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Cell B10 has a default formula for estimating annual recharge, in inches, through pervious surfaces. Recharge, R, is given by | Cell B10 has a default formula for estimating annual recharge, in inches, through pervious surfaces. Recharge, R, is given by | ||
− | <math> R_{pervious} = P * | + | <math> R_{pervious} = P * F_{Pp} </math> |
where | where | ||
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F<sub>P</sub> = is the fraction of annual precipitation that infiltrates through the soil, vadose zone, and into groundwater. | F<sub>P</sub> = is the fraction of annual precipitation that infiltrates through the soil, vadose zone, and into groundwater. | ||
− | The default for F<sub> | + | The default for F<sub>Pp</sub> in cell G10 is 0.2 based on a literature review. The user may change the value for F<sub>P</sub>. Recharge, calculated in cell B10, equals cellD4*0.01*G10*D2, where the 0.01 corrects for cell D4 (percent pervious) being expressed as a percent and cell D2 is P. |
F<sub>P</sub> is often known for an area. For example, USGS studies often publish this information as part of hydrologic studies in a watershed. If annual recharge through pervious surfaces is known, it may be input directly into cell B10. Note that substituting a value in cell B10 erases the formula. | F<sub>P</sub> is often known for an area. For example, USGS studies often publish this information as part of hydrologic studies in a watershed. If annual recharge through pervious surfaces is known, it may be input directly into cell B10. Note that substituting a value in cell B10 erases the formula. | ||
− | + | The default chloride concentration in recharge water is 50 mg/L. This is based on typical chloride concentrations in shallow groundwater in urban areas. The user can adjust this value based on local data or better information. For example, concentrations may be higher in high volume transportation areas and lower in park areas where deicer is not applied. | |
− | |||
− | ===Row 12: | + | ===Row 11: Loading from impervious surfaces=== |
+ | There is always some infiltration through areas considered to be impervious. This is due to cracks or other conduits through which water can move vertically into the underlying soil. The calculation for annual recharge, in inches, is the same as for pervious surfaces. This calculation is in Cell B11. Recharge, R, is given by | ||
+ | |||
+ | <math> R_{impervious} = P * F_{Pi} </math> | ||
+ | |||
+ | where | ||
+ | *P = annual precipitation (inches) and | ||
+ | F<sub>Pi</sub> = is the fraction of annual precipitation that infiltrates through impervious surfaces. | ||
+ | |||
+ | The default for F<sub>Pi</sub> in cell G10 is 0.05 based on a literature review. The user may change the value for F<sub>Pi</sub>. Recharge, calculated in cell B11, equals cellD4*0.01*G11*D2, where the 0.01 corrects for cell D4 (percent pervious) being expressed as a percent and cell D2 is P. | ||
+ | |||
+ | Note that infiltration through impervious surfaces decreases the amount of runoff from impervious surfaces. If F<sub>Pi</sub> is small (e.g. 0.05 or less), the user may choose to not correct for this decrease in impervious surface runoff. However, as F<sub>Pi</sub> increases, users should subtract the fraction (i.e. percent) of impervious surface in Cell D3 and Cells D5 through D7, as appropriate. | ||
+ | |||
+ | ===Row 12: Loading from piped inflow=== | ||
This input includes leakage from water distribution systems. There is always some leakage from these systems since they are under pressure. | This input includes leakage from water distribution systems. There is always some leakage from these systems since they are under pressure. | ||
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Users who have data for the volume of piped inflow should use that data. In this case, the formula in cell B12 would be rewritten as L times the annual volume of piped inflow divided by the area with piped inflow. For example, if the leakage rate is 0.15 the annual piped inflow is 1000 ft<sup>3</sup>, and the area with piped inflow is 100 ft<sup>2</sup>, the annual infiltration rate (I) equals 0.15 * 1000 / 10 or 1.5 inches per year. | Users who have data for the volume of piped inflow should use that data. In this case, the formula in cell B12 would be rewritten as L times the annual volume of piped inflow divided by the area with piped inflow. For example, if the leakage rate is 0.15 the annual piped inflow is 1000 ft<sup>3</sup>, and the area with piped inflow is 100 ft<sup>2</sup>, the annual infiltration rate (I) equals 0.15 * 1000 / 10 or 1.5 inches per year. | ||
+ | |||
+ | ===Loading from sanitary sewer leakage=== | ||
+ | |||
+ | ===Loading from storm sewer leakage=== | ||
+ | |||
+ | ===Loading from stormwater infiltration=== | ||
+ | |||
+ | ===Loading from surface water discharges=== | ||
+ | |||
+ | ===Loading from sedimentation practices=== | ||
+ | |||
+ | ===Loading from filtration practices=== |
This page provides guidance for using an Excel spreadsheet designed to estimate contributions of chloride to shallow groundwater from nine different sources. The calculator allows the user to adjust inputs for each source and produces an estimate, in pounds per acre or kilograms per hectare, from each source and cumulatively for all sources. The nine sources, described in greater detail below, include the following.
Before using the calculator, we strongly recommend reading the following.
All calculations in the spreadsheet are made on a 1 acre basis. This is why the spreadsheet includes fractions or percentages rather than areas. Inputting areas into cells will invalidate the results.
Cells A1 through D7 are for general inputs into the calculator.
The following conditions apply to the inputs in these cells.
Deciding if an area is impervious, pervious, or surface water is not always clear in more complicated runoff routing scenarios. Below are some recommendations, but the user will have to decide the appropriate accounting.
This term includes chloride loading from areas such as lawns, gardens, wooded areas, and cropped areas. It does not include loading from pervious areas in stormwater practices, such as a swale of filter strip.
Cell B10 has a default formula for estimating annual recharge, in inches, through pervious surfaces. Recharge, R, is given by
\( R_{pervious} = P * F_{Pp} \)
where
FP = is the fraction of annual precipitation that infiltrates through the soil, vadose zone, and into groundwater.
The default for FPp in cell G10 is 0.2 based on a literature review. The user may change the value for FP. Recharge, calculated in cell B10, equals cellD4*0.01*G10*D2, where the 0.01 corrects for cell D4 (percent pervious) being expressed as a percent and cell D2 is P.
FP is often known for an area. For example, USGS studies often publish this information as part of hydrologic studies in a watershed. If annual recharge through pervious surfaces is known, it may be input directly into cell B10. Note that substituting a value in cell B10 erases the formula.
The default chloride concentration in recharge water is 50 mg/L. This is based on typical chloride concentrations in shallow groundwater in urban areas. The user can adjust this value based on local data or better information. For example, concentrations may be higher in high volume transportation areas and lower in park areas where deicer is not applied.
There is always some infiltration through areas considered to be impervious. This is due to cracks or other conduits through which water can move vertically into the underlying soil. The calculation for annual recharge, in inches, is the same as for pervious surfaces. This calculation is in Cell B11. Recharge, R, is given by
\( R_{impervious} = P * F_{Pi} \)
where
FPi = is the fraction of annual precipitation that infiltrates through impervious surfaces.
The default for FPi in cell G10 is 0.05 based on a literature review. The user may change the value for FPi. Recharge, calculated in cell B11, equals cellD4*0.01*G11*D2, where the 0.01 corrects for cell D4 (percent pervious) being expressed as a percent and cell D2 is P.
Note that infiltration through impervious surfaces decreases the amount of runoff from impervious surfaces. If FPi is small (e.g. 0.05 or less), the user may choose to not correct for this decrease in impervious surface runoff. However, as FPi increases, users should subtract the fraction (i.e. percent) of impervious surface in Cell D3 and Cells D5 through D7, as appropriate.
This input includes leakage from water distribution systems. There is always some leakage from these systems since they are under pressure.
The default annual infiltration rate (I) is based on the following equation
\( I = P * F_{precipitation} * L \)
where
L is the leakage rate from the piped infrastructure, as a fraction of total piped inflow.
The term Fprecipitation is used because most literature expresses the volume of piped inflow as a percentage of precipitation. For example, studies suggest that a typical volume of piped inflow is about 50% the value of annual precipitation volume. Leakage represents an annual average value. For example, if 15% of the annual piped inflow is lost through leakage, the value for F is 0.15. The terms Fprecipitation and L are thus unitless.
Users who have data for the volume of piped inflow should use that data. In this case, the formula in cell B12 would be rewritten as L times the annual volume of piped inflow divided by the area with piped inflow. For example, if the leakage rate is 0.15 the annual piped inflow is 1000 ft3, and the area with piped inflow is 100 ft2, the annual infiltration rate (I) equals 0.15 * 1000 / 10 or 1.5 inches per year.