 



                                       
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            REGION IX AIR DIVISION










                          Technical Support Document 
                                      for
                              EPA's Rulemaking
                                    for the
                       Arizona State Implementation Plan
                                       
Pima County Department of Environmental Quality, Pima County Code Section 17.16.125, 
         Inactive mineral tailings impoundment and slag storage area 
                       within the Ajo PM10 Planning Area












                              
                              Christine Vineyard

                                  March 2020





RULE IDENTIFICATION 
Agency
Pima County Department of Environmental Quality (DEQ)

Subject of this TSD
Pima County Code (PCC), title 17 (Air Quality Control), chapter 17.16 (Emission Limiting Standards), article III (Emissions from Existing and New Nonpoint Sources), section 17.16.125 - Inactive Mineral Tailings Impoundment and Slag Storage Area within the Ajo PM10 Planning Area. 

Adopted  -  January 22, 2019
Effective  -  February 21, 2019
Submitted  -  May 10, 2019

Completeness Finding
Determination of Completeness letter: October 22, 2019


BACKGROUND  -  Pima County DEQ regulates most types of stationary sources within Pima County, Arizona. Two areas within Pima County are classified as Moderate nonattainment areas for the National Ambient Air Quality Standards (NAAQS) for particulate matter of ten microns or less (PM10). The Ajo planning area, located in northwest Pima County, is one of the two PM10 nonattainment areas in Pima County. Pima County Code (PCC) section 17.16.125 regulates emissions sources within the Ajo planning area.

Historically, the primary sources of PM10 emissions in the Ajo nonattainment area were fugitive dust from tailings piles, mining, milling, distilling, and smelting processes at the Phelps Dodge Corporation copper mine and smelter. Additional sources included Minerals Research & Recovery Inc. (MRRI), a slag reprocessing facility, vehicular traffic on Highway 85, a landfill, unpaved roads, construction, and windblown dust from open areas.

The Phelps Dodge Corporation copper mining, concentrating and smelting facilities, collectively known as the Phelps Dodge "New Cornelia Branch," were the largest permitted stationary sources in the Ajo nonattainment area. Fugitive dust originating from tailings impoundments contributed the largest share of anthropogenic PM10 emissions in the nonattainment area. The Ajo mine ceased operation in 1984 and the smelter deactivated in April 1985. A resource reclamation and salvage program was initiated in January 1995 and completed in March 1996, effectively dismantling the smelter and copper ore concentrator structures at the facility. The drying surfaces of tailings piles can become friable, easily crumbled or reduced to powder, thereby contributing to windblown particulate emissions. To minimize windblown emissions from the inactive tailings impoundments, Phelps Dodge engaged Terra Contracting to cover (or cap) more than 1900 acres of the tailings with 2-4" diameter crushed rock between May 1990 and October 1991.To prevent disturbance, access to roads and service areas around and on the tailings continues to be restricted (i.e., property is posted and fenced).

Minerals Research & Recovery Inc. (MRRI) was a slag reprocessing facility adjacent to the Ajo tailings piles. MRRI utilized byproducts of the copper smelting process (slag) to make products such as abrasives and grinding materials, roofing granules, and asphalt fillers. Sources of process emissions and fugitive dust at the Ajo facility included three main production areas; raw stockpile and waste storage areas, a primary crushing and screening plant, and a secondary crushing and screening plant. In addition, there was an access road to nearby Highway 85 and haul roads to the stockpile areas. MRRI filed a notice of intent to terminate its air quality operating permit in October 2015. Demolition of all facility structures was accomplished between July 1, 2015 and October 31, 2015. To reduce future windblown fugitive emissions, mitigation measures were implemented including application of a slag dust cap on selected process areas. Stabilization of the worksite was completed by the end of 2015. To prevent further disturbance, access to roads and service areas at the former reprocessing facility are restricted (i.e., property is posted and fenced).

Application of control measures at the Ajo tailings impoundment and slag processing/storage areas were completed in 1991 and 2015, respectively, as discussed above. Pima County Code section 17.16.125 was developed by Pima County DEQ to provide permanence and federal enforceability for those measures already implemented, and, thereby, to support ADEQ's request for redesignation of the Ajo planning area from nonattainment to attainment for the PM10 NAAQS.    

RULE SUMMARY  -  New PCC Section 17.16.125 will provide permanence and enforceability for control measures that have already been implemented.  Owners and operators are required to implement and maintain required PM10 control measures on applicable sources to meet visible emissions and stabilization requirements, to ensure continued particulate matter emissions reductions in the Ajo PM10 Planning Area.  The inactive tailings area must be controlled to 20% opacity for fugitive emissions on the property.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

Specific rule elements include:

1.	An Applicability section is included to show that this rule applies to the owner or operator of the inactive mineral tailings impoundment and slag storage area within the Ajo PM10 Planning Area. 
                                          
2.	The following defined terms are included to clarify the rule: affected area, Ajo PM10 Planning Area, chemical or organic soil stabilizer, coarse, copper smelter slag, crushed rock, Department, gravel, high wind event, inactive, meteorological monitoring station, mineral tailings impoundment, opacity, particulate matter, PM10, slag storage area, and vegetative cover.

3.	The following control measures are included:
      a.  For the inactive mineral tailings impoundment, the owner or operator must implement and maintain at least one of the following reasonably available control measures:
 Application of crushed rock or gravel;
 Application of chemical or organic soil stabilizers;
 Application of water;
 Establishment of vegetative cover; or
 An equivalent method or technique approved by the Department and EPA Region IX.
            
b.  For inactive slag storage areas, the owner or operator must implement and maintain at least one of the following reasonable available control measures:
            Application of a cap consisting of coarse copper smelter slag material; or
            Any other equivalent method or techniques approved by the Department and EPA Region IX.
           
      c.  To prevent trespassing at the inactive mineral tailings impoundment and slag storage areas, the owner or operator must install and maintain the following:
            No trespassing signs; and
            Physical barriers such as fences, gates, posts, shrubs, trees, or other measures to effectively restrict access from the general public.
           
4. 	An opacity standard is included for the mineral tailings impoundment:
a.  The owner or operator must not cause or allow visible emissions to exceed 20% opacity.	 

b.  The 20% opacity standard does not apply during high wind events (i.e., hourly average > 25 miles per hour (mph) or instantaneous wind gust > 40 mph) if the owner or operator has implemented and maintained one of the reasonably available control measures described above and documented implementation and maintenance of the measure as set forth elsewhere in the rule.

5. 	Monitoring Requirements:
a.  To demonstrate compliance with the reasonably available control measures requirement for the inactive mineral tailings impoundment and the opacity standard, the owner or operator must conduct weekly visible emissions observations in accordance with 40 CFR part 60, appendix A, Reference Method 9 or  ASTM D7520-16.

	b.  To demonstrative compliance with inactive slag storage area reasonably 	available control measures, the owner or operator must conduct monthly 	inspections to assess the effectiveness.

	c.  To demonstrate compliance with requirements to prevent trespassing, the 	owner or operator must conduct monthly inspections of trespassing signs and 	physical constraints.

6.  	Recordkeeping Requirements:
a.  The owner or operator must maintain and make available to the Pima County DEQ or EPA Region IX the following records upon request:
 Reasonably available control measures implemented and maintained;
 Visible emission observations;
 Monthly inspection of the slag storage areas and trespassing signs and physical constraints;
 Records of test method certifications;
 Meteorological monitoring station data.
            
b.  If the owner or operator elects to conduct weekly visual observations in accordance with ASTM D7520-16 then certification documentation, data sheets and all raw unaltered data records are required to be maintained. 

c.  Records must be maintained by the owner or operator for a minimum of 5 years.

7. 	Notification Requirements:
a.   The owner or operator must provide written notification to the Pima County DEQ at least 30 days prior to initiating weekly visual observations.
b.  The owner or operator must provide written notice to the Pima County DEQ at least 30 days prior to using any meteorological monitoring station.

8.	Reporting Requirements:
a.  The owner or operator must report to the Pima County DEQ any visible emissions in excess of established opacity limit.
b.  Excess opacity report must contain certain specific types of information.
      c.  Certain specific reporting requirements apply to continuous or recurring excess opacity events.

EVALUATION CRITERIA  -  The following criteria were used to evaluate the submitted rule. 

1.	Enforceability - The Bluebook (Issues Relating to VOC Regulation Cutpoints, Deficiencies, and Deviations, EPA, May 25, 1988) and the Little Bluebook (Guidance Document for Correcting Common VOC & Other Rule Deficiencies, EPA Region 9, August 21, 2001) were used to help evaluate compliance with the Clean Air Act (CAA) §110(a)(2)(A) requirement for enforceability.  

2.	SIP Revisions - CAA §110(l) prohibits EPA from approving any SIP revision that would interfere with any applicable requirement concerning attainment and reasonable further progress (RFP) or any other applicable requirement of the CAA. In addition, CAA §193 prohibits the modification of any SIP-approved control requirement in effect before November 15, 1990, in a nonattainment area, unless the modification insures equivalent or greater emission reductions.

3. 	Stringency  -    Clean Air Act (CAA) §§ 172(c)(1) and 189(a)(1)(C) require that moderate nonattainment area SIP revisions include emissions reductions from existing sources of PM10 emissions, as may be obtained through reasonably available control measures (RACM) and reasonably available control technology (RACT).   

EPA EVALUATION  -  A summary of our evaluation of the three criteria follows.

      1. 	Enforceability  -  To help ensure enforceability, the rule requirements and applicability are clear, and the monitoring, recordkeeping, reporting and other provisions sufficiently ensure that affected sources and regulators can consistently evaluate and determine compliance with PCC Section 17.16.125.  Enforceable requirements include:
 Visible emissions cannot exceed 20% opacity as determined by EPA Reference Method 9 or ASTM D7520-16.
 Inactive mineral tailings impoundment and inactive slag storage areas must be stabilized through implementation and maintenance of at least one of the specific reasonable available control measures listed in the rule.
 To prevent trespassing the owner or operator must install and maintain no trespassing signs and physical barriers such as fences, gates, posts, shrubs, trees, or other measures to effectively restrict access from the general public.
 The owner or operator must report any visible emissions in excess of the 20% opacity emission limits.
            
      2.  	SIP Revisions  -  PCC Section 17.16.125 would not interfere with attainment or maintenance of any of the NAAQS, or any other requirement of the CAA. Rather, PCC Section 17.16.125 directly supports maintenance of the PM10 NAAQS in the Ajo planning area by providing permanence and enforceability to the fugitive dust measures that have brought the area into attainment. As such, EPA finds this SIP revision to be approvable under section 110(l). Section 193 does not apply to this SIP revision because PCC Section 17.16.125 post-dates the CAA Amendments of 1990.  

      3. 	Stringency  -  On February 8, 2006, EPA determined that the Ajo nonattainment area has attained the PM10 NAAQS and suspended the requirements for SIP revisions providing for reasonably available control measures (RACM) under CAA sections 172(c)(1) and 189(a)(1)(C). Therefore, we do not need to determine that PCC Section 17.16.125 meets the RACM requirement. Rather, the purpose of PCC Section 17.16.125 is to provide permanence and enforceability for the maintenance of fugitive dust control measures that have already been implemented at the inactive mineral tailing impoundment and inactive slag storage area within the Ajo planning area. We find that the rule is reasonably designed to achieve that purpose. 
      
EPA ACTION - The submitted Pima County Code Section 17.16.125 strengthens the SIP by providing for the long-term maintenance of the estimated 127 tons per year in emissions reductions that were achieved through closure and capping of the Ajo tailings impoundment and the slag reprocessing areas. The rule meets the relevant CAA § 110 and part D requirements. Therefore, EPA staff recommends approval of Pima County Code 17.16.125 pursuant to CAA §§ 110(k)(3) and 301(a). 

REFERENCES 

 "Issues Relating to VOC Regulation Cutpoints, Deficiencies, and Deviations," (a.k.a., Bluebook) EPA OAQPS, May 25, 1988.
 "Guidance Document for Correcting Common VOC & Other Rule Deficiencies," (a.k.a., Little Bluebook), EPA Region 9, August 21, 2001.
 Pima County Code, Title 17, Section 17.16.125, Inactive mineral tailings impoundment and slag storage area within the Ajo PM10 Planning Area, adopted January 22, 2019.

