S.B. County Groundwater Characterization Project: Santa Ynez River Groundwater Basin (2019)

Onsite Wastewater Treatment Systems (typically referred to as septic systems or OWTS) located in the Santa Ynez River Valley, Santa Barbara County, have been linked to elevated nitrate levels in drinking water wells.

The highest risk to groundwater was found to be in Janin Acres, located adjacent to the Santa Ynez River with a relatively high density of OWTS and shallow groundwater. Two other areas at risk are the area northeast of Los Olivos and the Lompoc Plain, also characterized by shallow groundwater.

These are among the findings in a three-year study of the Santa Ynez River Valley Groundwater Basin, a cooperative effort of Heal the Ocean and the Central Coast Regional Water Quality Control Board. Funding from Heal the Ocean paid for intern Riley Haas, an environmental studies major from Cal Poly, San Luis Obispo, to work at the Regional Board offices in San Luis Obispo, compiling and digitizing water well data in five sub-basins from the Los Olivos area along the Santa Ynez River to Lompoc and Vandenberg Air Force Base.

The study, “Santa Barbara County Groundwater Characterization Project: Santa Ynez River Valley Groundwater Basin” which went through extensive review and hydrology analysis by Regional Board staff, is the most complete picture to date of water quality in the Santa Ynez-Lompoc Valley area.

Utilizing a US EPA risk model, the report provides a sophisticated and detailed analysis of water quality data in the study area based on geographic information system (GIS) mapping of various hydrogeologic parameters and other characteristics. It addresses chemical constituents, proximity to agricultural lands, density of OWTS, groundwater recharge rates, depth to groundwater, geologic features, and other variables.

According to Rick Merrifield, former Santa Barbara County Environmental Health Services director (and member for Heal the Ocean’s Advisory Board), the study “confirms concerns that have been noted for decades (since the 70’s) related to groundwater pollution and human health as a result of high-density development using OWTS in areas with shallow groundwater.” Commenting on Los Olivos in particular, Mr. Merrifield stated, “Onsite systems have been in constant use for sewage disposal in Los Olivos since the 1880s. That's almost 140 years!” Having studied the septic system situation in Los Olivos during his time as EHS director, Merrifield had noted the “extreme density” of systems (lots as small as 4,500 square feet whereas the Regional Board standard is at least one acre - 43,560 sf) - and the inability to expand aging systems because there is so little undeveloped area leads to shallow groundwater contamination. Merrifield also noted a river runs through the center of town, and that groundwater is as shallow as 10-12 feet deep.

The former Santa Barbara County EHS director notes that nitrates are useful as indicators of pollution from sewage disposal systems and/or agricultural fertilizers. The Santa Ynez River Valley Groundwater Basin report observes that while agricultural fertilizers are also a known source of nitrates, proximity to farmland has a much smaller impact than the density of septic systems. “While it's true that nitrate can come from livestock and crops, that typically happens only when the source of nitrate is somewhat concentrated, not on open pasture land,” says Merrifield. “The report states pretty clearly that there is a correlation between OWTS density and nitrate levels in the groundwater.”

For more details from the report, click here.