Investigation and Cleanup at the Caselton Site

Contamination at the Caselton Mine Area and Mill Site

The Caselton Mine Area and Mill Site has been contaminated from decades of mining and milling activities in the 1800s and 1900s. Mining-related wastes include waste rock and tailings, and the main contaminants of concern at the Site are metals, including lead and arsenic.

Waste rock consists of rock and sediment produced by digging and blasting for ore in mine shafts. The waste rock can have elevated concentrations of lead, arsenic, and other metals, and contaminated sediment can mobilize with stormwater.

Tailings are byproducts from mining and milling that are contaminated with metals and chemicals. Because tailings are fine-grained, they can migrate with surface water to move contamination. Stormwater is the primary mechanism for transporting tailings downstream and around the Site.

Current Activities and Work

  • The Multistate Environmental Response Trust (Multistate Trust) is prioritizing, evaluating, and addressing tailings located on the Tank Road Parcel (Tank Road Tailings) in OU1, due to their proximity to residential areas in the Town of Pioche.

  • The U.S. Environmental Protection Agency (EPA) is conducting environmental site assessment activities at and near the Caselton Mill Site (OU4) through its Targeted Brownfields Assessment Program.

  • The Bureau of Land Management (BLM) has received funding through the Bipartisan Infrastructure Law for its “Caselton Mine & Mill and Impacted Watershed Restoration” project. BLM is using the funding to complete a comprehensive remedial investigation and feasibility study to evaluate watershed impacts from Site-related contamination in OU4 and OU5.

Operable Units

The Multistate Trust and the Nevada Division of Environmental Protection (NDEP) have divided portions of the Site into five distinct geographic areas to investigate different parts of the Site and develop area-specific cleanup goals and remedial strategies based on their environmental conditions. These areas are called operable units (OUs). The five OUs at the Site are:

  • OU1: Treasure Hill

  • OU2: Caselton Heights Residential Yard Soils

  • OU3: Caselton Mine Site

  • OU4: Caselton Mill Site and Adjacent Tailings

  • OU5: Caselton Wash Tailings

Overview of Investigations and Work

What are risk-based cleanup levels?

Established contamination limits (for contaminants such as lead and arsenic) based on risks to human health and the environment and on anticipated future land uses (such as residential, recreational, and commercial).

OU1 – Treasure Hill

OU1 is located in the Town of Pioche, upgradient (uphill) of homes and businesses, and contains the abandoned Caselton Mine Shaft No. 1. The Multistate Trust conducted investigations at Treasure Hill, including a remedial investigation (sampling waste rock sediment and tailings), screening-level human health risk assessments, and soil sampling in yards of residential parcels (where access was granted) located downgradient (downhill) of OU1. Results showed contaminants in soils, such as lead and arsenic, exceed risk-based cleanup levels.

The NDEP and Multistate Trust prioritized removing contaminated soils from residential parcels with existing homes along Tank Road, Newark Street, and Ely Street.

  • ±2,300 cubic yards of contaminated soils were excavated from 18 parcels.

  • Excavated soil was replaced with clean backfill.

Sampling also identified tailings on a private parcel (Tank Road Parcel) along Tank Road (Tank Road Tailings). In 2022, Lincoln County acquired the Tank Road Parcel to facilitate cleanup.

  • In November 2022, the Multistate Trust performed additional environmental investigations to better understand the tailing characteristics (e.g., thickness and volume) and contamination levels.

  • Results confirmed that lead and arsenic are above risk-based cleanup levels and that soils beneath the tailings are contaminated. The Tank Road Tailings are consistent in characteristics and contaminant concentrations with OU4 and OU5 tailings.

OU2 – Caselton Heights Residential Yard Soils

OU2 is in the Caselton Heights subdivision. The Multistate Trust collected soil samples from residential yards and adjacent vacant land and found Site-related soil contaminants to be below risk-based cleanup levels for residential land uses. Therefore, no remedial or cleanup action was needed. In 2018, the Multistate Trust transferred the land beneath each home to the respective homeowner. The remaining vacant land was transferred to Lincoln County.

OU3 – Caselton Mine Site

OU3 consists of the abandoned Caselton Mine Shaft No. 2 and abandoned mine buildings. The area is secured to deter trespassing and does not require investigation. OU3 and OU4 together make up the area known locally as the Caselton Mine and Mill Site.

OU4 – Caselton Mill Site and Adjacent Tailings

The former Caselton Mill Site and related contaminants make up OU4. Remedial investigations showed that the former mill site, tailings, and disposal pond sediments contained contaminants from past mining and milling operations. Surface water drains toward the Caselton Wash (located in OU5), and contamination can migrate with water runoff, especially during precipitation. The Multistate Trust prepared an initial assessment of potential remedies to mitigate contaminant discharge and prevent human exposure to the Caselton Mill site. OU4 was recently divided into OU4A (Caselton Mill Site) and OU4B (less impacted area south of the mill site) to facilitate reuse.

OU5 – Caselton Wash Tailings

The Caselton Wash is an ephemeral stream that held wastewater ponds from past milling operations. The land is not owned by the Multistate Trust and is managed by the Bureau of Land Management (BLM). The ponds contain tailings, and years of rain and flooding have caused the tailings to migrate down the Caselton Wash. The Multistate Trust and the NDEP have partnered with the University of Nevada, Reno to collect data to support remedial investigations and evaluate the potential for tailings contamination to affect groundwater.  

Metals concentrations do not exceed established drinking water standards. The Multistate Trust collected soil samples in the Caselton Wash over an 8-mile reach downstream of the tailings ponds. Wash soils are not expected to have an unacceptable health risk to recreators, and tailings in the wash are not expected to impact surrounding groundwater wells.

Our Beneficiaries and Regulatory Framework

The Multistate Trust performs environmental actions under the oversight of and as approved by the Site’s Lead Agency, the NDEP. The Site cleanup is managed under the NDEP’s Abandoned Mine Lands Program, which focuses on mitigating potential human health and ecological concerns from legacy heavy-metal mining operations.

The Multistate Trust works with state and federal beneficiaries for the Site:

  • The State of Nevada, represented by the NDEP

  • The United States, represented by EPA and BLM

Both the NDEP and EPA, in consultation with the U.S. Department of Justice, must approve the sale, transfer, or disposition of all or any portion of the Site.