the tampa bay regional reservoir project tech3.pdf · 52 • february 2004 • florida water...

50 • FEBRUARY 2004 • FLORIDA WATER RESOURCES JOURNAL

Tampa Bay Water is a governmentalagency within the state of Florida thatprovides wholesale drinking water to

six member governments: HillsboroughCounty, Pasco County, Pinellas County, NewPort Richey, St. Petersburg, and Tampa. Thesemember governments, in turn, provide drink-ing water to approximately 2 million people.

Tampa Bay Water was created in 1998,with assistance from the Florida Legislatureand the governor, by restructuring the WestCoast Regional Water Supply Authority froma cooperative association into a true publicutility. The agency began supplying surfacewater to its member governments in 2002.

The surface-water supply system is madeup of the Alafia River Pump Station; theTampa Bypass Canal Pump Station; theTampa Bay Regional Surface Water TreatmentPlant; the 13-mile, bi-directional, 72-inchdiameter South-Central HillsboroughIntertie; the 15-billion-gallon (46,000 acre-feet) Tampa Bay Regional Reservoir; and theeight-mile, bi-directional, 84-inch diameterReservoir Transmission Main. The capital costfor the entire surface-water system is $350million. The cost for the reservoir and thereservoir transmission main is $148 million.

The Tampa Bay Regional ReservoirProject is a necessary component of the sur-face-water system because the allowed with-drawals from the pump stations vary withflows in the river systems, with no with-drawals allowed during low-flow conditions.During the rainy season, surface-water with-drawals could be as high as 202 million gal-lons per day, or three times the 66-million-gallons-per-day capacity of the surface-watertreatment plant. When withdrawals exceedthe capacity of the treatment plant, the extrawater will be routed south to the reservoir forreserve capacity to help meet demand duringthe dry season without withdrawing waterfrom traditional sources.

A total of 11 permits were required for thereservoir project before construction couldbegin. In addition, the U.S. EnvironmentalProtection Agency (EPA) prepared an environ-mental impact statement (EIS) because over$48 million in federal funding has been allo-cated to the project to date. The EIS was pre-pared under a third-party consultant agree-ment that allowed Tampa Bay Water to fundthe study but let EPA retain control over itsdirection. The Final EIS was issued onNovember 9, 2001, and the record of decisionwas issued on January 14, 2002.

The major permit for the reservoir proj-ect is a state-issued environmental resourcepermit (ERP) that covers the design of theembankment as well as all environmentalissues, such as wetland impacts and mitiga-tion. No design criteria for this facility existwithin the rules ofthe Florida Depart-ment of Environ-mental Protectionbecause this is thefirst facility of its typein the state. The rulethat would mostclosely fit is for earth-en dams used inphosphate mining(Chapter 62-672),but that rule wasdeemed not applica-ble because phos-phate industry stor-age embankments aretemporary structureswith very differentseepage potentials.

The Tampa Bay Regional Reservoir ProjectAmanda E. Rice

Amanda E. Rice, P.E., is a project man-ager with Tampa Bay Water

Hillsborough River

Tampa Bypass Canal

Alafia River

Treatment Plant

Pump Station

To Regional System

Reservoir

Pump Station

Hillsborough River

Tampa Bypass Canal

Alafia River

Treatment Plant

Pump Station

To Regional System

Reservoir

Pump Station

Hillsborough River

Tampa Bypass Canal

Alafia River

Treatment Plant

Pump Station

To Regional System

Reservoir

Pump Station

HillsboroughBay

Alafia

River

Tampa Bay

Regional Reservoir

Pipeline Route

Alafia River Intake

Area enlarged.

Continued on page 52

Figure 1. Enhanced Surface Water System

Figure 2. Location of Tampa Bay Regional Reservoir

52 • FEBRUARY 2004 • FLORIDA WATER RESOURCES JOURNAL

Florida DEP,Chapt. 62-672

Corps ofEngineers

EM 1110-2-1902

Soil ConservationService, TR-60

State of GeorgiaDNR, Chapt. 391-

3-8

AdoptedFactor of

SafetyEND OF CONSTUCTION, Both upstream and downstream slopes

Norequirement

1.3 general case 1.3 strong found. 1.3 no restrictions 1.3

RAPIND DRAWDOWN, Upstream slopesNo

requirement1.0 from max.

pool1.2 emerg.spillway

1.3 no elevationdef.

1.3

PARTIAL POOL, Upstream slopeNo

requirement1.5 No requirement No requirement 1.5

STEADY SEEPAGE, Downstream slope1.75 base of

fill1.5 within fill

1.5 from max.pool

1.4 from sur. pool1.5 from spillway 1.5

1.751.5

EARTHQUAKENo

requirement1.0 1.1 1.1 NA

No. of SamplesType of Exploration

No. ofExplorations

TotalFootage Soil Rock

No. of In-Situ Tests

Rotary-Wash Boring 18914,896

(5,827)*2,905 1,218 --

CPTU Sounding 139 4,063 -- -- --

Dilatometer Sounding 18 474 -- -- 438

Auger Boring 60 900 180 -- --

Soil Probe 49 -- -- -- --

Hand Auger 23 -- 21 -- --

Trench 4 1,450 58 -- --

Borehole Hydraulic Conductivity 4 -- -- -- 17

Piezometers 124 -- -- -- --

Aquifer Pump Tests 8 -- -- -- --

Table 2. Geotechnical Investigation Program Components

Table 1. Comparison of Factors of Safety for Stability Analyses

The project team proposed designcriteria from the state of Georgia,the U.S. Army Corps of Engineers,and the Soil Conservation Service.The proposed criteria were accept-ed and governed the design. Table 1compares these criteria.

Regulatory concerns during thepermitting stage included potentialkarst conditions and the ability of thefacility to retain stored water. Theproject team developed an originalgeotechnical investigative programto determine suitability of the sub-surface for the embankment founda-tion and borrow material, and todefine the sinkhole potential withinthe reservoir footprint. This investi-gation, conducted in 1999 and 2000,became part of the ERP application,and included 14,000 man-hours ofstudy, three miles of subsurface coreinvestigation, 30 linear miles ofground penetrating radar, and 18 lin-ear miles of seismic work. Table 2lists the total quantity of explorationsperformed at the site.

The reservoir will be a rimdike earthen structure with anembankment length of five miles.The embankment height will varyfrom 30 to 65 feet, with an averageembankment height of 55 feet andan average water depth of 45 feet.Some portion of the reservoir stor-age will be provided below theexisting land surface as a result ofexcavation of materials requiredfor the embankment. The facilityfootprint will cover 1,100 acres ona 5,229-acre site. The prominentembankment design details are:• The flexible, textured geomem-

brane liner within the embankmentthat will reduce water losses, lowerthe phreatic surface in the embank-ment, and increase upstream anddownstream slope stability.

• A soil-cement course on theupstream slope that will protect theembankment from erosion effects.

• A soil-bentonite mix cut-off wallthat will reduce water losses from thereservoir, lower the phreatic surfacein the embankment, and reducegroundwater seepage into the reser-voir excavation during construction.

• A horizontal blanket and toedrain that will control the phreat-ic surface in the downsteam por-tion of the embankment and willprovide a means to collect and

Continued from page 50

Figure 3. Embankment Cross Section

discharge embankment seepage. The blanket drain materialis tailing sand from a local phosphate mine. The tailing sandis a clean, uniform-size material that is economical due to itsclose proximity to the construction site.

Construction of the Tampa Bay Regional Reservoir willimpact approximately 173 acres of wetlands and other surfacewaters. Table 3 lists the acreages for the various types of wetlandmitigation that will be constructed as part of the project.

The reservoir has been under construction since July 2002.The construction phase was expected to take 25 months, so thefacility was scheduled to begin filling in August 2004. The con-struction schedule for the project has been impacted by theheavy rains of December 2002 and June 2003. Over 19 inches ofrain were recorded at the site during each of those months. Thenew scheduled filling date is November 2004, but the contractorhas been steadily regaining time through the current dry season.To date, the contractor has moved and placed approximately 9million of the total 11 million cubic yards of embankmentmaterial. Based on average climatic conditions, once complete,the filling phase is expected to take about one year.

Type AcreageCREATION

Forested Creation 62.81Herbaceous Creation 150.82Wetland Scrub Creation 7.60Open Water Creation 16.32Open Water in Marsh 2.90

Subtotal 240.45ENHANCEMENT

Forested Enhancement 85.18Herbaceous Enhancement 110.70Open Water in Marsh 14.77

Subtotal 210.65Total Mitigation 451.10Upland Buffers 597.14

Grand Total 1,048.24Table 3. Reservoir Project Mitigation Requirements

FLORIDA WATER RESOURCES JOURNAL • FEBRUARY 2004 • 53