WATER QUALITY ASSESSMENT ALONG GALLINAS CREEK SURFACE WATER AND GROUNDWATER PATHWAYS, LAS VEGAS, NEW MEXICO

We report preliminary results of a pilot study that compared the chemistry of surface water and ground water within the Gallinas Watershed. Gallinas Creek originates in the southern Sangre de Cristo Mountains and flows southeast towards the high plains desert community of Las Vegas, New Mexico. A large percentage of flow is diverted to the Storrie Lake Water Project and divided among multiple users, including the city of Las Vegas, Las Vegas National Wildlife Refuge, and farmers and ranchers. We studied changes in water quality within different regions of the diverted water system. Samples were collected at four primary locations: the surface water source (Upper Gallinas River), diverted surface water (McCallister Lake), ground water seeps (springs along Gallinas Canyon) and ground water receptor (Lower Gallinas River). This study hypothesized that as water infiltrates through the subsurface, the area’s highly alkaline soils and the shallow bedrock aquifer contribute dissolved constituents to ground water. To test this hypothesis, surface water and ground water samples from Gallinas Creek sources were collected and analyzed for various water parameters. Our results indicate that Ca, Mg, Na, Si, Cl, SO4, and CaCO3 concentrations are 1.6 to 7.2 times higher in ground water. Likewise, hardness, alkalinity, conductivity, and total dissolved solids are also appreciably higher (increased by factor of 1.4 to 2.0). These results suggest that soils and bedrock are leaching dissolved constituents to ground water. McCallister Lake exhibits elevated Ca (402 mg/L), Na (1165 mg/L), Cl (678 mg/L), SO4 (3525 mg/L), and electrical conductivity (11,200 micromohs/cm) concentrations that suggest high evaporation is enriching dissolved salt concentrations. Continued drought conditions will enhance evaporation rates and lead to increasing accumulation of dissolved salts and minerals potentially threatening the vitality of the lake ecosystem.