January 23, 2018 – A large-scale effort to remove sediment from the Loma Rica Reservoir has reclaimed lost water storage of about 12,000 cubic yards of material. That means NID has regained water storage of about 2.4 million gallons (or 7.4 acre-feet) that can be used for community supplies.
Just east of Nevada County Air Park, the reservoir stores raw water delivered through the Cascade Canal and the 48-inch diameter Banner Cascade Pipeline from Deer Creek to the Loma Rica Water Treatment Plan. It also is a supply route for the Chicago Park Canal for raw-water customers, although it is not directly connected with any local creeks nor does it discharge to any natural water bodies or streams.
In addition, the Grass Valley Air Attack Base uses reservoir water to mix retardant dropped by tankers dispatched from the local airport to fight wildfires regionally and around the state. Last year NID contributed 1 million gallons of water to the air attack base free of charge as part of its community firefighting support. For comparison, it takes 660,430 gallons to fill an Olympic-sized swimming pool.
In previous years, NID has contributed the following amounts of water to the county’s Air Attack Base:
- 2016 – 714,000 gallons
- 2015 – 871,420 gallons
- 2014 – 878,900 gallons
When first constructed in the early 1960s, Loma Rica Reservoir had a capacity of 31.6 million gallons (96.9 acre-feet). Since then, silt and vegetation growth has significantly decreased that overall capacity.
NID Directors authorized a $200,000 contract with Lorang Brothers Construction of Colfax on Oct. 25, to clean out the reservoir with assistance from NID maintenance workers.
Heavy metals mercury and arsenic related to past gold mining activities plague much of the county’s waterways. Sediment often carries these hazardous waste metals through streams which are then deposited in lakes and reservoirs. Because the Loma Rica Reservoir receives water from man-made canals and upper country water sources, it was anticipated that these heavy metals would not be at levels indicating past mining activities.
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“It is anticipated that heavy metal concentrations associated with sediment that will be removed during this project will approximately the same as background soil levels typically found in non-mining associated soils in Nevada County,” noted the project’s negative declaration document from 2013.
That indeed was the case, based on soil testing of removed sediment in November. Samples were collected and analyzed by BSK Associates Laboratory for toxics, including arsenic and mercury. The firm conducted soil testing from 10 different sites. The tested samples indicated mercury was ND or “Non Detect.” This means that mercury was not detectable at the legally reportable limit of .50 mg/kg, which is the best possible result.
“Thus, we tested and no issues were present other than normal, clean dirt for the area,” said Gary King, NID’s engineering manager.
The Loma Rica cleaning effort is an example of how NID is committed to finding ways to optimize capacity of its existing infrastructure in order to ensure a resilient water supply for its customers now and into the future.