Bacteria TMDLs for Clear Creek

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Bacteria TMDLs forClear Creek
March 6, 2008
PARSONS
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Outline

• Pollutant source assessment
• LDCs for non-tidal segments
• Tidal Prism methodology for tidal segments
• TMDL Calculations

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Clear Creek Watershed

• 200 square miles
• Located within 4 counties (Harris, Galveston,
  Brazoria, Fort Bend)
• Average Annual Rainfall 53 inches (PRISM Group
  2006)

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Land Use/Land Cover
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Water Quality Stations
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Outline

• Pollutant source assessment
• LDCs for non-tidal segments
• Tidal Prism methodology for tidal segments
• TMDL Calculations

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TPDES Facilities
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SSOs
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Permitted Stormwater
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Sampled Runoff Sites 2006
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Stormwater Loads 2006 Data
Orange Color indicates Max and Green indicates
Min Load.
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Pipe Recon 05-06
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FC from GCHD Discharge Data
Yellow indicates 200 400 cfu/100 ml and orange
indicates gt 400 cfu/100ml
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Dry weather PipeBacteria Loading
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Livestock/Manure
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OSSFs
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OSSF Loads
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Domesticated Animals
X 109
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Outline

• Pollutant source assessment
• LDCs for non-tidal segments
• Tidal Prism methodology for tidal segments
• TMDL Calculations

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TMDL WQ Stations
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LDC Schematic
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Chigger Creek LDC
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Reductions for Freshwater Segments
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Outline

• Pollutant source assessment
• LDCs for non-tidal segments
• Tidal Prism methodology for tidal segments
• TMDL Calculations

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Tidal Boundary
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Tidal prism model

• Volume of water between low and high tide levels
• Model incorporates the following sources of ENT
• Storm water runoff loadings
• WWTP point source loadings
• Tidally-influenced loadings
• ENT removal mechanisms include
• Net estuarine flow loadings
• Decay (first-order)

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Tidal prism conceptual model
Removal/decay rate (k)
Downstream reach boundary
Upstream reach boundary
Q flow C conductivity N Enterococci
Control
volume
Tidally-influenced loading (Qu, Cu, Nu)
Tidally-influenced loading (Qd, Cd, Nd)
Freshwater loading (Qf, Cf, Nf)
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Tidal prism model for Clear Creek Tidal

• Time variable (1 hour time steps)
• 11 reaches in main stem and 6 for major
  tributaries
• Simulation period 1/1/2000 to 9/30/2006

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Tidal prism final model segmentation
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Input data
Tide elevations from NOAA gage at Clear Lake
Support volume and flow calculations
Cross-sectional areas for boundaries of reaches
Flows and concentrations for u/s freshwater
streams
Boundary conditions for five headwaters. Load is
QC
Storm water runoff daily flows and concentrations
WWTP daily flows and maximum 30-day geomean
concentrations
Flows and loads to the system. Load is QC
Flows and concentrations for tributaries with no
reach in the model
First-order decay rate

Removal mechanism
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Conductivity calibration
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Enterococci calibration
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Enterococci calibration time series
Station 11448 (Reach B)
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Enterococci calibration time series contd
Station 16573 (Reach K)
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Enterococci calibration time series contd
Station 16475 (Reach O)
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Outline

• Pollutant source assessment
• LDCs for non-tidal segments
• Tidal Prism methodology for tidal segments
• TMDL Calculations

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Required reductions geometric mean
Clear Creek Tidal
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Required reductions single sample criterion
Clear Creek Tidal
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Required reductions geometric mean
Tributaries
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Required reductions single sample criterion
Tributaries
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Summary required percent reductions
a Reductions are calculated assuming that the
upstream freshwater segment (addressed using LDC)
meet the WQS of 35 counts/dL b Overall reduction
for the entire main stem The bacteria indicator
in tidal segments is Enterococci
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TMDL calculations for tidal segments
a Sum of WWTP, stormwater runoff, and tributary
loads discharging directly to the WQ segment that
result in attainment of the WQ criteria b
TMDL0.05 c Sum of loads from the WWTP
discharging to the segment. Individual loads are
calculated as permitted flow35 cfu/dLconversion
factor d MS4 WLA (TMDL MOS WWTP
WLA)percent of drainage area covered by MS4
permits e LA TMDL MOS WWTP WLA MS4 WLA