TPDES 02120 FOR TEXAS MUNICIPAL POWER AGENCY’S 

GIBBONS CREEK STEAM ELECTRIC STATION 

SUPPLEMENTAL INFORMATION for 316(b) 

DETERMINATION of BEST TECHNOLOGY AVAILABLE

 

 

 

 

Prepared by: 

PBS&J and 

Texas Municipal Power Agency 

P O Box 7000 

Bryan, Texas 77805 

August 2006 
GIBBONS CREEK STEAM ELECTRIC STATION 

SUPPLEMENTAL INFORMATION FOR SECTION 316(b) DETERMINATION OF BEST 

TECHNOLOGY AVAILABLE 

Section 316(b) of the Clean Water Act requires that the location, design, construction, and 

capacity of cooling water intake structures (CWIS) reflect the best technology available (BTA) 

for minimizing adverse environmental impact (AEI). Under current regulations, existing 

facilities are subject to Section 316(b) conditions that reflect BTA for minimizing AEI on a caseby-case, best professional judgment (BPJ) basis (40 CFR 125.90[b]). 

In July 2007, the Environmental Protection Agency’s (EPA) Phase II Section 316(b) rule for 

existing facilities was remanded to the EPA in Riverkeeper, Inc, et al. v. EPA. As a result, the 

EPA is presently revising the rule and has provided interim guidance to the states through a draft 

guidance document issued in December 2007 titled Development of BPJ-Based Section 316(b) 

NPDES Permit Condition. Although the guidance is draft and is not a requirement, it offers the 

general basis for the development of a BPJ-based evaluation. 

The Section 316(b) permitting process that the Texas Commission on Environmental Quality 

(TCEQ) is presently considering requires facilities to submit information with permit renewals 

that allows permit writers to make BPJ-based decisions. Upon issuance of the permits, the TCEQ 

may require a permit reopener provision and requirement for the facility to submit IM data or 

other information to support AEI analysis. 

The Texas Municipal Power Agency (TMPA) owns and operates Gibbons Creek Steam Electric 

Station (GCSES) [TPDES Permit No. 02120], located in Grimes County near Bryan, Texas. 

GCSES withdraws once-through cooling water from Gibbons Creek Reservoir and is regulated 

under Section 316(b). The following information is provided to show that the GCSES existing 

technologies are BTA, when compared to the effectiveness, applicability, cost and/or energy 

penalty of other technologies for minimizing AEI. 

Facility Description 

GCSES consists of one coal-fired, generating unit that is rated at 480 megawatts and withdraws 

cooling water from Gibbons Creek Reservoir (Figure 1). Gibbons Creek Reservoir is a 2770-acre 

impoundment of Gibbons Creek, which is a tributary of the Navasota River (Segment No. 1209). 

Make-up water for the reservoir is withdrawn from the Navasota River. 
GCSES has one CWIS that is located at the end of an excavated intake channel that is 

approximately 1,500 feet (ft) long. The depth of the excavated channel is approximately 20 ft 

deep and extends to a point that joins the 20-ft contour depth in the reservoir. Approximately 500 

ft of the excavated channel in front of the CWIS forms an intake canal (Figure 2). 

The CWIS consists of seven bays. Four bays house each of four circulating-water pumps two 

bays house the serves two auxiliary cooling-water pumps and the two service-water pumps and 

one bay houses the Firewater System pump. The pumps are protected by seven 12-foot wide 

vertical traveling water screens (screens) and trash racks. All of the CWIS pumps withdraw from 

a common embayment behind the screens. 

The screens consist of 3/8-inch square steel mesh, which can be rotated and cleaned with a spraywash system. The screens generally remain stationary, but are rotated and washed daily to 

prevent the accumulation of debris and head loss. The screen wash is carried through a sluice to a 

debris basket. The wash water is returned to the intake canal. The trash racks are constructed of 

3.5 x 0.5-inch steel plated placed on 3-inch centers, which are approximately 5 feet in front of the 

screens. 

Since the pumps withdraw water from a common embayment behind the screens, through-screen 

velocity depends on the number of pumps in operation. The maximum design flow of the facility 

is 564 million gallons per day (mgd). At normal reservoir pool elevation, the maximum throughscreen velocity is approximately 1 ft/second. However, facility flows generally lower than design 

flow (e.g. <500 mgd), where through-screen velocities are less than 1 ft/s. 

Reservoir Fishery Data 

Gibbons Creek Reservoir is open to the public for fishing and other recreation. The Texas Parks 

and Wildlife Department (TPWD) manages the fishery in the reservoir. The TPWD surveys the 

fish community in the reservoir approximately once every 3 years. Their surveys consist of 

qualitative sampling techniques, including boat electrofishing, gill netting, and trap-net surveys 

for the purpose of sport-fish management. A summary of the data collected by the TPWD are 

available through the Federal Aid in Sport Fish Restoration Act Performance Reports. The most 

recent survey for which the report is available was conducted in 2002 (TPWD, 2003). 

Bluegill (Lepomis macrochirus) is considered the prominent prey species, with electrofishing 

catch rates ranging from 130/hour to 297/hour over recent survey periods. Threadfin shad 

(Dorosoma petenense) and gizzard shad (D. cepedianum) are also important prey species. 
Threadfin shad electrofishing catch rates are somewhat variable, ranging from 77/hour in 2002 to 

172/hour in 1999. Electrofishing catch rates for gizzard shad ranged from 80/hour in 1999 to 

155/hour in 2002. 

Recent angler creel surveys indicated that largemouth bass (Micropterus salmoides), blue catfish 

(Ictalurus furcatus), and crappie (Pomoxis spp.) are the most popular sport fish. Largemouth bass 

electrofishing catch rates varied over recent survey periods from 26/hour in 2001 to 99/hour in 

2002. Gill net catch rates for blue catfish ranged from 18/net night in 1998 to 27/net night in 

2003. Trap net catch rates for crappie ranged from 2/net night in 1995 to 1/net night in 1998. 

Impingement and Reservoir Sampling 

As per the recent 316(b) Phase II rule, impingement monitoring was conducted by the TMPA. A 

total of 26 impingement samples were collected biweekly from December 2006 through 

November 2007. Each impingement sample included collection of fish from the screens over a 

24-hour period, basic water quality measurements, and observations of facility and environmental 

variables. The total number of fish collected during all sample events combined was 2,663 

representing 19 species. The overwhelming majority (92%) was threadfin shad followed by 

pirate perch (Aphredoderus sayanus) [3%], and bluegill [2%]. Recreationally important species 

made up approximately 1% of the fish impinged. 

Gibbons Creek Reservoir is sampled approximately once every 3 years by the Texas Parks and 

Wildlife Department. Data collected by the TPWD allow for qualitative assessments of target 

species, but do not provide a basis for quantifying pelagic species or juvenile life stages that may 

be susceptible to impingement. In particular, there were no data that described the pelagic 

segment of the threadfin shad population. 

Due to the paucity of data describing the segment of the fish community that is susceptible to 

impingement (e.g. clupeids), the TMPA conducted a field study to quantify threadfin shad, 

juvenile gizzard shad (D. cepedianum), and other pelagic species through the use of a pairedframe trawl (trawl). The purpose of the study was to collect information to support AEI and BTA 

analysis with respect to the existing CWIS design and operation. The trawling was performed 

quarterly, for 1 year, during approximately the same period in which the impingement sampling 

was conducted. The trawl survey included the collection of pelagic fish that would allow for 

developing population metrics, such as density, standing crop, and production. In addition, trawls 

were conducted in the intake canal to quantify the spatial and temporal difference in the fish 

populations. 
Results of the trawl study provided significant insight into the shad populations that is not well 

described through the TPWD routine monitoring. However, detailed analysis of the data has not 

been performed. Of particular interest are the threadfin shad population statistics. The mean 

density of threadfin shad, considering all sample locations and sample events, was approximately 

3,000/acre-ft. The mean number (all sample events averaged) of threadfin shad in the reservoir 

was estimated at approximately 95 million with a mean standing crop of 420,000 lbs. 

Information also gleaned from the trawl study indicated that the location of withdrawal from the 

reservoir and the depth of the intake canal also provide some fish-protection benefits. 

Preliminary analysis of the data indicates that the lowest densities of shad exist in the main body 

of the reservoir, which is where cooling water is withdrawn. In addition, a portion of the cooling 

water is withdrawn from depths >10 ft. Results of the trawl study indicate that some of the 

lowest densities of shad and other species exist in the deeper water of the intake canal. 

EPA Modeled Technologies 

As part of the Section 316(b) Phase II rule-making process, the EPA modeled 14 fish-protection 

technologies (technology) and costs for facilities (EPA, 2004). Of the 14 technologies considered 

by the EPA, only two were applicable for reducing IM. These were the addition of fish-handling 

and return systems to existing traveling water screens (fish handling and return system) and the 

addition of fish-net barrier systems (barrier net). The most common modeled technology for 

reservoir facilities was the addition of fish-handling and return systems. 

There was no technology modeled for GCSES. However, the CWIS that serves GCSES is the 

same technology that is used at other similar facilities where costs were modeled. While there 

can be differences among the facilities that would affect costs, the costs provided by the EPA for 

similar facilities could be used to approximate the annualized capitol, operation, and maintenance 

costs for GCSES. 

The estimated annualized cost for the addition of fish handling and return systems for facilities 

similar to GCSES ranged from approximately $500,000 to $2,000,000. The estimated annualized 

cost for the installation of fish-barrier nets ranged from $30,000 to $100,000. It is important to 

note that many utilities argued that the EPA costs underestimated the true costs of these 

technologies for various reasons. The existing traveling-screen technology employed at these 

facilities is not conducive for fish handling since they do not have fish-handling troughs on the 

screen frames. Therefore, to make the system functional, the existing screens must be modified 

or replaced to include this structure, which would require the facility shutdown and loss of 
revenue. Many utilities commented that the lost revenue that would result from this retrofit was 

not accurately represented in the EPA costs and would result in higher costs than those modeled. 

The use of barrier nets in biologically productive southern waters was also questioned. Due to 

debris loading and biofouling, utilities argued that the maintenance cost was not thoroughly 

considered. In some cases, the installation of this technology would possibly require facility shut 

down and lost revenue and permitting, which was not considered in the modeled cost. 

Technologies Considered for GCSES 

In addition to the fish handling and return system and barrier nets, the use of fish deterrents 

(deterrents) may also help to reduce impingement at reservoir facilities, although deterrents were 

not specifically listed by the EPA as a modeled technology. While cost-benefit analysis was 

specifically remanded from the rule by the court, the cost-effectiveness of such technologies is 

expected to provide a practical screening tool for determining which, if any, technology might be 

considered BTA only after analysis of the IM data indicate possible significant AEI. The 

following sections provide a brief overview of the applicability and efficacy of these technologies 

at GCSES. 

Fish Handling and Return System – This technology would require extensive modification of 

the CWIS as well as extended outage of the facility during construction. Due to the design of the 

existing screens, retrofitting a fish-handling system (e.g. fish buckets or toughs) would not be 

possible. Instead, the existing traveling screens would be replaced with a coarse-mesh Ristroph 

or comparable screen. Furthermore, the surface-area of the screens would need to be enlarged to 

further reduce through-screen velocity to <0.5 ft/s, which would require major structural 

modifications to the screen embayments 

Presently, the screens are rotated and washed approximately once-per-day to prevent debris 

accumulation. For a fish handling system to be effective, the screens would need to be operated 

continuously or at least during periods of impingement, which would increase operation and 

maintenance (O&M) costs. 

In addition to the screen replacement, a new fish-return system would need to be built that would 

carry the impinged fish to the reservoir, a distance of approximately 1,000 feet. The return 

system would need to be covered or screened to prevent predation by birds, raccoons, etc. 
Given the relatively low through-screen velocity (0.5 to 1 ft/s) at GCSES, it is believed that 

healthy fish could avoid impingement and many of the impinged fish were believed to be 

moribund or dead upon impingement. In particular, the large majority of impinged fish were 

threadfin shad, most of which were in poor condition or dead upon collection. It is unlikely that 

the use of a fish handling and return system would significantly reduce IM. Threadfin shad are 

very sensitive to handling stress and the survival of healthy individuals would probably be low. 

Conversely, other impinged species, including pirate perch, bluegill, and crappie, if healthy when 

impinged, would probably survive with the use of this technology. However, the number of these 

species that are impinged is exceptionally low, which would suggest that the technology is would 

not be cost-effective. 

Barrier Net – A properly-designed barrier net would exclude fish from the intake screens, which 

would prevent impingement. There are three key compliance features for a barrier net – a mesh 

size slightly smaller than the 3/8-inch square-mesh intake screens, reduction of through-net 

velocity to <0.5 ft/s, and an installation that would prevent passage of fish under or around the 

barrier net. Based on the previous rule, it is assumed that reducing velocity to <0.5 ft/s would 

prevent impingement of healthy fish on the barrier net and would be an acceptable compliance 

alternative. 

The approach velocity in the intake canal is approximately 0.4 ft/s. A 1⁄4-inch mesh net would 

occupy approximately 50% of the cross section of the intake canal, resulting in through-net 

velocities >0.5 ft/s. To reduce the through-net velocity to <0.5 ft/s, the net area would need to be 

approximately twice that of the intake canal cross section. Therefore, the net placement would 

need to extend from the intake canal and into the reservoir. Depending on the design, the barrier 

net system may require permitting. 

There are several barrier net designs that could be employed at GCSES. All of which require 

permanent structures to hold the barrier nets in place and to secure the bottom and ends to prevent 

fish passage. Barrier nets require cleaning and/or replacement to reduce biological fouling and 

debris loading. As such, a second barrier net is typically used so that one net is always in place 

while the other net is being cleaned. In addition, verification monitoring might be required to 

insure that the net is properly working. 

Since the barrier net placement would probably extend into the reservoir, there would be a large 

area behind the barrier net in which fish would reside. Many larval fish and eggs will be able to 

pass through the barrier net and some of them will mature in the area between the barrier net and 

the intake screens. Therefore, it is likely that some level of IM would persist. In addition, the 
barrier net would also restrict angler access to this area of the reservoir, part of which is presently 

open to public access. 

Fish Deterrents – Fish deterrents, including lights, sounding devices, and electrical barriers have 

been used to varying degrees of success for specific applications. There are no known studies of 

the efficacy of deterring threadfin shad using these types of technologies. Furthermore, there are 

no known installations of these technologies in the region that would provide some insight into 

their efficacy. It is likely that these technologies would be the least costly to install and operate; 

however, a site-specific study would be needed to evaluate efficacy. 

It is important to note that fish deterrents are only useful for deterring larger, healthy fish that are 

capable of responding to stimuli. In some cases, fish can acclimate to lighting and sound 

deterrents, resulting in reduced efficacy over time. The use of lighting in Gibbons Creek 

Reservoir would be of limited used due to the high turbidity. It is likely that significant costs 

would be incurred through pilot studies, which would be used to identify the appropriate 

technology, if any, that would be applicable at GCSES. Since many impinged fish are believed to 

be moribund or dead upon impingement, deterrents would likely have a low efficacy. 

AEI/BTA Considerations 

As previously discussed, IM-reduction technologies modeled by the EPA do not represent BTA 

for GCSES since AEI is presently avoided using existing technology and since any incremental 

IM reduction would not be cost effective. Other technologies that might have some application, 

such as fish deterrents, are not proven technologies and would probably not substantially reduce 

IM. The existing technology at GCSES is believed to represent BTA for minimizing AEI for a 

number of reasons, as described below. 

1. GCSES withdraws water from a reservoir that was specifically built as an industrial 

cooling-water impoundment and has operated on and has withdrawn water from the 

reservoir since the reservoir was impounded (1981); 

2. The cooling system at GCSES meets the definition of a “closed-cycle recalculating 

system” as described in EPA (2004); 

3. In addition to its use as an industrial cooling-water impoundment, the construction of 

Gibbons Creek Reservoir created over approximately 2,800 acres of aquatic habitat for 

fish and wildlife; 

4. The TMPA developed public access facilities and allows public access for a variety of 

outdoor recreation opportunities that would not exist absent the facility and reservoir; 

5. The TPWD stocks and manages the fishery in the reservoir; 

6. The TPWD (2008) describes the largemouth bass and catfish fishery in Gibbons Creek 

Reservoir as “excellent”, the crappie fishery as “good”, and the sunfish fishery as “fair”. 
Numerous largemouth bass over 10 lbs. have been caught from the reservoir (TPWD, 

2008); 

7. The TPWD has never listed IM as a concern for the reservoir fishery nor is the predatory 

fish population limited by the forage species that are impinged (e.g. threadfin shad); 

8. The number of fish (2,663) impinged was relatively low and consisted of very few 

recreationally important species. In addition, no threatened or endangered species are 

know to exist in the reservoir, nor were any collected in impingement samples; 

9. Operation of the reservoirs as a cooling-water impoundment results in biological 

productivity that is higher than other “non-cooling” reservoirs in the region; 

10. IM of all species appears to be a very small fraction (e.g. <1%) of the reservoir’s standing 

crop, density, and production; 

11. The location and design of the intake canal and CWIS provides some fish-protection 

benefits; and 

12. The existing through-screen velocities are relatively low (e.g. usually <1 ft/s) for this type 

of facility, which helps reduce impingement. 

In summary, the existing CWIS design and operation at GCSES is BTA, which is documented by 

the results of the recent impingement study. Preliminary analysis of the reservoir fishery data 

indicates that there is little potential for AEI with respect to the reservoir fish community. 

Furthermore, the construction of Gibbons Creek Reservoir as a cooling-water impoundment 

resulted in the creation of extensive aquatic habitats and extensive public recreation opportunities 

that would not otherwise exist. The installation and operation of more stringent fish-protection 

measures would probably not yield measureable environmental benefits and, therefore, are not 

necessary or cost effective. 

Literature Cited 

Environmental Protection Agency (EPA). 2004. National Pollutant Discharge Elimination 

System – Final regulations to establish requirements for cooling water intake structures at 

Phase II existing facilities. Environmental Protection Agency, Washington D.C. Vol. 

69:131. 

Texas Parks and Wildlife Department (TPWD). 2008 Fishing Gibbons Creek Reservoir. 

Accessed on the internet on July 15, 2008 at: 

http://www.tpwd.state.tx.us/fishboat/fish/recreational/lakes/gibbons_creek/ 

TPWD. 2003. Federal Aid in Sport Fish Restoration Act, Performance Report for Gibbons Creek 

Reservoir. Texas parks and Wildlife Department, Austin.