La Escuela Normal Francesa.

Challenges associated with the use of recycled water as a supply in the MokeWISE program are listed below. These challenges will limit the ability to implement recycled water as part of the MokeWISE process.

 Timing and storage. Recycled water use can be limited by the timing of supply and demand. While supply is available year-round, demand is often limited to the summer months, particularly if the recycled water demand is largely irrigation. Because of this discrepancy in the timing of supply and demand, storage is needed. However, storage can be costly and space for storage limited, particularly in urban areas and in areas with limited groundwater recharge ability.

 Economic feasibility. Recycled water projects can be costly, potentially limiting the ability of agencies implement projects and support ongoing operation and maintenance costs. While there are various funding opportunities available to help offset initial capital costs, agencies may reach a point of diminishing returns on recycled water projects. That is, the marginal cost of implementing the last few recycled water projects may be significant and those projects may not be economically feasible. While this point of diminishing returns may change over time as technology advances, some of the recycled water theoretically available for MokeWISE may not be economically feasible.

 Coordination costs. Many recycled water projects require multiple agencies to implement. Coordination costs may be significant in large-scale projects that require multiple agencies. For example, while there is roughly 163,000 AFY theoretically available within the EBMUD water service area, only about 75,500 AFY of that is from EBMUD’s Main WWTP. Coordination with nine agencies would be required to utilize the 163,000 AFY. This level of coordination may significantly limit the quantity of recycled water that could realistically be achieved.

 Infrastructure requirements. In the case of EBMUD, it is difficult to retrofit facilities already using EBMUD potable water. Because infrastructure relies on current demands in established areas, issues may arise if potable demands decrease.

Furthermore, the EBMUD service area is not planned for much growth that could use recycled water, as the majority of planned growth is infill and densification.

 Benefit allocation. Increasing recycled water use outside of the Mokelumne River watershed could potentially create issues with how benefits are apportioned within the watershed. For example, recycled water use in southern California has supported additional growth rather than reducing imports from other regions.

 Market potential. Recycled water projects can only be implemented if sufficient market demand exists to use the supply. Recycled water is primarily used for nonpotable, outdoor demands, which represent a subset of total demand. While recycled water can also be used to meet potable demands through indirect or direct potable reuse, regulatory requirements for potable reuse are currently evolving in California, adding some uncertainty to the feasibility of implementation, particularly given high costs of treatment to potable quality. Depending on the extent of market potential, the amount of recycled water that can be used within the planning horizon of the MokeWISE program may change.

 Local considerations. Each local agency has a unique setting which must be considered prior to implementing recycled water projects. For example, the City of Stockton produces 49,300 AFY of treated effluent that could theoretically be reused. However, due to the structure of the City’s water rights, this amount would result in a need to secure additional supplies and would therefore not generate a net increase in available supply. Additionally, some agencies overlap with the EBMUD service area. Recycled water projects would need to be implemented within the overlap with the EBMUD service area to create benefits to the Mokelumne River watershed.

 Scalability. Small wastewater treatment plants may provide recycled water that is potentially available in the future. For instance, AWA’s leachfields produce small quantities and are not proximate to potential recycled water customers. As such, projects involving recycled water from these leachfields are considered infeasible.

 Groundwater basin proximity. Recycled water could potentially be used to recharge the Eastern San Joaquin Groundwater Basin. However, feasibility of a recycled water recharge project may depend on the origin of the recycled water. Because of the proximity to the Eastern San Joaquin Groundwater Basin, recycled water from the lower watershed would likely be the most feasible for use in a recharge project. Because Stockton’s assumed available supply is 0 AFY, only the 3,700 AFY of recycled water from Lodi or other valley cities could potentially be used for recharge. While recycled water supplies from EBMUD and the upper watershed could be used for recharge, this supply would only be feasible through an exchange.

 Downstream impacts. Recycled water, particularly on the municipal scale, must consider the downstream impacts. As with agricultural drainage water, reuse of recycled water could decrease this source for downstream users, thereby potentially decreasing the amount of water available for downstream users.

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Opportunities for Maximizing Recycled Water Use

The following are potential opportunities for maximizing recycled water use. These examples can be considered when discussing potential MokeWISE projects and programs.

 Non-potable uses. The use of recycled water for non-potable uses such as irrigation and toilet flushing is becoming increasingly common, and there is likely demand for expanded use of recycled water for these purposes. Use of recycled water for non- potable purposes requires a lower level of treatment than other potential uses of recycled water, such as indirect or direct potable reuse, though infrastructure requirements may be more significant. Dual-pipe systems could be used to support recycled water use in urban and suburban infill areas.

 Saline intrusion barrier. There are a number of areas within the San Joaquin Valley that are experiencing or are expected to experience saline intrusion, resulting in degradation of groundwater supplies. Wastewater agencies adjacent to areas experiencing saline intrusion could inject recycled water into the groundwater basin to provide a barrier against saline intrusion.

 Indirect potable reuse/direct potable reuse. Regulations are currently in place allowing indirect potable reuse of recycled water via groundwater recharge, and such programs could be implemented to develop this practice within the MokeWISE region. Surface water augmentation regulations for indirect potable reuse and state guidelines for direct potable reuse are expected in 2016, which may enable expanded use of recycled water for potable purposes.

 Direct injection. Recycled water could be directly injected into the groundwater basin to help stabilize groundwater levels and offset Mokelumne River water use.