Would offsite wastewater treatment be better than an onsite option in some neighborhoods in the Wastewater Management District (WWMD)? That’s the question that the Water Pollution Control Authority (WPCA) asked engineering consultants at Wright-Pierce to help them answer.

The initial $138,350 consulting contract was for assessing several large properties for their potential to accommodate a community wastewater system. The goal was to find alternatives to on-site treatment for neighborhoods with land characteristics that make on-site septic system upgrade solutions problematic.

In this model, wastewater would be collected from homes in these neighborhoods and pumped to a common pre-treatment location near the edge of a candidate site. At the community system site, a small building would be built with wastewater treatment equipment. Here, the wastewater stream would be pre-treated before subsurface disposal. This type of wastewater treatment system is already in use at sites like Water’s Edge and Tanger Outlets in Westbrook.

In a community system model, wastewater is collected from homes and piped by gravity and/or pumped to a common treatment facility. From this structure, the treated wastewater is then distributed in pipes out into a leach field where it slowly seeps into the surrounding soil.

What the engineering firm was asked to do was to assess if the candidate properties’ characteristics were favorable enough to warrant further study for a community system. Among the factors that could affect a site’s hydrological capacity are the parcel’s size, soil type, distance to groundwater, whether ledge is present, and the parcel’s subsurface structure.

Two parcels were selected at the end of the first phase for more study: the former Donnelly’s property and the Old Saybrook High School property.

On Nov. 9, the WPCA approved Amendment 1 to Wright-Pierce’s contract at a cost of $119,537. This added scope of work supports more detailed and site-specific studies by the firm’s engineers of the two candidate properties.

“Could these sites be effectively used as a community system?” was the question that WPCA Project Manager Steve Mongillo said this project would answer.

Mongillo noted that any on-site testing done in this phase by Wright-Pierce would need to be pre-approved by the two candidate sites’ owners.

“The preliminary hydraulic studies will be done by the end of December,” said Mongillo. “Monitoring of the study sites will likely continue into next year.

“Ultimately it has to make sense. We are looking for the most realistic solution that is cost effective,” said Mongillo. “Several hundred homes may be considered for inclusion in this community system if it is found viable.”

The WWMD in which the WPCA is implementing the septic system upgrade program includes about 1,900 lots in 15 different areas of town. With a nine-year build-out estimate, by the end of 2015, about 700 of the 1,900 properties in the WWMD will meet the remedial standards agreed to by Department of Energy and Environmental Protection.