History and Overview of Cleanup

Geothermal Inc The Geothermal Inc. (GI) property is the site of a former geothermal waste disposal facility that is located about 2.5 miles southeast of Middletown on Butts Canyon Road, Lake County, California (Site). The facility, which operated from 1976 to 1986, consisted of evaporation ponds and solid waste disposal trenches where companies disposed of non-hazardous mud and waste generated from exploration, development, and power generation operations at the nearby Geysers Energy Field. PG&E was one of 17 companies and agencies who used the facility and participated in site closure after the former facility operator, Geothermal Inc., went bankrupt. PG&E purchased the property in 2003 and took over the responsibility for facility closure and maintenance. All work is conducted under the oversight of the Central Valley Regional Water Quality Control Board (Water Board).

From 2003 to 2006, PG&E conducted the following Site closure activities in accordance with an approved closure plan:

Crews Installing Landfill
  • Solar evaporation of 21 million gallons of pond water and closure of 30 acres of former waste ponds and disposal trenches;
  • Consolidation of 186,000 cubic yards of waste into a six-acre on-site landfill;
  • Filling/re-grading the remaining waste evaporation ponds with clean soil;
  • Installation of an engineered cover over the top of the landfill to prevent surface water infiltration into the landfill;
  • Grading of 90-acres around the landfill to promote rain water runoff away from the landfill;
  • Lowering neighboring Freeman Lake and planting 32-acres of trees around the landfill to lower groundwater levels so as to prevent groundwater from coming into contact with the bottom of the landfill;
  • Installing water supply and irrigation systems for the tree plantations and fire protection; and
  • Constructing four acres of new wetlands and restoring additional habitat.

The final landfill cover consists of a layer of high-density plastic covered by two feet of clean soil. The soil was then planted with native grasses. Eucalyptus and poplar trees were specifically chosen for planting around the landfill to maximize groundwater uptake and lower groundwater in the vicinity of the landfill.

Since 2006, PG&E has performed post-closure maintenance activities that include inspection and maintenance of the closed landfill and tree plantations, and semi-annual groundwater and surface water monitoring. PG&E also uses goats to graze the area around the landfill to reduce the threat of wildfire.

Grasses on landfill Tree on landfill

Project Status Update

PG&E continues to perform the post-closure monitoring and maintenance activities to maintain the closed landfill and monitor groundwater conditions and elevations. Post Closure monitoring data indicates that all closure requirements have been met; except the year-round five feet of separation between the waste and groundwater at all locations beneath the landfill. PG&E conducted additional site studies and concluded that additional measures are needed to achieve the required separation.

PG&E has submitted a Waste Separation Feasibility Study and Corrective Action Plan to the Water Board, recommending the following additional closure activities:

  • Install drainage improvements to convey storm water away from the landfill; and
  • Design and install an underground barrier wall that would divert groundwater flow around the landfill

The Water Board is reviewing these recommendations and if approved, PG&E anticipates that preliminary field work will begin the summer of 2015 and installation will occur in 2016.

Connecting with our Community

Middletown High School Field TripAs part of its commitment to the local community, PG&E works with various organizations including Middletown High School. Recently, PG&E invited students from Middletown High School Advanced Placement Environmental Science class to learn more about the diversity of ecological habitats and wildlife at the site through bird and wildlife monitoring and hands-on science activities.

Wildlife Habitat Council Overview and Certification

Integrity of Landfill CapThe closure activities that PG&E implemented at the Site required the removal of some wildlife habitat – including wetlands, riparian areas and oak trees. Working with regulatory agencies, PG&E replaced these resources, creating new wetlands and replacing trees on the property.

Frequently Asked Questions

Wildlife Habitat Who oversees PG&E's work at this site?
The Central Valley Regional Water Board, part of the California Environmental Protection Agency, is the regulatory agency responsible for overseeing and approving the work. The Water Board is responsible for the water in this region of California and, along with other Water Quality Control Boards, helps protect California's water supply. Some work may also require permits from other agencies, including Lake County, the US Army Corps of Engineers, and the California Department of Fish and Wildlife.

What chemicals were found in the soil and groundwater?
Waste in the landfill contains drilling muds, construction debris, sulfur compounds from geothermal energy production, and naturally occurring mineral compounds and elements from the surrounding region. Elevated concentrations of total dissolved solids, chloride, boron, and sulfate are present in the groundwater in the vicinity of the landfill. Testing, confirmed by the Water Board, has determined that the geothermal waste material in the landfill is not hazardous.

Why did PG&E choose to consolidate and cap the wastes as opposed to removing them?
An evaluation of closure and cleanup alternatives was performed that was based on a nationally prescribed list of factors including effectiveness, feasibility, regulatory and public acceptance, overall protection of human health and the environment, and cost. As a result of this evaluation, the Water Board determined that consolidating and capping the wastes on-site was the best closure and cleanup alternative.

Vernal PoolsHas PG&E completed the closure of the landfill?
Consolidation of the wastes into the single closure cell was completed in 2006. Post closure monitoring data indicated that all closure requirements have been met except the required year-round five feet of separation between site groundwater and landfill waste at all locations beneath the landfill.

In April 2015, PG&E submitted a Waste Separation Feasibility Study and Corrective Action Plan to the Water Board for review and approval. This Report recommends a plan for additional closure activities to achieve the year-round separation between site groundwater and landfill waste by installing an underground barrier wall to divert groundwater flow around the landfill and, improving drainage around the landfill area.

Why do I see PG&E crews at the former landfill?
PG&E regularly performs post-closure maintenance activities at the site. This includes monitoring and maintaining the landfill, maintaining the tree plantations and property, and monitoring groundwater.

What will the additional closure activities work consist of?
If approved, the additional closure activities work will include installation of a storm drainpipe that will connect with existing storm water management features at the landfill and carry storm water farther away from the landfill. In addition, an underground barrier wall will be installed to divert groundwater flow around the landfill. The exact location of the barrier and method of installing the wall will be determined after further design and engineering studies are completed.

What will this work look like?
Community members can expect to see heavy equipment, such as drill rigs, backhoes, and excavators, during the work. PG&E will keep the community informed of this work throughout the project and will distribute a work notice prior to the start of each phase of work.

We are currently in a drought - will these enhancements be effective at separating site groundwater from waste at the bottom of the landfill during heavy rains?
Yes, the additional remedial actions recommended in the Waste Separation Feasibility Study and Corrective Action Plan take into account site water fluctuations in both periods of drought and heavy rain and will be suitable for future weather conditions at the site.

Is there any danger to local groundwater?
Since the commencement of site investigations and groundwater monitoring in the early 1990s, no water quality problems have been experienced by landowners down gradient of the site. Current data indicate that impacted groundwater is stable and is limited to the immediate vicinity of past landfill operations. PG&E performs regular monitoring of the groundwater at the site and has been installing additional groundwater monitoring wells to further refine its understanding of groundwater conditions.

Can surface water or impacted groundwater on the site spread to my property?
PG&E has a large network of groundwater monitoring wells and performs surface water and groundwater monitoring on a semi-annual basis; these results are submitted to the Water Board. Since 1992, monitoring results indicate the area of impacted groundwater remains stable and has not moved for over two decades. PG&E will continue to conduct semi-annual surface water and groundwater monitoring and report these results to the Water Board, consistent with the agency’s monitoring plan for the site.

What would happen if there was a fire and the tree plantations burned?
PG&E has a thorough fire prevention program that includes annual goat grazing and brush clearing to reduce fire hazards and on-site fire suppression facilities and water supplies to maintain the tree plantations. While a major tree plantation fire is unlikely, if trees were to burn to the point where they could not recover, PG&E would work actively with the Water Board to develop a replacement program to maintain groundwater levels.

What would happen to the landfill in an earthquake?
The landfill was designed to withstand an earthquake and the mixed waste and clean soil is firm enough that it is not expected to be damaged. The landfill would be inspected following significant earthquakes and any settlement repaired.

For More Information

Wildflowers Blooming Further information about this site as well as an archive of all quarterly reports can be found on the Water Board’s GeoTracker website at:

If you have any questions or concerns, the please contact either: