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Groundwater Professional Bulletin Board Posted: 06/26/2007 MTBE MonitoringWhen can MTBE monitoring cease? Soil and groundwater samples collected during any phase of the risk-based corrective action (RBCA) evaluation process must be tested for methyl-tertiary butyl ether (MTBE) per Chapter 135.19(455B). Testing is not required if during prior sampling events MTBE was an analyte, but was not found in any soil or groundwater samples (see below regarding detection levels). However, if MTBE was found during the previous sampling event, subsequent samples collected at a site must be analyzed for MTBE. For sites in monitoring, all monitoring wells, as well as drinking and non-drinking water wells, in the monitoring plan must be tested for MTBE, not just those that had previously detected MTBE. When MTBE is no longer detected in any of the soil or groundwater samples, analysis for MTBE can cease. Laboratories analyzing for MTBE must be able to meet a detection level of 15 ug/L (ppb) for water samples and 15 ug/kg (ppb) for soil samples. MTBE is considered not present if reported as < 15 ppb. MTBE is considered present if 1) the lab reports it as a positive quantified level below 15 ppb (e.g., 12 ppb) by using a detection level below 15 ppb, or 2) if the laboratory is reporting at a higher detection level (e.g.<16 ppb, <50 ppb, <200 ppb). Under these conditions, continued monitoring/ testing for MTBE is required. |
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