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O H-At 56 t R t INN 5 <br /> OSlvll contracted Geosy ntec Consultants to provide a list of regulated constituents in groundwater <br /> according to Regulation 41 The Basic Stcntclarcls'/or Grozm(l 1i acr 41.5 (C) (3) Interim Organic Pollutant <br /> Standards("I able A - Ground Water Organic Chemical Standards). Geosy ntec reviewed Table A in <br /> Regulation 41 for a list of analvtes that might reasonably be expected to exist in GW-4. In general, <br /> pesticides «ere evcluded as they are not expected in historic contamination and not expected in drill-rig- <br /> fluids. (ioesy ntec', recommendations are presented in Attachment 5. GW-4 was sampled by Purewater <br /> S\stems of Ridgway, Colorado on three separate dates(April 21. June 3, and June 17) for the Geosyntee <br /> identified constituents. Samples were sent to ACZ Laboratories in Steamboat Springs, Colorado for <br /> analyses. The ty\o June sampling dates included duplicates. Results for these analyses, discussed below, <br /> are summarized in .Attachment 2, with laboratory reports in Attachment 3 and field notes in Attachment T. <br /> Nearly all the constituents identified by Geosyntee as having a potential presence in GW-4 were non- <br /> detect in all analyses. Constituents that were detected include DEHP and di-n-butyl phthalate, both <br /> detected below the method Practical Quantification Limits PQL (Tables 2 and 3 of Attachment 2)or <br /> below the groundwater standard for the constituent. Di-n- butyl phthalate ryas only detected in one <br /> sampling event. DEHP was detected in 4 out of five samples(including duplicates). DEHP results ranged <br /> from non-detect(with a detection limit of 3.8 µg/L,above the lowest standard of 2.5 µg/L) to I I µg/L <br /> (below the lab PQL of 18.6) with an average of 8.1 ug/L. While DEHP has a groundwater standard of 2.5 <br /> u,,/L, it is a ubiquitous plasticizer and a very common laboratory and sampling contaminant. Regulation <br /> 41 provides specific direction for cases when a standard is below the PQL T1.5 (C) (4): <br /> "117tcncl•cr tlrc EYructical ytruntitcttion limit, or POL, tor•crl)nlltttunt is hlghcr (less .cirirlgC171) 117ct1t u <br /> �lcntclurclltslccl in szrhscclion? or 3 above, the POL shall he ucccl nt rc;,ulutrrr ,l attic urJhzJirs POL'r <br /> rout'he cNcthlishccl fir the crh/zlicuhlc ugcrtCV ut-in con.ctnc(rtiurt irtlh the 11 iatcr(hrctlitY <br /> Control Divi7 ion " <br /> Water Quality Control Division (WQCD) Clean Water Policy 6. Practical 011antific•ation Limits, <br /> provides a PQL of 25 µg/L for the WQCD approved analytical method for DEHP. The policy <br /> also provides a minimum PQLs of 3 µg/L (above the groundwater standard of 2.5 µg/L) for a <br /> method that has not been approved by the WQCD. ACZ Laboratories only performs the WQCD <br /> approved method (EPA Method M8270E, Semivolatile Organic Compounds by GUMS). Given <br /> that the \VQCD approved method for DEHP analysis has a WQCD PQL of 25 µg/L, and given <br /> that =41.5 (C) (3) states that when PQL is less stringent than standard the PQL shall be used in <br /> regulating activities. the estimated detections of DEHP in GW-4 fall below the regulatory <br /> threshold despite being above the interim standards presented in 41.5 (C) (3) Table A. <br /> Because DEHP was detected above the interim standard, but below- regulatory thresholds, OSMI <br /> proposes to plug and abandon GW-=4. <br /> Cessation of Visually Contingent Monitoring at SW-22 <br /> OSMI has performed monthly sampling of SW-22 for DRO on a visually contingent basis to evaluate the <br /> potential for organics impacts in Sneffels Creek under the sheen rule(TO CFR 110). No sheen has been <br /> observed in S\V-22 (Attachment 4). and therefore no laboratory anal\ses have been run. OSMI has <br /> notified the division of these results by letter. <br /> 21 <br />