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water standards. Response levels are established in conjunction with notification levels <br /> and represent the drinking water contaminant concentration at which additional steps <br /> are recommended to reduce public exposure. Both notification and response levels are <br /> issued by the Deputy Director of DDW. <br /> DDW has defined PFHxS notification and response levels of 3 ng/L (3 parts per trillion) <br /> and 20 ng/L (20 parts per trillion), respectively. The difference between the OEHHA <br /> notification level of 2 ng/L and the DDW notification level of 3 ng/L is due to limitations in <br /> laboratory analytical methods that can't reliably test to levels below 3 ng/L. HSC 116378 <br /> requires that for PFAS substances where detected levels of a substance exceed the <br /> response level, a public water system shall take the water source exceeding the <br /> response level out of use or provide public notification within 30 days of the confirmed <br /> detection. A response level exceedance will be based on a single, confirmed sampling <br /> event. <br /> On August 17, 2022, the final public notice the for PFHxS notification and response <br /> levels was completed by the State Water Board. In response, the State Division of <br /> Drinking Water has issued to the City a new monitoring order for PFHxS which requires <br /> the City to act if PFHxS concentrations exceed the designated levels in its drinking <br /> water supply sources based on a single, confirmed sampling event. PFHxS <br /> concentration in the City water supply wells (wells, 5, 6, and 8) are exceeding the <br /> notification and response levels. Quarterly PFHxS water sampling results for the wells <br /> are presented in Figure 1 below confirming continued PFHxS exceedances. Well 8 was <br /> taken out of service in June 2019 because it exceeded a similar response level related <br /> to other PFAS compounds. <br /> 35 PFHxS Test Values <br /> 30 <br /> 25 <br /> a <br /> a <br /> 20r \ Z RL=20PPT <br /> v 15 <br /> Well 5 PFHxS <br /> -•-Well 6 PFHxS <br /> 10 <br /> 5 <br /> NL=3 PPT <br /> 0 <br /> 0 2 4 6 8 10 12 14 16 <br /> Quarter <br /> (Quarter 1=April to June 2019) <br /> Page 3 of 5 <br />