Mr. Shawn M Garvin (3RAOO)

Regional Administrator RECElvp Region IIIU.S. Environmental Protection Agency JUN 142011

1650 Arch Street

Philadelphia, PA 19103-2029 Division Director (3APOO)

Dear Administrator Garvin:

On June 2, 2010, the U.S. Environmental Protection Agency (EPA) strengthened the

National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO 2)by adding a new 1-hourprimary standard of 75 parts per billion (ppb) (3-year average of the 99t1 percentile daily maximum

1-hour concentration). Section 107(d) of the Clean Air Act (CAA) requires the Governor of each

State to submit to the EPA a list of all areas (or portions thereof) in the State, designating each as

nonattainment, attainment, or unclassifiable. This letter fulfills Delaware’s obligations under Section

107(d) of the CAA.

Area Description and Monitoring Data

Delaware is composed of three counties, namely New Castle, Kent and Sussex, laying from

north to south. The northern portion of New Castle County lies above the Chesapeake and

Delaware Canal, a waterway that connects the Chesapeake Bay with the Delaware Bay. This part ofNew Castle County is more metropolitan and industrialized than the remainder of Delaware. The

remainder of Delaware lies south of the Chesapeake and Delaware Canal, and comprises the

southern portion of New Castle County, and all of Kent and Sussex Counties.

Delaware currently monitors SO2at its Wilmington, Bellefonte, Summit Bridge, and

Delaware City monitoring sites, which are all located in New Castle County. The measured ambient

SO2concentrations (1-hour average, 99t1 percentile) for 2007 through 2009’ at three of thesemonitors are shown in the table below. Summit Bridge data is not included due to incomplete data,

and the fact that it has historically recorded the lowest SO2concentrations.

99th percentile 1-hour

average (ppb) 3-year average (ppb)

Site 2007 2008 2009 2007-2009

Bellefonte 69 60 41 56.7

MLK/Wilmington 58 57 30 48.3

Delaware City 41 51 28 40.0

1 2010 data has not undergone quality assurance and is incomplete at this time.
The designation approach under this new SO2 NAAQS uses both air quality monitoring and

modeling information. EPA’s March 24, 2011 guidance indicates that States should identify areas asattainment, nonattainment or unclassifiable on the basis of available monitoring and modelingmforniation.

Based on available monitoring and modeling information, Delaware recommends that each

of its three Delaware counties be designated as “unclassifiable” for the 75 ppb 1-hour °2 NAAQs.

• Delaware has no available monitoring or modeling information that supports a

nonattainment designation.

• Delaware’s existing SO2monitoring network is not sufficient to support an attainment

designation.

• Delaware has not completed all of the air dispersion modeling necessary to support

either an attainment or nonattainment designation.

This recommendation is consistent with the EPA expectation outlined in the Stephen D.

Page, Director, EPA Office of Air QualityPlanning and Standards, March 24, 2011 memorandum,“A ra Designationsfor the’ 2010 RezisedPrimzry SulfiirDiadde NationalA niientA ir Quality Standrth.”This memorandum states, “Gizithe am 1ylinitedr’tzeok ofSO 2nvnitom, and cxtr exjmationthatstates

ui/i not )et haze coiçktedappivpriate nix/ding fa11 sigificant SO2scwzrs, ue antiapaw that nxt awas (ftmtiy ui/i / asignated ‘mdassy9able

Thank you for your consideration of this recommendation. If you have any questions

concerning this submittal or would like to discuss it further, please contact Mr. All Mirzakhahui, P.E.,

the Director of our Division of Air Quality; at (302)739-9402.

Sincerely,

Jack A. Markell

Governor

pc: Coffin O’Mara

Dave SmallAll MirzakhaliuiDiana Esher