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Final March 2004 On-Post Quarterly Groundwater Monitoring Report
Section 4 - Westbay�-Equipped Well Results
The four CSSA multi-port Westbay�-equipped wells were sampled monthly during the first quarter of 2004. Pressure head monitoring was conducted a minimum of twice monthly. Discrete interval groundwater samples were also collected following a major precipitation event or at a minimum of one per month. Parsons and CSSA personnel teamed to monitor wells CS‑WB01, CS‑WB02, CS‑WB03, and CS‑WB04 (located off-post) in January, February, and March 2004. Westbay sampling methods and profiling operations are described in more detail in the TO42 Well Installation Report (currently draft) and the September 2003 On-Post Groundwater Monitoring Report, Volume 5, CSSA Environmental Encyclopedia.
From January through March 2004, profiling was conducted on various dates for each Westbay well (January 12, 20, 21, 22, and 27; February 18, 25, 26, and 27; and March 10, 23, 24, 25, and 26, 2004). During each profiling and/or 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 potential heads or piezometric levels. These are the water levels that would occur if the well was constructed to be open to that specific depth interval. Potential head varies over time as the hydraulic pressure of each zone changes in response to hydrologic conditions.
Using standard Westbay sampling equipment and methods, discrete samples were collected from all zones that yielded water. At CS‑WB01, nine of the 10 intervals (LGR‑1 through LGR‑9) were sampled over four sampling dates: January 19 and 20, February 26, and March 25, 2004. Eight of the 10 intervals at CS‑WB02 (LGR‑1, and LGR‑3 through LGR‑9) were sampled January 20; February 26, and March 25, 2004. Seven of the 10 intervals from CS‑WB03 (intervals LGR‑3 through LGR‑9) were sampled on January 21, February 27, and March 26, 2004. Fourteen of the 17 intervals (LGR‑3, LGR‑4, LGR‑6 through LGR‑11, BS‑01 and BS‑02, CC‑01 through CC‑03) were sampled from CS‑WB04 on January 22, February 25, and over March 23 � 24, 2004. Westbay intervals not sampled were dry at the time of sampling, except CS‑WB04‑LGR‑5, which had a malfunctioning sample port. Samples were analyzed for the specific short list of volatile organic compounds (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]) by DHL Analytical, Round Rock, Texas. Westbay data are used for screening purposes only; trip blanks are analyzed, but no other quality assurance/quality control (QA/QC) samples are collected. The laboratory analytical results and profile data are used to monitor contaminant concentrations and water levels in specific hydrogeologic zones. Westbay 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 during the first quarter of 2004. Graphs of PCE, TCE and cis-1,2-DCE concentrations from sampled monitoring zones in the Westbay wells are presented in Figure 4-1 through Figure 4-4. The depths indicated for each monitoring zone represent the sampling interval open to the formation.
Detections of PCE, TCE, and cis-1,2-DCE occurred in all four Westbay wells during the first quarter of 2004. Contaminant concentration trends, with the exception of acetone and isopropyl alcohol (IPA), decreased or remained stable in most Westbay zones as water levels increased. In general, contaminant concentrations in Westbay zones decrease with distance away from Area of Concern (AOC) 65.
Concentrations of PCE within the CSSA Westbay monitoring network were highest and most prevalent in WB03. The maximum of 50.8 micrograms per liter (μg/L) was reported in CS-WB03-LGR‑06 after the January sampling event. The lowest PCE concentrations of the Westbay network were found in WB04. Westbay zones sampled during this quarter which were consistently non-detect for PCE were WB01 intervals LGR‑05 and LGR‑-06, and all WB04 zones except LGR‑09. The maximum TCE concentration reported (17.8 μg/L) occurred in WB01 interval LGR‑09 during the January sampling. Detections of TCE were reported in all WB02 and WB03 zones sampled this quarter, and in all WB01 zones except LGR‑01, LGR‑04, and LGR‑05. At WB04, TCE was found only in zones LGR‑06 through LGR‑09 this first quarter of 2004. Very low concentrations of cis-1,2-DCE were detected sporadically in the Westbay wells in intervals LGR‑03, LGR‑06, LGR‑07, LGR‑09, and CC‑01. All reported cis-1,2-DCE concentrations for this quarter were <1.0 μg/L and �J� flagged.
Acetone and IPA detections showed a range of detections from non-detect (<5.0 μg/L) to 1,160 μg/L for acetone and 21,400 μg/L for IPA in the Westbay-equipped wells. Decontamination techniques continue to be refined with the goal of eliminating the acetone and IPA detections. First quarter 2004 laboratory results showed no detectable concentrations of toluene, trans-1,2-DCE, or MEK in any Westbay groundwater samples.
Pressure data depth profiles for each of the Westbay wells are presented in Figure 4‑5. The Westbay data show an overall water level rise from January 2004 to March 2004 throughout the local Middle Trinity aquifer. This rising trend is a typical response to increased precipitation and cool temperatures. The increases in pressure head generally show greater magnitude with depth. The largest increase in potential head took place between January 12 and 27, 2004, with the deeper LGR zones showing the greatest rises. The maximum rise within a single zone during this quarter was 40.51 feet reported in WB03‑LGR‑09. All four Upper Glen Rose (UGR) zones remained dry through the first quarter of 2004, as well as shallow zone LGR‑02 in WB02, WB03, and WB04, and zone LGR‑01 in WB03. Figure 4‑5 shows similar potential water levels in most zones lying below 240 feet bgs.