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March 2005 On-Post Quarterly Groundwater Monitoring Report
Section 4 - Westbay�-Equipped Well Results
Four Westbay� (WB) wells equipped with multi-level completions were installed at CSSA in August 2003. WBs are equipped with discrete sampling ports in the LGR, BS & CC. Profiles of each WB zone�s pressure are conducted twice monthly or more frequently when rainfall exceeds 1� in a 24-hour period. Samples are collected monthly and following precipitation. Wells CS-WB01, CS-WB02, CS-WB03, and CS-WB04 were sampled January 25-26 and February 22-24, 2005. In March the equipment was shipped to Westbay� Instruments, Inc. in Canada for servicing, and was unavailable for March sampling. Westbay Instruments, Inc. equipment, sampling methods and profiling operations are described in more detail in the TO42 Well Installation Report (August 2004) and the September 2003 On-Post Groundwater Monitoring Report, Volume 5, CSSA Environmental Encyclopedia.
Profiles were measured on January 13, February 4 and 11, and March 1 2005. During each profiling and sampling event, the field team obtained pressure data from each zone and calculated potential pressure heads and vertical and horizontal gradients. Pressure data were converted into potential heads, or water levels. These are the water levels that would result from hydrostatic pressure within that interval if the well were constructed as a conventional well and screened through that specific depth interval. Potential head varies over time as the hydraulic pressure of each zone changes in response to fluctuating hydrologic conditions. Generally, changes in pressure head show greater magnitude with depth in the formations monitored at CSSA.
There were no precipitation-driven WB sampling events during the first quarter 2005. January and February groundwater samples were collected from intervals that yielded adequate water using standard WB equipment and methods. Samples were analyzed for tetrachloroethene [PCE], trichloroethene [TCE], cis-1,2-dichloroethene [cis-1,2-DCE], trans-1,2-dichloroethene [trans-1,2-DCE], isopropyl alcohol [IPA], acetone, toluene, and 2-butanone [MEK] by DHL Analytical, Round Rock, Texas. WB data are used for screening purposes only. Trip blanks are analyzed, but other quality assurance/quality control (QA/QC) samples are not normally collected. In February two equipment blanks were collected to monitor the equipment decontamination process (see 4.2 below). The analytical results and profile data are used to monitor contaminant concentrations and potential head in specific hydrogeologic zones.
Table 4.1 summarizes analytical results of samples collected for the first quarter 2005. Concentrations from sampled WB zones are graphically represented on Figures 4.1 to 4.4. The contaminant trend lines on the figures end in February because there was no sampling in March. The depths indicated for each monitoring zone is the sampling interval open to the formation.
Detections of PCE, TCE, and cis-1,2-DCE occurred in all four WB wells, though not in every interval. These concentration trends decreased or remained stable in most WB zones as water levels (head pressures) rose during the quarter. Concentrations increased in the upper WB03 zones from January to February. Contaminant concentrations in WBs decrease with distance away from AOC-65.
Concentrations of PCE within the CSSA WB monitoring network were highest in WB03. The maximum of 10,900 micrograms per liter (μg/L) was reported in WB03 UGR‑01 in February. The lowest PCE concentrations continue to be found in WB04. Zones, which were consistently non-detect for PCE this quarter, were intervals WB01‑LGR-04 to -LGR-06, WB02‑LGR-05, and all WB04 zones except LGR-05, -07, -09, -10, and CC-01 and CC-02. TCE concentration trends mirror PCE trends in each interval. The maximum TCE concentration reported was 226 μg/L in WB03-UGR-01 in February. Detections of TCE were reported in all WB02 and WB03 sampled zones this quarter, and in all WB01 zones except LGR-01, LGR-04. At WB04 TCE was found in zones LGR‑06 through LGR‑10, and all results were J-flagged except LGR-09.
Very low concentrations of cis-1,2-DCE were detected in February in the UGR-01, LGR-02, LGR-03, LGR-06, LGR-07, and LGR-09. Only WB03-UGR-01 and WB04-CC-01 had cis-1,2-DCE detections in January. Concentrations of cis-1,2-DCE ranged from 0.26 μg/L in WB04-CC-01 (January) to 7.14 μg/L in WB03-UGR-01 (February). All other cis-1,2-DCE concentrations were between 1.65 and 2.19 μg/L.
Periodic acetone and IPA detections continued to be found in the January WB sample analyses results. In February only WB03-UGR-01 through LGR-06 had acetone or IPA detections. These upper zones in WB-03 also contain the highest concentrations of VOC contamination. Acetone and IPA exhibited a very wide range of concentrations when detected, from 5.4 to 36.1 μg/L, and from 5.2 to 132 μg/L, respectively.
In February two equipment blanks were collected after sampling at WB03 was completed. First the equipment was decontaminated without any chemical rinse. A slug of laboratory-supplied de-ionized water was processed through the equipment in the normal manner of sample collection and sample collected (EB-1). Results for EB-1 showed neither acetone nor IPA detection. The normal sample collected prior to decontamination for EB-1 contained the maximum PCE concentration of the quarter (10,900 μg/L). A second sample (EB-2) consisting of rinse water from an intermediate rinsing stage was collected. This rinse water was also supplied by DHL. Results for EB-2 showed 8.0 μg/L acetone (J-flag) and no IPA detection. These results are inconclusive. The IPA and acetone detections that have been sporadically appearing in the normal monthly WB results are usually of higher concentrations. No explanation has yet been established for the sporadic appearances of acetone and IPA relative to field activities. A Parsons senior chemist is scheduled to visit DHL in April 2005 for an informal review of their laboratory equipment-handling procedures. The January and February 2005 laboratory results had no detections for toluene, trans-1,2-DCE, and MEK in any WB groundwater samples.
First quarter pressure data profiles for each of the WB wells are presented in Figure 4-1 through Figure 4-4. Water levels declined from December 2004 through January 2005. Water levels declined up to approximately 1.2 feet/day in the lower LGR zones (09 � 11), and about 0.9 feet/day in the BS and CC zones of WB04. Profiling then indicated a moderate rising water level trend in most of the intervals through February to March. Increases ranged from approximately 2 feet in the LGR-01 horizon to an average increase of 20 feet in the lower LGR zones, 15 feet in the BS, and 12 feet in the CC. The greatest water level rise within a single horizon during this quarter occurred in the LGR‑09 zones, approximately 20 to 25 feet. Trends from all the UGR monitoring points were flat. By the end of this quarter the groundwater elevations in the various WB intervals had returned to the same approximate levels as at the start of January.
WB03-UGR exhibited the only water present in a UGR zone. The UGR zones at WB01, WB02, and WB04 remained dry this quarter, as well as shallow zone LGR‑01 in WB03. This is unusual as WB03 has water present in the monitoring intervals above and below LGR-01. Although pressure readings from WB03-LGR-01 are greater than a dry interval�s pressure, sampling tubes from this zone come up empty. This may be due to trapped air under pressure from the perched water in the overlying UGR zone.