Mercury – a Part IIa

investigation

Mandy Dennis

Senior Environmental Protection Officer

An unlikely mix!

Always expect the unexpected!

Mercury (total)

found across the

site ranging from

0.7mg/kg to

390mg/kg

Plus arsenic –

naturally

occurring

1884

1952

1964

• Where did it come from?

• Anecdotal evidence of a

tannery

• Further investigation

• 15 further trial pits

• 32 soil samples

• Mercury 2.3mg/kg to

960mg/kg

• Highly leachable

• Geology – Made ground

over Northampton Sand

and Ironstone Formation

• Mercury found to depths

of 2m

Site history

• Tannery started between 1884 and

1900

• Closed in 1957

• Sold in 1965 and used as a garage

• 2000 sold for housing

Leather finishing• Tanned leather can be dry and hard

• Casein emulsion used to make leather supple and fix the

dyes

• Milk based casein has mercuric chloride added to it

• Acts as a bactericide

• Prevents the casein going off

• Usage largely finished by the 1950s

What is casein?

• Principle protein found in cows milk as a suspension of casein

micelles

• Family of phosphoproteins

• Gives milk the white colour

• Cheese is the coagulation of casein using rennet

• Used in processed food products

• Casein based glues used in woodworking and aircraft

manufacture

• Casein glue used to coat transformer board

• Leather finishing

What next – risk assessment

• Inorganic mercury

• SNIFFER assessment gave SSAC of 20mg/kg

• Installation of boreholes

• Mercury in groundwater 83ug/l in borehole and well

• Lots of discussion about compliance point

• Source removed

• Remediation surface strip

• Clay capping layer and topsoil

Digging out hotspot

Hotspot reinstated

Why Part IIa?• Missed section of land at back of site outside footprint of the

tannery had elevated levels of mercury max 50mg/kg at near

surface

• If mercury found here could it be in other adjoining properties

around the tannery/garage

11 – 116mg/kg

0.25 – 5.9mg/kg

Part IIa investigation• 12 properties investigated

• Criteria within 20 metres of site boundary

• Special site based on the presence of mercury on the Northampton

Sand and Ironstone formation

• Investigation undertaken by the Environment Agency

Museum of Leathercraft• Kelly’s Directory 1893 list a John Lee & Son trading in the

village

• In the Welland list no mention of this company on either the

1849 or 1874 lists

• In 1915 company name changed to John Lee & Son

(Grantham) Ltd

• Up to 1930s traded as furriers, hide and skin merchants

• In the late 1930s hatters was added to the list

• Possibly closed during war time

• Known for tanning rabbit hides

• Closed in 1957 possibly due to myxomatosis in rabbits

As Mad as a Hatter!

• Listed as furriers up to 1930s

• Late 1930s company listed as hatters

• Fur from small animals used to make felt for hat

making

• Suggested they specialised in treating rabbit

hides

Carroting!

• Nothing to do with the vegetable!

• Rabbit skins rinsed in a heated solution of mercuric

nitrate or brushed onto the pelt

• Pelts dried in an over or outside on racks

• Turned the rabbit skins a carrot colour

• Fur separated from the pelt put onto a cone shaped

colander and treated with hot water to consolidate

• Banned in US in 1941 not because of health risks

but that mercury fulminate was needed to make

detonators from WWII

• Suggested the site was not operational during the

war

• Banned in UK by 1941

Carroting

Carroting

Part IIa Investigation• Investigated 12 residential properties

• Criteria within 20 metres of the boundary of the tannery

• Communication strategy

• Involved all partners such as the PCT, HPA, GPs, etc

• Consultants engaged by the Environment Agency

• Sampling of gardens for all three forms of mercury

• Results ranged from 8.41mg/kg to 62.4mg/kg

• One garden reported levels of mercury up to 62.4mg/kg

(US95 32.2mg/kg)

• SSAC 11.1 – 14.2mg/kg

Further investigation

Voluntary remediation

Human health assessment criteria

inorganic mercurymg/kg

• ICRCL 1

• SNIFFER SSAC 20

• SGV 8

• SSAC 11.2 – 14.1

• SSAC without home grown produce 51

• SGV 170

• LQM/CIEH S4UL 40

• C4SL ND

THANK YOU FOR LISTENING

Mandy Dennis

Senior Environmental Protection Officer

01832 742037

mdennis@east-northamptonshire.gov.uk