PFOS/PFOA Weekly Sample Results

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On July 30, 2018, the City’s Water Resources Department began weekly sampling for perfluorooctane sulfonic acid (PFOS) and related chemical perfluorooctanoic acid (PFOA) at both Lake Brandt and the entry point to the distribution system from Mitchell Water Treatment Plant.

Listed below are the weekly sample results. The US EPA health advisory level (HAL) for PFOA and PFOS (individually or combined) in drinking water is 70 parts per trillion (ng/l).

Lake Brandt Raw Water - Mitchell Water Treatment Plant Source
Date sample
taken
Date result
received
Substance monitored Result Unit
 07/30/19  08/08/19   Perfluoroctanesulfonic acid (PFOS)   30  ng/l
 07/30/19  08/08/19   Perfluorooctanoic acid (PFOA)   4.2  ng/l
 07/23/19  07/31/19  Perfluoroctanesulfonic acid (PFOS)   26  ng/l
 07/23/19  07/31/19  Perfluorooctanoic acid (PFOA)   4  ng/l
 07/16/19  07/26/19  Perfluoroctanesulfonic acid (PFOS)   28  ng/l
 07/16/19  07/26/19  Perfluorooctanoic acid (PFOA)   4.2  ng/l
 07/09/19  07/26/19  Perfluoroctanesulfonic acid (PFOS)   37  ng/l
 07/09/19  07/26/19  Perfluorooctanoic acid (PFOA)   4.8  ng/l
 06/25/19  07/02/19  Perfluoroctanesulfonic acid (PFOS)   23  ng/l
 06/25/19  07/02/19  Perfluorooctanoic acid (PFOA)   3.7  ng/l
 06/18/19  07/02/19  Perfluoroctanesulfonic acid (PFOS)   17  ng/l
 06/18/19  07/02/19  Perfluorooctanoic acid (PFOA)   3.3  ng/l
 06/04/19  06/25/19  Perfluoroctanesulfonic acid (PFOS)   34  ng/l
 06/04/19 06/25/19   Perfluorooctanoic acid (PFOA)   4.4  ng/l
 05/28/19  06/19/19  Perfluoroctanesulfonic acid (PFOS)   31  ng/l
 05/28/19  06/19/19  Perfluorooctanoic acid (PFOA)   4.3  ng/l
 05/21/19  05/30/19  Perfluoroctanesulfonic acid (PFOS)  32 ng/l 
 05/21/19  05/30/19  Perfluorooctanoic acid (PFOA)   4.3  ng/l
 05/14/19  05/24/19  Perfluoroctanesulfonic acid (PFOS)   28  ng/l
 05/14/19  05/24/19   Perfluorooctanoic acid (PFOA)   3.9  ng/l
 05/08/19  05/15/19  Perfluoroctanesulfonic acid (PFOS)   28  ng/l
 05/08/19  05/15/19  Perfluorooctanoic acid (PFOA)   4.1  ng/l
 04/30/19  05/08/19  Perfluoroctanesulfonic acid (PFOS)   25  ng/l
 04/30/19  05/08/19  Perfluorooctanoic acid (PFOA)   3.5  ng/l
 04/23/19  04/29/19  Perfluoroctanesulfonic acid (PFOS)   22  ng/l
 04/23/19  04/29/19  Perfluorooctanoic acid (PFOA)   3.3  ng/l
 04/16/19  04/24/19  Perfluoroctanesulfonic acid (PFOS)   24  ng/l
 04/16/19  04/24/19  Perfluorooctanoic acid (PFOA)   3.6  ng/l
 04/09/19  04/15/19 Perfluoroctanesulfonic acid (PFOS)    29  ng/l
 04/09/19  04/15/19  Perfluorooctanoic acid (PFOA)   3.7  ng/l
 04/02/19  04/10/19  Perfluoroctanesulfonic acid (PFOS)   25  ng/l
 04/02/19  04/10/19  Perfluorooctanoic acid (PFOA)   3.5  ng/l
 03/26/19  04/02/19  Perfluoroctanesulfonic acid (PFOS)   24  ng/l
 03/26/19  04/02/19  Perfluorooctanoic acid (PFOA)  3.2  ng/l
 03/19/19  04/01/19  Perfluoroctanesulfonic acid (PFOS)   15  ng/l
 03/19/19   04/01/19  Perfluorooctanoic acid (PFOA)  2.4  ng/l
 03/12/19  03/19/19 Perfluoroctanesulfonic acid (PFOS)   18  ng/l
 03/12/19  03/19/19  Perfluorooctanoic acid (PFOA)  2.7  ng/l
 03/05/19  03/14/19  Perfluoroctanesulfonic  acid (PFOS)   16  ng/l
 03/05/19  03/14/19   Perfluorooctanoic acid (PFOA)  2.7  ng/l
 02/26/19  03/12/19  Perfluoroctanesulfonic acid (PFOS)   15  ng/l
 02/26/19  03/12/19   Perfluorooctanoic acid (PFOA  2.8  ng/l
 02/19/19  02/26/19  Perfluoroctanesulfonic acid (PFOS)   19  ng/l
 02/19/19  02/26/19  Perfluorooctanoic acid (PFOA)  2.8  ng/l
 02/12/19  02/26/19 Perfluoroctanesulfonic acid (PFOS)   24  ng/l
 02/12/19  02/26/19  Perfluorooctanoic acid (PFOA)  3.3  ng/l
 02/05/19  02/26/19 Perfluoroctanesulfonic acid (PFOS)     24  ng/l
 02/05/19  02/26/19 Perfluorooctanoic acid (PFOA)  3.4  ng/l
 01/22/19 01/30/19  Perfluoroctanesulfonic acid (PFOS)     18  ng/l
 01/22/19  01/30/19 Perfluorooctanoic acid (PFOA)  3.0  ng/l
 01/15/19 01/22/19 Perfluoroctanesulfonic acid (PFOS)     23  ng/l
 01/15/19 01/22/19  Perfluorooctanoic acid (PFOA)  3.5  ng/l
 01/08/19 01/14/19  Perfluoroctanesulfonic acid (PFOS)    19  ng//l
 01/18/19 01/14/19  Perfluorooctanoic acid (PFOA)
3.1  ng/l
 01/02/19  01/11/2019 Perfluoroctanesulfonic acid (PFOS)    15  ng/l
 01/02/19  01/11/2019 Perfluorooctanoic acid (PFOA) 2.9  ng/l

Mitchell Water Treatment Plant Point of Entry
Date sample
taken
Date result
received
Substance monitored Result Unit
 07/09/19  08/08/19  Perfluorooctanesulfonic acid (PFOS)  28  ng/l
 07/09/19  08/08/19  Perfluorooctanoic acid (PFOA)  4.2  ng/l
 07/23/19  07/31/19  Perfluorooctanesulfonic acid (PFOS)  26  ng/l
 07/23/19  07/31/19  Perfluorooctanoic acid (PFOA)  4  ng/
 07/16/19  07/26/19  Perfluorooctanesulfonic acid (PFOS)  28  ng/l
 07/16/19  07/26/19   Perfluorooctanoic acid (PFOA)  4.2  ng/l
 07/09/19  07/26/19  Perfluorooctanesulfonic acid (PFOS)  22  ng/l
 07/09/19  07/26/19   Perfluorooctanoic acid (PFOA)  3.8  ng/l
 06/25/19  07/02/19  Perfluorooctanesulfonic acid (PFOS)  20  ng/l
 06/25/19  07/02/19   Perfluorooctanoic acid (PFOA)  3.6  ng/l
 06/18/19  07/02/19  Perfluorooctanesulfonic acid (PFOS)  22  ng/l
 06/18/19  07/02/19   Perfluorooctanoic acid (PFOA)  3.7  ng/l
 06/04/19  07/02/19  Perfluorooctanesulfonic acid (PFOS)  33  ng/l
 06/04/19  07/02/19  Perfluorooctanoic acid (PFOA)  4.8  ng/l
 05/28/19  06/19/19  Perfluorooctanesulfonic acid (PFOS)  30  ng/l
 05/28/19  06/19/19   Perfluorooctanoic acid (PFOA)  4.3  ng/l
 05/21/19  05/30/19   Perfluorooctanesulfonic acid (PFOS)  34  ng/l
 05/21/19  05/30/19  Perfluorooctanoic acid (PFOA)  4.3  ng/l
 05/14/19  05/24/19   Perfluorooctanesulfonic acid (PFOS)  27  ng/l
 05/14/19  05/24/19  Perfluorooctanoic acid (PFOA)  4.1  ng/l
 05/08/19  05/15/19  Perfluorooctanesulfonic acid (PFOS)  26  ng/l
 05/08/19  05/15/19  Perfluorooctanoic acid (PFOA)  3.9  ng/l
 04/30/19  05/08/19   Perfluorooctanesulfonic acid (PFOS)  23  ng/l
 04/30/19  05/08/19   Perfluorooctanoic acid (PFOA)  3.6  ng/l
 04/23/19  04/29/19  Perfluorooctanesulfonic acid (PFOS)  21  ng/l
 04/23/19  04/29/19   Perfluorooctanoic acid (PFOA)  3.3  ng/l
 04/16/19  04/24/19  Perfluorooctanesulfonic acid (PFOS)  30  ng/l
 04/16/19  04/24/19  Perfluorooctanoic acid (PFOA)  4.0  ng/l
 04/09/19  04/15/19  Perfluorooctanesulfonic acid (PFOS)  23 ng/l 
 04/09/19  04/15/19  Perfluorooctanoic acid (PFOA)   3.4  ng/l
 04/02/19  04/10/19  Perfluorooctanesulfonic acid (PFOS)  23  ng/l
 04/02/19  04/10/19  Perfluorooctanoic acid (PFOA)   3.4  ng/l
 03/26/19  04/02/19  Perfluorooctanesulfonic acid (PFOS)  11  ng/l
 03/26/19  04/02/19  Perfluorooctanoic acid (PFOA)   2.4  ng/l
 03/19/19  04/01/19  Perfluorooctanesulfonic acid (PFOS)  15 ng/l 
 03/19/19  04/01/19  Perfluorooctanoic acid (PFOA)   2.2  ng/l
 03/12/19  03/19/19  Perfluorooctanesulfonic acid (PFOS)  13  ng/l
 03/12/19  03/19/19  Perfluorooctanoic acid (PFOA)   2.3  ng/l
 03/05/19  03/14/19  Perfluorooctanesulfonic acid (PFOS)  11  ng/l
 03/05/19  03/14/19  Perfluorooctanoic acid (PFOA)   2.4  ng/l
 02/26/19  03/12/19  Perfluorooctanesulfonic acid (PFOS)  21  ng/l 
 02/26/19  03/12/19  Perfluorooctanoic acid (PFOA)   3.1  ng/l
 02/19/19  02/26/19  Perfluorooctanesulfonic acid (PFOS)  25  ng/l
 02/19/19  02/26/19  Perfluorooctanoic acid (PFOA)   3.4  ng/l
 02/12/19  02/26/19  Perfluorooctanesulfonic acid (PFOS)  22   ng/l
 02/12/19  02/26/19  Perfluorooctanoic acid (PFOA)   3.2  ng/l
 02/05/19  02/26/19  Perfluorooctanesulfonic acid (PFOS)  23  ng/l
 02/05/19  02/26/19  Perfluorooctanoic acid (PFOA)   3.5  ng/l
 01/22/19  01/30/19 Perfluorooctanesulfonic acid (PFOS)  19  ng/l
 01/22/19  01/30/19 Perfluorooctanoic acid (PFOA)   3.1  ng/l
01/15/19 01/22/19  Perfluorooctanesulfonic acid (PFOS)   17  ng/l
01/15/19 01/22/19  Perfluorooctanoic acid (PFOA)    3.0 ng/l 
01/08/19  01/14/19 Perfluorooctanesulfonic acid (PFOS)  13 ng/l
01/18/19  01/14/19 Perfluorooctanoic acid (PFOA)    2.7 ng/l
 01/02/19  01/11/19 Perfluorooctanesulfonic acid (PFOS)  12 ng/l
 01/02/19  01/11/19 Perfluorooctanoic acid (PFOA)   2.7 ng/l

2018 Weekly Testing Results


Additional Information

Water Resources continues to take proactive measures to minimize the potential impact the higher results has on the city's water system. Recently completed measures include:

  • Flushing raw water lines from Lake Brandt to the Mitchell to accelerate system turnover
  • Draining more than one million gallons of water from Mitchell's drinking water storage tank prior to beginning intermittent pumping operations
  • Minimizing the amount of water pumped from Mitchell by continuing to rely on other sources of drinking water in accordance with operational protocol
  • Relying on beneficial mixing (with other drinking water sources) within the distribution system to minimize the area potentially impacted by water above the HAL.

Summary

The August 7, 2018 Lake Brandt Raw Water sample results are encouraging in that the PFOS/PFOA levels within the lake are below the HAL. These results confirm the water is now being pumped to and treated at Mitchell is lower than the HAL.

The order for a temporary powdered activated carbon (PAC) feed system is complete and the system should arrive by the end of August. Once the unit is set up and the state Division of Water Quality approval (to operate) is received, Water Resources will begin installation and testing to ensure proper and effective setup, which is needed before the equipment is fully operational.

The August 14, 2018 samples were pulled to confirm alignment of drinking water levels with raw water levels below the HAL.

Perfluoroctanesulfonic acid (PFOS)   
Perfluoroctanesulfonic acid (PFOS)   
 Perfluorooctanoic acid (PFOA)