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The aquifer risk map is being developed to fulfill requirements of SB-200 and is intended to help prioritize areas where domestic wells and state small water systems may be accessing groundwater that does not meet primary drinking water standards (maximum contaminant level or MCL). In accordance with SB-200, the risk map is to be made available to the public and is to be updated annually starting January 1, 2021. The Fund Expenditure Plan states the risk map will be used by Water Boards staff to help prioritize areas for available SAFER funding.
This layer contains summarized water quality risk per census block group, square mile section, and well point. The overall census block group water quality risk is based on five risk factors (1. the count of chemicals with a long-term average (20 year) or recent result (within 2 years) above the MCL, 2. the count of chemicals with a long-term average (20 year) or recent result (within 2 years) within 80% of the MCL, 3. the average magnitude or results above the MCL, 4. the percent area with chemicals above the MCL, and 5. the percent area with chemicals within 80% of the MCL). The specific chemicals that contribute to these risk factors are listed as well. Higher values for each individual risk factor contribute to a higher overall score. The scores are converted to percentiles to normalize the results. Higher percentiles indicate higher water quality risk. The water quality data is based on depth-filtered, de-clustered water quality results from public and domestic supply wells, collected following a similar methodology as the Domestic Well Needs Assessment White Paper. The methodology used to calculate the risk percentiles is outlined in the Aquifer Risk Map Methodology. To provide comments or feedback on this map, please email SAFER@waterboards.ca.gov or Emily.Houlihan@Waterboards.ca.gov.
Methodology for the draft aquifer risk map available for download.