Hidden Valley Landfill Thun Fld

The Hidden Valley landfill is a closed 92-acre municipal solid waste landfill. It is located at 17925 Meridian Ave E in Puyallup.

Pierce County ran the landfill from the mid-1960s until 1977 when LRI bought it. Waste disposed of at the site included solid, demolition, commercial, and industrial waste. LRI stopped disposal in 1998.

Studies in the early 1980s helped the Environmental Protection Agency (EPA) assess the site. Contaminants released from the landfill to groundwater and landfill gas included: methane (landfill gas), ammonia, nitrate, dissolved iron, manganese, chloride, sulfate, and volatile organic compounds (VOCs).

In 1989, the EPA placed the site on the Superfund National Priorities List. In 1987, LRI, Pierce County, and Ecology entered into a legal agreement (consent decree) to study the site more and explore cleanup options.

After reviewing cleanup options, Ecology, Pierce County, and LRI selected the following cleanup actions:

• Closing the landfill – Leachate capping, landfill gas control, and surface water and erosion control were actions implemented as part of the closure. The landfill was closed in phases from 1989 - 2000.
• Compliance monitoring – LRI and Pierce County have operated treatment systems and monitored groundwater and landfill gas.
• Institutional controls – An environmental covenant (EC) that ensures pollutants remaining on site aren’t released. A fence around the property ensures the public cannot access the site.

LRI continues to monitor and maintain the site, such as ensuring the cover system remains in place.

Periodic Review
In June - July 2015, Ecology held a public comment period on a periodic review report for the site. The review found that cleanup actions at this site are protective. The report is now final (see below).

Consent Decree Amendment and Groundwater Monitoring Plan
In June - July 2015, we also held a public comment on revising the groundwater monitoring plan, which is a part of the consent decree, to include testing for 15 more metals and other parameters. Monitoring frequency will also increase to four times a year for one year. After one year, we will evaluate the monitoring schedule. These changes meet the state landfill law that was updated in 2012. The consent decree amendment was finalized on September 9th 2015.