Preliminary study of sources and processes of enrichment of manganese in water from University of Rhode Island supply wells

Abstract

about 1'f years. The wells are about 10 feet apart and are screened at different depths in stratified glacial drift, one from 50 to 70 feet, the other from 111 to 131 feet below land surface. A third well screened from 113 to 138 feet below land surface and located about 280 feet from the pond has yielded water containing little or no manganese since its construction in 1958. Concentrations of dissolved iron in water pumped from all three wells have been generally less than 0.3 milligrams per liter throughout their pumping history. Field investigations during 197'* and 1975 by the U.S. Geological Survey in cooperation with the Rhode Island Water Resources Board indicate that oxides and other forms of manganese that occur as stains and coatings on aquifer materials may be the most important source of the manganese contained in the well water. Organic-rich sediments on the bottom of the pond and river, through which infiltration is induced when the supply wells are pumped, constitute a significant but seemingly less important source material. Manganese enrichment in water in the well field seems to be related to the infiltration of surface water through the organic-rich sediments on the bottom of the pond and river. Data from an observation well screened from 3.5 to 5.8 feet below a 1.5~foot layer of organic material in the pond show that highly oxidized water in the pond becomes strongly reduced when passing through the organic sediments. The reduced infiltrate dissolves manganese and iron from aquifer materials and probably also from the lower layers of organic sediments. Concentrations of iron and manganese in the water from this observation well were as high as kQ and 1.2 milligrams per liter, respectively. Because concentrations of manganese were as high as 3.3 milligrams per liter in the deepest supply well, it is assumed that concentrations of manganese must either increase as infiltration moves to greater depths in the aquifer or that greater concentrations are developed beneath other parts of the pond. Also, because the supply wells yield water containing little or no dissolved iron, iron must be removed from solution by precipitation, or some other process, as the infiltrated water moves to greater depths in the aquifer. Hydrologic analysis indicates that most of the infiltration induced from the pond and from the Chipuxet River which flows through it is diverted to the two supply wells that yield water high in manganese. The low manganese content in water from the well farthest from the pond is attributed to the fact that this well pumps relatively little of the water induced into the aquifer from the pond and river.

Mobilization and retardation of reduced manganese in sandy aquifers: Column experiments, modeling and implications

“…Groundwater contamination with Mn is a well know phenomenon (Silvey and Johnston, 1977;Thomas et al, 1994;Bourg and Bertin, 1994;Klinchuch and Delfino, 2000;Buschmann et al, 2007). High Mn concentrations appear in wells long time after the onset of water production from the aquifer.…”

Hydrology, water quality, and ground-water-development alternatives in the Chipuxet ground-water reservoir, Rhode Island

“…Results of aquifer tests in the Chipuxet study area have been described by Dickerman (1984). A preliminary study of the source and causes of enrichment of manganese in water pumped from supply wells in the Chipuxet area has also been completed (Silvey and Johnston, 1977) .…”

“…16-B). Silvey and Johnston, 1977) At the Liberty Lane aquifer-test site, analyses of water from exploratory wells SNW 1121 and SNW 1122, which were drilled in a potato field ( fig. 19) Three 8-inch diameter test wells (SNW 1082, SNW 1085, and SNW 1086 were drilled at the edge of the potato field by the RIWRB.…”

“…Because manganese enrichment of water from heavily pumped municipal and industrial supply wells is a common and troublesome problem in Rhode Island, a study of the problem was made at the Thirty Acre Pond well field (Silvey and Johnston, 1977) .…”

“…Also, the addition of one or more additional wells on the opposite side of the pond would increase the opportunity to intercept potential ground-water runoff to the pond and stream, thereby reducing the amount of water passing through organic bed materials. Silvey and Johnston, 1977) Based on the study at Thirty Acre Pond, it is concluded that the manganese-enrichment problem can be minimized by avoiding siting supply wells adjacent to water bodies having organic-rich bottom sediments. Where this is not feasible, the problem may be minimized by siting the well(s) as far as possible from the recharge source so as to maximize interception of potential ground-water runoff and minimize induced stream infiltration.…”