Presented by: David Albus, RCE, GE

Definitions Percolation Rate- Rate that water falls in a percolation test Dependent on water pressure and geometry of test Infiltration Rate- The straight-path velocity at which water enters into soil Is dependent on the water pressure More pressure= higher infiltration Permeability Rate- Also known as Hydraulic Conductivity Is an intrinsic value - does not vary due to pressure All three have units of length/time- leads to confusion

Flow of water through Soil

Flow of water through Soil SATURATED FLOW TOTAL HEAD= PORE PRESSURE + ELEVATION Hydraulic Gradient

Flow of water through Soil Element Adjacent Elements K i (X-direction) K i (Y-direction) Boundary Flux Change in Water Content

Infiltration in a Basin

Infiltration in a Basin Impounding layer caused by soil with lower permeability

Infiltration in a Basin

Other Basin Systems Arched Chamber Systems Stackable Block Systems

Dry Well System

Types of Percolation Testing

Shallow Percolation Pit - Falling Head

Deep Percolation Pit - Falling Head

Single-Ring Infiltrometer Constant Head

Double-Ring Infiltrometer Constant Head

Well Permeameter - Constant Head USBR 7300-89

Well Permeameter - Constant Head

Laboratory Testing for Comparison

Laboratory Testing for Comparison Kozeny-Carmen Equ. from Chapuis & Aubertin (2003) A2 a constant in the range of 0.29-0.51; commonly 0.29 is used. Gs the specific gravity of solids, 2.65. S e k the specific surface (m2/kg) void ratio hydraulic conductivity in m/s

Design of Chamber or Basin

Design of Chamber or Basin Ratio of Clearance to Aquitard/width of BMP Effective Infiltration Rate 2.25 0.75U + 0.25L 1.5 0.5U + 0.5L 0.75 0.25U + 0.75L U= Upper Permeability L= Lower Permeability

Design of Chamber or Basin Depth of Ponding (in) Percent of Infiltration for 12 inches of ponding 9 75% 6 50% 3 25%

Design of Chamber or Basin

Design of Dry Well

Well Permeameter Equations

Well Permeameter Equations Ave. water level of segment Find Q at ave. water level and Volume of segment T 1 =V 1 /Q 1 Find Q 2 and V 2 T 2 =V 2 /Q 2 Find Q 3 and V 3 T 3 =V 3 /Q 3 Find Q 4 and V 4 T 4 =V 4 /Q 4 Find Q 5 and V 5 T 5 =V 5 /Q 5 Find Q 6 and V 6 T 6 =V 6 /Q 6 Add up for Total Time

Well Permeameter Equations K=saturated permeability T1 & t2= Times of interest H1 & H2= height of water in well at t1 & t2 L= Length of well screen r= Well radius

Computer Model of Dry Well Water Surface Upper Chamber Impermeable Layer (fill) More permeable layer Lower Well Less permeable layer Radial Distance of Saturation

Computer Model of Dry Well 95 Invert Chamber Section 80 Gravel Section 60

Computer Model of Dry Well TIME= 0 HR Groundwater

TIME= 1.7 HR Computer Model of Dry Well

TIME= 5.5 HR Computer Model of Dry Well

TIME= 9.7 HR Computer Model of Dry Well

TIME=13.6 HR Computer Model of Dry Well

Computer Model of Dry Well 40 35 40-foot deep, 4-foot diameter: Height of Water in Dry Well Height of Water in Well (ft) 30 25 20 15 10 5 0 0 2 4 6 8 10 12 14 16 18 20 Time (hrs)

Design Parameters Infiltration Basin/Chamber- Infiltration rate = permeability if ponding is 12 or more Reduce infiltration rate for ponding less than 12 using linear reduction Adjust rate in consideration of impeding layers or GW If impeding layer or GW more than 3X width, minimal effect If shallower than 3X Width, roughly weighted to proportion of distance Provide a second infiltration rate for down draw determination Use ½ of the value appropriate to the max ponding depth Dry Well- Infiltration rate permeability Need Q value for specific well configuration Use computer software or closed-form equation if suitable Effective Infiltration rate = Q/wetted area Effective Infiltration Rate will be much greater than permeability Don t be surprised to get rate that is 5X to 20X of permeability Use finite step method or Horslev equation for explicit draw down Or use computer model to determine drawdown time

Questions & Answers