The Northwestern States Portland Cement Company (NWSPCC) facility, now known as Holcim (US) Inc, has manufactured cement since 1908 in an area referred to as the West Quarry site, which was mined for limestone until 1950. From 1969 to 1985, NWSPCC used the quarry for the disposal of approximately 2,000,000 tons of waste kiln dust. When disposal activities ceased the quarry's unfilled area had been reduced to 40 acres and contained about 420 million gallons of water. In 1979, two seeps emerged from the northeastern portion of the filled part of the quarry and flowed overland to Calmus Creek. During a 1984 study by the IDNR, Calmus Creek was found to have elevated pH downstream from the seeps. In September 1986 fish kill occurred in Calmus Creek and the IDNR conducted additional stream sampling and found pH downstream from the seep area ranged 10.2 to 10.5. In 1987 EPA conducted a Superfund site inspection (SI). Based on the findings from the SI the site was proposed for the Superfund National Priorities List (NPL) and the NPL listing was finalized in 1989. NWSPCC conducted a remdial investigation/feasibility study (RI/FS) in cooperation with the IDNR (the lead Superfund agency at that time) beginning in 1988. Based on the RI/FS a Superfund Record Of Decision (ROD) was completed in June 1990.. The major health and environmental concern at NWSPCC is contaminated surface water and groundwater resulting from contact with waste cement kiln dust in the West Quarry. The kiln dust includes calcium oxide (CaO), which reacts with water and releases hydroxide ions (OH-) into solution. The hydroxide ion concentration directly controls the pH level in a liquid. The site has caused local groundwater and surface water to be impacted by high pH values, an increase in total dissolved solids, and elevated concentrations of potassium, sulfate, and sodium. Remedial action . Implementation of the remedial activities prescribed in the ROD were initiated in 1992 and completed in 1993. NWSPCC ontinues to be perform remedial action under the terms of an agreement with EPA, who is now the lead overasight agency. The remdial action has involved isolation of the kiln dust by the sequential implementation of the following remedial technologies: • The West Quarry was drained in September 1989. • A permanent drain system in the floor of the de-watered quarry was completed prior to the ROD. The system is inspected on an annual basis and repaired as necessary. • Bedrock de-watering wells on the quarry floor were completed in 1992. • Kiln dust monitoring wells were installed in 1992. • An engineered cap was placed over the kiln dust in 1993. The cap is inspected on an annual basis and repaired as necessary. • Treatment, in compliance with a state NPDES permit, of extracted waters is conducted prior discharge to Calmus Creek. A new treatment facility was completed in 1993. treatement consists of acid neutralization. • Quarterly groundwater monitoring for two years was conducted after the completion of remedial construction in October 1993. Sampling is now conducted on an annual basis. The latest study of Calmus Creek was completed in August 1995. Based on the results, the water quality of the creek complies with the state requirements for a Class B warm-water stream. The EPA completed a five-year review of the site in 2002. The EPA concluded the remedial action has been protective and recommended continued operation and maintenance of the remedial system. Another 5-year review was bugun in 2006.