m |
m |
||
Line 1: | Line 1: | ||
The section on [[Integrated stormwater management|integrated stormwater management]] outlines a cost estimation method which site planners could use to compare the relative construction and maintenance costs for structural best management practices. These curves are excellent for purposes of comparison; however, it is recommended that construction and maintenance budgets should be based on site specific information. Utilizing the table below and the cost estimation worksheet, will allow designers to avoid over or under estimation of fixed costs. | The section on [[Integrated stormwater management|integrated stormwater management]] outlines a cost estimation method which site planners could use to compare the relative construction and maintenance costs for structural best management practices. These curves are excellent for purposes of comparison; however, it is recommended that construction and maintenance budgets should be based on site specific information. Utilizing the table below and the cost estimation worksheet, will allow designers to avoid over or under estimation of fixed costs. | ||
− | {{: | + | {{:Design infiltration rates}} |
{{:Infiltration basin cost estimate worksheet}} | {{:Infiltration basin cost estimate worksheet}} |
The section on integrated stormwater management outlines a cost estimation method which site planners could use to compare the relative construction and maintenance costs for structural best management practices. These curves are excellent for purposes of comparison; however, it is recommended that construction and maintenance budgets should be based on site specific information. Utilizing the table below and the cost estimation worksheet, will allow designers to avoid over or under estimation of fixed costs.
Design infiltration rates, in inches per hour, for A, B, C, and D soil groups. Corresponding USDA soil classification and Unified soil Classifications are included. Note that A and B soils have two infiltration rates that are a function of soil texture.*
The values shown in this table are for uncompacted soils. This table can be used as a guide to determine if a soil is compacted. For information on alleviating compacted soils, link here. If a soil is compacted, reduce the soil infiltration rate by one level (e.g. for a compacted B(SM) use the infiltration rate for a B(MH) soil).
Link to this table
Hydrologic soil group | Infiltration rate (inches/hour) | Infiltration rate (centimeters/hour) | Soil textures | Corresponding Unified Soil ClassificationSuperscript text |
---|---|---|---|---|
Although a value of 1.63 inches per hour (4.14 centimeters per hour) may be used, it is Highly recommended that you conduct field infiltration tests or amend soils.b See Guidance for amending soils with rapid or high infiltration rates and Determining soil infiltration rates. |
gravel |
GW - Well-graded gravels, fine to coarse gravel GP - Poorly graded gravel |
||
1.63a | 4.14 |
silty gravels |
GM - Silty gravel |
|
0.8 | 2.03 |
sand |
SP - Poorly graded sand |
|
0.45 | 1.14 | silty sands | SM - Silty sand | |
0.3 | 0.76 | loam, silt loam | MH - Elastic silt | |
0.2 | 0.51 | Sandy clay loam, silts | ML - Silt | |
0.06 | 0.15 |
clay loam |
GC - Clayey gravel |
1For Unified Soil Classification, we show the basic text for each soil type. For more detailed descriptions, see the following links: The Unified Soil Classification System, CALIFORNIA DEPARTMENT OF TRANSPORTATION (CALTRANS) UNIFIED SOIL CLASSIFICATION SYSTEM
Source: Thirty guidance manuals and many other stormwater references were reviewed to compile recommended infiltration rates. All of these sources use the following studies as the basis for their recommended infiltration rates: (1) Rawls, Brakensiek and Saxton (1982); (2) Rawls, Gimenez and Grossman (1998); (3) Bouwer and Rice (1984); and (4) Urban Hydrology for Small Watersheds (NRCS). SWWD, 2005, provides field documented data that supports the proposed infiltration rates. (view reference list)
aThis rate is consistent with the infiltration rate provided for the lower end of the Hydrologic Soil Group A soils in the Stormwater post-construction technical standards, Wisconsin Department of Natural Resources Conservation Practice Standards.
bThe infiltration rates in this table are recommended values for sizing stormwater practices based on information collected from soil borings or pits. A group of technical experts developed the table for the original Minnesota Stormwater Manual in 2005. Additional technical review resulted in an update to the table in 2011. Over the past 5 to 7 years, several government agencies revised or developed guidance for designing infiltration practices. Several states now require or strongly recommend field infiltration tests. Examples include North Carolina, New York, Georgia, and the City of Philadelphia. The states of Washington and Maine strongly recommend field testing for infiltration rates, but both states allow grain size analyses in the determination of infiltration rates. The Minnesota Stormwater Manual strongly recommends field testing for infiltration rate, but allows information from soil borings or pits to be used in determining infiltration rate. A literature review suggests the values in the design infiltration rate table are not appropriate for soils with very high infiltration rates. This includes gravels, sandy gravels, and uniformly graded sands. Infiltration rates for these geologic materials are higher than indicated in the table.
References: Clapp, R. B., and George M. Hornberger. 1978. Empirical equations for some soil hydraulic properties. Water Resources Research. 14:4:601–604; Moynihan, K., and Vasconcelos, J. 2014. SWMM Modeling of a Rural Watershed in the Lower Coastal Plains of the United States. Journal of Water Management Modeling. C372; Rawls, W.J., D. Gimenez, and R. Grossman. 1998. Use of soil texture, bulk density and slope of the water retention curve to predict saturated hydraulic conductivity Transactions of the ASAE. VOL. 41(4): 983-988; Saxton, K.E., and W. J. Rawls. 2005. Soil Water Characteristic Estimates by Texture and Organic Matter for Hydrologic Solutions. Soil Science Society of America Journal. 70:5:1569-1578.
Infiltration trench and infiltration basin cost estimate worksheet.
Link to this table
Project Title | ||||
Owner | ||||
Location | ||||
Project Number | ||||
Date | ||||
Description | Units | Quantity | Unit Cost | Total Estimated Price |
---|---|---|---|---|
Site Preparation | ||||
Tree removal - up to 12" diameter | each | $350.00 | $0.00 | |
Clear and grub brush | square yard | $1.50 | $0.00 | |
Tree protection - temp. fence | lineal foot | $3.00 | $0.00 | |
Infiltration area protection - silt fence | lineal foot | $2.00 | $0.00 | |
Topsoil - 6" depth, salvage on site | square yard | $4.50 | $0.00 | |
Site Formation | ||||
Excavation - 6' depth | square yard | $8.00 | $0.00 | |
Grading | square yard | $1.50 | $0.00 | |
Hauling off-site - 6' depth | square yard | $10.00 | $0.00 | |
Structural Components | ||||
Inlet structure | each | $1,500.00 | $0.00 | |
Multi-stage outlet structure | each | $2,500.00 | $0.00 | |
Site Restoration | ||||
Sod filter strip | lineal foot | $1.50 | $0.00 | |
Soil preparation | square yard | $5.00 | $0.00 | |
Seeding - above outlet elevation | square yard | $0.50 | $0.00 | |
Planting - below outlet elevation | square yard | $30.00 | $0.00 | |
Mulch | square yard | $2.00 | $0.00 | |
Subtotal | $0.00 | |||
10% Contingencies | $0.00 | |||
Subtotal | $0.00 | |||
Apply MN Location Factor | $0.00 | |||
TAL CONSTRUCTION COST | $0.00 | |||
Annual Operation and Maintenance | ||||
Replace planting media | square yard | $12.00 | $0.00 | |
Debris removal | per visit | $50.00 | $0.00 | |
Mow filter strips | per visit | $50.00 | $0.00 | |
Sediment removal | per year | $500.00 | $0.00 | |
Replace plants | per plant | $5.00 | $0.00 | |
Erosion repair | square yard | $75.00 | $0.00 | |
Gate / valve operation | per visit | $125.00 | $0.00 | |
Inspection | per visit | $125.00 | $0.00 | |
Subtotal | $0.00 | |||
Apply MN Location Factor | $0.00 | |||
TOTAL ANNUAL O&M COST | $0.00 | |||
Minnesota Location Factors | ||||
Bemidji | 0.963 | |||
Brainerd | 1.003 | |||
Detroit Lakes | 0.962 | |||
Duluth | 0.991 | |||
Mankato | 0.990 | |||
Bemidji | 0.963 | |||
Minneapolis | 1.035 | |||
Rochester | 0.983 | |||
St. Paul | 1.000 | |||
St. Cloud | 1.002 | |||
Thief River Falls | 1.042 | |||
Willmar | 0.961 | |||
Windom | 0.935 | |||
Note: Suggested unit costs are based on RS Means prices for Spring, 2005, then factored into an area basis based on typical design features for Constructed Wetlands BMPs. To be used for preliminary cost estimation
The table below lists the specific site components that are specific to infiltration practices. Not included in this table are those cost items that are common to all construction projects, such as mobilization, traffic control, erosion and sediment control, permitting, etc.
Summary of infiltration practices cost components.
Link to this table
Implementation Stage | Primary Cost Components | Basic Cost Estimate | Other Considerations |
---|---|---|---|
Site Preparation | Tree & plant protection | Protection Cost ($/acre) * Affected Area (acre) | Removal of existing structures, topsoil removal and stockpiling |
Infiltration area protection | Silt fence cost ($/’foot) * Perimeter of infiltration area | ||
Clearing & grubbing | Clearing Cost ($/acre) * Affected Area (acre) | ||
Topsoil salvage | Salvage Cost ($/acre) * Affected Area | ||
Site Formation | Excavation / grading | X-ft Depth Excavation Cost ($/acre) * Area (acre) | Soil & rock fill material, tunneling |
Hauling material offsite | Excavation Cost * (% of Material to be hauled away) | ||
Structural Components | Vault structure (for underground infiltration) | ($/structure) | Pipes, catchbasins, manholes, valves, vaults |
Media (for infiltration trenches) | Media cost ($/cubic yard) * filter volume (cubic yard) | ||
Geotextile | Geotextile cost ($/cy) * area of trench, including walls | ||
inlet structure | ($/structure) | ||
Overflow structure | ($/structure) | ||
Observation well | ($/structure) | ||
Site Restoration | Soil preparation | Topsoil or amendment cost ($/acre) * Area (acre) | Tree protection, soil amendments, seed bed preparation, trails |
Seeding | Seeding Cost ($/acre) * Seeded Area (acre) | ||
Filter strip | Sod cost ($/square foot) * filter strip area | ||
Planting / transplanting | Planting Cost ($/acre) * Planted Area (acre) | ||
Annual Operation, Maintenance, and Inspection | Sediment removal | Removal Cost ($/acre) * Area (acre) * Frequency (1 time per 5 years) | Vegetation maintenance, cleaning of structures |
Debris removal | Removal Cost ($/acre) * Area (acre) * Frequency (2 time per year) | ||
Inspection | Inspection Cost ($) * Inspection Frequency (6 times per year) | ||
Mowing (for some vegetative filters) | Mowing Cost ($) * Mowing Frequency (6 times per year) |