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Montana water data · Community in Lake County

Big Arm: well depth, groundwater and water rights

What the public record says about water in Big Arm: how deep wells go, where the water table sits, what wells produce, which water rights are on file, and which documented environmental sites are nearby. Area statistics orient you; a property report analyzes the records around one specific parcel.

Updated September 2026 · Based on 253 public records from MBMG GWIC, Montana DNRC, Montana DEQ, EPA UST Finder, US Census (place boundary)

Wells on record

82

15.1 per sq mi

Median well depth

255 ft

half of wells 190–390 ft

Median static water level

39 ft

51 measurements

Median tested yield

20 gpm

69 pump tests

Well depth

How deep are wells in Big Arm?

Of 80 wells with a recorded total depth, the median is 255 feet. Half were drilled between 190 and 390 feet; one in ten went deeper than 576 feet and one in ten found water shallower than 132 feet. Depth is set by local geology and position on the landscape, both of which change over short distances, so the spread matters as much as the median.

under 50 ft
1%
50–100 ft
4%
100–200 ft
23%
200–300 ft
34%
300–500 ft
23%
500 ft and deeper
16%

Static water level

39 ft

median depth to water at rest · half between 8 and 101 ft

The static level is how far below ground the water stands before pumping, measured by the driller at completion. It affects pump setting and operating cost, and it moves with season and with neighbouring use.

Well yield

20 gpm

median tested yield · half between 12 and 50 gpm

6% of tested wells produced under 5 gallons per minute and 58% produced 20 or more. These are short completion tests, not sustained-capacity tests; a household typically needs 3 to 5 gpm with storage.

Drilling activity

Recent well drilling in Big Arm

9 wells have been completed here since 2016, 2 of them in the last twelve months. The newest log on file was completed May 4, 2026. Records run back to 1960.

What the wells are for

  • Domestic72
  • Stockwater10
  • Irrigation8
  • Public Water Supply4
  • Unused2

How they were drilled

  • Rotary43
  • Forward Rotary11
  • Air Rotary7
  • Cable3

Drillers filing well logs in Big Arm

  • Ace Drilling3 since 2016 · 2024
  • Oh Well Drilling And Pump3 since 2016 · 2026
  • Castlio Drilling16 all-time · 2000
  • Liberty Drilling & Pump Co13 all-time · 1997
  • O.k.8 all-time · 1979
  • Allwest Drilling Inc8 all-time · 2014
  • Camp Well Drilling3 all-time · 1989

Ranked by well logs filed with GWIC, public record only. Not an endorsement, a referral or a paid listing; we have no business relationship with these companies. Verify licensing with the Montana Board of Water Well Contractors before hiring.

Water rights

Water rights on file in Big Arm

Montana DNRC lists 163 water rights with a point of diversion inside this area: 94 groundwater and 69 surface water, 121 of them active. The median priority date is 1981, and the oldest claim dates to 1855.

Types of right

  • Statement Of Claim59
  • Ground Water Certificate39
  • Registration Certificate32
  • Provisional Permit19
  • Domestic Allowance5

Purposes

  • Domestic66
  • Domestic; Lawn And Garden16
  • Multiple Domestic15
  • Lawn And Garden11
  • Lawn And Garden; Domestic7

DNRC basins

  • 76LJ162
  • 76L1

Area totals describe the neighbourhood, not any one parcel. Montana publishes no authoritative link between a parcel and a water right; whether a right attaches to a specific property is a property-level question that our reports answer with the DNRC abstract linked.

Aquifers and geology

What wells in Big Arm draw from

Drillers record the aquifer a well is completed in. The units below account for the wells here that carry an aquifer assignment; the median depth beside each is for wells completed in that unit.

  • Ravalli Group29 wells · 58% · median 283 ft
  • Glacial Drift9 wells · 18% · median 175 ft
  • Alluvium (pleistocene)6 wells · 12% · median 198 ft

Aquifer assignments are the driller's, recorded at completion, and many older logs carry none. Absence of an assignment is not evidence about the geology.

Environmental groundwater screening

Documented environmental sites in Big Arm

Petroleum releases

4

1 open · 3 resolved

Superfund program sites

0

none on the National Priorities List

Registered tank facilities

4

underground storage tanks, current and historical

A documented release or site in the area is not evidence that any particular well is affected. Whether a release reaches a well depends on groundwater flow direction, geology, well depth and construction, the extent of the plume and the cleanup performed. The most recent release reported here dates to 2021. A property report screens the sites within a quarter, half and one mile of a specific parcel and links the agency records.