STORMWATER MANAGEMENT REPORT

Transcription

1 STORMWATER MANAGEMENT REPORT

2 STORMWATER MANAGEMENT REPORT GOLDEN GLADES INTERCHANGE PD&E STUDY Miami-Dade County, Florida Financial Management Number: Efficient Transportation Decision Making (ETDM) Number: Prepared for Florida Department of Transportation - District Six Miami, Florida Prepared by: Stantec Consulting Services, Inc. 901 Ponce de Leon Boulevard, Suite 900 Coral Gables, Florida Stantec.com April 2014

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4 EXECUTIVE SUMMARY This report provides the drainage documentation required to support the Project Development and Environment (PD&E) Study prepared for the Golden Glades Interchange (GGI) project area. This report identifies possible locations for stormwater treatment ponds. In addition, it also evaluates the Right-of-Way (R/W) needed to accommodate the stormwater management facilities. The purpose of this project is to provide a system-to-system connection for the SR 826/Palmetto Expressway eastbound to I-95 northbound movement and to improve the Turnpike southbound to I-95 southbound connection. The ultimate phase will evaluate a system-to-system connection between new express lanes on SR 826/Palmetto Expressway and the existing 95 Express Lanes System. The GGI is located in northeastern Miami-Dade County, Florida. The study area covers approximately 512 Acres and is located in Section 13, Township 52 South and Range 41 East. Discharge from the study area is bifurcated by the South Florida Rail Corridor (SFRC). Runoff from the area north of the SFRC ultimately drains northwesterly, within the Turnpike swales, towards the C-9 Canal. The area south of the SFRC generally drains south, within 2-72 asphalt coated ultra-flow metal pipes under I-95, towards the C-8 Canal. The project area was divided into seven main drainage systems. The naming convention was chosen so that the first two characters represent the receiving water body followed by an abbreviation of the general location of the system. The western portion of the study corridor is within the Anodyne contamination plume. A one-mile buffer around the contamination plume covers most of the study area. The Florida Department of Environmental protection (FDEP) discourages the use of wet ponds or exfiltration trenches within one mile of a superfund site. As such, water treatment facilities proposed by this study, which fall within the 1-mile Anodyne buffer, consist of dry-retention and/or dry-detention. Stormwater management systems proposed by this study meet current water quality standards as set forth in Chapter of the Florida Administrative Code. The approach to meeting water quality requirements is to provide treatment for the increase in impervious area and restore or replace existing treatment facilities impacted by this project. This approach was discussed with SFWMD during an interagency monthly meeting held on September 20 th Golden Glades Interchange Stormwater Management Report ii

5 TABLE OF CONTENTS SECTION PAGE EXECUTIVE SUMMARY... ii TABLE OF CONTENTS... iii LIST OF TABLES... vi 1. INTRODUCTION Project Description and Location DATA COLLECTION Vertical Datum Regional Watershed and Receiving Waterbodies Seasonal High Ground Water Table Soil Properties Wellfields Existing Drainage Concerns DESIGN CRITERIA Standards Water Quality Discharge Limitations PRELIMINARY DRAINAGE ANALYSIS Stormwater Management Systems System C8_I95-S Existing Condition Ultimate Build Alternative Interim Build Alternatives System C8_PR Existing Condition Ultimate Build Alternative Interim Build Alternatives System C8_GGI Golden Glades Interchange Stormwater Management Report iii

6 4.4.1 Existing Condition Ultimate Build Alternative Interim Build Alternatives System C8_I95-N Existing Condition Ultimate Build Alternative Interim Build Alternatives System C9_GGI Existing Condition Ultimate Build Alternative Interim Build Alternatives System C9_TPK Existing Condition Ultimate Build Alternative Interim Build Alternatives System C8_NW17th Existing Condition Ultimate Build Alternative Interim Build Alternatives Drainage Analysis Summary FLOODPLAIN CROSS DRAINS WATERBODY CROSSINGS I-95 over C-8 Canal (Bridge No ) NW 167 th Street over NW 17 th Avenue Canal (Culvert Extension) NW 165 th Street over NW 17 th Avenue Canal (Proposed Culvert) PERMITTING Existing Permits Proposed Permits CONCLUSIONS REFERENCES Golden Glades Interchange Stormwater Management Report iv

7 LIST OF FIGURES FIGURE PAGE Figure 1-1 Project Location... 1 Figure 2-1 Regional Watersheds... 3 Figure 3-1 Anodyne Superfund Site Contamination Plume & Buffer Figure 4-1 Stormwater Management Systems Figure 4-2 Drainage System C8_I95-S Figure 4-3 Drainage System C8_PR Figure 4-4 Drainage System C8_GGI Figure 4-5 Drainage System C8_I95-N Figure 4-6 Drainage System C9_GGI Figure 4-7 Drainage System C9_TPK Figure 4-8 Drainage System C8_NW17th Figure 5-1 FEMA Floodplain Map Figure 7-1 Bridge No (I-95 over C-8 Canal) Figure 7-2 Culvert Extension (NW 167 th ST Over NW 17 th Ave. Canal) Figure 7-3 Proposed Culvert (NW 165th ST Over NW 17 th Ave. Canal) Golden Glades Interchange Stormwater Management Report v

8 LIST OF TABLES TABLE PAGE Table 2-1 Datum Conversion from NGVD 29 to NAVD Table 2-2 Percolation Rates within Project Area... 4 Table 2-3 Soil Corrosion Properties... 4 Table 2-4 Miami-Dade County Soil Types within Project Area... 5 Table 3-1 Design Criteria... 6 Table 3-3 SFWMD Water Quality... 9 Table 4-1 Drainage System Characteristics Table 4-2 Preliminary Calculation Summary Golden Glades Interchange Stormwater Management Report vi

9 LIST OF APPENDICES Appendix A: Figures and Maps A-1: Project Aerial A-2: USGS Quad Map A-3: NRCS Soil Survey Maps A-4: Miami-Dade County Average October Ground Water Level Map A-5: Miami-Dade County Wellfield Map A-6: FEMA Flood Insurance Rate Map A-7: Vertical Datum Conversion Appendix B: Calculations B-1: Drainage Areas B-2: Water Quality Treatment Calculations B-3: Water Quality Impact Evaluation Appendix C: Project Correspondence and Meeting Minutes C-1: RER exemption January 13 th 2012 C-2: SFWMD Interagency Meeting April 19 th 2012 C-3: SFWMD Interagency Meeting September 20 th 2012 C-4: RER Meeting October 15 th 2012 C-5: FDOT Maintenance Teleconference October 24 th 2012 Appendix D: Geotechnical Data D-1: Geotech Structural Report Excerpts D-2: Geotech Percolation and Infiltration Report Appendix E: Excerpts from Previous Projects E-1: Drainage Map from SPN E-2: Drainage Map from SPN E-3: Drainage Map from SPN E-4: Drainage Report from SPN Golden Glades Interchange Stormwater Management Report vii

10 Appendix E: Excerpts from Previous Projects (Continued) E-5: Drainage Report from FPID E-6: Drainage Plans from SPN E-7: Drainage Plans from FPID Appendix F: Excerpts from Previous Permits F-1: SFWMD Permit S, Application X F-2: SFWMD Permit S, Application F-3: SFWMD Permit P, Application F-4: DERM Permit OF 401 Golden Glades Interchange Stormwater Management Report viii

11 1. INTRODUCTION This report provides the drainage documentation required to support the Project Development and Environment (PD&E) Study prepared for the Golden Glades Interchange (GGI) project area. Possible locations for stormwater treatment ponds, Right-of-Way (R/W) needed to accommodate the stormwater management facilities and a preliminary hydraulic analysis of the area are contained in this report. 1.1 Project Description and Location The purpose of this project is to provide a system-to-system connection for the SR 826/Palmetto Expressway eastbound to I-95 northbound movement and to improve the Turnpike southbound to I-95 southbound connection. The ultimate phase will evaluate a system-to-system connection between new express lanes on SR 826/Palmetto Expressway and the existing I-95 Express Lanes system. The Golden Glades Interchange (GGI) is located in northeastern Miami-Dade County, Florida (See Figure 1-1). The study area covers approximately 512 Acres and is located in Section 13, Township 52 South and Range 41 East. A USGS quadrangle map of the study corridor is located in Appendix A. Figure 1-1 Project Location Golden Glades Interchange Stormwater Management Report 1

12 2. DATA COLLECTION 2.1 Vertical Datum The primary vertical datum used in this report and the calculations is NGVD 29. This datum was chosen due to the fact that all existing data for the interchange is in NGVD 29. Moreover, government agencies such as the Army Corps of Engineers (ACOE), Federal Emergency Management Agency (FEMA), South Florida Water Management District (SFWMD) and Miami-Dade Department of Regulatory and Economic Resources (RER) currently use NGVD 29. Where practical, elevations are shown in both NGVD 29 and NAVD 88 since NAVD 88 is the Florida Department of Transportation (FDOT) standard datum. The vertical datum shift was identified for the approximate centroid of the study area by using the National Geodetic Survey VERTCON online tool. Coordinates of the centroid are shown below in Table 2-1. The datum shift used to convert NGVD 29 to NAVD 88 within the study area is (-)1.562 feet. See Appendix A for National Geodetic Survey VERTCON datum shift. Table 2 1: Datum Conversion from NGVD 29 to NAVD 88 Location Latitude Longitude Shift (ft) Study Area Centroid (-) Regional Watershed and Receiving Waterbodies The study corridor lies within South Florida Water Management District (SFWMD) Basins C-7, C-8, and C-9 East (See Figure 2-1). Discharge from the study area is bifurcated by the South Florida Rail Corridor (SFRC). Runoff from the area north of the SFRC ultimately drains northwesterly, within the Turnpike swales, towards the C-9 Canal. The area south of the SFRC generally drains south, within 2-72 asphalt coated ultra-flow metal pipes under I-95, towards the C-8 Canal. An exception to this statement is the southwestern corner of the project, which is north of the SFRC but drains into a local canal that runs along NW 17 th Avenue and discharges into the C-8 Canal. Golden Glades Interchange Stormwater Management Report 2

13 Figure 2-1 Regional Watersheds 2.3 Seasonal High Ground Water Table Geotechnical information provided by HR Engineering Services states that test borings, conducted during 2012, showed groundwater levels varying from elevation 2.1 to 2.6 ft- NGVD 29 (0.5 to 1.0 ft-navd 88). The geotechnical report recommended a Seasonal High Ground Water Table (SHGWT) of 4.6 ft-ngvd 29 (3.0 ft-navd 88). A review of the Miami-Dade County Design Standards indicates that the average elevation of the October ground water table for the project area is approximately 2.5 ft-ngvd (0.9 ft-navd). As such, the SHGWT value of 4.6 ft-ngvd 29, recommended by the geotech report, is considered conservative and will be used in the preliminary drainage design for this study. See Appendix D for the geotech reports and Appendix A for Miami-Dade County average October ground water level. Golden Glades Interchange Stormwater Management Report 3

14 2.4 Soil Properties Five percolation tests (Exfiltration) and seven double ring infiltrometer tests (Infiltration) were performed, during the geotechnical exploration, to estimate the hydraulic conductivity of the soils within the project area. Two additional percolation tests, from the nearby Turnpike Connector project, were also provided in the geotechnical report. Test results indicate that the percolation rates are poor to moderate and increase with depth, as shown in Table 2-2. The effective infiltration rate varies from 0.04 to 3.5 inches/hour for an average of 1.5 inches/hour. Calculations conducted to support the preliminary drainage analysis described in this report consider exfiltration trenches to be installed at a depth of 20-ft having a hydraulic conductivity of 1.5E-05 cfs/ft 2 -ft of head. Dry-retention pond recovery will be estimated using an infiltration rate of 1.5 inches/hour. These values were chosen as they are expected to yield reasonably conservative results. Table 2 2: Percolation Rates within Project Area Depth (ft) Hydraulic Conductivity (cfs/ft 2 -ft of head) E-06 to 3.2E E-06 to 2.3E E-05 to 2.4E-04 As an element of the geotechnical evaluation, soil and water samples were obtained to identify the soil corrosion properties outlined in Table 2-3. Testing of the soil and water samples revealed that drainage culverts will be subject to a moderately aggressive environment. Table 2 3: Soil Corrosion Properties Resistivity (ohms-cm) ph Sulfates (ppm) Chlorides (ppm) 1,460-3, Golden Glades Interchange Stormwater Management Report 4

15 The geotechnical report for this project suggests that unsuitable materials are not anticipated within the project area based on a review of the soil map published by the United States Department of Agriculture (USDA). There are four general mapping units (soil types), as shown below in Table 2-4. See Appendix D for the geotech reports and Appendix A for the project soils map. Table 2 4: Miami-Dade County Soil Types within Project Area Map Unit Symbol 10 Map Unit Name Udorthents, limestone substratum- Urban land Typical Profile 0 to 55 inches: Extremely Gravely Loam 55 to 59 inches: Unweathered Bedrock 15 Urban land N/A 40 Pomello sand 0 to 80 inches: Sand 99 Water 100 percent Water 2.5 Wellfields There are no wellfields within the project area. See Appendix A for a wellfield map of Miami-Dade County. 2.6 Existing Drainage Concerns The Study Team contacted FDOT District Six maintenance personnel to discuss maintenance concerns as they relate to drainage. Items of particular concern were localized ponding in the swales/infields or flooding in the travel lanes. Based on information obtained, incidents of flooding have been reported at the NW 7 th Avenue extension to US 441. Flooding at this location has been reported as early as 2004 and as late as Most of the flooding issues seem to be attributed to deficiencies in the drainage system as well as clogged drainage inlets. See teleconference notes and correspondence located in Appendix C. FDOT District Six drainage personnel have been made aware of the reoccurring ponding taking place at the NW 7 th Avenue extension to US 441. During the Final Design stage of this project, drainage design engineers are advised to further explore existing flooding conditions to ensure that they are corrected as part of the interim improvements proposed for the interchange. Golden Glades Interchange Stormwater Management Report 5

16 3. DESIGN CRITERIA 3.1 Standards Drainage design and construction criteria for the proposed improvements will adhere to FDOT Standards for the design of such roadways and will comply with the recommended standard practices as set forth in Table 3-1. Table 3 1 Design Criteria DESIGN ELEMENT CRITERIA SOURCE Design Frequency Storm Sewer - 10-Year design frequency standard (1, 8, 24-hour) - Check 100-Year storm (1,8, 24 hour) - 50-Year design frequency for interstate facility sag vertical curves which have no outlet other than a storm drain system D.M. Section 3.3 Cross Drains 50-Year design frequency D.M. Section 4.3 Design Tailwater All Conditions Conditions vary with outfall D.M. Section 3.4 Time Of Concentration (TOC) Minimum T.O.C. of 10 Minutes D.M. Section Other T.O.C calculations to follow NRCS TR-55 Pipe Slopes Minimum Min. slope to produce v=2.5 ft/sec flowing full D.M. Section Manning's "n" Coefficient Pipes (smooth pipes) (corrugated pipe) D.M. Section Asphalt (rough texture) Asphalt Pavement S.D. Table 3-2 Grades Longitudinal Gutter Grade minimum gutter grade is 0.3% D.M. Section Spread Standards Design Speed 45 Keep ½ lane clear 45 < Design Speed 55 Keep 8-ft of lane clear D.M. Section 3.9 Design Speed >55 No encroachment Pipe Size And Length Trunk Line 18-in Minimum Diameter. D.M. Section Length Between Structure 18-in Pipe=300ft., 24in 36in=400ft,>42-in =500ft D.M. Section Exfiltration Trench Pipe Diameter 24-in minimum D.M. Section Golden Glades Interchange Stormwater Management Report 6

17 Table 3 1 Design Criteria DESIGN ELEMENT CRITERIA SOURCE Exfiltration Trench (continued) Pipe Lengths Access through both ends: 300-ft 24-in to 30-in pipes; 400-ft for 36-in and larger pipes. Access through only one end: 150ft 24-in to 30-in pipes; 200-ft 36-in and larger pipes D.M Pipe Perforations Perforated pipes preferred in District 6 Skimmers/Baffles Trench Width Trench Depth Drainage Structures Other District 6 Preferences Ground Water Clearance Required at each entrance to exfiltration trench Minimum 4-ft, maximum 8-ft Maximum of 20-ft 2-foot sediment sump for inlets and catch basins FDOT District 6 Exfiltration Trench Reference Manual E.T.R.M Section 3.1 Dry Retention Pond bottom minimum 1-ft above SHGWT B.M.P. Section VIII Freeboard Storm Drain Ponds Permanent Pool Pond Depth Hydraulic Gradeline Minimum 1-ft below theoretical gutter elevation 1.13-ft below E.O.P. for Types E & F curb and gutter 1-ft below grate elevation for inlets Standard Index, Minimum 1-ft above peak design stage, measured from the inside edge of the maintenance berm. S.D. Section 5.0 D.M. Section Wet Detention 4-ft minimum depth, 8-ft maximum depth S.M.F. Section Stormwater Management System Water Quality Water quality standards, as set forth in Chapter , Florida Administrative Code. V - IV Section 5.0 Discharge Limitations Historic Discharges, Post <= Pre V - IV Section 6.1 Bridge Clearances Horizontal Vertical Center span 25 feet clear bent spacing, measured perpendicular to the channel. Approach bents 20 feet between faces of bents. 6 feet above seasonal high optimum water control elevation, or 2 feet above the design water surface, whichever produces the greater elevation. V - V Section IX B 7 feet above mean high water for Miami-Dade Canals RER Meeting 10/15/2012 Golden Glades Interchange Stormwater Management Report 7

18 Table 3 1 Design Criteria DESIGN ELEMENT CRITERIA SOURCE Bridge Clearances (continued) Vertical 2 feet minimum clearance between design flood stage and the low member of bridge to allow for debris P.P.M passage. 6 feet above Normal High Water for controlled canals Abbreviations D.M. FDOT Drainage Manual; January 2013 E.T.R.M FDOT District 6 Exfiltration Trench Reference Manual; January 2008 P.P.M. Plans Preparation Manual Volume 1, January 2012 S.D. FDOT Storm Drain Handbook; January 2012 S.M.F. FDOT Stormwater Management Facility Handbook; January 2004 V-IV SFWMD Permit Information Manual Volume IV; 2012 V-V SFWMD Permit Information Manual Volume V; 1999 B.M.P SFWMD Best Management Practices for South Florida Urban Stormwater Management Systems; April Water Quality Stormwater management systems proposed by this study meet existing water quality standards as set forth in Chapter of the Florida Administrative Code. The approach to meeting water quality requirements is to provide treatment for the increase in impervious area and restore or replace existing permitted treatment facilities impacted by this project. Table 3-2 summarizes the methodology used to calculate the treatment volume. An emphasis was placed on providing treatment for the increase in impervious area rather than providing treatment for the entire project area since the project is geometrically constrained due to the linear nature of the facility and heavily urbanized areas surrounding the study area. This approach will be followed for the increase in impervious area as it relates to the total project area and not dependent on whether the increase in impervious area is due to roadway widening or total road reconstruction, as discussed in the South Florida Water Management District (SFWMD) interagency monthly meeting held on September 20 th See Appendix C for meeting minutes. Golden Glades Interchange Stormwater Management Report 8

19 Table 3 2: SFWMD Water Quality Type of Treatment Wet-detention Dry-detention Dry-retention Treatment Volume* 2.5 inches times the increase in impervious area 75% of wet detention volume 50% of wet detention volume *Note: SFWMD agreed to this approach due to corridor constraints. During the development of the Contamination Screening Evaluation Report (CSER) for this PD&E, a superfund site named Anodyne was identified. There is evidence that waste from this site was discharged directly onto the ground. Furthermore, a 90-foot deep injection well was allegedly used to dispose of spent solvents during the manufacturing phase of the facility s operation. The Anodyne contamination plume, as estimated in 2010 by the TerranearPMC groundwater remediation study, extends into the western portion of the study corridor. A one-mile buffer around the contamination plume covers most of the study area, as shown below in Figure 3-1. The Florida Department of Environmental protection (FDEP) discourages the use of wet ponds or exfiltration trenches within one mile of a superfund site. As such, this study proposes dry-retention and/or dry-detention stormwater treatment facilities for areas which fall within the 1-mile Anodyne buffer. The use of solid pipe is FDEP s preferred method of conveyance through contaminated areas. A Phase II contamination study is recommended by the CSER to further quantify impacts to the project due to the contamination from the Anodyne superfund site as well as other smaller contamination sites within the study area. The CSER is prepared as part of the PD&E Study. Golden Glades Interchange Stormwater Management Report 9

20 Figure 3-1 Anodyne Superfund Site Contamination Plume & Buffer 3.3 Discharge Limitations As mentioned earlier in Section 2.2, the main receiving water bodies for this project are the C-8 and C-9 Canals. According to the South Florida Water Management District (SFWMD) Permit Information Manual, Volume IV, the allowable off-site discharge is essentially unlimited by gravity connection for both the C-8 and C-9 Canals. Given the preliminary nature of this study, the post development peak discharge has been attenuated to predevelopment levels in order to avoid impacting adjacent land uses. This is particularly important for systems discharging into the C-9 Canal, which must first flow through the Turnpike s existing system. The peak discharge for this project was estimated by using the SCS runoff curve number method as described in Technical Release 55 (TR-55), published in 1986 by the United States Department of Agriculture (USDA). Golden Glades Interchange Stormwater Management Report 10

21 4. PRELIMINARY DRAINAGE ANALYSIS The preliminary drainage analysis conducted for this study consisted of evaluating the project area to estimate the stormwater treatment and conveyance needs. The term stormwater treatment is used throughout this section to refer to both the water quality and peak attenuation requirements for a particular system. Typically the greater of the two is provided to insure both requirements are met. Preliminary calculations show that for most of the drainage systems in this project, the water quality and peak attenuation requirements are very close. Preliminary calculations are located in Appendix B. A summary of the analysis is provided in this Section. It follows the general format of identifying existing conditions and then providing recommended improvements that would be needed to accommodate additional runoff expected from the increase in impervious area (pavement) in the post development condition. The analysis was conducted for the roadway Ultimate Build Alternative and Interim Build Alternatives 3A, 3B, 3C, and 4 as described in the Preliminary Engineering Report. 4.1 Stormwater Management Systems The project area was divided into six main drainage systems, as shown below in Figure 4-1. A seventh system around NW 17 th Street was delineated based on potential connectivity mitigations to SR 826/Palmetto Expressway; this is further explained in Section 4.8. System limits were determined using existing drainage divides, which included changes in elevation, transportation facilities and water bodies. The naming convention was chosen so that the first two characters represent the receiving water body followed by an abbreviation of the general location of the system. These systems combined have a total area of 310 Acres. Golden Glades Interchange Stormwater Management Report 11

22 Figure 4-1 Stormwater Management Systems 4.2 System C8_I95-S Existing Condition System C8_I95-S covers the area of I-95 between SR 916/NW 135 th Street/Opa-Locka Boulevard and the C-8 Canal. It is slightly over a mile long and within the 1-mile buffer of the Anodyne contamination plume. Most of the drainage system consists of a network of inlets and closed pipes connecting to a main outfall trunk line, which discharges into the C-8 Canal. There is, nonetheless, a segment of the southbound lanes, between NW 151 st Street and the C-8 canal, which has a small swale system with a 24-inch outfall pipe into the canal. The main outfall trunk line in this system consists of concrete culverts, which progress in size from 30-inch to 42-inch. The trunk line runs the length of the basin and is on the west side of I-95 from Opa-Locka Boulevard to just south of NW 151 st Street. It then crosses under I-95 to connect to a 54-inch trunk line running east towards the canal. A desktop review of the limited plans available for the area indicates that the 54-inch trunk line services both I-95 and the adjacent residential community. The existing stormwater management system, for this segment of I-95, appears to be a direct discharge system with no formal water treatment being provided. Golden Glades Interchange Stormwater Management Report 12

23 Figure 4-2 Drainage System C8_I95-S Ultimate Build Alternative Most of the proposed roadway work within Drainage System C8_I95-S, under the Ultimate Build Alternative, is focused on the southbound lanes of I-95. Impervious area (pavement) is being added in order to provide direct managed lane connections between Florida s Turnpike and I-95 Express southbound managed lanes. The new pavement will add 2.0 Acres of impervious area and increase the roadway footprint towards the west. Preliminary calculations indicate that 0.21 Ac-ft of additional dry-retention will be needed to meet water quality requirements. Several parcels, in the vicinity of NW 6 th Court between NW 146 th Street and NW 151 st, will be acquired to accommodate the roadway improvements. A review of the proposed roadway geometry suggests that 1.8 Acres will be available for storm water treatment in the area where parcels will be acquired. This area can be used to accommodate a dry-retention pond with a bottom area of 1.2 Acres and a depth of 1.0 ft to provide a dry-retention treatment volume of 1.2 Ac-ft. The pond would Golden Glades Interchange Stormwater Management Report 13

24 provide 1.0 Ac-ft of surplus treatment since only 0.2 Ac-ft of treatment is required for this system. Surplus treatment provided in this pond could be used to compensate for required treatment in adjacent systems that also outfall into the C-8 Canal. This pond will need to be connected to the system trunk line in order to provide an outfall for overflows into the pond. A connection will have to be made to the trunk line before it crosses to the east side of I-95 in order to avoid needing to Jack & Bore or needing to open trenching across both lanes of I-95. It is anticipated that the surface drainage for the roadway can be accomplished by extending the existing closed pipe system and placing inlets as needed to control the spread. A note is made that contamination has been identified in the general vicinity of the proposed dry-retention pond. The site is identified as Jimmy s Shell located at NW 7 th Avenue and it poses a minimal potential of environmental impacts if dewatering is needed during construction activities. See environmental documents for specific contamination issues along the corridor Interim Build Alternatives Under Build Alternative 3A, there is minor work occurring within Drainage System C8_I95. The increase in impervious area is limited to the southbound lanes of I-95 between NW 151 st Street and the C-8 Canal. Preliminary calculations indicate that the impervious area will increase by 0.4 Acres and will require 0.04 Ac-ft of dry-retention. This amount of treatment is small enough that it can easily be accommodated in an adjacent system. In the event that surplus treatment is not available in a nearby system, a small dry-retention pond can be placed in the western swale of I-95, just north of NW 151 st Street, to provide the required water quality treatment. The western swale can accommodate a dry retention pond with a bottom area of 0.3 Acres and retention depth of 1-ft to provide a dry-retention treatment volume of 0.3 Ac-ft. Overflows into the pond can be discharged by using a control structure connected to the existing 24-inch outfall pipe, which discharges into the C-8 Canal. Under Build Alternatives 3B and 3C, the proposed improvements are the same, within this system, as in the Ultimate Build Alternative. As such, drainage improvements needed to meet water quality requirements for Build Alternatives 3B and 3C are the same as what is needed for the Ultimate Build Alternative in this drainage system. For Build Alternative 4, the proposed improvements and added impervious area are the same, within this system, as in Build Alternative 3A. Golden Glades Interchange Stormwater Management Report 14

25 4.3 System C8_PR Existing Condition System C8_PR consists of the Park & Ride, Municipal Parking facility and SR 9. The system is bound by the South Florida Rail Corridor (SFRC) on the north and the Turnpike Connector on the east, as shown in Figure 4-3. It is partially within the Anodyne contamination plume and completely within the 1-mile buffer of the plume. Stormwater runoff from this system is generally conveyed southeasterly through the Municipal Parking facility s piped drainage system. Ultimately, the runoff is discharged through a 42-inch culvert into the adjacent drainage system (C8_GGI), which outfalls into the C-8 Canal. See Appendix E for the Municipal Parking Facility drainage map (SPN ). The existing stormwater management system appears to be a direct discharge system with no formal water treatment being provided. Figure 4-3 Drainage System C8_PR Golden Glades Interchange Stormwater Management Report 15

26 4.3.2 Ultimate Build Alternative Roadway improvements proposed within Drainage System C8_PR, under the Ultimate Build Alternative, are geared towards providing a direct connection between SR 9 and I-95 in the northbound direction as well as widening the I-95 connector to facilitate movements from the Turnpike and SR 826 onto I-95 southbound. The new pavement will add 2.3 Acres of impervious area. Preliminary calculations indicate that 0.24 Ac-ft of dry-retention will be needed to meet water quality requirements. The required treatment can be provided through compensation in System C8_I95, which outfalls into the same receiving water body and is anticipated to have surplus treatment capacity when the Ultimate Build Alternative is constructed. In the event that surplus treatment is not available in C8_I95 or a nearby system, a 1-ft ditch block can be provided before runoff enters the Municipal Parking facility s piped drainage system. This would result in the retention of runoff within the southbound and northbound lanes of SR-9. Two small dry-retention ponds would be created that would have a combined bottom area of 1.6 Acres and a treatment volume of 1.6 Ac-ft, which exceeds the treatment volume of 0.24 Ac-ft required for this drainage system. A surplus of 1.36 Ac-ft would be available to be used as compensation in an adjacent system. Excess runoff into the ponds would overtop the ditch block and outfall through the Municipal Parking facility s piped drainage system. The minor stage, created in the retention ponds, is not anticipated to impact the existing roadway base clearance since the roads in this area are several feet above the existing ground level Interim Build Alternatives Within Drainage System C8_PR, Interim Build Alternatives 3A, 3B and 3C will widen the Turnpike connector. Interim Build Alternative 3A will add 1.9 Acres of impervious area and require 0.20 Ac-ft of dry-retention while both Interim Build Alternatives 3B and 3C will add 2.2 Acres of impervious area and require 0.23 Ac-ft of dry-retention. For Build Alternative 4, the proposed improvements and added impervious area are the same, within this system, as in Build Alternative 3A. In all cases, the potential stormwater treatment methods described for the Ultimate Build Alternative are applicable. Namely, using surplus treatment in an adjacent drainage system or providing a 1-ft ditch block to create a treatment volume of 1.6 Ac-ft. Golden Glades Interchange Stormwater Management Report 16

27 4.4 System C8_GGI Existing Condition System C8_GGI consists of the southern part of the Golden Glades Interchange (GGI). The system is bound by the South Florida Rail Corridor (SFRC) on the north and the C-8 Canal on the south, as shown in Figure 4-4. Most of this drainage system is within the 1-mile buffer of the Anodyne contamination plume. This drainage system receives runoff from System C8_PR as described in Section A review of available plans and permit information indicates that stormwater in this system is being collected and treated via dry-retention in the various infield areas between ramps before being discharged to the C-8 Canal. The I-95 northern segment of this drainage system has two concrete storm sewer trunk lines, which direct runoff south towards the GGI infield areas. One trunk line is located under each of the outside shoulders. Both trunk lines begin as an 18-inch round culvert near the northern limits of the drainage system and transition through several sizes of elliptical pipe before discharging into the GGI areas. The trunk line, located under the northbound outside shoulder ends as a 54-inch round culvert near NW 2 nd Avenue while the trunk line under the southbound outside lane ends as a 36-inch round culvert near the infield area between I-95 and SR 9. Excess runoff generated within the interchange portion of the system is generally conveyed south towards a double 72-inch asphalt coated metal trunk line that is located under the southbound shoulder of I-95 between the Park & Ride ramp and the C-8 Canal. See the drainage map for State Project (Appendix E) for more information on the existing trunk lines. The drainage report submitted to the Miami-Dade Department of Regulatory and Economic Resources (RER), to obtain permit OF 401 for project , states that Ac-ft of retention/detention is being provided in the aforementioned infield areas. Improvements that have occurred in this drainage system, since the RER permit was issued, have had little impacts to the amount of impervious area or treatment volume. See Appendix F for permit excerpts. Golden Glades Interchange Stormwater Management Report 17

28 Figure 4-4 Drainage System C8_GGI Ultimate Build Alternative Proposed roadway improvements within Drainage System C8_GGI, under the Ultimate Build Alternative, facilitate connections between the major roadways within this drainage system. A new flyover ramp to connect SR 826 eastbound to I-95 northbound as well as various widening and roadway realignments are being provided to meet this goal. The Ultimate Build Alternative will add 6.0 Acres of impervious area to the drainage system. This will require 0.63 Ac-ft of dry-retention to meet water quality. In the southern end of the project, improvements to the I-95 southbound lanes will move the travel lanes towards the west, which will result in the double 72-inch outfall pipes, and corresponding manholes, being in the travel lanes. Relocation of the double 72-inch outfall pipes (appx. 1,400-ft) is recommended to avoid having manholes in the travel lanes. Likewise, in the northern end of the drainage system, a portion of the 54-inch trunk line (appx. 2,800-ft) will also need to Golden Glades Interchange Stormwater Management Report 18

29 be relocated for the same reason since the I-95 northbound lanes will be shifted towards the east to create a median area that will accommodate the managed lanes. The control elevation for one of the existing dry-ponds, near the proposed flyover ramp, can be raised by 0.5-ft to increase the treatment volume from 0.95 Ac-ft to 1.67 Ac-ft in order to provide 0.72 Ac-ft of treatment volume, exceeding the required volume needed. The dry pond is identified as Area 20 in the plans for project A ditch block is currently being used to provide the control elevation. It can be raised by adding more earth to the ditch block and providing a concrete topping per SFWMD requirements. During final design, a detailed infiltration analysis will be required to ensure the pond recovers within 24-hours using the in-situ soil since an exfiltration trench to aid in pond recovery will not be allowed because the dry pond is within the Anodyne 1-mile buffer. The roadway base clearance is not anticipated to be impacted by the minor stage increase in Area 20. An alternative approach to meet water quality requirements for this drainage system, under the Ultimate Build Alternative, is to provide a dry retention pond within the infield area that will be created between NW 7 th Ave and the I-95 ramp. This approach would require a careful review of existing contamination since the adjacent parcels in this area are currently industrial. Should contamination be identified in the immediate area, a dry retention pond poses a potential of displacing the contamination plume Interim Build Alternatives Within Drainage System C8_GGI, Interim Build Alternatives 3A, 3B, 3C, and 4 will add 0.4, 1.1, 3.6, and 1.0 Acres of impervious area, respectively. Interim Build Alternative 3A will require 0.04 Ac-ft of dry retention. This small amount of treatment can easily be accommodated in a nearby drainage system. Interim Build Alternatives 3B, 3C, and 4 will require dry-retention treatment of 0.13, 0.38, and 0.13 Ac-ft respectively. The drainage solutions discussed in Section to meet water quality requirements for the Ultimate Build Alternative would be applicable to Build Alternatives 3B, 3C, and 4. Any surplus storage created during these interim phases would be available for the Ultimate Build Alternative. All four Interim Build Alternatives would require the relocation of the double 72-inch outfall pipes, located in the southern end of the drainage system. Golden Glades Interchange Stormwater Management Report 19

30 4.5 System C8_I95-N Existing Condition System C8_I95-N spans from just south of NE 1 st Avenue to NE 183 rd Street (Miami Gardens Drive). It is slightly less than a mile long and is outside of the Anodyne 1-mile buffer. This drainage system consists of roadside swales on both sides of the roadway with equalizer pipes connecting them and a retention area located in the western swale where I-95 turns away from the South Florida Rail Corridor (SFRC). The retention area provides 0.35 Ac-ft of dry-retention treatment. See the drainage report excerpts from FPID , located in Appendix E for more information on the existing retention area. In general runoff is conveyed from the eastern swale to the western swale, which abuts the SFRC, and runs south towards Drainage System C8_GGI. A note is made that the drainage report for FPID states that the area served by this drainage system ultimately discharges to the C-9 Canal; however a review of existing plans did not show a connection to move runoff across NE 183 rd Street. As such, the study team concluded that this drainage system ultimately discharges south along the SFRC swale towards the C-8 Canal rather than across NE 183 rd Street towards the C-9 Canal. Figure 4-5 Drainage System C8_I95-N Golden Glades Interchange Stormwater Management Report 20

31 4.5.2 Ultimate Build Alternative Under the Ultimate Build Alternative, within Drainage System C8_I95-N, proposed roadway improvements provide an additional lane in each direction for the I-95 express lanes located between the northbound and southbound lanes of the I-95 mainline. The express lanes are accommodated by shifting out the mainline by approximately 14-ft on the west side and 19-ft on the east side. The Ultimate Build Alternative will add 2.2 Acres of impervious area to the drainage system. In order to meet water quality, 0.23 Ac-ft of dry-retention will be needed to account for the increase in impervious area and 0.18 Ac-ft will be needed to offset encroachments into the existing retention area for a total of 0.41 Ac-ft of dry-retention needed for this drainage system. Proposed roadway improvements will greatly reduce or eliminate the existing swales being used for conveyance. A drainage trunk line (appx. 2,500-ft of 42-inch) will be needed to replace the function of the swales. Preliminary calculations indicate that the required 0.41-Ac-ft of dry-retention can be provided by installing 2,000-ft of 20-ft deep exfiltration trench in series with the new trunk line. The use of exfiltration trench in this drainage basin is acceptable because there is limited R/W available for a dry pond, the drainage system is outside of the 1-mile Anodyne contamination buffer and the anticipated exfiltration rate is 1.7E-05 cfs/ft 2 -ft of head. A note is made that this basin is located near several isolated contaminated sites, according to RER and FDEP records. See the Contamination Screening Evaluation Report (CSER) for details of these sites Interim Build Alternatives Interim Build Alternatives 3A, 3B, 3C, and 4 will not add any additional impervious area to Drainage System C8_I95-N. As such, no improvements are needed to this drainage system under the interim build alternatives. Golden Glades Interchange Stormwater Management Report 21

32 4.6 System C9_GGI Existing Condition System C9_GGI consists of the northern part of the Golden Glades Interchange (GGI) and an adjacent section of SR 826 (Palmetto Expressway), as shown in Figure 4-6. It is partially within the Anodyne contamination plume and completely within the 1-mile buffer of the plume. Stormwater runoff from the SR 826 segment of this system is conveyed east, through trunk lines along both sides of the roadway, towards the GGI interchange infield area. Runoff from the SR 826 southern swale is conveyed through a 24-inch x 38-inch cross drain under SR 826 to unite with runoff from the northern swale and flows north along the outside western Turnpike swale. In general, runoff generated within this drainage system is directed towards the GGI infield areas and then north towards the Turnpike (Drainage System C9_TPK) where it is conveyed by a 36-inch culvert through the Toll Plaza area and ultimately into the C-9 Canal. Based on a review of available construction plans and permitting information, the existing stormwater management system was not designed to provide a specific amount of water quality treatment. Figure 4-6 Drainage System C9_GGI Golden Glades Interchange Stormwater Management Report 22

33 4.6.2 Ultimate Build Alternative Proposed roadway improvements within Drainage System C9_GGI, under the Ultimate Build Alternative, facilitate connections between the major roadways within this drainage system. A new flyover ramp to connect SR 826 eastbound to I-95 northbound as well as widening of the Turnpike connector to I-95 southbound are being provided to meet this goal. The Ultimate Build Alternative will add 7.3 Acres of impervious area to the drainage system. This will require 0.78 Ac-ft of dry-retention to meet water quality. Proposed right-of-way acquisition of the warehouse area located in the Sunshine Industrial Park found in the southwest quadrant of the Golden Glades Interchange (GGI) can provide an appropriate location for water quality treatment. The proposed right-of-way acquisition area is part of Interim Build Alternative 4, which will be used to provide for the NW 12 th Avenue on-ramp to SR 826 that continues connecting to I-95 southbound. This potentially acquired area can accommodate a 4.2-Acre dry-retention pond. A depth of 0.5-ft can yield 2.10 Ac-ft of dry-retention treatment in the pond, thereby providing surplus treatment since only 0.78 Ac-ft of treatment is required for this system. Surplus treatment provided in this pond could be used to compensate for required treatment in adjacent systems that also outfall into the C-9 Canal. In order to get runoff from SR 826 to the proposed pond, trunk lines along both sides of SR 826 will need to be extended (Appx ft) and increased in size from 24-inch to 36-inch pipes. The north trunk line would need to cross under SR 826 and connect to the south trunk line before reaching the SR 826/I-95 ramp. The final discharge point, of the extended southern trunk line, would then be on the eastern side of the pond by the SR 826/I-95 ramp. Excess runoff into the pond could be discharged using the existing 24-inch x 28-inch cross drain under SR 826 and then continue to flow north along the outside western Turnpike swale towards the Turnpike Toll Plaza and eventually into the C-9 Canal. The required treatment volume for this drainage system can also be provided by creating a dry-retention pond in the FDOT owned vacant lot, folio , located just north of the railroad and bordered by both the SR 826 and Turnpike Connectors. This vacant lot can accommodate a 3.6-Acre dry-retention pond while avoiding impacting the Intelligent Transportation System (ITS) existing building on the site. A depth of 0.5 ft will yield 1.80 Ac-ft of dry-retention treatment in the pond thereby providing surplus treatment Golden Glades Interchange Stormwater Management Report 23

34 for this system. As mentioned before, available surplus treatment could be used to compensate for required treatment in adjacent systems that also outfall into the C-9 Canal. The aforementioned vacant parcel has been used in the recent past as a debris staging area to facilitate disaster recovery after hurricanes. If the parcel is used as a stormwater treatment pond, it will no longer be available for use as a debris staging area. See Appendix C for notes of a teleconference held with the FDOT Maintenance Department. In order to get runoff from SR 826 to the proposed pond, trunk lines will be needed along both sides of the roadway to get the runoff to the Turnpike Connector infield area. The trunk line on the north side will need to cross under the SR 826 mainline with a 42-inch culvert (Appx. 300-ft). The trunk line on the south side will need to cross under the SR 826/I-95 ramp with a 42-inch culvert (Appx. 150-ft). A 54-inch culvert (Appx. 250-ft) will need to be installed under the Turnpike Connector to get the runoff from the infield area to the pond. Given the relative height of the roadways to the surrounding ground, the Jack & Bore installation method will likely be the most economical way to install the needed culverts. Excess runoff into the pond can be discharged using the existing culverts to convey runoff towards the Turnpike Toll Plaza and into the C-9 Canal. A review of plans for proposed improvements to the Turnpike Toll Plaza (FPID ) indicates that the existing 36-inch culvert, used as this systems outfall and described in Section 4.7.1, will remain in operation after the improvements are constructed. See Appendix E for excerpts from the plans for the Toll Plaza improvements Interim Build Alternatives Within Drainage System C9_GGI, Interim Build Alternatives 3A, 3B and 3C are focused on widening the Turnpike Connector. Interim Build Alternative 4 also focuses on the Turnpike Connector widening but is more distinctly concerned with maintaining the NW 12 th St on-ramp open, to SR 826. Interim Build Alternative 3A, 3B, 3C, and 4 will add 3.3, 3.6, 3.8, and 3.5 Acres of impervious area, respectively. In all cases, the increase in impervious area is roughly half of the increase estimated for the Ultimate Build Alternative. As such, the potential stormwater treatment methods described for the Ultimate Build Alternative are applicable. However, the dry-retention pond potentially available due to the prospective right-of-way acquisition is only a viable treatment alternative for Interim Build Alternative 4. A note is made that there is a potential of encountering contamination during pond excavation due to the proximity of the Anodyne contamination plume and localized fuel Golden Glades Interchange Stormwater Management Report 24

35 spills from traffic accidents in the interchange. Final designers of the selected interim build alternative may want to limit excavation of the pond to the amount needed to meet water quality requirements for the interim design rather than excavating the pond for the Ultimate Build Alternative. 4.7 System C9_TPK Existing Condition System C9_TPK covers the area of the Turnpike between the Toll Plaza and the Golden Glades Interchange (GGI) loop ramps. It is approximately half a mile long and is within the 1-mile buffer of the Anodyne contamination plume. In general, runoff from this system is conveyed along the Turnpike swales towards the C-9 Canal. This drainage system receives runoff from Drainage System C9_GGI. For the purposes of quantifying the increase in impervious area, the existing condition in Drainage System C9_TPK was considered as the condition that will result once project FPID is constructed. A review of the proposed plans indicates that the existing 36-inch culvert, used as this system s outfall, will remain in operation after the improvements are constructed. See Appendix E for excerpts from the plans for the Toll Plaza improvements. Project FPID will convert the Toll Plaza to an All Electronic Tolling (AET) facility. Consequently, the facility s impervious footprint will be reduced allowing water quality treatment to be provided in the roadside swales. Documentation for permit P, Application , indicates that the water quality treatment provided in the widened swales is to compensate future improvements to the Turnpike mainline. See Appendix F for excerpts from permit P Ultimate Build Alternative Proposed roadway improvements within Drainage System C9_TPK, under the Ultimate Build Alternative, focus on widening the Turnpike connector to I-95 southbound. The Ultimate Build Alternative will add 0.9 Acres of impervious area to the drainage system. This will require 0.09 Ac-ft of dry-retention to meet water quality. The treatment volume requirement for this system can be met by providing compensating treatment in Drainage System C9_GGI, which has surplus capacity in its dry retention pond. Golden Glades Interchange Stormwater Management Report 25

36 Figure 4-7 Drainage System C9_TPK Interim Build Alternatives In this drainage system, roadway improvements proposed for Interim Build Alternatives 3A, 3B, 3C, and 4 are the same as the improvements proposed for the Ultimate Build Alternative. As such, the potential stormwater treatment methods described for the Ultimate Build Alternative are applicable for the interim build alternatives. Golden Glades Interchange Stormwater Management Report 26

37 4.8 System C8_NW17th This drainage system was delineated due to potential considerations in closing the NW 12 th Avenue on-ramp to SR 826. To maintain connectivity to SR 826, NW 17 th Avenue would be widened at the intersections to provide additional turn lanes and a new bridge at NW 165th Street crossing the NW 17 th Avenue Canal would be provided Existing Condition System C8_NW17th covers the area of NW 17th Avenue from NW 163rd Street to the SR 826. It is slightly less than half a mile long and within the 1-mile buffer of the Anodyne contamination plume. NW 17th Avenue is a County owned two lane undivided rural road with no dedicated drainage system. There are, however, a few drainage inlets mostly along the western swale area, as shown in Figure 4-8, but there is no formal conveyance system to get runoff to the inlets. Construction plans for NW 17th Avenue were unavailable from Miami-Dade County at the time of this study. The assumption is made that each of the sparsely placed drainage inlets is connected to an exfiltration trench of undetermined length and condition. The roadway is crowned such that runoff from the southbound lane sheet-flows into a flat swale area shared with a residential neighborhood while runoff from the northbound lane sheet-flows into a 15-ft wide flat strip of sod before overflowing into the NW 17th Avenue canal. In general, runoff generated within this system overtops NW 17th Avenue and flows into the NW 17th Avenue canal, which discharges into the C-8 Canal Ultimate Build Alternative In the Ultimate Build Alternative, the NW 12 th Avenue on-ramp to SR 826 will remain open, thus not requiring alternative connectivity to SR 826. There are no roadway improvements proposed within Drainage System C8_NW17th under the Ultimate Build Alternative Interim Build Alternatives Roadway improvements proposed within this drainage system, under Interim Build Alternatives 3A, 3B, and 3C will add 1.2 Acres and 0.13 Ac-ft of dry-retention will be needed to meet water quality requirements. There are no roadway improvements proposed within Drainage System C8_NW17th under Interim Build Alternative 4. Options to meet water quality needs within this system are limited by the NW 17 th Avenue Canal on the east side and residential development along the west side. The geometric constraints of the system area leave little room for stormwater treatment outside of the Golden Glades Interchange Stormwater Management Report 27

38 roadway R/W. Furthermore, the use of exfiltration trench in this system is discouraged by FDEP because it is within the 1-mile buffer of the Anodyne contamination plume. The approach to meeting water quality is to provide as much treatment within the existing R/W and provide compensating treatment in adjacent system to balance any shortcomings in this drainage system. A review of the potential roadway typical section for this system indicates a shallow ditch that can be utilized as a dry-retention swale for the southbound lane. The ditch is divided into two separate swales by NW 166 th Street. Each swale would need an outfall into the NW 17 th Avenue Canal and it would be beneficial to have an equalizer pipe connecting the swales under NW 163 rd Street. The ditches would have side slopes of 1H:3V, average width of 5.5-ft, a combined length of 1,100-ft and a retention depth of 0.5-ft to provide 0.07 Ac-ft of dry-retention treatment. The remaining 0.06 Ac-ft of dry-retention treatment would need to be provided in an adjacent drainage system with surplus capacity. Coordination with Miami-Dade Department of Regulatory and Economic Resources (RER) will be needed to obtain a permit for construction of an outfall into the NW 17 th Avenue Canal. Figure 4-8 Drainage System C8_NW17th Golden Glades Interchange Stormwater Management Report 28

39 4.9 Drainage Analysis Summary Preliminary water quality and attenuation calculations performed for the study are located in Appendix B. They are also summarized in Table 4-1 and Table 4-2, shown below. The treatment/storage quantity provided for each receiving water body exceeds the required amount for each Build Alternative. Table 4 1: Drainage System Characteristics Drainage System Existing Ultimate Build Alternatives Interim Interim 3A 3B Interim 3C Interim 4 TA EI EP PI PP PI PP PI PP PI PP PI PP C8_I95-S C8_PR C8_GGI C8_I95-N C8_NW C9_GGI C9_TPK NOTES: 1. TA = Total Area in drainage system (Ac). 2. EI = Existing Impervious Area (Ac). 3. EP = Existing Pervious area (Ac). 4. PI = Proposed Increase in impervious area (Ac). 5. PP = Proposed Pervious area (Ac). Golden Glades Interchange Stormwater Management Report 29

40 Table 4 2: Preliminary Calculation Summary Drainage System Build Alternatives Ultimate Interim 3A Interim 3B Interim 3C Interim 4 WQ ATT PRV WQ ATT PRV WQ ATT PRV WQ ATT PRV WQ ATT PRV C8_I95-S C8_PR C8_GGI C8_I95-N C8 NW C9_GGI C9_TPK Build Alternatives Receivin g Water Body Ultimate Interim 3A Interim 3B Interim 3C Interim 4 WQ ATT PRV WQ ATT PRV WQ ATT PRV WQ ATT PRV WQ ATT PRV C-8 Canal C-9 Canal NOTES: 1. WQ = Required treatment volume to meet water quality requirements (Ac-ft). 2. ATT = Required storage volume to attenuate peak discharge (Ac-ft). 3. PRV = Treatment/storage volume provided by proposed design (Ac-ft). 4. Treatment/storage quantity provided for each receiving water body exceeds the required amount. Golden Glades Interchange Stormwater Management Report 30

41 Golden Glades Interchange PD&E Study 5. FLOODPLAIN According to the Flood Insurance Rate Maps published by the Federal Emergency Management Agency (FEMA), a portion of the study area is within Special Flood Hazard Zone AE while the remainder of the study area is outside of the floodplain. See Figure 5-1 below. The 1% annual chance flood (100-year or Base Flood) in Zone AE is estimated to range from Elevation 6.0-ft to 7.0-ft NGVD. Areas identified within Zone X or Zone X-500 are estimated to have less than one foot or no flooding at all during the Base Flood. Roadway improvements proposed by this project are estimated to be no lower than elevation 9.0 NGVD, based on elevations extrapolated from limited As-built plans. As such, the facility is anticipated to be open to traffic during the Base Flood. There are no regulated floodways within the project limits. See Appendix A, for the Location Hydraulics Memorandum. Figure 5-1 FEMA Floodplain Map Golden Glades Interchange Stormwater Management Report 31

42 6. CROSS DRAINS There are no major cross drains in this project. 7. WATERBODY CROSSINGS Roadway improvements proposed by this study will involve work within the C-8 Canal and the NW 17 th Avenue Canal. The C-8 Canal is under the jurisdiction of South Florida Water Management District (SFWMD) and the Army Corp of Engineers and the NW 17 th Avenue Canal is under the jurisdiction of Miami-Dade Department of Regulatory and Economic Resources (RER). 7.1 I-95 over C-8 Canal (Bridge No ) Existing Bridge , shown below in Figure 7-1, carries I-95 northbound and southbound traffic over the C-8 Canal. Interim Build Alternative 3A widens the bridge while Interim Build Alternatives 3B, 3C and the Ultimate Build provide a new bridge for southbound traffic. In Build Alternative 3A, improvements to the Bridge will widen the footprint towards the west and require piles in the C-8 Canal. Preliminary calculations indicate that the existing bridge low member elevation of 7.66 ft-ngvd 29 (6.10 ft-navd 88) can be maintained for the widening in Build Alternative 3A as it meets the 2.0-ft minimum vertical clearance over the Normal High Water of the Canal. For the partial bridge replacements for Build Alternatives 3B, 3C and the Ultimate Build, the bridge will need to be raised to meet minimum vertical clearance requirements, as the anticipated widening for these alternatives would reduce the vertical clearance below acceptable limits if maintained at the existing elevation. The portion of the existing bridge carrying northbound traffic will remain for the aforementioned alternatives. New piles placed in the C-8 Canal will be aligned with existing piles to minimize hydraulic impacts (head loss) in the Canal. For more information on improvements to this bridge, see the Bridge Analysis Report-Interim Build Alternatives and the Bridge Analysis Report-Ultimate Build Alternative prepared as part of the PD&E Study. Golden Glades Interchange Stormwater Management Report 32

43 Figure 7-1 Bridge No (I-95 over C-8 Canal) 7.2 NW 167 th Street over NW 17 th Avenue Canal (Culvert Extension) Potential considerations in closing the NW 12 th Avenue on-ramp to SR 826 will require improvements to the NW 17 th Avenue interchange with SR 826 that will widen it towards the north and south. This will require extending the existing culvert in the NW 17 th Avenue Canal by approximately 15-ft on the northern end and 10-ft on the southern end to accommodate the widened footprint of NW 167 th Street. See Figure 7-2 below. Existing plans show that the culvert at this location was built in the early 60 s and consists of 10-in reinforced concrete walls with inside dimensions of 10-ft by 10-ft. In general, RER agreed to allow culvert extension at this location. The culvert extension proposed for this location will have dimensions of 10-ft by 10-ft to match the existing culvert. See Appendix C for notes of the meeting held on 10/15/2012. Golden Glades Interchange Stormwater Management Report 33

44 CULVERT EXTENSION NW 17TH AVENUE N Figure 7-2 Culvert Extension (NW 167 th ST Over NW 17 th Ave. Canal) 7.3 NW 165 th Street over NW 17 th Avenue Canal (Proposed Culvert) A new roadway connection from NW 165th Street to NW 17th Avenue, across the NW 17th Avenue Canal, is proposed by this study to provide alternate connectivity and mitigate the potential removal of the NW 12th Avenue on-ramp to SR 826. The Bridge Analysis Report, prepared as a part of this PD&E study, recommends a culvert for the NW 17th Avenue Canal crossing and approximately 500 linear feet of bulkhead along the western bank of the canal. The Study Team met with RER on October 15 th 2012 to confirm that a culvert crossing would be acceptable at this location. In general, RER agreed to allow a culvert at this location as long as certain requirements are met such as providing a maintenance access pad on either side of the culvert and hydraulic modeling as needed. See Appendix C for meeting notes. Golden Glades Interchange Stormwater Management Report 34

45 Existing plans show that the culvert (SR 826 crossing), just north from NW 165th Street, was built in the early 60 s and consists of 10-in reinforced concrete walls with inside dimensions of 10-ft by 10-ft. For the purposes of estimating a project cost, two Alternatives based on the existing upstream culvert were considered for the proposed culvert. Alternative 1 provides a single 10-ft x 10-ft culvert while Alternative 2 provides two 10-ft x 10-ft culverts, as shown in Figure 7-3 below. If this crossing is needed, the actual dimensions of the proposed culvert will be determined during the design phase of this project when the Bridge Hydraulics Report is prepared for this crossing. Figure 7-3 Proposed Culvert (NW 165th ST Over NW 17 th Ave. Canal) 8. PERMITTING 8.1 Existing Permits The South Florida Water Management District (SFWMD) and Miami-Dade Department of Regulatory and Economic Resources (RER) were contacted to obtain existing permits within the study area. Relevant permits are summarized below. See Appendix F for excerpts from these permits. SFWMD Permit 6P79-103, Application X Issued Golden Glades Interchange Stormwater Management Report 35