NEW JOB, FIRST ASSIGNMENT or Uh Oh, I Don’t Remember Any Calculus

1. NEW JOB, FIRST ASSIGNMENTorUh Oh, I Don’t Remember Any Calculus By Dick Bogaert Wetlands Biologist/Analyst Mt. View Sanitary District

2. Moorhen Marsh • Constructed marsh receiving highly treated wastewater. • One of the first marshes to receive wastewater for marsh enhancement. • Raised concerns about the quality of habitat produced.

3. Flow Scheme in Moorhen Marsh • Treated effluent flows first to pond D, then splits to pond C and E. These two recombine to flow to Fat Slough then split again to enter ponds A or B. Pond E Pond D Pond C Peyton Slough Pond B Pond A-2 Pond A-1 Treatment Fat Slough

4. How Does the Water Really Travel—the Flow Regimen? • Regulatory agencies were concerned that there might be pockets of low dissolved oxygen or that the water would rush through without interaction with the marsh. • Mosquito abatement was concerned that stagnant areas would produce mosquito breeding pockets. • A flow regimenwould reveal stagnation, short circuiting or high flow flushing.

5. Characterize the Water Flow Regimen Through the Marshes • The flow regimenreveals obstacles and short circuits that alter the actual time a liquid remains in a volume. • Residence time in a container or pond can be calculated directly knowing the volume of the container and the rate of liquid flow. • In a marsh, contours, vegetation, and relation of entry and exit points affect how long a portion of water remains in the marsh.

6. Use Flow, Concentration and Time to Show the Flow Regimen in Moorhen Marsh • Use a tracer to imitate and detect flow through the marsh. • Use a conservative tracer—bromine, a substance that is not absorbed, adsorbed or otherwise taken from the marsh system • Measure water flow out of the subject marsh through a V-notch weir. • Collect samples at known times and flow.

7. Tracer Flow Through a Typical Marsh • The tracer imitates water flow. • Water plus bromine tracer flows through the marsh as clouds of concentration. • Samplers at the exit will sample patches of high or low concentration. Bromine Tracer

8. Theoretical Curves for Bromine Concentration • In the Conc vs Time graph, the higher curve indicates shorter retention time. • In the “% Br Emitted” graph, the shape of the curve provides clues as to how the water flows through a marsh. Conc. Vs. T Conc. Time % Br Emitted % Emit’d Time

9. Combine Concentration, Flow and Time Data • After nine days, bromine concentration fell back to background level. • But does the water short circuit or stagnate? mg/L Br CFS Br Flow Background Br Days

10. Integration Cutout & Weigh • Integrate mass and flow over time…DUH!... • Cut out each section representing a time and mass. • With an analytical balance, weigh the sections. • Each section is proportional to the real mass.

11. Interpretation • Plot mass against time. • Chart now shows how much bromine was emitted against time in days. • The slight bulge in the curve indicates some bromine was retained. • Retention of flow could produce stagnant areas. 100% 80% 60% 40% 25%