Annual Permit Limits for Nitrogen and Phosphorus for Permits Designed to Protect Chesapeake Bay and Its Tidal Tributaries from Excess Nutrient Loading under the National Pollutant Discharge Elimination System

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Annual Permit Limits for Nitrogen and Phosphorus for Permits Designed to Protect Chesapeake Bay and Its Tidal Tributaries from Excess Nutrient Loading under the National Pollutant Discharge Elimination System


By: James A. Hanlon

Date: March 19, 2004

Source: Hanlon, James A. "Annual Permit Limits for Nitrogen and Phosphorus for Permits Designed to Protect Chesapeake Bay and Its Tidal Tributaries from Excess Nutrient Loading under the National Pollutant Discharge Elimination System." March 19, 2004. 〈〉 (accessed March 16, 2006).

About the Author: James (Jim) Hanlon was appointed as director of the U.S. Environmental Protection Agency (EPA) Office of Wastewater Management (OWM) with the Chesapeake Bay Program in April 2002. The OWM is a body that is responsible for issuing wastewater discharge permits to industries and municipalities. Prior to this, Hanlon was appointed as Director of the Municipal Construction Division in 1984. His responsibilities included managing funds and grants for construction projects. He also provided assistance to various municipalities for the construction of various wastewater infrastructure projects. In his capacity as Deputy Director of Science and Technology in the Office of Water since 1991, he was responsible for providing the scientific and technological foundation for federal water quality and various safe drinking water programs. He also served as Acting Deputy Assistant Administrator for the same office between 2001 and 2002. Hanlon holds a Bachelor of Science Degree in Civil Engineering from the University of Illinois and a Master of Business Administration from the University of Chicago.


Dissolved nutrients like nitrogen and phosphorus are an important source of nutrition and growth. However, when these are present in excess, they pose a significant hazard to the presence of the existing biodiversity. Excessive nutrients can cause the formation and growth of harmful algae and phytoplankton (organisms that usually drift in fresh water). Their presence reduces the amount of sunlight available to aquatic plants. Decomposing algae can reduce the amount of dissolved oxygen in the water necessary for aquatic life. This can lead to disastrous consequences for any ecosystem, and also lead to its ultimate death.

The Chesapeake Bay is the largest estuary (an arm of the sea that extends inland to meet the mouth of a river) located on the eastern coast of the United States. It is encompassed by seven states that include New York, Pennsylvania, Delaware, Maryland, Virginia, West Virginia, and the District of Columbia. Connected by nine major tributaries, the bay is a complex, vast, and diverse ecosystem that supports a large variety of plant and animal life. This includes many species of small sharks, blue crab, various exotic oysters, and a myriad of species of birds.

Since the 1990s, the ecosystem of Chesapeake Bay has been under threat of varied degrees from many forms of land, air, and water pollution. The most serious form of pollution the bay faces is that of excessive nutrient loading. In other words, there is an excessive discharge of nutritive content like phosphorus and nitrogen into the bay that can prove extremely harmful to aquatic life.

Earlier, much of the excessive nutrient was held back by wild marshes (wet soft land near water) and farmland. However, due to rapid industrialization, these areas have given way to cities and industrial zones. Industrial discharge into the bay also contains elements like nitrogen and phosphorus, leading to an overall increase in the nutrient levels in the bay ecosystem.

To tackle this problem, the Chesapeake Bay Program—a cooperative program between the U.S. Environmental Protection Agency Regions I & III, and the member states—was formed in 1983 to encompass the bay and its tributaries within their jurisdiction.

The twin goals of the Chesapeake 2000 agreement and The Clean Water Act initiated the Chesapeake Bay Program. The program involves the EPA and partner states setting nutrient discharge limits for the National Pollution Discharge Elimination System—a national-level program aimed at reducing discharge of pollutants into water resources—in the Chesapeake Bay and its tributaries.

Hanlon's memorandum was written to Jon Capacasa, Director of the Water Permits Division of EPA Region 3, and Rebecca Hammer, Director of the Chesapeake Bay Program Office. Briefly, the memo establishes annual limits for the discharge of nutrients under the National Pollution Discharge Elimination System (NPDES). It describes practical difficulties in setting daily, weekly, or monthly discharge limits for nutrients like phosphorus, nitrogen, and ammonia.



This memo responds to your proposal to use National Pollutant Discharge Elimination System (NPDES) permit effluent limits for nitrogen and phosphorus expressed as an annual limit in lieu of daily maximum, weekly average, or monthly average effluent limitations, for the protection of Chesapeake Bay and its tidal tributaries from excess nutrient loading. Based on the information provided by your staff and for the reasons and under the circumstances outlined herein, I concur that permit limits expressed as an annual limit are appropriate and that it is reasonable in this case to conclude that it is "impracticable" to express permit effluent limitations as daily maximum, weekly average, or monthly average effluent limitations. This memo describes the scientific and policy rationales that support this approach.

EPA Region 3 has developed recommended water quality criteria for certain parameters designed to protect water quality in Chesapeake Bay and its tidal tributaries. The main cause of water quality impairment for these parameters in the main stem of the Bay is loading of nutrients, specifically nitrogen and phosphorus, from point and nonpoint sources throughout the entire Chesapeake Bay watershed. The States are in the process of adopting revised water quality standards based on EPA Region 3's recommended water quality criteria and developing wasteload allocations for point sources discharging to the Chesapeake Bay watershed that are designed to protect water quality in Chesapeake Bay and its tidal tributaries from excess nutrient loading.

Establishing appropriate permit limits that implement nitrogen and phosphorus wasteload allocations for discharges that cause, have the reasonable potential to cause, or contribute to excursions of water quality criteria for Chesapeake Bay and its tidal tributaries is different from setting limits for other parameters such as toxic pollutants because: the exposure period of concern for nutrients loadings to Chesapeake Bay and its tidal tributaries is very long; the area of concern is far-field (as opposed to the immediate vicinity of the discharge); and the average pollutant load rather than the maximum pollutant load is of concern. Thus, developing appropriate effluent limitations requires innovative implementation procedures.

Applicablility Your proposal addresses implementation of wasteload allocations for nitrogen and phosphorus designed to achieve compliance with water quality standards of Chesapeake Bay. Your proposal and the rationale discussed in this memorandum are not intended to address wasteload allocations to meet other water quality standards in areas outside of Chesapeake Bay and its tidal tributaries. Smaller scales such as embayments and smaller tributaries than the major Eastern and Western shore rivers were not examined and therefore the rationale in this memorandum does not address and may not apply to the protection of these smaller scale situations.

This rationale also does not apply to parameters other than nitrogen and phosphorus that may exhibit an oxygen demand to waters of the Bay. Such parameters include dissolved oxygen, biochemical oxygen demand, and ammonia.

Of course, all local water quality standards apply and must be met when evaluating appropriate point source permit effluent limits. States are developing water quality standards for nutrients to be applied to local waters as stand-alone criteria. In any case where the nutrient wasteload allocations for protection of water quality in a river, tributary, or other part of Chesapeake Bay are expressed on a shorter term basis, i.e., seasonal, monthly, weekly or daily values, the permit limits that derive from and comply with the wasteload allocation expressed on such shorter term basis must be used. Shorter averaging periods might be appropriate and necessary to protect against local nutrient impacts in rivers or streams in the basin.

Additionally, it is important to note that the nutrient dynamics of the Bay may not be unique. The establishment of an annual limit with a similar finding of "impracticability" pursuant to 40 CFR 122.45(d) may be appropriate for the implementation of nutrient criteria in other watersheds when: attainment of the criteria is dependent on long-term average loadings rather than short-term maximum loadings; the circumstances match those outlined in this memo for Chesapeake Bay and its tidal tributaries; annual limits are technically supportable with robust data and modeling as they are in the Chesapeake Bay context; and appropriate safeguards to protect all other applicable water quality standards are employed.

Why are annual loadings appropriate for wasteload allocations for nutrients for Chesapeake Bay and its tidal tributaries? The nutrient dynamics of Chesapeake Bay and its tidal tributaries are complex. Unlike toxics and many conventional pollutants that have a direct and somewhat immediate effect on the aquatic system, nutrients have no direct effect, but instead are "processed" in several discreet steps in the Bay ecosystem before they have their full effect. Each processing "step" further delays and buffers the time between the time of nutrient discharge in an effluent and the resultant nutrient effect on the receiving waterbody. Chesapeake Bay and its tidal tributaries' biological and physical processes can be viewed as "integrating" variations of nutrient load magnitude over time. The integration of nutrient loads from all sources over time ameliorates intraannual load fluctuations from individual sources, with the Bay responding to overall loads on an annual scale, while showing little response to monthly variations within an annual load.

EPA has conducted complex modeling of the effect of nutrient loading to the Bay specifically from individual point source discharges. Based on the results of the model, EPA concluded that Chesapeake Bay and its tidal tributaries in effect integrate variable point source monthly loads over time, so that as long as a particular annual total load of nitrogen and phosphorus is met, constant or variable intraannual load variation from individual point sources has no effect on water quality of the main bay.

Based on the model, EPA and the affected States are developing "tributary strategies" that will assign wasteload allocations expressed as annual loads for the point source dischargers to the Bay and it tributaries that achieve the water quality standards of Chesapeake Bay and its tidal tributaries.

Why is it impracticable to express limits for nutrients on a daily, weekly or monthly basis? The NPDES regulations at 40 CFR 122.45(d) require that all permit limits be expressed, unless impracticable, as both average monthly limits and maximum daily limits for all dischargers other than publicly owned treatment works (POTWs), and as average weekly limits and average monthly limits for POTWs.

The Office of Wastewater Management cautions that the steady-state statistical procedures described in EPA's Technical Support Document for Water Quality-based Toxics Control (TSD) are not applicable or appropriate for developing nutrient limits for the main stem of Chesapeake Bay and its tribal tributaries. Developing permit limits for nutrients affecting Chesapeake Bay and its tidal tributaries is different from setting limits for toxic pollutants because the exposure period of concern for nutrients is longer than one month, and can be up to a few years, and the average exposure rather than the maximum exposure is of concern. The statistical derivation procedure described in the TSD for acute and chronic aquatic life protection is not applicable to exposure periods more than 30 days. If the procedures described in the TSD for aquatic life protection (i.e., criteria with 1-day and 4-day averaging periods) were used for developing permit limits for nutrients (with much longer averaging periods), both the maximum daily limit or the average weekly limit (as appropriate) and average monthly limit would be less stringent than the wasteload allocation necessary to protect the criteria. Thus, even if a facility was discharging in compliance with permit limits calculated using these procedures, it would be possible to constantly exceed the wasteload allocation. Such an approach clearly is unacceptable.

The TSD in Section 5.4.4 provides guidance for establishing daily and monthly effluent limits for human health protection based on long term exposure periods. However, this approach is also not appropriate for deriving permit limits for nutrients. This is because this TSD procedure is a steady-state approach that assumes that the distribution of effluent load is constant. However, the efficiency of treatment of nutrients by biological nutrient removal is highly sensitive to ambient temperature and is not effective at lower temperatures. Thus, the effluent loading of nutrients is not constant due to seasonal temperature fluctuations in northern climates. Even a simple steady-state model for permit development such as dividing the annual limit by 12 and establishing that value as the monthly limit is therefore, not appropriate. Such a limit does not account for seasonal fluctuations in effluent loading. To establish appropriate weekly or monthly limitations, due to the effect of temperature on treatment efficiency for nutrients, the permitting authority would need to be able to predict with some accuracy the expected annual temperature over that time frame, which is virtually impossible to do given the normal temperature variability in any given week or month. Because of the effect of temperature on the treatment efficiency and the normal variation in ambient temperature over shorter time periods, it is impracticable to develop appropriate daily, weekly or monthly limits for nutrients that are protective of the wasteload allocation expressed as an annual load.

Thus, we conclude that due to the characteristics of nutrient loading and its effects on the water quality in Chesapeake Bay and its tidal tributaries and because the derivation of appropriate daily, weekly or monthly limits is not possible for the reasons described above, that it is therefore "impracticable" to express permit effluent limitations as daily maximum, weekly average, or monthly average effluent limitations.

Recommendations for implementing an annual limit The permit should state the method for determining compliance with the annual limit. When expressing an effluent limit as an annual value, it is recommended that the permit provide the ability to assess compliance at interim dates.

The frequency of compliance monitoring should also be specified in the permit. The Office of Wastewater Management recommends that the effluent discharge volume should be monitored continuously. Nutrient monitoring should be specified on at least a weekly basis, and the monthly mass load should be summarized based on the total flow during the month and reported as a monthly load.


Pollution of water resources and important ecosystems has been a topic of great concern in the United States. Overexploitation of natural resources, coupled with land, water, and air pollution emanating from industries in ecosystems, such as the Chesapeake Bay area, have contributed to the increased threat to plant and aquatic life in these regions.

As with many other ecosystems, the Chesapeake Bay has suffered in varying degrees from pollutants from numerous sources. Although there was a considerable reduction in the nutrient discharge into the Chesapeake Bay after the implementation of the Chesapeake Bay program, experts were of the opinion that there still needed to be a further reduction in the discharge.

Consequently, since the 1990s and early 2000s, there have been talks of imposing daily or weekly nutrient discharge nutrient limits in the region. Member states issuing nutrient discharge permits need to ensure that nutrient discharge remains within acceptable limits. However, there are legitimate hindrances in determining the nutrient discharge on a maximum daily, average weekly, or monthly basis.

This memorandum, issued in 2004, enumerates various scientific and policy grounds that give basis to this approach. It sets the pace for allowing member states to issue nutrient discharge permits with the specification of annual limits for nutrient disposal into the Chesapeake estuary and its supporting components.

Hanlon argues on the basis of various scientific and technical interpretations that it is more practical to implement a permit system based around the annual limits of discharge allowed rather than a system permitting daily maximum, weekly, or monthly average discharge of nutrients into the bay.

Through the early 2000s, various companies still continue to discharge nutrients into the river, based upon the amounts allowed in the EPA issued permits. The problem of growing nutrient pollution in the bay is not completely resolved. The bay's natural capacity to repair itself is fairly limited, though evidence suggests that the bay system integrates out the nutrient overload over a duration of time.

Though the EPA has tried to keep the levels of nutrient discharge into the bay system under the limits specified, the states that encompass the bay system within their jurisdiction and various industries still discharge nutrients, albeit controlled by EPA permits. This, experts assert, could cause major environmental concerns in the long run.


Web sites

"Chesapeake Bay: Measuring Pollution Reduction." U.S. Geological Survey. 〈〉 (accessed March 16, 2006).

Chesapeake Bay Program. "Nutrient Pollution." 〈〉 (accessed March 16, 2006).

U.S. Environmental Protection Agency. "Decision on Petition for Rulemaking to Address Nutrient Pollution from Significant Point Sources in the Chesapeake Bay Watershed." U.S. Environmental Protection Agency. 〈〉 (accessed March 16, 2006).

――――――. "NPDES Permitting Approach for Discharges of Nutrients in the Chesapeake Bay Watershed." U.S. Environmental Protection Agency. 〈〉 (accessed March 16, 2006).

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Annual Permit Limits for Nitrogen and Phosphorus for Permits Designed to Protect Chesapeake Bay and Its Tidal Tributaries from Excess Nutrient Loading under the National Pollutant Discharge Elimination System

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