The attachment shows two sets of histograms, showing nitrate and total organic carbon (TOC) concentrations in each groundwater block of the London Basin region.
(a) I would like to know the spatial distribution of elevated nitrate levels in groundwater. What factors might explain this distribution?
(b) What is the spatial distribution of elevated TOC levels in groundwater? What factors might explain this distribution?
(c) The Chalk aquifer and the Middle Thames Gravels are both exploited in the London Basin block. Why do they show differences in chemistry and in contamination?
(a) Leatherhead, London Basin, and Lower Greensand have very little variation in nitrate concentrations and the majority of samples have very low concentrations at nearly 0 mg/L. Loddon-Wey and Malborough and Berkshire downs also have very low concentrations (0 mg/L) of nitrogen but there is more variation in samples. Middle Thames Valley Gravels and Chiterns have high standard deviations but nitrate concentrations average in in the 5-10 mg/L range. Lee Valley seems to have the highest nitrate concentrations, closer to 10 mg/L and high variation.
The maximum acceptable concentration for nitrate in drinking water in most places is anywhere from 10 to 45 mg/L and none of the sites seem to exceed this threshold. However, concentrations larger than 3mg/L usually indicate human or environmental impact that is impairing the groundwater quality. Otherwise, groundwater levels of nitrate are very low if unimpaired and often below 1 mg/L. The areas with higher nitrate concentrations may be affected by leaching of ...
The expert examines evaluated spatial distributions.