Table Of Content

BEST COPY AVAILABLE MISMO STATEMENT Pon Be meee fk Hung of ame Managemen ic susie the host Grecrety ane Prodanm h 6 tt pei umd ter Tac wer amd Chee RCR of frewctr anc future PONCRAT t y teeS s m BLWMY P L _-03/004+ 1310 RrmeeE BLANK PAGE Chapter4 BEST COPY AVAILABLE iSO ee. Sie ten Sate ea BLANK PAGE ee ee eee comsequences) that sould rowull ‘vom impiementapon of the Proposed AL nee and alternatwes Aa cowwonmencs! cffect of comsegucnce ss defined » 1 modficanon of change m the CUsimg cmv ironment brought adout Oy the achon waken Effects can be dorect. mderect. or cumulamwe and can de temporary (short term) of perma(nlocng ntetrm ) §f feccatm svar y m degree. ranging from only a shgit drscernabic change to 2 drastx change wm the environment. For the ES. short-term cffects are defined = occurmng dumng the construchon and driling compiebon phases Long-term cffects are Caused by construchon and operaions that woukd remas. Songer The analyses cvaiuated the cffects that would occur m the Proyect Arca. regard- tess of land ownersiup However. the diecrssoms on thes proyect by the BLM and FS would apply only to federal lands [he effects reported for non- federal lands may occur regardless of the BLM ami FS decrssons. Effects on non-federlaanld s are included to provide a full disclosure of effects for the compicte proyect and to support other environmental permitting associated with the proyect Groundwater Dumnng development of CBM. a pornon of the water contained in the coal aquifer is removed from CBM wells as produced water The pnmary effects on groundwater resources would be associated with the removal of groundwater stored in coal seams and the subsequent recharge of aquifers through infiltranon or injec- ten of producweadte r The combined effects of coal miming and other existing or reasonably foreseeable conditions on groundwater resources also are descnbed witthhisi chnapt er The effects of development of CBM on groundwater resources would be seen as a drop in the water level (drawdown) in nearby water wells completed im the developed coal aquifers and underlying or overlying sand aquifers. Drawdowni s observed when a loss in hydraulic pressure head occurs in the developed coal aquifers or in the overlying and underlying sand aquifers. The hydraulic pressure head 1s the vertical distance between the water level in a water well and the top of the confined aqurfer in which the well ts completed. Partial removal of groundwater from a coal seam (through coal miming opera- hens or development of CBM) would reduce the hydraulic ~wressure head and create a hydraulic gradient toward the weil or excavation. There would be a pro- gressive decline in hydraulic pressure head with time and distance as groundwater flows into a pumping well or excavation. The effect: wobue selen das p ro- gressive declines in the water level (drawdown) within nearby water wells completed in and near the developed coal aquifers. BEST COPY AVAI4L] ABLE PRB O) & G FEIS a A RR er ce 7 - — Gay ¢— Gee Cenge Leakage of groundwater ‘rom undertying and overtyimg units into the Coal aqui fer would smate recovery m scarby water weils completed in the Coa! aquifer Recovery would comtmuc a CBM produced water that infiltrates the surface reaches the sand and cosi apufers However. contumued leakage of nfiltratcd produced water from owertving and underiving sands into the coats would detay notceattc recovery of the sands uni removal of water ends Water levels on acarby water wells would De cxpected to recover after removal of water ends The rate of recovery mnaily would be raped because of the re-cquilibranon of pressure heads within the coal and leakage from overtving and undertying units The rate of recovery m the coal and sand aquifers would decrease progressively dumng the recovery penod as the enhanced infiltramon of produced water de- ches Other potennal effects on cxsting water wells ‘vould include changes in water yield and quality or methanc emissions Other cffects on groundwater resources would consist of potential changes im groundwater chemistry. in the nature of groundwater discharge w the surface. or recharge to the aquifers The natureo f groundwater discharge > the surface as spmngs. seeps. or base flows of surface draumcoauldg cehasng e Surface discharge of evtracted groundwater from ( BM operations into surface dramages. flow-through stock resernons. upland or bot tomiand infiltranon mmpoundments. or upiand containment impoundments « ould enhance recharge of shallow aquifers below creek and impoundment areas |njec- non of CBM produced water would recharge the aquifer units in which the inyec- hon wells are completed. Overview: Regional GroundwatMeodre ! Hydrogeologic Groups A detailed descnpnon of the geology and hydrology of the area is provided in Chapter 3. This analysis focuses on the coal seams of the upper part of the Fort Umon Formation, the sands of the ov_riying Wasatch Formation. and the ailu- vium that underhes surface drainages. The Wasatch Formation 1s exposed at the surface over most of the Proyect Arca and overlies the Fort Union Formatnon. The Wasatch Formation consists of fine- grained sandstones. siltstones. claystones, and coals. The sandstones tend to be discbout anre utsedi locnallyu foor wauter ssup ply Coal zones generaalrle yno t economic for miming or development of CBM. except im the area of Lake De Smet near the western margin of the PRB. Siitstones and claystones typically are of low permeability and form hydraulic confining units (or aquitards) within the Wasatch sequence. The Fort Umon Formation consists of coals. sandstones. siltstones. and claystones. The coals of the upper Fort Umon Formation show great vamation in thickness and continurty over the PRB. Coal seams spiit and merge over dis- tances of a few miles so it 1s more approprate to consider the coals as part of a hydrogeologic group rather than as individual aquifers. The upper sequence of Frt.e* e PRB O & G FEIS 42 Guy ¢— Gee Cage geologic groups defined on "+ hasss of the straneranine correlane:. of Coal seams (GoFionieyt. ansd Asbsociyates. 200 0). All four coal groups can be idennfied im the northern part of the PRB. Groups |. 2. and 3 merge to form a thick coal unit, known as the Big George. in the central pornon of the PRB. Only Group 4 1s prevent in the southeastern part of the PRB. where « ss locally known as the Wyodak coal. The outcrop areas of the coal seams are charabcy tthee prreseincez oef dhigh ly permcleinkear tbhati focrms a rechareaa fror gthee co al. Assumpfotr iGroounndwsate r Recharge to groundwater aquifers occurs from direct infiltranon of precipitanon (ran and snowmelt). runoff in creck valleys and standing water in playas. Infil- trahen is si uficamt im areas of more permeable surface geologsc units. wach as sandstone or the clinker that occurs in outcrop areas of the Fort mon and Wa- saich Formanons. Direct infiltranon of preciprtanon provides a minimal vource of recharge over most of the area because the climate and surface features prohibit vigm ‘icant infiltranon: Earty (pre-mine) data on water levels indicate that hydrauln gradients for the coal and clinker are steep near the outcrop with highest potentials in the clinker. suggesting that the clinker provides recharge to the coal Howevthee rrat.e o f recharg: from the clinker units to the coal 1s often limited by a relanvely jow- permeability. clay-mch zone that typically occurs af the contact between the clinandk tehe rcoa l. Infiltranon of surface water in creek valleys 1s considered an important sourcc of recharge to the undertying alluvium and the shallow bedrock aquifers A USGS study of two ephemera! dramages in the southern part of the PRB indicated stream losses of between 0)4 3 and | 44 acre-feet per mile from individual storm runoff events (Lenfest !987) and these values were acknowledged to be underes- umated. Recharge to shailow aquifers from stream valleys ranged from } 56 to 26 $ acre-feet per mile for individual storm runoff events in the same study Re- cent studies of the losses of surface water in several dramages of the PRB that receive CBM produced water during dry weather indicate that conveyance losses range from 64 percent to |00 percent of inflows (Babb |99%. Meyer 2000bA.HA 2001b). Conveyance losses include both cvapotranspiratioen and leakage into alluvium and bedrock that underlie the streams FEv apotranspiranon vanes seasonaily. but probably accounts for less than 20 percent of the conveyance losses over the course of a year A monthly water balance caiculanon for the Wild Horse Creek dramage found that cvapotranspiration accounted for |8 percent of the conveyance loss associated with the surface discharge of CBM produced water within the dramage basin (HydroColnsoultganits ci nc. 2601) Rechofa srhalglowe a g- uifers through ieakage from rivers or streams probably accounts for more than 80 percent of the conveyan|coevs . Discharge of CBM produced water to surface dramages was assumed for this analysis io result im a 20 percent total conveyance loss, of which 82 percent 43 PRO 4BG F EIS a "°° ~ ——— would be caused by infiltranon and |8 percent would de a result of ¢. apotranspiranon. These values are considerably lower than were demvcd in some studies of surface water losses m several dramages of the PRB (Lenfest !987. Babb |9 98. Mever 1000b, AHA 2001b) and represent a net recharge to shallow groundwater of just over |6 percent of the water produced. Higher values for convevancloes s would correspond to unsaturated stream channe! conditions Perenmiail flows hkety would be associated with the surface discharge of CBM produced water and would create saturated stream channe! conditions. Lower values for conveyance loss would apply to saturated conditions. This analysis assumed that water discharged into infiltranon ompoundments would result in 85 percent of the total volume cv aporating of infiltrating ato the shallow groundwater system (28 percent cvaporation, $7 percent infiltranen) Fifteen percemt of the total volume discharged into infiltration impoundments would resurface and contnbute to surface flow This estimate of infiltramowans used in the analyses to ensure that the environmental effects that could result from substantial infiltranon of produced water are Considered in the ground ater mode! analysis, This anatysis also assumed produced water discharged ww large Contamment impoundments that are Constructed to allow negligible infiltranon and minumal loss to sor morsture (10 percent) would not infiltrate into the shallow aquifer svsiem There would be no recharge to shallow groundwater from thi. water handhng opten Furthermore. the analysis assumed that all of the produced water usert for land apphcanon disposal would be used comsumptvely There would >> no net recharge from this water handling option Injechon of CBM produced water results in recharge to the sone of injechon Injection was assumed in this analyses to occur on somes decper than the For | o- von coal zone There would be no net recharge to the Wasatch sands or the coal cones within the Fort ( neon Formation from ths water handling upton Recharge w the Fort Lm on coal zone and higher units by infiltroafn o( nB M produced water ss summanzed by wub- watershed for cach alternative in | adie + | An estemated | 5 to 33 percent of the CBM produced water would infiltrate the surtace and recharge the coal zone aquifer under Alternative | Hydraulic connection Netween the sands of the Wasatch Formanen and the -oals of the upper Fort (mon Formation is lumited because of the low permeabelity claythats setparaote nthe etwos un its However. if the hydrauix head ( water level) on the coal ts naturally lower than in the overfyimg sands. then there 1s potential for leakage from the sands into the coal Based on oMservation of «ater levels im nested nonitormng wells. comsiderabdic leakage into developed coals 5 expected only where Wasr'ch sands occur within |00 feet abeve or Delow the cos! zone. The rate of leakage typically would be extremely small, but can amount to a significant portion of the total recharge into the coal taken over a large arca. fuuvecsengseeeseRlssyee e ‘7 As sands in the Wasatch Formation tend to be discontunuous. the amount of leak - IReaEtme we O age would also be lymuted by the arcal event of sands within | 00 feet of the coal. Locally. the hydraulic connection between the coal zone and Wasatch sands may be enhanced if the inteynty of the confining layer ss compromised Dy water sup- ply wells that are screened throuy Doth the coal come and the overtying sands. by detenoraing well casings. of Dy poorly plugged o2/ and gas wells of exp/-ra- tory dri! holes. Leakage irom the Wasatch sands into the coal zone also may Le enhanced |f water levels in the coal ore lowered as a result of dewatermg A sg- oficamt penod (typrcaily several years) would likely pass defore nonccabdic drawdown (drop im water level) in the wands would De apparent Decause of the meted hydraulxc Communication between the Coal come and the or criving Wa sateen wands Parnal solanon of the sand aquifers that overic the coal » indicated im the re- suits of the BLM s groundwater monitonng of (he Vearguiss ( BM propect. «fact has the longest hestery of operanon (since 1993) The BLM has monitoreodw o sets of pawed wells sunce the proyect began. in one set of wells. the MP l2OC weil ss completed m the coal and MP 22S weil ss competed in the firs overiving sand zone. 40 feet adowe the coal A decline in the water icve! of more than WO feet has been ofserved in the coal monitonng well, wile a devine im the water level of 20 feet has Been ofserved im the overiving sand cquifcr after more than / ‘ars of monmo(Frigumre g+ |) A lag ome of about 4 years cocurred before any measurable drawdown was soen in the weil Completed in ite wandisione =\ second paw of wells m the arca (MP 20 and MP 2S) shows. molar trend The two pass of monitonng wells m the Marques field are the waly sourceo f long-term monitonmng data 4. aladic for Wasatch sandsteecs in a BM dev ctop- ment arce withen the PRB that has O-ce active for sewera! years The BL has been active in setting up and monstomng paired wetls im other areas of the PRB_ Dut the hestory of data for these wells is retanvety fort However the data trom these nested weiis can De used w cvaluate the vernal perm cadility and icakage rate through the 40-foot theck claystone unit that separates the cual from tie sandstone in thes area ( AHA and Greystone 2002) +5 PRB O 4 & FEES BEST COPY AVAILABLE :