5.2 TYPES OF DATA NEEDED

In considering the rate structure, there are many ways to categorize billing policies used to calculate individual fees. For the purposes of this chapter, four issues will be considered:

1. Billing Units - The definition of equity is the foundation for the billing system and data collection process.
2. Impervious/Pervious - Almost all stormwater utility fee structures in the United States are based upon the impervious and, sometimes pervious, area for each parcel.
3. Vacant Property - Data are required for "empty" properties.
4. Agricultural Property - Data are also needed for developed but rural properties.

Issues regarding rate policy and data support are presented. It should be noted that stormwater utility fees are typically based upon either the amount of impervious area or an area-weighted amount of impervious and pervious area on the customer's property. To eliminate the multiple references to the amount of area, for the purposes of this chapter, the phrase "reference area" will refer to either impervious only area or impervious and pervious area.

5.2.1 Definition of Billing Units

For any stormwater utility fee, the definition of the billing unit provides the justification for equity. If the stormwater utility revenues are based on a special assessment, then the definition of billing unit is the foundation of the legal requirement that the assessments are fairly and reasonably apportioned among the benefited properties. If the utility revenues are based on a user fee, then the definition of the billing unit is the foundation of the connection (or nexus) between the governmental service provided and the customer. Either way, data requirements for billing units are important to the legality, public acceptance, and implementation of the stormwater utility. To discuss the definition of billing units, this section considers the customer, equivalency, uniform versus variable rates, and credits and exemptions.

Customer

For the purpose of this chapter, the "customer" is the person (or entity) to whom the stormwater utility assessment or fee is applicable.

Special Assessment
For special assessments, the customer is the property owner or escrow account. In other words, since the billing process through the tax collector is directed toward the property owner, special assessments are also associated with the owner. Therefore, data required for stormwater utility special assessment must be related to the property owner and the property owned. Land uses, impervious and pervious areas, location within incorporated areas, and other factors (see below) must be related to the property boundaries and, in fact, the primary key for assessment databases is the parcel identification number used by the Property Appraiser and Tax Collector.

User Fee
For user fees, the customer can be defined in a number of ways. If the fee is to be billed along with other existing utilities, then the customer is the existing customer for the other utilities. Many of the cities with existing stormwater user fees associate the stormwater fee with either the electric or water utility fees. In these cases, the customer is the electric or water customer. For user fees associated with other utilities, the customer can be either the owner or the tenant. The basis for the user fee database is generally the existing utility customer and the primary key for the database is the existing customer utility account number.

Equivalency

In the definition of Billing Units, there are a number of ways in which adopted utilities have established rates. In the same manner as other types of utility rates, most stormwater utility fees are based upon an equivalent unit, most commonly related to an average residential unit. According to the 1997 FASU survey, there are two common ways this relationship has been established:

1. Single Family Unit Equivalency - - In this method, the stormwater utility fees are related to an average single-family unit measurement for the unit of measure. To use this method, the average reference area for all single-family units in a municipality, or at least a statistically significant sample, must be obtained. Most of the stormwater utilities in Florida use a statistically significant sample to define the single-family unit average. The unit defined by this method has been referred to as a SFU (single-family unit) or SFE (single-family equivalent).
2. Residential Unit Equivalency - In this method, all residential types (single-family, multi-family, condominiums, and mobile homes) are included in the average reference area calculation. When residential parcels other than single-family are considered, additional data on the number of dwelling units are required. Most of the stormwater utility fees that use this method in Florida are based upon a statistically significant sample of reference area measurements for each dwelling unit type. The unit defined by this method has been referred to as an ERU (equivalent residential unit).

Methods for collecting residential area data and number of dwelling units are discussed in detail in Section 5.3. For the purposes of this chapter, the average equivalency area will be referred to as A_ERU whether it refers to the single-family or residential equivalency.

Variable Residential Rates

Notwithstanding the use of a single-family or dwelling unit equivalency, stormwater utility fee structures can be uniform or variable for residential customers, and are almost always based on a uniform rate related to impervious area for non-residential customers. Most commonly used methods for residential rates are presented below.

Uniform Single-family Rates

Stormwater utility rates in Florida are most commonly based upon a single rate for residential customers. The fee for a single-family unit customer, using this method, is calculated as the uniform rate times one. In other words, single-family units pay a fee equal to one times the uniform rate. The uniform rate is usually in units of dollars per month (or year) per equivalent unit (SFU or ERU).

Mathematically, this can be expressed as:

Single-Family Customer Fee = R_r

where R_r is the uniform residential rate. In this case, the only information necessary to calculate the fee for the customer is whether the customer is a single-family unit or not.

Variable Single Family Rates

Two other methods for calculating single-family fees have also been used both of which require significantly more data that for uniform single-family fees. In both cases, the rates would depend on the amount of reference area on the property in question. For the first type, the rate is tiered; that is, the rate would depend on where the amount of reference area would fall within three or more categories. As an example, if three categories were defined (less than A₁, between A₁ and A₂ and greater than A₂), then the fees would be calculated as:

where A is the amount of reference area. In this case, the smaller single-family units would pay less than the larger ones.

Significantly more data are required for this rate structure than for a uniform single-family rate structure. The reference area must be measured or obtained for every single-family unit customer, and these data would have to be maintained on a regular basis (i.e., changed frequently to account for modifications to homes). The overall size of the billing database would also be significantly higher than for a uniform rate.

The second method for calculating variable single-family unit fees is to calculate the fee based upon the actual reference area for each single-family unit. The calculation method would be similar to a non-residential fee calculation with the measured reference area divided by an SFU or ERU average reference area. Data requirements are the same as for a tiered single-family rate structure.

It should be noted that single-family unit customers generally represent a significant fraction of the utility customers, usually above 80 %. A database with all residential and non-residential reference areas is significantly larger than one with non-residential data only. If residential customers are 80% of the total number of customers, then the total database is five times larger than the non-residential database. This means that there is a greater administrative responsibility to maintain the database and there will be greater numbers of customers requesting specific information on their parcel. Thus, using a detailed single-family fee calculation requires increases in administrative costs for maintenance and customer service.

Variable Non-Single Family Residential Rates

Regardless of the equivalency or single-family unit rates, rate structures for residential customers can have both uniform and variable rates for non-single-family residential classes: apartments (multi-family), condominiums, and mobile homes. Alternatives are discussed below:

Uniform Rate Based on Dwelling Units

In this alternative, non-single-family residential units are assigned a fee based upon a uniform rate (usually the same as the single-family rate), and the number of dwelling units associated with the customer's property. In other words, if R_r is the uniform residential rate and N_u is the number of units, then:

Residential Customer Fee = R_r x N_u

where N_u is one for condominium units, single mobile homes on single parcels and multi-family units billed by individual apartment; and N_u is more than one for multi-family units using multi-unit meters or master meters.

For this type of fee calculation, the data required includes the number of dwelling units associated with the customer's property. Methods to collect these data are discussed in Section 5.3.3 below.

Uniform Rate Based on Reference Area

Another common alternative is for a uniform rate to be applied to non-single-family residential customers based upon the reference area in the same manner as a non-residential customer. If A is the reference area for the customer's property, then the fee is:

To implement this rate structure, information on the reference area for each non-single-family unit is required. While this data set is not as difficult or extensive to obtain as for single-family units, there are generally more non-single-family residential properties within municipalities than there are non-residential properties.

Variable Rates

The last alternative to be discussed includes variable rates depending on the residential class. These rates are generally multiplied times the number of dwelling units for convenience; however, they can be multiplied times the reference area. Thus, if the variable rates are R_r-mf, R_r-c and R_r-mh for multi-family, condominiums and mobile homes respectively, then:

where N_u is the number units.

To implement variable rates, some rationale is needed for setting the rates. One method used in Florida is to sample the reference areas for the various types of residential classes and calculate an average reference area per dwelling unit for each residential class. The rate is the ratio of the average reference area for the class and the single-family unit average reference area. An example is given in Table 5-1.

Table 5-1

Example Residential Average Impervious Areas

In this example table, the average impervious areas for residential classes are compared to the average impervious areas of single-family units. Rounding to the nearest tenth, the mobile homes in parks would pay 0.9 the rate of a single-family home, and apartments and condominiums would pay 0.4 times the rate of a single family. Other methods can be devised to justify the variable rates. Generally, whatever the variable non-single-family residential rate structure, information on the number of dwelling units and average reference area per dwelling unit are required.

Non-residential Rates

Unless there are different rates for service areas or specific basins for capital improvements, almost all rate structures for stormwater utilities have a uniform rate for non-residential property. The calculation for the fees for uniform rates is simple:

where R_r is the rate for each ERU, A_n is the reference area for the property, and A_ERU is the equivalent reference area. For this calculation the only information required is the reference area for the property.

Experience has shown that, unlike residential reference areas, non-residential reference areas are highly variable and that use of an average value to represent general classes is not valid. Averages can be used only to make general estimates of revenues. However, because they are highly variable, individual reference area measurements must be made for each non-residential customer.

Credits and Exemptions

For the purposes of this chapter, credits and exemptions are defined as follows:

• Credit - A reduction in fees owed to the municipality for an individual customer or class of customers.
• Exemption - The exclusion of a potential customer (or a portion of the fee) due to special reasons.

While both of these policy issues are related to equity and fairness, credits and exemptions are not the same. A credit is given to a customer or class of customers generally because the stormwater utility rate structure gives them a break for some reason. For example, if a commercial customer maintains the municipal stormwater system adjacent to the property, then a credit may be allowed because the stormwater service being provided to the property is reduced. If a portion of a customer's property drains away from the municipal storm sewer system, then the utility policy may exempt or exclude that portion of the property from any utility fee calculation. Clearly, whatever the credit or exemption policy authorized, individual customer and property data are required, and the type of credit or exemption will define the type of data collected. A number of types of credits are discussed below along with the data needs to support the policy.

Retention/Detention Ponds

In Florida, lands developed after 1985 have been required to satisfy Rule 62-25, Florida Administrative Codes (FAC) and other state, regional (i.e., water management district), and local regulations controlling the discharge of stormwater from the post-development sites. There are four major changes to stormwater runoff that occur because of land development: the peak runoff increases; the volume of runoff increases; the timing of the peak runoff changes (generally the peak shows up earlier in the storm event); and the quality of the runoff changes (generally worsens). State, regional, and local regulations attempt to minimize the negative effects of these changes by requiring the post-development peak runoff to be attenuated to the pre-development peak runoff, and by requiring the post-development runoff to be treated with best management practices such as wet detention ponds and retention. Lands developed after 1985, therefore, generally provide a measure of post-development improvements for peak runoff and runoff quality, and lands developed earlier do not.

It should be noted that, except when retention is used, the increase in post-development runoff volume is not mitigated; and treated, post-development runoff, while better than untreated runoff, worsens because of the change in runoff chemical makeup. Furthermore, to function properly, stormwater best management practices (BMPs) must be maintained. Poorly maintained facilities do not provide proper treatment.

Some stormwater utilities in Florida offer customers credit for stormwater facilities built in compliance with state, regional, or local stormwater regulations. The justification is that the customer's property on which BMPs are constructed provides an improvement in runoff quantity and quality that are not provided by property without BMPs. However, in most cases, such facilities must be maintained to earn the credit: either the municipality inspects the BMP each year, or the customer must provide the municipality with a certification of maintenance.

Credits for onsite BMPs have been offered in stormwater utility rate structures in two basic ways: a flat fee reduction, and a variable reduction based upon attenuation volume. For the first, an amount or percentage of the fee is eliminated for property with BMPs as follows:

Final Fee = Regular Fee x C

where C is a number less than 1. For the second credit calculation, the fee is reduced variably depending on the amount of attenuation or stormwater quality treatment provided. Mathematically, this credit can be expressed as follows:

where V_BMP is amount of attenuation or treatment provided by the customer's BMP and V_max is the ideal amount of attenuation or treatment authorized. Slightly more complicated alternatives to these offer a credit for only a portion of the fee. A base fee is required to pay for those portions of the stormwater management program unaffected by onsite BMPs (e.g., management, planning, enforcement, engineering, etc.) and a land development portion of the fee, which can be reduced with onsite BMPs:

Final Fee = F_B + F_LD x C

or

where F_B is the base fee and F_LD is the land development component of the fee.

Data requirements for these types of credits depend on the complexity of the credit structure. For the flat reduction, the billing database needs information on whether a parcel of land has a maintained stormwater facility or not. For the variable fee, additional information about the type and properties of the stormwater facility are also required. Therefore, the greater the complexity of the stormwater facility credit, the greater the expenditure of revenues to administer the credit itself.

Maintenance Credits

Similar to the onsite stormwater facility credit, a credit can be offered to customers who provide for the maintenance of municipal facilities themselves. An example would be a homeowner association's maintenance of a residential retention or detention pond. The municipality may own the facility, but a homeowner's association maintains it. As long as the municipality is supposed to do the maintenance, but the private entity is actually doing the maintenance, a credit can be offered according to municipal standards. An agreement between the municipality and private entity to ensure proper maintenance needs to be executed. Generally, the credit reduces the portion of the fee that is related to the maintenance portion of the stormwater management program offered by the municipality.

Data for this credit include whether the customer's property drains to a privately maintained, municipal stormwater facility or not. Proper maintenance must be demonstrated before the credit is authorized, so that annually, the database must record maintenance certification.

No Discharge Exemption

A type of exemption offered to properties is when all, or a portion, of the property does not discharge stormwater runoff to the municipal stormwater management system. Since the runoff from all or a portion of the property does not discharge to the municipality, the municipality does not provide the same level of stormwater service as it would to another parcel from which all of the runoff enters the municipal system. This credit is generally offered only in rural settings such as counties and is rarely offered in cities. Also, the credit usually affects non-residential customers. The credit can be represented as follows:

where A_ND is the portion of the reference area which does not discharge to the storm sewer system.

Information required for this credit includes specific data on runoff patterns from each non-residential parcel. For each parcel, the reference area must be measured and the runoff patterns defined with contours. The reference area applicable to the utility fee would be the total reference area minus the portion of the area that flows away from the stormwater management system. In agricultural areas where flow patterns are altered frequently, such calculations must be modified frequently.

5.2.2 Impervious and Pervious Areas

As noted in the introduction of Section 5.2, stormwater utility fees in Florida are based on either the impervious area or a combination of impervious and pervious areas for the customer's property. For simplicity, this chapter has referred to the area(s) used as the reference area. The purpose of this section is to define the data requirements to supply reference area information for the billing database.

Definitions

For the purposes of this chapter, the following definitions are applied to impervious and pervious areas:

• "Impervious Area" means the horizontal projection of areas on a customer's property that do not allow the infiltration of rainfall. Examples of impervious area include roofs of buildings, driveways, parking areas, sidewalks, tennis courts, etc. For a multi-story building, only the base area is considered part of the impervious area.
• "Pervious Area" means the horizontal projection of areas on a customer's property that allow infiltration of rainfall. In other words, the pervious area is the total property area minus the impervious area. Examples include grassed and forested areas.

Difficult Areas to Categorize as Impervious or Pervious Areas

While these definitions seem straight forward, there are a few exceptions that ultimately need to be considered as policy decisions. These are discussed below.

Shell, Gravel, and Sand

In numerous locations within a municipality, driveways, parking lots and roads are covered with what might be considered semi-impervious materials: shell, gravel, or sand. In each of these cases in an urban environment, the semi-impervious materials are underlain with compacted soil, so infiltration is impeded and reduced. Some stormwater utilities adopted in Florida have included these materials as impervious area and some have excluded them. The point of this discussion is that shell, gravel, and sand need to be categorized at the onset of the data collection process.

Swimming Pools

Clearly, the decking around swimming pools impedes the infiltration of rainfall and is impervious area. The pool itself, however, collects stormwater and does not create runoff. Therefore the question is: "Is a swimming pool pervious or impervious area?" As with semi-impervious materials, stormwater utilities in Florida have considered swimming pools either way. However, it should be noted that excess pool water does not generally have an opportunity to infiltrate into the soil as does rainfall striking pervious, or even semi-impervious, areas. Excess pool water is drained to the sanitary sewer or to the storm sewer. In the latter case, pool water becomes runoff and the area of the pool should be considered impervious area. As in the previous example, how a swimming pool is categorized should be decided early in the data collection process.

Wetlands and Private Lakes

Another policy issue to consider is that of private lakes and wetlands on private property, especially agricultural land uses. This issue is not as important to city governments as it is to county governments and to those that choose the reference area to be a combination of pervious and impervious areas. The issue is that private lakes and wetlands do allow rainfall to collect and eventually infiltrate to the ground; however, during certain rain events, they can discharge stormwater directly to ditches and canals that are owned and operated by the municipality. Should these lakes be considered impervious areas or pervious areas?

There are a few factors that argue in favor of private lakes and wetlands being pervious areas. First, by their nature, they cannot be developed further such that water quantity increases or stormwater quality decreases. Second, such lakes and wetlands do provide a measure of stormwater treatment by mechanical (settling), chemical (transformation), and biological (uptake) means. Therefore, the creation and maintenance of private lakes and wetlands should be encouraged. For these reasons, most stormwater utilities in Florida do not consider private lakes and wetlands to be impervious areas.

Rights-of-Way

Another type of area that is difficult to classify is a right-of way (ROW). For the purposes of this chapter, a ROW includes residential streets and roads, and other public roads (city, county, state and interstate). A ROW is clearly impervious and contributes stormwater to the municipal stormwater management system. On the other hand, many times the municipal stormwater management system discharges excess stormwater to the ROW and the ROW transports and stores rainwater (flooding in streets). Should ROW be included in the impervious area calculation?

Private roads and streets (e.g., internal roads in a mobile home park) which are neither owned nor maintained by the municipal government discharge to the municipal storm sewer system and act, for all practical purposes, like other impervious areas within the parcel. For this reason, most municipalities count private roads as impervious areas in the utility fee calculation.

Residential streets and other public roads can convey stormwater runoff to attenuation and treatment facilities and provide storage of runoff. State and interstate transportation systems are also constructed with a high drainage and stormwater quality level of service, and in some cases, accept runoff from municipal stormwater systems. Therefore, most if not all stormwater utilities adopted in Florida do not include public roads (ROW) as impervious areas to be included in the stormwater utility calculation. In essence, the ROW is considered part of the stormwater management system that is paid for by separate funding methods (e.g., gas taxes).

Land Use Factors

The final issue related to impervious and pervious areas is land use factors. In an attempt to minimize the data collection effort to generate stormwater utility fees, stormwater utilities can employ land use multipliers or factors that define the percent imperviousness of property depending on general land use types. For example, all commercial properties would be assigned an intensity of development factor of 0.7 because, on the average, commercial land uses are about 70% impervious. All properties with the same land use then would be assigned imperviousness with the same factor defined by ordinance. Therefore, the only data needs would be the total property area for the customer. According to the 1997 FASU Stormwater Utility Survey, only one community in Florida uses this method.

5.2.3 Vacant Property

Most stormwater utilities in Florida divide properties into at least two categories: developed and undeveloped. At first glance, these categories appear easy to distinguish. However, vacant lands can often get confused with undeveloped lands, so policy definitions are needed. For the purposes of this chapter, the following definitions will be used:

• "Developed Lands" are properties that have been altered from their natural state for the purposes of urban or agricultural use. General categories of developed lands include residential, commercial, industrial, institutional, agricultural, and governmental. Some stormwater utilities simplify this definition even further by defining developed lands as ones with impervious areas.
• "Undeveloped Lands" are properties that have not been altered from their natural state.

The definitions provided are consistent with many of the stormwater utility ordinances adopted in Florida and make a distinction between undeveloped lands and vacant ones. Vacant lands have developed land uses but there are no tenants. In the case of a utility fee that is sent to the tenant, this definition is important. In the case of an assessment that is sent to the owner, the definition is not important since the owner pays the bill whether there is a tenant or not.

Vacant versus undeveloped property is an issue related to data collection for the utility billing database because undeveloped and vacant properties can constitute 10% of the number of parcels to be considered. Therefore, a policy regarding undeveloped and vacant properties must be developed prior to initial billing. Some data may be collected first to help consider the policies. The vacant and undeveloped parcels are considered further below.

Developed But Vacant Parcels

As indicated above, the importance of vacant parcels depends on the type of funding program provided by the utility. A stormwater assessment is billed to the property owner so issues regarding tenants are not important. A stormwater user fee is normally billed to the tenant, so vacancy issues may be important. In both cases, whether the reference area is impervious area alone or is a combination of impervious and pervious area, is also important. Three types of vacant properties are discussed in this section:

1. Vacated Tenant - Property which has been developed (i.e., has impervious area) is considered vacant if no tenant is present. Because the property is developed, runoff exits the property whether the tenant is present or not. For a user fee, especially those billed in association with other utilities such as water or wastewater user fees, the absence of a tenant usually means the absence of other utilities. For administrative ease, most stormwater utilities do not send a separate bill for the stormwater user fee when no other utility bill is sent. However, this is a policy decision that must be considered as the stormwater utility fee database is being prepared.
2. Seasonal Customer - Another type of developed property that may be vacant has seasonal tenants. In Florida, this is very common, and seasonal changes in utility service needs can be significant in some communities. These customers should be addressed in the same manner as other utility customers during the vacated period.
3. Platted but Vacant - Finally in some communities, especially in south Florida, many parcels of land have been platted and infrastructure installed, yet they have never been fully developed. These lands have been significantly altered from their natural state and are developed, and municipal governments have to maintain the infrastructure. Therefore, these properties receive stormwater management services even though there are neither buildings nor tenants present. A policy for these types of parcels should be developed using specific information on a sample set of such parcels.

Undeveloped Properties

Undeveloped properties do not have impervious areas and have not been altered from their natural state. If the reference area includes impervious areas only, then undeveloped properties simply have to be identified in the utility billing database but no additional information is required. If the reference area includes pervious area as well, then total parcel area must be defined for each undeveloped property. It should be noted that undeveloped properties receive little or no benefit from a normal stormwater management program, and they also provide infiltration and recharge benefits to the municipality. This means that great care should be taken in assessing undeveloped lands a utility fee or assessment.

5.2.4 Agricultural Lands

Agriculture is the last category of land use that affects the development of the stormwater utility database and how the data are collected. Agricultural lands vary in uses including cropland, timberland (silviculture), grazing lands, orchards, dairies and feedlots, and nurseries. Generally, agricultural lands have small impervious areas and large pervious areas. Water use is usually controlled since water and pumping costs reduce profits. For agricultural lands other than for grazing, property can be altered from its natural state to improve drainage and irrigation, and many agricultural uses require pesticides and fertilizers to increase crops. Pesticides and herbicides can be carried by runoff to potentially impact surface waters. Sediment loads from agricultural lands can also be significant. Furthermore, some types of crops (e.g., strawberries) require temporary cover: aerial photographs appear to show significant impervious areas, yet rainfall is retained onsite. On the other hand, stormwater management programs generally do not provide agricultural lands with significant service since the rural stormwater system requires minimal maintenance. Because of these issues, some stormwater utilities charge agricultural lands a user fee or assessment and some do not, regardless of the choice of reference area.

How agricultural lands are to be addressed in the stormwater utility should be decided early in the database development process. In very urban environments (e.g., cities), agricultural lands are not significant so inclusion or exclusion generally does not affect utility revenues. For counties, on the other hand, rural lands can be significant in size but are generally few in number. Because the quantity and quality of runoff from agricultural lands varies during the year and depends on the current crops, some municipalities have chosen to collect detailed information on agricultural lands, such as types of crops, seasonal rotations, soils, water use and drainage, grazing lands, and pesticide uses, to name a few. An understanding of the agricultural practices (e.g., irrigation and best management practices) is important to consider whether agricultural areas discharge at all. In areas where water quality is important and agricultural lands significantly affect runoff quality, such information can be useful for a stormwater utility. However, detailed information can require significant administrative costs to collect and maintain.