Landfill gases, while invisible, are far from harmless - they can endanger public health and pollute the air. In 1991, EPA proposed rules to control emissions of carbon dioxide (CO2 ) and meth-ane (CH4), with traces of nonmethane organic carbons (NMOCs) such as ethane, toluene and benzene.
EPA's proposal includes NSPS for new and modified MSW landfills (those accepting waste after May 30, 1991), along with emission guidelines for states to regulate existing facilities (those accepting waste on or after November 8, 1987).
If sites exceed certain exemption criteria (see table), an active landfill gas collection system must be installed, which includes mechanical blowers or compressors that create a pressure gradient to extract the gas.
To estimate NMOC emissions, EPA has created the computerized, three-tiered Landfill Air Emissions Estimation Model with specific default values. If Tier 1 yields an emission rate exceeding the cutoff, Tier 2 analyzes the landfill gas using the site-specific NMOC concentration. Field testing (Tier 3) also may be conducted.
Although EPA's NSPS and emission guideline criteria may exempt a facility, the gas migration control requirements of Subtitle D ss 258.23 could still mandate a landfill gas control system. Operators should consult the state regulatory agency.
Design And Monitoring EPA's ss 60.758 provides owners and operators with design specifications for active vertical collection systems. Alternate designs must be approved by the state or EPA.
Collected landfill gas must be routed to an open flare in accordance with ss 60.18 or to an alternative system, such as an enclosed combustion device, which reduces the weight of NMOC concentrations by 98 percent, or the gas may be routed to a treatment system for a beneficial end-use.
The EPA considers active systems the most cost-effective way to collect landfill gas and prevent emissions. Passive systems will be allowed only if the operator can show that the wells collect gas from all areas of the landfill and that the landfill is fully contained with synthetic liners to prevent gas migration.
Emission control responsibility does not end when an active gas collection system is installed. The proposed ss 60.755 requires that the gauge pressure in the gas collection header at each well be monitored at least monthly to verify that the system functions efficiently.
Open flares must include a device that indicates a continual flame and a flow indicator on the header feeding the flare. The appropriate regulatory agency will determine monitoring procedures for other devices.
In the latest proposed changes to the NSPS and emission guidelines, EPA added monthly surface monitoring requirements, in which a technician walks a grid pattern on the landfill surface with a flame ionization detector. Any areas exceeding 500 ppm methane must comply within a time frame determined by the state regulatory agency.
When the new federal rules are promulgated, states will have nine months to adopt and submit implementation plans. Landfills then will have three years to comply under the following schedule:
* Initial reporting (90 days). For new facilities, ss 60.756 requires the initial design capacity report within 90 days of the construction or operating permit or within 30 days of construction. If the exemption capacity is exceeded, the first annual NMOC emission rate report must be submitted within 90 days of startup.
For existing facilities that are exempt, the initial design capacity report fulfills reporting and record-keeping requirements. For those not exempt, the design capacity report and the first annual NMOC emission rate report must be submitted within 90 days of the state plan's effective date. * Further site-specific testing, system design and installation (2.5 years). If Tier 1 indicates NMOC emission rates exceeding the regulatory level, site-specific testing (Tier 2 and optionally Tier 3) may be performed. Then the collection system is designed, reviewed by the state a-gency and installed.
* Performance testing (90 days). Installation of an approved landfill gas control system exempts facilities from the annual NMOC emission report requirements. Nevertheless, a semiannual monitoring and performance report of the control system is required, starting with an initial report within 90 days of installation and startup, and the system's downtime must be documented.
A landfill closure report must also be filed. If the landfill gas control system is deactivated and removed, a report must be submitted to the EPA.
Potential Effects The final NSPS and emissions guidelines will have a significant financial impact on facilities requiring an active gas collection system. Other site-specific considerations will also have an effect.
Operators will face decisions that will determine system installation costs and the yearly maintenance budget. Choices include above- or below-ground collection systems, open or enclosed combustion devices and the extent of preinstallation testing.
Open candle flares cost less and need less monitoring and maintenance than enclosed flares. But an enclosed system may be necessary to reduce flame visibility in nearby neighborhoods or to meet state emission control regulations.
The method and materials used to install the collection system will directly affect the landfill budget, as will salaries of monitoring and maintenance personnel, safety training, vehicles and monitoring equipment.
The collection system also will affect facility operations. During installation, access roads are commonly blocked to construct header road crossings.
A fulltime monitoring and maintenance crew will probably be required to ensure that the control system operates efficiently. Installing required controls in twoyear-old waste also may affect the landfill's waste sequencing.
Of all the criteria involved in designing and operating the gas control system, safety is the most critical. Proper design and operation can minimize the dangers of landfill gas. Monitoring and maintenance personnel must understand the system's purpose and proper safety procedures. Investing in safety will improve the site's record, reduce compensation cases and improve the morale of employees working with the control system.
One way to assess the impact of the new rules is to run sitespecific Tier 1 calculations as soon as possible to determine the facility's emission status. Getting involved in the formation of the state implementation plan will also minimize surprises.