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September 2002 Off-Post Quarterly Groundwater Monitoring Report

Section 2 - September 2002 Groundwater Monitoring Procedures

Twenty off-post wells were sampled during the September 2002 quarterly monitoring event (Figure 1.1). Twenty-seven samples were submitted for laboratory analysis, consisting of twenty individual well samples and seven post-GAC samples. Off-post groundwater monitoring was performed from September 16 through September 20, 2002. 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. 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 September 2002 quarterly event. Table 1.1 illustrates the sampling rationale for selecting wells based on the Plan and project DQOs. All wells sampled in September 2002 were sampled previously as part of the quarterly groundwater program. No additional wells that would provide data in support of DQOs were identified for testing this quarter.

Off-post wells sampled in September 2002 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, the 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. Field notes, including well purging data are included in Appendix C.

Each groundwater sample collected was analyzed for VOCs using SW846 Method 8260B by APPL Laboratory in Fresno, California (APPL). Samples for NAPs analyses were also collected from selected wells during the September 2002 event. Methane, ethane, and ethene (MEE) were analyzed using method RSK-175; chloride using method SW9056; dissolved organic carbon (DOC) using method SW9060 by Severn-Trent Laboratories (STL) in Arvada, CO. Also analyzed were volatile fatty acids (VFAs), phospholipid fatty acids (PLFAs), and dissolved hydrogen (DH) analyzed by Microbial Insights in Rockford, TN. Twenty-seven groundwater samples, two field duplicate samples, two Matrix Spike/Matrix Spike Duplicate (MS/MSD) pairs, and three trip blanks were submitted to APPL. Twelve NAP samples were collected and submitted to STL and Microbial Insights Laboratories. The Parsons internal data packages TO 0042-#36, #37, #38, #39, and #40 contain the analytical results for this sampling event. Laboratory results were reviewed and verified according to the guidelines outlined in the AFCEE QAPP, version 3.0. Data packages were received by Parsons October 10-17, 2002, the APPL data verification reports were submitted to AFCEE on October 30, 2002 and November 8, 2002, and AFCEE approved these data packages on December 5, 2002.

2.1 - Introduction to Natural Attenuation Parameter Sampling

CSSA has initiated a program of periodic NAP monitoring for both on-post and off-post groundwater sampled under the groundwater monitoring program. Analytes will be sampled that help to determine whether natural attenuation is a viable remediation option at CSSA. The September 2002 sampling event was the first NAP sampling event for both on-post and off-post groundwater monitoring. The Annual Groundwater Monitoring report to be prepared for CSSA will provide additional interpretation of the NAP analytical results from the September 2002 event. Additional reports which incorporate future NAP sampling events will interpret changes in NAP data over time to evaluate whether natural attenuation is a viable remediation option for CSSA.

Natural attenuation is a combined product of several mechanisms, classified as either destructive or nondestructive. Nondestructive attenuation mechanisms include that of volatilization, sorption, dispersion, and dilution from recharge, while biodegradation is the most substantial destructive mechanism. The determination of whether groundwater contamination presents a significant threat to human health and the environment relies upon an accurate estimation of the potential for natural biodegradation to occur. Evidence to scientifically establish that degradation of contaminants at a rate protective of human health and the environment is occurring must be used. Three general lines of evidence that can be used are:

1. An observed reduction in concentrations of contaminants downgradient of the source of contamination;

2. Analysis of chemical and geochemical analytical data, including that of decreasing parent chemicals, increasing daughter chemicals, the depletion of electron acceptors and donors, and the increase of metabolic byproduct concentrations; and

3. Microbial data to support the development and rate of biodegradation.

The continuation of NAP on- and off-post groundwater monitoring program, with a subsidiary objective of assessing whether there are apparent trends (decreasing or increasing) in contaminant levels over time in the sampled wells, fulfills requirements needed to obtain the first line of evidence and the majority of the second. Parameters specific to natural attenuation are needed to trace the depletion of electron acceptors and donors, and the increase of metabolic byproducts. Microbial data, in addition to the standard parameters included in the monitoring program are needed to obtain the third line of evidence (Wiedemeier et al., 1996).

2.2 - Natural Attenuation Procedures and Analysis

Twelve off-post wells were sampled in conjunction with the September 2002 sampling event for a natural attenuation study. Off-post wells sampled for this study were selected based on previous sampling results. The study focused on the wells with historically higher concentrations of contaminants, primarily chlorinated volatile organic compounds. Groundwater was tested in a temporary field analysis area created on-post, immediately after sampling, for parameters that could be analyzed with sufficient accuracy and reliability while still utilizing field procedures.

Parameters requiring specialized procedures were submitted to STL and Microbial Insights Laboratories.Parameters analyzed for in groundwater and submitted to STL included: methane, ethane, and ethene (MEE) using method RSK-175; chloride using Method SW9056; dissolved organic carbon (DOC) utilizing method SW9060. Volatile fatty acids (VFA, method 8015M), phospholipid fatty acids (PLFA), and dissolved hydrogen (DH) were analyzed for in groundwater samples submitted to Microbial Insights. The analytical results were reported to Parsons and were reviewed and verified according to AFCEE guidelines. Table E.1 summarizes off-post NAP laboratory results. Detailed descriptions of the various NAPs and their purpose in evaluating the occurrence of natural attenuation are provided in Table 2.1. 

Field analyses included that of alkalinity, carbon dioxide, ferrous iron, hydrogen sulfide, manganese, nitrate, nitrite, and sulfide utilizing the Hach testing methods of chemical-specific test kits and spectrophotometry using a Hach colorimeter. Standard solutions were made weekly and checked daily against all field procedures. Direct readings were taken immediately prior to sampling each well location using a YSI digital water quality probe. Readings included pH, conductivity, redox potential, dissolved oxygen, and temperature. Field NAP results for off-post wells are summarized in Appendix E, Table E.2. Further interpretation of the NAP results will be incorporated in the Annual Groundwater Monitoring Report to be prepared under TO 0042, as well as future Annual Reports including future NAP results.

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