Bliss Area Sewage System

1. Bliss Area Sewage System Groundwater Monitoring Pete Ganzel Washington County Department of Public Health & Environment

2. Agenda • System History • Local Geology • Collection System • Treatment System • MPCA Discharge Permit • Monitoring • Site Evaluation & Design • Evaluation of Piezometer Data • Discussion • Questions

3. System Overview Historical • Big Marine Lake • Bliss, Holiday Beach Plats 1950s • Uncontrolled Flooding 70s and 80s • Flood Control • 201 Program, Individual and Collector • Cost-$1.5 Million • System in Operation Since 1987

5. Local Geology • St Croix Moraine • Two Glaciations • Ice Block Lake • Ice Walled Lake Sediments • Outwash • Perched Shallow Aquifer

9. Additional site evaluation • More rigorous analyses of • Site • Soil • Stratigraphy • Hydrogeology • 7 additional pits (10 total) • Field permeability testing • Lab characterization • Shallow soil saturation monitoring (piezometers)

10. Results from further site evaluation • Site 10-20’ above nearby lake • 30-40’ above Big Marine Lake • 15-30’ above springs • Depressional area on southern edge of proposed soil treatment area • Lamellae bands common (19-250 cm/d) • Saturated zone within 15’ of surface • CONCLUSIONS: • -site limitations for in-ground sewage treatment system, mounding likely an issue • -Need to assess magnitude of mounding

11. Assessing Mounding Magnitude • Horizontal hydraulic conductivity of overlying soils (275-500 cm/d) • Analytical modeling (Khan et al., 1976) • 22000 gpd • 350’ length x 100’ width • Vertical permeability (assumed negligible) • OUTPUT – 31.5’ mounding height • CONCLUSION: Further analysis required

12. Assessing Mounding Magnitude continued • Numerical modeling approach (Prickett-Lonnquist, Illinois State Water Survey) • More complex site parameters • Compared (validated) to ambient conditions and correlated to observed piezometer readings • 300 days = mounding height of 10.7’; 5 years = 11.3’ (near or at soil surface) • Re-ran model with 50% flow (11000 gpd) • Mounding height of 6.8’ (within 4’ of surface elevation)

13. Overall Conclusions • Site not suitable for flows, loading rates if in-ground soil treatment • Alternative treatment options investigated • Treatment of water • Infiltration rates • Lessen mounding threat to environment • Ultimately alternative treatment employed • Monitoring of separation distances/mounding

14. System OverviewCollection System • 75 Dwellings • Septic Tanks • Shared Step Stations • Gravity Mains • Two Main Lift Stations • Force Mains

18. System OverviewTreatment System • 7500 Gallon Settling Tanks • Sand Filters and Dosing Station • Drainfields and Dosing Station

22. Incoming Effluent (LS3)

23. Sand Filter Effluent (LS4)

24. Guess Which?

25. MPCA Discharge Permit • Requires Licensed Operator- Class D Facility • Renewed Every 5 Years • Goal: Protecting Water Quality • Reporting • Monthly- Flow, Precipitation • Permitted 19,800 gallons per day • Quarterly- Groundwater Monitoring, Effluent Sampling

26. Monitoring • 9 Piezometers • Groundwater/system separation (water level) • 8 Groundwater Monitor Wells • Groundwater Quality • Nitrogen, Phosphorus, Chloride • Effluent Sampling • BOD- Biochemical Oxygen Demand • Waste Strength • VOC- Volatile Organic Compounds

27. Effluent Monitoring

29. VOC Monitoring • Volatile Organic Compounds • Evaporate easily, aromatic • Variable solubility in water, usually low • Solvents, Thinners, Degreasers, Fuels • Many petroleum derived or synthetic • Some Carcinogenic, Teratagenic • Air pollution-smog • Gas Chromatography • Scan for 68 compounds • Sample effluent only • RAW effluent • Sand Filter Effluent • Sample once per year in July • Not Routinely Done in Sewage Plants • Costly Test- $120 per sample, lab cost

31. Compounds Found

32. Some Perspective • Estimated Volume • System Volume-13,000 gallons • 1300 parts per billion is 80 ml of acetone in 13,000 gallons. • 8 parts per billion is 0.5ml of p-isopropyltoluene in 13,000 gallons. • Volumes probably more because of volatilization within the collection system. • Hit and Miss catching “slugs” of contaminants with limited sampling.

33. Piezometer Data • Separation to Drainfield Trenches • Operation of System

34. Bliss Separation 1987-1996

35. Bliss Separation 2001-2005

36. Site Evaluation 1985 Included analysis of Groundwater Elevation Soil Conductivity Projected Mounding

38. Example Soil Description

39. Conductivity Analysis

44. Groundwater Contours 1985

45. Estimated Groundwater Contours

49. Groundwater to Surface

50. Discussion/Questions???