Managing Peak Wastewater Flows

Transcription

1 Metropolitan Council Environmental Services Managing Peak Wastewater Flows Presented at the American Public Works Conference September 12, 2005 Donald Bluhm Interceptor Services Dept.

2 Inflow and Infiltration Peak I/I During a Wet Weather Event has Become a Major Issue Within the Metropolitan Area. System Design Start by making average flow projections for each community based on proposed Land Use Guidelines Interceptor system design: Peak to Average Ratios published and used by MCES since 1970 s Thus each community has a Peak flow allocation implied by the design practice Peak to Average Ratio MCES P/A Ratio Ten States Standards Observed DWF Average Flow

3 Allowable I/I The difference between the Actual Observed Peak Flow Ratios versus the Design Peak Flow Ratios result in an allowable I/I of approximately 1 million gallons per 1000 acres served. Affects of I/I on Sewer Capacity Growth Capacity Allowable I/I Design Peak Flow Base Flow

4 Affects of I/I on Growth Capacity Excessive I/I Growth Capacity Allowable I/I Design Peak Flow Base Flow I/I Background Some service areas are reaching peak flow allocation long before average flow allocation Metro Needs in 2030 Facilities Needed in 2030 if MCES standards are met

5 Design of WWTP I/I Effects on Hydraulic Capacity Affects peak hour Affects peak month flow and peak week flow (permit conditions) Peak Week Impacts Metro Plant Ultimate Design Capacity (350 MGD) Derated Plant (300 MGD) gpapd = 62,500 acres Blue Lake Plant Ultimate Design Capacity (80 MGD) Derated Plant (70 MGD) gpapd = 12,500 acre

6 Inflow and Infiltration Strategy Since it is extremely unlikely that a new Metro Plant or Blue Lake Plant could be sited and constructed MCES will work with communities to initiate an I/I reduction program whereby I/I is eliminated at its source. Long-term Storage is not a preferred alternative because it would result in the derating of our WWTP resulting in a potential lost of economical growth within the Region.

7 Inflow and Infiltration Strategies The Council will limit increases in service within those communities where excessive I/I jeopardizes MCES s ability to convey wastewater without an overflow or backup occurring, or limits the capacity in the system to the point where the Council can no longer provide additional wastewater services. Starting in 2013, the Council will limit future increases within those communities that have not met their I/I goal (s) until the problem is solved. Inflow and Infiltration Strategies Starting in 2013, the Council will institute a wastewater rate demand charge program for those communities that have not met their I/I goal(s).

8 Peak Wet Weather Treatment...To Blend or not to Blend? By Bob Matthews and Mike McGhee, CDM On May 19, 2005 the U.S. House of Representatives passed the EPA Appropriations Bill which included a provision which restricted EPA from spending any funds on a national blending policy or effectively prohibits EPA from finalizing its proposed Blending Policy. This action is very important to all utilities that have conducted wastewater blending in the past or desire to implement blending in the future. Background As an exception to the requirement of no discharge of pollutants, the Federal Clean Water Act required publicly owned treatment works (POTW's) to achieve, as a minimum, effluent limitations based upon secondary treatment. EPA passed regulations in 1982 that allowed bypasses, which was defined as "any intentional diversion from any portion of a treatment facility", only in very limited circumstances. In particular bypasses were allowable only where there was "no feasible alternative to the bypass". The NPDES permitting regulations further allowed the permitting authority (EPA or authorized State) to allow for anticipated bypasses in permits consistent with those regulations. Without specific guidance on the term "no feasible alternative" there was a wide range of bypass allowances or blending made by EPA Regional Offices and States across the country. Some areas of the country seemed to not allow blending under almost any circumstances, while other areas seemed to allow it even to avoid modest cost consequences. The result was inconsistent application of the law and regulation. Since December 2001, EPA has attempted to develop guidance for a more consistent application of blending as they applied to a variety of wet weather discharges. Utilities Have Struggled with High Peak Flows As many POTW's struggled with how to deal with excessive peak flows at their wastewater treatment facilities the concept of fully treating normal flows and partially treating peak flows and blending them together prior to discharge was often viewed as a technically feasible and an economical alternative--thus the concept of "blending". Blending was a process EPA allowed in combined sewer systems and many POTW's wanted to use the process on separate sewer systems. Because of the inconsistent application of the bypass regulations, EPA and the States were also inconsistent in the application for this particular peak wet weather situation. EPA Proposed a Draft Blending Policy In an attempt to remedy this inconsistent handling of blending, EPA formally proposed a national draft policy on blending in November, In essence the policy would have allowed blending only if six provisions were met, including: when the blended discharge meets permits limits based on secondary technology limits; when the permit application for the facilities specifies the treatment scenario that would be used for peak flow management; when the blended effluent has undergone at least primary treatment; when the permits requires

9 monitoring to ensure compliance; and when wastewater treatment facilities properly maintain and operate all parts of their collection system. EPA received approximately 96,000 comments on the proposed policy and a barrage of efforts ensued both for and against the policy until recently. (Note over 60,000 comments were the same message) House of Representatives Opposes EPA s Blending Policy On May 19, 2005 the House of Representatives passed the EPA Appropriations Bill which included a provision which effectively prohibits EPA from finalizing the proposed Blending Policy. In the Congressional Record which documented the discussion on this Bill, it was clear the sponsors intended Blending to be allowed only where other alternatives are not feasible. All concerned interests seem to agree that this effectively kills the proposed policy regardless of the final fate of the Appropriations Bill. EPA has made a few public statements since then which indicate they will provide some guidance to EPA Regions and States along the line of blending will be allowed only where there is no feasible alternative. EPA also states that there are instances that a facility may demonstrate that [blending] is the only feasible solution. What Happens Now? This, of course, circles back to question of what is "feasible". We don t know for sure how EPA will act to clarify new criteria at this point. If this wording is included in the final EPA Appropriations Bill, EPA may provide guidance that further defines feasible. In historic Clean Water Act actions EPA has used economic analyses such as 2% percent of the median family income to interpret terms like attainable, excessive cost, etc. POTW's wanting to pursue blending may have to provide a comprehensive analysis on a case by case basis, similar to those in an EPA CMOM analysis, of their system along with costs with and without blending.

10 Peak Wet Weather Treatment...To Blend or not to Blend? By Bob Matthews and Mike McGhee, CDM On May 19, 2005 the U.S. House of Representatives passed the EPA Appropriations Bill which included a provision which restricted EPA from spending any funds on a national blending policy or effectively prohibits EPA from finalizing its proposed Blending Policy. This action is very important to all utilities that have conducted wastewater blending in the past or desire to implement blending in the future. Background As an exception to the requirement of no discharge of pollutants, the Federal Clean Water Act required publicly owned treatment works (POTW's) to achieve, as a minimum, effluent limitations based upon secondary treatment. EPA passed regulations in 1982 that allowed bypasses, which was defined as "any intentional diversion from any portion of a treatment facility", only in very limited circumstances. In particular bypasses were allowable only where there was "no feasible alternative to the bypass". The NPDES permitting regulations further allowed the permitting authority (EPA or authorized State) to allow for anticipated bypasses in permits consistent with those regulations. Without specific guidance on the term "no feasible alternative" there was a wide range of bypass allowances or blending made by EPA Regional Offices and States across the country. Some areas of the country seemed to not allow blending under almost any circumstances, while other areas seemed to allow it even to avoid modest cost consequences. The result was inconsistent application of the law and regulation. Since December 2001, EPA has attempted to develop guidance for a more consistent application of blending as they applied to a variety of wet weather discharges. Utilities Have Struggled with High Peak Flows As many POTW's struggled with how to deal with excessive peak flows at their wastewater treatment facilities the concept of fully treating normal flows and partially treating peak flows and blending them together prior to discharge was often viewed as a technically feasible and an economical alternative--thus the concept of "blending". Blending was a process EPA allowed in combined sewer systems and many POTW's wanted to use the process on separate sewer systems. Because of the inconsistent application of the bypass regulations, EPA and the States were also inconsistent in the application for this particular peak wet weather situation. EPA Proposed a Draft Blending Policy In an attempt to remedy this inconsistent handling of blending, EPA formally proposed a national draft policy on blending in November, In essence the policy would have allowed blending only if six provisions were met, including: when the blended discharge meets permits limits based on secondary technology limits; when the permit application for the facilities specifies the treatment scenario that would be used for peak flow management; when the blended effluent has undergone at least primary treatment; when the permits requires

11 monitoring to ensure compliance; and when wastewater treatment facilities properly maintain and operate all parts of their collection system. EPA received approximately 96,000 comments on the proposed policy and a barrage of efforts ensued both for and against the policy until recently. (Note over 60,000 comments were the same message) House of Representatives Opposes EPA s Blending Policy On May 19, 2005 the House of Representatives passed the EPA Appropriations Bill which included a provision which effectively prohibits EPA from finalizing the proposed Blending Policy. In the Congressional Record which documented the discussion on this Bill, it was clear the sponsors intended Blending to be allowed only where other alternatives are not feasible. All concerned interests seem to agree that this effectively kills the proposed policy regardless of the final fate of the Appropriations Bill. EPA has made a few public statements since then which indicate they will provide some guidance to EPA Regions and States along the line of blending will be allowed only where there is no feasible alternative. EPA also states that there are instances that a facility may demonstrate that [blending] is the only feasible solution. What Happens Now? This, of course, circles back to question of what is "feasible". We don t know for sure how EPA will act to clarify new criteria at this point. If this wording is included in the final EPA Appropriations Bill, EPA may provide guidance that further defines feasible. In historic Clean Water Act actions EPA has used economic analyses such as 2% percent of the median family income to interpret terms like attainable, excessive cost, etc. POTW's wanting to pursue blending may have to provide a comprehensive analysis on a case by case basis, similar to those in an EPA CMOM analysis, of their system along with costs with and without blending.