memorandum 

February 19, 2009 Thermal Discharge Constraints at 316(b) Facilities 1

Environment and Resources

55 Wheeler Street, Cambridge, MA  Tel: 617 492-7100  www.abtassociates.com

Date February 19, 2009 

To Erik Helm and Josh Hall 

From Dominick Tribone and Michael Fisher 

Subject Key Concepts and Issues Surrounding an Analysis of Savings to 316(b) Facilities from 

Relaxation of Thermal Discharge Constraints

Steam power plants are often subject to thermal discharge limits as part of their overall NPDES limits. In 

some instances, particularly during periods of warm ambient water temperature, plants with once-through 

cooling water systems may need to curtail generation to remain within these limits. Such curtailments of 

output will lead to a loss of revenue and operating income. Installation of a cooling tower would generally 

eliminate the need to curtail generation to remain within thermal discharge limits. The avoidance of this 

output reduction would constitute a financial benefit that would offset, potentially in a material way, the 

cost of cooling tower installation as a compliance response to a 316(b) regulation. For facilities that 

curtail output because of a thermal discharge limit, failure to account for this potential financial benefit 

will tend to overstate the cost and financial burden of cooling tower installation. Below, we review 

concepts for assessing the financial gain from relaxation of thermal discharge constraints due to 

installation of a cooling tower. We also provide a few examples of thermal discharge values relative to 

discharge limits for 316(b) facilities. These examples suggest that some facilities may be operating in 

such way that they would need to curtail output to remain within their discharge limits. 

1 Overview of Methodology and Issues to be Addressed 

Our understanding of potential approach and issues in analyzing the financial benefits from relaxation of 

thermal discharge constraints is informed in part from our previous analyses to support development of a 

thermal discharge permit for the Brayton Point Generating Station in Massachusetts. In that effort, Abt 

Associates quantified increased opportunities for revenue generation (termed “avoided load loss”) 

anticipated at this power plant if it were to install a recirculating system, as it was constrained in its 

generation during lucrative peak summer hours by thermal discharge limits in its NPDES permit. This 

calculation hinged on four pieces of information: 

3⁄4 A schedule of periods during which the facility was limited in its generation due to thermal 

discharge limits 

3⁄4 An estimate of the curtailment in generating output required to keep the facility below its thermal 

discharge limits 

3⁄4 A schedule of wholesale electricity prices that would otherwise have been received by the 

company had the facility been able to generate electricity at a higher capacity 

3⁄4 A schedule of fuel costs for the generating units that curtailed output due to thermal discharge 

limitations. 

Abt Associates Inc., 
1.1 Determining the Extent to Which Generation is Constrained 

For the Brayton Point analysis, the company provided detailed information of the number of hours per 

year that the facility restricted output due to its thermal discharge limit; this is not likely to be feasible for 

the current facility set. In the case of the in-scope 316(b) facilities, we may be able to use permit 

compliance information from EPA’s PCS1

 and ICIS2-NPDES databases to identify time periods during 

which facilities are constrained by their thermal discharge limits. There are several questions related to 

the use of this information: 

3⁄4 What is the parameter used to limit thermal discharges? Several are present, including (but not 

limited to): maximum temperature of discharged water, average temperature of discharged water, 

temperature difference from upstream/downstream monitoring sites, total BTUs discharged over 

a period of time, and combinations of two or more limits (in the case of Brayton Point, there were 

limits on both the temperature of the discharged water at any given point and the total amount of 

thermal input over a given period). 

3⁄4 When are facilities being constrained by thermal discharge limitations, and for how long? This 

question is related to the previous one, as the timing and duration of a generating constraint will 

depend on the stipulations of a specific facility’s permit, the characteristics of a plant’s normal 

operations, and the temperature of intake and receiving water. 

3⁄4 How often is monitoring conducted? Initial searches for individual facilities returned monthly 

monitoring data, which does show some facilities hitting or slightly exceeding their thermal 

discharge limits in months where water temperature – and power demand – are usually high (July 

and August). It is unclear if this information is detailed enough for a rigorous analysis.3

1.2 Determining the Magnitude of a Generation Constraint 

An estimate of the extent to which generation was curtailed to meet thermal discharge limitations was 

also provided by the company in the Brayton Point case. For 316(b) facilities, we would need insight 

from either the EPA regions and state permitting authorities or from the 316(b) project engineers to 

determine an appropriate concept for approximating the potential “lost” production due to thermal 

discharge limits that could be “avoided” if a recirculating system is installed. 

1.3 Valuing the Revenue Loss from a Generation Constraint 

Both wholesale electricity prices and fuel costs are used in the IPM Market Model Analysis, and may be 

sufficient for valuing this “avoided load loss.” Combined with the timing and generation information, this 

would allow the calculation of a monetary benefit to facilities installing recirculating systems that also 

face thermal discharge constraints. However, market prices may be significantly higher during peak 

operating hours, which would increase the opportunity cost of curtailing operations due to thermal 

discharge constraints during these hours, and thus the benefit from avoiding such curtailments. If 

information on electricity prices by time period and by NERC region/Independent System Operator could 

be obtained, this would provide the most accurate estimate of the financial gain from avoided load loss. 

 

1

 Permit Compliance System 

2

 Integrated Compliance Information System 

3

 Another consideration is whether the thermal discharge limit is actually a binding constraint on the output for these 

facilities? Or are the penalties of non-compliance outweighed by revenue gained in such way that the facilities would not 

gain from installation of cooling towers? 

Abt Associates Inc., February 19, 2009 Thermal Discharge Constraints at 316(b) Facilities 2
1.4 Incorporation into 316(b) Economic Analysis 

There are essentially two ways to incorporate the information regarding avoided load loss into the 316(b) 

Economic Analysis. If EPA judges that effect warrants a formal analysis and we can obtain the 

information detailed above, we can develop a framework to calculate this effect for each facility and 

incorporate the savings into the overall cost analysis. Alternatively, we could provide several case studies 

(including Brayton Point) that provide anecdotal evidence of the financial benefits that facilities may 

experience from installing a recirculating cooling system. As outlined above, either effort would entail 

working with EPA Region and state permitting authorities and/or the EPA project engineers to develop 

estimates of the generating loss resulting from thermal discharge limits. 

To help inform this decision, several examples of the information provided by PCS and ICIS are provided 

in following section. 

2 Observed Thermal Discharge Trends at 316(b) Facilities 

Using EPA’s Online Tracking Information System (OTIS), we examined thermal discharge effluent 

charts for a small sample of facilities (see figures below). In the following figures, horizontal lines

represent limits set by the NPDES permits: solid lines indicate a limit on the maximum temperature and 

dashed lines indicate a limit on the average temperature; both may vary (as in Figure 3 and Figure 6). The 

symbols represent reported discharge values for the facilities: upward triangles are maximum reported 

values, diamonds are average reported values, and downward triangles are minimum reported values. 

Shading indicates a value reported over the permit limit. 

A preliminary look at these charts shows that these facilities’ thermal discharge limits are being reached 

and sometimes slightly exceeded during peak summer months, suggesting that their generating output 

may be restricted by their permitted thermal discharges. Looking at a random sample of 20 facilities, 11 

had both limits and monitoring data available for temperature. Of these 11 facilities, 10 were operating at 

90% or more of their limit during peak summer months. This leads us to believe that the limits may pose 

generation constraints during summer months for a substantial number of facilities. Below are sample 

charts of the effluent information available through OTIS. 

Figure 1: Discharged Water Temperature at Danskammer Generating Station, Newburgh, NY – Outfall 2 

Abt Associates Inc., February 19, 2009 Thermal Discharge Constraints at 316(b) Facilities 3
Figure 2: Discharged Water Temperature at Danskammer Generating Station, Newburgh, NY – Outfall 4 

Figure 3: Temperature Difference between Effluent and Upstream at Roseton Generating Station, Newburgh, 

NY 

Figure 4: Discharged Water Temperature at Roseton Generating Station, Newburgh, NY 

Abt Associates Inc., February 19, 2009 Thermal Discharge Constraints at 316(b) Facilities 4
Figure 5: Temperature Difference between Effluent and Upstream at Deepwater Generating Station Delaware 

River, Pennsville, NJ 

Figure 6: Discharged Water Temperature at Laskin Power Plant, Aurora, MN 

Figure 7: Discharged Water Temperature at Basin Electric Power L Olds, Stanton, ND 

Abt Associates Inc., February 19, 2009 Thermal Discharge Constraints at 316(b) Facilities 5