Environmental Contaminants Restoration of Hazardous Waste Sites

Cleveland Mill

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Located at the headwaters of a small tributary of the Little Walnut Creek, 5.5 miles north of Silver City, in Grant County, New Mexico is the Cleveland Mill Superfund Site. This Site is an abandoned lead, zinc, and copper mine and mill that operated in the early part of the century. It covers about 4 acres in mountainous terrain and about 14 acres which extend down a drainage area and into the streambed of Little Walnut Creek. The Site is located in a rapidly developing residential area that is adjacent to the Gila National Forest and private lands.

Tailings from the mill were uncovered, unstabilized and unlined, and had washed into Little Walnut Creek causing the waters to be acidified and contaminated with metals. Residential wells installed along the creek, though not contaminated with toxic substances, detected indicator parameters which indicate that they have been affected by the mine tailings. An on site reservoir is used for recreational purposes. The population within a 3 mile radius of the Site is estimated to be 1,200. In 1990, the Environmental Protection Agency (EPA) performed a remedial investigation/feasibility(RI/FS) study from the Superfund Trust Funds. The RI/FS and Proposal Plan were released to the public in April 1993. A Record of Decision (ROD) for the Site was signed in September 1993, by the EPA with consultation with the New Mexico Environment Department (NMED) that would have addressed the threats to human health and the environment at the Site. However, the ROD remedy was not implemented because the search for an acceptable off-site disposal facility was ultimately unsuccessful, and, during the search, unanticipated weather events caused extensive contaminant migration at the Site. This increased the potential risk to human health and the environment and made the risk more immediate. Therefore to address the immediate risks, on July 11, 1997, the EPA with concurrence of the NMED, issued an Action Memorandum that authorized a time-critical removal action to physically address the Site contamination and to restore affected surface areas at the Site.

Through an Administrative Order on Consent (AOC), effective on September 23, 1997, with the EPA and participation of Potentially Responsible Parties (PRPs) the action was implemented. The removal action included: excavation of contaminated tailings and sediment from the mine area, the mill area, and the streambed; neutralization of the acidic excavated material through admixing with limestone; disposal of the neutralized material in a limestone cell constructed at the Site covered with a multi-layer cap; construction of erosion control measures such as terraces, and reseeding of the disturbed areas of the Site and the disposal cell cap. An amended ROD, September 20, 1999, for the Site stated that no further response action was necessary, however the contamination of ground water and surface water monitoring, operation and maintenance (O&M) of the constructed remedy would continue. Implementation of institutional controls would also continue, limiting the use of ground water and advising future owners about the risks of disturbing the cover and/or the underlying material. Confirmatory sampling of the Site has verified that the 1993 ROD remediation goals were achieved, and that all cleanup actions specifies in the Site RODs and the Site Action Memorandum have been implemented. The Site risks associated with the tailing and sediment have been eliminated or reduced to acceptable levels through institutional controls, excavation, treatment, and onsite disposal. This Site meets with all the site completion requirements as specified in OSWER Directive 9320.2-09A-P, Closeout Procedures for National Priorities List Sites. The Cleveland Mill Superfund Site was deleted from the National Priorities List (NPL) on July 23, 2001.

The Cleveland Mill Site had the potential to cause severe impacts on human health and the environment. However, State and Federal agencies and non governmental organizations, have joined efforts to secure a cleaner environment for the people, plants and animals of southwestern New Mexico. The area is rapidly developing and residents are being educated on the importance of long term care of our natural resources.

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