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 ColumbiaWater and Sewer Authority

EPMC 3B2

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 3B3

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 3B4

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 3B5

Schematic flow routes R1 through R11 are color-coded

Diagram shows interconnections and pathways to Blue Plains

JOINT-USE FLOW-ROUTE DIAGRAM

EPMC 3B6

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 3B7

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 3B8

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 STATIONSSuburban 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 MAINSSuburban 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)

Min Max Min Max Min Max Min Max Min Max

R1 Little Falls Trunk Sewer 60.4% 100.0% 0.0% 39.6%

R2 Upper Potomac Interceptor 33.6% 100.0% 0.0% 21.1% 0.0% 11.2% 0.0% 2.5% 0.0% 47.0%

R3Upper Potomac Interceptor Relief Sewer 29.7% 39.5% 21.5% 36.7% 10.3% 21.1% 2.3% 4.7% 8.0% 19.4%

Rock Creek Main Interceptor 26.9% 100.0% 0.0% 73.1%

Rock Creek Relief Sewer 1 62.6% 87.1% 12.9% 37.4%

Rock Creek Relief Sewer 2 60.5% 76.0% 24.0% 39.5%

Rock Creek Relief Sewer 3 23.3% 58.2% 41.8% 76.7%

Potomac River Force Main -1 96" Force MainPotomac River Force Main -2 72" Force Main

R6 B Street New Jersey Avenue Sewer 3.1% 16.3% 83.7% 96.9%

Anacosia Siphon 6.1% 6.1% 93.9% 93.9%

East Outfall Sewer "UP" 7.1% 7.1% 92.9% 92.9%

West Outfall Sewer 7.1% 7.1% 92.9% 92.9%

East Outfall Sewer "Down" 7.1% 7.1% 92.9% 92.9%

Anacostia Force Main 75.8% 93.0% 7.0% 24.2%

NIBS & SIBS 75.8% 75.8% 24.2% 24.2%

Watts Branch Trunk Sewer 70.1% 100.0% 0.0% 29.9%

Anacostia Main Intereceptor 12.2% 28.7% 71.3% 87.8%

Upper Oxon Run Trunk Sewer

Lower Oxon Run Relief SewerOutfall Sewer from Potomac Pumping StationOutfall Sewer from Anacostia Force Main

PUMPING STATIONS

87.8%

93.9%

33.6%

Main Pumping Station

Poplar Point Pumping Station

6.1%

12.2%

0.9% 42.9%

50.0%

Rock Creek Pumping Station

Potomac Pumping Station 28.5% 13.6% 6.4% 1.4%

R11

WSSC Share of Flow Along Flow Routes

0.0% 44.3%

28.5% 13.6% 6.4% 1.4% 50.0%

55.8% 100.0%

R8

R10

43.0%

LCSA Share of Flow Along Flow Routes

Fairfax Share of Flow Along Flow Routes

8.9% 4.2%

R7

R5

Joint-Use FacilityFlow Route

Table 4-1 Summary of Flow Share

11.8% 6.3% 1.4% 46.9%

DC Share of Flow Along Flow Routes

Others Share of Flow Along Flow

Routes

R9

R4

No. Enabling Legislation JUF Route Recommended JUF Comment

1 Little Falls Trunk Sewer R1 Little Falls Trunk Sewer

2 Upper Potomac Interceptor R2 Upper Potomac Interceptor

3 Upper Potomac Interceptor Relief Sewer R3 Upper Potomac Interceptor Relief Sewer

4 Rock Creek Main Interceptor R4 Rock Creek Main Interceptor

5 Rock Creek Main Interceptor Relief Sewer R4 Rock Creek Main Interceptor Relief Sewers 1, 2 & 3

6 Potomac River Interceptor Sewer Potomac River Interceptor Sewer Not included in study

7 Potomac Pumping Station Potomac Pumping Station

8 Potomac River Force Mains R5 Potomac River 96 inch Force MainPotomac River 72 inch Force Main

R6 B Street New Jersey Avenue Sewer Added JUF

9 Outfall Sewers (Sewers from Main PS) R7 Anacostia SiphonsEast Outfall “UP” – above STR 4East Outfall “Down” – below STR 4West Outfall

Anacostia Siphons added JUF

10 Anacostia Force Main (Project 89 Sewer) R8 Anacostia FMNorth Interconnecting Branch SewerSouth Interconnection Branch Sewer

NIBS & SIBS Added JUF

11 Watt Branch Trunk Sewer R9 Watts Branch Trunk SewerAnacostia Main Interceptor

AMI Added JUF

12 Anacostia Force Main & Gravity Sewer

13 Lower Oxon Run Trunk Sewer Not JUF

14 Upper Oxon Run Trunk Sewer R10 Upper Oxon Run Trunk SewerLower Oxon Run Relief Sewer

15 Lower Oxon Run Relief Sewer R10

16 Upper Oxon Run Relief Sewer Not JUF

17 Outfall Relief Sewers (Sewers from Potomac PS) R11` Outfall Sewer From Potomac PSOutfall Sewer from NIBS and SIBS at STR 2A

18 Blue Plains WWTP Not included in study

19 Potomac Interceptor Sewer Included in Route 3

Rock Creek PS Added JUF

Main PS Added JUF

Poplar Point PS Added JUF

EPMC 3B11

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