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Final September 2002 On-Post Quarterly Groundwater Monitoring Report
Section 4 - September 2002 Analytical Results
Groundwater sampling was performed September 9-13, 2002. Twenty-eight on-post wells were sampled using dedicated low-flow pumps: CS-1, CS-2, CS-9, CS-10, CS-11, CS-D, CS-G-LGR, 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, CS-MW10-CC, CS-MW16-LGR, CS-MW17-LGR, CS-MW18-LGR, and CS-MW19-LGR. A bladder pump was not installed in well CS-H-LGR as of September 2002 and well CS-H was not sampled due to blockage within the well casing. A sample was also not collected from Well CS-I due to malfunction 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), newly installed wells (CS-MW17-LGR, CS-MW-18-LGR, and CS-MW19-LGR), and recently upgraded wells (CS-MW1-LGR, CS-MW2-LGR, CS-G-LGR, and CS-MW16-LGR) were 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 number (short list) of VOC analytes which were approved by U.S. Environmental Protection Agency (EPA) and the Texas Commission on Environmental Quality (TCEQ), formerly known as the Texas Natural Resource Conservation Commission, on October 5, 1999. The short 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.
Twenty-one on-post wells were sampled in conjunction with the September 2002 sampling event for a natural attenuation study of CSSA. On-post wells sampled for this study were selected based on previous sampling results. The study focused on the wells with historically higher concentrations of contaminants, primarily chlorinated compounds. For parameters that could be analyzed with sufficient accuracy and reliability the samples were tested on-post, immediately after collection. Parameters requiring specialized laboratory analyses were shipped off-post to STL and Microbial Insights Laboratories for analyses.
Natural attenuation parameters submitted to STL included methane, ethane, and ethene (MEE) using Method RSK-175; chloride using Method SW9056; dissolved organic carbon (DOC) utilizing Method SW9060. Volatile fatty acids (VFAs) with Method 8015M, phospholipid fatty acids (PLFA), and dissolved hydrogen (DH) were submitted to Microbial Insights. The analytical results were reported to Parsons and were reviewed and verified according to AFCEE guidelines. Table C-1 in Appendix C summarizes on-post natural attenuation parameter (NAP) laboratory results.
Field analyses included alkalinity, carbon dioxide, ferrous iron, hydrogen sulfide, manganese, nitrate, nitrite, and sulfide. Field analyses were conducted using Hach� test equipment and methods, including chemical-specific test kits and spectrophotometry using a Hach� colorimeter. Standard solutions were prepared weekly and instruments were calibrated daily for all field procedures. Direct parameter readings were recorded immediately prior to sampling each well location using a YSI digital water quality probe. These measurements included pH, conductivity, redox potential, dissolved oxygen, and temperature. A malfunction was reported in the conductivity meter during the sampling dates of September 9, 2002 through the majority of September 11, 2002. Conductivity data for these sample dates was considered non-usable. Field NAP results for on-post wells are summarized in Table C-2 in Appendix C.
The Parsons data package ID numbers TO42 #29, #30, #31, #32, #33, #34 and #35 contain the analytical results for this sampling event. The data packages were received by Parsons in October 2002 and subsequently validated and submitted to AFCEE November 8, 2002. AFCEE approval of the various packages was received December 5, 2002. All detected concentrations of metals and VOCs are presented in Table 4-1. Full analytical results 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-MW16-LGR, CS-MW1-LGR, and CS-D in the September 2002 event. The detected concentrations are summarized as follows:
CS-MW16-LGR - The PCE concentration was 54.0 micrograms per liter (�g/L), the TCE concentration was 61.0 �g/L, the cis-1,2-DCE concentration was 59.0 �g/L, the trans-1,2-DCE concentration was 0.23 �g/L, the chloroform concentration was 0.071 �g/L, and the toluene concentration was 0.45 �g/L. PCE and TCE concentrations were above the MCL, while cis-1,2-DCE was above the reporting limit (RL) in CS-MW16-LGR.
CS-D - The results for the compounds PCE, TCE, and cis-1,2-DCE in CS-D were 170.0 �g/L, 250.0 �g/L and 230.0 �g/L respectively. Well CS-D had a trans-1,2-DCE concentration of 1.5 �g/L, a chloroform concentration of 0.2 �g/L, and a 1,1-DCE concentration of 0.12�g/L in the September 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 12.0 �g/L, 25.0 �g/L, and 17.0 �g/L, respectively in September 2002. Also detected were trans-1,2-DCE at 0.19 �g/L, chloroform at 0.085 �g/L, and 1,1-DCE at 0.045 �g/L. The PCE and TCE MCLs were exceeded in CS-MW1-LGR in the September 2002 event.
The concentration trends over time for these three wells, including CS-MW2-LGR, and these contaminants of concern (COCs) are shown in Figure 4-1, Figure 4-2, Figure 4-3, Figure 4-4, Figure 4-5 and Figure 4-6. CS-MW16-LGR VOC concentrations from the September event decreased since June 2002 and are below concentrations detected in 1998. Concentrations in well CS-D for September 2002 were the maximum result since monitoring began in 1991. The VOC concentrations have been 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 since 1998 and both trend graphs show increases in concentrations in early 2001 and a decline in concentrations from September 2001 to September 2002. Screening data from Well CS-D (December 2001) are included on the figures for comparison of concentration trends over time.
Additional wells had VOC detections that were below the MCLs. CS-MW2-LGR had five VOC detections. PCE, TCE, cis-1,2-DCE, trans-1,2-DCE, and toluene concentrations were detected at concentrations of 2.9 �g/L, 2.0 �g/L, 1.1 �g/L, 0.055 �g/L, and 0.071 �g/L, respectively. PCE and TCE were above the RL and below the MCL.
CS-MW5-LGR had three VOC analytes detected. PCE was detected at a concentration of 0.32 �g/L, which is below the RL. TCE was detected at 0.4 �g/L and cis-1,2-DCE was detected at 0.46 �g/L. Concentrations of PCE, TCE, and cis-1,2-DCE have remained somewhat stable since CS-MW5-LGR was initially sampled in June 2001. Wells CS-MW7-LGR and CS-MW7-CC had PCE at concentrations of 0.073 �g/L and 0.13 �g/L, respectively. Methylene chloride was reported from December 2001 through June 2002 and 1,1 DCE was reported in June 2002. Methylene chloride is a common laboratory contaminant. This is the first detection of PCE in these wells; the concentrations are above the method detection limit (MDL) and below the RL.
Well CS-MW8-LGR had a VOC concentration of PCE at 0.59 �g/L. This concentration was above the 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 reported again until the March 2002 event.
CS-MW10-LGR had three VOC detections for PCE, TCE, and chloroform at concentrations of 2.2 �g/L, 0.56 �g/L, and 0.12 �g/L, respectively. PCE was above the RL and below the MCL while the TCE and chloroform concentrations were above the MDL and below the RL. These results are consistent with concentrations detected since the well was initially sampled in December 2001.
CS-MW10-CC also had a PCE detection above the MDL and below the RL at a concentration of 0.58 �g/L. This is the first detection of PCE in this well since it was first sampled in December 2001. The only other VOC detected in CS-MW10-CC was methylene chloride in March 2002.
All of the water supply wells, (CS-1, CS-9, and CS-10) had VOC concentrations detected above the MDL, but below the RL. CS-1 had detections of PCE, TCE, and chloromethane at concentrations of 0.08 �g/L, 0.2 �g/L, and 0.17 �g/L, respectively. Well CS-10 had PCE, chloroform, and chloromethane at concentrations of 0.086 �g/L, 0.4 �g/L, and 0.12 �g/L, respectively. PCE was not detected in CS-9 during this monitoring event after being detected for the first time in this well in March 2001. Well CS-9 had one detection of chloromethane at a concentration of 0.092 �g/L. Well CS-11 (a former drinking water well) had a concentration of 1,1 DCE at 0.032 �g/L, which was also above the MDL and below the RL.
Well CS-2 had a PCE detection of 0.073 �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 had cis-1,2-DCE detected above the MDL and below the RL at a concentration of 0.14 �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.
Well CS-MW17-LGR was installed in August 2002. This is the first quarterly sampling event for this well. Five VOCs were detected in this well. PCE was detected at a concentration of 0.083 �g/L. Toluene, 1,1-DCE, 1,2,4-TMB, and 1,3,5-TMB were detected at concentrations of 0.14 �g/L, 0.055�g/L, 0.097 �g/L and 0.064 �g/L, respectively. All concentrations were above the MDL and below the RL.
Well CS-MW18-LGR was also installed in August 2002. This is the first quarterly sampling event for this well. Four VOCs were detected in this well. Toluene, 1,2,4-TMB, 1,3,5-TMB, and o-xylene were detected at concentrations of 0.75 �g/L, 0.35 �g/L, 0.14 �g/L, and 0.078 �g/L. All concentrations were above the MDL and below the RL.
Well CS-MW19-LGR was installed in August 2002. This is the first quarterly sampling event for this well. Detections of PCE, toluene, methylene chloride, and 1,2,4-TMB were reported in this well. The concentrations were 0.28 �g/L, 0.22 �g/L, 0.61 �g/L, and 0.067 �g/L, respectively. All concentrations were above the MDL and below the RL.
Wells CS-MW3-LGR, CS-MW6-LGR, CS-MW6-BS, CS-MW6-CC, CS-MW8-CC, CS-MW9-LGR, CS-MW9-BS, and CS-MW9-CC had no VOC analytes detected above either the MDL or RL. Well CS-G-LGR reported a sub-RL toluene concentration.
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 all the wells tested during September 2002, only one on-post monitoring well, CS-MW17-LGR, had a detection of a metal above the appropriate MCL, action level (AL), or secondary standard. Nickel was detected in CS-MW17-LGR at a concentration of 150 �g/L (The MCL for nickel is 100 �g/L). This was the first sampling event for this well. No other CSSA wells exhibited metals levels that surpassed the MCLs/ALs during this monitoring event.
4.3 Natural Attenuation Parameters
4.3.1 Conditions of Natural Attenuation
Biodegradation, or natural attenuation, is the most active process in the removal of contaminants from groundwater. Natural attenuation is a combined product of several mechanisms, classified as either destructive or nondestructive. Nondestructive attenuation mechanisms include that of volatilization, sorption, dispersion, and dilution from recharge, while biodegradation is the most substantial destructive mechanism. The determination of whether groundwater contamination presents a significant threat to human health and the environment relies upon an accurate estimation of the potential for natural biodegradation to occur. Lines of evidence that will scientifically establish that degradation of contaminants at a rate protective of human health and the environment, is occurring must be established. Three general lines of evidence that can be used are:
An observed reduction in concentrations of contaminants downgradient of the source of contamination.
Analysis of chemical and geochemical analytical data, including decreasing parent chemicals, increasing daughter chemicals, the depletion of electron acceptors and donors, and the increase of metabolic byproduct concentrations.
Microbial data to support the development and rate of biodegradation.
The continuation of the on- and off-post groundwater monitoring program, with a subsidiary objective of assessing whether there are apparent trends (decreasing or increasing) in contaminant levels over time in the sampled wells, fulfills requirements needed to obtain the first line of evidence and the majority of the second. Parameters specific to natural attenuation are needed to trace the depletion of electron acceptors and donors, and the increase of metabolic byproducts. Microbial data, in addition to the standard parameters included in the monitoring program are needed to obtain the third line of evidence (Wiedemeier et al., 1996).
Table 4.2 is a list of each of the natural attenuation parameters sampled, and their relevance, for the September 2002 sampling event.
4.3.2 Natural Attenuation Parameter Results
The results of the natural attenuation field and laboratory analysis of on-post groundwater wells are summarized in Table C-1 and C-2 within Appendix C. A brief discussion of the results is provided below.
The field analysis Hach� testing yielded uniform results. Ferrous iron, hydrogen sulfide, manganese, nitrate, and nitrite results were either very low or non-detect. Sulfate and carbon dioxide results for on-post wells are within a consistent range, but offer little insight into possible geographical trends. Alkalinity results are consistent with historical levels in the area of CSSA (Bluntzer, 1992). Direct readings during field sampling resulted in reasonably neutral pH levels, with the exception of CS-MW8-LGR and CS-MW9-LGR; which had lower reported pH levels of 5.43 and 4.2, respectively. All reported temperatures were normal. Redox potential and dissolved oxygen results showed varied results with no noticeable geographic trend.
Laboratory analysis of methane and chloride yielded consistent results for all on-post wells. All of the results for chloride were above sample quantitation limits (SQL) and laboratory RL, but were consistent with average historical chloride levels for northern Bexar County (Ashworth, 1983, Bluntzer, 1992). Methane results were above the SQL but below the RL for every well, except for CS-1, CS-11, CS-MW2-LGR, and CS-MW6-LGR, which were also above the RL. All of the VFA analysis resulted in non-detects. Dissolved hydrogen reported range was between 0.14 and 59 nM, with no geographical trend. Well CS-MW16-LGR had a reported dissolved hydrogen result of 59 nanomole (nM), while CS-MW5-LGR resulted in 0.14 nM. The average dissolved hydrogen result for the remaining wells was 2.12 nM.
Phospholipid fatty acid results indicated fairly inconsistent results for all of the on-post wells sampled. The quantitative profile of the microbial population in seventeen of the on-post wells resulted in a majority of the microbial biomass consisting of the monoenoic (monos) PLFA structural group, found in Gram-negative bacteria; and normal saturated (Nsats), ubiquitous in both prokaryotic and eukaryotic organisms. A small total percentage of the biomass for the same seventeen wells consisted of eukaryotes of the polyenoic PLFA structural group, found in organisms such as fungi, protozoa, algae, higher plants, and animals; as well as terminally branched saturated (TerBrSats), representative of Gram-positive bacteria. Bacterial biomass is based on PLFA specifically attributable to bacteria, and eukaryotic biomass is PLFA analogous with higher organisms. Total biomass content (Pmole/mL) is the total amount of PLFA extracted from a given sample. Growth rates for the seventeen wells ranged from 0.16 to 1.03. CS-MW4-LGR reported the lowest growth value of 0.16, whereas CS-MW10-LGR reported the highest rate of 1.03.
Wells CS-9, CS-10, and CS-MW5-LGR resulted in 100% total biomass consisting of normal saturated (Nsats), but with lower total biomass concentrations. Comparison of the majority of on-post groundwater wells indicates a diverse community structure. Anaerobic metal and environmental stress levels were either low or non-detect for all wells.
CSSA has initiated a program of NAP monitoring for both on-post and off-post groundwater sampled under the groundwater monitoring program. The NAPs will be sampled to determine whether natural attenuation is a viable remediation option at CSSA. The September 2002 sampling event was the first NAP sampling event for both on-post and off-post groundwater monitoring. The Annual Groundwater Monitoring report to be prepared for CSSA will provide additional interpretation of the NAP analytical results from the September 2002 event. Additional reports which incorporate future NAP sampling events will interpret changes in NAP data over time to evaluate whether natural attenuation is a viable remediation option for CSSA.