Cleveland Mill

Overview

Cleveland Mill is a former gold, silver, and copper mining and milling operation about 5.5 miles north of Silver City, New Mexico. Mining left behind tailings piles containing heavy metals that threatened Little Walnut Creek and a nearby tributary. The site was listed on the National Priorities List in March 1989 after residents raised concerns about stream quality. The surrounding area is now a growing residential community, with roughly 1,200 people living within three miles and most relying on private wells for drinking water.

EPA identified nine contaminants of concern at the site: arsenic, beryllium, cadmium, copper, lead, mercury, silver, and zinc. These contaminants were found in soil, groundwater, and sediment. Copper and mercury were detected only in groundwater. The tailings also created acidic water conditions in the creek.

Cleanup included excavating and treating contaminated tailings and sediment, then placing the material in an on-site disposal cell with erosion controls. Unusually heavy summer rains in 1998 triggered a time-critical removal action after mine tailings washed into the creek and caused dangerous acidity levels. EPA sampling found elevated sulfate levels in two residential wells but no heavy metal exceedances in private or monitoring wells. The long-term remedy, updated in 1999, requires no further excavation. It calls for continued groundwater and surface water monitoring and institutional controls. Potentially responsible parties maintain the site under state and federal oversight. Construction was completed September 23, 1999, and the site was deleted from the National Priorities List on July 23, 2001. Human exposure is considered under control, and the site is ready for its anticipated use.

Annual groundwater sampling continues under an EPA-approved Operation and Maintenance Plan. The sixth Five-Year Review started in May 2026 and is expected to finish by May 2027. This review checks whether the remedy continues to protect human health and the environment. The most recent completed Five-Year Review was finished on May 13, 2022, and the next scheduled review is estimated between September and November 2027. Note that one source states the next review will begin in February 2026, while another states it started in May 2026. Both claims are included here as stated.

Community members can share their experiences and concerns by contacting EPA or the New Mexico Environment Department directly. EPA and NMED are conducting interviews to gather community input as part of the ongoing Five-Year Review. Media inquiries can be directed to the EPA Press Office at (214) 665-2200.