Evaluation of UDEQ Water Quality Data Following the Tibble Fork Reservoir Sediment Release
September 9, 2016
Mayor and City Council:
The city received a copy of an updated screening analysis by the Utah Division of Water Quality for discharge flows from the American Fork River. Three additional sites were tested. They include the ditch in Heritage Park, Highland Glenn Park Reservoir, and the Manila Reservoir in Pleasant Grove. None of these additional locations proved to exceed water screening limits for agriculture, recreation, or aquatic life limits. This is consistent with data previously received. The City of Cedar Hills is safe to use American Fork River water in the pressurized irrigation system. As always, irrigation water is not safe for human consumption, nor has it ever been.
The findings by the Utah Division of Water Quality and a link to the 24-page Evaluation are provided below.
David H. BunkerCity Manager/EngineerCity of Cedar Hills
Timeline of Tibble Fork Reservoir Sediment Release
On August 23, 2016, the Division of Water Quality was notified of an unplanned release of sediment from Tibble Fork Reservoir into the North Fork of the American Fork River. DWQ collected water chemistry and sediment samples on August 23 through August 30 to characterize the impact the release had on human health, the aquatic environment, and downstream water users. The National Park Service at Timpanogos National Monument collected data on August 22, 2016. These data sets have been evaluated in the context of human health, aquatic life, and agricultural uses of American Fork River. The data support the following main findings:
Dissolved and total metal concentrations in water quality samples collected on August 23 through August 28, 2016 below Tibble Fork Reservoir are 2 to 10 times higher than the concentrations of metals above Tibble Fork Reservoir.
Total metal concentrations collected below the reservoir on Monday August 22, 2016 are significantly higher than the samples collected by DWQ on Tuesday through Sunday, August 23-28, 2016. This suggest that the DWQ samples are not representative of the worst conditions in the river that occurred between August 20 and August 22, 2016.
Measurements of water clarity (turbidity and total suspsended solids) indicate clear violations of Utah’s narrative and numeric water quality standards.
Concentrations of dissolved metals in water quality samples collected above and below Tibble Fork Reservoir on August 22, 2016 do not violate Utah’s water quality standards for aquatic life or agricultural uses.
Concentrations of total metals in the water column collected on August 22 through August 28 below Tibble Fork Reservoir do not exceed human health screening values for recreational exposures.
Sediment metal concentrations collected below Tibble Fork Reservoir exceed human health screening values for lead and exceed aquatic life screening values for arsenic, cadmium, copper, lead, manganese, nickel, and zinc.
Sediment metal concentrations collected above Tibble Fork Reservoir on August 23, 2016 also exceed freshwater aquatic life screening values for arsenic, cadmium, lead, and zinc. The magnitude of these exceedances are not as pronounced as the data for samples collected below the reservoir.
At the request of local city governments, water samples were taken from Highland Glen Reservoir, Heritage Park, and Manila Reservoir on August 31, 2016. These recreation sites are downstream from the canyon and are all fed by irrigation water drawn from American Fork Creek. Analysis of total and dissolved metals in the samples confirmed the levels do not exceed the EPA screening standards for recreational use, agriculture, or aquatic life.
View the 24-page Evaluation of the Utah Division of Water Quality