Title: CSO-Related Bypass in Long-Term Control Plans (Maximizing Treatment at the Existing POTW Treatment Plant)

Identification Number: Water-015

Date Originally Effective: April 11, 2008

Dates Revised: None

Other Policies Repealed or Amended: None

Brief Description of Subject Matter: The appropriate use of the CSO-Related Bypass as part of the long-term CSO control strategy.

Citations Affected: Federal Bypass Rule at 40 CFR 122.41(m)

Disclaimer: This nonrule policy document (NPD) is intended solely as guidance and does not have the effect of law or represent formal Indiana Department of Environmental Management (IDEM) decisions or final actions. This NPD shall be used in conjunction with applicable laws. It does not replace applicable laws, and, if it conflicts with these laws, the laws shall control. This NPD may be put into effect by IDEM 30 days after presentation to the appropriate board. Under IC 13-14-11.5, this policy will be available for public inspection for at least 45 days prior to presentation to the appropriate board. If the nonrule policy is presented to more than one board, it will be effective 30 days after presentation to the last board. IDEM will submit the policy to the Indiana Register for publication. Revisions to the policy will follow the same procedure of presentation to the board and publication.

The purpose of this policy is to assist CSO communities to understand the requirements of the federal Bypass Rule at 40 CFR 122.41(m) and to appropriately utilize the CSO-Related Bypass as part of the long-term CSO control strategy. Under certain circumstances described by this NPD and the federal Bypass Rule, a CSO community may be approved by IDEM to allow a bypass of a portion of wet weather flow as part of the long-term CSO control strategy.

This policy affects CSO communities, IDEM's review of the communities' Long-Term Control Plans (LTCPs) and compliance with them.

Part II.C.7 of the national Combined Sewer Overflow (CSO) Control Policy (Policy), Federal Register/Vol. 59, No. 75/Tuesday, April 19, 1994, recognizes that a permitting authority may approve a CSO-Related Bypass, under certain conditions, to a portion of wet weather flow as a part of the long-term CSO control strategy. The Policy further states that the study of feasible alternatives (discussed below) in the Long-Term Control Plan may provide sufficient support for obtaining approval of CSO-Related Bypasses in permits.

The following definitions apply to the defined term as used in this NPD:

Long-Term Control Plans submitted by CSO Communities are reviewed for approval by the Office of Water Quality's Wet Weather Section.

40 CFR 122.41(m), the bypass rule, prohibits a bypass and provides that the Director may take enforcement against a permittee for bypass unless the following conditions are met:

The CSO-Related Bypass discussion is found in Part II.C.7., 'Maximizing Treatment at the Existing POTW Treatment Plant', on Page 18693 of the Policy. The Policy states the CSO-related bypass provision in an NPDES permit should make clear that all wet weather flows passing the headworks will receive at least:

• primary clarification;

• solids and floatables removal and disposal;

• disinfection, when necessary; and

• any other treatment that can reasonably be provided.

A CSO-Related Bypass scenario may include the use of a disinfection unit and outfall separate from those used for the fully treated discharge from the POTW.

In a CSO-Related Bypass scenario, the diversion is considered an "anticipated" bypass, meaning that the permittee is required to submit advanced notice of the need for a bypass. An anticipated bypass can be approved by IDEM, if, after considering its adverse effects, IDEM determines that the anticipated bypass will meet the conditions listed in the bypass rule, including the no feasible alternatives condition.

The CSO-Related Bypass may involve recombination of the bypassed flow with the final effluent prior to disinfection. The term "recombination", in the context of long-term control plan alternatives for wastewater treatment plants that receive flow from combined sewer systems, refers to the following scenario:

During high influent flow conditions due to wet weather events, wastewater flow at or below a specified flow rate receives full treatment, i.e., treatment through each unit treatment process present at the wastewater treatment plant. However, due to treatment process capacity restrictions, wastewater flow in excess of the specified flow rate receives partial treatment, i.e., treatment through some but not all of the unit treatment processes present at the wastewater treatment plant. The fully treated wastestream and the partially treated wastestream "recombine" prior to discharge through the wastewater treatment plant outfall to the receiving stream. The recombined flow must continue to meet permit limits.

Under both state and federal law, the intentional diversion of a wastestream from any portion of a treatment facility constitutes a bypass. While EPA reviews how recombination fits into the overall approach for treatment of wet weather flows from separate sanitary sewer systems, the approved bypass approach under the Policy is a way to account for recombination for the treatment of flows from combined sewer systems in the regulatory process. The Policy indicates the need for the conditions of the bypass rule, including the "no feasible alternatives" condition.

The Policy discusses the need for a permittee to document, among other things, the technical or financial infeasibility of providing secondary treatment for greater amounts of wet weather flow, including an assessment of the feasibility of increasing plant capacity through construction of additional treatment units or storage equipment. The Policy further discusses the need for the permittee to consider, as part of a feasible alternatives analysis, additional treatment options.

To demonstrate that there are no feasible alternatives other than the use of a CSO-related bypass in the CSO Long-Term Control Plan, a permittee should provide the following types of information in the alternatives analysis portion of the LTCP:

IDEM staff will review the facility's compliance and enforcement records, including the record of past bypassing. In addition, the permittee may also wish to provide information to IDEM to aid in this evaluation. Examples of the type of documentation that may be reviewed include, but are not limited to, the following information/records:

Examples of documentation that should be provided include, but are not limited to, the following information/records:

The permittee must evaluate various options for achieving a range of reductions in bypassing (e.g., zero bypasses, 1-3 bypasses, 4 bypasses, etc.) in the documentation, including:

• construction of additional secondary treatment facilities;

• storage of wet weather flows that exceed the secondary treatment system capacity;

• nonbiological secondary treatment; and

• enhanced primary treatment (such as chemical addition);

for a range of capacities, including capacity equal to peak wet weather primary treatment capacity. For each option and capacity, the permittee must identify the projected costs and the expected performance (i.e., impact on effluent quality for each pollutant present in the wastewater treatment plant influent).

If financially infeasible, then the permittee must provide a benefit-cost analysis* demonstrating that conveyance of wet weather flow to the WWTP for primary treatment is more beneficial than other CSO abatement alternatives, such as storage and pump back for secondary treatment, recombination, sewer separation, or satellite treatment.

*This evaluation should be done in accordance with the following sections of the Policy:

• under what conditions the CSO-Related Bypass occurs; and

• the cutoff point at which the flow will be diverted from the secondary treatment portion of the WWTP.

Additionally, the permittee must develop standard operating procedures (SOP) for dry weather and wet weather conditions at the WWTP. The wet weather SOP must describe:

• under what conditions a CSO-Related Bypass occurs; and

• the cutoff point at which the flow will be diverted from the secondary treatment portion of the WWTP.

The permittee must justify the cutoff point by providing flow rate data of the primary effluent, secondary effluent, and tertiary effluent (if applicable) at the WWTP.

If using recombination, the permittee will be required to sample the recombined wastestream and provide IDEM with the data.

The state of New York has developed the Wet Weather Operating Practices for POTWs with Combined Sewers manual. The manual can be found at: