Environmental Engineering Reference
In-Depth Information
TABLE 17.1
Distributions of Hazards by Census Tract
Number of
Tracts with at
Least 1 Site
Number of
Tracts with
No Sites
Number of
Tracts with
HDI Score > 0
Number
Tracts with
0 HDI Score
Number
of Sites
Type of Hazard
CERCLIS
412
122
344
305
161
LQGs
117
65
401
231
235
TRI
119
58
408
192
274
TSDF
13
11
455
47
419
Any hazard
sited in tract
661
156
a
310
a
361
a
105
a
a
Numbers do not sum as some sites are included in more than one hazard category.
To summarize research findings, of the 466 tracts in Maricopa County, 105 (about 22%)
tracts are untouched by 1 km buffers around hazardous sites. By comparison, 310 tracts
(67%) do not actually contain any of the four types of hazards studied. There are strong,
statistically significant relationships between the proximity of a hazard and the income
and race of residents. As presented in Table 17.2, tracts with CHDI scores greater than zero
had median family incomes that averaged more than $9000 less than “clean” tracts and
had significantly higher percentages of Latino, African American, and Indian residents.
Taking each hazard type individually, the same pattern holds. Tracts with a hazard score
greater than zero for each of the four types of hazards are significantly poorer and house
significantly higher proportions of Latino, Black, and Indian residents compared to tracts
with a hazard score of zero for the same hazard type. Affected tracts have significantly
lower median household incomes and higher proportions of minority residents. This
methodology reveals significant social inequalities in the distribution of four major types
of technological hazards in Phoenix.
To further specify the areas of highest hazard burden in the city of Phoenix, we next
identify those tracts in the 90th percentile of hazard scores, yielding 20 high hazard tracts.
Figure 17.1 presents a map of the Phoenix “riskscape” showing major urban features as
well as the locations of the highest scoring tracts. These 20 tracts comprise our study area
for the discussion to follow. To illustrate the gradients of hazard density values across
the metro area, Figure 17.2 presents a contour map of CHDI scores with the most heavily
shaded areas denoting the highest hazard scores. Notable in Figure 17.2 are the high
concentrations of hazards in older neighborhoods of South Phoenix (discussed later) and
in a mixed industrial/residential zone immediately west of the central business district
(CBD). For the high hazard study area tracts identified in Figure 17.1, all 20 are within
4.3 mile of Phoenix's CBD covering an area of 49.8 mile
2
. Taken together, these tracts form
a roughly L-shaped zone following rail and highway corridors around the CBD from Sky
Harbor airport on the east, across historic minority neighborhoods to the aging suburbs of
west central Phoenix. These tracts make up approximately 4% of the urbanized area and
have an average CHDI score of 6.4 (maximum is 16.4), compared to a metro- wide CHDI
average of .9. Recall too that approximately one quarter of metropolitan tracts, all on the
urban periphery, have hazard density scores of zero.
The study area captures an expanding zone of hazardous land uses: from the original
core in South Phoenix, it has extended with post-WWII industrial development east into
Sky Harbor airport and west into older suburban areas. Seventy-two percent of the housing
stock here was built prior to 1970 compared to a metropolitan average of 30%. These 20
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