Scott Waterman

You would probably liberate chlorine gas if you allowed dissolved hypochlorite to contact hydrogen peroxide.  I only use hypochlorite to temporarily disinfect a water system.  I have not seen any peroxide systems used for home treatment systems.  I have used it for insitu contaminant cleanup projects, but most have switched over to permanganates probably due to safer shipping and handling.  

Mineral scale in your plumbing system is a function of the background water chemistry which is altered by the pressure, temperature, and chemical changes (e.g. exposure to atmospheric oxygen) at the surface versus in the aquifer.   You will see rapid scaling a lot in water heaters where you are rapidly heating "hard" groundwater and precipitating calcium carbonate.  

The ozone system that I mentioned in the previous post was installed on a well in the lower Clark Fork River valley of SW Montana.  The groundwater had naturally occurring levels of arsenic (80 ppb), iron (2 ppm) and dissolved hydrogen sulfide gas that made it objectionable to use in a house, hence the treatment system.  The treatment train consisted of particulate filtration, softener (iron and manganese removal), arsenic removal unit, and ozone treatment for h2s removal.  This type of system costs about $3-4K and requires some regular operation and maintenance...and grid power.

In the public water supply world we use the term sanitary seal.  This means no outside entry of anything and slope the ground away from the collection system and make sure there is no surface ponding of stormwater.  Seal the top of the spring box except for a NSF vent and a gasketed access port to chlorinate or grab a sample.  Also erect a fence with a general radius of 50 feet around the entire spring collection system and use gradational small animal wire that is buried.  

The Sulphur odor (hydrogen sulphide gas) can be treated with oxidation ( ozone, peroxide, chlorine...).  First make sure you have thoroughly chlorinated the system....maintain 200 ppm free chlorine for 24 hours.  Also slug the well with chlorinated water to force some treatment into the aquifer.  The last h2s system I did used an ozone unit.  Around $1500 IIRC.  

Check the published geologic and hydrologic information in your area.  Start with ANR Dept. Of Environmental Conservation.  They work for you, use them to help you with options.  Good luck and report back what you find.  

Ke.  Measure the depth to the standing water level in the well and also to the bottom of the well and report back.  I would test pump the well.. it before investing in any equipment.  A local well service contractor should be able to help and even run the test.  You need to determine the long term yield that the well is capable of and proceed from there with designing a system.  

Colter.  I am a hydrologist located near Helena, MT.  I have worked all over the state for the last 30 years.  It was not uncommon in the early days for oil exploration holes to be turned over to the surface owner for stock watering or even domestic use. Unfortunately these wells were not designed as water wells and depending on many factors, can produce formation fines and further well development may not ever alleviate this problem. So you are left with treatment if you want to use this water in your house.  Since you desribe the water as high sulfate I assume you are located in Central or eastern MT where the Cretaceous units typically have this water quality issue.  Contact one of the water treatment vendors in you part of the state to discuss your options.  If you want to use the well you should go ahead and file a water right application with the Montana DNRC.  The DNRC Oil & Gas Board also maintains a GIS mapping application that should have a record of the original well.  You can reach me at azhydro1992@gmail.com if you have further questions.

The hydraulic response of the well to pumping stress will be different in confined versus unconfined aquifers..
See:  https://pubs.usgs.gov/circ/circ1186/html/boxa.html

You can often tell from the drillers log, if available, or talk to a local drilling contractor or hydrogeologist familiar with your area.

The majority of domestic wells are shallow and completed in unconfined aquifers.  

Kyle.   Your water quality issues are not insurmountable.   Have you located a well log for the well that describes the geology?  

I doubt there would be a salt water intrusion problem, for a couple of reasons,  a low yield aquifer (1.25 gpm) would not be as susceptible as a higher yield aquifer that has more hydraulic communication with the estuary you mention, also 920 uS would not be that indicative of seawater intrusion...most seawater is over 40,000 uS.... chloride levels would also be very high.  

Coliform is only an indicator of bacteria in the groundwater, the lab should have also checked to see if e.coli is present.  If the well has not been used for a long time and surface leakage that found a way in and could be the source. Bacteria is common in near surface soils and in shallow groundwater (<25 ft below ground surface).  Sealing the well head and shock chlorination may take care of the problem.  If not a chlorination or UV disinfection could be used.   At <2 gpm you will probably be pumping to a storage cistern and a inexpensive pellet chlorinator could be fitted.  UV systems alcan problematic with high iron groundwater unless you remove the iron first.

The iron levels you report are not that high.  A simple ion exchange water softener will drop out these iron levels and manganese too.

Higher a reputable well service contractor to redevelop and chlorinate the well and then purge it before collecting new lab samples.  Then take the results to a knowledgeable water treatment contractor ...if needed.  Do this as a contingency to purchase and definitely before committing to any new construction.

Good luck.