Susan Cormier and Charles Lane Environmental Protection Agency Scott Neimela and Joel Chirhart, U.S. Minnesota Pollut

1. Eco-epidemiological Screening to Design a Sampling Plan for TMDLs: Susan Cormier and Charles Lane Environmental Protection AgencyScott Neimela and Joel Chirhart, U.S. Minnesota Pollution Control Agency, U.S.A. Groundhouse River, Minnesota

2. Impetus for Causal Assessment • The Groundhouse River in central Minnesota did not meet minimum criteria for aquatic life uses. • Beneficial uses and was listed as impaired under Clean Water Act (CWA) Section 303(d).

4. Groundhouse River, MN (474) Ogilvie Mechanical treatment plant - trickling filter/chlorine disinfection - continuous discharge - avg. annual design flow 200,000 gpd - violates CBOD and TSS limits with some frequency

5. POTW Outfall

8. Candidate Causes?

9. Candidate Causes • Loss of suitable habitat from unstable or unsuitable substrates • Hypoxia associated with excessive nutrients • Altered food resources • Chronic or episodic toxic exposures

10. Loss of suitable habitat from unstable or unsuitable substrates Co-occurrence Stressor-Response Causal Pathway Analysis

11. Co-occurrence Stressor-Response Causal Pathway Hypoxia associated with excessive nutrients Analysis

12. Altered food resources Co-occurrence Stressor-Response Causal Pathway Analysis

13. Co-occurrence Stressor-Response Causal Pathway Chronic or episodic toxic exposures to ammonia Analysis

14. Probable Cause Scoring Table

15. Probable Cause Scoring Table

16. Siltation resulting in Loss of Habitat • Physical Interaction: Evidence of increased siltation compared to upstream • Sequential Dependence: • Source of sediment • Factors that increase siltation • Sufficiency: Level of %fines reported to cause biological impairments

17. Hypoxia associated with Nutrients • Physical Interaction: DO levels were greater at site 3 than upstream site 2 which was less impaired • Sequential Dependence: No point sources were found; e.g. combined sewer overflow • Sufficiency: Dissolved Oxygen levels were substantially higher than criteria

18. Altered Food Resource • Physical Interaction: No algal growth observed within the study reach, although there was some growth downstream of the treatment plant outfall. • Physical Interaction: Allocthonous input, but no leaf packs • Sequential Dependence: • Sources of leaf input • No additional sources of nutrient input found (no CSO)

19. Chronic or Episodic Toxicity • Physical Interaction: Ammonia levels were slightly greater at site than upstream site • Sequential Dependence: No known sources of other toxicants. Power line sprays herbicides not pesticides • Sufficiency: Ammonia levels orders of magnitude below acute and chronic toxicity values

20. Outcome • Since the analysis was based on unreplicated observations obtained in different years, uncertainty was high. • Additional sampling was recommended with special attention: • to determining the boundaries of the biological impairment, • to characterizing natural sediment regimes, and • to developing exposure-response associations using state monitoring data.