SHALLOW SALINE AQUIFER MONITORING AT NAVAL AIR STATION LEMOORE IN WESTERN SAN JOAQUIN VALLEY, CALIFORNIA

The Naval Air Station Lemoore (NASL) is located in the western central part of California’s San Joaquin Valley which has long been affected by soil and groundwater salinization due to drainage of irrigated agricultural fields. The drainage problem is caused by naturally saline soils and imported water, as well as the valley’s distinctive geological makeup which prevents effective natural drainage in certain areas.

A DoD supported field monitoring project was carried out to: (1) evaluate the existing monitoring system and update it with modern technologies; (2) develop recommendations for planting, soil amendments and groundwater management based on soil physics and chemistry studies; and (3) develop program recommendations based on scientific analyses and management needs. A total of 94 observation wells were monitored in 10 field surveys in 2010-12 water years, 28 new wells were installed from which core samples were taken for lab study.

The overall results show that the groundwater salinity was highly variable in space, with electric conductivity (EC) varying from 0.3 dS/m (fresh water) to 100 dS/m (similar to sea water or brine). But the seasonal variation was minimal. The average EC values varied in a narrow range between 7.8 and 9.5 dS/m (brackish water) over the entire 2010-2012 monitoring period. By the end of 2012, the saline groundwater area (EC = 4-12 dS/m) was wide spread and the groundwater table elevated to within 5-ft below surface which can cause soil salinization. The severely saline groundwater areas (EC > 12 dS/m) were invariably located deep beneath the paved areas where there is limited groundwater recharge. Lab studies were conducted to delineate the material composition, physics and chemistry of the aquifer based on 450 core samples obtained from 28 new wells. Three-dimensional solid models of the aquifer were developed using Rockware, which will be used in hydraulic simulations. Results of these studies will be reported separately in this meeting.