Monitoring

As part of our routine monitoring services at landfills, we typically also measure explosive gas concentrations. At some facilities, this is accomplished by measuring concentrations in the ground-water monitoring wells. Other facilities have gas probes specifically for this purpose. Generally, we install normally closed quick connect fittings on the cap such that the concentration can be measured without removing the cap. We have several gas measuring devices; however, some of our clients prefer that we use their device.

We installed, calibrate and maintain two continuous explosive gas monitoring systems. One is in the crawl space beneath an office and the other, beneath a cashier building at the landfill entrance. In order to maintain acceptable concentrations beneath the cashier building, a continuous forced air venting system was designed and is currently operating.

Design

Our first involvement with landfill gas control system design was in 1992 when we assisted Laidlaw Gas Recovery with the design of the active venting system installed at the Denver Regional Landfill (North). Our involvement primarily related to specification of appropriate total depths and perforated intervals for the vents; however, we also prepared the bid documents for the work. In 1995, we prepared a detailed design for the phased construction of an active system at the Denver Regional Landfill (South) involving both vertical and horizontal vents. A portion of the vertical vent system was constructed in 1995 in accordance with our design (again, we prepared the specifications and bid documents for the work). We later assisted SCS Engineers in the development of the vent design details for the portion of the system that was installed in 1998 at the Denver Regional Landfill (South).

Between 1999 and 2001, we designed a passive boundary control system utilizing 10 vertical passive vents for the closed Longmont Landfill. The vent spacing used in the design was based on detailed analysis of gas flow to and head drops around the vents. Perforation and surface seal lengths were selected such that the system could be converted to active operation, if necessary to achieve appropriate control. Detailed construction specifications were prepared for bidding and construction quality control purposes. This system has been constructed and appears to be functioning as designed.

During 2000 and 2001, we also prepared detailed designs for two closed facilities in the Denver metropolitan area for Clear Creek Development and Pecos Investments. Again, vent spacings were based on detailed analysis of gas flow to the vents.

Permitting

As we all know, permitting of methane emissions is a somewhat thorny issue. Depending on the size of the facility, emissions may be subject to the emission guidelines. Alternatively, a simple APEN for non-methane organic emissions may be required. Our experience with air permitting includes obtaining the air permits (APENs) for both of the Denver Regional Landfill operations. We also prepared initial design capacity reports (or equal) for three sites and performed a Tier 2 investigation at one of these.

Construction Management & Quality Control

We provided this service during the construction of the gas control systems at the Denver Regional Landfill (North) in 1994, the Denver Regional Landfill (South) in 1995 and 1998, and the closed Longmont Landfill (2000 and 2001). As part of the service, we developed health & safety plans for the work and oversaw the implementation of the plans. We inspected all materials and construction techniques for compliance with the specifications and made field decisions regarding completion details based on the design concepts when subsurface conditions were found to differ from those anticipated.

As-Built Documentation

We prepared detailed as-built documentation of the system constructed at the Denver Regional Landfill (North), the two systems constructed at the Denver Regional Landfill (South) and the system at the closed Longmont Landfill. The documentation included descriptions of construction methods, subsurface conditions, construction materials, and as-built details. Photographs, boring logs, completion diagrams, survey data, and maps showing vent locations and appurtenant structures were all provided. The project specifications and health & safety plans were also attached.