AWWA ACE59994

The Green Swamp of central Florida covers an area greater than 500,000 acres and is importantto the region in terms of water resources, wildlife, surface water, flood water detention, and waterquality. It is designated by the State of Florida as an Area of Critical State Concern. A mosaic ofrivers, swamps, uplands and forests, the Green Swamp contains the headwaters of four majorriver systems. Careful water supply planning, which includes aquifer performance testing,groundwater flow modeling, and evaluation, is essential to ensure that proposed development willnot interfere with the function of the Green Swamp.The City of Lakeland was issued a water use permit in 1993 that authorized the withdrawal ofwater from the Floridan aquifer at the City's northwest and northeast wellfields. The northeastwellfield, which is currently not in operation, is located within the Green Swamp area and issurrounded by wetlands on and off the wellfield site. Conditions of the water use permit requiredthat the City conduct a long-term aquifer performance test (APT), sufficient in duration todetermine the connection between the surficial and Floridan aquifers if any, and to predict thepotential impact to wetlands from the proposed withdrawals of 9 million gallons per day (MGD)annual daily demand and 16 MGD maximum daily demand.Since the initial 72-hour APT was run in 1989, two additional tests were run including a 7-daytest in 2000 and a 12-day test in 2003. The three constant rate discharge tests were run underdifferent hydrologic conditions. The surficial aquifer in 1989 was saturated and portions of thesite were inundated before and during the APT. In 2000, the surficial aquifer was essentially dry,and during the APT potentiometric head in the Floridan aquifer varied widely in the region inresponse to agricultural pumping for freeze protection. A large rain event occurred in the 2003test just before initiation of the APT, and then no rain occurred during the 12-day pumpingportion of the test. This led to a recession of water levels in the surficial aquifer thatoverwhelmed minute drawdown effects from APT pumping.The results of analyzing the time/drawdown data from all three tests showed that no matter thelength of the test from 3 days to 12 days or the antecedent and current rainfall events, the valuesof transmissivity, storage and leakage are essentially the same. It was determined that thecontrolling factor preventing the fluctuation of surficial aquifer water levels was the extremely lowleakage value between the surficial and Floridan aquifers resulting from over 20 feet of lowpermeability clay. This paper presents the testing and analyses that have spanned 14 yearsresulting in very similar solutions. It shows that as long as the source aquifer is saturated andconfined, and the underlying and overlying aquifers are saturated or nearly so, valid results ofhydraulic parameter analyses are possible. Includes 14 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

12

File Size:

1 file , 1.5 MB