Postconstruction stormwater regulators generally require hydrologic designs generated by approved science-based tools. They then review those designs to ensure that all pertinent rules and codes are met. This design-review sequence is done in various ways, but unfortunately the pass/fail bar is often not clearly defined, making the roles of both designer and reviewer more difficult than necessary. We herein describe a system built to integrate and improve the process, taking into account feedback from both reviewers and regulators while incorporating a physically based model accurately describing site hydrology. We hope this experience and lessons learned will help others develop similar design-review approaches for postconstruction stormwater or other natural resource development. Comprehensive design-review must aim toward a common ultimate goal. The US Environmental Protection Agency (USEPA) promulgated postconstruction stormwater rules, establishing local regulatory bodies as Municipal Separate Storm Sewer System (MS4) entities based on their management of infrastructure collecting urban stormwater runoff and discharging it to streams and rivers (USEPA 2018). Each MS4 must develop a comprehensive plan using ordinances, permits, education, and guidance to encourage progress so that discharges will ultimately meet expectations. The rules hold both for individual permits for larger communities (Phase 1 MS4s) and for state general…

Core Ideas Spontaneous imbibition was measured in rock fractures using neutron radiography. Early‐time uptake of water displacing air showed a square root of time dependency. Fracture sorptivity was quantified from the slope of the early‐time uptake data. Fracture sorptivity increased with increasing fracture aperture width. Fracture sorptivity decreased with increasing fracture surface roughness. Fractures in low‐porosity rocks can provide conduits for fluid flow. Numerous researchers have investigated fluid flow through fractures under saturated conditions. However, relatively little information exists on spontaneous imbibition in fractures, whereby a wetting fluid displaces a non‐wetting fluid by capillarity. We investigated spontaneous imbibition of water displacing air in a suite of fractured low‐porosity sedimentary and igneous rock cores (5.08‐cm length by 2.54‐cm diameter). Mode I fractures were induced in the cores by compression between opposing parallel flat plates. The following physical properties were measured: bulk density, ρb; solid‐phase density, ρs; porosity, ϕ; contact angle, θe; fracture aperture width, xgeo; and fracture surface roughness, Wr. The wetting front in each fracture was imaged using dynamic neutron radiography. Early‐time uptake exhibited a square root of time dependency, and was quantified by linear regression, with the slope equal to the fracture sorptivity, Sf. Estimates of Sf ranged from 10.1 to 40.5 mm s−0.5, with a median value of 25.0 mm s−0.5. There was a statistically significant effect of rock type on Sf, with igneous rocks generally having lower mean values than sedimentary rocks. Differences in ρb, ρs, ϕ, and θe between the rock types did not contribute significantly to the variation in Sf. However, xgeo and Wr were significantly correlated with Sf. These correlations indicated that Sf increases with increasing xgeo, as predicted by early‐time capillary theory, and decreases with increasing Wr, analogous to the decrease in fracture permeability with increasing surface roughness observed under saturated flow conditions.

This study provides a new mathematical description of pendular rings that allows for continuous solutions of the geometric and physical properties (i.e., volume, meridional curvature, azimuthal curvature, pressure difference, and total capillary force) that were previously not fully understood due to difficulty in obtaining the mathematical solutions. This new solution has also allowed for calculation of volume limit for a pendular ring, beyond which the dimensionless mean curvature obtained by iterative calculation does not converge. The new continuous solutions were validated by comparison to previously published results of an analytical solution for a succinct number of tabular input values. The resulting fits are excellent with root-mean square error of 0.00021.

Stormwater is a leading source of pollutants that when transported to surface waters may damage aquatic habitat, decrease reservoir capacity, and contaminate drinking water. In order to evaluate whether a pervious concrete detention system can remove stormwater pollutants from the runoff, water quality was monitored at a site with both impervious asphalt and pervious concrete parking areas. The stormwater flowed across asphalt pavement before infiltrating into the pervious concrete and an aggregate sub-base below. The runoff was sampled exiting the asphalt but prior to entering the pervious concrete, and after it passed through the pervious concrete detention system, representing pre- and post-treatment sampling. Results showed statistically significant (p < 0.05) decreases in concentrations of total suspended solids, nitrite, chemical oxygen demand, and polycyclic aromatic hydrocarbons compared to untreated asphalt runoff. Zinc concentrations were apparently reduced, but not quite to statistically significant levels (p = 0.054). Values of pH and sulfate both showed statistically significant (p < 0.05) increases.

This research developed a new approach for calculating the area over which water spreads after being released from a confined conduit onto a sloped planar surface with defined roughness. In particular, the goal was to predict how stormwater would spread onto a sloped grass lawn after being discharged from a disconnected gutter downspout or through a parking lot curb cut. The need for this stems primarily from regulators increasingly requiring developers to infiltrate more of the runoff created by site development, but designers not having good tools for estimating the infiltration area associated with such “overflow” practices. The model is largely based on Manning’s equation applied at multiple cross-sectional areas of flow downslope, with additional modifications allowing the water to spread laterally. The model results were compared to laboratory experiments of water spreading across a roughened painted surface and two different artificial turfs. The new model predicted the wetting area with average absolute errors of 6.0% and 5.9% for a fine-bladed artificial turf and a coarse-bladed artificial turf, respectively. In addition, while validating the modeled flow spreading across a range of roughnesses, the model had an absolute error of 5.2% for a rough painted surface meant to represent unfinished concrete.

Contact angle measurements for gas-liquid-rock systems are important for modeling multi-phase flow and transport in the subsurface. These data are needed in applications such as the extraction of oil and gas resources, geologic sequestration of carbon dioxide, contaminant fate and transport, and aquifer recharge through the vadose zone. Contact angles are frequently measured with the sessile drop method. Previous research has largely ignored the dynamic behavior of sessile droplets on geologic materials. This study investigates the dynamic behavior of sessile water droplets on prepared rock surfaces in the presence of air. Droplet diameter and advancing contact angle were determined at 0.5 s intervals for similar to 90 s on flat polished disks of Burlington limestone, Crossville sandstone, Mancos shale, Sierra White granite, Vermilion Bay granite, and Westerly granite using a Krtiss DSA 30 Drop Shape Analyzer. The droplet diameter and advancing contact angle data sets were nonlinearly regressed against time using two different two-parameter models. The median coefficients of determination for the fits were 0.85 and 0.96, respectively. The resulting parameter estimates were used to compute the apparent equilibrium contact angle, theta(e), for each disk following droplet diameter stabilization. Estimates of theta(e) ranged from 37.2 degrees for Mancos shale to 75.6 degrees for Burlington limestone. Analysis of variance indicated statistically significant differences in O e between the rock types at the 95% confidence level. The variability of O e on the polished rock surfaces, as quantified by the coefficient of variation (CV) for theta(e), varied between similar to 3 and similar to 9%; there were no significant differences in CV between the rock types. Neutron radiography indicated changes droplet morphology over time were due to the spontaneous imbibition of water into the rock matrix. The transient analysis employed in this study permits a more meaningful estimate of the equilibrium contact angle for rocks than taking the initial value or averaging over time as is frequently done.

Sediment-laden runoff is the primary pollutant in many watersheds, so sediment basins are commonly used to remove sediment before it leaves the site. In fact, for construction sites such basins are often required by statute. Sediment basins are usually drained by perforated vertical risers and more recently by floating skimmers. Whereas a traditional riser discharges primarily from its lower orifices because of the higher heads that exist at greater depths, skimmers drain the cleaner water at the top of the water column, thereby increasing sediment retention. The authors have developed an alternative solid state skimmer (given the moniker solid state because it has no moving parts) that provides a similar skimming function, but also provides the additional benefits of varying flow rate with head and serving as its own principal spillway. The solid state skimmer is comprised of two concentric vertical risers. Columns of orifices cut into each riser act in series such that the flow into the outer riser is always dominated by flow through the uppermost wetted orifices, enabling skimming of water from a basin for the purpose of increasing sediment retention.

A multifunctional heat pulse probe (MFHPP) can measure soil thermal and hydraulic properties. Though its successful implementation has been documented, previous studies have reported some limitations. One specific cause of the limitations is the absorption of the generated heat pulse within the probe itself, which creates error in the measurements. The objective of this study was to develop and evaluate a new calibration method to account for measurement error due to heat loss to the probe. A MFHPP was constructed and tested in six soil types using both a traditional method and the newly developed calibration method. The new calibration utilizes heat pulse response curves from real soils with thermal conductivities similar to that of the MFHPP rather than the traditional agar-stabilized water solution. This new approach significantly reduced average measurement errors from 9.1% to 2.4% for heat capacity and 13.5% to 4.5% for volumetric water content.

Abstract. Mixing models help describe the contribution of liquid, gas, and solid phases to the bulk dielectric permittivity of porous materials. They are particularly useful when studying the electromagnetic properties of the vadose zone using TDR or GPR techniques. The objective of this research was to evaluate the Lichtenecker Mixing Model applied to undisturbed and repacked soil data collected with a 50 MHz impedance sensor. These data along with four different applications of the Lichtenecker Mixing Model were used to predict the α parameter and/or solid phase permittivity. The four models employed were: (1) the Complex Refractive Index Model, α = 0.5 (CRIM); (2) dual varying of both α and solid phase permittivity (LI); (3) the direct-weighted average model, α = 1 (DW); and (4) a two-phase simplification of the Lichtenecker model (TM). Overall, the CRIM, LI, and TM models estimated the solid phase permittivity, α, and soil bulk permittivity within the ranges previously reported in the scientific literature, while the other model proved to be of little practical value. Further validation with glass beads showed that the simple CRIM model was the best predictor for soil bulk permittivity when compared to the two-parameter LI model. A regression model was also developed that accurately predicted the volumetric water content of glass beads from soil bulk permittivity, solid phase permittivity, and porosity.

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.

This study focuses on the discharge coefficient (Cd) for flow into orifices cut with a circular bit perpendicular to and along the centerline of a round pipe, a common configuration on perforated risers installed as the principal outlets for stormwater detention or sediment basins. When predicting flow, the orifice area is generally defined as the area of the bit used to cut the hole, but the true orifice area is larger than the bit due to the curvature of the riser pipe. Four different descriptions for orifice area were tested while attempting to fit Cd to measured discharge experiments. The tests showed that Cd decreases as the orifice diameter approaches the diameter of the riser. Photographic imagery shows that the reduced Cd is due to lateral flow from the riser's curved sides decreasing the vena contracta area more than what normally occurs during flow through an orifice in a flat plate. In contrast, but to a lesser extent, Cd increases as the water surface approaches the top of the orifice. Best fit equations to model Cd were developed to better estimate flow, with the most applicable having an R2 of 88.8% and a root-mean squared error of 0.028. Orifice elevation above the tank floor was measured and initially modeled but was ultimately not included in the Cd model because the R2 improved by only 0.6%.

Selenium (Se) is a trace element that can cause human physical deformations due to selenosis, and mutagenic changes on a range of sensitive macro-organisms. Previous studies indicated that Se enrichment is significantly greater in coal than in other rock units, suggesting a correlation between Se and coal bed proximity. Since coal extraction can cause a release of Se, some regulatory authorities have responded by requiring sampling of coal seams and adjacent rock for Se prior to issuing coal mining permits. This sampling is done under the assumption that Se in a small number of samples will be correlated to the Se concentrations throughout the strata they represent. For example, in one case a single continuous deep rock core was sampled for Se to estimate the concentrations of Se across a 2.52 km(2) proposed surface coal mine. This project examined the adequacy of such an approach using univariate statistics and variograms to determine the spatial variability and correlation of Se concentrations collected from six Appalachian coal seams. The results from all analyses showed no significant spatial correlation of Se within any coal seam examined. Given this lack of measured Se spatial correlation in Appalachian coal seams for scales as small as 0.10 km, it is unlikely that a Se spatial correlation exists in adjacent rock units at similar scales either, which is currently the assumption being made for sampling to minimize Se pollution from surface coal mining.

This study presents 2‐D analytical solutions for advective solute transport within a macropore with simultaneous radial diffusion into an unbounded soil matrix. Solutions for three conditions are derived: (1) an instantaneous release of solute into a macropore, (2) a constant concentration of solute at the top of a macropore, and (3) a pulse release of solute into a macropore. A system of two governing equations was solved by the Laplace transform method for solute concentration as a function of space and time. Substituting the asymptotic approximations of the modified Bessel functions, we also obtained approximate solutions for all three cases. For instantaneous and pulse‐type releases of solutes, the solutes initially diffuse into the soil matrix and then reverse direction away from the matrix as they diminish in the macropore. The matrix behaves as a long‐term contaminant source creating long tails in the breakthrough curves. Comparisons between the exact and approximate solutions for all three conditions show that the asymptotic approximations are accurate for relatively short periods of solute movement, with increasing error as time and transport distances increase. The analytical solutions were compared with one set of experimental data and also numerical simulations for contaminant transport in a cylindrical dual‐porosity medium. The analytical solutions for case 3 represented the experimental data reported in the literature well. Comparisons with numerical simulations in a two‐dimensional cylindrical domain that included dispersion in the macropore and advection in the matrix showed that the error caused by neglecting these two processes was minimal when a relatively low permeability matrix was considered for case 2.

In small communities, the number of residential units is a more stable indicator of wastewater volume than population. Large communities benefit from averaging because the likelihood of having concurrent large flows from all users is small. In contrast, a single septic system connected to a single residence must be designed to accommodate large flow variations. The objective of this study was to determine the risk of assigning various daily wastewater volumes to residential units. Risk was based on the probability of underestimating daily volume and, therefore, exceeding the capacity of the system. This study concluded that assigning a value of 950 L/d per residence (250 gpd per residence) is appropriate for communities with 15 or more residences, and that assigning a value of 850 L/d per residence (225 gpd per residence) is appropriate for communities with 30 or more residential connections.

Pore solution electrical conductivity (σw) is an important measurement for agricultural and environmental applications. Salt concentration can be predicted from σw and used to trace and monitor the transport of ionic solutes. Most models for predicting σw rely also on measurements of volumetric water content (θv). However, θv dependent estimations of σw are difficult to obtain because θv measurements are not always available and because of the complex nature of physicochemical interactions between soil and water. Electromagnetic sensors offer an alternative approach because estimations of σw can be obtained without direct knowledge of θv. We developed two semi-empirical formulae for predicting σw that are mathematically independent of θv. The new models are dielectric equivalents of the Rhoades type two-pathway models that are based on linear and power law solutions for the transmission coefficient. The models were fitted by nonlinear regression to a data set collected from different soil textures, and disturbance treatments, to predict known electrical conductivities of ∼0, 1.23, 2.41, 2.02 and 3.96dSm−1. Average σw predicted by the new models compared well to known saturating solution conductivities (average R2=0.82 and average root mean square error of 0.80dSm−1). The new models also compared well to models reported in the literature. The precision and accuracy of the estimates increased as σw increased, which might be related to a reduction of the influence of soil solid phase components on the estimates as σw becomes much higher than the solid phase conductivity.