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I-10 Twin Peaks Traffic Interchange, Environmental Assessment

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Affected Environment and <strong>Environmental</strong> Impacts October 2005<br />

The monitoring data indicate that the study area generally meets the NAAQS for<br />

monitored pollutants; however, particulate matter and CO are of general concern<br />

in the study area and Pima County. The project area lies completely within the<br />

boundaries of the Rillito Planning Area, which has been designated by EPA as a<br />

moderate nonattainment area for PM<strong>10</strong>. As opposed to the remainder of Pima<br />

County, which is under the auspices of PDEQ, the ADEQ has regulatory authority<br />

in the Rillito Planning Area. The primary sources of particulate emissions in this<br />

area include the Arizona Portland Cement Company, construction, unstabilized<br />

river banks, agriculture, unpaved roads, and unstabilized road shoulders. The<br />

Rillito PM<strong>10</strong> State Implementation Plan (SIP) was submitted to EPA in April 1994,<br />

but was never approved by EPA. However, the SIP does not include extraordinary<br />

particulate (dust) control mechanisms. According to ADEQ, compliance with Pima<br />

County’s Natural Events Action Plan (discussed in the following paragraph),<br />

ADOT standard specifications for dust suppression during construction, and the<br />

completion of a SWPPP would comply with the submitted Rillito Planning Area<br />

SIP.<br />

Table 4-5. National and State Ambient Air Quality Standards<br />

National and State Standards<br />

Pollutant Averaging Period Primary Secondary<br />

Carbon Monoxide<br />

(CO)<br />

Suspended<br />

Particulate Matter<br />

(PM<strong>10</strong>)<br />

8-Hour 9 ppm No Standard<br />

1 Hour 35 ppm No Standard<br />

24-Hour<br />

150 µg/<br />

m 3<br />

Same as Primary Standard<br />

Annual Arithmetic<br />

50 µg/ m<br />

Mean<br />

3 Same as Primary Standard<br />

Source: EPA (49 CFR 50).<br />

Abbreviations: ppm: parts per million, µg/m 3 : micrograms per cubic meter<br />

Although still considered an attainment area, Pima County exceeded the PM<strong>10</strong><br />

NAAQS six times in 1999. As a result, PDEQ developed a Natural Events Action<br />

Plan (NEAP) to protect public health, educate the public about high wind events,<br />

mitigate health impacts from future events, and identify and implement control<br />

measures for man-made sources of dust. The NEAP (and the ensuing Pima County<br />

ordinance) requires an activity permit from the PDEQ before activities such as<br />

earthmoving, trenching, or road construction are conducted. The ordinance also<br />

limits the amount of dust generated from these activities to a maximum opacity<br />

(cloudiness) of 20 percent. In addition to the NEAP, dust generation is also limited<br />

through grading permits issued by the Town of Marana and by ADOT standard<br />

specifications for dust suppression during construction.<br />

Interstate <strong>10</strong> <strong>Traffic</strong> <strong>Interchange</strong> at<br />

<strong>Twin</strong> <strong>Peaks</strong>/Linda Vista<br />

4-46<br />

Project No.: NH-0<strong>10</strong>-D (AIW)<br />

TRACS No.: <strong>10</strong> PM 236 H5838 01D

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