City of Indianapolis / County of Marion

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

Stormwater User Fee

The stormwater user fee for nonresidential property is based on the quantity of impervious area located on the lot or parcel and is paid by the owner of the property. The stormwater user fee is two dollars and twenty-five cents ($2.25) per ERU.

Calculation of user fee based on ERUs.

Nonresidential properties.

The monthly stormwater user fee for each nonresidential property is 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.

The user fee is 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.

Excluded cities.

Lots or parcels located within the geographic boundaries of the excluded City of Beech Grove, the excluded Town of Speedway and the included Town of Cumberland shall not be charged the stormwater user fees imposed by this article because Speedway and Cumberland established a stormwater utility under IC 8-1.5 and Beech Grove withdrew from the Marion County Stormwater Management District.

Credits.

Credit availability.

For purposes of this subsection, the following definitions apply:

  1. Credit means an on-going reduction in a stormwater user fee based on certain qualifying conditions or activities which mitigate the impact of increased stormwater runoff from the property on a continuing basis and/or reduce the department's cost of providing stormwater management services to the property.
  2. Code means the Code or the Revised Code of the Consolidated City and County.
  3. Stormwater Specification Manual means the City of Indianapolis Department of Public Works Stormwater Design and Construction Specification Manual effective August 23, 1995, as subsequently amended.
  4. Stormwater Credit Manual means the manual, recommended by the department and approved by the board, which shall set forth the details of the credit system, including parameters of credits and application procedures.

A credit to the stormwater user fee imposed on nonresidential property may be available, upon application to the department, for property which meets one (1) or more of the following criteria:

a. Location in relation to major waterway. Credit shall be granted for private stormwater facilities based on the location of the property to a major waterway of the United States, if the property directly discharges its stormwater to that waterway in compliance with all requirements of the Code, the stormwater specification manual, and state and federal regulations. White River, Fall Creek and Big Eagle Creek below Eagle Creek Reservoir shall be considered major waterways for the purposes of this section. A two (2) percent credit shall be granted from the total monthly stormwater user fee for each three (3) percent of the stormwater from the property which directly discharges to the major waterway.

b. Construction in compliance with the stormwater specification manual and the Code. Credit shall be granted from the total monthly stormwater user fee for private stormwater facilities, such as retention/detention facilities, constructed either prior to the effective date or after the effective date of the stormwater specification manual, if those facilities either meet or exceed:

1. The requirements of the stormwater specification manual; and

2. The requirements of the Code in effect at the time of construction.

c. Two-tiered credit availability. Property owners of private stormwater facilities, such as retention/detention facilities, eligible for credit under this subsection may, at their option, apply for either a Tier One or a Tier Two credit as set forth below. Details of the tier system and other matters relating to applying for and receiving credits shall be included in the stormwater credit manual.

1. Tier One. Tier One credit is intended for minor basins with watershed less than five (5) acres but is available for larger basins at owner's option.

Credit amount: Twenty-five (25) percent

Application fee: Not to exceed fifty dollars ($50.00)

Application process: Basic information shall be supplied by the owner. Such information shall include name of owner, location, parcel number, size and shape of basin, type and size of outlet. The owner shall rate the condition of basin as "good, fair or poor" and indicate how many times per year basic maintenance (such as erosion control and/or mowing) activities are performed. The owner shall be required to sign a statement certifying that information is correct and acknowledging that the credit determination will be based on information provided. A later determination that the information was inaccurate may result in loss of credit.

2. Tier Two. Tier Two credit is intended for basins with watershed equal to or greater than five (5) acres but is available for minor basins at owner's option.

Credit amount: Thirty-five (35) percent

Application fee: Not to exceed two hundred fifty dollars ($250.00)

Application process: More detailed technical information shall be supplied by the owner and the owner's engineer. Such information shall include as-built data, routing the storm event for the two (2), ten (10), twenty-five (25), fifty (50) and one hundred (100) year-storm events, comparison of pre-development and post-development conditions, total storage volume and emergency spillway configuration. To receive a Tier Two credit, stormwater facilities must provide control to a pre-development level for all the above storm events.

3. Additional Credit. Additional credit, above the thirty-five (35) percent described in subsection 2. above, shall be granted to properties with private stormwater facilities if the facilities reduce the stormwater discharge from the property to a level below the pre-development one hundred (100) year storm event. A one (1) percent credit shall be granted from the total monthly stormwater user fee for each two (2) percent reduction of discharge below the pre-development one hundred (100) year storm event.

d. Public stormwater facilities located on land owned by local, state or federal governments shall be eligible for credit under subsections a., b. and c. above in the same manner that private stormwater facilities are eligible for credit.

e. The descriptions in this section of circumstances in which credit shall be granted are not intended to be all inclusive. The stormwater credit manual may allow credit for stormwater facilities and circumstances not described in this subsection.

Each credit granted shall be conditioned on the continuing compliance with the design, operation and maintenance requirements of the Code, the stormwater specification manual and the requirements set forth in the stormwater credit manual.

Upon written notice to the property owner or other person designated by the property owner to receive such notice, the department may revoke the credit for good cause, including, but not limited to, failure to comply with minimum maintenance requirements. The department's revocation of the credit may be appealed by following the review procedures set forth in this article.

(b) Credit procedures.

Application for credit or an appeal of a credit determination shall not constitute a valid reason for non-payment of the stormwater user fee for which a credit is being requested.

Application for credit shall be made on forms provided by the department and shall be accompanied by the applicable application fee.

The department shall be responsible for reviewing credit applications and shall provide a written determination of credit within sixty (60) days of receipt of a complete credit application. The written determination shall set forth the effective date of the credit and any conditions applicable to receipt of the credit.

Fee adjustment reviews, credit determination reviews and credit revocation reviews.

(a) Any person subject to this article may petition the director for an adjustment of the stormwater user fees assessed against him, provided:

(1) That the petitioner has paid the disputed stormwater user fees in full;

(2) That the petitioner has good cause to believe that such stormwater user fees were erroneously assessed against him, or that because of extraordinary circumstances unique to his property, his property does not impact or benefit from the stormwater system of the district, or that because of extraordinary circumstances unique to his property, equity can be served only by adjusting the stormwater user fees assessed against his property; and

(3) That within six (6) months of the petitioner's receipt of the bill for the disputed stormwater user fees, the director receives from the petitioner a written petition for adjustment of fees and a brief statement of fact demonstrating the petitioner's right to an adjustment. The petitioner may include with his petition any additional information he deems relevant. If the petitioner wishes to have an informal hearing on his petition, a request for a hearing must be included with his petition.

(b) (1) The director shall appoint an account review officer (ARO) to review and resolve petitions for adjustment of fees. The ARO may be a qualified independent contractor or an employee of the city who serves as a hearing officer as part of his duties.

(2) The ARO shall consider the petitioner's statement of fact, as well as any other relevant and material evidence available in determining whether the petitioner is entitled to an adjustment of the stormwater user fee.

(3) If a hearing has been requested as provided in this article, the hearing shall be before the ARO and shall be held within thirty (30) days of the receipt of the request for hearing, unless a continuance is requested by the petitioner or requested by the department and agreed to by the petitioner. At the hearing the petitioner and the department may present any evidence that is, in the ARO's view, relevant and material to the dispute.

(4) Based on the petitioner's statement of fact, evidence presented at the hearing, if one (1) was requested, and any other relevant and material evidence available, the ARO shall issue a written decision on the petition. The ARO may grant, deny or modify the petition.

(5) The ARO's decision shall be final and binding and shall be issued to the petitioner within ninety (90) days of receipt by the director of the petition for adjustment if no hearing was requested, or ninety (90) days from the conclusion of the hearing.

(c) The petitioner may appeal the ARO's final determination to the board, provided that the board has received written notice of appeal within thirty (30) days of the petitioner's receipt of the ARO's final determination.

(d) The board shall notify the petitioner of the time and place of the hearing on the petitioner's appeal. The petitioner shall have the burden of proving that he is entitled to an adjustment of the stormwater user fees.

(e) At the hearing, the board shall consider any relevant and material evidence available in determining whether the petitioner is entitled to an adjustment of the stormwater user fees. The hearing shall be recorded by audiotape.

(f) The board may grant, deny or modify the petition for adjustment. If the board determines that the petitioner is entitled to an adjustment of the stormwater user fees, the board may, in its sole discretion, make such adjustment in the form of a refund or a credit against future stormwater user fees, or both.

 

Prohibited Discharges

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.

Operations and Maintenance Manual

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:

  1. Owner name, address, business phone number, home phone number, email address, cellular phone number, pager number;
  2. Site drawings (8½” by 11” or 11” by 17”), showing both plan and cross-section views, showing the infrastructure and applicable features, including dimensions, easements, outlet works, forebays, signage, etc., as well as an overall site map of the development showing all structures;
  3. Guidance on both owner-required periodic inspections and inspections to be performed by City representatives, including reference to the use of applicable checklists and reference to applicable inspection fees from the IndyGov web-site under the Department of Metropolitan Development;
  4. Requirement of owner to perform maintenance specified by City inspection, if any;
  5. Guidance on routine maintenance, including mowing, litter removal, woody growth removal, signage, etc.;
  6. Guidance on remedial maintenance; such as inlet replacement, outlet works maintenance, etc.;
  7. Guidance on sediment and trash removal, both narrative and graphical, describing when sediment removal should occur in order to insure that BMPs and other infrastructure remain effective as water quality and/or quantity control devices;
  8. A statement that the City‟s representatives have the right to enter the property to inspect the infrastructure;
  9. A tabular schedule showing inspection and maintenance requirements; and
  10. Identification of the property owner as the party responsible for all maintenance, including cost.

Maintenance of drainage facilities.

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.

Inspection and Maintenance

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.

Stormwater Ponds

Wet detention ponds can be designed to meet both water quality and water quantity requirements.

Advantages

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

Disadvantages

1. Potential for thermal impacts downstream

2. Dam height restrictions

3. Attractive to waterfowl, resulting in bacteria increases, unless shape and vegetation discourage waterfowl

Maintenance

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

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

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 pretreament 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.

Advantages

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

Disadvantages

1. Requires extensive landscaping

2. Not recommended for areas with steep slopes

Maintenance

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

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.

  1. The bioretention area should be vegetated like a terrestrial forest ecosystem, with a mature tree canopy, subcanopy of understory trees, scrub layer and herbaceous ground cover. Three species of each tree and shrub type should be planted.
  2. Perennials, grass-like plants, and ground-cover plants shall be healthy, well-rooted specimens. Plantings shall be designed to minimize the need for mowing, pruning, and irrigation.
    1. The following quantities per 100 square feet of bioretention area are suggested:

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.

  1. Woody vegetation should not be planted at inflow locations or near subsurface drainage pipes.
  2. After the trees and shrubs are established, the ground cover and mulch should be established.
  3. Use native plants, selected based upon hardiness and hydric tolerance.
  4. Landscaping plans shall be provided according to the guidance provided by Department of Public Works and Department of Metropolitan Development.

Micro-Bioretention

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.

Maintenance Criteria:

The following items should be addressed to ensure proper maintenance and long-term performance of micro-bioretention practices:

  • The top few inches of filter media should be removed and replaced when water ponds for more than 24 hours. Silts and sediment should be removed from the surface of the filter bed when accumulation exceeds one inch.
  • Where practices are used to treat areas with higher concentrations of heavy metals (e.g., parking lots, roads), mulch should be replaced annually. Otherwise, the top two to three inches should be replaced as necessary.
  • Occasional pruning and replacement of dead vegetation is necessary. If specific plants are not surviving, more appropriate species should be used. Watering may be required during prolonged dry periods.

Rain Gardens

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.

Maintenance Criteria:

The following items should be addressed to ensure proper maintenance and long-term performance of rain gardens:

  • Rain garden maintenance is generally no different than that required of other landscaped areas.
  • Privately owned practices must have a maintenance plan and shall be protected by easement, deed restriction, ordinance, or other legal measures preventing its neglect, adverse alteration, and removal.
  • The top few inches of the planting soil should be removed and replaced when water ponds for more than 48 hours. Silts and sediment should be removed from the surface of the bed as needed.
  • Where practices are used to treat areas with higher concentrations of heavy metals (e.g., parking lots, roads), mulch should be replaced annually. Otherwise, the top two to three inches should be replaced as necessary.
  • Occasional pruning and replacement of dead vegetation is necessary. If specific plants are not surviving, more appropriate species should be used. Watering may be required during prolonged dry periods.

Sand Filters

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.

Advantages

1. Applicable to small drainage areas

2. Good for highly impervious areas

3. Good retrofit capability

Disadvantages

1. High maintenance

2. Not recommended for areas with high sediment content in stormwater.

3. Relatively costly

4. Possible odor problems

Maintenance

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.

  1. A stormwater management easement and maintenance agreement is required for each facility. The maintenance covenant must require the owner of the sand filter to annually clean the structure. A copy of the easement should be included in the digital copy of the BMP operations and maintenance manual.
  2. Scrape off sediment layer buildup during dry periods with steel rakes or other devices.
  3. Replace some or all of the sand when permeability of the filter media is reduced to unacceptable levels, which shall be specified in the design of the facility. A minimum infiltration rate of 0.5 inches per hour shall be used for all infiltration designs.

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.

Advantages

1. Typically well accepted in residential settings

2. Inexpensive.

3. Combines water quality treatment with runoff conveyance.

4. Reduces runoff velocities.

5. Low maintenance.

Disadvantages

1. Cannot be used on steep slopes.

2. Can provide a limited amount of stormwater quantity control.

3. Shown to export bacteria to stormwater

Maintenance

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.

  1. A stormwater management easement and maintenance agreement is required for each facility. The maintenance covenant must require the owner of the grassed swale to periodically clean the structure. A copy of the easement should be included in the digital copy of the BMP operations and maintenance manual.
  2. Provide adequate access for inspection and maintenance.
  3. Dry swales shall be maintained to keep grass cover dense and vigorous.
  4. At a minimum, maintenance shall include periodic mowing, occasional spot reseeding, and weed control. Swale grasses must never be mowed close to the ground. Grass heights in the 4 to 6 inch range are recommended.
  5. Fertilization of grass swale shall be done when needed to maintain the health of the grass, with care not to over-apply the fertilizer.
  6. Remove sediment accumulated in forebay when it is 50% full.
  7. The planting soil should be removed or replanted when ponding time exceeds 36 hours.

 

Biofilters

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.

Advantages

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.

Disadvantages

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.

Maintenance

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:

  1. Provide an overflow weir to pass storm events larger than the design storm.
  2. Catch basin inserts must meet the 80% TSS removal rate. Verification of the TSS removal rate must be provided by independent testing, not manufacturer testing.
  3. If variations of the insert or filter media are available that remove bacteria, hydrocarbons, dissolved metals, or other pollutants verification of those removal characteristics must be provided.
  4. If multiple filter media are required to meet site-specific pollutant removal requirements the impact of multiple filter medias on discharge characteristics must be provided showing that the design storms still pass through the insert to the City’s standards.
  5. Each design for catch basins can have specific maintenance needs or issues. Maintenance requirements must be clearly defined, and a specific maintenance agreement submitted to the City for review and approval.

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.

 

LINKS:

Constructed Wetlands Operations, Maintenance, and Management Inspection Checklist for BMP Owners

Stormwater Pond Operation, Maintenance, and Management Inspection Checklist for BMP Owners

Sand Filter Operations, Maintenance, and Management Inspection Checklist for BMP Owners

Water Quality Swale Operation, Maintenance, and Management Inspection Checklist for BMP Owners

Biofilter and Buffer Operation, Maintenance, and Management Inspection Checklist for BMP Owners

Bioretention Operation, Maintenance, and Management Inspection Checklist for BMP Owners