Digital Geodata Series
DGS09-2 Coastal Plain Sediments with Potential to Form Acid (Sulfate) Soils

(677KB) 08-24-2009

Abstract

The New Jersey Department of Agriculture, Division of Agricultural and Natural Resources, State Soil Conservation Committee requires that plans for controlling erosion during land disturbances (such as construction) must be designed in accordance with a comprehensive set of erosion control practices known as the Standards for Soil Erosion and Sediment Control Act (P.L. 1975, chapter 251, N.J.S.A. 4:24-39 et seq.).  This map is intended to provide Federal and State agencies, and the public with fundamental geologic information on potential acid-producing (sulfate) sediments for use in natural resource planning and environmental analyses.

Soil pH is the measure of the pH of soil water, which depends on the hydrogen ion (H+) activity in solution. Soils become naturally acidic for three major reasons: rainfall and leaching, acidic parent material, and decay of organic matter which produces hydrogen ions. Sulfide-bearing (pyritic) Cretaceous and Paleogene (formerly the Tertiary period) marine and estuarine sediments, depicted on this map, are potential acid-soil producers. The development of acid-sulfate soils occurs when sulfide minerals, such as pyrite and/or elemental sulfur, in reduced sulfidic sediments oxidize upon air exposure through drainage or earth-moving operations. The overall acid-sulfate, soil-forming process involves a complex chain of reactions that connect the oxidation of iron sulfides to the release of iron oxyhydrates (+ hydronium jarosite, H₃OFe₃+3(SO₄)₂(OH)₆ ) and sulfuric acids. For pyrite and marcasite, the overall reaction is:

FeS₂    +     3.75O₂ + 3.5 H₂O   -- >    Fe(OH)₃       +     2H₂SO₄
(pyrite/marcasite)                             (iron oxyhydrate)    (sulfuric acid)

Acid-sulfate soil formation occurs if the reduced sulfur components exceed the acid-neutralizing capacity of adsorbed bases and easily weatherable silicate and carbonate minerals. Natural Resource Conservation Service reports (see for example Soil Survey of Monmouth County) demonstrate that soils developed on these sulfidic, non calcareous, marine sediments are strongly (pH < 5.5) to extremely acid (pH < 4.5).

Depicted in the GIS data are the sedimentary units with the potential to produce acid (sulfate) soils: Kirkwood, Shark River, Manasquan, Hornerstown, Tinton, Sandy Hook Member of the Red Bank, Navesink, Wenonah, Marshalltown, Englishtown, Woodbury, Merchantville, Cheesequake, Magothy, and Raritan Formations.

This map is for illustration purposes only.