COST ANALYSIS OF PUBLIC WASTEWATER VERSUS ONSITE WASTEWATER Danna L. Revis 1

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1 COST ANALYSIS OF PUBLIC WASTEWATER VERSUS ONSITE WASTEWATER Danna L. Revis 1 ABSTRACT A cost analysis of constructing and operating an onsite sewage system versus constructing a connection and subscribing to a public wastewater utility indicates that while conventional onsite sewage systems are less expensive to construct and operate over a 30 year period, alternative onsite sewage systems are more expensive to construct and operate than public sewer for a homeowner with a four bedroom house. Current large scale wastewater utilities benefit from economies of scale with respect to smaller systems and especially in comparison with soil dispersal systems. In microeconomics, economies of scale are the cost advantages that enterprises obtain due to size, output, or scale of operation, with cost per unit of output generally decreasing with increasing scale as fixed costs are spread out over more units of output. (Wikipedia, 2017) While larger soil dispersal systems could be constructed to address community needs and also benefit from economy of scale, the onsite wastewater industry must navigate a paradigm shift to take better advantage this approach. Explicit rather than implicit safety factors, design and operation strategies that facilitate flexibility in the ability to serve wastewater customers, and a requirement for pretreatment for high strength customers could go a long way towards making wastewater systems that disperse effluent into the soil more financially competitive with traditional discharging plants and help bring wastewater infrastructure to communities that cannot build discharging POTWs to accommodate decentralized areas. INTRODUCTION Comparing the cost of wastewater treatment between public sewer and onsite sewage systems as a whole is difficult to do. For an individual homebuilder whose property lies at the edge of a public sewer collection system, the problem is easier to navigate. What is the cost of connecting to public sewer compared to the cost of constructing an onsite sewage system on my property? The homebuilder can calculate the cost of a tap fee for connecting to sewer, the cost of the materials required for the connection, and the cost of construction, and compare those costs to the cost of constructing an onsite sewage system. This homebuilder can also project the cost of maintenance for the onsite sewage system against monthly sewer fees and make a decision. The decision is also clear when a homebuilder has property far outside the reach of the collection system or when the homebuilder has property clearly within the public sewer collection system 1 Danna L. Revis, Training Coordinator, Virginia Department of Health; danna.revis@vdh.virginia.gov

2 and is required to connect by law. In those cases, there is no decision to make: the course is clear since no alternative is available. Research into the costs for a homeowner to operate an onsite sewage system, either conventional or alternative, did not provide more accurate information than developing estimates of the costs involved based on anecdotal information and educated estimates. While both an onsite sewage system and a public sewer system will be designed to meet a specified flow, for an onsite sewage system, the specified flow figure often incorporates a safety factor tied to soil as a receiving environment. For commercial or industrial applications, additional safety factors may be applied to an onsite sewage system design based on wastewater characterization. Although maintenance for AOSS is currently required in Virginia and other locations around the US, the requirement is recent and many onsite sewage solution manufacturers have incorporated controls designed to be automatic to allow maintenance-free operation. Since onsite sewage systems are usually designed for a specific facility or small community, the design of the system often includes components to address specific treatment challenges that would be considered pretreatment, the responsibility of the specific customer, in a public sewer system. All of these differences in design paradigms for wastewater solutions lead to differences in the cost of designing, constructing, and operating onsite sewage systems and public sewer that confound comparison. Primarily, the differences in cost are tied to safety factors, flexibility and controls, and pretreatment Research into sewer costs indicates some variability in the cost of the monthly sewer bill depending on local challenges within the US. Circle of Blue, an online water news source, surveyed 30 US cities for sewer costs in 2010 (Walton, 2010). They found a wide variation in sewer costs when comparing the monthly bill for a family of four using 100 gallons per day per person. Salt Lake City came in lowest at $13.92 per month while Atlanta came in on the high side with a bill of $ per month. The author found that the differentials were largely due to repayments for capital improvements in the wastewater system. For instance, Salt Lake City has been delaying construction of a new wastewater treatment plant whereas Atlanta has been carrying out a $4 billion plan for modernization and expansion of the wastewater system, including remediation of combined sewer overflow (CSO) issues. Since the numbers for onsite sewage construction and maintenance estimates in this paper are based on Virginia costs, the numbers used for sewer cost estimates are also based on Virginia utility rates. A small utility that includes both decentralized and publicly-owned treatment works (POTW) systems on the Eastern Shore of Virginia is the Northampton Public Service Authority. According to documentation on their website, there are two rates for monthly sewer fees among their systems: $42/month for residents near Eastville, and $63/month for residents of Cape Charles (Northampton County, Virginia, 2015). The overall average monthly sewer charge in Virginia was $41.47 in (Draper Aden Associates, 2016) The next page provides the cost comparison between onsite sewage and public sewer for a four bedroom home over 30 years:

3 Table 1: Comparison of costs for onsite wastewater and public sewer in Virginia 4 BR home over 30 years Type of sewage solution Initial Installation Maintenance event Cost of maintenance Multiplier (over 30 years) Subtotal (maintenance) Total Cost Cost per year (30 years) Conventional - gravity $5, pump out $ $2, $7, $ Conventional - pump $7, pumpout $ $2, $12, $ pump repl $1, $3, AOSS - grav $20, pumpout $ $2, $40, $1, component repl $1, $4, O&M contract $ $13, AOSS - pressure $30, pumpout $ $2, $52, $1, component repl $1, $6, O&M contract $ $13, Sewer - low $6, monthly charge $ $15, $21, $ Sewer - high $6, monthly charge $ $22, $28, $956.00

4 DISCUSSION While using actual data rather than estimates may change some of the specific values in the above comparison, the proportional comparison is likely to remain the same: public sewer costs approximately twice as much as a conventional onsite sewage system (COSS) over 30 years, and an alternative onsite sewage system (AOSS) costs approximately twice as much as sewer for a single family home over the same time period. $2, $1, $1, $1, $1, $1, $ $ $ $ $0.00 Cost per year (30 years) Conventional - gravity Conventional - pump AOSS - grav AOSS - pressure Sewer - low Sewer - high Figure 1: Cost per year of onsite wastewater vs. public sewer The design and operation paradigms associated with each wastewater strategy onsite sewage vs. big pipe sewer -- are deeply engrained and worth exploring to better understand the struggle to find funding for onsite sewage systems and to help place soil treatment strategies more in the mainstream of wastewater infrastructure. At the community level, making a decision about pursuing a soil dispersal wastewater option vs a treatment plant to discharge highlights the differing paradigms. At this level, the community must consider the cost of undertaking construction or expansion of a wastewater plant, the cost of constructing or expanding a collection system, and the short-term and long-term financial future of the community. Driving the cost of providing the utility too high will damage the community s immediate financial future, drive away residents and businesses, and cause the community to fall into financial ruin. Ideally, the community will find the perfect solution for wastewater to serve its current residents affordably while enabling the community to expand and attract new businesses and tax base at just the right pace to benefit everyone.

5 Currently, large scale soil dispersal systems are rare and the design and operation strategies are different than the design and operation strategies for large discharging plants. Some key principles for design and operation of soil dispersal that differ from the principles in designing and operating discharging plants center on safety factors, flexibility and controls, and pretreatment. Safety factors In designs for soil dispersal systems in Virginia, the regulations require designs to have the capacity to accommodate peak flows. In a very old policy that has not been rescinded, Guidance Memorandum and Policy (GMP) , previously known as GMP 35, the policy states that the standard safety factor in Virginia design flows for soil absorption field design is 1.4. Following this premise for design, a four bedroom system designed for 600 gallons per day under Virginia onsite regulations would be expected to have an average flow of about 428 gallons per day, much closer to the figure used in engineering designs the Northampton Service Authority for an Equivalent Residential Connection or ERC of gpd. Since soil dispersal systems cannot accommodate extra flow because exceeding the application rate could shorten the life of the dispersal area, including a safety factor in the basis for its design makes sense, however burying the safety factor in the design specifications rather than making the safety factor explicit causes complications in designing alternative onsite sewage systems. For a treatment system to operate properly, both design flow and wastewater characterization are crucial elements in balancing treatment. Including a safety factor in the design flow makes it difficult for the designer to calculate for proper aeration and for nutrient reduction. Changing the basis for design to average or actual flow and requiring an explicit safety factor through storage or other means of flow equalization would allow designers and operators to better adjust the treatment process. In designing treatment, a designer must specify a treatment train that provides proper treatment based on the anticipated wastewater characterization. The design strategies commonly employed in designing treatment trains in POTW commonly include mixing, storage, and monitoring by the operator to assure that the design accomplishes proper treatment. These designs must be based on an accurate wastewater characterization. Incorporating a soil dispersal safety factor into the design flow for the system overall overestimates the volume of flow at the design stage resulting in underloading of the treatment system in operation and poorer performance of the treatment component in onsite sewage systems. Using industry standards for designing the treatment component of onsite sewage systems and applying necessary safety factors to the dispersal design would help operation of alternative onsite sewage systems in general. For individual residential systems where mixing, storage, and monitoring are less feasible to address fluctuations in wastewater strength, additional measures would be necessary to assure successful operation. Some operators in Virginia currently use a return loop to address fluctuations in strength and flow, but perhaps other strategies, such as flow equalization ahead of treatment, could be employed as well. Flexibility and controls Strategies for flow equalization in general could greatly help address the flexibility dichotomy between soil dispersal designs and discharging plant designs. The paradigm for operation of soil dispersal systems has always been that the owner can install it and forget it until if fails many

6 decades in the future. Even though drip irrigation has complex controls that require maintenance, the design strategy for drip is to use mechanical zoners and/or electrical solenoids based on timer controls to alternate zones automatically. Even for a large scale drip irrigation system, most of the prescribed O&M is focused on the treatment plant that discharges to the drip field. The drip field controls operate automatically to dose the dispersal area and require less frequent maintenance than the maintenance scheduled for the plant. While this automation appears to be a benefit, in some cases, especially for large decentralized systems, less automation and a more intentional approach to operating dispersal systems could be beneficial. Having the option to manually operate different zones or sections in the dispersal area could allow a system to better accommodate seasonal flows as well as to allow an operator to take a field off-line for maintenance without requiring the entire system to be shut down. For a large scale discharging plant, O&M protocols are based on having a resident operator to make decisions about the optimum stages of treatment at several points along the treatment train. Current discharging plants use SCADA systems for controls, and a dedicated operator can make adjustments in the operation of the plant based on observed conditions from his or her cell phone as well as from within the plant, giving the operator a lot of control in managing the function of the plant and allowing the utility a lot of flexibility in the types of customers the plant can accommodate. In general, large discharging wastewater treatment plants have no problems accommodating variable flows due to seasonal uses. College towns, beach communities for these and other communities that have seasonal migrations of customers, the local discharging wastewater plant operators can make adjustments to assure consistent treatment throughout the varying flow conditions. In contrast, large soil dispersal systems tend to be designed to accommodate only the original use of the facility they serve. If a strip mall on a soil dispersal system wants to change out a hardware store tenant for a restaurant tenant, major changes to the system would be required to accommodate higher strength waste and higher flow. Under the current paradigm for soil dispersal systems, the design of the treatment train would require changes and additional land for soil dispersal would likely be required. If a more universal design were provided from the beginning and the operator could use SCADA or even manual controls, an operator of a soil dispersal system could make adjustments that would accommodate changes in water use. Pretreatment In the case of a new use, changes in wastewater characterization for customers of POTW are generally addressed through a pretreatment ordinance that defines limits on the characterization of the wastewater that will be sent to the plant. A customer with high strength wastewater is required to pretreat the wastewater before sending it to the POTW. Alternative Onsite Sewage Systems face similar challenges when flow contributors produce high strength waste. Currently, for AOSS,, what would be considered pretreatment for a customer of a POTW becomes part of the treatment train for an AOSS. While this design paradigm addresses the needs of the customer using the system when it is designed, should a different business or industry move into the building, the primary treatment train may require redesign and modification. Since soil dispersal systems are currently usually privately owned, perhaps the provisions for high strength waste or other treatment challenges could be developed contractually placing the burden on the customer to

7 address pretreatment requirements rather than on the initial system designer.. If this type of arrangement were in place to address wastewater strength, only changing flows would need to be addressed by the system operator. CONCLUSION A cost analysis of constructing and operating an onsite sewage system versus constructing a connection and subscribing to a public wastewater utility indicates that while conventional onsite sewage systems are less expensive to construct and operate over a 30 year period, alternative onsite sewage systems are more expensive to construct and operate than public sewer for a homeowner with a four bedroom house. Current large scale wastewater utilities benefit from economies of scale with respect to smaller systems and especially in comparison with soil dispersal systems. In microeconomics, economies of scale are the cost advantages that enterprises obtain due to size, output, or scale of operation, with cost per unit of output generally decreasing with increasing scale as fixed costs are spread out over more units of output. (Wikipedia, 2017) While larger soil dispersal systems could be constructed to address community needs and also benefit from economy of scale, the onsite wastewater industry must navigate a paradigm shift to take better advantage this approach. Explicit rather than implicit safety factors, design and operation strategies that facilitate flexibility in the ability to serve wastewater customers, and a requirement for pretreatment for high strength customers could go a long way towards making wastewater systems that disperse effluent into the soil more financially competitive with traditional discharging plants and help bring wastewater infrastructure to communities that cannot build discharging POTWs to accommodate decentralized areas. LITERATURE CITED Draper Aden Associates. (2016). The 28th Annual Virginia Water and Wastewater Rate Report Blackburg, VA. Northampton County, Virginia. (2015, June 22). Northampton County/Administration. Retrieved August 2017, from Wastewater Project: Walton, B. (2010, 8 26). Circle of Blue. Retrieved August 2017, from The Price of Wastewater: A Comparison of Sewer rates in 30 US Cities: Wikipedia. (2017, August 28). Economies of scale. Retrieved September 3, 2017, from Wikipedia: