Lecture 22: Groundwater Contamination I

Transcription

1 Lecture 22: Groundwater Contamination I Key Questions 1. What causes seawater intrusion? 2. What is the Gyben-Herzberg Relation (z = 40h) 3. Why are islands susceptible to sea-water intrusion? 4. What are some examples of point sources of groundwater contamination? 5. What are some examples of non-point sources of groundwater contamination? 6. Why is nitrate the most common groundwater pollutant? 7. Why is the Abbotsford-Sumas aquifer susceptible to nitrate contamination? Niigata Japan, 1964 liquefaction

2 Seawater Intrusion

3 In a U - tube, water seeks its own level Δ = Δ =

4 Hydraulic equilibrium between two fluids with contrasting densities Δ = Δ = fresh water sea water interface between the fresh water and sea water

5 Sea water is denser so it displaces the fresh water upward Δ = Δ = fresh water sea water interface between the fresh water and sea water

6 Δ = h Δ = fresh water sea water z interface between the fresh water and sea water

7 ρ s = sea water density ρ f = fresh water density Δ = h Δ = z z + h ρ s ρ f fluid pressure P A = ρ s g z A B P B = ρ f g (z + h)

8 ρ s = sea water density ρ f = fresh water density Δ = h Δ = z z + h ρ s ρ f fluid pressure P A = ρ s g z A B P B = ρ f g (z + h)

9 hydraulic equilibrium Δ = h Δ = z z + h ρ s ρ f P A = ρ s g z A B P B = ρ f g (z + h) P A = P B

10 hydraulic equilibrium if Δ = h Δ = P A = P B then ρ s z ρ s g z = ρ f g (z + h) ρ f solving for z yields z = ρ f ρ f ρ s - h ρ s = sea water density ρ f = fresh water density

11 Ghyben Herzberg relation Δ = h Δ = z = ρ f ρ f ρ s - h if ρ s z ρ s = g/cm 3 ρ f ρ f = g/cm 3 then z = 40h

12 Ghyben Herzberg relation (static water conditions) sea level h water table seawater freshwater z z = 40 h The depth to the freshwater/seawater interface (z) is about 40 times the height of the freshwater above sea level (h).

13 Ghyben Herzberg relation (static water conditions) sea level h water table z = 40 h

14 Ghyben Herzberg relation (static water conditions) drop in the water table sea level z = 40 h rise in the interface

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16 Pumping wells create a cone-of-depression in the water table

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18 Seawater Intrusion on Islands

19 Chloride Concentrations are an indication of seawater intrusion Greater than 100 mg/l means intruded Greater than 250 mg/l means above drinking-water standard

20 Seawater Intrusion on Islands

21 Seawater Intrusion on Islands

22 Lopez Island

23 Lopez Island

24 Seawater Intrusion on Islands

25 Whidbey Island

26 Seawater Intrusion on Islands

27 Lummi Island

28 Seawater Intrusion on Islands

29 Seawater intrusion problems around the northern coastal region. Guemes Island

30 More Sources of Groundwater Contamination

31 Examples of Point Sources On-site septic systems Leaky tanks or pipelines containing hydrocarbons Leaks or spills at manufacturing facilities Municipal landfills Livestock wastes (manure lagoons) Leaky sewer lines Spills related to highway or railway accidents Examples of Non-point Sources Fertilizers on agricultural land Pesticides on agricultural land and forests Contaminants in rain, snow, and atmospheric fallout Source: Adapted from: Cherry, John A. "Groundwater Occurrence and Contamination in Canada." In M.C. Healey and R.R. Wallace, Canadian Aquatic Resources, eds., Canadian Bulletin of Fisheries and Aquatic Sciences 215: 395. Department of Fisheries and Oceans: Ottawa, 1987.

32 Agricultural Pollutants Pesticides (organic chemical) Herbicides (organic chemical) Fertilizers (nutrients)

33 Nitrate is the most common world-wide groundwater pollutant NO 3 -

34 Nitrogen fertilizers are major sources of nitrate Nitrogen inorganic commercial and organic manure fertilizers are added to the soil to supplement nutrients for crops

35 Liquid manure spreading in Whatcom County

36 Mineralization and Nitrification Excess nitrogen in the soil is converted to nitrate by the help of bacteria

37 Non-Point Nitrate Contamination Nitrate derived from fertilized fields is called a non-point source contaminant because it covers large surface areas on the aquifer.

38 Nitrate Leaching Rainfall (or irrigation water) percolating into the soil transports nitrate in the soil to the surface of the aquifer (water table).

39 Nitrate is transported through an aquifer by groundwater

40 Why is nitrate in drinking water a problem? Nitrate can affect red blood cells and reduce their ability to carry oxygen to the body. In most adults and children these affected blood cells rapidly return back to normal. However the blood cells of infants can take much longer to return to normal. As a result, infants who are given water with high levels of nitrate (or foods made with nitrate contaminated water) may develop a serious health condition due to the lack of oxygen. This condition is called methemoglobinemia or blue baby syndrome. The above information was extracted from a State of Washington Department of Health Fact Sheet (DOH PUB. # ).

41 How is nitrate in drinking water regulated? The U.S. EPA has established a Maximum Contaminant Level (MCL) of 10 milligrams per liter (mg/l) for nitrate. Public water systems are required to sample for nitrate on a regular basis. There is no required sampling of private individual wells. The above information was extracted from a State of Washington Department of Health Fact Sheet (DOH PUB. # ).

42 Groundwater is vulnerable to nitrate contamination where there is a combination of rainfall (or irrigation) agricultural land use permeable soils shallow water table

43 Nitrate Vulnerability Map USGS Fact Sheet FS The red areas on this map indicate regions that are highly susceptible to groundwater nitrate contamination.

44 Abbotsford-Sumas Aquifer USGS Fact Sheet FS

45 The lowlands over the aquifer are agriculturally productive. Whatcom County s Raspberry Industry is # 1 in the Nation. WWU

46 Whatcom County s Dairy Industry is # 2 in the State (~60,000 cows) Liquid manure spreading in Whatcom County

47 Southern British Columbia is dominated by raspberry and poultry industries

48 Groundwater flows south from BC into Whatcom County

49 Problem Elevated nitrate concentrations in the aquifer are due to agricultural practices on both sides of the border. The concentrations can exceed the US-EPA maximum contaminant level (MCL) of 10 mg-n/l. N S Well water with nitrate greater than 10 mg-n/l is not safe to drink. Δ BC WA

50 Problem Nutrient management in Whatcom County is difficult to assess because of nitrate transport from BC N S Δ BC WA

51 International Mitigation Strategy In 1992 the Abbotsford-Sumas International Task Force was formed to coordinate groundwater protection efforts in the aquifer. Members represent government agencies, tribes, cities and counties on both side of the border. Their goals are to Collect and Coordination Scientific Data Manage Activities Threatening the Aquifer Assist with Legislation and Policy Advice