Massachusetts Port Authority

  June 10, 2003

 Subject:  Questions Raised at May 20, 2003 HFAC Meeting About Hanscom Deicing Study

 At the May 20 HFAC meeting, several technical questions were raised about the recently completed Hanscom Field Deicing Study.  The questions are listed below, along with a response based on discussions with Massport’s environmental consultant CDM.

 Question 1: What are the maximum safe levels of deicing compound that could be used at Hanscom Field?

The modeling methods used in the deicing study to determine potential deicer concentrations and changes to dissolved oxygen concentration in the river were based on highly conservative assumptions (e.g. no in-stream dilution) for a specific scenario (2015 Moderate Growth).  Using the same model and aquatic toxicity standards would give highly misleading results regarding an allowable level of deicer application.  Also, it is not feasible to calculate a maximum safe level for human exposure since the deicers studied are not considered toxic to humans. 

 In order to ensure the safety of new deicing practices at Hanscom, Massport will undertake a monitoring program to compliment the modeling results. 

Question 2: What is the proposed scope of the Hanscom Field deicer monitoring program?

A preliminary outline for a water quality monitoring program has been developed for use at Hanscom Field during deicing events.  The objective of the monitoring program is to characterize the airfield runoff water quality during deicing events. This information will then be compared to the analysis in the deicing study.

 Monitoring Program Outline

Locations

5 Hanscom Field outfalls

2 in-stream locations (Shawsheen and Elm Brook)

Frequency

            Baseline testing prior to deicing

4 deicing events during the winter of 03-04

2-6 samples at each location per event depending on duration of deicing activities

Testing Parameters

Dissolved oxygen

Chemical oxygen demand

Biological demand

Glycol concentration

pH

Sodium

Conductivity

Temperature.

Question 3: What are the standards for sodium in drinking water and potential effects of deicing on sodium levels in downstream drinking water supplies?

The Massachusetts DEP has established a guideline for sodium in drinking water.  The guideline is 20mg/L and normally applies to people on a sodium-restricted diet.  Water suppliers are required to notify customers if their drinking water exceeds the guideline.  The water supplier is not required to treat the water.

Regarding the potential sodium concentrations in the study, it is important to note that the actual concentrations seen at downstream water supplies will be significantly less then the values reported in the deicing study for two reasons. First, the analyses used assumed no dilution would occur as the sodium traveled downstream.  In reality, there is significant dilution by tributary runoff before the Bedford well area and even more dilution by the Burlington intake.  Also, a portion of the deicer will be trapped in the stockpiled snow around the airfield and will enter the waterways slowly as the snow melts over time.  Secondly, in the case Bedford ’s groundwater wells, any river water that reaches the wells must first travel through the subsurface sand and gravel between the river and wells before it can be used.  This infiltration is a relatively slow process, which means that only a small fraction of river water passing by during a deicing event would enter the subsurface and be available at the wells.

Question 4: What are the baseline dissolved oxygen levels in the river and decreases due to the deicing compounds?

Massport proposes to collect baseline dissolved oxygen data as part of the proposed water quality monitoring program.  This data will then be used to determine what effects, if any, deicer use actually has on the water bodies.

The Massachusetts DEP has established a dissolved oxygen standard for the Shawsheen River and Elm Brook, which are defined as Class B waters.  Dissolved oxygen should be greater than 5 mg/l or greater than 60 percent of the saturated dissolved oxygen concentration.  For the winter months, the second criteria (i.e.greater than 60 percent saturation) is expected to be met since dissolved oxygen levels are higher in winter months due to the inverse relationship between temperature and dissolved oxygen.