Hanna (2014), from a combination of CPCB online and print records. The dataset spans the whole of India and runs from 1986-2004; an observation is a pollution monitor-month.

The national dataset contains information from 470 monitors situated along 162 rivers in 28 states. Excluding all areas outside the Ganga Basin leaves us with 101 unique pollution monitors along 29 rivers, in 62 districts representing 10 states; these are mapped in Figure 2. Over our 19-year period of observation, as many as 46 different measures of water quality are recorded at these monitoring stations, but only a few measures are consistently recorded over the entire sample time frame. The data are noisy, suggesting significant measurement error, and the panel is imbalanced. To mitigate these problems, we collapse monitor-level observations to the district level and construct moving averages of the data over a four-month window. These steps produce 8,725 district-month observations in the Ganga Basin with at least one non-missing value from our pollution measures of interest.

Our main indicator of river quality is BOD. This common, broad-based indicator of water pollution captures the amount of dissolved oxygen needed by water-borne, aerobic organisms to break down organic material present at a certain temperature (usually 20 degrees Celsius) and over a specific time period (usually five days). Its units are milligrams of oxygen consumed per liter (mg/l). Reduction of BOD is the primary goal of waste treatment plants in general (Brown and Caldwell 2001), but BOD is a particularly good choice for pollution measurement in the setting of Kanpur. Pollution from the tanning process primarily comes from two sources: the animal hides themselves, and the chemicals used to tan them. Both of these sources contain large amounts of organic matter, resulting in abnormally high BOD levels in tannery effluent. According to the United Nations Industrial Development Organization (UNIDO), effluent discharge into surface water typically is required to have BOD below 30-40 mg/l, while the typical BOD in _raw_ tannery effluent is approximately 2,000 (UNIDO 2011).

Use of a broad-based indicator of pollution raises the issue that it is likely affected by a variety of factors, not just the activities of tanneries. During the Supreme Court hearings, lawyers representing the tanneries argued that other firms, a negligent Kanpur municipality, and other negligent municipalities were contributing to the pollution around the tanneries (Mehta 2009: 78–82). This argument, however, was eventually dismissed in light of a report from the CPCB which demonstrated that the specific pollutant readings in the river were not even theoretically capable of being generated by any entity other than the cluster of tanneries (Mehta 2009: 83–84). Field reports of Jajmau report no other major industry in the area (Alley 2002).

In most of our analysis, we parameterize BOD as a dummy variable equaling one if average BOD in a district-month exceeds the national standard of 3 mg/l for bathing in surface water.<sup>2</sup> This 3-mg/l threshold is also a stated goal of the National River Conservation Plan, and is consistent with the crit-

> 2In addition to this BOD standard, suitability for outdoor bathing requires a total coliforms concentration of less than 5 per ml, pH between 6.5 and 8.5, and dissolved oxygen levels exceeding 5 mg/l.

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