PB Agenda Packet 3-4-26 - Laserfiche WebLink

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29 • Yield o Drawdown testing ■ A 24-hour drawdown test is used to determine a sustainable yield for the well(gallons per minute) • Wells are meant to be run 12 hours per day; 24 hours is used to strain test. ■ Weather can affect the drawdown, but at a general, regional level (supply is for a much greater distance than you might expect) ■ Seasonal changes in drawdown results are mostly due to the demand for watering lawns—in the short term, this is more immediately apparent than the impact of rain or drought ■ A long-term regional dewatering study would be helpful to ensure sustainability of water supply • Orange County has 13 wells that they monitor where data is collected 24 hours per day(Orange County WellNet). The County also monitors on the Eno River and in the Falls Lake and Jordan Lake watersheds. ■ If a drawdown test is found to interfere with another well, it's not a valid drawdown test o How much yield is needed? ■ Up to the discretion of the manager of the site; lots of design and management to understand what type of well is right for your system. ■ A good rule of thumb is one gallon per minute per residence ■ Generally much more use in the mornings and the evenings • Quality o Water quality samples are collected during drawdown testing and tested for contaminants o Quality testing results advising on filtration requirements o A significantly larger sample spread is used for public supply wells than for private wells, and standards are more strict o In Orange County, pretty much every well will have iron and manganese and will need to filter for those. Usually filtering for these is not complicated o PFAS are generally from local contaminants o Radiological problems are common constituents that preclude development of a community well because it can be cost-prohibitive ■ Constituent= naturally appears in water supply ■ Contaminant= comes from somewhere else