Yield Determination Purpose Groundwater Classification Yield Methods Recent Issues

Why Yields Important Determine hydrogeology Help determine GW Classification – Zones exceed UPUS – 3 Classes Evaluate upper zone is a confining unit or GW Response requirements

Well Yield Volume of water per unit time (gpm) Obtain from published maps/data Obtain from testing – Yield and other aquifer parameters Not from well development

Well Testing Slug (hydraulic conductivity) Modified Slug (hydraulic conductivity) – Pressure – Vacuum Pump Test (yield) – Step drawdown – Constant rate

Well Requirements Manufactured screen Four-inch diameter screen in eight-inch borehole Two-inch diameter screen in a six-inch borehole – Yield must be multiplied by factor of % penetrating well screen Sufficient number Properly developed

Partially Penetrating Correction Factor Percent Intake LengthCorrection Factor

Yield Threshold Criteria Pumped at or below Unsustainable threshold value, yield is less Signs of unsustainable threshold – Dry well – Over 24 hours recovery Helps determine ground water classification

Ground Water Classification Critical Resource Class A Class B Only for zones that exceed UPUS

Critical Resource Ground Water GW zone used by a public water system In drinking water source protection area Part of unconsolidated zone – Threshold yield of over 100 gpm over 24 hrs In a consolidated sole source aquifer

Class A Groundwater GW zone used for potable purposes within ½ mile Threshold yield > 0.1 gpm to 100 gpm or less TDS < 3,000 mg/L Doesn’t meet Critical Resource GW criteria

Class B Ground Water Yield < 0.1 gpm and meets definition of GW – Yield of 1.5 gallons within 8 hours of purging – Hydraulic conductivity > 5.0 X cm/sec Two other ways to define By comparison By depth

Class B GW Comparison Method Threshold yield < 3 gmp Other GW zone must be – Beneath property – Yield 2Xs zone being classified – GW zone likely potable source within 1 mile

Class B GW Depth Method GW in unconsolidated zone Threshold yield > 3 gpm Within 15 feet of ground surface Lower zone yields not compared

Yield Determination Rules Sufficient locations/testing to represent yield Bias to high yield areas Properly constructed and developed wells Account for spatial variation (heterogeneity) Temporal consideration – Statistical average – Maximum

Site Yield Determination Methods Maximum yield Average yield

Maximum Yield Test at times of maximum yield – Typically March through May in Ohio – Evaluate historical and current precipitation and GW levels – Other times if representative of historic maximum Higher than normal water levels Parts of June this year

Average Yield Average locations over 12 month period – Quarterly Demonstrate yield below threshold criteria from several quarters – If site average yield is 35% below, annual average won’t either

Evaluate for Confining Unit Evaluate uppermost saturated zone is a ground water zone or confining unit – Can use 2-inch diameter 5-ft long manufactured screen in 6-inch borehole – In situ hydraulic conductivity – Sufficient wells Groundwater resource maps – Ohio Department of Natural Resources (ODNR) – Other published/verified data

Recent Issues Not enough wells to characterize site Same GW zone classified 3 different ways No seasonal data collected Not biasing to higher yield areas Well screens less than 80% of GW zone

Summary Threshold criteria to classify water – Yield part of criteria to classify Methods to determine yield – Confining Unit – Demonstrate yield below threshold criteria ODNR map – Average – Maximum Questions