The Green Swamp of central Florida covers an area greater than 500,000 acres and is important
to the region in terms of water resources, wildlife, surface water, flood water detention, and water
quality. It is designated by the State of Florida as an Area of Critical State Concern. A mosaic of
rivers, swamps, uplands and forests, the Green Swamp contains the headwaters of four major
river systems. Careful water supply planning, which includes aquifer performance testing,
groundwater flow modeling, and evaluation, is essential to ensure that proposed development will
not interfere with the function of the Green Swamp.
The City of Lakeland was issued a water use permit in 1993 that authorized the withdrawal of
water from the Floridan aquifer at the City's northwest and northeast wellfields. The northeast
wellfield, which is currently not in operation, is located within the Green Swamp area and is
surrounded by wetlands on and off the wellfield site. Conditions of the water use permit required
that the City conduct a long-term aquifer performance test (APT), sufficient in duration to
determine the connection between the surficial and Floridan aquifers if any, and to predict the
potential 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-day
test in 2000 and a 12-day test in 2003. The three constant rate discharge tests were run under
different hydrologic conditions. The surficial aquifer in 1989 was saturated and portions of the
site 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 in
response to agricultural pumping for freeze protection. A large rain event occurred in the 2003
test just before initiation of the APT, and then no rain occurred during the 12-day pumping
portion of the test. This led to a recession of water levels in the surficial aquifer that
overwhelmed minute drawdown effects from APT pumping.
The results of analyzing the time/drawdown data from all three tests showed that no matter the
length of the test from 3 days to 12 days or the antecedent and current rainfall events, the values
of transmissivity, storage and leakage are essentially the same. It was determined that the
controlling factor preventing the fluctuation of surficial aquifer water levels was the extremely low
leakage value between the surficial and Floridan aquifers resulting from over 20 feet of low
permeability clay. This paper presents the testing and analyses that have spanned 14 years
resulting in very similar solutions. It shows that as long as the source aquifer is saturated and
confined, and the underlying and overlying aquifers are saturated or nearly so, valid results of
hydraulic parameter analyses are possible.
Includes 14 references, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 06/17/2004 |
