ALBANY, N.Y. — The Environmental Protection Agency says New York regulators should set limits for radioactive materials in gas-drilling wastewater sent to public treatment plants before allowing any hydraulic fracturing of natural gas wells in the state.

The federal agency made that suggestion and others related to radiation from gas-drilling activities in 44 pages of comments submitted Wednesday night on the state Department of Environmental Conservation's proposed rules for high-volume hydraulic fracturing.

DEC Commissioner Joe Martens said Wednesday that the state agency received an unprecedented number of comments on its environmental review, which began in 2008. DEC spokeswoman Emily DeSantis said Thursday that 32,100 comments have been tallied so far and the number is expected to exceed 40,000 when all are counted.

The EPA is conducting its own review of high-volume hydraulic fracturing, or "fracking," which releases gas from deep shale formations by injecting wells with chemically treated water at high pressure to break up surrounding rock. Initial research results of the EPA study, which focuses on the vast amount of fresh water used and wastewater produced by fracking, will be released this year.

In its comments on DEC's study, the federal agency recommends that the DEC develop a Geographic Information System-based display that shows the location of permitted gas wells and update it at least monthly with the stage of operations on each site. The publicly accessible map should also show public water wells and intakes, EPA said.

Environmental groups, some of which have called for a ban on fracking instead of regulations, say the activity is a threat to drinking water supplies. DEC's proposed rules would ban hydraulic fracturing in the watersheds of New York City and Syracuse, an exclusion supported by EPA.

The industry, citing a long history of problem-free drilling in watersheds and through aquifers, says the state's rules are unnecessarily restrictive.

One of the biggest problems related to a boom in gas development in the Marcellus Shale formation underlying parts of New York, Pennsylvania, Ohio and West Virginia is how to dispose of the millions of gallons of polluted wastewater produced by fracking. Municipal water treatment plants aren't designed to remove some of the contaminants found in the wastewater, including radioactive elements.

While the state's review says flowback water coming out of fracked wells is not expected to contain significant levels of naturally occurring radioactive materials, EPA pointed out its own data from six natural gas companies in Pennsylvania that show elevated levels of radioactive materials in wastewater.

EPA advises that DEC sets a limit for radioactivity in drilling wastewater sent to treatment plants. It also notes that both EPA and DEC have to approve a treatment plant's analysis of natural gas wastewater before the waste is accepted for disposal. The analysis must include identification of any potential effects on the plant's operations.

The federal agency noted that some of the out-of-state treatment plants listed by DEC as potential disposal sites for gas drilling wastewater would be unable to handle New York's wastewater.

EPA also recommends that DEC prohibit the spreading of all gas well wastewater on roads for de-icing because the liquid would have elevated levels of contaminants, including radioactive elements.

Environmental groups criticized the DEC document for its lack of a definite plan for disposal of wastewater.

Permitting for shale gas wells has been on hold since the DEC review began in 2008, and won't be issued until after all the comments are considered and taken into account in a final document, likely later this year.