Understanding Point Source vs. Nonpoint Source Pollution

By Ella Lunny, MT DEQ Nonpoint Source and Wetland Section

When working in watershed restoration, it’s important to understand the difference between the terms “point source” and “nonpoint source” to most effectively identify what funding and partnerships are available to you.
This informative blog is the second in Water Activities Work Group Restoration Series, which discusses restoration strategies, funding opportunities and tips for watershed restoration planning and implementation.

How is Pollution Addressed in Montana?

Under Montana law, pollution of state waters is illegal (75-5-605, MCA). To protect our watersheds, DEQ uses three primary approaches to reduce pollution:

• Voluntary Implementation: Supporting landowners and local groups in adopting Best Management Practices (BMPs) to address nonpoint source runoff.
• Permitting & Compliance: Regulating point source discharges through the Montana Pollutant Discharge Elimination System (MPDES) permit program to ensure standard criteria are met.
• Enforcement: Taking formal action when unpermitted discharges occur or permit conditions are violated.

Understanding which approach applies is key to identifying where watershed groups can take action.

Key Differences

• Point Source: Regulated, permit-based, easier to monitor and enforce.
• Nonpoint Source (NPS): Typically unregulated, diffuse, requires cooperative and voluntary efforts.

Point Source Pollution

Definition: A point source is a discernible, confined, and discrete conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, from which pollutants are or may be discharged (75-5-103(26).

How it is Regulated: Surface water point sources are regulated under the Montana Pollutant Discharge Elimination System (MPDES) program, which implements the Montana Water Quality Act and the Federal Clean Water Act.

• Types of MPDES permits:
  • Individual Permits: Specifically tailored to an individual facility.
  • General Permits: Cover categories of similar discharges statewide, such as pesticide applications, fish farms, domestic lagoons, concentrated animal feeding operations, construction dewatering operations, sand and gravel operations, produced water from oil and gas operations, and disinfected water and hydrostatic testing.

Management Approach:

• Permits set effluent limits, monitoring, and reporting requirements.
• Montana DEQ conducts enforcement activities.
• Where one exists, total maximum daily loads (TMDLs) are incorporated in permits authorizing discharge to impaired waters.

Why This Matters: Point source pollution is typically addressed through permits and enforcement action, meaning there are fewer opportunities for watershed groups to conduct voluntary restoration work in this space.

Nonpoint Source (NPS) Pollution

Definition: Diffuse pollution from land runoff, precipitation, atmospheric deposition, drainage, or seepage. NPS is not traceable to a single discharge point.

Common Sources: Agriculture (fertilizers, pesticides), grazing, forestry, abandoned mines, septic systems, urban runoff, streambank erosion.

Important Sources in Montana:
Agriculture and Livestock Operations: Livestock operations that meet the regulatory definition of a Concentrated Animal Feeding Operation (CAFO) (MCA 75-5-801) are regulated as point sources. This includes operations that confine animals for long periods of time and either meet a numeric threshold of animals or discharge pollutants into state waters, either directly or through a constructed ditch, pipe, or other man-made conveyance.
By contrast, runoff from pastures, cropland, or open grazing areas caused by rainfall or snowmelt is legally classified as agricultural stormwater discharge. This is considered a nonpoint source (NPS).
For watershed groups, this distinction matters; restoration efforts often focus on working with producers to address NPS by implementing BMPs such as manure management, runoff controls, grazing management plans and alternative water systems.

Abandoned Mine Lands: Abandoned mines are a significant source of pollution in Montana, particularly in historic mining areas. Some abandoned mine lands (AML) sites may have identifiable discharge points, while many others have discharges that are diffuse and challenging to address. Watershed restoration may address this pollution through waste removal, capping, and streambank stabilization.
Unlike point source pollution, many NPS issues do not have a clear responsible party. This is especially true for legacy pollution from AML. In some cases, the original party no longer exists. Because of this, NPS pollution is typically not addressed through enforcement. Instead, pollution reduction relies heavily on
voluntary partnership-driven restoration activities.

Management Approach:
Voluntary Best Management Practices (BMPs): Examples include the installation of riparian buffers, erosion control, nutrient management, and livestock watering alternatives.

Funding & Partnerships: DEQ administers Section 319 grants and other funding sources to support restoration projects. These projects often involve collaboration between watershed groups, conservation districts, landowners, and agencies.

Watershed Restoration Planning (WRPs): WRPs provide a roadmap for addressing NPS pollution. DEQ acceptance of a WRP is often required for eligibility for certain funding sources.

Monitoring and State Support (including AML): State and federal agencies play an important role in:

• Monitoring water quality
• Identifying and prioritizing impaired waters and restoration sites
• Implementing large-scale or complex restoration projects, including AML cleanup

Education & Outreach: It is essential for State and local levels to raise awareness about NPS pollution, its sources and effects, and actions that can be taken to improve water quality and to foster sustainable behavior change that protects water quality from NPS pollution.

Why This Matters: NPS pollution is largely addressed through voluntary, locally driven restoration efforts. Watershed groups and conservation districts frequently support these efforts by identifying local priorities, coordinating projects, and securing funding.

Stormwater Management

Stormwater as a point source: As a regulated point source, stormwater is covered under MPDES permits for:

• Industrial activity
• Construction activity (≥1 acre disturbance; or <1 acre but part of a “larger common plan of development or sale (larger common plan)” whose “total area” is ≥1 acre)
• Municipal separate storm sewer systems (MS4s)

Stormwater as a nonpoint source (NPS): Stormwater is primarily a NPS and thus eligible for Section 319 funding. Stormwater is typically considered a NPS when it flows across landscapes without a single point of
origin, such as a pipe or conveyance. Common NPS sources are:

• Agricultural runoff
• Small-scale residential
• Silviculture

Why This Matters:
Section 319 grants cannot be used to fund activities required by an MPDES permit, these regulated areas are generally ineligible for standard 319 restoration funds. Point source and nonpoint source stormwater require implementation of BMPs to reduce pollutant discharge. Stormwater often represents an opportunity for collaboration between regulated entities and watershed groups, particularly through green infrastructure and runoff reduction projects. Funding eligibility depends on what type of stormwater you are treating and will be discussed later in this informational series.

Looking Ahead

Understanding the difference between point and NPS pollution is the foundation for effective watershed restoration.

In the next installment of this series, we’ll explore funding opportunities for restoration projects and tips for developing a Watershed Restoration Plan.