Appendix 7 Acute Impacts Refined Analysis FiguresRefined Acute Modeling Approach

Initial acute screening risk calculation s were performed with the HEM-3 model. HEM-3 estimates acute (1-hour) impacts at both polar and census block receptors. It is assumed for this short period of time that an exposed individual coul d be located at any off-site location. The lack of readily av ailable detailed property boundary information for many of the facilities evaluated made it difficult to determine whether receptors were

on- or off-site. In the absence of such info rmation, the first ring of polar receptors was placed 100 meters from the plant center for ma ny facilities. However, these polar rings

often transected on-site locati ons, restricting public access to exposures at these levels and thereby overestimating exposures.

The screening approach used by HEM-3 to estimate maximum 1-hour exposures also likely overestimates. To estimate ma ximum 1-hour concentrati ons at each receptor,

HEM-3 sums the maximum concentrations at tributed to each source, regardless of

whether those maximum concentrations occurr ed during the same hour. In other words, HEM-3 assumes that the maximum impact from each source at each receptor occurs at the same time. In actuality, maximum imp acts from different sources may occur at

different times.

This appendix includes the results of refined acute assessments performed for

facilities that exceeded short-term health benchmarks using the HEM-3 approach. The

refinements can address both areas of cons ervatism described above. The simplest refinement is to plot the HE M-3 polar grid results on aerial photographs of the facilities;

This allows the assessment of off-site loca tions that may be accessible to the public ( e.g., roadways and public buildings.). In cases wh ere this refinement results in lower acute

risks no further refinement was conducted. Howeve r, if acute risk sti ll remain at or near

levels of concern a further refinement is conducted. This second refinement includes remodeling with the AERMOD model directly (instead of using HEM) to estimate maximum 1-hour concentrations at each recepto r by pairing individual source impacts in time and space. The AERMOD results are then plotted on aerial photographs as noted above to determine off-site impacts. Modeling with AERMOD also allows the estimation of the frequency of higher impacts at or above the health levels of concern. The modeled 1-hour concentration of a pollu tant divided by its short-term health benchmark) at the polar receptors near the f acility was below a HQ of 1. Refer to below for a brief summary;

• NEI23077; Acute Risk Screening HQ was equal to 4.2 for glycol ethers, initial evaluation of the map indicated the HQ was on-site, with an off-site HQ of 2. This site required a refined assessment with AERMOD, in which the off-site HQ

was less than 1. The acute REL value for ethylene glycol methyl ether was used as a surrogate for all glycol ethers.Shipbuilding and Ship Repair Facilities:(Refined Acute Risk Assessment)• Figure 1 – NEI23077; maximum offsiteacute HQ(REL)for glycol ethers less than 1,North of the facilityFigure 1 – NEI23077 Acute Glycol Ethers HQ (REL)