Aquifer Risk Map 2021

<div>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.<br /></div><div><br /></div><div>Methodology for the draft aquifer risk map <a href='https://gispublic.waterboards.ca.gov/portal/home/item.html?id=5f94cf5ca2a04f66a3dcfab29cf6c764' rel='nofollow ugc' target='_blank'>available for download</a>.<br /></div><div><br /></div><div>Water quality risk: </div><div>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 four risk factors (the count of chemicals with a long-term average (20 year) or recent result (within 2 years) above the MCL, the count of chemicals with a long-term average (20 year) or recent result (within 2 years) within 80% of the MCL, the average magnitude or results above the MCL, and the percent area with chemicals above the MCL or 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. The water quality data is based on depth-filtered, declustered water quality results from public and domestic supply wells, collected following a similar methodology as the Domestic Well Needs Assessment White Paper. This layer also displays the total estimated count of domestic wells per census block group, based on the Department of Water Resources Online System for Well Completion Reports, and the total estimated count of domestic well user population, based on the United States Geological Survey Road-Enhanced Methodology (Johnson and Belitz, 2019). To provide comments or feedback on this map, please email [e-mail] or [e-mail]. </div><div><br /></div><div>Individual chemicals: </div><div>This layer shows declustered water quality data for arsenic, nitrate, 1,2,3-trichloropropane, uranium, and hexavalent chromium per square mile section. The intent of the aquifer risk map is to help prioritize areas where domestic well users and state small water systems may be accessing groundwater that does not meet primary drinking water standards (maximum contaminant level or MCL) and will be updated annually starting January 1, 2021. </div><div>The section water quality data is based on depth-filtered water quality results from public and domestic supply wells, collected following a similar methodology as the Domestic Well Needs Assessment White Paper. This layer contains the long-term average (20 years) as well as the count of recent results (within 2 years) above the MCL, between 80% - 100% of the MCL, and below 80% of the MCL for each square mile section. </div><div><br /></div><div>Drinking water users: </div><div>This layer shows the locations of state small water systems and domestic well density. The state small water system locations were collected by the Rural Community Assistance Corporation. The locations are approximate and may not exactly represent well locations or service boundaries. The domestic well density per square mile is based on well completion report data from the Department of Water Resources Online System for Well Completion Reports. This layer also contains the public water system boundaries (available on the <a href='https://gispublic.waterboards.ca.gov/portalserver/rest/services/Drinking_Water/California_Drinking_Water_System_Area_Boundaries/MapServer' rel='nofollow ugc' target='_blank'>State Water Board REST endpoint</a>) for reference.</div><div><br /></div><div>Reference layers: </div><div>This layer contains several reference boundaries, including boundaries of CV-SALTS basins with their priority status, Groundwater Sustainability Agency boundaries, census block group boundaries, county boundaries, and groundwater unit boundaries.</div><div><br /></div>