The aquifer that is underneath Gallatin Valley, at four

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The aquifer that is underneath Gallatin Valley, at four Powered By Docstoc
					         Public concern has been raised regarding the impact of The Zoot Enterprises
development on groundwater. Zoot Enterprises is in the western half of section 11 in
township 2S and range 4E northwest of Four Corners in Gallatin County (Fig. 1). At
present the company has installed six monitoring wells. Three of the wells serve as a
public water supply for employees and visitors to Zoot Enterprises. These wells were
also designed for use by future homes and businesses in the Galactic Park Subdivision.
These three public- use wells are west of the building (Fig. 1). Presently these wells are
reported to produce no more than 35 gpm. The other three supply the cooling system for
the building and the fuel cells that are used for power in the building. Two of the cooling
water wells are along the east side of the building with the third east of the northeast
corner of the building (Fig. 1). The water used for the cooling system is discharged back
into the ground, with little net consumptive use, via an infiltration gallery to the
northwest of the building as labeled on the map. Currently there is a temporary septic
drainfield east of the building. There is also a gravel pit just to the Northwest of the
injection gallery. All of these features are within a quarter to a half of a mile of the
Gallatin River.
The aquifer that underlies Gallatin Valley, in the area around Zoot, and Four Corners, lies
within the Quaternary age Gallatin River alluvium, which averages about 55 feet thick
but is found to be as much as 80 feet thick in that vicinity. The alluvium is said to be
uniformly coarse and permeable. The coefficient of transmissibility has been found to
range from 170,000 gpd per foot to 380,000 gpd per foot (Hackett et al., 1960).
Underneath the alluvium are Tertiary silts and Archean gneiss (Fig. 4).
         The main source of groundwater recharge in this area is thought to be irrigation.
Some recharge also comes from the streams that enter the valley on either side of the
river. Most of the groundwater then discharges into the Gallatin or leaves the area as
underflow to the north, with some water lost to evapotranspiration.
         Based on available research (Hackett et al., 1960) (Slagle, 1995) the Gallatin
River is thought to be a gaining stream as inferred from ground water contours lines (Fig.
2 and 3). In the area of interest, the groundwater flow direction is to the northwest at
340° from north (Fig. 2 and Fig. 3). However the data used to draw the contours is for
the whole valley and is based upon wells which are often spaced a mile or more apart.
Only one well was monitored in the section in which the development has taken place or
is planned. There are four more wells in the whole township, only two of which are
within a half- mile of the river. Although monitoring wells installed prior to development
generally support the ground water flow direction, more detailed data is needed to test the
flow direction and flow gradient postulated by the USGS researchers.
         The public has expressed several concerns about Zoot’s groundwater use and
impact. One concern is that the wells that are to be used for public use may lower the
water table and may be having an effect on the flow of the Gallatin River, if not now then
in the future when Galactic Park subdivision has bee n built. A second concern is that the
water used for the cooling system is raising the temperature of the groundwater and
consequently the river once it is has been discharged back into the ground via the
infiltration gallery. A third concern is that the septic system is contaminating the
groundwater, which is consequently contaminating the river.
         These concerns can be assessed with a monitoring plan for the area. This
monitoring plan needs the following elements:
        1. An assessment of gradient, flow direction, and flow quantity to the river by
continuously monitoring pr1, pr2, and pr4 east of the river and, pr5, pr6, and pr7 west of
the river, as well as quarterly monitoring of existing Morrison Maerle monitoring wells
and pr3 (Fig. 1).
        2. A measurement of gain or loss of water to and from the river by measuring the
discharge manually in the reach above and below Zoot for gain and loss.
        3. An assessment of nutrient and microbial contamination by quarterly sampling
of mm12 and mm9 downflow of the septic drainfield and mm4 upflow of the.
        4. An assessment of change in groundwater temperature by monitoring and
comparing groundwater temperature upflow of the infiltration gallery at mm3 and
downflow at pr3 and pr1.
        5. A study of the timing of groundwater level rise and changes in stage in the
Gallatin River at the U.S. Geological Survey gage at Gallatin Gateway and in the Spain-
Ferris Ditch, and the ground water withdrawal from wells at Zoot.
        6. An examination of long-term changes in ground water level in response to
changes in water withdrawal at Zoot to see if there is a detectable trend, particularly a
trend that might reflect a change in ground-water discharge to or from the Gallatin River
in response to withdrawal of ground water by wells.

        Both short term and long term monitoring are needed to help better understand
potential cumulative, climatic, and other effects on the system.

         Seven wells are needed (Fig. 1) in addition to those installed by Morrison-Maerle
(Fig. 1).
         In order to continuously monitor water level and temperature, a water
level/temperature sensor/data logger will be needed in each of the wells proposed for
continuous monitoring above (mm3, pr1, pr2, pr3, pr4, pr5, pr 6, pr7, Spain Ferris Stage).
In addition, quarterly monitoring will be required at the remaining Morrison-Maerle
monitoring wells (mm4, mm 9, mm10, mm11, mm12, mm13, mm14). Monitoring of the
pumping wells for cooling and water supply are not practical due to well construction and
well pumping activity. Stage measurements in the Spain-Ferris ditch require a
capacitance rod because of the possibility of freezing which might damage pressure
transducers proposed for wells. While capacitance rods are less expensive they are not
adequate for the wells because they are not capable of measuring the full range of water-
level fluctuation in most wells (>2m (6 ft) (Fig. 4 and 5). Also the wells will need
locking caps to guard against theft and vandalism. Quarterly monitoring for Nitrate-
nitrogen and microbes is needed at mm4, mm9, and mm12. Temperature loggers are
needed in the gravel pit and in the Gallatin River above and below Zoot to monitor
temperature changes continuously and to help assess temperature effects.

       Drilling and well installation will be supervised by Dr. Steve Custer. Monitoring
work and data analysis will be done by students under the supervision of Dr. Custer.
Data will be submitted to the Montana Bureau of Mines and Geology Ground Water
Information Center which makes the data availab le on the world wide web.