1. Western Slope Bible Camp OWTS Hydrogeological Risk Assessment
Hydro G Logic
Dean R. Goebel

3. PURPOSE Evaluate Potential Water Quality Impacts
Collect Site-Specific Data
Determine Groundwater Perching Phenomena at Lithological Sandy Clay Geologic Contact
Obtain State Discharge Permit to Expand OWTS to Treat 56,250 gpd

4. METHODS Interval Soil Core & Grab Samples Groundwater Monitoring Wells
Nitrogen Modeling
Groundwater Dilution Modeling

6. Surface Geology
Tertiary Basin-Fill Deposits & Quaternary Alluvial & Outwash Deposits
0-55’: Gravels: GP-GC, GW-GM, GP-GM (USCS) or Very Bouldery and Gravelly Sand (NRCS)
’: GM or Sandy Pebbly Clay
’: Sands: SP, SP-SM, SW-SM

9. Top of Sandy Clay

12. Unconfined Aquifer Main Aquifer 134 to 142 feet Water Table
Water Table Fluctuation 8 feet
Perched Aquifer Water Table 11 to Not Present
Up to 44 feet Water Table Fluctuation

13. Well Hydrographs

15. Potentiometric Surface Map

16. Groundwater Quality Main Aquifer
Nitrate-Nitrogen <0.05 to 0.21 mg/L
Total Coliform 0.0 to 2.0 MPN
E. coli 0.0 MPN

17. Groundwater Quality Perched Groundwater
Nitrate-Nitrogen <0.05 to 0.16 mg/L
Total Coliform 0.0 to MPN
E. coli 0.0 MPN

18. Irrigation Water Quality
Total Nitrogen to 1.38 mg/L

19. Wastewater Quality Leachfield Distribution Box
Nitrate-Nitrogen 2.4 to 1.99 mg/L
TSS 60 mg/L
Sulfate 14 mg/L
Chloride 28 mg/L
BOD 69 mg/L
Total Coliform MPN

20. Untreated Domestic Wastewater Characteristics (Crites and Tchobanoglous, 1998)
TSS 100 to 350 mg/L
Sulfate 20 to 50 mg/L
Chloride mg/L
BOD 110 to 400 mg/L
Total Coliform 106 to 109 MPN

21. N-CALC

22. STUMOD Upper 55 Ft.

23. STUMOD Lower 65 Ft.

24. Nitrogen Dilution Potential
(Mass/Year) ÷ (Volume/Year) Recharge Volume Onsite Wastewater Treatment= 2,751,187 ft3/yr Groundwater Volume Turnover = 422,582 ft3/yr Recharge Precipitation & Irrigation Seepage = 11,719 ft3/yr Total Recharge = 3,185,488 ft3/yr = 90,149 m3/yr

25. Nitrogen Loading
Mass/Year ÷ Volume/Year 47,687 g/yr ÷ 90,149 m3/yr = 0.53 g/m3 = 0.53 mg/L Nitrate-Nitrogen 651,726 g/yr ÷ 90,149 m3/yr = 7.23 g/m3 = 7.23 mg/L Nitrate Nitrogen

26. Conclusions Perched Groundwater Conditions Persist
Sandy Clay Lithological Contact Leaky Confining Layer
Perched Groundwater Ephemeral Dilution Potential