Development of a Groundwater Flow Model for Hungry Valley, Washoe County, Nevada

The Reno-Sparks Indian Colony (RSIC) has reservation land located on 1,960 acres in Hungry Valley, Washoe County, Nevada; located approximately 10 miles north of Reno. Future growth of the community is dependent on sustainable groundwater development. Previous hydrogeologic assessments and pumping tests have consistently concluded that the aquifers are of limited extent. The aquifers are characterized by low transmissivities with storativity values indicating the aquifers to be confined. Groundwater pumping began in 1991 and a decline in static water levels began to occur. With an alternate pumping strategy implemented in 2004 and additional production wells implemented in 2005 static water levels have improved and most appear to have stabilized with measurements taken through March 2010. There are currently four production wells: Well Nos. 4, 5, 7 and 8. The objective of this groundwater flow model is to develop optimization strategies to maintain the static water levels as high as possible, minimize the cost of groundwater pumping, and keep arsenic levels below drinking water standards (through blending of pumped groundwater), while meeting the supply needs of the RSIC. The modeling protocol according to Anderson and Woessner (2002) was generally followed to develop the model; and the construction of the model was accomplished through the GMS User Interface for MODFLOW. Optimization was performed using a trial and error approach. The model results indicate that a pumping scenario of 70% for Well Nos. 7 and 8 and 30% for Well Nos. 4 and 5 appears to balance drawdowns in the two aquifers. Additionally, it appears that the pumping average from 2000 through 2009 (excluding 2005) of 193 cubic meters/day (57 acre-feet per year) can be supported by the current well field. Future water demand, estimated to be 243 cubic meters/day (72 acre-feet per year), can also supported by the current well field with additional decreases in static water levels. This decrease in static water levels is modeled to be greatest at Well Nos. 4 and 5 at 3.7 meters and can be minimized by utilizing Well No. 3 as a production well and/or considering an additional production well.