Mercury a Part IIa investigation Mandy Dennis Senior - - PowerPoint PPT Presentation

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

• ccurring

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
• ver Northampton Sand

and Ironstone Formation

• Mercury found to depths
• f 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 mercury

mg/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