Combined Sewer System Long Term Control Plan - DC Water

Selection of Final LTCP
Parameter
Table 11-13
Final Alternatives Comparison (ENR= 6383)
Existing
Phase I +
P.S. Rehab
Draft LTCP
B1 C3 D70A D70B D70C D70J D70M
Phase I
+ 10% LID + 50% LID
No Phase I Controls & Draft + 10%
(Equal (Equal
Controls P.S. Rehab LTCP LID + 50% LID Performance) Performance)
Tunnel Storage Volume (mg)
Anacostia 0 0 108 108 108 99 71
Potomac 0 0 35 35 35 30 24
Rock Creek 0 0 4 4 4 3 2.5
Total 0 0 147 147 147 132 98
No. Overflow/Avg. Yr.
Anacostia 82 75 4 3 1 4 4
Potomac 74 74 9 7 4 9 9
Rock Creek (Piney Branch/Others) 30 30 4 / 4 3 / 4 2 / 3 4 / 4 4 / 4
CSO Overflow Vol. (mg/avg yr.)
Anacostia 2,142 1,282 93 71 16 102 110
Potomac 1,063 639 153 134 78 162 149
Rock Creek 49 49 13 12 8 12 10
Total 3,254 1,970 259 217 102 276 269
Capital Cost ($M)
LID-R $0 $0 $3 $129 $646 $129 $646
Anacostia $0 $115 $856 $886 $886 $873 $834
Potomac $0 $12 $189 $209 $209 $199 $190
Rock Creek $0 $0 $38 $42 $42 $42 $41
Blue Plains $0 $0 $22 $22 $22 $22 $220
Total $0 $127 $1,108 $1,288 $1,805 $1,265 $1,931
Operation & Maintenance ($M/yr) $0 $0 $12 $16 $35 $16 $35
20 Yr. Net Present Worth $0 $0 $1,275 $1,524 $2,311 $1,498 $2,430
% Above Draft LTCP - - 0 20% 81% 17% 91%
$M/day gained compared to Draft
LTCP - - - $45 $44 >$100 >$100
Water Quality Performance
(Avg. Yr.)
# days FC>200 (CSO Only)
Anacostia @ Navy Yard 212 120 11 9 2 12 13
Potomac @ Memorial Bridge 57 44 10 9 5 10 11
Rock Creek @ Zoo 22 22 4 3 2 4 4
# days FC>200 (All Loads)
Anacostia @ Navy Yard 239 200 183 183 182 183 183
Potomac @ Memorial Bridge 142 133 107 107 107 108 108
Rock Creek @ Zoo 294 294 294 294 294 294 294
Blue Plains
Excess Flow Existing Existing Existing Existing Existing Existing Existing
Tunnel Dewatering - - BP 002 BP 002 BP 002 BP 002 BP 002
BP002 Dewatering Rate (mgd) - - 450 450 450 450 450
Dewatering Time (hrs) - - 44 44 44 40 29
IMA Impacts - Increase in Avg.
Flow (mgd) Baseline +3.5 +8.2 +6.5 +0.1 +6.3 -0.4
\\Gh-wash\eng 1160\LTCP\LTCP Final\Sec 11.doc 11-28 FINAL - July 2002