“Table 1Threshold values for assessing groundwater chemical status

Parameter	Unit	To examine if groundwater abstraction is causing saline or other intrusions	>To examine if groundwater is providing a significant contribution to the failure of the environmental objectives of associated surface water bodies	To examine if the quality of groundwater that is abstracted for potable use is deteriorating, possibly resulting in a need for increased purification	To examine the spatial extent of a groundwater body or group of bodies that are exceeding an EU Standard or threshold value
Ammonium	mg/l				0.29
Arsenic	μg/l				7.5
Atrazine	μg/l				0.075
Cadmium	μg/l				3.75
Chloride	mg/l	25
Electrical Conductivity	μS/cm	800		1875
Lead	μg/l				7.5
MCPA	μg/l				0.075
Mecoprop	μg/l				0.075
Mercury	μg/l				0.75
Nitrate (as NO3)	mg/l			37.5	37.5
Nitrite	μg/l			375	375
Simazine	μg/l				0.075
Sulphate	mg/l				187.5
Tetrachloroethylene	μg/l			7.5	7.5
Trichloroethylene	μg/l			7.5	7.5
Any pollutant in relation to which a surface water environmental standard has been set(1)			0.5 x (surface water standard divided by dilution factor)(2)

(1)

The surface water environmental standards are set out in Schedule 1 to The Water Framework Directive (Classification, Priority Substances and Shellfish Waters) Regulations (Northern Ireland) 2015(S.R. 2015 No. 351).

(2)

The “dilution factor” is taken to be the fraction of the average annual river flow derived from groundwater inflows. It can be estimated from established hydrological indices such as the baseflow index, or from the ratio of catchment groundwater recharge to effective precipitation.”