The primary objective of proper wastewater disposal is to reduce and/or eliminate the potential contamination of groundwater, surface water, or the environment and its inhabitants. All projects that use onsite wastewater disposal require Land Use review, permitting, inspection, and, in some cases monitoring. Napa County Environmental Management is responsible for all onsite sewage disposal systems in the county. Sewer connections within Napa City limits and some unincorporated areas of the County are served by Napa Sanitation District.
In this link Countyofnapa.org/
Title 13 of the building code relates to Water, Sewers and Public Services. This link will lead you to information on drilling wells, abandoning wells, permit requirements, classes of permits, septic tanks, holding tanks, undergrounding utilities and so much more. Drilling wells and installing septic systems is complex because of the setbacks, not only on your property but setbacks from neighboring wells and septic tanks and leach lines. For detailed information click on this link and then on Title 13. http://library.municode.
You will find almost everything you need to know about building and development in Napa County in this link: Countyofnapa.org/