SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

KLE/NFELOER yn e.oe:.nynesomro�. • e.; 1) Five of eleven groundwater monitoring events conducted to date by Kleinfelder revealed nitrate-nitrogen, in the monitoring well upslope (upgradient) of the nursery, above the MCL. The concentrations of the nitrate-nitrogen in this upgradient well (MW-2) are below the concentration in the downgradient wells (MW-5 and MW-8). The concentrations are decreasing in MW-2 in a similar pattern to last year at the same time. The changes in concentration may correlate with the last half of the rainy season (see Chart 1). It is unknown what the source of the perched water and nitrate-nitrogen is, that existed upslope of the nursery. Natural recharge, springs, vernal pools and the cattle grazing may be the explanations. 2) In October 1999, three groundwater monitoring wells were installed by Kleinfelder within the Barbagelata orchard south of Potter Creek. The wells were installed to monitor shallow perched groundwater conditions in the area. Since that time the monitoring wells have been developed, surveyed, purged, sampled and monitored. Reports documenting those findings are in the process. Additionally, attempts were made to install a shallow groundwater monitoring well north of Potter Creek, which yielded no shallow perched groundwater to a depth of approximately 18'/ feet below grade. Groundwater gradient in the shallow perched aquifer in October 25, 1999, December 27, 1999, March 23, 2000, and April 27, 2000 ranged from 0.002 to 0.004 feettfoot to the south southwest, south, northwest and south-southwest, respectively. Perched groundwater flow in the area of the Potter Creek bridge has not been noted to flow towards the north, towards the Eason and Dodge properties. Rather, the shallow perched groundwater flow appears to be away from Potter Creek and is confirmed by the lack of perched groundwater to a depth of 18-1/2 feet in the Barbagelata's orchard north of Potter Creek. However, in areas of flat groundwater gradients such as this site, • groundwater flow directions may significantly fluctuate due to rainfall, groundwater recharge, groundwater pumping, etc. Therefore, changes in groundwater flow directions may vary at this site with time. 3) There may be multiple sources of nitrate in the shallow perched groundwater. These include Potter Creek, an area near MW-8 within the Barbagelata's orchard and an area near the northwest corner of the nursery. Additionally, the above-noted data together with elevated concentrations in the perched groundwater to the east of the nursery (MW-2) suggests a regional problem in the shallow perched aquifer which varies seasonally and is affected by many agricultural operations in the area. This theory is further supported by the elevated concentrations of nitrate in the soil samples obtained in the Barbagelata orchard. 4) In late November 1999, three deep groundwater monitoring wells were installed within the nursery property. The purpose of the wells was to evaluate groundwater quality of the first aquifer beneath the site at a depth of approx. 150 feet below grade. The reason for evaluating the deeper groundwater was to evaluate the potential for the nursery to be impacting the drinking water wells on the nearby Dodge and Eason properties north of the nursery. Since that time the monitoring wells have been developed, surveyed, purged, sampled and monitored. Reports documenting those findings are in the process. In general, groundwater flow on both December 28, 1999 and March 21, 2000 was calculated to be 0.003 feettfoot to the southwest. This flow direction matches the San Joaquin County Flood Control and Water Conservation District data detailed in Section 2.4.4. No obvious impact of the nursery's operations on deep groundwater quality was noted. The report for this installation and monitoring is forthcoming. • 117226.E02/ST012R0696 Page 14 of 43 September 14, 2012 Copyright 2012 Kleinfelder