FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

I. Additionally, the soil samples collected from the monitoring well soil borings showed higher concentrations of TKN, nitrate as NO3, ammonia as N, and phosphate in MW-2 versus the concentrations noted in MW-1 and MW-3. All of the concentrations noted in each of the monitoring well soil samples decrease with depth. Only sulfate increased with depth in MW-2 from 10 mg/kg (1-foot) to 30 mg/kg (10-foot). There are no regulatory PRGs for TKN, nitrate as NO3, ammonia as N, phosphate or sulfate. As noted from the results of the shallow soil samples collected and analyzed from across the site; the areas near the tank washout sump and rinseate collection tank, and the former fuel AST area appear to display the highest relative concentrations of residual pesticides and/or Carbarnates and the fertilizer constituents TKN and nitrate as NO3 compared to the other portions of the site examined. The pesticides and Carbamates concentrations were below the respective PRGs for each reported constituent and the fertilizer constituents concentrations diminish with depth. A total of four groundwater samples were collected from the site. Three samples were collected from the three monitoring wells installed and one was collected from the domestic water supply well on site. There were no detected concentrations of metals above the Water Quality Goals (WQGs) as referenced to applicable Primary or Secondary Maximum Contaminant Levels (MCLs), Suggested No Adverse Response Levels (SNARLs), California State Action Levels, or Agricultural Water Quality Limits. There were however, detected concentrations of nitrate as NO3, and Total Dissolved Solids (TDS) above the applicable MCLs. Ammonia as N was detected above the WQG for ammonia as N (30 mg/1 SNARL) in the sample collected from MW-2 (56 mg/1). Nitrate as NO3 was detected in each sample and exceeded the PMCL (45 mg/1) in MW-1 (86 mg/1), MW-2 (131.6 mg/1), and the domestic well sample (47.2 mg/1). The TDS concentrations ranged from 400 mg/1 (MW-3) to 1,120 mg/1 (MW-2). The TDS concentrations in three of the four water samples exceeded the SMCL (500 mg/1) for TDS. Only 1,2-Dibromoethane (EDB) was detected in MW-2 with a concentration of 0.00004 mg/l. The PMCL for EDB is 0.00005 mg/1 and was not exceeded. No other pesticides, carbamates, or organophosphates were detected in any of the water samples collected for analyses at or above the applicable laboratory reporting limits. The groundwater results showed higher concentrations of TKN, nitrate as NO3, ammonia as N, sulfate, and phosphate in MW-2 versus the other water sample locations tested. MW-2 is located approximately 100 feet north and generally cross-gradient of the tank washout sump and rinseate collection tank. At this time it is not certain if the groundwater quality encountered in MW-2 is a result of the operations that had taken place in the tank washout and rinseate collection sump area or if it is a result of past regional agricultural activities. With the current calculated groundwater flow direction, MW-2 is located downgradient of one identified former vehicle parking areas identified on the site. It should be noted that nitrate as NO3 was also detected in MW-1 (upgradient well) with a concentration of 86 mg/1 and in the domestic well (47.2 mg/1), suggesting an offsite source. The downgradient concentration of nitrate as NO3 as seen in MW-3 was 10.9 mg/l. It is apparent that the shallow water quality entering the site at MW-1 exhibits elevated concentrations of nitrate as NO3, while the groundwater quality exiting on site at MW-3 shows improved quality, suggesting a denitrifying condition. I. 27125.E01 / STO4R181 Page 2 of 23 © 2004 Kleinfelder, Inc. February 13, 2004 KLEINFELDER 2825 East Myrtle Street, Stockton, CA 95205-4794 (209) 948-1345 (209) 948-0621 fax