Harihar Nepal

Nepal H., C. Monohan, J. Fleck and D. Brown. Sediment and Mercury Loads and Sources at Humbug Creek from Malakoff Diggins. California State University, Chico. Summer 2013.


Mine tailings and mercury-enriched sediment from legacy mines continue to be sources of inorganic Hg to the environment in the Sierra Nevada Mountains after the California Gold Rush. The outflow from Malakoff Diggins, once one of the largest hydraulic mines in California during the Gold Rush, continues to be a source of Hg and sediment to Humbug Creek. The purpose of this study was to estimate the load of particulate bound Hg and suspended sediment in Humbug Creek for Water Year 2012 and to identify the sources of Hg and sediment in Malakoff Diggins.

Grab samples were analyzed for total Hg, dissolved Hg and total suspended sediment (TSS) and instantaneous discharge (Q) was measured at the time of sample collection. The annual load of suspended sediment and particulate bound Hg in Humbug Creek were calculated using relationships established from continuous monitoring of turbidity and total suspended sediment (n = 23, y = 0.69x, R2 = 0.75) and particulate bound Hg (n = 16, y = 0.1412x, R2 = 0.84) from grab samples taken during multiple storm events.

For Water Year 2012, the load of particulate bound Hg was calculated to be approximately 350 grams per year and TSS to be approximately 1,800,000 kg per year in Humbug Creek. Approximately 50% of the annual sediment load for 2012 in Humbug Creek was from Hiller Tunnel, which drains Malakoff Diggins, and about 70% of the annual particulate bound Hg load for 2012 was from three storm events and nearly 50% was from a single storm event in March 2012.

Sources of suspended sediment and particulate bound Hg in Malakoff Diggins were identified by sampling 19 locations in the pit within a four-hour period during a single large rain event in December 2012. The load of particulate bound Hg did not vary in the same pattern as sediment load in the pit. The highest load of particulate bound Hg came from the east end of the pit (3,600 ng/s) whereas; the highest load of suspended sediment came from the north side of the pit (24,000 mg/s from SS12).

Student Bio

Harihar graduated from CSU Chico 2013 with B.S. in Environmental Science with a chemistry option and in 2014 with an M.S. in Environmental Science. While in graduate school, he worked under Dr. Carrie Monohan, and studied sediment load and inorganic mercury load in Humbug Creek. In the same project, he also worked to identify sources of sediment and mercury in the Malakoff Diggins abandoned mine site. In 2014, Harihar joined USGS Nevada Water Science Center (USGSNWSC), focused on flow (direct, indirect, ADCP computation), survey datum, and water quality (ground water and surface water) of the region (from Lake Tahoe to Pyramid Lake). Harihar currently teaches organic chemistry (CHEM220) and general environmental science(ENV100) in Truckee Meadow community college (TMCC) Reno since 2015.