Who this article is for: Authority users who manage discharge limits.
Overview
Discharge limits are the measurable thresholds your pretreatment program uses to define what an Industrial User can discharge at each outfall. Each limit targets a specific analyte (pollutant or parameter), specifies how compliance is measured (the limit type), and is assigned to an outfall.
A limit on its own defines the threshold. What gives it regulatory authority is its connection to a legal control — either a General Control (sewer use ordinance) or a Specific Control (discharge permit). SwiftComply tracks these connections through the Enforceability section on each limit, so you can see exactly which legal controls back each limit.
Key Concepts
Analyte — The pollutant or parameter being measured (e.g., BOD, TSS, pH, Lead).
Limit Unit — The unit of measurement (e.g., mg/L, lbs/day, SU). Units are filtered based on compatibility with the selected analyte and limit type.
Limit Type — How the limit is evaluated. Defines the statistical method or timeframe used for compliance determination.
Limit Definition — Whether the limit is for compliance enforcement or notification only.
Limit Rationale — The regulatory basis for the limit.
Limit Types
SwiftComply Pretreatment supports 18 limit types:
Limit Type | Description |
Instantaneous | Single point-in-time measurement. |
Instant Range (High-Low Values) | Range between high and low instantaneous values. Used for parameters like pH that have both a minimum and maximum. |
Daily Maximum | Highest value in a 24-hour period. |
Daily Minimum | Lowest value in a 24-hour period. |
Daily Average | Average of all values in a 24-hour period. |
4 Day Consecutive Average | Average over 4 consecutive days. |
Weekly Average | Average over 7 days. |
30 Day Average | Average over 30 days. |
Monthly Average | Average over a calendar month. |
6 Month Average | Average over 6 months. |
4 Quarter Rolling Average | Rolling average over 4 quarters. |
Annual Average | Average over a calendar year. |
Split Sample Average | Average of split sample results. |
Daily Total | Total mass in a 24-hour period. |
4 Day Consecutive Total | Total over 4 consecutive days. |
Weekly Total | Total over 7 days. |
Monthly Total | Total over a calendar month. |
Annual Total | Total over a calendar year. |
💡 Tip: Analyte, Limit Unit, and Limit Type are interdependent. When creating or editing a limit, selecting one filters the available options for the others based on compatibility. This three-way filtering ensures only valid combinations can be created.
Limit Definitions: Compliance vs. Notification
Every limit has a definition that determines how it is treated in the system:
Definition | Description | Enforceability |
Compliance | An enforceable discharge limit. Exceeding it can trigger a compliance violation. | Has an Enforceability section on the limit detail page. Can be connected to General Controls and Specific Controls. |
Notification | A monitoring threshold. Exceeding it triggers an alert but does not create a formal violation. | No Enforceability section. Not connected to legal controls. |
This distinction is important: only Compliance limits have enforceability tracking. If you don't see the Enforceability section on a limit's detail page, the limit is set to Notification.
Limit Rationales
The rationale records the regulatory basis for the limit:
Rationale | Description |
CFR | Code of Federal Regulations — federally mandated categorical limits. |
Local limits | Locally developed discharge limits based on your POTW's capacity and receiving water requirements. |
Authority (other) | Other authority-determined limits not covered by CFR or local limits. |
Surcharge | Limits related to surcharge fee calculations. |
Notification | Limits set for notification and monitoring purposes. |
TRC | Technically-based local limits derived from technical analysis of your treatment system's capacity. |
How Limits Connect to Legal Controls
Limits are created at the outfall level. Their enforceability comes from connections to legal controls. There are two ways limits get connected:
Connecting to General Controls (Manual)
You manually connect a Compliance limit to a General Control from the limit's detail page using the + General Control button. This is how you establish that a limit is backed by a sewer use ordinance or other broad regulation. A limit can be connected to multiple General Controls.
General Controls do not have expiration dates the way permits do — they remain in effect until explicitly terminated. A limit connected to a General Control is enforceable as long as that General Control is active.
For the step-by-step process, see Managing Discharge Limits.
Connecting to Specific Controls / Permits (Through Permit Creation)
Limits are connected to permits through the permit template's system tables during the permit creation process. When a permit template includes a limits system table (such as Compliance Limits or Limits and Requirements), the limits configured on the IU's outfalls are pulled into the permit document automatically.
Limits that remain in the system table when the permit is signed become associated with that permit. To exclude a limit from a specific permit, delete its row from the system table during Step 2 (Fill Form) of the permit wizard. Excluding a limit from the permit document does not delete or modify the limit itself — it only removes it from that particular permit.
A limit connected to a permit is enforceable for the duration of that permit's effective and expiration dates. Once the permit expires or is terminated, the limit is no longer enforced under that permit. If the IU is reissued a new permit, the limit would be connected to the new permit through the same permit creation process.
For details on system tables and the permit creation workflow, see Understanding Permit Templates and System Tables and How Permits and Sample Report Configurations Work Together.
Multiple Connections
A single limit can be connected to any combination of General Controls and Specific Controls simultaneously. For example, a BOD limit might be backed by both the sewer use ordinance (General Control) and the IU's discharge permit (Specific Control). The Enforceability table on the limit detail page shows the status and dates for each connection.
Where Limits Live
Limits are assigned at the outfall level. To view limits:
Click Industrial Users in the left sidebar.
Select an IU.
Select an Outfall.
View the Discharge Limits section on the outfall detail page.
Limits can also be viewed under a General Control's detail page in the Discharge Limits expandable section.
FAQ
Q: What is the difference between Compliance and Notification limits?
A: Compliance limits are legally enforceable and can be connected to legal controls through the Enforceability section. Notification limits are monitoring thresholds that do not have enforceability tracking.
Q: Can one outfall have multiple limits for the same analyte?
A: Yes. You can have different limit types for the same analyte on the same outfall — for example, both a Daily Maximum and Monthly Average limit for BOD.
Q: How do limits get into a permit?
A: Limits are pulled into the permit document through system tables during permit creation (Step 2: Fill Form). The permit template determines which system tables appear. Limits that remain in the table when the permit is signed are associated with that permit.
Q: What happens to a limit's enforceability when a permit expires?
A: The limit is no longer enforced under that permit. If the limit is also connected to a General Control, it remains enforceable under that control. The limit itself is not modified or deleted.
Q: What units are available for limits?
A: Over 20 units are available including mg/L, ug/L, ng/L, g/L, degrees C, degrees F, SU, gpd, gpm, lbs/day, kg/day, lbs, kg, Gallons, and more. Available units depend on the selected analyte and limit type.