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Rapid City Air Quality History

Rapid City Air Quality History

In 1978, a portion of Rapid City failed to meet the Environmental Protection Agency Total Suspended Particulate (TSP) Standard. As a result, the Environmental Protection Agency (EPA) designated a 10 by 10 square mile area of Rapid City as a nonattainment area for TSP. Non-attainment means that Rapid City did not attain the air quality standard required by the EPA for particles in the air. At that time, City street sanding operations and the northwest industrial complex were identified as sources of TSP. In response to the nonattainment designation, Pennington County adopted a local ordinance in 1978 to control fugitive dust emissions. The ordinance required reasonably available control technology, permits for construction activities, compliance plans for continuous operations, and an enforcement mechanism. The Pennington County Air Quality Review Board and an air quality officer were appointed to implement the fugitive dust requirements.

In 1986, the EPA TSP standard was changed to PM10. PM10 is airborne particles that are 10 microns in size, or smaller. Air quality monitoring data indicated that City street sanding operations were still an issue. This was confirmed after the initial three years of monitoring. During this time Rapid City was trying to convince the EPA that it deserved an "attainment" status, rather than the "unclassified" status that it carried with the advent of PM10. Three years is the length of time it would have taken to convince the EPA that Rapid City was in attainment of the standard. As a general rule of thumb for a rather complex computation, if one exceeds the standard three times in three years, a fourth exceedance becomes the trigger for a review process by the EPA.

In 1992, there were two exceedances, and in response, on February 11, 1996, the South Dakota Department of Environment and Natural Resources adopted street sanding and deicing regulations. During this period, changes in the City street sanding operations were implemented. After that, exceedances at the library site, in downtown Rapid City, no longer occurred. However, problems still existed in western Rapid City due to the northwest industrial complex.

In 1996, there were three exceedances, followed by a fourth in 1997. This triggered the review process referred to above. At this time, the northwest industrial complex was identified as the primary source of fugitive dust. The EPA wanted to know what the industrial complex sources would do to avoid these exceedances during future high wind events. In 1996, the South Dakota Department of Environment and Natural Resources developed a Natural Events Action Plan (NEAP) which includes measures to be implemented within specific time frames in order to be prepared for the high winds that Rapid City is prone to. The NEAP was reviewed and approved by the EPA on July 1, 1998. For the industrial sources, these measures require that Best Available Control Measures be applied for paved and unpaved roads, trackout areas, crushers, storage piles, waste pits, heavy equipment, and reclamation. In addition to the NEAP, the City of Rapid City controls the street sanding operations and regulates construction activities, wood burning and open burning. When an alert is called, industry is asked to minimize their activities, but the bulk of the control measures are applied continuously.

There is a difference between an exceedance and a violation. An exceedance simply means that a measurement was higher than the standard. The EPA determines if an exceedance is a violation. Determination of a violation is based on surrounding circumstances, which may or may not give the EPA reason to excuse the exceedance. Since the EPA accepts the NEAP, and it has been implemented as planned, then the EPA accepts the Department of Environment and Natural Resources’ contention that these past exceedances are due to natural events. As long as the EPA accepts the NEAP and industrial sources follow through with using the best available control measures, future exceedances during high wind events can be excused. The Department of Environment and Natural Resources submitted its first high wind exceedance from May 6, 1999 to the EPA for exclusion under the NEAP in December 1999. Additional exceedances occurred on December 18, 2000 and May 23, 2001. The EPA has acknowledged these exceedances as high wind events that would not be counted toward a violation under the NEAP.

In 2001, the implementation of the local air quality program was transferred from Pennington County to the City of Rapid City. The City of Rapid City adopted a fugitive dust ordinance and added a Rapid City Air Quality Program to implement and enforce the ordinance. The Rapid City Area Air Quality Board was appointed to oversee the local program. It was then determined that the City of Rapid City did not have the authority to implement its ordinance on state-owned property. On July 1, 2002, the Department of Environment and Natural Resources adopted regulations to control fugitive dust emissions from temporary and continuous construction activities on state-owned property to ensure all fugitive dust emissions sources were regulated.

Additional exceedances of the PM10 standard occurred on July 31, 2002 and August 16, 2002. The EPA has determined that these exceedances are also excluded under the NEAP.

Historically, all exceedances have been for the 24-hour standard, and only on days with sustained winds in excess of 20 miles per hour, and gusts over 50 miles per hour. Rapid City is unique in that it is the only region that has exceeded the 24-hour standard (150 micrograms per cubic meter) without ever having also exceeded the annual standard (50 micrograms per cubic meter). What that says is that, while we do have occasional exceedances above the 24- hour standard, in general, our air quality is in compliance.  In 2006, the PM10 annual standard was revoked. 

As required by the EPA, a five-year review of the NEAP was completed by the Department of Environment and Natural Resources in 2005 and was approved by EPA on August 4, 2005. The five-year review concluded that the NEAP was fully implemented and working to minimize PM10 fugitive dust emissions during high wind events.

The Department of Environment and Natural Resources reviewed the ambient air monitoring data to determine if the Rapid City area should be redesignated from unclassifiable to attainment for PM10. The data demonstrated compliance with the National Ambient Air Quality Standards for both the 24-hour and annual PM10 standards. On September 30, 2006, the Department of Environment and Natural Resources submitted a request to the EPA to redesignate the Rapid City area from unclassifiable to attainment of the PM10 standards. On April 5, 2006, the EPA announced that Rapid City was officially designated as in attainment of the Federal National Ambient Air Quality Standard for PM10.