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<br /> Appendix A:Response to DRMS Adequacy Review No.1
<br /> ' Comment Number Comment Letter Bullet number Comment Response Section/Table/Text
<br /> 1) The groundwater evaluation provided in TRA 0 is based solely on the assumption that groundwater flow at the site
<br /> occurs primarily along the contact of the Niobrara Formation and Codell Sandstone.The evaluation does not discuss other
<br /> t potential pathways for groundwater flow,specifically fracture flow,and/or other conduits.However,documentation in the
<br /> 1- permit file indicates alternative pathways for groundwater flow may exist at the site,including: See below. NA
<br /> a. A groundwater investigation conducted at the site in 1990 by Stewart Environmental Consultants,Inc.(SEC;received on
<br /> March 23,1998)to determine whether the site could be used as a county landfill.The results of the investigation led SEC to
<br /> ' conclude the site would be difficult to permit as a landfill due to its complex geology and groundwater hydrology associated
<br /> with fracture and/or conduit flow.SEC found that groundwater monitoring at the site would be difficult because the joint
<br /> structure of the formation is unknown,appropriate groundwater monitoring would depend on intersecting saturated joints,
<br /> 1 a and any continuity of the joints could be an avenue for contaminate migration. Text has been added to section 3.2 Section 3.2
<br /> ' b. A hydrogeologic and geochemical assessment of the site conducted by SECOR International Inc.in 1998(SECOR;
<br /> received on December 11,1998),which noted that groundwater flow at the site is likely limited to the most highly fractured
<br /> zones or interfaces between geologic strata,and that estimated conductivity was highest where fractures were noted during
<br /> 1 b drilling. Text has been added to section 3.2 Section 3.2
<br /> ' The SEO certified Pond Nos.2,B and C in 2015 as having achieved the design standard for
<br /> groundwater seepage for lined reservoirs under the 1999 SEO Guidelines. Beginning in June of 2016,
<br /> Holcim submitted monthly accounting to the SEO and the Division 1 Engineer based upon pressure
<br /> ' transducers installed in the ponds and a weather station installed adjacent to the ponds.That
<br /> monitoring demonstrated that seepage rates into the ponds continued to be well below the SEO's
<br /> design standards and,in December of 2017,the Division Engineer approved discontinuing
<br /> c. While the Office of the State Engineer(SEO)initially certified three ponds at the site(mined pits with ponded water)in monitoring of the ponds.
<br /> ' 2015 as having achieved the design standard for groundwater seepage for lined reservoirs in accordance with the 1999 SEO
<br /> Guidelines,after reviewing monthly water accounting submitted for the site,the SEO later determined an augmentation plan The SEO has not changed its position that groundwater seepage from the pits"is below the design
<br /> is required for the groundwater exposed in the pits.Therefore,regardless of the low permeability of site bedrock, standard referenced in the 1999 SEO Guidelines" See Sept.21,2015 SEO letter re Groundwater
<br /> groundwater seepage into the pits exceeds the SEO's allowable leakage rates.This determination by the SEO suggests Seepage Evaluation(emphasis in original). The SEC's requirement to submit an augmentation plan is
<br /> groundwater movement at the site may be subject to a fracture flow regime. not specific to groundwater and does not suggest or imply that the SEO's design standards are not
<br /> ' being met. To the contrary,the monitoring submitted by Holcim to the SEO,and the Division
<br /> Engineer's approval to discontinue that monitoring,demonstrates that any seepage is well below
<br /> those standards. Thus,there is no later determination by the SEO that would suggest a fracture flow
<br /> regime as stated in Comment 1.c. This is also consistent with the DRMS Fiscal Year 2017-2018 SB 89-
<br /> ' 181 Annual Report which,at page 14,states"[glgroundwater monitoring to date indicates a very
<br /> tight formation with deep groundwater and little groundwater movement"at the Holcim Boettcher
<br /> 1 c Quarry site.
<br /> d. On page 2 of TR-10,the operator describes the curve/band in the hogback located in the CKD disposal area A2 as being
<br /> ' a change in strike of the Niobrara Formation deposits,representing a zone of flexure.Found within these flexure areas,are
<br /> some minor changes in dip and minor faulting(with small displacements).Fracture areas are commonly associated with this
<br /> geologic feature.Evidence of fracturing is found in the borehole logs provided for all but well MW4.These logs describe
<br /> '
<br /> fracturing present in most of the wells,and some slickensides observed in well MW-7(indicating fault movement).1 d Text has been added to section 3.2 Section 3.2
<br /> The 1998 EPA report indicated the potential for immature karst for the sites it reviewed based on
<br /> Additionally,a draft report titled Technical Background Document on Ground Water Controls at CKD Landfills,published"The presence of a soluble rock formation such as limestone(as indicated on geologic maps)is an
<br /> by the EPA in 1998,indicates the site is situated in an immature karst hydrogeologic setting in which the groundwater system indicator of a potential karst area." For the Boettcher Quarry this was based on a 1975 geological
<br /> ' may have conduit-flow characteristics.Please be sure the groundwater evaluation provided in TR-10 addresses all potential map produced at the State scale. While limestone is present at site,we are not aware of
<br /> pathways for groundwater flow at the site,including fracture flow. identification or documentation karst features in the area of the site.Furthermore,the closest
<br /> known karst features are approximately 2 miles south of the site,as documented in the Colorado
<br /> 1 e Geological Survey paper OF-12-02(2012)). none
<br /> ' The most recent work-plan to install wells at the site,which was submitted to the DRMS on October
<br /> 2) On page 3,the operator states that no groundwater monitoring wells screened similarly to the downgradient site wells 25,2012,specified the locations of the more recently installed wells(MW-5 through MW-7). There
<br /> have been installed outside of the areas of CKD disposal.Please explain why this has not been done at this site,as the data was no comment at that time as to the need for additional well other than the three specified in the
<br /> ' obtained from such wells could potentially be very useful in evaluating CKD impacts. work plan. This work plan was discussed in a meeting with the DRMS on November 15,2012,which
<br /> was summarized in Golder's November 20,2012 letter summarizing the meeting and submitted to
<br /> 2- the DRMS for concurrence.Text has been modified in section 2.2 in response to this comment. Section 2.2
<br /> 3) Wells MW-1,MW-2,and MW-3 are installed across the Niobrara/Codell contact,the screened lithology of well MW-
<br /> ' 4 is unknown,and wells MW-6 and MW-7 are screened above the contact in the Niobrara Formation.Please discuss how As discussed in section 4.1,the screened Ilthology(and depth)greatly influence the observed
<br /> these differences in screened lithology may explain differences observed in groundwater quality at these wells,if .atalf. - concentrations in groundwater samples collected from the different wells.The text in this section
<br /> 3- has been modified to make this connection more clear. Section 4.1
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