Industry Insight: Long Island’s wastewater treatment plants and the nitrogen in it’s groundwater

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Throughout many areas of the country, and particularly on Long Island, entire communities are unable to connect to centralized sewer districts. In place of sewer connections, these homes have their own cesspools, which are designed to treat waste but only do so at the most basic level. In actuality, the waste that dissipates into the ground from these cesspools is nitrogen-rich, with high amounts linked to having hazardous effects on humans, animals and the environment. In an attempt to protect Long Island’s groundwater, there has been a recent push by government officials, the public, and industry experts to update the Island’s infrastructure by adding wastewater treatment plants. While space is hard to come by in many of the densely populated areas, wastewater treatment plants and centralized sewer districts have emerged, playing a vital role in the renaissance of certain Long Island communities. We sat down with Chris Weiss, one of H2M’s Senior Wastewater Engineers, to discuss the issue. Can you give us an overview of the issue with nitrogen in Long Island’s groundwater? We luckily have a very large sole source aquifer under the ground that all of our drinking water comes from. It’s not until you get into the city that it comes down from reservoirs. So, you have to be careful to protect that groundwater from saltwater intrusions. You can’t pump too much saltwater into the ground, otherwise it replaces the groundwater and you could get plumes of toxins.

That’s why we have wastewater treatment plants. Could you talk more about the wastewater treatment plants? What’s their purpose? 90% of Long Island’s treatment plants discharge to groundwater. Not to the oceans, streams or anything like that. So, basically all the treatment plants are required to remove all the biological pollution from the water. The only thing left after you do that is nitrogen. The whole concept is treatment plants will effectively lower the nitrogen levels to discharge below 10 milligrams of nitrogen. Suffolk County makes you reduce your nitrogen loading down to 10 milligrams per liter if you’re going to put it into groundwater and to 4 milligrams per liter or less if you’re discharging into the ocean. That is well below any danger level that would ever affect the groundwater source.

On Long Island, there are not that many treatment plants. We have over 200 treatment plants but there’s a heck of a lot more houses than that. I think less than 30 or 40% of the Island is connected to sewers. What about the homes not connected to sewers? Most of the houses are just connected to cesspools that do no treatment whatsoever. Nitrogen loading, if you put it into the ground, will dissipate. The ground will do its own natural treatment to a certain degree as long as you don’t have too much nitrogen going into one spot. The big concern is you have entire neighborhoods of cesspools that just take the solids out and you’re putting very nitrogen-rich effluent into the ground. It’s the only treatment that happens. Everything going into the ground at that point is biological stuff that naturally decays, so that’s not the problem.

You’re probably looking at 15-75 milligrams per liter of nitrogen, though. And if you multiply that by the number of homes, there’s a concern. How much of that could we put into the groundwater that the groundwater can dissipate and dilute? What’s the solution? The most prevalent solution is a centralized treatment district. It’s simple because you only have one place to maintain. But it’s a crowded island. Where do you put these big treatment plants? If there isn’t any room, could there be another solution? The other idea that everyone has been kicking around is to come up with something better than a septic tank—a homeowner’s personal treatment system. We did a study for Suffolk County evaluating different treatment plants that could be used for small commercial establishments and houses to meet the 10 milligram per liter requirement like a full-scale treatment plant. We found a bunch that could do that, but they’re costly. Are they cumbersome? They take up a little bit more space than a standard septic tank or leeching pool system—maybe 50% more space—but it’s underground, so you really don’t see it. All you need is some area on your property to install it. Are there any drawbacks?

There are some. In order to treat sewage to that level, you need mechanical equipment. Unlike a septic tank that has none and requires minimal maintenance, this setup would need something moving the water around, introducing air into it. Usually pumps do that with injection. You would need a control panel, float switches, and other controls. So now you have mechanical and electrical equipment. For most, that would require someone who knows how to operate the system to make sure it’s treating it properly. Then you have the need for repairs because of its components. So, it’s an added expense to the homeowner? It could cost you $20,000 or more to install one in the ground, plus paying an operator approximately $1,500 a year to run it. It’s a high expense compared to a septic tank and cesspool, which cost around maybe $7,000 total to install and it maintains itself with intermittent cleaning for 30 to 40 years. It’s really a question of coming up with an economical idea to protect our groundwater that people can afford. Are there more economical ideas? Not really, which is why the County and local government is pushing so hard to sewer all these areas rather than installing all these other systems. It would take the responsibility away from the homeowners. If private homeowners don’t maintain these systems, you’re essentially going to have the same, nitrogen-rich wastewater going out the door. So what problem did you solve? And how could you possibly monitor thousands of homes to make sure each one of them is maintaining their private little treatment plant? You would never be able to keep up with it.

Then what’s the solution? Do you make them smaller to accommodate each area? That’s one of the ideas. Technology has come a long way, and treatment plants are getting smaller. You can now do much more in a smaller footprint. It’s expensive, but they take up a lot less space. The problem is that nobody wants a treatment plant as their neighbor. It’s tough to find a plot of land on Long island that’s nowhere near someone else’s house, where the residents will say, “Oh, go ahead. Put a treatment plant there.” How do you approach it if nobody wants treatment plants in their neighborhood? There’s been a tendency to look at all these municipalities that already have municipal sewer plants, like Patchogue, Riverhead and Hauppauge. You start realizing that there are already treatment plants there, and there’s room at these treatment plants to give them extra capacity by improving the technology that will let them process more. What you do is start extending the sewer districts out and start taking in more areas to make those treatment plants centralized sewer districts, as opposed to just village sewer districts. Why doesn’t Suffolk County centralize? Because Suffolk County is looking at Nassau County and saying they don’t want to run themselves. Suffolk County differs from Nassau County in that Nassau has all of its sewer districts under one umbrella. Suffolk County is a collection of different municipal sewer districts.

Now Nassau is hiring a management company to run its sewer districts because it was not able to. What Suffolk is trying to figure out is how to help these municipal sewer districts expand and take in more areas. Are there any success stories for a municipal sewer district? It was hugely essential for Patchogue, which had a really good vision. They understood the treatment plant’s importance. They took an old, outdated sewer plant, which was designed for 500,000 gallons per day, and expanded it to take in more of the district and allow their downtown to grow. They increased the treatment plant to a highly efficient 800,000 GPD, which could easily expand to 1.2 million GPD. Now they have branches that go out and connect all these lovely commercial and housing developments, allowing Patchogue to flourish. Without a treatment plant, the revitalization never happens. What about areas that don’t already have a treatment plant in place? An area like Bellport is on the fence about either connecting to Patchogue or building their own sewer treatment plant. Bellport has options, but they know that without choosing one, they can’t stabilize their commercial district, which could increase property values of homes outside of the commercial district.

The commercial district creates the lifeblood of the community. As it relates to wastewater treatment plant expansion on LI, what would you like to see going forward? I’d like to see the expansion and branching out of the sewer districts, making the municipal districts centralized. The only way to get private homes on sewers is to do that. Find some land to either build a new centralized sewer district or connect them, like Mastic and Shirley are looking to do. All the existing treatment plants should try to take in as many residential and commercial areas around them as they possibly can to maximize their use, rather than being little islands unto themselves. Chris Weiss, P.E. is H2M’s Senior Wastewater Engineer. You can reach Chris at