A draft report by the engineering firm hired to evaluate soggy areas of Ocean Park concludes that while several wastewater treatment beds under the park are failing, “there is a strong likelihood” that the majority of the problem is from irrigation and storm-water runoff.
Oak Bluffs was ordered to do an engineering study in a notice of non-compliance, issued last September by the state Department of Environmental Protection. The Hyannis environmental engineering firm Stearns & Wheler conducted the study.
For several years, mushy ground and sometimes standing water have interfered with use of the public park in the month of August. Testing determined that some of the water was treated effluent from the town’s wastewater treatment plant, which pumps treated wastewater into leaching beds under the park.
“It’s a combination of everything, wastewater, irrigation, and storm water,” said wastewater plant manager Joe Alosso.
According to the report, four test excavations conducted on December 15 determined that many factors contribute to the ponding of water in the lowest part of Ocean Park.
Engineers said changes to irrigation, aeration, and turf management would reduce the ponding. They said removing some sprinkler heads in the affected area, and installing a rain sensor, so the sprinklers won’t turn on during a rain, would help.
Mr. Alosso has long contended that too much water is used to irrigate Ocean Park in the summer months. He said the irrigation system is turned on, rain or shine, for five days per week in August, dumping 186,400 gallons of water on the park. By contrast, he said the typical family home uses about 75,000 gallons of water for all uses, during an entire year.
“I have never said that the ponding in Ocean Park is from irrigation,” said Mr. Alosso. “But I do maintain that the inability of the treated wastewater to percolate down through the ground is affected by the amount of irrigation water and rain water that is applied to the site. The site needs recovery time for all this water to move down through the sand.”
Engineers determined that topsoil in some areas of the park is too thick and compacted to provide good drainage.
“There’s way too much topsoil, it’s not getting any oxygen into the sand and the soils below it,” said Mr. Alosso. “For the leaching beds to work properly you have to have some oxygen getting down in there. It’s upwards of a foot of topsoil in some places.”
Engineers also suggest that installation of underground irrigation pipes, electrical conduits, and other infrastructure may have the unintended effect of channeling drainage water to lower parts of the park. When trenches were excavated for the pipes, they may have created aerated soil that provides a path of least resistance for the water to drain. When the water reaches more compacted areas, it puddles on the surface. Another part of the problem may be a clogged catch basin. Engineers documented one catch basin in the lower part of the park full of water to within four inches of the surface. Other nearby catch basins were empty.
The engineers found that a leaching bed between the grandstand and Sea View Avenue was draining the effluent at a rate “significantly” less than it was designed to do. Engineers found large amounts of biological material (biomat) clogging the leaching fields. Biomat is a general term for living organisms that grow in a rich nitrogen environment. The excavation of the bed confirmed data from monitors that measured drainage over several months. On the basis of those findings, the engineer recommended shutting down four leaching beds located between the grandstand and Sea View Avenue. Flow to those beds has already been stopped. The report concludes that four more beds in the area generally surrounding the small concrete pond may have to be disconnected in the near future, because soil and biomat conditions are similar to the poorly functioning bed.
“We’ll talk about different options,” said Mr. Alosso. Among the options is permanent shutdown of leaching beds, or refurbishing them with new drainage material. “Fortunately it looks like it’s one section of the park. The other areas looked okay.”
The engineers concluded that even if the beds are shut down, the rest of the leaching field has the capacity to absorb all of the town’s wastewater. There are a total of 28 beds under the park.
Mr. Alosso said the town would continue work on an alternative site for leaching fields. The town is evaluating land known as the Leonardo property, located near the wastewater plant, which is located at the intersection of Pennsylvania Avenue and County Road. “We need to do something,” said Mr. Alosso. “I still think additional capacity is the good long-term answer.”
Copies of the engineering report were distributed to selectmen, park commissioners, and wastewater district commissioners. Mr. Alosso asked for comments from the public officials, which will be submitted to the engineering firm. “They will make any adjustments they think are warranted based on the comments, and then we’ll send it off to the state.”
The state will use the engineering report to determine the best way to solve the problems.