Three workers are doing the patrol of the tank area to spot the leaks. These are the assembled tanks as opposed to welded, held together by rivets and packing (whose effective life is about 5 hours, and that doesn't assume radiation).
The tanks contain highly contaminated waste water after cesium absorption treatment and desalination treatment (currently Reverse Osmosis only), high in beta nuclides including strontium. The beta radiation levels are about 2,000 mSv/hr, give or take 200, at 70 micrometer dose equivalent measured at 5-centimeter distance. (For more, read my posts on the topic, here.)
Workers are to examine the tanks and any water puddles closely, and measure the radiation. The area looks huge, and there is no way to distinguish the actual leak from the rainwater puddle until and unless they actually measure the radiation.
TEPCO released the video on September 4, 2013, which was taken on September 3.
By the way, there is a job listing posted on September 3, 2013 at the government job agency "Hellowork" in Fukushima Prefecture to recruit workers to do the tank patrol at Fukushima I Nuclear Power Plant. The listing was posted by one of the subcontractors (of the subcontractors, most likely).
According to the job listing, the tank patrol has three 8-hour shifts, and the workers will be paid between 10,000 yen to 14,000 yen per day with no benefit. There is no risk benefit either, even though they will be in very close proximity of the high beta source.
From Hellowork (9/3/2013):
Type of job: Full-time, contract
Job description: Monitoring tanks that store contaminated water at Fukushima I Nuclear Power Plant
Shifts: three (08:00～17:00, 16:00～01:00, 00:00～09:00)
Break: 60 minutes
Overtime: 10 hours per month average
Wages: 10,000 to 14,000 yen [100 to 140 dollars] per day
Details of work: to monitor tanks that store contaminated water at Fukushima I Nuclear Power Plant. You will patrol the compound with survey meter with another worker, and visually inspect the tanks and write reports. One round takes about 30 to 40 minutes, and you are expected to do 4 to 6 rounds of patrol per one shift. The work will be intermittent, and the effective hours of work per day will be about three hours. When you are not doing the patrol, you will wait in the room that is shielded from radiation inside the plant. Trial workers are also wanted.
Required education: none
Required work experience, license, certificate: none
If the national government is serious about tackling the problems at Fukushima I Nuke Plant, the very first thing they should do is to change this employment scheme of subcontracting pyramid which gives each layer profit by skimming off workers' wages and gives the top contractor(s) plausible deniability that they do not know about work conditions of the workers in the lower layers of the pyramid and therefore they are not responsible for the workers.
But I fear the government is not serious, and only interested in evading their responsibility and finding others to blame for any failure, past, present, and future.