According to Coker, once the chemical system is installed and running, 77 drums of chemicals a month would go in one end of the plant and come out the other as sludge. He added that in his 10 years working in waste-water treatment, the costs both of chemicals and sludge disposal had gone only up, a trend he did not see changing.
"Chemical treatment is the only way to meet the compliance deadline," he said.
Coker said he preferred a biological method that would remove not only phosphorus from the waste water but nitrogen and ammonia as well. He said the plan called for a conversion from the chemical to the biological method once the state's deadline had been met.
But Mark Malarich of Gannett Fleming, DARA's consulting engineer, warned against that plan.
Malarich said that so far the state Department of Environmental Resources had not required that nitrogen or ammonia be removed from the waste water before it was discharged into the Brandywine Creek. He questioned burdening DARA with the extra costs of removing them.
"It is our position that until we know what the nitrogen-removal limits are, we can't even proceed with a study," Malarich said after the meeting. He added, though, that he supported the biological method, which in the long run
avoids the high costs associated with the chemical method.
In freshwater streams like the Brandywine, phosphorus, nitrogen and ammonia - all components of fertilizer - can devastate the ecological balance by causing excessive plant growth that robs other stream organisms of life-giving oxygen.
Although the Downingtown plant meets the DER's standards, experts claim the waters of the Brandywine are suffocating from an overload of the three nutrients.
"Getting the nitrogen and phosphorus out of the stream would do a lot for it," said John Johnson, president of the West Chester Fish, Game & Wildlife Association. "Although this does nothing to replace the groundwater, at least it would help protect the stream."
DARA has challenged the DER's timetable for implementing the latest discharge limits, including the phosphorus-removal requirement, before the state Environmental Hearing Board. Malarich would not say whether, even if DARA won the appeal and the July 1991 deadline was pushed back, the extra time would be used to install the biological method with the chemical treatment as backup.
In other business, the DARA board authorized Engineering-Science to advertise for bids to remove asbestos-containing materials and equipment from the Downingtown plant.
The action came after DARA lawyer Edward G. Conroy warned the board about taking on what could be perceived as E-S's operating responsibilities by withholding money for improvements that E-S recommends at the plant.
"That puts the authority dangerously close to operating responsibility," said Conroy, adding that such a path could lead to individual and joint liability, which are not covered by DARA's insurance. "Only with great care do we go against the recommendations of E-S," he said.