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Comments on the National Pollutant Discharge Elimination System Draft Permit for the Indian 

River Generating Station 

April 4, 2008 

Chris Bason, Science Coordinator, Delaware Center for the Inland Bays 

The Delaware Inland Bays have historically provided productive spawning grounds, nursery areas, and 

adult habitat for a variety of commercially and recreationally important shellfish and finfish. Over the 

past century, cumulative impacts have severely degraded fish and shellfish habitat and thus the 

recreational and economic value of the fishery of the Inland Bays. These impacts include conversion of 

estuarine habitat to other landuses, chronic eutrophication and associated habitat degradation, and a 

reduction in lower-salinity habitats due to the stabilization of the Indian River Inlet. Another lessdiscussed but long-standing impact on the fishery of the Inland Bays is the Indian River Generating 

Station (IRGS). The IRGS is currently permitted to use once-through condenser cooling that withdraws 

water from Indian River and discharges heated water to Island Creek off Indian River. Data from two 

studies that were contracted by NRG (2001 & 2003) to assess the environmental impacts of the cooling 

water intake and discharge demonstrated that 1) the fish habitat value of Island Creek and portions of the 

adjacent Ware Cove is degraded by the IRGS thermal discharge and 2) the cooling water intake annually 

kills the equivalent of millions of adult fish and hundreds of thousands of adult blue crabs. This results in 

a) significant degradation of the Indian River and Bay and the Rehoboth Bay as nursery habitat, b) 

significant contribution to the degradation of the economically important Inland Bays recreational fishery, 

and c) alteration of the entire food web of the Inland Bays. The conclusion of these studies was, however, 

that the IRGS had no adverse environmental impacts. Generally, these conclusions were made by using 

inappropriately large scales as the frame of reference for which to determine an impact to local 

ecosystems. For example, the hundreds of thousands of adult blue crabs killed annually by the plant were 

related to the entire blue crab population of Maryland and Delaware and thus characterized as 

insignificant. The federal Clean Water Act and the State of Delaware Water Quality Standards require 

that best available technologies be applied to power plants to minimize any adverse environmental 

impacts. A closed-cycle water system with a cooling tower in this case appears to be the best available 

technology because a cooling tower was constructed on IRGS unit 4 which was permitted under these 

federal requirements. The above studies were required of NRG by DNREC approximately 15 years ago 

to provide sufficient information to determine if an appreciable environmental impact to Island Creek and 

the Inland Bays fishery from the IRGS was occurring. The draft permit requires new studies to determine 

if best available technology is needed. Now requiring additional studies to make this determination again 

based on future scenarios of IRGS operation appear to be in conflict with the DNREC’s previous requests 

for the above referenced studies that, once completed, demonstrated appreciable environmental impact yet 

resulted in no requirement for applying best available technology. It is recommended that DNREC not 

issue the current draft permit and promptly develop a new draft permit with the requirement that the IRGS 

expeditiously employ best available technology to minimize all fishery and habitat impacts for its power 

generating unit number three, if it intends to maintain this unit under this requirement. It is recommended 

that, as a condition of the permit, estuarine ecosystem restoration and enhancements projects to be 

formulated and agreed upon by the Center, DNREC, and NRG, be implemented in the Inland Bays by 

NRG in coordination with the above parties as mitigation for impacts from power generating units 

number one and two until their shutdown per the 2007 consent order between NRG and DNREC. The 

following is a brief review of the information used to formulate these recommendations. 

Background 

The IRGS has three coal-fired steam electric generating units that withdraw cooling water via an intake 

canal from the Indian River at a maximum rate of 411 million gallons per day (mgd). For purposes of 

comparison, this is approximately 21 times the average flow of the freshwater Indian River. Each year 

millions of fish and hundreds of thousands of crabs are killed through entrainment and impingement 
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associated with the plants’ cooling water intake structures. Entrainment is when small aquatic organisms 

are (fish eggs & larvae) are drawn through the plant’s cooling water intake screen, pass through the 

condensors and exit. They can be killed or injured such that they later die as an indirect result. 

Impingement is when organisms that are too large to be entrained and that can not escape intake are 

caught on the intake screen. They can die directly or indirectly from wounds. Environmental impacts 

from the plant also result from the heated cooling water that is discharged via a canal into the upper 

reaches of Island Creek. Island Creek is an approximately 2 miles long tidal tributary of the Indian River 

Bay that comprises approximately 150 acres of estuarine habitat. The IRGS has had a long an unusual 

permitting history. A timeline of the major events associated with the permitting of the facility is 

presented as an attachment. It is important to note that IRGS power generating unit 1 and unit 2 are 

scheduled to go offline in 2011 and 2010 per a consent decree between DNREC and NRG. 

Regulatory and Permitting Matters 

The Delaware Inland Bays are Waters of Exceptional Recreational or Ecological Significance (ERES). 

Under the State of Delaware Water Quality Standards the Department of Natural Resources and 

Environmental Control shall assure that 1) there shall be achieved the highest statutory and regulatory 

requirements for all new and existing point sources 2) in order to be permitted, a discharge must be the 

least environmentally damaging practicable alternative, and 3) a permit shall not be issued or reissued for 

an existing source unless the applicant demonstrates a utilization of all economically feasible and 

reasonably available waste minimization practices and technologies, and the lack of feasible alternative 

production processes and disposal options. Potential water quality impairment associated with a thermal 

discharge must be consistent with Section 316 of the Federal Water Pollution Control Act (Clean Water 

Act). Section 316(a) allows a variance from meeting effluent thermal limits if no appreciable harm has 

resulted from the normal component of the discharge. Section 316(b) requires that a point source shall 

require that the location, design, construction, and capacity of cooling water intake structures reflect the 

best technology available for minimizing adverse environmental impact. NRG contracted two studies 

completed by Entrix in 2001 and 2003 that suggested no adverse environmental impacts from the thermal 

discharge and intake. NRG thus requested a variance from the 316(a) and (b) requirements. Currently, it 

appears that no official federal guidelines exist for determining an adverse environmental impact that 

would require best available technology. In this case, best available technology appears to be a closed 

cycle cooling water system with a cooling tower. Individual states must now use Best Professional 

Judgment to determine an adverse environmental impact that would require best available technology. 

Upper Indian River Bay including Island Creek is on the 303d list of impaired waters and is impaired for 

bacteria, nutrients, DO, and temperature. The Indian River/Bay also has a Total Maximum Load for 

Temperature. DNREC, and supposedly the EPA, have concluded that no appreciable harm to the aquatic 

environment has occurred from the thermal discharge but have not granted NRG’s request for a 316(a) 

variance. No 316(b) variance was issued either. The draft permit requires additional study that appears 

designed to determine if adverse environmental impacts are occurring or will be occurring after the 

scheduled shutdown of units 1 and 2. 

Assessment of Environmental Impacts 

Impingement and Entrainment 

The 2003 316(b) was clearly designed to determine whether the IRGS was causing an adverse 

environmental impact (AEI) to the Indian River and Rehoboth Bay study area (page 1-3). AEI occurs 

when the ecological function of species are reduced such that populations decline, reductions in the 

optimum sustainable yield to fisheries results, or an unmitigable loss to the aquatic ecosystem occurs. 

The protection of a balanced indigenous community and long term sustainability of fish and blue crabs in 

the vicinity of the IRGS were two selected endpoints to determine an AEI. The endpoints were 

determined by modeling 1) the proportion of eggs, larvae and juveniles lost due to entrainment relative to 

the number of eggs, larvae and juveniles present in the study area (Empirical Transport Model (ETM)), 2) 

the number of adults lost due to the mortality of entrained eggs, larvae, and juveniles (Equivalent Adult 
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Model (EAM)), and 3) the commercial and recreational value of foregone production for commercially 

and recreationally important RIS. 

The study selected representative important species (RIS) based partly on their vulnerability to 

entrainment and impingement, recreational and economic importance. The species were bay anchovy, 

menhaden, spot, croaker, winter flounder, and blue crab. Anchovy and winter flounder spawn within the 

Inland Bays, their larvae use the Bays as nursery grounds, and adults of both species use the Bays almost 

year round. Menhaden, spot, and croaker generally spawn offshore and their juveniles migrate into the 

nursery grounds of the Bays. Full adults generally use the Bays for only part of the year. All the species 

play an integral role in the food web converting plankton and benthic animal biomass into the biomass of 

the birds and fish that eat them. For example, the study states “the bay anchovy play an integral role in 

the estuarine food web, representing an important link between plankton and [fish eating] fish and 

birds.... Serving as the primary forage fish for many avian and aquatic species, they have a long list of 

predators that includes herons, egrets, terns, weakfish, bluefish, striped bass, summer flounder, and blue 

crab... bay anchovy are one of the most ecologically important species within the Mid-Atlantic Region.” 

The major results of the study are summarized in the tables below and are followed by definitions of the 

model results. On average, 2,397,533 equivalent adult individuals of the RIS are estimated to be killed 

each year by the plant. This equivalent number is modeled from the many times more fish eggs and subadult individuals that were killed. In addition, 300,000 adult blue crabs are estimated to be killed each 

year. The magnitude of the impact of the plant intake on the bay anchovy population of the bays is 

particularly surprising. A bay anchovy spawned in the Inland Bays has an average 32% chance of being 

killed by the plant intake before it reaches non-entrainable size. The cumulative impact of the 

impingement and entrainment undoubtedly has a major effect on the food chain of the Bays by limiting 

the upwards flow of energy. For example, the study estimated that each year an additional 213 tons of 

menhaden and anchovy alone would be available to predators if not for the plant. Further, the numbers 

presented only include five of the over sixty species of fish found killed by the plant. It is reasonable to 

believe the total number of individual fish of all different life stages killed by the plant each year is 

multiple orders of magnitude higher than what is presented. 

 

One important fish species that was not examined as an RIS was the weakfish. During the first year of 

study, weakfish were the fifth most abundant species killed by impingement of 60 species found 

impinged. They were also the 7th and 4th most entrained species in year 1 and year 2, with entrainment 

losses greater than all RIS except anchovy in year 2. The weakfish population is of particular concern 

because of its economic value, its recent population declines, and its local relative abundance. The 

weakfish was considered as an RIS in the earlier 316(a) study and it was unclear why it was not selected 

for the 316(b) study. The Department should consider the weakfish as another RIS when determining an 

AEI. 
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Table 5-1. Output from the Empirical Transport Model (ETM), Equivalent Adults Model (EAM), and 

Equivalent Yield Model (EYM) 

Total EYM (kg)2 Species ETM (% 

CMR) 

EAM (EQ1)1 

Entrainment Impingement Total 

Year 1 

Bay anchovy 33 2,656,218 N/A N/A N/A 

Atlantic menhaden 16 12,488 406 15,209 15,615 

Spot 2 961 207 183 390 

Atlantic croaker 5 518,910 32,793 5,593 38,386 

Winter flounder 1 798,888 69,998 99 70,097 

Year 2 

Bay anchovy 31 636,272 N/A N/A N/A 

Atlantic menhaden 20 110,618 3,592 142 3,734 

Spot 2 0 255 0.1 255 

Atlantic croaker 12 24,823 1,634 171 1,805 

Winter flounder 7 35,887 3,408 0.9 3,409 

Table 5-2. Results of the Production Forgone Model 

Year 1 Production Foregone (kg) Year 2 Production Foregone (kg) Species Entrainment Impingement Entrainment Impingement 

Bay anchovy 119,824 19 130,673 14.5 

Atlantic menhaden 4,219 76,187 55,721 710 

Empirical Transport Model, % Conditional Mortality Rate -- the percentage reduction in a species abundance 

attributable to the plant intake, or the percentage of the entrainable population that would be lost if entrainment were 

the sole source of mortality. 

Equivalent Adult Model – the estimate of the number of adults fish lost that would have lived if not for the plant. 

Equivalent Yield Model – the biomass that would have been harvested by commercial and recreational fisheries in 

the absence of entrainment and impingement. Calculated for coastal stocks. 

Production Foregone Model – the biomass of the prey species that would have been available to predators in the 

absence of entrainment and impingement. 

The study concluded no AEI because its risk characterization phase related the losses from impingement 

and entrainment to the size of mid-Atlantic coastal fish stocks and the total fishery landings of Delaware 

and Maryland. This basis for determining an AEI to the Inland Bays is wholly inappropriate for the 

following reasons: 

1. the study “was designed to collect the appropriate data to evaluate whether the current operations 

at the IRGS are likely to cause an AEI to the aquatic resources within the Indian River Estuary 

and Rehoboth Bay study area,” not to coastal stocks. 

2. The endpoints selected to determine the likelihood of an AEI were a) the protection of a 

Balanced Indigenous Community of fish and blue crab in the vicinity of the IRGS and b) the 

production of the long-term sustainability of fish and blue crab populations in the region 

influenced by the IRGS cooling water intake structure. 

By relating losses to coastal stocks in its risk characterization phase, the study compromises its stated 

design to evaluate both the Inland Bays and the vicinity of the IRGS. Further, it is not reasonable to 

believe that one power plant in isolation could influence the sustainability of the entire mid-Atlantic RIS 

fishery, and so it is here interpreted that the region influenced corresponds to the Inland Bays. Using the 

approach of this study it is reasonable to conclude that no AEI to the RIS would occur even if the entire 

RIS population of the Bays were killed each year by the plant. 
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The study attempted to support their determination of an AEI on the local RIS populations by relating 

trends in the State of Delaware Inland Bays finfish monitoring trawl data from 1986 through the study 

period to the plant. The study found no long term trends in fish populations and assumed no AEI. This is 

an unreasonable assumption because 1) there is no method to distinguish the affect of the power plant on 

populations from the myriad of interacting environmental factors such as coastal stock fluctuations, 

habitat quality, and climate and 2) the trawl data began years after the units came online and thus included 

no means to reference pre-existing conditions to determine population change from the plant. 

 

It appears that benchmark values suggested to determine an AEI were referenced but then not used in the 

determination of AEI for this study. Conditional mortality rates, or the percentage reduction in that 

species abundance attributable to the plant intake, of the RIS were compared to values of 10% for nonforage species and 15% for forage species. These benchmark rates were borrowed from assessments 

made on the New Jersey Deep Water Generating Station on the Delaware River. It is not clear if these 

benchmarks are appropriately transferable between two greatly different estuaries. The study found 

conditional mortality rate of 33% for bay anchovy, over twice the recommended value for the Delaware 

River. An average rate of 18% was found for menhaden, again over the 15% value for forage species. It 

is unclear why these benchmarks were compared to study data but then apparently not used in the 

determination of an AEI. The benchmarks alone suggest the occurrence of an AEI. 

Based on the data presented in the 316(b) report it is clear to the author that the impingement and 

entrainment of the plant is having an adverse environmental impact on the Inland Bays ecosystem. One 

would have a hard time trying to find an independent professional fisheries scientist that would, in their 

best professional judgment, disagree. According to State and Federal law, this requires the application of 

best available technologies to the IRGS. 

316(a) 

The 316(a) study was briefly reviewed. The report assessed the affects of elevated water temperatures on 

eight representative important fish species: bay anchovy, menhaden, winter and summer flounder, 

croaker, spot, striped bass, and weakfish. The important effects of the thermal discharge are the potential 

avoidance and subsequent reduction of available habitat and associated services experienced by the target 

species and other organisms inhabiting the study area. The study found that juvenile and adult target 

species were not required to permanently avoid major segments of the Indian River and lose the habitat 

services associated with these segments. The study concluded no adverse effect, or no appreciable harm, 

on the fish and shellfish populations in the Indian River and Bay. The author agrees with these 

conclusions. However, the study concludes and clearly demonstrates that, during the warmer months, the 

discharge has an adverse effect on Island Creek and sometimes the adjacent Ware Cove. Island Creek 

and Ware Cove is a large estuarine segment that provides relatively important fish and crab habitat. Its 

lower salinity and position in the larger estuary is attractive to RIS such as bay anchovy, spot, and 

menhaden larvae, and young blue crabs. The potential mortality associated with sub-adult stages of fish 

and crabs and the avoidance of the area by sub-adult and adult fish is proportional to the size of the area 

affected which is large. The creek is about two miles long and, including parts of the cove, is 150 acres of 

estuarine habitat. Further, reductions in dissolved oxygen associated with the discharge were substantial 

(mean = 0.6 mg/l) even in Ware Cove. These reductions are in addition to cumulative effects of 

eutrophication on the widely fluctuating diel cycling dissolved oxygen concentrations of tidal tributaries 

to the Inland Bays. Island Creek is a significant tidal tributary of the Inland Bays and the determination 

of plant effects should focus on Island Creek and Ware Cove. The existing study is sufficient to make 

this determination and no new study is needed. It is clear that Island Creek and, during some time of the 

year, Ware Cove experiences appreciable harm from the discharge, and BAT should be applied. 

On the Rationale for Requesting Further Study 

It was stated by representatives of DNREC that part of the rationale for issuing the current draft permit 

without requiring BAT was that AEI from impingement and entrainment were expected to decrease such 
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that the protection of a balanced indigenous community could result. However, no evidence was 

provided as to the likelihood that this would occur. What little evidence that can be drawn from the 

existing studies as is, appears to not support this because unit 3, the unit that will remain online for the 

near future, accounted for 72% of the total impingement losses whereas unit 1 accounted for only 28%. 

This makes sense because unit 3 is much larger than 1 and 2. Unit 2 was not directly sampled, so its 

relative contribution to total losses is unknown. 

Both entrainment and impingement sampling was accompanied by the volume of circulating water or 

flow rate based on the number of circulating water pumps in operation and/or the pumping rates. In fact, 

the Empirical Transport Model determined entrainment as a simple function of the plant’s measured 

intake flow rates. This suggests that the existing data could be used to determine the relationship between 

pumping rates and both impingement and entrainment useful for estimating the risk of an AEI after unit 1 

and 2 have gone offline. Before issuing a permit requesting additional study, DNREC should attempt to 

use the existing data to estimate an AEI after units 1 and 2 have gone offline. 

It is likely that similar modeling can be conducted with data from the 316(a) report to estimate if 

appreciable harm will occur to the fish assemblage of Island Creek after units 1 and 2 have gone offline. 

Given the legal status of the Inland Bays and their tributaries and their impaired condition from 

cumulative impacts, it is recommended that a highly precautionary approach be used when estimating the 

potential for an AEI in the future. 

Consideration of Cumulative Impacts 

Finally, there was no indication in the rationale for issuing the permit that the impacts of the plant were 

evaluated cumulatively with other impacts to the fishery of the Inland Bays or with trends in regional 

populations. By not specifically considering cumulative impacts to the fishery, the justification for 

regulating individual impacts is weakened. DNREC should describe and consider the cumulative impacts 

to the fishery when determining the issuance of this and other individual permits. 

General Recommendations 

It is recommended that DNREC not issue the current draft permit and promptly develop a new draft 

permit with the requirement that the IRGS expeditiously employ best available technology to minimize all 

fishery and habitat impacts for its power generating unit number three, if it intends to maintain this unit 

under this requirement. It is also recommended that, as a condition of the permit, estuarine ecosystem 

restoration and enhancements projects to be formulated and agreed upon by the Center, the Department, 

and NRG, be implemented in the Inland Bays by NRG in coordination with the above parties as 

mitigation for impacts from power generating units number one and two until their shutdown per the 2007 

consent order between NRG and DNREC. 

 

 

 
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IRGS TIMELINE 

DEC 1976 316(a) thermal discharge demonstration report prepared by Ecological Analysts Inc. for 

Delmarva Power & Light Co. was released. 

??? 1978 316(b) entrainment and impingement demonstration report prepared by Ecological Analysts 

Inc. for Delmarva Power & Light Co. was released. 

???? 1980 IRGS Unit Four using closed cycle cooling comes online. 

MAY 1983 NPDES Permit issued for the facility. 

SEP 1988 Delaware NPDES Permit issued for the facility. 

???? 1990 DNREC contracted Versar to review the 316(a) and (b) compliance of 12 Delaware facilities 

including IRGS. Versar concluded that the studies from the 70s were outdated and the 

resulting data not representative of current conditions. Versar recommended DNREC 

conduct a formal review of the original 316(b) findings. 

???? 1990 Delaware NPDES Permit amended to change flow and loading limits, biomonitoring 

requirements, copper monitoring requirements, and toxicity limits. 

???? 1992 Based on Versar report DNREC determined original 316 (b) findings outdated. 

SEP 1992 Delaware NPDES Permit expired. 

???? 1993 Versar, contracted by DNREC, recommends that DNREC require the then owners of IRGS 

to conduct updated 316(b) studies prior to the next permit renewal. 

???? 1997 According to Peder Hansen, DNREC started working on the issue of impacts in earnest. 

JAN 2001 316(a) (thermal discharge) ecological risk-based demonstration report prepared by Entrix for 

Conectiv. 

AUG 2003 316(b) (entrainment and impingement) ecological risk-based evaluation report prepared by 

Entrix for Conectiv 

JUL 2004 EPA Promulgates Requirements for Cooling Water Intake Structures at Phase II Existing 

Facilities (affects IRGS?). This requires establishes performance standards that are 

projected to reduce impingement mortality by 80 to 95 percent and, if applicable, 

entrainment by 60 to 90 percent. Details Best Available Technologies. 

JUL 2004 DNREC IRGS visited to observe operations to develop permit limitations and conditions. 

DEC 2004 EPA established a TMDL for temperature for the Indian River Bay 

JAN 2007 EPA suspends the Cooling Water Intake Structure Regulations for existing large power 

plants. This suspension is in response to the 2nd Circuit Court of Appeals decision in 

Riverkeeper, Inc., v. EPA. State permitters are still required to establish section 316(b) 

requirements on a BPJ basis for existing facilities not subject to categorical section 316(b) 

regulations. 
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NOV 2007 DNREC releases public notice of NPDES permit 

???? 2008 Effective date of the new permit 

MAY 2010 NRG required to have shut down Unit 2 

MAY 2011 NRG required to have shut down Unit 1 

???? 2012 Expiration date of the new permit.