Wastewater treatment plant leak causing shellfish harvest restrictions

MILFORD — For the second time this year, DNREC has had to suspend shellfish harvest in the Delaware Bay and inland rivers due to wastewater discharge from Kent County’s sewer system — this time from the county’s treatment plant itself.

Since July 5, the Kent County wastewater treatment plant has been discharging “undertreated” wastewater because of operational issues, said Kent County Public Works director Andrew Jakubowitch. In an ordinary day, the plant expels about 10 million gallons of fully treated wastewater subject to several different standards concerning nutrient, bacteria and suspended solid limits. One bacteria they screen for, enterococcus, was significantly elevated.

“Our plant limit for our permit for enterococcus colonies is 33 per 100 mL,” said Mr. Jakubowitch. “Ordinarily we get that down to about 1 or 2 because we run really efficiently. Over the past 15 days the numbers have been all over the place from the hundreds to the thousands.”

Although highly concentrated, the undertreated wastewater diffuses quickly as it enters the Murderkill River.

“We’ve been monitoring the levels closely and the two recent tests we pulled from the mouth of the river were 41 and 50 colonies per 100 mL,” he added. “It’s elevated but diffused. The limit where the state recommends not swimming is 104 I’m told.”

Kent County has altered DNREC to the issue and is working closely to monitor the nearby rivers. On Tuesday, Secretary Shawn Garvin issued an emergency order for the closure of recreational shellfishing in the Delaware Bay north of the entrance to the Mispillion Inlet in response to the discharge from the plant. DNREC also advised not swimming in the affected area of Delaware Bay or other physical contact with the water but has not issued any warning about drinking water.

The emergency shellfish closure will remain in effect until 21 days after the “ongoing” issue has been resolved and water quality returns to acceptable effluent levels.

The closure only impacts the harvest of bivalve molluscan shellfish, — clams, oysters and mussels — and does not affect the legal harvest of other shellfish species such as crabs and conchs. DNREC noted that commercial oystering is not currently taking place in the Delaware Bay, but recreational harvest of hard clams is common this time of year.

The closure was necessary because as “filter feeders,” these types of shellfish “bioaccumulate” hazardous material found in the water column and can cause illness if eaten within a certain time frame, noted DNREC officials. The closure time frame is based on US Food and Drug Administration Guidelines under the National Shellfish Sanitation Program, and provides adequate public health protection for pathogens of concern, including viruses.

In February, DNREC suspended shellfish harvest for 21 days after an estimated 300,000 gallons of raw sewage was spilled into the Saint Jones River in Dover. According to the county, that incident stemmed from complications associated with emergency repair work on a broken 30-inch concrete sewer line outside Postlehwait Middle School. Although a much larger volume of wastewater is concerned with the recent incident at the treatment plant, it is undertreated wasterwater being discharged rather than raw sewage — which is far more hazardous per gallon.

What happened?

The issue began with a mechanical malfunction in one of the county’s wastewater plant’s 10 million gallon aeration basins — large holding or treatment ponds which promote the biological oxidation of wastewater. The plant has two of these basins, but one was in the process of being repaired when the other basin’s lining developed a hole.

“While we were working on the first basin, the other developed what’s called a ‘Whale,” said Mr. Jakubowitch. “This is when the liner fails and a large gas bubble forms in it and rises to the surface. The only way to remove the bubble is to puncture it, which makes another hole and causes more whales to form. When this is going on, that basin becomes very inefficient, and the water being released is no longer up to our standards.”

Mr. Jakubowitch said it is not uncommon for liners to fail, but to have it happen while the other basin was being repaired — thus unable to pick up the slack — it caused the issue to snowball.

“In addition, we’re receiving an extraordinarily high level of suspended solids into the plant right now,” he said. “Occasionally those levels will surge at intervals during the year, but when we’re already impaired, it just made our bad situation worse.”

What’s being done?

Although the wastewater being discharged is still in violation of the plant’s required standards, they’re beginning to dial back as the basin that was down for repairs comes back online.

“We have the other basin back online now with brand new diffusers,” said Mr. Jakubowitch. “We switching everything over to that basin now so the basin with whales in it can have the liner repaired. That process could take a few months, but the other basin has enough capacity to last us for a very long time and bring the levels back into compliance.”

Working closely with DNREC fisheries and enforcement officials, Mr. Jakubowitch says the state’s 21 day restriction on shellfishing will likely begin in the next few days as wastewater discharge quality returns to normal. Additionally, the county will continue to monitor bacteria levels in the Murderkill River and report their findings to DNREC.

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