Title
Accept report regarding management and mitigation at the San Ardo Landfill.
Report
RECOMMENDATION:
It is recommended that the Board of Supervisors accept report regarding management and mitigation at the San Ardo Landfill.
SUMMARY/DISCUSSION:
The San Ardo closed landfill is a former Class III landfill located near the intersection of Cattleman Road and U.S. Highway 101. Solid waste disposal operations were conducted at the site between 1980 and 1984, at which time filling operations were curtailed and the landfill was capped with a soil landfill cap and closed. Landfill capping is a containment technology that forms a barrier between the solid waste and the surface, thereby shielding humans and the environment from harmful effects of the solid waste and limiting the migration of both landfill gas and contamination originating from the solid waste.
Currently, the landfill is being used exclusively as a refuse transfer station. Refuse operations are managed by King City Disposal Company, a subsidiary of Waste Management, Inc., which has an exclusive unified franchise agreement with the County. The transfer station is open to the local public on Saturdays and closed the rest of the week.
A deformation in the cap was observed in November 2009 near the center of the landfill. At that time, the area was approximately 23 feet by 14 feet in size. A five (5) foot deep void was observed in the west end of the depressed area and a smaller, 18-inch-deep void was observed at the southeast corner of the distressed area. In December 2009, the depressed area was repaired
by excavating soils in the area, replacing and recompacting.
During the 2013-14 rainy season, a geologist from the consulting engineering firm that provides inspection, monitoring and reporting services, observed the cap subsiding in several locations across the landfill. Continual subsidence and the creation of a sinkhole was apparent during the 2014-15 rainy season and a recommendation was made to perform a cap repair.
The cap repair was completed in May 2016 which involved excavating and backfilling the sink hole, grading the landfill surface and reestablishing the stormwater surface flow direction, upgrading the stormwater collection basin, and repair of fissures on the cap surface. Hydroseeding was applied to the entire cap to reestablish native vegetation.
Inspection reports indicate the cap performed well during the 2016-17 rain season except for the reappearance of a small sink hole, which reappeared between January 2 and 23, 2017. The sink hole was approximately eight (8) feet in diameter and was located in a 35 feet by 26 feet area containing fissures of various sizes and lengths. All fissures were filled with soil and no new displacement has been observed. In early fall, the small sink hole was filled with soil and compacted and there is no evidence that the area is continuing to sink.
The area is inspected by a landfill consultant monthly during the rainy season who will notify staff should there be a need for continued fill and compaction activities. Recommended action by the landfill consultant is to continue monitoring the area and add fill dirt and compact in an as needed basis. This maintenance will be provided by the San Ardo Road District 4 maintenance crews.
FINANCING:
Annual expenses related to closed landfills (e.g. monitoring consultant) are funded by the General Fund 001. Nominal annual lease revenues in the amount of $425 are received for use at the Chualar closed landfill. Maintenance funds are budgeted on an annual basis to provide for wet weather preparedness and other necessary maintenance expenditures. The 2016 cap repair was funded by Fund 401. It is anticipated that current funding levels will be sufficient for any additional backfilling and compacting activities that are necessary if the sink hole shows signs of reappearing.
BOARD OF SUPERVISORS STRATEGIC INITIATIVES:
Maintenance, inspection, reporting, testing of the San Ardo closed landfill is mandated by State and Federal agencies specifically to monitoring ground and surface water for pollutants (Federal Clean Water Act, Safe Drinking Water Act, State NPDES Program, Title 27 CCR, Waste Discharge Order No. R3-2004-2006, et.al.)
__ Economic Development
__ Administration
X _ Health & Human Services
_ Infrastructure
X Public Safety
Prepared by: Lynette Redman, Management Analyst III, (831) 796-6038
Approved by: Shawne Ellerbee, RMA Deputy Director of Administrative Services
Approved by: Carl P. Holm, AICP, RMA Director
Attachments:
Attachment A - Closed Landfill Budget Sheet
(Attachment on file with the Clerk of the Board)