joint groundwater report - Texas Commission on Environmental ...

29 chemical parameters. Subsequent samples were taken quarterly, semi-annually, or annually, as required inthe facilities’ permits or by the GWMT, and were analyzed for an abbreviated number of parameters. Sitesthat closed prior to the October 9, 1993, or April 9, 1994, deadlines are presently following theserequirements during their post-closure care periods.The RCRA Subtitle D <strong>groundwater</strong> monitoring requirements are phased in for active landfills based onproximity to the nearest drinking water intake (including any surface water intake, domestic well, publicwater supply well, etc. utilized for human consumption). These requirements include the following: athorough <strong>groundwater</strong> characterization study; an approved certification of the site's <strong>groundwater</strong> monitoringsystem; an approved Groundwater Sampling and Analysis Plan (GWSAP); a modified and expanded list ofanalytical parameters including 47 volatile organic compounds; at least four background sampling events[depending on the statistical method(s) utilized]; a semiannual sampling schedule during detectionmonitoring; and, statistical analysis of <strong>groundwater</strong> analytical data. An annual sampling schedule may beallowed under certain conditions.Prior to the Subtitle D rules, when <strong>groundwater</strong> analyses indicated a departure from background or historicallevels, or if other evidence of possible contamination was present, the GWMT required re-sampling ofexisting monitor wells, often including additional analytical parameters. If further investigation indicatedprobable contamination, the permittee was required to initiate a remedial investigation, potentially leading tocorrective action and/or remediation.Under the Subtitle D rules, the permittee conducts background monitoring as prescribed in an approvedGWSAP. Upon completion of background sampling, the permittee is required to conduct detectionmonitoring sampling and to initiate statistical analysis of the <strong>groundwater</strong> analytical data and to continueperforming statistical analysis of the data in subsequent detection monitoring events. If statistical analysisindicates that a statistically significant change (SSC) in constituent concentrations has occurred frombackground concentrations, the site must notify the TNRCC of the SSC. The facility may resample toconfirm the SSC and/or demonstrate within 90 days of the notification that the SSC has occurred due to asource other than the landfill. If the demonstration is not satisfactory, the owner/operator becomes subject tothe requirements of assessment monitoring, which includes analysis for an expanded list of constituents. Ifone or more assessment monitoring constituents are detected at statistically significant levels aboveestablished <strong>groundwater</strong> protection standards [which could be maximum contaminant levels (MCLs),background concentrations, or health-based concentrations] the owner/operator must initiate an assessment ofcorrective measures and must characterize the nature and extent of the release. At this time, the facility willbe added to the list of MSWLFs with known <strong>groundwater</strong> contamination. After the assessment of correctivemeasures and before the selection of the remedy, the permittee is required to conduct a public meeting todiscuss the results of the assessment of corrective measures with affected and interested parties. This, in turn,will lead to the selection of the remedy and the implementation of the appropriate corrective action/remedialaction.Status of Groundwater Contamination. Approximately 3,900 samples were collected from all the wellssampled in 1997. Groundwater contamination has been confirmed at the 26 MSWLF sites listed by county inTable 1 under the heading "MSW.” Of those 26 sites, contamination has been found in approximately 144samples from an estimated 69 monitor wells. None of the 26 contamination cases are new and none of themrequired the notification of local officials under <strong>Texas</strong> Water Code, §5.236. Two sites listed in the 1996<strong>report</strong> were removed because actions were completed.41