TOTAL MAXIMUM DAILY LOAD (TMDL) For Fecal Coliforms In C-25 Canal West (WBID 3160) and C-25 Cowbone Creek (WBID 3189) Prepared by: US EPA Region 4 61 Forsyth Street SW Atlanta, Georgia 30303 October 2008 SEPA United States Environmental Protection Agency In compliance with the provisions of the Federal Clean Water Act, 33 U.S.C §1251 et. seq., as amended by the Water Quality Act of 1987, P.L. 400-4, the U.S. Environmental Protection Agency is hereby establishing Total Maximum Daily Loads (TMDLs) for fecal coliforms in the ------- C-25 Canal West (WBID 3160) and C-25 Cowbone Creek (WBID 3189). Subsequent actions must be consistent with these TMDLs. James D. Giattina Date Director Water Management Division ------- Page Intentionally Blank ------- TABLE OF CONTENTS 1. INTRODUCTION 6 2. PROBLEM DEFINITION 9 3. WATERSHED DESCRIPTION 9 4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION 12 5. WATER QUALITY ASSESSMENT 13 6. SOURCE ASSESSMENT 16 6.1. Point Sources 17 6.2. Nonpoint Sources 17 6.3. Wildlife 17 6.4. Agricultural Animals 18 6.5. Onsite Sewerage Treatment and Disposal Systems (Septic Tanks) 18 6.6. Urban Development 19 7. ANALYTICAL APPROACH 20 7.1. Percent Reduction Approach for TMDL Development 20 8. DEVELOPMENT OF TOTAL MAXIMUM DAILY LOADS 21 8.1. Critical Conditions 22 8.2. Margin of Safety 22 8.3. Determination of TMDL, LA and WL A 22 8.4. Waste Load Allocations 22 8.5. Load Allocations 23 8.6. Seasonal Variation 23 8.7. Recommendations 23 REFERENCES 24 APPENDIX A: Water Quality Data 25 ------- LIST OF TABLES Table 1: Land Cover Distribution for WBID 3160 12 Table 2: Land Cover Distribution for WBID 3189 12 Table 3: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3160 13 Table 4: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3189 14 Table 5. Summary of Fecal Coliform Monitoring Data 14 Table 6. Livestock Inventory by County (source: USDA, 2002) 18 Table 7. County Estimates of Septic Tank Installations 19 Table 8. Summary of Fecal Coliform TMDL Components 22 Table 9: Guide to Water Quality Remark Codes (Rcode column in data tables) 25 Table 10. Fecal Coliform Data Collected in WBID 3160 (Source: IWR Run 32) 25 Table 11. Calculation of Percentiles 26 LIST OF FIGURES Figure 1: FDEP Group 2 River Basins 7 Figure 2: St. Lucie / Loxahatchee River Basin 8 Figure 3: C-25 Basin 1 Planning Unit 11 Figure 4: Water Quality Monitoring Stations in WBID 3160 15 Figure 5. Comparison between fecal coliform concentrations in C-25 Canal and rainfall..16 in ------- LIST OF ABBREVIATIONS AFO Animal Feeding Operation BMP Best Management Practices BPJ Best Professional Judgment CAFO Concentrated Animal Feeding Operation CFS Cubic Feet per Second CWA Clean Water Act DMR Discharge Monitoring Report EPA Environmental Protection Agency F.A.C. Florida Administrative Code GIS Geographic Information System LA Load Allocation MGD Million Gallons per Day MOS Margin of Safety MPN Most Probable Number MS4 Municipal Separate Storm Sewer Systems NASS National Agriculture Statistics Service NLCD National Land Cover Data NPDES National Pollutant Discharge Elimination System NRCS Natural Resources Conservation Service OSTD Onsite Sewer Treatment and Disposal Systems RM River Mile SFWMD South Florida Water Management District SLE St. Lucie Estuary S TA Storm water Treatm ent Area STORET STORage RETrieval database TMDL Total Maximum Daily Load USD A United States Department of Agriculture USGS United States Geological Survey WBID Water Body Identification WCD Water Control District WLA Waste Load Allocation WQS Water Quality Standard WWTF Wastewater Treatment Facility IV ------- SUMMARY SHEET Total Maximum Daily Load (TMDL) 1. 303(d) Listed Waterbody Information State: Florida Major River Basin: St. Lucie River Basin Impaired Waterbodies for TMDLs (1998 303(d) List): WBID 3160 3189 Segment Name and Type C-25 Canal West C-25 Canal West River Basin St. Lucie St. Lucie County St. Lucie, Indian River and Okeechobee St. Lucie, Indian River and Okeechobee Constituent(s) Fecal Coliform Fecal Coliform 2. TMDL Endpoints (i.e., Targets) for Class III Waters (fresh and marine): Fecal Coliform: 400 MPN/lOOml and 800 MPN/lOOml 3. Fecal Coliform Allocations: Stream Name / WBID C-25 Canal (3 160) C-25 Canal (3 189) Criterion used to develop TMDL 800 MPN/lOOml 400 MPN/lOOml WLA Continuous N/A N/A MS4 95% reduction N/A LA 95% reduction 97% reduction TMDL 95% reduction 97% reduction Notes: 1) To meet the 400 MPN/lOOml criterion in WBID 3160, a 67 percent reduction is required and to meet the 800 MPN/lOOml criterion in WBID 3189, a 95 percent reduction is needed (see Section 7.1); and 2) margin of safety is implicit in both TMDLs. 4 Endangered Species (yes or blank): Yes 5 EPA Lead on TMDL (EPA or blank): EPA 6. TMDL Considers Point Source, Nonpoint Source, or both: Both 7. Major NPDES Discharges to surface waters addressed in TMDLs: St. Lucie County MS4 (FLR04E029) Indian River County MS4 (FLR04E068) Larson Dairy Barn #3 (FLA139254) Note: MS4 permittees will only be responsible for reducing the anthropogenic loads associated with stormwater outfalls they own or otherwise has responsible control over. ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 TOTAL MAXIMUM DAILY LOAD (TMDL) FECAL COLIFORM IN C-25 CANAL WEST (WBIDS 3160 AND 3189) 1. INTRODUCTION Section 303(d) of the Clean Water Act (CWA) requires each state to list those waters within its boundaries for which technology based effluent limitations are not stringent enough to protect any water quality standard applicable to such waters. Listed waters are prioritized with respect to designated use classifications and the severity of pollution. In accordance with this prioritization, states are required to develop Total Maximum Daily Loads (TMDLs) for those water bodies that are not meeting water quality standards. The TMDL process establishes the allowable loadings of pollutants or other quantifiable parameters for a waterbody based on the relationship between pollution sources and in-stream water quality conditions, so that states can establish water quality based controls to reduce pollution from both point and nonpoint sources and restore and maintain the quality of their water resources (USEPA, 1991). The State of Florida Department of Environmental Protection (FDEP) developed a statewide, watershed-based approach to water resource management. Under the watershed management approach, water resources are managed on the basis of natural boundaries, such as river basins, rather than political boundaries. The watershed management approach is the framework FDEP uses for implementing TMDLs. The state's 52 basins are divided into 5 groups. Water quality is assessed in each group on a rotating five-year cycle. The Group 2 basin is shown in Figure 1 and includes the St. Lucie and Loxahatchee River Basin (Figure 2). The St. Lucie and Loxahatchee Basin encompasses many square miles. To provide a smaller-scale geographic basis for assessing, reporting, and documenting water quality improvement projects, the FDEP subdivided the Group 2 area into smaller areas called planning units. Planning units help organize information and management strategies around prominent subbasin characteristics and drainage features. To the extent possible, planning units were chosen to reflect subbasins that had previously been defined by the South Florida Water Management District (SFWMD). The St. Lucie and Loxahatchee Basin contains eight planning units: C-25/Basin 1, North St. Lucie, C-24, C-23, South St. Lucie, C-44, Loxahatchee, and Coastal. Water quality assessments were conducted on individual waterbody segments within planning units. Each waterbody segment is assigned a unique waterbody identification (WBID) number. Waterbody segments are the assessment units or polygons that have historically been used by the FDEP to define waterbodies in their biannual inventory and reporting of water quality to EPA under Section 305(b) of the federal Clean Water Act. The same WBIDs are also the assessment units identified in the FDEP's biannual lists of impaired waters submitted to EPA as part of their reporting under Section 303(d) of the Clean Water Act. ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Apalachicola -Chipol Mid die St. Johnsj Tampa Bay TributariesL I V | Charlotte Harbor | St. Lucia - Loxahatehe Figure 1: FDEP Group 2 River Basins ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 St. Lucie - Loxahatchee Group 2 Verified Listed Waters Interstates US Routes Major Rivers (lines) Major Rivers TMDL by Year | 12005 1 WBID I |2Q1n j 1998303d I Planning Units County Boundaries Figure 2: St. Lucie / Loxahatchee River Basin ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 2. PROBLEM DEFINITION Florida's final 1998 Section 303(d) list identified WBIDs 3160 and 3189 in the St. Lucie River Basin as not supporting water quality standards (WQS) due to coliform bacteria. After assessing all readily available water quality data, EPA determined fecal coliform TMDLs are needed in WBIDs 3160 and 3189. The locations of these WBIDs are shown in Figure 2. The TMDLs addressed in this document are being proposed pursuant to EPA commitments in the 1998 Consent Decree in the Florida TMDL lawsuit (Florida Wildlife Federation, et al. v. Carol Browner, et al., Civil Action No. 4: 98CV356-WS, 1998). WBIDs 3160 and 3189 are designated as a Class III fresh water. The designated use of Class III waters is recreation, propagation and maintenance of a healthy, well-balanced population offish and wildlife. Class III waters are further categorized based on fresh or marine waters. Water quality criteria for fecal and total coliform do not vary between Class III fresh or marine waters. 3. WATERSHED DESCRIPTION FDEP manages water resources based on river basins. The river basins are organized from large groups of major river basins to smaller watersheds called planning units, and finally to small waterbody polygons called WBIDs. The following information is from FDEP's Basin Status Report for St. Lucie and Loxahatchee (FDEP, 2003). In the St. Lucie Basin, most of the land in non-coastal areas is used for the production of citrus crops and beef cattle. The extensive network of canals that drain these agricultural areas transport stormwater runoff containing nutrients, sediment, bacteria, and other pollutants. These reach the natural drainage-ways (such as the North and South Forks of the St. Lucie River) and ultimately the St. Lucie Estuary and the South Indian River Lagoon. The St. Lucie Canal (C-44), the inland waterway that connects Lake Okeechobee to Florida's east coast, transports regulated releases of water from Lake Okeechobee and runoff from agricultural areas within the C-44 basin. Other major canals also transport storm-water from inland agricultural areas to the estuary. Canals C-23 and C-24 discharge water into the North Fork of the St. Lucie River and the C-25 Canal discharges to the Indian River Lagoon. Urban and residential areas continue to expand in the coastal areas, with polluted urban stormwater runoff and seepage from septic tanks also contributing to the water quality problems in streams and canals. As a result, portions of the St. Lucie Estuary (SLE) appear to be impaired by nutrients, copper, and low levels of DO. Other evidence of impairment was gathered for the SLE segments in a FDEP South East District biological survey (Graves et al., 2002). Sediment accumulation, decline of sea-grasses and oysters, algal blooms, fish kills, and low diversity of benthic macroinvertebrates in the SLE comprise this body of evidence. WBIDs 3160 and 3189 are in the C-25 Canal planning unit of the St. Lucie Basin. These two WBIDs are covered by this TMDL report since WBID 3189 is surrounded by and flows into WBID 3160. The planning unit includes the watershed of the C-25 Canal (also known as Belcher Canal), which transports water eastward across northern St. Lucie County from near the St. Lucie-Okeechobee County border. It includes the C-25, Basin 1, and C-25 East subbasins that are defined by SFWMD. The USGS includes all of these but Basin 1 in the Southeast Florida Coast ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 hydrologic unit. Basin 1 lies in the Indian River South hydrologic unit, as defined by USGS. The planning unit includes a complex network of canals primarily for agricultural drainage that has created a conveyance for discharge to the IRL. Runoff from the western part of the planning unit can discharge southward to the C-24 Canal via the C-25 extension (C-25 EXT). Runoff from the eastern and central portions of this subbasin is conveyed eastward through the S-99 structure on the C-25 Canal. Basin 1, east of S-99, receives drainage from the Ft. Pierce Farms Water Control District (WCD) that was established under Chapter 298, Laws of Florida. The Ft. Pierce Farms WCD Canal #1 is the primary surface water conveyance for Basin 1, providing drainage of the agricultural area and inhibiting saltwater intrusion. Canal #1 and C-25 discharge into the South IRL through the mouth of Taylor Creek at Ft. Pierce. The eastern part of this planning unit includes the northern edge of the Ft. Pierce city limits. Figure 3 is a composite map of this planning unit that shows potentially impaired waters and potential point sources of pollution. Approximately 10 percent of the planning unit area is defined as wetland and 15 percent listed as pine flatwoods. The largest contiguous wetland area, an extension of the St. Johns Marsh, is located in the northwestern corner of St. Lucie County. One state-managed natural area exists in the C-25/Basin 1 planning unit. The Green Swamp Preserve is located in the northwestern corner. Most waterbodies within this planning unit are agricultural canals used for drainage and/or irrigation that feed the conveyance system provided by C-25 and other SFWMD canals. Although classified as Class III waters, canals are not capable of supporting the diverse ecosystems characteristic of natural streams. The C-25/Basin 1 planning unit is primarily an agricultural area. Efforts to reduce pollutant loadings to storm-water from individual agricultural land holdings are tied to the active participation of local citrus growers and cattlemen in agricultural best management practices (BMP). These actions are assisted by Department of Agriculture and Consumer Services, University of Florida Institute of Food and Agricultural Science, U.S. Department of Agriculture Natural Resources Conservation Service and the FDEP Under the Indian River Lagoon South Feasibility Study, a regional water storage reservoir and a storm-water treatment area (STA) are proposed within this unit. This project will include a 741-acre aboveground reservoir and a 163- acre STA at the S-99 structure on the C-25 Canal. The system will be used to capture local runoff from the C-25 subbasin and the Ft. Pierce Farms WCD. The purpose of this component is to provide peak flow attenuation, a water supply for irrigation, and reductions in concentrations of nutrients, pesticides, and other contaminants. Water quality will be improved in the canal east of the STA and the southern Indian River Lagoon. WBID 3160 is a large polygon of over 96,000 acres that surrounds the much smaller WBID 3189 that contains only 741 acres. Cowbone Creek is a channelized stream system in the western part of the planning unit that makes up WBID 3189. Land cover in WBIDs 3160 and 3189 is mostly agriculture and wetlands, with about 81 and 52 percent agriculture and 12 and 43 percent wetlands, respectively. The land cover distribution for this and other cover types is shown in Table 1 for WBID 3160 and Table 2 for WBID 3189. Land cover is based on a 1999 coverage provided by the SFWMD. WBID 3160 includes most of the C-25 Canal planning unit. 10 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 * Oomestc and industrial waslewattff facilliv discharging to surface water * Domestic and industrial waslewater facility discharging to ground water O Wastewater facility greater than 0,1 MGO 4- Aciiva landfill (Class I, II, III, CSDj Q State-funded hazardous wasfe siie Superfund hazardous waste site n SFWMD structure Area o( toown ground wator contamination C-25/Basin 1 Planning Unit Walsrbody identification boundary Outstanding Florida Waters 303d listed waterbody segment PotenlBly impaired waterbotfy s^menl Sasec! on lmf>aimd Waters Ryle evaluatkm ftote: Featyms from legend not shown on this planning ynii m^j were not reported as being present. ~^r Figure 3: C-25 Basin 1 Planning Unit 11 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Table 1: Land Cover Distribution for WBID 3160 Land Cover Residential (1100-1390) Commercial, Industrial, Public (1400, 1500, 1800) Agriculture (2000 series) Rangeland (3000 series) Forest (4000 series) Water (5000 series) Wetlands (6000 series) Barren & Extractive (7000, 1600) Transportation & Utilities (8000 series) TOTAL (acres) Acreage 260 42 78448 686 1074 3022 11278 1063 563 96436 Percentage 0% 0% 81% 1% 1% 3% 12% 1% 1% Table 2: Land Cover Distribution for WBID 3189 Land Cover Residential (1100-1390) Commercial, Industrial, Public (1400, 1500, 1800) Agriculture (2000 series) Rangeland (3000 series) Forest (4000 series) Water (5000 series) Wetlands (6000 series) Barren & Extractive (7000, 1600) Transportation & Utilities (8000 series) TOTAL (acres) Acreage 0 0 386 0 21 12 322 0 0 741 Percentage 0% 0% 52% 0% 3% 2% 43% 0% 0% 4. WATER QUALITY STANDARD AND TARGET IDENTIFICATION The water quality criteria for protection of Class III waters are established by the State of Florida in the Florida Administrative Code (F.A.C.), Section 62-302.530. The individual criteria should be considered in conjunction with other provisions in water quality standards, including Section 62-302.500 F.A.C. [Surface Waters: Minimum Criteria, General Criteria] that apply to all waters unless alternative or more stringent criteria are specified in F.A.C. Section 62-302.530. Fecal coliforms are a subset of the total coliform group and indicate the presence of fecal material from warm-blooded animals. Total coliform bacteria generally indicate the presence of soil-associated bacteria and result from natural influences on a water body such as rainfall runoff as well as sewage inflows. The most probable number (MPN) or membrane filter (MF) counts per 100 milliliter (ml) of fecal coliform bacteria shall not exceed a monthly average of 200, nor exceed 400 in 10 percent of the samples, nor exceed 800 on any one day. Monthly averages shall be expressed as geometric means based on a minimum of 10 samples taken over a 30-day period. The geometric mean criteria reflect chronic or long-term water quality conditions whereas the 400 and 800 values reflect acute or short-term conditions. The target for these TMDLs are is the 12 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 daily 800 MPN/100 ml and the "not to exceed 400 in 10 percent of the samples" criteria, since insufficient monthly data were collected to evaluate the monthly average 200 criteria. 5. WATER QUALITY ASSESSMENT To determine the status of surface water quality in Florida, three categories of data, chemistry data, biological data, and fish consumption advisories, were evaluated to determine potential impairments. The level of impairment is defined in the Identification of Impaired Surface Waters Rule (IWR), Section 62-303 of the Florida Administrative Code (F.A.C.). The IWR defines FDEP's threshold for identifying water quality limited WBIDs to be included on the State's 303 (d) list. In addition, all waters on the 1998 303 (d) list that were not delisted remain on the current 303 (d) list and require TMDLs. WBIDs 3160 and 3189 are on FDEP's planning list for fecal coliform bacteria. EPA assessed these WBIDs using data reported in IWR Run 32 and concluded that they are impaired and fecal coliform TMDLs are required (see Appendix A). FDEP maintains ambient monitoring stations throughout the basin. Table 3 provides a list of the monitoring stations in WBID 3160 used in the development of the TMDL. The spatial distribution of the monitoring stations is shown in Figure 4. Data were not collected in WBID 3189; however, stations 21FLA26010429 and 21FLBRA3160-C are located downstream of WBID 3189 and are the only data available to characterize WBID 3189 (see Table 4). Therefore, the data collected at these two stations were used in the development of the TMDL for WBID 3189. Table 5 summarizes the fecal coliform monitoring data by station in the two WBIDs. Violations of the fecal coliform criteria often occur in response to rainfall events. Precipitation data collected at the St. Lucie County Airport (National Oceanic Atmospheric Administration Station 12895) located near WBID 3160 was plotted with the fecal coliform results in WBID 3160 to identify conditions when violations occurred (see Figure 5). In most instances, exceedances of the criteria occur in response to rain events while at other times exceedances occur during dry conditions. Implementation of this TMDL should address controlling nonpoint sources during both wet and dry weather conditions. Rainfall data were not available in WBID 3189, so a precipitation plot with fecal coliform correlations could not be developed for WBID 3189. Table 3: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3160 Station ID 21FLA 26010429 Station Name COWBONE CREEK AT SR 68 Number of Observations 12 Start Date 2/15/1996 End Date 8/4/1998 13 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 21FLBRA3160-A 21FLBRA3160-B 21FLBRA3160-C 21FLWPB28042331 21FLA 26010429 3 160 - Cowbone Creek - Header Rd dead ends at canal 3 160 - Cowbone Creek - Bridge W of Header Canal Rd station 3 160 - Cowbone Creek - Cowbone Creek off 68 CC1 - C-25 @ N HEADER CANALRD COWBONE CREEK AT SR 68 10 9 1 5 12 3/28/2006 6/6/2006 10/19/2006 2/7/2007 2/15/1996 10/19/2006 10/10/2006 11/7/2007 8/4/1998 Table 4: Monitoring Stations used in the Fecal Coliform TMDL for WBID 3189 Station ID 21FLA 26010429 21FLBRA3160-C Station Name COWBONE CREEK AT SR 68 3 160 - Cowbone Creek - Cowbone Creek off 68 Number of Observations 12 1 Start Date 2/15/1996 10/19/2006 End Date 8/4/1998 Table 5. Summary of Fecal Coliform Monitoring Data Number of Samples 21FLA 26010429 21FLBRA3160-A 21FLBRA3160-B 21FLBRA3160-C 21FLWPB28042331 % Samples > 400 (MPN/lOOml) 92% 0% 0% 100% 0% % Samples > 800 (MPN/lOOml) 50% 0% 0% 100% 0% Minimum Concentration (MPN/lOOml) 180 1 1 1000 2 Maximum Concentration (MPN/lOOml) 17100 315 036 1000 096 Notes: Insufficient data collected to evaluate geometric mean criterion 14 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Figure 4: Water Quality Monitoring Stations in WBID 3160 15 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Rainfall and Fecal Coliform Data in WBID 316ol 1400 T_ fecal coliform nmifirr m M fl Pirn 1700 1 "1 E --MOOO o E S 800 -I ^ z Rnn s 1 OĢ. 400 onn r| |-ŧ Rainfall TP'ff "f" '" 'I" 8/1/2003 9/4/2004 10/9/2005 a^n* ^^~^^~ 11/13/2006 12/18/ 0 2 a o 4 "2 - o w 8fl^ " 10 2007 Figure 5. Comparison between fecal coliform concentrations in C-25 Canal and rainfall 6. SOURCE ASSESSMENT An important part of the TMDL analysis is the identification of source categories, source subcategories, or individual sources of coliform bacteria in the watershed and the amount of pollutant loading contributed by each of these sources. Sources are broadly classified as either point or nonpoint sources. A point source is defined as a discernable, confined, and discrete conveyance from which pollutants are or may be discharged to surface waters. Point source discharges of industrial wastewater and treated sanitary wastewater must be authorized by National Pollutant Discharge Elimination System (NPDES) permits. NPDES permitted facilities discharging treated sanitary wastewater or stormwater (i.e., Phase I or II MS4 discharges) are considered primary point sources of coliform. Figure 3 shows permitted wastewater treatment facilities, landfills, and delineated ground water contamination areas in the planning unit. Most of the facilities are in the eastern part of the planning unit and do not impact WBIDs 3160 or 3189. Nonpoint sources of coliform are diffuse sources that cannot be identified as entering a waterbody through a discrete conveyance at a single location. These sources generally, but not always, involve accumulation of bacteria on land surfaces and wash off as a result of storm events. Typical nonpoint sources of coliform include: Wildlife Agricultural animals Onsite Sewer Treatment and Disposal Systems (septic tanks) Urban development (outside of Phase I or IIMS4 discharges) 16 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 A geographic information system (GIS) tool was used to display, analyze, and compile available information to characterize potential bacteria sources in the impaired WBID. This information includes land use, point source dischargers, soil types and characteristics, population data (human and livestock), and stream characteristics. 6.1. Point Sources Larson Dairy Barn #3 (FLA139254) is a confined animal feeding operation (CAFO). The facility discharges to a spray irrigation land application site in the Gomez Creek watershed within WBID 3160. Gomez Creek is a tributary to Cowbone Creek, and therefore this facility is a potential source of pollutants in both WBID 3160 and 3189. CAFOs are point sources, as defined by the CWA [Section 502(14)]. To be considered a CAFO, a facility must first be defined as an Animal Feeding Operation (AFO). Animal Feeding Operations (AFOs) are agricultural operations where animals are kept and raised in confined situations. AFOs generally congregate animals, feed, manure, dead animals, and production operations on a small land area. Feed is brought to the animals rather than the animals grazing or otherwise seeking feed in pastures. Animal waste and wastewater can enter water bodies from spills or breaks of waste storage structures (due to accidents or excessive rain), and non-agricultural application of manure to crop land. AFOs that meet the regulatory definition of a CAFO have the potential of being regulated under the NPDES permitting program. The NPDES permit for a CAFO does not allow discharge to surface waters except under extreme conditions. Municipal Separate Storm Sewer Systems (MS4s) may also discharge bacteria to water-bodies in response to storm events. Large, medium, and small MS4s serving populations greater than 50,000 people, or with an overall population density of 1,000 people per square mile, are required to obtain a NPDES storm water permit. There are three MS4 permits in St. Lucie County, five in Indian River County, and none in Okeechobee County. Only the St. Lucie County MS4 (FLR04E029) and the Indian River County MS4 (FLR04E068) are near WBID 3160 and are likely to discharge in the WBID. There are no MS4s near WBID 3189. 6.2. Nonpoint Sources Based on Level I and Level II land use summary information (SFWMD, 1995), the predominant land use in the C-25/ Basin 1 planning unit is agriculture (approximately 65 percent of area). The agricultural lands are used for cultivation of citrus (approximately 34 percent of planning unit area) and improved pasture (approximately 28 percent of area). Only 5 percent of the planning unit area is designated as urban/built-up. These land uses can be associated with nonpoint discharges of pollutants and eroded sediments. 6.3. Wildlife Wildlife deposit bacteria in their feces onto land surfaces where it can be transported during storm events to nearby streams. Bacteria load from wildlife is assumed background, since the contribution from this source is small relative to the load from urban and agricultural areas. Water fowl (e.g., egrets, ducks, wood storks, herons) often frequent storm-water ponds. Depending on the number of birds, the contributions of fecal coliform could result in stream 17 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 concentrations above the criteria. 6.4. Agricultural Animals Agricultural animals are the source of several types of coliform loadings to streams, that impact water quality. This source includes agriculture runoff from pastureland and cattle in streams. The land use within the impaired WBIDs is 81 and 52 percent agricultural (Table 1 and Table 2), so this landuse likely discharges a significant amount of the bacteria load. The USDA National Agricultural Statistics Service (NASS) compiles Census of Agriculture data by county for virtually every facet of U.S. agriculture (USDA, 2002). The "Census of Agriculture Act of 1997" (Title 7, United States Code, Section 2204g) directs the Secretary of Agriculture to conduct a census of agriculture on a 5-year cycle collecting data for the years ending in 2 and 7. In 2002, NASS reported 221,537 acres of farmland in St. Lucie County, 191,333 acres in Indian River County, and 392,495 acres in Okeechobee County. Livestock inventory from the 2002 Census of Agriculture reports are listed in Table 6. Cattle and calves are the predominate livestock. CAFOs are not known to operate in either St. Lucie or Indian River County; however, dairy farm CAFOs, such as the Larson Dairy discussed previously, are present in Okeechobee County. Table 6. Livestock Inventory by County (source: USDA, 2002) Livestock (inventory) Cattle and calves Hogs and Pigs St. Lucie 31,944 394 Okeechobee 142,656 82 Indian River 25,139 271 6.5. Onsite Sewerage Treatment and Disposal Systems (Septic Tanks) Onsite sewage treatment and disposal systems (OSTDs) including septic tanks are commonly used where providing central sewer is not cost effective or practical. When properly sited, designed, constructed, maintained, and operated, OSTDs are a safe means of disposing of domestic waste. The effluent from a well-functioning OSTD is comparable to secondarily treated wastewater from a sewage treatment plant. When not functioning properly, OSTDs can be a source of nutrient (nitrogen and phosphorus), pathogens, and other pollutants to both ground water and surface water. The State of Florida Department of Health publishes septic tanks data on a county basis (www.doh.state.fl.us/environment/ostds/statistics/ostdsstatistics.htm). Table 7 summarizes the cumulative number of septic systems installed since the 1970 census. The data does not reflect septic tanks removed from service. 18 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Table 7. County Estimates of Septic Tank Installations County St. Lucie Indian River Okeechobee Number Septic Tanks (1970-2002) 43,022 34,174 11,432 6.6. Urban Development Fecal coliform loading from urban areas is attributable to multiple sources including storm-water runoff, leaks and overflows from sanitary sewer systems, illicit discharges of sanitary waste, runoff from improper disposal of waste materials, leaking septic systems, and domestic animals. Urban land uses include residential, industrial, extractive and commercial categories. Fecal coliform loading from urban areas (whether within an MS4 jurisdiction or not) is attributable to multiple sources including storm water runoff, leaks and overflows from sanitary sewer systems, illicit discharges of sanitary waste, runoff from improper disposal of waste materials, leaking septic systems, and domestic animals. In 1982, Florida became the first state in the country to implement statewide regulations to address the issue of nonpoint source pollution by requiring new development and redevelopment to treat stormwater before it is discharged. The Stormwater Rule, as outlined in Chapter 403 of the Florida Statutes (F.S.), was established as a technology-based program that relies upon the implementation of BMPs that are designed to achieve a specific level of treatment (i.e., performance standards) as set forth in Chapter 62-40, F.A.C. Florida's stormwater program is unique in having a performance standard for older stormwater systems that were built before the implementation of the Stormwater Rule in 1982. This rule states: "the pollutant loading from older stormwater management systems shall be reduced as needed to restore or maintain the beneficial uses of water" (Section 62-40-.432 (5) (c), F.A.C.). In 1994, state legislation created the Environmental Resource Permitting program to consolidate stormwater quantity, stormwater quality, and wetlands protection into a single permit. Presently, the majority of environmental resource permits are issued by the state's water management districts, although DEP continues to issue permits for specific projects. Nonstructural and structural BMPs are an integral part of Florida's stormwater programs. Nonstructural BMPs, often referred to as "source controls", are those that can be used to prevent the generation of NPS pollutants or to limit their transport off-site. Typical nonstructural BMPs include public education, land use management, preservation of wetlands and floodplains, and minimizing impervious surfaces. Technology-based structural BMPs are used to mitigate the increased stormwater peak discharge rate, volume, and pollutant loadings that accompany urbanization. 19 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 7. ANALYTICAL APPROACH The approach for calculating coliform TMDLs depends on the number of water quality samples and the availability of flow data. When long-term records of water quality and flow data are not available, the TMDL is expressed as a percent reduction. Load duration curves are used to develop TMDLs when significant data are available to develop a relationship between flow and concentration. Flow measurements are not available in either WBID 3160 or 3189, nor were sufficient information available to estimate flow; therefore, these TMDLs are expressed as a percent reduction. 7.1. Percent Reduction Approach for TMDL Development Under this "percent reduction" method, the percent reduction needed to meet the applicable criterion is calculated based on a percentile of all measured concentrations. The (p X 100) percentile is the value with the cumulative probability of p. For example, the 90th percentile has a cumulative probability of 0.90. The 90th percentile is also called the 10 percent exceedance event because it will be exceeded with the probability of 0.10. Therefore, considering a set of water quality data, 90 percent of the measured values are lower than the 90th percentile concentration and 10 percent are higher. Since the water quality standard states the fecal coliform concentration shall not exceed 400 counts per 100 ml in 10 percent of the samples, 400 should be targeted with a percentile slightly larger than 90 to ensure less than 10 percent of the values exceed 400. For this TMDL, 400 counts per 100 milliliter was targeted as the 95th percentile. This will meet the water quality standard and provide a margin of safety by ensuring that only 5 percent of the data exceed a concentration of 400. There are many formulas for determining the percentile and these can be found in many text books on statistics. In these TMDLs the Hazen formula was used since it is recommended in Hunter's Applied Microbiology (2002) article concerning bacteria in water. Application of the Hazen formula to data collected in WBID 3160 is provided in Appendix A and summarized below. The percent reduction was also calculated using the maximum concentration measured in the WBID and the 800 criterion. The larger of the two percent reduction values was selected as the TMDL. The TMDL percent reduction required to meet the coliform criteria is based on the following equation: Percent Reduction = (existing 95th percentile concentration - criteria) / existing 95th percentile concentration x 100 (Equation 1) For WBID 3160, the existing 95th percentile concentration is 1,226 MPN/100 mL, and a 67 percent reduction is necessary to meet the water quality target of 400 MPN/100 mL 95 percent of the time. The "not to exceed 800" standard would result in a reduction of about 95 percent because of the maximum reported value of 17,100 counts per 100 mL. The 97 percent reduction is selected for the TMDL to comply with both acute and the chronic criteria in the water quality standards. For WBID 3189, the existing 95th percentile concentration is 14,727 MPN/100 mL, and a 97 percent reduction is necessary to meet the water quality target of 400 MPN/100 mL 95 percent of 20 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 the time. The "not to exceed 800" standard would result in a reduction of about 95 percent because of the maximum reported value of 17,100 counts per 100 mL. The 97 percent reduction is selected for the TMDL to comply with both water quality standards. 8. DEVELOPMENT OF TOTAL MAXIMUM DAILY LOADS The TMDL process quantifies the amount of a pollutant that can be assimilated in a waterbody, identifies the sources of the pollutant, and recommends regulatory or other actions to be taken to achieve compliance with applicable water quality standards based on the relationship between pollution sources and in-stream water quality conditions. A TMDL can be expressed as the sum of all point source loads (Waste Load Allocations (WLA)), nonpoint source loads (Load Allocations (LA)), and an appropriate margin of safety (MOS), which takes into account any uncertainty concerning the relationship between effluent limitations and water quality: TMDL = E WLAs + E LAs + MOS As discussed earlier, the WLA is broken out into separate subcategories for wastewater discharges and stormwater discharges regulated under the NPDES Program: TMDL = X WLAswastewater+ Ģ WLASNPDES Stormwater + Ģ LAs + MOS The various components of the TMDL equation may not sum up to the value of the TMDL because: a) the WLA for NPDES stormwater is typically based on the percent reduction needed for nonpoint sources and is also accounted for within the LA; and b) TMDL components can be expressed in different terms (e.g., the WLA for stormwater is typically expressed as a percent reduction, and the WLA for wastewater is typically expressed as mass per day). WLAs for stormwater discharges are typically expressed as "percent reduction" because it is very difficult to quantify the loads from MS4s (given the numerous discharge points) and to distinguish loads from MS4s from other nonpoint sources (given the nature of stormwater transport). The permitting of stormwater discharges also differs from the permitting of most wastewater point sources. Because stormwater discharges cannot be centrally collected, monitored, and treated, they are not subject to the same types of effluent limitations as wastewater facilities, and instead are required to meet a performance standard of providing treatment to the "maximum extent practical" through the implementation of BMPs. This approach is consistent with federal regulations (40 CFR § 130.2(i)), which state that TMDLs can be expressed in terms of mass per time (e.g., pounds per day), toxicity, or other appropriate measure. TMDLs for the C-25 WBIDs 3160 and 3189 are expressed as a percent reduction. The TMDLs are expressed as daily loads by multiplying the water quality target by an estimate of flow in the WBID. The C-25 Canal is an ungaged waterbody and therefore it is not possible to estimate flow with the available data. However, it is recommended that flow be measured at the time of sampling to ensure compliance with the TMDLs. The maximum one day load the Canal can transport in any 30-day period and maintain water quality standards is calculated by multiplying 800 MPN/100 ml times the flow (in cubic feet per second) and a conversion factor to obtain units of fecal coliform counts/day. 21 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 8.1. Critical Conditions The critical condition for nonpoint source coliform loading is an extended dry period followed by a rainfall runoff event. During the dry weather period, coliforms build up on the land surface, and are washed off by rainfall. The critical condition for point source loading occurs during periods of low stream flow when dilution is minimized. Water quality data have been collected during both time periods. Most violations occur in response to rain events. Critical conditions are accounted for in the analyses by using all water quality data available for the WBIDs. 8.2. Margin of Safety TMDLs shall include a margin of safety (MOS) that takes into account any lack of knowledge about the pollutant loading and in-stream water quality. In these TMDLs, lack of knowledge concerns the data, how well it represents the true water quality in the WBIDs, and the estimation of the exceedance probability. There are two methods for incorporating a MOS in the analysis: 1) implicitly incorporate the MOS using conservative model assumptions to develop allocations; or 2) explicitly specify a portion of the TMDL as the MOS and use the remainder for allocations. In these TMDLs, an implicit MOS was used by targeting reductions that will result in no more than 5 percent of the samples exceeding a concentration of 400 counts per 100 ml even though the standard requires less than 10 percent exceedance. In addition, the TMDLs require very high reductions. 8.3. Determination of TMDL, LA and WLA The TMDL values represent the maximum daily load the stream can assimilate and maintain water quality standards. The TMDLs are based on the daily 800 counts per 100 ml and the "not to exceed 400 in 10 percent of the samples" Class III WQS, and are expressed as percent reductions. TMDL components for the impaired water-bodies required to achieve the numerical criterion are summarized in Table 8. Table 8. Summary of Fecal Coliform TMDL Components Stream Name / WBID C-25 Canal (3 160) C-25 Canal (3 189) Criterion used to develop TMDL SOOMPN/lOOml 400MPN/100ml WLA Continuous N/A N/A MS4 95% reduction N/A LA 95% reduction 97% reduction TMDL 95% reduction 97% reduction Notes: 1) To meet the 400 MPN/lOOml criterion in WBID 3160, a 67 percent reduction is required and to meet the 800 MPN/lOOml criterion in WBID 3189, a 95 percent reduction is needed (see Section 7.1); and 2) margin of safety is implicit in both TMDLs. 8.4. Waste Load Allocations It is not applicable to assign a waste load allocation (WLA) to the Larson Dairy Barn #3 (FLA139254) because the CAFO permit does not allow the facility to discharge to surface 22 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 waters, except under extreme conditions. CAFOs have management plans that describe how the waste will be treated so that no waste water is discharged. The WLA for municipally separated storm sewer systems contributing pollutants to WBID 3160 is a 95 percent reduction from existing concentrations. There are two MS4 permits near WBID 3160: St. Lucie County MS4 (FLR04E029) and Indian River County MS4 (FLR04E068). It should be noted that any MS4 permittee will only be responsible for reducing the anthropogenic loads associated with stormwater outfalls that it owns or otherwise has responsible control over, and it is not responsible for reducing other nonpoint source loads in its jurisdiction. 8.5. Load Allocations There are two modes of transport for nonpoint source coliform bacteria loading into the stream. First, fecal coliform loading from failing septic systems and animals in the stream are considered direct sources of coliform to the stream, since they are independent of precipitation. The second mode involves coliform loadings resulting from accumulation on land surfaces transported to streams during storm events. Data from these WBIDs shows violations during wet weather and dry weather, so both direct and indirect sources should be targeted by the reductions. 8.6. Seasonal Variation Seasonality was addressed by using all water quality data associated with the impaired WBIDs, which was collected during multiple seasons over several years. 8.7. Recommendations It is recommended that flow be measured at the time of sampling so that loads can be calculated. The available data indicates violations of the acute criteria occurred at the stations in Cowbone Creek near State Route 68. Locating BMPs in the subbasins draining into these stations should be a priority during implementation. Determining the source of bacteria in waterbodies is the initial step to implementing a coliform TMDL. FDEP employs the Basin Management Action Plan (B-MAP) as the mechanism for developing strategies to accomplish the necessary load reductions. Components of a B-MAP are: Allocations among stakeholders Listing of specific activities to achieve reductions Project initiation and completion timeliness Identification of funding opportunities Agreements Local ordinances Local water quality standards and permits Follow-up monitoring 23 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 REFERENCES Cleland, Bruce, 2003. TMDL development from the "bottom up " - Part III: Duration curves and wet-weather assessments. America's Clean Water Foundation, Washington, DC. September 15,2003. Florida Administrative Code (F. A.C.). Chapter 62-302, Surface Water Quality Standards. FDEP, 2003. Basin Status Report, St. Lucie and Loxahatchee Basin, FDEP Division of Water Resource Management, Group 2 Basin, February 2003. Graves, Gregory A., Wan, Yongshan and Fike, Dana L., 2004. Water Quality Characteristics of Storm Water From Major Land Uses in South Florida, Journal of the American Water Resources Association, December 2004, 40(6): 1405-1419. Hunter, P.R., 2002. The Society for Applied Microbiology, Letters in Applied Microbiology. 34. 283-286. USDA, 2002. 2002 Census of Agriculture, Volume 1, Geographic Area Series, Part 9, U.S. Department of Agriculture, National Agricultural Statistics Service. AC02-A-9, June 2004. USDA, 1997. 7997 Census of Agriculture, Volume 1, Geographic Area Series, Part 42, U.S. Department of Agriculture, National Agricultural Statistics Service. AC97-A-42, March 1999. USEPA, 1991. Guidance for Water Quality -based Decisions: The TMDL Process. U.S. Environmental Protection Agency, Office of Water, Washington, DC. EPA-440/4-91-001, April 1991. 24 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 APPENDIX A: WATER QUALITY DATA Table 9: Guide to Water Quality Remark Codes (Rcode column in data tables) Remark Code A B E I J K L Q T U < Z Definition Value reported is mean of two or more samples Result based on colony counts outside the acceptable range Extra sample taken in compositing process The value reported is less than the practical quantification limit and greater than or equal to the method detection limit. Estimated. Value shown is not a result of analytical measurement. Off-scale low. Actual value not known, but known to be less than value shown Off-scale high. Actual value not known, but known to be greater than value shown Sample held beyond normal holding time Value reported is less than the criteria of detection Material was analyzed for but not detected. Value stored is the limit of detection. NAWQA - actual value is known to be less than the value shown Too many colonies were present to count (TNTC), the numeric value represents the filtration volume Use in TMDL Data included in analysis as reported Data included in analysis as reported Data included as average Data included in analysis as reported Data included in analysis as reported Data included in analysis as reported Data included in analysis as reported Data used in analysis - holding samples on ice slows the metabolism of the organisms resulting in no appreciable growth. Actual concentration is expected to be at least as high as the value reported. Data included in analysis if the reported value is below criteria; otherwise, reported value is not used in the analysis Data not included in analysis Data included in analysis Data not included in analysis Table 10. Fecal Coliform Data Collected in WBID 3160 (Source: IWR Run 32) Station Date Depth Result Rcode 25 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-C 21FLGW 20026 21FLGW 20105 21 FLWPB 28042331 21 FLWPB 28042331 21 FLWPB 28042331 21 FLWPB 28042331 21 FLWPB 28042331 2/15/1996 4/10/1996 8/1/1996 10/1/1996 11/20/1996 2/19/1997 7/8/1997 8/5/1997 11/5/1997 1/22/1998 6/2/1998 8/4/1998 3/28/2006 6/6/2006 6/15/2006 7/12/2006 7/20/2006 8/4/2006 8/20/2006 9/8/2006 10/10/2006 10/19/2006 3/28/2006 6/6/2006 6/15/2006 7/12/2006 7/20/2006 8/4/2006 8/17/2006 9/8/2006 10/10/2006 10/19/2006 8/19/2003 10/21/2003 2/7/2007 3/28/2007 8/1/2007 9/26/2007 11/7/2007 0.98 0.33 0.98 0.66 0.33 0.66 2.95 0.98 0.98 2.62 1.31 0.98 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.35 0.50 0.10 0.10 0.10 0.10 0.10 1280 1100 810 410 1010 950 610 520 17100 720 180 670 5.1 170 5.1 35 315 1 20 96 5.2 15 5.2 11 8.5 7.5 2 1 5.2 36 7.5 1000 880 10 11 2 96 78 14 J J U B B B Table 11. Calculation of Percentiles Date 8/4/2006 8/4/2006 7/20/2006 3/28/2007 3/28/2006 6/15/2006 10/10/2006 Station 21FLBRA3160-A 21FLBRA3160-B 21FLBRA3160-B 21 FLWPB 28042331 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A Result 1 1 2 2 5.1 5.1 5.2 Rcod e U Rank 1 2 3 4 5 6 7 Percentile by Hazen method 1% 4% 6% 9% 12% 14% 17% 26 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 Date 3/28/2006 8/17/2006 7/12/2006 10/10/2006 6/15/2006 10/21/2003 6/6/2006 2/7/2007 11/7/2007 10/19/2006 8/20/2006 7/12/2006 9/8/2006 9/26/2007 9/8/2006 8/1/2007 6/6/2006 6/2/1998 7/20/2006 10/1/1996 8/5/1997 7/8/1997 8/4/1998 1/22/1998 8/1/1996 8/19/2003 2/19/1997 10/19/2006 11/20/1996 4/10/1996 2/15/1996 11/5/1997 Station 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLBRA3160-B 21FLGW 20105 21FLBRA3160-B 2 1FLWPB 28042331 2 1FLWPB 28042331 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-A 21FLBRA3160-B 2 1FLWPB 28042331 21FLBRA3160-A 2 1FLWPB 28042331 21FLBRA3160-A 21 FLA 26010429 21FLBRA3160-A 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21FLGW 20026 21 FLA 26010429 21FLBRA3160-C 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 21 FLA 26010429 Result 5.2 5.2 7.5 7.5 8.5 10 11 11 14 15 20 35 36 78 96 96 170 180 315 410 520 610 670 720 810 880 950 1000 1010 1100 1280 17100 Rcod e B B J J B Rank 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Percentile by Hazen method 19% 22% 24% 27% 29% 32% 35% 37% 40% 42% 45% 47% 50% 53% 55% 58% 60% 63% 65% 68% 71% 73% 76% 78% 81% 83% 86% 88% 91% 94% 96% 99% In this TMDL the Hazen formula was used since it is recommended in Hunter's Applied Microbiology (2002) article concerning bacteria in water. To use the Hazen formula to calculate the percentile associated with the sample concentrations, the data are first sorted by concentration, lowest to highest. A ranking is assigned to each sample, with the lowest concentration having a rank of 1 and the highest concentration having a rank equivalent to the total number of samples collected. The percentile is calculated as follows: Percentile = (Rank - 0.5)/ (total number of samples collected) For example, on October 19, 2006 a fecal coliform concentration of 1000 MPN/lOOml was measured at station 21FLBRA3160-C. This concentration ranks number 35 out of 39 samples collected in WBID 3160. The associated percentile is calculated as: Percentile = (35-0.5)739 = 0.88 = 88% 27 ------- Fecal Coliform TMDLs for C-25 Canal West (WBIDs 3160) and C-25 Cowbone Creek (WBID 3189) September 2008 This implies that 88 percent of the time the instream concentration is less than 1000 MPN/lOOml. 28 ------- |