Combined Sewer Overflow (CSO)

When a Combined Sewer System (CSS) discharges untreated or partially treated sewage and other wastes directly into streams, rivers, coastal waters, or other water bodies. Also see CSS.


Combined Sewer System (CSS)

A system using shared pipes for transporting stormwater runoff and sewage to wastewater treatment plants. Common in older cities, these systems were once thought to be efficient  because they used rainwater to intermittently flush pipes and culverts, preventing backups and the build up of sewer waste. To prevent catastrophic failure at wastewater treatment plants during heavy rains, these systems often have multiple overflow points, where above capacity flows are directed directly to rivers, creeks, or coastal waters. Green infrastructure has become a major strategy for retaining, slowing the flow of, diverting, and evaporating stormwater so it does not enter the CSS during rain events.


Community Land Trust

A non-profit, legal mechanism for acquiring and managing land for the benefit of a specified community.



The result of being exposed to a particular event. These effects can be positive or negative depending on the situation, the nature of the event, and the dispersal of its impacts. Harmful consequences are a key component of risk evaluation. Desired consequences are usually referred to as benefits, and their overall social benefit depends upon both context and distributions.



The reality within which decisions are made and consequences are experienced, sensitive to the conditions of a particular time and place. Key components of context involve how information is presented, the experiences of those affected by decision making processes, and the ability to process and understand prior and current events and information. For green infrastructure, the ways in which it is able to provide benefits and manage risks ultimately depends on its context.



Formally referring to the distribution of difference within a given population. For cities, this can refer to the multitude of streetscape forms, densities, socio-economic conditions, races, ethnicities, nationalities, and political orientations, among other characteristics. Intersectional understandings of identity should inform the discussion of what constitutes social diversity. Recognizing diversity is often the first step of building more inclusive processes that work for individuals and communities from various backgrounds and orientations. Measures of diversity are scale sensitive, so that estimating diversity at the neighborhood or block level may be very different from the city or metropolitan level. Best practices would include multiple measures estimated at different spatial scales for both the biological diversity supporting green infrastructure’s resilience, as well as the social diversity of cities.


Environmental Hazards

Dangers or risks to humans resulting from ecological or earth processes or biological agents, including extreme weather events, sea level rise, earthquakes, tsunamis, biological toxins (algal blooms), and vector borne diseases (Covid-19, malaria, Zika Virus). In some cases, industrial wastes and other types of human-created pollution are also considered environmental hazards. For the purposes of this project, the broadest possible definition has been retained – those hazards present in the surroundings of individuals and communities. However, specific language is used regarding particular hazards wherever possible.



Fairness in process and outcomes, including the allocation of resources based upon need. The factors and processes that determine Equity are dynamic and may change over space and time, as new circumstances (i.e. climate change) and understandings arise. 



The intersection of an individual, community, or physical or psychological asset to a particular event (good or bad). In general, exposure refers to negative events and is fundamental to risk assessment for all humans and planning processes. Exposure to positive events or amenities is usually referred to as accessibility.


Exposure, Differential

The ways in which exposure to hazards is not distributed evenly in space, time, and across society. Distinct from, but related to, differential vulnerability.


Green Infrastructure

Green infrastructure (GI) refers to a system of interconnected ecosystems, ecological-technological hybrids, and built infrastructures providing social, environmental, and technological functions and benefits. As a planning concept, GI brings attention to how urban ecosystems and built infrastructures function in relation to each other to achieve socially negotiated goals. 

The Green infrastructure concept has emerged out of traditions of landscape conservation and design, often informing regional conservation strategies, as well as efforts to make stormwater systems more sustainable, championed in the US by the Environmental Protection Agency (EPA).


Housing Co-Operative

Housing cooperatives, a subset of real-estate cooperatives, are organized expressly for the purpose of providing housing to member-owners. Generally members pay a fee or share in order to have ownership of their residential unit and annual or monthly fees to cover costs associated with utilities, upkeep, maintenance, and upgrades. These ownership structures can also place housing outside of market rates, by setting a base price for what constitutes a share (essentially buying an apartment within the cooperative), or limiting the equity of individual members, eliminating profit motives in the ownership and transfer of housing.  Cooperatives have often formed following real estate market crashes, allowing tenants to purchase buildings, and form a significant portion of affordable housing in cities like Washington D.C. and NYC. 



A principle closely related to accessibility that demands that those to be affected by decision making are included in the processes of decision making. Inclusion is a key component of participatory planning approaches, but by itself is insufficient to address the long standing inequalities in access to resources, agenda setting, and social power that shape how planning takes place.



Originally a legal term, intersectionality was coined for popular use by professor Kimberlé Crenshaw in 1989. It has come to describe how race, class, gender, sexual orientation, political orientation, and other individual or community characteristics overlap to affect social positions and treatment by other individuals, communities, and institutions. 



Justice involves recognizing unfairness and harms (past and present) perpetuated against individuals and groups, finding satisfaction for those harmed, and ensuring that such harms do not recur. Justice means different things to different people and requires those who have been harmed to define it in context. See recognitional, restorative, and transformative justice.


Justice, Design

A community-led design concept and practice which centers those who will be directly impacted by policies, programs, and projects, as opposed to the vision of the designer. In this sense, the designer serves as an instrument – essentially a professional in service of the needs and priorities of the communities they have been charged to assist. 


Justice, Recognitional

Recognitional justice involves recognizing past and current harms, and acknowledging that injustices have occurred against individuals and social groups. Often this is the first step in any type of social process to address injustice. Without restorative and transformative elements however, recognitional justice can be used to delegitimize calls for justice by relegating injustice to the distant past rather than as something with consequences felt in the present.


Justice, Restorative

Restorative, or reparative, justice refers to the allocation of resources for the reparation,  restitution, and ‘making whole’ of individuals and groups that have been subjected to injustice.


Justice, Transformational

Transformational, or transformative justice, recognizes that in order for justice and equity to be achieved, the systems, ways of thinking, and lifestyles perpetuating harm must be transformed in line with the demands, desires, and visions of those who are harmed by them.


Justice, Environmental (EJ)

Environmental Justice refers to the fact that certain individuals and groups are unfairly impacted by environmental hazards. Often, polluting industrial activities are placed in BIPOC and/or low-income neighborhoods and communities, where residents have not been included in decision making processes. These same communities may also have been made more vulnerable to present-day climate hazards due to historical policies influencing their location, infrastructure investments, and other factors.

Remedies for past and present wrongs require supporting EJ communities in developing, implementing, and enforcing social policies and processes in order to address the unfair distribution of environmental risks and benefits, and provide requested resources for remediating past harms.


Justice, Critical Environmental

An emerging understanding of environmental justice issues as explicit forms of structural violence and ecological genocide and not simply the result of unequal enforcement of environmental laws. Critical EJ scholarship and practice formed in opposition to narratives that certain races and classes are incapable of advocating for their own self interest in an otherwise fair system.


Justice, Indigenous Environmental

A framework for addressing the environmental injustices caused by the dispossession of Indigenous lands and purposeful destruction or undermining of Indigenous systems of governance. IEJ reframes EJ concerns as core questions of who has authority to permit environmental and social harms, not solely as questions of social difference, such as race, gender, or class.


Long Term Control Plans

A specific type of regulatory plan overseen by the US Environmental Protection Agency (EPA) pertaining to the regulation and mitigation of combined sewer overflows (CSOs). While historically focused on increasing sewer and wastewater treatment plant capacity, increasingly they rely on green infrastructure approaches to reduce the inflow of stormwater runoff into combined sewer systems.

Municipally owned and operated stormwater sewer systems using separate pipes to manage surface stormwater runoff and discharge that flow directly into local surface waters. MS4s are not connected with city wastewater system infrastructure. Stormwater runoff, especially in urban areas, is a major source of contaminants, including lawn and automotive chemicals, heavy metals, and other non-point source pollutants, and is increasingly treated using green infrastructure facilities and approaches.



Interests, perspectives, and experiences of diverse groups, individuals, disciplines, and sectors  in society are recognized and considered valid as knowledge for framing and addressing problems. Pluralism is essential for the development of democratic policy and planning. 


Rent Burden

Historically, a household or individual was considered rent burdened if  >25% of their income was spent for housing. Many now use 30% as the cutoff. However, with wage stagnation and rising housing costs, the original definition was determined to be more appropriate for this project.


Real Estate Co-Operative

A Co-operative created for the express purpose of owning real estate for and by commercial, non-profit, and residential tenants that can be co-owned by non-occupants, such as shareholders or member owners of commercial enterprises. Cooperatives in various forms became increasingly prominent during periods of rapid industrialization in Europe and the USA, seeking to create working models of economic democracy. When applied to real estate, cooperatives combine different levels of financial investment with voting rights and various forms of responsibilities. They are increasingly employed as means of raising capital for major investments from diverse sources while retaining community control of development projects and ensuring that profits from ventures are directly reinvested or otherwise stay in the community.



A federal policy begun in the 1930’s, redlining created institutional forms of discrimination by classifying particular neighborhoods of certain racial, ethnic, and socio-economic characteristics as having a higher level of risk for real estate financing. This limited residents’ access to capital for home ownership and renovation, and fueled cycles of neighborhood disinvestment. 

Redlining is widely understood to have significantly influenced the economic mobility of affected communities, with persistent impacts upon the quality of housing stock, residents’ exposure to environmental hazards, and their ability to accumulate wealth. Scholars contend that current methods of real-estate evaluation have allowed redlining to persist in various forms, even though the practice was explicitly banned by the Fair Housing Act of 1968. The FHA stipulates that individuals can not be denied access to financing based race, color, national origin, religion, sex, familial status, and disability. 



The possibility of something bad or undesirable happening. Risks take many forms and depend upon context and exposure to potential harms. The formal definition of risk includes the probability of an event occurring multiplied by its consequences. Thus, low probability events with high consequences (e.g. death) can be high risk, as can low level chronic events (e.g. daily exposure to sub lethal air pollution can still constitute a high risk). The idea is often applied to financial, economic, and social decisions and programs to aid in the evaluation of the potential negative outcomes of decision making. Current thinking on risk has shifted to understand risk in multiple ways at once (risk pluralism).


Sanitary Sewer Overflows (SSOs)

Dedicated Sanitary Sewer Systems that are not connected to stormwater runoff control can still have overflow events from poor system planning and large demand increases, as well as connections to ground and surface water resulting from leaky pipes or other structural failures. In general these appear to have lower environmental impacts, as the sanitary sewer system, in theory, treats all the sewage within the city.


Sanitary Sewer System  

A system of underground pipes, distinct from storm sewers, that convey sewage from buildings to waste water treatment facilities. Common in newer cities and in some older cities, like Baltimore, that decided early on to keep flows separate. 


Total Maximum Daily Load (TMDL)

The maximum daily load of regulated contaminants allowed to be discharged into a water body, so that water body continues to meet water quality standards specified by the EPA. Formal regulatory plans must be submitted to keep pollution below this level. Pollution sources are designated as either point sources (single, identifiable sources, such as pipes) or nonpoint sources (roads, lawns, and contaminated lands). Green infrastructure has become a dominant strategy for managing the Load Allocations (LA) from nonpoint sources, as well as reducing the severity and incidence of some point-sources of contaminants, like those from CSOs.


Universal Good

The idea that some goods are beneficial and experienced by everyone. A guiding idea of environmental policy and regulation is that improvements in environmental quality benefit all individuals equally; in practice, this has been shown to be untrue. A primary challenge of achieving universal benefits is the harmonious realization of all individual perceptions of good, requiring attention to pluralism and the ways in which green infrastructure improvements are experienced by diverse communities.



A moral and ethical philosophy that supposes human ethical principles can be applied to everyone, irrespective of social context, culture, upbringing, or individual characteristics.



Similar to susceptibility or sensitivity, vulnerability deals with the severity of impact resulting from exposure to a specified event will have on an entity such as an individual, community, society or system.


Vulnerability, Differential

The idea that some groups and individuals have been made more vulnerable to hazards over time, meaning they experience more severe consequences than other groups as a result of exposure to the same events. Causes can include pre-existing conditions and reduced access to resources to plan, recover, and adapt. It is important to examine hazard vulnerability in context and not based on generalized attributes of populations.



Generally defined as the physical boundaries of an area of land wherein all rainfall drains into a single outlet, such as a river or stream mouth. This is closely related to the concept of ‘sewer shed’, which is the surface area draining into a particular sewer system or sub-section. Complicated by modern water infrastructures that transfer both source (e.g. drinking) and waste (e.g. storm and sewer) water between basins. The watershed boundary is often used to guide water quality interventions, integrated water system and resource planning, as well as ecological restoration programs.