Due to historical water quality degradation of the Los Osos Groundwater Basin ("Basin"), new development is contingent to implementation of the Basin Plan for the Los Osos Groundwater Basin ("Basin Plan") and the County's Retrofit-to-Build program. To ensure that growth does not result in further degradation of the groundwater basin, the County's Growth Management Ordinance serves as the tool for metering out residential construction permits (for more information regarding growth rate, see "Residential Growth Rate" section below). In addition, the LOCP would only allow for the approval of new discretionary land use permits if the proposed development can be accommodated by the sustainable yield of the Los Osos Groundwater Basin without causing seawater intrusion (as identified in the Basin Plan and annual monitoring reports), unless the proposed development offsets the net increase in water demand at a 1:1 ratio or, for new structures, the 2:1 ratio required by the County's Retrofit-to-Build program.
Los Osos Groundwater Basin ("Basin")
The Basin is identified as a Level III severity. The Basin is made up of several aquifer layers, underlying the Los Osos community and surrounding areas. The Upper and Lower Aquifers are the main sources of municipal and domestic water supplies. Nitrates from historic use of septic systems in Los Osos has caused the degradation of water quality in the Upper Aquifer, and in response, water purveyors increased pumping water from the Lower Aquifer. However, the increased groundwater extractions exceeded the sustainable yield of the Lower Aquifer in the western area, resulting in seawater intrusion. The groundwater issues Los Osos faces pre-date the drought and the current development restrictions.
To address the groundwater issues, the County and water purveyors developed the Basin Plan (approved on October 14, 2015), which calls for many infrastructure projects. These projects, along with their funding, fall into two phases.
- Phase 1 Infrastructure Projects intend to stabilize the Basin to serve current development with no or marginal future development
- Phase 2 Infrastructure Projects intend to increase the sustainable basin yield to allow new development and buildout of the Los Osos community
The Phase 1 Basin Plan Projects are fully funded and partially implemented. The Los Osos Groundwater Basin Management Committee ("BMC") is responsible for implementing the Basin Plan and preparing annual reports documenting the status of infrastructure improvement projects, estimated sustainable basin yield, and monitoring data to evaluate Basin conditions.
The BMC Board of Directors is scheduled to hold regular meetings on the third Wednesday of every month, starting at 1:30 p.m. Meetings are currently held remotely due to COVID-19 concerns (previously, meetings were held at the South Bay Community Center, located at 2180 Palisades Avenue, Los Osos).
For more information regarding the Basin Plan and BMC (including annual reports and meeting agendas), visit the following website:
Los Osos Basin Management Committee Website
Residential Growth Rate
The County's Growth Management Ordinance ("GMO") requires the Board of Supervisors to approve an annual growth rate for the number of new dwelling units allowed to be constructed each fiscal year to ensure new residential development is appropriate based on the availability of community resources. The GMO specifies that, each fiscal year, 65% of new dwelling units allowed are reserved for single-family dwellings and 35% of new dwelling units allowed are reserved for multi-family dwellings; while the following types of residential development would be exempt from the growth rate in Los Osos: affordable housing, accessory dwelling units, and agricultural worker housing. Currently, the residential growth rate is 0% for undeveloped properties in the Los Osos sewer service area.
On December 15, 2020, the Board of Supervisors tentatively approved the following growth rates:
- Before the Phase 1 Basin Plan Programs are implemented - 0% growth rate
- After the Phase 1 Basin Plan Programs are implemented - 1.3% growth rate
The proposed growth rate has not yet taken effect and is subject to change, as it will be reviewed annually for appropriateness, based on ongoing basin monitoring data. The Board of Supervisors Tentatively Adopted Growth Management Ordinance Amendment (2020) is available at the following weblink:
Tentative Residential Growth Rate for the Los Osos Urban Reserve Line (as of December 15, 2020)
On October 27, 2021, in conjunction with transitioning to an adaptive management groundwater model that seeks to halt further seawater intrusion while the basin plan programs are being implemented, the BMC unanimously approved a new sustainable yield estimate of 2,380 acre-feet per year (AFY) for the Basin for calendar year 2022, a 380 AFY reduction from the 2020 estimate. The County may propose an amended residential growth rate for Los Osos based on this new data and the results from the water offset study to update the Retrofit-to-Build program.
Retrofit-to-Build Program & Water Offset Study
The Retrofit-to-Build program (under Title 19) requires all new structures that use water from the Basin to retrofit older plumbing fixtures in existing homes and businesses to save twice the amount of water the new development will use prior to issuance of a construction permit to mitigate water supply impacts.
The County is hiring a consultant to prepare a water offset study to update the water usage assumption estimates, water savings calculations, and water conservation measures for the Retrofit-to-Build program. This study is anticipated to be completed by March 2022.
The Retrofit-to-Build program requirements and description of the water offset study are available at the following weblinks:
Retrofit-to-Build Program Requirements
Los Osos Water Offset Study Updates