TABLE 3—
Generalized Additive Model Results Estimating the Association Between Sociodemographic Variables and 2011–2019 Mean Groundwater Contaminant Levels Among Domestic Well Areas: California
| Dependent Variables | Arsenic ≥ 1/2 MCL (n = 1782), PRa (95% CI) | Nitrate ≥ 1/2 MCL (n = 1917), PR (95% CI) | Cr(VI) ≥ 1/2 MCL (n = 1597), PR (95% CI) | Cumulative Contaminant Indexb (n = 1587), Bc (95% CI) |
| % Latinxd | 1.13 (1.05, 1.21) | 1.19 (1.11, 1.28) | 1.23 (1.13, 1.34) | 0.14 (0.09, 0.19) |
| % non-Latinx people of colord | 1.21 (1.07, 1.37) | 1.07 (0.93, 1.24) | 1.11 (0.94, 1.30) | 0.10 (0.01, 0.19) |
| % renterd | 1.07 (0.99, 1.16) | 1.06 (0.98, 1.16) | 1.06 (0.95, 1.17) | 0.07 (0.01, 0.12) |
| Central Coaste | 0.96 (0.37, 2.48) | 0.82 (0.35, 1.91) | . . .f | 0.22 (‒0.42, 0.86) |
| Eastern Sierra | 0.83 (0.31, 2.25) | 0.14 (0.01, 1.40) | . . .f | 0.10 (‒0.60, 0.80) |
| Imperial Valley and Mojave Desert | 2.48 (0.34, 18.16) | 1.13 (0.15, 8.56) | . . .f | 0.04 (‒1.21, 1.28) |
| Northern California | 0.51 (0.18, 1.50) | 0.41 (0.07, 2.28) | . . .f | −0.37 (‒1.14, 0.40) |
| Northern Sierra | 1.30 (0.56, 3.00) | 1.11 (0.33, 3.77) | . . .f | 0.41 (‒0.22, 1.04) |
| San Joaquin Valley | 1.91 (0.91, 3.99) | 1.31 (0.55, 3.12) | . . .f | 0.90 (0.37, 1.44) |
| Southern California | 2.58 (0.61, 10.96) | 0.17 (0.04, 0.30) | . . .f | 0.04 (‒0.90, 0.97) |
| AIC | 1 700.72 | 1 466.24 | 1 028.27 | 6 339.41 |
| Log-likelihood | −821.32 (df = 29.05) | −702.40 (df = 30.72) | −492.48 (df = 21.66) | −3140.16 (df = 29.55) |
| Moran’s I P | .82 | .63 | .96 | .54 |
Note. AIC = Akaike information criterion; CI = confidence interval; MCL = maximum contaminant level. The California MCL for arsenic is 10 µg/L. The MCL for nitrate as N is 10 mg/L. Cr(VI) does not currently have an MCL; we used the most recent MCL of 10 µg/L, which was rescinded in 2017 and is in the process of being revised.
PRs are prevalence ratios obtained by exponentiating the binomial model regression coefficients.
The cumulative contaminant index (CCI) is the sum of individual mean contaminant concentrations (arsenic, nitrate, and Cr[VI]) divided by half of their respective MCLs. CCI ranged from 0.0 to 112.6 with a mean of 1.8 across all DWAs in the state.
Estimates represent a mean difference obtained from Gaussian model regression coefficients.
Continuous dependent variables were scaled by 10%.
Comparison group is the San Francisco Bay Area region.
Region excluded from this model because Cr(VI) is a more localized contaminant than arsenic or nitrate.