Ambient Air Monitoring Program for the Agua Fria River Basin

WESTON conducted a 4-month ambient air quality study along the Agua Fria River basin in the Sun City area. Residents in the vicinity of several sand and gravel manufacturing (SGM) operations located in the Agua Fria River basin had complained of dust and asphalt odors. The study was conducted in response to those complaints. The study focused on particulate matter and polynuclear aromatic hydrocarbons (PAHs).

Particulate matter was measured over two particle size ranges: particles less than 10 microns aerodynamic diameter (PM10), and particles less than 2.5 microns aerodynamic diameter (PM2.5). PM10 was selected because it is primarily made up of suspended dust from roads, soil, and construction, while PM2.5 was selected because it is primarily made up of fine particles from combustion sources (e.g., vehicle exhaust, residential wood combustion, fuel oil). The continuous monitoring was done to compare the local results to the U.S. Environmental Protection Agency’s (EPA) established 24-hour average Primary National Ambient Air Quality Standards (NAAQS) for PM10 and PM2.5 that are protective of public health. PAHs were targeted in the study because they are emitted by hot-mix asphalt (HMA) operations, which are present at some of the SGMs. The sampling results at the monitoring locations were compared to the State of Arizona’s 24-hour Ambient Air Guideline (AAG) concentrations for three PAH compounds–benzo(a)pyrene, benzo(a)anthracene, and naphthalene.

The objectives of the study were as follows:

• Evaluate the potential for residents living near, in, and immediately adjacent to the Agua Fria River basin to be exposed to particulate concentrations above the 24-hour NAAQS for PM10 and PM2.5

• Evaluate 24-hour ambient air concentrations of PAH hazardous air pollutants (HAPs) in conjunction with Arizona AAG concentrations

• Collect continuous monitoring data for particulates to provide information regarding acute, short-term air quality impacts

• Collect meteorological data to assist in the interpretation of the ambient air sampling and monitoring data

The study recorded data concurrently at six locations. The six locations were broken down into two primary locations, two secondary locations, and two mobile locations. The two primary locations collected continuous data for PM10 and PM2.5, with one also collecting periodic samples for PAHs and periodic confirmatory samples for PM2.5. The two secondary locations collected continuous data for PM10, with one being the location of the meteorological station, periodic confirmatory sampling for PM10, and periodic sampling for PAHs. The mobile locations collected continuous data for PM10 only and were designed to be moved to different sites if deemed necessary throughout the sampling program.