Finance Committee - Agenda - 3/2/2022 - P40
Exhibit A
Scope of Services
The City of Nashua currently utilizes anaerobic digestion to produce Class B biosolids for land application; reduce
the total quantity of dry solids; and to create biogas for beneficial use. The digested sludge is dewatered with one
of three inclined screw presses and then disposed of through a 3-year contract with RMI. The current contract is
scheduled to expire on June 30, 2022. The City is currently paying $62/wet ton and this rate is anticipated to
increase significantly with the next contract due to significant changes in the biosolids/sludge disposal market
related in great part to the emergence of PFAS compounds as a critical concern.
The City has also experienced capacity concerns with the current level of raw solids production in the primary egg-
shaped digester but have been able to maintain the necessary detention time required for Class B criteria by
adjusting the digester feed schedule and holding more solids in the digester tanks.
Until there are clear regulatory criteria for PFAS compounds in wastewater sludges, there will be uncertainty with
any plan to continue with beneficial use. However, current indicators appear to favor processing biosolids to meet
Class A criteria. Likewise, reducing the wet weight of the final product will reduce ultimate disposal costs whether
the biosolids are beneficially used, landfilled, or incinerated. As such, the City would like to implement sludge
drying of the anaerobically-digested sludge to meet Class A criteria. This will include an investigation of drying
technology alternatives to determine the preferred approach based on product quality characteristics and
preliminary design development to assess overall project requirements and costs.
Based on our understanding of the needs of the City, we propose to perform the following tasks to identify the
preferred drying technology, develop a detailed facility design concept including capital and operational costs, and
assess the impact on future biosolids disposal /beneficial use costs. Once the preferred technology has been
selected, preliminary design documentation (report, plans and cost estimate) will be developed.
A. Initial Kick-off Meeting and Preliminary Planning Session.
B. Validate Existing and Future Sludge Quantities. The sludge generation numbers developed for the Facility
Plan will be updated using data from 2020 and 2021. The updated existing sludge quantities will be used to
estimate future quantities using the methodology developed for the 20-Year Facility Plan.
C. PFAS Assessment.
1. Collect existing PFAS monitoring data for the digested solids and conduct two additional rounds of
PFAS testing on the digested sludge.
2. Compare PFAS levels in Nashua’s digested sludge to available benchmarks (Maine’s screening
standards, Michigan’s land application guideline, available international standards for land
application). Compare results for Nashua’s digested sludge with monitoring data for other
biosolids in New England and beyond.
3. Identify potential impacts of anticipated PFAS regulations on disposal options, based on current
levels in Nashua’s digested solids.
4, The budget for this scope item includes a $5,000 allowance for contract testing services.
D. Baseline conditions assessment.
1. Based on the continued use of the existing anaerobic digesters and the existing and projected
future sludge quantities, assess the technical feasibility of continuing to meet Class B criteria over
the 20-year planning period.
WRIGHT-PIERCE = 1 of 3
Engineering a Beller Environment
