Model Update By Upper Trinity Water Quality Compact Will Benefit Permittees

1. Model Update ByUpper Trinity Water Quality Compact Will Benefit Permittees By Peggy W. Glass, Ph.D. Alan Plummer Associates, Inc. Texas Association of Clean Water Agencies September 27, 2013

2. Once upon a time, in a galaxy far, far away . . . (NOT!!) “ The flow below Dallasfor many miles does notimpress one as being that ofa river. A stench from its inky surface putrescent with the oxidizing processes to whichthe shadows of overarching treesadd Stygian blackness and the suggestion of some mythological river of death.” Report on 1924-1925 survey of Trinity River, State Health Dept of Texas

3. Federal Water Quality Act of 1972 This act required a wasteload allocation (WLA) to be performed for any water body where secondary treatment would not result in compliance with water quality standards.

4. Upper Trinity RiverWasteload Allocation 1974

5. Upper Trinity RiverWasteload Allocation 1986

6. Upper Trinity RiverCurrent Wasteload Allocation

7. Revision of Current Wasteload Allocation To Provide for Additional Growth • Study Conducted by • Freese & Nichols, Inc. • Alan Plummer Associates, Inc. • Study Conducted for UpperTrinity Water Quality Compact

8. Upper Trinity Water Quality Compact • Fort Worth, Trinity River Authority, Dallas, North Texas Municipal Water District • Organized in 1975 to work effectively with each other and regulatory agencies to manage wastewater treatment in the Dallas/Fort Worth Metroplex.

9. Re-evaluation of Seasonal Base Flows in River • Stream reach: West Fork Trinity River belowLake Worth to just below the USGS Trinidad gage • Stream distance: 259 kilometers/161 miles

10. Study Area • 7 USGS gages • 9 major municipal discharges • 2 major tributaries

11. Study Methodology Base Flow = (Gage Flow) – (Discharge Volume) • Six years of data (2002 — 2007) • Daily gage flows and daily discharge volumes for 9 major facilities • Permitted flows for non-majors 0.5 MGD and greater • Plants permitted for less than 0.5 MGD not included

12. Statistical Calculations • Summer (June through August) andWinter (December through March) values were calculated • 10, 15, and 25 percentile values • 7Q2 flows 7Q2 flows recommended for model

13. Comparison of Historic (and Current Base Flows Summer 7Q2 Condition

14. Comparison of Historic (and Current Base Flows Winter 7Q2 Condition

15. Results of Revised Model • Based on current WLA flows and concentrations, the predicted increases in DO concentrations along the Upper Trinity River are as follows: ‒ Winter: 0.13 mg/L to 0.59 mg/L, depending on location. ‒ Summer: 0.10 mg/L to 0.35 mg/L, depending on location. • Overall increase in assimilative capacity is approximately 15%.

16. Conclusions • In spite of discharges that have increased2.4 times, treatment limits have remainedwithin capability of generally available technology. • Validity of the model is confirmed by the fact that none of the Upper Trinity River segments are on the 303(d) List for Dissolved Oxygen.

17. Take-away Message • It is important to periodically re-evaluate WLA models. • Site-specific data is essential for accurate predictions. • The willingness of the Upper Trinity Water Quality Compact to work cooperatively and support technical studies has resulted in dramatic improvements in the quality of theriver without unduly burdensome treatment requirements.