The lag in the completion of new power stations, equipment breakdowns, and insufficient water reserves for hydroelectric stations have caused frequent power shortages, particularly at peak load hours. Elaborate official measures have been introduced to regulate the consumption of electricity and to eliminate waste, including a bonus system for saving electricity. These measures have not proved sufficiently effective, and some enterprises have been reported to earn bonuses by the simple expedient of overstating their requirements in the formulation of the annual economic plans. The State Inspectorate for Industrial Power and Power Control, it was stated by officials, was not in a position to solve the problem of economizing electric power without the active cooperation of every enterprise, plant, and trade union. Additional unspecified measures affecting industry were reported to have been taken in 1973 to reduce peak power loads, and the population was advised to use electricity more sparingly between 6:00 P.M. and 9:00 P.M. RAW MATERIALS In 1970 about 54 percent of the manufacturing industry's output was based on industrial materials, and 46 percent was derived from agricultural raw materials; the proportion of industrial materials in manufacturing continued on its post-World War II upward trend in the 1960-70 period from a level of 24 percent in 1948 and 49 percent in 1960. This trend was sustained by the relatively rapid rise in the production and imports of industrial materials compared to the slower increase in agricultural output and imports. Because of the limitation of domestic resources, further industrial expansion will necessitate ever larger material imports. Iron and Steel The main deposits of iron ore are located at Kremikovtsi, northeast of Sofia, and at Krumovo in the lower Tundzha valley. Other small deposits of little or no commercial value are scattered in the Strandzha mountains, in the western Stara Planina, and at several locations in the Rodopi (or Rhodope Mountains). The ore in the Kremikovtsi deposit is of low grade; it has a mineral content of about 33 percent and requires beneficiation. Reserves at Krumovo were reported to be of better grade but much smaller. Available evidence suggests that mining at this deposit was discontinued after the mid-1960s. Its site is far removed from the country's two iron and steel mills.