{"schema_version":"1.2","pwsid":"IL1570100","system_name":"CHESTER","city":"CHESTER","state":"IL","population_served":8407,"source_type":"SW","summary":"CHESTER serves approximately 8,407 people in CHESTER, Illinois. Based on contaminant analyses from EPA ECHO, EPA UCMR5, 0 contaminants have been measured above federal EPA standards (MCL) and 1 exceeds health-based guidelines. The most significant finding is Lead (90th Percentile) at 0.0018 mg/L, which is 9x the health guideline. Data is drawn from source-level compliance monitoring and covers 2017 through 2025. Results reflect conditions at the point of collection (wells, treatment plants), not necessarily at the tap.","data_period":{"start":"2017-12-31","end":"2025-12-31"},"contaminants_tested":31,"contaminants_detected":5,"exceedances":0,"guideline_exceedances":1,"contaminants":[{"name":"Lead (90th Percentile)","code":"PB90","cas_number":"7439-92-1","group":"lead_copper","section":"guideline_exceedance","measured_value":0.0018,"unit":"mg/L","sample_date":"2025-12-31","source":"EPA ECHO","source_scope":"federal_program","health_guideline_value":0.0002,"health_guideline_source":"OEHHA PHG","epa_mcl_value":null,"status":"exceeds_guideline","detection_limit":null},{"name":"Lithium","code":"lithium","cas_number":null,"group":"other","section":"pfas","measured_value":13,"unit":"ug/L","sample_date":"2024-12-03","source":"EPA UCMR5","source_scope":"federal_program","health_guideline_value":null,"health_guideline_source":null,"epa_mcl_value":null,"status":"detected","detection_limit":9},{"name":"PFBA (Perfluorobutanoic Acid)","code":"PFBA","cas_number":null,"group":"pfas","section":"pfas","measured_value":0.0083,"unit":"ug/L","sample_date":"2024-12-03","source":"EPA UCMR5","source_scope":"federal_program","health_guideline_value":null,"health_guideline_source":null,"epa_mcl_value":null,"status":"detected","detection_limit":0.005},{"name":"PFBS (Perfluorobutane Sulfonate)","code":"PFBS","cas_number":"375-73-5","group":"pfas","section":"pfas","measured_value":0.0032,"unit":"ug/L","sample_date":"2024-12-03","source":"EPA UCMR5","source_scope":"federal_program","health_guideline_value":null,"health_guideline_source":null,"epa_mcl_value":null,"status":"detected","detection_limit":0.003},{"name":"Pfpea","code":"PFPeA","cas_number":null,"group":"other","section":"pfas","measured_value":0.0031,"unit":"ug/L","sample_date":"2024-09-10","source":"EPA UCMR5","source_scope":"federal_program","health_guideline_value":null,"health_guideline_source":null,"epa_mcl_value":null,"status":"detected","detection_limit":0.003}],"sources":[{"name":"EPA ECHO","url":"https://echo.epa.gov/"},{"name":"EPA UCMR5","url":"https://www.epa.gov/dwucmr/fifth-unregulated-contaminant-monitoring-rule"}],"pfas_combined_display":null,"well_counts":{"active":0,"retired":0,"facilities_synced_at":"2026-09-06T14:49:36.593Z"},"historical_wells":[],"has_only_historical_data":false,"pfas_hazard_index":{"value":0.0016,"compounds_used":["PFBS"],"is_partial":true,"threshold":1,"components":[{"code":"PFBS","value_ng_l":3.2,"hbwc_ng_l":2000,"ratio":0.0016}]},"tthm_lraa":[],"haa5_lraa":[]}