Pesticides and Water Quality - Texas Center for Policy Studies

D. Drinking Water MonitoringThis section reviews pesticide monitoring data for drinking water supply systems. Water utilities servingat least 25 persons or 15 connections at least 60 days a year are required to monitor for a number oforganics, including pesticides. (Many of these systems, however, can apply for waivers from theserequirements). Toxic pollutant monitoring requirements for drinking water systems began as a result ofthe 1986 Safe Drinking Water Act. Currently, there are 54 organic chemicals for which MaximumContaminant Levels, or MCLs exist, and 33 additional organic compounds that must be monitored for,even though no MCL currently exists. Of these organics, 23 of the regulated MCL and 10 monitoredcontaminants are used or have been used as pesticide active ingredients. 32 If the average of fourconsecutive quarterly samples of these chemicals is above the MCL, then it is considered to be a violationof both state and federal drinking water standards. TNRCC implements the requirements of the federalSDWA and related Texas law.As described in more detail in Appendix A, some systems have waivers from pesticide monitoringrequirements. These waivers are granted after TNRCC conducts a “vulnerability assessment”, anevaluation of various factors to determine whether the water source is “vulnerable” to contamination. Thevast majority of waivers are granted to systems relying on ground water. About one-half of the over5,700 community and non-transient, non-community water systems in Texas have received waivers fromall pesticide monitoring based on TNRCC determinations that they are not “vulnerable” tocontamination. 33 In addition, TNRCC has granted statewide waivers for four pesticides: endothall anddiquat (primarily used as aquatic herbicides), glyphosate (a widely used herbicide) 34 anddibromochloropropane.In those systems conducting sampling for pesticides, atrazine is the most frequently detected pesticide. Anumber of Texas systems have detected atrazine in finished drinking water (i.e. drinking water that goesto the tap) and a few have had individual quarterly samples above the MCL for atrazine (see Map 3 andAppendix B, Table B-1). In 1997 alone, for example, atrazine was detected in the tap water provided over60 public water supply systems. 35 These systems served at least four million people. Between 1995 and1997, over 80 public water supply systems detected atrazine in finished drinking water one or more times.Overall, nine water systems have exceeded the atrazine MCL at least once since drinking watermonitoring for organics began in 1993. In addition, the Aquilla Water Supply District in Hillsboro, HillCounty was in violation of the atrazine MCL and has exceeded the alachlor MCL on two occasions(Table 13). 36 Statewide, most of the MCL exceedences have been found in the spring, when atrazine useis higher and when rains are most likely to wash it into surface waters. 37In addition to the detections and exceedences of the MCL for alachlor and atrazine in some systems,many drinking water systems have detected other pesticides with frequency. Other pesticides that have32 Does not include two aldicarb breakdown products on unregulated contaminants monitoring list.33 Texas Natural Resource Conservation Commission, “Vulnerability Assessments”, www.tnrcc.state.tx.us /water/wu/swap/vapp.html, May 19, 1998. These systems still must sample once every three years for pesticides andother contaminants.34 TNRCC’s waiver for glyphosate is based on (1) glyphosate being reduced or eliminated by chlorination orozonation and (2) that the MCL for glyphosate is very high.35 Texas Natural Resource Conservation Commission, TNRCC Executive Management Briefing Paper Subject: AtrazineOccurrence in Public Drinking Water (Austin: TNRCC, August 19, 1997).36 Information from Organic Drinking Water Sampling Database, Water Quality Division, Texas Natural Resource ConservationCommission.37 Texas Natural Resource Conservation Commission, TNRCC Executive Management Briefing Paper Subject: AtrazineOccurrence in Public Drinking Water (Austin: TNRCC, August 19, 1997).17