Land based disposal

As I sat at the back of the courtroom for three weeks, the question people kept asking was “exciting isn’t it?”.  Of course, the implication was that the slow pace was like watching paint dry.

But once you get into the rhythm of it, you realize that there is a lot of information being presented that just isn’t as directly available elsewhere.  If you want to understand the dilemma that our town faces, the primer on land based disposal was very informative.  Here’s what I got out of it:

Basically, waste water systems have two components.  First there is a treatment facility that essentially does all of the serious cleanup of removing solids and in our case cleaning up the organic components with bacteria that essentially eats it and settles out.  The resultant effluent is bacteriological inert but contains a high level of the nutrients nitrogen and phosphorus.  Those nutrients are the first two of the three numbers on a bag of fertilizer.  Like 5-10-5 contains 5 parts nitrogen, 10 phosphorus, and 5 potash.

We all know that the DES tries to prevent people from using fertilizers near the waterfront because the runoff can cause algae blooms and weeds.  The treated effluent from the Waste Water Treatment plant isn’t much different.  The nitrogen and phosphorus can actually be lower than the standard for drinking water, yet it cannot be released into a lake or pond in large quantities because it will “fertilize” the lake and cause unwanted growth.  It is a form of pollution.

So after treatment, the effluent must be disposed of in a way that doesn’t affect lakes, ponds, or even nearby property.  Most large municipal systems discharge into moving rivers, where the effluent is diluted so much that it is virtually undetectable downstream, and the moving water cannot produce algae.

When there is no suitable river available, the problem gets very complicated.  You need to dispose of the effluent over land.  The basic methods are:

  • Rapid Infiltration
  • Slow Infiltration
  • Spray Irrigation

When the effluent travels through the ground (groundwater), it naturally loses it’s nitrogen and phosphorus, to the point where it can later emerge from the ground as surface water and be as benign as rainwater.  Both Rapid Infiltration and Slow Infiltration are methods of getting the effluent to sink into the ground, merge with existing groundwater, and clean up as it travels to some discharge point months later.  Slow infiltration uses the drip irrigation concept with buried pipes.  Unlike spray fields, it can be designed to operate year round.  Spray irrigation results in some amount of groundwater “recharge” and also benefits from evaporation and transpiration through plants.

According to testimony at the trial, Rapid Infiltration is by far the most economical form of land-based disposal.  The other methods involve much larger tracts of land as well as miles of pipe and/or tubing.  But the most significant factor for Wolfeboro is the geology of the town.  According to testimony, most of the land in town has a very shallow depth to bedrock, and so the carrying capacity of the unsaturated “overburden” soil in many places is unsuitable for any type of infiltration.

One geologist who testified said that looking at a topographical map of Wolfeboro, there were only a few formations that would appear to a geologist to be suitable for land-based disposal.  Those areas were obvious glacial deposits that would be composed of a lot of sand and be free of bedrock.

The town currently disposes of about 20%-25% of it’s effluent, about 30 million gallons,  on about 46 acres of spray fields.  That’s about 650,000 gallons per year per acre.  Extrapolating the town’s needs of about 160 million gallons per year, the current spray field equivalent is about 250 acres of spray fields.

Without a doubt, better suited land can be found and switching to a year-round technology would double the capacity and halve the land requirement.  So maybe 100 well selected drip acres could dispose of the town’s current needs of 160 million gallons, or say 135-150 acres of drip to get an equivalent of the 600,000 gpd that the RIB was supposed to provide.

The cost comparisons between RIB and other land based disposal methods include all of the life-cycle costs.  While our RIB system has been expensive to operate because of the problems, most ribs have very low operational costs.  The various forms of slow infiltration like spray and drip will have higher maintenance and operational costs because of the complexity of miles of pipes and dozens of monitoring wells.

So I hope the town thinks through the whole plan for the next 20 years or so before deciding there is a surplus from the punitive damages they extract from Wright Pierce.



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