Transcript Muddy Creek TMDL Team - Northern Virginia Regional Commission

Commonwealth of Virginia
Fecal Coliform Bacteria TMDLs
Four Mile Run
Public Meeting #1
June 14, 2001
What is A TMDL?
• Process or plan to attain and maintain water
quality standards
• Consist of 3 basic actions:
– identifies sources of pollution
– quantifies pollutant loads from each source
– quantifies allocations or reductions needed to
attain and maintain water quality standards
TMDL Equation
TMDL =  WLAs +  LAs + MOS
Where:
• WLA is pollutant load allocated to all
point sources.
• LA is pollutant load allocated to all
nonpoint sources.
• MOS is the margin of safety to account
for uncertainity in calculations.
TMDLs and Standards
• TMDLs have put
spotlight on Virginia’s
WQ standards.
• Bacteria issues
– application to stream
– wildlife
– all waters designated and
protected for primary
contact swimming use.
Application of Virginia’s Fecal
Coliform Standard
• geometric mean* - 200
• 2 or more samples every 30 days
• instantaneous* - 1000 at any time
• 0 violation rate
* colonies / 100 ml
Application of Virginia’s
Bacteria Standard
• One criterion, never both, applies to a
data set
• 303(d) assessment
– Use instantaneous 1000 and EPA’s 10%
violation rate
• TMDLs
– TMDL based on geometric mean of 200
– impossible to meet instantaneous 1000
Public Response to Bacteria
TMDLs
• Public wants good information on
source identification
– Performing bacteria source tracking (BST)
studies on all fecal coliform TMDLs
• Public is concerned about primary
contact (beach) protection for all waters
– Limited access & minimal stream depth
Four Mile Run BST Study
• “Wildlife” - 56%
• Human, canines, other - 44%
• TMDL must address human and other
anthropogenic sources
• Will water quality standards be attained
if all anthropogenic contributions are
removed?
Wildlife and Bacteria Standard
• In some other TMDLs, bacteria source
tracking and wildlife densities show
significant contributions by wildlife
– critical conditions occur during base flow
– water quality is not attained with 100%
removal of human related pollutants
• Public has expressed concerns
– staged targets in TMDL
– standards change may impact TMDL?
TMDL Allocation Scenario
Percent reductions
Scenario Wildlife in Livestock
Stream
in Stream
Upland
Areas
1
0
100
100
Percent
Violation of
Standard
39.9
2
25
96.5
0
60.5
3
75
99
0
16.0
4
70
100
0
0
Bacteria Indicator Change for
Protection of Swimming Use
• All of Virginia’s waters designated and
protected for primary contact swimming use
– EPA proposing “ 4 levels” of use
• EPA believes there are better indicators than
fecal coliform for human health protection
• Virginia is proposing changing to
– E. coli for freshwater
– Enterococci for marine water
EPA’s New Swimming Use
and Bacteria Criteria*
Contact
E. coli
Enterococci
Beach
235
61
Moderate
298
89
Light
406
108
Infrequent
576
151
Geo. mean
126
33
* Colonies / 100 ml
Preliminary Evaluation of Impact
100 Stations
N = 336
Type
Fecal Beach
Fecal Beach
E.coli Beach
E.coli Mod
E.coli Light
E.coli Infreq
Threshold *
1000
400
235
298
406
576
% Exceed
33
50
48
44
35
30
* Colonies / 100 ml
TMDL Impacts
• TMDLs to be adopted by SWCB as
regulations
• VPDES must be consistent with TMDLs
• EPA HQ developing TMDL / MS4
guidance
– case-by-case decision
– TMDL to include numeric limits if practical,
or BMPs if impractical
– DEQ to include only BMPs in TMDLs