MILFORD TOWN OF

Milford's plant blows past its new phosphorus limit during drought recovery

On August 8, Milford's wastewater treatment plant, which discharges to the Souhegan River, reported a phosphorus violation of 652 percent over its permitted limit, alongside a repeat copper exceedance the same day. The copper problem is not new; it echoes a violation from late March that was already the facility's second consecutive one. What makes the phosphorus number especially striking is how young that limit is: it comes from a general permit that only took effect this past February, so a blowout of this size arrived within the permit's first six months. EPA currently lists the plant as one of only three facilities in significant non-compliance across this watershed. The timing sharpens the concern. This stretch of the Souhegan is already on the state's impaired-waters list for nutrients, and a pollution reduction plan for phosphorus loading here exists precisely because this has been a recognized problem before. The violation also landed as Hillsborough County was climbing out of a severe drought, with over 80 percent of the county still in moderate-or-worse drought conditions in late July, easing to roughly a fifth of that by mid-August. Low summer flows matter here because they mean less river volume to dilute whatever the plant releases. Excess phosphorus in slow, warm water is exactly the kind of load that feeds algal growth and can drive down dissolved oxygen for the fish and mussels downstream. Flow and oxygen readings at the outfall itself were not available, but the conditions on the river this summer were set up for exactly that kind of stress.

Copper discharge threatens mussels during summer low flow

The Milford wastewater treatment plant released copper at nearly double its permitted level last quarter — marking the second consecutive violation for the facility. The timing is particularly acute: summer low flows concentrate whatever enters the water, and Eastern Elliptio mussels (Unionidae) inhabit these rivers and are exquisitely sensitive to copper toxicity. These native filter-feeders rely on clean water to survive. Copper bioaccumulates in their tissues and disrupts their metabolism even at low concentrations. With the plant now running a pattern of non-compliance and river flows at their annual minimum, the margin for the mussel populations narrows considerably.