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March 2002 On-Post Quarterly Groundwater Monitoring Report
Section 4 - March 2002 Analytical Results
Groundwater sampling was performed March 11, 2002 through March 14, 2002. Twenty-seven on-post wells were sampled using dedicated low-flow pumps: CS-1, CS-2, CS-9, CS-10, CS-11, CS-16, CSD, CS-G, CS-H, CS-I, CS-MW1-LGR, CS-MW2-LGR, CS-MW3-LGR, CS-MW4-LGR, CS-MW5-LGR, CS-MW6-LGR, CS-MW6-BS, CS MW6-CC, CS-MW7-LGR, -CS-MW7-CC, CS-MW8-LGR, CS-MW8-CC, CS-MW9 LGR, CS-MW9-BS, CS-MW9-CC, CS-MW10-LGR, and CS-MW10-CC. Wells CS-G, CS-H, and CS-MW5-LGR were sampled with a bailer during this sampling event. Bladder pumps had not been installed in wells CS-H and CS-G as of March 2002. Well CS-MW5-LGR was sampled with a bailer due to malfunction of the dedicated low-flow pump.
The analytical program for on-post monitoring wells includes short list volatile organic compound (VOC) analysis and nine metals. Samples from the drinking water supply wells CS-1, CS-9, and CS-10, are analyzed for the full list of VOCs as well as nine metals. The metals analyzed include arsenic, cadmium, lead, barium, chromium, copper, nickel, zinc and mercury. All other on-post monitoring wells were analyzed for a reduced list of VOCs which was approved by Environmental Protection Agency (EPA) and the Texas Natural Resource Conservation Commission October 5, 1999. The reduced list included bromodichloromethane, chloroform, dibromochloromethane, 1,1-dichloroethene (DCE), cis-1,2-DCE, trans-1,2-DCE, methylene chloride, tetrachloroethene (PCE), trichloroethene (TCE), and vinyl chloride.
The Parsons data package ID numbers TO42 #1, #2, #3, and #4 contains the analytical results for this sampling event. The data packages were received by Parsons in April 2002 and subsequently validated and submitted to AFCEE in May 2002. AFCEE approval of the various packages is pending. All detected concentrations of metals and VOCs are presented in Table 4. Full analytical results for March 2002 are presented in Appendix B. Cumulative VOC and metals data from this round and all previous sampling events can be found in Tables 6 and 7, respectively, of the Introduction to the Quarterly Groundwater Monitoring Program (Parsons 2001) (Volume 5, Groundwater).
4.1 - Volatile Organic Compound Analyses
Maximum contaminant levels (MCLs) were exceeded in wells CS-16, CS-D, CS-MW1-LGR, and CS-MW2-LGR in the March 2002 event. The detected concentrations are summarized as follows:
| CS-16 - The PCE concentration was 28.0 micrograms per liter (�g/L), the TCE concentration was 26.0 �g/L, the cis-1,2-DCE concentration was 22.0 �g/L, and the trans-1,2-DCE concentration was 0.052 �g/L. PCE and TCE concentrations were above the MCL in CS-16. | |
| CS-D - The results for the compounds PCE, TCE, and cis-1,2-DCE in CS-D were 100.0 �g/L, 160.0 �g/L and 150.0 �g/L respectively. Well CS-D had a trans-1,2-DCE concentration of 1.5 �g/L and methylene chloride was detected at 4.9 �g/L in the March 2002 event. The PCE, TCE and cis-1,2-DCE levels exceeded MCLs | |
| CS-MW1-LGR - The concentrations of PCE, TCE, and cis-1,2-DCE in CS-MW1-LGR were 19.0 �g/L, 30.0 �g/L, and 26.0 �g/L, respectively. The PCE and TCE MCLs were exceeded in CS-MW1-LGR. | |
| CS-MW2-LGR - PCE and TCE concentrations were also above the MCLs in CS-MW2-LGR at 9.1 �g/L and 7.1 �g/L, respectively. A cis-1,2-DCE concentration of 4.0 �g/L was also detected as well as trans-1,2-DCE at 0.1 �g/L. |
The concentration trends over time for these four wells and these compounds are shown in Figure 4-1, Figure 4-2, and Figure 4-3. Trends over time in well CS-16 show variation in VOC concentrations. VOC levels noted during the March event are the lowest concentrations detected since 1994 and have been generally decreasing since 1998. Concentrations in well CS-D were generally increasing over time until the December 2001 event and declined at the March 2002 event. Wells CS-MW1-LGR and CS-MW2-LGR have been monitored for less time than wells CS-16 or CS-D, and both trend graphs show increases in concentrations the first part of 2001 and a slight decline in concentrations since September 2001 to March 2002. Screening data from Well CS-D (December 2001) are included on the figures to enable comparison of concentration trends over time.
CS-MW5-LGR had four VOC analytes detected. PCE was detected at a concentration of 1.1 �g/L, which is below the reporting limit (RL). TCE was detected at 1.9 �g/L and cis-1,2-DCE was detected at 2.1 �g/L. Methylene chloride was detected at a concentration of 0.22 �g/L and is considered a laboratory contaminant. Concentrations of PCE, TCE and cis-1,2-DCE have remained somewhat stable since CS-MW5-LGR was initially sampled in June 2001.
Well CS-MW8-LGR had VOC concentrations of PCE, TCE, and methylene chloride at concentrations of 0.85 �g/L, 0.057 �g/L, and 0.53 �g/L, respectively. All concentrations were above the method detection limit (MDL) and below the RL. Concentrations of PCE have remained stable, and below the RL, since the well was first sampled in June 2001. TCE was initially detected in June 2001 and not again until this March 2002 event.
Well CS-MW9-LGR had a sub-RL PCE concentration of 0.041 �g/L. This was the first detection of PCE since CS-MW9-LGR was first sampled in June 2001.
CS-MW10-LGR had three sub-RL VOC detections for TCE, methylene chloride, and chloroform at concentrations of 0.72 �g/L, 0.49 �g/L, and 0.12 �g/L, respectively. CS-MW10-LGR also had a detection of PCE above RL at a concentration of 2.1 �g/L. These results are consistent with concentrations detected since the well was initially sampled in December 2001.
The water supply wells, CS-1, CS-9, and CS-10, did not have any VOC concentrations detected above the RL. Off-post Well CS-1 had sub-RL PCE, TCE, toluene, and methylene chloride detections at 0.12 �g/L, 0.47 �g/L, 0.24 �g/L, and 0.49 �g/L, respectively. PCE was not detected in CS-9 and CS-10 during this monitoring event after being detected for the first time in these wells in March 2001. Wells CS-9 and CS-10 had one VOC analyte detected, methylene chloride at concentrations of 0.25 �g/L and 0.46 �g/L, respectively. Well CS-11 (a former drinking water well) had concentrations of PCE at 0.062 �g/L and chloroform at 0.15 �g/L, both above the MDL and below the RL.
Wells CS-2 and CS-MW4-LGR had no VOC analytes detected above either the MDL or RL. Wells CS-G, CS-H, CS-I, CS-MW3-LGR, CS-MW6-LGR, CS-MW6-BS, CS-MW6-CC, CS-MW7-LGR, CS-MW7-CC, CS-MW8-CC, CS-MW9-BS, CS-MW9-CC, and CS-MW10-CC reported sub-RL methylene chloride concentrations. Methylene chloride has been reported in samples from on- and off-post wells since 1992. However, each time methylene chloride has been detected in a sample, it has also been consistently present in the analysis method blank, indicating the likelihood that this analyte was introduced as a laboratory contaminant and is not present in the groundwater. Methylene chloride is considered a common laboratory contaminant and there are no known historical uses of methylene chloride on-post.
Of the nine metals regularly analyzed for at CSSA, lead, copper, and iron do not have an MCL established by the EPA. An action level (AL) for a treatment technique to control corrosiveness of water is defined by the EPA to be 1.3 milligrams per liter (mg/L) (1300 mg/L) for copper and 0.015 mg/L (15 mg/L ) for lead. An additional guidance set by the EPA for iron is a secondary standard for iron of 0.3 mg/L (300 mg/L).
One on-post agricultural/livestock well, CS-I, had a detection of a metal above the appropriate MCL, AL, or secondary standard in the March 2002 sampling event. Lead was detected above the AL (15 mg/L) at a concentration of 87.0 mg/L. Lead has been consistently detected in CS-I since June 2001 at concentrations of 34.9 �g/L, 19.3 �g/L, and 82.7 �g/L in June, September, and December 2001, respectively. No other CSSA wells exhibited metals levels that surpassed the MCLs/ALs during this monitoring event.