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	Annual Toxics Summary San Francisco-Arkansas Street FAQs Perchloroethylene parts per billion

Read About Estimated Risk

Year	Months Present	Minimum	Median	Mean	90th Percentile	Maximum	Standard Deviation	Number of Observations	Detection Limit	Estimated Risk
2023		0.005	0.005	*	0.005	0.01	0.002	19	0.01	*
2022		0.005	0.005	0.008	0.02	0.03	0.006	30	0.01	0.9
2021		0.005	0.005	*	0.02	0.08	0.016	23	0.01	*
2020		0.005	*	*	*	0.01	0.003	9	0.01	*
2019		0.005	0.005	0.006	0.005	0.02	0.003	30	0.01	0.7
2018		0.005	0.005	0.008	0.02	0.02	0.005	31	0.01	1
2017		0.005	0.005	0.009	0.02	0.04	0.008	30	0.01	1
2016		0.005	0.005	0.011	0.02	0.08	0.014	31	0.01	1
2015		0.005	0.01	0.015	0.03	0.05	0.011	30	0.01	2
2014		0.005	0.005	0.011	0.02	0.03	0.007	30	0.01	1
2013		0.005	0.01	0.012	0.02	0.07	0.012	31	0.01	1
2012		0.005	0.005	0.010	0.02	0.07	0.013	29	0.01	1
2011		0.005	0.02	0.018	0.03	0.04	0.011	31	0.01	2
2010		0.005	0.02	0.022	0.04	0.06	0.015	29	0.01	3
2009		0.005	0.01	0.021	0.05	0.07	0.018	28	0.01	2
2008		0.005	0.02	0.020	0.04	0.06	0.015	31	0.01	2
2007		0.005	0.03	0.031	0.06	0.10	0.025	29	0.01	4
2006		0.005	0.03	0.030	0.05	0.07	0.019	30	0.01	3
2005		0.005	0.02	0.026	0.05	0.10	0.020	31	0.01	3
2004		0.005	0.04	0.040	0.07	0.08	0.019	30	0.01	5
2003		0.005	0.03	0.038	0.06	0.10	0.022	31	0.01	4
2002		0.02	0.05	*	0.16	0.19	0.054	16	0.01	*
2001		0.01	0.05	0.074	0.07	0.65	0.112	30	0.01	9
2000		0.02	0.06	0.068	0.14	0.20	0.044	28	0.01	8
1999		0.02	0.07	*	0.15	0.17	0.050	18	0.01	*
1998		0.02	0.05	*	0.25	0.43	0.104	26	0.01	*
1997		0.01	0.04	0.065	0.13	0.25	0.054	29	0.01	8
1996		0.01	0.06	0.084	0.18	0.42	0.085	31	0.01	10
1995		0.02	0.07	0.092	0.19	0.38	0.083	29	0.01	11
1994		0.01	0.07	0.105	0.19	0.39	0.100	30	0.01	12
1993		0.01	0.10	*	0.30	0.48	0.110	27	0.01	*
1992		0.03	0.11	0.130	0.23	0.36	0.081	31	0.01	15
1991		0.03	0.19	0.229	0.41	0.81	0.182	26	0.01	27
1990		0.04	0.15	*	0.38	0.39	0.105	27	0.01	*
1989		0.08	0.20	0.269	0.44	0.97	0.197	23	0.01	31

	Notes:	Values below the Limit of Detection (LoD) assumed to be ½ LoD. Means and risks shown only for years with data in all 12 months. "*" means there was insufficient or no data available to determine the value.