Surface runoff

There are three main methods to dispose of releases from thermal relief valves. Discharge around a block valve (isolation circumvention) is widely used in most situations, however where this is not practical or economical disposal to a sewer or release to surface runoff can be specified in certain cases. 

Where the fluid is the same on each side of the isolation means, and no contamination will result this is the optimum choice for thermal relief release. Consideration of the possibility of backpressure onto the thermal relief valve, rendering the valve ineffective, should be evaluated before an analysis is finished. 

A process oily water sewer system is a convenient location to direct oily wastes. The oily water system normally collects into a sump. If several lines connect into a common header, care should be taken to prevent backflow into another outlet source. In such cases use of an air gap, i.e., drainage in to a collection ftinnel has be advantageous. 

Only when other alternatives are not available should a fluid release to the open environment be considered a viable disposal method. Additionally it should only be considered when the release is small and does not create an additional hazard - either from fire safety or environmentally. The relieved liquid should always be directed to a level surface away from other equipment, for containment by the facility surface runoff accommodations to mitigate any environmental or fire hazard. In no cases should discharge to the atmosphere be contemplated as it would create an immediate explosion or fire hazard and could also be considered an immediate environmental pollutant. 

Compaction of the fill will generally result in a reduction of the permeability and, hence, of the infiltration capacity. In moderate and (sub)arctic climates the upper zone of the fill may be frozen during certain periods of the year. This will cause a strong reduction of the permeabihty near the surface which will hamper the infiltration capacity. In particular at the end of a frost period (melting of snow and ice), this often results in ponding and an increase of the surface runoff. 

As a result of the hydraulic placement method a thin crust of fine-grained, aggregated soil can develop at the fill s surface that may act as a low-permeable seal, hindering natural infiltration and promoting ponding and surface runoff. 

The most important parameters that control the permeability are the grain size distribution and the density of the fill. A first estimate of the permeability can be obtained from the particle size distribution by empirical formulae proposed by Hazen (1911), Kozeny-Carman (Carman, 1956) and others. In particular the fines content has a strong influence on the permeability. 

The storage capacity is defined as the volume of pores in the unsaturated zone that is available to store infiltrated water. It mainly depends on the grain size distribution, the density and water content of the soil and the depth to the groundwater table. 

A rising groundwater table or compaction of the fill will reduce the storage capacity and, hence, the infiltration capacity. A high natural water content of the fill mass will also adversely affect the storage capacity. 

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Protects water quality in lakes, rivers, aquifers, and coastal areas by regulating ivastewater discharges monitoring bodies of water, and controlling surface runoff... 

Fig. 6-6 Hydrograph showing the rapid contribution of surface runoff and more steady baseflow. Runoff in cubic feet per second, precipitaion in inches. (From Langbein and Wells, 1955.)...

Surface runoff. Hydrologists have identified two processes for generating surface runoff over land. The first, saturated overland flow (SOF), is generated when precipitation (or snowmelt) occurs over a saturated soil since water has nowhere to infiltrate, it then runs off over land. SOF typically occurs only in humid environments or where the water table rises to intersect with a stream. Horton overland flow (HOF or infiltration-limited overland flow) occurs when precipitation intensity exceeds the infiltration capacity of the soil in a non-saturated environment. In this case, only the excess precipitation (that exceeding the infiltration capacity) runs off over the surface. Both types of overland runoff generate relatively rapid flows that constitute the surface water contribution to the hydrograph (Fig. 6-6). 

Runoff sensitivity, particularly in arid and semi-arid climates, is largely a result of sensitivity in soil moisture response. If rainfall amount and frequency decrease, more soil moisture is lost to evapotranspiration, creating a soil moisture deficit that must be replaced before surface runoff or significant ground-water flow returns. The converse also tends to... 

Bonan, G. B. (1996c). Sensitivity of a GCM simulation to subgrid infiltration and surface runoff, Clim. Dyn. 12,279-285. 

Fig. 2 Relative changes (between 2080-2099 and present, 1980-1999) of annual surface runoff on the globe, from results of several climate models forced by emissions of scenario AIB. Dashed areas indicate that more than 90% of models agree with the sign of change. Taken from IPCC [1]...

Fig. 7 Comparison of observed present AF in the Sau Reservoir and results of the AF model solved assuming a decrease in surface runoff by 20-40% during the present century, and an additional effect of lack of dilution of labile DOC in the tributary. Shaded areas represent uncertainty of predictions...

Effluents from manufacturing and formulating facilities and surface runoff from treated croplands are sources of releases of the compound to surface waters. Endosulfan has been detected in rivers draining industrial areas where manufacturers or formulators of the compound are located (WHO 1984) and in streams adjacent to treated fields (NRCC 1975). For example, about 0.6% of the 5.6 kg/hectare of endosulfan applied to soybean fields in Mississippi was lost from the fields in runoff Endosulfan residues were detected up to 3.5 kilometers (km) downstream from the treatment area for about 3 weeks following the last application of the compound (Willis et al. 1987). 

It will prevent surface runoff, which carries contaminants to rivers and to places where the contaminants will infiltrate and percolate into soil and groundwater. 

Sedimentation basins can be used to collect and store surface water flow and to settle suspended solid particles. Seepage basins and ditches can be used to discharge uncontaminated or treated water downgradient of the site. It is important to separate clean surface runoff from contaminated water and store and treat them separately. Table 16.4 summarizes the surface water control methods. 

Factors Affecting Amount and Rate of Surface Runoff from ET Landfill Covers... 

Surface runoff (Q) is the second-largest part of the hydrologic water balance for ET landfill covers at many sites in humid regions. Even at dry sites where surface runoff is small, errors in estimates of Q are important, and especially so if the model estimates significant Q on days with no runoff. Estimates of Q are therefore important to the design process at all sites. 

Surface runoff can begin only after (1) rainfall or snowmelt fills storage by plant interception and surface ponding and (2) the rainfall or snowmelt rate exceeds the soil infiltration rate. Excellent sources for technical details include Chow et al.,50 ASCE Manual 28,53 and Linsley et al.56 Factors affecting Q are listed in Table 25.1. 

Increase surface runoff by replacing the second layer of soil—for example, 6-12 in.—with clay soil, or use clay soil for the top 6 in. of the cover however, maintain the same soil thickness as required for a one-layer soil. 

Development of the Environmental Policy Integrated Climate (EPIC) model and its predecessor, the Erosion Productivity Impact Calculator, began in the early 1980s.69 70 The first version of EPIC was intended to evaluate the effects of wind and water erosion on plant growth and food production. More recent versions also evaluate factors important to other environmental issues. EPIC is a onedimensional model however, it can estimate lateral flow in soil layers at depth. All versions of EPIC estimate surface runoff, PET, AET, soil-water storage, and PRK below the root zone—these complete the hydrologic water balance for an ET landfill cover. 

UNSAT-H sets infiltration equal to the precipitation rate unless the surface soil becomes saturated. It does not simulate the soil crust that develops on the soil surface however, the user may describe a constant soil crust as a thin surface soil layer. It does not simulate runoff explicitly 80 however, it assigns excess precipitation that does not infiltrate into the soil as surface runoff. 

Examination of Table 25.3 and the comments above clearly demonstrate that both HYDRUS and UNSAT-H are likely to produce very good estimates of water movement within the soil profile. However, they do not estimate snowmelt, model mixed plant communities, directly estimate surface runoff, or consider the effect of soil density on root growth and water use.14... 

Land disposal sites result in soil contamination through leachate migration. The composition of the substances produced depends principally on the type of wastes present and the decomposition in the landfill (aerobic or anaerobic). The adjacent soil can be contaminated by direct horizontal leaching of surface runoff vertical leaching and transfer of gases from decomposition by diffusion and convection. The disposal of... 

The hydrologic cycle, or moisture cycle — that may encompass the processes of rain infiltration in the soil, exfiltration from the soil to the air, surface runoff, evaporation, moisture behavior, groundwater recharge and capillary rise from the groundwater. All these processes are interconnected and are frequently referred to as the hydrologic cycle components. 

From the hydrologic cycle temporal resolution of soil moisture surface, runoff, and groundwater recharge components, by inputting to the model the net infiltration rate into the soil column and... 

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