Bldg Dept Addendum 1.pdf

City of Peachtree City 151 Willowbend Road Peachtree City, GA 30269 Phone: 770-631-2515 Fax: 770-631-2507 PeachtreeCityGA.gov Purchasing Department

CITY OF PEACHTREE CITY

BUILDING DEPARTMENT SERVICES AND EROSION CONTORL REVIEW & INSPECTION

25-124PPZ

ADDENDUM #1

1. QUESTION: Under the City’s current contract, the current company supplies a Planning & Zoning Technician. However, the RFP does not mention this role. Do you want proposers to include this service in their proposals? CITY’S RESPONSE: No, do not include.

2. QUESTION: Do you require copies of our staff’s certifications or is listing them sufficient? CITY’S RESPONSE: Responses need to include both a listing and copies.

3. QUESTION: Is the City’s expectation that the Plan Reviewer and the building Official be two separate full-time employee? CITY’S RESPONSE: Yes, this would constitute two distinct roles; however, the Building Official should have the necessary knowledge to perform plan reviews where needed.

4. QUESTION: Referring to Attachment C: Terminations Form (page 15/19), does the City want documentation for terminated projects with Peachtree City or for other municipal clients? CITY’S RESPONSE: Other municipal clients.

5. CLARIFICATION: The City requires that the company have a professional engineer that can review commercial site development plans, road construction plans, and erosion control plans according to the attached checklist and the City’s local design manual.

This individual must also be a certified Level II design professional by the Georgia Soil and Water Conservation Commission.

6. CLARIFICATION: The City also requires a company that will be able to perform erosion control inspections on all active sites with a Land Disturbance Permit (LDP) every week and after every rain event over 0.5 inches. The inspections shall conform to the attached Enforcement Response Plan and utilize the attached Site Inspection Form.

The City also needs the company to be able to perform the initial erosion control inspections prior to the issuance of the LDP. Persons performing the inspections must be certified by the Georgia Soil and Water Conservation Commission in the appropriate areas.

7. CLARIFICATION: The City needs the company to be able to supply the results of the erosion control inspections with photographs. In addition, the City needs the inspection results in the same tabular format as used by the Flint River Soil and Water Conservation District quarterly, and semi-annual reports.

Attachments

Final Site Plan and Road Construction Plan Review Checklist Local Design Manual Enforcement Response Plan Site Inspection Form

June 19, 2025

Engineering Department 209 Mcintosh Trail Peachtree City, GA 30269 Phone: 770-487-5183 Fax: 770-631-2552 www.peachtree-city.org

Version 1/2/2025

CHECKLIST FOR REVIEW OF SITE PLANS AND ROAD CONSTRUCTION PLANS

DEVELOPMENT NAME: ____________________________

LOCATION: _____________________________________

REVIEWED BY:_____________________________________ DATE: _____________

Note: Plans must adhere to standards in the latest edition of the Georgia Stormwater Management Manual (GSMM), the Peachtree City Local Design Manual, the Manual for Erosion and Sediment Control in Georgia, and the AASHTO Policy on Geometric Design of Highways and Streets!

NOTE:

1. -All changes required are to be called out in the form of ballooning or call outs on the re-submitted plans!

2. -Redlined Drawings must be returned with subsequent submittals!

Otherwise re-submittals will be rejected.

3. If Stormwater checklist in Appendix A of Local Design Manual is not provided plans will be automatically rejected.

Item has been met Item has NOT been met (red font) Item is not applicable

A. BACKGROUND INFORMATION ON PLANS

1. Stormwater Hydrologic and Hydraulic Checklist from Appendix A in Local Design Manual filled out and provided?

2. Add note on cover “Plans expire 12 months from approval date unless a Land Disturbance Permit has been issued by development inspector.” Expiration date shall also be noted on the cover sheet.

3. Development name, address and legal description of site

4. Engineer’s seal and signature, address and telephone

5. Developer’s name, address, and telephone number

6. Date and vicinity map

7. Site matches the approved Preliminary Plat/Concept Plan?

8. GADOT approval for access to State Route prior to plan approval.

9. WASA approval for sewer

10. Fayette County Water System approval for water

11. Environmental Health Approval for septic system

12. Evidence of acquisition of all applicable local and non-local permits (To be completed upon plan approval)

13. Evidence of acquisition of all necessary legal agreements (e.g., easements, covenants, land trusts, etc.)

B. PLAN SHEETS

1. Show proposed and existing R/W lines and lot lines, pavement width and curb and gutter

2. Give FEMA map number based on field located survey (datum must match FEMA datum) and date and note about project in/out of floodplain, if any are located on or near the site they must be delineated. Also show City calculated floodplain as well if applicable.

http://www.peachtree-city.org/

(1) Any fill in FEMA floodplain or City Floodplain? (Not permitted in most cases – see City Engineer)

(2) Future Conditions flood study performed?

3. Show that lots have at least 70% of minimum lot area for that zoning district out of floodplain.

4. Is there stream with drainage basin of 100 acres or greater on the property? If so existing/future floodplain study must be conducted if City has not already done so.

(1) If develop in future flood, no rise certification and other conditions must be met – see City Engineer

5. Minimum Finished Floor Elevations (MFFEs)

(1) Adjacent to floodplain – structures elevated to at least 3ft above existing flood or 1 ft above future flood, whichever is greater.

(2) Adjacent to stormdrain structures – structures elevated to at least 1 ft above point where water would by-pass the system (i.e. low point in road, etc.). Depending on situation this could be increased to 1 ft above future 100-yr assuming system blocked.

6. Show all existing and proposed street names

7. Show all proposed and existing storm sewers

8. Show north arrow on each sheet

9. Show all drainage easements, pond access /maintenance easements, pipe easements, path easements and greenbelts to be dedicated to City. Show 20’ minimum, more specific below.

(1) For paths between platted lots use 50’ width greenbelt.

(2) For ditches/channels show easement equal to total top width of conveyance (including side slopes) plus 5 feet either side?

(3) City pond access easement from closest street 20 ft wide minimum and 4:1 longitudinal slope.

(4) City pond maintenance easement around pond 20 ft wide minimum and 4:1 longitudinal slope.

(5) For City maintained pipes see formula in Local Design Manual.

10. Delineate all cart path locations, widths, and easements. Must meet city design and cross section, ADA slopes. All transitions at roads/parking lots must meet ADA requirements for a pedestrian ramp.

11. Location of existing and proposed roads, buildings, parking lots and other impervious areas.

12. Location of existing and proposed utilities (e.g., water, sewer, gas, electric) and easements.

13. Show all existing and proposed lakes with surface area and dam height (Dam breach analysis may be required on new/existing lakes. Any CAT.II dams close by/upstream)

14. Show storm sewers extending from right-of-way to rear of residential lots

15. Show ponds and BMPs outside of creeks/streams and buffers. Ponds must not be on residential lots but in greenbelt.

16. General maximum fill slope is 2:1, maximum cut slope is 2:1

17. Provide traffic signage/striping plan (including street names) with note stating that all traffic control devices shall meet the requirements of the latest edition of the M.U.T.C.D. (with specifications put on plan).

(1) Add appropriate street detail sheet from Local Design Manual.

(2) Add cart path stop signs at all transitions from multi-use paths to roads/parking lots.

18. Delineate the width and length of acceleration and deceleration lanes if appropriate.

19. Label length of cul-de-sac streets. Max length is 1,200 ft. (Cul-de-sac required on all streets, provide temporary cul-de-sacs with right-of-way if not intersecting with another city street)

20. Label radius of curb returns curb radius should be minimized for pedestrian safety where appropriate.

21. Delineate the horizontal and vertical centerline of all new roads. Stationing shall be at minimum 100 ft intervals including at the stations for the PC, PT, and the centerline of intersections.

22. Delineate the horizontal profile of all new roads and provide centerline curve data including delta, arc, chord and tangent.

23. Delineate all perennial and intermittent streams

24. Location and dimensions of proposed channel modifications, such as bridge or culvert crossings

25. Delineate all streams and wetlands with appropriate buffers (see Article X of Land Development Ordinance) (Refer to River Basin Profiles https://storymaps.arcgis.com/collections/f60598f6c6b24777a38f40d400ae17b8?item=3iver for buffer delineations)

(1) State Waters Buffers

(2) Wetland Buffers

(3) Metro North Georgia Stream Buffers

(4) Watershed Protection Buffers

(5) Wetland Protection District (National Wetland Inventory Maps)

26. Has field run topography been provide for the proposed site?

27. The City shall not approve the construction of private streets in single family detached residential subdivisions.

C. PROFILE SHEETS

1. Show centerline profile of all streets with % grade, PVC, PVT, PVI and low point elevations

2. Show centerline profile of all storm sewers with structure number, % slope, grade/gage of material, size, and material type, etc. (AASHTO type ______)

3. Show catch basin top and invert elevations

4. Show storm sewer invert elevations

5. Show minimum clearance between storm sewers and other buried utilities (6”) and base course (18”) from street or parking lot

6. Show centerline profile (vertical and horizontal) of existing streets to the appropriate distance left and right of new intersection to determine adequate sight distance.

D. DETAIL SHEETS

1. Add Pond or lake dam detail with emergency spillway, anti-seep collar/collar drain, mud mat, permanent cleanout marker, etc. Refer to 3.2 of Local Design Manual for details to be added for specific type of pond.

(1) No roads allowed over any dam.

(2) City maintained ponds must be on separate parcels dedicated to City as Greenbelt.

2. Outlet control structure details (Check for trash rack, floatation, freeboard, and submergence)

(1) Need structural drawings?

3. Trash rack required for all openings that have smallest dimension less than 1 ft. Some dry pond specifications area as follows. See GSMM for specifications for wet pond trash racks.

(i) Area is at least ten times larger than the control outlet orifice

(ii) Trash rack bars are proportioned to the size of the smallest outlet protected

1. Opening space for pipes under 6 inches should be less then the pipe diameter

2. Opening space for pipes greater then 6 inches should be no greater then 6 inches

(iii) The rack has hinged connections at the top for easy clean out https://storymaps.arcgis.com/collections/f60598f6c6b24777a38f40d400ae17b8?item=3

(iv) The inside of the outlet structure for a dry basin should be below the ground level, at least equal to the diameter of the outlet, to minimize clogging due to sedimentation

(v) The slope of the should be about 3H:1V to 5H:1V to allow trash to slide up the rack with flow pressure and rising water level

4. Ditch or channel cross section detail provided?

5. Add typical section of R/W from Local Design Manual with pavement design (shoulder widths, sidewalks, utility placement, etc.) Will utilities cut through storm drains?

6. Typical section of curb and gutter. (L-back only)

7. Add Drainage structure details headwalls, drop inlets, storm sewer manholes, catch basins, etc. (Georgia D.O.T.

details needed for these) outlet structures, embankments, spillways, grade control structures, conveyance channels, etc. No hooded grate inlets are allowed in city right-of-way or easements without prior approval.

8. Pipe construction details. Add pipe material, bedding class, pipe gage, backfill methods, minimum cover, maximum lift thickness, compaction specifications, etc. Show design customized for particular project with anticipated minimum and maximum depths. See Local Design Manual for specifics.

9. Road sub grade fill details (compaction specifications, maximum lift thickness, etc.) Add details from Local Design Manual and reference it for specifications.

10. Stormwater quality BMP details match requirements in GSMM and Local Design Manual and are site specific?

11. Cart path detail needed? Use detail from Local Design Manual.

12. Landscape irrigation detail showing rain sensor shut-off switches per O.C.G.A 12-5-6.

E. MINIMUM DESIGN STANDARDS

I. STORMWATER QUANTITY

1. All City maintained storm drain pipes shall have a minimum diameter of 18 in. and be of material in Local Design Manual. For RCP show 12 inches minimum cover between top of pipe and GAB (unless manufacturer require more). For all other show 48 inches minimum cover.

(1) Minimum pipe velocity is 2.5 ft/s for the 2-year storm.

(2) Minimum pipe slope is 1%.

(3) Maximum pipe velocity is 12ft/s for the design storm. Otherwise need reinforcement at joints and manholes and other pipe-restraining methods.

(4) Maximum storm-drain pipe slope is 10% for concrete and 14% for others. Need profile.

(5) Maximum drop in storm-drain manhole is 10ft. Maximum manhole depth is 15ft.

(6) Maximum continuous length of pipe is 300 ft without a manhole/inlet.

(7) Note: Private maintained pipes may be specified to standard of owner and their engineer; however, shall still meet specifications outlined in Section 2.2.2 of Local Design Manual.

2. Energy dissipation must be employed when outlet velocity exceeds 4.0 ft/s or the erosion velocity of receiving area (whichever is less) for the 25-year storm. Design according to GSMM. Evaluation of stability of downstream channel must take place to see if additional downstream protection/stabilization is required due to increased flow volumes for 25-yr event.

3. Ditches/channels must be designed to same level of services as projects culvert/pipe systems.

(1) If convey flow to detention pond, ditch must be sized for 100-yr storm.

(2) ½ foot freeboard provided?

(3) 1% minimum slope.

(4) 3:1 side slopes .

(5) 3 ft minimum bottom width.

(6) Maximum velocity of 4 ft/s for the 25-year design storm. If over 4 ft/s adequate scour protection must be designed with rip-rap, etc.

4. For gutter spread see Local Design Manual page 9.

5. Ponds Dedicated to Peachtree City: See Section 3 of Local Design Manual for specifics on dam height, freeboard, compaction, principal spillway material. Some specifics below to be put on detail sheets.

(1) Show and label clearing limits at least 10 ft from toe of dam.

(2) Show aquatic and safety benches as appropriate.

(3) Outlet structures shall be concrete.

(4) Construct emergency spillway such that flows exceeding 100-yr storm shall pass through the spillway.

(5) Emergency spillway shall be separate structure from principal spillway.

(6) 1.0 ft of freeboard minimum is required between the calculated 100-year pond elevation (using both principal and emergency spillway discharges) and the lowest point on the top of the dam, not counting the emergency spillway.

(7) The emergency spillway must be able to discharge the entire developed 100-yr inflow routed through the pond (assuming the principal spillway is blocked) without over topping the dam.

6. Private Ponds not dedicated to City: See Section 3 of Local Design manual for specifics on dam height, freeboard, compaction, principal spillway material. Some specifics below to be put on detail sheets.

(1) Must meet all applicable standards in Section 3.2 of Local Design Manual and the GSMM and be shown on plans.

(2) Show aquatic and safety benches as appropriate.

(3) Dam height appropriate?

(4) Freeboard correct?

(5) Principal and Emergency spillway designed correctly?

7. Fencing requirement? - See Pond Fence Policy dated 9/2017. Ponds dedicated to City must have fence. Other ponds can be designed as to not have a fence if slopes and safety bench meet GSMM standards.

8. Use correct design storm for Storm drains and culvert design? See Local Design Manual page 8.

9. Show Hydraulic Grade Line (HGL) remain in pipe for applicable design storm and delineate on plans? Example page 8 Local Design Manual.

(1) Additionally, show 100-yr HGL and determine impact regardless of design storm.

10. For the design storm show HGL to be no less than 18” below the point at which water would bypass the inlet (i.e.

low point in road etc.) and maintain a HW/D ≤ 1.2.

11. Inlets shall not impact/back water up on upstream inlet and reduce upstream system performance.

12. Culverts with drainage areas over 25 Acres designed to 24-hr storm and not Rational Method?

II. STORMWATER QUALITY

1. 1.0 inch run-off reduction volume (RRv) met for site?

(1) Does off-site area affect and how deal with it?

(2) If can’t meet then:

(a) Must submit Runoff Reduction Feasibility Form

(b) site must be designed to treat 1.2 inch rain event. See Local Design Manual for more information.

(3) Must have Geotechnical Report to justify above information.

2. Channel Protection provided?

3. Follow all design recommendations from GSMM and Local Design Manual on structural BMPs?

(1) If using proprietary BMP for water quality, on approved list from Metro North Georgia?

4. Credits calculated according to GSMM and Local Design Manual?

5. Maintenance/Operation Plan specified on the plans for each BMP?

(1) Name, legal address and phone number of responsible parties for maintenance activities

(2) Description and schedule of maintenance task

(3) Description of applicable easements

(4) Description of funding source

(5) Access and Safety issues

(6) Procedures for testing and disposal of sediments, if required

6. Maintenance Agreement signed? This will be required for Land Disturbance Permit.

7. Landscape Standards followed and specified on the plans (Appendix D, of the GSMM)?

8. In Groundwater Recharge Area? See Ordinance Section 1008 of Article X of Land Development Ord.

9. Delineated all wetlands, lakes, ponds or other setbacks or have certification none on site?

(1) 404 permit needed?

10. Provide a location for concrete truck washout

F. ROAD DESIGN AND LAYOUT

1. Max change in grade is 1% without VC.*

2. Avoid steep grades and sharp VC at intersections. Street leveling may be required. (See Land Development Ordinance for Max grades and speed limits)

3. Geometry (AASHTO Standards)

(1) Vertical Curves

(2) Horizontal Curves

(3) Reverse Horizontal Curves – Tangents

(4) Min/Max Grade allowable

(5) Superelevation

4. See City Engineer for Bridges and Tunnels. Special requirements in ordinance and Local Design Manual.

5. Curb cut spacing adequate? (Refer to zoning ordinance section 913 and Land Development Ordinance section 803 for specifics. No residential access to arterial or collector. Keep curb cuts directly opposite each other and not offset.

6. Sight distance adequate? (AASHTO Standards with 6” object for new roads). Intersection sight distance will use

AASHTO eye and object standard heights.

G. GENERAL HYDROLOGY AND HYDRAULICS

1. Hydrology Report Certification Statement page from Appendix A of Local Design Manual provided?

2. No increase in floodplain (FEMA or not) elevations allowed off site.

3. Check upstream and downstream for sensitivity. Analyze 25-yr and 100-yr down to 10% point and check for downstream controls that warrant restriction. Analyze at all culvert or road crossings along the way. See Local Design Manual for larger watershed exemptions.

4. Pre-developed conditions/baseline conditions can be modeled as existing conditions. No increase in discharge rate (reported to nearest 0.1 cfs) in the 2-100 year storms allowed at any point on property line stormwater is discharged.

5. Show no increase in drainage area to a single discharge point over 10% of total predevelopment drainage area or 1.0 acre, whichever is less. If over this limit see Local Design Manual.

6. Delineate all drainage areas to each structure and check for offsite drainage potential.

7. For culvets/stormdrains design storm- Increase C factor for undeveloped offsite conditions according to future land use.

(1) Also check 100-yr future land use as check storm to see where flooding occur regardless of design storm.

8. Delineate all drainage areas, pre-developed and post-developed in master hydro-study, including off-site areas and their flow paths. How deal with off-site areas? (See Local Design Manual)

9. Check adequacy of tc, “C” factors and Drainage Areas, P values, storm type, shape factor , etc. in both master hydrology study and for each drainage structure.

10. In general SCS Method required for detention analysis and pipes draining over 25 acres. Check Local Design Manual and model usage limits, acreage limits, Cf, ponding ratio, Ia, IDF curves, etc.

11. Outlet structure hydraulics ok? Stage-Discharge curve developed according to proper hydraulic formulas and constraints?

12. Where will overflow/backup go if drainage system design storm is exceeded? Affect structures? (i.e., where 100-yr go if not designed for that storm?)

13. Final sizing calculations for structural stormwater controls including contributing drainage area, storage, and outlet configuration

H. EROSION AND SEDIMENT CONTROL

1. Refer to applicable erosion control plan checklist

2. Add Note on plans, “All persons involved in land disturbance activities must be certified in erosion and sediment control by the GASWCC or supervised by someone who is.”

3. Show and label Limits of disturbance on all phases of ESPC Plans.

REVIEW COMMENTS:

ENGINEERING DEPARTMENT

RESUBMIT:__________________ APPROVED_________________

DATE: ______________________ DATE______________________

RESUBMIT__________________ APPROVED_________________

DATE_______________________ DATE______________________

Direct questions regarding the above issues to:

Danny Chow, P.E.

Charles Abbott Associates, Inc.

27201 Puerta Real, #200 Mission Viejo, CA 92691 Toll Free: (866) 530-4980

(949) 367-2850

(e) dannychow@caa.inc

David A. Borkowski, P.E., City Engineer 209 McIntosh Trail

Peachtree City, Georgia 30269

(p) 770.631.2538

(f) 770.631.2552

(e) dborkowski@peachtree-city.org

Other policies and checklists can be found at Peachtree City Engineering Department Policies and Standards | Peachtree City, GA - Official Website mailto:dborkowski@peachtree-city.org https://www.peachtree-city.org/287/Development-Standards https://www.peachtree-city.org/287/Development-Standards

LOCAL DESIGN MANUAL

2021 EDITION

dborkowski Typewritten Text Revision to page 6 on RRv approved by City Council on January 7, 2021.

City Engineer - 01/08/2021 dborkowski Dave Signature

CITY OF PEACHTREE CITY

LOCAL DESIGN MANUAL | 2016 EDITION

October 2016

Contents

PART I | STORMWATER

1. Forward

1.1. Meeting the Stormwater Management Requirements of the City

1.2. Definitions

2. Design Performance Requirements

2.1. Discharge Standards to Adjacent Properties and Right-of-Ways

2.2. Conveyance Systems Standards

2.3. Flood Elevation Impacts

2.4. Minimum Finished Floor Elevation Adjacent to Stormwater Structures

3. Materials and Design Specification Requirements

3.1. Conveyance Structures

3.2. Detention Ponds

3.3. Water Quality Best Management Practices

3.4. Easement Requirements

4. Approved Hydrologic & Hydraulic Methods

4.1. Hydrologic Methods

4.2. Hydraulic Methods

4.3. Channel Protection Design

5. Special Districts

6. Hydrologic & Hydraulic Report Requirements

6.1. Hydrologic & Hydraulic Report Checklist / Certification

6.2. Project Narrative

6.3. Existing Conditions Hydrologic Analysis

6.4. Post-Development Hydrologic Analysis

6.5. Downstream Analysis

6.6. Stormwater Management System Design

6.7. Planting Plan (if applicable)

6.8. Operations & Maintenance Plan

PART II – TRANSPORTATION

APPENDICES

Appendix A – Stormwater Hydrologic & Hydraulic Checklist

Appendix B – American Concrete Pipe Association LRFD Fill Height Tables

Appendix C – General Peachtree City Technical Specifications for Drainage Systems

Appendix D – Construction Details

Part I | Stormwater

1. Forward This manual is meant to serve as a comprehensive guide to implementing stormwater management system requirements in The City of Peachtree City. Additionally, the manual is designed to supplement the

Georgia Stormwater Management Manual (GSMM) 2016 Edition, which shall serve as the technical manual for design and specification of individual components within the system.

1.1. Meeting the Stormwater Management Requirements of the City

The following outlines the process for developing a stormwater management plan for issuance and maintenance of a site development permit in the City.

Pre-Design Phase

Step 1 Check for new special district requirements with the City staff

Step 2 Check for concept plan submittal requirements

Step 3 Prepare concept plan (if required)

Step 4 Submit concept plan to the City and schedule concept pan meeting (if required)

Step 5 Meet with City staff to discuss concept plan (highly recommend)

Design Phase

Step 6 Prepare stormwater management plan

Step 7 Submit stormwater management plan to the City for approval

Construction Phase

Step 8 After receiving approval from the City begin construction

Step 9 Coordinate construction with the City inspection staff during construction

Post-Construction Phase

Step 10 After construction prepare As-Built Survey and As-Built Design Certification

Step 11 Adjust stormwater structures if necessary

Step 12 Execute stormwater inspection and maintenance agreement for all private on-site stormwater management facilities

Step 13 Secure Certificate of Occupancy / Final Plat

1.2. Definitions

“Adverse impact” shall apply to situations where the post development discharge rates, up to and including the 100-year storm event, exceed those determined for the pre-developed conditions per basin at the property line of individual property lines at the time of development. It shall also include situations where development will cause an increase in flood elevations on adjacent properties.

“Freeboard” area of containment above the design storm event.

“Hotspot” is defined as a land use or activity on a site that produces higher concentrations of trace metals, hydrocarbons, or other priority pollutants than are normally found in urban stormwater runoff.

Examples of hotspots include gas stations, vehicle service and maintenance areas, industrial facilities such as salvage yards (both permitted under the Industrial General Permit and others), material storage sites, garbage transfer facilities, and commercial parking lots with high-intensity use.

“Low cord” the lowest part of the bridge deck structure or stringers whichever is lower.

“Site” means the area of development or redevelopment.

“Structural development” means construction, installation or expansion of a building or other structure.

“Impervious development” means the creation or addition of impervious surfaces, or the replacement of impervious surface not part of routine maintenance.

2. Design Performance Requirements

2.1. Discharge Standards to Adjacent Properties and Right-of-Ways

Development plans including site grading and drainage plans should be developed to minimize disruption of natural drainage patterns on properties. The site shall be analyzed to determine the changes between the baseline conditions and proposed conditions for drainage area, discharge rate, and discharge volume at every point along the property line as stormwater is discharged onto an adjacent property or existing right-of-way. The baseline conditions shall be a based upon the existing conditions of the site and shall model any depression storage and / or detention storage if deemed necessary by the design professional of record for the project or City Engineer. If off-site areas discharge onto the site, the baseline conditions for these areas shall be analyzed based on the existing conditions at the time of the analysis.

The development shall be analyzed for the following storm events:

• 2-year 24-hour Design Storm

• 5-year 24-hour Design Storm

• 10-year 24-hour Design Storm

• 25-year 24-hour Design Storm

• 50-year 24-hour Design Storm

• 100-year 24-hour Design Storm

2.1.1. Discharge Rates

It is the policy of the City of Peachtree City that no increases in stormwater runoff discharge rates as reported to the nearest tenth of one cubic foot per second (0.1 cfs) shall be allowed above the baseline conditions from any point along the property line as stormwater is discharged onto an adjacent property or existing right-of-way.

2.1.2. Changes to Drainage Area

It is the policy of the City of Peachtree City that no increase in drainage area to a single discharge point greater than 10% of the total area of the predevelopment drainage area or 1 acre whichever is less for that point shall be allowed without considering the impacts to the total runoff volume. If drainage areas are substantially changed (greater than 10% or 1 acre whichever is less), then the design professional of record shall add a statement to the hydrologic and hydraulic report stating that in their professional opinion, no adverse impacts to downstream properties will occur as a result of the changes in the drainage basin areas. Where the City Engineer finds that there is a potential threat to downstream properties from proposed development activities, the City Engineer may require additional study to document the impacts on adjacent property.

For the purposes of satisfying the additional study requirements, the design professional of record shall:

• Document the increase in volume (measured in cubic feet) of stormwater runoff for each storm event as a result of basin transfer

• Identify existing downstream conditions and impacts from the proposed conditions including flow volumes and peak flow rates

• Document that the channel is capable of handling the additional volume without becoming unstable due to increased velocities and duration of flooding

In-lieu of this statement, the developer may secure a drainage easement between the developer and the downstream property owner(s) including, but not limited to, any parties that have a lien or security interest in the property to satisfy this requirement. A copy of the recorded easement must be included in the hydrologic and hydraulic report that includes language showing that the downstream property owner(s) acknowledges the increase in runoff and/or volume and holds harmless the City of Peachtree

City and its agents if the project is approved. Easements shall continue to a point downstream where the runoff would have naturally drained to in a pre-development condition or the downstream analysis point, whichever occurs first.

2.1.3. Downstream Analysis

All hydrologic analyses shall be continued to a point downstream where the site represents at least 10% of the total drainage area. The analysis shall include study points along the drainage path where the drainage path crosses the following:

• Property Lines / Rights-of-Way

• Culverts / Pipe Systems

• Detention Ponds / Ponds / Lakes

• Drainage Path Confluences of Significance

• Public Infrastructure (i.e. water, sewer, etc.)

Where a detention pond, pond, or lake is encountered, the design professional shall model the impacts of the proposed development on the detention pond, pond, or lake to determine if the development will cause an increase in the maximum water surface elevation at each storm event. If access cannot be reasonably obtained or as-built surveys of the facility are not available from the City or local government with jurisdiction, the design professional of record may add a statement to the hydrologic and hydraulic report stating that in their professional opinion, no adverse impacts including increases in maximum water surface elevations to the detention pond, pond, or lake will occur as a result of the development.

This statement shall include a description of the location of the detention pond, pond, or lake. A separate statement shall be required for each detention pond, pond, or lake not studied.

It is not the intent of this downstream analysis requirement to require the design professional of record to analyze streams or rivers with very large watersheds (greater than 2,000 acres) as part of this effort. The downstream analysis may be terminated at a point immediately upstream of a point (if the 10% requirement has not been met) where the site represents 0.5% of the total drainage area or 2,000 acres whichever is less. However, this modification shall not apply to developments that exceed 100 acres in size.

The downstream analysis shall be conducted to demonstrate that no increases in stormwater runoff rate occur downstream of the property / site for either the 25-year or 100-year storm event unless otherwise noted above. The City Engineer may require analysis of additional storm events where a downstream condition warrants further study.

Example A:

Suppose there is a 2-acre site draining into a small drainage feature (such as a swale or pipe system) that has a total drainage area of 15 acres and then discharges into a creek with a 4,000-acre drainage area. In this example, the design professional of record shall terminate the downstream analysis at the point where the total drainage area is 15-acres. Although the 10% rule has not been met since the drainage area would be 20 acres at a typical 10% analysis point, the requirement to analyze a 4,000 acre watershed would be overly burdensome to the developer and likely outside of the technical expertise of a typical site development engineer.

Example B:

Suppose there is a 2-acre site draining into a small drainage feature (such as a swale or pipe system) that has a total drainage area of 15 acres and then discharges into a creek with a 380-acre drainage area. In this example, the design professional of record shall terminate the downstream analysis at the confluence point of the small drainage area and the creek with the 380-acre drainage area and shall include the larger drainage area. At this point, the 10% rule has been satisfied without exceeding the 0.5% (400-acres) total drainage area limit for a 2-acre site or the

2,000-acre maximum drainage area.

The design professional of record is strongly encouraged to discuss the downstream analysis requirements with the City Engineer prior to beginning any design for the project to determine the specific requirements and study points / elements.

October 2016

2.1.4. Water Quality Standards

Stormwater management systems shall be designed to retain or treat the runoff from 85% of the storms that occur in an average year, and reduce average annual post-development total suspended solids loadings by 80%. Averaged from rainfall events across the state of Georgia, this equates to treating storm events of 1.2 inches or less, as well as the first 1.2 inches of runoff for all larger storm events.

The City Engineer will waive the water quality treatment requirement if 100% of the 1.0 inch runoff reduction volume (RRv) is achieved. If the entire 1.0-inch runoff reduction standard cannot be achieved, the remaining runoff from the 1.2-inch rainfall event must be treated by BMPs to remove at least 80% of the calculated average annual post-development TSS loading from the site. Infeasibility of implementing the RRv will be determined by the City Engineer by looking at groundwater table and infiltration rates.

This standard is quantified and expressed in terms of engineering design criteria through specification of the water quality volume (WQv), which is equal to the runoff generated on a site from 1.2 inches of rainfall. The WQV must be treated to the 80% TSS removal performance goal.

This standard assumes that BMPs will be designed, constructed and maintained according to the criteria in the GSMM. Stormwater discharges from land uses or activities with higher or special potential pollutant loadings may require the use of specific structural practices and pollution prevention practices. A detailed overview of BMPs is provided in Chapter 4 of the GSMM.

For further discussion on this standard, see Section 2.2.4.1 of the GSMM.

The City encourages the designer to implement specific stormwater credits for reducing the water quality treatment requirements on site. These credits can be found in Section 2.3.3 of the GSMM. However, the

City recognizes that water quality treatment of stormwater runoff from certain areas of a site is not feasible. As such, the following areas are exempt from water quality treatment.

• Impervious surfaces associated with the driveway located within the City’s existing right-of-way assuming that runoff from the driveway drains away from the site and into the right-of-way

• Portions of the site which will remain undisturbed and which does not drain to a water quality or detention facility / BMP. These undisturbed areas must contain at least 10,000 square feet of contiguous area. Additionally, these areas must not be used for any purposes during construction and must be protected from such activities by construction fencing or other means to prevent construction personnel ingress.

Additional water quality requirements will be required for hotspot land uses and activities regulated by the National Pollutant Discharge Elimination System (NPDES) Industrial General Stormwater Permit.

2.1.5. Channel Protection Standards

Channel protection shall be provided for each discharge point from the site unless meeting the exemption criteria (as determined by the City Engineer) outlined below. Channel protection shall be accomplished by providing for 24-hour extended detention of the 1-year 24-hour storm event.

Channel protection shall not be required if one of the following criteria is applicable to an outfall point on the site:

• Point discharges that do not exceed 2 cubic feet per second for the 1-year 24-hour storm in a post developed condition

• Sheet flow discharges that do not have more than 100 feet of contributing drainage area assuming that no impervious surfaces are within the contributing drainage area

• Point or sheet flow discharges from drainage areas consisting entirely of undisturbed lands on the site

• Point discharges which drain directly to a long piped drainage system and which the City has determined that the outfall of the system will not experience significant channel erosion as a result of not providing channel protection via extended detention of the 1-year 24-hour storm

• Point discharges which drain directly to streams, rivers, wetlands, lakes or other scenarios where reduction of the 1-year 24-hour storm will in the opinion of the City Engineer result in no impact to downstream channel integrity. Point discharges that drain to the buffer areas adjacent to large streams, rivers, wetlands or lakes will still require channel protection in most cases.

For additional discussion, see Section 2.2.4.2 of the GSMM.

2.1.6. Energy Dissipation

Energy dissipation shall be employed whenever the velocity of flows leaving a new stormwater facility exceeds the erosion velocity of the downstream area or 4.0 feet per second whichever is less for the 25-year storm. Energy dissipation shall be designed according to the standards in the GSMM. Evaluation of the stability of the downstream channel below the energy dissipation device/improvement must take place to see if additional downstream protection/stabilization is required due to increased flow volumes for the 25-year storm event.

2.2. Conveyance Systems Standards

2.2.1. Bridges

All new bridges shall be designed to accommodate the 100-year 24-hour design storm with the 100-year flood elevation 1-foot below the low cord of the bridge (i.e. the lowest part of the bridge deck structure or stringers whichever is lower). The 100-year flood elevation shall be the higher of the existing or future condition elevations. If such a flood elevation has not been computed, the flood elevation shall be computed with a means acceptable to produce FEMA floodplain elevations.

2.2.2. Culverts & Pipe Systems

The level of service provided by new culverts and pipe systems in the City is dependent on a number of different factors. These include the type of road that the system will service, the potential for upstream flooding, floodplain impacts and other service issues. Generally, the level of service to be provided by culverts in Peachtree City as outlined in the table below:

Roadway Classification* / Use Design Storm

Arterial/Emergency Evacuation Roadway/Community Collector

100-Year

Village Collector/Neighborhood Collector 50-Year

Local Roads/Parking Lots 25-Year

Roads with No Other Outlet 100-Year

Material Storage Areas/Landscape Areas 10-Year

*As shown on the City’s Thoroughfare Plan

The levels of service standards outlined above are considered minimum standards. Where warranted, in cases of a threat to property, structures or human safety, the level of service may be increased at the discretion of the designer or the City Engineer. Pipes shall be designed such that the hydraulic grade line

(HGL) shall remain within the pipe for the applicable design storm. For example, the HGL for a 48-inch

(4-feet) diameter pipe should not exceed 4 feet above the pipe invert. The City Engineer will allow exceptions on a case by case basis for pipes that are designed around extenuating circumstances

(generally excessive tailwater conditions, etc.).

Culverts with contributing drainage areas greater than 25 acres shall be designed to the 24-hour storm.

For example, if a culvert is to be designed to convey stormwater runoff from a 25-acre drainage basin under a neighborhood road, the design storm shall be a 25-year 24-hour storm.

The design must also take into account undeveloped offsite areas. An increase in the C-factor (or CN as applicable) for this area according to proposed land use must be added to the design as an added safety factor and the future condition 100-year design storm must be calculated based on the future land use plan for Peachtree City.

The hydraulic grade line must be calculated and shown on plans for the design storm. Additionally, a 100-year design storm shall be calculated and analyzed to determine the impact; regardless of the design storm.

If a culvert is designed to connect to an existing system of a differing design level of service, then the system with the greater design requirement will be used to size the proposed system.

If a drainage system is designed to discharge to residential property, it must be extended from the right-of-way or upstream structure to the rear of the residential lot.

The minimum pipe velocity for the 2-year storm shall be 2.5 feet per second unless otherwise approved by the City Engineer. The maximum pipe velocity for the design storm shall be 12 feet per second.

2.2.3. Inlets (Catch Basins, Yard Inlets, Drop Inlets, Hooded Grate Inlets and Flumes)

Inlets collecting stormwater runoff from street surfaces and area inlets shall be sized to capture the storm event specified for the pipe system to which it drains and a maximum flooding depth as determined by the following table:

Roadway Classification/Use Design Storm Flooding Depth

Arterial/Emergency Evacuation Roadway/Community Collector

100-Year ½ Lane Width + Gutter or 8 Feet Whichever is Less

Village Collector/Neighborhood Collector 50-Year ½ Lane Width + Gutter or 8 Feet Whichever is Less

Local Roads 25-Year ½ Lane Width + Gutter or 8 Feet Whichever is Less

Roads with No Other Outlet 100-Year ½ Lane Width + Gutter or 8 Feet Whichever is Less

Parking Lots (with a check of the 100-year storm flooding depth and maximum 1-foot depth)

25-Year Maximum 0.5 ft. Depth

Detention Areas utilized for other purposes with general public access (i.e. parking lot detention, etc.) with flood warning sign

100-Year Maximum 2.9 ft. Depth

Material Storage Areas / Landscape Areas with flood warning sign if area is utilized by the public (with a check of the 100-year storm flooding depth)

10-Year Maximum 1.5 ft. Depth

*Gutter spread measured from face of curb.

**Inlets and grading adjacent to habitable structures shall be designed to prevent stormwater runoff from entering the structure during the 100-year design storm.

2.2.4. Inlets (Headwalls, Flared End Sections, etc.)

Inlets that utilize the opening of the pipe as the inlet (i.e. headwalls, flared end sections, etc.) shall be sized to capture the storm event specified for the pipe system to which it drains. The HGL should be designed to be no less than 18 inches below the point at which water would bypass the inlet (i.e. low point of the road, bypass to another inlet, etc.). Additionally, the headwater to diameter, as determined by the height of the pipe if not round, or Hw/d ratio shall not exceed 1.2

The headwater conditions induced by the inlet should not cause an impact on any upstream drainage structures such that the upstream structure will realize a loss in performance due to elevated tailwater conditions. In simpler terms, the headwater from an inlet should not back water into another culvert or drainage system. This requirement may be waived by the City Engineer in situations where it would not be feasible to design the culverts due to proximity of the culverts or shallow grades between the culverts.

In these cases, the design professional of record shall provide a detailed analysis showing no impacs to structures or overtopping of roadways will occur due to the proposed design.

2.2.5. Roadside Ditches / Drainage Channels

Roads constructed without curb and gutter shall incorporate ditches where necessary that are designed to the specific design storms. The level of service provided by the ditches shall match the level of service provided by a comparable pipe system as outlined above. A minimum of ½ foot of freeboard shall be required for all ditches or channels. The level of service standards are considered minimum standards, where warranted the level of service may be increased at the discretion of the designer or at the request of the City of Peachtree City when a threat to property, structures or human safety is present.

Culverts traversing a roadside ditch shall be sized to the same standard as the ditch it crosses. The culvert shall be sized such that the headwater from the culvert does not cause runoff to overflow the ditch cross section and drain to other areas. All other pipe requirements for the culvert shall apply as required in this manual.

For constructed drainage channels designed to convey stormwater runoff either from or to a culvert, the channel should be sized, at a minimum, to accommodate the same storm event specified for the pipe system. Channels designed to convey stormwater runoff to detention ponds shall be sized to accommodate the 100-year design storm.

2.3. Flood Elevation Impacts

It is the policy of the City of Peachtree City that raising the elevation of flooding (regardless of whether it is in a studied FEMA floodplain or not) on an adjacent property either upstream or downstream shall not be acceptable. As such, the level of service standards outlined above shall be considered minimum standards. Where flood elevations on an adjacent property will be increased due to development and/or construction of a drainage system, the level of service may be increased by the City to result in no impact on flood elevations to the adjacent property. This requirement may be waived at the City Engineer’s discretion if the adjacent property owner provides a permanent drainage easement between the two property owners sufficient to cover the area of any increase in flood elevation to the adjacent property.

The easement shall provide that the owner of the impacted property acknowledges that an increase in flood elevations will occur on their property as a result of the proposed development, and must also include the approval of any other persons who have an interest in the property including, but not limited to, any parties that have a lien or security interest in the property. Additionally, the easement shall include at a minimum a map showing the extent of the pre-development and post-development 100-year flood elevations. The easement must be provided to the City with Hydrologic & Hydraulic Report and recorded with the deed records at the Office of the Clerk of the Superior Court of Fayette County, Georgia, as an attachment to the affected property’s land deed and shall be binding on all future property owners. Finally, any proposed increases in flood elevation that would occur within a FEMA identified floodplain will also comply with all applicable FEMA regulations for increases in flood elevation.

2.4. Minimum Finished Floor Elevation Adjacent to Stormwater Structures

The provisions of the Peachtree City Flood Damage Prevention ordinance shall apply to all developments within the City of Peachtree City. However, if a structure, as defined in the Flood Damage Prevention ordinance, is located upstream of a public or private stormwater system, the structure may be required to be elevated above the standards of the Flood Damage Prevention ordinance. Generally, the City will require the minimum finished floor elevation to be at least 1-foot above the point at which water will by-pass the system. It is the intent of this provision to ensure that structures will not be flooded by runoff if the stormwater system were to become inoperable due to damage or blockage by debris. If the City

Engineer believes or determines that the 1-foot minimum elevation will not be sufficient to protect upstream homes, the City Engineer may increase the requirement. In these cases, the City Engineer may increase this requirement to 1-foot above the 100-year flood elevation during the 100-year 24-hour future conditions design storm event assuming that the applicable stormwater system is inoperable.

For example, suppose several residential homes are to be constructed adjacent to a drainage channel.

Immediately downstream of the homes is a road crossing with a low roadway…