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Monday, Oct 15, 2018
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Study explains water levels

NEW PORT RICHEY - Prompted by a mid-April request from New Port Richey Mayor Scott McPherson, Tampa Bay Water has taken a look at why the water levels in Moon Lake and Crews Lake don't seem to be rebounding as well as other lakes in the region. The Clearwater-based regional water wholesaler compiled data and reviewed past studies and concluded a combination of factors influence recharge of the two lakes in northwestern Pasco County. On factor is the lakes' heavy dependency on rainfall, which stifles rapid lake-level recovery. While Moon and Crews lakes have risen about 4 feet and 6 feet, respectively, as of April, both remain noticeably below their regulatory minimum lake level as established by the Southwest Florida Water Management District. They are in this condition despite rainfall totals between November 2009 and April 2010 that are 3.54 inches above average at Crews Lake and 6.63 inches above average at Moon Lake. Both Pasco lakes hit their lowest levels ever recorded in 2009. Though the lakes are slowly recovering, McPherson said, he was curious as to why they remain below regulatory minimum level since it was reported that the overall aquifer level rose 7 feet.
Porous geology McPherson is New Port Richey's representative on the Tampa Bay Water board. The utility's other member-customers are Tampa and St. Petersburg, and Pasco, Pinellas and Hillsborough counties. One factor that affects both bodies, said Warren Hogg, Tampa Bay Water's senior manager of evaluations and permitting, is the porous geology of north-central Pasco. Because the area has little in the way of clay layers providing subsurface confinement, water quickly drains from the Upper Florida Aquifer to the surficial aquifer, he said. In southern Hillsborough, Hogg said, the two aquifers are separated by from 20 to 50 or more feet of clay between upper layers of sand and lower layers of limestone. Traveling farther north, though, that clay layer thins out "to the point where it's almost like looking at a flat slice of Swiss cheese," he said. In addition, sinkholes help drain water away from the surface in northern Pasco. In dramatic cases, large sinkholes opening underneath lakes are capable of completely draining them, Hogg said. Hampering recharge Furthermore, the uncommonly small watershed of the area around Moon Lake hampers its recharge, the report states. The driving factor behind the recovery of both lakes is sustained periods of above-normal rainfall, Hogg said. "It just takes them a long time to bounce back from long, chronic dry periods." Data tracking lake levels, rainfall and wellfield pumping rates seem to bolster that theory. The levels of neither Moon Lake nor Crews Lake have deviated with any statistical significance or consistency in relation to increases or decreases from groundwater pumping stations in their respective areas over the years. In regard to Moon Lake, pumping at Starkey wellfield dropped from an average of about 12 million to 4 million gallons per day since December 2007. "Right around a wellfield, if it's pumping really hard, you can have some drawdown effects from that wellfield," Hogg said. Even though Tampa Bay Water has reduced pumping at both its Starkey and Cross Bar Ranch wellfields, the positive impact on the levels of Moon and Crews lakes has been minimal, he noted. Swiftmud urged Tampa Bay Water to reduce its wellfield pumping in response to complaints that the water withdrawals were causing damage around its wellfields.
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