SARASOTA BAY NATIONAL ESTUARY PROGRAM

POINTINON-POINT SOURCE -- 

## I POLLUTION LOADING ASSESSMENT PHASE I

JANUARY 10. 1992 

# Camp Dresser & 

# McKee

### TABLE OF CONTENTS

Section

1.0 INTRODUCTION

1.1 Background of the Sarasota Bay National Estuary Program 1.2 Purpose and Scope of Point and Nonpoint Pollution LoadingAnalysis 1.3 Organization of Report

2.0 STUDY AREA CHARACTERISTICS 2-1

2.1 Introduction 2.2 Watershed Delineation 2.3 Existing Land Use 2.3.1 Sarasota County 2.3.2 Manatee County 2.3.3 City of Sarasota 2.3.4 Barrier Islands 2.4 Future Land Use 2.4.1 5-Year Future. 2.4.2Buildout Future 2.5 Soils Characteristics 2.6 Water Quality Characteristics 2.7 Sources of Pollution 2.7.1 SurfaceRunoff 2.7.2 Baseflow 2.7.3 Point SourceDischarges 2.7.4 Septic Tanks 2.7.5 Rainfall

3.0 METHODOLOGY FOR POLLUTION LOADING PROJECTIONS 3-1

3.1 Introduction 3.2 RainfalllRunoff Relationships 

### 3.2.1 Rainfall and Streamflow Data 3.2.2 Pervious Area Runoff 3.2.3 Impervious Area Runoff 3.2.4Baseflow 3.3 Nonpoint Pollution Loading Factors 3.3.1 SurfaceRunoff

### TABLE OF CONTENTS (Continued)

Section

3.3.2 Baseflow 3.4 Point SourceLoadings 3.5 Septic TankLoadings 3.5.1 Failing Septic Tanks 3.5.2 Working Septic Tanks 3.6 Rainfall Loadings

4.0 LOADING TRANSPORTTO BAY

4.1 Model Description 4.2 Model Parameters 4.2.1 Tidal Influence 4.2.2 Tributary flows 

### and Loadings 4.2.3 Tributary Geometries 4.2.4 Pollutant SettlingParameters 4.3 Modeling Procedure 4.4 Model Results

5.0 POLLUTIONLOADING PROJECTIONS FOR EXISTING LAND USE CONDITIONS 5-1

5.1 Average Annual Loading Result 5.1.1 Loadings by

### Watershed 5.1.2 Loadings by Source 5.1.3 Loadings by Jurisdiction 5.2 Wet Season and Dry Season Results 5.3 Wet Year and 

### Dry Year Results 5.4 Summary

6.0 POLLUTION LOADINGPROJECTIONS FOR FUTURE LAND USE CONDITIONS 6-1

6.1 Five-YearFuture Land Use 6.2 BuildoutFuture Land Use

7.0 SUMMARY 7-1

8.0 REFERENCES 8-1

### CONTENTS
(Continued)

Section 

### &

APPENDICES

APPENDIX A 

### - STORET Water Quality Data forTributaries to SarasotaBay

APPENDIXB 

## - TechnicalMemorandum on Septic Tank Literature Review and Analysis

APPENDIX 

### C

## - Statistical Analysis of Banier Island and Mainland Rainfall DataLIST OFTABLES

Watershedsin SarasotaBay NEP Study Area Land Use Categories and Associated Percent Imperviousness Existing Land Use by Jurisdiction in Sarasota Bay

### NEP Study Area Existing Land Use by Watershed in Sarasota~ay 

### NEP Study Area 

## - SarasotaCounty Existing Land Use by Watershed in Sarasota Bay 

### NEP Study Area 

### - Manatee County Existing Land Use by Watershed in Sarasota Bay 

### NEP Study Area 

### - City of Sarasota Existing Land Use by Watershed in Sarasota Bay 

### NEP Study Area 

### - Barrier Islands Five-Year Future Land Use by Watershed in the Sarasota Bay NEP Study Area 

### - Sarasota County Buildout Future Land Use by Watershed in the SarasotaBay NEP Study Area

## - Sarasota County Buildout Future Land Use by Watershed in the SarasotaBay 

### NEP Study Area

## - Manatee County Septic Tank Coverage for Sarasota Bay

### NEP Study Area
Precipitation Data for Gages in Sarasota Bay NEP Study Area Streamflow Data for Gages in Sarasota Bay

### NEP StudyArea Event Mean Concentration Values for Sarasota Bay NEP Study Point Source Discharges in SarasotaBay NEP StudyArea Point Source Flows and Concentrations for Existing Conditions Point Source Flows and Concentrations for Five-Year Conditions Point Source Flows and Concentrations for Buildout Future Conditions Septic Tanks Flow Rates forVarious Land Uses Parametersfor Analysis ofWorking Septic Tanks
Delivery Ratios for Major Tidal Tributaries

iii

### LIST OFTABLES (Continued)

Average Annual Loadingsby 

### Watershedfor Existing Land Use Conditions Average Annual Loadingsby 

### Sourcefor Existing Land Use Conditions Average Annual Loadingsby 

### Jurisdictionfor ExistingLand Use Conditions Wet Season Loadingsby 

### Watershed for ExistingLand Use Conditions Dry Season Loadings by 

### Watershed for Existing Land Use Conditions Wet Season and Dry Season Loadingsby 

### Source for Existing Land Use Conditions Wet Season and Dry Season Loadingsby 

### Jurisdictionfor Existing Land Use Conditions Wet Year Loadings by 

### Watershed forExisting Land Use Conditions Dry Year Loadingsby 

### Watershed for Existing Land Use Conditions Wet Year and Dry Year Loadings by 

### Source for Existing Land Use Conditions Wet Year and Dry Year Loadingsby 

### JurisdictionforExisting Land Use Conditions Average Annual Loadingsby 

### WatershedforFive-YearFuture Land Use Conditions Average Annual Loadingsby 

### SourceforFive-YearFuture Land Use Conditions Average Annual 

### Loadingsby 

### Jurisdictionfor Five-Year Future Land Use Conditions Wet Season Loadings by 

### Watershed for Five-Year Future Land Use Conditions Dry 

### Season Loadingsby 

### Watershed for Five-Year Future Land Use Conditions Wet Season and Dry Season Loadingsby 

### Source for Five-Year Future Use Conditions Wet Season and Dry Season Loadingsby 

### Jurisdiction for Five-Year Land Use Conditions Wet Year Loadingsby 

### Watershed for Five-Year Future Land Use ConditionsLIST OF TABLES (Continued)

Dry Year Loadings 

### by Watershed for Five-Year Future Land Use Conditions Wet Year and Dry Year Loadings 

### by Sourcefor Five-Year Future Land Use Conditions Wet Year and Dry Year Loadings

### by Jurisdiction for Five-Year Future Land Use Conditions Average Annual Loadings 

### by Watershed forBuildout Future Land Use Conditions AverageAnnual Loadings 

### by Sourcefor Buildout Future Land Use Conditions AverageAnnual Loadings 

### by Jurisdiction forBuildout Future Land Use Conditions Wet Season Loadings 

### by Watershed for Buildout Future Land Use Conditions Dry Season Loadings 

### by Watershed for Buildout Future Land Use Conditions Wet Season and Dry Season Loadings 

### by Source for Buildout Future Land Use Conditions Wet Season and Dry SeasonLoadings 

### by Jurisdiction for Buildout Future Land Use Conditions Wet Year Loadings 

### by Watershed for Buildout Future Land Use Conditions Dry Year Loadings 

### by Watershed for Buildout Future Land Use Conditions Wet Year and Dry Year Loadings 

### by Source for Buildout Future Land Use Conditions Wet Year and Dry Year Loadings

### by Jurisdictionfor Buildout Future Land Use Conditions

### LIST 

### OFFIGURES



### Figure

2- 1 Sarasota Bay NEP Study Area Septic Tank Total 

### N Concentration at Various Distances from ReceivingWater

WASP4 Model Segmentationfor PhilippiCreek WASP4 Model SegmentationforWhitakerBayou WASP4 Model Segmentationfor Hudson Bayou WASP4 Model Segmentationfor BowlessCreek WASP4 Model Segmentationfor Cedar Hammock

Runoff Distribution by Watershed in 

### SarasotaBay 

### NEP Study Area Total P Distribution by Watershed in Sarasota Bay NEP Study Area Total 

### N Distribution by Watershed in SarasotaBay NEP Study Area Lead Distribution by Watershed in SarasotaBay NEP Study Area Zinc Distribution by Watershed in Sarasota Bay NEP Study Area Runoff Distribution by Sourcein SarasotaBay 

### NEP Study Area Total P Distribution by Sourcein 

### SarasotaBay 

### NEP Study Area Total 

### N Distribution by Sourcein Sarasota Bay NEP StudyArea Lead Distributionby Source

### in SarasotaBay NEP Study Area Zinc Distribution by Sourcein 

### SarasotaBay NEP Study Area1.0 INTRODUCTION



### 1.1 BACKGROUND OFTHE SARASOTA BAY NATIONAL ESTUARY PROGRAM

Sarasota Bay was identifiedin Section 317 of the Water Quality Act of 1987 as an estuary to be given priority consideration for inclusionin the National Estuary Program 

### (NEP). As 

### aresult, Governor Bob Martineznominated Sarasota Bay to the NEP, in a May 19, 1987letter to EPA AdministratorLee Thomas. According to the Act, documentation was required to support the nomination. This documentation would evaluate the need for a management conference, likelihood ofprogram success, and need

to protect water quality beyond existing controls.

In 1987, the EPA establisheda cooperative agreement with Mote Marine Laboratory to gather dataregarding environmental status, trends and problems in SarasotaBay. These data were to be used as the documentation to support the Bay's nomination to the NEP. The report developed by Mote was presented at a workshop of federal, state and local governmentrepresentatives on March 17, 1988. Through the workshop, additional information on Sarasota Bay was obtained.

The Florida Department of Environmental Regulation (FDER) used the Mote report 

### as the basis for the completion of the Governor's nomination document. The supporting documentation was submitted on May 31, 1988to the EPA Office of Marine and Estuary Protection. After EPA's evaluation, the Bay was designated as a member of the 

### NEP on July 18, 1988.



### In May of 1989,the Sarasota Bay NEP released a Request for Proposal 

### (RFP)for work related to the preservation,restoration and enhancement of the Bay. The RFPincluded the following areas:0 Baywide Segmentation and Mapping

0 Wetland Habitat Assessment

0 Estuarine Bottom Habitat Assessment

0 Regional BeachhletManagement

0 Impacts of Sea Level Rise

0 Fishery Resource Assessment

0 Shellfish Contamination Assessment

0 Point and Nonpoint Pollution Loading Assessment, Calibration,Verification, and Projections

0 Resource Access and Use Assessment

0 Data Management

The information gathered in these areas will lead to the developmentof a comprehensive conservation and management plan.

1.2 PURPOSE 

### AND SCOPE OFPOINT AND NONPOINT POLLUTION LOADING 

### ANALYSIS

CDM was selected to conduct the analysis of point and nonpoint source loadings to SarasotaBay. Basically, the objective of the analysisis to quantify the loadings of nutrients and metals to the Bay, to identify the areas that are contributing the largest share of the total load, and to analyze alternative measures for reducing the loadings.

For purposes of this study, assessment of pollutant loadings was restrictedto total nitrogen, total phosphorus, lead and zinc. Sources of loadings evaluated include baseflow,

storm event runoff, atmospheric, and point source loadings. While it is

### fully recognized that there are other contaminating substances entering SarasotaBay through a variety of other sources, these parameters were chosen as surrogatesfor 

### &non-point and point source loadings. These parameters represent contaminantswhich are well characterized in 

### \ the literature, and for which documented relationships with land-use exist. As such, this 

# \ \study does not attempt to characterizeall pollutant loadings,nor all sources of pollution, but rather focuses on the major loadings delivered to Sarasota Bay.

The analysis

### is divided into three distinctphases. In Phase 1,existing data are used to estimate current loading levels. Phase 

### 2 

### is designed to collect field measurementsor other data required to improve the estimates developed in Phase 

### 1. Analysis of future loadings, based on projected changes in population, land use, and otherfactors,isperformed 

### in Phase 

### 3. Evaluation of alternative managementprograms is also part of Phase 

### 3.

Thisreport documents the results generated in Phase 1. This phase includes the estimation of existing point and nonpoint source loadings. Even though future loading estimates are part of the Phase 3 analysis,preliminary estimates of future loadings also are included here in Phase 

### 1.

1.3 ORGANIZATIONOFREPORT

Chapter 2 summarizes the study area characteristics that are pertinent to the analysis of point and nonpoint sources loadings. The methodology used to develop loading estimates ispresented 

### in Chapter 

### 3. Chapter

### 4 documents the modeling of water quality constituentsin the tidal tributaries of the major watersheds. The estimated loadings for existing and future land uses are presented in Chapter 

### 5 and 

### 6,respectively. Chapter 

### 7 evaluates and summarizesthe results presented in Chapters 

### 5 and 

### 6. The references used in the study are listed in Chapter 

### 8.2.0 STUDYAREA CHARACTERISTlCS

2.1 INTRODUCTION

This chapter describes the NEP study area characteristics that are essential to the pollutant loading analyses. These characteristics include watershed boundaries, existing and future land use, soil classifications 

### ,water quality, and sources ofpollution.

2.2 WATERSHEDDELINEATION

The SarasotaBay NEP study area is shown in Figure 2-1. The area extends to the north

as far asAnna Maria Island and Perico Island, and to the south 

### as far 

### as Casey Key. The watersheds in the study drain not only to SarasotaBay itself, but to several smaller bays to the south including Roberts Bay, Little SarasotaBay, Dryman Bay, and Blackbum Bay.
In this report, the term "Sarasota Bay" will include all of the bays listed above.

Delineation of the total study area draining to SarasotaBay, and delineationof major watersheds within the study area, was done on 

### 1"= 2000' USGS quadranglemaps. These
maps were combined 

### in a mosaic to create one large map which was used asa project work map for the study. 

### In some cases, additional information was required to delineate watershed boundaries due to the lack of topography. Previous studies 

### (CDM, 1987; Briley and Wild, 1984)were used to check the delineation and to provide guidance where map topography was lacking.

Table 2-1 lists the watersheds that were defined in the delineation process. 

### In addition, the table shows the drainage area andjurisdiction or jurisdictions 

### in which each watershed islocated. 

### In 

### all, the study area contains approximately 150square miles of land area, plus 52 square miles of water surface.TABLE 2-1
WATERSHEDS INSARASOTA BAY NEPSTUDYAREA

Jurisdiction(s)

Cityof Sarasota SarasotaCounty Manatee County Cityof Sarasota Ciiyof Sarasota SarasotaCounty Manatee County Cityof Sarasota Sarasota County Manatee County Cityof Sarasota SarasotaCounty Cityof Sarasota Sarasota County Sarasota County
SarasotaCounty Sarasota County

SarasotaCounty Manatee County

ManateeCounty

ManateeCounty Manatee County Manatee County

Barrier Islands

Barrier Islands

Barrier Islands

Barrier Islands

Barrier Islands Watershed

PhillippiCreek

Hudson Bayou

BowleesCreek

West Bowlees

Whitaker Bayou

Directto Bay

MathenyCreek

Catfish Creek

North Creek

SouthCreek

PalmaSola Creek

PalmaSola2

West Bradenton
SouthBradenton
Cedar Hammock
Siesta Key

Anna Maria Island

Perico Island Longboat Key
Other Islands Drainage area (Acres)

36.417

1,595
6,489

1,559

5,015

4,241

3,800
3,360
1,920
12,995

900
1,120
4,395
4,635
1,930
1,385

919

860
1,697

900. 2.3 EXISTING 

### LAND USE

Existing land use was establishedin the study area based on Real Estate Data Inc. (REDI) maps. These maps include aerial photographs and corresponding zoning maps. From the aerials, developed and undeveloped areas were identified. The type of developmentin urban areas was determined based on the zoning maps.

The study area was classified accordingto the following land uses:
Cropland Forested Uplands RangelandlWoodlands Openhtecreation Wetland Citrus Low Density Single Family Residential Medium Density Single Family Residential High Density Single Family Residential Multi-Family Building MobileHome CommerciallServices Institutional Industrial Transportation Waterbody Sewage Treatment and Power Plants

Table 

### 2-2 summarizes the assumed directly connected impervious area (DCIA) established foreach urban land use category. The DCIA value isimportant because it determines the

amount of surfacerunoff that is generatedby precipitation. The values in the table were selected based on literature values and previous CDM studies. For urban land use, industrial and commercial areas tend to have the highest percentage of impervious area. In residential areas, the DCIA value increases with the density of the development (i.e., number of dwellingsper acre).TABLE 2-2 IMPERVIOUSCOVER FOR URBANLANDUSECATEGORIES

LandUse
Low Density Single Family Residential Medium Density Single Family Residential High Density Single Family Residential Multi-family Building Mobile Home CommerciaVServices Extractive Institutional Industrial Transportation STP and Power Plants DirectlyConnected ImperviousArea 

### ("4

20 30 40 50 60 85 70 40 70 90 40Table 2-3 presents the existing land use byjurisdiction forthe study area. As shown in the table, Sarasota Countyhas the largest contributory area to the Bay, accountingfor 65 percent of the total land area. The City of Sarasota, Manatee County, and the barrier islands make up 8, 21 and 6 percent of the total land area, respectively.

In the study area, slightlymore than half of the land area consists of urban development (residential, commercial, industrial and institutional land uses), and the rest 

### is rural. Of the urban development, about 81percent isresidential, primarily medium density and high density. For the rural areas, about 18 percent is either cropland or citrus, and the rest 

### is primarily rangeland/woodlands,openlrecreation and forested uplands.

The following sections discussland use distributionsfor eachjurisdiction.

2.3.1 SARASOTA COUNTY

The existing land use distribution for Sarasota County, broken down by watershed,is presented in Table 2-4. The values in the table indicate that PhillippiCreek accountsfor

over half of the total drainage area in the County. South Creek accountsfor about 21 

### perc_e&gf$e L~~-~c~ 7%*---~c,L-- of the total area.

In the County, approximately 42percent of the land area consists of urban development and the remaining 58 percentisrural. The urban developmentis most prevalent in the land areas closest to the Bay (i.e., the western sections of each watershed), and rural areas

are typically located in the eastern sections of each watershed. Of the urban development, about 87 percent is residential,primarily split between low, medium and high density single family residential. For the rural areas, about 17 percent is either cropland or citrus, and the rest isprimarily rangelandlwoodlandsor openlrecreation.TABLE 2-3

EXISTING LAND USE BYJURISDICTION IN SARASOTA BAY NEPSTUDYAREA

Land Use
Cropland Forested Uplands Rangeland~Woodlands OpenIRecreation Wetland Citrus Low DensitySingle Family Residential Medium DensitySingle Family Residential High DensitySingle Family Residential Multi-family Building Mobile Home CommerciaVSe~ices Institutional

Industrial Transportation Waterbody SewageTreatmentand Power Plants

Total 

### Ciof Sarasota

0 168 126 650 0 4 368 1,320 2,164

946 0 926 529 521

17 75 30

7,844 Sarasota County

3,756

673 15,544 11,688

1,449 2,278 7,375 6,827 5,163 1,983 1,065 1,485

647 1,106

203 1,028 30

62,301 AREA (Acres)

Manatee County

1,912 1.052 1,253 2.222

415 209 292 2,012 3,422 2,677

862 654 365 1,989

633 228

30

20,226 Barrier Islands

130

44 19 1,373

403 0 388 1.641

741 754

37 169

0 40 15 2 5

5,761 Total

5,798 1,937 16,942 15,933 2,267 2,491 8,423 11,800 11,490

6,360 1,964 3,234 1,541 3,656

868 1,333 95

96,132TABLE2-4

EXISTING LAND USE BYWATERSHED INSARASOTA BAY NEPSTUDYAREA

## - SARASOTACOUNTY

Land Use
Cropland Forested Uplands RangelandMloodlands OpenIRecreation Wetland Citrus Low DensitySingle Family Residential Medium DensitySingle FamilyResidential High Density Single FamilyResidential Multi-family Building MobileHome CommerciaVSewices Institutional Industrial Transportation Waterbody Sewage Treatmentand Power Plants

Total Total

3,756

673 15,544 11,688

1,449 2,278 7,375 6,827 5,163 1,983 1,065 1,486

647 1,106

203 1,028 30

62,301 Phillippi Creek

3,612

570 5,304 5,353

436 1,938 4.770 4.997 3,685

896 423 588 496 542

65 542

30

34,247 Matheny Creek

0 15 675 444

14 104 1 45 114 1,176

307

30 435 0 221 0 120

0

3,800 Catfish Creek

0 20 2,202

171 199 50 227 257 0 73 42 30 20

0 0 69

0

3,360 AREA

Norlh Creek

48 20 728 655

57 10 191

70

0 5 35 35

0 25

0 41

0

1,920 Bowlees Creek

0 0 7 7 0 0 0 0 0 0 0 0 7 0 135

4 0

160 (Acres)

South Creek

65

0 6.41 0 4,502

565 120 636 133 140 109

80 30 75 10 0120 0

12,995 West Bowlees

0 0 0 0 0 0 0 38

0 0 0 13

0 0 0 0 0

51 Whitaker Bayou

31 29 29 499 3 4 578 291

80 317 31 4 105

21 308 2 98

0

2,710 Direct toBay

0 19 189 57 175 52 828 927

82 276 141 250

28

0 0 34

0

3,058

### 2.3.2 

### MANATEE COUNTY

The existing land use distribution for the watershedsin Manatee County ispresented in Table 

### 2-5. The largest watershedsin the County includeBowlees Creek, South Bradenton, and West Bradenton. These three watersheds account for 

### 75 percent of the total drainage area in the County.



### In Manatee County, about 

### 64percent of the land area consistsof urban development and the other 

### 36 percent isrural. Generally, the areas immediately south and west of the City of Bradenton are undeveloped, whereas the remaining areas are developed. Roughly 

### 72 percent of the urban area isresidential, primarily divided between medium and high density single family and multi-family building. In the rural areas, about 

### 29 percent 

### is either cropland or citrus, and the remaining 71percent 

### is typically either rangeland/woodlandsor openlrecreation.



### 2.3.3 CITY OF SARASOTA

Table 

### 2-6 presents the existing land use distributionfor the watersheds in the City of Sarasota. The largest watersheds in the City includeWhitakerBayou, Phillippi Creek and Hudson Bayou. These watersheds accountfor 

### 75 percent of the City drainage area. In addition, another 

### 15 percent drains directly to SarasotaBay.

In the City, 

### 87 percent of the land area consists of urban development and the other 

### 13 percent 

### is rural. Most of the rural area 

### is located in the far 

### eastern part of the City, and the majority of the rural area actually consists of golf course and park land that 

### will not be urbanized in the future. Residential developmentaccounts for 

### 70percent of the total urban land use, and it isprimarily split between medium density and high density single family residential and multi-family building.EXISTING LAND USE BYWATERSHED INSARASOTA BAY NEPSTUDYAREA

## - MANATEE COUNTY

LandUse
Cropland ForestedUplands RangelandMloodlands OpenIRecreation Wetland Cirus Low Density Single Family Residential Medium Density Single Family Residential HighDensity Single Family Residential Multi-family Building Mobile Home CommerciaVSe~ices Institutional Industrial Transportation Waterbody Sewage Treatment and Power Plants

Total Total

1,912 1,052 1,253 2,222

41 5 209 292 2,012 3.422 2,677

862 654 365 1,989

633 228

30

20,226 Phillippi Creek

0 0 87

0 0 0 63

0 0 0 0 0 0 0 0 0 0

150 Palma Sola2

0 65 45 385 0 0 0 0 295 180 70

0 0 80

0 0 0

1,120 West Bowlees

0 0 41 77

0 0 0 319 246

41 101

25

0 31

0 0 0

881 Bowlees

Creek

16 32 345 365 0 204

24 958 621 481 461 294

95 1,663

633

24

0

6,215 Palma Sola Creek

250 135

20 55

0 0 0 20 35 310 0 0 75

0 0 0 0

900 South Bradenton

1,486

625 525 610 110 0 0 315 285 250 130

85

0 40

0 144 30

4,635 AREA (Acres)

West Bradenton

160 180 160 720 305 5 125 280 1.540

550

20 1

45 80 80

0 45

0

4,395 Cedar Hammock

0 15 30 10

0 0 80 120 400 865

80 105 115

95

0 15

0

1.930TABLE 2-6

EXISTING LAND USE BYWATERSHED INSARASOTA BAY NEPSTUDY AREA

## - CITY OF SARASOTA

Land Use
Cropland Forested Uplands RangelandMloodlands OpenlRecreation Wetland Citrus Low DensitySingle Family Residential Medium DensitySingle Family Residential High DensitySingle Family Residential Multi-family Building Mobile Home CommerciallSe~ices Institutional Industrial Transportation Waterbody Sewage Treatment and Power Plants

Total Direct to Bay

0 10

0 52

0 0 39 484 229 0 0 279

39 30 15

6 0

1.183 Total

0 168 126 650 0 4 368 1,320 2,164

946 0 926 529 521

17 75 30

7,844 AREA (Acres)

Bowlees

Creek

0 9 35

0 0 0 0 3 1 25

0 19 19

0 0 3 0

114 Phillippi Creek

0 38 27 370 0 4 55 356 574 306 0 99 113

38

0 39

0

2,020 West Bowlees

0 0 6 59

0 0 77 21 0 170 5 0 46 54

0 0 0 0

627 Hudson Bayou

0 0 0 65

0 0 0 150 635 240 0 305 180

20

0 0 0

1,595 Whitaker Bayou

0 111

57 104

0 0 197 117 555 370 0 178 124 433 2 27 30

2,3052.3.4 BARRIER ISLANDS

The existing land use distribution for the barrier islands draining to Sarasota Bay 

### is presented in Table 2-7. Siesta Key, Anna Maria Island, Perico Island and Longboat Key are the major land areas contributing to the Bay. 

### A group of smallerislands, including Lido Key, St. Armands Key, Coon Key, Bird Key, Otter Key and Casey Key, was combined under the category of "Other Islands".

For the barrier islands, 

### 66 percent of the land area consists of urban development and the other 34percent isrural. Most of therural areaislocated on Longboat Key and Perico Island, whereas Siesta Key and Anna Maria Island are predominantly urbanized. Of the urban area, 94percent is residential. Medium density single family makes up almost haIf of the residential area, and the rest 

### is split primarily between low and high density single family residential and multi-family building. Cropland and citrus account for only 

### 7 percent of the totalrural area on the islands. Over 

### 70 percent of the rural area

### is openlrecreation.

2.4 FUTURE LAND USE

Even though the focus of Phase 

### 1is determinationof existing loads to Sarasota Bay, preliminary projections of future loadings were developed to get a preliminary estimate of the incremental increases in loadings that are expected due to future development. Consequently, future land use data were developed aspart of the analysis. Two future land use scenarios were developed: 5-year future and a buildout future.

The 5-year future land use was developed based on the Developments of Regional Impact (DM) data provided by Sarasota and Manatee Counties. The 

### DRI information was screened to determine which projects were located in the SarasotaBay study area. The appropriateprojects were located on the existing land use maps to determine the watershed in which the developmentwould occur, and the type of land that would beTABLE 2-7

EXISTING LAND USE BYWATERSHED INSARASOTA BAY NEP STUDYAREA

## - BARRIER ISLANDS

Land Use
Cropland Forested Uplands RangelandMloodlands OpenIRecreation Wetland Citrus Low Density Single Family Residential Medium Density Single Family Residential High DensitySingle Family Residential Multi-family Building Mobile Home Commercial/Sewices Institutional Industrial Transportation Waterbody SewageTreatmentand Power Plants

Total -

Other Islands

'0 6 19 137

57

0 155 394 0 65

0 30

0 20 15

2 0

900 Longboat Key

0 38

0 689 8 0 34 459

95 31 1

25 38

0 0 0 0 0

1,697 Perico Island

130

0 0 330 290 0 0 0 15 80

0 0 0 15

0 0 0

860 AREA(Acres) Anna Maria Island

0 0 0 172 0 0 0 0 621

55 12 59

0 0 0 0 0

919 Total

130 44 19 1.373

403 0 388 1,641

741 754

37 169

0 40 15

2 5

5,761 Siesta Key

0 0 0 45 48

0 199 788

10 243 0 42

0 5 0 0 5

1,385converted to urbanized area. Because some of the DRI projects are alreadyunderway and some are not due to be completed 

### 5years from now, the increasein urban area during the 5-yearplanning horizon was estimated to reflect the amount of developmentexpected to

occur between 1991and 1996. For example, 

### a DRI with a scheduled construction start date of 1991 and buildout date of 2001 would be assumed 

### 50 percent complete in the 5- year planning horizon.

The ComprehensivePlans forManatee and Sarasota Counties were used to develop the buildout future land use scenario. Development ofrural areas in the two counties was evaluatedby locating rural areas on the existing land use maps, and consulting the comprehensiveplans to determine the future land use.

For both scenarios, the City of Sarasota and the barrier islands were not included in the analysis. The City of Sarasotais approachingbuild-out, and future development will be limited. The barrier islands were excluded because they represent only 

### 6 percent of the land area in the study, and because comprehensive plans forthe island communitieswere not available when the analysiswas conducted.

2.4.1 

### 5-YEAR FUTURE

After screening the DRI data for Sarasota and Manatee Counties, the following developments were included 

### in the 5-year future land use analysis:



# . Palmer Ranch, Increments 

### I-V, in Catfish and Matheny Creek watersheds, of Sarasota County



# . Gateway Development, in Phillippi Creek Watershed, of SarasotaCounty



# . SawgrassHollow Development,in PhillippiCreekWatershed, of Sarasota County

### Based on information in the 

### DRIreports and the existing land use maps, the development of 1,686 acres of rural land was projected. Note that all of these developmentsarein Sarasota County.

The 5-year future land use for Sarasota Countyispresented 

### in Table 2-8. Overall, 248

acres of open/residential, 1,350 acres ofrangeland/woodlands and 88 acres of citrus are developed to create 1,319 acres of medium density single family residential, 120 acres of industrial, 20 acres of institutional and 227 acres of commercial area. In addition, 87 acres are shifted from low densityto medium densityresidential to account for increased densities in developmentswhich.were only partly developed under existing land use conditions.

2.4.2 BUILDOUT

### FUTURE

Tables 2-9 and 2-10 present the buildout future land use distributions for Sarasota and Manatee Counties,respectively. Between the two counties, almost 31,000 acres of undeveloped land 

### are converted to urban uses in going from the existing to the buildout future scenario. Of the 31,000 acres, about 85percent is developed intoresidential land

* 

### use, and the remaining 15percent isprimarily converted to commercial or industrialuse.

The Comprehensive Plans for Manatee and SarasotaCounties do not specify the planning horizon that isrepresented by the buildout scenario. However,by comparing the 23,000

acres of developmentfor Sarasota Countyin the buildout scenario to the 1,686 acres of d&elopment in the 5-year scenario, the buildout scenariois estimated to

### represent a planning horizon of roughly 68 years (23,000 acres divided by 1,686 acres, times 

### 5years). This estimate involves two assumptions. One is that the current rate of development

### is representative of the long-term rate, and the other is that the 5-year estimate of land developmentis 

### accurate. While the 5-year estimate isbelieved to be accurate, itmay be less than the overalllong-term rate of development due to the weakness of the economy at this time.TABLE 2-8

FIVE

## - YEAR FUTURE LAND USE BYWATERSHED INTHE SARASOTA BAY NEP STUDY AREA

## - SARASOTACOUNTY

LandUse
Cropland Forested Uplands RangelandMloodlands OpenlRecreation Wetland Citrus Low DensitySingle Family Residential Medium DensitySingle Family Residential High Density Single FamilyResidential Multi-family Building Mobile Home CommerciaVSe~ices Institutional Industrial Transportation Waterbody SewageTreatment and Power Plants

Total Total

3,756

673 14,194 11,439

1,449 2,190 7,288 8,233 5,163 1,983 1,065 1,712

667 1,226

203 1,028 30

62,301 Phillippi Creek

3,612

570 5,114 5,118

436 1,850 4,770 5,408 3,685

896 423 689 496 542

65 542

30

34,247 Matheny Creek

0 15 403 430

14 104 121 304 1,176

307

30 435 0 341 0 120

0

3,800 AREA

North Creek

48 20 728 655

57 10 191

70

0 5 35 35

0 25

0 41

0

1,920 Catfish Creek

0 20 1,314

171 199

50 164 1,062 0 73 42 156 40

0 0 69

0

3,360 (Acres)

South Creek

65

0 6,410 4,502

565 1

20 636 133 140 109 80 30 75 10

0 120

0

12,995 ' Bowlees

Creek

0 0 7 7 0 0 0 0 0 0 0 0 7 0 135

4 0

160 West Bowlees

Creek

0 0 0 0 0 0 0 38

0 0 0 13

0 0 0 0 0

51 Whitaker Bayou

31 29 29 499 3 4 578 291

80 317 314 1

05 21 308 2 98

0

2,710 Direct toBay

0 19 189 57 175 52 828 927

82 276 141 250

28

0 0 34

0

3,058TABLE 2-9

BUILDOUT FUTURE LAND USEBYWATERSHED INTHE SARASOTABAY NEP STUDY AREA SARASOTA COUNTY

Land Use
Cropland ForestedUplands RangelandNVoodlands OpenlRecreation Wetland Citrus Low DensitySingle Family Residential Medium Density Single Family Residential High Density Single Family Residential Multi-family Building Mobile Home CommerciaVSewices Institutional Industrial Transportation Waterbody SewageTreatment and Power Plants

Total Total

1,695 33 3,582 5,221 1,449

369 12,738 22,114

5,163 1,983 1,065 1.775

667 3,186

203 1,028 30

62,301 Phillippi Creek

1,655 6 1,167

677 436 353 7,763 13,448

3,685

896 423 765 496 1,840 65 542

30

34,247 Matheny Creek

0 5 90 21 14

0 145 729 1,176

307

30 455 0 708 0 120 0

3,800 Catfish Creek

0 20 64 65 199 0 227 2,285 0 73 42 51 40 225 0 69

0

3,360 AREA

North Creek

9 0 0 0 57

0 339 1,364 0 5 35 45

0 25

0 41

0

1.920 (Acres)

South Creek

0 0 2,249 4,382

565

12 2,868 2,355

140 109

80 30 75 10

0 120 0

12,995 Bowlees Creek

0 0 0 0 0 0 0 14

0 0 0 0 7 0 135 4 0

160 West Bowlees

Creek

0 0 0 0 0 0 0 38

0 0 0 13

0 0 0 0 0

51 Whitaker Bayou

31

2 2 49

3 4 578 725

80 317 314 105

21 378 2 98

0

2,710 Direct toBay

0 0 10 27 175 0 818 1,156 82 276 141 31I

28

0 0 34

0

3,058TABLE 2-10

BUILDOUT FUTURE LAND USE BYWATERSHED INTHE SARASOTA BAY NEP STUDY AREA 

### - MANATEECOUNTY

Land Use
Cropland Forested Uplands RangelandMloodlands OpenlRecreation Wetland Citrus Low Density Single Family Residential Medium Density Single Family Residential High Density Single Family Residential Multi-family Building Mobile Home CommerciallSewices Institutional Industrial Transportation Waterbody Sewage Treatmentand Power Plants

Total Total

0 39 88 325 415

93 685 4,132 5,650 3.240

862 824 365 2,452

633 228 195

20,226 Phillippi Creek

0 0 0 0 0 0 63

0 0 0 0 87

0 0 0 0 0

150 Palma Sola2

0 0 20

0 0 0 0 108 495 315

70 32

0 80

0 0 0

1,120 Bowlees Creek

0 0 0 0 0 88 24 1,151

713 616 461 294

95 2,116

633

24

0

6,215 AREA (Acres)

West Bradenton

0 21 18 315 305 5 518 658 1,579

555

20 196

80 80

0 45

0

4,395 Cedar Hammock

0 15 30 10

0 0 80 120 400 865

80 105 115

95

0 15 0

1,930 Palma Sola Creek

0 3 20

0 0 0 0 20 417 365 0 0 75

0 0 0 0

900 West Bowlees

Creek

0 0 0 0 0 0 0 437 246

41 101

25

0 31

0 0 0

881 South Bradenton

0 0 0 0 110

0 0 1,638 1,800

483 130 85

0 50

0 1 44 195

4,635With the exception of the West Bradentonwatershed in Manatee County and the Phiippi and South Creek watershedsin Sarasota County, 

### all of the watershedsare almost completely developed in the buildout scenario. The West Bradenton watershed includes

area near Perico Island that isplanned for conservationpurposes. Both the Philippi and South Creek watersheds include area east of 1-75that is designated 

### asrural land use in the Sarasota County ComprehensivePlan.

2.5 SOILSCHARACTERISTICS

The soils characteristicsforthe study area were determined using the Soils Conservation Service Soil Surveysfor Manatee and Sarasota Counties. The SCS hydrologic soils
groups (A, 

### B, C, and D) indicate the relativeinf~ltration characteristicsof a soil after prolonged wetting. In the SCS system, an 

### 'A' soilisthe most well-drained and a 'D' soil is the most poorly-drained.

Review of the soils data indicated that most of the area is characterized by BID soils. In the Manatee County part of the study area, three soils associations make up most of the total area. These are the Eau Gallie-Floridana, Wabasso-Bradenton-Eau Gallie, and Delray-Floridana associations. The soiltypes in these associations 

### are classified as B/D by SCS. For Sarasota County, the major soil types shown on the soil survey maps were Eau Gallie and Myakka fine sands, and Pineda fine sand. Each of these soilsis classified

as B/D by SCS. Based on these data, the entire study area was considered 

### to be B/D soils for this analysis.

2.6 WATER 

### OUALlTY CHARACTERISTICS

Based on reports from the Florida Department of Environmental Regulation (FDER, 

### 1990; FDER, 1987), SarasotaBay isgenerally characterized 

### as having "fair" water quality, and its tributaries are characterized ashaving "poor"to "fair" water quality. The classifications were established by analyzing water quality data 

### in EPA's Storage andRetrieval System (STORET), as well asUSGS data. The monitoring data were transformed by FDER into Water Quality Indices (WQI) and Trophic State Indexes (TSI) for tributaries and various areas of the Bay.

Tributarieswith "fair" water quality ratings include Phiilippi Creek, Matheny Creek and Catfish Creek. Whitaker Bayou has a "poor" water quality rating. 

### In most cases, elevated nutrient levels are the reason for the poor to fairratings. The elevated nutrient levels are usually attributed to urban runoff and wastewater treatment plant effluent.

Several studies (Hey1 and Dixon, 1987; CDM, 1990) have explored the trends in Sarasota Bay water, quality since the mid-1960s. These studies have identified a downward trend in salinity and nutrient concentrations over time. Rainfall patterns, changes in agricultural land use, changes in point source loadings and other factors were considered 

### as reasons for the identified trends.

The changes in land use appear to be one plausible reason for declining salinity and nutrientsin the Bay. The transformation of certain types of agricultural land to urban residentialland use results in increased surface runoff, which in turn results in more freshwater dilutionin the Bay. 

### In addition, a previous local study (CDM, 1987)forthe Braden River projected a decrease in nutrients 

### as agriculturalland was converted to low densityresidential use. It should be noted that the study also projected an increase in heavy metals loading as a result of urbanization. Unfortunately,water quality trends for metals in Sarasota Bay could not be assessed due to a lack of monitoring data.

Recent improvements

### in wastewater treatment and disposal should continue to improve water quality in the Bay. The City of Sarasota WastewaterTreatment Plant 

### (WWTP), which dischargesto WhitakerBayou, has recently upgraded treatment 

### from secondary to advanced waste treatment 

### (AWT). In addition, the quantity of effluent discharged to Whitaker Bayou has been reduced through a recently implemented reuse irrigation system. Manatee County has developed a deep-well injection system to accept excess effluentfrom the WWTP with the largest flow in the SarasotaBay study area, and has improved its reuse irrigation system.

2.7 SOURCES OFPOLLUTION



### In this study, five different sources of pollution to SarasotaBay have been considered. They include the following:



# . Surfacerunoff



# . Baseflow



# . Point source discharges



# . Septic tanks



# . Rainfall

A brief summary of each pollution source

### is presented below.

2.7.1 SURFACE RUNOFF

During a rainfall event, the volume ofrainfall that cannotinfitrate into the soilbecomes surfacerunoff which enters numerous tributaries and ultimately istransported to Sarasota Bay. En route to the tributaries, the surfacerunoff picks up pollutants that have accumulated on the land surface. Examplesof suchpollutants include nutrients such as nitrogen and phosphorus, which are applied to lawn areas for fertilization, and metals such



### as lead and zinc, which are deposited on streetsby automobiles.

Because 

### 60 percent of the study area 

### is currently characterized by improved land uses (e.g., agricultural, residential, industrial,commercial),itislikely that surfacerunoff 

### is a significant contribution to the total pollution loading to the Bay. Cropland, citrus, commercial, industrial, and the more denseresidential land uses can be expected to contribute high concentrationsof nitrogen and phosphorusto tributaries. With the exception of cropland and citrus, these same land uses will also contributerelatively high metals concentrations.The baseflow loading accountsforpollution conveyed by groundwater. The fraction of total watershed loading that is due to baseflow becomes smaller asthe watershed develops,because more of the rainfall is converted to surface runoff and less infiltrates into the soil. The concentration of pollutants inthe groundwater 

### is based on the natural composition of the soil.



### 2.7.3 POINT SOURCE DISCHARGES

Point source discharges in the study area include wastewater treatment plants (WWTPs) that discharge treated wastewater from municipal and industrial sources. Municipal

sources accountfor almost all of the total point source discharge.

Anna Maria Island, Longboat Key and the portion of Manatee County within the study

area are all served by the Southwest RegionalWWTP. The plant currently has an average daily flow rate of 

### 12.8 million gallons per day (mgd). The effluent 

### is used forirrigation
purposes, primarily at the Manatee Fruit Company site and several golf courses. 

### In addition, effluent can also be dischargedinto a deep well injection system during wet weather conditions. 

### In effect, no effluent is directly discharged to surfacewaters.

The City of Saraso-taand some areas in SarasotaCounty are served by the City of Sarasota

### WWTP. 

### In 1990,the average discharge from the plant was 

### 6.9 mgd. The plant has recentlybeen upgraded from secondary treatment to 

### AWT. Disposal of the effluent consists of irrigation on pasture land and golf courseproperty with intermittent surface

water discharge. Loadings to Sarasota Bay from discharge to Whitaker Bayou have decreased considerably since these improvementswere implemented. Additionalreuse sites, which will further reduce loadings from thispoint source, are planned.Siesta Key and parts of Sarasota County are served by a number of smallpackage plants and privately-owned wastewater treatment utilities. The total flow for these plants 

### is approximately7.4 mgd. Some of these facilities achieve

### AWT standards. Most of the facilities discharge via irrigation, drain fields, and percolation ponds, though several of the larger plants discharge directly to surface water.

2.7.4 SEPTIC TANKS

Septic 

### tanks (also referred to as onsite disposal systems) are used in some cases to treat
waste from individual homes, multi-family buildings, and commercial and industrial areas. Basically, a septic tank achievesprimary treatment (i.e., settling)in 

### an anaerobic environment, and discharges the effluent to a drainfield. Presumably, further pollutant transformation and removal occurs as the effluent percolates downward through the drainfield to the water table. Further dilution and removal isexpected to occur 

### as the effluent mixes with and moves along with the groundwater flow.

Table 2-1 1shows septic tank coverage informationfor the Sarasota Bay 

### NEP study area. Septic tanks are used throughout the SarasotaCounty mainland and 

### in the barrier islands.
For Casey Key, all of the residential development (157 acres) 

### is served by septic 

### tanks.
In Sarasota County, the percentage of land use servedby septic tanks depends on the type of land use. Forresidential land use, about 58 percent of the low and medium single family residentialland use is served by septic 

### tanks,whereas the percent served for high density single family residential, multi-family building and mobile homes are estimated to be 38, 13, and 3 respectively. The percent served for commercial, industrial and institutionalland uses are estimated to be 21, 23, and 9, respectively.

The pollutants of concern from septic tanks are total nitrogen and, to a lesser extent, total phosphorus. Both total nitrogen and total phosphorus are discharged athigh concentrationsfrom a septic tank. Typical effluent concentrations are 40 to 80mg/L forTABLE 2-11

SEPTICTANK COVERAGE FORSARASOTA BAY NEP STUDYAREA

NOTES:

1. Septic tank areas inSarasota County estimatedbasedonmapping providedby Countystaff.

2. Small numberof septic tanks are stilladveIn Manatee Countyandthe Cityof Sarasota, butwere excludedfrom theanalysis. Land Use

Low DensitySlngle Family Resldentlal Medium Density Single FamilyResidenUal Hlgh Density Single Family Residential Multl-familyBuilding Moblle Home CommerciallSe~ices InstiMional industrial Manatee County

Area Sewedby Septic Tanks (acres)

0 0 0 0 0 0 0 0 Percent of Total Area

0% 0% 0% 0% 0% 0% 0% 0% Ciyof Sarasota

Area Sewedby Septic Tanks (acres)

0 0 0 0 0 0 0 0 Percent of Total Area

0% 0% 0% 0% 0% 0% 0% 0% Barrier Islands

Area Sewedby Septic Tanks (acres)

155

0 0 0 0 0 0 0 Percent of Total Area

40%

0% 0% 0% 0% 0% 0% 0% SarasotaCounty

Area Sewedby Septic Tanks (acres)

4272 3897 1963 252

34 311

59 252 Total

Percent of Total Area

58% 57% 38% 13%

3% 21%

9% 23Y9 Area Sewedby Septic Tanks (acres)

4427 3897 1963 252

34 31 1

59 252 Percent of Total Area

53% 33% 17% 4% 2% 10% 4% 7%total 

### N and about 

### 15 mgLfor total 

### P, as compared to 

### 3 mg/L total 

### N and 1mgLtotal 

### P for 

### AWT. 

### In most instances, soil is effectivein removing total 

### P, such that 

### 90 percent or

more isretained in the soil through adsorption. For total N, however, much of the mass in the effluent reaches the water table, with ammonia nitrogenbeing convertedto nitrate nitrogen under aerobic conditionsin the soil. Nitrate nitrogen isknown to be very mobile in groundwaterand can have serioushealth effects

### if drinking water concentrations are too high.

Loadings to SarasotaBay also are contributed by rainfall on the Bay surface. Considering that the water surface is about 

### 52 square miles 

### (34 percent of the total drainage area to the Bay), rainfall could have a significant impact on pollution loading. Precipitation totals for the study area are discussed in Section

### 3.2, and rainfall qualityis discussedin Section 

### 3.6.3.0 METHODOLOGY FOR POLLUTION LOADING PROJECTIONS

3.1 INTRODUCTION

This section presents the methodology and assumptionsused to estimate pollution loadings

to SarasotaBay. The discussion includes the relationship between rainfall and streamflow, and the selection of nonpoint pollution loading factors. Data regarding quantity and quality of point sources, septic 

### tanks and rainfall are also presented.

3.2 RAINFALL/RUNOFFRELATIONSHIPS

The annual loadingsfor surface runoff and baseflow are based upon the streamflowfrom the watershed, mean pollutant concentrationsof the surface runoff and baseflow, and the distribution of streamflow between surface runoff and baseflow. To calculate annual streamflow volumes for the study area, long-term monitoring data from USGS gages and local raingages were analyzed. 

### In additionto analyzing average annual conditions, rainfall and streamflow volumesfor the wet season (June

## - September) and the dry season (October

## - May) that comprise the average annual conditions were also determined. Finally, the data were also analyzed to establish a wet year and a 

### dry year scenario.

3.2.1 RAWFALL AND STREAMFLOWDATA

Table 

### 3-1 shows rainfall data for two long-term gages in the vicinity of the study area. The average year totals for the Bradenton and Myakka gages were determined by averaging the annual totals over the entire period of record. Similarly, the wet season and dry season volumes were calculated by averaging the total rainfall during each season over the period of record. The wet year and 

### dry year values were establishedby ranking the annual rainfall totals from lowest to highest, selecting the 10thpercentile value 

### as the dry year total and the 90th percentile value as the wet year total.TABLE 3-1
PRECIPITATIONDATA FORGAGES IN

SARASOTA BAY NEP STUDYAREA

PRECIPITATION(INCHES)

BRADENTONGAGE(104YEARSOF RECORD1

AVERAGEYEAR 54.6



## - WET SEASON 33.7



## - DRYSEASON 20.9

WET YEAR 69.7

DRYYEAR 41.7

MYAKKA GAGE (44YEARS OF RECORD)

AVERAGE YEAR 54.3

-WET SEASON 32.5



## - DRYSEASON 21.8

WETYEAR 69.6
DRYYEAR 40.4

BRADENTON GAGE (44YEARS OF RECORD1

AVERAGEYEAR 53.3



## -WET SEASON 31.8



## - DRYSEASON 21.5

WETYEAR 69.7

DRYYEAR 42.6The values generatedfor the Bradenton gage were selected for the runoff analysis. As shown in Table 

### 3-1, the results for the same 44 years of record at the Bradenton and Myakka gages were comparable. Because the rainfall values for the kvo gages are similar, it is appropriate to use the values forthe gage with the longestperiod ofrecord. Thus, an average annual

### rainfall total of 

### 54.6inches was assumed for the study area. Of the 

### 54.6 inches, 

### 33.7 inches 

### (62percent) occurs during the months of June through September, and the remaining 

### 20.9 inches 

### (38 percent) occurs during the other eight months. The annual values for a wet year and a 

### dry year are 

### 69.7 and 

### 41.7 inches, respectively. These values are 

### 28 percent higher and 

### 24percent lower than the average annual rainfall total.

Streamflow data for two USGS gagesin the vicinity of the study area are presented 

### in Table 

### 3-2. For the Lake Manatee and Myakka River gages, streamflowvalues for average annual, wet season, dry season,wet year and dry year scenarioswere establishedin the

same manner as the rainfall values.

Because the two gages had comparable periods ofrecord, the streamflow values used in the runoff analysis were the average of the values forthe two gages. 

### As shown in Table 

### 3-2, the average annual streamflow volume is 

### 14.8 inches, with 

### 9.9inches 

### (67 percent)
occumng during the wet season and 

### 4.9 inches occumng during the 

### dry season. The wet
year and dry year streamflowvalues are 

### 22.9 and 

### 7.6 inches, respectively. Both values
vary by roughly 

### 50 percent from the average annual value.



### 3.2.2 PERVIOUS 

### AREA RUNOFF

The streamflow volume due to surfacerunoff from pervious areas was estimated by assigning a runoff coefficient. Therunoff coefficient was multiplied by the rainfall volume to calculate the surfacerunoff volume from pervious areas. A single value was established to estimate the average annual runoff, given the averagerainfall total.TABLE3-2
STREAMFLOW DATA FORGAGES IN SARASOTA BAY NEP STUDY AREA

STREAMFLOW (INCHES) 

## - LAKE MANATEE GAGE (50YEARSOF RECORD1
AVERAGEYEAR 15.0



## - WET SEASON 10.3



### - DRY SEASON 4.7

WET YEAR 22.6

DRYYEAR 9.0

MYAKKA GAGE (50YEARS OF RECORD)
AVERAGE YEAR 14.5



## - WET SEASON 9.5



## - DRY SEASON 5.0

WETYEAR 23.2

DRY YEAR 6.1

AVERAGE OF LAKEMANATEEAND MYAKKA GAGES

AVERAGE YEAR 14.8

-WETSEASON 9.9



## - DRY SEASON 4.9

WETYEAR 22.9

DRY YEAR 7.6

### An 

### average annualrunoff coefficient of 0.15 was established for pervious areas. In this analysis, the runoff coefficient of 0.15 combined with an annual rainfall total of 54.6 inchesresults in an annualrunoff of 8.2 inches. By subtracting the 8.2 inches from
average annual streamflow volume of 14.8 inches, an annual groundwaterbaseflow volume of 6.6 inches 

### is calculated. Thus, based on a runoff coefficient of 0.15, about 15 

### percent of rainfall becomes surface runoff, 12percent contributes to streambaseflow, and the remaining 73percent (39.8 inches) is lost via evapotranspiration.

3.2.3 IMPERVIOUS 

### AREA RUNOFF

The streamflowvolume due to surfacerunoff from impervious areas was also determined using runoff coefficients. For allimpervious area, a runoff coefficient of 0.95 was assumed.

3.2.4 BASEFLOW

The baseflow volume at the USGS gages was calculated as the differencebetween streamflow volume and surface runoff, with gage drainage areas assumed to be rural (i.e., pervious). For undeveloped areas, baseflow was calculated to contribute about 45 percent of the streamflow.

For individual watershedsin the study area, the baseflow volume was reduced as a direct function of the percentage of urban impervious area. For example, if 

### the drainage area

was 50percent impervious due to residential and commercial development, then the baseflow volume was reduced by 50percent. Thus, the percentage of streamflow due to baseflow diminishes

### as development occurs in the watershed. However,itis not only because baseflow diminishes, but alsobecause surfacerunoff increases.3.3 NONPOINT POLLUTIONLOADING FACTORS

For both surfacerunoff and baseflow, the pollution loadings were calculatedby multiplying the flow volume by an appropriatepollutant concentration. 

### In the case of surface runoff, event mean concentration (EMC) data developed through studies such 

### as EPA's Nationwide Urban Runoff Program 

# m) were used to characterize runoff concentrations. For baseflow, local ambientmonitoring data were used to develop the concentrations.

3.3.1 SURFACE RUNOFF

Since the completion of EPA's Nationwide Runoff Program (NURP) in the early 1980's (USEPA, 1983),there is a general consensusin the field of nonpoint pollution management that local monitoring studies of singleland use watersheds are no longer required to characterizeurban nonpoint pollution loadingsformanagement studies. In place of an expensive local monitoringprogram, available literature values for nonpoint pollution Ioading factorscan be used to formulate the watershed managementplan. 

### In addition to the transferability evaluationsin the EPA

### NCTRP study, this approachhas worked out well in previous watershed management studieswhere mixed land use monitoring data were availablefor comparison.

In the SarasotaBay 

### NEP study, pollutantloading analyses were limited to the constituents for which considerableloading data 

### are reported in the literature. The following four pollutants were included: total phosphorus (total P), total nitrogen (total

### N), lead, and zinc. Total 

### P and total N are included because they may be responsiblefor adverse eutrophicationimpacts. Lead and zinc are heavy metals which typically exhibit higher nonpoint pollution loadings than other metals found 

### in urban runoff, and therefore, transferableloading factors 

### are availablein the literature. These heavy metals may be viewed as surrogates for a wide range of toxicants that have been identified in previous field monitoring studies of urban runoff pollution (USEPA, 1983).The EMC values to estimate surfacerunoff loadings are presented in Table 

### 3-3. Again, the values are based primarily on data from the EPA NURP study, although values for land uses such as cropland (which tend to vary substantiallyfrom one location to another) are also based on local data. These same values have been applied successfully in several other studies in the State of Florida (CDM, 1990).

For nutrients (total

### N and total P), the EMC values are highestfor cropland, citrus, and low and medium density single family residential land uses. This is due to fertilization of the cropland and the lawns of the residential areas. Commercial, industrial and unimproved areas have the lowest EMC values fornutrients, less than half aslarge 

### as the agricultural and residentialvalues.

It should be noted, however, that the pollutant loading depends on the EMC value the volume of surfacemnoff for a particular land use. Because commercial and industrial land uses have a much greaterpercentage of impervious areathan residential land use, they tend to produce greater loadingsin terms of lbdaclyear, even though they are characterizedby lower EMC values. For example, the average annual surfacerunoff loads for commercialand medium density single familyresidential land uses are relatively similar 

### (1.6 lb/ac/yr for commercial and 2.1 lb/ac/yr for residential) for total P, even though the EMC is much higher for the residential area. The loadingsfortotal N are 12.3 and 10.1lb/ac/yr for commercial and medium density residential land uses, respectively. Thus, EMC values alone cannotbe used to determine the relative loading impacts of different land uses.

For lead and zinc, Table 

### 3-3 showsthat unimproved and agricultural land uses have EMCs of zero, whereas residential, commercial, industrial and other urban land uses are shown to generate loadings of metals. The EMC values increase asthe percent imperviousness of the land use increases. Because more impervious areas will also generate more runoff, the loadings from commercial and industrial areas will be substantially higher than the loadings from the residential areas.TABLE 3-3

EVENT MEANCONCENTRATION VALUES FOR SARASOTA BAY NEP STUDY

LandUse
Cropland Forested Uplands e Rangeland/Woodlands OpenIRecreation Wetland Citrus Low Density Single Family Residential Medium Density Single Family Residential High Density Single Family Residential Multi-family Building MobileHome CommerciallSe~ices Institutional Industrial Transporlation Waterbody STP and Power Plants

. Event Mean

Total Phosphorus

1.13 0.16 0.16 0.16 0.03 0.41 0.39 0.39 0.33 0.33 0.33 0.15 0.15 0.15 0.15 0.15 0.15 Values

Total Lead

0.000 0.000 0.000 0.000 0.000 0.000 0.049 0.049 0.076 0.076 0.076 0.235 0.235 0.235 0.235 0.006 0.235 Concentration

Total Nitrogen

3.74 1.02 1.02 1.02 0.25 0.92 1.87 1.87 1.65 1.65 1.65 1.18 1.18 1.18 1.18 0.82 1.18 in mgll

Total Zinc

0.000 0.000 0.000 0.000 0.000 0.000 0.054 0.054 0.060 0.060 0.060 0.120 0.120 0.120 0.120 0.146 0.120Baseflow loadings, like surfacerunoff loadings, were calculated by determining the flow volume and the flow concentration. Based on analysis of existing water quality data, the following values were selectedfor baseflow concentrations:



# . Total 

### P: 0.30 mg/L



# . Total N: 1.00 mg/L



# . Lead: 0.003 mg/L



# . Zinc: 0.05 mg/L

The total N and total P values were selected after analyzing concentration-frequency

curvesfor several STORET stations. It was assumed that the median concentrationsfor these stations were representativeof dry weather conditionswhere baseflow was predominant, and that the stationswere located in areaswhere dry weather flows are not affected by point source discharges or septic tank impacts. Unfortunately, the same stations did not include metals data. The values shown above for metals were selected based on a limited number of STORET values for raw water monitoring at various water

treatmentplants in and around the study area.

A summary of available STORET data ispresented in Appendix A.



### 3.4 POINT SOURCE LOADINGS

Table 3-4 lists the point source discharges included in the loading analysis. These represent all of the dischargeslocated 

### in the study area that have a daily average flowrate exceeding0.1 mgd. Together, these plants account for over 95 percent of the total point source dischargein the study area. In all, the total discharge from these treatment plants isroughly 

### 27 mgd.

Data shown in the table include the watershed, average flow, level of treatment and method(s) of disposal. In Sarasota County and the City of Sarasota, discharges occur inTABLE 3-4

POINT SOURCE DISCHARGESINSARASOTA BAY NEPSTUDYAREA

Disposal Method(s)
Irrigation Deepwell Injection

Percolationponds lrrigation
Irrigation

Percolationponds
percolation ponds Surfacewater

Percolationponds irrigation

Percolationponds lrrigation

Percolationponds lrrigation

Percolationponds

Percolationponds

Percolationponds

,
Surfacewater

Irrigation Surfacewater

Percolationponds irrigation

Permiationponds Irrigation

Surfacewater

Drainfieids Discharge
Southwest RegionalWWTP

## -

Manatee County

Southeastern-Bent Tree

Atlantic Utilities

Dolomite

### - Fruitville

FloridaCities

### -

Southgate
Kensington Park

Utilities

## - 27th St.

MeadowoodUtilities

Tamaron Utility Authority

Camelot

Sorrento

CentralCounty Utilities

Florida Cities

## -

Gulf Gate

SarasotaCity WWTP

Dolomite

## -Tri Par

Kensington Park Util..

Monica Pkwy.

Siesta Key Utilities
Southbay Utilities Watershed

South Bradenton

PhillippiCreek

PhiliippiCreek
PhillippiCreek
PhiliippiCreek

PhiliippiCreek

PhiilippiCreek

PhiilippiCreek

PhiilippiCreek
MathenyCreek
Matheny Creek
MathenyCreek

Whitaker Bayou

Whitaker Bayou

Whitaker Bayou

Siesta Key

Directto Bay Average Flow (mgd)

12.80

0.26

0.77

0.14

1.10

0.09

0.47

0.11

0.1 0

0.25

0.31

1.37

6.90

0.23

0.36

1.82

0.13 Level of Treatment
Secondary

Secondary

Secondary
Secondary

AWT

.

Secondary

Secondary

Secondary

Secondary
Secondary
Secondary

AWT

AWT

Secondary

Secondary

AWT
Secondarythe Phillippi Creek,Matheny Creek and Whitaker Bayou watersheds. Disposal methods include a combination of irrigation, percolationponds, and surface water discharge.
Manatee County, Anna Maria Island and Longboat Key are served by the Southwest Regional WWTP, which disposes of effluent through irrigation and deep well injection. Siesta Key is served by Siesta Key Utilities, which disposesof effluent via surface water discharge.

To estimate the point source pollution loadings, a number of assumptions were made. Assumptionsregarding effluent quality (i.e., concentrationsofpollutants in the effluent) were made based on limited monitoring data supplemented by literature values. For disposal methods other than surface water discharge, the fraction of effluent load reaching Bay tributaries was assumed.

The effluent concentrations assumed for the point source analysis are presented below:

Secondary treatment:

Advanced waste treatment: Total N =20 mg/L Total P =

### 4 mgL Lead = 25 ugL zinc = 100ugn Total N =

### 3 mg/l Total P = l mgL Lead 

### =25 ugL Zinc = 100ugL

Nutrient values for secondary treatment were established based onmonthly operating report (MOR) datafrom several of the SarasotaCounty dischargers, and the nutrient values for AWT were based on the typical standards includedin NPDES permits. The reviewed data did not include any lead or zinc concentrations,so these values are strictly based on literature data. The values are in the mid-range of concentrationsthat may be expected,based on effluent data from 12CaliforniaWWTPs that use effluent for

### irrigation (Lewis, 1985)as well as typical influent concentration and removal efficiency data developed in 

### an EPA 

### study ofprioritypollutants in publicly owned treatment works @PA, 

### 1982).

For land disposalof wastewater, the fraction of the mass load reaching Bay tributaries dependsupon the type of disposal. It was assumed that no load would reach the Bay for deep well injection. For percolation ponds and drainfields, a removal 

### rate of 90percent

was assumed for allpollutants. A 

### previous CDM study (CDM, 1985)found that the 90 percent value was appropriate for retention and exf~ltration best managementpractices (BMPs). A 

### slightly higher removal 

### rate of 95percent was assumed forirrigation practices, with the higher efficiency attributed 

### to plant uptake.

Based on the assumptions above, the point source loadings shown in Table 3-5 were developed for existing conditions. The flow rates represent only the surfacewater dischargesplus a fraction of the dischargeto percolationponds and drainfield. This fraction was set equal to 0.27, which is theratio of streamflow toprecipitation. The concentrations of nutrients and metals were established such that theproduct of flow and concentration was equalto the combined mass ofpollutant from surfacewater and percolation pondldrainfield discharges. Surface dischargesfor annual, wet season and dry season are constant for all watersheds exceptWhitakerBayou, which receives discharge from the City of Sarasota. The City of Sarasota discharge of 3.30 mgd represents a projected discharge of 7 mgd for a total of 172 days during 1991,based on a mid-year estimate (CDM, 1991). Of the 172 days, 75 are during the wet season (June through September) and 97 are during the dry season (October through May). Consequently, the average flow rates during the wet and dry season are 4.30 and 2.79 mgd, respectively. The remaining 0.17 mgd attributed to Whitaker Bayou comes from


### two smallpackageplants. For the South Bradenton watershed, the flow value of 2.08 mgd represents 27 percent of 7.7 mgd attributedto irrigation. Recent data indicate that about 60percent of the SWWWTPeffluentisused for irrigation, and the remaining 40 percent is discharged via deep well injection.TABLE 3-5

POINTSOURCE FLOWSAND CONCENTRATIONSFOR EXISTING CONDITIONS

WATERSHED
PhillippiCreek
Matheny Creek
Whitaker Bayou

Directto Bay

Siesta Key

South Bradenton DISCHARGE (rngd)

ANNUAL

1.63

1.52

3.47

0.04

1.82

2.08 CONCENTRATION (rng/L)

TOTAL P

1.03

1.05

1.02

1.48

1 .OO

0.74 WET SEASON

1.63

1.52

4.47

0.04

1.82

2.08 DRY SEASON

1.63

1.52

2.96

0.04

1.82

2.08 TOTAL N

3.78

3.44

3.20

7.38

3.00

3.69 LEAD

0.015

0.019

0.019

0.007

0.020

0.004 ZINC

0.076

0.094

0.097

0.037

0.100

0.018Point source flows for the 5-year future scenario were estimated using available data. 

### In Manatee County, linear interpolation was used to estimate a 5-year flow rate of 14.1 mgd, given the existing rate of 12.8rngd and the 20-year projected rate of 18 mgd. 

### In addition, it was estimated that 9.8 mgd out of the 14.1rngd would be used for irrigation. For the othw localities, the total flow rate was estimatedby evaluatingchanges inresidential land

use, The total number of dwellingunits in the localitiesfor the existing and 5-year scenarios was calculated by assigning densities (dwellingsper acre) to each residential land use. The ratio of future to existing dwellingunits was then multiplied by the existing total point source flow rate in order to estimate the 5-yeartotal flow ;ate. Based

on this method, a value of 15.9 mgd was calculated.

The 5-year future point source flow rate was then distributed between the City of Sarasota plant and the other existing utilities and package plants. The City was assigned a flow

rate of 9.0 mgd, based on available flow projections. The remaining 6.9 rngd was equivalent to the sum of the existing dischargesin the Phillippi Creek, Matheny Creek, Direct to Bay and Siesta Key watersheds. Consequently, the 5-year future surface water discharge values for facilities other than the City of SarasotaWWTP were set equal to the existing discharge values.



# .
The same methodology was used to estimate the buildout future total point source flow

rate in Sarasota County and the City of Sarasota. 

### As a result, a total flow of 23.0 mgd

was estimated. The City of Sarasota was assigned a flowrate of 13.0 mgd, the current design capacity of the plant. The remaining 10.0 rngd was divided between utilities and package plants, with the increase in flow applied mainly to the Manatee and Phillippi Creek watersheds. The relative proportionsof disposal via surface discharge, percolation ponds, drainfields, and irrigation were consistentwith existing conditions. For Manatee County, the 20-year estimates of 18mgd (16 rngd irrigation and 

### 2rngd deep well injection) were used for the buildout scenario.

### Table 3-6 presents the point source loading data for the 5-year future scenario. The value of 1.61 rngd for the City of SarasotaWWTP isbased on a flow of 9.0 rngd discharging

### to surface water for a total of 59 days per year plus package plant discharge of 0.17 mgd. The 59 days of discharge isconsistent with an NPDES permit that is currentlybeing sought by the City WWTP. The SouthwestWWTP discharge of 2.66 rngd reflects 

### 27 percent of the 9.8 rngd attributed to irrigation. The other surfacewater discharge rates are equal to the rates for existing conditions.

The point source data for the buildout future scenario 

### are presented in Table 3-7. The value of 2.10 rngd for the City of Sarasota

### WWTPreflects a 

### 13 rngd surface water discharge for a total of 59 days per year. In 

### the other watersheds, the surface water discharges are higher than the 5-year future discharges. Futwe package plants and utilities are assumed to operate similarly to existing facilities. 

### In other words, discharge is distributedbetween surfacewaters, percolation ponds, draifields, and irrigation.

3.5 SEPTIC TANK 

### LOADINGS

Some of the existing developmentsin Sarasota County 

### are serviced by septictanks. The SarasotaCounty Health Department estimates that there are approximately45,000 septic tanks within the County, and the majority of these are probably within the 

### NEP study area. On Casey Key, all of the residential areais served by septic tanks, and the number of permitted tanks is 330.

The assessment of septic tank loadings included a literature review designed to better quantify the impacts of failing and working septic 

### tanks. Previous CDM studies have focused on the impacts of failing septic tanks. 

### Reasons for septic tank failure include high

water table, structural failure, and direct connection between septic tank and receiving water. These failing septic tanks are expected to dischargehigh concentrationsofTABLE 3-6

POINT SOURCE FLOWS AND CONCENTRATIONS FOR FIVE-YEAR FUTURE CONDITIONS

WATERSHED
Phillippi Creek
Matheny Creek
Whitaker Bayou

Directto Bay
Siesta Key

South Bradenton DISCHARGE(rngd)

ANNUAL

1.63

1.52

1.61

0.04

1.82

2.66 CONCENTRATION (rnglL)

TOTAL 

### P

1.03

1.05

1.05

1.48

1 .OO

0.74 WET SEASON

1.63

1.52

2.19

0.04

1.82

2.66 DRY SEASON

1.63

1.52

1.33

0.04

1.82

2.66 TOTAL N

3.78

3.44

3.43

7.38

3.00

3.69 LEAD

0.015

0.019

0.019

0.007

0.020

0.004 ZINC

0.076

0.094

0.094

0.037

0.100

0.018TABLE 3-7

POINT SOURCE FLOWSAND CONCENTRATIONSFOR BUILDOUT FUTURE CONDITIONS

WATERSHED
PhillippiCreek
Matheny Creek
Whitaker Bayou

Directto Bay
Siesta Key

South Bradenton CONCENTRATION(mg/L) DISCHARGE(mgd)

TOTAL

### P

1.03

1.05

1.OO

1.48

1.OO

0.74 ANNUAL

2.62

2.45

2.10

0.04

1.82

4.34 LEAD

0.015

0.019

0.020

0.007

0.020

0.004 TOTAL N

3.78

3.44

3.00

7.38

3.00

3.69 ZINC

0.076

0.094

0.100

0.037

0.100

0.018 WET SEASON

2.62

rir 2.45

2.94

0.04

1.82

4.34 DRY SEASON

2.62

2.45

1.68

0.04

1.82

4.34

### nutrients. For working septic tanks, a methodologywas established to estimate pollutant loadingsbased on of the literature review. Appendix 

### B contain a technical memorandum summarizing the findings of the literaturereview.

The septic tank evaluation conducted for purposes of this study was limited to the contaminants identified 

### in section 1.2; namely total nitrogen, totalphosphorus, lead and zinc. The evaluation focused on relative (to other sources evaluated) loading contribution from on-site disposal systems. As such, human health issues (such asproximity to drinking water sources, bacterial and viral issues) of septic systems were not explicitly evaluated.

3.5.1 FAILING SEPTIC TANKS

Nutrient concentrations for failing septic tanks were developed from 

### a review of septic tank 

### leachate monitoring studies. The typical concentrations established based on the literaturevalues are as follows:

TotalN 30 mglL Total P 2 mglL

Generally, these values are

### in the range of groundwater concentrationsmeasured at or

near septic

### tank discharges. Thevalues reflect pollutantremoval 

### within the soil of roughly 50percent for total N and 90percent for total P, based on average effluent concentrations cited in the literature.

Nutrient loadings for specific land uses were calculated by multiplying the concentrations by a flow rate. The flow rate for a particular land use dependedupon the number of residentsper acre, and theper capita flow rate.

Table 3-8 shows the septic tank flow rates developed for various land uses. For 

### all land

uses, a per capita flow rate of 75 gallonsper day was established. This value is at theTABLE3-8

SEPTIC TANKS FLOW RATESFOR VARIOUS LAND USES

Flow Rate (gallacrelday)

150 675 1125 1350 1350 1350 1350 1350 PerCapita Wastewater

Flow Rate (gaVdaylperson)

75 75 75 75 75 

## - Persons Per Dwellingunit

2 2 2 2 2 Land Use

LDSF Residential MDSF Residential HDSF Residential Multi-family Bldg Mobile Home CommerciallSe~ices Institutional Industrial DwellingUnits PerAcre

1 4.5 7.5

9 9 

## - -high end of the range of flow rates documented in the literature, and reflects local water

use data. For the residential areas, values of dwellingunits per acre were determined based on the descriptions of various land uses in the SarasotaCounty Comprehensive Plan and densities observed in aerial photographs. Each dwelling unit 

### is assumed to have 2.0 people, based on household size estimatesfor Sarasotaand Charlotte Counties and the City of North Port as cited in the City of North Port Comprehensive Plan. 

### Thisvalue is somewhat lower than the national average, because some of the populationis seasonal and because the population distribution is weighted more heavily toward retired persons who would tend to have a smallerhousehold size. For commercial and industrial areas, the flow values were assumed equal. to the highest residentialvalue.

A final considerationin the loading analysis for failing septic tanks 

### is the failurerate

## - that is, what percentage of the septic tanks are failing. These datawere established based

on permitting data from the Sarasota County Health Department. The Health Department requires a permit for repair or replacementof septic 

### tanks. During the period 1980 through 1990, an average of 740 repairs per year was recorded. Based on the estimate of 45,000 septic 

### tanksin the County, the annual repair rate is 1.6 percent. Recognizing that failure may occur for a number of years before repair isinitiated, the failure rate at any time islikely to be higher than 1.6 percent. 

### In previous studies,the annual failure rate has been multiplied by a factor of 

### 5, which implies that septic systems on average fail for 

### 5 years before repairs are made. For SarasotaCounty, the resulting failurerate is 

### 8 percent. This value compared favorably with the results of a septic 

### tank survey conducted in Jacksonville,FL by the Department of Health and Rehabilitative Services.
In the study, an inspection of more than 800 sites revealed about 90 violations, or a ' failurerate of 12percent Failure calculations also were done specificallyfor Casey Key, which had a higher annual repairrate. The failurerate establishedfor Casey Key was 20 percent.3.5.2 WORKING SEPTIC TANKS

Based on the literature review of septic 

### tanks, a methodology for assessing impacts of working septic tanks was developed. The methodology uses data such as suIficial aquifer transmissivity, recharge volume, typical distancesfrom septic tanks to receiving waters, and pollutant decay rates to determinehow much of the total

### N and totalP discharged from septic tanks will reach the Bay tributaries. 

### A detailed description of the calculations isprovided in a technical memorandum developed in Phase 

### 2 of the Sarasota Bay 

### NEP study (seeAppendix B). 

### An overview of the methodology ispresented below.

The methodology 

### is based on equations developed by Dupuit (Todd, 1985)to define baseflow to a stream. 

### In the septic 

### tank analysis, the baseflow was set equal to the recharge rate, which was defmed as the sum of natural baseflow calculated during the hydrologic analysis plus drainfield flow contributed by septic 

### tanks. It was assumed that the recharge to the surficial aquifer occurred uniformly between the stream and the most distantrecharge point. By inspection of USGS quadrangle maps, the typical maximum recharge distance (i.e., typical maximum distance to a perennial stream) was set equal to 3,000 feet. Thus, at any distance from the stream, the flow could be calculated. Furthermore, by establishing typical values of aquiferthickness, transmissivity and porosity, the velocity at any distancefrom the stream could also be determined. These calculations were performed at 10-foot incrementsto establish cumulative travel times from the septic tank to the receiving stream 

### as a function of distance. By applying a fvst order decay coefficient uniformly between the minimum distance and the maximum distancebetween septic tank andreceiving stream, an overall delivery ratio was established. The minimum distance was set at 

### 75 feet, which is the DERrequirement for septic tank implementation, and the maximum distance was set at 3000 feet, the maximum recharge distance.

Initially,the first order decay rate was establishedbased on work done by Ostendorf (1986). Ostendorf developed a model to simulate total N, chloride,boron and methylene

### blue active substances WAS)downgradient from the Otis 

### Air ForceBase in Massachusetts. The base has discharged an average flow of0.53 mgd since 1941. Sampleswere taken at various distances downgradientfrom the inf~ltration beds in order

to test the model's predictive ability. Chloride, a conservative substance, was simulated fust to test the model accuracy. Results showed a very good agreementbetween predicted and measured concentrations. When total N and MBAS were modeled 

### as conservativesubstances, the model overpredicted the concentrations. Consequently, first order decay rates were established for these constituents. For total N, a rate of 1.69

### X 10-g/second was established. At this rate, the total N concentrationwould be reduced by 5 percent after a travel time of 

### 1year, 41percent after 10 years, and 93percent after 50
years.

Other parameter values used in 

### the septic tank 

### analysis arepresented in Table 3-9. Values for aquifer thickness, porosity and conductivity werebased on review of the soil
survey for SarasotaCounty and a SouthwestFloridaWater Management District report on groundwaterresource availability in Sarasota County (SWWMD, 1988). 

### In addition, the minimum travel distance of 75 feet was based on septic tank regulations, and the maximum distanceof 3,000 feet was based on inspection of USGS maps.

To evaluate the methodologyand the fust-order decay rate, the septic 

### tank analysis results were applied 

### to the drainage areas of two STORET stations 

### in the Phillippi 

### Creek watershed. These include the Main A Canal at Palmers Boulevard Bridge (Station 24010630) and PhillippiCreek at Bahia Vista Street Bridge (Station24010625). The Palmers Boulevard station has a drainage 

### area of about 8 square miles, which consists primarily of cropland, rangeland, and low and medium density singlefamily residential land uses. 89 percent of the low density and 66percent of the medium density residential

areas are served by septic

### tanks, and there areno substantial point sourceloads. The Bahia Vista Street station has a drainage 

### area of44 square miles, comprised mainly of cropland, rangelands, open space, and low and medium density residential land uses. 53 percent of the low density, 41 percent of the medium density, and 37percent of the highTABLE 3-9

PARAMETERSFOR ANALYSIS OFWORKING SEPTIC TANKS

Source
SWFWMD, 1988
SWFWMD, 1988
SWFWMD, 1988

FDER
USGS maps Parameter
Aquifer Conductivity
Aquifer Thickness
Porosity

MinimumTravel Length

MaximumTravel Length Value

8.0 inlhr

60.0 ft

0.3

75ft

3000ft

### density residential areas are served by septic tanks. Unlike the Palmers Boulevard station, the water quality at Bahia Vista Streethas been impacted by the Atlantic Utilities and Kensington Park Utilitiespoint sources, which had been directly discharging secondary effluent

### to Phillippi Creek during the STORETperiod ofrecord. It ispossible that other smallerpoint sources may have also been discharging directly, rather than through percolation ponds and irrigation, during theperiod ofrecord.

The results of the analysisindicated that nitrogen concentrations were oversimulated when the low first-order decay rate was used. At the Palmers Boulevard station, the average annual total 

### N concentrationwas oversimulatedby 49 percent. The oversimulation of total
N 

### atthe Bahia Vista Street station was only 11

### percent, but sensitivity analyses indicated that significantly higher first-orderdecay rates would still result in reasonable total N predictions. Consequently, higher decay rates (which would result 

### in 

### a lower delivery ratio) were investigated.

After analyzing various first order decay rates, a conservativevalue of 0.00055lday was established. Thevalue was selected such that the observed and simulatedtotal N concentrations atthe BahiaVista Street station matched. When the samevalue was used forthe Palmer Street station, the simulated totalN concentrationexceeded the observed concentration by about 20 percent. This may indicatethat the analysis methodologyis better suited for stationswith larger drainage areas likethe BahiaVista Street station. It is alsopossible that the septic tankloading is conservatively high, and that additionalpoint

sourceloadings (rather than septic 

### tank loading) areresponsible for the high total N 

### concentrations at the Bahia Vista Bridge station.

Figure 3-1 shows total 

### N concentration of septic tank effluent as a function of distance from the receiving water, based on the conservativefirst order decay rate of 0.00055lday. As shown in the figure, most of the total N ispredicted to reach the receiving water at a distance of 75 feet. AWT conditions (totalN = 

### 3 mg/L) are not met unless the distance

### from the septic tank to the receiving wateris almost 1000 feet. Consequently, a setback distancein excess of 75 feet would appear to be appropriatefor water quality protection in the study area.

3.6 RAWFALL LOADINGS



### In order to account forrainfall loadings on the Bay water surface, concentrations representing rainfall loadings were included in the analysis. The Bay surface areais about 52 square miles. For the average annualprecipitation, the rainfall total of 54.6 inches per
year spread over the Bay surface results in an equivalent flowrate of 135mgd.



# .

The pollutant concentrations selectedforrainfall were based on monitoring data from the Tampa Bay NURP 

### study (Priede-Sedgwick, 

### Inc., 1982). The values are listed below:

Total N 0.82 mgL Total P 0.15 mgL Lead 6 u& Zinc 146ugL



### * The nitrogen concentrationsfrom the Tampa Bay NURP Study are consistentwith other local data, based on a review of other Tampa Bay loading studies and ofrainfall monitoring data from Pinellas County. Unfortunately, the studies and monitoring data did not include concentrationsfor total 

### P, lead or zinc.

For the average rainfall year, the calculated rainfallloads inlblyr are 

### 337,400 for total N, 61,700 for total P, 2,500 forlead, and 60,100forzinc. The significanceof these loads with respect to the other sources discussedpreviously in this section will be evaluatedin subsequent sections of this report.4.0 LOADING TRANSPORT TOBAY

The surfacerunoff pollutant loadings described in Section 

### 3.3represent estimates of loadings which have been discharged into a storm sewer, swale or stream channel. However, it ispossible that the loading to these conveyance systems (particularly stream channels) will be reduced enrouteto the Bay by processes such 

### as settling. Because many of the watersheds are relatively small, and storm flows will typically result in turbulent stream conditions, sign5cant load reductions 

### are not likely to occur in the free-flowing sections of the Bay tributaries. On the other hand, some removal may occurin the tidal portions of the tributaries,where flowsmay tend to be more quiescent.

Computer modeling using the EPA's WASP4 model (EPA, 1990)was conducted to evaluate the potential for pollution removal within the major tidal tributaries. The following tributaries were included 

### in the analyses:



# . Phillippi Creek



# . Whitaker Bayou



# . Hudson Bayou



# . Bowlees Creek



# . CedarHammock

The watersheds of these tributaries account for 

### 55 percent of the total land area, and 

### 64 percent of the total improved (e.g., urban and agricultural)land area. Most of the remaining improved area drains directly to the Bay instead of discharging to a major tributary.

The analysis focused strictlyon the removal of suspended pollutants by means of settling. Thus, dissolvedpollutants were assumed to exhibit 100percent delivery to the Bay. Settling of suspended pollutants was influenced by the assumed settling rate, water depth, and tidal flushing effects.4.1 MODEL DESCRIPTION

The Water Quality Analysis Simulationprogram -4 (WASP4) consists of two separate subprograms

## - the hydrodynamics program DYNHYDS and the water quality program WASP4. DYNHYDS solves the one 

## - dimensional equationsof continuity and

momentum in order to calculate water surface elevations, velocities and flow rates at various points within the modeling system. WASP4 solves the conservation of mass equation in order to calculate pollutant concentrationswithin the system.

Both programs use the "link-node"method of simulation. The water body 

### is represented in the model as a series of storagepoints (nodes)interconnected with a series of channels (links). For each time step during the simulation, the model solves the equation of

momentum for each link to calculateflow between connected nodes, and solves the equation of continuity to determine water surface elevations at each node. Water quality
constituents are transported between nodes by the flows in each 

### link. In addition, loads
may be added to each node via point sources or nonpoint sources. For each node, the

mass balance equationis solved to calculate the mass of pollutant, and this value is divided by the node volume (afunction of the node water surface elevation) to determine the pollutant concentration.

Figures 4-1 through 4-5 show the model segmentationdeveloped for each major tributary. The model segmentationwas designed to extend upstream from the mouth to most distant

extent of tidal influence. Segmentsin individual systems were sized according to recommendationsin the WASP4 User's Manual (EPA, 

### 1990). Generally,it

### is best to segment the system sothat the water volumes areroughly the same. 

### This guideline allows larger time steps and results in greater numerical accuracy.FRUITVILLE ROAD



## SARASO 

## BAY 

# 3

-I CITY LIMIT
Q CtiI

### a c-. 

### a C

r--- 

# -- 7



# -

0 1000 2000 3000 DISTANCE 

### IN FEET



### Figure4-1. WASP4

. . 

### ModelSegmentation

### for PhillippiCreek.

### Figure 4-2. 

### WASP4 Model Segmentationfor Whitaker Bayou.

### Figure4-3. 

### WASP4 

### Model Segmentationfor Hudson Bayou.

### Figure 4-4. 

### WASP4 

### Model Segmentationfor BowleesCreek.

### BAYSHORE GARDENS PARKWAY 

# /

DISTANCE IN FEET 

# SARASOTA 

# BAY

Figure4-5. 

### WASP4 ModelSegmentationfor 

### Cedar Hammock.4.2 MODEL PARAMETERS



### In modeling the Bay tributaries a number of parameters were evaluated. These included tidal influence, channel geometry, suspended pollutant settling rate and surfacerunoff loadings and flows. The evaluation of these parametersis discussed below.

4.2.1 

### TIDAL INFLUENCE

One of the major forcing functions in each of the tributaries is the inflow and outflow of the tide. In the model, a lunar semidiurnal tide was specified,with a period of 12.5 hours. Key values that were established are the water elevation at mean tide, and the mean tidal range.

Based on data from the 1991 Tide Tables, the selectedparameter values for tidal effects

were 1.0 ftNational Geodetic Vertical Datum (NGVD) 

### as the mean tide elevation, and 2.0 feet as the mean tidal range. The mean water elevation

### is consistent with a review of Phillippi Creek cross-sectional data developed for the Sarasota County Stormwater Master Plan report (CDM, 1987). The value of 1.0 ft NGVD was the mid-range of water elevations measured at the cross-sections in the tidal part of the creek.

The other major forcing functionin each tributary

### is the flow and associated surface runoff pollutant loading from the watershed. Generally,because runoff from the large majority of the drainage area enters the stream above the first model segment, the total flow and load was assigned to the fistsegment. The exception was Hudson Bayou, where 60percent of the flow and load was assigned to Segment 

### 1and 40 percent was assigned to Segment

### 3, based on drainage area to each segment.The loadings and flows were simulated as steady input values, calculatedfrom the average annual results generated by the spreadsheetmodel. Streamflowvalues, calculated by the model in terms of inches per year over the drainage area, were converted to a steady inflow in units of cubic meters per second. Similarly, the annual loading values in pounds
per year were converted to a steady loading in kilograms per day.

Sensitivity runs were conducted to determine whether wet year, dry year, and seasonal flows and loadingswould generate substantially different results then the average year flows and loadings. Results showed that the deliveryratios (the percentage of surface runoff loading that reaches the Bay) were not substantially differentfor any of these cases. Consequently, the delivery ratios determined for average annual conditionswere used for all rainfall scenarios.

4.2.3 TRIBUTARY GEOMETRIES

The depth, width, length and cross-sectional geometries of the tributaries were established based on existing data. Bowlees Creek and Phillippi Creek were the tributaries having the

most detailed data. Cross-sections were developed for Phillippi Creek aspart of the
SarasotaCounty Stormwater Master Plan (CDM, 1987), and Bowlees Creekhad previously been modeled using the U.S. Corps of Engineers HEC-2 model. Data for the other tributaries were developed based on USGS quadranglemaps, NOAA nautical charts and Florida Department of Transportationbridge records and field inspections.

The cross-sectional data were used to developHEC-2 datasets for each tributary, and these datasetswere used to develop the input data required by the WASP4 model. For each tributary, the HEC-2 model was run at the average stream flow and mean tidal height, producing values of depth, volume and surface area 

### This output was used to specify the depth, volume and surface area of each of the segments

### in the WASP4 model.

### 4.2.4 POLLUTANT SE'I%ING 

### PARAMETERS

The WASP4 model was run for each tributary assuming that settling of suspended pollutants was the only pollutant removalprocess. Twokey factors

### in determining how much removal will occur are the pollutant settling rate, and the fraction of total pollutant that is in the suspendedform.



### A settling rate of 1.0 foot per day was selected based on a review of the 

### literature. A review of previous modeling studiesindicated that calculated settling velocitiesfor suspended solids in quiescent waters have ranged from 0.1 to 5.0 meters per day (Delos

et al, 1983). In 

### studies of the Flint River (Richardson et 

### al, 1983)and the Deep River (Metcalfe etal, 

### 1984),calibrated settling rates ranged from 0.2 to 0.65 meters per day (0.7

to 2.1 feet per day). In contrast, literature settling rates for phytoplanktonrange from 0.0
to 30.0 meters per day, with most in the rage of 0.02 to 0.6 meters per day (EPA, 1985). Consequently,a settlingrate of 1.0 feetper day (0.30 meters per day) isin the mid-range of typical settlingvalues.

Sensitivityruns were conducted to determine the effect of increasing or decreasing the settlingrate. The analysis evaluated settling rates of 0.5 and 1.5 feetper day, which represent a 50 percent variation from the selected rate of 1.0 feet per day. Results indicated that the changein deliveryratio ranged from 2 to 20 percent, and was generally less than 10percent. Thus, it appears that the delivery ratio results are not sensitiveto these changes in the settlingrate.

The settlingrate was applied to the suspendedfraction of each pollutant, which was also establishedbased on a literaturereview. The selected values for the constituents analyzed
in the study area, based on typical values for urbanized areas, are 

### as follows:



# . Total 

### N 25% suspended



# . Total P 40% suspended

# . Lead 90% suspended



# . Zinc

' 40% suspended

These values are typical of monitoring data from the

### NURe study. Based on these values lead 

### is the pollutant that will exhibit the highest degree of settling in the tributaries, and total 

### N will exhibit the lowest degree of settling.



### 4.3 MODELING PROCEDURE

The data described in Section 4.2 were used in the WASP4 model to determine the delivery ratio for each of the major tributaries. The model was run for a simulation period of 

### 30 days, with a repeated semi-diurnal tide and constant streamflow and pollutant loading, to establish steady-state conditions (i.e., concentrationsdid not vary from one day

to the next). The WASP4 model output included a mass balance file that summarized the outflow of pollutant from the tributary. The pollutant outflow was compared to the constant loading to establish the delivery ratio for each polIutant.

A slightly different procedure was used for Cedar Hammock, due to the presence of two sediment traps in the non-tidal part of the tributary. Figure 4-2 shows the location of these traps at FloridaBoulevard and Harvard Avenue. The areas upstream of the traps could not be modeled within the WASP4 framework. City records regarding sediment accumulation in these traps suggest that substantialpollutant removal may be occurring there, unlike salinity barriers or other minor structuresthat 

### are unlikely to promote significant settling.

The pollutantreduction due to the sediment traps was estimatedin a spreadsheet. Based

on ihe average flowrate and the weir length and elevation, the water elevation behind each weir was determined. Cross-sectional data from a survey of the area were entered into a HEC-2 model dataset to determine water depth, volume and surface area. Usingthese data along with the values for settling rate and suspended fraction of pollutant, removal due to settling was calculated.

To run the WASP4 model for Cedar Hammock the pollutant parameters were adjusted to
account for the settlingin the sedimenttraps. The average pollutant loading was reduced

to reflect the settling. In addition, the suspended fraction of each pollutant had to be changed, because the suspended fraction to the Bay was lower than the suspended fraction to the sedimenttraps. For example, if a 100pound per day load to the sediment traps contains 40 pounds of suspended pollutant (i.e., suspended fraction 

### is 40 percent), and 20 pounds per days of suspended pollutant are removed 

### in the sediment traps, then 20 pounds
per day of suspended pollutant remains in the 80pounds per day of pollutant reaching the Bay, resulting in a suspended fraction of 

### 25 percent, rather than 40 percent.

4.4 MODEL RESULTS

The delivery ratios developed for each tidal tributary are presented in Table 4-1. 

### As one would expect, the deliveryratios are highest for total 

### N, which had the lowest suspended fraction, and lowest for lead, which had the highest suspended fraction. Bowlees Creek, Hudson Bayou and Whitaker Bayou exhibit little reduction in loadingsto the Bay, with delivery ratios of over 90percentfor all pollutants. PhiUippi Creek provided 30 percent removal of lead in the tributary, but delivery of zinc, total 

### N and total P are still in the neighb&hood of 90 percent. Cedar Hammock exhibits the most pollutant removal, chiefly because of the sediment traps in the non-tidal tributary.

As presented in Chapter 5.0, these delivery ratios were applied to the surfacerunoff loads for the major tributaries. For the areas draining directly to the Bay, and forthe other
tributaries that were not modeled, 100 percent deliverywas assumed. Theratios were not applied to point source discharges, septic 

### tank discharges, baseflow and rainfall, because the pollutants for these type of discharges are expected to be primarily in the dissolved form.TABLE4-1

DELIVERY RATIOS FOR MAJOR TIDALTRIBUTARIES

Tributary

PhillippiCreek

Whitaker Bayou

HudsonBayou

BowleesCreek

Cedar Hammock DeliveryRatio (%)

Zinc

87

97

92

96

82 Total P

87

97

92

96

82 Total N

93

100

96

99

90 Lead

71

92

82

89

585.0 POLLUTIONLOADING PROJECTIONS FOR EXISTING LAND USE CONDITIONS

The data presented in the previous chapters were used as input to a spreadsheet model which calculated pollutant loadings to SarasotaBay for existing land use conditions. The results were analyzedin a number of ways. Totalloadings to the Bay were analyzed to determine the relative impacts of surface runoff, point sources, septic 

### tanks,baseflow and rainfall. 

### In addition, the loadings attributedto each of the study area jurisdictions, and each of the watershedsin the study area were calculated. For the average annual rainfall, the percentage of the totalloading occuning in the wet and 

### dry seasons was also established. Finally, the analysis considered the loadings for a wet year and a dry year, comparing the loadings with those of an averageyear.



### 5.I AVERAGE'

### ANNUAL LOADINGRESULTS

5.1.1 LOADINGS BY WATERSHED

Table 5-1 presents the average annual loading results by watershed for existing land use conditions. The results include the impacts of surface runoff, baseflow, septic 

### tanks,point source discharges and rainfall. Values in the table include total area, total runoff, and loadig data for total P, total N, lead and zinc. The loadigdata include the total mass in pounds; the unit load in pounds per acre, and the flow-weighted concentrationin milligrams per liter. The last line in the table represents the values for the entire study

area, including the land areas 

### and the Bay water surface.

For total P, the watershedsthat exhibit the highest to@ loadings, unit loadings and concentrations include PhillippiCreek, Whitaker Bayou, SouthBradenton and Siesta Key. Phillippi Creek, SouthBradenton and Whitaker Bayou account for 

### 40 percent of the total P load to the Bay. Though the total load from Siesta Key 

### is not nearly as high as for

### Phillippi Creek and Whitaker Bayou, the unit loading and concentration from the watershed ishigher than any other watershed. Surface water discharge ofpoint sourcesis 

### the major reason for high total 

### P concentrationsin the Siesta Key watershed.

The same four watersheds, along with Matheny Creek and the areas in western Sarasota County that drain 

### directlyto the Bay, alsohave high loading and concentration values for total N. About 36 percent of the total N loading to 

### the Bay comes from Phillippi Creek and WhitakerBayou. Surface water discharge ofpoint sourcesisthe major reason for high total N concentrationsin the Matheny Creek and Siesta Key watersheds.

Phillippi Creek,Bowlees Creek and WhitakerBayou are the largest loading sourcesfor lead. These three watersheds account for 54percent of the total Bay loading. Surface runoff isthe major source of lead in Bowlees Creek, whereas a combinationof surface runoff and point source discharge are the major contributorsin Phillippi Creek and Whitaker Bayou. Relatively high lead concentrations were calculatedforHudson Bayou and CedarHammock. This can be attributed to surface runoffin these two watersheds.

Other than rainfall, which accountsfor 65 percent of the zinc loading to the Bay, major zinc loadings are attributed to PhiippiCreek, Bowlees Creek and WhitakerBayou. The high zinc concentration in the rainfall, which was assumedbased on Tampa Bay

## NLTRP data,isresponsible forthe large rainfall loading. Surfacerunoff and point source discharge are the major factors in Phillippi Creek and Whitaker Bayou, and surface runoff isthe major factorin Hudson Bayou.

The values in Table 5-1 do not include the effects of pollutant settling in the tidal tributaries. Pollutant settlingwas assumedto apply only to the loading from surface runoff. When the delivery ratios presented inTable 

### 4-1 were appliedto the tributaries, the reduction in surface runoff loadings was only 6 percent for total 

### P and zinc, 3 percent for total N, and 13percent for lead. When considering the total loading from all sources,

### the loading reductions due to settling were 3 

### percent fortotal 

### P, 12percent for lead, and 2 

### percent fortotal N and zinc.

5.1.2 LOADINGS 

### BY SOURCE

Overall loading statistics as a function of pollution source 

### arepresented in 

### Table 5-2. 

### The sources included in the table are surface runoff, baseflow, septic tanks, point sources, and rainfall. The total runoff and loadings of total P, total 

### N, lead and zinc are presented, as isthe percentage of the total loading attributed to each source. Generally, the results indicate that surfacerunoff and rainfall are the two largest sources ofpollutant loadings to the Bay. Together,these two sources account for 71

### percent of the total P, 

### 73

### percent of the total N, 98 percent of the lead and 91 percent of the zinc loadings. Surface runoff is the major source of total P, total N and lead, while rainfallisthe major source of zinc;

These 

### are several reasons why these two sources dominatethe total loadings. One isthat the two sources account for 

### 84percent ofthe total flow that reaches the Bay. Another is that the remaining 16 

### percent of the total runoff is primarily attributed to baseflow, which has rather low pollutantconcentrations.

Septic tanks 

### and point source discharges contribute a relatively small percentage of total loadings. The values in the table show thatthe combined loadings of septic 

### tanks and point sources are 

### 16to 

### 18percent of the total loadingsforthe nutrients, and 1

### to 

### 3 percent for the metals. Point source loadings are limited by the implementationof AWT standards atwastewater treatment plants, alongwith a shift from surface water discharge to land applicationof wastewater. Septic 

### tank loadings are limited by the relatively low failurerate of 

### 8percent. 

### In addition, as aresult of the substantial travel time from septic 

### tanks to the Bay and its tributaries, a relatively small fraction of septictank effluent loading reaches the Bay.TABLE 5-2

AVERAGE ANNUAL LOADINGSBY SOURCE FOR EXISTINGLAND USE CONDITIONS

Note: Loadingtotalsdo not include pollutant settling intidaltributaries. Seetextfor discussionof settlingintributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

14.58 42.6% 3.84 11.2% 0.70 2.0% 1.10 3.2% 14.04 41.0% 34.26 AVERAGE YEAR POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL 117,830 46.6% 33,810 13.4%

8,230 3.3% 31,110 12.3% 61,730 24.4% 252.710 TOTALN %OF (Ib) TOTAL 609,990 47.2% 112,700 8.7% 123,520 9.6% 109,230 8.4% 337,460 26.1% 1,292,900 LEAD %OF (Ib) TOTAL 33,790 91.2% 300 0.8% 0 0.0% 490 1.3% 2,470 6.7% 37,050 ZINC %OF (Ib) TOTAL 24,890 26.7%

5,620 6.0% 0 0.0% 2,510 2.7% 60,080 64.5% 93,100The values in Table 5-2 do not include the effects of pollutant settling in the tidal tributaries. When the delivery ratios presented in Table 4-1 were applied to the tidal tributaries to assess the impact on the source distribution percentage, the results were only slightly different than the results generated without considering the delivery ratios. The percentage of loading due to surfacerunoff changed by 2 percentage points orless, and the percentages for the other sources changed by no more than 1percentage point. Thus, the relative distribution of the sourcesremained essentially the same, with surface runoff, baseflow and rainfall providing the highest percentages of the total pollutant loadings.

5.1.3 LOADINGS BY JURISDICTION

Loading totals were also calculatedbyjurisdiction, and these totals are presented in Table 5-3. The jurisdiction list includes Sarasota County, Manatee County, the City of Sarasota, the Barrier Islands, and the Bay Water Surface. The Barrier Islands were initially included in a separate group because itwas speculatedthat rainfall totals for the barrier islands could be significantly different than mainland rainfall totals. However, a statistical analysis ofrainfall data indicated that the barrier island and inland rainfall data were very similar (See Appendix C). For eachjurisdiction, the table lists the area, the runoff volume, and loadings of total 

### P,total 

### N, lead and zinc. The percentage of the total runoff and loadings attributed to eachjurisdiction 

### are also included.

Table 5-3 shows that the largest areas generallyproduce the highest percentage ofrunoff volume and pollutantloading. Sarasota Countyis the largestjurisdiction, comprising49 percent of the total land and water surface area. TheBay Surface

### is next largest at 26 percent, followed by Manatee County at 16 percent. Together, these three jurisdictions account for 89percent of the total runoff, and 78 to 

### 92percent of the pollutants listed in the table.

For total 

### P and total 

### N, Sarasota County accounts for about44 percent of the loading to the Bay, and Manatee County and the Bay surface accountfor another40to 42percent.TABLE 5-3

AVERAGE ANNUAL LOADINGSBYJURISDICTION FOR EXISTING LAND USE CONDITIONS

Note: Loading totals do not includepollutantsettling intidaltributaries. Seetext for discussion of settling intributaries. JURISDICTION

SARASOTA CO. SARASOTACITY MANATEECO. ISLANDS BAY SURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33,280 129,412 RUNOFF %OF (in) TOTAL

11.94 34.8%

2.20 6.4% 4.66 13.6% 1.42 4.1% 14.04 41.0% 34.26 AVERAGE YEAR POLLUTANT LOADING Total P %OF

(Ib) TOTAL 108,900 43.1%

25,230 10.0% 41,240 16.3% 15,610 6.2% 61,730 24.4% 252,710 LEAD %OF (Ib) TOTAL 14,720 39.7%

6,170 16.7% 11.830 31.9%

1,860 5.0% 2,470 6.7% 37,050 Total N %OF

(Ib) TOTAL 575.960 44.5% 109.970 8.5% 204.350 15.8%

65,160 5.0% 337,460 26.1% 1,292.900 ZINC %OF (Ib) TOTAL 16,790 18.0%

5,170 5.6% 8,820 9.5% 2,240 2.4% 60,080 64.5% 93,100Sources of nutrientsin Sarasota County include surface runoff, baseflow, septic tanks and point sources. Of these, surface runoff is the major contributor. Surfacerunoff is also the key factor for Manatee County. Loading to the Bay surface occurs through rainfall.



### In comparison to nutrients, the values forlead indicate a higher percentage contribution from the City of Sarasota and Manatee County. This is primarily due to the surface runoff from the highly developed areas within the City and parts of the County. 

### In contrast, rainfall has a much lower relative contribution due to the low lead concentration assumed, based on Tampa 

### NURP data.

Due to the high concentration of zinc in rainfall (based on the Tampa 

### NURP study), the Bay surface loading accounts for 

### 65 percent of the zinc loading to the Bay. 

### As with lead, the zinc loadings from the City of Sarasota and Manatee County tend to be more significant with respect to the loading from Sarasota County, due to urban surfacerunoff.

For all of the pollutants, the islands 

### are responsible for 

### 7 percent or less of the total loadings. The relative contribution of nutrients ishigher than the relative contribution of metals for the islands. This can be attributed to the somewhathigherrate of septic tank 

# - failure assumed for Casey Key 

### (20 percent compared to 

### 8 percent for other watersheds), and the surface water discharge from Siesta Key, in addition to surfacerunoff and baseflow loadings.

The values in Table 

### 5-3 do not include the effects of pollutant settling in the tidal tributaries. When the delivery ratios presented in Table 

### 4-1 were applied to the tidal tributaries to assess the impact on the loading distribution betweenjurisdictions, the results were only slightly different than the results generated without considering the delivery ratios. The relative percentages of loading attributed to the various jurisdictions did not change by more than 1percentagepoint.5.2 WET SEASON

### AND DRY SEASON RESULTS

Separate analyses were conducted to evaluate loadings during the wet season (June through September) and the dry season (Octoberthrough May) of an average year. The results were used to determine how the total annual load was distributed between the two

seasons. In addition, the results for each season were compared to the annualresults to identify changes in loading distributions by source and byjurisdiction.

Tables 

### 5-4 through 5-7 present the results of the seasonalloading analysis. Loadings by watershed for the wet season and dry season are listed in Tables 5-4 and 5-5, respectively. Table 5-6 includes loading values by pollutant source for both the wet and the dry season. Loading values byjurisdiction for both seasons are shown in Table 5-7.

Based on the data in Tables 5-4 and 5-5, about 60percent of the annual loading occurs during the wet season, and 40 percent occurs during the dry season, for all four of the analyzed pollutants. Because surface runoff and rainfall are major load contributors, one would expect that the loading distribution would reflect the precipitation distribution between wet and dry season. As shown previously 

### in Table 3-1, 20.9 inches ofrain was established for the dry season and 33.9 inches of rain was established for the wet season. This results in a rainfall distribution of 38percent in the dry season and 62 percent in the wet season, which is almost identical to the loading distribution. The runoff distribution is also very similar, with 62 percent of the runoff attributed to the wet season and 38 percent of the runoff attributed to the dry season.

A review of the values in Table 5-6 indicates that the distributionsof loadings between the various pollutant sources during the wet and dry season are very similar to the average annual distribution. The largest changes occur for point sourcesloadings. Unlike the other sources of pollution, point sources and septic tanks actuallyhave a greater total flow volume during the 8-month dry season than during the 4-month wet season.WETSEASON LOADINGSBYWATERSHED FOR EXISTING LAND USE CONDlTiONS

WATERSHED

Note: Loading totals do not include pollutantsenling in tidaltributaries. Seetextfordiscussionof settling intributaries.TABLE 5-5

DRY SEASON LOADINGSBYWATERSHED

FOR EXISTING LAND USE CONDITIONS

Note: Loading totals do not include pollutant settling in tidaltributaries. Seetextfor discussionof settling intributaries.TABLE 5-6

WET SEASON AND DRY SEASON LOADINGSBY SOURCE FOR EXISTING LAND USECONDITIONS

SOURCE

SURFACE BASEFLOW SEPTIC POINT SOURCE RAINFALLTOTAL

Note: Loading totals do not include pollutant settling in tidaltributaries. Seetextfordiscussionof settlingintributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINT SOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL 9.00 42.6% 2.82 13.4% 0.23 1.1% 0.40 1.9% 8.67 41.1% 21.12

RUNOFF %OF (in) TOTAL 5.58 42.5% 1.03 7.8% 0.47 3.6% 0.69 5.3% 5.37 40.9% 13.14 WET SEASON POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL

72,640 48.1% 24,790 16.4%

4.120 2.7% 11,450 7.6% 38,100 25.2% 151.100

DRYSEASON POLLUTANT LOADING TOTAL P %OF (lb) TOTAL

45,050 44.4%

9,030 8.9% 4,130 4.1% 19,660 19.4% 23.630 23.3% 101.500 TOTALN %OF (lb) TOTAL 376,520 49.0%

82,600 10.7% 61,740 8.0% 39,780 5.2% 208,290 27.1% 768,930

TOTAL N %OF (Ib) TOTAL 233.420 44.6%

30,090 5.7% 61.820 11.8% 69.440 13.3% 129.170 24.7% 523,940 LEAD %OF (Ib) TOTAL 20.880 91.6% 200 0.9% 0 0.0% 190 0.8% 1,520 6.7% 22,790 ZINC %OF (Ib) TOTAL 15,360 26.7%

4,110 7.1% 0 0.0% 950 1.7% 37,090 64.5% 57,510

LEAD %OF

(Ib) TOTAL 12,970 90.8% 50 0.4%

0 0.0% 310 2.2% 950 6.7% 14.280 ZINC %OF (Ib) TOTAL

9.520 26.7% 1,510 4.2% 0 0.0% 1,570 4.4% 23,000 64.6% 35,600TABLE 5-7

WET SEASON AND DRYSEASON LOADINGS BYJURISDICTION .FOR EXISTING LAND USE CONDITIONS

JURISDICTION

SARASOTA CO. SARASOTACITY MANATEECO. ISLANDS BAY SURFACE TOTAL

Note: Loadingtotals do not include pollutant settlingintidaltributaries. See text for discussionof settlingintributaries. JURISDICTION

SARASQTACO. SARASOTACITY MANATEECO. ISLANDS BAY SURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33.280 129,412

AREA

(ac) 62,301

7,844 20,226

5,761 33,280 129.412 RUNOFF %OF (in) TOTAL 7.39 35.0% 1.32 6.3% 2.90 13.7% 0.85 4.0% 8.67 41.0% 21.12

RUNOFF %OF (in) TOTAL

4.55 34.6% 0.88 6.7% 1.77 13.4% 0.57 4.3% 5.37 40.9% 13.14 WET SEASON POLLUTANT LOADING

DRY SEASON POLLUTANT LOADING Total P %OF

(Ib) TOTAL 66.080 43.7% 13.790 9.1% 24,850 16.4%

8,280 5.5% 38,100 25.2% 151,100

Total P %OF

(Ib) TOTAL 42.760 42.1% 1 1,360 11.2% 16.410 16.2%

7,340 7.2% 23,630 23.3% 101.500 LEAD %OF (Ib) TOTAL

9,070 39.8% 3,760 16.5% 7,330 32.2% 1,110 4.9% 1,520 6.7% 22,790 Total N %OF

(Ib) TOTAL 340.160 44.2%

62,460 8.1% 121,860 15.8% 36,160 4.7% 208,290 27.1% 768,930 ZINC %OF (Ib) TOTAL 10,600 18.4% 3,030 5.3% 5,530 9.6% 1,260 2.2% 37,090 64.5% 57,510

Total N %OF

(Ib) TOTAL 235.840 45.0%

47,440 9.1% 82,490 15.7% 29,000 5.5% 129,170 24.7% 523,940 LEAD %OF (Ib) TOTAL

5,660 39.6% 2,390 16.7% 4,550 31.9%

730 5.1% 950 6.7% 14,280 ZINC %OF (Ib) TOTAL

6,190 17.4% 2,140 6.0% 3,290 9.2%

980 2.8% 23,000 64.6% 35.600Consequently, the percentage of the total loading due to point sourcesis substantially higher during the dry season, and lower during the wet season. Even during the dry

season, however, the point source loadings for total 

### P, total 

### N and zinc are less than the loadings due to surface runoff orrainfall.

A comparison between Tables 5-3 and 5-7 reveals that there 

### is little differencein the distribution of runoff and loadingsbetween the various jurisdictions during the wet season, dry season and average year. In almost all cases, the changein the distribution values

were less than one percentage point. The values for the wet season tended to be more similar to the average annual vaesthan were the dry season values.

The values in Tables 5-4through 5-7 do not include the effects of pollutant settlingin the tidal tributaries. 

### As discussedin Section 5.1, the applicationof the delivery ratios determined for the tributaries did not produce substantial changes in total loadings or the distribution of loadingsbetween sources or jurisdictions.

5.3 WET 

### YEAR 

### AND DRY YEAR RESULTS

Analyses were also conducted to evaluate loadings during a wet year and a dry year. 

### As discussed in Section 

### 3.2,the 10thpercentile and 90th percentile value for annual precipitation and annual streamflow were used to represent the wet and dry years. Results were used to determine the changes in total loadings to the Bay, and to assess changes 

### in load distributionby source and byjurisdiction.

Tables 5-8 through 5-11 present the results of the wet and dry year loading analyses. Loadings by watershed for the wet year and the dry year are listed in Tables 5-8 and 5-9, respectively. Table 5-10 includes loading values by pollutant sourceforboth the wet and the dry year. Loading values byjurisdiction for both wet and dry years are shown in Table 5-11.TABLE 5-8

WET YEAR LOADINGSBYWATERSHED FOR EXISTING LAND USE CONDITIONS

BAY SURFACE

Note: Loading totals do not include pollutant settling in tidal tributaries. See textfor discussion of settling in tributaries.TABLE 5-9

DRYYEAR LOADINGS BYWATERSHED FOR EXISTING LAND USECONDITIONSTABLE 5-10

WET YEAR AND DRYYEAR LOADINGS BY SOURCE FOR EXISTINGLAND USE CONDITIONS

SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL

Note: Loading totalsdo not include pollutant settling in tidaltributaries. Seetextfordiscussionof settling intributaries. RUNOFF %OF (in) TOTAL

18.62 40.9%

7.23 15.9% 0.70 1.5% 1.10 2.4% 17.92 39.3% 45.57

SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

11.14 45.6% 0.78 3.2% 0.70 2.9% 1.10 4.5% 10.72 43.9%

. 24.44 DRY YEAR POLLUTANT LOADING WET YEAR POLLUTANT LOADING

TOTAL P %OF (Ib) TOTAL

89,990 49.1%

6,870 3.7% 8.230 4.5'/0 31.110 17.0% 47,150 25.7% 183,350 ZINC %OF (Ib) TOTAL 31,750 26.1% 10,620 8.7% 0 0.0% 2,510 2.1% 76.700 63.1% 121,580 TOTAL P %OF (Ib) TOTAL 150,380 45.3%

63.640 19.2%

8,230 2.5% 31,110 9.4% 78,800 23.7% 332.160

LEAD %OF (Ib) TOTAL 25,820 91.4% 40 0.1%

0 O.OO/o 490 1.7% 1,890 6.7% 28,240 TOTAL N %OF (Ib) TOTAL 465.91 0 47.6%

22,920 2.3% 123,520 12.6% 109,230 11.2% 257.730 26.3% 979,310 ZINC %OF (lb) TOTAL 18,980 27.7%

1,150 1.7% 0 O.OO/o 2,510 3.7% 45,890 67.0% 68,530 TOTAL N %OF (Ib) TOTAL 778,600 47.1% 212,200 12.8% 123.520 7.5% 109,230 6.6% 430,790 26.0% 1,654,340 LEAD %OF (Ib) TOTAL 43.140 91.0% 640 1.3% 0 0.0% 490 1.0% 3.150 6.6% 47,420WETYEAR AND DRYYEAR LOADINGS BYJURISDICTION FOR EXISTING LAND USECONDITIONS

JURISDICTION

SARASOTACO. SARASOTA CITY MANATEECO. ISLANDS BAYSURFACE TOTAL

Note: Loadingtotals do not include pollutantsettling in tidaltributaries. Seetext for discussionof settling intributaries. AREA

(ac) 62,301

7,844 20,226

5.761 33,280 1'29.412

JURISDICTION

SARASOTACO. SARASOTA CITY MANATEECO. ISLANDS BAY SURFACE TOTAL DRYYEAR POLLUTANT LOADING RUNOFF %OF (in) TOTAL

16.59 36.4%

2.86 6.3% 6.31 13.9% 1.89 4.1% 17.92 39.3% 45.57

AREA

(ac) 62,301

7,844 20,226

5,761 33.280 129,412 RUNOFF %OF (in) TOTAL 7.86 32.1% 1.63 6.7% 3.22 13.2% 1.00 4.1% 10.72 43.9% 24.44 Total P %OF (Ib) TOTAL 74,270 40.5% 20.630 11.3% 29,140 15.9% 12.160 6.6% 47,150 25.7% 183,350 WET YEAR POLLUTANTLOADING

LEAD %OF

(Ib) TOTAL 11,140 39.4%

4.750 16.8% 9,020 31.9% 1,440 5.1% 1,890 6.7% 28,240 Total N %OF

(Ib) TOTAL 433,080 44.Zo/o

88.060 9.0% 150,150 15.3% 50,290 5.1% 257,730 26.3% 979,310 ZINC %OF (Ib) TOTAL 10,810 15.8%

3.980 5.8% 6,200 9.0% 1,650 2.4% 45,890 67.0% 68,530 ZINC %OF

(Ib) TOTAL 23,570 19.4%

6,540 5.4% 11,870 9.8%

2,900 2.4% 76.700 63.1% 121,580 LEAD %OF

(Ib) TOTAL 18,890 39.8%

7,840 16.5% 15,180 32.0%

2,360 5.0°/0 3.150 6.6% 47,420 Total P %OF

(Ib) TOTAL 148,220 44.6%

30.440 9.2% 55,100 16.6% 19,600 5.9% 78,800 23.7% 332.160 Total N %OF (Ib) TOTAL 739,160 44.7% 135,280 8.2% 266,780 16.1%

82.330 5.0% 430,790 26.0% 1,654,340Based on a comparisonwith the average year loadings, the values in Tables 5-8 and 5-9 show that loadings for all pollutants will be 28 to 31percent higher during the wet year, and 24 to 27 percent lower during the 

### dry year. These values correspond closely to the differences in rainfall and runoff values between the wet year, dry year, and average year. During the wet year, rainfall was calculatedto be 28 percent higher than average, and the runoff total shown in Table 5-8 

### is 31percent higher than the average year. For the dry year, rainfall was calculated to be 

### 24 percent lower than average, and themofftotal shown in Table 5-9 is 29 percent lower than the averageyear. Theresults presented in Table 5-10 indicate that the wet year and dry year load distributions by source are very similar to the average year distribution. The largest change occurs for point source discharges, because the total loading is assumed to be the sameregardless of the annual precipitation volume. Thus, the percentage of loadings due to point sources are noticeably higher during the dry year and lower during the wet year. Even during the dry year, however, the point source loadingsfor total P, total 

### N and zinc are less than the loadings due to surfacerunoff and rainfall.

A comparison between Tables 5-3 and 5-11reveals that there 

### is little differencein the distribution ofrunoff and loadings among the wet, dry and average years. For virtually
alljurisdictions and pollutants, the change in the distribution values were less than one percentage point. Values for the wet year tended to be more similarto the average year than were the dry year values.

The values in Tables 5-8 though 5-11 do not include the effects of pollutant settling in the tidal tributaries. As discussed in Section5.1, the applicationof the delivery ratios determined for the tributaries did not produce substantial changes in total loadings or the distribution of loadings between sourcesorjurisdictions.5.4 

### SUMMARY

The results from the analysis of existing loads indicates that, 

### as one would expect, the largestrunoff volumes and pollutant loadings are generated within the largest watersheds. However, small but highly urbanized watersheds can also contribute substantialloads from surface water runoff and point sources. Overall, surfacerunoff and rainfall account for the majority of the pollutant loading, to the Bay. Point sources and septic 

### tanks combined

account for 16to 18percent of the total nutrient loadings and 1to 

### 3 percent of the metals loadings, and baseflow provides an even lower percentage of the total loading.

Analyses of wet and dry seasons, and wet and 

### dry years, revealed that the distribution of loadings betweenjurisdictions and between sources of pollution remain relatively similar to the average year distributions. Point source loadings tend to be more prominent during dry periods, but are still lower than surfacerunoff and rainfall loadings.6.0 POLLUTIONLOADING PROJECTIONS FOR FUTURE LAND USE CONDITIONS

Preliminary loading estimates were also developed for two futureland use scenarios. The scenarios included the five-year future and the buildout future land uses. The methods used to develop these land use scenarios were presented in Section 2.4 of this report.

The results of the future land use analyses are presented in this section. Similar to the existing land use analysis,results are presented for average annual, wet and 

### dry season, and wet and dry year rainfall conditions. Tables are presented which quantify loadings by watershed,by source and byjurisdiction. The values are compared to the existing land use results to identify local and Bay-wide changes.

6.1 FIVE-YEAR FUTURE LAND USE

Tables 6-1 through 6-11 present the loading results for the five-year future land use analysis. The results for the average annual rainfall condition are shown in Tables 6-1 through 6-3. Wet season and dry season results are listed in Tables 6-4 through 6-7, and wet year and dry year results are presented in Tables 6-8 through 6-11.

Table 6-1 shows the average annual loadings by watershed. 

### A comparison of Tables 

### 5-1 (existingland use conditions)and 6-1reveals a small decrease in overall total P loadings, and a small increase in total 

### N and metals loadings. The projected shift in point sources from surface water discharge to land application accounts for reductionsin pollutants, particularly nutrients, in point source loadings. This reduction is offsetby an increase in surfacerunoff loadings due to new development. PhillippiCreek and Whitaker Bayou are still the major contributorsof all four pollutants, and Bowlees Creek is a major contributor of metals loadings.TABLE 6-1

AVERAGE ANNUAL LOADINGS BYWATERSHED FOR FIVE -YEAR FUTURE LAND USE CONDITIONS

Note: Loadingtotals do not include pollutant settling intidaltributaries. Seetext for discussionof senling intributaries. OTHER ISLANDS DIRECTTO BAY BAYSURFACE TOTAL 900 4,241 33,280 129,412 27.94 31.85 54.60 34.32 1.640 8,850 61,730 250,600 1.82 2.09 1.85 2.12 0.29 0.29 0.15 0.30 8.360 51,430 337,460 1,294,680 9.29 12.13 10.14 10.22 1.47 1.68 0.82 1.47 310 2,340 2,470 38,090 0.34 0.55 0.07 0.42 0.054 0.076 0.006 0.060 290 1,880 60.080 93.290 0.32 0.44 1.81 0.46 0.051 0.061 0.146 0.061TABLE 6-2

AVERAGEANNUAL LOADINGS BY SOURCE FOR FIVE

## - YEAR FUTURE LAND USE CONDITIONS

Note: Loadingtotalsdo not include pollutant settlingintidaltributaries. Seetextfor discussionof settling intributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

14.81 43.1% 3.81 11.1% 0.70 2.0% 0.96 2.8% 14.04 40.9% 34.32 AVERAGE YEAR POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL 120,300 48.0%

33,490 13.4%

8,260 3.3% 26,820 10.7% 61,730 24.6% 250,600 LEAD %OF (Ib) TOTAL 34,930 91.7% 300 0.8% 0 0.0% 390 1.0% 2,470 6.5% 38,090 TOTAL N %OF (Ib) TOTAL 622,830 48.1% 11 1,660 8.6% 123,890 9.6%

98,840 7.6% 337,460 26.1% 1,294,680 ZINC %OF (Ib) TOTAL 25.660 27.5%

5,570 6.0% 0 0.0% 1,980 2.1% 60,080 64.4% 93,290

# . TABLE6-3

AVERAGE ANNUAL LOADINGSBYJURISDICTION FOR FIVE 

### - YEAR FUTURE LAND USECONDITIONS

Note: Loading totals do not includepollutantsettling in tidaltributaries. Seetext for discussionof senling intributaries. 

### -

JURISDICTION

SARASOTA CO. SARASOTACITY MANATEECO. ISLANDS BAYSURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33,280 129,412 RUNOFF %OF (in) TOTAL

12.13 35.3% 2.01 5.9% 4.72 13.8% 1.42 4.1% 14.04 40.9% 34.32 AVERAGE YEAR POLLUTANT LOADING Total P %OF

(Ib) TOTAL 111,080 44.3%

19,630 7.8% 42,550 17.0% 15,610 6.2% 61,730 24.656 250,600 LEAD %OF (Ib) TOTAL 15,860 41.6%

6,060 15.9%



# .

11,840 31.1%

1,860 4.9% 2,470 6.5% 38,090 Total N %OF

(Ib) TOTAL 588,130 45.4%

93,060 7.2% 210,870 16.3%

65,160 5.0% 337,460 26.1% 1,294,680 ZINC %OF (Ib) TOTAL 17,510 18.8% 4,610 4.9% 8,850 9.5O/o 2,240 2.4% 60,080 64.4% 93,290TABLE 64

WET SEASON LOADINGSBYWATERSHED

FOR FIVE-YEAR LAND USE CONDITIONS



### I
I Note: Loading totals do not include pollutantsenling in tidaltributaries. Seetextfor discussionofsettling Intributaries.TABLE 6-5

DRY SEASON LOADINGS BYWATERSHED FOR FIVE-YEAR LAND USE CONDITIONS

Note: Loadingtotals do not include pollutantsettling intidal tributaries. Seetextfor discussionof senllng intributaries.TABLE 6-6

WET SEASONAND DRY SEASON LOADINGSBY SOURCE FOR FIVE

## - YEAR FUTURE LAND USE CONDITIONS

SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL

Note: Loading totals do not include pollutant settling intidaltributaries. Seetext for discussionof settling intributaries.

. . .... ,..: ,,.,<\,cs.; SOURCE

SURFACE BASEFLOW SEPTIC POINT SOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL 9.14 43.2% 2.79 13.2% 0.23 1.1% 0.34 1.6% 8.67 40.9% 21.17

RUNOFF %OF (in) TOTAL 5.67 43.1% 1.02 7.7% 0.47 3.6% 0.62 4.7% 5.37 40.9% 13.15 WET SEASON POLLUTANTLOADING

DRY SEASON POLLUTANTLOADING TOTAL P %OF (Ib) TOTAL

74,170 49.3% 24,550 16.3%

4130 2.7% 9.610 6.4% 38.100 25.3% 150,560 LEAD %OF (Ib) TOTAL 21,590 92.1% 200 0.9% 0 0.0% 140 0.6% 1,520 6.5% 23,450 TOTAL N %OF (lb) TOTAL 384,470 49.8%

81,840 10.6% 61,900 8.0% 35,130 4.6% 208,290 27.0% 771.630

TOTAL P %OF (Ib) TOTAL

46,000 46.0%

8,940 8.9% 4,140 4.1% 17,210 17.2% 23,630 23.6% 99,920 ZINC %OF (Ib) TOTAL 15,830 27.4%

4,070 7.1% 0 0.0% 730 1.3% 37,090 64.3% 57,720

LEAD %OF

(Ib) TOTAL 13,410 91.5% 50 0.3%

0 0.0% 250 1.7% 950 6.5% 14,660 TOTALN %OF (lb) TOTAL 238,330 45.6%

29,810 5.7% 61,980 11.9% 63.700 12.2% 129,170 24.7% 522,990 ZINC %OF (Ib) TOTAL

9,820 27.6% 1,510 4.2% 0 0.0% 1,260 3.5% 23.000 64.6% 35,5901 TABLE 6-7

WET SEASONAND DRY SEASON LOADINGS BYJURISDICTION FOR.FIVE -YEAR FUTURE LAND USECONDITIONS

JURISDICTION

SARASOTACO. SARASOTA CITY MANATEECO. ISLANDS BAYSURFACE TOTAL

Note: Loadingtotalsdo not include pollutant settling in tidaltributaries. See text for discussionof settlingintributaries. 

### -

JURISDICTION

SARASOTA CO. SARASOTA CITY MANATEEGO. ISLANDS BAY SURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33.280 129,412

DRY SEASON POLLUTANTLOADING RUNOFF %OF (in) TOTAL 7.50 35.4% 1.24 5.9% 2.92 13.8% 0.85 4.0% 8.67 40.9% 21.17 WET SEASON POLLUTANT LOADING

AREA

(ac) 62,301

7,844 20,226

5,761 33,280 129,412 RUNOFF %OF (in) TOTAL 4.63 35.2% 0.77 5.8% 1.80 13.7% 0.57 4.3% 5.37 4O.go/o 13.15 ZINC %OF (Ib) TOTAL

6,490 18.2% 1,810 5.1% 3,310 9.3%

980 2.8% 23,000 64.6% 35,590 Total P %OF

(Ib) TOTAL 43,630 43.7%

8,050 8.1% 17,270 17.3%

7,340 7.3% 23,630 23.6O/. 99.920 ZINC %OF (Ib) TOTAL 11,030 19.1%

2,800 4.9% 5.540 9.6% 1,260 2.2% 37,090 64.3% 57,720 LEAD %OF

(Ib) TOTAL

9,780 41.7% 3,710 15.8% 7,330 31.3% 1,110 4.7% 1.520 6.5% 23.450 Total

### P %OF

(Ib) TOTAL 67,380 44.8% 11,500 7.636 25,300 16.8%

8,280 5.5% 38,100 25.3% 150,560

Total N %0c (Ib) TOTAL 240,630 46.0%

37,420 7.2% 86,770 16.6% 29,000 5.5% 129,170 24.7O/o 522.990 Total N %OF

(Ib) TOTAL 347,510 45.0%

55,570 7.2% 124,100 16.1% 36,160 4.7% 208,290 27.0% 771,630

LEAD %OF (Ib) TOTAL

6,100 41.6% 2,330 15.9% 4,550 31.0%

730 5.0% 950 6.5% 14,660TABLE 6-8

WET YEAR LOADINGSBYWATERSHED FOR FIVE -YEAR FUTURE LAND USE CONDITIONS

Note: Loading totalsdo not include pollutantsettling intidaltributaries. See textfordiscussionofsenling intributaries.

# . TABLE 6-9

DRYYEAR LOADINGSBYWATERSHED FOR FIVE

## - YEAR FUTURE LAND USECONDiTlONS

Note: Loading totals do not includepollutant settling intidal tributaries. Seetext fordiscussionof sealing intributaries.TABLE 6-1 0

WET YEAR AND DRYYEAR LOADINGS BY SOURCE FOR FIVE-YEAR FUTURELAND USECONDITIONS

SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL

Note: Loadingtotalsdo not includepollutant settling intidaltributaries. Seetextfordiscussionof settling intributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

18.91 41.4% 7.17 15.7% 0.70 1.5% 0.96 2.1% 17.92 39.3% 45.66

RUNOFF %OF (in) TOTAL

11.31 46.2% 0.77 3.2% 0.70 2.9% 0.96 3.9% 10.72 43.8% 24.48 WETYEAR POLLUTANT LOADING TOTAL P %OF (16) TOTAL 153,500 46.5%

63,060 19.1%

8,260 2.5% 26,820 8.1% 78.800 23.8% 330,440

DRY YEAR POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL

91,860 50.8%

6,800 3.8% 8,260 4.6% 26.820 14.8% 47,150 26.1% 180,890 TOTALN %OF (Ib) TOTAL 795,000 47.9% 210,260 12.7% 123,890 7.5%

98.840 6.0% 430,790 26.0% 1,658,780

TOTAL N %OF (Ib) TOTAL 475,710 48.6%

22,710 2.3% 123.890 12.7%

98,840 10.1% 257.730 26.3% 978.880 LEAD %OF (Ib) TOTAL 44,600 91.4% 630 1.3% 0 0.0% 390 0.8% 3,150 6.5% 48.770 ZINC %OF (Ib) TOTAL 32,740 26.8% 10,520 8.6% 0 0.0% 1,980 1.6% 76,700 62.9% 121,940

LEAD %OF

(Ib) TOTAL 26.690 92.0% 40 0.1%

0 0.0% 390 1.3% 1,890 6.5% 29,010 ZINC %OF (Ib) TOTAL 19,570 28.5%

1,140 1.7% 0 0.0% 1,980 2.9% 45,890 66.9% 68,580TABLE 6-1 1

WET YEAR AND DRYYEAR LOADINGSBYJURISDICTION FOR FIVE -YEAR FUTURE LAND USE CONDITIONS

JURISDICTION

SARASOTACO. SARASOTA CITY MANATEECO. ISLANDS BAY SURFACE TOTAL

Note: Loading totalsdo not includepollutantsettling intidaltributaries. See text for discussionof settling intributaries. JURISDICTION

SARASOTACO. SARASOTACITY MANATEECO. ISLANDS BAY SURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33,280 129.412

AREA

(ac) 62,301

7,844 20,226

5,761 33,280 129.412 RUNOFF %OF (in) TOTAL

16.81 36.8%

2.66 5.8% 6.37 14.0% 1.89 4.1% 17.92 39.3% 45.66

RUNOFF %OF (in) TOTAL 8.02 32.8% 1.44 5.9% 3.28 13.456 1.00 4.1% 10.72 43.8% 24.48 WET YEAR POLLUTANT LOADING

DRY YEAR POLLUTANT LOADING ZINC %OF (Ib) TOTAL 24,460 20.1%

5,980 4.9% 11,900 9.8%

2,900 2.4% 76,700 62.9% 121,940 LEAD %OF

(Ib) TOTAL 20,340 41.7%

7,730 15.8% 15,190 31.1%

2,360 4.8% 3,150 6.5% 48,770 Total P %OF

(Ib) TOTAL 150,790 45.6%

24,840 7.5% 56,410 17.1% 19,600 5.9% 78,800 23.8% 330.440

Total P %OF

(Ib) TOTAL 76,100 42.1% 15,030 8.3% 30.450 16.8% 12,160 6.7% 47,150 26.1% 180,890 Total N %OF (Ib) TOTAL 753.990 45.5% 118,370 7.1% 273,300 16.5%

82,330 5.0% 430,790 26.0% 1,658,780

LEAD %OF (Ib) TOTAL 12,010 41.4%

4,640 16.0% 9,030 31.1% 1,440 5.0% 1.890 6.5% 29,010 Total N %OF

(Ib) TOTAL 443,040 45.3%

71,150 7.3% 156,670 16.0%

50.290 5.1% 257,730 26.3% 978,880 ZINC %OF (Ib) TOTAL 11,390 16.6%

3,420 5.0% 6,230 9.1% 1,650 2.4% 45,890 66.9% 68,580 

## -The average annual loadings by source are presented in Table 

### 6-2. The results for the five-year future land use are similar to the results forthe existing land use. The total runoff for the study area increased slightly, from 

### 34.26 to 

### 34.32inches per year. The percentage of the total runoff due to surface runoff increased slightly (from 

### 42.6% to 

### 43.1%),while the percentagesfor the other sources were the same or slightlylower. For pollution loadings, the percentage of total loading due to point sources decreased noticeably, whereas the nonpoint source percentage exhibited the largest increase. Again, a decrease in the amount of pollution due to point sourcesis projected based on a shift from surface water discharge to land application. Increases in nonpoint source loadings are due to future development. Baseflow loadings decrease slightly, because new development results in less groundwater recharge and 

### a corresponding reduction in baseflow quantity. Septictank and rainfall loadings are assumed to be the same as for existing conditions. Surface runoff 

### is still the major source of total N, total 

### P and lead, whereas rainfall is the major source of zinc.

Table 

### 6-3 lists the average annual loadings byjurisdiction. 

### A comparison to the results for the existing land use condition (see Table 

### 5-3) shows an increase 

### in loadingsfor Sarasota County and Manatee County, a decrease in loadingsfor the City of Sarasota,and the same loadings for the BarrierIslands. No changes were projected forthe Barrier Islands during the 5-yearplanning horizon because no 

### DRIs were identified in the study

area, and the load to the Bay surface due to rainfall was not expected to change. 

### In Sarasota County, the new development and corresponding increase in surfacerunoff is the

reason for the loading increases. Transition from surface water dischargeto land applicationfor the City of Sarasota wastewater treatment plant is the reason for the reduced loadings from the City. In Manatee County, increased wastewater flows account .for the loading increases. Similar to existing conditions, the jurisdictions of Sarasota County, Manatee County and the Bay Surface together account for 

### 90 percent of the total runoff and 

### 79 to 

### 93 percent of the pollutants analyzed.The wet season and dry season results for the five-year future land use scenario, as presented in Tables 6-4 through 6-7, show the same trends that were identified in the analysis for existingland use conditions. Based on the data in Tables 6-4 and 6-5, about 60 percent of the annual loading occurs during the wet season, and 40 percent occurs during the dry season, forsunoff, nutrients and metals. Surface runoff and rainfall are the major loading sources for all of the pollutants, as shown in Table 6-6. Surfacerunoff tends to provide a larger percentage of loading during the wet season than during the dry season, whereas point sources and septic

### tanks provide a larger percentage of the 

### total loading during the dry season than during the wet season. However, the total contribution due to point sources and septic tanks 

### is less than contributions due to surfacerunoff and rainfall. 

### In Table 6-7, the distributionsof runoff and loadings byjurisdiction for the wet and the dry seasons are only slightly different than the distributions for the average annual loadings, shown 

### inTable 6-3.

Tables 6-8 through 6-11 present the five-year futureland use scenario results for the wet
year and dry year analysis. In comparison with the average annual five-year future loadings, the values in Tables 6-8 and 6-9 show that loadings for all pollutants will be 28

to 32 percent higher during the wet year, and 24 to 28 percent lower during the dry year. Results in Table 6-10 indicate that the wet year and dry year load distribution by source are similar to the distribution for the averagerainfall year. Similarly, the results in Table 6-11indicate that the wet year and dry year distributions byjurisdiction are virtually the

same as for the average rainfall year.

The values in Tables 6-1through 6-11 do not include the effects of pollutant settling

### in the tidal tributaries. As discussed in Section 5.1, the application of the delivery ratios establishedfor the tidal tributaries did not produce substantial changes

### in total loadings or the distributionof loadings between sources orjurisdictions. The reduction in surface loadings due to the delivery ratios was only 6 percent for total 

### P and zinc, 

### 3 percent for total N and 13percent for lead. When considering the loadings from all sources, the loading reductions due to settling were 3 percent for total 

### P, 12percent for lead, and 1percent for total 

### N and zinc. With regard to source distribution, the percentage of total loading due to surfacerunoff changed by 2 percentagepoints or less, and the percentages for the other sourceschanged by no more than 1percentagepoint. Distribution by jurisdiction remained essentially unchanged, with differences alwaysless than 

### 1 percentage point.

6.2 BUILDOUTFUTURE 

### LAND USE

Tables 6-12 through 6-22 present the loading results forthe buildout future land use analysis. The buildout future land use includes development in all areas identified in the ComprehensivePlans for Manatee and SarasotaCounties. The results for the average annual rainfall condition are shown in Tables 6-12 through 6-14. Wet season and dry season results are listed in Tables 6-15 through 6-18, and wet year and dry year results are presented in Tables 6-19 through 6-22.

Table 6-12 shows the average annual loading results by watershed. 

### A comparison of Tables 5-1 (existingland use conditions) and 6-12 show an overall increase from existing loadings for all pollutants. The increase 

### in loading for total 

### P, total 

### N and zinc ranges from 10to 15percent, whereas the increase for lead is 35percent. The percent increase in loadings for zinc and the nutrients 

### is relatively small because of the substantial loadings attributed to rainfall and baseflow. Lead, on the other hand, has very low concentrations in baseflow and rainfall but moderate to high values in runoff from urbanized areas. Consequently,projected increases in urban area result in a substantially larger annual loading of lead from the study area.

In some cases, watersheds that had minor impacts under existingland use conditionshave a substantially larger contributionin the buildoutfuture scenario. For total 

### P, Phillippi Creek and South Bradenton are still the largest watershed contributors, but the loading from South Creek has increased 46percent, suchthat the total loading from South Creek 

### is greater than the Whitaker Bayou loading. The Phillippi Creek, SouthBradenton, South

# . TABLE 6-12

AVERAGEANNUAL LOADINGSBYWATERSHED FOR BUILDOUTFUTURE LAND USE CONDITIONS

Note: Loading totals do not include pollutant settling intidaltributaries. Seetextfor discussionof settling intributaries.TABLE 6-13

AVERAGE ANNUAL LOADINGS BY SOURCE FOR BUILDOUTFUTURE LAND USE CONDITIONS

Note: Loading totalsdo not include pollutant settling in tidaltributaries.Seetextfor discussionof settling intributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINT SOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

17.79 47.7% 3.34 9.0% 0.70 1.9% 1.39 3.7% 14.04 37.7% 37.26 AVERAGEYEAR POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL 151,340 52.4% 29,380 10.2%

8,270 2.9% 37,940 13.1% 61,730 21.4% 288,660 TOTAL N %OF (Ib) TOTAL 790,360 53.0%

98,030 6.6% 124,060 8.3% 141,230 9.5% 337.460 22.6% 1,491,140 LEAD %OF (Ib) TOTAL 46,900 93.5% 260 0.5% 0 0.0% 550 1.1%

' 2,470 4.9% 50,180 ZINC %OF (Ib) TOTAL 34,990 34.1%

4,910 4.8% 0 0.0% 2,740 2.7% 60,080 58.5% 102,720TABLE 6-14

AVERAGE ANNUAL LOADINGSBYJURISDICTION FOR BUILDOUT FUTURE LAND USE CONDITIONS

Note: Loadinglotalsdo not include pollutant settling in tidaltributaries. Seetext for discussion of settling intributaries. JURISDICTION

SARASOTACO. SARASOTA

### CITY MANATEECO. ISLANDS BAY SURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33,280 129,412 RUNOFF %OF (in) TOTAL

14.17 38.0%

2.06 5.5% 5.57 14.9% 1.42 3.8% 14.04 37.7% 37.26 AVERAGE YEAR POLLUTANTLOADING Total P %OF

(Ib) TOTAL 139.670 48.4%

20,880 7.2% 50,770 17.6% 15,610 5.4% 61.730 21.4% 288.660 Total N %OF (Ib) TOTAL 731,660 49.1%

95,430 6.4% 261,430 17.5%

65,160 4.4% 337,460 22.6% 1,491,140 LEAD %OF (Ib) TOTAL 24,440 48.7%

6,100 12.2% 15,310 30.5%

1,860 3.7% 2,470 4.9% 50,180 ZINC %OF (Ib) TOTAL 24,380 23.7%

4,790 4.7% 11,230 10.9%

2,240 2.2% 60.080 58.5% 102,720TABLE 6-15

WET SEASON LOADINGSBYWATERSHED FOR EUlLDOUT FUTURE LAND USECONDiTlONS

Note:Loadingtotals do not include pollutantseniing in tidal tributaries. Seetextfor discussionof seniing Intributaries.TABLE 6-17

WET SEASON AND DRY SEASON LOADINGS BY SOURCE FOR BUILDOUT FUTURE LAND USE CONDITIONS

SOURCE

SURFACE BASEFLOW SEPTIC POINT SOURCE RAINFALLTOTAL

Note: Loadingtotalsdo not includepollutantsettling in tidaltributaries. Seetext for discussionof settlingintributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

10.98 48.1%

2.45 10.7% 0.23 1.0% 0.49 2.2% 8.67 38.0% 22.82

RUNOFF %OF (in) TOTAL 6.81 47.2% 0.89 6.2% 0.47 3.2% 0.90 6.2% 5.37 37.2% 14.44 WET SEASON POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL

93,290 54.7% 21.550 12.6%

4,130 2.4% 13,520 7.9% 38,100 22.3% 170,590

DRY SEASON POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL

57,880 49.1%

7,830 6.6% 4,140 3.5% 24,410 20.7% 23,630 20.0% 117,890 TOTALN %OF (Ib) TOTAL 487,860 55.5%

71,860 8.2% 61,990 7.0% 49,710 5.7% 208.290 23.7% 879,710

TOTAL N %OF (Ib) TOTAL 302,480 49.5%

26,170 4.3% 62,070 10.2% 91,540 15.0% 129.170 21.1% 611,430 LEAD %OF (Ib) TOTAL 28,950 93.8% 180 0.6%

0 0.0% 210 0.7% 1,520 4.9% 30.860 ZINC 'OF (Ib) TOTAL 21,580 34.1%

3,580 5.7% 0 0.0% 1,000 1.6% 37,090 58.6% 63,250

LEAD %OF

(Ib) TOTAL 17,980 93.1% 40 0.2%

0 0.0% 340 1.8% 950 4.9% 19,310 ZINC %OF (Ib) TOTAL 13,390 33.9%

1,330 3.4% 0 0.0% 1,750 4.4% 23,000 58.3% 39,470

# .. TABLE 6-1 8

WET SEASONAND DRY SEASON LOADINGSBYJURISDICTION FOR BUILDOUTFUTURE LAND USE CONDITIONS

Note: Loading totalsdo not include pollutant settling in tidaltributaries. Seetextfor discussionof settlingintributaries. JURISDICTION

SARASOTACO. SARASOTACtTY MANATEECO. ISLANDS BAYSURFACE TOTAL WET SEASON POLLUTANT LOADING

JURISDICTION

SARASOTA CO. SARASOTACITY MANATEECO. ISLANDS BAYSURFACE TOTAL AREA (ac) 62,301

7.844 20,226

5.761 33,280 129.412

RUNOFF %OF (in) TOTAL 5.51 38.1% 0.79 5.5% 2.19 15.2% 0.57 4.0% 5.37 37.2% 14.44 AREA

(ac) 62,301

7,844 20,226

5,761 33,280 129,412 RUNOFF %OF (in) TOTAL

8.67 38.0% 1.27 5.6O/~ 3.38 14.8% 0.85 3.7% 8.67 38.0% 22.82 ZINC %OF (Ib) TOTAL 15,060 23.8%

2,890 4.6O/o 6,950 11.0% 1,260 2.0% 37,090 58.6% 63.250 LEAD %OF

(Ib) TOTAL 15,050 48.8%

3,730 12.1%



# .9,450 30.6% 1.110 3.6% 1,520 4.9% 30,860 Total P %OF

(Ib) TOTAL 82,960 48.6% 12,120 7.1% 29,130 17.1%

8.280 4.9% 38.100 22.3% 170,590

DRY SEASON POLLUTANT LOADING Total N %OF

(Ib) TOTAL 428,910 48.8%

56,800 6.5% 149,550 17.0% 36.160 4.1% 208,290 23.7% 879,710

ZINC %OF (Ib) TOTAL

9,310 23.6% 1,900 4.8% 4.280 10.8%

980 2.5% 23,000 58.3% 39,470 LEAD %OF

(Ib) TOTAL

9,410 48.7% 2,350 12.2% 5,870 30.4%

730 3.8% 950 4.9% 19,310 Total P %OF

(Ib) TOT& 56,620 48.0%

8,680 7.4% 21,620 18.3%

7,340 6.2% 23,630 20.0% 117.890 Total N %OF (Ib) TOTAL 302,740 49.5%

38,570 6.3% 111,950 18.3% 29,000 4.7% 129.170 21.1% 611,430TABLE 6-19

WETYEAR LOADINGSBY WATERSHED FOR BUiLDOUT FUTURE LAND USE CONDITIONS

Note: Loading totalsdo not include pollutant senlingintidaltributaries. Seetext for disarssionof senllng Intributaries. OTHER ISLANDS DIRECTTO BAY BAY SURFACE TOTAL 38.53 43.93 69.70 49.02 900 4.241 33,280 129,412 2.260 12,210 78,800 373,540 2.51 2.88 2.37 3.1 1 0.29 0.29 0.15 0.31 11,090 67,510 430,790 1,889,530 12.32 15.92 12.94 14.96 1.41 1.60 0.82 1.47 400 3.250 3.150 64,060 0.44 0.77 0.09 0.65 0.051 0.077 0.006 0.065 400 2.670 76.700 133,310 0.44 0.63 2.30 0.69 0.051 0.063 0.146 0.065TABLE 6-21

WETYEAR AND DRY YEAR LOADINGS BY SOURCE

FOR BUILDOUT FUTURE LAND USE CONDITIONS



### -

SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL

Note: Loadingtotalsdo not include pollutant settlingintidaltributaries. Seetextfordiscussionof settling intributaries. SOURCE

SURFACE BASEFLOW SEPTIC POINTSOURCE RAINFALLTOTAL RUNOFF %OF (in) TOTAL

22.71 46.3%

6.29 12.8% 0.70 1.4% 1.39 2.8% 17.92 36.Vh 49.02

RUNOFF %OF (in) TOTAL

13.59 50.2% 0.68 2.5% 0.70 2.6% 1.39 5.1% 10.72 39.6% 27.08 WET YEAR POLLUTANT LOADING TOTALP %OF (Ib) TOTAL 193,150 51.7%

55,380 14.8%

8,270 2.2% 37,940 10.2% 78,800 21.I% 373,540

DRY YEAR POLLUTANT LOADING TOTAL P %OF (Ib) TOTAL 115,620 54.8%

5,990 2.8% 4,140 2.0% 37,940 18.0% 47,150 22.4% 210,840 TOTAL N %OF (Ib) TOTAL 1,008,890 53.4%

184,560 9.8% 124,060 6.6% 141,230 7.5% 430.790 22.8% 1,889,530

TOTALN %OF (lb) TOTAL 603,760 52.7%

19,950 1.7% 124,060 10.8% 141,230 12.3% 257,730 22.5% 1 ,I 46.730 LEAD %OF (Ib) TOTAL 59,830 93.4% 530 0.8% 0 0.0% 550 0.9% 3.150 4.9% 64.060 ZINC %OF (Ib) TOTAL 44,660 33.5%

9.210 6.9% 0 0.0% 2,740 2.1% 76.700 57.5% 133.310

LEAD %OF

(Ib) TOTAL 35,860 93.6% 30 0.1%

0 0.0% 550 1.4% 1,890 4.9% 38,330 ZINC %OF (Ib) TOTAL 26,720 35.0%

1,000 1.3% 0 0.0% 2,740 3.6% 45.890 60.1% 76.350TABLE 6-22

WETYEAR AND DRYYEAR LOADINGS BYJURISDICTION FOR BUILDOUTFUTURE LAND USE CONDITIONS

Note: Loadingtotalsdo not include pollutant settlingintidaltributaries.Seetextfor discussionof settling intributaries. JURISDICTION

SARASOTACO. SARASOTACITY MANATEECO. ISLANDS BAYSURFACE TOTAL

JURISDICTION

SARASOTA CO. SARASOTA CITY MANATEEGO. ISLANDS BAYSURFACE TOTAL AREA (ac) 62,301

7,844 20,226

5,761 33,280 129.412 RUNOFF '10 OF (in) TOTAL

19.15 39.1%

2.72 5.5% 7.33 15.0% 1.89 3.9% 17.92 36.6% 49.02

AREA

(ac) 62,301

7,844 20,226

5,761 33,280 129,412 WET YEAR POLLUTANT LOADING Total P %OF

(Ib) TOTAL 183,840 49.2%

26,090 7.0% 65,210 17.5% 19.600 5.2% 78.800 21.1% 373,540

RUNOFF %OF (in) TOTAL

9.82 36.3% 1.50 5.5% 4.04 14.9% 1.00 3.7% 10.72 39.6% 27.08 Total N %OF (Ib) TOTAL 925,240 49.0% 120.740 6.4% 330,430 17.5%

82,330 4.4% 430,790 22.8% 1,889.530

DRY YEAR POLLUTANT LOADING LEAD %OF

(Ib) TOTAL 31,230 48.8%

7,770 12.1% 19,550 30.5%

2,360 3.7% 3,150 4.9% 64.060

Total P %OF

(Ib) TOTAL 101,110 47.0%



### . 16,290 7.6% 38,260 17.8% 12,160 5.7% 47.150 21.9% 214.970 ZINC %OF (Ib) TOTAL 32,790 24.6%

6,160 4.6% 14,760 11.1%

2,900 2.2% 76,700 57.5% 133,310

TotalN %OF (Ib) TOTAL 563,320 49.1%

73,600 6.4% 201,790 17.6%

50,290 4.4% 257,730 22.5% 1,146,730 LEAD %OF (Ib) TOTAL 18,610 48.6% 4,700 12.3% 11,690 30.5%

1,440 3.8% 1,890 4.9% 38,330 ZINC %OF (Ib) TOTAL 17,040 22.3% 3,610 4.7% 8,160 10.7% 1,650 2.2% 45,890 60.1% 76,350

### Creek and Whitaker Bayou watersheds are also the largest contributors of total N in the study area. PhillippiCreek, Whitaker Bayou and Bowlees Creek are still the major contributors of lead and zinc loadings. Like South Creek, Matheny Creek also exhibits substantialloading increases, such that the loading from Matheny Creek iscomparable to the WhitakerBayou loadingsfor all of the analyzed pollutants.

The average annual loadingsby source arepresented in Table 

### 6-13. A 

### comparisonof Tables 

### 5-2 and 

### 6-13 shows that the total study area flow increased from 

### 34.26inches to 

### 37.26 inches. Surfacerunoff 

### is the major factor, increasing from 

### 14.58inchesto 

### 17.79 inches. Point source flows also increase, whereas baseflow is 

### lower, and septictank 

### and rainfall flows are the same. As 

### expected, the increasein surfacerunoff also generates increased surfacerunoff loadings,with increases ranging from 

### 28 percent for total P to 41 

### percent for zinc. The increase in surfacerunoff due to urban development also results in

a decreasein baseflow quantity, sobaseflow loading isless forthe buildout scenario. Point source loading is 

### greater than existing conditionsforthe buildout scenario, due to the increase in wastewaterflows generatedby the buildout population. Rainfall and septic tank loadings are assumed to be the same for the existing and buildout scenarios, the lam because all future developmentwas assumed to be sewered rather than servedby septic tanks. 

### Overall, the major sources of nutrients and metals are surface runoff and rainfall.

Table 

### 6-14lists the average annual loadingsbyjurisdiction. A 

### comparison of these results with the results forthe existing land use condition (see Table 

### 5-3) shows an increase in loadingsfor Sarasota and Manatee Counties, a decreasein loadingsfor the City of Sarasota, and the sameloadings for the Barrier Islands and the Bay Surface. Future land use changes forthe islands were not considered because comprehensive planning documents were not available. 

### In Sarasota County, loading increases ranged from 

### 27 percent for total N to 

### 66 percent for lead, primarily due to surfacerunoff. 

### In Manatee County, future urbanization accounted for loading increases ranging from 

### 23 percent for total P to 

### 29 percent for lead. Reductionsin City of Sarasota loadings ranged from 1 

### percent for lead to 

### 17 percent fortotal P, due to transition from surface waterdischarge to land application of wastewater. Because most of the future developmentis in Sarasota County, the relative percentage of total loading contributed by Sarasota County increased, whereas the percentage contributedby each of the other jurisdictions typically either decreased or remained the same.

The wet season and 

### dry season results for the buildoutfuture land use scenario, 

### as presented in Tables 

### 6-15 through 

### 6-18, show trends similar to those identifed in the analysis of existing land use conditions. Based onthe datainTables 

### 6-15 and 

### 6-16, about 

### 60 percent of the annual loading occurs during the wet season, and 

### 40 percent occurs during the dry season,forrunoff, nutrients and metals. Surfacerunoff and rainfall are the major loading sources for all of the pollutants, as shownin Table 

### 6-17. Surfacerunoff tends to provide a larger percentage of loading during the wet season than during the dry season, whereas point sources and septic tanks provide a larger percentage of the total load during the 

### dry season than during the wet season. 

### In fact, the combination of point

source and septic tank nutrient loadings actually exceed the rainfall nutrient loadings during the dry season. 

### In Table 

### 6-18, the distributions ofrunoff and loadings by jurisdiction for the wet and dry seasons 

### are only slightly different than the distributions for the average annual loadings, shown in Table 

### 6-14. 

## .



# .
Tables 

### 6-19 through 

### 6-22 present the buildout future land use scenario results for the wet
year and 

### dry year analysis. In comparison with the average ye&loadings, the values in Tables 

### 6-19 and 

### 6-20 show that loadings for 

### all pollutants are 

### 27 to 

### 30 percent higher during the wet year and 

### 23 to 

### 26 percent lower during the dry year. Results in Table 

### 6-21
indicate that the wet year and dry year loading distributions by source 

### are essentially the

same 

### as the distribution forthe average rainfall year. Similarly,the results in Table 

### 6-22 indicate that the wet year and dry year distributions byjurisdiction are virtually the same

as for the average rainfall year.

The values in Tables 

### 6-12through 

### 6-22 do not include the effects of pollutant settlingin the tidal tributaries. As discussed in Section

### 5.1, the application of the delivery ratiosestablished for the tidal tributaries did not produce substantial changes in total loadings or the distribution of loadingsbetween sources orjurisdictions. The reduction in surface loadings due to the deliveryratios was only 

### 6 percent for total 

### P and zinc, 

### 3 percent for total 

### N and 

### 13percent for lead. When considering the loadingsfrom 

### all sources, the loading reductions due to settling were 

### 3 percent fortotal P, 

### 12percent for lead, and 1 percent for total 

### N and zinc. With regard to source distribution, the percentage of total loading due to surfacerunoff changed by 

### 2 percentage points or less, and the percentages for the other sources changed by no more than 

### 1percentagepoint. Distribution by jurisdiction remained essentially unchanged, with differences alwaysless than 

### 1 percentagepoint.7.0 SUMMARY



### In Phase I of the Sarasota Bay National Estuary Program Point and Nonpoint Source Loading Assessment, existing data were used to quantify the loadings of nutrients and metals to Sarasota Bay. Loadings were estimated forthree different land use scenarios: existing, fiveyear future and buildout future. The three scenarios were investigated to establish current loading trends and to project how these trends may change in the future.

The results of the analysis for the average rainfall year are presented graphicallyin Figures 7- 1 through 7-10. Figures 7-1 through 7-5 are stacked bar graphs which show the distribution of average annual loadingsbetween the watersheds that comprise the study area. Results are presented for total runoff, total P, total N, lead and zinc. In Figures 7-6 through 7-10, the bar graphs show the distribution by source for the same five constituents. 

### In all of the figures, values are presented for all three land use scenarios.

Figures 7-1 through 7-5 show that the Phillippi Creek, Whitaker Bayou, Bowlees Creek and South Creek watersheds account for over half of the runoff and total loadingsto the Bay, excluding rainfall. Phillippi Creek and Whitaker Bayou contribute a large percentage of the total loadings for both the nutrients and the metals. In contrast,Bowlees Creek has a greater relative impact on metals loadingsthan on nutrient loadings, and South Creek has a greater relative impact on nutrient loadings than on metals loadings. This isbecause Bowlees Creek is highly industrialized relative to the other watersheds, whereas South Creekisprimarily rural.

The figures also show that five-year futureloadings will be similarto existing loadings, but that the buildout future loadings will be considerably higher. The results show a very small increasein total runoff volume, a small decrease in total P loadings, and a small increase in total N and metals loadings for the five-year scenario. Loading increases due to increased urbanization are offsetby loading reductions due to changesin wastewater disposalmethods.

### EXISTING 5-YR 

### FUTURE BUllDOUl

Land Use Scenario Rainfall PhilippiCreek Whitoker Bayou Bowlees Creek 

# 1223South Creek 

# a Other

Figure 7-1. Flow Distributionby Watershed in Sarasota Bay

### NEP Study Area.EXISTING 5-YR FUTURE BUllDOUI

Land Use Scenorio 

## @ Rainloll PhilippiCreek Whiloker Boyou Bowlees Creek 

### [Za South Creek 

# a Other

~i~ure 7-2. Total P Distribution byWatershed inSarasotaBay NEPStudyArea.EXISTING 5-YR FUTURE BUllOOUT

Land Use Scenario Rainfall philippi Creek Whitaker Bayou BowleesCreek 

## jZS]Saulh Creek Olher

Figure 7-3. TotalNDistributionbyWatershed inSarasota Bay NEPStudy Area.EXISTING 5-YR FUTURE BUllOOUT

Lond Use Scenario Rainfall Philippi Creek 

# a Wnitoker Bayou 

# 618]BowleesCreek 

## [m South Creek Other

Figure7-4. LeadDistributionbyWatershed inSarasotaBay NEPStudyArea.EXISTING 5-YR FUTURE BUILDOUT

Lond Use Scenario Roinfoll ~hlippi Creek Whitaker Boyou BowleesCreek 

## IZZ]Soulh Creek Other

Figure 7-5.Zinc Distributionby Watershed inSarasota Bay NEPStudyArea.EXISTING 5-YR FUTURE BUILDOUT

Lond Use Scenario Roinfoll Point Source Septic Tanks Bosefiow Surfoce Runoff

Figure 7-6. Flow DistributionbySource in Sarasota BayNEPStudyArea.EXISTING 5-YR FUTURE BUILDOUT

Land Use Scenario Rainfall Point Source Septic Tanks 

### [aSI Boseflow 

# 1ZZ]Surfoce Runoff

Figure7-7. Total PDistribution by Source inSarasotaBay NEPStudyArea.. EXISTING 5-YR FUTURE BUllDOUT

Land Use Scenario 

## @Rainfall Painl Source Seplit Tonks 

## 188] Boseflow 

# a Sutfoce Runoff

Figure 7-8. Total NDistributionby Source inSarasota Bay NEPStudyArea." EXISTING 5-YR FUTURE BUILDOUT

Land Use.Scenario Rainfall 

# a Point Source Septic Tonks Boseflow Surfoce Runoff

Figure7-9. Lead Distributionby Source inSarasota Bay NEP StudyArea.EXISTING 5-YR FUTURE BUllOOUT

Lond Use Scenaria Rainfall Point Source 

# a Seplic Tanks Baseflow Surloce Runoff

Figure7-10. Zinc DistributionbySource inSarasdta Bay

### NEP StudyArea.

### For the buildout scenario,however, loadings are higher for all 

### constituents. The figures generally show increased loadings for all 

### of the watersheds, due to impacts of increasing urbanization.

Figures 7-6through 7-10 indicatethat surface runoff and rainfall are currently the most important factors in determining total loadings to the Bay. The two major sources account for 84percent of the total runoff, and 71to 98 percent ofthe nutrient and metal loadings. Of the two sources, surfacerunoff 

### is the largest source of total 

### P, totalN and lead, whereas rainfalI is the largest source of 

### zinc.



# . As shown 

### in the figures, point sources and septic 

### tanks are less significant than surface runoff and rainfall. Point source loadings 

### are relatively low becausemost of the treatment facilities achieve Advanced WastewaterTreatment (AWT) standards. Most of the facilities also discharge via land application (irrigation, percolationponds, drainfields) which removes much

or all of the effluent pollutant load via plant uptake or soilremoval mechanisms. Septic 

### tank loadings are not a major contributorfor several reasons. One is 

### that Sarasota County and Casey Key are the only parts of the study area in 

### which septic 

### tanks are in 

### use. In 

### addition, the failurerate of septic tanks in Sarasota County isbelieved to be low, based on repair permit data from the CountyHealth Department Finally, because of the low hydraulic conductivity and hydraulic gradients in the surficial aquifer, the travel time from any septic tank to the Bay or one of its tributaries isprobably on the order ofmonths oryears. With some pollutant removal occurring as the waste travels through the aquifer, itislikely that
most of the septic tank 

### effluentloading does not reach the Bay. However, the septic tank 

### loadings may result in localizedwater quality impacts,particularly in areas ofhigh septic 

### tank densities, relatively steephydraulic gradients, and relatively short travel distances from the septic tanks 

### to the receiving waters.

A 

### comparison of existing and future distributions indicatesthat surface runoff wiU have an increasing impact on Bay loadings, while the impact of other sources will decrease orremain the same. With increased urban development, more surfacerunoff is 

### generated and lessrecharge occurs, resulting in lower baseflow quantities. Because new development

### is typically served by collection systemsrather than septic tanks, the septic tank loading is not expected to increase in the future. Wastewater quantities will increase in the future asthe population increases, but the combination of 

### AWT effluent quality and land application of the effluent results in a relatively low contribution to 

### Bay loading. Rainfall loadings 

### are assumed

to be constant

The estimates presented here will be used as input 

### to Phase 

### 3 of the Sarasota Bay NEP Point and Nonpoint Source Loading Assessment. In Phase 

### 3, alternativemanagement strategies for control of Bay loadings will be identified and evaluated. These strategiesmay include nonstructural controls (e.g., land use controls), structural stormwater controls (e.g., wet detention basins, infiltrationbasins) and point source controls (e.g., increased use of effluent for irrigation). Both the water quality benefits and the costs of alternative strategies will be assessed. Based on the analysis, selected management strategies will be recommended.

### 8.0 REFERENCES

Ambrose,R.B., T.A. Wool, J.P. Connolly, and R.W. Schanz, "WASP4, A Hydrodynamic and Water Quality Model

## - Model Theory, User's Manual and Programmer's Guide (Draft)," U.S. Environmental Protection Agency, Office of Research and Development, Environmental ResearchLaboratory, Athens, Georgia,August 1990.
Bowie, G.L., W.B. Mills, D.B. Porcella, C.L. Campbell,J.R. Pagenkopf, G.L. Rupp, K.M. Johnson,P.W.H. Chan, S.A. Gherini and 

### C.E. Chamberlin, "Rates, Constants, and Kinetics Formulationsin 

### SurfaceWater Quality Modeling (Second Edition)," EPAl60013-851040, U.S. EnvironmentalProtection Agency, Office of Research and Development, EnvironmentalResearch Laboratory, Athens, Georgia, June 1985.
Briley 

### ,Wild & 

### Associates, Inc., "Master Stormwater Drainage Plan Areas "A" and "B"," prepared for Manatee County Public Works Department, 1984.
Camp Dresser & 

### McKee, "Southeast Area Study Model Update," prepared forManatee County Planning and Development Department, March 1987.
Camp Dresser &

### McKee, "Sarasota Bay Water QualityTrend Evaluation, Progress Report No. 1,"prepared for Mote Marine Laboratory, November 1990.
Camp Dresser &

### McKee, "LakeManatee Watershed Water Resources Development Report (FinalDraft)," prepared for the Manatee County Public Works Department,May 1991.
Camp Dresser & 

### McKee, "Sarasota County Stormwater~&ter Plan Final Report," prepared for the SarasotaCounty Commission and the Sarasota County Transportation Department,March 1987.
Camp Dresser &

### McKee, "An

### Assessment of StormwaterManagement Programs," prepared for the Florida Department of EnvironmentalRegulation, December 1985.
Delos, C.G., W.L. Richardson, 

### J.V. DePinto, P.W. Rogers, K. Rygwelski, J.P. St. John, W.L. Shaughnessy, T.A. Faha, and W. N. Christie, "Technical Guidance Manual for PerformingWasteload Allocations, Book 11: 

### Streams and Rivers, Chapter 3, Toxic Substances,"EPA-44014-84-022, U.S. Environmental ProtectionAgency, Office ofWater Regulations and Standards, Washington, DC, 1984.
Hand, J., 

### V. Tauxe, M. Friedemann and L. Smith, "1990 Florida Water Quality Assessment 305(b) TechnicalAppendix," Florida Department of Environmental Regulation, Division ofWater Management, Bureau of Surface Water Management, Standards and Monitoring Section, June 1990.

### Hand, J., V. Tauxe, and M. Friedemann, "Sarasota Bay Basin Technical Report: An Appendix of the 305(b)Water Quality Assessment for the State of Florida," Florida Department of EnvironmentalRegulation, Division ofWater Managemenf Bureau of Surface Water Management, Standards and Monitoring Section, July 1988. Heyl, M.G. and L.K. Dixon,"WaterQuality 

### Status and Trendsin Sarasota Bay (1966- 1986)," presented at the SarasotaBay Area ScientificInformation Symposium, April 1987.
Metcalfe,

### J., R. Wagner and A. Stoddard, "Development of Heavy Metal Wasteload Allocationsfor the State of North Carolina," prepared for the U.S. Environmental Protection Agency, Washington,DC, 1984.
Ostendorf,D.W., Modeling Contamination of ShallowUnconfined Aquifers through Infitration Beds," Water Resources Research, Vol. 22, No. 

### 3, March 1986, pp. 375-382.
Pettygrove,G.S. and T. Asano (editors), "Irrigationwith Reclaimed Municipal Wastewater



### - A Guidance Manual," prepared by the Department of Land, 

### Air and Water Resources, University of California,Davis, prepared for the California State Water Resources Control Board, Lewis Publishers,Inc., 1985. Priede-Sedgwick,Inc., "Tampa Bay Nationwide Urban Runoff Program Study, Phase 11, 

### Task II.3: Precipitation Quantity and Quality," February 1983.
Richardson, W.L., R. Brown, F. Gawronski, K. 

### McGunagle, and R. Wethington, "User's Manual for the Transport and Fate Model MICHRN," U.S. Environmental Protection Agency, Large Lake Research Station, Grosse nle, Michigan, 1983.

Southwest Florida Water Management District, "GroundwaterResource Availability: Sarasota County, Florida," ResourceManagement and Planning Department, March 1988.

U.S. EnvironmentalProtection Agency, "Fate of Priority Pollutantsin Publicly Owned Treatment Works, Final Report, Volume 

### I," EPA 44011-821303, Effluent Guidelines Division, Washington, DC, September 1982.

U.S. EnvironmentalProtection Agency, "Results of the Nationwide Urban Runoff

. 

### Program: Volume I 

### Final Report," Water Planning Division, Washington, DC, December 1983.
Wanielista,M.P., "Evers Reservoir Hydrologic Study," University of Central Florida, Orlando, Florida, September 1989.APPENDIX A

STORET WATER QUALITY DATA FOR TRIBUTARIES TO SARASOTA BAYWHITAKER BAYOUATTRI-PAR DR 

### - BRK

TOTAL P (MGIL)

0.170 0.298 0.234 0.325 0.609 0.762 1.092 0.398 0.944 0.404 0.193 0.132 0.351 0.320 0.554 0.406 0.188 0.226 0.307

0.300 0.445

0.551 0.354 0.353 0.386

0.425 0.431 0.282 0.444 0.246 0.378 0.729 0.318 0.456 0.480 YEAR

75 

## n 78 78 80 80 80 81

82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 85 86 86 86 87 87 87 87 88 88 88 88 89 89 MONTH

1 11

1 3 4 9 10

2



# . 6 1 4 2 3 4 5 10

1 2 4 7 11

1 3 8 10 11

1 3 6 1 3 6 9 1 5 9 11

1 4 DAY

27 15 17 27 28 15 13

2 15

5 5 8 28 25 31 24 23 27

2 9 26 21 25 20 28 18

6 31 16 20 23

8 22

4 2 26 14 17 24 STATION

24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 24010558 TOTAL N (MGIL)

0.63

1.22 1.66

1.07 1.32 1.01 0.87 0.93 0.92 0.76 0.67 0.82 0.82 0.91 0.69

0.73 0.80 0.82

1.25 0.69 1.54

0.82 0.63 0.66 0.86 0.94 0.98 1.51 0.98 0.80 0.80WHITAKER BAYOUON27TH STREET

YEAR

75 75 77 78 78 80 80 80 81 81 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 89 89 TOTAL 

### P (MGIL)

1.300 1.300 1.328 0.865 1.358 1.023 0.737 1.768 1.295 1.466 1.387 0.764 0.323 0.559 0.776 0.895 1.118

1.230 1.330

1.722 1.982

1.062 1.850 1.492 1.736 1.810 0.517 1.139 1.371 0.867 0.706 0.389 0.358 0.394 0.358 0.595 0.960 MONTH

1 1 11

1 3 4 9 10 2 6 1 4 2 3 4 5 10

1 2 4 7 11

1 3 8 10 11

1 3 6 12

1 3 6 9 1 5 9 11

1 4 STATION

24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 24010553 DAY

27 27 15 17 27 28 15 13 2 15

5 5 8 28 25 31 24 23 27

2 9 26 21 25 20 28 18

6 31 16

1 20 23

8 22

4 2 26 14 17 24 TOTAL N (MGIL)

5.77 3.08 3.21 6.13 2.39

5.68 3.30 5.25 3.42 1.88 1.46 4.50 2.20 1.70 2.73 5.09 6.35

5.64 6.56 3.03 2.93 7.00 5.83 2.02 3.40 1.65 2.10 1.99 1.06 1.83 1.78 1.52 1.86 1.58 2.30 2.18PHILLIPPI CREEKAT FRUlNlLLEROAD

TOTAL P (MGIL)

1.662 1.634 1.177 1.733 0.900

1.861 0.551 1.007 1.656 0.561 0.400 0.520 0 847 0 513

0.591 0.555 0.673

2.071 1.509

1.535 0.393 0.696 0.569 1.002 0.821 1.298 1.539 0.728 0 460 0.462 0.401 0.307 0.542 YEAR

75 77 77 78 78 79 80 80 81 81 82 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 89 89 STATION

24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 24010626 TOTAL N (MGIL)

5.20 4.38 4.03 4.54

5.79

9.04 1.22 7.34 4.36 1.63 6.28 1.14 5.97 3.64

2.59 3.46 4.81

8.64 6.51 9.71 2.72 10.54

7.10 1.14 2.04 2.09 3.68 4.22 3.30 4.31 1.73 1.36 1.18 0.99 1.OO 0.69 MONTH

1 11 12

2 4 10

3 12

5 9 3 6 10

1 3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

5 7 10 11 12

2 5 DAY

10

1 6 7 11

9 10

1 18

8 1 7 5 18

7 16 18 27

3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 31 26 17 29 27 27 22PHILLIPPICREEKAT 17THSTREET BRIDGE

YEAR

75 77 77 78 78 79 79 79 79 80 80 80 81 81 82 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 88 89 89 MONTH

1 11 12

2 4 1 3 4 10

1 3 12

5 9 3 6 10

1 3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 5 7 10 11 12

2 5 DAY

10

1 6 7 11 24

5 24

9 21 10

1 18 8 1 7 5 18

7 16 18



### - 27 3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 31 26 17 29 27 27 22 TOTAL N (MGIL)

0.79 1.01

1.44 0.59 0.53

1.97 2.13

1.29 1.01 1.25 1.15 1.40 1.53 3.29 0.74 0.83

1.15 1.OO 1.30

0.83 0.65 0.74 1.01 1.23 1.11 0.96 0.95 1.33 1.16 3.19 0.96 0.96 0.56 1.13 1.11 1.22 1.05 0.94 0.82 STATION 

# ------

24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 24010627 TOTAL 

### P (MGIL)

0.468 0.51 1 0.438 0.498 0.585 0.532 1.193 0.579 0.985 0.420

0.428 0.451 0.549 0.791 0.357 0.208 0.750 1.426 0.402

0.306 0.329 0.416

0.353 0.418 0.290 0.350 0.270 0.672 0.432 0.445 0.427 0.681 0.450 0.440 0.279 0.480 0.413 0.420 0.362 0.421 0.348 0.659PHILLIPPICREEKAT l7THSTWEST BRIDGE

TOTAL 

### P (MGIL)

0.976

1.101 0.945 1.187

1.568 3.664 1.489

1.920 0.845 1.161 0.874 1.783 1.447 5.969 0.716 1.299 0.661 0.603 0.562 0.613 0.794 STATION

24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 24010670 DAY

1 21 10 3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 26 17 29 27 27 22 YEAR

79 80 80 83 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 89 89 TOTAL N (MGIL)

1.88 9.71 8.55

8.34 7.67

16.32 18.59

13.14 19.23 12.82

0.88 3.06 3.57 6.64 2.56 5.61 3.30 2.20 0.93 0.91 0.80 1.31 0.81 MONTH

10

1 3 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 7 10 11 12

2 5CLARKS LAKE DRAINAGEATWlLKlNSON ROAD

YEAR

77 79 80 80 80 81 82 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 88 89 89 TOTAL N (MGIL)

1.Ol 1.OO 3.35 2.70

1.13 1.40 1.85 2.38 1.50 2.13 0.82 0.93

1.59 1.36 1.84

0.69 1.28 1.29 1.10 1.18 0.76 1.26 1.16 1.39 1.56 1.46 1.54 1.39 0.81 0.95 1.34 1.28 1.32 1.38 1.09 MONTH

10

9 1 3 12

9 3 6 10

1 3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 5 7 10 11 12

2 5 TOTAL P (MGIL)

0.415 0.414 0.608

0.451 0.349 0.617 0.485 0.256 0.358 0.492 0.718

0.265 0.267 0.297

0.235 0.438 1.276 0.214

0.423 0.413 0.232 0.305 0.441 0.450 0.398 0.199 0.440 0.433 0.280 0.321 0.421 0.286 0.736 DAY

25 24 21 10

1 8 1 7 5 18

7 16 18 27

3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 31 26 17 29 27 27 22 STATION

24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642 24010642MAINA CNLAT CATTLEMANS ROAD BRIDGE

YEAR

74 78 78 79 80 80 80 81 81 82 82 82 83 83 83 83 83 84 84 84 64 84 85 85 85 85 86 86 87 87 87 87 88 88 88 88 88 88 89 89 MONTH

11

1 4 10

1 3 12 5



# . 9 3 6 10

1 3 5 7 9 1 3 4 8 10

1 3 5 8 7 10

1 3 8 11

2 5 7 10 11 12

2 5 DAY

19 24

4 1 21 10

1 18

8 1 7 5 18

7 16 18 27

3 5 9 27 15 14 18 20 12 28 20 26

2 24

2 16 31 26 17 29 27 27 22 STATION

24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 24010629 TOTAL N (MGR)

1.31

2.04 2.86 1.53

1.79 1.52 1.46 1.65 1.62 0.87 1.12 0.81 0.95

1.59 1.15 1.39

1.29 2.72 0.67 1.52 2.37 1.30 2.43 2.29 1.72 1.49 1.57 0.67 1.04 1.20 1.42 1.33 0.89 2.71 TOTAL

### P (MGR)

0.150 0.328 0.310 0.965 0.606 0.210

0.553 1.027 0.458 0.791 0.602 0.250 0.177 0.323 1.273

0.286 0.185 0.297

0.510 0.817

0.619 0.529 1.022 0.469 0.628 0.358 0.820 0.787 0.240 0.562 0.341 0.307 0.446PHILLIPPICREEK AT BAHlAVISTA STREET BRIDGE

TOTAL P (MGIL)

1.041 1.109 0.492 1.520

0.772 1.888 0.695 0.420

2.188 1.111 1.114 0.642 0.944 0.583 1.I 74 0.985

0.653 0.637 0.673

1.215 1.857

0.413 0.754 0.590 1.002 0.704 0.942 0.537 1.099 0.846 0.801 0.663 0.822 1.472 1.646 TOTAL N (MGIL)

2.62 2.73 2.18 2.78 2.37 1.70 2.20 0.91 2.88

5.03 3.73 2.57 1.89 4.38 2.57 3.47 1.76

2.43 2.52 2.84

4.70 2.93 5.07 1.53 5.94 4.60 1.42 2.36 2.16 3.55 2.39 2.77 2.06 2.63 2.62 3.23 2.77 3.16 4.84 6.19 STATION

24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 24010625 DAY

10

1 6 7 11 24

5 24 24 10

1 18

1 7 5 18

7 16 18 27

3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 31 26 17 29 27 27 22 YEAR

75 

## n 77 78 78 79 79 79 79 80 80 81 82 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 88 89 89 MONTH

1 11 12

2 4 1 3 4 9 3 12 5 3 6 10

1 3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 5 7 10 11 12

2 5MAIN A CNLAT BAHlAVISTA ST BRIDGE

YEAR

75 79 79 79 79 80 80 80 80 80 81 82 82 82 82 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 88 89 89 DAY

10 24

5 24 24 21 21 10 10

1 18 18

1 7 5 7 16 18 27

3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 31 26 17 29 27 27 22 MONTH

1 1 3 4 9 1 1 3 3 12

5 

### I 3 6 10

3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 5 7 10 11 12

2 5 STATION

24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 24010628 TOTAL N (MGIL)

1.87 1.51 0.94 0.29 3.95 4.41 2.65 2.54

5.03 2.14 2.96 2.00 1.84 2.39 3.28 1.18

2.01 2.73 1.95

3.55 3.08 5.89 1.10 4.89 9.61 1.70 2.12 2.34 4.76 2.48 2.33 2 13 4.93 2.24 2.26 3.22 2.11 2.77 5.15 TOTAL P (MGIL)

0.632 0.691 0.705 1.061 1.061 0.420 0.420

3.043 0.761 1.385 0.894 0.702 0.832 1.040 2.874

0.367

0.435

1.293 1.374 1.934

0.948 0.569 1.282 0.704 0.754 0.438 1.959 0.866 0.380 0.723 0.421 0.532 1.937PHILLIPPI CREEKAT SARASOTA, FL

TOTAL P (MGIL)

2.500 1

### .OOO 0.880 2.600 0.350 1.600 2.400 0.700 3.200 0.510 0.940 0.430 1.160 0.750 STATION

2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 2299800 DAY

14 11

6 21 13 27

2 15 14 20

1 16

2 12

8 YEAR

68 70 70 71 71 72 74 74 75 75 76 76 77 77 78 TOTAL N (MGIL)

3.04

3.09 1.50 3.10 1.70 MONTH

5 6 10

4 10

4 5 10

4 10

6 9 5 10

5MAINA CNLAT PALMERS BLVD BRIDGE

YEAR

74 77 77 78 78 79 79 79 79 80 80 80 81 81 82 82 83 83 83 83 83 84 84 84 84 84 85 85 85 85 86 86 86 86 87 87 87 87 88 88 88 88 88 88 89 89 MONTH

11 11 12

1 4 1 3 4 10

1 3 12

5 9 3 6 1 3 5 7 9 1 3 4 8 10

1 3 5 8 1 4 7 10

1 3 8 11

2 5 7 10 11 12

2 5 DAY

19

1 6 24

4 24

5 24

1 21 10

1 18 8 1 7 18

7 16 18 27

3 5 9 27 15 14 18 20 12 20 21 28 20 26

2 24

2 16 31 26 17 29 27 27 22 STATION

24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 24010630 TOTAL N (MGIL)

0.88 1.90 1.33

0.95 1.99 0.54 1.61 2.51 3.05

0.75 1.46 1.51 1.56 1.03 1.28 0.89 1.28

1.61 1.50 1.29

0.69

0.57 1.72 0.84 0.74 1.10 1.42 3.07 1.52 1.73 1.12 4.35 0.69 1.07 2.27 1.60 1.06 0.48 4.10 TOTAL P (MGIL)

0.160 0.194 0.527 0.270 0.417 1.652 0.681 0.658 0.886 0.606

0.252 0.877 0.291 0.820 0.148 0.225 0.209 0.965

0.224

0.137 0.697 0.058 0.389

0.384

0.155 0.285 0.461 0.391 0.251 0.318 0.240 0.472 0.160 0.362 0.140 0.061 0.484APPENDIX 

### B

TECHNICAL MEMORANDUM ON SEPTIC TANK LITERATURE REVIEW AND ANALYSISMEMORANDUM

TO : Mike Heyl, CDM/Sarasota
FROM : Rich Wagner, CDM/Annandale
SUBJECT: Literature Review of Septic Tank Loadings

DATE : January 27, 1992

INTRODUCTION

CDM conducted a literature review to evaluate the pollutant loadings contributed by septic tank systems. Data gathered as part of this review include septic tank wastewater flow rates and effluent characteristics, pollutant removal mechanisms and efficiencies in drainfields, and delivery of loadings to surface waters. These data were used to assess the pollution impacts of septic tanks in the Sarasota Bay NEP study area.

LITERATURE SEARCH
Sources of information were obtained through a computerized literature review in conjunction with manual research of sources based on previous work. The initial computer search was conducted through the United States Geological Survey (USGS) on-line library system. Key words such as "septic tank","onsite disposal system", and "groundwater contamination" were used to identify potential
sources of data in technical journals, textbooks, and conference proceedings. In addition, sources were identified by examining the literature review that is published annually by the Journal of the Water Pollution Control Federation (WPCF). The review includes a segment devoted specifically to on-site alternatives for treatment and disposal.

After the USGS and WPCF listings had been reviewed, specific journal articles, reports and conference proceedings were obtained. These sources were reviewed to provide data for the septic tank loading assessment. In addition, the sources included other references that were reviewed in order to identify other apparent data sources, which were then obtained and reviewed.

In all, over 50 articles and reports 

### were reviewed as part of the septic tank loading evaluation. Those that were used in the evaluation are identified in the bibliography of this memorandum.
DEFINITION OF LOADING PARAMETERS
The data found during the literature was used to define a nuniber of loading parameters for the analysis. These parameters include the following:0 

### Typical effluent flow rate (gal/capita/day)



### o Typical effluent water quality characteristics (e.g., concentrations of various pollutants)



### o Typical removal processes and efficiencies that characterize effluent percolation through the soil o Processes occurring after the effluent reaches the groundwater and is ultimately transported to surface waters
Of these parameters, effluent quantity and quality were documented in many studies. Removal processes during percolation are also well-documented, and efficiencies are listed or can be estimatedby analysis of monitoring data in the literature. Unfortunately, processes occuring between the drainfields and surface waters and estimation of surface water loadings due to septic tanks are not well-documented. However, several articles have considered the far-field impacts of septic tank loadings, and these were used to develop a methodology for estimating septic tank impacts for Sarasota Bay.
Effluent Flow Rate
Table 1 presents a listing of effluent flow rates in gallons/capita/day (gpcd) that were either measured or assumed by various authors. Typically, the values range between 40 and 80 gpcd. Local water usage data for the study area indicate that the per capita wastewater flow rate for the study area is expected to be about 75 

### gpcd, which is at the high end of the identified range. Based on the local data, a value of 75 

### gpcd was selected as a typical flow rate for septic tank systems in the study area.

Effluent Oualitv

Water quality characteristics for septic tank effluent are presented in Table 2. 

### These values were either measured or assumed by various authors. The table focuses on total nitrogen (total N) and total phosphorus (total P), because nutrient impacts are typically the major concern for septic tanks. For each source, the table indicates the number of samples and the average concentration for total N and total P.

As shown in Table 

### 2, both the concentration and the range of concentrations for total N is larger than for total P. Total N 

### values in the literature ranged from 40 to 130 mg/L, with most of the values in the 40 to 80 mg/L range. For the purposes of this study, a mid-range value of 60 mg/L was selected for the total N 

### effluent concentration. In contrast, the total P effluent concentratins ranged from 4 to 16 

### mg/L. A 

### number of the observations fall between 13 and 16 

### mg/L, so a value of 15 

### mg/L wasselected for the purposes of this study.

Removal Processes and Efficiencies in Unsaturated Zone

In the case of total PI the main removal process inthe unsaturated soil zone between the septic tank and the water table is adsorption. Many articles have concluded that most or virtually all of the total P in the effluent will be captured in the drainfield, such that adverse water quality impacts on groundwater
or surface waters are unlikely. Several articles have indicated that pollution due to total P may ultimately occur when the adsorptive capacity of the soil 

### is exceeded, but this would require
a substantial, long-term discharge.
Removal of total N 

### is not as complete nor as simple as that of total P. Of the total N, typically about 20 percent is in the organic form, and the remaining 80 percent 

### is present as ammonia nitrogen. The organic nitrogen is likely to be removed during effluent percolation via filtration. The ammonia nitrogen, on the other hand, will primarily remain in solution rather than being removed through adsorption. In most cases, the ammonia nitrogen is completely converted to nitrate nitrogen in the drainfield, if aerobic conditions are present. Nitrate nitrogen 

### is very mobile in solution, and very little nitrate removal would be expected in the drainfield under aerobic conditions. If part of the drainfield 

### is anaerobic, however, and a sufficient carbon source is present, denitrification may occur, converting nitrate nitrogen tonitrogen gas. This would reduce the amount of nitrogen entering the groundwater and, ultimately, surface waters.
Based on the literature data, it 

### is difficult toprecisely quantify the removal of total N and total P between the septic tank and the water table. In some cases, nutrient concentrations are reported in the soil near the septic tank, but the septic tank effluent concentrations are not specified. In other cases, a removal percentage is defined without specifying the effluent and soil concentrations. Also, the removal efficiency may vary at a particular site depending upon the conditions at the 

### time of the monitoring.
After a review of the data, it was assumed that the concentrations of total N and total P after percolation to the water table are 30 mg/L and 2 mg/L, respectively. Given the assumed total N effluent concentration of 60 mg/L, the water table concentration of 30 mg/L presumes that 50 percent of the total N 

### is removed as the effluent percolates through the soil. This concentration and percent removal are consistent with the results presented by Andreoli 

### & al. (1980), Walker et a1. (1973a), Ellis (1983), and Cogger et al. 

## - (1988). For total PI an assumed water table concentration of 2 mg/L implies a removal of about 90 percent during the effluent

### percolation, based on the assumed effluent concentration of 15 mg/L. Numerous studies, such as Jones and Lee (19791, Gilliam and Patmont (1983), Reneau et al. (1989) and Sawhney and Starr (1977) have concluded that 90 percent or more of the total 

### P remains in the soil. Thus, both of these assumed values are reasonable with respect to findings of other studies.

Surface Water Impacts Though most of the focus in the literature has been on effluent quality and groundwater concentration in the immediate vicinity of individual septic tanks, several studies have analyzed the potential extent of large-scale septic t'ank impacts on groundwater quality and surface water quality. Surface water studies typically used monitoring data to identify areas with septic tank loadings, and to quantify the loadings, whereas groundwater studies typically developed a modeling framework to assess loadings. Several of the modeling studies are described below.

Bauman and Schafer (1984) have developed a method of estimating groundwater impacts for nitrogen based on a mass balance approach. The approach requires an evaluation of the water budget and the nitrogen budget within the surficial aquifer. Water budget and nitrogen budget components include groundwater flow, natural recharge and septic system effluent. By determining the volume of water from each source and defining a nitrogen concentration for each source, the concentration of the combined sources can be calculated. Groundwater flow is calculated by determining aquifer thickness, width, hydraulic conductivity and hydraulic gradient, and groundwater concentration is based on local monitoring data. Similarly, recharge volume and concentration is determined from local data, and septic tank data are estimated based on population density and typical effluent characteristics.

A transport model for pollutants in the water table aquifer has been developed by Anderson et a1 (1987) as part of the Florida Onsite Disposal System (OSDS) project. The model is more complex than that of Bauman and Schafer, simulating transport as a steady, one-dimensional flow field with three-dimensional dispersion, retardation, and first-order decay. Though more complex, required data for this model are similar to those required for the mass balance model, including septic tank flows and .loadings, as well as aquifer hydraulic conductivity and hydr'aulic gradient. Dispersivity factors are also required to quantify the dispersion of the effluent down gradient of the source.

A third approach to modeling surficial aquifers affected by septic tank effluent was presented by Ostendorf (1986). This model simulates the near field mixing and- routing of effluent and groundwater as a linear reservoir, and simulates far field pollutant concentrations based on a first order decay rate. As with the other models, the essential data include effluent flow,

### effluent water quality characteristics, and aquifer characteristics (e.g., hydraulic conductivity, hydraulic.gradient, thickness).

The Ostendorf model was applied at the Otis Air Force Base in Massachusetts, which has discharged an average effluent flow rate of 0.53 

### mgd to its drainfields since 1941. 

### Concentrations of chloride, boron, total N and methylene blue active substances

(MBAS) were measured in the groundwater at various distances downgradient of the drainfields. Using the input data described above, the model was tested first for chloride, a conservative constituent, to determine if the model transport simulation was accurate. The results showed an excellent agreement between predicted and measured concentrations downgradient of the drainfields. Then, the model was applied for the other constituents, including the calibration of total N and MBAS by the evaluation of a first order decay rate.
After reviewing these modeling approaches, a methodology for estimating septic loads that reach receiving waters was developed. The methodology uses some of the components of these models. The development of the methodology is discussed in the next section.

MODELING METHODOLOGY
Calculation of septic tank loadings to surface waters is performed within the NPS spreadsheet model. The existing model already includes a method for calculating loads due to failing septic tanks. As part of the Sarasota Bay NEP Study, the model has been modified to include the calculation of loads due to septic tanks that are not failing. The calculation method for both failing and working septic tanks are presented below.
Failina Septic Tanks
Nutrient concentrations for failing septic tanks were established based on the literature review. It was assumed that the concentrations for a failing septic tank are equivalent to the concentrations established for the effluent at the water table. These were as follows:

o Total N 30 

### mg/L



### o Total P 2 

### mg/L
The values reflect pollutant removal within the soil of roughly 50 

### percent for total N and 90 

### percent for total 

### P.
Nutrient loadings for specific land uses were calculated by multiplying the concentrations by a flow rate. The flow rate for
a particular land use depended upon the number of residents per acre, and the per capita flow rate.

### Table 

### 3 shows the septic tank flow rates developed for various land
uses. For all land uses, a per capita flow rate of 75 gallons per day was established. For the residential areas, values of dwelling units per acre were determined based on the descriptions of various land uses in the Sarasota County Comprehensive Plan and densities observed in aerial photographs. Each dwelling unit is assumed to, have 2.0 people, based on household size estimates for Sarasota and Charlotte Counties and the City of North Port, as cited in the City of North Port Comprehensive Plan. This value is somewhat lower than the national average, because some of the population is seasonal and because the population distribution is weighted more heavily toward retired persons who would tend to have a smaller household size. For commercial and industrial areas, the flow values were assumed equal to the highest residential value. The literature indicates that commercial and industrial flows can vary widely, but it was assumed that any large industrial or commercial wastewater source would be served by sewers.



### A final consideration in the loading analysis for failing septic tanks is the failure rate 

## - that is, what percentage of the tanks are failing. These data were established based on permitting data from the Sarasota County Health Department. The Health Department requires a permit for repair or replacement of septic tanks. During the period 1980 through 1990, an average of 740 repairs per year was recorded. Based on the estimate of 45,000 septic tanks in the County, the annual repair rate is 1.6 percent. Recognizing that failure may occur for a number of years before repairs are initiated, the failure rate at any time is likely to be higher than 1.6 percent. In previous studies, the annual failure rate has been multiplied by a factor of 5, 

### which implies that septic systems on average fail for 5 

### years before repairs are made. For Sarasota *County, the resulting failure rate is 8 percent. This value compares favorably with the results of a septic tank survey conducted in Jacksonville, FL 

### by the Department of Health and Rehabilitative Services. In the study, an inspection of more than 800 sites revealed about 90 violations, or a failure rate of 12 percent. Failure calculations also were done specifically for Casey Key, which had a higher annual repair rate. The failure rate established for Casey Key was 20 percent.
Workins Septic Tanks

The surface water loading due to effluent from working septic tanks is calculated based on the modeling frameworks that were found in the literature (Bauman and Schafer, 1984; Ostendorf, 1986)


# . The model assumes that a load of total N and total P enters the surficial aquifer below the septic tank after percolating through the unsaturated soil zone. The load then travels along with the surficial aquifer flow, subject to a first order decay rate that reduces the mass over time. The load that is left when the surficial aquifer reaches a permanent water body is assumed 

### to discharge to the water body.Figure 1 shows the theoretical basis of the septic tank analysis. It 

### is assumed that recharge of the surficial aquifer occurs at a constant rate (W)


## . Under steady flow conditions, this recharge rate 

### is equivalent to the discharge rate in the receiving stream, assuming no leakage to the lower aquifer layers. By determining factors such as the length (L), the aquifer thickness at the receiving stream ha, and the hydraulic conductivity of the aquifer, groundwater flow equations can be used to calculate the water table height and flow velocity at various distances from the receiving stream. The velocity values can then be used to determine travel times to the receiving stream. The travel time, combined with the first order decay rate, determines the fraction of septic tank loading that reaches the receiving stream. Equations developed by Dupuit (Todd, 1985) were used toperform the groundwater flow and velocity calculations. These equations have been used in models such as DRAINMOD to simulate subsurface water movement into drain tubes or ditches. One of the basic equations used in the analysis is

where

x = distance from the point of maximum water table elevation (ft)

q, = groundwater flow per unit of stream length (ft2/day)

W = groundwater recharge (ft/day)

In the septic tank analysis, the value of W was calculated 

### as the
sum of the natural recharge determined by the hydrologic analysis plus the flow contributed by septic tanks. For the areas with septic tanks, an average value of 7 inches/year (0.0016 ft/day) was calculated. Using equation 

### (I), the flow rate at any distance from the point of maximum water table elevation can be calculated. The other basic equation 

### is

where h, = water table height at distance 

### x from maximum

- water table elevation (ft)
ha = water table height at receiving stream (ft)

K = hydraulic conductivity of aquifer (ft/day)L = distance from point of maximum water table elevation to centerline of stream (ft)
This equation can be used to calculate water table height at any point between the stream and the location of the maximum water table elevation. These two equations were used to develop a third equation, that determines the velocity at various distances from the receiving stream. The equation 

### is as follows:

where
V, = velocity at distance x from location of maximum water table elevation (ft/day)

P = porosity of surficial aquifer Velocity is an important parameter in the analysis because it influences the travel time from the septic tank to the surface water, which in turn affects the extent of pollutant decay en route to the surface water.
The aquifer values established for the Sarasota Bay study area are presented in Table 4. The values represent an average of the data obtained at a number of monitoring sites in the vicinity of the study area. Values for aquifer thickness ha, porosity (P) and conductivity 

### (K) are based on review of the Soil Survey for Sarasota County and a Southwest Florida Water Management District (SWFWMD) report on groundwater availability in Sarasota County (SWFWMD, 1988)



## . The maximum distance value 

### (L) of 3,000 feet was selectedbased on inspection of USGS quadrangle sheets covering the study area, and the recharge value of 7 inches/year was based on the hydrologic simulation.
Travel 

### times at distances up to 1000 feet from the receiving stream are shown in Figure 2. The cumulative travel times shown in the figure were developed in a spreadsheet which generates values at points established at 10 foot increments, from 0 to 3000 feet from the stream. At each point, the spreadsheet calculates the velocity, and then determines the travel 

### time across the 10-foot distance between that point and the previous point. By summing travel times from consecutive 10-foot intervals, cumulative travel times are also calculated. Thus, at any point between 0 and 3000 feet from the stream, the total travel time to the stream 

### is determined. Figure 2 shows that the travel distance in one year ranges from 60 to 110 feet, with higher velocities in the areas closest to the stream. These travel times translate into velocities of 0.16 to 0.30 feet per day.Assuming a first order decay rate, the reduction in pollutant mass as a function of travel time 

### is determined by the following equation :

where

f = fraction of pollutant removed after 

### time t
k = first order decay coefficient (l/days)

t = time since the effluent entered the surficial aquifer (days)
This equation was also included in the spreadsheet todetermine the pollutant reduction associated with each 10-foot increment. In this way, the fraction of pollutant delivered at various distances from the stream were determined. In addition, an overall average delivery ratio was established by averaging the delivery ratios at each 10-foot increment.

APPLICATION OF MODEL
The methodology presented above was incorporatedinto a spreadsheet model that calculates pollutant loadings from surface runoff, baseflow and point sources as well as septic tank loadings. This model was used to estimate loadings at two water quality stations located on Phillippi Creek. In estimating septic tank loadings, initial model runs were conducted assuming the first order decay rate of 0.00015/day that was established in the Ostendorf study. The results indicated a very high delivery of working septic tank loadings to the receiving streams, which could not be verified by analysis of stream water quality monitoring data inthe study area. Subsequently, the first order decay rate was adjusted upward so t h a t t h e loadings were more consistent with observed instream water quality. Once an appropriate decay rate was established, the model
was applied to each watershed in the study area to determine the relative significance of septic tank loadings. Comparison of Observed and Simulated Instream Water Oualitv
The methodology and first-order decay rate were evaluated by comparing observed and simulated water quality data at two monitoring stations in the Phillippi Creek watershed. The STORET stations used in the analysis 

### were the Main A Canal at Palmers Boulevard Bridge (Station 24010630) and Philrippi Creek at Bahia Vista Street Bridge (Station 24010625). The Palmers Boulevard Bridge station has a drainage area of about 8 square miles, which consists primarily of cropland, rangeland, and low and medium density single family residential land uses. 89 percent of the low

### density and 

### 66 percent of the medium density residential areas are served by septic tanks, and there are no substantial point source loads. The Bahia Vista Street station has a drainage area of 

### 44 square miles, comprised mainly of cropland, rangeland, open space, and low and medium density residential land uses. 53 percent of the low density, 41 percent of the medium density and 37 percent of the high density residential areas are served by septic tanks. Unlike the Palmers Boulevard station, the water quality at the Bahia Vista Street station has been impacted by the Atlantic Utilities and Kensington Park Utilities point sources, which had been directly discharging secondary effluent to Phillippi Creek during the STORET period of record. It is possible that other smaller point sources may also have been discharging directly, rather than through percolation ponds and irrigation, during the period of record.
The results of the water quality analyses for the two monitoring stations are presented in Table 5. 

### The table includes results for three different first-order decay rates, which are as follows:



### o The initial Ostendorf decay rate of 0.00015/day

o Decay rate of 0.00170/day based on assumed removal via percolation ponds and irrigation

o Decay rate of 0.00055/day based on calibration of Bahia Vista Street station loadings

For each decay rate, the results include the overall percent delivery from septic tanks, and a comparison of observed and simulated instream concentrations on an annual and seasonal basis. The overall percent delivery includes the impacts of both failing and working septic tanks, and reflects the fraction of nitrogen loading that is transported from the drainfield to the receiving water. The methodology used to determine the simulated and observed instream concentrations are described below.

The simulated instream concentrations were determined by calculating loadings from septic tanks, surface runoff, point
sources and baseflow for an averase rainfall year, divided into a wet season (June through September) and a dry season (October through May)



## . The calculations were conducted by using a spreadsheet model developed by CDM, which has been applied in a number of water quality studies in Florida and other states. The model uses long-term precipitation and streamflow data, along with runoff coefficients for pervious and impervious area, to determine the relationship between rainfall, surface runoff and baseflow. Loadings associated with surface runoff are calculated by using event mean concentration (EMC) values. The EMC represents the flow-weighted concentration of pollutant in surface runoff during a typical storm event. Distinct EMC values are specified for different types of land use (e.g., residential, commercial,

### agricultural)



## . Baseflow loadings are calculated assuming a constant baseflow concentration. Point source loadings are included by specifying wastewater flows and concentrations, and septic tank loadings are calculated using the newly developed methodology described in this memorandum. The results of the modeling include total loading (e.g., pounds of nitrogen) and the total runoff depth (e-g., inches of flow distributed over the drainage area) for the modeling period. Given these output values and the size of the drainage area, a flow-weighted instream concentration can be calculated.

Because the simulated results include a flow-weighted instream concentration, the monitoring data were also analyzed to provide flow-weightedinstream concentrations. The concentration data were sorted by month, and an average concentration was calculated for each month. Monthly flows were estimated using the same long-term streamflow records used in the spreadsheet model, and the percentage of annual flow attributedto each month was established. Usingthis information, a flow-weighted concentration was developed
on an annual and a seasonal basis.

As shown in Table 5, nitrogen concentrations are substantially oversimulated when the Ostendorf decay rate was used. At the Palmers Boulevard station, the average annual total 

### N concentration was oversimulated by 49 percent, and both wet season and dry season concentrations were oversimulated by more than 40 percent. The oversimulation at the Bahia Vista Street station was only 11 percent for the annual average analysis, but was 

### 23 percent for the wet season analysis. Sensitivity analyses indicated that higher first-order decay rates would still result in reasonable total N 

### predictions at the Bahia Vista Street station, while improving the predictions at the Palmers Boulevard station. Consequently, higher decay rates (which would result in a lower delivery ratio) were investigated. Using a decay rate of 0.00170/day produces results that appear to be more reasonable that those developed using the Ostendorf rate. Based on the typical surficial aquifer velocity, this decay rate translates into 20 percent delivery (i.e., 80 percent removal) for sources at a distance of 300 feet from the receiving water. Together with the previous assumption of 50 percent total N 

### removal in the unsaturated soil above the water table, the overall delivery is reduced to 10 percent. This value is consistent with the 90 percent removal value assumed for percolation ponds, which in many cases are located only a few hundred feet from receiving waters.
The simulation results indicate an oversimulation of total N 

### at the Palmers Boulevard station and an undersimulation of total N 

### at the Bahia Vista Street station for the annual average analysis. However, both sets of simulated results are within 20 percent of the observed values. Given the uncertainty associated with the monitoring data and the calculation of the surface runoff, baseflow

### and point source loads, these results appear to be reasonable. The largest discrepancy between simulated and observedvalues occurs in the dry season analysis for the Bahia Vista Street station. During the dry season, the loading due to surface runoff is less significant, whereas point sources and septic tanks account for a greater percentage of the overall loading. Thus, one possible explanation of the total N 

### undersimulation is that the point source loading during the monitoring period was underestimated. As mentioned earlier, two relatively large plants were discharging directly to Phillippi Creek, and it is possible that some of the smaller plants were also discharging directly to the creek at that time



## . In addition, the Florida South 'Gate plant discharges directly to the creek downstream of the Bahia Vista Street station, and some of that loading may influence the water quality at the station due to dispersion and tidal transport. Alternatively, the undersimulation may indicate that the loading due to septic tanks has been underestimated.
A third set of results was generated in which the decay rate was established such that the simulated and observed total N 

### concentration at the Bahia Vista Street station matched for the average annual simulation. Through a calibration process, a decay rate value of 0.00055/day was established. The corresponding overall delivery from the drainfield to the receiving water is 

### 20 percent, which is one-half of the delivery ratio calculated using the Ostendorf decay rate and twice the delivery ratio calculated using the decay rate of 0.00170/day.
The results show that there is good agreement between simulated and observed values at the Bahia Vista Street station, but that total N 

### is oversimulated at the Palmers Boulevard station. As discussed above, the annual average simulated results match the observed values because that was the basis of the decay rate calibration. The results from the seasonal analyses for the Bahia Vista Street station shgw simulated total N 

### concentrations that are somewhat higher than observed values during the wet season, and somewhat lower than observed values during the dry season. However, in both cases the difference between simulated and observed values is less than 20 percent. Given the uncertainty associated with the monitoring data and the calculation of the surface runoff, baseflow and point source loads, these results appear to be reasonable. For the Palmers Boulevard station, there is an oversimulation of total N 

### for the annual and seasonal analyses. In all cases, the simulated loads are about 20 percent higher than the observed loads.

Due to the uncertainty in estimating loads and measuring instream concentrations, it is impossible to determine the loading due to septic tanks with any certainty. The results using the Ostendorf decay rate appear to generate excessive total N 

### loadings from septic tanks. The results based on the other two decay rates both appear to give a reasonable estimate of septic tank loadings. Therate of 0.00170/day seems reasonable for the annual and seasonal analyses, with the percent difference between simulated and observed total N concentrations ranging from +14 to -20. In comparison, the results for the decay rate of 0.00055/day show percent differences ranging from +26 to -16. The overall septic tank delivery ratio for the two alternative decay rates are 10 percent and 20 percent, respectively. Thus, based on the analysis described above, a delivery ratio of 10 to 20 percent is assumed to be representative for septic tank loadings in the study area.
In the final calculation of study area loadings, the more conservative delivery ratio value of 20 percent was selected. Because the relatively high delivery ratio was selected, it is likely that the impacts of septic tank loadings will not be underestimated, and in fact may be overestimated. Average Annual Loadings for Studv Area Watersheds
The average annual loading results for the watersheds in the study
area are shown in Table 6. Because nutrients are the major concern for septic tanks, total P and total N results are included in the table. The results are shown separately for those watersheds that do have septic tanks, whereas the watersheds without septic tanks have been combined into one category. For each watershed, the table lists the total loading inpounds attributed to septictanks, the total loading from all sources, and the percentage of the total loading attributable to septic tanks. The total loading includes septic tanks plus surface runoff, baseflow, point sources, and precipitation falling directly onto the Bay surface.
The results presented in Table 6 indicate that septic tanks account for only a small fraction of the total study area loadings, but that the impact of septic tanks varies between watersheds. Overall, septic tanks account for 3.3 percent of the total P loading and 9.6 percent of the total N loading to the Bay. For total P, the septic tank contribution 

### is less than the contribution of any of the other four pollution sources (surface runoff, baseflow, point sources and rainfall). For total N, the septic tank contribution is less than that of surface runoff and rainfall, but is slightly higher than the contribution due to point sources or baseflow. Watersheds that have 

### a relatively high percentage of septic tank contribution include Phillippi Creek, Matheny Creek and the areas along the 

### west coast that drain directly to the Bay. Phillippi Creek alone accounts for 71 percent of the septic tank loading for total N.

SUMMARY

CDM conducted a literature review to evaluate the pollutant loadings contributed by septic tank systems. Data gathered as part of this review included septic tank wastewater flow rates andeffluent characteristics, pollutant removal mechanisms and efficiencies in drainfields, and delivery of loadings to surface waters. Methods for estimating pollution loadings due to working and failing septic tanks were developed, based on previous studies and the literature review. When these methods were applied to the Sarasota Bay study area, the results indicated that the septic tank loadings may have significant local water quality impacts, but do not appear to be a major factor i n t o t a l pollution loadings tothe Bay.

### REFERENCES Alhajjar, B.J., et al., "Indicators of Chemical Pollution from Septic Systems,

### " Ground Water, Vol. 28, No. 4, July-August 1990, pp. 559-568. Alhajjar, B.J., et al., "Detergent Formula and Characteristics of Wastewater in Septic Tanks," Journal of Water Pollution Control Federation, Vol. 61, No. 5, May 1989, pp. 605-613. Alhajjar, B.J., et al., "Detergent Formula Effect on Transport of Nutrients to Ground Water from Septic Systems," Ground Water, Vol. 27, No. 2, March-April 1989, pp. 209-219. Alhajjar, B.J., "Groundwater Contamination from Septic Systems Receiving Detergents of Two Types of Formulation," PhD dissertation, University of Wisconsin-Madison, 1985.
Anderson, D.L., et a1



### .

## , "Ground Water Modeling with Uncertainty Analysis to Assess the Contamination Potential from Onsite Sewage Disposal Systems (OSDS) in Florida," Proceedinss of the Fifth National Svmposium on Individual and Small Communitv Sewaae Svstems, American Society of Agricultural Engineers, Chicago, Illinois, December 1987, pp. 264-273. Andreadakis, A.D., "Organic Matter and Nitrogen Removal by an On Site Sewage Treatment and Disposal System," Water Resources, Vol. 21, No. 5, 1987, pp. 559-565. Andreoli, A., et al., "Nitrogen Removal in a Subsurface Disposal System," Journal of Water Pollution Control Federation, Vol. 51, No. 4, 

### April 1979, pp. 841-854.
Bauman, B.J. and W.M. Schafer, "Estimating Ground-Water Quality Impacts From On-Site Sewage Treatment Systems," Proceedinss of the Fourth National Svmposium on Individual and Small Communitv Sewaae Svstems, American Society of Agricultural Engineers, New Orleans, LA, December 1984, pp. 285-294. Bicki, T.J., 

### "Hydroqen Peroxide Treatment of Septic Systems and Its Negative ~ffects on-ShallowGround Water,

### " ~roind water Monitorinq Review, Vol. 8, No. 4, 1988, pp. 108-111.
Brandes, M., "Characteristics of Effluents from Gray and Black Water Septic Tanks,

### " Journal of Water Pollution Control Federation, Vol. 50, No. 11, November 1978, pp. 2547-2559.
Canter, L.W. 

### and R.C. Knox, Septic Tank Svstem Effects on Ground Water Oualitv, Lewis Publishers, Chelsea, Michigan, 1985.

### Chen, M., "Pollution of Ground Water by Nutrients and Fecal Coliforms from Lakeshore Septic Tank systems," Water, Air and Soil Pollution, Vol. 37, No. 3, 1988, pp. 407-418.
Cogger, C.G., et al., "Septic System Performance on a Coastal Barrier Island," Journal of Environmental Oualitv, Vol. 17, No. 3, 1988, pp. 401-408.
Cogger, C.G. and B.L. Carlile, "Field Performance of Conventional and Alternative Septic Systems in Wet Soils," Journal of Environmental Oualitv, Vol. 13, No. 1, 1984, pp. 137-142.
Ehrenfeld, J.G., "The Role of Woody Vegetation in Preventing Ground Water Pollution by Nitrogen from Septic Tank Leachate," Water Resources, Vol. 21, No. 5, 1987, pp. 605-614. Ellis, B.G., "Nitrate Cbntamination of Groundwater on the Old Mission Peninsula: Contribution of Land Reshaping and Septic Drainfield," prepared for the U.S. Department of the Interior, March 1982. Gilliom, R.J. and C.R. Patmont, "Lake Phosphorus Loading from Septic Systems by Seasonally .PerchedGroundwater," 

### Journal of Water Pollution Control Federation, Vol. 55, No. 10, October 1983, pp. 1297-1305. Gilliom, R.J. and C.R. Patmont, "Lake Phosphorus Loading from Septic Systems by Seasonally Perched Ground Water, Puget Sound Region, Washington," Open File Report 82-907, U.S. Geological Survey, Reston, Virginia, 1983.
30nes, R.A. and G.F. Lee, "Septic Tank Wastewater Disposal Systems
as Phosphorus Sources for -Surface Waters," ~ournal of -water Pollution Control Federation, Vol. 51, No. 11, November 1979, pp. 2764-2775. Kaplan, O.B., Septic Systems Handbook, Lewis Publishers, Chelsea, Michigan, 1987.
Kerfoot, W.B., "Septic System Leachate Surveys for Rural Lake Communities: A Winter Survey of Otter Tail Lake, Minnesota," Individual Onsite Wastewater Systems: Proceedinqs of the Sixth National Conference 1980, ed. Nina I. 

### McClelland, Ann Arbor Science, Ann Arbor, MI, 1980.
Lance, J.C., "Effect of Sludge Additions on Nitrogen Removal in Soil Columns Flooded with Secondary Effluent," Journal of Environmental Oualitv, Vol. 15, No. 3, 1986, pp. 298-301. LaPointe, B.E., et al., "Nutrient Couplings Between On-Site Sewage Disposal Systems, Groundwaters, and Nearshore Surface Water of the Florida Keys," Bioseochemistrv, Vol. 10, 1990, pp. 289-307.

16

### Miller, F.P. and D.C. Wolf, "Renovation of Sewage Effluent by the Soil," Individual Onsite Wastewater Svstems: ~roceedincrs

## 05 the Second National Conference 1975, National Sanitation Foundation and U.S. Environmental Protection Aaencv Technoloav Transfer Proaram.

< 

### Ann Arbor, Michigan, 1975. Nagpal, N.K., "Effect of Soil and Effluent Characteristics on Phosphorus Sorption in Dosed Columns," Journal of Environmental Oualitv, Vol. 15, No. 1, 1986, pp. 73-78.
Novak, L.T. and D.C. Adriano, "Phosphorus Movement in Soils: SoilOrthophosphate Reaction Kinetics," Journal of Environmental Qualitv, Vol. 4, No. 2, 1975, pp. 

### 261-266.
Ostendorf, D.W., "Modelinq Contamination of Shallow Unconfined Aquifers Through- 1nfiltratyon Beds,

### " Water Resources Research, Vol. 22, No. 3, March 1986, pp. 

### 375-382. Piluk, R.J. 

### and 0.

### J. Hao, "Evaluation of On-Site Waste Disposal System for Nitrogen Reduction," Journal of Environmental Enuineerinq, Vol. 115, No. 4, August 1989, pp. 725-740. Pitt, W .A., et al., "Ground-Water Quality in Selected Areas Serviced by Septic Tanks, Dade County, Florida," Open File Report 75-607, U.S. Geological Survey, Tallahassee, Florida, 1975. Reddy, M.R. and S.J. Dunn, "Effect of Domestic Effluents on ~rouiidwater Quality: A Case Study," The Science of the Total Environment, Vol. 40, 1984, pp. 115-124.
Reneau, R.B., et al., "Fate and Transport of Biological and Inorganic Contaminants from On-Site Disposal of Domestic Wastewater, " 

### Journal of Environmental Oualitv, Vol. 18, No. 2, April-June 1989, pp. 135-144. Sawhney, 

### B.L. and J.L. Starr, "Movement of Phosphorus from a Septic System Drainfield," Journal of Water Pollution Control Federation, Vol. 49, No. 11, November 1977, pp. 2238-2242. Sawhney, B.L. and D.E. Hill, "Phosphate Sorption Characteristics of Soils Treated with Domestic Waste Water, " 

### Journal of Environmental Qualitv, Vol. 4, No. 3, 

### 1975, pp. 342-346. Smith, T. and M. 

### Ince, "Septic System Density and Groundwater Contamination in Illinois: A Survey of State and Local Regulation, Final Report," prepared for the Illinois Department of Energy and Natural Resources, March 1989.
Southwest Florida Water Management District, "Groundwater Resource Availability: Sarasota County, Florida," Resource Management and Planning Department, March 1988.

### Starr, J.L. and B.L. Sawhney, "Movement of Nitrogen and Carbon from
a Septic System Drainfield," Water, Air, and Soil Pollution, Vol. 13, 1980, pp. 113-123.
Suzuki. T. and G. Yamaura. "Natural Recoverv of Chemical Comwonents ~ccumuiatedin Soil By wastewater ~~~lication," Water ~esburces, Vol. 23, No. 10, 1989, pp. 1285-1291.

U.S. Environmental Protection Agency, Manaqement of Small Wastewater Flows, Municipal Environmental Research Laboratory, Cincinnati, Ohio, 1978.
Walker, W.G., et al., "Nitrogen Transformations During Subsurface Disposal of Septic Tank Effluent in Sands: 

### I. Soil Transformations," Journal of Environmental Oualitv, Vol. 2, 

### No. 

### 4, 1973, pp. 475-480.
Walker, W.G., et al., "Nitrogen Transformations During Subsurface Disposal of Septic Tank Effluent in Sands: 11. 

### Ground Water Quality," Journal of Environmental Oualitv, Vol. 2, No. 4, 1973, pp.521-525.
Waller, B.G., et al., "Effluent Migration from Septic Tank Systems in Two Different Lithologies, Broward County, Florida," WaterResources Investigations Report 87-4075, U.S. Geological Survey, Tallahassee, Florida, 1987.
Whelan, B.R., "Disposal'of Septic Tank Effluent in Calcareous Sands," Journal of Environmental Oualitv, Vol. 17, No. 2, 

### 1988, pp. 272-277.
Whelan, B.R. and Z.V. 

### Titamnis, "Daily Chemical Variability of Domestic Septic Tank Effluent," Water, Air, and Soil Pollution, Vol. 17, 1982, pp.131-139. Wilson, S.A., et al., "Effect of Tile Drainage on Disposal of Septic Tank Effluent in Wet Soils,"

' 

### Journal of Environmental Quality, Vol. 11, No. 3, 1982, pp. 372-375.
Yates, M.V., "Septic Tank Density and Ground-Water Contamination," Groundwater, Vol. 

### 23, No. 5, September-October 1985, pp. 586-591.TABLE 1

FLOW RATES FOR SEPTIC TANK EFFLUENT

TABLE2

NUTRIENT CONCENTRATIONS INSEPTIC TANK EFFLUENT Reference Waller et al., 1987 Sawnhey and Starr, 1977 Cogger andCarlile, 1984 Starr and Sawhney, 1979 Alhaggar et al., 1989 Andreoliet al.. 1979 Pilukand Hao, 1989 Reneau et al., 1989 Brandes, 1978 Reddyand Dunn, 1984 Flow Rate (gal/capita/day) 75 50 50 50 36-47

60 66 45 41-45 40-80

Notes:

1. n = numberof samples 2. NIA = not available Reference Waller et al., 1987 Walker et al., 1973 Whelan andTitmanis, 1981

Gilliamand Patmont, 1983 Alhaggar et al., 1989 Andreoli et al., 1979 Piluk and Hao, 1989 USEPA, 1978 Reneauet al., 1989 Coggeret al., 1988 Total P Total N
n 5 NIA NIA

54 357 N/A NIA NIA N/A

32 n 5 NIA NIA NIA 356 NIA NIA NIA NIA

32 (mg/l)

, 4.1 NIA

15 15 7.9-14 NIA 8.3

13 16 6.2 (mgll) 39 80 100 NIA

73 61.3 69.4

45 40-80 28TABLE 3

SEPTIC TANKS FLOW RATES FOR VARIOUS LAND USES

TABLE4

PARAMETERSFOR ANALYSIS OF WORKINGSEPTICTANKS Land Use

LDSF Residential MDSF Residential HDSF Residential Multi-family Bldg Mobile Home CommercialIServices Institutional Industrial Dwelling Units Per Acre

1 4.5 7.5 9 9



## -

Source

SWFWMD. 1988
SWFWMD, 1988
SWFWMD, 1988

FDER

USGS maps Parameter
Aquifer Conductivity
Aquifer Thickness
Porosity
Minimum Travel Length
Maximum Travel Length Value

8.0inlhr

60.0 ft

0.3

75ft

3000ft Flow Rate (gavacrelday)

150 675 1125 1350 1350 1350 1350 1350 Persons Per Dwelling unit

2 2 2 2 2



## -

- PerCapita Wastewater

Flow Rate (gaVday1person)

75 75 75 75 75



## -

-TABLE5 SIMULATEDAND OBSERVEDTOTAL N DATA PALMERS BOULEVARD AND BAHlAVISTA STREET STATIONSTABLE 6 AVERAGE ANNUAL LOADINGS FOR STUDY AREA WATERSHEDS EXISTINGLAND USE CONDITIONSAPPENDIX C

STATISTICAL ANALYSIS OF BARRIER ISLAND AND MAINLAND RAINFALL DATAAPPENDIX C STATISTICAL ANALYSIS OF BARRIER ISLAND AND MAINLAND RAINFALL DATA

The climate in the Sarasota Bay National Estuary Program study area is subtropical, with a mean daily temperature of about 78 degrees. The weather is influenced by latitude, low elevation, wind patterns and proximity to the Gulf of Mexico and to Sarasota Bay. Average annual rainfall for the study area is about 54 inches, with approximately 60 percent of the total precipitation falling during the summer months of June through September. The summer rainfall patterns typically consist of short duration, intense convective thunderstorms occurring in the late afternoon. Rainfall in the winter months is generally associated with cold fronts moving across the region. Compared to summer rainfall events, winter rainfall events usually have a longer duration and lower intensity. Typically, continuous monthly rainfall totals in excess of 25-30 years period of record are used in estimating annual, or seasonal non-point source pollutant loadings. Of the local rain gage data available, data from only one station (Bradenton ESE) meets the criteria, although except for 

### a 15 month gap in record keeping, the Myakka River rainfall record meets the duration criteria. The Bradenton station is located in the upper northeastern portion of the study area. It was felt that use of this gage alone was insufficient to represent the rainfall over the entire study area, and the Myakka gage record was extrapolated to provide gage data in the southern portion of the study area. There are two rain gages within the Myakka River State Park. The Myakka River NWS (National Weather Station # 6065-04) rainfall record is lacking three consecutive months in 1966, and all of 1967. In order to obtain a long-term rainfall record in the southern portion of the NEP study area, the 1966 rainfall records for the two stations for the nine months were.compared,and deemed sufficiently close to allow substitution of the missing three months in the NWS station.
Except for 1967, the Bradenton ESE and Myakka NWS station data were averaged for each month of the period of record, and annual totals derived. The Bradenton ESE rainfall totals were used for the year of 1967.
The question of dissimilar distribution, and rainfall totals between the seaward barrier islands and the inland rainfall totals was investigated. Monthly, and annual rainfall totals from several local rain gages, including three stations located on barrier islands were compiled and statistically compared with four inland gages and one composite rainfall record. Rainfall totals were obtained as hard copy from the South West Florida Water Management District for the following stations : Station Name Sarasota Bradenton Cutter Siesta Key Tallevast Approximate Location Airport South Longboat Key (barrier island) North Siesta Key (barrier island) US 301 North of AirportRainfall data for City Island was obtained from Mote Marine Laboratory as daily digital data, and was totalled by month and year. Myakka River State Park was obtained as daily totals from National Climatic Data Center (NOAA) in digital form from 1957-1985, and totalled by month and year. This data was supplemented with climatological bulletins published by National Climatic Data Center (NCDC)


## . Bradenton ESE (NWS station 0945-04) rainfall totals were also taken from climatological bulletins. Data prior to 1981 were taken from microfiche of earlier bulletins.
Arithmetic averages of monthly totals (except as previously noted) were derived from the Myakka NWS and Bradenton ESE stations, and are designated as BRAdenton-Easka (BRAMYK)


## . - The descriptive statistics of each rainfall record are given below in Box 1. In accordance with USEPA (EPA-600/4-82-029) guidelines, all stations except Tallevast and Bradenton appear to be normally distributed (coefficient of skewness < 0.7). These two stations were deleted from further parametric evaluation and subjected to non-parametric tests.

Box 1

years df mean s.d. var

## . skew kurt.

CITY ISL. 9 8 48.20 10.20 104.05 0.6361 2.987 MYAKKA 4 6 45 55.70 11.56 133.65 0.2009 2.238 CUTTER 10 9 50.14 11.04 121.98 0.2345 2.026 SARBRA 10 9 49.52 9.40 88.41 -0.5432 2.692 SIESTA 12 11 49.31 8.78 77.12 0.3334 2.721

TALLY 39 38 58.04 15.25 232.64 0.8702 4.479 BRADENTON 51 50 54.54 11.30 127.76 0.7224 4.314 BRADtMYAK 4 6 45 55.48 7.95 63.28 0.4167 2.299

Prior to using parametric means tests (Student's 't' test), the equality of variance must be established. The 'F' ratio was used to determine if the variance of the station pairs were statistically similar. The results, given in Box 2, indicate that the following station pairs had statistically different variances (two-tailed significance < = 0.05): Myakka/Tallevast, Siesta/Tallevast, Bradenton/Tallevast, BRAMYK/Tallevast, BRAMYK/Bradenton and BRAMYK/Myakka. Non-parametric tests were conducted for these station pairs.Box 2
two-tailed Stations Compared F df/df signif. City Is1 vs. Myakka 1.2845 45/8 0.3764 City Is1 vs. Cutter 1.1723 9/8 0.4166 City Is1 vs. SarBra 1.1769 8/9 0.4036 City Is1 vs. Siesta 1.3492 8/11 0.3151 City Is1 vs. Tally 2.2358 38/8 0.1154 City Is1 vs. Bradenton 1.2279 50/8 0.4066 City Is1 vs. BRAMYK 1.6443 8/45 0.1392 Myakka vs. Cutter 1.0957 45/9 0.4771 Myakka vs. SarBra 1.5117 45/9 0.2614 Myakka vs. Siesta 1.7330 45/11 0.1629 Myakka vs. Tally 1.7407 38/45 0.0376 Myakka vs. Bradenton 1.0461 45/50 0.4366 Myakka vs. BRAMYK 2.1120 45/45 0.0068 Cutter vs. SarBra 1.3797 9/19 0.2642 Cutter vs. Siesta 1.5817 9/11 0.2335 Cutter vs. Tally 1.9072 38/9 0.1524 Cutter vs. Bradenton 1.0474 50/9 0.5123 Cutter vs. BRAMYK 1.9276 9/45 0.0720 SarBra vs. Siesta 1.1464 9/11 0.4085 SarBra vs. Tally 2.6314 38/9 0.0625 SarBra vs. Bradenton 1.4451 50/9 0.2873 SarBra vs. BRAMYK 1.3971 9/45 0.2180 Siesta vs. Tally 3.0166 38/11 0.0267 Siesta vs. Bradenton 1.6566 50/11 0.1833 Siesta vs. BRAMYK 1.2187 11/45 0.3028 Tally vs. Bradenton 1.8209 38/50 0.0236 Tally vs. BRAMYK 3.6764 38/45 0.0000 Bradenton vs. BRAMYK 2.0190 50/45 0.0091

Station pairs consisting of normally distributed data and equivalent variances were then evaluated for statistical similarity of annual means, without pairing of occurrence. The null hypothesis evaluated was that there is no difference in the annual mean rainfall totals. The results are given in the top half of Box 3, and indicate that twelve pairs were statistically equivalent at, or above the 0.05 significance level, and two pairs were not equivalent at the 0.05 level.
Next, the station pairs were subjected to 

### a 't' test of paired annual means. The results are illustrated in the bottom half of the previous box. Station pairs with significance levels less than 0.05 are considered statistically different. Eight were found to be different, and six pairs
were found to be statistically equivalent at the 0.05 significance level.

For station pairs that could not be evaluated with parametric techniques due to non-normality, or unequal variances, a Mann-Whitney test of similarity was employed. The results for annual, unpaired rainfall totals are given in the lower portion of Box 3. The results indicate that none ofthe annual mean comparisons excluded from parametric testing were significantly different (at the 0.05 significance level).

Box 3 two-sided significance level: unpaired t-test of annual means 2 3 4 5 6 7 8 0.0568 0.6956 0.7745 0.7970 /<non-normal>/ 0.0566 0.1620 0.0787 0.0417 /<non-normal>/ (F-test) It' 3 0.2735 0.0012~ 

# , 0.8930 0.8490 Icnon-normal>/ 0.1631 test 4 0.6794 0.0062 0.6408 0.9581 1cnon-normal>/ 0.0740 (two- 5 0.4841 0.0086 0.1767 0.9225l /<non-normal>/ 0.0345 sided) 6 I<----------- non-normal-------------> I f-) (F-test) 

### 1 7 I<----------- non-normal--------------- 

# I (F-test) 8 0.0021 (F-test) 0.0012 0.0020 0.0032 (F-test) (F-test)

Non-Parametric;two-sided significance level: Mann- Whitney test 1 2 3 4 5 6 7 8 l1 0.0684 0.1086 2 

## I 0.6753 0.5463 0.9906 3 0 .I538 0.2973 0.1467 0.3252 Mann 

## - Whitney Comparison for 5l 10.0637 0.1132 non-normal stations, or unequal variances. 6 0.2509 0.7276 7[ 

### -- 0.4902

1 = City Island, 2 = Myakka, 3 = Cutter, 4 = Sarasota Bradenton AOP 5 = Siesta, 6 = Tallevast, 7 = Bradenton ESE, 8 = (Bradenton+Myakka)/2
Italics type indicates either non-normal distributions based on the coefficient of skewness, or unequal variances as determined by the F'test. Bold faced type are significance levels <= 0.05.

The monthly totals were compared using a linear least squares regression. The regression test, by definition, is a 'paired' comparison. The following illustration (Box 4) indicates that there is no significant difference in the seasonal distribution of any station pair, suggesting that monthly variationbetween stations is consistent. In other words, when the monthly rainfall at one station is higher, it is likely to be relatively higher at all stations, although the magnitude of increase may vary between stations. In essence, the 'wet season' occurs at all stations during the same time of the year. All pairs were significant at P < = 0.0000, although it should be noted that station pairs including Tallevast and Bradenton are not normally distributed and thus may not be accurately represented by 

### a least squares evaluation based on a normal.distribution assumption.Box 4

rA2 of linear regression (monthly totals) 1 2 3 4 5 6 7 8 1 

## -------- 0.7444 0.8831 0.8466 0.8574 0.7691 0.5900 0.7317 2 

### -------

## - 0.7331 0.8029 0.7584 0.7461 0.7513 0.9322 3 

## -------- 0.8582 0.8815 0.7881 0.8269 0.8089 4 

### -

## ------- 0.8744 0.9478 0.8969 0.8870 5 (Note : Significance of all 

### ----

## ---- 0.8350 0.8491 0.8387 6 Comparisons < = 0.0000) 

### ------

## -- 0.8668 0.8451 7 

## -------- 0.9350 8 

### ---

## ----

## -

The results of the statistical evaluations indicate the following points:
1) The wet and dry seasons occur synchronously at all stations evaluated.
2) Taken as pairs of annual rainfall totals, there are significant differences among the stations evaluated. When the station locations are considered, the differences appear to be related to distance from the coast. For example, the results from the Myakka (and BRAMYK, which includes the Myakka results) were statistically different from the coastal stations, but not from the other inland stations. Station pairs exhibiting differences in paired annual means include the following:
Myakka and a) Cutter, b) Sarasota-Bradenton, c) Siesta, d) City Island. BRAMYK and a) Cutter, b) Sarasota-Bradenton, c) Siesta, d) City Island.
3) When evaluated as unpaired annual totals, the number of significant differences were minimal, with the Siesta Key annual rainfall differing from both the Myakka results and the BRAMYK results.

For the present annual NPS loading evaluation, 'whenf an annual rainfall total occurs is immaterial, and the unpaired comparisons are more appropriate than the paired comparisons. Considering the relatively short

(10-12 years) period of the coastal stations, use of the longer records of the inland stations is appropriate.