HARRISBURG — Companies rushing to drill for natural gas in the rich Marcellus Shale reserve a mile below Pennsylvania have tallied more than 1,400 violations of state laws since January 2008, according to an environmental advocacy group's analysis of state data.

The Pennsylvania Land Trust Association said 952, about two-thirds, of the violations caused or had the potential to cause environmental damage, from chemical spills to improperly lined sludge pits. The rest were classified as safety or administrative violations.

More than half the environmental violations involved improper construction of a wastewater pit or improper control of erosion during earth-moving activity, both of which can result in water pollution. One in six of the environmental violations, or 154, dealt with industrial waste spills while one in 10, or 100, dealt with unspecified violations of the state's waterway protection law.

The modern-day gas rush has poured billions of dollars into the Marcellus Shale region, which underlies New York, Pennsylvania, West Virginia and Ohio. Many residents have complained the drilling techniques used are unsafe, but the drilling companies say that's untrue.

A portion of the report sorts the violations by company and divides by the number of wells each company drilled, giving a snapshot of the best performers against the worst offenders.

The association's project coordinator, Elana Richman, said the staff had been reading news reports of the violations and wondered how many more violations were happening.

"We felt like there was more out there that we weren't seeing and we wanted to know what really was going on," Richman said Tuesday.

The association filed a Right-to-Know request with the Department of Environmental Protection and received information on spreadsheets.

Some of the violations reported in the media were not included in the spreadsheets, a discrepancy the association has been unable to resolve with the department. The numbers also do not include violations by trucks hauling wastewater away from drilling sites.

The association did not take a position on whether the number is too high, but two conservation groups cited the report in calling for more state inspections.