The twenty-mile Union Pacific Railroad (UPRR) causeway across the Great Salt Lake separates the lake into a North Arm and South Arm of different salinities. Between 2011 and 2013, UPRR applied for and received a federal Clean Water Act Section 404 permit from the U. S. Army Corps of Engineer (USACE) to close two culverts in the rock-fill causeway that were at risk of imminent collapse. Several agencies, including the Division of Water Quality (DWQ), and GSL stakeholders expressed concerns about potential changes to the lake’s ecological resources and uses from culvert closure. In response, UPRR proposed construction of a 180-foot bridge intended to replicate the water and salt transfer previously accomplished by the free-flowing exchange of the lake water through the culverts. After completing water and salt balance modeling for the lake, UPRR determined that a 150-foot bridge would better duplicate the water-salt exchange accomplished by the culverts.
Culvert closure and bridge construction required a 404 permit from USACE and a corresponding state 401 Water Quality Certification (2.6 MB) with conditions from DWQ. The 401 Water Quality Certification included conditions to ensure protection of GSL water quality. These include requirements for monitoring causeway opening morphology, flow volume through the causeway, and salinity in the lake. Conditions also include performance measures for causeway opening morphology and salinity values in the lake to ensure that the new opening matches the water and salt exchange of the previous causeway culverts.
Direct connectivity between Gilbert (south arm) and Gunnison Bays (north arm) via the new causeway bridge was restored in December 2016. Monitoring and evaluation of the bridge opening and water quality impacts commenced following the opening of the causeway bridge.
Permit performance standards
The intent of the causeway bridge and opening is to compensate for the impacts to GSL from the emergency closure of the previously active causeway culverts. Therefore, the performance standards target the duplication of conditions prior to culvert closure. The performance standards associated with the 401 Water Quality Certification and 404 Permit are laid out in a compensatory mitigation and monitoring plan (CMMP) (9.3 MB). The CMMP specifies conditions for both salinity in Gilbert Bay of GSL and the geometry of the causeway bridge and opening.
As required in the 401 Water Quality Certification of this project, “UPRR will conduct the required monitoring until the results demonstrate that the Salinity Performance Standard Ranges are being met and trends indicate they will continue to be met into the future. The UPRR may request cessation of monitoring and adaptive management by submitting a Completion Report that includes no less than 5 years of monitoring results after the most recent causeway modification affecting water and salt transfer,” and, “6. Determination of compliance with the Causeway Opening Geometry Performance Standards will be made semi-annually for the first two years after bridge completion and then annually until cessation of monitoring is granted,” by DWQ.
Annual monitoring reports
- 2019 Monitoring Results (3 MB)
- 2018 Monitoring Results (3.7 MB)
- 2017 Monitoring Results (3.5 MB)
- 2016 Monitoring Results (2 MB)
- 2015 Monitoring Results (1.8 MB)
- 2014 Monitoring Results (4 MB)