CITY OF TAMPA INVESTIGATIONS OF HILLSBOROUGH BAY SEDIMENTS 
FDER Wasteload Allocation 
In 1981, the Florida Legislature repealed a statue requiring 
advanced wastewater treatment (AWT) for domestic wastewater treatment 
facilities constructed after 1972. The statue was replaced by a mandate 
requiring the Florida Department of Environmental Regulations (FDER) to 
specify wasteload allocations on a case-by-case basis for domestic point 
sources. The FDER began a "wasteload allocation" study to evaluate the 
dissolved oxygen and nutrient impacts of Tampa Bay (including 
Hillsborough Bay) surface water dischargers for long-term wastewater 
planning and permitting. A "wasteload allocation" draft report 
(McClelland 1984) was released by FDER in 1984 for review by interested 
parties. Several criticisms of that draft report were communicated to 
FDER by individuals of the local scientific community and the Tampa Bay 
Management Study Commission (Tampa Bay Management Study Commission 1985). 
One major criticism was that the contribution of sediment pollution 
sources was based on insufficient data. 
The City of Tampa (COT) operates an advanced wastewater treatment 
plant with a permitted discharge into Hillsborough Bay of 60 mgd. It was 
in the interest of the COT to cooperate with FDER in obtaining the most 
accurate data for their wasteload allocation study. The Bay Study Group 
(BSG) of the COT Sanitary Sewer Department, in agreement with the FDER, 
launched a two phased sediment project in Hillsborough Bay to, (1), map 
the surface sediment composition, and (2), quantify dissolved nutrient 
fluxes between the water column and sediments through i_n situ 
measurements of sediment oxygen demand (SOD) rates and nutrient exchange 
rates (NERs). Detailed results of the BSG sediment project have been 
submitted to the FDER in two reports (COT 1986a, 1986b). 
Distribution and Description of Hillsborough Bay Surface Sediments 
Phase 1 of the BSG’s sediment project produced a map of 
Hillsborough Bay identifying areas of "sandy" and "muddy" sediments, and 
estimated the areal coverage of those sediment types. Continuous depth 
recording soundings (200KHz transducer) along 29 transects were used in 
conjunction with sediment grain size analyses from 19 stations to produce 
a sediment map. "Mud" was assumed to occur at locations where 50% or 
more (by weight) of sediment particles passed through a 63um mesh sieve. 
"Sand" occurred where less than 50% of sediment particles (by weight) 
passed through a 63um mesh sieve. Grain size analyses revealed that 
sediment compositions, depending on location, ranged from 95.3% "sand" to 
98.9% "mud." 
"Mud" sections along the 29 transects were interconnected based on 
bottom topography and dredging information, thereby producing the map 
shown in Figure 1. The largest expanse of "mud" covered the deeper zones 
of west-central Hillsborough Bay. The BSG concluded the areal coverage of 
"mud" constituted approximately 24% of the bottom of Hillsborough Bay. 
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