Strategic Management Implications of Water Reclamation and Reuse on Water Resources

As stewards of our natural resources it is incumbent on us to give careful consideration to effects on future generations of decisions we make to address today's problems. We recognize that high quality water sources are limited and that we are approaching or have surpassed the prudent levels of waste discharges to surface waters of the State. It is time for North Carolinians to examine how we currently meet our demand for water.

Water management decisions are based on both the existing condition and the potential of the resource base at the time decisions are made. The present demand on water resources represents a combination of demands from all users which has evolved over time. Currently in most public water supply systems, these demands are met by supplying water that has been treated to drinking water quality to all users even though not all users require water of such high quality. Responsible water supply planning is needed to support the current level of growth and development in North Carolina and to ensure appropriate quality water is available to meet intended uses. With the increasing limitations on the way we are accustomed to using water, it is necessary to explore alternatives to better use and protect our water resources for current and future citizens of North Carolina.

Recent changes in water treatment regulations require higher levels of treatment for public water supplies. As a result, the cost of delivering treated water to the end-users of public systems has increased. At the same time, higher levels of treatment for wastewater discharges are becoming necessary in order to meet environmental and permitting requirements. These two trends have helped stimulate an examination of alternatives to our current approaches to water resource use in water supply and collection systems to answer the following question. What possibilities are available to use highly processed wastewater discharges to meet non-potable water demands and extend the life of current supplies and treatment infrastructure?

Wastewater treatment plants (WWTPs) using advanced wastewater treatment (AWT) technologies can produce treated water of high quality. See Thompson, et al. for the results of a study in San Diego indicating that discharges from an AWT system produced water of a higher quality than the raw water used as a source for the City's potable water. Having been almost exclusively considered waste to date, treated water from AWT plants is beginning to be recognized as a source of water to meet a portion of total demand. Using reclaimed wastewater for non-potable needs has the potential to reduce withdrawals required to satisfy current demand, and decrease the volume of effluent discharged to receiving waters. Evaluations of reuse proposals must consider effects on other demands that have been satisfied by the water to be reused as well as the potential to provide for additional growth without increasing withdrawals.

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The effect of a reuse project on streamflow varies depending on where in the system streamflow is measured and whether or not an interbasin transfer is involved. For example, a system with one withdrawal point and one corresponding downstream discharge point as shown below, could implement a water reuse project that recycled a percentage of the waste stream back to the system to offset the potable demands. The withdrawal and discharge would both be reduced by the same amount that is recycled. Therefore, the amount of flow below the discharge point is the same whether or not the system recycles. For this same system, however, the flow in the intervening reach between the withdrawal and discharge would increase by the recycled amount. For this single basin example, there is no impact on the downstream flow amount due to the water reuse. However, the reduced withdrawal is a beneficial impact on the intervening reach. To illustrate the concept, the graphic below shows the result of reuse on streamflow for a system with a 10 mgd water demand, 3 mgd reuse, and 2 mgd consumptive loss, where all of the reuse offsets the water demand.

If the reuse does not offset a potable water demand, in effect a new demand has been created that would not otherwise exist. The withdrawal, therefore, cannot be reduced and the streamflow below the discharge will be reduced as compared to a system without reuse. This could hurt aquatic habitat and limit downstream users. The potential effects of reduced discharges on minimum flow requirements could affect the availability of water for withdrawal and discharge. If reused wastewater does not offset an existing water demand, the more appropriate term to apply is wastewater disposal rather than water reuse.

For a system with an interbasin transfer, the difference from the above illustrations is that the change in flows are permanent. Since the withdrawal is lower due to the reuse, the amount of flow below the point of withdrawal is greater than it was before the reuse, by the amount of water that is reused. Similarly, flows in the receiving basin are reduced by the amount of the reuse, because less water is discharged. Whether this flow reduction is perceived as a benefit or detriment to the receiving basin depends upon the perception of the impact of the wastewater. This will vary with the characteristics of the receiving body and proximity to the discharge. Downstream users that depend on a consistent flow may see the reduction as detrimental, while users with water quality concerns near the discharge point may see the reduction as beneficial.

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How our water resources are dedicated to meet current needs has evolved from historical decisions on how water is to be used. Decisions about withdrawals are made based on projected effects on habitat as well as other users. Discharges are permitted considering assimilative capacity, water quality regulations, and effects on other users. The resulting arrangement represents a dynamic equilibrium defined by the current state of withdrawals, discharges, and the basins hydrogeological characteristics. It is imperative that reuse options be considered within a regional context since changes in use patterns will force adjustment to the dynamic equilibrium among interconnected water resources and water uses.

Diverting current wastewater discharges for reuse may generate effects on other water users. If historic discharges have been included in the 7-day 10-year low flow (7Q10) calculations used to issue discharge permits, diversion of discharges could have significant effects on water quality, downstream users, habitat, and/or ground water recharge. Investigation of potential effects on water resources throughout a basin or system of linked basins is crucial to maximizing the benefits possible from the use of reclaimed water. In the initial phases of water reuse efforts the effects of decreased discharges may not be significant. However, if efforts prove successful and a significant percentage of discharges are shifted to reuse, consideration of effects on downstream users will become even more critical.

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Reclamation of used water has the potential to improve allocation of water resources by providing an alternative source of water to meet system demands which do not require high quality, potable water. If the benefits of this possibility are to be realized, focus should be on the displacement of existing uses of potable water and the development of a reliable supply of non-potable water. Most water supply systems will have a certain percentage of uses which do not require water treated to drinking water standards. Substitution of reclaimed, non-potable water for uses which do not require potable water (e.g. some industrial uses and irrigation) could reduce demand on current potable water supplies, extending the life of the current source and treatment capacity. A beneficial aspect of reduced demand is the potential to postpone enlargement of treatment capacity and to avoid the impacts associated with development of new raw water sources.

Reclaimed water is a potential "new" water source. Reusing water to serve non-potable needs can reduce the existing potable water demand. Once the existing potable water is freed up, it can be used for expansion or future needs without requiring any additional withdrawal. A system with a water shortage response plan, practicing water conservation and reuse might be able to extend their water supply to meet projected growth needs. The adjoining example demonstrates the ability of our example system to increase their demand from 10 to 13 mgd, with no increase in the withdrawal. The reduction in streamflow below the discharge is due to the increase in the consumptive use (still 20 percent) due to the increased water use. The downstream flow is unchanged as compared to a system with no recycling.

Additionally, decreasing demand on current sources has the potential to decrease the operating costs for raw water treatment by reducing the quantity of water needing to meet drinking water standards. This may prove particularly true as treatment standards become stricter and associated costs rise. Of particular interest is the possibility of reducing demand on current sources in capacity use areas and areas already experiencing source limitations due to factors such as salt water intrusion.

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As noted above the use of reclaimed water could have a beneficial effect on ground water supplied systems. Beyond the obvious advantage of displacing demand there is the possibility of using reclaimed water to recharge aquifers. Although currently prohibited in North Carolina, other coastal states such as California and New Jersey have programs to use reclaimed water to recharge aquifers. This may be of particular interest to water users in the coastal region. Given that individual septic systems and land application of WWTP effluents often function as aquifer recharge mechanisms, supplementing this input with reclaimed water in areas with WWTPs has the potential to recharge the surficial aquifer with higher quality water and increase the pressure and quantity of fresh water resisting salt water intrusion. A state which depends heavily on coastal tourism, as North Carolina does, may benefit from augmenting the recharge of coastal aquifers to protect and extend the life of drinking water supplies essential to the support of local economies. It is assumed that any efforts of this nature would be accompanied by a conscientious program of demand management and water conservation.

The City of Perth Amboy, New Jersey, designed a system of two open-water recharge reservoirs to supplement recharge to the ground water aquifers the city relies on to supply drinking water. The goal was to increase pumping to meet increasing demand and to inhibit salt water intrusion (Neuner et al., 1992). Los Angeles County Sanitary District has been using surface spreading of wastewater to recharge local aquifers since the 1960s (Crook et al., 1990). The Orange County (CA) Water District operates a reclamation facility to inject reclaimed water to create a hydraulic barrier to salt water intrusion (Mills, 1993, Crook et al., 1990). In Clayton County, Georgia discharges from several WWTPs are collected and piped for land application to the watershed of the system's major water source. This reclaimed water returns as surface flow, subsurface flow, and ground water discharge (Reed and Bastian, 1991). While hydrologic conditions in the above regions are different than North Carolina, the experience and data available from these efforts will facilitate discussions of the potential of aquifer recharge in areas of North Carolina where it could play a beneficial role in protecting and preserving our water resources.

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The need to upgrade existing WWTPs to meet stricter discharge standards offers plant operators a potential revenue stream in the form of marketable reclaimed water. The potential for offsetting costs associated with system upgrades by marketing reclaimed water, particularly in service areas with large irrigation or industrial consumption, should be investigated during the planning and design phase of WWTP construction. Likewise, projections prepared for potable water treatment plant expansions should consider the potential application of reclaimed water for non-potable uses on demand management options. At the same time, demand projections should integrate water conservation efforts which are expected to induce permanent changes in water use patterns. Water conservation activities have the potential to produce significant reductions in demand without some of the infrastructure changes required by reuse.

In most cases reclaimed water use will require the construction of a separate distribution system for non-potable water to comply with public health requirements. Water supply systems considering the use of reclaimed water in the foreseeable future should consider requesting the installation of non-potable water distribution systems during site development on new development projects. One study in Florida estimated that retrofitting a system to allow non-potable water use for residential irrigation was almost twice as expensive than installation during initial infrastructure development (Paret and Elsner, 1993). New development projects using new or upgraded WWTPs may want to consider dual (potable and non-potable) distribution systems in association with AWT to facilitate management of demand and discharge volumes.

Dual system development should get careful consideration in areas experiencing rapid growth and development with a concurrent need to expand water supply, as well as areas experiencing restrictions on additional development due to limitations in water supply or the ability to increase discharge loads to receiving waters. It must be emphasized that irrigation with reclaimed water solely to reduce discharges, while likely beneficial to the aquatic ecosystem, does not necessarily represent a reduction in demand on the system and is more accurately viewed as an alternative disposal procedure rather than as supply protection.

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Entangled with the goal of displacing current use is the need to assure reliable supplies of non-potable water for adequate periods of time to make the necessary infrastructure investments practical. Planning and development for the beneficial use of water resources requires locating and securing water supplies adequate to meet projected demand over an extended planning horizon. Sources which can only be guaranteed for limited periods of time will not have a significant impact on the need to secure guaranteed long-term sources. If water reuse is to ultimately ease demands on surface water and ground water resources, the ability to form long- term arrangements between consumers and suppliers is essential.

The process of securing an adequate, reliable supply of reclaimed water will necessitate negotiations between the consumers and the suppliers of reclaimed water. Successful negotiations will have to settle the issues of quantity, quality, duration, and price among parties that are likely to be a mix of public and private entities. Consumers will seek to secure a dependable supply, of sufficient quality, at an acceptable price, and for a period of time adequate to allow securing and repayment of associated debts. A prudent supplier seeing the potential demand for reclaimed water increasing will seek to maintain flexibility to sell water to the highest bidder. If suppliers' prime motivation to market reclaimed water is to reduce effluent discharges, they will likely also desire long-term contracts and the conflicts noted above may not be an issue. However, if the motivation is to supplement their revenue stream the likelihood of contract time limits or price escalation clauses may increase uncertainty and limit the development of long-term uses of reclaimed water.

Contracts between suppliers and consumers will have to be of a duration long enough to ensure the securing and payback of financing for infrastructure, or in some way be structured to ensure the reliability of supply. If reclaimed water is to be considered a component of the State's total water resources it will have to enter the planning process as a long term supply option. Limitations imposed by contractual arrangements will serve to limit the infrastructure development necessary for beneficial water reuse.

It should be noted that, while use of reclaimed water displaces current potable water use the key value lies in postponing the investments associated with expansion of supply. Therefore, the price of reclaimed water should reflect the marginal cost of expanding capacity not merely the current cost of existing capacity. Keeping this in mind, the motivation to pursue the use of reclaimed water may not arise until the prospect of price increases associated with financing of additional treatment capacity becomes imminent.

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As this discussion shows, there are potential benefits to water reclamation and reuse from the perspective of using and protecting water resources for the current and future residents of North Carolina. Utilization of reclaimed water will require a shift in the way water resources are considered. To date water use has been primarily considered a linear process: water is removed from the natural resource pool, treated to meet drinking water quality standards, distributed to consumers, and the wastewater generated is disposed of in a manner designed to protect the public health and environment. Reclamation of used water requires adjusting perspective to envision the system as a cycle where a portion of the wastewater discharges are returned to the system as a source of water for users who do not require potable quality water. Given that a goal of water resource planning and development is the provision of water resources in the quantities and qualities that are best for the intended uses, then integration of reclaimed water into water use planning is a logical step.

Wastewater discharges are commonly located some distance downstream from water intakes. This arrangement may limit the practical reuse of effluent from a WWTP by the people who finance and contribute water to the plant in question. It is likely that in at least some cases the most efficient use of reclaimed water may be by consumers who are located in a different service area than the one which supplies the reclaimed water. Such cases will require interjurisdictional negotiations to arrive at an arrangement acceptable to all parties. The difficulty and time required for these negotiations will generate transaction costs, which will add to the total cost of efforts to use reclaimed water. If these transaction costs, be they calculated in dollars, time, or increased levels of distrust, add significantly to the difficulty of developing workable methods to use reclaimed water, then the full benefits may not be realized.

The example above is only one possible scenario. There will probably be as many variations on issues to be addressed as there are attempts to negotiate an agreement. The key point here is that anything which inhibits negotiation of agreements will increase the amount of resources necessary to reach an acceptable contract and add to the total costs of projects. If these additional costs are significant, a dampening effect could be expected on the efforts to develop reuse projects.

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Experiences in other areas of the country suggest that there are benefits to be realized by reclaiming wastewater and using it to meet non-potable water demands. The abundance of reliable water sources in North Carolina compared to states like California and Florida will likely limit the consideration of reuse potential to the situations where individual systems are forced to face the prospect of capital investments in treatment facilities and/or limitations on wastewater discharges. Several issues arise when considering the potential for using reclaimed water.

What are the potential effects on other demands of the water body, such as water quality, off stream uses or ground water recharge, from changes in discharge volumes? Changes in water use patterns will have impacts throughout the set of water resources linked to the system in question. Reuse decisions have to be made considering potential correlative effects.

If reclamation is to contribute to preserving and protecting current water supplies it must offset current demands on potable water. Optimum allocation of water resources implies delivering appropriate quality of water for its intended use. If reclaimed water use does not release a portion of current high quality water for uses which require it, the change in distribution of resources will not move us closer to the optimum, and may have some negative consequences for streamflows.

Using reclaimed water for aquifer recharge may provide relief to areas of the State experiencing diminishing ground water supplies and/or salt water intrusion. Success of projects throughout the country over several decades indicate aquifer recharge with reclaimed water can be an effective method to help preserve and protect the water resources that support our current and planned levels of economic activity.

Reclaimed water use will require adjustments to our current approaches to water resource management. Water management is organized through a system that has evolved over time reflecting adaptations to changing needs. Entities involved in water management decision making will have to explore the possibilities available to them to encourage the most beneficial aspects of reuse and minimize the potential drawbacks. In particular, the potential need to create interjurisdictional agreements may have the unfortunate potential to spark turf battles between parties which could limit use and infrastructure development.

Reclamation and reuse, while worthy goals, will only provide a temporary solution to water supply problems if they are not instituted in the context of a well structured water conservation effort. Water conservation efforts may yield more benefits in terms of demand reduction and should be encouraged at every opportunity. Increasing the water available to meet current demands without improving the efficiency with which we use our water resources will only shift the problem to future generations of North Carolinians. As stewards of the water resources of the State, we are all charged with encouraging the highest and best use of the resources while protecting and preserving them for current and future generations.

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Crook, J., T. Asano, and M. Nellor, 1990, Groundwater Recharge with Reclaimed Water in California, pages 67-74 in Municipal Wastewater Reuse: Selected Readings On Water Reuse, United States Environmental Protection Agency, Washington, D.C., EPA 430/09-91-022

Mills, W.R. Jr., 1993, Groundwater Recharge Success, Water Environment & Technology, 5(2):40-44.

Neuner, R.G., B. Schwenneker, A.X. Kozak, and T. Ramadan, 1992, Perth Amboy Turns Water Crisis in Its Favor, Public Works, 123(11):44-45.

Paret, M. and M. Elsner, 1993, Reclaimed Water Perspectives, Water Environment & Technology, 5(2):46-49.

Reed, S. And R. Bastian, 1991, Potable Water via Land Treatment and AWT, pages 59-66 in Municipal Wastewater Reuse: Selected Readings On Water Reuse, United States Environmental Protection Agency, Washington, D.C., EPA 430/09-91-022

Thompson, K., R.C. Cooper, A.W. Olivieeri, D. Eisenberg, L.A. Pettegrew, and R.E. Danielson, 1992, City of San Diego potable reuse of reclaimed water: Final results, in Desalting and Recycling: Meeting Today's Water Challenges, Proceedings of the National Water Supply Improvement Association 1992 Biennial Conference, NWSIA, St. Leonard, MD.

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