Nitrate in Groundwater – Implementing Groundwater Monitoring Requirements for Irrigated Agriculture and Ensuring Safe Drinking Water in the Central Coast Region of California
Central Coast Water Board
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Protecting groundwater that serves as a drinking water source is among the highest priorities for the Central Coast Regional Water Quality Control Board (Central Coast Water Board). In March 2012, the Central Coast Water Board adopted an updated Conditional Waiver of Waste Discharge Requirements for Dischargers from Irrigated Lands (Agricultural Order No. R3-2012-0011), including the requirement for growers to conduct groundwater monitoring and report data electronically to the Central Coast Water Board. The objectives of these initial groundwater monitoring requirements are to evaluate groundwater conditions in agricultural areas, identify areas at greatest risk for excessive nitrate discharge and loading and exceedance of drinking water standards, and identify priority areas for nutrient management. Growers enrolled in the Central Coast Water Board’s Irrigated Lands Regulatory Program (ILRP) must sample all domestic drinking water wells and also the primary irrigation well, or participate in an approved cooperative groundwater monitoring program. As of January 2016, the Central Coast Water Board received groundwater monitoring data for approximately 4000 groundwater wells in agricultural areas. Consistent with existing reports, the data confirms wide-spread nitrate impacts to groundwater in the Central Coast Region. In general, nitrate concentrations ranged from less than the detection limit to 870 mg/L Nitrate (as N) – a maximum that is 87 times the drinking water standard for nitrate (10 mg/L Nitrate as N). Overall, approximately 26% of the groundwater wells sampled region wide exceeded the nitrate drinking water standard, including both domestic drinking water wells and irrigation wells. In Monterey County, approximately 38% of the groundwater wells sampled exceeded the nitrate drinking water standard. Well construction information is limited; however the distribution of nitrate concentrations with depth demonstrates that in general, nitrate concentrations decrease with depth. In response to these data, the Central Coast Water Board is implementing the Agricultural Order to control excessive nitrate loading from agricultural operations. In addition, the Central Coast Water Board and the State Water Resources Control Board - Division of Drinking Water (DDW) are coordinating together with county health departments to ensure safe drinking water by notifying domestic well owners and providing technical and financial assistance to small community water systems to implement innovative nitrate treatment solutions. Consistent with California’s Human Right to Water Law, Central Coast Water Board staff is also coordinating with environmental justice organizations to support disadvantaged communities affected by nitrate contamination to help ensure they have safe, clean, affordable, and accessible water adequate for human consumption, cooking, and sanitary purposes. The Central Coast Water Board is responsible for protecting and restoring water quality in the approximately 300 mile long coastal region from southern San Mateo and Santa Clara counties to the northern part of Ventura County. DDW is a statewide agency that regulates public water systems; oversees water recycling projects; permits water treatment devices; and supports and promotes water system security. Groundwater data submitted to the Central Coast Water Board is available to the public on the Water Board’s GeoTracker data management system (https://geotracker.waterboards.ca.gov/gama/).