Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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idle for 10 minutes. Water trucks would be used during the mass grading and fine grading construction phases. The water trucks were assumed to travel a 5 mph for 8 hours per day for 16 days during mass grading and 20 days during fine grading. The projected construction schedule and DPM emission calculations are provided in Attachment 1 along with other assumptions included in the modeling. The U.S. EPA ISCST3 dispersion model was used to predict concentrations of DPM at existing residences surrounding the project site. The ISCST3 modeling included a single area source to represent the on-site construction. An emission release height of 6 meters was used for the area source. The elevated emission release height represents the elevated exhaust stacks and buoyant plumes. Emissions were modeled as occurring daily between 7 am - 4 pm. Emissions for each of the construction years were modeled. The model used a 4-year data set of hourly meteorological data from San Carlos Airport (years 2002 through 2005), located about 3.5 miles northwest of the project site. Annual DPM concentrations from construction activities were predicted for 2013 and 2014, with the concentrations for each construction year based on the 4- year average concentrations from modeling 4 years of ineteorological data. DPM concentrations were calculated for three heights at each receptor location; 1.5 meters, 4.55 meters, and 7.6 meters, representative of the first, second, and third stories of nearby apartments and houses. The maximum concentration occurred at a receptor adjacent to the southern boundary of the project site at the second floor level. The location of this receptor is also shown in Figure 1. Increased cancer risks were calculated using the maximum modeled annual concentrations and BAAQMD recommended risk assessment methods for both a child exposure (3rd trimester through 2 years of age) and for an adult exposure. Since the modeling was conducted assuming emissions occur 365 days per year, the default OEHHA exposure period of 350 days per year was used. Nearly continuous infant and child exposures were assumed at the nearby residences through the entire construction period. Results of this assessment indicate an incremental residential child cancer risk of 8.3 cancer cases per million and a residential adult incremental cancer risk of 0.4 cancer cases per million. These cancer risks are below the BAAQMD's threshold of 10 excess cancer cases per million. The maximum annual PM2.5 concentrations would be 0.10 µg/m3. Potential non-cancer health effects due to chronic exposure to DPM were also evaluated. The chronic inhalation reference exposure level (REL) for DPM is 5 µg/m3. The maximum predicted annual DPM concentration from construction activities is 0.10 µg/m3, which is much lower than the REL. The Hazard Index (HI), which is the ratio of the annual DPM concentration to the REL, is 0.014. This HI is much lower than the BAAQMD significance criterion of a HI greater than 1.0. Attachment 1 includes the emission calculations used for the construction area source modeling and the cancer risk calculations. The cancer risks would be below the significance thresholds. However, mitigation measures are recommended to ensure that construction emissions are properly controlled to avoid significant exposures to construction emissions. 4