417.5 MW

Lancaster County

Same type9 mi away

Compare with this plant

Units and generators

Operating generator records and technology attributes reported through EIA-860.

Generator	Capacity	Technology	Operation	Status
1	134 MW 134 MW summer	Hydroelectric Pumped Storage Water · PS	Apr 1967	Operating
2	134 MW 131.7 MW summer	Hydroelectric Pumped Storage Water · PS	Apr 1967	Operating
3	134 MW 134 MW summer	Hydroelectric Pumped Storage Water · PS	Apr 1967	Operating
4	134 MW 134 MW summer	Hydroelectric Pumped Storage Water · PS	Jun 1967	Operating
5	134 MW

Performance

Monthly EIA generation history and recent market-resource behavior where linked telemetry is available.

Peer context

Technology capacity: 1,072 MW; Hydroelectric Pumped Storage
National rank: #7; of 39 operating peers
PA rank: #1; of 2 operating peers

Monthly generation

Download CSV

Latest 12 months

1.94 TWh

Reported gross generation

Latest report

Jun 2026

EIA-923 monthly filing

2025 net exchange

-502.5 GWh

Generation less station charging

Grid and market context

Deterministic links to ERCOT market resources, price records, outage disclosures, queue records, and nearby infrastructure. Candidate joins remain labeled until corroborated.

Nearby substations

HIFLD infrastructure inventory

MUDDY RUN

IN SERVICE · 230 kV

0.0 km

FACE ROCK

Commercial, land, and environmental record

Source-backed project transactions, agreements, land records, permits, and environmental disclosures. Portfolio and adjacent-project facts remain explicitly scoped.

Land and environmental record

Environmental-Compliance Milestone

Aug 14, 2023

2026 DEP fact sheet reports no open violations; July 20, 2020 administrative inspection found treatment units online and operable; August 14, 2023 routine inspection found field results within permitted limits

These are the specific compliance milestones reported in the renewal fact sheet.

Source

Federal-Land Status

Mar 11, 2015

The Muddy Run and related Susquehanna River hydroelectric projects do not occupy federal land

Final environmental-impact material states that the projects do not occupy federal lands.

FERC Project-Boundary Acreage

2012

Approximately 2,793 acres within FERC project boundary

Lands within the FERC Project boundary comprise approximately 2,793 acres, including 1,000 acres impounded by upper power and recreation reservoirs.

2.0 PURPOSE AND GOALS OF

Internal Wastewater Monitoring Point

Mar 25, 2026

Outfall 401: internal monitoring point with design flow of 0.0069 MGD

DEP's fact sheet identifies Outfall 401 as an internal monitoring point associated with the facility's permitted discharge system.

Source

NPDES Industrial-Wastewater Permit

Jun 1, 2026

NPDES Permit PA0009741 effective June 1, 2026 and expires May 31, 2031

Pennsylvania DEP's final industrial-wastewater permit authorizes discharge from Muddy Run Pumped Storage Facility to the Susquehanna River in Lancaster County under Permit PA0009741.

AUTHORIZATION TO DISCHARGE UNDER THE NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM DISCHARGE REQUIREMENTS FOR INDUSTRIAL WASTEWATER FACILITIES

Related parties and identifiers

Parties, market resources, and identifiers tied to this asset, with owner, operator, developer, EPC, compliance provider, and interconnecting entity roles kept separate.

Relationship graph

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AssetOwner / operator

Parties and identifiers

OrganizationRoleBasis

plant:plant-3164Grid selectionCanonical asset page /assets/facilities/muddy-run.

Reporting portfolio

EIA reporting entity

Constellation Power, Inc

Entity 6035

Timeline and sources

Project milestones and public references behind the asset profile.

Project timeline

1966
1966
Commercial Operation BeganMuddy Run P...
Constellation states that Muddy Run began providing electric power to the regional transmission system in 1966.
Apr 1967
Apr 1967
Generators enter operation

Largest reported plants in this portfolio
Largest reported plants	Capacity	State
Handley	1,314.8 MW	TX
Wolf Hollow II	1,231.2 MW	TX
Colorado Bend II	1,230.3 MW	TX
Muddy RunCurrent	1,072 MW	PA
Eddystone Generating Station	861.6 MW	PA
Croydon CT Generating Station	546.4 MW	PA
Conowingo	530.8 MW	MD
Exelon West Medway II LLC	263.6 MW	MA

Muddy Run