1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Variance 1+ Variance 2+

Triennial 

review

State rulemaking 

and EPA approval 

of initial WQS 

variance

Triennial 

review

Reevaluation at 

permit reissuance.

More stringent HAC 

not found.

No change to WQBEL.

Reevaluation at 

permit reissuance.

More stringent HAC 

identified.

Modified WQBEL 

derived from more 

stringent HAC.

Triennial 

review

Triennial 

review

provides 

additional 

information

State rulemaking 

and EPA approval 

of subsequent 

WQS variance

Permit 5

Permit 1 Permit 2 Permit 3 Permit 4

Hypothetical Example of 20-year WQS Variance

Reevaluations Synchronized to NPDES Permit Cycle

Triennial 

review

Triennial 

review

Reevaluation at 

permit reissuance 

using additional 

information from 

triennial review.

More stringent HAC 

identified.

Modified WQBEL 

derived from more 

stringent HAC.

WQBEL

Year

Permit reissuance.

Designated use not 

attainable, but additional 

progress possible.

Adopt WQS variance.

Derive WQBEL from HAC 

of WQS variance.

+ Meets all statutory and regulatory requirements.

WQBEL – Water Quality Based Effluent Limit

HAC – Highest Attainable Condition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Variance 1+ Variance 2+

Triennial 

review and 

reevaluation.

More 

stringent HAC 

not found.

State rulemaking 

and EPA approval 

of initial WQS 

variance

Permit reissuance.

No change to WQBEL.

Permit reissuance.

Modified WQBEL 

derived from more 

stringent HAC.

Triennial 

review and 

reevaluation.

More 

stringent HAC 

identified

State rulemaking 

and EPA approval 

of subsequent 

WQS variance

Permit 5

Permit 1 Permit 2 Permit 3 Permit 4

Hypothetical Example of 20-year WQS Variance

Reevaluations Synchronized to Triennial Review Cycle

Triennial 

review and 

reevaluation.

More 

stringent HAC 

not found.

Triennial 

review and 

reevaluation.

More 

stringent HAC 

not found.

Permit reissuance.

Modified WQBEL 

derived from more 

stringent HAC.

Triennial 

review and 

reevaluation.

More 

stringent HAC 

not found.

Triennial 

review and 

reevaluation.

More 

stringent HAC 

identified

Permit reissuance.

Designated use not 

attainable, but additional 

progress possible.

Adopt WQS variance.

Derive WQBEL from HAC 

of WQS variance.

+ Meets all statutory and regulatory requirements.

WQBEL – Water Quality Based Effluent Limit

HAC – Highest Attainable Condition

WQBEL

Year
WQS Variance 1

Hypothetical Example of Coordinating a Discharger-specific

WQS Variance and a Permit Compliance Schedule

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Permit 1 Permit 3

After 15 years, the state could:

1. Establish a new WQBEL derived from the underlying designated use (and a compliance schedule if needed) if 

the underlying designated use is now attainable;

2. Consider adopting a subsequent WQS variance with a new HAC and WQBEL (and compliance schedule if 

needed) if uncertainty remains about the attainability of the underlying designated use;

3. Consider modifying the designated use if it remains unattainable.

Year

Underlying 

designated 

use

WQS HAC and 

permit WQBEL

Current 

effluent 

condition

Permit 2

Permit Compliance Schedule 1

The underlying designated use is not attainable. The highest attainable condition (HAC) can be identified as an 

effluent condition, but the discharger requires 15 years to attain it. The state is able to justify and adopts a 15-year 

WQS variance specifying the HAC, and establishes a water quality-based effluent limit (WQBEL) equal to the HAC. 

The state also provides the permittee with a 15-year compliance schedule that will lead to attainment of the WQBEL 

“as soon as possible” (in this case 15 years).

1 Meets all statutory and regulatory requirements.