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Section 4 - Westbay®-Equipped Well Results
The four CSSA multi-port Westbay-equipped wells were sampled monthly during the fourth quarter of 2003. Pressure head monitoring was conducted a minimum of twice monthly. Discrete interval groundwater samples were also collected following major precipitation events 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 December 2003. Westbay sampling methods and profiling operations are described in more detail in the TO42 Well Installation Report and the September 2003 On-Post Groundwater Monitoring Report, Volume 5, CSSA Environmental Encyclopedia. The monitoring port at WB04 zone LGR-05 was determined to be defective and has been removed from the monitoring schedule.
From October through December 2003, profiling was conducted on various dates for each Westbay well (October 7, 15, 16, 20, and 21; November 18, 19, and 20; and December 3, 17, 18, 2003). 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 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
Discrete samples were collected from all zones in the Westbay®-equipped wells that yielded water. Nine of the 10 intervals (LGR‑1 through LGR‑9) at CS‑WB01 were sampled over four sampling dates: October 7 and 21, November 18, and December 17, 2003. Eight of the 10 intervals at CS-WB02 (LGR‑1 and LGR‑3 through LGR‑9) were sampled on October 7 and 20; November 19, and December 17, 2003. Seven of the 10 intervals from CS-WB03 (intervals LGR‑3 through LGR‑9) were sampled on October 15, November 19, and December 18, 2003. Fourteen of the 17 intervals (LGR‑3, LGR‑4, LGR‑6 through LGR‑11, BS‑01 and BS‑02, and CC‑01 through CC‑03) were sampled from CS‑WB04 on October 16, November 20, and December 18, 2003. All other WB‑04 sampling intervals were dry. Samples were analyzed for the specific short list of volatile organic compounds (VOC) (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.
Sampling of WB‑01 and WB‑02 was conducted October 7 and 8, 2003. Samples were shipped to the laboratory, but misrouted by Fedex during shipping. Once the error was corrected and shipments forwarded to the laboratory, the ice was melted and samples were no longer usable. These samples were re-collected on October 15, 2003.
Table 4-1 summarizes analytical results for samples collected during the fourth quarter of 2003. Graphs of PCE and TCE concentrations from sampled monitoring zones in the Westbay wells are presented in Figure 4-1 and Figure 4-2. The depths indicated for each monitoring zone represent the sampling interval open to the formation.
Detections of PCE and TCE occurred in all four Westbay wells and cis-1,2-DCE was detected in four zones within WB04. Contaminant concentration trends, with the exception of acetone, decreased or remained stable in most Westbay zones as water levels declined through the fourth quarter. In general, contaminant concentrations in Westbay zones decrease with distance away from area of concern (AOC)-65.
Concentrations of PCE were highest in WB03 during October, showing a maximum of 81.5 micrograms per liter (μg/L) in WB03 interval LGR‑09. The lowest PCE concentrations were reported in WB04. Westbay zones sampled during this quarter which were consistently non-detect for PCE were WB04 zones LGR-01 through LGR-06, CC-01, and CC-03. The maximum TCE concentration reported (19.1 μg/L) occurred in WB01 interval LGR-09 during the October sampling. Detections of TCE were reported in all Westbay zones sampled this quarter except for WB04 zones LGR‑01, LGR‑03, and LGR‑04. Low concentrations of cis-1,2-DCE were detected sporadically in a few Westbay zones with a maximum concentration of 1.6 μg/L in WB02 interval LGR‑09.
Acetone detections ranged from less than the method detection limit (MDL) to 76.2 μg/L in WB01 interval LGR-02 (October). Two equipment blanks (EB) were collected October 20, 2003, following WB‑02 sampling, one after a hexane wash and one after an (isopropyl alcohol (IPA) wash. The IPA EB result was non-detect for acetone, and the hexane EB result showed acetone at 13 µg/L. Hexane was eliminated from decontamination procedures after a review of the results. The EB sampling results proved inconclusive as acetone detections continued in the following months after hexane was eliminated from sample decontamination procedures. Consequently, a higher grade of IPA (nanograde) was purchased for the Westbay sampling equipment decontamination and results are pending. There is no known history of acetone usage at CSSA. Laboratory results showed no detectable concentrations of toluene, trans-1,2-DCE, and MEK in any Westbay groundwater samples this quarter.
Pressure data depth profiles for each of the Westbay wells are presented in Figure 4‑3, Figure 4-4, Figure 4-5, and Figure 4‑6. The Westbay data show an overall water level decline from September 2003 to December 2003 throughout the local Middle Trinity aquifer. This decline is a continuing trend from the previous quarter in response to a lack of precipitation. The declining trend is measured in inches in the shallower zones of the LGR and generally increases in magnitude with depth. The greatest declines are shown in the WB02 and WB04 data occurring in the lower LGR, the BS, and the major water-bearing portion of the CC Formations. The largest decrease in potential head took place between November and December 2003, with the deeper zones in WB02 and WB04 decreasing by 20 feet. From September to December 2003, the lower zones of the LGR and BS showed an overall decline in potential head approximately 3 feet greater than in the CC zones. The maximum decline within a single zone during this quarter was 34.53 feet reported in WB02 zone LGR‑09. All four Upper Glen Rose (UGR) zones remained dry from September to December 2003, as well as shallow zone LGR‑02 in WB02, WB03, and WB04, and zone LGR‑01 in WB03. Water levels in the LGR and CC zones are often at similar depths. Figure 4‑3, Figure 4-4, Figure 4-5, and Figure 4‑6 show similar potential head in most zones below 240 feet below ground surface. One exception occurs in CS‑WB03, where there is a difference of about 7 to 10 feet between zones LGR‑08 and LGR‑09.