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William Hahn, P.G. Professional Hydrogeologist 6589 Elaine Road, Evergreen CO 80439

Presentation to the Jefferson County Board of County Commissioners April 16, 2019 Conifer Heights Rezoning Request 18-107113RZ. William Hahn, P.G. Professional Hydrogeologist 6589 Elaine Road, Evergreen CO 80439. Credentials – Basis for My Professional Opinions.

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William Hahn, P.G. Professional Hydrogeologist 6589 Elaine Road, Evergreen CO 80439

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  1. Presentation to the Jefferson County Board of County CommissionersApril 16, 2019Conifer Heights Rezoning Request18-107113RZ William Hahn, P.G.Professional Hydrogeologist 6589 Elaine Road, Evergreen CO 80439

  2. Credentials – Basis for My Professional Opinions • B.S. Geology Additional Studies in Hydrology , Numerical Modeling • Practicing Hydrogeologist with >45 Years Experience • Expert Witness-State Water Courts-Federal District Court-US Supreme Court (KS v CO) • Published Papers on Fractured Crystalline Rocks • Design, Construction, and Testing > 250 Water Supply Wells • Research, Design, and Testing of Facilities for Recharge of Treated Wastewater

  3. Principal Findings • Investigations flawed • Design was based on “averages” -Size of development (# units) overestimated -Required capacity of on-site wells underestimated • Failed to demonstrate adequate on-site water supply • Risk to quality of water supply (on -site disposal of treated wastewater) • Long-term sustainability of the water supply for this development has not been proven These all point to a water supply that could fail! Further discussion provided in my letter report of April 10, 2019

  4. Size of the DevelopmentWhy “Averages” Don’t Work • Legal Supply = 16 acre-feet per year (5.2 million gallons per year) (this is fixed) • Assume “average” daily demand = 137 gallons per day/unit • No margin of safety • Then we can supply 104 units (Applicant builds 101 units) • If our estimate of “average” is off by 5% (i.e. real demand turns out to be 144 gallons per day/unit • We fall short of water!

  5. Calculate the Size of the Development(Preferred Approach)(with apologies for the math) Start with 5.2 million gallons Adopt the Applicant’s number of 137 gallons per day /unit Introduce a safety factor (typically a factor between 1.5 and 2.5) Using low end of range, we have:137 gpd per unit x 1.5 = 206 gpd/unit The number of units that can be supported: 5.2 million gallons = about 70 units (not 101 units) 206 gpd/unit

  6. What is the Required Well Capacity? Applicant: “…gross demand rate of just under 9 gpm…” “…drilling of up to 8 wells should produce sufficient water…” Analysis was based on “average”

  7. Why “Averages” Don’t Work • Assume “average” daily demand = 137 gallons per day/unit • For 101 units we need 13,800 gallons (for an average day) • Friday (an average day) the development uses 13,800 gallons • Saturday and Sunday the development uses 1 ½ times the average (it’s the weekend?) • We can meet the weekend demand if we have storage • But, by Monday, we again have to supply the “average”PLUSwe need to replace the storage depleted over the weekend

  8. What is the Required Well Capacity?Preferred Approach Preferred approach: 1) if we adopt the Applicant’s number of 137 gpd/unit 2) introduce a safety factor of 1.5 (low end of range) 3) we have: 137 gpd/unit x 1.5 = 206 gpd/unit For 101 units we need: 206 x 101 = 20,800 gallons per day = 14 gpm (not 9 gpm)

  9. Perspectives on Supply My Well (#145043) 3.5 gpm Village at Elk Crossing 10 – 46 gpm Formal Well Test Well 1 (72 hours) 10 gpm, 86 % of water in well still available

  10. What Can the On-Site Wells Produce? Well 1 (Existing House Well on Property) “…can hold a pumping rate of 1.5 gpm for 8 hours” (then what?) Well 3 No formal testing <0.5 gpm? Well 4 tested for < 4 hours <1.7 gpm? Conclusion: Well testing was completely inadequate .

  11. Why an 8-hour well test is insufficient Water Level at 70 hours 80 feet Water Level at 8 hours 24 feet Water Level Decline in feet The water level never stabilized! Decline more than doubled! Time in minutes Well test – the Village at Elk Crossing Jefferson County, 2002

  12. Risk to Quality of Water SupplyfromOn-Site Disposal of Treated Wastewater • Exfiltration galleries for wastewater disposal located on-site surrounded by 8 wells • High probability of capture by on-site wells • Travel time (from discharge at surface to capture by wells) may be short…days? weeks? months?

  13. Risk to Water Quality Capture of Wastewater by On-Site Wells SupplyWell SupplyWell Exfiltration Gallery Infiltrating Wastewater Groundwater Moving to Wells

  14. Long-Term Sustainability of Supply • Underlying assumption of WAA faulty- WAA compares local pumping withdrawals with regional values of storage and recharge- This assumes the groundwater system is able to “rebalance” itself, i.e. replace withdrawals from one area with water moving in from other areas- Allocating water in this manner likely to lead to mining of groundwater (creating “holes” in storage)

  15. Summary • Flawed investigations (methods and conclusions) • Size of development (101 units) is overestimated • The need for on-site water supply (wells) is underestimated • The ability to develop the needed water supply has not been demonstrated • Significant risk of shortfall in supply • Significant risk that the on-site supply will be degraded by on-site wastewater disposal • Sustainability of supply not proven • Need for more aggressive review by JeffCO Thank you

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