High Wind Dust Alerts & Natural Events Action Plan for Rapid City, SD.

Natural Events Action Plan High Wind Dust Alerts

Area of Impact: Applies only in West Rapid City beginning at the "Gap".

Meteorological Criteria:
If the following weather conditions exist, a high wind dust alert will be called:

  1. Five consecutive days of 0.02 inches or less of precipitation each day, excluding dry snow;
  2. The forecasted peak wind gust greater than 40 mph; and
  3. The forecasted average hourly wind speed greater than 20 mph.

The high wind dust alert will be discontinued when the following weather conditions exist:

  1. Wind speeds decrease below 12 mph on an hourly average and peak wind gusts are below 30 mph; or
  2. There is greater than 0.02 inches of precipitation in a 24 hour period excluding dry snow.

High Wind Dust Alert issuance: An alert will be issued and subsequently cancelled by the National Weather Service. The National Weather Service will notify the media as well as the Rapid City Air Quality Program or the department in the following sequence: Sam Nesbitt, SD DANR - Rapid City (work 394-2229) or Air Quality Coordinator, Rapid City Air Quality Program (work 394-4120).

Health Precautions: During an alert, elderly citizens, young children and individuals with respiratory problems should avoid excessive physical exertion and minimize outdoor activities. Although these people are the most susceptible to health impacts, it is recommended that everyone take precautions to avoid being exposed to these poor air quality conditions.

Voluntary actions to reduce air pollution levels: To minimize pollution levels, it is recommended that any manipulation of soils (i.e. construction, or industrial or agricultural activity) cease or be minimized during these events. It is also recommended that pollution controls for soil stabilization, process equipment, waste pits, stock piles and construction sites (i.e. watering or chemical treatment) be increased.

Basis for criteria selection: High wind/dust conditions typically occur after extended dry periods during the colder months of the year and have, on occasion, caused air pollution problems during warmer months. Therefore, high wind dust alerts will be called year-round. High air pollution levels occur when peak wind gusts reach 40 to 70 miles per hour and average hourly wind speeds are greater than 20 miles per hour for an extended period of time. The high winds strip away the top crusted layer of the soil and suspend the finer dust particles in the air. The high wind events can last from one to eight hours depending on the strength of the storm system.

During these events, the hourly dust concentrations have ranged from 100 ug/m3 to 900 ug/m3 per hour. A violation of the dust health standard is a reading over 150 ug/m3 averaged over a 24-hour period. This standard has been violated during these conditions in West Rapid City. Therefore, air pollution alert for dust will only be called for the West Rapid City area. A review of monitoring data indicates that high concentrations only occur in this area of town during these high wind events.

Natural Events Action Plan

In a memo dated May 30, 1996, by Mary D. Nichols, Assistant Administrator for the Office of Air and Radiation, the Environmental Protection Agency (EPA) established a Natural Events Policy to address National Ambient Air Quality Standards for PM10 (particulate matter less than 10 microns) violations or exceedances that occurred during natural events. One of the three natural events identified in the memo was high winds.

Rapid City experiences PM10 exceedances that could lead to violations of the National Ambient Air Quality Standard. Past history has shown that the majority of these exceedances occur during high wind events. In 1997, the South Dakota Department of Environment and Natural Resources began to develop a Natural Events Action Plan, which is the compliance mechanism to the Natural Events Policy. A coordinated effort between the department, the Pennington County Air Quality Board, the City of Rapid City, Pennington County, and the industries in the Northwest Industrial Complex was undertaken to complete the plan. The plan was finalized on July 1, 1998.

Download the Natural Events Action Plan
Download the NEAP 5 year review
Download the NEAP Appendices

The purpose of the plan was to identify the Natural Events that have resulted in past PM10 exceedances and to develop or identify controls for PM10 sources to reduce or eliminate future PM10 exceedances in West Rapid City during high wind events. If the proposed Best Available Control Measures and public notice of an event are implemented, any future exceedance occurring during a high wind event, as defined in the plan, would not be counted towards a violation.

Area of Implementation
This plan will be implemented in West Rapid City where the PM10 exceedances have occurred. West Rapid City lies in the middle of the geological formation termed the limestone racetrack that surrounds the Black Hills National Forest. It is bordered on the west and south by the Black Hills and on the east by a series of hogback hills, creating a bowl-like formation ideal for air pollution problems. The city's main industrial and mining complex is located in this section of the city. The area of implementation for this plan will be between a line extending north and south from the "Gap" to 5 miles west of the city's western city limit. The "Gap" is a geographic marker that is drainage for Rapid Creek out of the Black Hills that runs through Rapid City. Map of the NEAP Control Area.

Identification of Contributing Sources
It is stated in the Natural Events Policy that all sources contributing to a PM10 violation are required to have Best Available Control Measures implemented. This plan identifies fugitive dust sources within the industrial complex as the main contributors to the PM10 exceedances. It also identifies the proposed Best Available Control Measures for these sources and the process of implementation.

Other sources having the potential to contribute to the exceedances include point sources in the area, street sanding operations, construction activities, paved and unpaved parking lots/alleys, woodburning, and open burning. Best Available Control Measures have already been implemented for these sources because of past particulate pollution problems in other sections of the city. They are desscribed in the plan. Since the implementation of these measures, particulate pollution problems in other areas in the city have been significantly reduced or eliminated.

Development and Implementation of BACM
The 1996 policy stipulates that Best Available Control Measures must be federally enforceable. The controls for industrial fugitive dust sources are implemented through the industrial sources' state air pollution permits. These are either in the state's Part 70 permit or minor permit, both of which are federally enforceable through South Dakota's State Implementation Plan (SIP). Controls for other sources contributing to the violation, such as reentrained street dust, unpaved parking lots/alleys, woodburning, construction activity, and open burning, have been established either under state regulations or the local Pennington County Air Quality Ordinance #12.

Public Education and Notification of High Wind Events
A review of meetings held to notify the public of high concentrations and to discuss the Natural Events Action Plan is provided in the plan along with the process for calling high wind dust alerts for future high wind events.

Particulate Matter Background History
Historically, the Rapid City area has had problems with high particulate levels. Due to recorded exceedances, Rapid City was classified as nonattainment for total suspended particulate (TSP) in 1978. In 1986, the dust standard was changed to PM10. With the change in standards, Rapid City became designated "unclassifiable" for PM10. Rapid City met the new standard for several years.

In October 1992, two samples collected at Jaehn's Business Supply site in West Rapid City violated the PM10 standard and triggered the nonattainment process with EPA. The department submitted information to EPA requesting the samples be flagged as exceptional events under 40 CFR Part 50 Appendix K as a result of abnormally dry conditions coupled with high winds. It was stated these samples should not be used to determine the air quality status of Rapid City. The department made several appeals to EPA for a favorable ruling.

In a letter from EPA to Governor Janklow dated July 19, 1995, EPA did not agree with the department's position and planned to go forward with the nonattainment designation. EPA based their decision on the belief that high wind events are recurring. However, the department convinced EPA the designation would be counterproductive to all the work the city, county, industry, and state had done to improve the air quality. EPA decided to suspend the designation if the following conditions were met:

  • The department submitted an analysis of the Rapid City air monitoring data to EPA;
  • New requirements to control fugitive emissions for street sanding operations and industry were implemented;
  • The department continued to operate the air monitoring network in Rapid City; and
  • No further violations of the air quality standards in Rapid City were documented.

DANR established some fugitive dust controls in the sources' permits, but the controls were not implemented in all the permits due to the then recent development of the Part 70 permitting program and the Natural Events Policy.

In January, February, and December 1996 and May 1997, four exceedances of the daily PM10 standard occurred at the Family Thrift Center site in Rapid City. The department flagged these exceedances as exceptional events in the Aeromatic Information Retrieval System (AIRS) database. Although the four exceedances occurred on high wind days, the exceedances could not be considered exceptional events under 40 CFR Part 50 Appendix K because, according to EPA, the conditions could recur.

On May 30, 1996, EPA issued its Natural Events Policy to address PM10 violations that occur during natural events. The policy covered natural events such as wildfire, volcanoes, and high wind with the requirement that best available control measures be applied to sources contributing to the PM10 violation even if the event could recur. On August 7, 1997, the department notified EPA that the policy would be applied to the three exceedances and any future exceedances caused by high wind events to the Natural Events Action Plan the department developed for Rapid City. The plan was reviewed by EPA and accepted by them on July 1, 1998.

The department submitted its first high wind exceedance (May 6, 1999) to EPA for exclusion under the Natural Events Action Plan. In a letter dated December 20, 1999, to the department, EPA acknowledged the exceedance as a high wind event that would not be counted towards a violation under the Natural Events Action Plan.

NEAP Controls

This portion of the plan discusses the air pollution controls that were required to be implemented by the industrial facilities. The controls are referred to as Best Available Control Measures (BACM).

Identifying why existing controls failed
The Natural Events Action Plan describes the weather conditions in Rapid City which contributed to the PM10 exceedances. Following is a discussion of the reasons why existing controls for fugitive dust emissions can fail under these conditions.

Hourly Wind Speed: When winds exceed 20 mph (hourly average), the soil or dust crust covering stockpiles, waste dust pits, land, and haul roads deteriorates. This allows the dust to become airborne. It has been identified that PM10 concentrations increase from 100 ug/m3 per hour up to 900 ug/m3 when average hourly winds are greater than 20 mph. Conversely, the concentrations drop below 100 ug/m3 when hourly average wind speeds decrease below 20 mph.

Peak Wind Speed: When peak winds exceed 40 mph (one minute average), the soil or dust crust deteriorates at a faster rate, and the dust becomes airborne. These wind speeds also reduce the effectiveness of any water control practices because the strength of the wind makes it difficult to apply the water where needed.

Soil Moisture Content: It has been documented in studies that soil erosion caused by wind can begin at 13.4 mph and is highly accelerated at winds of up to 50 mph. These studies were conducted on agricultural, construction and industrial soils in separate studies by W.G. Nickling, J.A. Gilles, D.W. Fryrear, D.A. Gillete, J. Adams, A. Endo, D. Smith, R. Kihl, L.D. Stetler, K.E. Saxton. The parameters established in this plan are consistent with these wind rates. Soil moisture content is also a vital component in the rate of wind erosion, although there are no data available discussing the relationship between soil moisture, wind speeds and PM10 concentrations for this area.

Consecutive Days of No Precipitation: Three or more days of little or no precipitation also results in conditions favorable to generating dust. First, when there is no precipitation for several consecutive days, there is no creation of a natural crust on fugitive dust sources. Second, the moisture content in the existing crust evaporates, leaving the dust vulnerable to reentrainment. There is also a new buildup of dust from the industrial processes during this time period. Long-term dry periods reduce vegetative cover and cause fugitive dust to become airborne during high winds, even in reclaimed quarry areas.

Temperature: When the temperature is below 32 degrees F., the industrial sources do not apply water, which was the main source of dust control. Water is not applied during freezing periods because it has the potential to cause unsafe working conditions. Equipment used to apply the water (water trucks or crusher spray bars) can also freeze. The freezing and thawing effect also increases the erodibility of the crustal surfaces, contributing to high PM10 concentrations on windy days.

BACM Determination for Industrial Fugitive Dust Sources
The Best Available Control Measures determination was based on finding controls that could provide the best and economically feasible control of fugitive dust during high winds and freezing conditions. The search began with reviewing Best Available Control Technologies (BACT) implemented in PM10 nonattainment areas with similar air pollution problems as Rapid City. Nonattainment area controls in Reno and Las Vegas, Nevada, Spokane and Puget Sound, Washington, and South Coast, California were reviewed. The search indicated accepted controls of chemical application on fugitive dust sources such as haul roads, stockpiles, and waste pits with enclosures and installation of pollution control devices on limestone rock crushing and processing. Water for dust suppression was an accepted control in milder climates; however this type of control would not always be effective in Rapid City's colder winter months when water is not used due to safety and mechanical problems associated with freezing.

The department also reviewed EPA's "Best Available Control Technologies for Fugitive Dust Sources." The review indicated the BACM developed by the department for sources in West Rapid City were comparable to the controls in EPA's document. This book did not provide controls for crushing operations. Therefore, a search for Best Available Control Measures for rock crushing was conducted in EPA's "RACT/BACT/LAER Clearinghouse." The clearinghouse identifies acceptable level of controls for new and modified sources that have to comply with requirements in nonattainment areas as well as EPA's New Source Review and Prevention of Significant Deterioration rules. The results of this search indicated water spray bars are the accepted control for rock crushing operations processing aggregate other than limestone. Limestone crushing operations are required to enclose the operation and install a pollution collection device. Again, because of the colder seasons, water spray control systems are not acceptable in the Rapid City area except for a wet scrubber system, which is considered a pollution control collection device.

To conclude the search on fugitive dust controls and to determine if the controls were economically feasible to implement, a review of controls already implemented by similar industries in the Rapid City area was conducted. A couple of the industries were implementing most of the proposed fugitive dust and crushing controls, but the majority of industries were implementing only a few of the proposed controls. Many of the proposed controls were implemented within the last three to four years. The implementation of these controls is reflected in the reduction of days with greater than 100 ug/m3 of PM10 per year.

BACM for Particulate Emissions
The following Best Available Control Measures, based upon the review described above, were developed for fugitive dust sources in the industrial complex in West Rapid City. The Best Available Control Measures have been reviewed by EPA's Region VIII and Headquarters, the Rapid City industries, the Pennington County Air Quality Board, and the department.

The Best Available Control Measures apply to the following industries and to any new industry locating in West Rapid City:

  • Birdsall Sand and Gravel;
  • Black Hills Power and Light Company;
  • Dakota Block Company;
  • Fisher Sand and Gravel;
  • Hills Materials Company;
  • J.E. Simon Construction;
  • Pete Lien and Sons, Inc.; and
  • South Dakota Cement.

Standard of Control
Best Available Control Measures for particulate matter sources are techniques and/or controls that achieve the maximum degree of emission reduction from a source as determined on a case-by-case basis considering technological and economic feasibility. (59 FR 42010, August 16, 1994).

Alternative Techniques and Controls
The owner or operator shall have the option to implement other techniques and/or controls that are as efficient in reducing or eliminating particulate matter as the controls listed. If the owner or operator decides to pursue other alternative techniques and/or controls, the owner or operator shall notify the department in writing of the alternative technique and/or controls. The notification shall include an explanation as to what the owner or operator proposes, testing results, emission projections, and a timeline for installing the control measure. The department shall review the proposal and notify the owner or operator in writing within 30 days of receiving the proposal, that the owner or operator may proceed as proposed or with changes outlined in the department's written response. The department shall be receptive of proposals that are as efficient as existing techniques and/or controls. Failure of the department to notify the owner or operator within 30 days shall be deemed to be acceptance of the owner or operator's alternative techniques and/or controls.

Crusher Control Options
The owner or operator shall enclose any primary, secondary or tertiary rock crusher along with the associated screens, transfer points and load-outs (from hoppers or conveyors to other than stockpiles). Any captured particulate matter shall be disposed of in a manner that will not allow the captured particulate matter to become reentrained into the ambient air.

The term "enclosure" shall be defined to be either a complete enclosure around one or more pieces of equipment or an enclosure of those points on the equipment from which particulates are emitted. To qualify as an enclosure, the enclosure shall be:

  • Constructed of materials impermeable to air. The actual shell of a piece of equipment may be considered as the enclosure or part of the enclosure.
  • Designed and constructed to minimize the number and size of openings through which air may enter or exit the building or enclosure. Openings shall be covered by a curtain or other method to minimize the opening to the size reasonably needed for the movement of materials, equipment, personnel, and air necessary for operation and ventilation of occupied areas.
  • Designed and constructed so that the discharge of air from the building or enclosed structure on the unit associated with movement of materials shall be minimized as much as is reasonably possible.
  • Include a method of control, either (1) treating, capturing or removing particulate matter emissions generated from the material being processed with wet suppression, baghouse or wet scrubber for complete enclosed buildings, and/or (2) capturing or removing particulate emissions generated with a baghouse or wet scrubber for an enclosure of an emission point. Wet suppression may not be used as a control for option (2). At least one control method shall be used when equipment is operated.
  • Whenever reasonably possible, the control shall have a negative pressure.
  • Designed and constructed together with the controls to allow for the removal of particulate emissions which have settled out of the air inside the enclosure or have been removed from the air by controls.
Air emissions from the enclosure shall be subject to the 20 percent opacity emission limit or the applicable New Source Performance Standards. Limitations in sealing off enclosures from airflow that will impact worker safety and health standards for indoor particulate emission limits will be considered when reviewing the plans.

Unpaved Roads Controls
For Unpaved Road Controls the owner or operator shall implement one of the following:

  • Apply a chemical stabilizer to all main haul roads in sufficient quantity and frequency to suppress particulate matter generation to comply with opacity standards as identified in the plan, and apply a chemical stabilizer or water to all secondary haul roads that have daily vehicular traffic at a frequency to suppress particulate matter generation to comply with opacity standards identified in the plan; or
  • Pave main haul roads and secondary haul roads with tack seal, asphalt, recycled asphalt or concrete.

Main haul roads are defined as passageways between the mining area and the processing facility or between the processing facility and the storage area in which material is transferred on a road.

Secondary haul roads are defined as passageways in which there is daily vehicular traffic on normal work days other than the main haul roads.

Chemical stabilizers include magnesium chloride, calcium chloride, or on-specification used oil as defined in ARSD 74:28 that is applied to a scarified road surface. To receive approval for an additional chemical stabilizer, the owner or operator shall submit a written proposal to the department demonstrating the proposed chemical will not violate surface or ground water standards upon run-off or leaching and is equivalent to the approved chemical stabilizer for controlling particulate matter. Delays for application of chemical stabilizers up to 30 days will be allowed during freezing conditions or when conditions are not favorable for application.

Paved Roads and Parking Area Control
The owner or operator shall sweep and water flush or vacuum and water flush all paved roads and parking areas to remove particulate matter that has the potential to be resuspended. The frequency of cleaning will be on an as needed basis to comply with opacity standards.

Track Out Area Control
For Track Out Area Controls the owner or operator shall implement one of the following:

  • Pave (asphalt or concrete) a track out area to maintain a stabilized surface starting from the point of intersection with the public paved surface into the facility boundary for a total distance of at least 100 feet and a width of at least 20 feet; or
  • Install a wash station and require all haul truck vehicles leaving the facility to remove track out materials through the use of water.
For temporary track out areas (in use for less than 60 days in a calendar year), techniques and/or controls shall be implemented so as to prevent particulate matter from becoming entrained in violation of the opacity standard identified in the plan. The controls and/or techniques shall require DENR approval unless it is a control or technique approved in this section.

Track out areas are defined as driving surfaces from the owner or operator's facility to public roadways upon which particulate matter has been deposited by transport vehicles.

Reclamation Control

  • Reclamation Plan: The owner or operator shall submit to the department for approval, a plan to reclaim lands that have a wind erosion potential within 90 days of the issuance of the Part 70 Operating Permit. Upon approval of the plan by the department, the plan shall remain in effect as the BACM for lands with wind erosion potential, until reclamation has been completed at the facility and approved by the department. The department will approve a plan that makes reasonable progress toward reclaiming land with a wind erosion potential.
  • Plan Approval: The department shall notify the owner or operator within 90 days after issuance of the owner or operator's operating permit if the plan is approved or, in the alternative, which portions are not approved and the reason why the portions have not been approved. The owner or operator shall resubmit a revised plan within 90 days of notification. When the department finds the owner or operator's plan or revised plan to be acceptable, it shall provide written notice to the owner or operator. The accepted plan shall remain in effect until further modification.
  • Plan Modification: The owner or operator may propose further modification of an approved plan by written notice to the department. The department shall respond in writing within 90 days of the owner or operator's proposed modification.
  • Reclaimed Lands: Lands which have been successfully reclaimed, as approved by the department, shall no longer be subject to the approved plan requirements, as long as they remain reclaimed.

Reclaimed land is defined as an area which meets the requirements for reclamation in SDCL 45-6 for licensed mining operations or established in the reclamation plan of a mining operation permitted under SDCL 45-6B.

Lands with a wind erosion potential are all areas within the facility except those that have a hard rock surface, are paved (concrete or asphalt), have a building structure over it, the working face of the quarry, or have been reclaimed.

Front-end Loader Control
Control Development: Controls for particulate matter generated by front-end loader operations are being researched. At the time a control is determined and agreed upon, it will be placed in each permit as necessary.

Open Storage Pile Control
For open storage pile controls the owner or operator shall implement one of the following:

  • Apply chemical stabilizer in a sufficient quantity and frequency to suppress particulate matter generation to comply with the opacity standard identified in the plan; or
  • Apply water to the surface area of all open storage piles on an as needed basis to comply with the opacity standard between May 1 to October 1; or
  • Install at least a two-sided enclosure with walls which extend, at a minimum, to the top of the pile to comply with the opacity standard.

Open storage piles are defined as a storage pile with a silt content of four percent or greater, has a height of three feet or more, and a total surface area of 150 square feet or more. Silt content will be determined by sampling and analysis in accordance with the ASTM C-136 or other equivalent methods approved by the department. Silt is defined as any material with a particulate size less than 74 micrometers in diameter and passes through a number 200 sieve.

Chemical stabilizer delays - Delays for application, up to 30 days, will be allowed during freezing conditions or when conditions are not favorable for application.

Waste Pit Control
For waste pit areas, the owner or operator shall implement one of the following:

  • Apply a soil cement or similar application that is approved by the department between October 1 and March 31 and apply a water spray to adequately create a crusted surface over the entire waste pit area to adequately control particulate matter between April 1 and September 30; or
  • Implement a combination of wind protection (wind-fence, wind-screen, three wall enclosure) and water spray application on an annual basis; or
  • Eliminate the waste pit by developing a market for the waste.

Waste pits are defined as areas where waste particulate matter from process equipment or pollution control units are deposited or disposed.

Blasting Controls
No blasting shall be allowed when a high wind air quality alert is in effect. The only exception is if the detonation charges have been set in the blasting holes prior to being notified of the high wind air quality alert. This exception is allowed for safety reasons and Mining Safety and Health Administration blasting requirements.

Comments and Proposed Controls:
Comments on the controls or suggestions on new controls are always welcome. To submit comments or proposed new controls, please call or write the department at the address and phone number below or send an email to the state contact:

Rick Boddicker, Environmental Scientist Manager
Air Quality Program
523 E. Capitol
Pierre, South Dakota 57501
(605) 773-3151