Orchard Site, Arsenic Exceedance, and Public-System Status
A 20-unit condominium proposes a new 8-inch bedrock well on a 1.5-acre site that was an apple orchard until 1985. The well is 400 ft deep with 60 ft of casing and yields 25 gpm. First sample results are arsenic 22 µg/L, manganese 0.6 mg/L, iron 1.2 mg/L, pH 5.8, lead 8 µg/L first-draw, nitrate 3.0 mg/L, and total coliform absent. The board wants to use the well as the sole source and avoid treatment 'because the water looks clear.' The local board of health has issued a well construction permit; the condominium has 20 service connections and 45 residents year-round. The driller must submit a well completion report.
1. Is this a public water system, and what regulatory approvals and monitoring apply?
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Yes. A system with 20 service connections and 45 year-round residents meets the Massachusetts public water system threshold of 15 service connections or 25 people served at least 60 days per year. It cannot be handled as a private well. The condominium must obtain MassDEP approval for the source and treatment, have a certified operator, conduct initial and routine monitoring under 310 CMR 22.00, issue a Consumer Confidence Report, and meet public-notice requirements. The arsenic result of 22 µg/L exceeds the 10 µg/L MCL; manganese 0.6 mg/L exceeds the 0.05 mg/L secondary standard; pH 5.8 is corrosive, and the 8 µg/L first-draw lead, although below the 15 µg/L action level, signals a corrosion-control problem. The board of health construction permit is necessary but not sufficient. The driller should submit the well completion report and provide the owner with yield and water-quality data.
2. Recommend a treatment train and explain the sequence.
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The water has arsenic, iron, manganese, low pH, and corrosion potential. First oxidize with chlorine, ozone, or aeration to convert As(III) to As(V) and precipitate iron and manganese. Then filter through an oxidizing filter medium such as manganese greensand or catalytic carbon followed by filtration to remove the oxidized metals and particulate arsenic. If dissolved arsenic remains above 10 µg/L, add an arsenic-adsorptive medium, anion exchange, or reverse osmosis for drinking water. Because iron at 1.2 mg/L and manganese at 0.6 mg/L can foul arsenic media, remove them first. After filtration, adjust pH to about 7.5-8.0 with soda ash or caustic to reduce corrosion and lead leaching, then disinfect with chlorine or UV to maintain a residual. Do not simply install a water softener; it will not reliably remove arsenic and can worsen corrosion. Pilot-test and monitor arsenic speciation and treated-water effluent.
3. What confirmatory sampling, reporting, and wellhead-protection steps are needed before occupancy?
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Resample arsenic with a certified laboratory and request speciation of As(III) and As(V); also rerun manganese, iron, pH, alkalinity, lead first-draw, nitrate, and coliform. Use proper preservation and collect at the wellhead and at a representative tap after flushing. If arsenic remains above 10 µg/L, the system is out of compliance and must not serve water without treatment or required public notice. Report exceedances to MassDEP as required; MCL violations trigger public notice. Submit the well completion report and as-built details: casing depth, grout, screen, yield, and pump setting. Establish a wellhead protection area and inspect the former orchard for arsenic and lead residues, fuel tanks, and floor drains. The well should be upslope and properly sealed. Record all sampling and treatment performance for the operator.