Environmental Engineering Reference
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between the iron and surrounding sandy soil matrix. The long-screened
wells were installed with the intention of monitoring groundwater veloc-
ity and direction with in situ velocity probes (gauging groundwater depths
ultimately became a more reliable method of doing this).
In October 2000, two bundle piezometers were added, installed in the iron
bed 0.2 m from the front face (to measure CTC—see Section 12.6).
12.6 Groundwater Sampling and Analysis
The groundwater monitoring program was developed by Woodward-Clyde.
Groundwater samples were typically collected and analyzed for
• Vol at i le CHCs
• Organics—Dissolved and total organic carbon (DOC and TOC), and
chemical and biological oxygen demand (COD and BOD)
• Inorganics—Ferrous and total dissolved iron, dissolved and total
manganese, sulfide, sulfate, alkalinity, total dissolved solids (TDS)
• Field parameters such as electrical conductivity, dissolved oxygen,
redox potential (Eh), and pH
Several key performance parameters were closely monitored:
• Percent mass reduction (MR)—The percentage reduction of total
CHCs across the barrier thickness (in a given vertical and horizontal
transect) relative to the influent total CHC concentration
• Degradation of half-lives of key contaminants—particularly CTC
and PCE—calculated assuming first-order reaction kinetics (expo-
nential decay)
• TOC (elevated TOC concentrations could hinder degradation of tar-
get CHCs, especially PCE)
• Hydraulic gradient into, through, and out of the barrier (which could
be indicative of fouling or preferential flow paths and also residence
(flow-through) time in the barrier)
• Sulfide, sulfate, Eh, and pH (changes could be indicative of mineral
formation, precipitation, and consequent fouling)
• Ferrous (dissolved) iron downgradient of the barrier (as dissolved
iron could adversely impact surface water quality in Springvale
Drain and then Botany Bay)
The initial sampling program comprised groundwater samples being col-
lected at 1, 3, and 6 months (late March, early June, and early September
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