Element 1 - Effluent Limits Determination

Determining effluent limits in state operating or National Pollutant Discharge Elimination System (NPDES) permits is an important component in the implementation of water pollution control in the State of Missouri. All permit limits or conditions are developed to be protective of water quality standards. While wastewater, concentrated animal feed operations (CAFOs), or stormwater permits are developed to be protective of water quality standards, they may vary widely in specific limits, best management practices, or conditions based on the nature of the discharge and the type of receiving waters.

Permitting for Domestic Wastewater Treatment Systems
The Missouri Clean Water Commission regulations define domestic wastewater as: “Wastewater originating primarily from the sanitary conveniences of residences, commercial buildings, factories and institutions, including any wastewater which may be infiltrated the sewers.”  Domestic wastewater treatment systems are often associated with municipal or publically owned treatment works (POTWs) but also include smaller and privately owned systems that serve smaller populations such as subdivisions, resorts and mobile home parks.

Domestic waste NPDES permits include effluent limitations, monitoring and reporting requirements, special conditions and standard conditions.  Limitations can be categorized as either technology-based effluent limitations (TBEL) or water quality-based effluent limitations (WQBEL).  The Clean Water Act requires a permit to include the most protective of the two limitation types when addressing a specific pollutant of concern (POC) within an operating permit.  The discharge from these facilities must be monitored, utilizing approved and sufficiently sensitive methods and, the results submitted at frequencies specified within in the permit.  Permits also include special conditions, required of a specific permitted facility, and standard conditions which apply to all permitted facilities.  Examples of special conditions include the development and implementation of a Stormwater Pollution Prevention Plan (SWPPP), Operation and Maintenance Plan or best management practices (BMPs).  Standard conditions include specific record keeping requirements and retention timeframes as well as sludge management and reporting requirements.  Stormwater information used to determine the requirements of the permit, such as a facility’s performance history, regulatory citations, policies, and mathematical calculations, as documented in a fact sheet, accompany the permit through the permitting process.

Industrial Activity Permits
Missouri industrial activities which generate process wastewater that discharge to waters of the state, are required to have a general or site-specific permit in accordance with 10 CSR 6.010. Waters of the state are defined in 10 CSR 20-2.010(82). If the industrial activity generates a process wastewater but is operated as without discharge a permit is required in accordance with 10 CSR 20-6.015.

Discharges of stormwater associated with industrial activity may need a permit if the activity is listed among categories and meet certain requirements as outlined in 10 CSR 20-6.200. An industrial activity listed in 10 CSR 20-6.200 may be excluded from a stormwater permit if the activity does not expose materials to stormwater as stated in 10 CSR 20-6.200 (1)16. Qualified industries seeking exemption must submit a completed No Exposure Exclusion Certification form (USEPA form 3510-11) to the Missouri Department of Natural Resources each permit cycle. This form is available at the following link: http://www.epa.gov/npdes/pubs/msgp2008_appendixk.pdf.

The Water Protection Program's Water Pollution Control Branch recognizes the need for a consistent strategy and rationale in the development of effluent limitations and monitoring requirements for discharges to waters of the state, i.e. technology based or, water quality based limits, most protective of water quality to prevent the degradation of the water.

Based Limits
When developing effluent limitations, a water quality reviewer (the permit writer) must consider limits based on both the technology based effluent limits to control the pollutants and water quality based effluent limits, protective of the water quality standards of the receiving water. According to the Clean Water Act, permits must reflect the more stringent of either the technology-based or water quality-based limits for all pollutants of concern. The effluent limit determination and derivation process considers current effluent requirements, background water quality, nearby discharges and antidegradation requirements supported by best professional judgment. Technology based limits represent a level of treatment that can be typically achieved through the use of common control technologies. The program's rules define the technology-based treatment requirements for various discharges.  Absent defined technology-based treatment requirements, permit writers must make a best professional judgement determination of what the best available pollutant control technology is for a specific pollutant.

Final permits may contain numerical effluent limits, special conditions and, those requirements that the Branch determines are necessary to protect water quality. These conditions or requirements again, may be a Stormwater Pollution Prevention Plan (SWPPP), a sludge management plan, best management practices or, pollutant of concern (POC) effluent sampling and monitoring frequency.

Waterbodies are assessed over time to determine if water quality standards are being maintained. Theses assessments are published in the 305(b) report and the 303(d) list of impaired water bodies.

Missouri Revised Statutes, Chapter 644, water pollution control and, the Water Quality and Antidegradation Review Assistance: A Technical Reference Guide that includes effluent limits guidance discussion to  protect water quality, human health and the environment. The procedures for developing many water quality based effluent limits in the guidance are derived from EPA's guidance document, Technical Support Document for Water Quality-Based Toxics Control.

Permit Writer determines permitting conditions, effluent limits and requirements in accordance with the Missouri Clean Water Law and its implementing regulations, and guidance documents such as:

  • The department’s Water Pollution Control Permit Writer's Manual
  • Guidance that supplements the Missouri Antidegradation and Implementation Procedure, May 2012:
  • Guidance for Water Quality and Antidegradation Review Assistance: A Technical Reference Guide
  • EPA guidance document: Technical Support Document For Water Quality-based Toxic Control (EPA/505/2-90-001)
  • Missouri Revised Statutes Chapter 644
  • Permitting for Concentrated Animal Feeding Operations (CAFOs)

CAFOs must be designed constructed, operated and maintained as “no-discharge” facilities. This means the operation must contain all of the wastewater to be land-applied when conditions are favorable. Operating permits are required for Class I CAFO animal confinement areas and waste management features. The operating permit must be obtained prior to placing animals in the confinement areas. Design and engineering requirements are located in 10 CSR 20-8.300. CAFOs must have a nutrient management plan incorporated into the no-discharge permit. The department’ guide to Animal Feeding Operations provides an overview of Missouri’s CAFO regulatory program and the department’s public appeals process. Additional information can be found by visiting the department’s CAFO Web page at: http://www.dnr.mo.gov/env/wpp/cafo/index.html

Permitting for Storm Water Discharges
Polluted stormwater runoff is a leading cause of impairment to the nearly 40 percent of surveyed United States water bodies which do not meet water quality standards. Over land or by storm sewer systems, polluted runoff is discharged, often untreated, directly into local water bodies. When left uncontrolled, this water pollution can result in the destruction of fish, wildlife, and aquatic life habitats; a loss in aesthetic value; and threats to public health due to contaminated food, drinking water supplies, and recreational waterways.

In 1987 the federal Clean Water Act was amended to include the regulation of certain stormwater classes which lead to the establishment of the National Pollutant Discharge Elimination System (NPDES) permitting program. The NPDES program requires the implementation of controls designed to prevent harmful pollutants from being washed as stormwater runoff into local water bodies.

Regulated entities listed in 10 CSR 20-6.200 must obtain coverage under an NPDES stormwater permit and implement stormwater pollution prevention plans (SWPPPs) or stormwater management programs (SWMPs). Either requirement should outline best management practices (BMPs) that effectively reduce or prevent the discharge of pollutants into receiving waters.

Guidance for Best Management Practices for stormwater control is in the Protecting Water Quality field guide, see below, as well as the “Missouri Guide to Green Infrastructure:  Integrating Water Quality into Municipal Stormwater Management” (http://dnr.mo.gov/env/wpp/stormwater/mo-gi-guide.htm) and pollution prevention guides for various industries located at http://dnr.mo.gov/pubs/index.html#PollutionPrevention.

General Permits
General permits cover a group of similar discharges under one permit. These permits simplify the process for dischargers to obtain authorization to discharge, provide permit requirements for any discharger that applies for coverage, and reduce the administrative workload for NPDES permitting authorities. General permits for stormwater management require owners or operators of certain facilities or those with land disturbance projects to manage their practices in ways that are beneficial to the environment and to Missouri streams. These permits generally specify that stormwater discharges shall not cause water quality violations.

Site-Specific Permits
Many facilities have discharges that cannot be covered under a general permit and so are required to obtain a site-specific permit. A site-specific permit may be for a discharge that results from the storage of toxic materials or large amounts of potential contaminants on site that are exposed to rainfall. These permits require additional attention from the permit writer in determining how existing practices effects the environment and what requirements will be needed to ensure the environment and Missouri streams are not adversely impacted.  In other instances the Branch has determined that discharges to certain sensitive waterbodies or settings require facilities to obtain a site specific permit in order to address the sensitive nature of the discharge scenario. 

Stormwater Permits
The law requires that stormwater discharges from three broad activities are required to obtain a NPDES operating permit.  The three activities are: 1) Construction [i.e., land disturbance activities of 1 acre or greater, or less than 1 acre but part of a larger common plan of development or sale], 2) Municipal as part of the Municipal Separate Storm Sewer System (MS4), and 3) Industrial with certain Standard Industrial Classification (SIC) codes. All activities are required to obtain either a general permit or a site-specific permit prior to beginning their regulated activity.

Land Disturbance Permit
The primary pollutants of concern from construction activities are silt and sediment, but other pollutants such as oils and grease, vehicle fluids, and debris are present as well. The removal of vegetation exposes bare soil which is much more vulnerable to erosion, resulting in sediment moving into receiving waters. Sedimentation can destroy aquatic habitat and high volumes of runoff can cause streambank erosion. The volume and rate of runoff are typically increased, providing a larger capacity to transport pollutants to rivers and lakes.

State law requires land disturbance activities of one acre or greater, and those less than one acre if part of a common plan of development or sale to be covered under a permit prior to the onset of construction activities.

The primary requirement of the land disturbance permit is development and implementation of a Stormwater Pollution Prevention Plan (SWPPP). The purpose of the SWPPP is to ensure the proper design, implementation, management and maintenance of BMPs in order to reduce the amount of sediment and other pollutants in stormwater discharges.

The plan must be accessible on-site. Plans do not need to be sent to the Missouri Department of Natural Resources unless specifically requested. The plan must be amended when changes in facility design, construction, operation or maintenance occur.

The permittee shall select, install, use, operate, and maintain appropriate BMPs for the permitted site. The following manuals are acceptable resources for the selection of appropriate BMPs. The permittee is not limited to the use of these guidance manuals; however, all BMPs should be described and justified in the SWPPP.

Stormwater Management for Construction Activities: Developing Pollution Prevention Plans and Best Management Practices, (Document number EPA 833-R-06-004) published by the United States Environmental Protection Agency (USEPA) in May 2007 as well as other information, including examples of construction SWPPPs, is available at the USEPA internet site below.

Protecting Water Quality: A field guide to erosion, sediment and stormwater best management practices for development sites in Missouri, published by the Missouri Department of Natural Resources, January 2011, is available on the department’s internet site below.

MS4 Permits
A MS4 is a conveyance or system of conveyances, including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains designated and utilized for routing of stormwater.  Additionally, MS4s do not include any waters of the state, is not part or portion of a combined sewer system, and is not part of a publicly owned treatment works (POTW).   MS4s are owned and operated by the United States, a state, city, town, borough, county, parish, district, association, or other drainage district, or other public body created or pursuant to the laws of Missouri having jurisdiction over disposal of sewage, industrial waste, stormwater, or other liquid wastes.  In order to be a regulated MS4 (i.e., subjected to the terms and conditions of a NPDES operating permit), the entity must be designated as either a Phase I or Phase II MS4.  Regulated Phase I and Phase II MS4s in Missouri can be found at: http://dnr.mo.gov/env/wpp/stormwater/sw-local-gov-programs.htm.

In 1990, the Environmental Protection Agency (EPA) promulgated rules establishing Phase I of the NPDES stormwater program.  The Phase I program for MS4s requires entities of “medium” and “large” MS4s, that is, those that generally serve populations of 100,000 or greater based on the 1990 decennial census by the United States Bureau of Census, to implement a stormwater management program as a means to control polluted discharges from the MS4.  There are only three Phase I regulated MS4s in Missouri, which are Kansas City, Independence, and Springfield. 

In 1999, EPA promulgated the Stormwater Phase II Rule to extend coverage of the NPDES stormwater program to include “small” MS4s; however, the 1999 Stormwater Rule took a slightly different approach to how the stormwater management program is developed and implemented.  A Phase II Small MS4 community is any MS4 that is not designated as a “medium” or “large” MS4.  In Missouri, Phase II Small MS4s are designated as a regulated MS4 if the MS4 serves a population of one thousand (1,000) or more within an urbanized area, or any MS4 located outside of an urbanized area serving a jurisdiction with a population of at least ten thousand (10,000) and a population density of one thousand (1,000) per square mile or greater.  Additionally, Phase II communities may be designated by the department when it is determined that discharges from the MS4 have caused or have the potential to cause an adverse impact on water quality. 

Both Phase I and Phase II regulated MS4 communities must develop and implement their Stormwater Management Program (SWMP) or portions thereof if the Phase II regulated MS4 community is utilizing a co-permittee approach.  In Missouri, both Phase I and Phase II MS4s implement the Phase II six minimum control measures, which are: 1) Public Education and Outreach; 2) Public Involvement and Participation; 3) Illicit Discharge Detection and Elimination; 4) Construction Site Runoff Management; 5) Post-construction Runoff Management; and 6) Pollution Prevention/Good Housekeeping in Municipal Operations.  In addition, Phase I MS4 communities also implement Stormwater Quality Assessment (i.e., water quality monitoring) and High-Risk Industrial Runoff Management. 

Phase I MS4 regulated communities and newly designated Phase II MS4 communities are required to submit annual SWMP status reports.  Existing Phase II MS4 communities (i.e., having the previous NPDES Phase II Small MS4 operating) are required to submit biennial (once every two years) SWMP status reports.  However, the report is required to contain two years’ worth of the required information.

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