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

2. 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).

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4. 4 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 Groundhouse River, MN (474)

5. 5 POTW Outfall

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8. 8 Candidate Causes?

9. 9 Candidate Causes 1)Loss of suitable habitat from unstable or unsuitable substrates 2)Hypoxia associated with excessive nutrients 3)Altered food resources 4)Chronic or episodic toxic exposures

10. 10 Causal PathwayStressor-ResponseCo-occurrence Analysis Loss of suitable habitat from unstable or unsuitable substrates

11. 11 Causal PathwayStressor-ResponseCo-occurrence Analysis Hypoxia associated with excessive nutrients

12. 12 Causal PathwayStressor-ResponseCo-occurrence Analysis Altered food resources

13. 13 Causal PathwayStressor-ResponseCo-occurrence Analysis Chronic or episodic toxic exposures to ammonia

14. 14 Candidate Causes Type of EvidenceSiltLow DO Altered Food Ammonia Spatial Co- Occurrence Causal Pathway Stressor Response (Field or Lab) Consistent Evidence Reasonable Explanation Probable Cause Scoring Table

15. 15 Candidate Causes Type of EvidenceSiltLow DO Altered Food Ammonia Spatial Co- Occurrence +0- - -+ Causal Pathway +0+NE Stressor Response (Field or Lab) +-0 - Consistent Evidence +--- Reasonable Explanation 0000 Probable Cause Scoring Table

16. 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. 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. 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. 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. 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.