SITE INFORMATION AND CORRESPONDENCE_CASE 2

Home Browse Search

INFORMATION SHEET 5 ORDER NO R5-2007- CITY OF TRACY AND LEPRINO FOODS COMPANY LAND DISCHARGE UNITS OF THE TRACY WASTEWATER TREATMENT PLANT SAN JOAQUIN COUNTY In 1991, Regional Water Board staff ordered the Discharger to conduct additional quarterly groundwater monitoring. This monitoring included the collection of samples from the ponds and monitoring wells, with analyses performed for TDS, pH, EC, and chlorides. The monitoring began in March 1992 and included six quarterly sets of data collected by the Discharger. The monitoring data appeared to confirm the holding ponds were not negatively affecting the water quality of the shallow groundwater. However, some data was contradictory. Continued concerns about potential degradation of groundwater remained and Regional Water Board staff ordered installation of a new background monitoring well, further upgradient from the ponds, due to concerns that the background monitoring well, MW-1, was not outside the influence of the ponds. The Discharger was also ordered to conduct additional groundwater monitoring, and surface water monitoring in Sugar Cut Slough, which is adjacent to the ponds. The City installed a new background well, MW-5, further upgradient from the holding ponds. Water quality sampling of the holding ponds, monitoring wells, Sugar Cut Slough, and an agricultural drainage ditch upstream of Sugar Cut Slough was conducted in September and November 1994 and March 1995. The samples were analyzed for TDS, EC, chlorides, and pH. The samples collected in November were also analyzed for major cations and anions. The data was analyzed and summarized in a 1995 report submitted by the Discharger. The 1995 Report concluded the unlined ponds percolated to the shallow groundwater, and that the shallow groundwater in the vicinity of the ponds was in hydraulic continuity with Sugar Cut Slough. Even though downgradient well samples showed higher salinity concentrations than background well samples, the 1995 Report concluded there was not adequate evidence that the ponds were causing the increases, because the underlying groundwater had higher concentrations than the ponds. The 1995 Report further concluded the ponds were not adversely affecting surface water in Sugar Cut Slough. The monitoring and reporting program contained in Order No. 96-104 required quarterly monitoring of the holding ponds and groundwater for TDS and EC. Based on monitoring from October 1999 through May 2004, it is evident the EC of the ponds has increased from the levels measured in 1994 and 1995, which were used to evaluate groundwater degradation caused by the ponds. Prior to 1997, Heinz Foods, Inc. discharged approximately 1.6 to 2.0 mgd of tomato wastewater to the ponds during the summer months. Since Heinz ceased its discharge to the Facility, the average EC concentrations of the ponds have increased. This may be due to lower flows through the ponds. Leprino discharges on average about 0.6 mgd. Lower flows result in longer detention times and increased evaporation may be causing the increase in EC in the ponds. This is corroborated by pond monitoring data from 2001 — 2004, which show increases in EC from March-October each year. Downgradient groundwater sampling shows that groundwater quality fluctuates with EC peaking in