Seawater Intrusion Protection

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Seawater Intrusion Protection

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1. Seawater Intrusion Protection

2. Saltwater Intrusion

3. portions of the aquifer may contain saltwater while other portions contain fresh water. Freshwater is less dense, floats on top of the saltwater Relationship based on density difference between saltwater and freshwater that can be used to estimate the depth to saltwater based on the thickness of the freshwater zone above sea level. The relationship is known as the Ghyben-Herzberg relationportions of the aquifer may contain saltwater while other portions contain fresh water. Freshwater is less dense, floats on top of the saltwater Relationship based on density difference between saltwater and freshwater that can be used to estimate the depth to saltwater based on the thickness of the freshwater zone above sea level. The relationship is known as the Ghyben-Herzberg relation

4. The boundary is not sharp, but a gradual change over a finite distance, and is known as the zone of diffusion or the zone of mixing. All our groundwater from precipitation, which creates a pressure distribution, highest in the center of the islands, lowering as you approach the shorelines. Leads to a flow in the aquifers, vertically downward near the center, radially outward toward the shore Two mixing processes (diffusion and dispersion) continuously move saltwater into the freshwater zone. Flow in the freshwater zone sweeps this mixed-brackish water toward the shoreline where it discharges at submarine seeps. Recharge, flow, mixing, and discharge all work to hold the interface position in a roughly stationary position. A change to these processes can result in a change in the position of the interface, an inland movement of the interface boundary is known as lateral intrusion. The boundary is not sharp, but a gradual change over a finite distance, and is known as the zone of diffusion or the zone of mixing. All our groundwater from precipitation, which creates a pressure distribution, highest in the center of the islands, lowering as you approach the shorelines. Leads to a flow in the aquifers, vertically downward near the center, radially outward toward the shore Two mixing processes (diffusion and dispersion) continuously move saltwater into the freshwater zone. Flow in the freshwater zone sweeps this mixed-brackish water toward the shoreline where it discharges at submarine seeps. Recharge, flow, mixing, and discharge all work to hold the interface position in a roughly stationary position. A change to these processes can result in a change in the position of the interface, an inland movement of the interface boundary is known as lateral intrusion.

5. When a well is pumped, water levels in the vicinity of the well are lowered, creating a drawdown cone. If a saltwater zone exists in the aquifer beneath the well, the saltwater will rise up toward the well screen. This rising up of saltwater is known as upconing and is the second type of seawater intrusion. When a well is pumped, water levels in the vicinity of the well are lowered, creating a drawdown cone. If a saltwater zone exists in the aquifer beneath the well, the saltwater will rise up toward the well screen. This rising up of saltwater is known as upconing and is the second type of seawater intrusion.

6. San Juan County Seawater Intrusion Policy The primary function of the policy is to trigger additional review (of potential for seawater intrusion) of new or expanding public water systems in areas where seawater intrusion appears to be occurring. The policy utilizes chloride concentrations in wells as its indicator of seawater intrusion and defines ‘risk zones’, drawing ½ mile circles around wells with elevated chloride concentrations. all wells within 1000’ have chloride concentrations less than 100 milligrams per liter (mg/l) is considered ‘low risk’. one or more wells have chlorides between 100 and 160 mg/l is considered ‘medium risk’, area with one or more wells with chloride concentrations greater than 160 mg/l is considered ‘high risk’. Drawing 1000’ circles around wells with elevated chloride concentrations yields the map shown in Figure 5 known as the Circle Map. The majority of the 1000’ circles fall along the shoreline, which makes sense in light of the conceptual model However there are exceptions to this pattern, where isolated circles, and even clusters of circles fall away from the shorelines toward the island interiors. This discrepancy suggests a problemThe primary function of the policy is to trigger additional review (of potential for seawater intrusion) of new or expanding public water systems in areas where seawater intrusion appears to be occurring. The policy utilizes chloride concentrations in wells as its indicator of seawater intrusion and defines ‘risk zones’, drawing ½ mile circles around wells with elevated chloride concentrations. all wells within 1000’ have chloride concentrations less than 100 milligrams per liter (mg/l) is considered ‘low risk’. one or more wells have chlorides between 100 and 160 mg/l is considered ‘medium risk’, area with one or more wells with chloride concentrations greater than 160 mg/l is considered ‘high risk’. Drawing 1000’ circles around wells with elevated chloride concentrations yields the map shown in Figure 5 known as the Circle Map. The majority of the 1000’ circles fall along the shoreline, which makes sense in light of the conceptual model However there are exceptions to this pattern, where isolated circles, and even clusters of circles fall away from the shorelines toward the island interiors. This discrepancy suggests a problem

8. Seawater Intrusion Protection

9. Chloride Based Trigger

10. Shoreline Buffer Trigger

11. Water Level Elevation Trigger

12. Island County Phase II Assessment

13. Phase II Data Analysis

14. Conceptual Model

15. Countywide Data

16. Triggering Mechanism Concepts

17. Chloride Trigger Selection

18. WLE Trigger Selection

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