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September 2000 Quarterly Groundwater Monitoring Report

Groundwater monitoring was scoped under the Air Mobility Command (AMC) Contract F11623-94-D0024, Delivery Order RL74 performed September 11 through 18, 2000 at Camp Stanley Storage Activity (CSSA). Groundwater monitoring under AMC Order RL74 was initiated in March 2000. AFCEE/ERD and AFCEE/ERC provide technical oversight of the monitoring program.

The current objectives of the groundwater monitoring program are to determine groundwater flow direction and water levels, determine groundwater contaminant concentrations for characterization purposes, and identify seasonal variations in physical and chemical properties. Appendix A identifies the DQOs for CSSA�s groundwater monitoring program, along with an evaluation of whether each DQO has been attained. Where this is true, the appropriate reference is provided in the second column. The objectives listed in the table also reference appropriate sections of the Order.

Overall DQOs for the investigations at CSSA are provided in Volume 1-1 behind the RFI Addendum tab (Section 11).

1.0 - Water Level Measurements

Twelve water level measurements were recorded during the September 2000 monitoring event. Water level measurements were taken in Wells 1, 2, 3, 4, 9, 10, 16, D, G, I, MW1, and MW2. A water level reading could not be obtained from Well 11 due to an obstruction in this well at 255.65 feet. All of the water levels were measured with an e-line except for Well 10, which was measured with an air-line apparatus.

Groundwater levels fell 6.34 feet on average between June 15, 2000 and September 11, 2000. The groundwater elevations calculated from the water level measurements are summarized in Table 1. On September 11, 2000, a difference in groundwater elevation of approximately 13 feet existed between Well 16 and Well D. According to historic groundwater elevations from October 1992 through March 2000, shown in Table 3 of the Introduction to the Groundwater Monitoring Program at Camp Stanley, this is not an unusual occurrence.

2.0 - Basewide Flow Direction and Gradient

A groundwater potentiometric map was generated from the September 2000 groundwater elevations and is shown in Figure 1. The September 2000 potentiometric map indicates that the general groundwater flow direction at that time was to the southeast and the groundwater gradient was approximately 0.006 ft/ft. Groundwater flow directions and gradients during past monitoring events are provided in Table 3 of the Introduction to the Groundwater Monitoring Program at Camp Stanley for comparison.

3.0 - Well 16 Water Level and Transducer Data

Precipitation data collected from the meteorological station at Well 16 between October 5, 1998 and September 11, 2000 is shown in Figure 2, along with water level data collected during the same period by the Well 16 transducer.

Groundwater levels fell 6.34 feet on average between June 15, 2000 and September 11, 2000. During this period, there were nine rainfall events, with a total precipitation 1.96 inches. During the previous quarter when groundwater levels rose 11.77 feet between March 21 and June 14, twenty-three rainfall events occurred, with a total precipitation of 11.1 inches.

4.0 - September 2000 Analytical Results

Nine onsite wells were sampled in September 2000: 1, 2, 9, 10, 11, 16, I, MW1, and MW2. In addition, one of the offsite wells, Well LS-7, was sampled during this monitoring event. As noted earlier, Well D was not sampled during this event because the water level was below the pump depth and Wells G and H were not sampled due to inoperable sucker rods in these wells. The data package RL74-10 contains the VOC and metals analytical results for this monitoring event. This data package was received by Parsons ES on October 16, 2000, validated and submitted to AFCEE on December 15, 2000, and is not yet approved by AFCEE. Approval is pending laboratory submittal of documentation for system performance check compounds. Analytical results for September 2000 are presented in Table 2. VOC trends over time for Well 16 are depicted graphically in Figure 3.

4.1   Volatile Organic Compound Analyses

Maximum contaminant levels (MCLs) for TCE, PCE, and cis-1,2-DCE were exceeded in Well 16. During the September 2000 monitoring event, the PCE concentration in Well 16 was 167.24 �g/L, and the TCE concentration was 180.9 �g/L.

These levels are higher than those recorded during recent monitoring events, and are among the highest recorded for these wells. In addition, a significant increase from recent sampling events of cis-1,2-DCE concentration in Well 16 was also observed. According to the weather station data, several rain events totaling 0.43 inches occurred in September at CSSA just prior to groundwater sampling at Wells 16 and MW1. This precipitation may have resulted in the increase in contaminant concentrations over recent levels seen in Wells 16 and MW1. Figure 3 shows how concentrations of these compounds in Well 16 during September 2000 compare to historical levels.

The only other major change in VOC levels in onsite wells during this sampling event occurred in Well MW1. Similar to the results for Well 16 during this monitoring event, Well MW1 was found to have PCE, TCE, and cis-1,2-DCE concentrations
(25.44 �g/L, 25.0 �g/L, and 26.38 �g/L, respectively) that exhibited large increases over all recent levels in this well. The concentrations of all three compounds were among the highest ever recorded for this well.

Concentrations of all three contaminants had generally been decreasing in Well MW1 since the November 1998 sampling event. TCE and PCE concentrations in Well MW1 exceeded the MCLs after falling below these levels during the last two sampling events. PCE reached its highest detected concentration in Well MW1 during September 2000. Conversely, concentrations of TCE, PCE, and cis-1,2-DCE have been relatively stable in Well MW2 since monitoring began in November 1998. In addition, levels of trans-1,2-DCE below the reporting limit (RL) were detected in Wells MW1 and MW2. The latest data support the assumption that it is possible that MW1 and MW2 are located on the outskirts of the same plume encompassing Well 16.

Concentrations of chloroform and TCE that were below the RL were found in Well 1. As in the previous two sampling events, Well 10 had a chloroform concentration that was below the RL. Chloroform was detected at a level below the RL in Well 11 after a non-detect during the last sampling event.

4.2   Metals Analyses

No significant changes in metal levels were detected and no metal concentrations exceeded the MCLs during this sampling event. The most recent above-MCL detection was lead (0.0172 �g/L) at Well 1 in March 2000.

4.3 - Offsite Groundwater Monitoring

A sample was collected from private Well LS-7 during this sampling event. No contaminant levels above MCLs were found, but a PCE concentration of 3.12 mg/L was detected. This concentration is a slight increase over the previous level of 2.2 mg/L recorded during the last sampling event and represents the highest detected concentration for this well. In addition, TCE and chloroform were detected at concentrations below the RL.

5.0 - Summary