Distributed Wastewater Management for Small North Carolina

DISTRIBUTED WASTEWATER MANAGEMENT FOR SMALL NORTH
CAROLINA COMMUNITIES
Victor D’Amato, PE, Tetra Tech, Inc., PO Box 14409, Research Triangle Park, NC 27709. (919) 485-2070.
[email protected]
ABSTRACT
Distributed wastewater management relies on the optimum combination of decentralized and centralized system
components for addressing the wastewater management of a service area. Many rural and exurban North
Carolina communities rely on individual subsurface soil absorption systems (septic systems) for the bulk of their
wastewater treatment needs. These septic systems have sometimes been implicated as reasons for water quality
degradation and a historical lack of proactive management has sometimes resulted in system malfunctions,
creating financial hardships – as well as potential health hazards – for homeowners.
A distributed approach to wastewater management looks at the full complement of options for serving a
community. In many small communities, lot density is not sufficient to make centralized sewering financially
feasible. This presentation will report on the results of several recent studies looking at the use of decentralized
alternatives where more traditional centralized service options were considered. These decentralized alternatives
include cluster systems with advanced treatment, enhanced management of individual system and traditional
water/sewer utility managed systems. The results of a recent Water Environment Research Foundation project
that evaluated 20 case studies will be presented along with a more local example where a small disadvantaged
community in Northeastern North Carolina is pursuing affordable decentralized systems for meeting the needs of
their residents.
Keywords: wastewater, decentralized, distributed, small community, water reuse.
INTRODUCTION
The manner in which the collection, treatment, and product management components of a wastewater system are
arranged within a given service area is sometimes called the system architecture. System architecture has a
profound but largely overlooked impact on system performance across a range metrics of importance to small
communities, including capital and recurring monetary costs.
Traditional system architectures, particularly in urban and suburban areas, rely on expansive wastewater
collection and conveyance systems feeding a centralized treatment facility. Alternative architectures are
developing for more efficient and effective wastewater management. These architectures combine traditional
centralized and new uses of decentralized system infrastructure in an approach termed distributed management.
Distributed water infrastructure systems are emerging in rural, suburban, and urban communities across the
United States and abroad. Communities are recognizing that these strategies—which integrate water
management at the individual site scale, to residential neighborhoods and small communities, to an entire
watershed or region—are more efficient and effective across a triple bottom line of environmental, social, and
economic considerations.
The research project, When to Consider Distributed Systems in an Urban and Suburban Context, analyzed 20
case studies where distributed approaches are being used to provide integrated water services across a range of
community-specific situations and management frameworks in the United States and Australia. This project was
sponsored by the Water Environment Research Foundation (WERF) and the National Decentralized Wastewater
Resource Capacity Development Project (NDWRCDP) to help planners, utility managers, engineers, developers,
regulators and other decision-makers determine whether they should consider using a distributed approach in
areas where users might normally be served by centralized systems.
DISTRIBUTED WASTEWATER MANAGEMENT
Distributed Wastewater Management for Small North Carolina Communities
Managed distributed infrastructure incorporates both decentralized and centralized elements to most efficiently
provide water-related services to users. The concept of distributed infrastructure as a key element of sustainable
water management has been embraced in the stormwater sector, where control – and often beneficial reuse – are
implemented close to the source using low impact design principles and various best management practices. For
wastewater systems, distributed management uses smaller-scale systems within more centralized management
frameworks. This involves integrating a range of system scales from onsite or onlot to cluster to regional to
centralized (Figure 1).
Figure 1. Distributed Wastewater Management Continuum.
An obvious advantage of decentralization is the proximity of systems to wastewater sources and reuse areas
(Figure 2) which minimizes or precludes energy inputs for conveyance. Distributed management has particular
advantages for small communities in North Carolina, where more densely developed “main street” and crossroads
areas lend themselves well to large cluster and semi-centralized systems while less dense areas can rely on
small clusters and managed individual onsite systems. Benefits of distributed wastewater management include
affordability and the ability to phase in system capacity as funding becomes available, the potential for water
reuse and resource recovery, and energy efficiency.
Figure 2. Distributed Management Versus Traditional Sewer Extension.
Infrastructure Funding
Traditional infrastructure projects are often characterized by large sunk costs. The financing and debt service
associated with these projects can be crippling to communities, particularly if projected revenues are not realized,
because, for example, an economic downturn slows or stops growth. The use of a distributed infrastructure
approach, by contrast, allows for a variety of adaptive funding approaches, such as systems funded by
developers that then turn them over to a utility for operation. Underserved communities can phase the installation
of systems, prioritizing the areas of greatest need as grant funding or slowly developing revenue streams become
available. Rapidly growing communities can increase treatment capacity by adding treatment modules to existing
systems or new cluster systems as demand increases. State and federal clean water funding specifically
Distributed Wastewater Management for Small North Carolina Communities
recognizes and includes decentralized wastewater systems in the 20% Green Project Reserve which is set aside
for environmentally superior projects.
Resource Recovery
Source control – for example, the separate management of graywater, blackwater, and even yellow-water or urine
– is more viable at decentralized scales, helps conserve energy associated with treatment, and facilitates
resource recovery and reuse. Distributed approaches help leverage the connections and synergies between land
use and water management and to close the loop on waste-related resource cycles. Rural communities can use
one of their greatest resources – land – for wastewater treatment, rather than costly mechanical treatment plants.
Doing so recharges aquifers rather than discharging to surface waters and helps restore the natural water cycle
and heal degraded hydrologic function. Recycling nutrients in wastes can support agriculture and food production
while recovering energy from waste helps offset imported sources.
Efficiency
Distributed systems can provide great efficiency advantages over traditional approaches. First and foremost treatment closer to the source and/or reuse area requires less energy for conveyance. Properly implemented,
decentralized reuse technologies can be very efficient as well. Table 1 provides power requirements for common
unit processes used in decentralized wastewater treatment and reuse systems. Table 2 presents operational
power requirements for various types of decentralized reuse systems based on the data in Table 1. The model
decentralized systems range from standard aquifer recharge systems to advanced attached growth-disinfection
systems capable of meeting stringent effluent quality requirements for unrestricted reuses. These power
requirements compare favorably with power requirements for traditional centralized systems. For comparison,
energy requirements for wastewater collection, treatment and discharge/recycling in California have been
estimated to range from 1,500 to 5,800 kWh/MG treated (CEC, 2005).
The model decentralized systems benefit from relatively short conveyance distances, requiring little or no energy,
along with low-energy treatment systems; for example, highly effective recirculating filters and soil dispersal
systems generally require no forced aeration to effectively treat regular-strength wastewater to reclaimed water
quality. Embedded and secondary energy impacts of decentralized reclamation and reuse approaches, while
highly context specific, are believed to have significant advantages over centralized approaches, although no
robust evaluations have yet been conducted to our knowledge.
Table 1. Electrical Energy Demand for Unit Processes in 5,000 Gallon per Day Decentralized Reuse Systems
(does not include energy requirements for maintenance activities or incidentals, e.g., lighting).
Unit Process
Gravity Sewer
Septic Tank
Pump Stations
Filter Pumps
Recirculating Filter
Effluent Pumps
UV Disinfection
Drainfield/Reuse
Power
0.0
0.0
1.0
1.6
0.0
1.0
0.3
0.0
Units
kWh/d
kWh/d
kWh/d
kWh/d
kWh/d
kWh/d
kWh/d
kWh/d
Notes
Does not include periodic solids removal
1 hp pump on 1 hr/d, 100 gpm @ 30' TDH (60% efficiency)
1/2-hp recirc. pump on 4 hr/d, 60 gpm @ 20' TDH (60% efficiency)
Passive aeration; all energy associated with filter pumps
1 hp pump on 1 hr/d, 100 gpm @ 30' TDH (60% efficiency)
Sanitron S5000 on 1 hr/d
Passive aeration; energy associated with effluent pumps to pressurize
distribution network
Table 2. Unit Electrical Energy Demand for Model 5,000 Gallon per Day Decentralized Reuse Systems.
System Type
Conventional Gravity Septic System
Pumped / Pressurized Drainfield System
Gravity Collection to Recirculating Filter
Gravity Collection to RF and UV Disinfection
Reuses
Aquifer Recharge
Aquifer Recharge
Irrigation
Unrestricted
Power
0.0
200.0
520.0
580.0
Units
kWh/MG
kWh/MG
kWh/MG
kWh/MG
Distributed Wastewater Management for Small North Carolina Communities
Pressure Sewer to RF and UV
Unrestricted
780.0
kWh/MG
New small-scale technologies are available that use smart control systems for effective remote monitoring of
multiple, dispersed systems; clean technologies to reclaim and recover resources at multiple scales – from
individual sites to neighborhoods; and green systems that mimic natural processes and can be integrated into
landscapes and buildings. The small, shallow collection sewers associated with decentralized systems are much
more infiltration-resistant and robust when compared with traditional collection systems.
Professional Management
Since the release of US EPA’s management guidelines in 2003 (see Table 3), a number of professionally
managed distributed systems have been implemented in communities throughout the United States and abroad.
These systems may consist of individual onsite or onlot systems, cluster systems that serve multiple residences
or establishments, systems serving entire developments or small communities, or a combination thereof. The key
to proper implementation of any combination of decentralized system approaches, however, is a well-defined
management program based on sustainability principles.
Table 3. EPA Management Models
Level I: Homeowner Awareness
• Prescriptive system designs
• Proactive maintenance encouraged through education and reminders
Level II: Maintenance Contracts
• Enhanced treatment on traditional sites
• Required maintenance contracts between owner and operator
Level III: Operating Permits
• Entry to performance-based programs
• Compliance based on performance rather than technology or design
Level IV: Responsible Management Entity (RME) O&M
• Responsibilities given to public or private RME
• Watershed-wide planning
Level V: RME Ownership and management
• Ownership and all management responsibilities with public or private RME
While ensuring adequate and sustained management has historically been a shortcoming of traditional septic
systems, concerted management programs that combine tracking and data management tools with physical
inspections and the use of remote monitoring telemetry have proven that distributed systems can be managed at
an equal or more professional level than can centralized systems. For this rapidly growing sector of the U.S. water
infrastructure industry, both public and private service providers have emerged to fill a critical business market
under a variety of creative structures adapted to the diversity of situations presented.
WERF CASE STUDIES
A recent Water Environment Research Foundation project looked at emerging uses for decentralized systems in
areas typically served by centralized sewers (WERF 2011). The cases studied identified a number of ways that
these distributed approaches are being implemented in communities across the country and around the world.
At the building or site scale, decentralized wastewater reclamation and reuse systems are being integrated into
building and landscape designs, often using multifunctional systems serving dual uses for recreation and
education. A number of small communities have embraced a distributed approach in order to maintain their fiscal
independence (i.e., not connecting to another community’s sewer system) and to preserve the character of the
community by discouraging unplanned development that sometimes comes with a sewer main. And an increasing
number of more traditional water and wastewater utilities are implementing decentralized systems to more
efficiently and effectively delivery service to their customers. This includes:
• Professional management of cluster systems for development outside of the core service area; and
• Sewer mining and satellite treatment systems where decentralized systems are used to provide a
localized source of reclaimed water. These smaller systems are usually physically connected to the main
sewer system for backup and for handling solids resulting from the treatment process.
Distributed Wastewater Management for Small North Carolina Communities
Wickford Village, North Kingston, RI
Substandard septic systems in densely settled Wickford
Village have long been implicated in nutrient enrichment of
adjacent Narragansett Bay. In lieu of connecting to a nearby
state-owned wastewater treatment facility, the town chose to
adopt a decentralized approach to ensure preservation of the
town’s historic character. The Town of North Kingston created
a wastewater management program that requires all
homeowners to regularly inspect and maintain septic systems
and report problems to the town. Repairs and upgrades of
onsite systems with advanced technologies were also
encouraged for homeowners in high-risk areas. Priority areas
were established to better match treatment technology and
grant funding with environmental sensitivity. North Kingston set
up a fund to help property owners pay for required system
improvements, which was initially funded through the Rhode
Island Housing and Clean Water Finance Agency.
Warren, VT
The small town of Warren, Vermont rejected a centralized
sewer approach for their village area triggering a significant
amount of scientific assessment, homeowner education and
outreach, and regulator education and outreach regarding
pretreatment technologies and decentralized cluster system
options. The community provides centralized management
(town administrator, sewage board, and contract technicians)
for a variety of decentralized systems, ranging in size from
individual onsite to a 30,000 gpd system. This project passed
a bond vote with strong public support.
Piperton, TN
The town of Piperton was facing pressure from increasing growth in the Memphis area and in need of wastewater
infrastructure. The city considered building its own centralized wastewater treatment plant and tying into the
adjacent town’s wastewater treatment plant, but ultimately decided on a distributed sewer network to
accommodate development. Since the population tax base was small compared with its future growth projections,
the city’s codes require developers to pay for their own infrastructure and then turn it over to the city to own and
operate, which eliminated the huge tax burden that would have been placed on existing residences if a
centralized plant had been constructed. In addition, the city created subdivision regulations that support open
space and creative land use planning, which led to smaller lot sizes and more open space preserved overall.
Because of its clear ordinances and well-established protocols, it is easier to permit developments in Piperton
than in the surrounding area. Therefore, developers have gravitated to Piperton, which now has more than
280,000 gpd of sewage treatment capacity serving six subdivisions. The cluster systems include septic tank
effluent pumping (STEP), septic tank effluent gravity (STEG), and low-pressure sewer collection systems, trickling
filter treatment, and UV disinfection with drip irrigation used for effluent dispersal. Developers have the advantage
of being able to sell homes with the benefit of having municipal infrastructure services described in their
covenants. Distributed treatment gives the city independence with its own infrastructure and is ultimately better for
public health and the environment than other alternatives considered. Perhaps the biggest benefit is the ability to
build when and where needed eliminating a huge capital outlay and burden on taxpayers for a central plant.
Bethel Heights, AR
Bethel Heights is an example of a community that pursued a distributed approach primarily for economic reasons.
Rather than connecting to an adjacent sewer or building one, large, overdesigned plant, the city manages two
more efficient cluster systems whose construction is phased in to accommodate increasing demands as the
population grows. Wastewater is transported via small-diameter pressure sewer systems to two regionally-located
modular treatment systems. Drip irrigation is used to disperse reclaimed effluent to hay fields which helps manage
Distributed Wastewater Management for Small North Carolina Communities
nutrients in this nutrient-sensitive watershed. Hay is harvested and shipped to farmers in a part of the state that is
nutrient-deficient.
The systems in both Bethel Heights and Piperton utilize septic tank effluent gravity (STEG) and/or septic tank
effluent pump (STEP) collection systems, another form of phased system installation where each building or pair
of buildings installs its own septic tank for pretreatment prior to their connection to the cluster system. Pretreating
wastewater in septic tanks before collection has a number of advantages including lower maintenance demands
on the collection piping and lower loadings to advanced treatment units, as well as the ability to use more
affordable, smaller, shallower collection piping that is accordingly less susceptible to infiltration and inflow (I/I)
than conventional collection systems. Total system costs for these two communities reportedly range between
$5,000 and $10,000 per residence.
Weston, MA
When inadequate grease traps serving commercial businesses in downtown Weston, Massachusetts stressed
their septic systems to failure, impacting an adjacent wetland, the Massachusetts Department of Environmental
Protection (MADEP) stepped in and required property owners to upgrade their systems. Property owners formed
a limited partnership to design, build, own, and manage a wastewater system designed based on natural
ecological processes to serve the core commercial area. A Solar Aquatic System (SAS) system was selected as
a way to provide a neighborhood-friendly wastewater treatment system that could meet stringent groundwater
discharge requirements. The system consists of several natural treatment stages including aeration, plant and
animal aquaculture, solar radiation, clarification, sand filtration, subsurface flow anoxic wetlands and UV
disinfection.
Construction of a conventional, municipally-owned wastewater treatment plant was opposed by residents at public
hearings because of concerns, based on the experiences of other towns, that developers would no longer be
restricted if public sewers were available and the character of the town could be negatively affected; additionally,
a suitable location could not be established. Preservation of community character and control of growth were thus
the primary reasons why a distributed approach was selected in Weston.
Mobile Area Water and Sewer System (MAWSS)
MAWSS includes 12 separate cluster systems, serving 90 to 270 homes each, implemented by three different
utility companies to serve the new suburban development pushing west from Mobile. These previously unsewered
communities are located in a drinking-water watershed and have a history of onsite system failure. To date,
operation of these small-diameter effluent sewer and packed-bed treatment systems has been efficient and
maintenance activity has been minimal. This case study provides a good analysis of capital costs ($7,500 to
$8,000 per home), operation costs, user fees, and financing options through developer investment and utility
management. Additionally, MAWSS owns and operates a demonstration sewer mining project that removes
wastewater from an interceptor sewer, treats it with cluster-scale onsite treatment systems (three different types
were evaluated), and uses the effluent to irrigate a new city park. The project was funded through U.S, EPA’s
National Community Decentralized Wastewater Demonstration Project.
Loudoun County, VA
Loudoun Water provides water and wastewater service for Loudoun County, VA (a Washington, D.C. suburb),
and includes approximately 56,000 central system customers and 1,000 community systems customers.
Loudoun County’s approach to wastewater service is for growth to pay for growth and for development outside of
the centralized service area to be guided by land use planning and zoning rather than the availability of sewer.
Loudon County, Virginia decided to rely on managed decentralized, cluster systems for sewer service for new
exurban development. Developers design and construct cluster wastewater facilities to Loudoun Water standards
and at no cost to Loudoun Water. For subdivisions and small communities, the developer transfers ownership of
the system to Loudoun Water for continued maintenance (Level V Responsible Management Entity (RME) under
US EPA’s management guidelines). The utility acts as a Level IV RME when operating (but not owning) treatment
plants for commercial facilities. The program is financially self-sustaining via rates and developer paid revenues.
Distributed Wastewater Management for Small North Carolina Communities
Figure 1. Cluster treatment system in Loudoun County, VA.
Pennant Hills Golf Club, Sydney, AUS
Sydney Water is a leading utility in Australia that was approached by a golf club that was struggling to maintain its
fairways and greens because of irrigation restrictions associated with the ongoing drought in Australia. Because
public water and sewer, but not reclaimed water, were available, the golf course entered into an agreement with
the utility to mine wastewater from an adjacent sewermain for localized treatment and reuse. Residuals from the
treatment system are discharged back into the collection system for conveyance to and treatment in the
centralized wastewater plant. The conveyance costs associated with more traditional centralized recycled water
systems often render satellite users, such as Pennant Hills Golf Course, uneconomic. Using average costs for
potable water and sewage disposal across the network can often distort the business case and drivers for
localized reuse. A privately-driven sewer mining project, MBR treatment system produces 172,000 gallons of
high quality water per day. Treated water is used to irrigate the 22 hectares (55 acres) of greens, tees and
fairways.
LOTT Alliance, WA
The LOTT Alliance is a wastewater and reclaimed water utility serving Lacey, Olympia and Tumwater in
Washington. The partner communities went through an extensive infrastructure planning process and ultimately
chose what they call their “highly managed option” for wastewater infrastructure implementation. So instead of
building a single, larger, overdesigned plant, they are building in smaller increments of capacity. This phased
approach allows the utility to adapt and take advantage of the latest advances in technology as regulations evolve
over time, while also minimizing upfront expenditures.
Their 20-year plan calls for construction of three satellite reclaimed water treatment plants; as currently planned,
each satellite would initially be built to treat at least 1 million gallons per day (mgd), expandable up to 5 mgd.
Building the satellites in small increments is intended to allow just-in-time construction to meet future wastewater
treatment needs (Klein and Zuchowski, 2008). Using this capacity development strategy, LOTT will save an
estimated $87 million over the course of its 20-year capital improvements planning period, while minimizing risk,
wisely managing community resources and taking advantage of the latest advances in technology.
MEADOWS SEWER DISTRICT
Tetra Tech was selected to help the disadvantaged rural community of Hollister, North Carolina study, develop
and begin implementing a plan to use decentralized wastewater systems serving clusters of homes and
businesses to meet their wastewater management needs.
Halifax County established the Meadows Sewer District in 2005 as a first step in providing residents of the
Hollister community with safe and effective sewage management. A previous engineering report estimated that
the upfront costs of connecting Hollister residents to the nearest sanitary sewer system would be prohibitively
high at over $8 million. A recent survey of individual onsite wastewater management systems in the area showed
that approximately 37 percent were non-compliant or had occupant-identified problems within the last two years,
including surfacing effluent, blackwater and laundry/graywater straightpipes to the ground surface or ditches, and
lack of indoor plumbing. The lack of adequate sewage management has led to further socioeconomic decline
because of the difficulty in siting new businesses in the community.
Distributed Wastewater Management for Small North Carolina Communities
The Meadows Sewer District includes a total of about 700 homes, spread out over roughly 20 square miles. The
proximity of relatively large undeveloped parcels to groups of residences creates an ideal opportunity to manage
wastewater using clustered treatment systems with treated effluent reused or dispersed on adjacent parcels.
Economies of scale allow cluster treatment systems to be more affordable than individual onsite systems, while
locating these systems near the residences being served reduces the costs and associated operation and
maintenance demands of collection and conveyance piping and energy demands associated with pumping
systems. An important advantage of a distributed approach for many communities is that wastewater service can
be phased in as need, funding availability and other factors dictate. A centralized approach, by contrast, would
require most costs to be sunk upfront to extend sewerlines to Hollister.
Tetra Tech’s scope of work includes developing a Preliminary Engineering Report (PER) that would, at the
completion of the study, provide the County and District with a roadmap for moving forward with implementation
of a decentralized service approach in the Meadows Sewer District. More detailed information will support the
design and permitting of early phases of implementation, where it is anticipated that typical cluster systems in the
area would serve between 10 and 50 homes (roughly 3,000-15,000 gallons per day each).
The distributed wastewater management plan for Halifax County has required close collaboration between the
Meadows Sewer District, Halifax County Public Utilities and Halifax County Environmental Health. The project
team is currently working with owners of large parcels of land where cluster systems could be sited, while also
investigating opportunities to reuse treated wastewater effluent to support local businesses (including tree farms)
and food production, as well as the potential for nutrient trading in the Tar-Pamlico River Basin.
Figure 2. Meadows Sewer District map of existing systems (colored circles) and potential treatment sites
(parcels outlined in blue).
Distributed Wastewater Management for Small North Carolina Communities
CONCLUSIONS
This paper uses the results of several recent research and planning projects to show how small communities can
utilize a distributed wastewater management approach as a viable, cost-effective alternative to centralized sewer
extension.
The Water Environment Research Foundation (WERF) project entitled When to Consider Distributed Systems in
an Urban and Suburban Context, identified and evaluated new applications for decentralized systems in areas
where sewer would traditionally be extended to provide service, including a number of small communities who
embraced a distributed approach in order to maintain their fiscal health and independence. These communities
relied on professional management of well-planned and designed cluster and individual onsite wastewater
treatment systems.
New distributed management approaches are being implemented in the Meadows Sewer District in Halifax
County, NC where a preliminary engineering report specific to decentralized, cluster systems is being prepared as
an alternative to a cost-prohibitive sewer extension to serve residents with failing or inadequate septic systems.
REFERENCES
CEC. Integrated Energy Policy Report: Committee Draft Report. CEC-100-2005-007-CDT. 2005
EPRI. Water and Sustainability (Volume 4): U. S. Electricity Consumption for Water Supply & Treatment—The
Next Half Century. Electric Power Research Institute. No. 1006787, Palo Alto, California. 2002.
Klein, A. and Zuchowski, T. “Dynamic Updating Program for Just In Time Design of Water Reclamation
Facilities.” Proceedings of WEFTEC08. Chicago, IL. October 2008.
WERF. “When to Consider Distributed
www.werf.org/distributedwater. July 18, 2011
Systems
in
an
Urban
and
Suburban
Context.”
Distributed Wastewater Management for Small North Carolina Communities