1 / 15

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

Presentation discussing inadequate water supply projections for Conifer Heights development, advocating for accurate assessments to prevent potential shortages and quality risks. Includes a professional's opinion on well capacities, sustainability, and risk factors.

dapril
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related