1

Site Visit Report

Williams Station

2242 Bushy Park Road

Goose Creek, SC 29445

February 9, 2009

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 typical facilities, including 

the site-specific 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. Williams Station (Williams) was selected for a site visit due 

to its use of a partially recirculating cooling water system.

2.0 Facility Description

Williams is located on approximately 470 acres.

1

 It began operation in 1973 and 

has 78 employees. It withdraws cooling water from the Back River Reservoir2

and discharges 450-500 MGD to the tidal Cooper River under NPDES permit 

number SC0003883 which was renewed on June 1, 2009. At the time of the site 

visit, the permit had expired; Williams had submitted permit renewals, but permit 

reissuance was still in progress. Williams is owned by GENCO, a wholly owned 

subsidiary of SCANA. The facility is operated by South Carolina Electric & Gas 

Company.

3.0 Electricity Generation and Transmission

Williams has a single 650 MW coal-fired generating unit. It was originally 

designed to use #6 fuel oil, but the plant converted in 1984 to utilize coal. 

Williams is a baseload unit operating at around 80 to 85 percent availability. 

Currently, Williams uses eastern bituminous coal, but has the capability to import 

coal from South America.

3

 The plant has two routine maintenance outages each 

 

1

Facility representatives estimated that the site was about 40% developed; 20% of the site was in use by 

the plant itself and another 20% of the area is covered by the treatment ponds.

2 Downstream of the point of withdrawal, the Back River has been dammed, creating a freshwater 

reservoir.

3 Williams added a barge loading facility to receive coal from South America. Domestic coal is received 

by rail only.
2

year (spring and fall) that typically last one week. About every three years, 

Williams has an 8-10 week outage for turbine overhaul.

The facility also has two 25MW gas turbines onsite for peaking power and to 

provide startup capabilities. There is not sufficient distribution infrastructure for

the facility to change to natural gas as its base fuel.

4.0 Cooling Water System and Intake Structure

Williams withdraws from the Back River Reservoir via a 1000 foot long canal. 

Where the canal reaches the highway at the facility entrance, water passes 

underneath the road via concrete culverts. Additionally, a surface boom upstream 

of the culverts removes floating debris and vegetation. After passing under the 

roadway, the canal “daylights” for another 500 feet before reaching the CWIS.

Williams has a single CWIS with a common trash rack and six bays; each pair of 

bays has two coarse mesh (3/8” square mesh) fiberglass traveling screens and one 

pump. The facility occasionally experiences a heavy debris load from uprooted 

aquatic vegetation that becomes impinged on the trash rack; the materials are 

removed from the trash rack by a claw system and deposited adjacent to the intake 

structure and eventually disposed of onsite. During a screen cleaning cycle, one

screen rotates continuously for 30 minutes, followed by subsequent individual 

screens.

4

 Materials and fish impinged on the traveling screens are also deposited 

in a trash bin at the CWIS; there is no fish return. In 1984, Williams added a 5 

mm debris filter downstream of the traveling screens (and prior to the condensers)

for additional debris removal.5

The intake pumps are rated at 375,000 gallons per minute (gpm), giving a design 

flow of 533 million gallons per day (mgd) and a through-screen velocity of 

approximately 0.72 feet per second (fps). The delta T for Williams’ cooling water 

system is 20°F.

Williams does not use biocides at its CWIS.

5.0 Impingement and Entrainment Information

In 1977, Williams conducted a 316(a) and 316(b) study with a biological focus on 

impingement. The 316(a) study was revised in 1989 (following the conversion to 

coal in 1984) and again in 1994. More recently (2005-2006), the facility

conducted a 316(b) study to explore impingement rates; the study was conducted 

in response to the expected requirements of the now-suspended 2004 rule. During 

the study, the facility impinged 52 taxa including 44 species of fish. Blueback 

 

4

Facility representatives stated that they previously replaced traveling screens every 3 years due to heavy 

use, but have recently switched to fiberglass materials and a less frequent screenwash regimen.

5

Facility representatives noted that the debris filter would very likely lead to zero through-plant 

entrainment survival, if such a measure were included in the revised rule.
3

herring and hog choker comprised 68 percent of the abundance and the top 8 

species represented more than 90 percent of the total aquatic life. Shellfish were 

observed in very small abundance. No major diurnal variation or seasonality was 

observed. Using information collected in this study, Williams estimated its 

annual calculation baseline to be 57,000 organisms, with an approximately 1 

order of magnitude variation year to year due primarily to cold shock events 

(primarily affecting the shad species). Facility representatives noted that most of 

the impinged organisms were young-of-the-year, indicating that biologically

productive years could lead to higher impingement rates at the CWIS.

Williams has not conducted any entrainment studies.6

6.0 Cooling Tower Feasibility

The plant originally had a 14 cell cooling tower that was destroyed in 1989 by

hurricane Hugo. The rebuilt (1990) cooling tower has 15 cells. Under normal

operations, the facility employs once-through cooling and uses the cooling tower 

as a “helper” tower to reduce the amount of heat discharged to the Cooper River.

7

 

However, for approximately 4 days per year, state resource agencies apply 

herbicides to the aquatic vegetation in the Back River Reservoir as part of routine 

maintenance. During this period, Williams operates its cooling towers as a 

closed-cycle system to increase the residence time of the herbicide within the 

reservoir.8,9 The facility loses between 50 and 150 MW of electricity generation 

when operating as closed-cycle, depending on variables such as ambient 

temperature, river temperature and relative humidity.

10

 Depending on seasonal 

temperatures, the facility is capable of operating as a closed-cycle system more 

often, but does not do so in order to maintain the flow to the Cooper River and to 

avoid the energy penalty associated with operating the towers.

According to facility representatives, the existing towers are reaching the end of 

their useful lifetime. 

Facility representatives stated that Williams has available land to construct 

additional cooling towers (enough to enable operations as a fully closed-cycle 

system), however it has not considered doing so.

 

6 The facility noted that none of SCEG’s plants would have been subject to entrainment requirements under 

the now-suspended 2004 Phase II 316(b) regulation.

7 Under normal operations (i.e., once-through with helper towers), only 67% of the cooling water passes 

through the helper towers. The other portion of the flow is directly discharged to the river.

8 Once-through flows at Williams are the primary driver for flow exiting the Back River reservoir. The 

next nearest natural channel to the Cooper River is several miles upstream.

9 The discharge from the cooling towers is not directly tied into the condenser—in closed-cycle mode, 

water is returned to intake canal, adjacent to the CWIS.

10 The facility does not have enough cooling tower capacity to operate at 100% of its generating capacity 

while using a closed-cycle system. Instead, the facility operates only 2 of its 3 intake pumps.
4

7.0 Debris Handling

As discussed in Section 4.0 above, Williams occasionally experiences high 

loadings of vegetation.

8.0 Repowering/Future Uses

Williams does not have current plans to repower or upgrade.

9.0 Cooling Ponds

Williams does not have cooling ponds. 

10.0 Ownership

Williams Station is owned by GENCO, a wholly owned subsidiary of SCANA. 

The facility is operated by South Carolina Electric & Gas Company. Its 

transmission system is owned by South Carolina Electric & Gas Company.

11.0 316(a)

316(a) permit requirements for thermal discharges were originally developed 

when the facility was a fuel oil facility and was updated to reflect coal operations. 

The state has requesting the 316(a) analysis be updated and reviewed to reflect 

current environmental conditions and a verification study is in progress. Current

thermal limits are set at a 17.5°F differential and a 104°F maximum discharge 

temperature. To meet these thermal limits, Williams has had to throttle back 

power production an average of once per year.11

12.0 Ash Handling

Williams does not have an ash pond. Ash is sent to a cement company or landfill.

13.0 Air Emissions Controls

At the time of the site visit, Williams was adding a wet flue gas desulfurization 

(FGD) unit; it was completed in October 2009. Resulting waste is sent to a low 

volume sedimentation pond, identified as “Pond C.” FGD water is discharged; no 

recycle or reuse loop is planned at this time. No additional neutralization is 

intended for FGD wastewater prior to discharge at this time. 

 

11 This has happened several times in 2010 due to unusual atmospheric conditions and equipment being 

out-of-service.
5

14.0 Additional Information

Following promulgation of the now-suspended 2004 Phase II rule, the facility

explored various impingement compliance alternatives.12 These alternatives 

include placing a barrier net in the intake canal, installing Ristroph traveling 

screens with fish return, and the addition of dual entry banks to reduce the intake 

velocity below 0.5 fps. The facility concluded that a barrier net may be 

problematic due to the high levels of vegetation that is impinged on the intake 

screens. The facility concluded that a fish return and handling system would not 

be viable, due to the approximately 3,000 foot distance to the reservoir; there 

were also concerns as to whether the location of the return would be sufficiently

far enough from the intake to avoid re-impingement. Dual entry screens were 

also eliminated from consideration, as facility representatives stated that the 

reduction in intake velocity was unlikely to be sufficient to reach the 0.5 fps 

threshold. The facility determined the most cost-effective solution would be a 

block net.

The facility also evaluated various scenarios for “multimode” operations of the 

cooling tower.13 Facility representatives concluded that the current configuration 

for the cooling towers would not permit recirculation back to the intake structure 

without adding additional pumps.

Williams also evaluated reducing the number of pumps in use (from 3 to 2), but 

found that this would only be feasible during winter, as ambient water 

temperatures in the summer inhibit heat rejection. The facility also concluded the 

variable speed pumps would not be especially effective in reducing the overall 

intake flow. The facility is still considering the use of variable speed controls on 

pumps for power savings reasons.

Facility representatives noted that Summer Nuclear Station (another SCANA 

facility) is proposing to add two new generating units. Both would utilize closedcycle cooling due to regulatory restrictions. However, they noted that evaporative 

consumption via the cooling towers is a concern. Facility representatives stated 

that the prevailing opinion is that dry cooling would not be effective, as ambient 

air temperatures in the summer would limit the heat rejection capability of the 

tower. Additionally, summer is the period of greatest energy demand from 

consumers.

Facility representatives described the hydrologic history of the region. In the 

1940s, the Army Corps of Engineers constructed two shallow reservoirs nearby

 

12 The facility did not explore entrainment technologies because it would not have been subject to 

entrainment requirements. The facility did not submit a Comprehensive Demonstration study (CDS) to the 

state.

13 Multimode refers to operating in various modes of recirculation, depending on the need to reduce intake 

flows at a given time. Williams may be capable of operating as fully closed-cycle, once-through with 

helper towers, or simply as once-through.
6

and re-routed the Santee River into the Cooper River. However, due to problems 

with siltation and other issues, the Corps diverted the flow back to the Santee 

River in 1984. As a result, flows in the Cooper River are lower than before. 

Facility representatives noted that there are several neighboring industrial sites 

that depend on the once-through flow from Williams to maintain low salinity

conditions in the Back River Reservoir; some sites advocate for Williams to pump 

even when not generating, as this improves the dissolved oxygen in the Cooper

River. Facility representatives added that the once-through flows also help to 

prevent salt water intrusion in the City of Charleston’s drinking water supply

upriver.

Attachments

Attachment A List of Attendees

Attachment B Aerial Photos

Attachment C Site Visit Photos
7

Attachment A--List of Attendees

Paul Shriner, EPA

Jan Matuszko, EPA

Kelly Meadows, Tetra Tech

Stephen Summer, SCANA Services, Corporate Environmental Services

Timothy Lucius, SCE&G

Milton Quattlebaum, SCANA Services, Corporate Environmental Services

Mark Ferguson, SCANA Services, Corporate Environmental Services

Terry Cheek, Geosyntec
Copyrighted page(s) have been removed from 

this document. 

Please contact the EPA Docket Center, Public 

Reading Room to view this document. 

Address: 

1301 Constitution Ave, NW 

Room 3334 

Washington, DC 20004 

Telephone: 

202-566-1744 

Fax: 

202-566- 9744 

Email: 

docket-customerservice@epa.gov
10

Attachment C—Site Visit Photos

Please see the attached materials.