Did the train derailment in East Palestine affect its water supply? Experts say more testing is needed.

After a Norfolk Southern train derailed in East Palestine, Ohio, more than two weeks ago, residents and health officials have expressed concern about the state of water in the area.

Homeowners in East Palestine have complained of symptoms that some in the town believe are tied to the release of chemicals from the derailed train cars.

The incident has also sparked environmental concerns. An estimated 3,500 fish -- such as minnows, darters and sculpin -- have died in creeks and rivers around the area, according to the Ohio Department of Natural Resources.

While many officials have said the town's water supply appears to be free of harmful levels of contamination, Kuldeep Singh, an assistant professor of earth sciences at Kent State University, told ABC News that long-term testing needs to be done to ensure the water supply is safe.

Singh said locations that previously showed clear results may not produce the same results two or three weeks down the road.

"What happens today is only a diagnostic of that space and time," he said. "What may not happen in one location might be another location, what may not be in one particular location in time could be in another location in time."

Cleaning up derailment site

According to Ohio Gov. Mike DeWine, most contaminants did not enter local waterways but are rather "pooling at the derailment site in puddles and ditches."

So far, Norfolk Southern said it has removed more than 1.5 million gallons of contaminated water from the site, with the company telling ABC News that 400,000 gallons of contaminated water were collected on Tuesday alone.

Neither Norfolk Southern nor the Environmental Protection Agency revealed which contaminants were found in the water, or the levels of contaminants found.

Several of the train cars were carrying dangerous materials on board, including vinyl chloride, ethyl acrylate and isobutylene, are considered to be very toxic -- possibly carcinogenic -- and could be unsafe for both residents and the environment.

"These are hazardous chemicals and have potential health impacts if they contaminate our air and water," Miranda Leppla, director of the Environmental Law Clinic at Case Western Reserve University's School of Law, told ABC News. "And so, it's really important that we make sure that the cleanup efforts are really looking at this on a long-term basis."

The risk is not just to humans. ODNR said the deaths of the fish in nearby creeks and rivers likely occurred from the immediate release of contaminants following the crash, although the agency does not believe there is currently any risk to aquatic life.

Testing water wells

According to the EPA's latest update Sunday, results from sampling municipal well water don't show quality concerns. The Columbiana County Health District has so far sampled 52 private water wells.

On a trip to East Palestine Tuesday, Gov. DeWine and EPA Administrator Michael Regan drank tap water while visiting a woman's home to prove the water is safe to drink, although some residents are encouraged to use bottled water until their well water testing results return.

Singh said it's possible the public supply wells are never contaminated because the aquifers -- which are the water-bearing rocks that transmit water to wells -- are deep underground and separated by hundreds of feet of sedimentary rock.

However, private water wells might be contaminated because their aquifers are shallower.

However, he added that to detect whether or not the private wells are contaminated, inspectors cannot examine them at random.

"If it's random testing, you might be testing in a direction where you would never go, for example, but if nothing shows up in their well, does not mean contaminants are not there and that's what my point is," Singh said. "Random testing does not ensure that they are not contaminated. It has to be mapped from the site where contamination started, and then move outwards."

Sampling groundwater

About a week after the accident, Norfolk Southern submitted an action plan to the Ohio Protection Agency saying it will install a number of monitoring wells to test groundwater.

"If you think about it, anything that spills, with simple gravity, would go into the soil and percolate down to the groundwater," Singh said. "That part is not visible. Often, our choices and fears are dictated by the visible components, not the invisible."

No reports have been released stating groundwater is contaminated but, if it is, it could feed to streams and rivers.

Additionally, because so much of groundwater is deep below the surface, "the effects of that contamination may take a longer time to appear," Leppla said.

Unlike cleaning soil, which is much easier because it can be picked up and moved, groundwater takes longer to be decontaminated.

"Groundwater is the most important being that is the most pristine freshwater abundant available to us," Singh said. "And once contaminated, may take forever. For example, cleanup, of…groundwater contamination might take 10 years. That takes a lot of costs on taxpayers."

ABC News' Sasha Pezenik contributed to this report.