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HJ-100

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Trichloroethene Optrode Detection System

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CASE STUDIES:

EDWARDS AIR FORCE BASE
Field Trials

The system was composed of a TCE optrode interfaced into the HJ-100 sampling/analytical module to allow for remote monitoring of 4-inch diameter ground-water wells. This configuration was employed at Edwards Air Force Base, California, from May 2002, to December 2002. The sampling/analytical unit containing the optrode is placed in an auxiliary well adjacent to the monitoring well to protect the unit and provide temperature control for the optrode. The design philosophy for mounting the optrode in the auxiliary well is that it is easier to transport a sample to a sensor than to mount a sensor in a monitoring well. The system was designed for ease of maintenance, and the elimination of possible contamination of the well from standards or other chemicals.

Ground-water samples were collected using a Burge Sampler. The Burge Sampler is designed to collect and transport 150 to 200 mL samples to the HJ-100 analytical system located in the auxiliary well. The Burge Sampler is capable of sampling from four different levels within a monitoring well. In this deployment, the system sampled two discrete levels.

The results of the ground-water monitoring from May 2002, to August 2002, are presented on Table I. The well has a total depth of 128 feet below ground surface (bgs) with a screened interval from 118 to 128 feet bgs. The static water level was approximately 40 feet bgs over the time period of the investigation. The system was configured to collect water samples from 99.5 and 123.5 feet bgs. One of the sampling ports was placed in the screened interval and the second sampling port was placed in the blank casing (stagnant water region). The historical TCE concentrations of the screened interval of the monitoring well ranged from 150 to 200 ppb.

Table I

Well-Mounted Optrode Results

May 2002-August 2002


Date	Lower Level Screened Interval (123.5 feet bgs)	Upper Level Blank Interval (99.5 feet bgs)


5/15/02	210	<1
6/17/02	209	108
7/03/02	224	NA
7/20/02	205	104
8/08/02	198	131

8/08/02 Laboratory A	210	170
11/20/02 Laboratory A	230	12
11/20/02 Laboratory B	178	9.4

The water samples collected from the blank interval indicate a high degree of variability based on the laboratory data collected on August 8, 2002, and November 20, 2002. Therefore, sampling of water in the blank casing is not a good basis for performance studies.

The results of the well-mounted sampling/analytical system samples collected from the lower level (screened interval) indicate good correlation with the laboratory samples collected on August 8, 2002, and November 20, 2002. The data from the sampling/analytical system is consistent indicating good precision.

The results of the monitoring program were documented in a report entitled “United States Air Force, Flight Test Center, Environmental Management Offic, Edwards AFB, CA, Sensor Evaluation Report For The Burge Environmental HJ-100 Automated Groundwater Monitoring System Main Base Flightline Operable Unit No.1 Edwards AFB, CA, Final” dated June 2003. The conclusions stated “In conclusion, the system is accurate and precise in measuring TCE concentrations in groundwater” and “The data appears to be comparable to data acquired from a fixed laboratory, at a substantial savings in cost of shipping, analyzing and validating the data”.

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