The Department of Public Works (DPW) is writing this letter in response to the outpouring of complaints that we are receiving regarding dirty / rusty water. We believe it important for residents to understand the complex nature of this problem; the potential solutions and the cost implications; as well as what the DPW is doing to remedy the problem.

The dirty water coming out of your tap is created from naturally occurring minerals (iron and manganese) found in the town’s groundwater. The iron and manganese are dissolved in the water coming out of the ground. When these dissolved minerals are oxidized they form precipitates that can come out of solution. The town of Pembroke utilizes chlorine for disinfection, which is a strong oxidizing agent and can increase the rate of precipitation of iron and manganese. Since the boil order in August, the DPW has been injecting chlorine into the system at an elevated rate to protect the system from future bacteria outbreaks. The iron precipitates collect in the distribution system over time and when water velocities through the pipe are increased either by opening a hydrant or a large increase in water demand, the iron is picked up into solution and can come out through the tap. Pembroke’s groundwater has fairly high levels of iron and manganese. Three of the five Town groundwater sources are currently treated (Well #1, #4 & #5). The other two sources (#2 & #3) have dissolved iron and manganese levels below the treatment standards, but still high enough to form iron precipitates when oxidized.

This is the same chemical reaction that occurs when a resident uses groundwater to fill their swimming pool or hot tub and then after “shock” treating the water with chlorine, the water turns brown.

The town has received approval from the DEP to lower the chlorine levels in the water system and have already begun the process of lowering the chlorine dose. The DPW also plans to completely flush the hydrants and water system this spring which should help with the dirty water complaints. In an effort to minimize overtime costs, the flushing will likely occur during the day. It will be important for residents to watch where this work is occurring for the next couple weeks to make sure that iron colored water does not end up in your laundry.

The DPW is hopeful that lowering the chlorine dose will solve the majority of dirty water problems. It will be important for residents to continue reporting information to the DPW while we undertake these chemistry changes. Our goal as a public water supplier is to provide safe drinking water of good quality at the lowest reasonable cost. We sincerely apologize for the inconvenience that this continues to cause you.

Sincerely,

The Department of Public Works – Water Division