Subsurface drains

Delineation/Verification of Gross Contamination Sampling and Analysis Interceptor Trench/Sump/Subsurface Drain Pump and Treat In-situ Treatment Temporary Cap/Cover... 

Principal Option for Containment/ Recovery Excavation Vacuum extraction Temporary cap/cover Hydraulic modification No action Groundwater pumping Subsurface drains Hydraulic barriers Low permeability barriers No action Overflow/underflow containment (i.e. oil booms) Run off/run on control Diversion/collection No action Capping/ nsulation Operations modifications Gas collection/removal No action... 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

Several studies have been conducted to measure methyl parathion in streams, rivers, and lakes. A U.S. Geological Survey (USGS) of western streams detected methyl parathion in five river samples taken from four states during a 14-month period in 1970 and 1971. The amount of methyl parathion detected ranged from 0.04 to 0.23 pg/L (Schultz et al. 1973). A later and more extensive USGS study analyzed water samples from major rivers of the United States four times yearly in the period of 1975-1985. Of the 2,861 water samples, 0.1% had detectable levels of methyl parathion (Gilliom et al. 1985). In a study of Arkansas surface waters, samples of lake and river/stream water were collected and analyzed over a three-year period (Senseman et al. 1997). Of the 485 samples collected, methyl parathion was found in one river/stream sample at a maximum concentration of 3.5 pg/L. Results from an EPA study in California detected methyl parathion in 3 of 18 surface drain effluent samples at concentrations of 10-190 ng/kg. Subsurface drain effluent water had concentrations of 10-170 ng/kg in 8 of 60 samples (lARC 1983). 

Subsurface drains include any type of buried conduits that convey and collect aqueous discharges by gravity flow (Figure 16.11). Water collected in a storage tank or a collection sump is then pumped for further treatment. Filters are usually needed in drain systems to prevent fine particles from causing clogging. 

Subsurface drains function like an infinite line of extraction wells, and can be used to contain and remove a plume or to lower the groundwater table (Figure 16.12). They are more cost-effective than pumping for shallow contamination problems at depths of less than 12 m (40 ft). Depths may be increased if the site is stable, if the soil has a low permeability, and if no rock excavations are encountered. 

FIGURE 16.12 Use of a one-sided subsurface drain for reducing flow from uncontaminated sources. 

Table 24.3 Triazine transport to subsurface drains from research studies worldwide...

In Indiana, small amounts of atrazine were detected in subsurface drain flow within 3 weeks of application - after less than 2-cm net subsurface drain flow from a poorly structured silt loam soil with low organic matter (Kladivko et al., 1991). The rapid appearance of atrazine indicated the possibility of preferential flow. Atrazine, DEA, and DIA were also found in subsurface drainage water in Iowa the order of concentration was atrazine > DEA > DIA (Jayachandran et al., 1994). Levels of triazines in subsurface drains ranged from 0.1 to 29 ig/L, with concentrations declining with time (Milburn et al., 1995). A spill on one of these plots, followed by 71 mm of rainfall within a few days, resulted in subsurface drain concentrations of 150 i,g/L. This concentration decreased to <3.0 i,g/L within 6 days of the initiation of subsurface drain flow. Atrazine has also been found in subsurface drainage in a clay soil with an average concentration of 0.4 a,g/L for 24-30 months after the last application (Buhler et al., 1993). 

Southwick, L.M., G.H. Willis, R.L. Bengston, and T.J. Lormand (1990b). Atrazine and metolachlor in subsurface drain water in Louisiana. J. Irrig. Drain. Eng., 116 16-23. 

Traub-Eberhard, U., K.P Henschel, W. Kordel, and W. Klein (1995). Influence of different field sites on pesticide movement into subsurface drains. Pestic. Sci., 43 121-129. 

Traub-Eberhard, U., Kordel, W., Klein, W. (1994) Pesticide movement into subsurface drains on a loamy silt soil. Chemosphere 28, 273-284. 

A preferential circulation area, in which the waters are still fresh far below the outcrop, occurs NE of the River Meurthe. The existence of higher permeabilities may account for this anomaly. In addition, several SSE—NNW faults, reaching the basement and serving as a subsurface drain system, bring water up from the deep-seated horizons. 

The wide range of end uses for these speciality fabrics, which keeps expanding, includes road paving stabilisation, landhll liners, subsurface drains, soil separation membranes, sediment control fabrics, and membranes for erosion control and weed management and suppression. 

I plumes existing at the Hanford site are largely confined to the 200 Areas where it was discharged to subsurface drains. The highest concentrations observed onsite are downgradient from the PUREX and REDOX Plants in the 200-East and 200-West Areas, respectively. The plume at the latter area is coincident with... 

The main drainage system must carry off the water to the discharge location(s) where it drains into natural open water. The system generally consists of shallow and/or deep collector drains that collect water of respectively the field surface drains or the field subsurface drains. Main drains transport the drainage water from the collector drains to the locations where the water is discharged into the river, sea or other open water. Outfalls (if required) are usually also considered to be part of the main drainage system. Shallow collector drains can be channels or ditches, while the deep collector drains include pipe drains and (deep) ditches. 

---