WINDHAM – The quality of groundwater in North Windham continues to worsen as a result of the area’s high level of commercial development, according to test-well data unveiled Tuesday.

“The effects of development on groundwater quality have been significant,” Robert Gerber told the Windham Town Council Tuesday. “As I study not only over the state of Maine but New England, which is the area that I cover in my work, this is one of the more dramatic examples I’ve seen of change in groundwater quality over time in relation to development.”

Gerber, a geologist with Sebago Technics who has tracked the quality of the North Windham Aquifer since the mid-1990s, was at the meeting to present for the first time the 2008 and 2009 data collected by the United States Geological Survey, which installed and annually tests North Windham wells.

The council, which has been discussing a possible sewer for North Windham and Windham Center more intensely in recent months and has already spent close to $100,000 to conduct initial surveys and research on possible sewer routes, made little comment on Gerber’s report Tuesday night, though the report confirmed what former and current councilors have publicly feared: higher pollution rates are being caused by the concentrated development in North Windham.

While there are individual test-well results that buck the rising trend, including ones at Chaffin Pond, groundwater overall is showing higher amounts of nitrates, chlorides and electrical conductivity, Gerber said.

“The trend is that the water quality in the aquifer is getting worse with time,” Gerber said. “It’s significantly worse particularly along the Route 302 corridor and down near Collins Pond.”

Gerber explained to councilors Tuesday night that nitrates are caused by manure, fertilizer, human waste and food waste leeching into the groundwater, and the chlorides can be traced to road salt used in winter road maintenance.

Nitrates, Gerber explained, are particularly harmful to pregnant mothers and infants.

“The nitrate turns to nitrite in their stomach and that inhibits the ability of the hemoglobin to carry oxygen around the body,” Gerber said. “There have actually been infant deaths as a result of them not being able to get oxygen … so it is a real serious parameter for people who are drinking the water.

“Fortunately,” he continued, “all of North Windham in most of the areas are covered by public drinking water supply from Portland Water District. If they are on private wells, it could be a concern.”

The North Windham Aquifer is a mass of underground sand and gravel that is more than 100 feet thick in spots, Gerber said. The aquifer covers much of the commercial district extending from Enterprise Drive in the north to below Collins Pond in the south, behind Wal-Mart on the west and east beyond Little Sebago Lake.

The USGS test wells range in depth from 25 feet in order to test water quality in the upper aquifer to deeper wells that test the lower aquifer. Gerber said the data show upper aquifer test wells are generally more polluted than the deeper test wells, primarily because pollutants are slow to seep to the deeper levels of the aquifer. Gerber expects those levels to rise as pollutants descend through the aquifer.

Two of the highest readings came in test wells off Route 115 near Collins Pond and at Wal-Mart, which in recent years has begun more intense food processing operations at its superstore. Since food waste can increase nitrate levels in groundwater, the rising trends don’t surprise Gerber, who said test wells near Wal-Mart and Collins Pond both show nitrate levels over or near 10 milligrams per liter, the federally recommended safety limit for nitrates in drinking water.

Gerber also reported higher levels of “specific conductance” of the groundwater, a measure of the electrical conductance of water that is closely associated with increased development pressures. Gerber said development in North Windham has introduced more solids and ions into the water, which can cause higher conductivity.

“There are a lot of large rapid increases along the Route 302 area, and some fairly high numbers,” Gerber said. “Background groundwater would typically be 150 microSiemens per centimeter and we’ve got numbers over 1,000 here. So, it’s quite a bit elevated over what would be normal groundwater that doesn’t have any influences from manmade stuff. So the rapid increases and high numbers definitely showing the effects of probably land alteration and combination of road salting and septic systems.”

While higher nitrate levels can cause oxygen transport problems in the human body, high sodium chloride content can cause problems in adults suffering from hypertension and blood pressure ailments.

“People that are required to be on low-salt diets, heavy people or people with hypertension or blood pressure issues, the doctors will tell them they need to be on low-salt diets,” Gerber said, “Some of these sodium levels are well over 100 mg per liter and that can be dangerous to people who have to be on a low-salt diet if they drank a lot of the water.”