Montana Bureau of Mines and Geology A Department of Montana Tech of The University of Montana Lolo-Bitterroot Area Map Area Dissolved Constituents Nitrate Arsenic R 21 W R 20 W ' 0 0 o R 19 W 4 1 1 R 21 W R 20 W ' 0 )" 0 L *# o R 19 W olo # 4 Cr Lolo * 1 )" Montana Ground-Water Assessmen 1 *# ut12 (! )" *#)" R 21 W t Atlas 4, Part B, Map 9 R 20 W ' 93 0 Open-File Version May 2006 t )" )" (! 0 u )" o R19 W ! *# (! *# 4 T 11 N ((! )"(! 1 (! (!)" 1 (! )("! (! (! Lolo Florence inset map T 11 N )" (! (!(! )"(! *# R 21 W (! (!!(! (! 2.89 ' )" ( (! R 20 W 0 Radon )" " r 0 ) o e C )"*# # (! ut93 4 R 19 W v * 1 i l (! 1 . a )" Lolo r ! R k ( *# O . )" *# t 2.21 (! o R 21 W C )" O o F (! R 20 W ' ! r 0 C ( L *# o (! *# r 0 )" o e R19 W A r 4 A " "*# t k ) 1 ) t *# i R L )" (! )" Lolo 1 4.82 T 11 N *# B E R U iver Eight Mile Fan *#)"(! (! (! Florence *# (! (! )"(! N O *# I Cr (! *# )" 894 Lolo-Bitterroot S ile (! *# M Florence tm *# *#*# # *# S igh ! 8.3 * *# Ground-Water Characterization Area I E ( T 11 N *# (!(! *#*# 3.2 2.0 T 10 N *# (!*# (! 4.9 M )" (!2.8 (! T 11 N (! (! # (! *# Lolo Sweeney Cr *#)"(! *# (! 2.45 * 4.75 MISSOUL T 10 N *# *# *#(! *# *# A CO. Three Mile Fan (! ! (! *# RAV r ( 2.4 *# ALLI CO. C *# (! 3.03 T 11 N(! Eightmile eek *# e (! *# *# *#(! Cr 3.5 il )" *# (! (! *# *# 3.8 T 11 N )" m *#*# (! 2.44 *# (! S e (! *# *#*#*#(! *# *#)" y Bass C e (!*# (! 2.53 e r a r 5.5 e h (! T 11 N g p *# l T *# (! *# (! l n 2.8 p (! (! *# *# *# a a )" 01 T 11 N h *# 7.17 (! r Line of Section *# R V i K e o *# Miles r oten (! *#*# (! (! t v a # e i * t C Florence (! *# Scale 1:80,000 i r #*# *#*#(!(!**#*#(!*#*#(! *# *# T 11 N o T 9 N ! (!*#(! *## R ( * o M *# )" *#*#(!*#(! *#*# *# o t North Bench (! (!# *#*# )" o ##* r * o **# o T 9 N *#*#*#! (! (!*# *#*# " *# Around Florence and in the Eightmile r ( # ) r # * *# o Stevensville N T 10 N )"*#**#*#(! # r u * # r (! *# * e . *# *# *# ! r B *#(! (! *# ( # drainage, nitrate was detected in 61 of o * t *# Florence (!(! *# n 46 30' *#*# e *# # *# e u (! * t *#(!(! *## t r (! *# (!*#*(! i t n (! t (! (!*# t t )" *#(!(! *# i T 10 N *# # t # # * *# 77 samples; concentrations ranged a S Fo ! *# * !*(! *# # o ( (! ( * B i . 46 30' *# B B r *# *# *#*#(! i u k (! *#*#*#(!! (! (!*# *#*# *# *# n rn Cr *# T 10 N *#*#*#*#(!(!( *# )" from non detectable to 8.30 mg/L. B t *# (!(! *# *# *# (! s F #*##(! *# (! *# *# ork *# **(! *# the boxed area (0.8 sq. mi.) In Florence (!*#(!(!*#*#*#*#*# *# Big C (! T 10 N (! *#(!*#(!(! )" *#*# Cr r (! *# there are (!*#*#(!(!*#(! *# *#*# Sunset Bench Florence inset map records of more than 115 septic *#*#*#! (! *# 5.4 *# 5.7 *#*#*#*#*#*#(! ( *# *# )" 880 . (! T 10 N )" (! *# 500 1080 by Cr systems (Norbeck and McDonald, *#(! *# *# 1080 *# T 8 N ugh # *# *# *#(!! *# Florence *# 1070 *# 20 0 20 illo *#* *# ((! *##710 10 W )" 2001) 7480 ") 760* T 8 N *# and nitrate was detected in all *# T 10 N *# *#810 *# *# *# !(*#410 510*# r but one of the samples suggesting that *# Swe *# T 10 N 580 810 550*#650 a Victor e *# *# *# Miles tho (! 3.53 *#660 use *# (! *# septic effluent is a source ground- Cr iv T 10 N Willoughby Fan (! *# water nitrate in this area. Scale 1:1,500,000 R *# (! Projection Montana State Plane t T 9 N *#(! *#*# *# o # Datum NAD83 *#* *# o (! (! *# *# )" T 9 N Map Area r (! T 7 N r *# T 9 N *#(! e o *# )" t 46 30' *# (! *# *# t T 7 N i *#(! Stevensville (! T 9 N T 9 N Ground-Water Quality of the Shallow Basin-Fill, B *# o *# )" 46 30' *# Corvallis ! o *# (!( (!*# 46 30' *# (! T 9 N Deep Basin-Fill, and Bedrock Aquifers, W Stevensville illo # T 9 N w C *# *#*# * o *# r (! *# *# # )" 46 30' * o Willow Creek Fan (! 46 30' *# Bitterroot Valley, Missoula T 6 N *# *# *# (! *# *# *# Stevensville T 9 N and Ravalli Counties, *# *# 2.34 Blodget T 6 N t Cr *# *# o G *# *# (! 46 30' T 8 N (! *# *# # 5.90 Southwest Montana ir *# *# !((! (! * o Canyon Cr d (! *#)" *# 46 30' C # !( (! *# 2.06 *# r * (! (! (! # Stevensville n *# * T 8 N *# *# Hamilto *# *# o by *# # 46 30' T 8 N * (!(! *# *# *# John I. LaFave )" *# (! Saw (! (! *## )" *# (! (! *# *# tooth Cr *# * )" (! T 8 N Author's Note: This map is part of *#*# (! T 8 N *# the Montana Bureau of Mines and Geology T 5 N Sk 3.76 (MBMG) Ground-Water Assessment Atlas fo al *#*# 3.43 )" *# (! ka *# (! *# (! )" (! (! T 8 N ho T 5 N *#(! )" *# intended to stand alone and describe a r the Lolo-Bitterroot Area. It is C *# (! *# r (! T 8 N study area, although many of the area'ssingle hydrogeologic aspect of the *# (! )" Sl (! )" For an integrated view of the hydrogeol hydrogeologic features are interrelated. Cama ee *# (! )" T 8 N s Cr pin *# ! *# *# ogy of the Lolo-Bitterroot Area the H g C *# (!( *#*# *# reader is referred to Part A (descrip ayes hi (! Cr ld C T 7 N )" Montana Ground-Water Assessment tiveAtlas overview) 4. and Part B (maps) of r *# *# r *#*# (! 3.27 *# e C (! T 7 N s )" (! *#*# 810 t Hor (! *#*# 6.98 Los *# *# *#*# )" T 7 N INTRODUCTION T 4 N (! T 4 N *# r 12.14 T 7 N C )" *# *# o k T 7 N om oc *# *# )" As part of the Montana Gr e C # *# *# ak R *# * (! ound-Water Assessment Program, L *# (! *#(! evaluated in the bedrock and basin- (! *# )" T 7 N fill aquifers in the Bitterroot Valleywater qualityin western was Darby *#*#(! (! *#*# )" *# Montana. This plate presents maps showing *#*# *# )" *# T 7 N the distribution of dissolved constituents, T 3 N *# (!)" *# (! well as nitrate, arsenic, and radon in the shal )")" *# *# *# *# *# (! (! 1170 (! *#!(*# 2.80 3.20 (! (! Hamilton inset map T 7 N low, deep, and bedrock aquifers of theas Tin C T 3 N *# *# *# )" Bitterroot Valley. Ground-water quality da u *# *# *# *# (! (! 2.85 *#*# )" ") o p *# *#*# *# 00' )" 46 C (! *# *#*# *## *#2.70 8.09 area (Mineral and Missoula Coun ta for the northern r T 6 N *# * (! part of the Lolo- *#*#*#*# ") (! (!)" (! 11.8 220 o *# Bitterroot 46 00' *# )" )" 2.30 *#*# *# *# (! (! ties) are presented on a separate plate (LaFave, 2006a). ! *# *# )" (! *#*#(! 2.52 (! ( *# (! *# 2.50 (! )" ") Rye Cr *#*# # T 6 N *# # *# 3.10 *# (! 7.8 *# The north-flowing Bitterroot River drains the 2,860 mi *# (!(! (! * (! (! *#*# *(!(! *# 2.37 *# *# 10.6 1460 (! (! )" T 6 N *# 21.5 ! !( 2 *# *# *#*#!*#*# )" 7.4 # ( *#5.1 490 and part of Missoula County )" ( )" *# *#*#(!*8.8 valley in Ravalli *# (! (! 3.60 *# *# 1950 ") . The Bitterroot Valley is a structurally controlledCounty Chaffin Cr *# *# T 6 N 11.8 Willow C intermontane basin framed by *# *#*# 5.3 8.8 reek !( 640 (! (!! (! (! *#*# )" *# # 350 the Bitterroot Range on Hamilton *# (!(! T 6 N # *# 6.4 1280 * Mountains on the east; the western an (! Hamilton inset map * 8.17 11.2*#*#*# )" 150 !( the west and the Sapphire T 2 N *# *# *# ") *# *# (! *# (! (! (! 8.0 5.38 10.8 d southern valley boundary is par *#*# )" T 6 N 230 380 Montana/Idaho border. Much of the Bitterroot (! (! *# 1.39 *# 200 t of the T 2 N (!(! *# ") *# Forest. drainage is within the Bitterroot National *# Hamilton 0*#.94 *# *# ! T 6 N *#150 ! *# )" ( *# 1100 2720 *#170 (! ( *## 1.0 *#(! *#* 2.85 *# !( 1120 !( R 21 W *# *# T 6 N ' (! *# 1130 0 (! 0 (! !( The Bitterroot Valley is an area of R 20 W o (! !(! 2.75 W ND !( 4 ( i Hamilton 1 (!(! " llo 0.85 910 1 R 19 W ) w (! (! !( rapidly growing population; the populatio T 5 N *#)" (!(! C )" 0.71 Willow Creek S Ravalli County increased 44 percent (fro )" )" *# (! 1.70 reek tock 1116 n of *# *# )"(! )" *# (! *#*# 1.81 *# 1523 m 25,010 to 36,070) betw *# (!1.24 2.50 # Most of the residents live on the valley floor between the towns of Darbyeen in1990 the southand 2000. and *# )" *# 725!*( )" T 5 N (! 2.30 *#1.07 Scale 1:300,000 (! 3.41 1.48 Hamilton Lolo in the north. Ground wate T 5 N )" (!(! r supplies most domestic and public water supply needs. Projection Montana State Plane 2.32 )" (! )"(! )" *# Datum NAD83 )" (! (! 2.52 05 (! *# *# T 5 *#N *# (! 1.40 (! Land use has long been dominated by ir 1.60 0.54 (!1.10 3.10 5.04 . (! T 5 N )" (!(! 8.38 Miles (! 1996). However, as noted by Briar and Dutton (2 rigated agriculture (Kendy and Tresh, )" 2.16 0.97 )" *# (! (!(! *#1.50 2.37 )" )" *# )" (! *#1.50 0.771.38 to residential home sites is the major 000), the conversion of agricultural land *# *# (! *# *# )" T 5 N land-use change occurring in the Bitterr (! (! )" 3.6 1.90 01 In Ravalli County, the amount of land in *# 4.91 T 5 N oot Valley. EXPLANATION # Miles Skalkaho Stock between 1993 and 2003 (Montana irrigated acreageAgri ha *#(! * )" Scale 1:80,000 (! s declined about 7 (! T 5 N percent )" *# *# Skalk www.nass.usda.gov/mt). cultural Statistics Service, *# Nitrate was detected in 28 of the 29 aho C Description of simplified geologic )" *# reek T 4 N *# (! )" *# samples from the Willow Creek\ Road units on water quality maps (!(! Willow GEOLOGIC SETTING )" Creek fan area; concentrations were Quaternary sediments *# T 4 N (! below 4.0 mg/L with a median (! (! T 4 N (! )" *# The Bitterroot Range rises prominently on Stream - alluvium, outwash (! concentration of 1.5 mg/L. *# *#(!(! sources of the widespread ground-Likely peaks ranging from 9,000 ft the west side of the valley, with rug o )" *# - alluvial fan deposits om e C T 4 N in the north to 10,000 f ged ak (! water nitrate in this area include T 4 N (! " Sapphire Mountains on the east side of the t above sea level in the south. The L ) *# 770 Lake (! septic effluent (! generally less than 8,500 valley are more subdued, with rounded pea # , domestic application of Tertiary sediments and sedimentary rocks *)" o fertilizer, ft above sea level.