Cold Spring Mobile Home Park: E. coli Positive, Repeat Positive, and a Well Integrity Problem
Cold Spring Mobile Home Park is a community water system serving 1,150 people year-round from two bedrock wells, chlorinated with sodium hypochlorite and fed to a 40,000-gallon storage tank; there is no other treatment. The system collects two routine total coliform samples per month. On Tuesday, June 9, the routine sample from the Well 2 pressure-tank tap is reported total coliform positive and E. coli positive. Free chlorine at that tap is 0.1 mg/L; at the Well 1 tap it is 0.7 mg/L. On Wednesday three repeat samples are collected - the original site, a tap upstream, and a tap downstream - and two come back total coliform positive, one of them E. coli positive. Well 2 has a cracked well cap, and the casing is in a shallow pit that floods every spring. The park manager wants to just add more chlorine and wait for the next sample. Your certification is Grade 1, and the system's only other certified operator is on vacation.
1. Lay out what must happen and when, starting from the positive result.
Read the worked answer
Timeline and reasoning:
- Repeat sampling within 24 hours of learning of the total coliform positive: original site plus upstream and downstream. That was done correctly on Wednesday.
- This is an E. coli MCL violation. A routine E. coli positive followed by a total coliform positive repeat at the original site meets the rule's MCL definition. The system does not get to wait for a cleaner sample to make it go away.
- Notify NH DES by the end of the next business day after the confirmation.
- Tier 1 public notice within 24 hours of the confirmed violation. That is the tightest deadline in the rule and it does not wait for lab re-confirmation or for the manager's agreement.
- Level 2 assessment within 30 days, conducted by the state or a party the state approves - not something a single Grade 1 operator signs off on alone during a staffing gap.
- Corrective actions on the state's schedule, which here means well integrity work.
Immediate operational moves: verify the chlorine feed is actually running and the dose is right; consider taking Well 2 out of service if the other well can carry the demand; check for cross-connections and backflow; and inspect the wellhead. The cracked cap and flooding pit are the obvious pathway for surface water to reach the supply - more chlorine in the tank is not a barrier against a compromised well.
2. What tier of public notice applies, how must it be delivered, and what must it say?
Read the worked answer
Tier 1 - immediate notice, 24 hours. E. coli in a confirmed MCL situation is a Tier 1 event because of the acute risk of gastrointestinal illness.
Delivery: hand delivery or another method that actually reaches every customer within 24 hours - door hangers, direct delivery, broadcast media, or posting in conspicuous places where service is intermittent, depending on what your state accepts. Mail alone is generally not sufficient for Tier 1. For a 1,150-person park, hand delivery to each unit plus posting at the office is realistic and defensible.
Content, in plain language:
- What happened and when (E. coli detected, repeat confirmed).
- The potential health effects and who is most at risk - infants, young children, the elderly, and immunocompromised people.
- What consumers should do right now: boil water for one minute and cool it before use, or use bottled water, including for drinking, brushing teeth, making ice, and food preparation.
- What the system is doing (chlorination verified, well evaluation, assessment scheduled).
- Who to call for questions, with a name and a working phone number.
Follow-through: a rescission notice when the state confirms the problem is corrected, delivery documentation retained, and the violation reported in the next Consumer Confidence Report with the required health-effects language.
3. The manager's plan is to raise the chlorine dose and re-sample. Evaluate that plan.
Read the worked answer
It is half a plan, and the wrong half first.
What is right about it: a 0.1 mg/L free residual at the Well 2 tap against 0.7 mg/L at Well 1 means something is consuming chlorine - contamination in the pressure tank, stagnant storage, or a hydraulic path that is not getting contact time. Restoring a reliable residual is necessary.
Why it is not sufficient:
- Chlorine is a barrier inside the pipe; it is not a barrier at a wellhead. A cracked cap and a casing in a pit that floods every spring is a direct pathway for surface water and shallow groundwater to enter the supply. Disinfecting water that is being re-contaminated at the source is a treadmill.
- Contact time matters. A residual of 0.7 mg/L at one tap and 0.1 at another suggests the distribution layout and storage, not just the dose, control the outcome.
- Waiting for the next sample means the boil water notice and the state notification are late. Those are rule violations on top of the MCL.
A defensible plan: keep the system on boiled or alternate water until sampling clears; fix the wellhead (extend the casing above grade and above flood level, seal the pit or eliminate it, sanitize the well, dye-test or inspect for annular leakage); verify chlorine contact and residual at the furthest points; then complete the Level 2 assessment with the state or an approved party. Also address operator coverage - a system this size cannot have its only certified operator on vacation and a Grade 1 alone in charge during an acute event.