Current as of September 17, 2026
Key Takeaways
- Latest chapter amendment: Effective July 11, 2026, updating stream designations and correcting drainage lists.
- Latest statewide chemical criteria revision: Effective December 20, 2025, addressing 17 toxic substances.
- Key values: The human health criterion for 1,4-dioxane is 0.3 µg/L. Carbaryl’s acute and chronic aquatic-life criteria are both 2.1 µg/L.
- Application matters: Check averaging periods, water hardness, stream designations and site-specific requirements before comparing results.
- Federal status requires a separate check: A state effective date does not establish EPA approval for Clean Water Act purposes.
Sources: 2026 final rule, 2025 final rule, EPA’s Pennsylvania standards page.
Pennsylvania’s Chapter 93 water quality standards have two recent updates environmental professionals should know:
- July 11, 2026: The latest chapter amendment updated stream designations, including High Quality protection for qualifying Class A wild trout waters, and corrected drainage lists. 2026 final rule
- December 20, 2025: The latest statewide numeric criteria revision updated or added criteria for 17 toxic substances and clarified averaging periods. 2025 final rule
Chapter 93 sets goals for surface-water quality that support aquatic life, water supplies, recreation and other protected uses. These goals inform discharge permits and pollution controls; individual permit limits depend on how the standards apply to the receiving water. Chapter 93
The December 2025 revision established the following human health criteria for the substances it addressed. All concentrations are in micrograms per litre (µg/L).
| Substance | Current human health criterion |
|---|---|
| 1,4-Dioxane | 0.3 |
| 1,2,4-Trimethylbenzene | 10 |
| 1,3,5-Trimethylbenzene | 10 |
| 1,2,3-Trichloropropane | 30 |
| Chloroform | 60 |
| Metolachlor | 700 |
| Barium | 1,000 |
| Boron | 1,000 |
| Formaldehyde | 1,000 |
| Xylene | 1,000 |
| 2,4-D | 1,300 |
| Resorcinol | 3,000 |
| Methyl ethyl ketone | 4,000 |
| Acetone | 6,000 |
The revision also addressed three substances for aquatic-life protection:
| Substance | Acute criterion (µg/L) | Chronic criterion (µg/L) |
|---|---|---|
| Carbaryl | 2.1 | 2.1 |
| Tributyltin | 0.46 | 0.072 |
| Cadmium, at hardness of 100 mg/L as CaCO₃ | 1.8 | 0.72 |
Cadmium values are dissolved concentrations calculated from water hardness. The example above must be recalculated for local conditions. Both tables summarize the criteria addressed by the revision; the complete toxic-substance table contains additional criteria and application notes. §93.8c, Table 5
The 2025 changes reflect updated toxicity information and exposure assumptions. They also clarify that, unless specified otherwise, acute aquatic-life criteria in Table 5 use a one-hour average, while chronic criteria use a four-day average. Table 3’s aquatic-life minimum and maximum values generally use a one-hour average, as does its pH criterion. Table notes and outdated references were also revised. 2025 final rule
The July 2026 amendment changes which protections apply to particular waters. Examples include High Quality–Cold Water Fishes designations for the Bradley Run basin and specified headwaters of Saucon Creek. It also corrects entries for Haldeman Quarries, Mill Creek and Logan Run. For project teams, this makes checking the receiving stream’s current designation as important as checking chemical concentrations. 2026 final rule and drainage lists
When applying the values, check basin-specific and site-specific requirements, including separate Great Lakes criteria. Also distinguish state effective dates from federal approval. EPA’s published Pennsylvania standards page currently lists a Chapter 93 version effective October 9, 2025; that listing does not establish EPA approval of the later amendments. Confirm the applicable EPA-approved provisions for Clean Water Act work. Chapter 93, EPA’s Pennsylvania standards page
FAQs
When were Pennsylvania Chapter 93 water quality standards last updated?
The latest chapter amendment took effect on July 11, 2026, covering stream designations. The latest statewide chemical criteria revision took effect on December 20, 2025. 2026 final rule, 2025 final rule
Are Chapter 93 criteria the same as discharge permit limits?
Chapter 93 criteria describe the water quality needed to protect surface-water uses. DEP uses applicable criteria when developing discharge permit conditions. A facility should assess compliance against its permit’s specific requirements. Chapter 93
Why does cadmium have different values at different sites?
Its aquatic-life criteria depend on water hardness. The table’s values apply at a hardness of 100 mg/L as calcium carbonate; use the prescribed equations for other conditions. §93.8c, Table 5
Does a state amendment automatically apply for federal Clean Water Act purposes?
EPA approval is a separate step. Check the federal approval status of the relevant provisions before applying a state amendment for Clean Water Act purposes. EPA’s Pennsylvania standards page
Glossary
| Term | Meaning |
|---|---|
| Acute criterion | A concentration intended to protect aquatic life from short-term exposure. |
| Chronic criterion | A concentration intended to protect aquatic life over longer exposure periods. |
| Designated use | A use assigned to a waterbody in the regulations, such as supporting cold-water fish. |
| Human health criterion | A concentration intended to protect people from exposure to a substance through pathways such as drinking water and fish consumption. |
| Water hardness | A water characteristic expressed as mg/L of calcium carbonate that affects the calculation of some metals criteria. |
| µg/L | Micrograms per litre, a unit of concentration. |
| DEP | Pennsylvania Department of Environmental Protection. |
| EPA | United States Environmental Protection Agency. |
| NPDES | National Pollutant Discharge Elimination System, the permitting program for regulated pollutant discharges. |
Source: Chapter 93 definitions and criteria.
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