**5. Conclusions and Policy Implication**

This paper presents an alternative approach to salt regulation and control that follows first attempts to implement the 2002 TMDL, when it was realized that TMDL policy objectives could not be achieved without potential annual costs to stakeholders in the millions of dollars annually, using typical penalty schedules for daily exceedance of a 30-day running average EC objective at a single downstream compliance site. These costs would have potentially risen with the inclusion of two additional upstream compliance monitoring sites adopted to protect agricultural riparian diverters from high salt concentrations in irrigation applied water. The novel concept of "Real-Time Water Quality management" relies on a continually updated forecasting model to provide daily estimates of salt load assimilative capacity in the San Joaquin River and assessments of compliance with salinity concentration objectives at three monitoring sites on the river, based on the 30-day running average EC. A water quality forecasting model WARMF was developed as part of this alternative regulatory schema, which served both as a compliance forecasting tool and the means by which salt load allocations and salt exports from each of the seven contributing subareas could be estimated and compared. The trading of salt loads between subareas is now feasible as both the regulatory salt load allocation and actual salt load discharge to the river can be quantified. The results of the study have shown that the policy combination of well-crafted river salinity objectives by the regulator and the application of an easy-to use and maintain decision support tool by stakeholders have succeeded in minimizing water quality (salinity) exceedances over a 20-year study period. The WARMF model improvements, and consequent increase in stakeholder and agency confidence in this decision support tool, suggest its potential application in other river basins facing similar challenges. Our framework allows farmers and regulators to jointly understand and evaluate the meaning of various regulatory policy interventions on the emission of salinity and on the cost to be incurred by farmers at various locations along the river. The results of the paper support the development of close collaboration between farmers and regulators in the application of non-point source pollution policy. The paper also suggests significant benefit from better cooperation and coordination among and between farmers and other dischargers of salt load who rely on the river for drainage disposal and who are already

organized into sensible subareas for salt management. This can provide a cost-effective pathway for agricultural sustainability.

**Author Contributions:** Conceptualization, A.D. and N.W.T.Q.; methodology, A.D. and N.W.T.Q.; validation, A.D. and N.W.T.Q.; formal analysis, A.D. and N.W.T.Q.; investigation, A.D. and N.W.T.Q.; resources, A.D.; data curation, A.D. and N.W.T.Q.; writing—original draft preparation, A.D.; writing—review and editing, A.D. and N.W.T.Q.; supervision, A.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded, in part, by the Gianni Foundation Mini-grant Program 2020 DAVIS CA, 95616, USA.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data used in this paper is reported in the various tables. Additional clarifications regarding the data can be obtained from the corresponding author upon request.

**Acknowledgments:** The work leading to this paper was funded by the Giannini Foundation of Agricultural Economics Mini-grant Program. Ariel Dinar would like to acknowledge support from the W4190 Multistate NIFA-USDA-funded project, "Management and Policy Challenges in a Water-Scarce World". Financial support for the development of the real-time salinity management concept has been provided by the US Bureau of Reclamation, Division of Planning, and the California Department of Water Resources through Proposition 84- funded grants.

**Conflicts of Interest:** The authors declare no conflict of interest.
