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September 2004 On-Post Quarterly Groundwater Monitoring Report
Section 4 - Westbay�-Equipped Well Results
Three of the four CSSA Westbay� system multi-port equipped wells were sampled in July 2004. The WB MOSDAX pressure monitoring string installed at WB01 in April 2004 was removed on August 11. All WBs were monitored normally in September. Pressure head monitoring (profiling) at the WB wells is generally conducted al least twice monthly. Additional profiling or discrete interval groundwater sampling may also be conducted following major precipitation events. In the third quarter of 2004 no major, unscheduled, event-driven sampling was conducted. Inclement weather conditions and consequent scheduling conflicts this quarter resulted in two comprehensive sampling events rather than the normal 3. Parsons and CSSA personnel teamed to monitor wells CS‑WB01, CS‑WB02, CS‑WB03, and CS‑WB04 (located off-post) in July, August, and September 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, CSSA Environmental Encyclopedia.
During the third quarter 2004, profiling was conducted on various dates for the WB wells: July 2, 12, 16, August 25, and September 7 (WBs 01 - 03) and 8 (WB04). Comprehensive sampling took place July 26-27, and September 2-3, 2004. In WB02 two upper zones (UGR01 and LGR02) that are normally dry were sampled on July 2 after profiling revealed they contained water. 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 wells were constructed open to those specific depth intervals. Potential head varies over time as the hydraulic pressure of each zone changes in response to hydrologic conditions.
Using standard WB sampling equipment and methods, discrete samples were collected from all zones that yielded water. Occasionally, sampling events are prolonged due to adverse weather. At WB01, nine of the 10 intervals (LGR01 through LGR09) were sampled on September 2, 2004. This was the only sampling event this quarter after removal of the MOSDAX monitoring string from WB01 in August. A WB well cannot be sampled with a MOSDAX string in place.
The 3 uppermost intervals at WB02 filled and drained intermittently throughout the quarter apparently in response to precipitation and subsequent changing of subsurface conditions. WB02 was sampled July 2 (zones UGR01 and LGR02 only) and 26, September 2 and 9 (zones LGR01 and LGR02 only), 2004. For the July 26 event all intervals contained water for sampling except the UGR zone. On September 2, 7 of the 10 WB02 zones (LGR03 through LGR09) contained sufficient groundwater for sample retrieval. While profiling on September 7 following a weekend of rain, zones WB02-LGR01 and LGR02 exhibited sufficient hydrostatic pressure and were therefore sampled.
At WB03 the same seven of 10 intervals (intervals LGR03 through LGR09) were sampled on July 26 and September 3, 2004. In WB04 all of the intervals except the UGR zone were sampled on July 27. On September 3, 2004 all WB04 zones except UGR01 and LGR02 were sampled.
Westbay� intervals not mentioned as being sampled were either dry or did not hold adequate groundwater at the time of sampling. 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. WB data are used for screening purposes; trip blanks are analyzed; 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. 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 during the third quarter of 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 generally remained flat in most WB zones through the third quarter 2004. The LGR09 interval shows the most consistent, or pervasive PCE and TCE contamination (though not always above the maximum historical levels) through all four WBs. In general, contaminant concentrations in the WB zones decrease with distance away from Area of Concern (AOC)-65.
Concentrations of PCE within the CSSA WB monitoring network continue to be most prevalent in WB03. The quarterly maximum of 33.9 micrograms per liter (μg/L) was reported in WB03-LGR06 after the July sampling event. The greatest increase is 7.3 μg/L exhibited in WB03-LGR07. The lowest PCE concentrations of the WB network are found in WB04. All WB04 intervals sampled this quarter were consistently non-detect for PCE except WB04-LGR09, which shows 6.67 and 7.87 μg/L, for July and September, respectively. This quarter presented the first sampling of an UGR interval. WB02-UGR01 was sampled in early July after several days of heavy rain. Laboratory results show low concentrations of PCE (3.45 μg/L) and TCE (2.12 μg/L) from the UGR water.
The TCE concentration trend in the WB monitoring wells mirrors that of PCE, though subdued in comparison. The maximum TCE concentration reported was 17.6 μg/L from interval WB03-LGR03 after the late July sampling. Detections of TCE are reported in all WB02 and WB03 zones sampled this quarter except WB02-LGR02 and LGR08. In WB01 TCE is reported in all sampled zones except LGR01 and LGR04. At WB04, TCE was found in zones LGR06 through LGR10 only this quarter, and all concentrations there are �J� flagged except zone LGR09.
Detections of cis-1,2-DCE are reported in only 3 areas this quarter. Very low concentrations of cis-1,2-DCE were detected in WB03-LGR03 and WB04-LGR06 after both sampling events, and also in WB04-LGR07 after the September event. All reported cis-1,2-DCE concentrations for this quarter were <1.0 μg/L (the RL) and therefore �J�-flagged. No cis-1,2-DCE was found in WB01 and WB02 during the third quarter 2004.
Acetone and isopropyl alcohol (IPA) detections have been greatly reduced after revision of decontamination techniques. No acetone or IPA was detected in any samples after the comprehensive September 2-3 event. The September 7 sample results for WB02-LGR02 show �J�-flagged detections (<15 μg/L) of acetone and IPA. Third quarter 2004 laboratory results reports show no detectable concentrations of toluene, trans-1,2-DCE, and 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 data show an overall water level rising trend between June and early July 2004 throughout the local Middle Trinity aquifer. This came in response to frequent and sometimes heavy precipitation received at the end of June. Water levels began to recede shortly thereafter, and a general decline followed, continuing through the remainder of July and the month of August. The decline reversed in early September in response to significant precipitation, with levels rising moderately.
The UGR interval at WB02 exhibited water for the first time during July 2 profiling due to precipitation from the previous week. The water present in WB02-UGR01 was temporary and the zone was dry by the July 26 sampling event. WB02-UGR01 was dry during the August and September monitoring. The other UGR monitoring points remained dry through the third quarter 2004, as well as shallow zones LGR01 and LGR02 in WB03. 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 also respond to changing weather conditions faster than the shallower zones.