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March 2003 Off-Post Quarterly Groundwater Monitoring Report

Section 2 - March 2003 Groundwater Monitoring Procedures

Off-post groundwater monitoring was performed March 10 through 13, 2003. Twenty‑five off-post wells were sampled during the March 2003 quarterly monitoring event (Figure 1.1). Thirty-five samples were submitted for laboratory analysis, consisting of 25 individual well samples, 7 post-filtration samples, and 3 non-purged samples, not including laboratory QA/QC samples. Off-post wells sampled during this quarterly monitoring event were selected based on previous sampling results and proximity to both the post boundary and wells with detections of PCE and TCE plume migration. Public and private supply wells located west and south of CSSA were selected for this event. Figure 1.1 illustrates locations of off-post private and public wells sampled during the March 2003 quarterly event. Table 1.1 illustrates sampling rationale for selecting wells based on the Plan and project DQOs. All wells sampled in March 2003 were sampled previously as part of the quarterly groundwater program. Well JW-30 had been sampled previously (December 1995 and September 1999), with no VOCs detected and was added to the March 2003 sampling as part of the quarterly monitoring program to be in compliance with the Plan.

Off-post wells sampled in March 2003 include (see Figure 1.1 for well locations):

All wells were sampled from a tap as close to the wellhead as possible. Most of the taps were installed by CSSA to obtain a representative groundwater sample before pressurization or storage and before it enters the water supply distribution system. Prior to sample collection, water was flushed to engage the well pump. While the well was pumping, pH, conductivity, and temperature readings were measured and recorded to confirm adequate purging. Generally, this required an average of 20 gallons to be purged prior to sample collection. In accordance with the Field Sampling Plan (FSP), adequate purging is determined when these parameters stabilize. During the March 2003 sampling event, three samples were collected without purging to verify that purging does not affect sample concentrations. Samples were collected from drinking water wells I10-7, JW-14, and LS-7 under non-purged conditions. These non-purged samples were collected to analyze results from water as it is used, directly from the drinking water well, and to determine if purging affects sampling concentrations.

Twenty-five groundwater samples, seven post-filtration samples, three non-purged samples, four field duplicate samples, two matrix spike/matrix spike duplicate (MS/MSD) pairs, and two trip blanks were submitted to APPL Laboratory (APPL) in Fresno, California for analysis. Each groundwater sample collected was analyzed for VOCs using SW-846 Method 8260. The EPA-approved list of VOCs analyzed for in off-post groundwater samples includes bromodichloromethane, chloroform, dibromochloromethane, cis-1,2-DCE, trans‑1,2‑DCE, 1,1-DCE, methylene chloride, PCE, TCE, and vinyl chloride. This list represents analytes which have either been detected in on-post groundwater samples or analytes which may result from natural degradation of the detected on-post compounds. Prior to the March 2003 monitoring event, CSSA reviewed the DQOs and opted to add bromoform, dichlorofluoromethane, naphthalene, and toluene to the list of target analytes due to previous low-level detections of these analytes.

The Parsons internal data package number TO 0042-#78 (group O) contains the analytical results for this sampling event. Laboratory results were reviewed and verified according to the guidelines outlined in the AFCEE Quality Assurance Project Plan (QAPP), version 3.0. Data packages were received by Parsons on April 16, 2003, and the data verification reports were submitted to AFCEE on April 25, 2003. AFCEE approved the data package on May 5, 2003.

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