Harrison Landfill

This recently closed MSW landfill was suspected of generating methane that was moving off site onto adjacent private property and was the subject of litigation. In addition, the landfill was suspected to be a source of volatile organic compounds (VOCs). HGC was retained to:

• conduct soil gas surveys to determine the extent of methane migration and VOC distribution,
• conduct soil and refuse characterizations to determine refuse biodegradability and LFG generation potential,
• perform barometric pressure tests to estimate in-situ LFG generation rates,
• conduct pressure testing of the existing LFG collection system to evaluate its performance,
• obtain air quality permits, and
• design, construct, and operate an LFG/VOC control system that will work in conjunction with the LFG collection system and remove VOCs.

The LFG/VOC control system that HGC constructed has been operating since August 1999, and has removed over 14,000 pounds of contaminants from the subsurface. LFG migration is well under control.

More information
APWA Projcet of the Year Award • Arizona Daily Star Article • APWA Reporter Article • City of Tucson Environmental Management Department • back to top

Silverbell and Broadway Landfills

Both MSW landfills are closed and unlined landfills and were suspected of generating methane and odors that were moving off the site onto adjacent private properties. In addition, both landfills were suspected to be sources of VOCs to groundwater. HGC was retained to:

• conduct an LFG survey to determine the extent of the off-site methane migration and VOC distribution,
• conduct refuse characterization to determine refuse biodegradability,
• perform barometric pressure and drawdown tests to determine vertical and horizontal air permeabilities and in- situ LFG generation rates,
• obtain air quality permits,
• develop an engineering design with extraction rates of 1,500 scfm, and
• complete construction and operation.

The LFG/VOC control system that HGC constructed has been operating since June 2000 for the central city landfill, and February 2001 for the west side landfill. LFG and odor at both sites have been sucessfully controlled.

More information
City of Tucson Environmental Management Department • AZ Daily Star Article 12-30-02 • back to top

Landfill Gas Measurement and Control at
Northwest Tucson Landfill, Arizona

A landfill gas control system was already in place at the site, but the available LFG was insufficient to operate the flare. The landfill was also suspected to be a source of VOCs in groundwater. HGC was retained to:

• Perform baro-pneumatic tests to measure in-situ LFG generation rates and permeability distribution
• Construct an LFG/VOC control system consisting of gas-extraction and air injection wells

HGC’s estimate of LFG generation was one-third to one tenth of previously obtained estimates, consistent with the low production obtained by the existing oversized LFG collection system. HGC’s LFG/VOC control system is now in place.

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Design of Alternative Cover, Closed Solid Waste Landfill
Former Superfund site, California

Hydro Geo Chem designed an alternative soil cover for a closed solid waste landfill that was part of a former Superfund site in northern California. This landfill is part of a Federal Superfund site that had been used for the disposal of municipal and industrial solid waste for over 50 years. HGC evaluated the thickness, soil water properties, and drainage requirements for the cover to prevent infiltration of rainwater into the underlying refuse. This work was performed to meet the cover requirements of the California Integrated Waste Management Board. This work involved:

• soil gas surveys to determine the extent of methane migration,
• drilling and sampling of the refuse,
• in-situ measurements of methane generation rates,
• evaluation of remedial alternatives including methane control systems, and
• design of a landfill cover and drainage that met State of California standards.

Earthen Cover Design • back to top