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Home My WebLink About20040100.tiff � r 1 GROUNDWATER MONITORING AND MITIGATION PLAN _...4,...,..,R4,4;,),.....,„...,- ....,Y . 'dJ t FOR HEIT AGGREGATE tlyp k t- ' i ly { � k RESOURCE OPERATION WELD COUNTY =E `' " AQUATIC AND WETLAND °� , ,, .� NURSERY AND COYLE " PROPERTIES c0,.. rnn ' f ]� 3Y Y F {{ ii rAYM ,a, M �jtj� a.%' .YLM:M i4 '. 1 Y b4 Y � ��ggjyyj vv n'YA',(� YV�� x 7f -7e , r�� Rae;. 5 �Y. ,y �, i41.} 'fie W -2,14: :, } -,,,0 p - _ - 's kiS 9 .yyf bi : a ''';?:',,,,,+- ' '. p f�`" ..1 Y is w 3 ;': Jul y 2003 2004-0100 1 GROUNDWATER MONITORING AND MITIGATION PLAN FOR HEIT AGGREGATE RESOURCE OPERATION WELD COUNTY AQUATIC AND WETLAND NURSERY AND COYLE PROPERTIES Prepared by: WRIGHT WATER ENGINEERS, INC. Denver, Colorado July 2003 021-110.030 TABLE OF CONTENTS P� 1.0 INTRODUCTION/PURPOSE 1 2.0 BACKGROUND 1 3.0 PROPOSED MONITORING PLAN 2 4.0 DATA EVALUATION AND DEFINITION OF "TRIGGER" 3 4.1 Trigger Definition 4 5.0 RECOMMENDED MITIGATION MEASURES 4 5.1 Construction of Pipe to Equalize Groundwater Levels 5 5.2 Deepening of Existing Wells 5 5.3 Drilling of New Well(s) 5 5.4 Delivery of Water from the Meadow Island Ditch 5 5.5 Relocation of Nursery Stock (for AWC only) 6 5.6 Excavation of Area for Nursery Stock (AWC only) 6 5.7 Emergency Pumping 6 6.0 SUMMARY 6 FIGURES (END OF REPORT) 1 Vicinity Map 2 Heit Pit&Adjacent Features Relative to Monitoring/Mitigation Plan 3 Proposed Monitoring Plan for Heit Pit APPENDIX (END OF REPORT) A Detail of the Piezometer Construction GROUNDWATER MONITORING AND MITIGATION PLAN FOR HEIT AGGREGATE RESOURCE OPERATION-WELD COUNTY AQUATIC AND WETLAND NURSERY AND COYLE PROPERTIES 1.0 INTRODUCTION/PURPOSE This report was prepared on behalf of the applicant of the proposed Heit Aggregate resource operation in Weld County to provide a recommended groundwater monitoring and mitigation plan for the Aquatic and Wetland Nursery (AWC) and Coyle properties adjacent to the operation. The scope of this plan includes: 1) a proposed groundwater monitoring program, 2) a recommended level of change in groundwater that would "trigger" implementation of mitigation measures, and 3) a discussion of potential mitigation measures. Wright Water Engineers, Inc. (W WE) completed a preliminary evaluation of potential effects on groundwater from the proposed pit in a report entitled Groundwater Evaluation for Proposed Heil Aggregate Operation, Weld County, Colorado (March 2003). This monitoring and mitigation plan was prepared based on the findings of this previous report, a meeting with Jay and Brad Windcll (AWC) and Laura Coyle on July 1, 2003, and subsequent evaluations. Additional work may be necessary to implement any of the recommendations in this plan, and the recommendations could be modified pending more fieldwork. 2.0 BACKGROUND The Heit Pit is a proposed aggregate operation on approximately 110 acres in the E '/2 of Section 13, T2N, R67W in Weld County. Figure 1 is a vicinity map. It is proposed to construct a slurry wall around the mine area prior to aggregate removal. This slurry wall will reduce effects on groundwater levels adjacent to the pit during mining and enable the site to be used for water storage after mining. Concern was raised by property owners with possible impacts from the mine on local groundwater levels. AWC operates a nursery on land immediately north of the proposed pit 021-110.030 Wright Water Engineers, Inc. Page 1 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County .-. Aquatic and Wetland Nursery and Coyle Properties (Figure 2). Nursery plants are reportedly irrigated by sub-irrigation from shallow groundwater and by several wells owned by AWC. Concern was expressed by AWC regarding possible impacts on their operation from lowered groundwater levels due to the pit. The Coyles own land southwest of the proposed pit (Figure 2) and reportedly rely on natural sub-irrigation of a pasture by shallow groundwater. They expressed concern with their pasture drying up due to lowered groundwater levels caused by the Heit Pit. Potential impacts on groundwater were assessed in the March 2003 WWE report using the U.S Geologic Survey's (USGS) MODFLOW-2000 computer model. Model boundary conditions and parameters were obtained from USGS reports with data from the late 1900s. It was assumed that a slurry wall would be constructed that meets state standards for an impermeable wall. The modeling predicted a slight rise of the groundwater table on the upgradient side of the proposed pit and a slight lowering on the downgradient side. Approximately 2 feet of drawdown was predicted immediately north of the wall, with 0.5 feet of drawdown approximately 1200 feet to the north. and southeast of the pit. Concern was expressed during the meeting on July 1, 2003 by AWC and Ms. Coyle that more current information was not available for use for the modeling in the March 2003 study. Accordingly, obtaining groundwater measurements for updating the modeling and to assess potential impacts was proposed by the applicant. 3.0 PROPOSED MONITORING PLAN Monitoring would be conducted for three purposes: I) establish pre-mining groundwater levels, 2) monitor groundwater levels during operation of the proposed pit to assess whether it was affecting groundwater levels, and 3) provide current groundwater level data that could be used to update the modeling, if necessary. It is recommended that groundwater be measured in several existing wells owned by AWC and the Coyles and in a series of piezometers constructed at key locations. Figure 3 shows the 021-110.030 Wright Water Engineers, Inc. Page 2 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County Aquatic and Wetland Nursery and Coyle Properties locations of three existing wells that we recommend be monitored (labeled "A-C") and the general locations of seven new piezometers. Permission will be needed from the well owners to enable monitoring, and the wells will have to be observed to assess the feasibility of monitoring. The proposed locations for the piezometers should be observed to confirm access and the feasibility of construction. Piezometers will be constructed of small diameter PVC pipe with slots in and near groundwater. The top of casing will be sealed with bentonite chips. Attachment A is a detail of the piezometer construction. The minimum recommended depth of piezometers is 10 feet; it may be necessary to go 15 feet at locations where groundwater is deeper. The top of casing of all wells and piezometers used for monitoring will be surveyed. It is recommended that groundwater be measured at least monthly in each well and piezometer for a minimum of one year prior to mining to enable determination of baseline conditions. This will allow for observation of annual fluctuations in groundwater levels and estimation of normal growing and non-growing season groundwater levels. 4.0 DATA EVALUATION AND DEFINITION OF "TRIGGER" Pre-mining groundwater data will be evaluated to determine baseline condition with respect to the following at each well/piezometer: 1) Average growing and non-growing season water level, and 2) Range of growing and non-growing season levels. Precipitation conditions (e.g., average year, dry year) will be considered when analyzing the data. The growing season will be defined as from May 15 through October 1. 021-110.030 Wright Water Engineers, Inc. Page 3 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County Aquatic and Wetland Nursery and Coyle Properties 4.1 Trigger Definition Groundwater levels should continue to be monitored on a monthly basis for at least the first year of mining. starting when de-watering operations for mining commence. This post-mining data should be compared to baseline data to assess whether the operation is affecting groundwater. It is proposed to define a level of change in baseline groundwater levels that would"trigger": 1) Immediate cessation of dewatering operations, 2) An evaluation of the data and factors causing the decline in readings (to confirm that the mining operation was responsible), and 3) Implementation of mitigation measures. For the purposes of this plan, it is proposed that potential impact to groundwater will result and the above actions will be triggered from post-mining data that show: 1) a lowering of the average (growing or non-growing season) groundwater by more than 2 feet, or 2) lowering of two or more consecutive readings by more than 2 feet compared to data taken at the same time of year prior to mining. Two feet is recommended as the limit of change in groundwater since the preliminary modeling indicates that this is the maximum change that will occur and since lowering of groundwater any further could limit sub-irrigation in the growing season. 5.0 RECOMMENDED MITIGATION MEASURES The mitigation measures described in this section could be used to alleviate an impact to groundwater where monitoring data triggers a determination of impact, as defined in the previous section. The mitigation measures have been evaluated at a conceptual level in terms of feasibility. The exact measure or combination of measures used should be determined based on consultation with the affected party. The cost for construction and maintenance of mitigation measures will be borne by the owner of the Heit Pit. 021-110.030 Wright Water Engineers, Inc. Page 4 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County Aquatic and Wetland Nursery and Coyle Properties The goal of the following potential mitigation measures is to: 1) restore groundwater levels to pre-mine conditions, or 2) alleviate a groundwater impact by another means. 5.1 Construction of Pipe to Equalize Groundwater Levels Initial calculations indicate that it may be possible to convey groundwater by gravity from the area of predicted mounding southwest (upgradient) of the proposed pit to the north onto AWC property where a small lowering of groundwater is predicted. Smooth wall pipe (at least 6 inch diameter) would be needed, and the pipe would have to be carefully constructed to maintain adequate slope. Initial calculations indicate that insufficient slope will exist between the southwest corners of the proposed pit to the Coyle property to permit a gravity pipeline. 5.2 Deepening of Existing Wells AWC owns several wells that are reportedly used to irrigate nursery stock (Figure 3). These wells could be deepened or other improvements made (e.g., new pipelines), if necessary, to increase their yield to offset lowered groundwater. Existing wells on the Coyle property could also be improved. 5.3 Drilling of New Well(s) A new well or wells could be constructed on AWC and/or the Coyles to provide additional water, if needed. 5.4 Delivery of Water from the Meadow Island Ditch The project applicant owns shares in the Meadow Island Ditch, which flows to the west and upgradient of AWC and the Coyles. Water from this ditch could be delivered via new or existing laterals for flood irrigation of either property. 021-110.030 Wright Water Engineers, Inc. Page 5 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County Aquatic and Wetland Nursery and Coyle Properties 5.5 Relocation of Nursery Stock (for AWC only) Nursery stock that is currently sub-irrigated could be moved to the north further away from the area of potential influence from the Heit Pit. Preliminary modeling shows that the extent of drawdown north of the proposed pit becomes small (0.5 feet or less) approximately 1,200 feet north of the pit on AWC property. 5.6 Excavation of Area for Nursery Stock (AWC only) An area could be excavated on AWC property to enable continued sub-irrigation with slightly lowered groundwater. 5.7 Emergency Pumping If necessary, water from the pit could be pumped to meet an emergency need (e.g., to maintain existing nursery stock). It may be possible to use the existing lake north of the Coyle's house for this purpose on their property. 6.0 SUMMARY The preliminary groundwater evaluation completed for the Heit pit found that only relatively small changes in groundwater levels are possible from the operation due to the presence of a slurry wall. However, it is recommended that the groundwater monitoring program in this plan be implemented for the adjacent AWC and Coyle properties. Groundwater measurements from the plan can be used to determine pre-mining conditions,post-mining levels, and for updating the modeling completed in our March 2003 report. If groundwater is lowered by more than 2.0 feet compared to pre-mining conditions by the operation, this will immediately trigger: I) Cessation of de-watering operations, 021-110.030 Wright Water Engineers, Inc. Page 6 July 2003 Groundwater Monitoring and Mitigation Plan for Heit Aggregate Resource Operation—Weld County Aquatic and Wetland Nursery and Coyle Properties 2) Verification that the lowering is due to the mine, and 3) Implementation of one or more mitigation measures to alleviate the problem. The specific mitigation measures to be used should be decided with input from the affected landowner. Also, additional monitoring should be conducted to assess the effectiveness of the mitigation measures. C\PP.U2I-11 U:LL3!mds`.I IFIT PLAN.AWCdoc 021-110.030 Wright Water Engineers,Inc. Page 7 July 2003 Figures M F�` ` awe ii 'i I.. - P y I°P°A ;1 _tr.T � 7. r. __1. -_- - .$ [ }a;t, ' ,,[: ' 1 v I ° - y . I o r. v [ 1 one v-__ 4 (/9 I PROPERTY ._ BOUNDARY a c 1�_ .: i. .Ns \\` It fl / .--I50, 1 \t ` I[ '4•v ] ..:f; la I' , VOLLMAR ,:: 1 v . ,1a 85 I 1 ,,r -C f r' ,: Q o I '' ♦ x44 ,+ i.. in l..... .. \,,, ,. s 19 76. �, I .c 1 \ j •ti I 1 v' I \ .. 1 I • I r . L L 0M •2 'Slphp' Flume A 0 ,2000 Feet 24 __ ; y e d •14867 _� 1-=2000' 'j'-' ` ; ' • � _HRISN UJ'021-11NHNI PI APH I1.1.x. �.. •, HEIT PIT FIGURE WRIGHTWATER ENGINEERS,INC 24ICINITY MAP 1 2490 W 26TH AVEAV E. 100A DENVER,CO.80211 (303)480-1700 I -'q " ' 4 O F --e4'4" ', I � x <a � ;Lam,;,. t Yr n,5� i�•i a AWC .F / UFt ERY • / rI� . ! F . i N© Y' r - r • ..t I . z 4 , ' K • L'l '•fig' \ - ‘ L... V . , . . is 4 1 ` ,trA �"'' ' _ k yy, T' t/ «� t6 y" LAKES 1 .n ', 1. I ---"-- 81'd ' . •e�,R i om �.�n'. FA s. NIG I _ , , ( a '. SPIT ..� 4�14 r? LR :ran 6a�. J .� � .. I CV } . X1 �) CbY ,r \„ i . -ROPER' b ' 44 a s 0 1000 Feei rLa _ A °- 4., F n 1..-1000 ! D- ` * ` �. 01 N --� �� HEIT PIT & ADJACENT A f i . FIGURE IWRIGHT WATER ENGINEERS,INC, FEATURES RELATIVE TO 2 2490W 26TH AVE DENVER,CO80211 MONITORING / MITIGATION PLAN DENVER,C.O.80211 (303)48(-1700 I iS .r y;'5a. e i 'f 6 ��y� '. fAY 3 . ' 3:x Photo 3. Closer view toward South Platte River looking across CR 25 east of Heit Mine site. Note oil and gars Iarili f; r ility adjacent to riparian habitat and agricultural land between road and river. .. • yr m;. t+ f : i. tk: �r/e 'er ,j."-'. !" }1 y 446',..I ' 'ar r't:It P F .S';4 t tW •�' }N r L�r te `41 y /u N j; ..,' ../.'',:' ‘I>N U s.' � i1 x r ,� r:„43.):A t w r r' i r P '' ✓ �' •c c i 3 ie xF)s� er -Lr Y; � [r,.x3 �yh` �/ r{. , /, . f e `I f :, r. ^tv 'J11� .ar9! R (eir .eO.1 A k sr •(1 \�• �� eq�t !.."..4' ihr_5�r !�),s�� tl1.e� k.r �rJ�.��1+ � ,!'� �/ t .. r •r r,: ;, i7.-i a el A'yts. y:1 ,."yLi,t igl•wT .;. y�Vy ✓ „.:4.1,,,„_,+ . .� ,.. 'e f4Tl . ..#1,..-t- �. r l V.. rMr ._A ! / �tser L,t),-....,,) ,,,z-,..,) ,z S ,4s,--: 71,-,7z � k,�+/ t ; :Li corridor f.- ?, a" �! r � ,.�- _ft 1+' t�•A► .•►'. . .2: .-: ... ', -' ti 1TS4. ;tom NwtM� +�' '•>"!1' 5•+.Mi Mixf}�'`t n•.• '•• '177^ f wh ��t Ai - ,•l'. .� drllre ^87� `g'Fa ...-414,744.''71:4-04.1,„."^"q.' "� r �+ �k , 1 'i 5 s. `•. p . •••t .,;.,rt sr tK •. rf ll ' • ,. ` , , i p i -t �� 1i ti 3 t zay '4 r{� 5 o ay { J 51! x'i + _Zr !. ;} Al •5 �f, .' �, yf7 i e • ,•':•-•"*" ;,, r.,1••.r..t-' ..!b. a .•.' �5 7_lf5r 4..' • •., '',..;e2,,� • a.•$:!! S'^ '"} 1"q)ti -.+a ° t1 {1f+j11!".''�� . wi t+ .r' r•-• ��•' ' 'r.'I• •'ill • ;V li p 1p5r - 1 - .e. • • tit..:• f w`-�` +' ••••••);- -it ;' :-..,-. ••.6,1-. . ,. - ,-•• ..- , ••.. 1 * ' _• ! ie.^.•':,•.•-.#1-4,—* `.!t 'L. r i 5' • ;; .:Arc; r•Y,T. t. . r 4 x• i7"-t ' .'t 14.''-iit. ` . r *. 14 '••` .r.�1.L c '.c;, t •, •L...c , _: t1 . .' :• ....\Sl: t M.. ..r..+4...„ ' Y t �� •• '•'•. •.I' ",J 1 ".'J.1K '�+' 1 jot 1 33• �'b '':i {�.eye `.jr' �'. ..• r. •• - 1 • . 4•x. // F 1 t ! .lL� 1'.< •l l� cL i p)) .'� ' s 'll' a r y • • x {r1.lk .-'!, :. ,-, 1p 1','u' s!Y .+$d ��1 `.it?. . Photo 5. View to northwest across wetland complex west of onion fields in western portion of Heit Mine property. Note mosaic of herbaceous wet3ard plants with scattered large trees (cottonwoods and green ash). This mosaic would not be affected by proposed sand and gravel mine. b - "7i t: -w .•,a, qr•S..«. .. ,+.•1 r L w.. .-4,...,, • .,'a%J!'P5.'1".•;<++i` ,tz : • . -.""*;','..-,,,71.- .�.... . 4Y,4k.„.yam.:l,'.. `t'" 3 s ',4 C ,I • • :1 :T...;4`;;;;.,.11..-1.4 •Q w ]�' ' y •t `�.' ' f ....: r �"'s Ifl,; . !•,;.t'.S• '•••e.•;1. . --y`'•' lit • t .l * • .ra•' `-s 4.•'.. •t,lr a \?R y' .,' ',.;'••• t; 474: k rr�y�t r}f * !.?'',,,t•.y ,'"4 , 1 '.714,...:•••411!..4...q.- • t t -• '•, r".. t !C ••ti toter i iL v f ri'�4 II itL~ ,:h"<,', ' i 9 l ^ 1. i. ^",'11tyi ,y t ' ''. a. r 1 1 .1 a # ' �) y • •• �•." ti, w, t 1,1 .,_ ....:,,:_,,,.,.„, .:.,., •'•.....,y.4"-_ ; ,... ... .... .,......,,.....,:,..„ .,...„...,.: ,..4„.„.,,. ....\:_, . 1' ` li, f., . .`. ,A '11• t�( u\,�. 1'. ,d4 - , .;,.........;:...,:.• -.s ,.-..,;,!,1- d, 2`: ,..1'...,--•. �' ..` -vr. r-y<w.,..' ••''''. F ' .!e.':cfv'•+ 1% h2......„,-4,-„,47.,,,,,-.....,;,.„.,...-.....;',.t -,,,,A.'14'.. ..-4-,,.....- • ti sN ,f `s p: - • 1 fc ft ,,..�, y�l ei r.1 .;�t•,.•" '�'� ,� •a Wp�.w• ;• Y _ J •� 1.-2 „f a:.-_-'f- --,...:-..•:-.N....1.•"• ...AL:.. Vii —'£ , 1, Photo 6 View to southwest AMISS wetland .;rrinplev. from :,tj . , . : . . :,; : Note rich mosaic of herbaceous wetlall(3 and wets i ri-mfirgir• . 1• ,i,, •i••;• absence of willows t;t Other -ip:triir: shrill).; .,:,. M y '5,..<:;fl k"'+.4 .+L.f ....+ Can M L 11 Ta a rYyL ,k .;; Photo 7 View to north along farm road between western sedge of Onion field frighti and eastern edge of wetland complex {lefts Marrow strip <,f xer+c >nland in loft or fence supports ci small colony of °lack-t.i; c•c' pr area' Itogs Praine ;jog., a1`,•: occupy wider xeric area west of wetland complex along rNester site boundary_ r ':tea va t.. . ,,Y, C Q A- M.gi rf /' ~ ,• .. +. 5� ara t �$k ti. .4 Y r i 3 • r Nr Photo d Vievf Lr ,,rth at southw< •_tern .r nn-, ;:t c.,1-J. ,no., 'ail MP 71'I-fh : ice: r Ditch r Y. r r,r No r- it ut thro..gh so 1 -westr e: �1etlar' , ,"It�t dr Ury Photos 5 through / extends northward fr_,rn ditct. Noto car roa: : rUh< r .2,1 .aita ' bulrush and seed canarygrass plow) hank- .if ditcr. • 3, f r � , e. u ,,,!;:4•74i-,•'; '� y. 5 ' • • } F .Ate• 6y�rg • • .: C `. ' K\ � •e i a •` , j r: , A8 '\ a ,b4 .y I, t ${ 6, E y 1.11,I,:*.: ..; Na. f 'd 0-Y, 4 & •' e••.$. I,• IAu r A . 1. , a y �, '! : k 0- .� dk Qr� F ,� f I x.� 1 Z.YJ✓ S� ..•_ �' a... \'r • M1 t.,• N 4-1.i; 'K 7* x .Wy . . (7 ,.'.4w•a a 0 1000 Feet 't EXISTING WELL TO MEASURE ,,t,,,-,-,r' = 1000 NEW PIEZOMETER ' a N ■ •ILS•IW PROPOSED MONITORING PLAN FIGURE I 1 WRIGHT WATER ENGINEERS,INC. FOR HEIT PIT 3 2490 W 26TH AVE 100A DENVER,CO 80211 (303)480-1700 Appendix .1 0 0 J TOP OF CASING ir J-CAP VARIES ) GROUT OR CONCRETE TYPICAL 12" TO 36" � TYPICAL 6" DEPTH GROUND SURFACE I \ \\ �\//\// /%/�% .\.//�i 7 /V / /\/ A - _I \„„ t, , , ", _ ___ /\ - \\�\j�\j�%j j - J, _ _ _ BENTONITE CLAY SEAL A - -= -� _ 2" PVC RISER PIPE ( _ NATIVE - - (TYPICAL) GROUND J ,_ - �- - - - UPPER PORTION LOWER PORTION ± 2 FEET �-. 1 ADDITIONAL SAND PACK _ ABOVE SCREEN a r COARSE GRADED I ± 4 DIAMETER 0.- I SAND PACK BOREHOLE j` . 10 FEET HORIZONTAL 0.010" .... SLIT SCREENED INTERVAL 1 1 I + END CAP t 4 TYPICAL VARIES WITH NATIVE GROUND COMPETENCY I AND REQUIRED INSTALLATION An - TOTAL DEPTH PENETRATED I FILE: PIEZO-1,DWG DETAIL: TYP. TEMP. PIE2OMETER WELL DETAIL NO. XXXXXXXX DESIGN: EFM DATE: 9/8/98 SCALE: NTS XXXX: X , DRAWN: EFTA Hello