Water & Gas Monitoring

Groundwater Monitoring Program

The groundwater monitoring network includes a network of seventeen (17) upgradient and downgradient monitoring wells that are located around the immediate perimeter of both the closed landfill (old original landfill) and active landfill portion (Cells A-D).

Asotin County submits quarterly and year-end (annual) groundwater monitoring reports to Ecology in accordance Ch. 173-351-410, WAC. These reports summarize the quarterly groundwater field measured parameters (such as groundwater flow rate and groundwater flow direction), statistical trend evaluation, comparison to maximum contaminant levels (MCL’s), and laboratory results.

Landfill Gas Control System

The landfill gas (LFG) control system was originally installed in 1993 at the ACRL to continuously collect gas from above the geomembrane component of the bottom liner of the modern landfill (and below the final cover system upon closure). Gas extraction from the modern landfill generally consists of horizontal gas collectors buried in the waste connected to monitoring stations on the south side of the landfill to control the gas flow rate (and methane concentration) going to the flare station. A series of vertical gas extraction wells were also installed at that time along the southern (upgradient) margin of the closed landfill.

The ACRL is required to comply with Washington State performance standards, namely WAC 173-351-200(4) and 173-351-200(5), that address explosive gas control and air quality criteria. Asotin County has implemented a routine explosion monitoring program at the ACRL as part of their operations, to ensure that methane concentrations do not exceed 25 percent of the lower explosion limit for methane in nearby facility structures and at the landfill property limits. Open burning of solid waste is prohibited at the landfill.

The ACRL also must comply with federal landfill gas regulations, namely 40 CFR Part 60, Standards of Performance for New Stationary Sources, subpart WWW – Standards of Performance for Municipal Solid Waste Landfills. The provisions of this regulation apply to each municipal solid waste (MSW) landfill that commenced construction, reconstruction, or modification on or after May 30, 1991. The control requirements apply to all MSW landfills with a design capacity equal to or greater than 2.8 million tons AND 3.3 million cubic yards. The ACRL has an expected capacity of 3,826,000 cubic yards at full buildout of all four cells (Cells A-D). At a variable effective density increase from 1,050 to 1,250 lb/cy over its life, the mass capacity of the landfill is expected to be around 2.2 million tons. It is estimated that the old original landfill area has approximately 1.3 million cubic yards in place, equating to about 500,000 tons. Therefore, the total facility at full development will have an estimated 5.1 million cubic yards and approximately 2.7 million tons of refuse in-place. Although the total waste is over the volume threshold but under the weight threshold, whereby not triggering NSPS, the County has instituted an active landfill gas control system at the ACRL as a best management practice to promote worker safety and environmental controls for both odor and gas migration.