Public Works and Utilities Committee

PUBLIC WORKS AND UTILITIES COMMITTEE AGENDA There will be a meeting of the Public Works and Utilities Committee on Tuesday, January 24, 2017 to begin at 3:30 p.m. at Founders Hall, Charles Towne Landing. The following items will be heard: A. Invocation B. Approval of Public Works and Utilities Committee Minutes December 6, 2016 – DEFERRED December 20, 2016 – DEFERRED January 10, 2017 – DEFERRED C. Request to Set a Public Hearing None D. Acceptance and Dedication of Rights-of-Way and Easements 1. Whitney Lake Phase 4 - Acceptance and dedication of Pole Cat Alley (25-foot right- of-way), Rose Mallow Alley (25-foot right-of-way), a portion of Celosia Alley (25-foot right-of-way), a portion of Sweetleaf Lane (55-foot right-of-way), and a portion of Sparkleberry Lane (variable width right-of-way). Sidewalk is bonded. a. Title to Real Estate b. Affidavit for Taxable or Exempt Transfers c. Plat (2) d. Exclusive Storm Water Drainage Easements E. Requests for Permanent Encroachments None 2 George Street, Suite 2100, Charleston, SC 29401-3506 · Phone (843) 724-3754 · Fax (843) 973-7261 F. Temporary Encroachments Approved By The Department of Public Service (For information only) None G. Miscellaneous or Other New Business 1. Update on Stormwater Policy for grandfathered commercial developments. Councilmember Rodney Williams Chairperson CITY OF CHARLESTON REDEVELOPMENT STANDARDS FOR STORMWATER AECOM | 24 January 2017 | FINAL EXECUTIVE REPORT TABLE OF CONTENTS TERMS AND ACRONYMS ………………… …………… …………… ………………2 EXECUTIVE SUMMARY…………… …………… …………… …………… ……………….4 SECTION 1 - INTRODUCTION TO STORM WATER ………………………... 9 Figure 1: Diagram depicting changes in runoff and infiltration ………………………………. 9 Figure 2: Diagram depicting role of wetlands in a watershed ………………… ………………...10 Figure 3: Cross-sectional diagram of an infiltration BMP ……………………………………...11 Figure 4: LID BMPs treating urban parking lot runoff …………………………………………..12 Figure 5: Residential LID …………………… ……………… ……………… ……………………………………12 SECTION 2 - STORMWATER REDEVELOPMENT IN CHARLESTON …..14 SECTION 3 - STORMWATER REDEVELOPMENT OPTIONS ……………..16 Table 1: Overarching Redevelopment Considerations ………………………… ………………...17 Table 2: Redevelopment Standards Based on Site Conditions ……………………………….18 Table 3: City and State Stormwater Redevelopment Standards Comparison ……………. 19 Table 4: Redevelopment Standards Comparison for SC Municipalities …………………….20 SECTION 4 - CURRENT CITY OF CHARLESTON STANDARDS ………..23 SECTION 5 - CURRENT STATE OF SOUT H CAROLINA STANDARDS...28 SECTION 6 - REFERENCES ………………… …………… …………… ……………...30 EXAMPLES ………………………………………………………………………32 Figure 6: Comparing redevelopment options for a s uburban site in Charleston……….... 33 Figure 7: Comparing redevelopment options for an urban site in Charleston……………. 34 Page 1 TERMS AND ACRONYMS BMPs Best Management Practices; structural controls or behaviors which are used to manage stormwater CGP Construction General Permit; NPDES permit issued by SCDHEC governing construction sites larger than one-half acre Channel Protection Standards intended to prevent erosion and damage to natural stream channels from stormwater discharges and pipes Coastal Zone Coastal lands and waters with critical areas designated by SCDHEC CWA Clean Water Act Design Storm A particular storm size (intensity a nd frequency) used to design a site’s stormwater control structures Detention Temporarily capturing stormwater runoff, in order to release it a slower rate DS Design Standards EPA US Environmental Protection Agency; establishes clean water standards FEMA Federal Emergency Management Agency; establishes floodplain standards Filtration Straining runoff through a mesh or sand/gravel media in order to remove pollutants Flood Control Standards intended to address large storms and prevent damage to downstream property and infrastructure Flowrate Combination of rate and volume; typically expressed as cubic feet per second Impaired Waters Water bodies which do not meet SC standards for their designated uses Impervious Areas Hard surfaces, such as roofs, pavement, and compacted soil, which prevent rainfall from soaking into the ground. Infiltration The process of water soaking into the underlying soil and groundwater LID Low Impact Development Modern Stormwater Addresses both water quantity and water quality; attempts to mimic and Management restore natural flow paths and treatment processes MS4 Municipal Separate Storm Sewer System; NPDES permit issued by SCDEHC governing stormwater management within a municipal area New Development Construction, installation, or alteration of land, a structure, impervious surface or drainage facility; soil disturbance; or any divi sion or subdivision of a lot, tract, parcel, or other divisions by plat or deed (Ch 27 City Code also uses this definition for Redevelopment) NPDES National Pollutant Discharge Elimination System; federal permit program for stormwater and wastewater, admi nistered by SCDHEC Pollutants Any substance or material not naturally present in water, or a natural substance which is present in excessive quantities, such as sediment Page 2 Pre-development The condition of the land at some time previous to a proposed new action (general); conditions which exist prior to the time the applicant commences any construction, development or re-development activity (DS definition) Rainfall Frequency How often a rain event of a given size occurs; typically expressed as “10-year storm”, “25-year storm”, etc Rainfall Intensity Amount of rainfall in a given time period; typically expressed as inches per hour Rate Speed of runoff; typically expressed as feet per second Redevelopment Construction, installation or land disturbance on a previously disturbed site (general); land disturbance that alters current use of land but does not necessarily alter pre-dev runoff characteristics (SC Reg 72-300) Retention Capturing runoff and storing on-site for infiltration, evaporation or reuse Riparian Buffer Vegetated area along stream channels which protects the stream from damage, filters runoff and maintains ecological function Runoff Water generated when rainfall travels over land rather than soaking in Runoff Reduction Reduce or eliminate runoff volume via infiltration, evaporation or reuse SCDHEC South Carolina Department of Health and Environmental Control Special Stormwater Areas which require additional control of stormwater quality and quantity Management Areas than that provided by minimum design standards Suburban Medium density developed areas SWDSM City of Charleston Stormwater Design Standards Manual SWMP Stormwater Management Plan; Ci ty of Charleston’s implementation plan to comply with MS4 Permit requirements Traditional Addresses primarily water quantity and focuses on impacts from flooding; Stormwater may not address water quality or other community interests Management TMDL Total Maximum Daily Load; state regulatory process to improve water quality of impaired waters Urban High density developed areas Volume Amount of runoff; typically expressed in cubic feet or acre-feet Water Quality Chemical and biological characteristics of runoff Water Quantity Amount (volume) and speed (rate) characteristics of runoff Watershed Land area draining to a common point Wetlands Partially submerged areas at the edge of land Page 3 EXECUTIVE SUMMARY Objective Provide an overview of stormwater and redevelopment i ssues and present options for stormwater redevelopment standards for the City of Charleston (City). Key Points  The current City stormwater design standards do not distinguish between new development and redevelopment. Redevelopment design standards are currently the same as standards for new development, producing very little drainage improvement when redevelopment occurs in built-out areas.  Redevelopment provides a rare opportunity to improve stormwater management in existing urban and suburban areas.  Updating the City’s stormwater design standards for redevelopment sites can and should align with the City’s current zoning standards for red evelopment sites. Zoning standards currently address buffers and setbacks, trees and landscaping, lane width, parking areas, permeable paving, low impact development, and other topics which intersect with stormwater requirements.  Redevelopment standards would allow for incremental improvement of stormwater management in previously developed areas as sites are redeveloped. This helps to address community concerns about growth and development, and associated flooding and water quality.  Modern stormwater management can improve aesthetics on a site, which is valued in the community. Improved stormwater management can also increase property value.  South Carolina stormwater requirements are not as stringent or as proactive as stormwater standards in nearby states. The City has the opportunity to lead the metro area in implementing modern stormwater management.  The timing is right to address redevelopment in the City. Redevelopment standards can be adopted as part of the overall update to the Stormwater Design Standards Manual, planned for 2017. Concepts In a natural condition, the land absorbs the majority of rainfall by infiltration. As the land is developed and becomes more urbanized, more of the land is covered by impervious surfaces, such as rooftops, pavement and compacted soil. An increasing amount of impervious surface results in less rainfall being infiltrated into the soil, and more running off. Impervious surfaces generate a larger volume of water and the runoff travels at a faster rate. Fast-moving, large Page 4 volumes of water cause erosion and flooding, and as the runoff travels, it picks up and transports pollutants. Traditional stormwater management was primarily focused on water quantity, and drainage systems were designed for temporary detention and controlled release of floodwater. Modern stormwater management addresses flooding as well as pollution, and is focused on both water quantity and water quality. Modern drainage systems are designed for retention, and Best Management Practices (BMPs) are structures or devices which slow the rate of runoff, reduce or eliminate excess volume, and provide treatment to re move or reduce pollutants. Low Impact Development (LID) BMPs are designed to mimic natural flow patterns, infiltration and treatment processes. Some BMPs provide basic filtration and capture sediment/debris. The City of Charleston has adopted a stormwater and floodplain Ordinance (Chapter 27 of the City Code), established stormwater Design Standards, and developed a Charleston-specific Municipal Stormwater Management Plan. Collectively, these address the design, construction and management of stormwater BMPs and the collection and conveyance system within the City of Charleston, and include requirements for redevelopment. Redevelopment in Charleston Analysis of the City’s existing stormwater management standards and discussions with City staff regarding growth and redevelopment have identified a number of issues, listed below:  Existing City stormwater design standards do not differentiate between new development and redevelopment.  Existing City water quantity standards are primarily flowrate-based, temporary detention standards.  Pre-development site condition and timeframe are not clearly defined.  Unclear terminology in standards creates confusion, loopholes, unintended outcomes.  Existing site conditions make quantity controls difficult, infeasible, or undesirable for some sites.  Existing City standards specify temporary “store and release” of a “water quality volume”.  Existing City standards specify “retention” for projects in the Coastal Zone only.  Existing City and State water quality standards are vague and at times, inconsistent. Page 5 Pre-development Considerations and Options  Pre-development may be defined in a variety of ways, depending upon the relative amount and timing of land disturbance. The pre-development condition in turn impacts the redevelopment requirements.  Pre-development may be defined as “pre-project” (the soil, vegetation and impervious conditions present immediately prior to submission of a project to the City).  Pre-development may be defined as “pre-Columbian” (the native vegetation and soil conditions prior to the arrival of settlers in North America).  Pre-development may be defined for a certain timeframe (number of years) prior to submission of a project to the City (thus allowing flexibility to the applicant for site status changes).  Pre-development may also be defined according to a certain threshold of acreage, or of overall development, such that prior development greater than, for example, 20% of a site, triggers redevelopment requirements, but prior deve lopment less than 20% of a site would instead trigger new development requirements.  Sites with prior development often have altered soil types and compaction, and potential contamination, therefore soil borings and testing are needed in order to determine existing site conditions.  Pre-development should be clearly defined in the design standards and aligned with desired zoning densities and style of development in a particular area. Different pre-development definitions could be used for redevelopment quantity and quality criteria. Redevelopment Considerations and Options New development and redevelopment design standards are typically tiered or cascaded with overarching site considerations addressed first. Then for redevelopment sites, the most effective standards can be established for sites with ideal conditions, followed by more flexible standards for sites with difficult site conditions, or where the City desires to encourage redevelopment. Design standards should be structured to account for the following types of requirements:  Natural resources (wetlands, riparian buffers, wildlife habitat)  Impaired waters  Flood control and channel protection (peak flow rate s and velocities)  Runoff reduction (volume)  Water quality (treatment) Design standards which encourage runoff reduction (volume) via on-site retention, infiltration and LID are suitable for sites with ideal conditions. Ideal site conditions include the following:  Clean soils with good infiltration  Deeper water table Page 6  Lower density suburban areas  Sufficient space on-site  Few site constraints Design standards with flexible requirements are appropriate for sites with more difficult conditions and where runoff reduction and infiltration are infeasible. Difficult site conditions include the following:  Small sites  High density urban areas  Desire to maintain character of streetscape  Poor or contaminated soils  Geotechnical hazards  Shallow water table  Complex existing infrastructure or other constraints There are a number of options for redevelopment standards in the City of Charleston. Options may include:  Adding a requirement for runoff reduction (volume)  Selecting a more stringent design storm (in order to require a larger amount of stormwater to be managed)  Capping the allowable percentage of impervious surface or requiring a certain amount of green space on a site (in order to reduce generation of runoff and to align with current zoning requirements)  Adding a requirement for channel protection  Considering the use of impact fees, in lieu of fees, or off-site mitigation or other credits Preliminary Recommendations Successful standards should define the terms new development, redevelopment and pre- development, as well as detention and retention. They should establish a minimum disturbance footprint and state whether the requirements apply to the entire site, disturbed area or impervious areas. A timeframe should be established for when the new standards will apply. Standards should also establish a threshold for switching from a runoff reduction (infiltration) requirement to a water quality treatment (filtration) requi rement, or to allow an in lieu of or offset fee or mitigation. Successful standards should be flexible enough to encourage responsible redevelopment while discouraging new impervious surfaces. Design standards should establish a tiered system for acceptable BMPs. Use of infiltration BMPs in site design is dependent on site soil characteristics, therefore implementation of infiltration BMPs should be on a site-specific basis with feasibility criteria. Site investigation and soil testing should be required in order to determine the appropriate tier. For acceptable soils, infiltration can be allowed. If site soils are too compacted or contaminated, or if site activities are likely to produce spills or contamination in the future, design standards should require filtration BMPs with a liner and prohibit any discharge to the groundwater or subsurface. Page 7 Design standards should establish prioritization for urba n and suburban BMPs. LID BMPs are more easily implemented in suburban and new development areas. High density urban and redevelopment areas require more space-efficient BMPs that make use of existing hardscape (rooftops, sidewalks, plazas, etc). A prioritization rankin g system should be established for allowable BMPs in the more urbanized areas, and in suburban areas, separately. Topics Covered in this Document Section 1 provides an introduction to stormwater and watersheds, with explanation of key terms and acronyms, and graphics. The introduction includes Stormwater 101 concepts, explanation of stormwater management techniques and BMPs, water quantity and quality controls, and legal drivers and implementation in South Carolina. Section 2 is an analysis of stormwater and redevelopment issues in the City. Section 3 summarizes options for stormwater redevelopment, and provides a comparison of redevelopment standards in other municipalities in coastal South Carolina, as well as in municipalities and states in the Southeast region. Section 4 lays out the City’s current stormwater standards in detail. Section 5 lays out the State of South Carolina’s current stormwater standards in detail. Section 6 contains reference citations for the sources a nd graphics used in this report. Page 8 SECTION 1 - INTRODUCTION TO STORMWATER Stormwater 101 During a storm, rainfall can either be intercepted by plants and trees, or fall on the land. In a natural condition, the land is able to absorb the majority of rainfall by a process called infiltration. As the land is developed and becomes more urbanized, more of the surface of the land is covered by impervious surfaces, such as rooftops, pavement and compacted soil. As shown in Figure 1, an increasing percentage of impervious surface results in less rainfall being infiltrated into the soil, and more of the rainfall running off. These hard surfaces generate a larger volume of water, and without the natural obstacles which would otherwise slow the water down, the runoff travels at a faster rate. Fast-moving, large volumes of water cause erosion and flooding, and can damage land and property downstream. Additionally, as the runoff travels over the land, it picks up pollutants. Pollutants are any substance or material not naturally present in rainwater or surface water, or a natural substance which is present in excessive quantities (such as sediment). Impaired waters cannot be used as intended, for recreation, water supply, fishing or shellfishing, etc. due to pollution, or may lose their ability to support aquatic life. Figure 1: Diagram depicting changes in runoff and infiltration with increasing amounts of impervious surface A watershed is an area of land which all drains to a single point, bounded by higher elevations at the edges. Within a watershed, water travels over land until it reaches a stream, and as the Page 9 water passes further downstream, draining a larger area, pollutants can accumulate. Ultimately, the rivers and streams reach the ocean, and any accum ulated pollutants are discharged into the ocean. In the Lowcountry, wetlands fringe the edge of the land, and many of the local streams and creeks enter wetlands before discharging to the ocean. Wetlands perform a crucial function in the watershed, intercepting pollutants carried downstream and removing them from the water in a natural treatment process. Additionally, the wetlands slow the water down, allowing some of the runoff to infiltrate or be stored in the wetlands and slowly released long after the storm has passed. Figure 2 depicts how wetlands work. Figure 2: Diagram depicting role of wetlands in a watershed Stormwater Management Traditional stormwater management was primarily focused on water quantity. Drainage systems were designed to capture the large volume, high-rate runoff, reducing the peak flowrate if possible, and then convey the runoff rapidly away from developed areas. This is why in older areas of most cities, the stormwater system consists primarily of catch basin drains and stormwater pipes to collect and convey floodwaters, and also often includes some type of detention basin or pond to temporarily detain and control the runoff, before releasing the water at a controlled rate. These traditional systems often do not adequately address water quality, environmental, aesthetic or other community issues. Modern stormwater management addresses flooding as well as pollution found in runoff, and therefore is focused on both water quantity and water quality. Modern stormwater management attempts to restore the natural function and connection of the streams in the watershed, and Best Management Practices (BMP) are used to slow the rate of runoff, reduce or eliminate the excess volume of runoff, and provide treatment to remove or reduce the Page 10 pollutants. BMPs are typically structures or devices whi ch capture and treat runoff. Some BMPs provide flow-through treatment only, filtration of the runoff or physical removal of trash and debris entering the BMP, with cleaner water flowing out. Some BMPs provide on-site retention of runoff, allowing the retained water to infiltrate into the ground, evaporate into the atmosphere, or be reused for landscape irrigation or oth er purposes. Note that BMPs may also be behaviors which can improve stormwater quality, such as picking up after a pet. Low Impact Development (LID) BMPs are designed to mim ic natural flow patterns across the land, as well as natural treatment processes. Figure 3 is a diagram of an LID BMP designed for infiltration of the runoff into the underlying soil. Figures 4A and 4B are photographs of infiltration BMPs, integrating stormwater management into the overall site design and landscaping. Figure 3: Cross-sectional diagram of an infiltration BMP Figures 4A and 4B: LID BMPs treating urban parking lot runoff Types of Stormwater Controls Page 11 In summary, stormwater controls can be categorized according to the following: I. Water Quantity – Peak Flow (rate) control, Volume control II. Water Quality – Treatment control (pollutants) III. Combination of Quantity and Quality Controls Modern stormwater management and LID require (III), a combination of water Quantity and Quality Controls. There are a large number of types of BMPs and controls, and these controls can be implemented in a variety of ways. Designs are strongly influenced by site characteristics, such as:  Topography  Soils and underlying geology  Groundwater  Proximity of wetlands or other water bodies  Climate and weather patterns  Natural resources and wildlife  Existing vegetation Because improperly managed stormwater has the potential to impact public health and safety, and/or cause damage to property, a number of Figure 5: Residential LID laws and regulations have been adopted. These federal, state and local requirements are intended to provide guidance and limitations for the design and management of stormwater systems, and implementation is ultimately done at the local level. The following paragraphs summarize the most important requirements which relate to development and redevelopment within the City of Charleston. Legal Drivers and Implementation Congress adopted the Clean Water Act (CWA) in 1972 . This law established a framework for managing water bodies in the United States, including c lassification of waters, water quality standards, and beneficial uses of waters. Since that time, the US Environmental Protection Agency (EPA) has adopted a number of regulatory requ irements, including the National Pollutant Discharge Elimination System (NPDES) Permit Program, to address pollutant sources from both stormwater and wastewater. CWA authority has been delegated to most of the states, including South Carolina, to manage water resources at the state level. The state of South Carolina administers the NPDES permit program, and delegates much of the local implementation and enforcement responsibility down to the municipalities. The State of South Carolina has enacted several stormwater regulations and general permits. These are targeted at specific industries and activities known to contribute to stormwater pollution.  SC Construction General Permit (CGP) (2013)  SC Small Municipal Separate Stormwater Sewer System (MS4) Permit (2014) Page 12  SC Regulation 72-300 through 72-316, Standards for Stormwater Management and Sediment Reduction (2002) The City of Charleston has been designated as a “Qualifying Local Program” with responsibility for implementing the above-listed NPDES permits and state regulations. Accordingly, in recent years, the City has adopted a stormwater and floodplain Ordinance (Chapter 27 of the City Code), established stormwater Design Standards, and has developed a Charleston-specific municipal Stormwater Management Plan (listed below).  City of Charleston Stormwater Management and Flood Control Ordinance (2013)  City of Charleston Stormwater Design Standards Manual (SWDSM) (2013)  City of Charleston Stormwater Management Plan (SWMP) (2014) These standards address the design, construction and management of stormwater BMPs and the collection and conveyance system within th e City of Charleston. Each of the aforementioned state of SC and City of Charleston stormwater requirements have been examined and analyzed with regards to new development and redevelopment. This analysis is presented in Section 2. Additional detail regarding each of the City and State requirements, including direct excerpts from the Design Standards, can be found in Sections 4 and 5. Note: The City is also responsible for implementing national floodplain regulations established by the Federal Emergency Management Agency (FEMA). These regulations are addressed under the 2013 Ordinance, and do impact new development and redevelopment, however they will not be revised and as such, are not discussed in this Executive Report. Page 13 SECTION 2 - STORMWATER REDEVELOPMENT IN CHARLESTON The City of Charleston encourages redevelopment and infill of previously developed areas, and needs design and zoning standards which appropriately direct this redevelopment. Many of the older areas of the City, in particular West Ashley, were developed during a time of traditional stormwater management. Redevelopment provides an opportunity to upgrade and modernize the stormwater system, restore natural function, and provide an aesthetic amenity. Analysis of the City’s existing stormwater management standards and discussions with City staff regarding redevelopment have identified a number of issues, listed below: 1. Existing City stormwater design standards do not differentiate between new development and redevelopment. 2. Existing City standards are primarily flowrate-based, temporary detention standards. Rate controls are specified for water quantity. Rate and volume controls are specified for projects in Church Creek basin only (and any other Special Stormwater Management Areas to be designated in the future).  Temporary detention and rate controls reduce flood damage, however they do not reduce the large volumes of runoff generated by impervious surfaces and provide minimal treatment for pollutants.  For a built-out site, the post-development runoff rate will not change much from the pre-development condition, therefore the req uirement to match post-development rates to pre-development rates has minimal effect and does not require the developer to upgrade the site’s stormwater management. The standard only requires that the runoff rate is not exacerbated by redevelopment. 3. Pre-development site condition and timeframe are not defined. If the previous site condition was more developed (more impervious) than the current site condition (ie: the site has been demolished and re-vegetation has occurred), developers request to consider the pre-development condition of the site as the more developed condition.  This is advantageous to the developer in that it reduces stormwater management requirements, and results in a lost opportunity for the City to upgrade the site.  Current City SWDSM requirements do not precisely define the pre-development timeframe or the threshold at which a site is considered previously developed.  City Engineering staff define pre-development as the condition as of the day before submittal of plan review package. The project is considered redevelopment if there is any amount of prior development on the site. 4. Unclear terminology creates confusion, loopholes, unintended outcomes. Existing SWDSM does not clearly define key terms such as: special protection area vs. special Page 14  stormwater management area; pre-development vs. pre-project; new development vs. redevelopment; detention vs. retention; etc. 5. Existing site conditions make quantity controls difficult, infeasible, or undesirable for some sites. This includes sites with small parcel size, city streetscape, shallow water table, poor soil characteristics, etc.  Current SWDSM uses an all or nothing approach. Smaller scale BMP implementation or other adaptations providin g flexibility for sites with difficult site conditions would be possible with revised standards. 6. Existing City standards specify temporary “store and release” of a “water quality volume”. This treatment requirement, and the specified volume, differs depending upon the situation (structural controls or ponds; engineered treatment devices; infiltration devices; projects in Church Creek Basin or other Special Stormwater Management Areas to be designated in the future; and/or projects near shellfish beds).  Differing volume requirements creates confusion for designers.  “Store and release” treatment does not reduce overall volume of runoff. This tends to result in installation of basic filtration devic es and a proliferation of traditional ponds, even for sites where more effective B MPs are feasible. 7. Existing City standards specify “retention” for projects in the Coastal Zone only.  “Retention” is defined in the SWDSM as collection and storage of runoff, without subsequent discharge. This standard would be beneficial throughout the City.  Coastal Zone projects have different requirements for volumes to be retained, for entire site vs. built upon area. This distinction is not made elsewhere in the SWDSM and would be beneficial. 8. Existing City and State water quality standards are vague. The City’s current SWDSM requires treatment for sites larger than 1-acre, for both new development and redevelopment. The MS4 permit requires treatment of 1-inch volume for new development, and specifies treatment as necessary for redevelopment, however it only specifies “improving the pre-development hydrology.” The CGP requires treatment via undisturbed buffer areas, during construction only. Buffers are a lso required under the City’s current SWDSM for projects discharging to impaired waters.  Revised standards specifying volume retention/reduction and water quality treatment, and with more specifics regarding types, location, sizing and other design requirements for a greater variety of BMPs would result in improved water quality as well as improved pre-development hydrology for redevelopment sites. Page 15 SECTION 3 - STORMWATER REDEVELOPMENT OPTIONS After analyzing the City of Charleston’s current requirements for redevelopment, it is instructive to take a look at national guidance regarding stormwater and redevelopment, and then to compare the City of Charleston’s requirements to stormwater redevelopment requirements in other cities, counties and states in the region. A variety of options are available for managing stormwater on redevelopment sites, depending upon site conditions. Standards should be selected based on the goals of the City (flooding, water quality, green space, aesthetics, impaired waters, etc.) New development and redevelopment standards are typically tiered or cascaded with overarching site considerations addressed first. Then for redevelopment sites, the most effective standards can be established for sites with ideal conditions, followed by more flexible standards for sites with difficult site conditions, or where the City desires to encourage redevelopment. Design standards should be structured to account for the following types of requirements and overarching site considerations:  Natural resources (wetlands, riparian buffers, wildlife habitat)  Impaired waters  Flood control and channel protection (peak flow rate s and velocities)  Runoff reduction (volume)  Water quality (treatment) Design standards which encourage runoff reduction (volume) via on-site retention, infiltration and LID are suitable for sites with ideal conditions. Ideal site conditions include the following:  Clean soils with good infiltration  Deeper water table  Lower density suburban areas  Sufficient space on-site  Few site constraints Design standards with flexible requirements are appropriate for sites with more difficult conditions and where runoff reduction and infiltration are infeasible. Difficult site conditions include the following:  Small sites  High density urban areas  Desire to maintain character of streetscape  Poor or contaminated soils  Geotechnical hazards  Shallow water table  Complex existing infrastructure or other constraints Page 16 On the following pages, a series of tables presents redevelopment standards for consideration in the City of Charleston:  Table 1: Overarching Redevelopment Considerations  Table 2: Redevelopment Standards Based on Site Conditions  Table 3: City and State Stormwater Redevelopm ent Standards Comparison  Table 4: Redevelopment Standards Comparison for SC Municipalities Table 1 presents overarching redevelopment considerations, based on national guidance for stormwater and redevelopment. Table 2 presents more specific redevelopment requirements by site condition, also based on national guidance, and categorized accordingly to the specific technical requirements. This same categorization is used in Table 3, to compare redevelopment standards for various cities, counties and states in the Southeast region. Finally, Table 4 presents a list of the South Carolina coastal communities which have adopted redevelopment standards more stringent than existing South Carolina state requirements. SC standards are less stringent than surrounding states, an d none of the cities or counties in the Charleston metro area have yet adopted standards more stringent than the state standards. The City has an opportunity to lead in modern stormwater management. Table 1: Overarching Redevelopment Considerations REDEVELOPMENT HOW TO IMPLEMENT CONSIDERATIONS Natural Resources - Overarching considerations regarding conservation easements, riparian buffers, wetlands, open space, reforestation, soil conservation, etc. Impaired Waters - Pollutant load-based standards, where applicable, or - Cumulative effect of BMP implementation strategy Groundwater Recharge - Where applicable Water Quantity – - Maintain stable channels and control flow rates for large Flood Control and storm events, where applicable Channel Protection - May require downstream analysis for large drainage areas (flow rate and velocities) - Incorporate with floodplain requirements Water Quantity – - Hydrograph-based volume capture and retain on-site Runoff Reduction (volume) - Assumes retention-based (volume) standard for new development Water Quality (treatment) - LID implementation; infiltration BMPs required and feasible Page 17  Table 2: Redevelopment Standards based on Site Conditions REDEVELOPMENT SITE HOW TO IMPLEMENT STANDARDS CONDITIONS Water Quantity – Ideal Conditions - Require entire post-development volume to be Runoff Reduction captured Difficult Conditions - Require x % of post-development volume to be captured, or demonstrate maximum achievable Design Storm Ideal Conditions - Specify 2-yr, 24-hr storm or 80th/85th/90th percentile Difficult Conditions - Allow 1-yr, 24-hr storm or less than 80th/85th/90th percentile storm Water Quality Ideal Conditions - Require entire post-development volume to be treated via on-site infiltration Difficult Conditions - Allow Flow-through BMPs (filtration) where infiltration is not possible, or to treat volume remaining that cannot be infiltrated - Allow reduced sizing for Microscale BMPs (smaller design storm) - Establish a prioritized suite of BMPs for difficult site conditions based on site and soil characteristics Impervious Surface Both - Establish a minimum % pervious Thresholds - Establish a maximum % impervious - Require reduction of x % impervious - Disconnection of impervious surfaces - Increase of < 50% impervious surface, capture and treat runoff from new and/or replaced areas - Increase of > 50% impervious surface, capture and treat runoff from entire site (new, existing and replaced i mpervious surfaces) - Capture and treat runoff from x % of existing impervious surfaces plus any new impervious surfaces Green Space and Both - Require addition of x % tree canopy Urban Tree Planting - Require s oil amendments and tilling to restore soil capacity for infiltration and plants in green spaces Financial Difficult Conditions - Impact Fees - In lieu of Fees or Offset Fees Off-Site Mitigation Difficult Conditions - Privately owned land elsewhere in the watershed - City/County mitigation project (wetlands, stream restoration, stormwater retrofit, other) Page 18  Table 3: City and State Stormwater Redevelopment Standards Comparison: REDEVELOPMENT MARYLAND VIRGINIA NORTH GEORGIA SOUTH FLORIDA REQUIREMENTS CAROLINA CAROLINA Definition of Considered Prior developed Any land disturbing Structural dev, Land disturbance Not specified. Redevelopment redevelopment if lands. activity that does create/add/replace that alters current State-level design St 40% imperv. Net increase in not result in a net imperv surfaces, use of land but standards not Requirements imperv area, apply incr in built-upon and land does not specified. apply for all new development area and provides disturb assoc with necessarily alter existing imperv standards to new greater or equal structural/imperv pre-dev runoff areas within limits areas of stormwater control dev on a previously characteristics (SC of disturbance redevelopment site than previous dev developed site Reg 72-300) General Flexible options: Focus on Standards Coastal LID in Coastal SC: Sttate law requires Comments Reduce imperv Chesapeake Bay established by communities Planning and 880% reduction of area by 50% or watershed River Basin and adopted more strict Design Guide av avg ann pollutant provide treatment water classif. Reqs standards; best reference lload that would for 50% existing based on density adopted statewide caause violation of imperv area, or in 2016. WQS; 95% for combination ORRW; not achieved Runoff Reduction Recharge volume Reqs increase for 1” statewide First 1” Recommends 1” Required (volume) fraction of WQ vol increased 1.5” coastal volume removed but not required ddrawdown 72 hrs depending upon impervious areas Rate 1-yr, 24-hr soil group and decrease for storm. Drawdown sites < 1ac. 48-120 hrs Water Quality WQ volume 1” BMPs required Neuse Basin max Treat remaining Vol Recommendations 1” or 2.5”x% eastern zone, 0.9” phosphorus load Nitr 3.6 lb/ac/yr; x 1.2 with 80% TSS only im mperv, whichever western zone. reductions Tar-Pam Basin load removal is greater Area adjusted 10-20% max Nitr 4 lb/ac/yr, ((SJRWMD and based on % imperv max Phos 0.4 SFWMD only); lb/ac/yr. Redev in poond depth not to Tar-Pam reduce exceed anoxic Nitr by 30%, no net depth incr in P load. Rem basins 85% TSS removal Channel Provide extended Peak rate 20% less Not specified as 1-yr, 24-hr storm, Not specified as Not specified Protection detention volume than predev rate x such. Riparian energy dissipation such (Peak flowrate) for 1-yr, 24-hr ratio of pre:post- buffer and various and preservation of storm. N/A for tidal dev runoff vol for setback reqs apply stream buffer discharges natural channels Flood Control Opt: control peak Peak discharge FEMA 25-yr, 24-hr rate Reduce discharge Esstablished in each (Peak flowrate) discharge from 10- match pre-dev rate, requirements (overbank prot) velocities to non- WWMD for canals, yr storm to pre-dev 10-yr, 24-hr storm. 100-yr, 24-hr erosive velocity or etc. rate. Dev excluded Impounding (extreme events) 10-yr, 24-hr storm from 100-yr structures designed pre-dev rate, floodplain. Eastern to withstand 100-yr, whichever is less Shore: control peak 24-hr storm. (SC Reg 72-307, disch for 2-yr specifies for CGP) storm. Green Infrastr. X ¥ ¥ ¥ X X Credits or Mitigation Credits (off-site BMP alt) Offset Fees X ¥ ¥ ¥ X X Latest edition 2009 2013 2007 2016 2014 2005 Page 19   Table 4: Redevelopment Standards Comparison for SC Municipalities MUNICIPALITY STORMWATER VOLUME CONTROL Beaufort County All stormwater from the 95th percentile storm (1.94 inches) must be Includes City of Beaufort retained on site. and Town of Port Royal In areas of Hydrologic Soil Groups A&B, the development shall control and infiltrate the first one inch of stormwater runoff from the entire Town of Bluffton development or maintain the pre-development hydrology for the Water Quality Design Storm Event (95th percentile storm = 1.95 inches), whichever is greater. Three Options: 1. Redevelopment projects must achieve a 10% reduction in runoff volume (from pre-redevelopment levels). Horry County 2. Reduce impervious cover on the site by at least 20%. 3. Reduce the post-development peak discharge rates by 20% for the 10- and 25-year, 24-hour storms. Jasper County The 85th percentile storm (1 .2 inches) must be retained on site. As a minimum, the first inch of rainfall from each storm over the City of Myrtle Beach developed portion of the site shall be retained on site. Minimum storage volume shall be provided to retain on-site the first inch City of North Myrtle of runoff generated by any storm event over the developed or Beach redeveloped portion of the site. The first flush runoff (0.5 to 1.0 inch) from paved streets and parking areas shall be filtered through vegetation, grass, gravel, sand or other Town of Hilton Head filter mediums to remove oil, grease, gasoline, particulates and organic matter is required before the runoff leaves the site or enters any natural or manmade waterbody. As a minimum, adequate storage volume shall be provided to retain Town of Surfside Beach on-site the first inch of runoff generated by any storm event over the developed or redeveloped portion of the site. MUNICIPALITY PEAK STORMWATER CONTROL Projects greater than 5 acres or redevelopment projects must reduce Horry County post-development peak discharge by 20% for the 10-year and 25-year storms. The post-development peak discharge shall not exceed the pre- City of Hardeeville development peak for developments from 0-299 acres (25-year storm); over 300 acres (50-year storm). Reprinted from Low Impact Development in Coastal South Carolina: A Planning and Design Guide, 2014. Note: The City of Charleston’s Stormwater Management Plan states an intent to adopt post-construction site performance standards to require treatment of the first 1-inch of runoff from impervious areas on new development and redevelopment sites. Page 20 Pre-development Considerations and Options  Pre-development may be defined in a variety of ways, depending upon the relative amount and timing of land disturbance. The pre-development condition in turn impacts the redevelopment requirements.  Pre-development may be defined as “pre-project” (the soil, vegetation and impervious conditions present immediately prior to submission of a project to the City).  Pre-development may be defined as “pre-Columbian” (the native vegetation and soil conditions prior to the arrival of settlers in North America).  Pre-development may be defined for a certain timeframe (number of years) prior to submission of a project to the City (thus allowing flexibility to the applicant for site status changes).  Pre-development may also be defined according to a certain threshold of acreage, or of overall development, such that prior development greater than, for example, 20% of a site, triggers redevelopment requirements, but prior deve lopment less than 20% of a site would instead trigger new development requirements.  Sites with prior development often have altered soil types and compaction, and potential contamination, therefore soil borings and testing are needed in order to determine existing site conditions.  Pre-development should be clearly defined in the design standards and aligned with desired zoning densities and style of development in a particular area. Different pre-development definitions could be used for redevelopment quantity and quality criteria. Redevelopment Considerations and Options There are a number of ways the City of Charleston can implement redevelopment standards. This may include:  Adding a requirement for runoff reduction (volume)  Selecting a more stringent design storm (in order to require a larger amount of stormwater to be managed)  Capping the allowable percentage of impervious surface or requiring a certain amount of green space on a site (in order to reduce generation of runoff)  Adding a requirement for channel protection  Considering the use of impact fees, in lieu of fees, or off-site mitigation or other credits Preliminary Recommendations Successful standards should define the terms new development, redevelopment and pre- development, as well as detention and retention. They should establish a minimum disturbance footprint and state whether the requirements apply to the entire site, disturbed area or impervious areas. A timeframe should be established for when the new standards will apply. Standards should also establish a threshold for switching from a runoff reduction (infiltration) Page 21 requirement to a water quality treatment (filtration) requi rement, or to allow an in lieu of or offset fee or mitigation. Successful standards should be flexible enough to encourage responsible redevelopment while discouraging new impervious surfaces. Design standards should establish a tiered system for acceptable BMPs. Use of infiltration BMPs in site design is dependent on site soil characteristics, therefore implementation of infiltration BMPs should be on a site-specific basis with feasibility criteria. Site investigation and soil testing should be required in order to determine the appropriate tier. For acceptable soils, infiltration can be allowed. If site soils are too compacted or contaminated, or if site activities are likely to produce spills or contamination in the future, design standards should require filtration BMPs with liner and prohibit any discharge to the groundwater or subsurface. Design standards should establish prioritization for urba n and suburban BMPs. LID BMPs are more easily implemented in suburban and new development areas. High density urban and redevelopment areas require more space-efficient BMPs that make use of existing hardscape (rooftops, sidewalks, plazas, etc). A prioritization rankin g system should be established for allowable BMPs in the more urbanized areas, and in suburban areas, separately. Page 22 SECTION 4 - CURRENT CITY OF CHARLESTON STANDARDS Types of Stormwater Controls: I. Water Quantity – Peak Flow (rate) control, Volume control II. Water Quality – Treatment control (pollutants) III. Combination of Quantity and Quality Controls Legal Drivers for City of Charleston Stormwater Standards:  City of Charleston Stormwater Management and Flood Control Ordinance (2013)  City of Charleston Stormwater Design Standards Manual (SWDSM) (2013)  City of Charleston Stormwater Management Plan (SWMP) (2014)  SC Construction General Permit (CGP) (2013)  SC Small Municipal Separate Stormwater Sewer System (MS4) Permit (2014)  SC Regulation 72-300 through 72-316, Standards for Stormwater Management and Sediment Reduction (2002) The following text is directly excerpted from the City’s SWDSM, with page numbers referenced at the end of each item. Several items have been condensed in the interest of brevity. Part (I) Water Quantity and part (II) Water Quality requirements are each broken out according to (A) Minimum Requirements for all Projects, and (B) Requirements for Special Stormwater Management Areas. Part (III) shows the Quality and Quantity controls combined and explains the requirements for Special Stormwater Management Areas. I. WATER QUANTITY The following bullets summarize the water quantity and quality requirements found in the City of Charleston’s SWDSM, unless otherwise noted: A. Minimum Requirements for all Projects o Runoff Rates: Post-development discharge rates shall not exceed pre-development discharge rates for the 2, 10 and 25-yr frequency, 24-hr duration storm. (pg 3-8) o Discharge Velocity: Post-development discharge velocity shall be reduced to provide non-erosive flow velocities from structures, channels or other control measures, or shall equal the pre-development discharge velocity for the 10-yr, 24- hr storm event, whichever is less. (pg 3-10) o Underground Detention Systems: Post-development discharge velocities shall be reduced to provide non-erosive flow velocitie s from structures, channels or other control measures, or shall equal the pre-development 10-yr, 24-hr storm velocities, whichever is less. (pg 3-9) o Recovery Time: Detained volume from all controls shall be drained from the structure within 72 hours. (pg 3-10) Page 23  o Ponds: Runoff is detained above the permanent pool elevation and released at a designed flow rate to reduce the downstream water quantity impacts. (pg 3-13) o 100-yr, 24-hr storm event: Shall be used to check all drainage designs for local flooding and possible flood hazards at adjacent structures and/or property. (pg 3-35) B. Requirements for Special Stormwater Management Areas o Church Creek Basin - Systems shall be designed and constructed to maintain the post-development peak flow rates at or below the pre-development peak flow rates, and to detain the excess runoff volume for th e 2, 10, 25, 50 and 100-yr frequency storms, with duration of 24-hrs. System must detain for a period of 24-hrs, with tolerances for a peak flow rate match for the 25 and 50-yr storm events being ± 10%, with all others matching pre-development conditions. Detention facilities shall contain the excess volume for the 24-hr period, and the volume required to release the post-development peak flow rates at or b elow the pre-development peak flow rates. (pg 3-4)  Note: pg 3-4 says Special Stormwater Management Area (Church Creek Basin) requirements only apply to new development, however pg. 3-5 states that redevelopment projects shall be governed by the same design criteria as new development, which would include redevelopment in Church Creek basin and any other Special Stormwater Management Areas. This conflict will be clarified in the next SWDSM update to ensure redevelopment standards will apply in Church Creek Basin. o Areas identified with flooding: The peak discharge rate is restricted to ½ of the pre- development rates for the 2 and 10-yr, 24-hr storm, or to the downstream capacity of the system, whichever is less; and the post-development runoff volumes for the 2-yr, 24-hr duration storm events above the pre-development level shall be stored for a period of 24-hrs on average before release. (pg 3-45) Page 24 II. WATER QUALITY A. Minimum Requirements for all Projects o Structural and Nonstructural Controls [generi c statements]: Stormwater runoff from construction, development and redevelopment shall be treated through the use of structural and nonstructural practices. (pg 3-5) Any water quality structures shall be designed to accommodate at least ½-inch of runoff from the entire site. (pg 3-22) o Water Quality Control Threshold: All sites which disturb one acre or greater shall have at least one permanent water quality structural BMP installed. (pg 3-22) o Water Quality Volume: Permanent water quality ponds/structures with a permanent pool elevation shall be designed to store and release the first ½-inch of runoff from the contributing area over a minimum period of 24-hrs. Permanent water quality structures without a permanent pool elevation shall be designed to store and release the first 1-inch of runoff from the site over a minimum period of 24-hrs. (pg 3-22) o Shellfish Beds: For a project located within 1,000 ft of shellfish beds, the water quality structure shall be designed to store and release the first 1½-inches of runoff from the site over a period of a minimum of 24-hrs. (pg 3-22) o Coastal Zone: Projects within ½-mi of a receiving water in the Coastal Zone must show that the first ½-inch of runoff from the entire site, or the first 1-inch of runoff from the built-upon area, whichever is greater, can be stored on-site. (pg 3-22) o Engineered Devices: The water quality volumes listed above may be waived if treatment is instead provided by engineered devices. The device must capture an equivalent amount of runoff as that captured by a dry pond with a volume capture of 1-inch. (pg 3-22) o Infiltration: Devices may be required on those sites which do not currently discharge stormwater runoff, have no existing outlet, or are in the Church Creek basin (ie: limits volume increases). In the post-development condition, devices shall be designed to infiltrate the runoff volume equivalent to the 2-yr, 24-hr storm, in 24 hrs. For the 10- yr and 25-yr, 24-hr storms, the discharge rate shall not exceed that of a site of equivalent size and slope with an SCS curve number of 39. (pg 3-11) Page 25  o Impaired Waters: Projects that discharge directly or indirectly into an impaired water body shall be required, via the installation an d implementation of measures, structural or non-structural BMPs, to reduce pollutant loads to levels required by the Total Maximum Daily Load (TMDL). (pg 3-22)  Not applicable in City of Charleston beca use the Ashley River/Cooper River/Charleston Harbor TMDL has not assigned loads to the City. o Post-Construction Standards: City of Charleston’s Stormwater Management Plan states an intent to adopt post-construction site performance standards to require treatment of the first 1-inch of runoff from impervious areas on new development and redevelopment sites. (SWMP, section 4.5.2).  These standards will be incorporated to the upcoming SWDSM update. B. Requirements for Special Stormwater Management Areas o Areas associated with TMDLs and Impaired Waters: Must meet water quality requirements listed above. Buffers are required to be established along perennial and intermittent streams adjacent to the project in a watershed where there is an established TMDL, and for other waters as dictated by the City. Base width is 50 ft plus 2 ft per 1% slope of the stream. All sources of contamination and degradation shall be excluded from buffer areas. (pgs 3-45, 3-46) III. COMBINATION OF QUANTITY AND QUALITY CONTROLS The City’s Stormwater Ordinance and Design Standards call for the designation of “Special Stormwater Management Areas.” This term has been defined as follows: “…areas which require additional control of stormwater quality and quantity than that provided by minimum design standards. Such areas may consist of watersheds corresponding to adopted TMDLs, known flooding problems and pollutant impairments, or other areas necessary to protect, maintain, and enhance water quality and the environment of the city and the public health, safety, and general welfare of the citizens of the city.” Currently Church Creek Basin in West Ashley is the only area in the City to have been designated as a Special Stormwater Management Area. Church Creek Basin requirements are listed below. The City of Charleston has initiated a series of watershed assessment studies, intended to update the Master Drainage Plan, evaluate existing conditions, model the system and make recommendations for improvements. Customized design standards for each watershed area and designations for Special Stormwater Management Areas will be included in the recommendations. o Church Creek Basin - Systems shall be designed and constructed to maintain the post-development peak flow rates at or below the pre-development peak flow rates, Page 26  and to detain the excess runoff volume for th e 2, 10, 25, 50 and 100-yr frequency storms, with duration of 24-hrs. System must detain for a period of 24-hrs, with tolerances for a peak flow rate match for the 25 and 50-yr storm events being ± 10%, with all others matching pre-development conditions. Detention facilities shall contain the excess volume for the 24-hr period, and the volume required to release the post-development peak flow rates at or b elow the pre-development peak flow rates. (pg 3-4)  Note: pg 3-4 says Special Stormwater Management Area (Church Creek Basin) requirements only apply to new development, however pg. 3-5 states that redevelopment projects shall be governed by the same design criteria as new development, which would include redevelopment in Church Creek basin and any other Special Stormwater Management Areas. This conflict will be clarified in the next SWDSM update to ensure redevelopment standards will apply in Church Creek Basin. o Areas identified with flooding: The peak discharge rate is restricted to ½ of the pre- development rates for the 2 and 10-yr, 24-hr storm, or to the downstream capacity of the system, whichever is less; and the post-development runoff volumes for the 2-yr, 24-hr duration storm events above the pre-development level shall be stored for a period of 24-hrs on average before release. (pg 3-45) o Areas associated with TMDLs and Impaired Waters: Must meet water quality requirements listed in B above. Buffers are required to be established along perennial and intermittent streams adjacent to the project in a watershed where there is an established TMDL, and for other waters as dictated by the City. Base width is 50 ft plus 2 ft per 1% slope of the stream. All sources of contamination and degradation shall be excluded from buffer areas. (pgs 3-45, 3-46) Page 27  SECTION 5 - CURRENT STATE OF SOUTH CAROLINA STANDARDS Types of Stormwater Controls: I. Water Quantity – Peak Flow (rate) control, Volume control II. Water Quality – Treatment control (pollutants) III. Combination of Quantity and Quality Controls Legal Drivers for State of SC Stormwater Standards:  SC Construction General Permit (CGP) (2013)  SC Small Municipal Separate Stormwater Sewer System (MS4) Permit (2014)  SC Regulation 72-300 through 72-316, Standards for Stormwater Management and Sediment Reduction (2002) Several State of South Carolina NPDES Permits and Regulations contain design requirements from the above-listed sources. The following text is directly excerpted from the State requirements, with sections referenced at the end of each item. Several items have been condensed in the interest of brevity. Standards are presented by (I) Water Quantity, (II) Water Quality, and (III) Combined Quality and Quantity Controls, in parallel with the City Standards in the previous section. Note: Many of the MS4 requirements are new, and will be included in the upcoming SWDSM update. I. WATER QUANTITY o Required volume and rate control are specified for during construction only. (CGP, section 3.2.10) o Basic post-development rates for conveyance and discharge velocity are stated in SC Reg 72-307 and CGP (sections 3.2.6 and 3.2.7), and are already reflected in the City’s current SWDSM. o Post-Construction BMPs are not mandated by the CGP, however both SC Reg 72- 307 and CGP (section 3.2.8) provide basic design guidelines for when permanent BMPs are included in a site design and CGP submittal. o Discharge velocities shall be reduced to provide a non-erosive velocity flow from a structure, channel, or other control measure or the velocity of the 10-year, 24- hour storm runoff in the receiving waterway prior to the land disturbing activity, whichever is greater. (SC Reg 307) II. WATER QUALITY Page 28  o Water Quality Controls [generic statements]: Controls are required in order to reduce discharge of pollutants from new development and redevelopment sites that disturb at least one acre and which discharge into an MS4. (MS4, section 4.2.5) o Controls must meet the performance standards (approximate pre-development conditions) to the maximum extent practicabl e. (MS4, sections 1.5 and 4.2.5) o Controls are required for discharges to impai red water bodies. (MS4, section 3.4) o Controls are required for discharges to specific classifications of waters. (MS4, sections 3.5 and 3.6) o Buffer Zones: Undisturbed buffer zone of 30 -ft is required during construction if surface waters are located on or immediately adjacent to the construction site. Extended buffer of 45-ft is required for sensitive waters. Reduction of the buffer width, or elimination of the buffer, are allowed under certain circumstances. (CGP, section 3.2.4.C) III. COMBINATION OF QUANTITY AND QUALITY CONTROLS o Water Quality Treatment Volume: New development standards can be one or a combination of design strategies, controls, practices or provisions that demonstrate the runoff reduction and pollutant removal necessary to approximate pre- development conditions. The first 1 inch of runoff must be addressed. (MS4, section 4.2.5) o Site Performance Standards: MS4 must describe the design strategies, controls and other practices deemed necessary to maintain, or in the case of redevelopment improve, pre-development hydrology and protect water quality. (MS4, section 4.2.5) Page 29 SECTION 6 - REFERENCES California State Water Resources Control Board. Waste Discharge Requirements for Stormwater Discharges from Small Municipal Separate Storm Sewer Systems (MS4), General Permit. Water Quality Order 2013-0001-DWQ, NPDES General Permit No. CAS000004, issued February 2013. Center for Watershed Protection. Managing Stormwate r in Your Community: A Guide for Building an Effective Post-Construction Program. EPA Publication No. 833-R-08-001, July 2001. City of Atlanta. Substitute Ordinance to amend Post Development Stormwater Management, Chapter 74, Article X – FINAL. Adopted February 2013. City of Charleston. Stormwater Design Standards Manual. Issued March 2013. City of Charleston. Stormwater Management Plan. Issued November 2014. City of Charleston. Why Does it Seem Like Charleston Always Floods When it Rains? City Stormwater Service. Undated. City of Clearwater. Stormwater Drainage Criteria Manual. Engineering Department, July 2015. Chatham County-Savannah Metropolitan Planning Com mission. Coastal Stormwater Supplement to the Georgia Stormwater Management Manual. April 2009. Ellis, K., C. Berg, D. Caraco, S. Drescher, G. Hoffmann, B. Keppler, M. LaRocco, and A. Turner. Low Impact Development in Coastal South Carolina: A Planning and Design Guide. ACE Basin and North Inlet-Winyah Bay National Estuarine Research Reserves, 2014. Florida Department of Environmental Protection. Florida Water Resource Implementation Rule. FAC 62-40, adopted 2005. Georgia Department of Natural Resources. Georgia Stormwater Management Manual, Vol 2: Technical Handbook. Environmental Protection Division, 2016 ed. Gwinnett County, GA. Stormwater Systems and Facilities Installation Standards and Specifications. 2006 ed. Harper, H. and D. Baker. Evaluation of Current Stormwater Design Criteria within the State of Florida, Final Report. Florida Department of Environmental Protection. June 2007. Maryland Department of the Environment. Maryland Stormwater Design Manual, Vol I. Center for Watershed Protection, May 2009 ed. North Carolina Department of Environmental Quality. Stormwater BMP Manual. “Chapter 2 - NC Stormwater Requirements.” Rev. 2009. Schueler, Tom. Stormwater Design for High Intensity Redevelopment Projects in the Chesapeake Bay Watershed. Chesapeake Stormwater Network, May 2011. Page 30 South Carolina Department of Health and Environmental Control. State of South Carolina NPDES General Permit for Storm Water Discharges from Regulated Small Municipal Separate Storm Sewer Systems (SMS4). Permit No. SCR 0300000, issued November 2013. South Carolina Department of Health and Environmental Control. South Carolina NPDES General Permit for Storm Water Discharges from Construction Activities. Permit No. SCR 100000, issued October 2012. South Carolina Department of Health and Environmental Control. Standards for Stormwater Management and Sediment Reduction: Regulation 72-300 through 72-316. Bureau of Water, issued June 2002. US Environmental Protection Agency. EPA Summary o f State Stormwater Standards, Draft. Jeremy Bauer, Office of Water, June 2011. Virginia Department of Environmental Quality. Virginia Stormwater Management Handbook. First ed., 1999. 2nd ed., Draft, 2013. Virginia Department of Environmental Quality. Virginia Stormwater Management Program (VSMP) Regulation. Eff. October 2013. Photo Credits Ellis, K., C. Berg, D. Caraco, S. Drescher, G. Hoffmann, B. Keppler, M. LaRocco, and A. Turner. Low Impact Development in Coastal South Carolina: A Planning and Design Guide. ACE Basin and North Inlet-Winyah Bay National Estuarine Research Reserves, 2014. Photos by A. Blair, D. Sanger, CWP, NEMO, RI DEM. US Environmental Protection Agency. “What is Green Infrastructure?” https://www.epa.gov/green-infrastructure/what-green-infrastructure. Accessed September 7, 2016. Capital Regional District, British Columbia, Canada. “How wetlands work.” https://www.crd.bc.ca/docs/default-source/Partnerships-PDF/image-download/wetlands- (jpg).jpg?sfvrsn=0. Accessed September 7, 2016. Page 31 EXAMPLES #1 Chuck E Cheese (1610 Sam Rittenburg Blvd, West Ashley) Fully developed (100% impervious) site, a few small trees, suburban area, little to no existing management of stormwater. #2 Abandoned site (corner of Morrison Drive and Romney Street) Previously developed site, demolished, now compacted gravel and grass, urban area (Poor soils?) City interest in site redevelopment to have urban streetscape in keeping with area. Indirect discharge via tidal creek to Cooper River. Special consideration TMDL. Page 32 Example #1: Chuck E Cheese 1610 Sam Rittenburg Blvd, West Ashley Site Conditions:  14 Acres  Soils unsuitable for infiltration  Suburban area, medium density development desired  Proximity to surface waters – not close Redevelopment Options:  Disconnect impervious areas, drain to landscaping  Use traditional detention basin for water quantity control  Incorporate flow-through bioretention for water quality treatment  Landscape site per zoning ordinance Figure 6: Comparing redevelopment options for a s uburban site in Charleston Page 33 Example #2: Abandoned Site Southeast corner of Morrison Drive and Romney Street Existing Conditions:  3.5 acres  Soils unsuitable for infiltration  Urban area, high density development desired  Proximity to surface waters – very close Redevelopment Options:  Disconnect impervious areas, drain to landscaping  Use traditional or reduced requirement for water quantity  Use permeable pavement in parking stalls, flow-thro ugh filtration tree box planters or green roof for water quality treatment  Landscape site per zoning ordinance Figure 7: Comparing redevelopment options for an urban site in Charleston Page 34