Achieving higher density development in areas without public water or sewer service presents special circumstances and unique challenges. Conventional septic systems require permeable soils, adequate depth to groundwater and numerous setbacks to lot lines, drinking water wells and wetlands. These physical and regulatory requirements can preclude the clustering of development. However, there are also a number of technological and regulatory opportunities to address these challenges. They include shared systems (multiple homes on one septic system), innovative and alternative septic systems, and small sewage treatment plants. Careful site planning using techniques such as Open Space Residential Design (OSRD) and Low-Impact Development (LID) can identify and set aside optimal locations for wastewater facilities and drinking water sources, thereby allowing the remaining land to be developed at a higher density.
Many of the smart growth techniques, including those that apply to rural areas, rely upon concentrating growth in higher-density configurations, such as a village or town center, and concurrently relieving development pressures in outlying areas that deserve preservation. Challenges to achieving this type of development pattern in rural areas often include wastewater treatment and disposal constraints, especially for on-site systems. There are also many existing small (non-conforming) lots along late shorelines that cause water quality problems.
In areas without existing public sewer service, wastewater options are commonly limited by low-permeability soils, shallow depths to groundwater and bedrock, and proximity to wetlands and other natural resource areas. Other common obstacles are cost and management structures. The unit costs of small wastewater treatment plants are significantly higher than standard septic systems and commonly become affordable only at higher densities. Shared sewage disposal systems and wastewater treatment plants also require a more elaborate management system to provide ongoing operation, maintenance, and repair. A condominium style legal agreement is typically necessary to provide this required management.
Properly planned and designed infrastructure can provide significant opportunities to create higher-density developments with less environmental impacts and more open space preservation. Through increased densities and enhanced real estate values, wastewater treatment plants can be cost-effective. Both shared systems and wastewater treatment plants offer the advantage of needing only one location for disposal rather than one for each dwelling unit or lot. Furthermore, the use of wastewater treatment facilities can significantly reduce the area requirements for the ultimate disposal of treated effluent.
Regulations and Policies
Two primary sets of regulations govern sewage disposal in Massachusetts: Title 5 and the Groundwater Discharge Permit Regulations. There are also a series of important wastewater policies that apply to facilities regulated under the Groundwater Discharge Permit program.
The State Environmental Code, Title 5 (310 CMR 15.000): Title 5 governs systems with design flows less than 10,000 gallons per day (the equivalent of approximately thirty 3 bedroom units or 200,000 square feet of retail space). Design flows are calculated according to a schedule that includes 110 gallons/day per bedroom for residential projects. Title 5 is administered by local Boards of Health and includes required minimum setbacks (such as 50 feet to wetlands and watercourses), requirements for suitable soils, and minimum depths to groundwater (four or five feet to the maximum groundwater elevation, depending on the soil type). The regulations also specify the engineering design requirements for the system components, as well as the soil and hydrologic testing needed to prove a complying system can be constructed on a site.
Title 5 also provides for the utilization of innovative and alternative septic technologies. A range of technologies has emerged that provide enhanced treatment (removal) of nitrogen and other pollutants associated with sewage. Consequently, they allow for higher densities of development than those supported by standard Title 5 systems, without increasing negative water quality impacts. Some alternative components allow a smaller footprint for the system, providing applications for new construction or upgrades on small village-scale lots.
The Groundwater Discharge Permit Regulations (314 CMR 5.00): These regulations govern wastewater treatment systems with design flows of 10,000 gallons per day or greater and are administered by the Massachusetts Department of Environmental Protection (MassDEP). The local Board of Health does not permit a system of this size unless they have a local health regulation that allows this to occur.
The state-level regulations require significant analysis of a proposed discharge site to insure the treated effluent will not create a public health or environmental nuisance in the future. This includes testing the suitability of subsurface soils, mapping groundwater flow, and identifying downgradient impacts including the cumulative impacts to drinking water supplies and coastal embayments. They also require an applicant to submit a fully engineered design for the disposal facility and an engineering report describing the overall design of the treatment facilities. Treatment plant designs must comply with MassDEP's Guidelines for the Design, Construction, Operation, and Maintenance of Small Wastewater Treatment Facilities with Land Disposal (MassDEP publication, April 2004).
Wastewater Reuse Policy: MassDEP has developed interim guidance for reuse of reclaimed wastewater, consistent with United States Environmental Protection Agency Guidelines. Allowable uses for reclaimed water in Massachusetts include golf course irrigation, landscape irrigation, toilet flushing, and aquifer recharge. Water must be treated to a high quality to meet reuse standards. There are specific standards for reuse water infrastructure as well as requirements for public notification. In addition, a wastewater facility constructed for water reuse must provide a full-sized disposal facility as a backup to the reuse option. This duplication of facilities has limited the use of reclaimed water and is being investigated as part of ongoing development of new reuse standards by MassDEP.
Nutrient Loading Approach: The Nutrient Loading Approach was established by MassDEP in 1999 to allow a property owner to utilize on-site septic systems in lieu of a wastewater treatment facility if certain water quality standards are met. The policy designates nutrient sensitive areas such as Zone II wellhead protection areas, coastal watersheds, and watersheds to freshwater ponds. It then sets performance standards that must be met on the property to protect these resources, including a site-wide nitrogen loading requirement to meet an average concentration of 5 mg/L in groundwater underneath the site. This policy provides flexibility in using on-site septic systems versus a centralized package treatment facility if these water quality standards can be met.
Private Sewage Treatment Plants For Multiple Lot Residential Developments: In 1999, MassDEP allowed the use of wastewater treatment facilities shared by residential properties on fee simple lots. The policy specifies the legal, institutional and financial requirements for individual homeowners to share a common wastewater facility. It also requires that the water quality standards of the Nitrogen Loading Policy be met for a facility to be approved.
Total Maximum Daily Loads (TMDL): Streams lakes and coastal estuaries are biologically productive water bodies and are very sensitive to pollutant additions from sewage-derived sources. Nitrogen concentrations well below the national and state drinking water standard of 10 mg/L can trigger algae blooms and fish kills in coastal waters. In some areas concentrations at or below 0.5 mg/L have been shown to cause eutrophication in coastal waters. Therefore, scientific studies are being conducted to determine the total maximum daily load (TMDL) of each estuarine system. These TMDLs will then be used to set standards for wastewater discharges within these coastal watersheds, likely requiring the connections to centralized facilities for many properties within the watershed currently using on-site septic systems. Similarly, lakes and ponds can be damaged by excessive amounts of phosphorous. TMDLs for phosphorous need to be established and wastewater treatment systems need to be considered to address this issue.
Wastewater Management Options
The options for managing wastewater can be divided into three groups based on their size, and the regulatory programs that govern their design and operation. They are:
- On-site septic systems for individual houses or commercial properties regulated under Title 5;
- Shared or cluster systems serving up to 20-30 residences, also regulated under Title 5; and
- Larger wastewater treatment systems regulated under the state’s Groundwater Discharge Permit program.
The potential for each of these wastewater options to support higher density developments varies. There are also differences in the water quality impacts of each approach along with variations in cost for both construction and operation and maintenance. These are described below.
On-site septic systems:
The use of on-site septic systems is commonplace in rural and suburban areas of Massachusetts. They typically consist of a septic tank that separates the solids and floatables from the liquid effluent. The effluent then flows through a distribution box to a leaching facility where it infiltrates into the ground and eventually mixes with the underlying groundwater. Little treatment of the effluent occurs before it reaches groundwater. Bacteria is removed through filtration in the subsurface sediments between the leaching facility and groundwater. However, nitrogen, phosphorus, household hazardous wastes, and viruses are not attenuated in an on-site septic system and may pose a threat to nearby private or public wells, fresh water ponds, or coastal embayments.
The typical four-bedroom home requires an area of approximately 3,900 square feet to construct a Title 5 system that meets all the appropriate property line and building setbacks, provided reasonable soils exist at the site. For a three-bedroom home, the area needed is about 3,300 square feet. In many historical villages, it may be difficult to comply with these space requirements for upgrading existing facilities. Sizing requirements can also limit the ability to create new small lots to match historical building patterns in Massachusetts villages.
The ability to site a system can also be affected by the need to meet setbacks to private wells (100 feet), and wetland resource areas (50 feet). Many towns have increased these setbacks through local health regulations and/or wetlands protection bylaws. In addition, the depth to groundwater and the permeability of the soils on a given lot will affect the ability to construct or upgrade a system. With tighter soils, the sizing estimates given above for typical bedroom counts can increase by 70% to 100%.
The density of development served by on-site systems is carefully controlled to protect groundwater quality in nitrogen sensitive areas which Title 5 defines as Zone II Wellhead Protection Areas, and Interim Wellhead Protection Areas. Those lots served by both a private well and a septic system while not defined as nitrogen-sensative areas, are subject to the same nitrogen loading limitations. MassDEP has reserved (but not acted upon) the ability under Title 5 to designate nitrogen sensitive embayments as nitrogen sensitive areas. However, MassDEP will likely manage wastewater disposal in these areas through the TMDL process mentioned above.
In a nitrogen sensitive area, the density of development is limited to a design flow of 440 gallons per day of effluent discharge for each builder's acre, or 40,000 square feet. This translates to a four-bedroom home on 40,000 square feet. If an approved alternative system is used to provide additional treatment of wastewater prior to discharge, the density can be increased to 660 gallons per day per 40,000 square feet. This translates to six bedrooms to the acre, or a three-bedroom house on a half-acre.
The use of on-site systems in a higher density development can be optimized by considering how wastewater effluent moves through groundwater. This allows planners to design a community to minimize conflicts between septic system effluent and nearby water resources. The Town of Nantucket has a private well regulation that requires developers to locate proposed well and septic system locations on a plan prior to subdivision approval. They must show that the private wells are upgradient of proposed septic systems so the plume of effluent from the septic system will not impact drinking water quality (Figure 2 - Nantucket Private well site plan graphic). This regulation has protected public health in the areas of Nantucket outside the main towns, while still allowing cluster development on small lots, preserving the historical character of the Island.
Septic systems require periodic inspection and maintenance to insure their performance. Systems should be pumped every two to three years to remove accumulated solids so they do not clog the leaching facility. This maintenance averages about $100 per year for a typical residence and is much less intense and costly than that required for larger treatment facilities. A full inspection is required at the time of a property transfer following specifications contained in Title 5.
Finally, as mentioned above, Title 5 does allow for the use of alternative systems to improve the quality of discharged effluent and allow for increased density. Increased density is allowed in nitrogen sensitive areas with alternative systems. Reductions in leaching facility size can also be accomplished on Remedial Use Systems, and in some cases with alternative systems, allowing smaller systems on constrained lots. Many of these approved systems, however, are designed to perform upgrades to existing systems where compliance with current Title 5 regulations is difficult without an alternative system. The use of individual alternative systems throughout a community or neighborhood as a tool to increase density may or may not be the most cost effective approach, as will be explained below. This is a function of both the added cost of the alternative system components and the additional maintenance and sampling requirements for these systems which may be cheaper to maintain if a system is shared between properties compared to each property taking care of its own. A full listing of the approved alternative systems under Title 5 can be found at the end of this section.
Shared or Cluster Systems:
Title 5 allows the use of shared systems for upgrades of existing facilities as well as for new construction. The use of shared systems in cluster developments has been encouraged through recent changes to Title 5, promoting conservation design and smart growth principles. The use of shared systems can be cost effective in comparison to individual on-site systems when alternative treatment is used in nitrogen sensitive areas. They can also be used in higher density areas where the location of individual leaching areas is impractical. Shared systems are approved by the local Board of Health; however, the approved design must then be submitted to MassDEP for review. MassDEP can approve the application, request modifications, or supersede the local board and deny the application.
A shared system is a traditional septic system that is used by two or more adjacent properties. With the exception of cluster developments, applicants proposing a shared system for new construction must prove that each lot connecting to the system can support a complying Title 5 system of their own. The 2006 changes to Title 5 remove this requirement for cluster developments that comply with local cluster bylaws adopted under M.G.L. Chap. 40A, Sec 9, or that provide 50% of the site as permanent open space. This provides flexibility to design a site to promote conservation design, especially on sites with shallow depths to groundwater or with areas of poor soils on a portion of the site that make it difficult to prove each individual lot can support its own system.
The minimum lot size for a property in a cluster development using a shared system does not have to be controlled by the septic system design as the system can be located on its own separate lot. As such, the density is controlled by the local zoning and subdivision codes. It should be noted that a shared system permitted under Title 5 cannot exceed a design flow of 10,000 gpd. Therefore, for a community of four-bedroom houses, approximately 22 homes can share a system. Up to 30 three-bedroom homes can share a system. If the system is in a nitrogen-sensitive area, a nitrogen agregation plan may apply.
To give an example of increased density with a shared system, consider a 30-acre parcel where the local zoning has a one-acre minimum lot size as a base requirement. If the development of thirty homes is clustered on 0.25-acre lots with a shared system, the development only requires 7.5 acres of land (plus some area for roads, wastewater disposal, and drainage facilities). In this manner, over 50% of the lot area can remain undeveloped. In this case the leaching field would be approximately 13,400 square feet in an area with permeable soils.
Title 5 has specific legal and institutional requirements for shared systems to insure they are operated properly and to insure the Board of Health or Department of Environmental Protection can step in to fix a problem that is a threat to public health or the environment. These include the requirement to register a Grant of Title 5 Covenant and Easement on the deed for the properties sharing the system. This easement gives the Board of Health or MassDEP the right to enter the site to fix problems associated with the facility, and also sets out the operation and maintenance requirements for the system users. It also requires a financial assurance mechanism, such as an escrow account or letter of credit that can be accessed by the approving authorities if they need to repair the system.
The use of a shared system provides some flexibility in how a leaching field is located in order to protect sensitive water resources. Depending on site conditions, it may be possible to site the facility so it is outside a nitrogen sensitive area (such as a Zone II). It is also possible to maximize setbacks to wetlands and surface waters to protect against phosphorus and pathogen transport. The siting of one shared system (instead of multiple individual systems), has the added advantage that the minimum required setbacks only have to be met once, at one location.
The addition of "innovative and alternative" treatment technologies is also more efficient in comparison to systems serving individual homes. The requirements for operation and maintenance of a shared system are not significantly different then that for an individual home system if both contain alternative treatment. There are the same requirements for system inspections, sampling, and reporting, such that cost savings can be achieved with the shared system. The ability to provide backup power to allow the system to operate during a power outage is also enhanced with a shared system.
However, many towns have legitimate concerns about the long-term operation of shared systems, especially those that include alternative treatment components. They question how well systems will be maintained, what treatment levels can be reasonably obtained and how systems will be managed if water quality goals are not met in the future. In an attempt to address these concerns, the Barnstable County Health and Environmental Department has begun collecting system performance data through the web-based database where system operators input information on the performance of the system. It also tracks compliance with required operation and maintenance activities. In other cases, municipalities have opted to take over the ownership and maintenance of these systems.
Wastewater Treatment Plants:
Any system that exceeds a discharge volume of 10,000 gpd requires treatment beyond that of an on-site or shared system and must be permitted through the Groundwater Discharge Permit regulations (314 CMR 5.00). Advanced tertiary treatment is necessary with the effluent meeting strict standards for nitrogen (10 mg/L) suspended solids and biological oxygen demand. The design of the facility, especially the disposal facilities, is closely reviewed by MassDEP and ongoing oversight by a certified operator is required.
The use of a wastewater treatment plant expands the options for higher density development as lot sizes are not controlled by the need to provide an on-site septic system. Instead of wastewater as a control, density is determined by local zoning and subdivision rules and regulations, providing flexibility in design and land use management.
The leaching field area requirements for wastewater treatment plants is significantly less compared to Title 5 systems due to the higher treatment and removal of solids that could otherwise clog leaching facilities. Disposal is often managed through subsurface trenches or fields or through open infiltration basins. With good soils, the infiltration rate can be up to six times faster than that for a Title 5 system, requiring significantly less land for the disposal facility.
There are two primary issues to consider with the use of a centralized treatment plant: cost and wastewater disposal constraints. New treatment plants are expensive to construct, upgrade, and maintain. As explained in the cost section below, the key to making a treatment plant affordable is to maximize the number of users to lower the capital cost as well as long-term operation and maintenance costs for those using the facilities.
However, the greater the number of users, the higher the flow through the plant and the greater potential for environmental conflicts in locating and designing an appropriate wastewater disposal site. There are two facets to this issue: the ability to transmit water into the ground (as permitting for surface water discharges is extremely difficult) and the impacts of the discharge on downgradient wells, wetland, and surface waters.
A wastewater disposal site must contain permeable soils with a sufficient depth to groundwater to accommodate the mounding of the water table that occurs as the effluent discharges into the ground. The presence of tight soils such as silt and clay or bedrock (ledge) can make it difficult to dispose of effluent properly. The depth to groundwater in low-lying areas such as floodplains or near large wetland complexes can also make it difficult to achieve the proper four to five foot separation between the system and the water table. Wastewater-reuse options, such as for irrigation or toilet flushing, can mitigate disposal issues. Although for many of these options a facility still must be able to permit and build a fully sized disposal system in case the reuse option becomes unworkable in the future. MassDEP is in the process of updating the current wastewater reuse policies and these may provide greater advantages in the future.
Impacts to water resources must be considered in designing a treatment plant. For new construction, one must consider how the effluent plume from the plant will affect downgradient wells and surface waters. A treatment plant discharge must be separated from a public supply well by a distance equal to a two-year time of travel for groundwater. If groundwater is moving at an average speed of one foot per day (typical of sandy soils), a treatment plant discharge must be a minimum of 730 feet from the well. Issues with phosphorus loading to fresh water systems downgradient of a discharge must be considered as phosphorus will move readily in a larger effluent plume.
Finally, in watersheds to coastal embayments, the nitrogen in discharged effluent can be of great concern. While the drinking water standard for nitrogen is 10 mg/L, coastal embayments suffer if nitrogen concentrations exceed 0.35 mg/L. As an example, the wastewater treatment plant for the Town of Falmouth must meet a 3mg/L discharge limit for nitrogen such that the overall nitrogen loading within the watershed will stay below a limit needed to protect West Falmouth Harbor. New facilities in coastal watersheds are facing similar discharge standards. In addition, facilities being designed to replace on-site systems in these watersheds will likely need to meet similar standards.
Given the strict nitrogen standards being developed for these watersheds, the use of a wastewater treatment plant may be the only option for management of a high-density development, as on-site or shared systems may not provide the necessary level of treatment.
Wastewater Facilities Management:
The management options for wastewater facilities of any size will depend on whether they are privately or publicly owned. These management structures are typically used for centralized facilities but have been used for the management and oversight of individual on-site systems as well. Examples include Block Island, Rhode Island and Orange County in North Carolina.
The ultimate cost of any sewage treatment or disposal system is very site specific and can be expensive in areas where the presence of poor soils, ledge, or shallow depths to groundwater complicate the system design. The installation of clean fill to replace low permeability silts or clays will raise construction costs. A mounded system, sometimes built with retaining walls to support the raised system may be needed to meet the minimum vertical separation distance between the leaching field and the water table, and this can add cost as well. Setting these site-specific constraints and associated costs aside there are some general cost patterns associated with the various sewage disposal options.
Standard Title 5 systems in suitable soils can generally be constructed for $5,000 - $10,000 per dwelling unit. A typical lifespan for a standard Title 5 system is 20-50 years.
Innovative and alternative systems utilize the standard system components and add specific treatment components to treat the effluent or reduce the size of the required leaching facility. In suitable soils, they can be typically constructed for $13,000 - $18,000 per dwelling unit, or about $8,000 more than a standard Title 5 system. Operation and maintenance costs are approximately $500 to $1,000 per unit for an individual system with the range depending on the water quality testing needed and the electrical costs for system operation. For a shared system, the construction costs are somewhat less than conventional individual septic systems ($5,000-$10,000 per dwelling unit) and the operational costs can range from $3,000 - $5,000. This cost can be allocated between as many as 20-30 residential units depending on the system design, reducing the annual cost to about $150-$200 per home.
Please be aware that other factors may affect annual cost. When a shared system exceeds 10,000 gallons per day, and a groundwater discharge permit is required, operating expenses and testing mandated by the Department of Environmental Protection will increase the annual cost per home. Also, the removal of total nitrogen to less than 3 mg/l, as required in some coastal estuaries, can add to both capital and operating costs.
Centralized wastewater treatment facilities serving smaller rural or suburban areas have been shown to cost between $30,000 - $60,000 per dwelling unit. The cost is dependent on the type of treatment system, the water quality requirements for the system, the distance between homes, and the resulting collection system expense. However, if used in a cluster or village setting, the collection system costs can be reduced. In addition, the greater number of units connected to the system the lower the per-unit cost. When one combines the wastewater treatment costs with the higher densities achievable through enhanced treatment and land costs, the benefits of clustered developments with sewage treatment become apparent. The following table provides an illustration of this cost analysis. For the purposes of comparison, a range of land values is presented ($50,000 - $300,000 per acre).
Wastewater Treatment and Smart Growth
When examining the relationship between wastewater management and smart growth, several common themes emerge:
- Standard Title 5 systems are often the preferred approach to on-site wastewater management because the permitting process is faster and the technique is more predictable.
- Without broader community-based planning efforts, it will be difficult to establish the patterns of development, the administrative capacity and the funding mechanisms often necessary to move away from a standard Title 5 approach.
- Without serious outreach (such as increased density) to the development community, we are unlikely to reverse the current trends toward "cookie-cutter" wastewater management.
For those communities with or without existing centralized wastewater infrastructure, creating new, or re-invigorating older, walkable neighborhoods requires a thoughtful approach to wastewater management. Several steps a community can take to assist in encouraging more centralized approaches include:
- Develop a Comprehensive Wastewater Management Plan
As a stand-alone document or as part of a larger Comprehensive Plan, comprehensive wastewater planning is an integral component of a local smart growth program. Among other items, these plans will help to delineate growth center boundaries, lay the ground work for Transfer of Development Rights (TDR), help to shape Open Space Residential Design (OSRD) and provide the foundation for significant environmental benefits. The essential sections of a Comprehensive Wastewater Plan include:
- Maps of growth centers, preservation lands and transitional areas between the two;
- A detailed discussion of the types of wastewater management strategies applicable to the community’s housing, environmental, fiscal and commerce-related goals;
- A discussion of the different densities of development that will occur within and surrounding identified growth centers;
- An examination of the community’s administrative capacity with regard to permitting innovative systems and/or establishing wastewater authorities;
- Cost estimates associated with construction, permitting, design, administration and maintenance of any intended public facilities;
- Identification of any existing bylaws or regulations that would conflict with the intended wastewater strategies; and
- Identification of any public funding opportunities associated with infrastructure development or financing.
- Identify Larger Projects as Anchor Opportunities
Communities in which a larger development project is being proposed may have an opportunity to leverage this investment toward a more inclusive wastewater service envelope. Due to the level of initial investment being provided by a third party, a local officials may be able create a public/private partnership to help service surrounding properties with a slightly larger system than what would be needed for the expanded project alone.
- Identify and Procure Sources of Public Funding
Certainly an important consideration to establishing any public wastewater facilities is cost to the municipality. When considering a public-based approach to more centralized sewer development, communities should investigate opportunities for state-level funding including those administered by the Executive Office of Housing and Economic Development. Specifically, District Improvement Financing (DIF), the Community Development Action Grant Program (CDAG) and the Public Works and Economic Development Program (PWED) could provide financial assistance communities wishing to make a large-scale investment in new or existing wastewater infrastructure.
- Use Innovative Financing Mechanisms
Outside of the DIF program mentioned above, Massachusetts legislation also allows for site specific tax incentives to be implemented by local governments. Most notable in this approach is the Tax Increment Financing (TIF) mechanism. Also of interest is the Chapter 40R program which is designed to provide cash to communities looking to create higher density developments. The cash incentives provided to local governments could be used to help pay back investment in wastewater infrastructure.
- Provide Density Incentives Where Appropriate
Planning for more compact patterns of development generally includes the identification of one or more growth centers or village in a community. Depending on the densities communities are comfortable with allowing, incentives could be included for developers willing to use more centralized wastewater approaches. This strategy may be particularly effective in smaller suburban or rural settings where village centers could operate on a single or several "neighborhood-scale" treatment plants.
- Be Aware of TMDL Programs and Nitrogen Sensitive Areas in Your Community
State and federal programs continue to study and place legal limits upon loading/discharging into water bodies and natural resource areas throughout the Commonwealth. As Nitrogen Sensitive Areas continue to be identified and TMDL allocations continue to be established, local authorities will need to be aware of their obligations and the potential leverage these standards will provide toward more advanced forms of wastewater treatment. Issues of environmental protection and existing regulatory programs are rapidly creating awareness within the development community that more compact forms of development are more environmentally friendly and can also be more profitable.