Figure 5.

Key risk factors regressed on private well contamination probability (log-binomial regression) or concentration (gamma regression): (A) detection probability for human-specific markers; (B) detection probability for any fecal marker; covariates: manure storage distance, bedrock depth, manure storage distance times bedrock depth interaction, rainfall 2-d antecedent cumulative; (C) estimated bovine-specific marker concentration (mean sum); (D) interaction between manure storage distance and bedrock depth for any fecal marker detection probability; covariates: septic system drainfields within $229\mathrm{m}$ of well, rainfall 2-d antecedent cumulative; (E) detection probability of ${\mathrm{NO}}_3^{-}\text{-N}>10\mathrm{mg}/\mathrm{L}$. Black line: regression estimates. Dashed lines: 95% pointwise confidence limits. Coefficients and p-values are reported in Table 5. Covariates in the multivariable models were fixed at their median values for the purpose of plotting.