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Final June 2002 On-Post Quarterly Groundwater Monitoring Report
Section 4 - June 2002 Analytical Results
Groundwater sampling was performed June 17-24, 2002. Twenty-three on-post wells were sampled using dedicated low-flow pumps: CS-1, CS-2, CS-9, CS-10, CS-11, CS-16, CS-D, CS-G, CS-H, 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 and CS-H were sampled with a bailer during this sampling event. Bladder pumps were not installed in wells CS-H and CS-G as of June 2002. Wells CS-MW1-LGR, CS-MW2-LGR, and CS-MW3-LGR were not sampled due to malfunction of the dedicated low-flow pump. A sample was not collected from Well CS-I due to improper function of the windmill.
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 were approved by EPA and the Texas Commission on Environmental Quality, (TCEQ) the regulatory agency formerly known as the Texas Natural Resource Conservation Commission on October 5, 1999. The reduced list includes 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 #5, #6, #7, #8 and #9 contains the analytical results for this sampling event. The data packages were received by Parsons in July 2002 and subsequently validated and submitted to AFCEE in August 2002. AFCEE approval of the various packages is pending. All detected concentrations of metals and VOCs are presented in Table 4-1. Full analytical results for June 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 2002) (Volume 5, Groundwater).
4.1 - Volatile Organic Compound Analyses
Maximum contaminant levels (MCLs) were exceeded in wells CS-16 and CS-D in the June 2002 event. The detected concentrations are summarized as follows:
| CS-16 - The PCE concentration was 95.0 micrograms per liter (�g/L), the TCE concentration was 100.0 �g/L, the cis-1,2-DCE concentration was 100.0 �g/L, the trans-1,2-DCE concentration was 3.9 �g/L, and the chloroform concentration was 0.096 �g/L. PCE, TCE, and cis-1,2-DCE concentrations were above the MCL in CS-16. |
The concentration trends over time for these four wells and these COCs 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 June event increased significantly since March 2002 but are below concentrations detected in 1998. Concentrations in well CS-D were generally increasing over time with the exception of the March 2002 event where concentrations declined. 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 from 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 1.3 �g/L, which is below the reporting limit (RL). TCE was detected at 1.5 �g/L and cis-1,2-DCE was detected at 1.6 �g/L. Trans-1,2-DCE was detected at a concentration of 0.041 �g/L, above the MDL but below the RL 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 a VOC concentration of PCE at 0.057 �g/L. This concentration was 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 the March 2002 event.
CS-MW7-CC had two VOC detections of 1,1-DCE at a concentration of 0.33 �g/L and methylene chloride at a concentration of 1.8 �g/L. The only other VOC detection in this well since it was first sampled in September 2001 was methylene chloride in December 2001 and March 2002. Methylene chloride is a common laboratory contaminant.
CS-MW10-LGR had two sub-RL VOC detections for TCE and chloroform at concentrations of 0.6 �g/L and 0.12 �g/L, respectively. CS-MW10-LGR also had a detection of PCE above RL at a concentration of 2.5 �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, had one VOC concentration detected above the RL. CS-1 had a detection of chloromethane at a concentration of 2.8 �g/L. All other VOC detections in well CS-1 were below the RL for PCE, TCE, and chloroform at concentrations of 0.11 �g/L, 0.63 �g/L, and 0.076 �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. Well CS-10 had two VOC analytes detected, chloroform at concentrations of 0.053 �g/L and 1,1-DCE at a concentration at 0.03 �g/L, respectively. Well CS-9 had no VOC detections in this sampling event. Well CS-11 (a former drinking water well) had a concentration of chloroform at 0.13 �g/L, which was above the MDL and below the RL.
Well CS-2 had a PCE detection of 0.52 �g/L. This concentration was above the MDL and below the RL. It has been periodically detected above the MDL and below the RL since November 1992. CS-2 had no other VOC detections.
Well CS-MW4-LGR has one VOC detection above the MDL and below the RL. Cis-1,2-DCE was detected at a concentration of 0.11 �g/L. This well was sampled for the first time in June 2001. The first reported detection of cis-1,2-DCE was also above the MDL and below the RL in December 2001.
Wells CS-G, CS-MW8-CC, CS-MW9-LGR, CS-MW9-BS, CS-MW9-CC, and CS-MW10-CC had no VOC analytes detected above either the MDL or RL. Wells CS-H, CS-MW6-LGR, CS-MW6-BS, CS-MW6-CC, and CS-MW7-LGR 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 and copper do not have an MCL established by the U.S. Environmental Protection Agency (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.
One on-post agricultural/livestock well, CS-11, had a detection of a metal above the appropriate MCL, AL, or secondary standard in the June 2002 sampling event. Lead was detected above the AL (15 mg/L) at a concentration of 15.4 mg/L. Lead has been consistently detected in CS-11 since March 2000 at concentrations of 7.2 �g/L, 6.3 �g/L, and 14.5 �g/L in March 2001, December 2001 and March 2002, respectively. No other CSSA wells exhibited metals levels that surpassed the MCLs/ALs during this monitoring event.