Monitoring the Removal of Phosphate from Ground Water Discharging through a Pond‐Bottom Permeable Reactive Barrier

Abstract

Installation of a permeable reactive barrier to intercept a phosphate (PO 4 ) plume where it discharges to a pond provided an opportunity to develop and test methods for monitoring the barrier's performance in the shallow pond-bottom sediments. The barrier is composed of zero-valent-iron mixed with the native sediments to a 0.6-m depth over a 1100-m 2 area. Permanent suction, diffusion, and seepage samplers were installed to monitor PO 4 and other chemical species along vertical transects through the barrier and horizontal transects below and near the top of the barrier. Analysis of pore water sampled at about 3-cm vertical intervals by using multilevel diffusion and suction samplers indicated steep decreases in PO 4 concentrations in ground water flowing upward through the barrier. Samples from vertically aligned pairs of horizontal multiport suction samplers also indicated substantial decreases in PO 4 concentrations and lateral shifts in the plume's discharge area as a result of varying pond stage. Measurements from Lee-style seepage meters indicated substantially decreased PO 4 concentrations in discharging ground water in the treated area; temporal trends in water flux were related to pond stage. The advantages and limitations of each sampling device are described. Preliminary analysis of the first 2 years of data indicates that the barrier reduced PO 4 flux by as much as 95%.

Phosphorus in groundwater discharge – A potential source for lake eutrophication

“…Pond in Cape Cod, as a permeable reactive layer directly into the lake bottom (McCobb et al, 2009). Also, the abstraction of contaminated near-shore groundwater to an off-site treatment facility may be a feasible option to remove P from the system.…”

Enriched Iron(III)-Reducing Bacterial Communities are Shaped by Carbon Substrate and Iron Oxide Mineralogy

“…Ashumet Pond is a freshwater kettle-hole pond that receives phosphate-laden groundwater from infiltration beds at a decommissioned wastewater treatment and disposal facility at the adjacent Massachusetts Military Reservation on Cape Cod. In 2004, a permeable reactive barrier containing zero valent Fe [3% Fe(0) by weight] was emplaced subhorizontally on the bottom of the pond (0.6 m deep) to intercept phosphate-laden water that discharges near the shore of Ashumet Pond (McCobb et al, 2009). Three shallow sediment cores were collected within the pond downgradient of the barrier with a water depth of ∼0.5 m. Upon sampling, the cores were stored on ice, transferred back to the laboratory and placed in an anaerobic chamber (94% N 2 : 6% H 2 ).…”

Groundwater – the disregarded component in lake water and nutrient budgets. Part 2: effects of groundwater on nutrients

“…Applicable techniques will be discussed briefly here; see Rosenberry et al (this issue) for further details. Additional criteria to consider when choosing a sampling method are accessibility, costs, robustness, unattractiveness for vandalism and aesthetical aspects (McCobb et al, ). All approaches listed in the succeeding text require multiplying the estimates of the water fluxes by the nutrient concentrations in the seepage water (e.g., Winter, ; Zimmermann et al, ; Robertson et al, ; Kroeger and Charette, ; Meinikmann et al, ).…”