OCT-15-2008 22:23 From: 

,\i€O 674 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 2771 1 

OCT 7 5 2008 

SUBJECT: Update of Analysis of. Proposed So lg Emissiotl Threshold 

FROM: Kevin Ca.vcnder, CIAQPSIAQADI 

TO: .Lead NAAQS 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 'Pb emission rate hat 

under reasonable worst-case coilditiotls (e.g., nlclcorological and cmission rclcasc conditions that 

lead .to poor 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 the proposed emission threshold correspvndcd to the 1-angc of the proposcd Pb NAAQS, 

rind assumed Ihc NAAQS would be based on,tnonthly averaging. Wc pointed out t,hslt the 

enlissioe threshold would nccd to be rcca.lallated ba.scd on the fina.1 Pb NAAQS lcvel, averiigilzg. 

time, and form. 

Decisions on the final Pb NAAQS have been nladc. The ma1ysi.s d~cumcl~rcd hare reflccrs a PbTSP NAAQS of 0.15 pg/m" based on a tnaxilnuin raIli,ng 3-month average ("the fjnal Pb 

NAAQS"). 

In the initial dcvelopmcnt of the einiss,ion threshold., 3 n~ethods were used to calcula[.e a.n 

emission thrcshold. 'Wc .use the simc metliods hcrc, but ha.vc rcvised U1c rncthods to update the 

ailelysis based on the final Pb NAAQS Icvcl., avera.ging time, 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-djustcd the valuc to account for-thc difference 
OCT-15-2008 22:23 From: 

in averaging pcriod (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.ta near Pb sourccs. Sourcc oricnted Pb monitors 

within one mile of a. Pb soume (identified rrom the 2002 National Emissi.ons Tnvcntory, 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-facility pa.irs tneetiilg thc criteria. Using data 

in AQS for Ihc years 2002-2005, wc developed an cstimate of hc msximum 3-m.onth avera.yc Pb 

concentration. Next wc obtained a ratio of the ma.xir~ium 3-month average concentration to the 

fa.cility annual emissions (a.s identi,ficd in the 2002 NGI) to provide an estimatc of the i~npa.cr 

fronl the faci1it.y in units of pg/tn3 per 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/m3 pcr 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.scd on M'onitoring Data 

In the third medlod, we perfomcd modeling utilizing EPA.'s SCREEN3 wodcl. SCICEEN3 is a 

single source Gxussian plumc in,odel which 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-aging dnx. 'For !.his anrtlysis, we used existing 

inonitoring da.ta to develop a scaling factor to convert the m;utin~um mo.nthly impa.ct. to a 

maximum 3-month average impact. LJsing daa in AQS fa: the ycms 2002-2005, the maximum 

mo.nthly conccntrrttion and the maximum rolling 3-month average concentrittion were calculated 

,using thc procedures in the final Appendix R tbr each Pb-TSl> monitoring sitc (see Table 2). 

O.nly sitcs with surficicnt data, ro calculrttc a. mwimum 3-tnonth average was used in this analyis, 

and only d.ata with miuri~num 3-month avera.gc .Pb-TSP concenlratious grca.tcr then 0.01 pg/m3. 
OCT-15-2BB8 22:23 From: 

The ratio of lhc ~naxitnurn 3-monlh a.vcra.gc co.ncentration to 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 0.375 tpy) 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. 
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OCT-15-2668 22:23 From: 

Rcfcrcnces 

Cavendcr, Kcvia, .March 3,2008, Memorandum to the Lead NAAQS Rcvi.cw ,Docket (OAK2006-0735), "Lcad NAAQS Ainbient Air Monitoring Nctwork: Network Design Options Under 

Consideration,"