OCT-15-2008 22:23 From:

,\i€O 674 UNITED STATES ENVIRONMENTAL PROTECTIONAGENCY RESEARCHTRIANGLE PARK, NC 27711 

## OCT 

## 7 5 

## 2008

SUBJECT: Update of Analysis 

### of. Proposed 

### So lg Emissiotl Threshold 

### FROM: Kevin Ca.vcnder,CIAQPSIAQADI 

### TO: .LeadNAAQS Review Docket 

### (oh%-2000-073

### 5) This memorandum updates the iinalysis conduct.cd it) developing the proposcd range for hc cmissian threshold (Cavendcr, 2008.) 

### BACKGROUND 

### Wc proposcd 

### a requiremcrlt for statc 

### and local monitoring agencies ("tn~ni.toring agencies") to conduct 

### Pb monitoring 

### in 

### areas near sources 

### of 'Pb that emitted more than rtn "emission tl~reshold." The emission threshold rcprcsents an estimate of the lowest 

### 'Pbemission rate hat under reasonable worst-case coilditiotls (e.g., nlclcorological 

### and cmission rclcasc conditions that lead .topoor dispersion and high 

### Pb concentrations) could lead to 

### Pb concentrations exceeding ' the 

### NAAQS. In thc piopossl notice, we proposcd a range: 

### Ibr tlic emission. threshold of 

### 200 to 

### 600 kdyr. 

### 'I'he rmgc of theproposed emission 

### threshold correspvndcd to 

### the 1-angc of the proposcd 

### Pb NAAQS, rind assumed Ihc NAAQS would be based on,tnonthlyaveraging. 

### Wc pointed out t,hsltthe enlissioe threshold would nccd to be rcca.lallatedba.scd 

### on the fina.1

### Pb NAAQS lcvel, averiigilzg. time, and form. Decisions on the final 

### Pb NAAQS 

### have been nladc. The ma1ysi.sd~cumcl~rcd hare reflccrs a Pb

### TSP NAAQS 

### of 0.15 

### pg/m" based on 

### a tnaxilnuin raIli,ng3-month average ("the fjnal 

### Pb NAAQS").



### In the initial dcvelopmcnt 

### ofthe einiss,ionthreshold.,

### 3 n~ethods were used to calcula[.e

### a.n emission thrcshold. 'Wc .usethe simc metliods hcrc, but ha.vcrcvised U1c rncthods to update the ailelysis based 

### on the final 

### Pb NAAQS Icvcl., avera.gingtime, 

### and fonn. 

### For the first mcthod, we scalcd the 5 tons per year (tpy) thrcshold, which was used lo identify cnndidatc sources for monitoring prior to the most rccent nmonitoring requircmenl:

### revisions based on the existing 

### 1.5 C1glrn3 Pb 

### NAAQS to the 

### ncw PI> N AAQS. Bascd on this approach, a valuc 

### is calcularcd as 

### 0.5 

### tpy (5 tpy *0.15/1.5). Wc also a-djustcdthe valuc to account for-thcdifferenceOCT-15-2008 22:23 From:

in 

### averagingpcriod (calendar quarter vs. rolling 3-monlh avcrage) using monitoring data (as described 

### below), but the adjustmctit was so minor it did not affect 

### thc rcsu1.t('i.e., thc 

### estimated value was still 

### 0.5 tpy sfer adj,ustrnent), and as sucll, 

### we don't detail thc adjustment hcre. The sccond method looked a1 monitoring da.tanear Pb sourccs. Sourcc oricnted 

### Pb monitors within one mile of 

### a.Pb soume 

### (identified rrom the 

### 2002 National Emissi.onsTnvcntory, 

### NET) were idenlificd.This goup of sites was then im-rowcd down lo sitcs near facilities emitting one tpy or more, 

### md then to sites which were only impacted by onc 

### Pb source. .Also,oilly thc highest reading monitor wa.s,used for 

### facilities where lllorc than one monitor was identified 'within one mile. From this :u~alysis, we identified 

### 7 moni1:or-facilitypa.irs tneetiilg thc criteria. Using data in 

### AQS for Ihc years 2002-2005, wc developed an cstimate of hcmsximum 3-m.onthavera.yc

### Pb concentration. Next wc obtained 

### a ratio of 

### the 

### ma.xir~ium 3-month average concentration to the fa.cilityannual 

### emissions (a.sidenti,ficdin the 2002 

### NGI) to provide an estimatc of the i~npa.cr fronl the faci1it.y

### in units of pg/tn3per tpy (scc Table I). As expected, this valuc varied greatly by 

### non nit or-source pa.ir.NoneLl~clcss, a median impact of 

### 0.2 Hg/m3pcr t.py and a maximum iinpa.ct of 

### 0.3 

### C~g/rn' per tpy wcre obtained from this list of sites. For 

### a final Pb 

### NAAQS of 0.15 yg/in", these ratios correspond to a vahc of'0.75 imd 0.5 tpy, respectively. Tab1.e 1. Wa.~a. Used to Estimate Facility In~pacts 

### Ba.scdon M'onitoring Data



### In the third medlod, 

### we perfomcd modeling utilizing 

### EPA.'s SCREEN3 wodcl. SCICEEN3 

### is a single source Gxussian plumc in,odelwhich provides maxim~un ground-level concentrations for point, 

### asca, flars, and vol~mnlc sources. The initial analysis providcd a inaximutn irnpac~ of 

### 0.6 

## pdrn3 per tpy for 

### a ~naxi~nutrl moilthly avel-agingdnx. 'For !.his anrtlysis, we used existing inonitoring da.tato develop 

### a scaling factor to convert the m;utin~um mo.nthly impa.ct. to a maximum 3-month average impact. LJsing 

### daain AQS 

### fa: the ycms 2002-2005, the maximum mo.nthlyconccntrrttion and the maximum rolling 3-month average concentrittion were calculated 

### ,usingthc 

### procedures in the final Appendix 

### R tbr each Pb-TSl> monitoring sitc (see Table 

### 2). O.nlysitcs with surficicnt data,ro calculrttc 

### a.mwimum 3-tnonth average was used in 

### this analyis, 

### and only d.atawith miuri~num 3-month avera.gc

### .Pb-TSPconcenlratious grca.tcrthen 

### 0.01 pg/m3.OCT-15-2BB8 22:23 From:



### The ratio of 

### lhc 

### ~naxitnurn 3-monlh 

### a.vcra.gcco.ncentrationto he 

### n~aximum monthly coa.centl-ation was 

### ca.lculdcd

### for each 

### site, 'md 

### thc 

### average of these 

### ratios (0.7) 

### was used to 

### col-rect the 

### maximum 

### monthly impact vitlctc (0.6 

### pg/~n\er tpy) to 

### a maximum 3-month 

### average 

### impact of 0.4 pg/m3

### pcr Ipy (Q.6*0.7).

### "I'his corresponds 

### to 

### a value of 0.375 

### tons for 

### a.final 

### Pb NAAQS 

### of 0.I 5 pg/m3. CONCLUSION 

### The updated 

### analysis provides four 

### diffcrcnt 

### values (0.5, 0.5, 0.75,,md 

### 0.375tpy) with 

### an 

### average 0.f 

### 0.5 

### rpy. Tablc 

### 2. Calculation of 

### Avcragc Ratio of M'aximum

### Rol.l.ing 3-Month 

### Average lo 

### Muim,um Moothly Average for the 

### Ycass 2002-2005.OCT-15-2008 22:23 From:OCT-15-2668 22:23 From:



### Rcfcrcnces Cavendcr, 

### Kcvia, .March 

### 3,2008, Memorandum 

### to the Lead

### NAAQS Rcvi.cw,Docket(OAK

### 2006-0735), 

### "Lcad NAAQS 

### Ainbient Air 

### Monitoring Nctwork: Network 

### Design Options Under Consideration,"