38. The method according to claim 37, further comprising: (h) sampling the flushed soil after treatment to determine the effectiveness of the treatment based on an amount of hexavalent chromium present in the flushed soil.
39. The method according to claim 38, further comprising repeating steps (g) and (h) until the amount of hexavalent chromium concentration is sufficiently reduced. 40. The method according to claim 38, wherein the treated soil after pumping has an amount of hexavalent chromium no greater than 5 mg/L.
41. A method for the in-situ reduction of hexavalent chromium to trivalent chromium in soil comprising hexavalent chromium, comprising:
(a) sampling soil comprising hexavalent chromium to determine a reaction amount of a reducing agent;
(b) providing a frame on a top surface of the soil;
(c) wetting the soil in the frame;
(d) spreading a reducing agent on the top surface of the soil in the frame;
(e) flushing the soil in the frame with water to dissolve the reducing agent;
(f) covering the top surface or the soil in the frame with a layer of clean soil free of hexavalent chromium.
42. The method according to claim 41, wherein the soil comprising hexavalent chromium to be reduced comprises a top layer which is free of hexavalent chromium, and the method further comprises removing the top layer of the soil which is free of hexavalent chromium before stop (c); and step (f) further comprises using the removed top layer of the soil as the layer of clean soil in step (f).