Well Chlorination + Shock Treatment

Why this matters

Well chlorination ("shock treatment") is the standard response to bacterial contamination in private well water - coliform bacteria, E. coli, iron bacteria, sulfate-reducing bacteria. The procedure is straightforward but requires careful chemistry, fixture protection, + customer follow-up. Service. Annual or after-event service. Routes with well customers (rural service area) have recurring chlorination work + the cross-sell to filtration systems.

When to chlorinate

Test-driven:

• Coliform positive on bacterial test
• 1. coli positive (urgent - boil-water status)
• Total bacteria count elevated even without specific pathogens
• Iron bacteria (slime in toilet tanks, orange staining)
• Sulfate-reducing bacteria (rotten-egg smell that comes and goes)

Event-driven:

• New well completion + commissioning
• Well repair (pump replaced, pitless adapter serviced, casing repaired)
• Flooding event (surface water entered well)
• Well sat unused 6+ months
• After water-quality complaint suggesting contamination

NOT a substitute for fixing the cause:

• Surface water infiltration = casing or well-cap repair
• Septic intrusion = septic system evaluation
• Cracked casing = casing repair OR well replacement
• Customer education: shock chlorination kills bacteria once; the contamination source must be addressed OR bacteria returns

Pre-chlorination

Customer briefing (written)

1. Water will be unsafe to drink for 24+ hours
2. Chlorine smell + taste expected for days post-treatment
3. Fixtures + appliances cleared of bottled water + alternative supply
4. Customer + family use bottled water until clear

Fixture preparation

1. Bypass water softener (chlorine destroys softener resin)
2. Bypass any reverse osmosis system (chlorine destroys RO membrane)
3. Bypass any carbon filter (chlorine reacts + destroys)
4. Open all hose bibs + drain enough water to refresh the well + pipes
5. Note all fixtures to flush

Chlorine source

Bleach (sodium hypochlorite - 5 - 6%)

• Common household bleach (Clorox, Walmart store brand)
• DO NOT use scented OR thickened bleach (additives contaminate well)
• 1 gallon treats ~100 gallons of well water at ~50 ppm

Calcium hypochlorite (HTH, granular pool chlorine - 65 - 75%)

• More concentrated; smaller volume
• Easier transport
• 2 oz per 100 gallons of water = 50 ppm
• Requires careful handling (oxidizer + dust irritant)

Liquid pool shock (10 - 12.5% sodium hypochlorite)

• More concentrated than household bleach
• Same chemistry; less volume
• 1 quart treats ~100 gallons at ~50 ppm

Most professional service uses household bleach OR liquid pool shock - handling is safer than granular.

Target chlorine concentration

50 - 200 ppm free chlorine in the well + plumbing for 12 - 24 hour soak.

Test strips: use the high-range pool chlorine strips (0 - 500 ppm) NOT low-range residential strips.

Procedure

Step 1: Calculate volume

1. Well casing diameter × casing depth × 0.163 = gallons in well

• 6-inch casing × 200 ft = ~78 gallons
• 8-inch casing × 150 ft = ~98 gallons

1. Add household plumbing volume estimate: ~30 - 60 gallons for typical home
2. Total: ~100 - 200 gallons typical residential

Step 2: Calculate chlorine amount

For 50 - 100 ppm in 150 gallons:

• Household bleach (5%): 1 - 2 quarts
• Liquid pool shock (10%): 1 - 2 cups
• Granular calcium hypo (70%): 1 - 2 oz

Many techs double the calculated amount to ensure adequate concentration; 100 - 200 ppm is in-spec + chlorine demand of the well consumes some.

Step 3: Open the well cap

1. Remove well cap (most are bolted or clamped)
2. Inspect: condition, vermin entry, water level
3. Set up hose for circulation

Step 4: Add chlorine to well

1. Pour calculated chlorine into well from cap
2. Bleach goes directly in; granular dissolved in 5-gallon bucket first then poured

Step 5: Circulate

1. Connect hose from outdoor spigot back into the well cap
2. Run for 30 - 60 minutes to circulate well water + mix chlorine
3. Smell at hose: chlorine smell = well + plumbing exposed to chlorine

Step 6: Run chlorine through every fixture

1. Indoor + outdoor every faucet + every shower / tub
2. Each fixture: open + run until chlorine smell evident
3. Includes: every kitchen + bathroom faucet, hose bibs, washing machine supply, dishwasher supply (advisable for full coverage), water heater (drain + refill cycle)
4. Goal: chlorine touches every part of the plumbing system

Step 7: Soak

1. Replace well cap
2. Customer doesn't use water for 12 - 24 hours
3. Reminder: shower, kitchen, dishwasher all OFF
4. Toilet flush limited

Step 8: Flush

1. After 12 - 24 hour soak, open outdoor hose
2. Run outdoor hoses until chlorine clears (use chlorine test strips at hose to verify <0.5 ppm)
3. Flush every indoor fixture next; let water run several minutes per fixture
4. Don't flush to septic (kills septic bacteria) - pump outdoor as much as possible

Step 9: Reinstall bypassed equipment

1. Reconnect softener, RO, carbon filter
2. Verify operations

Step 10: Test bacteria 1 - 2 weeks later

1. Wait for chlorine to fully clear before re-testing (5 - 10 days)
2. Take samples to state-approved lab
3. Coliform + E. coli negative = success
4. If positive, repeat chlorination AND investigate source

Common mistakes

• Insufficient concentration: biofilm needs 200 - 400 ppm + 24 - 48 hr soak (not standard 50 ppm)
• Skipping fixture flush: every fixture must run chlorinated for the protocol to work
• Not bypassing softener / RO / carbon: chlorine destroys all three; customer charges back damaged equipment
• Customer drinks too early: 50 - 200 ppm chlorine is harmful; written instructions + signature mandatory
• Not addressing source: chlorine kills bacteria once; cracked casing OR surface infiltration brings it back

References

• EPA + state drinking water standards
• NSF / ANSI 60 (chlorine for water treatment)
• State + local well construction codes
• CDC + EPA private well guidance
• Manuall internal: Well Water Systems Reference