Delon Hampton and Associates, Chartered EPMC 3B Joint-Use Facilities Capital Cost Allocation Study Presented to Environmental Quality & Operations Committee February 18, 2010 District of Columbia Water and Sewer Authority

EPMC 3B 2 INTRODUCTION PURPOSE  To develop a method to allocate capital costs among joint-use sewerage facility users that is proportional to the demands they place on the capacity of the facilities  To identify any previously unrecognized joint-use facilities BACKGROUND  DC WASA’s enabling legislation identified nineteen (19) joint-use facilities  DC WASA charges routine O&M costs to joint-use facility users based on metered flow  DC WASA now seeks to adopt a method to allocate capital costs among users for major rehabilitation of joint-use facilities included in the CIP

EPMC 3B 3 APPROACH Develop a capital cost allocation method compliant with existing legal structures:  WASA’s enabling legislation  Blue Plains Intermunicipal Agreement (IMA)  Anacostia Force Main Agreement  Potomac Interceptor Agreements Analyze joint-use flow pathways with the MIKE URBAN model used in developing the Long Term Control Plan for CSO Develop a logical capital cost allocation method using the model to replicate conditions under realistic peak demands

EPMC 3B 4 JOINT-USE FACILITIES MODELING  IMA peak flow allocations were modeled from the nine (9) suburban boundary inputs downstream through the system to Blue Plains, picking up peak District flows en-route  Four (4) previously unrecognized joint-use sewers that originate from a pumping station or a structure within the District were identified as joint use by the modeling  Eleven (11) joint-use flow routes were defined, mapped, and modeled under peak flow conditions  Suburban and District flow shares were calculated along each flow route

EPMC 3B 5  Schematic flow routes R1 through R11 are color-coded  Diagram shows interconnections and pathways to Blue Plains JOINT-USE FLOW-ROUTE DIAGRAM

EPMC 3B 6 MIKE URBAN MODEL ASSUMPTIONS  Suburban peak flow allocation inputs were used, because they are the maximum the IMA permits to be routed through the joint-use facilities  Peak flows collected within the District were added along the route of joint- use sanitary and combined sewers  In District joint-use sanitary sewers, peak hourly sanitary flows, and base groundwater, I/I, and stormwater allowances were added to suburban peak flows  In District joint-use combined sewers, stormwater runoff from a 15-year frequency design storm was added to peak hourly sanitary flows, groundwater and I/I allowances, and suburban peak flows

EPMC 3B 7 CONCLUSIONS  The model confirms that the suburban share of total peak flows routed through joint-use sewers decreases in an expected pattern from upstream input points to downstream termini  The model also confirms that the District share of total peak flows increases proportional to the accumulation of District inflows as flows are routed downstream  The model study was able to accurately predict each jurisdiction’s proportional flows in each joint use sewer and in finite sewer segments

EPMC 3B 8 GRAVITY SEWERS User shares of capital costs for a joint-use sewer are proportional to the computed flow shares attributable to suburban users and the District at peak flow PUMPING STATIONS Suburban users’ share of capital costs is proportional to the ratio of their computed peak inflow at a pumping station to its rated firm pumping capacity Ratio of remaining pumping station firm capacity to rated firm pumping capacity represents District’s share of capital costs FORCE MAINS Suburban and District capital cost shares are in the same ratio as their cost shares at the connected upstream pumping station, adjusted for District inputs en-route RECOMMENDED COST ALLOCATION METHOD (IN ACCORDANCE WITH IMA COST ALLOCATION PRINCIPLES)

No.Enabling Legislation JUFRouteRecommended JUFComment 1Little Falls Trunk SewerR1Little Falls Trunk Sewer 2Upper Potomac InterceptorR2Upper Potomac Interceptor 3Upper Potomac Interceptor Relief SewerR3Upper Potomac Interceptor Relief Sewer 4Rock Creek Main InterceptorR4Rock Creek Main Interceptor 5Rock Creek Main Interceptor Relief SewerR4Rock Creek Main Interceptor Relief Sewers 1, 2 & 3 6Potomac River Interceptor Sewer Not included in study 7Potomac Pumping Station 8Potomac River Force MainsR5Potomac River 96 inch Force Main Potomac River 72 inch Force Main R6 B Street New Jersey Avenue Sewer Added JUF 9Outfall Sewers (Sewers from Main PS)R7 Anacostia Siphons East Outfall “UP” – above STR 4 East Outfall “Down” – below STR 4 West Outfall Anacostia Siphons added JUF 10Anacostia Force Main (Project 89 Sewer)R8Anacostia FM North Interconnecting Branch Sewer South Interconnection Branch Sewer NIBS & SIBS Added JUF 11Watt Branch Trunk SewerR9Watts Branch Trunk Sewer Anacostia Main Interceptor AMI Added JUF 12Anacostia Force Main & Gravity Sewer 13Lower Oxon Run Trunk SewerNot JUF 14Upper Oxon Run Trunk SewerR10Upper Oxon Run Trunk Sewer Lower Oxon Run Relief Sewer 15Lower Oxon Run Relief SewerR10 16Upper Oxon Run Relief SewerNot JUF 17Outfall Relief Sewers (Sewers from Potomac PS)R11`Outfall Sewer From Potomac PS Outfall Sewer from NIBS and SIBS at STR 2A 18Blue Plains WWTPNot included in study 19Potomac Interceptor SewerIncluded in Route 3 Rock Creek PS Added JUF Main PS Added JUF Poplar Point PS Added JUF

EPMC 3B 11 NEXT STEPS  Finalize draft report by March 1, 2010  Present to Blue Plains Regional Committee timely to IMA negotiations  Detailed review and discussions with user jurisdictions