IM_Manual.pdf

In associa�on with

STORMWATER

SYSTEM

INSPECTION

AND

MAINTENANCE

MANUAL

March 2023

This manual complies with NPDES Stormwater (MS4) Permit

Number GAR041000

Current Permit: January 3, 2022-January 2, 2027

Original Permit: January 3, 2012 -January 2, 2017

Stormwater System Inspec�on and

Maintenance Manual

Prepared for:

Georgia Department of Transporta�on

Prepared by:

Arcadis U.S., Inc.

2839 Paces Ferry Road

#900

Atlanta

Georgia 30339

Tel 770 431 8666

Fax 770 435 2666

Our Ref.:

30106171

Date:

March 2023

This document is intended only for the use of the individual or en�ty for which it was prepared and may contain informa�on that is privileged, confiden�al and exempt from disclosure under applicable law. Any dissemina�on, distribu�on or copying of this document is strictly prohibited.

GDOT ● Inspec�on and Maintenance Manual i

Table of Contents

Version Control Revision No

Date Issued Location Description

1 March 2020 Section 2 Updated to four-tier condition assessment rating for post-construction BMPs.

Section 3 Added GDOT Policy 61612-1 Roadway Inspection Form instructions to Existing Maintenance Practices.

Section 4 Updated text to be consistent with the drainage inventory database terminology.

Section 5 Updated route inspection requirements and compliance inspection requirements. Added a discussion on special designs or alternative BMPs not in the manual.

Section 5 Revised filter strips and grassed channels to be inspected through Day Inspection policy.

Section 5-10 Removed OGFC inspection and maintenance information and replaced with text referencing the GDOT’s pavement management system.

Section 6-3 Deleted previous “Program Development” section. Revised description of schedule to reference and match permit requirements.

Appendix B Revised post-construction BMP inspection checklists to include note fields for major components.

2 March 2023 Whole Document

Updated the document to reflect the 2022 Permit and made slight modifications to follow the current process/standards.

GDOT ● Inspec�on and Maintenance Manual i

Version Control i

1 Introduction 1-1

1.1 Purpose 1-1

1.2 Use of this I&M Manual 1-1

2 GDOT Maintenance Policy 2-1

2.1 Extent of Service 2-1

2.2 Level of Service 2-1

3 GDOT Maintenance Practices 3-1

3.1 Exis�ng Maintenance Prac�ces 3-1

3.2 Inspec�on and Maintenance Performed By Contractors 3-4

3.3 Inspec�on and Maintenance Performed by Others 3-5

4 Drainage Structures 4-1

4.1 Pipe Systems 4-3

4.1.1 Descrip�on and Func�on of Structure 4-3

4.1.2 Inspec�on and Maintenance 4-3

4.2 Ditches, Channels, and Swales 4-5

4.2.1 Descrip�on and Func�on of Structure 4-5

4.2.2 Inspec�on and Maintenance 4-5

4.3 Manholes, Junc�on Boxes, Catch Basins, Inlets, and Outlets 4-7

4.3.1 Descrip�on and Func�on of Structure 4-7

4.3.2 Inspec�on and Maintenance 4-7

5 Post-Construction Stormwater Best Management Practices 5-1

5.1 Filter Strips 5-5

5.1.1 Descrip�on and Func�on of Structure 5-5

5.1.2 Inspec�on and Maintenance 5-6

5.2 Grass Channel 5-8

GDOT ● Inspec�on and Maintenance Manual ii

5.2.1 Descrip�on and Func�on of Structure 5-8

5.2.2 Inspec�on and Maintenance 5-9

5.3 Enhanced Swales 5-10

5.3.1 Descrip�on and Func�on of Structure 5-10

5.3.2 Inspec�on and Maintenance 5-12

5.4 Infiltra�on Trench 5-22

5.4.1 Descrip�on and Func�on of Structure 5-22

5.4.2 Inspec�on and Maintenance 5-23

5.5 Sand Filters 5-30

5.5.1 Descrip�on and Func�on of Structure 5-30

5.5.2 Inspec�on and Maintenance 5-32

5.6 Dry Deten�on Basins 5-42

5.6.1 Descrip�on and Func�on of Structure 5-42

5.6.2 Inspec�on and Maintenance 5-44

5.7 Wet Deten�on Ponds 5-54

5.7.1 Descrip�on and Func�on of Structure 5-54

5.7.2 Inspec�on and Maintenance 5-56

5.8 Stormwater Wetlands 5-64

5.8.1 Descrip�on and Func�on of Structure 5-64

5.8.2 Inspec�on and Maintenance 5-65

5.9 Bioslopes 5-74

5.9.1 Descrip�on and Func�on of Structure 5-74

5.9.2 Inspec�on and Maintenance 5-75

5.10 Bioreten�on Basins 5-83

5.10.1 Descrip�on and Func�on of Structure 5-83

GDOT ● Inspec�on and Maintenance Manual iii

5.10.2 Inspec�on and Maintenance 5-84

5.11 Open-Graded Fric�on Course 5-93

5.11.1 Descrip�on and Func�on of Structure 5-93

5.11.2 Inspec�on and Maintenance 5-94

5.12 Other Components 5-96

5.12.1 Inspec�on and Maintenance 5-96

6 Implementation 6-1

6.1 Key Staff, Roles, and Responsibili�es 6-1

6.2 Training 6-2

6.3 Compliance Inspec�on Schedule 6-2

7 Recordkeeping and Reporting 7-1

7.1 Recordkeeping 7-1

7.2 Repor�ng 7-1

Figures

4.1-1 Pipe Conveyance Blocked with Sediment 4-4

4.1-2 Pipe Separa�on 4-4

4.1-3 Pipe Conveyance with Trash 4-4

4.1-4 Severe Erosion and Collapse 4-4

4.2-1 Cracks and Joint Separa�on in Concrete Channel 4-6

4.3-1 Missing Proper Cover 4-7

4.3-2 Debris Accumula�on 4-7

4.3-3 Grate Blockage 4-8

4.3-4 Sediment/Debris Buildup 4-8

GDOT ● Inspec�on and Maintenance Manual iv

5.1-1 Channel between Filter Strip (top le�), Filter Strip around Drop Outlet (top right), Concrete Level Spreader and Filter Strip (bo�om le�), and Concrete Level Spreader under Construc�on (bo�om right) 5-5

5.1-2 Typical Filter Strip Configura�on and Components 5-6

5.2-1 Two Examples of a Roadside Grass Channel 5-8

5.2-2 Typical Grass Channel Configura�on and Components 5-9

5.3-1 Examples of a Dry (le�) and a Wet Swale (right) 5-11

5.3-2 Typical Enhanced Dry Swale Configura�on and Components 5-11

5.3-3 Typical Enhanced Wet Swale Configura�on and Components 5-12

5.4-1 Typical Infiltra�on Trench Configura�on and Components 5-22

5.5-1 Surface Sand Filter (le�) and Perimeter Sand Filter (right) 5-30

5.5-2 Typical Surface Sand Filter Configura�on and Components 5-31

5.5-3 Typical Perimeter Sand Filter Configura�on and Components 5-31

5.6-1 Dry Deten�on Basin with Low-Flow Channel (le�) and Dry Deten�on Basin with Landscaping (right) 5-42

5.6-2 Typical Dry Deten�on Basin Configura�on and Components 5-43

5.7-1 Wet Deten�on Pond as Part of a Conveyance Channel (le�) and a Wet Deten�on Pond at a DOT Maintenance Facility (right) 5-54

5.7-2 Typical Wet Deten�on Pond Configura�on and Components 5-55

5.8-1 Shallow Stormwater Wetland (le�) and Pocket Stormwater Wetland (right) 5-64

5.8-2 Typical Components and Configura�on for a Stormwater Wetland 5-65

5.9-1 Bioslope with Gravel Diaphragm 5-74

5.9-2 Typical Bioslope Configura�on and Components 5-75

5.10-1 Landscaped Bioreten�on Basin (le�) and Newly Planted Bioreten�on Basin a�er Storm Event (right) 5-83

5.10-2 Typical Bioreten�on Basin Configura�on and Components 5-84

5.11-1 OGFC (le�) and Conven�onal Asphalt (right) Cross Sec�ons 5-93

GDOT ● Inspec�on and Maintenance Manual v

5.11-2 OGFC with a Filter Strip for Added Stormwater Treatment 5-94

6.1-1 Key GDOT Staff for I&M Manual Implementa�on 6-1

Tables

Table 1 Drainage Structure Inventory and Inspec�on Database

Table 2 Maintenance Ac�vi�es and Frequency for Common Post-Construc�on BMPs

Appendices

A Drainage Structure Inspec�on Checklist

B Post-Construc�on Stormwater BMP Inspec�on Checklists

C MS4 Structure Inventory and Inspec�on Summary, Es�mated MS4 Structures Maintenance Summary, and Summary of Post-Construc�on Stormwater BMPs Inspec�ons

GDOT ● Inspec�on and Maintenance Manual ● Introduc�on 1-1

1 Introduc�on

1.1 Purpose

This Stormwater System Inspection and Maintenance Manual (I&M Manual) provides a basis for the inspection and maintenance of the Georgia Department of Transportation (GDOT) stormwater system, particularly those structures and conveyances associated with the Municipal Separate Storm Sewer System (MS4). This I&M Manual complies with the requirements of the General National Pollutant Discharge Elimination System (NPDES) Stormwater MS4 Permit No.

GAR041000 (MS4 Permit) requiring GDOT to develop and implement programs to prevent or reduce stormwater pollution from its facilities and to perform routine maintenance activities within the permit area.

This I&M Manual presents a program for the long-term inspection and routine maintenance of the drainage system (collection and conveyance) and post-construction stormwater best management practices (BMPs) designed for filtering and/or detention (e.g., detention ponds, wetlands, enhanced dry swales, bioretention basins, and filter strips, among others). It includes recommended inspection frequencies, checklists, and procedures for maintaining the drainage system and post-construction BMPs that are subject to the MS4 Permit. Post-construction stormwater BMPs are referred to as "post construction structures" in the MS4 Permit and they are permanent BMPs, as opposed to temporary BMPs used for erosion and sedimentation control on construction sites.

BMPs included in this manual are limited to those that are presently approved for construction by GDOT. The drainage structures that make up the stormwater collection and conveyance system are referred to as “MS4 structures” in the MS4 Permit.

This I&M Manual defines a level and extent of service for the inspection and maintenance of drainage structures within GDOT rights-of-way inside its MS4 designated areas. The program, where possible and with enhancements focused on water quality aspects, incorporates and tailors established GDOT inspection and maintenance policies and practices as mechanisms to achieve the ultimate goals of properly maintaining stormwater BMPs to meet permit requirements.

1.2 Use of this I&M Manual

The guidelines included in this I&M Manual define a standard of practice that is complementary to other standards of practice adopted and implemented by GDOT including the Manual for Erosion and Sediment Control in Georgia, which supports construction activity, and the GDOT Manual on Drainage Design for Highways. This manual may also be used as guidance for the maintenance of drainage structures and water quality structures not subject to MS4 permit requirements.

GDOT ● Inspec�on and Maintenance Manual ● Introduc�on 1-2

The objectives of the standards of practice defined in this I&M Manual are to:

• Define inspection and maintenance practices that meet the requirements of the MS4 Permit.

• Define the practices needed to keep stormwater management facilities and their components functioning in accordance with their respective design objectives.

The need to update this I&M Manual will be evaluated periodically and subsequent updates will be undertaken, as needed. Any revisions will be submitted to the Georgia Environmental Protection Division (EPD). The MS4 Permit requires GDOT to verify that procedures documented in this I&M Manual are properly implemented. GDOT will review implementation of the I&M Manual by evaluating the corrective actions identified during compliance inspections and tracking whether the corrective actions have been completed.

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Policy 2-1

2 GDOT Maintenance Policy

The Stormwater I&M Manual is part of GDOT’s program to perform routine inspections and maintenance of drainage structures and post-construction stormwater BMPs in accordance with GDOT’s MS4 permit requirements. The plan of operation, inspection, and maintenance presented in this manual is based on balancing MS4 Permit compliance, safety of the traveling public, legal obligations, and use of established GDOT maintenance policies and procedures. The plan of operation may change as warranted by modifications to one or more of these factors.

2.1 Extent of Service

For the purposes of GDOT’s MS4 program, GDOT’s extent of service for its stormwater system falls into two broad categories:

1. Category 1. Within GDOT properties and rights-of-way that are owned and operated by GDOT.

2. Category 2. Outside GDOT owned properties and rights-of-way but within GDOT permanent easements legally accepted by GDOT.

2.2 Level of Service

The policies for maintenance of GDOT’s stormwater management system, of which this manual is a part, are based on safety of the public and its employees, flood hazard reduction, environmental protection, asset management goals, regulatory compliance, and fiscal responsibility, among others. The manual defines the frequency and types of inspections and maintenance actions desired to maintain the stormwater conveyance system and asset operation at an acceptable level. GDOT determines drainage structure and BMP condition through field data collection as described in this manual and uses the condition assessment to evaluate if maintenance is required. For drainage structures, condition ratings meeting the criteria highlighted in yellow in Table 1 (located in the Tables section of this manual) are identified as needing work. Drainage structures whose conditions meet these criteria are further prioritized for maintenance by each field district.

For the post-construction stormwater BMPs, each inspection item is assigned a condition rating using a four-tier system:

• Level 1, Green. Good condition. No corrective action required.

• Level 2, Yellow. Good to fair condition. Monitor periodically for potential maintenance or repair needs. (see corrective action for further details).

• Level 3, Orange. Fair condition. Still functional, but needing non-critical repairs (see corrective action for further details).

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Policy 2-2

• Level 4, Red. Poor condition. Needing maintenance, repair, and/or replacement (see corrective action for further details).

Post-construction BMP components whose conditions meet Level 3 and Level 4 are further prioritized for maintenance by each field district.

Inspection procedures and checklists for MS4 structure and post-construction stormwater BMPs and other related information are provided in the following sections and appendices to this I&M Manual:

• Section 4 – Drainage Structures

• Section 5 – Post-Construction Stormwater Best Management Practices

• Appendix A – Drainage Structure Inspection Checklists

• Appendix B – Post-Construction Stormwater BMPs Inspection Checklists

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Prac�ces 3-1

3 GDOT Maintenance Prac�ces

GDOT has a multi-tiered approach to perform both routine and as-needed inspection, maintenance, and corrective actions for drainage structures and post-construction stormwater BMPs. The combination of internal GDOT policies and procedures, implementation of comprehensive maintenance contracts (CMCs), other maintenance services contracts with external contractors, and agreements with local municipalities allow GDOT to provide necessary coverage to achieve permit compliance. Historically, inspections have been centered on stormwater conveyance and condition assessment; however, this I&M Manual focuses on water quality issues, with parallel implementation of the GDOT Facilities Stormwater Pollution Prevention Plan (F-SWPPP) and Illicit Discharge Detection and Elimination Plan (IDDE Plan).

3.1 Exis�ng Maintenance Prac�ces

GDOT maintains a system of practices that address the inspection and maintenance of drainage structures within various operations. The procedures described in this I&M Manual are an integral part of this system, which includes guidelines from the following documents:

• Manual on Drainage Design for Highways. This manual provides an overview of drainage guidelines and references to appropriate design procedures to address environmental issues and other site-specific concerns. GDOT recently expanded this manual to include design guidance for post-construction stormwater BMPs.

• GDOT Policy 61612-1 Roadway Inspection Form Instructions. The policy provides instructions for completing a roadway inspection report and states that the Maintenance Area Manager is responsible for the condition of the entire roadway and roadside, including pavement system, drainage, shoulders, vegetation, guardrail, signs, pavement markings, and bridges. The roadway inspection form is an exception report where only items that are deficient or need correction are reported.

• Post-Construction BMP Maintenance and Construction Inspection Checklists. These checklists will be used to document the condition of newly constructed BMPs during final inspection. The Environmental Compliance Specialist (ECS) uses the construction and maintenance inspection forms to evaluate the BMP after construction is complete and to document acceptance of maintenance responsibility.

• Drainage Inspection Manual for Minor Drainage Structures. Apart from general guidelines for the drainage inspection of minor drainage structures, this manual summarizes the material handling and storage procedures for use during storm sewer system repair. The manual presents a program to be used for inspection of drainage structures, including MS4 classified structures. These inspections, scheduled from December 1 to March 31, are conducted by routine maintenance personnel, but the Assistant Area Manager of Maintenance is responsible for confirming that these

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Prac�ces 3-2 inspections and maintenance are performed correctly. Other non-routine inspections are performed and instances of repair, modification by construction, or abandonment are documented. The inspection procedures follow the GDOT Drainage Inspection Manual for Minor Drainage Structures.

Inspection criteria of the Drainage Inspection Manual for Minor Drainage Structures are as follows:

• Purpose of the inspection

• Inlet/outlet conditions

• Inlet/outlet ditch conditions

• Siltation, debris, pollutants.

The Biennial Drainage Structure Inspection Form includes:

• Structure location

• Stream type

• Pipe information

• Inlet and outlet headwall, apron, and end section details

• Structural conditions

• Corrective actions required for cleaning, repair, or replacement.

Acquired data from these inspections are entered into the Biennial Drainage Inspection Module of the Georgia Asset Management System (GAMS) or a similarly capable database that tracks the overall operational and structural conditions for drainage structures and corrective actions. Activity codes are used to describe and track certain maintenance activities. The following activity codes are MS4 relevant maintenance activities:

Activity 400: Manual Clean Drain Structure. This activity involves cleaning pipes, culverts, catch basins, drop inlets, and paved flumes by manually removing accumulated dirt and debris. A Special Performance Condition requires that structures be inspected routinely for cleaning based on the condition of the structure.

Activity 405: Mechanical Clean Drain Structure. This activity involves mechanical cleaning of pipes, structures, and retention/detention facilities, including follow-up reporting if a structure requires additional corrective actions.

Activity 410: Clean/Restore Ditches. This activity includes cleaning, reshaping, and re-establishment of vegetation of roadside and outfall ditches, and restoring the grade line if necessary to maintain adequate drainage. Special Performance Conditions require work as soon as practical in ditches where silt has accumulated or where obstructed or blocked drainage is evident.

Activity 415: Pipe Install/Repair. This activity includes repairs or new installations of items such as pipe, headwalls, wing-walls, and aprons to maintain adequate drainage.

Repairs may also be performed by internal lining or grouting.

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Prac�ces 3-3

Activity 420: Build/Repair Concrete Structure. This activity involves repairs or construction of catch basins, drop inlets, ditch paving, curb and gutter, and septic tanks, among other items.

Activity 540: Litter Patrol. This activity includes removal of unwanted and/or unauthorized objects from roadways and rights-of-way such as tire fragments, dead animals, and collected litter. Visual inspections of post-construction BMPs are performed during this activity.

Activity 545: Litter Pick-up/Full. This activity includes full-width cleaning of continuous sections of the right-of-way to remove unsightly objects and obstructions to drainage. Special Performance Conditions require scheduling throughout the year as required, especially prior to mowing.

Activity 550: Erosion Control. This activity includes the placement, maintenance, and removal of erosion control devices due to the performance of maintenance activities, which results in disturbance of erodible earth areas. This activity also includes all grassing and reseeding operations to maintain desirable vegetation cover.

Activity 821: Culvert Repair. Description includes patching and/or repairing a culvert or any of its associated structures such as head walls, wing wall, and aprons etc.

Special

Activity 822: Culvert Extension. This activity includes extending a culvert or any of its associated structures such as head walls, wing wall, and aprons etc.

Activity 900: Scheduled Inspections. Description includes performing annual Pavement Condition Evaluations, Day and Night Roadway Inspections, Drainage Inspections, and other assigned roadway inspections. Recommended procedures specify that inspections should be performed based on the most current GDOT policies, within the specified time frames.

GDOT will continue to perform preventive maintenance measures to reduce sources of sediment and debris from entering stormwater systems. These preventive maintenance measures may include highway sweeping efforts (both by GDOT and contracted) to remove dirt, grit, and sediment from the roadways and drainage system. GDOT will also continue trash and litter pick-up, with internal schedules for maintenance crews, and as part of right-of-way mowing contracts, CMCs, and other maintenance service contracts.

GDOT’s GAMS includes a summary which accounts for actual work quantities for a given period.

• General Facility Environmental Guidelines. These guidelines present procedures for material handling and storage for various activities conducted by GDOT. The guidelines are focused on GDOT operations, maintenance, storage, administrative, and public use facilities, each of which has some type of stormwater system.

Typically, facilities are inspected twice annually for safety, general housekeeping, GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Prac�ces 3-4 and facility handling of potential pollutants (e.g., fuels, oils, coolants, herbicides/pesticides, chemicals, used batteries, scrap tires, wash water, waste disposal). A Maintenance Facility Checklist, which is included in this document, identifies conditions found and provides guidance for any needed corrective actions.

With the parallel development and implementation of the GDOT Facilities SWPPP, each of these facilities within designated MS4 areas will undergo scheduled, site-specific MS4 inspections.

• Integrated Roadside Vegetation Management Herbicides Standards Manual. This manual summarizes the procedures for herbicide handling and storage.

• Environmental Compliance, Requirements for GDOT Maintenance Activities and Operations. This document presents requirements for GDOT maintenance activities and operations and outlines permit notifications that may be required by EPD and/or U.S. Army Corps of Engineers (USACE) for potential maintenance work. The tasks identified in the document include mechanical cleaning of drainage structures, ditch cleaning and restoration, storm drain pipe installation and repair, and culvert repair.

According to this document, none of these tasks require a Notice of Intent with EPD or a Preconstruction Notification with USACE (unless work will be performed in live streams).

• Drainage Maintenance Manual. GDOT’s maintenance personnel use this manual to identify drainage deficiencies and determine the best procedures for correcting them.

Drainage facilities included in the manual are pipe and box culverts, storm sewers, drop inlets and catch basins, high shoulders, low shoulders/edge ruts, ditches, slope drains, flumes, and curbs and gutters.

• Integrated Roadside Vegetation Management (IRVM) Straight Line Mowing Standards Manual. This manual establishes uniform mowing procedures throughout the state.

3.2 Inspec�on and Maintenance Performed By

Contractors

GDOT external specialty maintenance contracts will provide several services, including annual cleaning of identified storm drain structures. Whether included as an aspect of a district or statewide sweeping and (identified in Section 3.1 as a preventive measure) storm drain cleaning services contract or an interstate corridor-specific CMC, storm drainage structures will receive GDOT’s attention via these contracts.

Contracts to provide highway sweeping services also include provisions for cleaning storm drainage structures and pipes. The scope of storm drainage structure cleaning involves removal, as feasible, of covering grates for items such as median barrier wall box inlets, drop inlets, catch

GDOT ● Inspec�on and Maintenance Manual ● GDOT Maintenance Prac�ces 3-5 basins, gutter drains, ramp drains, and bridge end drainage inlets, and vacuum removal of debris from the throat and chamber areas of the structures and from 15 feet in each direction of the connecting piping. The location, e.g. global positioning system (GPS) coordinates, GDOT district, route designation, and nearest milepost are collected, as feasible and based on the contract terms, for each structure, as well as any notation of corrective action recommended. In addition, through highway sweeping, right-of-way mowing, or other contracts, litter and other debris encountered during these activities is removed, quantified, and disposed.

Other similar external contracts encompass a broader array of highway and right-of-way maintenance activities (e.g., inspecting drainage structures [biennially (or every other year)] and addressing inlet/outlet overgrowth of vegetation or erosion, damages due to siltation, cracking, joint failures, blockages).

Language requiring contractors to provide GDOT with maintenance records consistent with the drainage structure and post-construction stormwater BMP database will be included in all new maintenance contracts. District ECS and District Maintenance Contracts Managers should be aware of the reporting requirement for each maintenance contract.

3.3 Inspec�on and Maintenance Performed by

Others

GDOT will continue to enter into various contracts for maintenance of highways and memorandums of agreement with cities, counties, and other stakeholders in MS4 designated areas to perform new construction as well as maintenance of existing facilities under the terms of the agreements. These agreements will allow GDOT the necessary oversight to manage potential problems, conduct timely inspections, and perform corrective actions promptly and effectively.

Details of these efforts as they relate to drainage structures may be tracked using GAMS.

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-1

4 Drainage Structures

GDOT has installed, operated, and maintained stormwater drainage structures to provide safe and effective drainage along its highways. These same systems may also transport roadway pollutants as water flows from impervious areas and erodes less stable surfaces. These pollutants may discharge to streams, rivers, lakes, marshes, and other water bodies. GDOT has measures in place to lessen pollutant loads. These measures include increasing efforts to reduce and pick up roadside litter, performing highway sweeping operations, cleaning catch basins and inlets and enhancing stormwater system inspection programs.

Drainage structures are defined as collection and conveyance system components comprising pipes, ditches, channels, swales, manholes, junction boxes, catch basins, drop inlets, and other structures designed to manage and safely direct storm runoff from roadways and GDOT facilities.

Indicators of drainage structure problems include structural damage, erosion, corrosion, and blockages from animals, debris, siltation, and vegetation. Structural condition and the ability of drainage structures to allow water to flow through them relates directly to water quality. Failure or damage of these structures could lead to the release of sediment, debris, and potential pollutants to receiving waters.

The inspection and maintenance of drainage structures, as presented in this manual, extends the purpose of GDOT’s current inspection and maintenance policy and procedures to reduce the potential of adversely affecting water quality. Drainage structures do not include bridge structures or roadway culverts1 as defined by federal code and GDOT. The inspection and maintenance of these structures is not discussed in this manual.

Routine inspection and maintenance of drainage structures must be conducted so that the structures function as designed structurally and hydraulically, and to prevent the potential discharge of pollutants to receiving waters. Two types of inspections are performed on drainage structures: day inspections and compliance inspections.

Day Inspections

Drainage structures are scheduled to be inspected at least annually during day inspections according to GDOT Policy 6162-1 Roadway Inspection Form Instructions. The Roadway Inspection Report form will be an exception report. Only items that are deficient or need correction are reported. Deficiencies will include those items normally performed by the Routine Maintenance Crews and those items performed by others. It will be the responsibility of the Maintenance Area Manager to ensure that deficiencies are corrected. Completion of Roadway Inspection Reports are recorded in GAMS using Activity 900 Schedule Inspections with work description of Day/Night Time Inspections.

1If the clear span is more than 20 feet (Drainage Inspec�on Manual for Minor Drainage Structures).

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-2

Inspection may also include observation and corrective action of potential illicit discharges, as defined in the IDDE Plan. Completion of work is recorded in GAMS using applicable activity codes.

Compliance Inspections

The frequency of compliance inspections is identified in the MS4 Permit and a summary of inspections is required for the MS4 annual report. Compliance inspections are stored in GDOT’s MS4 drainage inventory database and are performed using detailed Drainage Structure Inspection Checklists provided in Appendix A. Although the checklists included in Appendix A provide the basics of the inspection criteria and may be manually used, an electronic process is the primary method for recording inspection data. Table 1, located in the Tables section of this manual, offers an abbreviated exhibit of the detailed attributes collected.

The State Maintenance Office identifies drainage structures for maintenance based on the condition assessment results from compliance inspections. Each district prioritizes the identified structures for maintenance, schedules, and completes the work. Districts send their prioritization and schedule to the Office of Design Policy and Support. The maintenance is performed following the maintenance approach and guidelines established in the Drainage Maintenance Manual and other existing maintenance practices. Completion of work is recorded in GDOT’s MS4 drainage inventory database and in GAMS using applicable activity codes. Work completed is summarized in the MS4 annual report.

The remainder of this section presents structure specific inspection and maintenance procedures and protocols, incorporating relevant inspection protocols from the Drainage Inspection Manual for Minor Drainage Structures.

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-3

4.1 Pipe Systems

4.1.1 Descrip�on and Func�on of Structure

Pipe systems are linear systems designed to collect, convey, and direct roadway runoff safely and effectively away from the roadway surface. These component structures are typically part of an interdependent conveyance system. The impairment of one pipe segment can compromise the functionality of the larger system.

Pipe structures are constructed from a variety of materials in accordance with GDOT specifications. The most common pipe structures include concrete and corrugated metal conduits that are designed or constructed primarily for subsurface stormwater runoff conveyance.

4.1.2 Inspec�on and Maintenance

Pipe systems are subject to functional impairment by a variety of conditions, including:

• Blockage or obstruction due to vegetation, debris, sediment or other objects

• Cracks and/or joint separation

• Collapsed pipe

• Corrosion

• Root intrusion

• Bent or chipped pipe ends

• Leakage

• Liner damage

• Lack of stabilization

• Moderate erosion

• Severe erosion

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-4

Figures 4.1-1, 4.1-2, 4.1-3, and 4.1-4 depict some of these conditions.

Figure 4.1-1 Pipe Conveyance Blocked with

Sediment

Figure 4.1-2 Pipe Separa�on

Figure 4.1-3 Pipe Conveyance with Trash

Figure 4.1-4 Severe Erosion and Collapse

The inspector observes and notes any of the following conditions on the checklist provided in Appendix A Form A-1 to determine appropriate actions to remedy functional impairments:

• Surface over the pipe system for settlement or lost cover.

• Scouring or undermining, including evidence of animal burrows.

• Blockage due to excessive vegetation, particularly trees or other woody vegetation.

• Blockage due to the deposition of sediment and other debris. The inspector should estimate the severity of the sediment or siltation by estimating the depth of the deposits relative to the diameter of the pipe and recording the information on the inspection form. Water, sediment, and other debris in the structure often prevent a

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-5 proper inspection of the structure. In these cases, every effort should be made to clear the structure so that an inspection can be performed.

• Pipe deformation or collapse. Pipes that have taken on a non-circular shape indicate a structural deficiency that could cause the structures to collapse and/or reduce the flow capacity of the system.

• Corrosion of metal pipes. Corrosion of the pipe reduces structural integrity and may create conditions for undermining and erosion. If the invert is rusted out and deformation is present, the pipe is in danger of collapse.

In some cases, due to the size, length, and/or condition of the structure, the inspector may not be able to perform the inspection. For these cases, blockage, erosion type, or defect attributes are noted as unknown. Districts should view these structures in the field to determine the type of maintenance corrective action required.

The inspector records the inspection, performance condition assessment, and recommend action on Form A-1 (Appendix A).

4.2 Ditches, Channels, and Swales

4.2.1 Descrip�on and Func�on of Structure

Ditches, channels, and swales are open, linear systems designed to safely and effectively collect, convey, and direct roadway runoff away from the roadway surface. These structures are typically part of a larger conveyance system with many interconnected components where the impairment of one component can compromise the functionality of the larger system.

These structures may be armored (e.g. concrete lined) but also include natural or grass channels.

Enhanced vegetated swales and channels designed for filtering and/or detention to provide water quality treatment are designated as post-construction stormwater BMPs.

4.2.2 Inspec�on and Maintenance

Ditch, channel, and swale systems are subject to functional impairment by a variety of conditions, including:

• Concrete liner cracks, including damage from equipment or motor vehicles,

• Joint separation, or blowout

• Obstruction due to debris, sediment, animal activity, excessive vegetation, or other objects

• Lack of stabilization due to undermining or scouring of soils beneath channel linings causing structural failures of the concrete

• Root intrusion

• Out of bank flow (surcharged flow)

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-6

• Lack of vegetative cover for grass-lined channels

• Moderate erosion

• Severe erosion

Figure 4.2-1 shows cracks and joint separation in the concrete channel. Note: removal of the vegetation may prevent further joint separation.

Figure 4.2-1 Cracks and Joint Separa�on in Concrete Channel

The inspector observes and notes any of the following conditions using Form A-2 in Appendix A to determine appropriate actions to remedy functional impairments.

Ditches, swales, and drainage channels should be maintained to the line, grade, depth, and cross section to which they were constructed or subsequently improved. Settlement should be corrected and repairs of broken or eroded surfaces should be made with appropriate materials.

Ditches, swales, and drainage channels should be kept reasonably clear of obstructing materials and kept clean of debris and trash that may impede the normal flow of water. These include gutters or curbs used along the side of a roadway surface to collect and control the flow of water and direct it to an inlet or outlet ditch, catch basin, or shoulder drain leading the water into a nearby stream or other natural watercourse.

The inspector records the ditch, swale, and drainage channel inspection, performance condition assessment, and recommended action on Form A-2 (Appendix A).

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-7

4.3 Manholes, Junc�on Boxes, Catch Basins, Inlets, and

Outlets

4.3.1 Descrip�on and Func�on of Structure

Manholes, junction boxes, catch basins, inlets and outlets are junction and connection points for the linear system described in Section 4.2 and are designed to safely and effectively collect, convey, and direct roadway runoff away from the roadway surface. These structures are typically part of a larger conveyance system with many interconnected components where the impairment of one component can compromise the functionality of the larger system.

These structures are constructed conveyances made from a variety of materials in accordance with GDOT specifications.

4.3.2 Inspec�on and Maintenance

These structures are subject to functional impairment by a variety of conditions, including:

• Structural damage including from motor vehicles

• Cracks/joint separation at inlet and outlet connections

• Leaking due to cracks and joint separation

• Top covers broken or missing

• Corrosion

• Blockage in structure due to debris, sediment, vegetation, or other objects

• Moderate erosion

• Severe erosion

Some of these conditions are shown on Figures 4.3-1 through 4.3-4.

Figure 4.3-1 Missing Proper Cover

Figure 4.3-2 Debris Accumula�on

GDOT ● Inspec�on and Maintenance Manual ● Drainage Structures 4-8

Figure 4.3-3 Grate Blockage

Figure 4.3-4 Sediment/Debris Buildup

The inspector observes and notes any of the following conditions using Form A-3 in Appendix A to determine appropriate actions to remedy functional impairments.

Like other drainage structures, manholes, junction boxes, catch basins, inlets and outlets are subject to structural degradation, blockage, and sediment and debris accumulation. They must be routinely inspected and maintained to continually function as designed structurally and hydraulically and to prevent the potential discharge of pollutants to receiving waters.

These structures are typically found at GDOT facilities and along the highway right-of-way, and therefore have the potential to collect and accumulate sediment, debris, and trash.

Catch basins designed with a sump at the base act to trap sediment and debris. It is important to remove and properly dispose of the accumulated material in the sump so that it can continue to function as designed and reduce the amount of sediment, trash, and other debris that enters the storm drain and is transported to surface waters.

The routine removal of trash and other debris from inlet and outlets structures reduces the potential for clogging during storm events and reduces the amount of sediment and debris released to receiving waters.

The inspector records the inspection, performance condition assessment, and recommended action on Form A-3 (Appendix A).

GDOT ● Inspec�on and Maintenance Manual ● Post-Construc�on Stormwater Best Management Prac�ces 5-1

5 Post-Construc�on Stormwater Best Management Prac�ces

Table 4.2.5 of GDOT’s Permit GAR041000, defines post-construction stormwater structures as those “designed for filtering and/or detention.” These structures/controls are engineered to filter, infiltrate, detain, and/or retain stormwater flows to allow the removal of pollutants prior to discharge into waterways. Post-construction structures, also referred to as post-construction stormwater BMPs or permanent BMPs, are designed to stay in place and treat runoff from impervious surfaces. These are different from temporary erosion and sediment control practices used during construction (e.g., silt fences, sediment basins). Unlike many temporary BMPs used for sediment control during construction, most of the post-construction stormwater BMPs included in this manual rely on healthy vegetation to maximize pollutant removal effectiveness. During design, vegetation is specifically selected for each BMP to provide:

• Filtration of sediments and attached pollutants

• Infiltration and evapotranspiration of runoff

• Protection of soil from erosion

Most BMPs need to maintain a healthy stand of vegetation to achieve their water quality objectives.

Post-construction stormwater BMPs are an important part of GDOT’s stormwater infrastructure and need to be identified, inventoried, maintained, and inspected. Once identified, they are inventoried and recorded in GDOTs post-construction stormwater database. Only those structures in the database are subject to the MS4 Permit requirements and this I&M Manual unless the department includes others constructed for purposes other than MS4 compliance.

Maintenance

Regular maintenance of post-construction stormwater BMPs keeps them functioning as designed and reduces the need for costly major repairs. Table 2, located in the Tables section of this manual, defines regular maintenance activities and activity frequencies for common post-construction stormwater BMP types.

Maintenance personnel may encounter situations where a BMP has become significantly overgrown, damaged, or require significant repairs. For situations requiring construction type activities or significant clearing, Office of Environmental Services (OEnvS) should be contacted to ensure that no environmental permitting will be required prior to beginning work activities. This guidance should be especially followed in cases where streams, lakes, wetlands, or stream buffers may be disturbed. A special email address that is regularly monitored for questions specific to environmental concerns has been created to ensure guidance is provided where appropriate. Email guidance requests to Ecology_Submittals@dot.ga.gov.

GDOT ● Inspec�on and Maintenance Manual ● Post-Construc�on Stormwater Best Management Prac�ces 5-2

Occasionally, maintenance personnel may encounter environmentally sensitive areas that require modifying the typical maintenance approach. ESAs are specifically designated areas that denote special conditions regarding environmental or cultural resources subject to protection by the state. These areas are indicated by ESA signage. Examples of protected resources can include but are not limited to:

• Threatened or endangered plant species

• Cultural or historical areas

• Stream buffers or wetlands

Encountering an ESA does not prevent maintenance on facilities such as BMPs but may require adjusting procedures to restrictions noted by the presence of the ESA. Examples of ESA restrictions that might be found include:

• Seasonal mowing restrictions due to threatened or endangered plant species

• Restrictions on the use of pesticides / herbicides

• Limits on digging due to nearby cultural / historical resources

• Limits on clearing due to buffers, etc.

It may not be possible to determine the restrictions imposed by ESAs while in the field performing work. Therefore, should ESA signage be encountered, maintenance personnel should stop work in and adjacent to the ESA and contact the OEnvS. OEnvS will research the ESA to determine what restrictions were put in place at the time the ESA was established. Email guidance requests for ESAs to Ecology_Submittals@dot.ga.gov. Once guidance has been provided by OEnvS, a maintenance plan should be developed to achieve required maintenance activities while complying with ESA restrictions.

Post- construction stormwater BMPs are subject to two types of inspections: route inspections and compliance inspections.

Route Inspections

Except for open-graded friction course (OGFC), post-construction stormwater BMPs are inspected at least annually during route inspections. Completion of route inspections are recorded in GAMS using Activity 540 Litter Patrol with a work description of MS4 Route Inspection. The frequency of route inspections may be increased depending upon past maintenance history or the risk associated with safety or non-compliance should the BMP fail to perform as designed. Route inspections may also be required after major storm events. Maintenance personnel performing route inspections at a minimum look for:

Typical ESA Sign

ESA Sign with Restric�on

Guidance

GDOT ● Inspec�on and Maintenance Manual ● Post-Construc�on Stormwater Best Management Prac�ces 5-3

• Erosion

• Trash

• Condition of vegetation

• Structure damage

• Damage to inlet or outlet structures

Corrective actions identified during route inspections are reported to the ECS for further investigation. Completion of maintenance or repair work is recorded in GAMS using applicable activity codes.

Compliance Inspections

The frequency of compliance inspections is identified in the MS4 Permit and the inspection results are required for the MS4 annual report. Compliance inspections are performed according to the BMP type. Compliance inspections for filter strips and grass channels are conducted during Day Inspections according to GDOT Policy 6162-1 Roadway Inspection Form Instructions. The Roadway Inspection Report form will be an exceptions report. Only items that are deficient or need correction are reported.

Compliance inspections for enhanced swales, infiltration trenches, sand filters, dry detention basins, wet detention ponds, stormwater wetlands, bioslopes, and bioretention basins are conducted using the inspection checklists provided in Appendix B. Although the checklists included in Appendix B provide the basics of the inspection criteria and may be manually used, an electronic process is the primary method for recording inspection data. OGFC BMP compliance inspections are conducted as part of GDOT’s pavement evaluation system (PMS) and are discussed in Section 5.11.

Maintenance needs or corrective actions identified during compliance inspections are reported to the ECS or Area Manager who prioritizes and schedules the work. The type of work and date completed is recorded by the ECS and submitted to the Office of Design Policy and Support (ODPS) to include in the annual report.

Sections 5.1 through 5.12 describe the major components, function, and inspection and maintenance requirements for:

• Filter Strips

• Grass Channels

• Enhanced Swales

• Infiltration Trenches

• Sand Filters

GDOT ● Inspec�on and Maintenance Manual ● Post-Construc�on Stormwater Best Management Prac�ces 5-4

• Dry Detention Basins

• Wet Detention Ponds

• Stormwater Wetlands

• Bioslopes

• Bioretention Basins

• Open Graded Friction Course

• Optional Components

The above post-construction stormwater BMPs are also identified and described in the GDOT Manual on Drainage Design for Highways (Drainage Design Manual). Inspectors should refer to the Drainage Design Manual for design and performance specifications. For BMPs not included in Section 5 of this manual, inspectors should reference project design drawings and specifications for specific maintenance information or manufacturer recommendations for manufactured devices.

BMPs designed prior to the Drainage Design Manual may be assigned to one of the BMP types and inspected using the corresponding inspection process.

GDOT ● Inspec�on and Maintenance Manual ● Filter Strips

5-5

5.1 Filter Strips

5.1.1 Descrip�on and Func�on of Structure

Filter strips are uniformly graded and permanent areas of dense vegetation located between runoff pollutant sources (e.g., road and highway shoulders, medians, other paved areas) and post-construction stormwater BMPs or receiving water bodies. Vegetated filter strips may be constructed of turf, meadow grasses, or other dense vegetation. Filter strips may also surround a drainage structure (e.g., drop inlet), as shown on Figure 5.1-1.

Figure 5.1-1 Channel between Filter Strip (le�), Filter Strip around Drop Inlet (right), Filter strips remove pollutants from stormwater runoff through increased sedimentation. Filter strips require sheet flow across the filter strip to perform as designed which may necessitate the inclusion of a level spreader at the top of the slope of the filter strip. Filter strips reduce the stormwater temperature and encourage filtration and infiltration, which are facilitated by vegetation. Figure 5.1-2 shows a typical filter strip configuration and components.

5-6

Figure 5.1-2 Typical Filter Strip Configura�on and Components

The following key functional features of filter strips must be maintained:

• Runoff sheet flows across the entire filter strip.

• Uniform sheet flow conditions at the interface of the filter strip and the adjacent land cover, such as the buffer shown on Figure 5.1-2.

• Energy dissipation structures (if present), such as flow spreaders or gravel diaphragms to control inflow velocity and erosive energy.

• Dense and uninterrupted vegetation.

Section 5.1.2 recommends inspection and maintenance practices for maximizing filter strip performance.

5.1.2 Inspec�on and Maintenance

Filter strips are preferred BMPs because they are adaptable in a linear setting and are highly cost-effective. Inspections of filter strips should be conducted at least annually during periodic route inspections. Compliance inspections of filter strips are conducted during Day Inspections according to GDOT Policy 6162-1 Roadway Inspection Form Instructions.