Deciding the fate of a sewage-fed lake
A 42-hectare lake on the edge of a Class II town receives about 3 million litres a day (MLD) of untreated sewage from 6,000 households. Dissolved oxygen falls to 1.2 mg/l, and fish kills were reported in April and May. Around the lake, 120 small farmers irrigate 90 hectares of vegetables, 60 families fish, and 30 households wash clothes and utensils. A real estate firm has offered ₹40 crore for 6 hectares of the lakebed for a convention centre, which the town says it could use to build a sewage treatment plant (STP) costing ₹18 crore plus ₹1.5 crore a year to run. An environmental economist estimates lake benefits at ₹4.5 crore a year: fisheries ₹0.4 crore, irrigation ₹1.6 crore, recharge and flood buffer ₹2 crore, recreation ₹0.5 crore. The municipal council must decide within a month.
1. Identify the economic problem. Who causes the damage and who bears it?
Read the worked answer
This is a negative externality combined with a common pool resource problem.
- The 6,000 households and the town gain from disposing of sewage cheaply, but the cost appears as a polluted lake. The cost is external to the decision-makers, so the sewage keeps flowing.
- The lake is a common pool resource: no single owner can exclude users, but one person's use reduces what is available to others. Each household's discharge is small; the combined effect kills fish. This is the classic logic of the tragedy of the commons.
Incidence of the damage:
- 60 fishing families lose their catch and income (₹0.4 crore a year).
- 120 farmers irrigating 90 hectares face contaminated produce, market rejection and health risk.
- 30 households lose a washing and domestic-water site.
- The town loses groundwater recharge and flood buffering worth ₹2 crore a year, and residents face higher health costs.
Selling 6 hectares would convert a common resource into private property and transfer the loss permanently. The first question for the council is not 'how much is the land worth' but 'who is currently paying for the pollution without being compensated'.
2. Compare building the STP with selling the lakebed, using the given figures and a ten-year horizon. What should the council choose?
Read the worked answer
Option 1: build and run the STP (keep the lake)
- Capital ₹18 crore + 10 years × ₹1.5 crore = ₹33 crore total cost
- Benefits 10 × ₹4.5 crore = ₹45 crore, undiscounted
- Net advantage ≈ +₹12 crore, before counting health gains, groundwater recharge and property values
Option 2: sell 6 hectares for ₹40 crore
- One-time receipt ₹40 crore, but the lake loses about 14% of its area and the sewage problem remains; an STP would still be needed somewhere.
- Forgone benefits are at least irrigation ₹1.6 + fisheries ₹0.4 + recreation ₹0.5 = ₹2.5 crore a year, plus part of the ₹2 crore recharge and flood buffer. Over ten years that is ₹25 crore or more, and the loss continues after year ten.
- A one-time ₹40 crore is not comparable with a perpetual annual stream unless discounted, and the sale is irreversible.
Judgement: choose the STP and lake restoration. Even with a discount rate that narrows the gap, the annual benefit stream, the health gains and the irreversibility of a lakebed sale dominate. The ₹40 crore figure looks large only because the annual benefits are not on the same line of the comparison.
3. The municipality has a revenue shortfall. Design a financing and management arrangement for the STP, and state one risk.
Read the worked answer
Financing mix:
- Polluter-pays sewage cess: 6,000 households × ₹50 a month = ₹3 lakh a month ≈ ₹0.36 crore a year. Small per household, visible on the bill, and directly linked to the service.
- Municipal budget contribution of about ₹0.6 crore a year from property tax, since the town gains the health and flood benefits.
- Betterment levy or development charge on new real estate around the lake, which captures part of the land-value gain created by public restoration.
- State wetland or urban infrastructure grant for the capital cost, so the O&M is not starved by construction spending.
Management: a lake management committee with the municipality, two farmer representatives, two fisher representatives and a scientist, publishing dissolved oxygen readings monthly. Ring-fence the cess and O&M money in an escrow account so it cannot be diverted to road works.
Risk: the cess is collected but O&M slips, or the STP is built and left without power and staff, returning the lake to its present state within two years. Mitigation: publish the DO data and the O&M accounts, and make the operator's payment conditional on effluent quality. A treatment plant is a recurring commitment, not a one-time construction event.