## TPDES 02120 FOR TEXAS MUNI CIPAL 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 2006GIBBONS 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 (CWI S) 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 Ag ency’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 As a result, the EPA is presently revising the rule and has provi ded interim guidance to the states through a draft guidance document issued in December 2007 titled Development of BPJ-Based Section 316(b)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 faciliti es 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 C ounty near Bryan, Texas. GCSES withdraws once-through cooling water fro m 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 e ffectiveness, 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 e nd 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 th e 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-wate r 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 th e 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 facilityis 564 million gallons per day (mgd). At normal reservoir pool elevation, the maximum throughscreen velocity is approximately 1 ft/second. Ho wever, 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 fi shing and other recreation. The Texas Parks and Wildlife Department (TPWD) manages the fi shery in the reservoir. The TPWD surveys the fish community in the reservoir approximately onc e 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 availa ble 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 ov er 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 fo r gizzard shad ranged from 80/hour in 1999 to
155/hour in 2002.

Recent angler creel surveys i ndicated 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 surv ey periods from 26/hour in 2001 to 99/hour in 2002. Gill net catch rates for blue catfish range d 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 co llected 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 major ity (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 TPW D allow for qualitative assessments of target species, but do not provide a basis for quantifying pe lagic 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 d esign 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 co llection of pelagic fish that would allow for developing population metrics, such as density, st anding crop, and production. In addition, trawls
were conducted in the intake cana l 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. Ho wever, 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 indi cated 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 exis t 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 reduci ng 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 a ffect 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 a pproximately $500,000 to $2,000,000. The estimated annualized
cost for the installation of fish-barrier nets ra nged from $30,000 to $100,000. It is important to note that many utilities argued that the EPA co sts underestimated the true costs of these technologies for various reasons. The existing tr aveling-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 ofrevenue. Many utilities commented that the lost revenue that would result from this retrofit was not accurately represented in the EPA costs and woul d 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 syst em 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 modele d 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 du ring 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-a rea 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 a pproximately once-per-day to prevent debris accumulation. For a fish handling system to be ef fective, 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-re turn system would need to be built that would carry the impinged fish to the reservoir, a distan ce 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 impinge ment and many of the impinge d 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 w ould 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, wh ich 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 barri er net and would be an acceptable compliance
alternative.

The approach velocity in the intake canal is a pproximately 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 velo city to <0.5 ft/s, the ne t area would need to be approximately twice that of the intake canal cro ss section. Therefore, the net placement would
need to extend from the intake canal and into th e 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 additio n, verification monitoring might be required to insure that the net is properly working.

Since the barrier net placement would probably ex tend 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 w ill 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, thebarrier 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 specifi c 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 ca ses, 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 likel y 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, deterre nts 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 technol ogies 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 operate d 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 cool ing-water impoundment, the construction of Gibbons Creek Reservoir created over approxima tely 2,800 acres of aquatic habitat for fish and wildlife; 4. The TMPA developed public access facilities a nd 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 “g ood”, 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 re latively 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 cooli ng-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 relativel y 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. Prel iminary analysis of the reservoir fishery data indicates that there is little potential for AEI w ith respect to the reservoir fish community. Furthermore, the construction of Gibbons Cr eek Reservoir as a cooling-water impoundment resulted in the creation of extensive aquatic hab itats and extensive public recreation opportunities
that would not otherwise exist. The installati on and operation of more stringent fish-protection measures would probably not yield measureable envi ronmental 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 require ments for cooling water intake structures at Phase II existing facilities. Environmental Protection Agency, Washington D.C. Vol. 69:131.

Texas Parks and Wildlife Depa rtment (TPWD). 2008 Fishing Gibbons Creek Reservoir. Accessed on the internet on July 15, 2008 at: http://www.tpwd.state.tx.us/fishboat/fis h/recreational/lakes/gibbons_creek/

TPWD. 2003. Federal Aid in Sport Fish Restor ation Act, Performance Report for Gibbons Creek Reservoir. Texas parks and Wildlife Department, Austin.