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December 2004 On-Post Quarterly Groundwater Monitoring Report
Section 4 - Westbay�-Equipped Well Results
The four CSSA Westbay� system multi-port equipped wells (WBs) were sampled monthly from September to December 2004. Pressure head monitoring (profiling) at the WB wells was conducted at least twice per month, occasionally in conjunction with sampling. Additional profiling or discrete interval groundwater sampling may also be conducted following major precipitation events under the Groundwater Monitoring Program DQOs. Parsons and CSSA personnel teamed to monitor wells CS‑WB01, CS‑WB02, CS‑WB03, and CS‑WB04 (located off-post) in October, November, and December 2004. WB sampling methods and profiling operations are described in detail in the September 2003 On-Post Groundwater Monitoring Report, and the TO42 Well Installation Report, Volume 5-2.3, CSSA Environmental Encyclopedia.
Regularly scheduled WB profiling was conducted October 4 and 26, November 15 and 22 (excluding WB04, due to flooding), and December 10. Rain event profiling was conducted on November 17 (WB01‑03) and 18 (WB04), after approximately 3.4 inches of precipitation fell within 24 hours November 16-17. Monthly sampling occurred October 4-7, November 29-December 2, and December 27-29, 2004. Rain event sampling of the UGR zones took place on November 18, 2004 when profiling data showed water in these normally dry intervals. This was the first time since installation that all the WB UGR intervals contained sufficient water for sampling. Rain event sampling of one zone, WB03-UGR01, occurred on November 24 as a result of the 4.42 inches of rain on November 22.
During each profiling and sampling event, the field sampling team obtained pressure data from each zone and calculated potential pressure heads and vertical and horizontal gradients. Pressure data were converted into piezometric levels. These are the water levels expected if the wells were constructed open to a specific depth interval. Potential head varies over time as the hydraulic pressure of each zone changes in response to hydrologic conditions. Using standard WB equipment and methods, discrete samples were collected from all zones that yielded water. Occasionally, sampling events are prolonged due to adverse weather or scheduling conflicts.
At WB01, nine of the ten intervals (LGR01 through LGR09) were sampled on October 4, 2004; and the UGR01 interval was dry. Profiling after November 16-17 rainfall indicated water in the WB01‑UGR01 zone as well as all lower zones. On November 18 the WB01‑UGR01 interval was sampled. Regular monthly sampling for November was delayed until December 2, and all ten zones were sampled. On December 27, WB01 zones LGR01 to LGR09 were sampled, with the UGR01 interval found dry.
At WB02, nine of the ten intervals (LGR01 through LGR09) were sampled on October 5, 2004. Rain event profiling on November 16-17 indicated water in the WB02‑UGR01 zone as well as all lower zones. On November 18 a sample was taken from WB02‑UGR01. All 10 zones were sampled on December 2. On December 29, WB02 zones LGR01 through LGR09 were sampled for the monthly event and WB02-UGR01 was again dry.
On October 6, 2004, seven of ten WB03 intervals (LGR03 through LGR09) were sampled. Profiling after the rains of November 16-17 indicated water was present for the first time in the WB03‑UGR01 zone. Unlike WB01, WB02, and WB04, the two zones immediately below UGR01 did not contain water. During November 18 profiling, water was present in both UGR01 and LGR01 and two samples were collected. The WB03-LGR02 interval remained dry. WB03-UGR01 was sampled on November 24 after 4.42 inches of rain fell on November 22. Regular WB03 monthly sampling for November was performed on the 29th, and nine samples were collected. Although profiling indicated the presence of groundwater, the sample bottle retrieved from WB03-LGR01 was empty. This is further discussed in Section 4.4. Monthly WB03 sampling on December 29 yielded the same sample quantity from the same intervals as in late November.
Fifteen of the 16 WB04 intervals (LGR01 through CC03) were sampled on October 7, 2004. Profiling following November 16-17 rainfall indicated water in the WB04‑UGR01 zone as well as all other zones. On November 18, a sample was taken from the WB04-UGR01 interval. On December 1, nine intervals were sampled. On December 28, 15 WB04 zones (LGR01 to CC03) were sampled, and UGR01 was dry.
Westbay� samples were analyzed for a project specific short list of volatile organic compounds (VOCs) (tetrachloroethene [PCE], trichloroethene [TCE], cis-1,2-dichloroethene [cis-1,2-DCE], trans-1,2-dichloroethene [trans-1,2-DCE], acetone, toluene, and 2-butanone [MEK]), and isopropyl alcohol [IPA]) by DHL Analytical, Round Rock, Texas. WB data are used for screening purposes only. Trip blanks are included and analyzed (one per cooler) and no other quality assurance/quality control (QA/QC) samples are collected. The laboratory analytical results and profile data are used to monitor contaminant concentration trends and water levels in specific hydrogeologic zones. WB monitoring methodology and data management conform to the CSSA Quality Assurance Project Plan (QAPP) and project DQOs.
Table 4-1 summarizes analytical results for samples collected from September to December 2004. Graphs of PCE and TCE concentrations from sampled monitoring zones in the WB wells are presented in Figures 4-1 through Figure 4-4. The depths indicated for each monitoring zone represent the sampling interval open to the formation.
Detections of PCE and TCE are reported in all four WB wells this quarter. Contaminant concentration trends did not increase or decrease in most WB zones through the monitoring period. Detections of PCE and TCE in the WB wells continue to show maximum concentrations in the WB03 column, which is closer to AOC-65. Together, the LGR09 zones from all four WB wells show the most pervasive lateral PCE and TCE contamination (though not at the maximum concentrations) than any other WB zone. Contaminant concentrations generally decrease with distance away from AOC-65.
The maximum detection to date was reported in WB03‑UGR01 (20 ft to 37 ft) at 13,900 μg/L after the November 18 rain event sampling. Every interval at WB03 shows PCE contamination. PCE concentrations decrease rapidly with depth to zone LGR03 (105fbgs), then range from 18 � 41 μg/L. The lowest PCE concentrations continue to be found in WB04. Most WB04 intervals sampled this quarter were consistently non-detect for PCE. WB04 zones UGR01 and LGR09 show concentrations ranging from 7.47 to 9.51 μg/L. Other detections in WB04-LGR06, -LGR07, -LGR10, and -CC01 are all �J�-flagged (below the RL [<2.0 μg/L]).
Following the November precipitation, all four UGR intervals contained water sufficient for sampling. The PCE concentrations were 6.58 (WB01), 7.02 (WB02), and 9.51 μg/L (WB04) in three of the WBs. WB03-UGR01 was sampled four times from November to December. Laboratory results show concentrations of PCE ranging from 9,170 � 13,900 μg/L. WB03‑LGR01 and ‑LGR02, also usually dry, were sampled and showed elevated PCE levels ranging from 363 μg/L in LGR02 to 560 μg/L in LGR01. PCE concentration trends in WB01 and 02 were relatively unchanged from previous quarters.
General TCE concentration trends in the WB monitoring wells mimic the PCE concentrations. Occasionally, in deeper zones TCE exceeds the PCE concentration. The maximum TCE concentration reported was 321 μg/L from interval WB03‑UGR01 after the late December sampling. Detections of TCE were reported in all WB02 and WB03 zones sampled this quarter. In WB01 TCE was reported in all sampled zones except LGR01 and LGR04. At WB04, TCE was found only in zones LGR06 through LGR10 this quarter, and all concentrations were �J�‑flagged except those from zone LGR09, which range from 7.6 to 9.87 μg/L.
Detections of cis-1,2-DCE were consistently reported in all WB03-UGR01 samples this quarter, ranging from 5.32 to 7.78 μg/L. These are the highest cis-1,2-DCE concentrations exhibited in any WB interval to date. October and November sampling in WB03‑LGR03 revealed concentrations of cis-1,2-DCE at 0.32 and 0.43 μg/L (both �J�-flagged), respectively. At WB04 concentrations were consistently reported in the LGR06 zone (0.79 to 1.22 μg/L) and once (November) in the LGR07 zone (0.27 μg/L). Reported cis-1,2-DCE concentrations <1.0 μg/L (lab RL) are �J�-flagged. No cis-1,2-DCE was reported in WB01 or WB02 during this fourth quarter of 2004.
Isopropyl alcohol (IPA) detections up to 32.2 μg/L continue to be reported in the WB sample analysis results, though most detections are lower than previous quarters. Acetone was detected in the WB03‑UGR01 sample collected on November 24 at 6.6 μg/L (J). Fourth quarter 2004 laboratory results had no detectable concentrations of toluene, trans-1,2-DCE, or MEK in any WB groundwater samples.
Pressure data depth profiles for each of the WB wells are presented in Figure 4‑1 through Figure 4‑4. The WB water level data show a shallow rising trend between October and mid-November 2004 throughout the local Middle Trinity aquifer. Precipitation received November 14 � 22 caused the levels to rise more sharply. The water levels peak in early December, and then exhibit a steady, slow decline to the end of December. After the November rain, some middle LGR WB intervals show no water level decline, but continue a slow, subdued increase. It appears from the data that intervals WB03‑UGR01 to ‑LGR05, and WB04‑LGR03 to ‑LGR04 contain perched water that is replenished faster than it is drained.
Following precipitation on November 16 and 17, all four UGR intervals contained water. This is the first time since Westbay� installation that all the UGR zones contained water simultaneously. The UGR zones in WB01 and WB02 drained over the next three weeks and were dry by December 10. WB03-UGR01 continued to contain water through December, draining during the second half of the month. WB04-UGR01 appeared to drain quickly, and was dry by December 1.
Interval WB03‑LGR01 profiling indicated water was present but could not be sampled. Groundwater was present here at the November 18 shallow zone sampling (described above). During the later November and December sampling events, WB03-LGR01 indicated pressures above ambient atmospheric pressure that suggested groundwater was present. However, the sampling team was unable to collect from this level. No equipment malfunction was detected. This could have resulted from trapped air being subjected to pressure from water‑filled zones above and below. Nearby AOC‑65 PZ‑4 and some LGR monitoring wells in other portions of CSSA have been observed releasing air due to pressure differences.
The most dynamic changes in potential head continue to appear in the lower portions of the LGR, specifically the LGR09 zones of the wells. Generally, changes in pressure head show greater magnitude with depth in the WB systems. The deeper, more permeable zones are observed to respond faster than the shallow zones as a result of changing weather conditions.