Seal Cove Critical Geotechnical Hazards Area Resident Updates

November 30, 2025 Update

Montara 1pg Seal Cove FAQ FINAL 11.26.25.pdf

Montara Water and Sanitary District (MWSD) staff and Board members have been concerned about increased land movement in recent winters that have affected Seal Cove homes and District infrastructure, such as sewer and water facilities.

What caused the land to move in Seal Cove?

Seal Cove has a long, well documented history of ground and soil movement. San Mateo County has completed various studies throughout the decades documenting an active landslide.

For example, in the 1960’s, the County noted that: “development in portions of the Seal Cove community was identified by the U.S. Geological Survey as being constrained by high geologic hazards due to active landsliding and accelerated coastal erosion.”

These County reports include:

  • Geologic Analysis of the Seal Cove Area Report William Cotton and Associates, August 1980
  • Geologic Report of Seal Cove and Moss Beach Area, F. Beach Leighton and Associates, October 15, 1971

Per the County’s website, the County is currently performing a study of the area’s geotechnical conditions, using a geotechnical consultant to prepare an updated report assessing the various geologic hazards affecting the Seal Cove area, along with recommendations about how to manage development and infrastructure strategically.

What has MWSD done to address damage to its infrastructure?

Buried pipelines are affected by the same land movement that impacts homes and public roads in the Seal Cove area. The landslide movement that buckles roads can pull apart or break buried pipes. In response to the land movement, the District declared an emergency on 3/27/2025. The District’s mainlines in the actively moving landslide have been repaired as quickly as possible to provide uninterrupted service.

Why is MWSD proposing to place above ground water lines in Seal Cove?

In early 2025, to maintain water service to certain Seal Cove properties on public roads closed by San Mateo County, MWSD staff installed temporary above ground water service lines connecting homes to a nearby District water main. Given the likelihood of additional land movement in Seal Cove, MWSD is prepared to address further leaks and continue to provide service to all residences with above ground connections.

Above ground permanent service connections allow property owners to visually inspect water service lines and repair any leaks rapidly. Where needed, above ground mainlines can continue to provide fire protection service to affected structures and can be monitored and repaired quickly by MWSD.

How is San Mateo County involved?

A map detailing geological hazard zones in Seal Cove, divided into Zones 1, 2, and 3, with street names and features.

 San Mateo County is the land use agency for the coastal zone, and is responsible for expertise on geotechnical conditions, ground movement, and land use planning for the Seal Cove area. The County controls all development to ensure consistency with the County’s coastal development and geologic hazard districts, and its Local Coastal Program (LCP) policies. This includes decisions about coastal hazards, geotechnical investigation, development standards, as well as critical public safety services – such as construction permitting (including permits for MWSD work in the streets), building inspection, as well as the construction and maintenance of public roads.

MWSD-owned infrastructure is located in public roads, which fall under County jurisdiction. The County has determined that some of the roadways in which Seal Cove infrastructure is located are unsafe to access or work in. MWSD continues to monitor the situation with the County to obtain access where it is safe to work.

What did MWSD do to address the damage to other sewer and water facilities affected by land movement?

District Code sections 3-5.1100(a) (sewer) and 5-4.225 (water) define the facilities that are the responsibility of the property owner.

After forming a special assessment district in 1983 that was primarily funded by Seal Cove residents benefitting from the Seal Cove Area Collection System Improvement Project, the District allocated surplus funds to address issues in Seal Cove, but those funds were eventually exhausted.

Following the most recent land movement in early 2025, the District has advised property owners to contact private contractors to repair these facilities, including in those situations where damaged private facilities are causing sewer effluent to escape. These obligations are applicable to all property owners within the MWSD jurisdiction.

  • 3-5.1100 Maintenance of Side Sewers.
    (a) Maintenance. The construction, installation, maintenance, repair and replacement of Side Sewers, Lateral Sewers, and Building Sewers shall be, and are, the responsibility, at no cost to the District, of the owner of the Parcel served thereby.
  • 5-4.225. Ownership of Mains
    Mains and appurtenances connected to the District’s distribution system shall become the property of the District, and shall be operated and maintained by the District. Dedication of such mains and appurtenances to the District shall be made, in a form acceptable for recording, prior to commencement of Service through the new system. Title to Service Pipes and appurtenances thereto shall be vested in the owner of the Premises served thereby. Said Owners shall be responsible, at their sole cost and expense, for the maintenance, repair and replacement of such Service Pipes.

Who should I contact for assistance?

Please contact MWSD at 650-728-3545 for emergencies, or send us an email at info@mwsd.net for non-urgent inquiries.

 July 17, 2025 Update

Termination of Seal Cove Geotechnical Hazards Area Emergency.

On July 17th, the MWSD Board took action to terminate our Seal Cove Emergency. Since the last significant rain events in March, no further water mainline leaks have developed in Seal Cove. Additionally, San Mateo County has assured MWSD that encroachment permits can be issued in the impacted areas based on a licensed engineer’s inspection, signature, and acknowledgment of potential impacts on the area.
Staff suggested terminating the emergency status due to the reduced land movement and subsequent reduced damage to District assets. Work continues to develop a conceptual design for above ground water service lines, and where necessary, to provide fire flows using above ground water lines for fire protection.

June 12, 2025 Update

June, 2025 Seal Cove Critical Geotechnical Hazards Area Resident Update

 What is the latest MWSD activity in Seal Cove?

MWSD has continued to keep all existing Seal Cove customers connected for both water and sewer services.

MWSD staff continue to assess options for affected Seal Cove infrastructure and associated costs. Continued land movement will require more repairs and replacement of the affected water mains, exceeding the typical repair and replacement lifecycle of these community paid assets.

Proposed solutions to maintain water and sewer services in the hazard area may include abandonment of water mains, meter relocations, and above ground permanent service lines - effectively a main replacement.

Please Remember:

  • Check and properly maintain your sewer lateral, shared sewer laterals, sewer sump and grinder pumps.
  • Leaks on your private water and sewer laterals may be repaired by a qualified plumber.
  • Sewer pump repairs should be completed by the service company (Signa Mechanical) listed on the electrical panels of the pumps.

New Geological Survey Report

MWSD was alerted to a new California Geological Survey report with a proposed revised Alquist-Priolo Earthquake Fault Zone affecting the Seal Cove area. These maps are released under the authority of the Alquist-Priolo Act, a state law designed to reduce the hazard from surface fault rupture during an earthquake.

Seal Cove is one of only two exposed onshore locations of the San Gregorio Fault. The Seal Cove Fault section extends for approximately 4 km from where the fault initially comes onshore in Moss Beach and continues southward along Pillar Point Bluff before heading back offshore south of Pillar Point Harbor. The report states ‘there is also clear evidence of active landsliding located over 100 meters inland from the top of the sea cliff.’

Full report online at www.conservation.ca.gov/cgs/publications/preliminary-releases

San Mateo County Seal Cove Community Meeting
Wednesday, June 11th 5:30-7:30PM
270 Capistrano Road, Half Moon Bay

Supervisor Ray Mueller is hosting a community meeting to address concerns in the Seal Cove area. Representatives from San Mateo County including Planning and Public Works will be in attendance, along with other resources for residents.

San Mateo County & Seal Cove

San Mateo County’s Planning and Building Department establishes land use policies and development regulations that protect public health and safety. This includes oversight of County streets and structures on private property.

In Seal Cove:

The Building Division has been performing visual inspections of impacted properties to determine if and how the use of these homes needs to be restricted.

Public Works personnel have been inspecting road conditions to evaluate the need for any immediate measures that can be taken to maintain the County roads and ensure the continued use by the traveling public.

Updates online at www.smcgov.org/planning/sealcoveinfo

Emergency Contact Numbers

Water Emergencies: Call MWSD at (650) 728-3545
Sewer Emergencies: Call SAM at (650) 726-0124
Dial 911 for life-threatening and safety

April 28, 2025 Update

Montara 1pg Seal Cove 042825 Update Final.pdf

MWSD Board Action on May 1st

On May 1st, the MWSD Board will consider continuing this District Emergency as declared at our March 27th Board meeting. A District Emergency allows for faster contracting and response to the emerging issues in the Seal Cove area. This emergency also authorizes the District to seek state and federal financial assistance.

We continue our investigations to recommend safe solutions for Seal Cove water and sewer infrastructure.

MWSD is committed to providing continued updates directly to our Seal Cove customers, and during MWSD Board Meetings.

What is the latest MWSD activity in Seal Cove?

Staff have continued active response in the Seal Cove area. This includes responding to and repairing additional leaks of water and sewer infrastructure, as well as continuing evaluation of safe solutions to maintain water and sewer services. Some key updates:

  • Everyone remains connected and served by both water and sewer systems.
  • On San Lucas Avenue, we have abandoned both our water and sewer mains west of the Del Mar Avenue intersection. We are no longer utilizing these pipes for any water or sewage flows.
  • The water main in San Lucas was reconfigured east of the Del Mar intersection. The main now crosses San Lucas, keeps the fire hydrant at the intersection operational, and connects into the water main in Del Mar Avenue.
  • We have continued to meet and coordinate with both Coastside Fire Protection District and San Mateo County as we assess our infrastructure in the affected area.
  • Our crews have seen increased land movement most recently on La Grande Avenue.
  • Water and sewer mains on the western ends of Madrone, La Grande and Los Banos Avenues, as well as the Park Street and Beach Street intersection, are being examined for safer configurations. This may include above ground pipelines, and relocation of water meters for private properties. Above ground pipelines provide increased flexibility and quick visual access, ensuring leaks are less frequent and caught quickly.

Please Remember:

  • Check and properly maintain your sewer lateral, shared sewer laterals, sewer sump and grinder pumps.
  • Leaks on your private water and sewer laterals may be repaired by a qualified plumber.
  • Sewer pump repairs should be completed by the service company (Signa Mechanical) listed on the electrical panels of the pumps.

History of Seal Cove Land Movement

Since the 1960’s there have been numerous, geotechnical studies of the Seal Cove area by San Mateo County, the land use authority for this area.

Study started in the 1960’s, when the U.S. Geological Survey slowed Seal Cove development due to active landsliding and accelerated coastal erosion. In 1971 and 1984 San Mateo County studies confirmed continued instability and geologic hazards. Structural damage due to landslide activity has been documented throughout this time.

San Mateo County

San Mateo County’s Planning and Building Department establishes land use policies and development regulations that protect public health and safety. This includes oversight of County streets and structures on private property.

Emergency Contact Numbers

Water Emergencies: Call MWSD at (650) 728-3545
Sewer Emergencies: Call SAM at (650) 726-0124
Dial 911 for life-threatening and safety