1. Update on PI Modeling and Nitrogen Removal at Blue Plains
Briefing Materials
Update on PI Modeling and Nitrogen Removal at Blue Plains
Presented to:
Blue Plains Regional Committee
By:
District of Columbia
Water and Sewer Authority
October 25, 2007

2. Agenda Fairfax request for additional flow in PI Nitrogen
Regulatory update
Cost allocation of nitrogen removal facilities
Poundage / allocation – upcoming issues

3. PI Model: Fairfax Request for Additional Flow
Approach:
Revise relationships predicting peak flow vs. rain based on new data
Obtain suburban & WASA flow data
Recalibrate model based on new data
Evaluate 5, 10 & 15-year storm
Field visit MH’s with predicted overflows
Assess whether additional flow can be added

4. Status of PI Work
Activity
Status
Comments
1. Obtain flow data
Received data from WASA, Fairfax, WSSC
No data from LCSA
LCSA data may not be available in useable form
Recommend using previously developed relationships
2. Develop wet weather relationships
Completed
Need to review with CH2M Hill
3. Recalibrate model
4. Evaluate 5,10, 15 yr storms
5. Field visit manholes
In progress
Should have results for December meeting (including CH2M Hill review)

5. Nitrogen Update: TN/WW Plan
Facilities Part of TN/WW Plan
Facilities in LTCP
Nitrogen Update: TN/WW Plan N
Northeast Boundary Tunnel
Anacostia CSO Tunnel
Existing Sewers
Extend CSO Tunnel to Blue Plains- 31 mg Added Storage
Current Facility Plan Alignment
Overflow to Tunnel
Main & O Terminus
RFK Stadium
TDPS at Blue Plains
Anacostia River Tunnel
Alternate alignment under consideration
Anacostia River
225 mgd
555 mgd
Excess Flow Treatment: ECF
Complete Treatment ENR
Bolling Overflow Tunnel
Tunnel to Blue Plains
Potomac River
Outfall 001
(CSO Bypass)
Outfall 002
Blue Plains
Tunnel Dewatering Pump Station & ECF at Blue Plains
Recommended Plan - Alternative D 5

6. Nitrogen Update: Recent Events
April 13, 2007 – Draft TN/WW Plan submitted to EPA
May to Sept 17, public comment period
Only received comments from EPA
Oct 12, 2007 – Submitted Final TN/WW Plan to EPA
Anticipate modifying LTCP Consent Decree to incorporate plan
Substantive changes between Draft & Final Plan:
Schedule in Final Plan
Place TN facilities in operation: July 1, 2014
Start TN compliance: 1st full calendar year after placing facilities in operation
Place Wet Weather Facilities in Operation: March 23, 2018
Item
Draft Plan
Final Plan
Complete treatment flow rates
555 mgd 1st 4 hrs
511 mgd next 24 hrs
450 mgd thereafter
511 mgd thereafter
Permitting Status of Outfall 001
Permit as CSO Bypass
Permit as CSO Outfall
Based on EPA approval of plan by 1/1/2008

7. Cost Allocation of Nitrogen Removal Facilities
BPWWTP Site
Off Site
Poplar Point
Spills to Tunnel when Q > complete treatment capacity
Up to 1076 from all sources
555/511
West P.S.
Outfall 002
Filters & Disinf.
ENR
Prim & Sec
555/511
East P.S.
Up to 521 mgd
Fine Screen & Grit for ECF
TDPS 225 mgd
Shaft
Outfall 001: CSO
New ECF 225 mgd
Anacostia CSO facilities
Disinf.
170 mgd
Tunnel
55 mgd
185/4 hrs= 31 mg
LEGEND
Existing facilities
Joint Use – split based on 370 mgd
Joint Use – split based on agreed LTCP split
Anacostia River

8. TN Allocation Issues: Outfall 001
NPDES Permit Modification
Allocates all mil lbs to 002
Didn’t address outfall 001
EPA says intent was for mil lbs to apply to sum of
001 loads are highly variable
Estimate about 0.18 mil lbs/average yr TN
Depends a lot on rain – both DC and suburban flow
WASA’s recommendation to EPA:
Make 002’s allocation = – 0.18 = mil lbs
Treat 001 as a CSO with an allocation of 0.18 mil lbs
No TN permit limit for 001, evaluate it based on post construction monitoring
Recognizes that TN for 001 will go up and down dramatically with rainfall
Consistent with CSO Policy & handling of CSOs in TMDLs

9. ANNUAL AVG FLOW AND TN ALLOCATION
TN Allocation Issues: Required Nitrogen Removal is not Proportional to Flow
ITEM
ANNUAL AVG FLOW AND TN ALLOCATION
TOTAL
D.C. MD VA
A. BP IMA Flow Allocations – MGD
1. D.C.
148.0
2. WSSC
169.6
3. Fairfax CO
31.0
4. P.I. Flows
▪ LCSA
13.8
▪ Town of Vienna + Dulles Airport 3
▪ Navy + NPS
0.1
▪ Future PI Users (D.C.)
4.5
Total – MGD)
370.0
152.5
169.7
47.8
B. Blue Plains TN Allocation. LBS/YR (Effluent Allocation)
4,689,000
2,115,000
1,993,000
581,000
1. MG/L Effluent Required at Flow Allocation
4.16
4.56
3.86
3.99

10. TN Allocation Issues: Impact of Flow Offloading
77,000 lb/yr reduction for BP flows going to Seneca
Blue Plains allocation reduced, but plant capacity not reduced
Options / Implications
Reduce plant capacity rating to match TN allocation
Improve nitrogen treatment (limit of technology)
Pay in proportion to nitrogen removed
TN Load Allocation (mil lbs/yr)
Source
EPA 7/28/2005 Letter
NPDES Permit Fact Sheet
DC CSO after LTCP
0.0053
DC BP CSO Bypass (001) -
DC non-point sources
0.28
DC portion of BP
2.115
Total DC
2.4
MD part of BP
2.007
1.993
Virginia part of BP
0.581
Total Suburbs
2.6510
2.574
Total Blue Plains
4.766
4.689