*4.2. Discussion*

As California battles another year of drought; records are being broken for climate extreme conditions impacting the sustainability of water resources and human-induced problems of water scarcity, quality, and misallocation. The State of California has taken aggressive action starting in 2014 with the passage of the Sustainable Groundwater Management Act and the formation of the stakeholder-led Central Valley salinity Coalition (CVSALTS) that together address problems of unsustainable groundwater pumping practices, problems of subsidence and water quality degradation of surface and groundwater resources, and the fertility of agricultural soils. Although salinity degradation of receiving waters, such as rivers and deep percolation of saline water to aquifers, have been studied for over 100 years and are well understood, there has been a reluctance of the state to commit to addressing this problem. The publication of the 2002 Total Maximum Daily Load (TMDL) by the federal EPA for salt and boron incentivized the search for effective and cost-effective policy tools to address salinity impairments in the San Joaquin River and to find a feasible and equitable schema that would be accepted by stakeholders and foreclose costly litigation that would result in a continuation of the status quo.

TMDL required the state government water quality regulator to set salt load objectives for the basin in 2002. However, the conservative nature of the TMDL computation and utilizing the lowest 10% average low-flow condition resulted in allocations that were unattainable without a major impact to the agricultural economy in each subarea. This created a need to replace the initial TMDL allocations with more flexible concentration objectives based on a 30-day running average electrical conductivity (EC) that will accommodate agricultural production and irrigation practices. A concentration objective allows agricultural producers and other salinity dischargers to utilize more of the available salt

load assimilative capacity in the SJR. This initial compliance monitoring objective has been supplemented with two additional upstream salinity objectives, ostensibly, to protect the water quality of agricultural diversions made by westside agricultural producers.

The adjustments of the quality standards to seasons and to the different locations (subareas) and the real-time reporting to the stakeholders allow farmers more flexibility in adjusting their practices and responding to the standards in a creative way. In that respect, the approach suggested in our work is similar to Doole [21], and Doole and Pannell [22], which take into account the differences in abatement cost and ability to address quality standards by different dairy farms in New Zealand. Hence, a differential standard is suggested for more cost-effective results at the regional level.

Adjustment of the salinity standard to the conditions in the river assimilative capacity and in each subarea along the river also allows introduction of trade in salinity disposal permissions among subareas as another way of handling the salinity load to the river. In that respect, the experience of the Hunter Basin of New South Wales, Australia [25,26], is similar to the suggested scheme in the SJR as discussed in our paper. The main idea of the scheme in the Hunter was to permit discharge of salt loads only when there was available salt load assimilative capacity in the river that drains the Hunter Basin. Details in Quinn [4], explain how salt load discharges to the river were scheduled by quantity, time, and location, based on stakeholder need and calculations of salt load assimilative capacity using a simple spreadsheet mass–balance model. While our work has not explored regional cooperative arrangements, such as trade in salt load permissions, or side payments for improvements in on-farm salinity load disposal, our future work will focus on such options.
