John S. Tyner

Increasing exfiltration from pervious concrete and temperature monitoring.

Pervious concrete typically has an infiltration rate far exceeding any expectation of precipitation rate. The limiting factor of a retention based pervious concrete system is often defined by how quickly the underlying soil subgrade will infiltrate the water temporarily stored within the concrete and/or aggregate base. This issue is of particular importance when placing a pervious concrete system on compacted fine textured soils. This research describes the exfiltration from twelve pervious concrete plots constructed on a compacted clay soil in eastern Tennessee, USA. Several types of treatments were applied to the clay soil prior to placement of the stone aggregate base and pervious concrete in an attempt to increase the exfiltration rate, including: 1) control--no treatment; 2) trenched--soil trenched and backfilled with stone aggregate; 3) ripped--soil ripped with a subsoiler; and 4) boreholes--placement of shallow boreholes backfilled with sand. The average exfiltration rates were 0.8 cm d(-1) (control), 4.6 cm d(-1) (borehole), 10.0 cm d(-1) (ripped), and 25.8 cm d(-1) (trenched). The trenched treatment exfiltrated fastest, followed by the ripped and then the borehole treatments, although the ripped and borehole treatments were not different from one another at the 5% level of significance. The internal temperature of the pervious concrete and aggregate base was monitored throughout the winter of 2006-2007. Although the temperature of the pervious concrete dropped below freezing 24 times, freezing concrete temperatures never coincided with free water being present in the large pervious concrete pores. The coldest recorded air temperature was -9.9 degrees C, and the corresponding coldest recorded pervious concrete temperature was -7.1 degrees C. The temperature of the pervious concrete lagged diurnal air temperature changes and was generally buffered in amplitude, particularly when free water was present since the addition of water increases the thermal capacity of the pervious concrete greatly. The temperature of the aggregate base was further buffered to diurnal changes, and no freezing temperatures were recorded.

SEAL FORMATION BENEATH ANIMAL WASTE HOLDING PONDS

The objectives of this study were to measure the sealing effectiveness of swine and dairy waste applied to a variety of soil textures and to develop a suitable model for describing the sealing process through time. Dairy and swine waste were applied to soil columns packed with sand, silt loam, or clay. A seal developed that reduced the infiltration rates to approximately 10-6 cm s-1 or less within the 54 to 60 day testing period. Throughout the test, the infiltration rates into the clay soil were lowest. Yet as time passed, the differences between soil types diminished. Swine waste applied to sand required more time to develop a seal than all other combinations of waste and soil. A model was developed that describes cumulative infiltration as function of elapsed time, waste height, waste total solids content, and soil hydraulic conductivity. After a stable seal develops, the model predicts that only the seal properties (not the soil properties) are responsible for limiting infiltration. During the seal-dominated phase, a plot of cumulative infiltration versus the square root of time is linear, and the respective slope is dependent on a lumped parameter (Kseal/a). A review of available waste infiltration datasets from the literature revealed that Kseal/a can be estimated from the total solids concentration of the waste (R2 = 0.87). Predictions of Kseal/a were not improved by including the hydraulic conductivity of the soil into the estimate or by analyzing the dairy and swine waste datasets separately. This suggests that neither soil hydraulic conductivity nor waste type greatly affect the infiltration rate during the seal-dominated phase of infiltration.

Chloride mass balance to determine water fluxes beneath KCl-fertilized crops.

The utilization of Chloride Mass Balance (CMB) to determine water fluxes generally has been restricted to applications in arid to semi-arid environments. Only in such environments does the chloride deposited by precipitation and dry fallout concentrate sufficiently by evapotranspiration for accurate measurement. This study successfully applied CMB to dryland winter wheat plots with 860 mm of precipitation per year. Soil cores were collected from long-term dryland winter wheat test plots located near Stillwater, Oklahoma, which had known constant applications of the fertilizer KCl for the past 29 years. This additional chloride was sufficient to allow for accurate chloride concentration measurement. Groundwater recharge rates of 12.2 to 38.9 mm/y were calculated with recharge increasing with fertilizer N. These fluxes may be overestimated by up to 20% based on anion exclusion measurements from adjacent soil cores. Numerical modeling of the chloride distributions beneath the plots supported the assumptions of CMB.

IDENTIFYING LONG-TERM PREFERENTIAL AND MATRIX FLOW RECHARGE AT THE FIELD SCALE

Preferential recharge from agricultural production fields can lead to agrochemical contamination of groundwater due to short-circuiting of the soil matrix. This research determines the relative amounts of preferential and matrix flow recharge from a no-till agricultural production field. The conservative tracer potassium bromide was surface applied to a 0.37 ha bermed field plot at a rate of 900 kg ha-1 as bromide. The site was instrumented to monitor precipitation and runoff from the bermed field plot. Three years after the bromide application, twenty-one 3.65 m continuous soil cores were collected from the bermed plot and analyzed for bromide. Based solely on the shape of the bromide profiles, most of the 21 soil cores showed no apparent preferential flow. However, up to 83% of the infiltrated bromide mass was absent from individual soil cores, presumably due to preferential flow. Using a mass balance approach, we estimated that 58% of the recharge was due to preferential flow and 42% was due to matrix flow.

INFLUENCE OF SEAL AND LINER HYDRAULIC PROPERTIES ON THE SEEPAGE RATE FROM ANIMAL WASTE HOLDING PONDS AND LAGOONS

Animal waste holding ponds and lagoons are often lined with soil and may leak leachate into the underlying media. Calculating the flux of leachate through a pond liner is typically predicted by applying Darcy’s law across the liner while assuming saturated conditions. The formation of a thin sealing layer atop holding pond liners is common due to the abundance of fines and organic material within animal waste. Research has shown that these seals are credited with reducing the flux from holding ponds by one or more orders of magnitude due to the very low hydraulic conductivity of the sealing layer. Because even compacted clay liners are likely to have hydraulic conductivities much larger than the overlying seal, a unit gradient forms within the liner such that it desaturates to the point that its unsaturated hydraulic conductivity is equal to the flux, a process similar to that of water infiltrating into a crusted soil. In this study, a two-layer (liner and seal) unsaturated model is presented for describing the flux of animal waste from holding ponds. The two-layer model predicts that flux is not a function of liner thickness, and is only a weak function of liner hydraulic conductivity. Instead, flux through the liner is primarily a function of seal hydraulic conductivity, seal thickness, and depth of waste. The van Genuchten-Mualem hydraulic parameters (. and n) of the liner are found to correlate well with flux, but the saturated hydraulic conductivity of the liner is found to be a poor predictor of flux.

CONSERVATION PLANNING FOR CONSTRUCTION SITES

Although conservation planning for agricultural lands has evolved to its current relatively stable form over many decades, conservation planning for construction sites is still in its infancy. This project drew on the resources of various agencies and researchers to develop a conservation planning tool specifically geared towards meeting construction site planning needs in Wisconsin, basing it on the Revised Universal Soil Loss Equation, version 2 (RUSLE2). The project began by deconstructing the planning process itself to determine possible approaches and critical elements, and used those pieces to build a rational new approach to construction site conservation planning. Although no changes were required to the erosion or sediment delivery calculations in RUSLE2, this new tool required substantial changes to the database, the interface, and how the results were presented and packaged. The lessons learned in this effort should be instructive to both a general discussion of the construction site planning process and to attempts to develop other tools that meet this need.

Fate and Transport of 17β-Estradiol beneath Animal Waste Holding Ponds.

Concentrated animal feeding operations typically store livestock waste in clay-lined ponds. Although these ponds are regulated to include a liner with a small hydraulic conductivity to limit leaching, previous studies have traced surface and groundwater contamination from such regulated animal waste ponds. This research examined the transport of 17β-estradiol (E2) and its primary metabolite, estrone (E1), through soil liners using field- and laboratory-based studies. Additionally, a potential engineering solution to limit hormone transport-applying biochar to new pond liners to act as a retardant-was studied. Soil cores 80 cm in length were collected beneath a mature dairy waste pond and analyzed for moisture content and hormone concentrations. Unsaturated conditions and E2 concentrations of 4 to 250 ng g were detected beneath the waste pond. In the laboratory portion of the study, hand-packed columns of sand or clay were subjected to infiltration by a 2.3-m head of dairy waste. A subset of the hand-packed sand columns was amended with powdered biochar to test its ability to retard E2 and E1. For 3 mo, column leachate was analyzed for hormone concentrations, and at the conclusion of the study E2 and E1 concentrations in the soil were measured. In the 44 d after sealing, the clay, sand, sand with a thin layer of biochar, and sand mixed with a biochar amendment leached a total of 0.54, 1.3, 0.09, and 0.45 μg of E2, respectively. The biochar amendments to the hand-packed columns considerably minimized E2 in the leachate.

Discussion of “Investigation of Flow through Orifices in Riser Pipes” by P. D. Prohaska, A. A. Khan, and N. B. Kaye

The referenced manuscript is a very useful contribution to the scientific literature because it describes the variation of Cd across a variety of parameters for a riser outlet commonly employed within stormwater systems. The authors conducted an excellent investigation of the discharge through orifices in riser pipes, but the area (A) used to calculate discharge in the orifice equation is not clearly defined. The manuscript states that the holes are cut with a bit, so it is assumed that A is the area of the bit (we will use the term Ab to distinguish the bit area), but this is not the area of the hole, because the hole perimeter formed by a circular bit drilling into a curved surface appears as a three-dimensional ellipsoid instead of a circle. If the actual orifice area encountered by the flowing water could be described, we hypothesize that it might be better correlated to flow than Ab. We can define two distinct areas that describe a hole cut perpendicularly by a circular bit into the center of a round pipe. The first describes an outer surface (Ao) and is equivalent to the area of pipe removed by the bit (Fig. 1). The second describes an inner surface (Ai) that curves into the riser (Fig. 1). Ao and Ai are always larger than Ab, but they approach the value of Ab as d=D approaches zero. Both Ao and Ai share a common perimeter described by Stockie (1998) as

LAGOON SEALING AND FILTER CAKES

A recent study presented a two-layer (liner and seal) unsaturated model to predict the flux from lagoons. The model predicted that flux is not related to liner thickness, is only weakly related to the saturated hydraulic conductivity of the liner, and is primarily controlled by the hydraulic conductivity of the seal. In this study, we evaluated those predictions by monitoring the flux of dairy waste through eight intact soil monoliths (silt loam) with large macropores. After applying a 2.3 m column of dairy waste (2.3% total solids) to the top of the monoliths, a seal developed within 2 d, and the leakage continued to decrease for the remaining 83 d of the test. The average leakage rate after 85 d was 0.70 mm d-1, and an average of 218 mm of waste infiltrated into the monoliths. Small holes drilled into the sides of the monoliths, just below the soil surface, failed to fill with liquid, which demonstrated that the soil was unsaturated and therefore was not limiting the leakage rate. The amount of waste required to initially seal the monoliths did not correlate to the seal growth rate, which also implies that the soil contributed little to the seal growth rate or leakage rate after seal development. A plot of cumulative waste infiltration versus the square root of time showed a strong linear relationship (R2 = 0.996), which suggests that the phenomenon of dairy waste sealing a soil is analogous to filter cake growth. Long-term studies with other soil and waste types are needed to confirm the findings of this research.

A Review of Construction Site Best Management Practices for Erosion Control

A literature review was conducted to determine the effectiveness of erosion control products and practices commonly applied at construction sites, limiting ourselves to studies providing useful information for erosion estimation within the USLE/RUSLE framework. We found that erosion control mats reduced erosion most, followed in descending order by mulches, composts, hydromulches and bonded fiber matrixes (BFMs), polyacrylamides (PAMs), and lastly compaction methods. Excluding compaction, all of the methods relied on surface cover for erosion control and exhibited average soil loss ratios (SLR) from 0.21 to 0.38, indicating erosion reductions of 62% to 79% from what would be expected for bare loose soil. The mean SLR for compaction methods was 0.63, but this value represents results from a single study. The literature yielded a tremendous variety of testing protocols applied to measuring the efficacy of cover products, making interpretation of the resulting data difficult regardless of the underlying conceptual model. Since erosion is inherently a highly variable process, additional variability from poorly defined protocols reduces the value of the resulting data. The erosion and sediment control community should work towards establishing and following validated erosion testing protocols to describe field-scale processes.