Sanitary Sewer Overflow Due to Heavy Rains

February  16, 2017

Napa, California – Despite the extensive efforts of NapaSan staff to divert wastewater away from potential overflow areas, there was a sewer overflow in the stormwater detention basin in the Lake Park neighborhood. An estimated 25,000 gallons of dilute wastewater entered into the five million gallon stormwater detention basin. As soon as the overflow began, NapaSan reported the incident to the California Office of Emergency Services, posted warning signs to alert residents to temporarily avoid use of the park, and took water samples to be analyzed to determine if wastewater had entered Lake Park. Sampling did show that enterococcus bacteria were present in the water within Lake Park. Enterococcus bacteria do not have a long survival period once outside of their host, because water temperature and exposure to ultraviolet light will kill the bacteria. Additionally, when water percolates into the grass and soil, the plant roots and soil itself naturally filter out contaminants, so it is not necessary to perform a formal cleanup effort. There will be no long-term contamination effects in the area related to the sewer overflow. NapaSan will continue to monitor the Lake Park neighborhood in the coming storms and alert residents to any overflow incidents or threats to public health.

The park is a stormwater detention basin, and should never be used for wading, swimming, or other recreational uses as stated on City of Napa signs posted around the area. The stormwater that runs into the basin can contain petroleum, pet waste, litter, and other contaminants. It is also important to keep pets out of this basin since they can carry bacteria and pollutants into your home after contact with the water.

During the winter, flow through the sewer system can increase dramatically due to rainwater and groundwater seeping into cracked or damaged sewer pipes. When stormwater flows into cracked pipes, it is called inflow and infiltration. This extra water can overwhelm the sewer system and lead to sewer overflows. NapaSan is working to replace the aging sewer pipes that allow storm and groundwater to seep into the sewer system, and will continue these efforts to minimize the occurrence and effects of sewer overflows and protect public health and the environment.

Napa Sanitation District (NSD) provides wastewater collection and treatment services to the residents and businesses in the City of Napa, Silverado Country Club, the Napa County Airport and several adjacent unincorporated areas. NSD also provides recycled water service to portions of southern Napa County. Covering 20 square miles, NSD has been serving the community since November 1945. For further information about the District, please see