What is a retrofit?

A retrofit is an upgrade, modification or refreshment to an existing facility, product or item. Retrofits can be done to improve effectiveness, improve energy efficiency, improve business efficiency, or to adapt to new needs.

Retrofits can be done on aging infrastructure to bring them into the modern age by utilizing modern technology. Retrofits can also be used to remove hazardous materials by replacing them with more environmentally friendly and efficient materials.

A machine can be retrofitted with modern equipment to make it more suitable for new technology. This can be an upgrade to sensors, materials, batteries, etc. to make the machine run more efficiently with new and modified parts.

A retrofit can be thought of as taking an aging piece of equipment or infrastructure and giving it a new lease on life by upgrading it with modern technology, material and parts.

Retrofits within the stormwater industry can be used to modify existing unmanaged or inadequately managed stormwater runoff in impaired watersheds.

What does retrofit mean?

An EPA document describes that "while new development is required to manage stormwater on-site, older developments may have been constructed before stormwater management was required or modern criteria was established. Retrofits include new installations or upgrades to existing Best Management Practices (BMPs) in developed areas where there is a lack of adequate stormwater treatment."

Oxford English Dictionary describes retrofitting as “a modification made to a product or structure to incorporate changes and developments introduced since manufacture or construction; the action or fact of modifying a product or structure in this manner.”^[2]

Merriam-Webster defines a retrofit as “to furnish (something, such as a computer, airplane, or building) with new or modified parts or equipment not available or considered necessary at the time of manufacture.”^[3]

The Ohio Environmental Protection Agency (EPA) defines retrofitting inside of the stormwater industry as “installation of storm water best management practices in areas where non previously existed, or improvement of existing storm water management practices so that they provide a water quality function.”^[4]

What is an example of a retrofit?

The goal of a stormwater retrofit may include the correction of prior design or performance deficiencies, flood mitigation, disconnecting impervious areas, improving recharge and infiltration performance, addressing pollutants of conern, demonstrating new technologies, and supporting team restoration activities.

Exmaples of stormwater retrofits described by the U.S. EPA include:

Bioretention in a municipal park
Bioswales at the edges, or within, a parking lot
Sand filters to treat parking lot runoff
Bioretention facilities

Examples of retrofits described by the Ohio EPA include:

Detention Basins with water quality enhancements
Green roofs
Rain barrels
Pervious pavement
Rain gardens

Pavement

Permeable pavers key feature of roadway retrofit in historic New York village

Kevin Earley

Nov. 17, 2023

A New York green infrastructure project that reduces stormwater runoff and pollutants from entering Chautauqua Lake used permeable pavers to achieve its goals.

What is the purpose of retrofit?

A retrofit within the stormwater industry can have multiple purposes.

Taking an existing detention basin and retrofitting it with natural vegetation and sediment to better filter out contaminants in the stormwater is a good example.

Using porous pavement that allows for better runoff is an example of how a roads pavement can be repurposed and retrofitted with new technology.

Municipal Separate Storm Sewer Systems (MS4s) can use retrofits to meet different demands.

One such demand is meeting the National Pollutant Discharge Elimination System (NPDES) MS4 Program that aims to eliminate pollution from rainfall runoff that flows through MS4s.

Retrofitting can be used to meet Total Maximum Daily Load (TMDL) reductions.

Existing developments, like watersheds, may be required to be retrofitted to meet pollutant reduction targets.

How to do a retrofit?

A U.S. EPA document titled Stormwater Retrofit Techniques for Restoring Urban Drainages in Massachusetts and New Hampshire details a "widely accepted approach (Schueler et al., 2007) to stormwater retrofitting at the small watershed scale."

A summarized eight step process as described by the U.S. EPA is below:

Evaluate local need and capacity for retrofitting in your MS4 and identify yout pollutant reduction requirements.
Using GIS, institutional knowledge and blueprints as apropriate, indentify potential retrofit locations at publicly-owned properties.
Conduct a retrofit investigation by visiting each location to verify current conditions and identify potential retrofit treatment options and constraints.
Develop an inventory of potential retrofit candidates, with concept sketches, site photos, and basic drainage calculations.
Evaluate and rate retrofit concepts based on predetermined factors such as pollutant reduction requirements and cost.
Model watershed treatment benefits for various implementation scenarios to determine the most cost-effective approaches to implementation.
Take the top projects to final design and construction stages.
Provide inspection and maintenance services for the life of the retrofit.