As with water quality, APEM have been fortunate to be able to develop a high level of expertise in sediment contamination particularly through our work in artificial grossly polluted dock environments. Analysis of sediment characteristics including particle size, organic carbon content and sediment oxygen demand has also been conducted with the Mersey Estuary and other estuarine environments. In this regard sediment contamination from heavy metals, organo chemicals and nutrients as well as issues relating to sediment oxygen demand (SOD) are all areas in which APEM have a specialised skill base.

Heavy Metal & Organo Chemicals

This work commenced in 1987 with a nationwide survey of disused dock basins throughout the UK. In addition to basic data collection of these systems' plant and animal life, water quality and sediment contamination studies were also undertaken to provide background data on environmental conditions which might be influencing dock ecology. In many cases, analysis of the sediments revealed that some contaminants present were amongst the highest concentrations to be found anywhere in Europe. This work has continued with a number of related studies in coastal ports and harbours throughout the UK including Stanlow, Poole Harbour, Harwich Haven and Middlehaven Dock, Middlesbrough. One of the most detailed studies to date was undertaken in conjunction with North West Water (now United Utilities) where APEM undertook a detailed three dimensional transect based study to evaluate the historic/recent contamination in sediment layers across the 50 hectares of highly contaminated sediment in the upper reaches of the Manchester Ship Canal. This work involved collection of sediment samples from numerous locations, with additional samples being retrieved from within the sediment column at 0.5m intervals within up to 4m of accumulated sediment.

Analysis for metals and organic chemical is undertaken externally at suitably UKAS accredited laboratories that specialise in this type of work, with the appropriate level of detection for the purposes required.

Plans to dredge areas of the South Liverpool Docks to provide a suitable boat draft involved extensive collection and analysis of sediments. Once the analysis was complete APEM used a number of European and North American guidelines to assess the likely ecological impacts of the dredging process. Unsurprisingly these sediments being from historically very active docks were highly contaminated and issues relating to disposal were therefore also raised and considered.

Nutrient Loading

Sediment contamination investigations do not always centre on industrial areas or conurbations. Following a liquid fertiliser spill into a brook located in rolling dales a number of down stream pools were impacted. Sediment within the pools became enriched with plant nutrients and excessive annual algal blooms resulted. Dredging and subsequent removal of the contaminated sediment was seen as the most cost effective and suitable method of improvement.

Sediment Oxygen Demand

In addition to our studies on chemical contamination of sediments we also undertake a considerable amount of work on organic sediment pollution, measuring sediment oxygen demand. This is now a key component of our mass flux models for aeration and destratification systems for example. Over the years we have experimented with a number of different approaches ranging from the conventional laboratory based WALRUS SOD estimation technique through to 'live' sediment core studies. However, following on from the extensive modelling and experimental oxygen injection work preceding the MSC Oxygenation Project, we believe that the most accurate results are obtained with an SOD chamber. This is a specially constructed device based on the current state of the art design from the USA that is deployed within the waterbody in question to measure SOD directly. We have undertaken SOD studies in a range of situations including lakes, rivers, reservoirs, canals and docks, and now consider it an essential component of our data gathering process for accurate and representative water quality models. Specific projects where the SOD chamber has been put to specific use include investigations of a fish kill in Cavendish Dock, Barrow-in-Furness, MSC and Salford Quays monitoring studies and modelling, pre and post dredging studies in lowland rivers and drains, and reservoir monitoring for water utilities.