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Site Visit Report

Mercer Generating Station

Lamberton Road

Hamilton Township, NJ 08611

May 26, 2010

1.0 Background and Objectives

The Environmental Protection Agency (EPA) is in the process of developing 

316(b) cooling water intake structure requirements that reflect the best technology

available (BTA) for minimizing adverse environmental impact for all existing 

power plants and manufacturing facilities. As part of this process, EPA staff is 

visiting electric generators and manufacturers to better understand the cooling 

water intake structure (CWIS) technologies in use at facilities, including the sitespecific characteristics of each facility and how these affect the selection and 

performance of CWIS technologies. EPA is also visiting facilities to better 

understand cooling water use and specific issues or technologies that can affect 

316(b) compliance. Mercer was selected for a site visit due to its proximity to 

EPA Headquarters and its location on a large tidally influenced freshwater river.

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2.0 Facility Description

Mercer is located on a 115 acre site outside of Trenton, along the Delaware 

River,2and began operations in 1960. The facility is owned by PSEG and 

employs approximately 125 people. The facility’s NPDES permit (NJ0004995) is 

due to expire on October 31, 2011.

3.0 Electricity Generation and Transmission

Mercer has two coal-fired generating units, each with a generating capacity of 300 

MW (600 MW total). The facility typically uses eastern bituminous coal from 

West Virginia.3 The coal (delivered by barge) is a premium grade with low sulfur 

content. Mercer is a load-following plant, with a capacity factor in recent years of 

approximately 50-70%.

The facility has routine maintenance outages approximately every 18 months.

Unit 3 is an old 8-turbine expander turbine generating unit (125 MW total) that is 

rarely operated and will be decommissioned in 2015.

 

1 EPA was unable to provide a copy of this report to the facility for review prior to publication.

2 Mercer is located in the freshwater portion of the Delaware River, but does experience tidal surges of up 

to 7 feet. Approximately 3 miles downriver, the Delaware is generally considered to be tidal/brackish.

3 The facility has 3 pulverizers to provide fuel to the generating units. These units can also burn natural gas.
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4.0 Cooling Water System and Intake Structure

Mercer uses a once-through cooling system and operates a shoreline CWIS. The 

intake structure is comprised of a trash rack/ice barrier followed by coarse mesh 

traveling screens (1/2 by 1/4 inch mesh). There are 4 screens, each with a single 

fixed speed circulating pump and a service water pump, with a total design intake 

flow of 610 million gallons per day (mgd).4 The design through-screen velocity is 

approximately 1.5 feet per second (fps). The facility is permitted to use chlorine 

as a biocide for up to three 20 minute cycles per day. The facility is also capable 

of redirecting heated effluent to the CWIS in the winter to prevent ice formation.

As part of the requirements in their current NPDES permit, Mercer will be 

installing new Ristroph screens with a new directional (i.e., will discharge fish in 

the direction of the tidal current) fish return and dual pressure spray wash next 

year. The screens will be continuously rotated from May to October. The new 

screens will cost approximately $8 million. PSEG selected the Ristroph screens 

over other designs due to the familiarity from using them at other sites and known 

performance. Mercer will be required to conduct 2 years of verification 

monitoring following the installation of the new screens.

5.0 Impingement and Entrainment Information

The facility conducted extensive impingement and entrainment studies in the 

1990s (one in 1991-1992 and another in 1998-1999) and did not find significant 

impingement, even during the large shad runs each spring.

6.0 Cooling Tower Feasibility

The facility has not extensively studied a potential retrofit to closed-cycle cooling. 

Facility representatives noted significant economic challenges (see Section 14.0), 

as well as space constraints; the facility’s recently constructed air emissions 

controls occupy much of the space near the facility. Facility representatives also 

noted a nearby highway that could be affected. See Section 12.0 below for 

information on other potentially available space.

Mercer has a wastewater treatment facility onsite and facility representatives 

assumed that it would be capable of handling additional flow from cooling tower 

blowdown if the site were required to retrofit to closed-cycle cooling.

7.0 Debris Handling

Mercer does not have significant problems with trash or debris. Episodic debris 

events occur in spring, when accumulated woody debris is flushed into the river.

 

4 Each circulating pump is rated at 105,000 gpm, while each service water pump has a capacity of 875 gpm.
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8.0 Repowering/Future Uses

Facility representatives stated that there are no plans to expand the facility; at 

present, Mercer provides PSEG with valuable fuel diversity in its generating fleet.

9.0 Cooling Ponds

There are no active cooling ponds on site. Two ash ponds are no longer in 

service; see Section 12.0.

10.0 Ownership

Mercer is owned by PSEG, an investor-owned company. PSEG has fossil plants 

in New Jersey, Connecticut, New York and Texas, plus nuclear plants in New 

Jersey.

11.0 316(a)

Mercer is subject to thermal discharge limits (discharge temperature, total heat 

load, and delta T) and has a 316(a) variance that was developed in the 1990s.

12.0 Ash Handling

Bottom ash is used for roofing and other products, while fly ash is also used for 

beneficial uses.

Mercer previously operated two ash ponds just northeast of the generating units, 

but decommissioned these ponds in the 1990s.

13.0 Air Emissions Controls

Mercer is constructing a dry scrubber for each generating unit to address SOx. 

These units will become operational in late 2010. The facility also installed 

electrostatic precipitators in the 1990s to collect dust and particulate matter. In 

2004, they added an SCR to address NOx emissions. By adding each of these 

control technologies, the facility has greater flexibility in the types of coal that it 

can use. Facility representatives noted that PSEG is closing 2000 MW of 

generating capacity as a result of compliance with air regulations. They added 

that new units are being added at some facilities, but that the company will not 

recover all of the lost capacity.

14.0 Additional Information

In response to the now-suspended 2004 Phase II rule, facility representatives 

stated that Mercer was likely to pursue the cost-benefit test, given the low 

impingement and entrainment rates at the site. They noted that NJDEP was likely
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to be supportive of this, as they generally consider Mercer to be a site with low 

biological impacts.

Facility representatives stated that the revised rule should contain a site-specific 

option, as cooling towers are not a sensible choice for facilities such as Mercer. 

They believe that a cost-benefit test is the most direct approach, but other options 

(such as pre-approved technologies for certain categories of facility) may also be 

available. Facility representatives note that PSEG operates a number of facilities 

that are only marginally profitable; a rule requiring closed-cycle cooling could 

have a significant effect.

Merryll Reservoir is a large off-river reservoir upstream of the site that was 

constructed by power plants in the area to provide supplemental water supplies in 

times of extreme drought.

PSEG deployed a Gunderboom at another facility (Bethlehem Energy Center) and 

experienced significant problems. The first-of-its-kind fixed panel barrier failed 

each season it was deployed for a variety of reasons.

Bergen is a sister station to Mercer and recently repowered to combined cycle 

with cooling towers (with plume abatement); a nearby WWTP supplies the 

makeup water for the towers.

Attachments

Attachment A List of Attendees

Attachment B Aerial Photos

Attachment C Site Visit Photos
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Attachment A--List of Attendees

Paul Shriner, EPA Headquarters

Erik Helm, EPA Headquarters

Tom Born, EPA Headquarters

Shari Goodwin, Tetra Tech

Kelly Meadows, Tetra Tech

Mark Strickland, PSEG

Carmine DeNicola, PSEG

Mark Schwartzkopf, PSEG
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Attachment C—Site Visit Photos

Please see DCNs 10-6558B through L accompanying this document.