[Home] [Master Table of Contents]
[Groundwater Report Index] [Next Section]
March 2000 On-Post Quarterly Groundwater Monitoring Report
Section 4 - Analytical Results
All groundwater samples collected as part of the RL74 monitoring program were analyzed for 1,1-dichloroethene (1,1-DCE), bromodichloromethane, chloroform, cis-1,2-dichloroethene (cis-1,2-DCE), dibromochloromethane, methylene chloride, trans-1,2-dichloroethene (trans-1,2-DCE), tetrachloroethene (PCE), trichloroethene (TCE), and vinyl chloride using USEPA Method SW8260.� This list of analytes was agreed upon by the USEPA at the February 3, 2000 TIMs, and by the TNRCC in a letter dated October 5, 1999.� The analytical results for VOC concentrations in groundwater samples are summarized in Table 4.� VOC trends over time for Well 16 are depicted graphically in Figure 9.
All groundwater samples collected as part of the RL74 monitoring program were also analyzed for arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, and zinc.� Metal analytical results are summarized in Table 5.
Well 16 was resampled for VOCs on April 27, 2000 due to the laboratory�s failure to analyze an undiluted sample.� The sample collected on March 22, 2000 was only analyzed at a 5-times dilution.� The sample collected on April 27, 2000 was analyzed both in its original undiluted form and at a 5-times dilution.� Only the April 27 results are reported here.
CSSA sampled Well LS-7 during March 2000; the samples were split with the USEPA.� The CSSA samples were shipped to O�Brien and Gere for analysis, while the USEPA samples were shipped to USEPA�s contract laboratory in Houston, Texas.� The CSSA samples analyzed by O�Brien and Gere were validated in accordance with the CSSA QAP.� The results for the CSSA samples have been incorporated into the summary table.
4.1�- Volatile Organic Compound Analyses
A total of nine wells were sampled in March 2000:� 1, 2, 9, 10, 11, 16, I, MW1, and MW2.� Well D was not sampled during this event because the water level was below the pump setting.� This monitoring event also did not include Well G because the down-hole pump was not operational in March 2000.� In addition, none of the offsite wells were sampled for this monitoring event.� Concentrations of TCE, PCE, and cis-1,2-DCE that exceeded maximum contaminant levels (MCLs) were detected in Well 16.� The results for Well 16 showed that cis-1,2-DCE, PCE, and TCE concentrations decreased somewhat as compared to the December 1999 sampling event and that the concentration of trans-1,2-DCE fell below detection limits for the first time since February 1996.� Well MW2 was found to have PCE and TCE concentrations that exceeded MCLs and a cis-1,2-DCE concentration that was below the MCL.� MW1 had concentrations of all three of these compounds that were below MCLs.� The latest data support the assumption that it is possible that MW1 and MW2 are located on the outskirts of the same plume encompassing Well 16.� In addition, levels of trans-1,2-DCE that were below the reporting limit (RL) but above the method detection limit (MDL) exist in Wells MW1 and MW2.� Concentrations of chloroform, TCE, and PCE that were below the RL were found in Well 1.� Well 10 had a sub-RL chloroform level while Well 11 had a concentration of this compound that was above the RL but well below the MCL.
A lead concentration of 0.0172 mg/l detected in Well 1 was the only metals level exceeding the MCL.� The MCL for lead is 0.015 mg/L.� A lead concentration of 0.0108 mg/l occurred in Well 11.