Since its inception, the El Sobrante Landfill has an excellent record in meeting and exceeding city, state and federal guidelines. Our commitment to the community’s environmental and social health means that we are continuously working to operate our facility in the safest way possible.
The El Sobrante Landfill is designed to dispose of non-hazardous solid wastes. The current permits require all disposal areas to be constructed with a composite liner system and leachate collection system. The leachate collection system gathers wastewater that is generated by the overlying municipal solid waste. It is then extracted and disposed of through evaporation or re-circulation into the landfill.
The primary liner consists of two synthetic high-density polyethylene (HDPE) layers encasing a geosynthetic clay liner (GCL). This liner system is underlain by a minimum of one foot of low-permiability clay or equivalent material, and protected above by a minimum two-foot thick soil layer. Together, these components of the liner system prevent overlying waste and its contaminants from penetrating through to the surrounding environment.
The leachate collection system consists of synthetic drainage material called a geocomposite. The geocomposite is comprised of high-density polyethylene channels manufactured to rapidly convey liquids such as leachate. It is considered to be an acceptable equivalent to one-foot of granular drainage material. A non-woven filter geotextile is attached to prevent infiltration of soil that will clog the geocomposite. Base grades are sloped to a central collection sump which is designed for subsequent removal of leachate to an onsite storage tank.
Following completion of the various liner components, landfill construction is accomplished by the area method. Open refuse is minimized by the construction of daily work areas sized to handle only each day's volume, and subsequently covered and sealed with cover material at the close of each operating period.
The current groundwater-monitoring program includes monitoring wells placed around the active areas of the El Sobrante Landfill. The locations of the wells are principally selected to intercept groundwater that flows beneath the landfills. The depths of the monitoring wells have been selected to monitor the uppermost groundwater. Monitoring wells are sampled and inspected on a regular basis in accordance with state and federal guidelines.
LANDFILL LINER CONSTRUCTION
All components of the liner system construction are supervised and inspected to ensure that the completed landfill will be protective of the environment. This includes manufacturing of the HDPE liner and installation of all components of the liner system during construction.
Preparation of the existing ground surface is performed prior to construction of the liner system to achieve the design subgrade configuration and remove rocks that could penetrate the liner. After preparation of the sub-base, a one-foot thick clay layer with a specific permeability is installed on the base of the landfill. A forty-mill HDPE liner is placed on top of the clay followed by a geosynthetic clay liner and a 60-mill HDPE layer. The geosynthetic layer is equivalent to a 2-foot of low permeability layer. Finally, a drainage geocomposite is placed above the HDPE liner followed by a minimum one-foot of #3 Pea gravel and two feet of operations soil.
The HDPE liner is fabricated, installed, tested and repaired in accordance with approved guidelines. Independent Quality Assurance personnel oversee al manufacturer's recommendations and installation procedures.
A brief summary of the construction guidelines is presented below:
- The liner installation contractor has been approved by the geomembrane manufacturer, and has the necessary personnel and equipment to perform the work.
- All personnel performing field liner seaming are qualified by experience or by passing field seaming tests.
- Field seams will be oriented parallel to slopes, and will not be located in areas of potential stress concentrations. Adjacent geomembrane panels will be overlapped a sufficient distance to permit peel tests which are to be performed on all field seams.
- Extrusion or fusion welds, using only equipment and materials specifically approved, will join Field seams. Prior to seaming, the entire seam area will be free of moisture, dirt, dust, foreign material and debris of any kind.
Final acceptance of the geosynthetic liner system is based on certification by the Quality Assurance/Quality Control (QA/QC) consultant that the geosynthetic materials have been properly installed.
Following approval of a lined area by the QA/QC inspector, overlying protective cover layer materials are placed.
LANDFILL GAS MONITORING
A regular gas-monitoring program has been in effect at the El Sobrante Landfill since its inception and includes permanent probes located along the perimeter of the landfill. The probes are installed to monitor the entire depth of waste to ensure that methane gas does not migrate off the landfill property.
LANDFILL GAS COLLECTION AND RECOVERY
The El Sobrante Landfill gas collection and recovery system is designed to achieve the following:
- 1. Reduce the potential for off-site landfill gas migration
- 2. Minimize landfill gas emissions from the surface of the landfill
- 3. Control landfill odors
A landfill gas recovery system is in operation on the active portions of the El Sobrante Landfill. The purpose of the system is to collect and incinerate methane gas that is generated by the decomposition of waste.
The gas recovery system is designed to provide continuous removal of landfill gas in active areas of the landfill and consists of gas extraction wells, gas collection piping, vacuum collection skid, and enclosed flare. Gas wells are installed at appropriate spacing to efficiently collect gas generated by the waste. The wells are connected to a pipe network that transmits gas to a high efficiency flare for destruction. A vacuum is applied to the gas well field by a blower system that is located adjacent to the flare.