Water Supply Not Sufficient in Los Osos — a letter to the County Board of Supervisors.

We join with the concerned residents of Los Osos who have urged you not to approve new development over the Los Osos Groundwater Basin until such time as it can be shown that the basin is capable of serving new development while continuing to serve existing homes and businesses while sustaining the habitat and wildlife that rely on it.

The Los Osos Community Plan should allow the approval of new development only in the presence of real evidence that the water supply is sufficient to support that development without permanently harming the basin, existing development, and ESHA. Absent such evidence, the proposed LOCP language is inconsistent with Public Works policy 1 and Watershed policies 1 and 2 in the Local Coastal Plan, Coastal Zone Land Use Ordinance Section 23.04.403, and Special Condition 5 of the Los Osos Wastewater Project requiring a guarantee of adequate groundwater for ESHA and maximized conservation measures.

We have reviewed the documents submitted to the Basin Management Committee pertaining to recent water level and chloride metrics and concur that the evidence shows that seawater intrusion has been rapidly advancing over the last two years, and is near the point of no return in the deep aquifer (2500 mg/l of chlorides.) Per the 2019 monitoring report, water levels ranged from sea level to eight feet below sea level, in stark contrast to the Basin Plan’s target of aquifer levels at eight feet above mean sea level in order to stop and reverse seawater intrusion.

It is clear to us that these metrics, not the degree to which residents have adopted retrofits or achieved water conservation goals, should govern the County’s decisions on proposed revisions to the Growth Management Ordinance exempting accessory dwelling units, affordable housing, and commercial-to-residential conversions from growth limits. Nor is proof of sustainable yield to be found in proposed LOCP language and revisions to the Growth Management Ordinance eliminating the requirement for determination of a sustainable water supply for certain new development, replacing that determination with a requirement for a 2:1 retrofit.

In short, it should be clear, per the standard in the proposed LOCP language, that new development cannot 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.”

We reiterate the recommendation we made in our August 25, 2015, letter to Kelly Brown, SLO County Dept. of Planning, for language in the LOCP:

“Prior to approval of any new development, conclusive evidence (well tests over time) must show that seawater intrusion has reversed and ample freshwater exists in the Basin to support the current population plus additional population…. All new development over the Basin shall be prohibited until the Basin Plan Water Level and Chloride Metrics have been exceeded, showing the Basin has ample reserves to sustainably support additional development while maintaining ample storage capacity to weather droughts and climate change. As an additional minimum requirement, no wells, including private wells and test/observation wells, shall have a chloride level above 100 mg/l or water levels below 9.5 feet above mean sea level (amsl) in the Lower Aquifer, 13.5 feet amsl in the deep aquifer, and 6 feet amsl in the Upper Aquifer. The amount of new development allowed will depend on the extent to which these minimum requirements are exceeded, indicating excess Basin capacity, and conservative estimates, based on water use and other data, of the amount of development the added capacity will support.”

Andrew Christie
Santa Lucia Chapter of the Sierra Club

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