From the report:
" An assessment (‘Phase 1’) of three geoarchaeological boreholes and 57 geotechnical boreholes drilled at Long Reach, Dartford, in 2010 demonstrated that strata of moderate to high palaeoenvironmental potential existed throughout the site within the Holocene sedimentary sequence. As a result a programme of bio- and geoarchaeological assessment (‘Phase 2’) was carried out by ARCA and Quaternary Scientific (Quest) between January and June 2012. The work focussed on cores recovered from two of the geoarchaeological boreholes drilled during the Phase 1 assessment and comprised mass specific magnetic susceptibility, palynological and diatom assessment and AMS 14C dating.

Following the Phase 2 works, and an additional geoarchaeological watching brief on further geotechnical boreholes, recommendations for a final analytical phase of works (‘Phase 3’) were made.
The Phase 3 works reported here comprised the drilling of three additional geoarchaeological boreholes, the production of updated deposit models for the site, AMS 14C dating of organic strata from to boreholes, and a programme of bioarchaeological assessment (ARCA BH6) and analysis (ARCA BH8) of pollen, diatom and waterlogged wood remains.

Deposit modelling at the site enabled the production of updated surface elevation and thickness models for the main sedimentary units encountered at Long Reach. The sedimentary sequence at the site consisted of four main stratigraphic units: at the base, bedrock of the undifferentiated Newhaven and Seaford Formations (Upper Chalk) outcropped at between -5.00m OD and -14.50m OD, sloping down towards the north; overlying the Chalk, deposits of sands and gravels of the Shepperton Member were encountered which were in turn overlain by strata of the Holocene Tilbury Member and finally Made Ground.

Tilbury Member strata at Long Reach thickened towards the north and were comprised of a sequence of three sedimentary units: the lower fine-grained mineral bed (LFGMB), middle organic bed (MOB), and the upper fine-grained mineral bed (UFGMB).

Organic strata within the LFGMB were 14C dated to the Mesolithic period (7400-7200 cal BP). 14C dating also demonstrated that the MOB formed from the Early Neolithic until the post-Roman period (1560-1410 cal BP). The MOB initially formed in an emergent saltmarsh environment, which was succeeded by freshwater carr and then by further reed peats and mineral intertidal strata. The UFGMB comprised mineral strata deposited in a subsequent mudflat environment overlain by a further reed peat dating to the Early Medieval period (1270-1090 cal BP).

Palynological investigations throughout the MOB provided evidence for a series of vegetation shifts both on the wetland and the surrounding dryland areas likely to have been the result of a number of human (e.g. Bronze Age woodland clearance and cultivation) and natural (e.g. changes in relative sea level) factors. Diatom analysis of ARCA BH8 meanwhile provided evidence for a general increase in saline influence in the upper part of the MOB from the Bronze Age onwards.

Although only indirect evidence for human activity has been found as a result of the geoarchaeological and palaeoenvironmental studies carried out at Long Reach, Dartford, the project has provided information of considerable palaeoenvironmental significance. The site provides a detailed Holocene sea level and palaeobotanical record in a part of the Lower Thames where investigations have previously been sparse. Consequently publication of the data reported here will contribute significantly to the understanding of the Holocene evolution of the Lower Thames."(1)

Thames Water Utilities, 2008, A Desk Based Assessment for an Extension at Long Reach Sewage Treatment Works, Dartford, Kent (Unpublished document). SKE16037.

<1> ARCA, 2013, Long Reach STW, Dartford, Kent: palaeolithic analysis (Unpublished document). SKE17417.