Risk and Monitoring System for Soil Concerning Nitrate Directive in Romania

7/30/2019 Risk and Monitoring System for Soil Concerning Nitrate Directive in Romania

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RISK AND MONITORING SYSTEM FOR SOIL

CONCERNING NITRATE DIRECTIVE IN

ROMANIA

Catalin SIMOTA

National Research and Development Institutefor Soil Science, Agricultural Chemistry and

Environment Bucharest ROMANIA


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ICPA performed a previous delineation of NVZs inRomania which was mainly based on the soil map.

The characteristics of the soil according to the variables

runoff and leaching capacity, provide the nitratevulnerability of the region.

As such this method provided for every soil typevulnerability scores for different criteria (e.g. wet front

hydraulic conductivity; maximum available water; thegeneral soil type; presence of an impermeable layer,etc.). By combining all these criteria for each soil type,general vulnerability scores were assigned.


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Whereas the method of ICPA mainly considers the leaching capacityof the soil, the vulnerability of groundwater is also affected by thestability of nitrate in the groundwater.

Similar to the previous method of RISSA, this stability can also beassessed as a function of different criteria such as hydraulicconductivity of groundwater layers, the hydraulic gradient and thepresence or absence of reducing compounds.

All these criteria can be combined in a general vulnerability score for

groundwater, considering both the leaching capacity of the soil andthe stability of nitrate in the groundwater reservoir.


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Delineation of Recharge Areas

The first step of the delineation of the NVZs wasthe delineation of the recharge areas, wheresurface water is allowed to enter into an aquifer.

These areas are particularly vulnerable tovarious pollutants present in the surface water.

Outside of the recharge areas the vulnerability ofgroundwater was not considered because theimpact of nitrate pollution can be neglected.


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The delineation of recharge areas was mainly

based on the phreatic groundwater map


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As phreatic aquifers chiefly occur in plains with clastic sediments, adelineation of these plains was prepared. This delineation wascompared to the information from a digital terrain model, in which

areas with slopes steeper than 8% are considered as mountainareas

In the code of good agricultural practice, distinction is made betweenplains, hills and mountains. For the sake of simplicity, only twoclasses are retained in the delineation of NVZ. Hills and mountainsare considered as one class.

Generally, in these mountain areas the impact of runoff will be moreimportant than the leaching effects towards groundwater bodies.


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A comparison of these two maps reveals that both delineations arequite similar.

Nearly all the phreatic aquifers are situated in the plains shown bythe extracted DTM map.

However, the few phreatic aquifers in the areas with slopes steeperthan 8%, are in karst regions or in fissured rock types. Theinfiltration rate can be high in these areas, and as such, thegroundwater table is vulnerable for nitrate pollution. These regionsare included in the recharge areas derived from the data layer withphreatic aquifers.

As a result, MAP 1 will be used as final delineation of the rechargeareas.


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Delineation of Nitrate Vulnerable Zones for

Surface Waters

Nitrates mainly reach surface waters by groundwaterdischarge. This effect has been accounted for in theassessment of groundwater vulnerability. To avoiddouble-counting, nitrate contamination of surface waters

by groundwater discharge will not be considered here.

Next to groundwater discharge, nitrates may also reachthe river system by superficial runoff or by flooding ofnitrate contaminated soils. In mountain areas, superficial

runoff can be considerable but the extent of floodingareas is usually rather small. On plains, the volume ofsurface runoff is very limited but large flooding areasmay appear.


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Surface Waters

On the one hand, the amount of runoff in mountain areas will beaffected by the soil type.

The higher the infiltration capacity of a soil, the smaller theprecipitation part that contributes the surface water runoff.

As such, the soil criteria affecting this infiltration (like the drainageclasses, the hydraulic conductivity, the maximum available water,the parental material and the texture) have an influence on thenitrate vulnerability of the surface water.

High vulnerability scores can be given for criteria that cause higherrunoff rates.


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Surface Waters

On the other hand, a vulnerability factor could be introduced forassessing nitrate vulnerability of surface waters in mountain areas,based on the distance of a place to the most nearby river.

In mountain areas, the risk that superficial runoff will actually reacha river network, is proportional to the distance to the nearest river.

The further the distance, the higher the chance that water willinfiltrate or evaporate and will never reach the river.

Vulnerable zones are consequently the zones nearby rivers.


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Surface Waters

On the plains, characterized by slopes of lessthan 8%, the effect of runoff can be neglected,

as mentioned earlier.

The vulnerable zones can be restricted to thepossible flooding areas, as nitrates in the soil

can reach the surface waters in a direct way onlyduring floods (i.e. not passing through majorgroundwater reserves).


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Groundwater

The delineation of nitrate vulnerable zones in the groundwater

bodies was only performed in recharge areas.

For the assessment of nitrate vulnerability, the subdivided aquifers(subzones) were connected in Hydrogeological Homogenous Zones

(HHZs), with comparable physical and chemical conditions and

where natural nitrate removal inside the aquifer systems follows

similar processes.


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Groundwater

The following type of subzones were united into one HHZ:

Adjacent subzones that are subdivided on the above mentionedaquifer map, as they fall within different river basins;

Adjacent subzones of similar geological age, similar type of aquiferand properties (e.g. conductivity, infiltration, rock material);

Adjacent subzones in the same floodplain, terraces or alluvium fromthe same river system;

Subzones that are not adjacent one to each other, but within a shortdistance and with the same geological age, similar kind of aquiferand similar properties (e.g. conductivity, infiltration, rock material).


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In order to assess the vulnerability of a HHZ, the risk that nitrates

can occur in the groundwater was determined. In fact, the presence

of nitrates in the groundwater depends on three factors:

the supply of nitrates from the surface to the groundwater table;

the distribution of nitrates by transport with the groundwater;

redox reactions, including a decrease of nitrate concentrations

due to reduction of the nitrates.


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The first of these factors, mainly depend on externalsources of contamination that cannot be connected tothe HHZ.

These external sources can be diffuse nitrate pollutiondue to agriculture (application of manure on the field), aswell as point pollution sources e.g. resulting from failingsewer systems.

On the other hand, the supply of nitrates to the phreaticgroundwater bodies is also affected by the leachingpotential of the soil.


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The other two factors (i.e. horizontal transport of nitratesand redox reactions) are solely related to the HHZ.

First of all, the distribution of nitrates, both horizontally

and vertically, will contribute to the vulnerability of anHHZ.

An HHZ will be more sensitive if nitrate can percolate

faster into the subsurface. HHZs with high infiltrationrates will thus be assessed as more vulnerable.


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The distribution of nitrates, and as such the vulnerability,also depends on redox conditions in the groundwater.

Nitrate is only stable when dissolved oxygen is present

in the groundwater.

Under oxic conditions, oxygen is used in oxidationprocesses (e.g. the oxidation of pyrite and/or organic

matter), but after the removal of oxygen, in anoxicconditions, nitrate will act as the oxydans during theseoxidation processes, resulting in the reduction of thenitrate


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Redox zones


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The nitrate vulnerability of the HHZs was basedon following criteria:

the hydraulic conductivity;

the hydraulic gradient;

the thickness of the unsaturated zone;

the oxidation status of the rocks during deposition orformation;

the thickness of the water saturated zone of the aquifer;


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For the conductivity of the groundwater

water, scores were based on the K values,

obtained from literature:

1 low vulnerability: K < 20 m/day

2 moderate vulnerability : K = 20100 m/day

3 high vulnerability: K > 100 m/day 4 extremely vulnerable: Karst and fissured rocks.

Discharge values (Q) are used instead of K values;


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The scores for the oxidation status during rock formationcould be divided in two groups: oxidation was possible or

difficult. As nitrate is more stable when oxygen is

available, the rocks that were possibly affected to

oxidation during formation, will be more vulnerable:

1 low vulnerability: Alluvial deposits;

2 vulnerable: Other type of rock formations;


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For the reduction capacity of the soil,scores were assessed by the presence orabsence of organic material or pyrite:

1 low vulnerability: presence of organic materialor pyrite;

2 vulnerable: absence of organic material orpyrite;


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The gradient of the groundwater table causes horizontal migration ofpollutants. Because there was no accurate information about

groundwater flow, the gradient was calculated as the gradient of the

ground surface (Digital Terrain Model). On plains the groundwater

table runs more or less parallel with the ground surface (->):

1 low vulnerability: gradient values 4;


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The thickness of the unsaturated zone is derivedfrom the soil map, with soils in flooding areas ofriver systems being saturated the most:

1 low vulnerability:recent soils

2 vulnerable: hydromorph soils

3 very vulnerable: supplementary class water

All other soil types were considered as notvulnerable (= 0).


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The sum of the scores of all criteria

resulted in a general score for the nitrate

vulnerability of each HHZ


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HHZ

Geological Age Catchment

Oxidationduring

Formation

Conductivity ReductionCapacity

Thickness ofUnsatured

Zone

Gradient FinalVulnerability

Score

ROGW01 Cuaternar Somes -Tisa 1 3 2 0 1 7

ROGW02 Paleogen-Cuarternar Somes -Tisa 2 4 1 0 3 10

ROGW03 Triasic-Cretacic Somes -Tisa; Crisuri 2 4 2 0 3 11

ROGW04 Cuaternar (depoziteHolocene-Pleistocene)

Somes -Tisa 1 3 1 0 2

7

ROGW05 Cuaternar Somes -Tisa 1 3 1 1 2 8

ROGW06 Precambrian Somes -Tisa; Siret 2 4 2 0 3 11

ROGW07 Cuaternar Mures; Crisuri 1 2 2 1 1 7

ROGW08 Cuaternar Mures 1 2 2 0 1 6

ROGW09 Cuarternar Mures 1 2 2 1 2 8

ROGW10 Paleozoic-triasic-Jurasic

Mures 2 4 2 0 3

11

ROGW11 Precambrian superior Mures; Banat 2 4 2 0 3 11

ROGW12 Paleozoic Mures 2 4 2 0 3 11

ROGW13 Jurasic-Cretacic Mures 2 4 2 0 3 11

ROGW14 Carbonifer inferior Mures 2 4 2 0 3 11ROGW15 Cretacic superior Mures 2 4 2 0 3 11

ROGW16 Precambrian superior-Paleozoic

Mures 2 4 2 0 3

11

ROGW17 Jurasic-Cretacic Mures 2 4 2 0 3 11


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Assessment per NVZ

For the assessment of the vulnerability of groundwater bodies andsurface waters, the data layer with nitrate concentrations wasattached to the corresponding nitrate vulnerable zone (NVZg andNVZs respectively).

As such, for each NVZg/NVZs the average and variation in thepollution data per NVZ can be presented. For each NVZ thesestatistics are provided separately for all measuring points inside andoutside of the communas.

The mean value of the actual nitrate pollution within one zone iscalculated with the data outside of the communas.

The data from inside of the communas will be used to locate anypoint pollution.


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Assessment per NVZ

In a next phase a score is provided based on the meanactual pollution.

The standard for nitrate in potable water of 50 mg/l (EU

Drinking Water Directive, 1998 and WHO, 2004) isconsidered as the upper threshold.

For the delineation of areas that are not affected by

nitrate pollution, the mean background values of nitratein EU groundwater of 10 mg/l is used (UNEP, 2004)


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Assessment per NVZ

0 no pollution (and natural contamination),values lower then 10mg/l;

1 little pollution, values between 10 and25mg/l;

2 moderately polluted, values between 25 and

50 mg/l;

3 heavily polluted, values higher then 50mg/l.


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Pollution matrix showing different classes of risk and

monitoring actions, based on potential vulnerability and

actual pollution

0 1 2 3

no A A C F

low A B C F

intermediate B B D G

high E E G Gpotential

vulnerability

actual pollution

A) low risk --> least concernB) monitoring results show low contamination, the potential risk is low to moderate

--> monitorring program to look for possible pollution

C) unexpected intermediate pollution values in areas with no or small potential risk--> look for reason, monitoring campaign need to be adapted (point source, bad delineation)

D) moderate values in an area weighted as intermediate

--> moderate monitoring, attention for pollution sources

E) low measurement values, but the area is weighted as high risk. A

--> precautions for pollution, no aggriculture, and many monitoring wells!F) High values measured, while no problem has been expected.

--> look for reason, monitoring campaign need to be adapted (point source, bad delineation)

G) important risk, higher pollution vallues

--> cleaning up, many monitorring wells


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Assessment per comuna

Subsequently, the selected communas are projected on the NVZswhich are combined with the data from wells.

Each communa is situated at least in one NVZ with a given potentialvulnerability.

If monitoring points are available inside the NVZ, the actual pollutionstatus of the communa can be estimated based on these monitoringdata.

For some NVZs, no monitoring wells were available. For example,in karst areas, nitrate concentrations in groundwater have not beenmonitored. In this case, an appropriate monitoring program will beproposed that aims to assess whether or not increased nitrateconcentrations appear inside the NVZ. The density of monitoring

wells is set proportional to the potential nitrate vulnerability. Each communa is thus evaluated together with the local NVZ. When

a communa is located on the border of two NVZs, the communa issplit in two parts and evaluated twice.


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HHZ pot act villages HHZ new code HHZ pot act

A low 0 1 A 1a A low 0

B high 3 + B 1b B high 3

C low 2 2 B 2b B high 3

3 C 3c C low 2


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Methodology for Groundwater Monitoring Wells

The location of the wells that are installed to detect and monitordiffuse pollution should be according to the following conditions:

inside arable land;

at a distance of minimum 100 m downstream of houses, farmsand industry;

at a distance of minimum five times the width of running surfacewater;

at a distance of minimum 100 m downstream of nature reservesand forests;

at a distance of minimum 100 m downstream of manure and

waste disposals; easily accessible to drilling companies and laboratories;

at a distance of minimum 100 m of watersheds and border zonesbetween different HHZs.


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Score A

If the combination of the scores for aselected communa is evaluated as A, then

both the potential vulnerability and theactual pollution is assessed as low. As aresult the selected communa is of leastconcern. The existing monitoring networkwill be sufficient in this case. There is noneed for additional monitoring.


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Score C or F If the combination of the scores for a selected communa is

evaluated as C or F, the actual pollution is not in line with theassessed potential vulnerability.

Although the potential vulnerability is assessed as low, the actualpollution shows respectively intermediate and high values.

In this case, it can be important to look for point pollution (i.e. highvalues within communas or the presence of outliers in the data set).In this case, appropriate measures should be taken in function of thetype of point pollution (e.g. wastewater treatment plant). To follow uppoint pollution problems more detailed monitoring campaigns needto be foreseen, with wells and surface water observation points

upstream an downstream of the point source. A sampling frequencyof once per several years is advised. This, way the long-termefficiency of pollution abatement strategies can be evaluated.

If no indication for point pollution was found, an evaluation as C or Fmay indicate an error of the delineation of the vulnerable zones.


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Score D If the combination of the scores for a selected communa

is evaluated as D, then an intermediate potentialvulnerability and a moderate actual nitrate pollution arecalculated.

Measures should be taken to reduce the production ofnitrates in the area and the evolution of the water qualityshould be closely monitored. Yearly or 2-yearly samplingis advised, with monitoring wells located upstream anddownstream of the village.

Depending on the density of the existing monitoringnetwork, a frequent (e.g. 2-yearly) sampling of theexisting wells may be sufficient or additional wells willneed to be installed.


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Score E or G If the combination of the scores for a selected communa is

evaluated as E or G, then the potential vulnerability is assessed ashigh.

No matter if the actual pollution is small (E) or high (G) themonitoring campaign should be rather intensive. A yearly sampling

frequency is advised. Existing wells can be used, but depending on the density of the

existing monitoring network, it will most probably be necessary toinstall additional wells, so that several measuring locations upstreamand downstream of the village are present.

Agricultural activities should be decreased, and precautions for

possible pollution need to be made. In case of an evaluation as G,measures should be taken in order to clean up the actual pollution.


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Soil monitoring

For each groundwater/surface water

monitoring site measurements of nitrate

concentration in soil (0-30, 30-60, 60-90

cm depth) in recharging areas are to bedone 2 times per year (spring/winter)

Sampling design needs to be adapted to

specific hydrogeological conditions, landuse and local agriculture practices

Documents

Risk and Monitoring System for Soil Concerning Nitrate Directive in Romania