Tidal forcing

We may think of each high tide as a flush: a bolus of toxified water is released, as from a toilet bowl, into the bay. Our proposal is to interpose a salt marsh, as a sort of septic tank or living machine, between the dump and the bay.
  • We assume that each high tide (over the level of the salt marsh) introduces a bolus of sea water into the dump (the capped volume of the landfill).
  • Within the landfill, the bolus of sea water mixes with a reservoir of water in which chemicals of concern (COCs) have dissolved.
  • As soon as the tide recedes below the level of the top of the salt marsh, this bolus leaches out into the salt marsh.
  • The leachate exits into the root system of the cordgrass (Spartina alterniflora), the upper 6 inch layer of the salt marsh.
  • The sediments of the salt marsh below the root system are perpetually saturated with water, are anoxic, and serve as a barrier to leachout from the dump.
  • Each high tide creates a single pulse of leach through the upper (root) layer of the salt marsh, of which a significant fraction consists of the rhizosphere of cordgrass.

Revised by Ralph Abraham 16 August 1998