Loma Rica Reservoir Cleaning Project

The Loma Rica Reservoir is located directly east of the City of Grass Valley, Nevada County, California, at an elevation of 3,154 feet above mean sea level (msl).  The reservoir is located on property owned by the Nevada Irrigation District (NID) and it is approximately 1,500 feet east of the Nevada County operated airport and public use runway.  The reservoir is part of the NID water-supply system and it stores raw water delivered through the Cascade Canal and the Banner Cascade Pipeline. The reservoir had a maximum capacity of 96.9 acre-feet (31.6 million gallons) when it was first constructed in the early 1960’s.  Since then silt and sediment deposited in the reservoir with the incoming water sources have significantly decreased its capacity. This decrease adversely effects capacity of NID’s drinking and irrigation water systems.

Water from the Loma Rica Reservoir supplies the Loma Rica Water Treatment Plant and the Chicago Park Canal, an NID supply route for raw-water customers. The reservoir is not directly connected with any local creeks nor does it discharge to any natural water bodies or streams.

The Project entails a multi-year process of removing accumulated sediment from the Reservoir. The Loma Rica Reservoir Cleaning Project began with the dredging of the Reservoir in the fall of 2017.  A second dredging period occurred in 2018. Approximately 40,000 cubic yards of sediment was removed during the last two years.

The removal of the sediment is accomplished by first draining the reservoir followed by approximately one month of drying. The sediment is then excavated using front-end loaders and excavators.  The excavated sediment is then placed on adjacent previously disturbed land in order to drain the sediment of remaining water and to allow for drying or transported off site to be recycled as fill material, if determined to be suitable for that purpose. The sediment removed in 2017 and 2018 was deposited on the Nevada County airport property that filled in a depression north of the runway.

The Reservoir cleaning generally occurs between September and January.  This time frame minimizes environmental impacts and takes advantage of lower water demands for the NID such that the reservoir inactivity will not significantly affect NID’s operation. The District anticipates that 2019 will be the last cleaning period for this project, with an estimated 15,000 to 30,000 remaining cubic yards of sediment to remove.

The identified potentially significant impacts of the project are less than significant with the incorporation of mitigation measures into the project.  The potentially significant project impacts and associated mitigation measures are included in the project’s Initial Study/Limited Negative Declaration dated April 5, 2013 and posted on this website page under “Project Documents”.

The adoption of this project occurred at the NID public Board Meeting on May 22, 2013.