Marion County has enacted a Stormwater Ordinance in to provide for the collection and disposal of stormwater in a manner that protects the public health, safety and welfare. The City of Indianapolis is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Indianapolis will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. Marion County will calculate and collect stormwater user fees. Stormwater credits are available for properties that maintain stormwater management facilities. The City of Indianapolis/Marion County, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Indianapolis/Marion County has the authority to inspect stormwater facilities and practices in order to ascertain that they properly maintained and functioning.
Marion County, IN Department of Public Works: 317-327-2015
The stormwater user fee shall be two dollars and twenty-five cents ($2.25) per equivalent residential unit ("ERU") until and including June 30, 2015, and shall be one dollar and ten cents ($1.10) per base billing unit ("BBU") beginning on July 1, 2015.
Calculation of user fee based on ERUs.
Until and including June 30, 2015, stormwater user fees shall be calculated as follows:
(1) Residential properties. Each residential property, as defined in this article, shall be assessed a monthly stormwater user fee based on one (1) ERU. An ERU, as defined in this article, shall be established at two thousand eight hundred (2,800) square feet.
(2) Nonresidential properties. Stormwater user fees for nonresidential properties shall be calculated as follows:
a. The monthly stormwater user fee for each nonresidential property, as defined in this article, shall be calculated by determining and assigning to that property an ERU multiple based upon the property's individually measured square footage of impervious area, divided by two thousand eight hundred (2,800) square feet, which is one (1) ERU. This division shall be calculated to the first decimal place.
b. The user fee shall be based on the nearest whole ERU. Rounding necessary to determine the nearest ERU shall be done according to mathematical convention, zero (0.0) to four-tenths (0.4) rounded down to the nearest whole ERU and five-tenths (0.5) to nine-tenths (0.9) rounded up to the nearest whole ERU.
(3) Exemptions from the assignment of ERUs shall be governed by section 131-422. Credits to the stormwater user fee shall be governed by section 676-403, fee adjustments shall be governed by section 676-304, and appeals shall be governed by section 676-304 of this Code.
Calculation of user fee based on BBUs.
Beginning on July 1, 2015, stormwater user fees shall be calculated as follows:
(1) Stormwater user fees for all parcels within the district, residential and nonresidential, shall be calculated as follows:
a. The monthly stormwater user fee shall be calculated utilizing the measured impervious area (IA) for each parcel and assigning the parcel to a group assigned one (1) base billing unit (BBU) or a multiple of BBUs following the convention 1—1,000 square feet of measured IA is assigned one (1) BBU; 1,001—2,000 square feet of measured IA is assigned two (2) BBUs; 2,001—3,000 square feet of measured IA is assigned three (3) BBUs and progressing in a manner such that each additional 1,000 square foot unit of IA is assigned an additional BBU. BBUs shall be assigned to each parcel proportional to each one thousand-square foot increment of IA contained on the parcel. No parcel containing measurable IA greater than one (1) square foot shall be assigned less than one (1) BBU unless exempted by section 131-422.
b. The impervious area measurement shall be rounded to the nearest whole square foot.
c. The impervious area measurement of a residential parcel shall not be assessed for more than twenty (20) BBUs.
(2) Exemptions from the assignment of BBUs shall be governed by section 131-422. Credits to the stormwater user fee shall be governed by section 676-303, fee adjustments shall be governed by section 676-304 and appeals shall be governed by section 676-304 of this Code.
(3) The stormwater user fee established in section 131-422 shall change annually subject to the automatic rate adjustment procedures outlined herein.
To the extent a sustainable operations and capital improvement program will be maintained and to meet indexing costs after 2019, a stormwater user fee adjustment shall occur automatically each year on January 1 at a rate of $0.05 per 1,000 square feet of impervious surface as defined herein through January 1, 2034 unless otherwise modified as allowed by the articles of this or other applicable ordinance.
The increased stormwater user fee shall be rounded up to the nearest whole cent per BBU.
General discharge prohibitions.
It shall be unlawful to discharge or cause or allow discharge to any natural outlet or watercourse within the city any wastewater or other polluted waters or hazardous materials, except where suitable treatment has been provided in accordance with regulations adopted by CWA Authority and other applicable federal, state and local law.
Prohibited discharges to public sewers.
(a) No person shall discharge or cause to be discharged any stormwater, surface water, groundwater, roof runoff or subsurface drainage into any sanitary sewer.
(b) Stormwater and all other unpolluted drainage may be discharged through existing structures to such sewers as are specifically designated as combined sewers or storm sewers. No additional flow shall be introduced. Industrial cooling waters or unpolluted process waters may only be discharged upon approval by CWA Authority.
(c) No person shall discharge or cause to be discharged to any public sewer wastewater or pollutants other than in compliance with the regulations adopted by CWA Authority, and all other applicable federal, state and local law.
An operations and maintenance (O&M) manual for all private infrastructure, including but not limited to pipes, ponds, ditches, and BMPs (when required), shall be submitted for the final plan approval and permit process. The manual will become a maintenance guide for the drainage infrastructure once development is complete. The final O&M manual will be provided to the City in both hard copy and digital formats.
The O&M manual maintenance agreement along with a site map showing the BMP locations shall be recorded with the final plat. The O&M manual will include the following:
The owner of property is responsible for maintenance of the property's drainage facilities. The granting of an easement to the City of Indianapolis does not alter the property owner's duty to maintain the property's drainage facilities.
Each BMP (a single practice or combination of practices that meet the treatment goal) on a site must be identified in the operations and maintenance plan. The maintenance plan must be submitted with the stormwater management plan and approved by the City. The approved operations and maintenance plan must be provided to the BMP owner.
Annual inspections of permanent BMPs will be performed by the City. Prior to stormwater management plan approval, the developer or owner of a site must pay a predetermined fee to cover the City’s costs for annual inspection for the first 3 years. After the first 3 years, the City will inspect the facility and bill the owner. The number of BMPs on a site will be determined as follows; for each distinct drainage area that requires a stormwater quality control measure either a single BMP or a treatment train (system of 2 or 3 BMPs) will be required. Each BMP system treating a single drainage area is deemed to be one BMP for inspection purposes.
Routine inspections are the responsibility of the BMP owner. Maintenance is also the responsibility of the owner. The approved maintenance plan and inspection forms provided at the ends of each BMP section should be used as guidance for performing maintenance activities. Completed inspection forms must be maintained by the BMP owner and produced upon request by the City. The City must be notified of any changes in BMP ownership, major repairs or BMP failure in writing within 30 days.
Wet detention ponds can be designed to meet both water quality and water quantity requirements.
1. High pollutant removal
2. High community acceptance, if designed and maintained correctly
3. Opportunity for wildlife habitat
4. Multi-objective use for water quality and quantity control
1. Potential for thermal impacts downstream
2. Dam height restrictions
3. Attractive to waterfowl, resulting in bacteria increases, unless shape and vegetation discourage waterfowl
Refer to the checklist provided in the links section for operation, maintenance and inspection of stormwater ponds. The checklist is for the use of the BMP owner in performing routine inspections. The City will perform annual inspections of BMPs, using a similar checklist. The developer/owner is responsible for the cost of maintenance and annual inspections. The BMP owner must maintain and update the BMP operations and maintenance plan. At a minimum, the operations and maintenance plan must include, but is not limited to:
1. Removal debris from inlet and outlet structures
2. Removal of invasive vegetation from all side slopes
3. Removal of sediment accumulation from forebay and permanent pool area when 50% full
4. Removal of woody vegetation from the embankment
Stormwater wetlands are artificial wetlands created for the purposes of stormwater pollutant removal and quantity control. It is the intent of the City and County to encourage regional stormwater wetlands and discourage artificial wetlands designed for individual sites. However, BMP plans will be reviewed on a case-by-case situation to determine feasibility.
Operation and Maintenance Recommendations
Each BMP must have an operations and maintenance plan submitted to the City for approval and maintained and updated by the BMP owner. Refer to links section for a checklist for routine operation, inspection and maintenance requirements for the BMP owner. The City will perform annual inspections, with a similar checklist. The BMP owner is responsible for the cost of maintenance and annual inspections.
1. A stormwater management easement and maintenance agreement is required for each facility. The maintenance covenant must require the owner of the wetland to annually clean the facility and outlet structure. The maintenance agreement must provide for ongoing inspection and maintenance, with more intense activity for the first three years after construction. The easement must include the BMP, all outlet structures and access to the BMP. A copy of the easement should be included in the digital copy of the BMP operations and maintenance manual.
2. The wetland must be maintained to prevent loss of area of ponded water available for emergent vegetation due to sedimentation and/or accumulation of plant material.
3. Sediment forebays must be cleaned when 50% full. Pocket wetlands without forebays must be cleaned after a six-inch accumulation of sediment.
4. The ponded water area may be maintained by raising the elevation of the water level in the permanent pond, by raising the height of the orifice in the outlet structure, or by removing accumulated solids by excavation.
5. Water levels may need to be supplemented or drained periodically until vegetation is fully established.
6. It may be desirable to remove contaminated sediment bottoms or to harvest above ground biomass and remove it from the site to permanently remove pollutants from the wetland.
Bioretention, micro-bioretention and rain garden areas, are structural stormwater controls that capture and temporarily store the Water Quality Volume using soils and vegetation in landscaped areas to remove pollutants from stormwater runoff.
Bioretention: Intended use for drainage areas 5 acres or less, however if hydraulic and hydrologic design criteria are met, sites may be designed to manage multiple 5 acre watersheds.
Micro-bioretention: Intended to be versatile and can be adapted for use anywhere there is landscaping. Contributing drainage area should be less than 20,000 square feet.
Rain garden: Typically used to treat runoff from small impervious areas like rooftops, driveways, and sidewalks. Rain gardens can also be used in retrofitting and redevelopment applications and in series where existing slopes require energy dissipation. Contributing drainage area should be less than 10,000 square feet.
Bioretention areas are engineered facilities in which runoff is conveyed as sheet flow to the “treatment area,” consisting of a pretreatment area, including a sediment forebay, ponding area containing vegetation with a planting soil bed, organic/mulch layer and gravel and perforated pipe underdrain system. The filtered runoff is typically collected and returned to the conveyance system, though it can be infiltrated into the in-situ soils in areas with porous soils (>1”/hour), though infiltration may not be permitted in Wellfield Zoning Districts or hotspot locations. If no perforated pipe underdrain system is used, a geotechnical investigation, soil infiltration testing, and a hotspot investigation must be completed.
Bioretention facilities can provide a limited amount of water quantity control, with the storage provided by the facility included in the design of any downstream detention structures.
Bioretention areas are designed for intermittent flow and to drain and aerate between rainfall events. Sites with continuous flow from groundwater, sump pumps or other areas must be avoided.
1. Applicable to drainage areas <5 acres
2. Often located in landscape islands
3. High pollutant removal
4. High community acceptance, if designed and maintained correctly
1. Requires extensive landscaping
2. Not recommended for areas with steep slopes
A BMP operations and maintenance plan is required for bioretention facilities. The plan must be approved by the City and maintained and updated by the BMP owner. Refer to links section for a checklist for BMP owners for the routine operation, maintenance and inspection of bioretention areas. The City will perform annual BMP inspections, using a similar checklist. The BMP owner is responsible for maintenance costs and inspection fees.
1. Inspect and repair/replace treatment components.
Landscaping is critical to the performance and function of the bioretention area. A dense and vigorous groundcover must be established over the contributing pervious drainage area before runoff can be diverted into the facility.
i.1 large tree
ii.2-4 small trees or shrubs
iii.6 ferns or grass-like plants (1-gallon containers)
iv. Groundcover plantings and wildflower plugs on 12 inch centers with triangular spacing.
v. A native grass/wildflower seed mix can be used as an alternative to groundcover planting.
Micro-bioretention practices capture and treat runoff from discrete impervious areas by passing it through a filter bed mixture of sand, soil, and organic matter. Filtered stormwater is either returned to the conveyance system or partially infiltrated into the soil. Micro-bioretention practices are versatile and may be adapted for use anywhere there is landscaping.
Micro-bioretention is a multi-functional practice that can be easily adapted for new and redevelopment applications in commercial and industrial projects. Stormwater runoff is stored temporarily and filtered in landscaped facilities shaped to take runoff from various sized impervious areas. Micro-bioretention provides water quality treatment, aesthetic value, and can be applied as concave parking lot islands, linear roadway or median filters, terraces slope facilities, residential cul-de-sac islands, and ultra-urban planter boxes.
The following items should be addressed to ensure proper maintenance and long-term performance of micro-bioretention practices:
A rain garden is a shallow, excavated landscape feature or a saucer-shaped depression that temporarily holds runoff for a short period of time. Rain gardens typically consist of an absorbent-planted soil bed; a mulch layer; a gravel filter chamber; and planting materials such as shrubs, grasses, and flowers. An overflow conveyance system is included to pass larger storms. Captured runoff from downspouts, roof drains, pipes, swales, or curb openings temporarily ponds and slowly filters into the soil over 24 to 72 hours.
Rain gardens can be primary or secondary practices on residential, commercial, industrial, or institutional sites. This practice is typically used to treat runoff from small impervious areas like rooftops, driveways, and sidewalks. Rain gardens can also be used in retrofitting and redevelopment applications and in series where existing slopes require energy dissipation.
The following items should be addressed to ensure proper maintenance and long-term performance of rain gardens:
Sand filters are structural stormwater controls that temporarily store stormwater and pass it through a filter bed of sand. Most sand filter systems contain two chambers. The first chamber is a sedimentation chamber that removes floatables and heavy sediments. The second chamber is the filtration chamber, which removes additional pollutants by filtering the runoff through a sand bed. The filtered runoff is typically collected and returned to the conveyance system, though it can be partially or fully exfiltrated into the surrounding soil in areas with porous soils.
Sand filters are primarily designed as off-line structures for stormwater quality and typically need to be used in conjunction with another structural BMP to provide water quantity control.
1. Applicable to small drainage areas
2. Good for highly impervious areas
3. Good retrofit capability
1. High maintenance
2. Not recommended for areas with high sediment content in stormwater.
3. Relatively costly
4. Possible odor problems
Each BMP must have an operations and maintenance plan submitted to the City for approval and maintained and updated by the BMP owner. Refer to links section for a checklist for BMP owner routine operation, maintenance and inspection of sand filters. The City will perform annual BMP inspections, using a similar checklist. The owner shall be responsible for maintenance costs and the annual inspection fee.
Water Quality Swales
Dry water quality swales are channels designed and constructed to capture and treat stormwater runoff within dry cells formed by check dams or other means. Dry water quality swales are also described as biofiltration swales. These swales are designed with a limited slope for slow, shallow flow to allow particulates to settle out and to promote infiltration. Water quality swales are limited to areas with low impervious acreage, such as residential and industrial developments.
1. Typically well accepted in residential settings
3. Combines water quality treatment with runoff conveyance.
4. Reduces runoff velocities.
5. Low maintenance.
1. Cannot be used on steep slopes.
2. Can provide a limited amount of stormwater quantity control.
3. Shown to export bacteria to stormwater
Each BMP must have an operations and maintenance plan submitted to the City for approval and maintained and updated by the BMP owner. Refer to links section for a checklist for BMP owner routine operation, inspection and maintenance of water quality swales. The City will perform annual inspections. The BMP owner shall be responsible for maintenance costs and the annual inspection fee.
Biofilters are densely vegetated sections of land, designed to treat runoff from and remove pollutants through vegetative filtering and infiltration. Biofilters must receive runoff from adjacent areas as sheet flow. The vegetation slows the runoff and filters out sediment and other pollutants. However, the TSS removal provided is less than 80 percent. Therefore, biofilters must be used in a treatment train in conjunction with other management practices to provide the 80 percent performance goal.
Biofilters are best suited to treating runoff from roadways, rooftops, small parking areas and pervious areas. They can be easily incorporated into residential development as land-use buffers and setbacks.
Allowable Biofilter Variations
Filter strip: A filter strip is a uniformly graded and densely vegetated strip of land. The vegetation can be grasses or a combination of grass and woody plants. Pollutant removal efficiencies are based upon a 50-foot wide strip. Uniform sheet flow must be maintained through the filter strip to provide pollutant reduction and to avoid erosion.
Riparian buffer: A riparian buffer is a strip of land with natural, woody vegetation along a stream or other watercourse. Besides the undergrowth of grasses and herbaceous vegetation, the riparian buffer includes deep rooted trees. The 20-foot zone closest to the stream or watercourse (Zone 1) contains the trees, while the outer 30 feet of the riparian buffer contains a dense stand of grasses. The overall width of the riparian buffer is 50 feet. Uniform sheet flow must be maintained through the filter strip to provide pollutant reduction and to avoid erosion.
1. Filter strips and riparian buffers can easily be incorporated into new development design.
2. Low maintenance once a dense ground cover is established in filter strips and level spreaders and once trees and other woody vegetation is established in riparian buffers.
3. Riparian buffers provide wildlife habitat.
1. Filter strips, riparian buffers and level spreaders have limited drainage areas.
2. Constructing a level lip on a level spreader can be difficult. Failure to construct a level lip makes the level spreader ineffective.
A BMP operations and maintenance plan is required for each BMP. The plan must be submitted to the City for approval and maintained and updated by the BMP owner. Refer to the links section for a BMP
Owner’s routine checklist for inspection and maintenance of filter strips and riparian buffers. The City shall perform annual inspections, using a similar checklist. The BMP owner is responsible for maintenance costs and the annual inspection fee.
Catch Basin Inserts
Many variations of catch basin insert designs exist. Catch basin inserts can be designed and installed in a storm drain system provided the following minimum criteria for the inserts are met:
Supporting documentation from the manufacturer to verify maintenance requirements and pollutant removal rates must be submitted to the City for verification and approval. A maintenance plan must be submitted to the City prior to stormwater management plan approval and maintained and updated by the BMP owner. The BMP owner is responsible for routine maintenance, operation and inspection. The City shall perform annual inspections. The BMP owner is responsible for maintenance costs and the annual inspection fee.
Stormwater User Rate and Credit Manual