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Item H5
� H.5 � � �, BOARD OF COUNTY COMMISSIONERS County of Monroe � ��r�i �r � s�� Mayor Heather Carruthers,District 3 The Florida.Keys Mayor Pro Tem Michelle Coldiron,District 2 Craig Cates,District 1 �e- David Rice,District 4 Sylvia J.Murphy,District 5 County Commission Meeting June 17, 2020 Agenda Item Number: H.5 Agenda Item Summary #6729 BULK ITEM: No DEPARTMENT: Planning/Environmental Resources TIME APPROXIMATE: STAFF CONTACT: Cynthia Guerra(305) 289-2588 NO AGENDA ITEM WORDING: Presentation of update on DEO Community Planning Technical Assistance Grant 4P0363 to improve Monroe County's stormwater management guidance and regulations. ITEM BACKGROUND: In October 2019, Monroe County received a Community Planning Technical Assistance grant from the Department of Economic Opportunity. The grant requires the County to update the Land Development Code for the management of stormwater and update two supporting guidance documents to be used by both County regulators and design professionals working within the County. The update will consider factors such as improving nutrient reduction in stormwater discharges and the effects of sea level rise. Updating the County's codes and guidance materials will focus on options to eliminate or reduce off-property discharges to decrease discharge to nearshore waters. The County has demonstrated its commitment to improving water quality through administrative and regulatory policies. The Coastal Management Element of the Comprehensive Plan states that we shall develop a comprehensive development plan that establishes specific goals for safe management and disposal of stormwater and conservation of our water resources. The county adopted Stormwater Management Ordinance Section 114-3 of the Land Development Code, which establishes guidelines for the safe management and disposal of stormwater from developed areas. This project includes the preparation of recommendations for Code amendments to Monroe County Code Sections 114-2(a)(5) and 114-3 to reflect the identified best practices in floodplain management ensuring consistency and streamlining the process. Monroe County developed a "Manual of Stormwater Management Practices" in 1994 to accompany the Monroe County Stormwater Management Ordinance. The Manual provided Best Management Practices (BMP's) that were appropriate for the time. The manual has not been updated since 1994 and no longer reflects advancements in stormwater management practices and standards. In conjunction with the Manual, Monroe County developed a "Layman's Brochure" that provided guidelines for incorporation of BMP's in the preparation of site plans for single family and duplex lots. The work provided for through this grant has resulted in updates to the Manual and Brochure and revisions for changes to Section 114-2(a)(5) and 114-3 of the Land Development Code. The drafted documents have been developed by the County's consultant, Jones Edmunds and Packet Pg. 1728 H.5 Associates, under the direction and guidance of Mike Roberts, Assistant Director Environmental Resources. To arrive at the recommended revisions, the consultant was required to prepare an analysis of existing principles and guidelines from various sources such as the South Florida Water Management District's Environmental Resource Permit Applicant's Handbook as well as stormwater manuals for other jurisdictions in the state with similar stormwater challenges and conditions. Further, the County and the consultant co-hosted two stakeholder engagement forum webinars to solicit the feedback from stormwater design professionals and County stormwater inspection and permit review staff. The forums were intended to gather information on building improved and more resilient stormwater management systems and to solicit ideas on BMP's for implementation. Information obtained through the analysis of existing principles and the forums were used to inform the draft revised Manual, Brochure and changes to Monroe County Code Sections 114-2(a)(5) and 114-3. The grant requires a public meeting to communicate the proposed code amendments and the revised Manual and Brochure. This meeting is required by the grant and provides an opportunity for the Board of County Commissioners and interested members of the public to review and provide feedback and direction on the draft documents and proposed Code revisions. The proposed Code revisions include references to the updated Manual and Layman's Brochure as appropriate. The code revisions also require that stormwater discharges meet net improvement criteria consistent with state standards or reduce the post-development annual average stormwater total nitrogen and phosphorous load by 95%. Compliance is attained when projects are designed, constructed, operated, and maintained in accordance with the BMPs requirements found in the manual of stormwater management practices. The proposed code revisions further eliminate the use of dry detention and wet retention as best management practices, as these options have been shown to not achieve the required net improvement in water quality. Section 114-3(h)(6)requires BOCC approval of the Manual, so the revised Manual and Brochure are included with this agenda item. PREVIOUS RELEVANT BOCC ACTION: CONTRACT/AGREEMENT CHANGES: n/a STAFF RECOMMENDATION: Staff requests feedback regarding the proposed updates of the Manual of Stormwater Management Practices, the Layman's Brochure and revised language in Monroe County Code Sections 114-2(a)(5) and 114-3. DOCUMENTATION: MCC Sec. 114-2 114-3 Final Draft SW-Manual Monroe Final Draft Monroe_County_Laymans_Final Draft FINANCIAL IMPACT: Packet Pg. 1729 H.5 Effective Date: Expiration Date: Total Dollar Value of Contract: Total Cost to County: Current Year Portion: Budgeted: Source of Funds: CPI: Indirect Costs: Estimated Ongoing Costs Not Included in above dollar amounts: Revenue Producing: If yes, amount: Grant: DEO CPTA Grant P0363, $40,000 County Match: $0 Insurance Required: n/a Additional Details: NA - The work is being funded through DEO CPTA Grant 4P0363 REVIEWED BY: Michael Roberts Completed 03/24/2020 9:11 AM Emily Schemper Completed 05/27/2020 5:57 PM Steve Williams Completed 05/28/2020 2:38 PM Assistant County Administrator Christine Hurley Completed 05/29/2020 9:32 AM Purchasing Completed 05/29/2020 9:49 AM Budget and Finance Completed 05/29/2020 11:40 AM Maria Slavik Completed 05/29/2020 11:41 AM Kathy Peters Completed 06/01/2020 8:52 AM Board of County Commissioners Pending 06/17/2020 9:00 AM Packet Pg. 1730 H.S.a Sec. 114-2. -Adequate Facilities and Review Procedures. (a) Level-of-Service (LOS) Standards. All development shall be served by adequate public facilities in accordance with the following standards: (1) Transportation/Roadways. c a. US 1 shall have sufficient available capacity to operate at LOS C for the overall arterial length and the 24 roadway segments of US 1, as measured by the US 1 Level of Service Task Force Methodology, at all intersections and roadway segments. In addition, all segments of US 1, as identified in the US 1 Level of N Service Task Force Methodology, which would be impacted by a proposed development's access to US 1, shall have sufficient available capacity to operate at LOS C. b. Development may be approved, provided that the development in combination with all other permitted development will not decrease travel speed by more than 5 percent below LOS C, as measured by the US 1 Level of Service Task Force CL Methodology. While development may be approved within 5 percent of LOS C, the proposed development shall be considered to have an impact that needs mitigation. Development mitigation may be in the form of specific improvements or proportioned shared contribution towards improvements and strategies identified by the County, and/or Florida Department of Transportation (FDOT) to address any LOS degradation beyond LOS C and/or deficiencies. 0 c. All paved County roads shall have sufficient available capacity to operate at or within 5 percent of a LOS D as measured by the methodology identified in the most recent edition of the Highway Capacity Manual. While development may be Cr approved within 5 percent of LOS D, the development shall be considered to have 2 an impact that needs mitigation. Development mitigation may be in the form of specific improvements or proportioned shared contribution towards m improvements and strategies identified by the County, and/or FDOT to address any LOS degradation beyond LOS D and/or deficiencies. d. The development of one single family residence on a single parcel shall be considered de minimis and shall not be considered to impact road capacity established in this Subsection. e. The County shall post on the Monroe County website informing the public of the available transportation capacity for each road segment of US 1 as described in the Ceounty's biennial public facilities capacity report. The available capacity shall be expressed in terms of number of trips remaining until the adequate i transportation facilities standard is exceeded. f. The County, in coordination with the FDOT, shall continue the systematic traffic monitoring program to monitor peak season traffic volumes at permanent count stations and travel speeds on the overall length of US 1 and on each of the CAI 24 study segments of US 1, and to determine the cumulative impact of development and through traffic. The County shall coordinate with municipalities in the review of the systematic traffic monitoring program to monitor traffic volumes and travel speeds of US 1 as well as on each of the 24 study segments Packet Pg. 1731 H.S.a on US 1. The County and municipalities shall coordinate with FDOT to evaluate segments with deficiencies of LOS to determine necessary improvements and strategies to address any degradation and/or deficiencies. 2 (2)Solid waste. Sufficient capacity shall be available at a solid waste disposal site at an 2 LOS of 11.41 pounds per capita per day. The county solid waste and resource recovery authority may enter into agreements, including agreements under Florida Statutes (FS) Section 163.01, to dispose of solid waste outside of the county. (3)Potable water. The County will coordinate with Florida Keys Aqueduct Authority y (FKAA) in its efforts to assure sufficient potable water from an approved and < permitted source shall be available to satisfy the projected water needs of the proposed development at the levels of service listed below. Approved and permitted sources shall include cisterns, wells, FKAA distribution systems, individual water condensation systems, and any other system that complies with state standards for potable water. CL a. Overall LOS: 100 gal./capita/day. b. Minimum pressure: 20 pounds per square inch at customer service point. c. Minimum quality: As defined by Chapter 62-550 Florida Administrative Code (FAC). (4)Sanitary Sewer. Sufficient wastewater treatment and disposal shall be available to satisfy the projected needs of the development or use according to the following LOS standards: Cr .S a. The capacity LOS standard: 167 gallons per day per equivalent dwelling unit 2 (EDU). b. The wastewater treatment LOS standards: Mg/L 2 BOD TSS TN TP On-site sewage treatment and disposal systems 10 10 10 1 Design flows less than 100,000 gpd (BAT) 10 10 10 1 Design flows greater than or equal to 100,000 'gpd 5 5 3 1 (AWT) BOD: Biochemical Oxygen Demand c?� TSS: Total Suspended Solids TN: Total Nitrogen TP: Total Phosphorus BAT: Best Available Technology AWT: Advanced Wastewater Technology (5)Drainage/stormwater. Treatment and disposal facilities shall be designed }c meet the U� design and performance standards established in 62 25 FAG the current edition of the County's Manual of Stormwater Management Practices and either demonstrate that post development total nitrogen and total phosphorous loads are less than pre- development loads to the receiving water body (net improvement) or demonstrate a Packet Pg. 1732 H.S.a ninety five percent (95%) reduction in stormwater total nitrogen load and total phosphorus load. Treatment and disposal facilities must be afrd-designed and operated so that off-site discharges meet State water quality standards. Fez G TOT b. oo. '7 ?!1'7 CA!` 2 (6)Schools. Sufficient school classroom capacity shall be available to accommodate all school-age children to be generated by the proposed development. (7)Recreation and Open Space. Sufficient available recreation and open space facility capacity shall be available at the levels of service listed below: N a. One and one-half acres per 1,000 functional population of passive, resource- based neighborhood and community parks; and b. One and one-half acres per 1,000 functional population of activity-based neighborhood and community parks within each of the Upper Keys, Middle Keys, and Lower Keys subareas. CL (b) Review of capacity. (1)Purpose. It is the purpose of this Subsection is to ensure that the purposes of the Monroe County Comprehensive Plan are achieved and to provide an orderly and c equitable procedure for the issuance of development permits, other than permits for additions to existing structures and other development activity not requiring LU additional public facilities. 0 (2)Service areas. For the purposes of this Subsection, the unincorporated areas of the county shall be divided into the following three public facilities service areas: Cr a. Upper Keys Service Area: The unincorporated areas of the county north of the Whale Harbor Bridge; b. Middle Keys Service Area: The unincorporated areas of the county between the Seven Mile Bridge and Whale Harbor Bridge; and 2 C. Lower Keys Service Area: The unincorporated areas of the county south and/or CL west of the Seven Mile Bridge. (3)Biennial Assessment of public facilities capacity. The Planning Director shall submit to the Board of County Commissioners (BOCC) a report of the capacity of available public facilities in each of the service areas established in Subsection (b)(2) of this i Section. The report shall be based on standard analytical methodologies and shall "? include a projection of the amount of residential and nonresidential growth that can be accommodated in each of the service areas during the ensuing year without cv� exceeding safe and efficient provision of essential public services. The report shall clearly identify areas of inadequate facility capacity, which are those areas with i capacity below the adopted LOS standards as provided in Subsection (a)(1)—(7) of this Section, and areas of marginally adequate facility capacity, which are those areas at the adopted LOS standard or which are projected to reach inadequate c) capacity within the next 12 to 24 months. In addition, the report shall include growth r_ trends and projections and a development permit monitoring system for each service 0) area. Packet Pg. 1733 H.S.a (4)Ratification of the service capacity report . The BOCC shall consider and approve or approve with modifications the assessment of public facilities capacity. In the event the BOCC acts to increase the development capacity of any service area, the BOCC shall make specific findings of fact as to the reasons for the increase, including the source of funds to be used to pay for the additional capacity required to serve additional development to be permitted during the next 12- to 24-month period. (5)Review procedure. a. Applicability. In the event the approved assessment shows that projected growth N and development during the next 12 to 24 months exceeds public facilities < capacity that will be available to serve the projected growth, development in one or more of the service areas that will require any of the public facilities enumerated in Subsection (a) of this Section that have insufficient capacity to provide safe and efficient public services shall be subject to the procedure established in this Section. Development that does not require the public facilitiesCL enumerated in Subsection (a) of this Section and that has sufficient capacity to provide safe and efficient public services shall not be subject to the procedure established in this Section. b. Application for development. As a condition of approval of a development order, all applicants for development shall file an application with the county in the form LU prescribed by the Planning Director, accompanied by a fee to be set by resolution of the BOCC. The application shall include a written evaluation (facilities impact report and traffic report) of the impact of the anticipated development on the levels of service for public facilities and services and demonstrate that publicCr S facilities and services are available prior to or concurrent with the impacts of development. c. Areas of inadequate facility capacity. The county shall not approve applications for development in areas of the county that are served by inadequate facilities 2 identified in the biennial assessment of public facilities capacity report, except the county may approve development that will have no reduction in the capacity of the facility or where the developer agrees to increase the LOS of the facility to the adopted LOS standard. An applicant, except for persons applying for a single- family residence, shall provide a facilities impact report that demonstrates that: 1. For potable water, solid waste, sanitary sewer, and drainage facilities and services, one or more of the following conditions are met: i. The necessary facilities and services are in place at the time a development permit is issued; or ii. The necessary facilities and services are in place at the time a certificate of occupancy, or its functional equivalent is issued. Prior to i commencement of construction, the applicant shall enter into a binding and legally enforceable commitment to the County to assure construction or improvement of the facility. 2. For recreational facilities, one or more of the following conditions are met: Packet Pg. 1734 H.S.a i. Conditions 1(i.) or 1(ii.), listed above; or ii. The necessary facilities are in place no later than 1 year after issuance of a building permit. Prior to commencement of construction, the applicant shall enter into a binding and legally enforceable commitment to the 2 County to assure construction or improvement of the facility; or iii. In the case of acreage (land) for such parks and recreational facilities, land shall be dedicated to or acquired by the County prior to issuance of a building permit, or funds in the amount of the developer's fair share are y committed no later than the approval to commence construction; or iv. An enforceable development agreement guarantees that the necessary facilities and services will be in place with the issuance of the applicable development permit. An enforceable development agreement may include, but is not limited to, development agreements pursuant to Section 163.3220, FS, or an agreement or development order issued CL pursuant to Chapter 380, FS. 3. For roads, one or more of the following conditions are met: i. Conditions 1(i.) or 1(ii.) listed above; or ii. A binding executed contract is in place at the time the development LU permit is issued which provides for the commencement of the actual 0 construction of the required facilities or provision of services; or iii. An enforceable development agreement guarantees that the necessary Cr facilities and services will be in place with the issuance of the applicable 2 development permit. An enforceable development agreement may include, but is not limited to, development agreements pursuant to a, Section 163.3220, FS, or an agreement or development order issued pursuant to Chapter 380, FS, or 2 iv. The proportionate share contribution or construction is sufficient to CL accomplish one or more mobility improvement(s) that will benefit a regionally significant transportation facility. d. Areas ofmarginally adequate facility capacity. In areas of marginal facility _ capacity as identified in the current biennial assessment of public facilities i capacity report, the county shall either deny the application or condition the approval so that the LOS standard is not violated. An applicant in these areas, except for persons applying for a single-family residence, shall provide a facilities impact report to demonstrate the standards in Subsection (b)(5)c. of this Section have been met. e. Facilities impact report requirements. The facilities impact report required by this i Section shall use acceptable professional methodologies and standards inclusive of a cumulative traffic impact analysis, where necessary, as provided by the Planning Director. Packet Pg. 1735 H.S.a (6)Exemptions. In addition to the exemptions from development described in Subsection (3) of the definition of "development" in Section 101-1, the following construction activities shall not be considered development for the purposes of this Section only: 2 a. The rebuilding or restoration of a single-family residence damaged or destroyed by fire, calamity, or natural disaster if the rebuilding or restoration takes place within the footprint of the destroyed or damaged structure and the use of the structure remains single-family residential; n b. The replacement of a mobile home upon the same lot where the original was < located as long as there is no increase in density or intensity of use; C. The construction of fences; d. The construction of concrete slabs for existing buildings; e. The construction of driveways; CL f. The construction of docking facilities and seawalls; g. The construction of tiki and chickee huts; 0 h. The construction of swimming pools; or LU i. The installation of storm shutters. j. Development that does not require the public facilities enumerated in Section 114-2(a) and that has sufficient capacity. .S k. Development that will not reduce the capacity of the affected facilities. Cr C 2 I. Notwithstanding the LOS established above, public transit facilities as defined and provided for within Section 163.3180(5)(h)2., FS, are exempt from transportation concurrency. m. Installation of solar collection systems on single-family residences. n. Work conducted by public utilities within the right-of-way. o. Installation of concrete cisterns for water collection. (Ord. No. 006-2016 , § 1(Exh. 1), 4-13-2016) S i Sec. 114-3. -Surface Water Management Criteria. r (a) Intent. It is the intent of this Section to establish guidelines and criteria for the safe management and disposal of stormwater runoff from developed areas that will minimize `V or eliminate any resultant adverse impacts on the surface water, groundwater, and other natural resources of the county. These guidelines consider the effects of sea level rise and encourage the use of low impact development and new stormwater i management approaches that reduce off-property discharges. These procedures are intended to assist in protection of the vital water resources of the Florida Keys, including the reservoir of freshwater on Big Pine Key and the near shore waters of the Gulf of Mexico, Florida Bay, and the Atlantic Ocean. Packet Pg. 1736 H 5.a (b) Applicability. Projects discharging to impaired waters or to Outstanding Florida Waters (OFW) are subject to additional requirements for mitigation of pollutant loads. Single- family and duplex residences are required to observe best management practices (BMPs) as identified in the sections of the current edition of the Ceounty's M+franual of sStormwaterMmanagement ppractices clearly labeled as applicable to single-family and duplex residences and are subject only to the criteria, administrative procedures, and maintenance/retrofitting requirements identified in Subsection (d) of this Section and other applicable provisions of the Comprehensive Plan and this Land Development Ln Code. All other applications for a county building permit are subject to all the criteria N established in this Section, except those identified in Subsection (c). Except as specifically exempted in Subsection (c) below, applications for a building permit for properties that are nonconforming to the standards of this Section shall be subject to the requirements of Section 114-110. .E (c) Exemptions. Notwithstanding any other provisions of this Land Development Code, the following activities are exempt from the requirements of this Section, unless otherwise CL required by State or Federal Law: (1) Maintenance work on existing mosquito drainage structures for public health and welfare purposes, provided that the activities do not increase peak discharge rate or pollution load; (2) Routine maintenance and minor modification of existing impervious area other than single family and duplex residences provided it meets one of the following conditions: .S a. The maintenance does not increase the existing impervious conditions of the site; Cr C 2 or CD b. The proposed maintenance is certified by a licensed engineer demonstrating that the maintenance will not increase the design peak discharge rate, volume pollution load of stormwater runoff, or impervious coverage of the site; or .2 c. The placement of a new structure does not change the designed peak discharge rate, volume or pollution load, or increase impervious coverage of site area of stormwater runoff from the site. (3) Emergencies requiring immediate action to prevent material harm or danger to _ persons when obtaining a permit is impractical and would cause undue hardship in i protection of property from fire, violent storms, hurricanes, or other hazards. A report of the emergency action shall be made to the county administrator as soon as practicable. All emergency action shall also be temporary in nature and be reversed n' or appropriately remedied after the emergency has passed; i (4) Single-family and duplex residences built on individual lots that are part of an existing subdivision, provided a stormwater management system approved by the i Monroe County Growth Management Division or South Florida Water Management U District (SFWMD) is in place, and is provided as part of the application materials; Packet Pg. 1737 H.S.a (5) Maintenance, repair, or installation of underground or overhead utility facilities, such as, but not limited to, pipes, conduits and vaults, including replacing the ground surface with in-kind material or materials with similar runoff characteristics; 2 (6) Installation of a new or replacement of an existing public drainage system, public 2 combined sewer, public sanitary sewer, or public water supply system; (7) Road and parking lot maintenance limited to the following activities: a. Pothole and square cut patching; v, N b. Overlaying existing asphalt or concrete or impervious brick pavement with `n asphalt or concrete without expanding the area of coverage; c. Shoulder grading; d. Reshaping or regrading drainage ditches; e. Crack sealing; and CL f. Vegetation maintenance. (d) Single-family and duplex residences. 0 (1) Criteria. All water-quality criteria in accordance with Subsection (f)(2) of this Section. U (2)Administrative procedures. At building permit review, stormwater management LU criteria will be applied, generally to assess the applicant's compliance with these criteria through the implementation of BMPs. An applicant's stormwater management plan must comply with the criteria listed in Subsection (f)(2) of this Section or, in the alternative, follow the guidelines outlined in the document entitled Layman's Cr C Brochure " " distributed by the county. CD C (3)Lot coverage expansion/retrofitting requirements. Those existing single-family and duplex lot owners wishing to expand impervious area shall bring the increase in impervious area into compliance with this Section. Any substantial improvements .2 shall be brought into compliance with the applicable provisions of the land development regulations. (e) General criteria. i cv i i i c� Packet Pg. 1738 H 5.a (1) Water management areas. Such areas shall be legally reserved to and maintained by the operational entity and be dedicated on the plat, deed restriction, or easements. Any change in the use of the property must comply with this regulation and any other requirements of the Comprehensive Plan and this Land Development Code. Stormwater management areas shall be connected to a public road or other location from which operation and maintenance means of access are legally and physically available to the operational entity, in accordance with county land development regulations governing subdivision of land. (2)Environmental impacts. All surface water management plans shall be reviewed by y the staff to evaluate anticipated impacts of the proposed work on the environment of the county. The following environmental features, among others, shall be used by the staff in evaluating impacts: a. Wetlands; b. Water bodies (including determination of discharge to impaired waters or OFW); CL c. Intermittent (seasonally wet) ponds; d. Mixed upland and wetland systems; 0 e. Pinelands; LU f. Dunes/beach berms; g. Hammock areas; h. Uplands areas; and Cr i. Preferred habitat of rare and endangered plant and animal species. 2 (3)Legal operational entity requirements. m a. An acceptable, responsible entity that agrees to operate and maintain the surface water management system shall be identified in the building permit application. .2 The entity must be provided with sufficient ownership so that it has control over all water management facilities authorized. The following are examples of entities that are acceptable: 1. Governmental agencies; 2. Nonprofit corporations, including homeowners' associations, property owners' i associations, condominium owners' associations, or master associations; or 3. The property owner as permittee, or his successors, if the property is wholly i owned by the permittee and is intended to be so retained. b. The entity must provide legally binding written documentation that it will accept the operation and maintenance of all surface water management systems prior to approval. cal c) Packet Pg. 1739 H.S.a (4) Water quality considerations. All new surface water management systems shall be evaluated based on the ability of the system to prevent degradation of receiving waters. All new surface water management systems shall be designed to either: 2 a. Meet net improvement criteria as defined in Section 114-2(a) (5); or 2 c b. Reduce the post-development annual average stormwater for both total nitrogen load and total phosphorus load by 95 N aeeeFdanee with ego,-r 4.091, FAG, and-aTe�ea--�-n--tTe €WFD. � (5) Water quantity considerations. All new stormwater management systems shall be evaluated on the ability of the system to prevent flooding of on-site structures, CL adjacent properties, roads, and road rights-of-way based upon antecedent rainfall conditions. (f) Technical criteria. c U (1) Water quantity. a. Discharge. Off-site discharge is limited to amounts that will not cause adverse off-site impacts. These amounts are: Cr 1. Historic discharges based on natural site drainage patterns; or 2 CD 2. Amounts determined in previous SFWMD or the county permit actions. . , m b. Drainage and flood protection criteria. The surface water management system shall be designed using a 24-hour rainfall duration and 25-year return frequency in computing allowable off-site discharge rate. Flood protection and floodplain CL encroachment standards shall be those established in the Monroe County Land Development Regulations and Comprehensive Plan. If post-development conditions are such that a volume greater than the retention and/or detention volume required for stormwater management is already being retained on site, that condition shall be maintained. (2) Water quality. i cv a. Degradation of receiving water quality prohibited. PFejeets _h^II be designed __that disehaFges de net degFade the ..ateF qHality, as set feFth On FAG Ghap ' i CeFs 62 3, G�77n and RH a 62 330.0 Proiects shall demonstrate � either of the following: i U a) Meet net improvement criteria; or U b) Reduce the post-development annual average stormwater for both total nitrogen load and total phosphorus load by 95%. Packet Pg. 1740 H 5.a b Retentef: �etentie~ er4t ~�, Presumption of Compliance. Projects designed, cu constructed, operated, and maintained in accordance with the BMPs requirements found in the Manual of Stormwater Management Practices are presumed to be in compliance with the requirements of this article.These eFit ._,, ,_., based eig the Fn++/��+mum Meet+�+e+�t�`-`-I�e�+e+� s-e,-- AG �',Ta I� 330.0Th_ __I-w,- that needs f_ be Fetam..._.-I eF detained is dependent en the N 1. Requirements for submittal include a stormwater pollution prevention plan, an v operational phase pollution prevention plan, site-specific water quality evaluation, grading plan, and all other requirements by permitting agencies. -_-----_-ll-- _...._._ the r_. __.._ _. ....r_. __ __._g_ dependent Hp en the r_. __.._ CL 0 T....-.t..........t ..I.......e cr 2. PFejeets that disehaFge diFeetly te sensitive teFs shall eeFnply with eendit+ens; and analysis, I M that r r FeElHiFed by Seet+eig 114 3,—�E2)b:'_ be eeigsodeFed. plan, and all etheF FeqHiFements by peFFnmttl-- I Packet Pg. 1741 H 5.a well, / eF / Fete ig toe ig deteigt'_ig 2 For the purposes of this Section, the term "disturbed area" includes the entire lot except that the areas covered by the following BMPs which shall be subtracted from the calculation of disturbed area: i. Forested upland areas/vegetative buffer strips (both natural and y manmade) which will be retained intact and over or through which v vehicular access or travel is not possible and will not occur; and ii. Open water surfaces and wetlands (salt marsh, buttonwood, mangroves, or freshwater marsh habitat types). .E It will be the responsibility of the applicant to affirmatively demonstrate that the BMPs used for the project are designed, constructed, and CL maintained properly. 3. For the purposes of this Section, the term "discharging directly to sensitive waters" means the discharge of runoff via a pipe or channel outfall to the near c shore waters, including canals, for which there is no intervening stormwater treatment system such as those listed in Subsection (g)(2)b.3. of this LU Section. Sensitive receiving waters are defined as Class I waters, Class II waters, Class III waters, OFWs, impaired water bodies as defined by 62-303, FAC, and/or canals connecting with these waters. Cr 4. Treatment storage recovery shall be estimated using a safety factor of two for 2 retention systems with supporting infiltration tests. Q '2 onnlinohlo (3) Construction considerations. After complying with the 2 water quantity and water quality criteria provisions of this Section as applicable, if discharge structures are necessary, the following design construction considerations ,W shall apply: a. Discharge structures. 1. All design discharges from the site shall be made through and controlled by structural discharge facilities. Earth berms shall be used only to disperse or collect sheet flows from or to ditches, swales, or other water channels, served by discharge structures. i 2 Discharge stFHetHFes sh-.II be stFHete d se that they aFe stab.,..-fy P, 2. Discharge structures shall include gratings for safety and maintenance purposes. Removal of trash is mandatory if the stormwater management i system discharges into surface waters and/or outstanding state waters. 3. Discharge structures shall include systems that would allow discharge from other than the top or bottom of the water column and shall include a 0) cleanable jump area for the sediment removal. Discharge structures from Packet Pg. 1742 H.S.a areas with greater than 50 percent impervious area or systems with inlets in paved areas shall include a baffle, skimmer, or other mechanism suitable for preventing oil and grease from discharging to and/or from retention/detention areas. 2 4. Direct discharges, such as through culverts, storm drains, or weir structures, will normally be allowed to receivinn e waters which by virtue of their large capacity and configuration, are easily able to absorb concentrated discharges. Such receiving waters might include existing storm sewer systems and y manmade ditches, canals, the bay, channels, and the ocean. v 5. Indirect discharges, such as overflow and spreader swales, are required where the receiving water or its adjacent supporting ecosystem might be degraded by a direct discharge. The discharge structure would therefore discharge into the overflow, spreader swale, or other channel, which in turn would release the water to the actual receiving water. Such receiving watersCL might include marshes, wetland, salt marshes and land naturally receiving overland sheet flow. b. Dry retention'-' R areas (not applicable to natural or mitigation wetland areas). 1. Dry retention'dn areas shall allow for the return of the groundwater LU level in the area to the control elevation. 0 2. On-site mosquito control ditches or other appropriate features for such purpose shall be incorporated into the design of dry retention'dnCr S areas. 2 CD 3. The design of dry retention;deteiqtieiq areas shall incorporate considerations for regular maintenance and vegetation harvesting procedures. m c. Wet ~detention areas. 2 1. Dimensional criteria (as measured at or from the control elevation). CL i. Depth. A minimum of 20 percent of the area shallower than 6 feet is req u i red. ii. Side slopes for purposes of public safety, water quality enhancement and maintenance. All wet retention/detention areas shall have side slopes no steeper than 4:1 (horizontal/vertical) out to a depth of 2 feet below the control elevation, or an equivalent substitute. Side slopes shall be i topsoiled, nurtured, or planted from 2 feet below to 1 foot above control ' elevation to promote vegetation growth. Littoral zone vegetation growth survival shall be a condition for operation permit issuance. 2. Support facility design criteria. Perimeter maintenance and operation easements of 10 feet (minimum preferable) width at slopes no steeper than U 4:1 (horizontal/vertical) should be provided beyond the control elevation water line. Control elevations must be set so as not to cause flooding in roadways and to protect road subgrades. Packet Pg. 1743 H 5.a d. Impervious areas. Runoff shall be discharged from impervious surfaces through retention areas, detention devices, filtering and cleansing devices, and/or subjected to some type of best management practice (BMP) prior to discharge from the project site. For projects that include substantial paved areas, such as shopping centers, large highway intersections with frequently stopped traffic, and high-density developments, provisions shall be made for the removal of oil, grease, and sediment from stormwater prior to discharge into the receiving waters of a watercourse. e. Stagnant water conditions. Configurations that create stagnant water conditions y shall not be allowed. (g) Stormwater management plans. It is the responsibility of the applicant to include in the stormwater management plan for the development sufficient information for the Planning Director or designee to evaluate the environmental and stormwater discharge characteristics of the affected areas, the potential and predicted impacts of theCL proposed activity on community waters, and the effectiveness and acceptability of those measures proposed by the applicant for reducing adverse impacts. The stormwater management plan shall contain maps, charts, graphs, tables, photographs, narrative descriptions, calculations, explanations, and citations to supporting references, and any additional information deemed necessary by the Planning Director. The Stormwater LU management plan must be sealed by an engineer registered in the state with experience in stormwater management and drainage design. (h) Manual of stormwater management practices and Lfavman's Bbrochure. Cr (1)The Planning and Environmental Resources Department staff shall compile a +Manual of sStormwater ffiManagement p.Practices for the guidance of persons preparing stormwater management plans and designing or operating stormwater management systems. The Mffianual of Stormwater Management Practices and Layman's Brochure shall be the primary implementation tool and shall be updated periodically to reflect the most current and effective practices. The+s Manual of Stormwater Management Practices wand Layman's Brochure shall be made available to the public. (2)The Manual of Stormwater Management Practices Fnaigual shall include guidance and specifications for the preparation of stormwater management plans. Acceptable techniques for obtaining, calculating, and presenting the information required in the stormwater management plans shall be described. cv (3)The Manual of Stormwater Management Practicesma n Ha 1 and Layman's Brochure bFeehHFe include guidance for acceptable BMPs for stormwater management �1 systems for single-family and duplex residences. It shall address the condition that a improvements to the land may result in water improvement, thereby creating i surface water over land that would otherwise not be wetland. (4)The Manual of Stormwater Management PracticesFnaigHal and Layman's Brochure bFeehHFe include guidance in the selection of environmentally sound practices E for the management of stormwater and the control of erosion and sedimentation. Packet Pg. 1744 H.S.a The development and use of techniques that emphasize the use of natural systems shall be encouraged. (5)The Manual of Stormwater Management PracticesFnaigual shall also establish minimum specifications for the construction of stormwater management facilities. 2 Construction specification shall be established in accordance with sound engineering practices. (6)The Planning and Environmental Resources Department shall submit the Manual of Stormwater Management Practices and subsequent revisions of it to the y BOCC for review and approval. The Manual of Stormwater Management Practices < manual may also be submitted for review to the Florida Department of Environmental Protection's Nonpoint Source Management Section in Tallahassee, Florida, and SFWMD. .E (7)Adherence to these regulations shall be based on the guidelines outlined in the Manual of Stormwater Management Practices. CL (i) Administration. (1) Permit application procedures. The stormwater management plan shall be submitted as part of an application for development approval outlined in this Code, unless otherwise herein exempted. All conditions, approvals, and fees shall apply. LU (2) Plan adherence. The applicant shall be required to adhere to the plans as approved and permitted. Any changes or amendments to the individual stormwater management plan must be approved by the Planning and Environmental Resources Department prior to construction. Cr (3) If required, a permit from the SFWMD must be obtained prior to final concurrency determination. a, (j) Maintenance and inspection. (1)The installed systems required by these regulations shall be maintained by the owner or approved operating entity, except that the county may select certain systems for -- county maintenance. The selection of critical areas and/or structures to be maintained by the county shall be recommended to the BOCC by the Planning Director and the County Engineer. All areas and/or structures to be maintained by _ the county must be dedicated to the county by plat or separate instrument and i accepted by the BOCC. The systems to be maintained by the owner or approved operating entity shall have adequate access and easements to permit the county right of entry to inspect and, if necessary, to take corrective action should the owner fail to maintain the systems to be maintained by him. The Planning Director shall give such owner written notice of the nature of corrective action necessary. Should the owner fail, within 30 days from the date of the notice, to take corrective action, the BOCC may take the necessary corrective action and place a lien on the property of the owner to recover the costs thereof. (2)The applicant shall arrange with the Planning Director for scheduling the following inspections (these inspections may be scheduled along with other required inspections): Packet Pg. 1745 H.S.a a. Erosion and sediment control inspection. As necessary during and after construction to ensure effective control of erosion and sedimentation. Control measures shall be installed and stabilized between any waters and any areas cleared prior to land clearing. 2 b. Bury inspections. Prior to the burial of any underground drainage structure. c. Final inspection. When all work, including installation of all stormwater management system facilities, has been completed. The Code Compliance Officer who inspects the work shall either approve it or v notify the applicant in writing in what respects there has been a failure to comply with the requirements of the approved permit. Any portion of the work that does not comply shall be corrected by the permittee within a time frame deemed reasonable by the Planning Director depending on the time needed to correct the violation and the effect of the violation on water and habitat quality, or the applicant shall be subject to the penalty provisions of Subsection (k) of this CL Section. There shall be a fee for inspections as established by the BOCC, and no certificates of occupancy shall be issued without approval of the Planning Director. 0 (k) Enforcement and penalties. LU (1)Enforcement. If the Planning Director determines that the project is not being carried out in accordance with the approved plan or if any project subject to these regulations is being carried out without a permit he is authorized to: a. Issue written notice to the applicant that specifies the nature and location of the Cr alleged noncompliance and includes a description of the remedial actions 2 necessary to bring the project into compliance; and b. Direct the Building Official to issue stop-work orders directing the applicant or persons in possession to cease and desist all or any portion of the work that 2 violates the provisions of these regulations until the remedial work is completed. The applicant shall then bring the project into compliance or be subject to denial of certificate of occupancy for the project. Any order issued pursuant to this Subsection not adequately addressed within ten working days shall be forwarded to the Code Compliance Department. With the E exception of single-family and duplex residences, the Planning Director shall require a sealed, as-built topographic survey detailing the completed stormwater management system of the development. i (2)Penalties. Penalties will be assessed pursuant to FS Chapter 163. i (1) Appeals. Any person aggrieved by the action of any official charged with the enforcement of these regulations as the result of the disapproval of a properly filed i permit application, issuance of a written notice of violation, or an alleged failure to properly enforce these regulations in regard to a specific application, shall have the right to appeal the action to the Planning Commission pursuant to Section 102-185. (Ord. No. 006-2016 , § 1(Exh. 1), 4-13-2016) Packet Pg. 1746 H.S.b E c c DRAFT fi C. E 0 JJI! P UJ Cr r 4 t t S f� w 0 MANUAL OF STORMWATER MANAGEMENT PRACTICES To Be Used In Conjunction With The Monroe County Land Development Code March 2020 Packet Pg. 1747 H.S.b DRAFT c c UPDATED MANUAL OF STORMWATER MANAGEMENT PRACTICES Original Manual published by Monroe County in 1995 — Updates performed by )ones Edmunds & Associates, Inc. .E CL .E Prepared for: Monroe County Department of Planning & Environmental Resources 102050 Overseas Highway Key Largo, Florida 33037 Cr .S 2 CD Prepared by: Jones Edmunds &Associates, Inc. .2 2240 Palm Beach Lakes Blvd Suite 300 — West Palm Beach, Florida 33409 W i 2 r- 0 i Jones Edmunds Project No.: 13015-001-01 March 2020 Packet Pg. 1748 H.S.b TABLE OF CONTENTS DRAFT 1 INTRODUCTION ............................................................................................ 1-1 2 APPLICABILITY............................................................................................. 2-1 3 CONTENTS OF A STORMWATER MANAGEMENT PLAN..................................... 3-1 4 METHODS OF STORMWATER TREATMENT...................................................... 4-1 4.1 Wet Detention............................................................................................4-2 4.1.1 Definition.............................................................................................4-2 4.1.2 Requirements as Expressed in this Manual ...............................................4-2 4.1.3 Method of Achievement .........................................................................4-3 .E 4.2 Retention...................................................................................................4-3 4.2.1 Definition.............................................................................................4-3 .E 4.2.2 Requirements as Expressed in this Manual ...............................................4-3 4.2.3 Method of Achievement .........................................................................4-3 U 4.3 Low Impact Development or Design ..............................................................4-4 4.3.1 Definition.............................................................................................4-4 0 4.3.2 Requirements as Expressed in this Ordinance...........................................4-4 4.3.3 Method of Achievement .........................................................................4-5 Cr S CONTROL STRUCTURES................................................................................. S-1 CD 5.1 Definition...................................................................................................5-1 5.2 Purpose.....................................................................................................5-1 5.3 Types of Control Structures..........................................................................5-1 6 CRITERIA FOR SINGLE-FAMILY/DUPLEX LOTS ............................................. 6-1 LIST OF FIGURES Figure 1 Schematics of Four Basic Detention/Retention Stormwater Runoff Management Systems..........................................................................4-2 Figure 2 Spreader Swale (Indirect Discharge) .....................................................5-2 Figure 3A Orifice Weirs.....................................................................................A1-1 i Figure 3B V-Notched Weir.................................................................................A1-2 Figure 3C Rectangular Weir...............................................................................A1-3 Figure 4A Pollution -Retardant Catch Basin .........................................................A2-2 Figure 4B Pollution- Retardant Catch Basin with Removable Down-turned Pipe........A2-3 Figure 4C Pollution -Retardant Catch Basin with Removable Downturned Pipe .........A2-4 Figure 5 Typical Exfiltration Trench ..................................................................A4-2 13015-001-01 June 2020 Table of Packet Pg. 1749 H.S.b DRAFT LIST OF TABLES Table 1 Required Retention Depths for Stormwater Treatment .............................4-4 Table 2 Required Retention Depth for Single Family/Duplex Lots ..........................6-2 APPENDICES 2 Appendix 1 Control Structures N Appendix 2 Catch Basins and Pollutant Retardant Structures Appendix 3 Wet-Detention Facilities Appendix 4 Dry-Retention Facilities CL Appendix 5 Stormwater Management Plan Checklist Appendix 6 Sample Calculations for Single Family/Duplex Lots Appendix 7 Bibliography U 0 rr .S 2 m 2 0) i 2 r_ 0 i U 13015-001-01 June 2020 Table of Packet Pg. 1750 H.S.b DRAFT I INTRODUCTION Monroe County has a unique, water-oriented environment and because of the importance of its aquatic environment, both aesthetic and economic, a Stormwater Management Ordinance (hereinafter referred to as the "Ordinance") has been adopted to help protect 12 these resources from the harmful effects of stormwater runoff. Stormwater is the water that results from a rain event. Runoff is defined as the portion of stormwater that does not percolate into the ground, evaporate, and is not intercepted N before reaching a stormwater management system. Stormwater runoff from undeveloped < lands usually does not present a management problem since it is relatively clean, and the volume usually is minimal. When natural land is converted to some other land uses, stormwater becomes a problem and should be managed. Soil is often paved over and impervious surfaces are created. When impervious surfaces are created, stormwater is no longer able to percolate into the ground and accumulates on the surface causing flooding in CL some areas. These impervious areas also allow for pollution accumulation, degrading the quality of stormwater runoff and rendering it a pollution source. For these two reasons, flooding (water quantity) and pollution (water quality), stormwater management practices are implemented in developed areas. U Stormwater runoff quality varies with land use. A multitude of pollutants exist in stormwater LU runoff as well as the sources for these pollutants. These pollutants can consist of nutrients, solid waste, litter, lead, petroleum products (from automobiles), chemicals, fertilizers, and herbicides applied to lawns, and atmospheric deposition. Higher nutrient loads are generated by residential and industrial land uses and commercial, mixed urban, and Cr roadways generate higher concentrations of metal contamination. Heavy metals are of 2 concern because several are known to be toxic to many aquatic plant and animal species. Motor vehicles and road surfaces are the main sources of heavy metals in stormwater runoff. Nutrients and pesticides from lawn fertilizers and atmospheric deposition can cause algal blooms and similar occurrences if untreated runoff is allowed to enter surface waters. During a rainfall event, stormwater runoff flows over these surfaces, picking up pollutants, and carrying them to surface waters. Stormwater not only causes adverse environmental impacts, but economic impacts as well. An increase in the number of impervious surfaces increases the potential for flooding and property damage. Stormwater can also lead to reduced fisheries production because of the _I degradation of water quality. For these reasons, stormwater management practices have been implemented throughout Florida and the United States. This manual is designed as a guide to Best Management Practices (BMP's) for stormwater management in Monroe 1 County. A stormwater management practice is one that shapes and improves the quality and quantity of stormwater runoff being discharged to receiving waters. BMPs for stormwater are those that meet discharge quantity and quality criteria at a minimal cost (Wanielista and Yousef, 1985). Section 114-3 of the Monroe County Code addresses the issue of flood protection and water quantity management. Although this stormwater management ordinance does have general 13015-001-01 June 2020 Intr Packet Pg. 1751 H.S.b DRAFT criteria for water quantity and flood protection, the purpose is to control stormwater- generated pollution and is water quality based. The practices and procedures described in this manual are those in common usage throughout Florida and also apply to Monroe County. The bibliography at the end of this 2 manual lists some of the relevant sources of additional information on this subject. This manual will be used to review and approve stormwater management systems permitted by the County and will be modified as appropriate technology dictates. CL U 0 rr m 2 0) i 2 r- 0 i U 13015-001-01 June 2020 Intr Packet Pg. 1752 H.S.b DRAFT 2 APPLICABILITY This manual is to accompany the Monroe County Stormwater Management Ordinance. This Ordinance was incorporated into the Monroe County Land Development Code by amendment to the Comprehensive Plan. A Stormwater Management Plan will be required as part of all building permit applications (except those projects exempted pursuant to Section 114-3(c) of the Land Development Code). The definitions used in this manual are consistent with those in the Land Development Code and the Monroe County Stormwater Management Ln Ordinance. CL 0 U 0 rr .S 2 0) i 2 r- 0 i U 13015-001-01 June 2020 App Packet Pg. 1753 H.S.b DRAFT 3 CONTENTS OF A STORMWATER MANAGEMENT PLAN A stormwater management plan is required pursuant to Section 114-3 (g) of the Land Development Code for those projects not exempted pursuant to Section 114-3 (c). A Plan is to be submitted as part of the Monroe County building permit application. The Plan will indicate how project design will incorporate the required stormwater treatment criteria. The following is an outline of those elements that may be required as part of a stormwater management plan. Appendix 5 contains a check-list of these elements. This will allow v, County staff to determine which of the elements a specific plan should or should not require N for each site. Some of these elements are required for other parts of a County building permit, but also need to be considered as part of the Stormwater Management Plan. In these instances, specific criteria are the same as those already required by the County and are not discussed further in this Manual. 1. Site Information: CL a. Detailed location sketch. b. Description of vegetative cover, including wetlands. c. Location and size of preservation or mitigation areas. d. Paving, grading, and drainage plan. e. Vegetation protection plan. f. Soils map and percolation test results. g. Wet-season water table elevation. h. Future wet-season water table elevation (30-year). Cr S i. Description of measures to be used during construction to eliminate adverse off-site 2 impacts, such as increased turbidity or siltation, if applicable. j. Recent aerial photograph. k. Map of drainage basin boundaries. I. Map of floodplain and elevations. 2. Master Stormwater Management Plan: a. Location of all existing and proposed on-site water bodies, including wetlands. b. Location of all off-site wetlands, water courses, and waterbodies affected by on-site drainage patterns. _I c. Location and detail of all major control structures and elevations. Preliminary construction plans may be submitted for conceptual approval. d. Right-of-way and easement locations for stormwater management systems including all areas reserved for stormwater management purposes. e. Location and size of on-site stormwater management facilities. f. Square footages, acreages, and percentage of property proposed as: (1) Impervious surface (excluding waterbodies). (2) Impervious surface (waterbodies). (3) Pervious surface. (4) Total square footage or acreage of the project site. g. Proposed grading plan. 13015-001-01 June 2020 Contents of a Stormwater Managem Packet Pg. 1754 H.S.b DRAFT h. Treatment volumes and discharge rates (if applicable) for stormwater runoff. 3. Legal and Institutional Information: E a. Entity responsible for operation and maintenance of surface water management 2 system. 12 b. If the operational and maintenance entity is to be a public body, a letter from the public body confirming this must be submitted before staff approval. If the entity is a homeowners' association, documents verifying the existence of such organization n and its ability to accept operation and maintenance responsibility must be submitted (n before staff approval. .E CL .E 0 U 0 rr m 2 0) i 2 r- 0 i U 13015-001-01 June 2020 Contents of a Stormwater Managem Packet Pg. 1755 H.S.b DRAFT 4 METHODS OF STORMWATER TREATMENT Stormwater treatment facilities are designed to treat stormwater runoff to a level that results in the pollutant loads discharged after development either being less than the 2 pollutant loads discharged before development (a net improvement) or that results in pollutant loads being reduced by 95 percent. The volume to be treated depends on the type of stormwater management facility(ies) used and the land use of the property. The two most commonly used methods of stormwater treatment are wet detention and dry Ln; retention. A detention facility collects and temporarily stores a treatment volume to provide v for treatment through physical, chemical, or biological processes with subsequent gradual release of the stormwater to a surface water system. A retention facility is designed to prevent the discharge of a given volume; however, it is slowly released from the facility. A retention or detention facility built above the groundwater table is "dry." A facility with the bottom below the control elevation is "wet." Figure 1 conceptually illustrates the differences between each. The wet-season water table plays an important part in the functioning of CL retention systems. To ensure that stormwater practices continue to function, a stormwater design will need to include a determination of the wet-season water table and an estimate of the future wet-season water table. The future wet-season water table will be assumed to be increased by the difference in sea level in the year that the wet-season water table determination was made and the projected sea level 30 years after the permitting. The LU estimated sea level rise projections adopted the Southeast Florida Climate Change Compact must be used for this determination. A newer approach to stormwater management is called Low Impact Development or Design Cr (LID). This approach seeks to replicate a more natural hydrologic function on the landscape 2 and uses a combination of stormwater management practices to meet the objective stated above. Some of these practices include pervious pavement, vegetated swales, vegetated a, filter strips, bioretention systems, cisterns, and green roofs. Very often a stormwater management system incorporates a combination of treatment methods. It is unfeasible to describe all the possible combinations in this manual. The criteria for each individual type of treatment is detailed. The intent is to ensure that the proper volume of runoff is treated in an appropriate manner for the land use. References to guidelines for LID approaches to stormwater management are also provided. Appendices 3 through 6 provide the design criteria for each form of management. 2 r_ c i 13015-001-01 June 2020 Methods of Stormwater Tr Packet Pg. 1756 H.S.b DRAFT Figure c atiic f Four Basic Detention/Ret tii Stormwater Runoff Management Systems WET DETENTION BASIN DRY RETENTION BASIN E c INFLOW CONTROLLED INFLOW NO OUTFLOW L. {3UTFLOW EVAPORATICIN ♦ ♦ ® EVAPORATION i DETENTION ; y STORAGE PERCOLATION e�e PERCOLATION CL Source: Adapted from Whalen and Cullum, 1988. 4.1 T DETENTION c U ..1.1 DEFINITION Wet detention is the collection and temporary storage of stormwater runoff—before controlled discharge into receiving waters—in a permanently wet impoundment in such a manner as to provide for treatment through physical, chemical, and biological processesCr S with subsequent gradual release of the stormwater. A wet detention facility is a basin or 2 pond with a bottom elevation below the wet-season water table or control elevation. ..1.2 REQUIREMENTS As ExPRESSED IN THIS MANUAL Stormwater designs must demonstrate a net improvement in nutrient loads or a 95 percent reduction in pollutant loads. This can be demonstrated through methods that are accepted by the South Florida Water Management District (SFWMD). An example of one of these methods is using BMP Trains, which is freely available from the University of Central Florida Stormwater Management Academy (https:!lstars.library.ucf.edulbmptrains!). As an alternative to demonstrating net improvement or 95-percent reduction, wet detention i with pretreatment that meets the following criteria can be used as a stormwater practice and will be presumed to meet the County stormwater treatment objectives: • i Provide a treatment volume sized to the first 1 inch of runoff from the site or the total of 2.5 inches times the percent of impervious area, whichever is greater. • One-half inch of the detained volume must be released through a control structure within 24 hours. • Wet detention cannot be used as the sole form of stormwater treatment. Projects using wet detention must provide at least 2.5 inch of runoff pre-treatment in dry retention E before discharging into a wet detention facility. 13015-001-01 June 2020 Methods of Stormwater Tr Packet Pg. 1757 H.S.b DRAFT 4.1.3 METHOD OF ACHIEVEMENT � Man-made lakes or ponds on the site are generally used for wet detention. These lakes or ponds must meet the design criteria in Appendix 3 of this manual. The retention volume can be achieved using the guidelines in Section 4.2 and Section 4.3 of this manual. 2 4.2 c RETENTION ..2.1 DEFINITION Dry retention is a stormwater system designed to prevent the discharge of a given volume N of stormwater runoff into surface waters by complete on-site storage of that volume. A dry- retention facility has a bottom elevation at least 1 foot above the future condition wet- season water table and is usually dry. Stormwater is released only during times of heavy rainfall or flooding. .E ..2.2 REQUIREMENTS As ExPRESSED IN THIS MANUAL CL Stormwater designs must demonstrate a net improvement or a 95 percent reduction in pollutant loads in nutrient loads. This can be demonstrated through methods that are accepted by the SFWMD. An example of one of these methods is using the BMP Trains, which is freely available from the University of Central Florida Stormwater Management Academy (https:!lstars.library.ucf.edulbmptrains!). LU As an alternative to demonstrating net improvement or 95-percent nutrient load reduction, dry-retention systems that retain the retention depth listed in Table 1 multiplied by the total project area will be presumed to meet the County stormwater treatment objectives. Cr S 2 4.2.3 METHOD OF ACHIEVEMENT Examples of dry-retention facilities include infiltration systems (vegetated swales, m bioretention systems), and seepage systems (exfiltration trenches, pervious pavement, exfiltration vaults). Of these two, infiltration systems provide better pollution attenuation. The vegetation takes up a percentage of the nutrients commonly found in stormwater runoff. Most heavy metals bind with the soils above the water table, and the potential for them entering the groundwater is reduced. Seepage systems consist of an underground facility which that relies on a mostly outward _ dispersion of stormwater from the facility to the groundwater. These structures are i constructed a minimum of 1 foot above the future wet-season water table. These systems are most suitable for areas where the aquifer has a high transmissivity, such as Monroe County. However, they do not provide the nutrient uptake that is offered with vegetated i infiltration systems. Infiltration systems and seepage systems need a highly permeable substratum to allow the stormwater runoff to percolate into the ground. Seepage systems do not require as much land area as infiltration systems, since they can be installed underground. However, the future wet- season water table at the project site must be at least 1 foot below the seepage structure. 13015-001-01 June 2020 Methods of Stormwater Tr Packet Pg. 1758 H.S.b DRAFT Table 1 Required RetentionDepths for Stormwater Treatment Percent Impervious Required Retention Depth (Inches) 20 1.40 c 25 1.47 30 1.59 35 1.71 40 1.88 Ln 45 2.02 50 2.1`7 55 2.33 � CD 60 2.49 S .E 65 2.65 CL 70 2.81 75 2.99 80 3.16 c U 4.3 Low CT DEVELOPMENT OR DESIGN 4.3.1 DEFINITION LID is an approach to stormwater and land use management that aims to replicate a more natural hydrologic function by promoting infiltration, filtration, storage, and evaporation or Cr C stormwater runoff. This approach should focus on conservation, use of on-site natural features, site planning, and distributed stormwater management practices that are integrated into a project's design, especially its landscaping and open space. Stormwater management through LID often includes a treatment train consisting of several different stormwater management practices that combine to meet the stormwater quality objectives for the site. Examples of practices that are often included in LID are: • Minimizing clearing, grading, soil disturbance, and compaction on a site. • Minimizing impervious area on site. • Pervious pavement. • Shallow bioretention systems. 0)1 c • Vegetated or grassed swales. • Vegetated filter strips. • i Minimizing directly connected impervious area. • Cisterns. Stormwater harvesting. 4.3.2 REQUIREMENTS As ExPRESSED IN THIS ORDINANCE � Using a LID approach for stormwater management is encouraged in Monroe County. However, stormwater designs must demonstrate a net improvement or 95-percent reduction in pollutant loads. This can be demonstrated through methods that are accepted 13015-001-01 June 2020 Methods of Stormwater Tr Packet Pg. 1759 H.S.b DRAFT by SFWMD. An example of one of these methods is using BMP Trains, which is freely available from the University of Central Florida Stormwater Management Academy (https:llstars.library.ucf.edulbmgtrains/). E c 4,33 METHOD OF ACHIEVEMENT 2 c A LID approach to stormwater management starts during the planning and site evaluation and continues through the selection and design of the most appropriate stormwater treatment practices for the site. The goal of stormwater management should be to retain, detain, recharge, filter, and use as much stormwater as possible on a site. A variety of LID N design manuals in Florida describe this approach to stormwater management. These include but are not limited to the following: Low-Impact Development and Green Infrastructure: Pollution Reduction Guidance for Water Quality in Southeast Florida Sarasota County Low-Impact Development Guidance Document CL Duval County Low-Impact Development Stormwater Manual Pinellas County Stormwater Manual The manuals listed above provide design guidelines for a variety of LID Stormwater c practices, which include: • Grassed conveyance swales. • Shallow bioretention. • Pervious pavement. • Stormwater harvesting. Cr S • Green roofs. 2 • Rainwater harvesting (cisterns). • Detention with biofiltration. Monroe County will generally accept the LID practices and design consideration described in .2 the LID manuals referenced above, although it should be noted that the performance curves and tables provided in these manuals do not necessarily apply to Monroe County's hydrologic conditions. Pollutant load reductions will need to be determined by the appropriate Florida-registered and -licensed professional. W i c r_ c i 13015-001-01 June 2020 Methods of Stormwater Tr Packet Pg. 1760 H.S.b DRAFT 5 CONTROL STRUCTURES 5.1 DEFINITION A control structure is a device through or over which water is discharged from a stormwater management system. Direct discharge occurs when stormwater is released through a control structure to the receiving water body. If the discharge from the stormwater management system is by a means other than a control structure (e.g., sheet flow or spreader Swale), it is considered indirect discharge. y 5.2 PURPOSE The primary purpose of a control structure in a detention facility is to release the calculated runoff volume slowly over a specified period. In a retention facility the control structure allows for volumes in excess of the calculated retention volume to leave the system in a manner that provides for adequate downstream flood protection. CL 5.3 TYPES F CONTROL STRUCTURES Direct discharge from a water management facility to the receiving body is usually achieved U through control structures such as weirs and orifices. The following criteria must be met for LU all methods of direct discharge: 0 1. Trash-collecting gratings must be on the intake of all structures that discharge to surface waters. .5 2. Detention facilities must be discharged from the mid-depth of the water column. Cr C 3. If the property is greater than 50-percent impervious or contains a system with inlets in paved areas, discharge structures must include a baffle, skimmer, or other suitable mechanism for preventing oil and grease from being discharged. (Appendix 2 describes these mechanisms, which are part of a catch basin). 2 4. Direct discharge will only be allowed to those areas that by virtue of their large capacity or configuration are able to absorb concentrated discharges. .� When using indirect discharge to release stormwater, a spreader swale is commonly used. The swale is positioned parallel to the receiving body, and the side adjacent to the receiving body is lower than the side opposite the receiving body. Figure 2 illustrates this form of discharge. The swale allows the water to flow into the receiving body but not flood the adjoining property. This method works well when trying to maintain a proper water level in wetlands that are used for stormwater management. The spreader swale is also a treatment facility for stormwater runoff. Runoff in excess of the first flush is allowed to enter the wetland system via sheet flow. 13015-001-01 June 2020 Control St Packet Pg. 1761 H.S.b DRAFT Figure 2 St° t° Swale (Indirect i c r ) E 0 dry retention Swale wetland ` N vi H=depth of swale required W to treat runoff (example- 1st half inch of runoff) CL LU rr m 2 W 2 r- 0 13015-001-01 June 2020 Control St Packet Pg. 1762 H.S.b DRAFT 6 CRITERIA FOR SINGLE-FAMILY/DUPLEX LOTS Single family and duplex homes may be exempted from filing a Stormwater Management Plan pursuant to Section 14-3(d), provided guidelines established in the "Layman's Brochure" are used to treat stormwater. The Layman's Brochure and the following design criteria generally use vegetated swales. However, other retention practices may be used. The retention volume specified in these design criteria will provide adequate stormwater treatment on a single-family/duplex lot to meet the criteria of Section 114-3 (f) (2). Ln However, calculations demonstrating a net improvement or 95 percent reduction in nutrient N loads may be submitted as an alternative to using the retention volume specified in these design criteria. These stormwater calculations must be completed by an appropriate Florida- registered and -licensed professional. r The retention volume depends on the lot size and the stormwater management system used. Stormwater treatment can also be provided through the use of other retention CL systems such as pervious pavement, exfiltration trenches, or shallow stormwater vault systems. Required retention depths for single-family/duplex lost are provided in Table 2. U If swale(s) are used, they must meet the following criteria: • Runoff from site must be drained to Swale. • Swale length must be greater than its width. • Swale side slope must be 4:1 or shallower (horizontal to vertical). Cr • Swale must be placed so that any natural areas to be preserved are not disturbed. 2 • Swale must be at least 6 inches deep. • Swales should be vegetated. If a Swale is not vegetated, then a 6-inch layer of soil amendment formulated to reduce nutrient loading must be installed directly below the Swale. Specifications and published nutrient reduction test results for the media must be .2 provided at the time of testing. Examples of acceptable media are NutriGoneTM (distributed by EcoSense International) and Bold and Gold® (distributed by Environmental Conservation Solutions) Retention systems must discharge off-site to prevent flooding. For retention systems, a _ control structure will allow runoff in excess of the volume of the Swale to be discharged to i the receiving body. There may be More than one retention system may be present on the property, provided each meets these criteria and the total volume of the swales is at least the calculated volume. Vegetated swales may be incorporated into the set-back criteria i required by the Monroe County Code. Appendix 6 contains sample calculations for single- family/duplex lots. Florida-Friendly LandscapingT"' is encouraged for vegetated swales. 13015-001-01 June 2020 Criteria for Single Family/Du Packet Pg. 1763 H.S.b DRAFT Table 2 Required RetentionDepth for Single Family/Duplex lots � Effective Impervious Area Required Retention Required Retention to Disturbed Area Ratio Depth Depth (Step 5) (feet) (inches) 0.20 0.138 1.66 0.25 0.146 1.75 0.30 0.153 1.84 Ln 0.35 0.164 1.97 v 0.40 0.177 2.12 0.45 0.188 2.26 0.50 0.`203 2.44 0.55 0.215 2.58 CL 0.60 0.228 2.74 0.65 0.243 2.92 0 U 0.70 0.`256 3.07 LU 0.75 0.271 3.25 0 0.80 0.286 3.43 rr .S 2 w i r- 0 i 13015-001-01 June 2020 Criteria for Single Family/Du Packet Pg. 1764 H.S.b E c c DRAFT CL Appendices 0 The Appendices contain the specific design criteria for the BMPs discussed in this manual. These criteria are based on best available knowledge in Cr the area of stormwater management. As technology dictates, these criteria will change. W 2 C 0 Packet Pg. 1765 H.S.b E c c DRAFT CL L) Appendix 1 Control Structures w 2 C 0 Packet Pg. 1766 H.S.b DRAFT APPENDIX I — CONTROL STRUCTURES This Appendix contains details on the designs for four types of control structures: a triangular orifice, a circular orifice, a v-notched weir, and a rectangular weir. 2 Orifices and V-notched weirs are generally used with control structures associated with detention facilities. These structures are commonly referred to as bleed-down mechanisms and allow for controlled release of a portion of detained volume over a specified period (usually 1/2 inch in 24 hours). Rectangular weirs are commonly used with detention and N retention facilities. In retention facilities, a rectangular weir allows for the runoff in excess of the retained volume to leave the facility. Rectangular weirs serve the same purpose in detention facilities, using a circular or triangular orifice as the bleed -down device. Figures 3A through 3C illustrate these different types of control structures and their use. The retained and detained volumes used in the determination of the dimensions of the control structures are calculated from the equations following each drawing. CL Figure 3A OrificeWeirs OQOO npOoDaoODoSOQO0000nO9Dpao�ooOOQ00000OD00000OO000000.Oa0000Oo,OtlOOOpO0,On0000poO0OtlOOOpOG0pn0Qc000pO0D9OOCOOpCC.Ca0oocQoO0Uo,OOO 0O0p.0Qooao$Ooo0t.0000O0Op'n00aooDO5 opOOO SGODpQO`$npG0ooDooUOQn009o$ooaoCJno00ooao^O00oop flDoD0oG0 a0apD0a0CoD4�o0ooQp0000OoD0D�Da0oaa0coa0ppnDCOaCGo^oDOaooC50Coa�0$ooOoD08$pD0.CO$aDoDOO�OGo'FCorCOcGG^' pO�nom0G00G0CCOv0f 0000000000000 C0OcD 0O�o 0DOo0CopDoo�p0pa0Co$o0og0^0op0o 0oCo Cfl_op�D0aOOD0 GeCG0 e'0 GOr.o'0,a.x.GvD.zOnD.nO_Op aC0000O,OCcO_0O. C:00D__0pQx00 O � OOa C�o3©© 0D0 px_0 0_O0 p_p'J ^0 O 000C00000p O OO 00800co0 OpDOOOODOOO000Opp90000ppD0060OQ0a000 - O0000Qpp0D Lev gO000040 000 040000000 000C000OOpppp00000000D00 �00 O OOOOpD0pp000Q0000000Ca0 pOp 000 00C" 060000Q3 0000000 OOCOOCODO OS �OOppp 8 8009 8 8 2GG 000000000000 DQOOOODOOO 0000 pO pppp0000 000000080000pa00000909 o O OOpppW00fl O 000 0000000a0g o 9Oo000SS 9 00000008 � DSoaoocoGpoOopO po 0 p 00 ooao©9000OOC ppO 0000000po OOao 00 0 a0000 control cont: ao 0o35 000oc lev.000000paaoD 90a Celevtin Sa0e000000 n0 000a00000_RaOpORr000G Coo5 ., Triangular Orifice Circular Orifice A = Q 4.8H 3/2 Q = discharge (cfs) Q) i A= Area of orifice (square feet) r_ 0 H=Head above orifice centroid* (feet) i *Centroid for a circular orifice is the center; centroid for a triangular orifice is two-thirds the distance from the vertex. The first is a circular orifice. As the name and illustration implies, it is a round opening. The bottom of the opening is at the control elevation. In the case of dry detention, the bottom of the circle is at the ground elevation. The most common method for constructing a circular orifice is placing a PVC pipe in the control structure. This pipe then discharges to the receiving body or to a conveyance system discharging to the receiving body. 13015-001-01 June 2020 Appendix 1 - Control St Packet Pg. 1767 H.S.b DRAFT The second type of orifice is a triangular orifice which is an inverted triangular opening in the control structure. The vertex of the orifice is at the control elevation. If the facility is a dry detention facility, the vertex is at the ground elevation. For maintenance purposes, the cross-sectional area of the orifice in any control structure 2 must be greater than 6 square inches to ensure that the structure allows for free flow of water and does not become clogged. The above formula is used to calculate the cross- sectional area of the orifice. The following is an example calculation for an orifice in a control structure which is part of a y wet detention facility. The following assumptions are made. • H = 3 feet • One-half inch of retained stormwater = 400,000 ft3 • First, the discharge rate (Q) must be calculated: CL Q.sao,aoo ri-1 x 1► . zi haws 3600 Bm Q=4.63 cfs [? a 4.8 n are A 4�M3 1lzf Iti-1-63 9.31 A=0.56 fit cr This meets the minimum dimensional criteria for orifices in detention facilities. 2 m Figure 3 t f1Weir C ^j000t7 = 00000 JJ O_ �.MO000 aoaoocCCc�oo 00000coo ^ as —,T--control elevation 0000._..O 00000CCC00000000CC000 ooco0o0oco000CCoo0oc0a000ccocc ©©ooc0000000c0000000000000cCcc^ 000000000oggg000000000000000^O OOOOOOOOOOOOCOCOOCOJO000000000 000000000000000000000000000006 000000000000000000000OCOCCOOO C.^.0000OOOOCOCCpp00==0000000C 000000000000000000000000000000. �I OOOO0000000000000C000000000000 OOOOCOOOOOCOOOCCCC0000000000C0 Op000000000000000000000000COOD 8000 000 0000 O�y00000O0000000000000000JC QO00c000000C0OCOO 00000C00OOOO000000000000OO000000 00000OCOOJCDCCCCOOCCCCJC^""C C., 6000000C^a'O�CJOOOOCOOCCC."'..C©^� _ 0�_OQOO�J�_00QQOCQO_.r_R?za�. _I V-N©LCt"ed 'weir �=2arctan (0.492- ) ' —notch angle (degrees) Vdet=1/2 inch of detention volume to be released (acre-feet)' H=distance from weir crest to vertex angle ifeet) 1 cubic foot = 2.29x 10'5 acre-feet 13015-001-01 June 2020 Appendix 1 - Control St Packet Pg. 1768 H.S.b DRAFT V-notched weirs are used with wet- and dry- detention facilities. The configuration of the opening allows for slow discharge of detained water over time. The rate of discharge depends on the angle of the V-notch. When designing a control structure with a V-notch weir, the angle is calculated using the above formula. Vdet refers to 1/2 inch of the detained volume that must be discharged within 24 hours. 2 0 For maintenance and functional purposes, the angle of the V-notch should not be less than 200 being the minimum to allow for adequate flow of water and to prevent blockage of the weir. The following is an example calculation for a V-notched weir, which is part of a 2-foot-deep < dry-detention facility, making the following assumptions: H=2.0 feet (depth of detention facility) V,w=500 ft2 , therefore, Vd,=0.01 acre feet tbels. t8 CL -&=2 arctan (0.492) ((Vd,/}i2-s)) =2 arctan (0.452) ((0.01/22s)) -&=2 arctan (0.03) -&=3.14 degrees 0 Since the calculated angle is less than 200, and the angle of the V-notch must be at least LU 200, this facility will need a 200 angle. Because most of the stormwater management facilities reviewed by County staff will be small, calculations in which the angle of the notch is less than 200 will be common. rr Figure °tan Mat Weir 'OJOQO00 QOOOOOC u00000C ppp��yyppQQ 000 00C 9G i! �!.�.� O000000 - CCcoo00 v..JJ-VVUU OOOQO00 ODcocO o° W00000000O00oo0000000000000000000 OCCOOC oD00c _ DooIleoocoOQ0D0000000CQ water level $°0O°°° pooQD c C 00OooQ000DC0o0oQQ0a0000000000000o g 000COo c 000c�ca�o O00oc _ pO000pGOOQOOOOO00000000000008000000D0C OflO0000QO0000000 OOOCCO3 _ 0000D0000QOOOC900000000000000000000^ p� �7ppnnnnnnnn 0 control C00000000000000000000000000000000000 800 00 000000-M j C MIC�°1no0O 00000000000000000000000000000000oocC Oc00000000000O000DO000C 0000000 cc0 0000Q000000000000000000000000Q00--�� 000000 OODOO®OOCOOG00000 OCCOOOCO a evati= OOOODOOflODO00000Q00000000000000000"" - ^ "' (� 00000000000QQ000 00000000Oo0O0D000CD 0000000000000000 OOOOCOOOCOCCC_ ODD 7060000C90O0'000� O r OOOCCOCDOS�00000 0000000000000 G C0O0 ^000000000000,.0 OC O OOOOOOOOOOQ000 OODOODOOODDDO O G DOOOOOOOOQOO"CCC CDOC 000:H0000 OQOOOC ^OOQOCOGDOCCGCC ^DD C G000 �OOCOQOOOC 0C;.0 OOOCOCOOOQCOO^aO �O° _ control OO O0 C cOoco 0 0 O C OCcoOOooG occoD �c ^ coODeoDDecDc elevation G_ o ��^ O COOO:CCCC Occ © DODO QG,ce cxncg - Ooc - _ I oflc occOO oc^ a0c�g OD000gOCCOS - DQo^ccco _ OOO Oc 000c000c x :_ cQ' c _ �r ..--- -----------.,..__Q�.:ccoccc..„_c:�= OOOCOCCOC C C CD JOn.zr: .. OOQOOCCc C D ^v DCC CO00000� OO C„� OCOOr" 0000cOco...._S_TCo_CDoc__:Ooccc ;, Z= W= width of control structure circular orifice H= distance above control elevation needed to retain required volume A rectangular weir is a structure that allows excess volumes of water to leave a stormwater ' management facility. A rectangular weir is used with retention facilities to discharge runoff in excess of the retained volume. A rectangular weir can also be used in conjunction with a detention facility that has an orifice for the delayed release of stormwater runoff. The rectangular weir allows for the discharge of excess runoff during severe rain events. The weir is constructed on top of the control structure. Rectangular weirs are used in areas 13015-001-01 June 2020 Appendix 1 - Control St Packet Pg. 1769 H.S.b DRAFT where a receiving water body exists for excess runoff or a method of conveying excess runoff to a receiving water body. Control structures can be made of several different types of materials. Those commonly used include concrete, cement, aluminum, and earthen material. Polyvinyl chloride (PVC) 2 pipe is often used as a bleed-down mechanism (circular orifice). All control structures must discharge to a receiving body of water that has the capacity to handle the discharge. If no receiving water body exists adjacent to the stormwater management facility, some system for conveying the stormwater must be provided and is y commonly done by using swales, culverts, or similar mechanisms. However, an assurance < that water will not stand in enclosed structures (i.e., culverts) for extended periods must be provided since this may lead to water quality problems. CL U 0 rr m 2 0) i 2 r_ 0 i U 13015-001-01 June 2020 Appendix 1 - Control St Packet Pg. 1770 H.S.b E c c DRAFT CL L) Appendix 2 Catch Basins and Pollutant- Retardant Structures w 2 C 0 Packet Pg. 1771 H.S.b APPENDIX 2 — CATCH BASINS AND POLLUTANT- RETARDANT STRUCTURES DRAFT c Catch basins are often used to collect stormwater from areas with large percentages of 2 impervious surfaces and convey it to a treatment facility. These structures need to be designed and certified by a professional engineer and be equipped with pollutant -retardant structures. The structures in Figures 4A through 4C will allow for pollution control and sedimentation before discharge to the stormwater treatment facility. In Figure 4A, the v, center column acts as a baffle. Oils, greases, and debris will remain on top of the water v column in the right- hand chamber. Only water below the baffle will be able to flow out of the pipe. In Figures 413 and 4C, the down-turned pipe serves the same purpose. This pipe is removable so it can be cleaned and maintained. Periodic cleaning and maintenance are necessary to prevent clogging, ensure adequate treatment, and prolong the life of the facility. CL U c rr m 2 0) i c r_ c i 13015-001-01 June 2020 Appendix 2 - Catch Basins and Pollutant Retardant St Packet Pg. 1772 BuluuBld A4!unwwoo 03a aOl paimb a lea ailgn ) UBJa l l — Oa O —I n - :4u9wg3e44 Cl) Jq n a_ m ac U tC c L (Q J-� 1_ (Q J-� M 0 CL (Q Ln C V",71 �i I t L co_ 1 E I t 1 � wqi H ' 1C.31 IL.ff U man. 1 man. � i-i X lu .ql (W > : > 4.i Q E oe 'CT p o y C a F I s f/1 is 1.1 C S7'; G 6i G a C E E p R I O L u i E� �4+ C d' R > 40 ,� = _a r. y tlCS > i 66 0 { Z 0 r-I Kx O O O 0O �N 0 H.S.b DRAFT Figure ollu ion- Retardant Catch Basin with Removable Down-turned PipeL. E 0 inlet grate y Giro ut V Connecting Band(Typ) '----- r to retention I down-rturnedll OP pip � l._ detention facility 0 o� 1 Cr 31 CI CD 21 2 i W 2 (Votes: 0 1. Inverts of pipes to be placed to achieve intent of design ar: to accomodate hydraulic requirements. i 2. Adalted from Broward County, 1987. 13015-001-01 June 2020 Appendix 2 - Catch Basins and Pollutant Retardant St Packet Pg. 1774 BuluuBld A4!unwwoo 03a aOl paimb a lea ailgn ) UBJa l l — Oa —I n - :4u9wq3e44V LO s3 ram. *ri a_ m ac U tC c L (o J-� 1� P � ar J n. W G "0 . a C a co Go r H w � c U � N ° X � * C }a p E Q 2 A' ram. ay Q � lA I I "' +� - c �.c 4 � V O 0 rz- 01AMETERt a"."aides Vortos •�2N' T."i C.C 1 v� C- Z e > n a * O 'i O 0 0 N 0 H.S.b E c c DRAFT CL u Appendix 3 0 Wet-Detention Facilities Cr 2 C 0 Packet Pg. 1776 H.S.b DRAFT APPENDIX 3 - WET-DETENTION FACILITIES A wet -detention facility is usually wet and allows for 1/2 inch of the required detained volume (1 inch or the total of 2.5 inches times the percent of impervious area, whichever is greater) to be discharged through a control structure in no less than 24 hours. Catch basins, pipes, swales, or channels are used in areas with large amounts of impervious surface to collect runoff and convey it to the detention facility. The required design criteria of a wet detention facility are detailed below.: v, • The lakes must be at least 0.25 acre and be at least 50 feet wide for lakes in excess of 100 feet in length. • Irregularly shaped lakes may be narrower than 50 feet in some portions but should average 50 feet in width. • Projects with single-owner entities or entities with a full-time maintenance staff with obvious interests in maintaining the areas for water quality purposes may have the areaCL and width criteria waived. • The lake slopes should be at least 4:1 (horizontal to vertical), to a depth of 2 feet for safety reasons and to allow a littoral habitat to form. • Discharge should be from the center of the water column. • The control structure is at one point in the detention facility. Trash collection screens are LU required on structures discharging to all surface waters. • The control structure must be opposite from where the runoff enters the facility to prevent hydraulic short-circuiting and ensure full treatment. .5 Wet detention cannot be used as the sole form of stormwater. If wet detention is used, at Cr C least 2.5 inches of dry retention must be provided before discharging into a wet-detention facility. m 2 0) i c r_ c i 13015-001-01 June 2020 Appendix 3 - Wet-Retention Packet Pg. 1777 H.S.b E c c DRAFT CL L) Appendix 4 Dry-Retention Facilities w 2 C 0 Packet Pg. 1778 H.S.b DRAFT APPENDIX 4 - DRY- RETENTION FACILITIES Two types of dry-retention facilities exist — infiltration facilities and seepage facilities. The most common form of infiltration is vegetated swales or basins. Runoff is routed to a vegetated area, either directly or through a catch basin and conveyance system. A control structure, usually a rectangular weir, is at one end of the swale or basin to allow for excess runoff to be discharged to a receiving body. A spreader swale can also be used in conjunction with this form of treatment. This type of discharge is most often used to release N water through sheet flow to wetland areas or to prevent erosion. The seepage method of dry retention involves allowing the water to disperse outward from an underground facility. The runoff is routed to a catch basin and is conveyed to a seepage system. Exfiltration trenches are the most commonly used types of seepage systems. They are used in conjunction with catch basins and consist of a perforated pipe surrounded by coarse rock. Figure 5 shows that the system is in the ground, but above the wet-season CL water table. Water enters the pipe and seeps out. The retained volume will exfiltrate over 1 hour. The length of the pipe is dependent on several factors — the volume of runoff to be treated, the width of the trench, the depth to the water table, and the hydraulic conductivity c of the soils. When calculating the volume of an exfiltration trench, a safety factor of 2 is used to allow for geologic uncertainties. LU The formula shown in Figure 5 illustrates how to design an exfiltration trench. An overflow system allowing for volumes in excess of the retained volume is usually located at the end of the trench opposite the point where the runoff enters the system and discharges to theCr 5 receiving waters. Although exfiltration trenches provide adequate stormwater treatment and 2 allow more land for development, they must be inspected regularly and cleaned from time to time. The pipe can become clogged and not allow proper seepage. When this occurs, the pipe acts like a conduit for untreated stormwater. Ensuring that the catch basins are maintained is one way of preventing failure of the trench. .2 Required retention depth is based on Table 1. 0) i c r_ c i 13015-001-01 June 2020 Appendix 4 - Dry-Retention Packet Pg. 1779 H.S.b DRAFT Figure Typical Wiltration Trench BASE SELECT BACKFJI-1 >; 12INCHES JBACKFILL H2 UNSATURATRENCH 6ICtiES PIPE COVER Du 'DEPTH MINIMUM PIPE 12INCMIS PERFORATED MINIMUM PIPE DIAMETER T) D �� GIDARSE MiN MtAA INCHES PIPE BED 5 TRENCH WIDTH CL V L- K(HZW+2H2Du-ou2+2H2DS)+(1$9XId )WDU 0 Lz LENGTH OF TRENCH REOUIREDIFEET) c Vs VOLUME TREATED (ACRE-INCHES)* . Ws TRENCH WIDTH (FEET) Ks HYDRAULIC CONDUCTIVITY (CFS/FT=-FT.HEAD)** rr HZ- DEPTH TO WATER TABLE.(FEET) Du. NON-SATURATED TRENCH DEPTH (FEET) w DS- SATURATED TRENCH DEPTH (FEET) CUBIC FOOT = 2.75 X 10,14 ACRE-INCHES i HYDRAULIC CONDUCTIVITY (K) IS OBTAINED FROM THE PERCOLATION TEST 0 C c i 13015-001-01 June 2020 Appendix 4 - Dry-Retention Packet Pg. 1780 H.S.b E c c DRAFT CL L) Appendix 5 Stormwater Management Plan Checklist w 2 C 0 Packet Pg. 1781 H.S.b CHECKLIST DRAFT c Required Not Requ red Sufficient A. Site Information Detailed location sketch T) ® ' Description of vegetative cover y Location and size of preservation or mitigation areas ® Vegetation protection plan Soils map CL ® Percolation test results Current wet season high water table c U ® Future wet-season water table Measures to be taken to eliminate off-site adverse impacts, such as turbidity, flooding, etc. .S ® Recent aerial photo (if available) Cr CD Map of drainage basin boundaries ® Map of flood pain and elevations 2 B. Master Stormwater Management Plan Location of all existing and proposed on-site waterbodies (including wetlands) Location of all off-site wetlands and waterbodies to i be affected by on-site drainage patterns c Location of all major control structures and i elevations (preliminary construction plan may be submitted for conceptual review) Right-of-way and easement locations for stormwater management systems, including all areas reserved for stormwater management purposes 13015-001-01 June 2020 Appendix 5 - Stormwater Management Plan Packet Pg. 1782 H.S.b DRAFT Required Not Sufficient Required Location and size of on-site water management facilities 2 Square footages, acreages, and percentage of property proposed as: • Impervious surface (excluding waterbodies) v, • Impervious surface (waterbodies) N • Pervious surface • Total square footage or acreage of project site ® ' Proposed grading i plan .E Treatment volume and discharge rate (if applicable) for stormwater management system CL .E C. Legal and Institutional Information Entity responsible for operation and maintenance of stormwater management facility* * If the operational and maintenance entity is to be a public body, a letter from the public body confirming this must be submitted before staff approval. If the entity is a homeowners'association, documents verifying the existence of such organization and its ability to accept operation and maintenance ability must be submitted before staff approval. Cr CD 2 W i c C c i U 13015-001-01 June 2020 Appendix 5 - Stormwater Management Plan Packet Pg. 1783 H.S.b E c c DRAFT CL L) Appendix 6 0 Single-Family/ Duplex Lot Sample Calculations w 2 C 0 Packet Pg. 1784 H.S.b APPENDIX 6 — SINGLE-FAMILY/DUPLEX LOT SAMPLE CALCULATIONS DRAFT c An orifice is a device that allows for discharge from the center of the control structure. 2 Simply put, it is an opening in the structure that lets water slowly pass. Detention facilities use orifices. The rate that water is discharged depends on the cross-sectional area of the orifice. Figure 6 shows the two types of orifices. An 8,000-square-foot lot with a house, deck, and driveway using dry -retention swales: N • House 1,600 square feet (800 directly connected and 800 unconnected) • Driveway 650 square feet • Concrete Patio 840 square feet .E Total impervious 3,000 square feet CL Effective Impervious 2,600 square feet Total lot size 8,000 square feet c U Ration of effective impervious area = 37.5 percent.to lot area 0.33% LU Since the impervious area is less than 40 percent of the total lot size, the following equation is used: • Swale volume (cubic feet) = total lot size (square feet) x 0.415-foot required retentionCr S depth (feet) 2 • Swale volume = 8,000 x 0.0415.164 • Swale volume = 332 ft3 = 1,312 cubic feet Assuming a 4:1 (horizontal to vertical) slope for the swales to a 1-foot depth, the cross- .2 sectional area (A) of the Swale is 4.0 square feet. Therefore, the length of the Swale is determined as follows: Length of Swale (feet) = volume (A). Length of Swale = 1,312/4. i Length of Swale = 328 feet. 2 r_ In areas where there is a receiving water body is adjacent to the property, a rectangular c weir should be placed at one end of the Swale for discharge of excess runoff. To reduce the i required length of the Swale opportunities to reduce the directly connected impervious area, replace impervious surfaces with pervious surfaces, and minimize site disturbance could be evaluated. These changes would reduce the required Swale length. 13015-001-01 June 2020 Appendix 6 - Single Family/Duplex Lot Sample Cal Packet Pg. 1785 H.S.b E c c DRAFT N CL L) Appendix 7 Bibliographycr w 2 c 0 Packet Pg. 1786 H.S.b DRAFT APPENDIX 9 - BIBLIOGRAPHY Ammon, D.C.,; W.C. Huber, WC; and J.P. Heany, JP. 1981. Wetlands'Use for Water Management in Florida. J. Water Res. Planning Management Div. Proceeding of ASCE 107 (WR2):315-327. Branscome, J,. and R. S. Tomasello, IS. 1988. Field Testing of Exfiltration Systems. South Florida Water Management District, Tech. Pub. 87-5, West Palm Beach, Florida. 50 pp. Camp Dresser and McKee, Inc. (CDM). 1985. An Assessment of Stormwater Management v Programs. J.P. Hartiganm, S.V. Plante, L.A. Rosner., Maitland, Florida. Chesters, G,. and L.J. Schierow, LJ. 1985. A Primer on Nonpoint Pollution. J. Soil Water Conserv. 40(1):9-13. Cox, J.H. 1985. Overview of BMP's and Urban Stormwater Management. Proceedings: CL Stormwater Management - "an update' M.P. Wanielista and Y.A. Yousef, Eds. Univ. of Central Florida Environ. Systems Engr. Institute, Pub. #85-1,. Orlando, Florida. Duval County. Duval County Low-Impact Development Stormwater Manual. Jacksonville, FL c U Ferrara, R.A. 1982. Stormwater Detention and Nonpoint Source Pollution Control. In the International Symposium on Urban Hydrology, Hydraulics, and Sediment Control, University of Kentucky, Lexington, Kentucky, pp. 91-91. Florida Department of Environmental Protection. 2019. Low-Impact Development and Green Cr Infrastructure: Pollution Reduction Guidance for Water Quality in Southeast Florida. Harper, H.H.,; Y.A. Yousef, YA; and M.P. Wanielista, MP. 1984. Efficiency of Roadside Swales in Removing Heavy Metals from Highway Associated Nonpoint Source Runoff. Conference on Options for Reaching Water Quality Goals, American Water Res. Assoc. Livingston, E.H. 1985. Overview of Stormwater Management. Florida Department of Environmental Regulation, Tallahassee, Florida. Mass, R.P.; M.D. Smolen, MD; and S.A. Dressing, SA. 1985. Selecting Critical Areas for Nonpoint-Source Pollution Control. J. Soil Water Conserv. 40(1):68-71. i Mason, Jr., J.M. 1984. Development of a Stormwater Management Plan. In the international symposium on Urban Hydrology, Hydraulics, and Sediment Control, University of Kentucky, Lexington, Kentucky, pp. 201-205. i Sarasota County .2015. Sarasota County Low-Impact Development Guidance Document. Sarasota FL. South Florida Water Management District (SFWMD). In review. An Assessment of Land Use and Related Stormwater Runoff Quality Treatment Efficiencies Associated with Selected Stormwater Management Systems. Resource Planning Department, West Palm Beach, FL. 13015-001-01 June 2020 Appendix 7 - Bibli Packet Pg. 1787 H.S.b DRAFT South Florida Water Management District (SFWMD). Environmental Resource Permit Applicant's Handbook, Vol II. West Palm Beach, FL. Wanielista, M.P., and Y.A. Yousef, YA. 1985. Overview Stormwater Manage Practices. Proceedings: Stormwater Management - "an update' M.P> Wanielista and Y.A. Yousef, Eds. Univ. of Central Florida, Environ. Systems Engr. Institute, Pub. #85-1., Orlando, Florida. Whalen, P.J. and M.G. Cullum. 1988. As Assessment of Urban Land Use/Stormwater Runoff Quality Relationships and Treatment Efficiencies of Selected Stormwater Management y System. Technical Publication 88-9, South Florida Water Management District. West < Palm Beach, Florida. .E CL .E c U c rr .S m m 2 W i c r- c i 13015-001-01 June 2020 Appendix 7 - Bibli Packet Pg. 1788 H.5.c E c 0 CL E { t E 0 0 rr CD Photo Credit:Mayte Santamaria(Monroe Count LAYMAN"S BROCHURE W Guidelines for preparation of a site plan for single family and duplex lots in Monroe County N' March 2020 0 A. Stormwater Management..-an important element of the site plan ........ 2 l 0 B. Guidelines to prepare your site plan ...................................................... 3i1 b 4 S tt C. Guidelines to address star water management in your site plan........... 4r { D. Sample construction techniques ........................................................... 7 E. Guidelines for expansion of existing homes............................................ 1 Packet Pg. 1789 A. Stormwater Management — an important element of the siteI E WHY all the fuss, you ask?Here's why... 2 0 Monroe County is home to the Florida Keys, lush islands surrounded by clear, aquamarine waters, and a myriad of 4i underwater wonders. Most of the year,the Keys enjoy a sunny, near-tropical climate, but there comes a rainy 9 season,from May through October. During these months,frequent thunderstorms last from a few minutes to a few days. Heavy seasonal rains cause stormwater to run off commercial and residential rooftops,yards, and streets.This stormwater normally collects in the streets and works its way towards the nearest waterway. While street flooding is CL a temporary nuisance,the pollutants carried in the stormwater create a less visible but longer lasting effect.These pollutants include automobile oil and grease, lawn fertilizers and pesticides, a variety of chemicals from commercial/industrial areas, and silt and floating debris from highways. Continued pollution of Florida's coastal area has severely degraded our most valuable resource,the coral reefs. Pollution also has negatively affected the quality and clarity of our waters. It has reduced our fish and wildlife populations. Cr Stormwater running off into the streets also wastes a valuable resource.After the rainy season come the dry months of November through April. With few exceptions, Monroe County's drinking water comes from the mainland via a single pipeline. In the event of a hurricane, power and this water supply may be discontinued for days. 2 Monroe County has adopted a comprehensive development plan that establishes specific goals for safe CL management and disposal of stormwater and conservation of our water resources.To achieve these goals and to begin reversing the current negative trends,we must significantly reduce the potential pollution from new construction. 76 Our adopted Stormwater Management Ordinance Sec. 114-2 and 114-3 of the Land Development Code establishes y guidelines for the safe management and disposal of stormwater runoff from developed areas.The ordinance is applicable to all developments and requires that all applications for building permits must contain a stormwater i management plan. 0 The guidelines and recommendations in this brochure are designed to help you to address stormwater management d 0 in the site plan for your single family or duplex lot. Sample engineering calculations supporting the guidelines of the 0 brochure are available in the current version of Monroe County's "Manual of Stormwater Management Practices". 2 Packet Pg. 1790 B. Guidelines to prepare r site plan E OKAY, what must 1 do to prepare a site plan for my single family or duplex home? 2 0 In order to prepare a site plan, it is necessary to assess the existing site conditions, evaluate the proposed improvements and make provisions for stormwater management.This process begins with the collection of site- N specific data, by performing a lot survey.The lot survey is then used as a base to locate the proposed improvements and grade the lot in order to control stormwater runoff.The following steps detail the type of data to be collected for the lot survey and the information to be provided in the site plan. CD STEP ONE—SURVEY DRAWING CL Obtain a boundary survey and topographic information (either from survey or LiDAR data)for your lot.The survey must be performed by a professional land surveyor licensed to practice in the State of Florida. The survey drawing must provide this information: a. Legal description of lot. b. Property line dimensions, bearings and/or angles. c. Location of existing improvements,to include adjacent street and waterway(if any). d. Three cross-sections, showing elevations from the street, across lot lines and center of the property. e. Location and identification of existing trees. Cr C f. Location sketch and identification of a nearby Mile Marker g. Scale (1"=10' recommended)and north arrow. h. LiDAR-based elevations may be used if available. STEP TWO—SITE PLAN 2 Prepare a site plan showing the proposed improvements, utilities, site grading and landscaping.The site plan,which must meet the guidelines described later in this brochure, should be prepared at a recommended scale of 1"=10' and provide the following information: 76 a. Locations,dimensions, and types of construction materials of the building, roof, patio, screened porch, deck, �+ shed, pool, driveway, septic tank and drainfield. b. Proposed site grading showing existing and proposed elevations and/or contours. c. Proposed drainage directions and areas draining to each retention system. Site grading must drain towards retention system. d. Locations,dimensions, and types of materials to be used in landscaping features, such as planters,walks, 0 privacy walls,fences,trees and shrubs. U e. A cross-section (elevation view)across the center of the lot showing proposed improvements and site 0) 0 grading. 0 Packet Pg. 1791 C. Guidelines to address stormwater managemenin your site plan E c HOW do 1 address stormwater management in my site plan? Much of Monroe County is beautiful and ecologically sensitive to manmade pollutants, many of which are carried to the ocean by stormwater runoff. Monroe County's objective is to keep the resident coral reef,fish, and animals alive N and healthy,while allowing you to occupy the same bit of Florida paradise.To achieve this objective, Monroe County requires your new home to meet the following design and construction guidelines: CD • Preserve Roadside Swales (Plate 2) 1. Maintain the pervious cover of swales. 2. Preserve existing swale elevations. CL • Reduce Lot Fill (Plate 2) 1. Carefully consider the need to import any fill for the lot. 2. Limit building pad elevations to eight inches above the adjacent roadway. • Flood Protection (Plate 3) 1. Elevate the first habitable floor above the Federal Emergency Management Agency Base Flood Elevation using stilt-construction techniques. • Reduce Impervious Surfaces 1. Use pervious materials, such as gravel, pervious pavers on sand, native grasses,grass-covered porous pavement and wood for the construction of other site and landscaping improvements. Florida-Friendly Landscaping'" is encouraged. Cr 2. Do not place impervious layers, such as roofing paper or plastic under paved or landscaped areas. 0) • Conserve Water(Plate 4&5) 1. Use cisterns to collect roof runoff and recycle for non-potable water uses. 2. Use native plant materials for landscaping. • Reduce Direct Discharges to Waterways (Plate 6) 2 1. Use berms to contain runoff onto adjacent waterways. 2. If your lot has an existing bulkhead, lower the adjacent ground to provide a minimum of 6" difference �- between the finished lot and the top of the bulkhead. • Reduce Discharges to Roadway 1. Use berms to contain runoff from lot onto adjacent roadways. 2. Use traffic rated trench drains across driveways to reduce discharges to the roadway.These trench drains should be drained to an onsite retention area.Trench drains are not needed where the driveway is below or at the same elevation as the roadway Swale. • Calculate required retention volume using the following steps: 1. Determine square feet of impervious area on the site that is directly connected to the proposed retention system (typically this would be an onsite Swale). Directly connected would be any area when stormwater runoff passes over less than 20 feet on pervious area (e.g.grassed or landscaped area) before entering the onsite retention system. Pervious pavers would not be considered an impervious area. U 2. Determine square feet of impervious area on the site that is unconnected to the proposed retention system and has to drain over 20 feet or more of pervious area before entering the retention system.An example of this would be an area of the roof that is drained from a downspout but flows over 20 feet of landscaped c area before reaching the onsite Swale. 3. Calculate the total effective impervious area by summing the directly connected area with half the m unconnected area. 4 Packet Pg. 1792 4. Determine the square feet of lot area that is disturbed during construction.This is any area that is accessibl H 5.c' to construction vehicles or construction staff during construction. Undisturbed areas need to be clearly sig posted and taped off during construction. 5. Calculate the ratio of the effective impervious area to the disturbed area. 6. Use Table 1 below to determine the required retention depth.The effective impervious area to the disturbed area ratio from Step 5 should be rounded to the nearest ratio in Table 1. 7. Determine the required retention volume (cubic feet) by multiplying the required retention depth in feet E (Step 6) by the disturbed area in square feet (Step 4). c 0 Table 1. Required Retention Depth 0.20 0.138 1.66 0.25 0.146 1.75 0.30 0.153 1.84 0.35 0.164 1.97 CL 0.40 0.177 2.12 0.45 0.188 2.26 0 0.50 0.203 2.44 0.55 0.215 2.58 0 0.60 0.228 2.74 0.65 0.243 2.92Cr W 0.70 0.256 3.07 0.75 0.271 3.25 W 0.80 0.286 3.43 U If swale(s)are used they must meet the following criteria: 76 • Runoff from site must be drained to Swale. - • Swale length must be greater than its width. cn� • Swale side slope must be 4:1 or shallower(horizontal to vertical). • Swale must not disturb any natural areas. • Swale must be 6 inches or deeper. • Swales should be vegetated. If a Swale is not vegetated than a 6-inch layer of nutrient sorption soil amendment formulated to reduce nutrient loading must be installed directly below the Swale.Specifications 0 and published nutrient reduction test results for the media must be provided for County review at the time Ui of permitting. Examples of acceptable media are NutriGoneTM (distributed by EcoSense International)and 0 Bold and Gold° (distributed by Environmental Conservation Solutions). 0 Packet Pg. 1793 If exfiltration trenches or french drains are used on single-family or duplex lots they must meet the following criteri • Minimum of 8 inches of cover. • Use at least a 4 inch or greater perforated pipe.A prefabricated shallow vault or drainage well may be used. • Inlets to exfiltration system must include a fabric filter. • Exfiltration system must not be within 10 feet of a building. • Exfiltration systems cannot be installed under driveways or other areas that may receive frequent vehicular traffic, unless designed by a Florida-registered and -licensed professional engineer. • Bottom of exfiltration system must be more than 12 inches above the wet season water table. Wet season 2 water table can be determined using the USDA Web Soil Survey(hops.//webso'ilsurvey.sc.egov.usda.gov), SoilWeb app available on Android or iPhone devices,or determined by an appropriate Florida-registered and -licensed professional. • Volume of an exfiltration trench in cubic feet can be approximated as:V= L x W x(D—0.96)x 0.4,where L= length in feet,W=average trench width, and D=average trench depth in feet. y CD TOP OF PAVEMENT OR FINISHED GRADE CL SACKFILL OR EMBANKMENT AGG rREGATE FILTER FABRIC LU I BD 0 f� F1 TR � PERF RA � �� _ TREATMENT �FAIR SLOTMD HI I HT PIPE VOLUME � (PTV), Cr a- TRENCH WIDTH � ' RECOVERY IL II ' IL SEASONAL HIGH GROUND WATER TABLE LP(SHGWn CONFINING NIT - I y TYPICAL "DRY" EXFILTRATION TRENCH -SEA Ids Source.Florida Department of Environmental Protection and Water Management Districts Environmental Resource Permit Stormwater Quality Applicant's Handbook(March 2010—Draft) 0 CJ I 0 The following diagrams illustrate the above design and construction guidelines and a sample site plan (Plate 7). If you have other questions, call the Planning and Environmental Resources Department at at 305-289-2500. e 6 Packet Pg. 1794 D. Sample construction techniques ""0E CL `l 9 v o 0 c U _ Existing Native Shoreline Vegetation to be Preserved E Existing Ground (Plate 1) 0 Cr 0) Rear Setback Building Pad Front Setback Swale Swale 76 Raised Pad S Berm g"Maximum y riginal Natural Rear lot Swale Front lot Swale 6" Deep Minimum Ground Line g° peep Minimum CJ Existing Native Shoreline Vegetation to be Preserved Lot Grading (Plata 2) 7 Packet Pg. 1795 0 0 c� Breezeway CD Stilt Construction CL T E Existing Native Shoreline o Vegetation to be Preserved House Elevation (Plate 3) 0 Cr 0) i 0 '� Above Ground Cistern �I 2 Existing Native Shoreline Vegetation to be Preserved Water Conservation (Plate 4) 8 Packet P�. 1796 E 0 rydrITiry A_ 11 i I a. cn y U Native Vegetation Existing Native Shoreline Vegetation to be Preserved CL Water Conservation (Prate 5) 0 u EMangrove CD m cr Berm W e E E '"'�`" Bulkhead (if existing) cn s. I a• •« CJ 4� c 0 Side and Rear Lot Details (Plate 6) Packet Pg. 1797 Exisiing klevailor7 5'(3 1-Existing Pumbo Limbo tree to remain 43--Proposed �.. _ _ _ L- silver button wood I shrubs/24"'Will ,I I + Above Ground - Cistern 3 gal.containers,` M planted 2'apart t i tes wo Row � Berm N E- ROADWAY� to _15" Residence Driveway A II _. Tile Roof 4 Proposed — _ - i\ 15'Thatch Palm �!/ \ silver button wood shrubs/24"tall/ ___ 1-Existing 3 gal.containers/ Gumbo Lim kao tree planted 2'apart to remain SITE PLAN 0 2 CL Berm 12"high t Wood deck"a Bi�'ilding pad Edge pf pavement 6"above crown of road CANAL Existing elevation \e Above Ground Cistern Swale 6"below PC> Swale 6"deep crown of road its CROSS SECTION Existing Native Shoreline A—A Vegetation to be Preserved I (Plate 7) 0 10 Packet Pg. 1798 1—Existing Gumbo Limbo tree Proposed t0 remain Elevation 5'K Swale E Proposed Elevation 5'8' + •. li ll,ine Above Ground SWale`f Cistern JJJ 1 — u7 Wood Deck =' Row ROADWAYS _.......e1 Residence (.gavel — a6 Driveway r A =1 A — Proposed rile Roo — Elevation 5 8" Proposed Down _ 15'Thatch Palm EL 1 Existin Proposed — Gumbo Limbo tree Elevation 5'8" Existing to remain Elevation 5 2„ Existin Property Line 9 Elevation 4'B" LU SITE PLAN 0 Cr 0) CD Proposed Edge of Pavement CL Elevation= Elevation 1'Deep Swale Drainage Deter. RETENTION DETENTION �Proposed Elevation= Type of Storage: Bottom Of Swale DRY A 1.4i Sire _ sq,ft, B Impervious Area .,._ sq,ft. C RImperv2 SECTION A—A D Rainfall=2.5.5 x%Impervious�"(1"min) Disturbed Area impervious Other Other Other _ Total E Cubic ft..req,=Disturbed Area x Rainfall w E x D m ¢' 12 12 Low Density Foliage Lot Cubic ft.suppled_. Cu.ft. N.T.S. I � 1 1 4 4 CROSS SECTION SUPPLIED SWALE .l..l. Packet Pg. 1799 Existing Existing Elevation 5' " Elevation 4"5" 1—Existing Gumbo Limbo tree Proposed to remain ,Elevation 5'8" Proposed - _ Etevatidn.4'8" 4- - Below Ground R/w Une Cistern t I Wood Deck , Row _ �. <--ROADWAY— > _ Inverted 't-- 10 Residence ""G vel 0 4 ' Swale c Driveway Swale on drive only or in row only ctt -- N Existing LElevadtion14'8Propos d _"` rile riot Elevation 4'8'" p- ��� •• Proposed DownCD 15'Thatch Palm \1—Existing Proposed Gumbo Limber tree Elevation 5`8"' SITE PLAN Existing to remain Elevation 5'2" Property Line 0 U SECTION A—A 0 E. Guidelines for expansion of existing WHAT if 1 just want to expand my home? Any impervious area expansion of existing lot coverage,that is, roofs, decks, patios, pools, and pavements, must provide for the retention of two and half inches of runoff from the expansion area.Typically,this retention requirement can be met by construction of a shallow Swale alongside the expansion's area. However, other CL approaches to retaining stormwater on the site will be considered.The following table shows the proportional ICU stormwater retention storage required for every 25 feet of new impervious area: 76 Provisions for swales must be s ®g shown on the site plans �I submitted with your permit 25 5 application.Just remember, 50 10 you should still follow the steps outlined in this brochure, 75 16 but you don't need to meet all 0 of the design and construction t�l 100 21 criteria required for new 125 26 homes. 150 31 175 36 200 42 12 Packet Pg. 1800 7j Ily ■V rrww s V L O O 'a .a IM O � ;� O 4 _ I= = i E .E ,o O � E 0 O • V = _ E 0m (a O LV L E V a L. Z W r. 0 O 00 VN O Q 0�0 n i N O O li f9 V d e CL O ate. C cO gyp/�// Li. 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