Superfund Site: NORTHWESTERN STATES PORTLAND CEMENT CO., MASON CITY, IA
Superfund Site Profile
The Northwestern States Portland Cement Company Site consists of an area within the Holcim (US) Inc., (Holcim) former cement manufacturing facility, located just north of Mason City, Iowa, near the intersection of 25th Street and U.S. Highway 65. Cement was manufactured at the site from 1908 until 2009. The area referred to as the West Quarry was mined for limestone, a raw material for cement production, until 1950. The West Quarry had reached a depth of approximately 40 feet and covered an area of about 150 acres. In 1969, the company began using the West Quarry for the disposal of waste cement kiln dust (CKD). When disposal activities ceased in 1985, approximately two million tons of CKD had been placed in the quarry and the quarry’s unfilled area had been reduced to approximately 40 acres. The open portion of the quarry, filled with approximately 420 million gallons of water, was known as the West Quarry pond.
In 1979, two seeps emerged from the northeastern portion of the filled West Quarry and the water traveled overland and into Calmus Creek. The Iowa Department of Natural Resources found that downstream from the West Quarry, the creek water pH was elevated and the total dissolved solids were also elevated. In October 1980, water samples obtained from the West Quarry pond had a pH value of about 12.5. (pH is considered neutral at 7.0. A pH value lower than 7.0 is referred to as acidic and a value higher than 7.0 is referred to as alkaline.) A fish kill occurred in Calmus Creek in September 1986.
The major concerns at the site were contaminated surface water and groundwater resulting from contact with waste CKD in the West Quarry. CKD is composed of a primary cement component, calcium oxide, which reacts with water and releases hydroxide ions into solution. The hydroxide ion concentration directly controls the pH level of an aqueous solution. Local groundwater and surface water have been impacted by high pH levels, and by an increase in total dissolved solids content, as well as elevated levels of potassium, sulfate and sodium. Trace amounts of heavy metals and phenol have also been detected sporadically. Of the contaminants identified, only arsenic is a possible carcinogen.
Following cleanup, EPA removed the site from the Superfund program’s National Priorities List (NPL) in 1995. Monitoring and maintenance activities are ongoing.