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K. Holder <br />January 28, 2002 <br />Page 2 of 3 <br />Arsenic was the •oraly metal detected in concentrations axceedinghnman-health based SROs. However, <br />with the exception of one sample (22 mgJkg in SB-9), all detections were within or below the site•specifio <br />background sage of approximately 3 to 15 nrg/kg, based on soil satrrples collected isombackgrouad <br />borings. Total chromium was detected in several samples roughly coineideat with the TPH <br />contamination in the northem half of the site at concentrations exceeding the soil concentration protective <br />of groundwater SRO and site-specific background ranges. <br />Two wells installed and aatrapled in the area (1vIW-1 and MW-3) for'VOCs, SVOCs, and dissolved metals <br />did sot contain concentrations exceeding Colorado human health groundwater standards, with the <br />exception ofbenzene, detected at 5.2-6 ug/1, Free phase pmduct (approximately 4 inches apparent <br />thicJmess) was detected in a third well (MW-2) ins~lled during this investigation near the northern <br />boundary of Subarea 3 (Attachment n, <br />Dgtr-r~nination end additional Requirements <br />is accordance with Paragraph 29 of the Order and based on the results of the SCP, the Division has determined <br />that the nature and extent of contamination in Subarea 3 wader the current conditions (i.e,, pre-mixing) has been <br />adequately characterized, with the exception of SVOCs in soils and the product detected inwell MW-2. <br />Because the detectian limits for SVOCa exceeded the industrial SROs approved in the SCP, in many cases by <br />several orders of magnitude, no deteratiaation can be made as to whether S VOCs are present in concentrations <br />exceeding the applicable SROs, However, based on the very high TPkT coracentrationa associated with these <br />samples, the Division believes that the sail is the northern half of Subazea 3 would exceed many of the industrial <br />with Paragraph 30 of the Order, or FMM may presume tfiis area "dirty" and proceed to corrective action, As this <br />axes is slated for mining activities, FMM has indicated a preference to manage and dispose of these soils as solid <br />waste during implementation of the Waste Management Contingency Plan (WMCP), To the extent that any of <br />this area is not excavated doting mining anti disposed in accordance with the WMCP, additional confiratatory <br />sampling, axd coaective action for any remaining contaminated soil, will bs required. <br />The 6outliem half of Subarea 3 had significantly lower TPH concentrations (29-1,570 mg/lcg) in soil samples <br />collected from the area, However, laboratory detection limits for the single sample analyzed for SVOCa from this <br />area else exceeded many of the industrial SROs. While the Division does sot expect soil is this area to contain <br />SVOC concentrations exceeding SROs, additional sampling and aaelysie will be needed to verify this. These <br />samples cans be eollected,dvring aPhase 2 investigation prior to mining, during mining when this overburden is <br />removed and stockpiled on site, or following mining reclamation when the material is ra-graded on site. <br />The extent of free phase product in well MW-2 must be delineated prior to training ix the northern half of Subarea ,~~ ~ `, <br />3. Therefore, an additional well (proposed MW-4) must be installed approximately 300 feet southwest of MW-2 ~ r„°,~~ - <br />and screened across the water table. This well will also serve ae a `°seatry waIl" to monitor potential movement of <br />product during mining dewateriag activities, sad must be added to those that will be routinely monitored for fluid <br />levels once devs%ater3ag commences. Mitigation of any free product encountered during mixing is fltrther <br />addressed in rite WMCP, <br />Because continued dewatering over an extended time period may significantly change the current groundwater <br />coaditiaas and potentially result fn the creation of a pertnaneat surface water body, following completion of <br />mining, FMIvI will also be required to conduct water quality verification taonitoring/aampliag. Any See phase <br />product, or surface water or groundwater contamination remain+ng in Subarea 3 above applicable State standards, <br />will require additional corrective action, <br /> <br />