Subsurface Discharge Research Articles

The groundwater geochemistry of the Bengal Basin: Weathering, chemsorption, and trace metal flux to the oceans

Sixty-eight groundwater samples from the Ganges-Brahmaputra floodplain in the Bengal Basin were analyzed to assess the groundwater geochemistry, the subsurface hydrology, the buffering effects of sediments on trace metal concentrations and their isotopic compositions, and the magnitude of the subsurface trace element flux to the Bay of Bengal and to the global ocean. Samples obtained from depths of 10 to 350 m were measured for major and trace elements, dissolved gas, and tritium. On the basis of the 3He/ 3H ages, the groundwater at depth (30–150 m) appears to be continually replenished, indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the Bay of Bengal. Using the 3He/ 3H groundwater age–depth relationship to calculate a recharge rate of 60 ± 20 cm/yr, we estimate a subsurface discharge into the Bay of Bengal of 1.5 ± 0.5 × 10 11 m 3/yr, or 15% of the surface Ganges-Brahmaputra river (GBR) flux. Several trace elements, especially Sr and Ba, display elevated concentrations averaging 7 to 9 times the surface GBR water values. The submarine groundwater fluxes of Sr and Ba to the oceans are 8.2 ± 2 × 10 8 and 1.5 ± 0.3 × 10 8 mol/yr, or 3.3 and 1.2%, respectively, of the world total, or equal to the surface GBR Sr and Ba estimated fluxes. Our groundwater flux for Ba agrees with the estimate of Moore (1997) (3 × 10 8–3 × 10 9 mol/yr), on the basis of measured Ba and Ra excesses in the Bay of Bengal. Other trace metals, such as U and Mo, are at low but measurable levels and are not major contributors to the global flux in this river system. A comparison of the Sr and Ba concentrations, plus 87Sr/ 86Sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core, suggests that weathering of carbonates and minor silicates, coupled with cation exchange plus adsorption and desorption reactions, controls the trace element concentrations and 87Sr/ 86Sr isotopic compositions in both the groundwater and river water. Our data also imply that other coastal floodplains (e.g., the Mekong and the Irrawaddy rivers) that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the Sr isotopic evolution in seawater.

Simulation of high-latitude hydrological processes in the Torne–Kalix basin: PILPS Phase 2(e): 1: Experiment description and summary intercomparisons

Twenty-one land-surface schemes (LSSs) participated in the Project for Intercomparison of Land-surface Parameterizations (PILPS) Phase 2(e) experiment, which used data from the Torne–Kalix Rivers in northern Scandinavia. Atmospheric forcing data (precipitation, air temperature, specific humidity, wind speed, downward shortwave and longwave radiation) for a 20-year period (1979–1998) were provided to the 21 participating modeling groups for 218 1/4° grid cells that represented the study domain. The first decade (1979–1988) of the period was used for model spin-up. The quality of meteorologic forcing variables is of particular concern in high-latitude experiments and the quality of the gridded dataset was assessed to the extent possible. The lack of sub-daily precipitation, underestimation of true precipitation and the necessity to estimate incoming solar radiation were the primary data concerns for this study. The results from two of the three types of runs are analyzed in this, the first of a three-part paper: (1) calibration–validation runs—calibration of model parameters using observed streamflow was allowed for two small catchments (570 and 1300 km 2), and parameters were then transferred to two other catchments of roughly similar size (2600 and 1500 km 2) to assess the ability of models to represent ungauged areas elsewhere; and 2) reruns—using revised forcing data (to resolve problems with apparent underestimation of solar radiation of approximately 36%, and certain other problems with surface wind in the original forcing data). Model results for the period 1989–1998 are used to evaluate the performance of the participating land-surface schemes in a context that allows exploration of their ability to capture key processes spatially. In general, the experiment demonstrated that many of the LSSs are able to capture the limitations imposed on annual latent heat by the small net radiation available in this high-latitude environment. Simulated annual average net radiation varied between 16 and 40 W/m 2 for the 21 models, and latent heat varied between 18 and 36 W/m 2. Among-model differences in winter latent heat due to the treatment of aerodynamic resistance appear to be at least as important as those attributable to the treatment of canopy interception. In many models, the small annual net radiation forced negative sensible heat on average, which varied among the models between −11 and 9 W/m 2. Even though the largest evaporation rates occur in the summer (June, July and August), model-predicted snow sublimation in winter has proportionately more influence on differences in annual runoff volume among the models. A calibration experiment for four small sub-catchments of the Torne–Kalix basin showed that model parameters that are typically adjusted during calibration, those that control storage of moisture in the soil column or on the land surface via ponding, influence the seasonal distribution of runoff, but have relatively little impact on annual runoff ratios. Similarly, there was no relationship between annual runoff ratios and the proportion of surface and subsurface discharge for the basin as a whole.

The use of stream flow routing for direct channel precipitation with isotopically-based hydrograph separations: the role of new water in stormflow generation

Understanding the pathways by which event water contributes to stream stormflow provides insight into stormflow generation mechanisms. We analyze the impact of storm size on the relative contribution of event water to stormflow by using natural variations in the oxygen isotopic composition of precipitation and stream water to separate multiple stormflow hydrographs from a single fourth-order, 1212 ha catchment. We extend previous isotope-based hydrograph separations by independently accounting for the contribution of event water via direct channel precipitation to the stream hydrograph. The direct channel precipitation contribution is determined using a numerical model of stream flow routing though the catchment, taking precipitation and digital elevation data as input variables. For the range of storm sizes sampled, having recurrence intervals ranging from less than a week to ∼4 months, essentially all the event water in stream stormflow can be attributed to direct channel precipitation. Event water not directly falling on the stream channel indirectly contributes to stormflow by increasing the subsurface discharge of pre-event water to the stream. Neither the hydrograph separation data, field observations during the precipitation events, nor experimental observations of flow in a large-scale natural soil column extracted from the watershed are consistent with macropore flow or groundwater ridging as the primary mechanism responsible for increasing subsurface discharge. Results from a series of artificial rain experiments using the unsaturated natural soil column are consistent with a preferential kinematic flow model and indicate that the discharge of pre-event water to the stream during a storm event may be controlled by kinematic flow processes within the watershed soils.

Subsurface Response Model for Storm Events within Susquehanna River Basin

A three-equation model for subsurface response is presented. The model is based on storm events for various sized watersheds within the Susquehanna River Basin. The equations represent the peak flow, time to peak, and time base of the subsurface response. The model was developed using multiple variable regression and numerical optimization. The variables used in the regression analysis are related to the physical processes causing subsurface response and were obtained from streamflow and precipitation gauges, a digital elevation model, and land use and soils data. The measured peak subsurface discharge, time to peak, and time base required for the regression analysis were obtained by separating storm hydrographs into direct runoff and subsurface responses. A linear separation from the initial rise of the hydrograph to the inflection point on the recession limb was utilized. The model was developed from a dataset of 50 watersheds by 20 storms (1,000 watershed-events), with the watersheds ranging in size from 14 km2 to 67,000 km2. The results indicate that the measured and predicted subsurface response variables agree well, considering the great variation in the observed responses and the time and space scales of the available data.

Hydrological Changes and Their Effect on the Radiological Characteristics in the Chernobyl Abandoned Zone

The effect exerted by the engineering reconstruction activities in the Pripyat River floodplain and changes in the functional state of the melioration systems in the Chernobyl Abandoned Zone on the transformation of runoff characteristics within the period after Chernobyl accident is considered. Multivariate analysis is applied to study the environmental radiological situation resulting from the changes that have taken place. The distribution and migration of radionuclides within ameliorated watersheds are shown to be controlled by the specific features of the current state of melioration systems, cessation of operation, and damming of canals. These factors has affected the area waterlogging; the surface and subsurface water regime, their nutrition, discharge, and secondary pollution.

Hydraulic gradient reversal by trees in shallow water table areas and repercussions for the sustainability of tree-growing systems

Tree planting is often considered an environmentally `friendly' option for water table control in irrigation areas where water tables are shallow. This paper presents and discusses tree/water table interactions at two sites in Kyabram, Northern Victoria, Australia: one non-irrigated and planted to a range of Eucalyptus spp. and the other irrigated and planted to E. grandis at variable spacings. The non-irrigated (except for the first 7 years after planting) plantation was established in 1976. A network of observation bores and piezometers was installed in 1982. During the monitoring period 1982–1993, water tables underneath the plantation were lowered by between 2 and 4 m, compared with the adjacent paddocks. However, the impact of the trees on the piezometric levels, measured in the aquifer underneath the plantation, was less pronounced. The trees reversed the hydraulic gradient underneath the plantation, essentially converting the plantation site into a `sub-surface discharge area.' This resulted in a build-up of soil salinity under the trees over 1984–1994. Salinity also increased in the groundwater under the plantation. A similar hydraulic gradient reversal effect was found under the irrigated variable spacing tree site. About 4 years after planting, the higher tree density (3 m spacing interval) started to lower the water table and 2 years later a similar result was found in the 7.3 m spaced trees. The deeper (10 m) piezometric pressure was not affected at any of the tree densities. This lack of impact on deeper piezometric pressures, combined with the lowering of the water table, caused a reversal of the hydraulic gradient under the high density trees (3 m spacing) 5 years after planting, which was conducive to salt movement to the base of the root zone. In spite of irrigation water being applied, the trees progressively lowered the water table, with high-density trees showing the greatest effect. It is concluded that the low transmission characteristics of the soils restrict the depth of wetting from both irrigation and rainfall, leaving uptake from the capillary fringe above the water table to supply additional transpiration in coping with demand. The long-term sustainability of deep-rooted tree plantings growing on shallow water tables is questioned; engineering mechanisms such as groundwater pumps or tile drains may be needed to sustain long-term tree growth under these conditions.

Methane input and evasion in a hardwood forest stream: Effects of subsurface flow from shallow and deep pathway

Streams are typically supersaturated and emit methane to the atmosphere. Much of this gas appears to be imported from groundwater and riparian zones, where anoxia and methane production are common. We investigated how methane evasion and the concentration in groundwater discharge varied between five stream sections with differing rates of groundwater discharge along the east fork of Walker Branch in eastern Tennessee. Evasion and groundwater concentration were determined from measurements of methane in surface water in conjunction with coinjection of conservative solute and volatile gas tracers. Methane in surface water was supersaturated, varying from 0.67 to 1.56 µg CH4 liter−1, which translates to concentrations 17.6–41.4 times greater than those at atmospheric equilibrium. Methane evasion rates ranged from 0.4 to 13.2 mg CH4 m−2 d−1. Differences in methane concentration and evasion were related to variation in subsurface discharge and concentration in groundwater. All study sections gained flow, although the rate of subsurface discharge into the second study section (section 2) was particularly low. Furthermore, the specific conductance of groundwater flowing into section 2 averaged only 82.3 µS cm−1, compared with 110–125 µS cm−1 in the other study sections, indicating that groundwater discharge was derived from riparian soils as opposed to deeper flow from fractured bedrock. The mean concentration of 549.2 µg CH4 liter−1 in subsurface water flowing into section 2 was notably greater than in the other sections, where average groundwater concentration ranged from 158.9 to 376.2 µg CH4 liter−1. Our results suggest that subsurface flow from riparian soils appears to be the major source of methane to streams, although deeper bedrock flow also supplies methane at a lower concentration to surface waters.

Key Factors Affecting Subsurface Contamination of Natural Waters near Sour-gas Plants

Hydrocarbon contamination of lakes and rivers from subsurface discharge of ground-water is a common environmental problem in many countries. This source of contamination, particularly dissolved phase hydrocarbons, can significantly reduce the quality of natural waters. Laboratory results show that the aqueous solubility of benzene can be predicted by Raoul's Law for BTEX mixtures and for gas condensate. In contrast, the solubility of total xylenes was up to three times higher than the calculated results using Raoul's Law. A comparison of these finding with the composition of BTEX in groundwater at a sour-gas plant, indicated that the mole fraction and groundwater flow velocity were two principle factors affecting the discharge concentration of benzene and xylenes to natural waters.;Hydrocarbon contamination of lakes and rivers from subsurface discharge of ground-water is a common environmental problem in many countries. This source of contamination, particularly dissolved phase hydrocarbons, can significantly reduce the quality of natural waters. Laboratory results show that the aqueous solubility of benzene can be predicted by Raoul's Law for BTEX mixtures and for gas condensate. In contrast, the solubility of total xylenes was up to three times higher than the calculated results using Raoul's Law. A comparison of these finding with the composition of BTEX in groundwater at a sour-gas plant, indicated that the mole fraction and groundwater flow velocity were two principle factors affecting the discharge concentration of benzene and xylenes to natural waters.

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed, northern Japan

Surface flow and suspended sediment discharge from the head hollow of the Jozankei Experimental Watershed in Hokkaido, northern Japan, were measured to clarify the implications of subsurface hydrology for soil movement. Subsurface discharges during the extremely large storms of 1993 to 1994 were measured in a V-notch weir installed at a natural spring near the bottom of the head hollow, and shallow groundwater levels were observed in the wells excavated in the hollow. Sediment samples whose particle size range from 0·001 to 0·1 mm were manually and automatically collected at 15 to 60 min intervals, by use of 1 or 21 polyethylene bottles. Maximum concentration and flux of suspended sediment during the storms preceded the peak discharge of subsurface flow by several hours. Neither the changes in concentration (mg l−1) nor flux (mg s−1) of suspended sediment coincided with those in subsurface discharge (l s−1). Furthermore, sediment concentration was poorly correlated with the rate of change in subsurface discharge (l s−2) during the rising limb of the hydrograph. Suspended sediment flux during the acceleratory limb, however, was closely correlated with the rate of change in subsurface discharge. The relationship between suspended sediment flux and rate of change in subsurface discharge were in inverse proportion to initial subsurface discharge before the storm runoff and they represented rare seasonal variation. Subsurface hydraulic erosion and transport of suspended sediment resulting from changes in rate of change in subsurface discharge actively occur during the acceleratory rising limb of the hydrograph. Accordingly, subsurface hydraulic erosion during the acceleratory rising limb of the hydrograph can be physically understood by analysing suspended sediment flux associated with rate of change in subsurface discharge and initial subsurface discharge. © 1997 John Wiley & Sons, Ltd.

Subsurface Discharge and Suspended Sediment Yield Interactions in a Valley Head of a Small Forested Watershed

Sediment hield caused by hydraulic agents is believed to be one of the most important geomorphic processes in headwaters. Observations of shallow groundwater levels and suspended sediment yield were used to develop relationships between subsurface discharge and sediment movement in a valley head of a small forested watershed in Hokkaido, northern Japan. Drainage capacity of the soil was closely correlated with subsurface soil movement in the valley head. An increase in subsurface discharge associated with an increase in the drainage capacity of the soil depended heavily on the discharge of fine-grained particles originating from the soil. Clogging created by the fine-grained particles in the soil caused a decrease in subsurface discharge associated with the decline in the drainage capacity. In addition, neither the drainage capacity of the soil nor subsurface discharge changed because of the sediment unavailability within the subsurface flow system. Accordingly, as shown by the changes in the drainage capacity of the sedimentary soil, subsurface discharge and suspended sediment yield from the valley head showed strong interactions.

Pipe flow significance on subsurface discharge from the valley head of a small watershed

Pipe flow significance on subsurface discharge from the valley head of a small watershed

Petroleum-Based Hydrocarbon Investigations: Are Groundwater Resources Adequately Protected by Present Practice?: ABSTRACT

Conventional demonstration of petroleum-based hydrocarbon soil contamination through soil matrix sampling has severe systemic limitations long ignored. Aromatic volatile organic compound (VOC) soil contamination is frequently understated by so-called {open_quotes}standard practice{close_quotes}, which is to obtain a relative few soil matrix samples in sometimes dubious fashion, often from excavations left open to rainfall accumulation, analyze with low-priced TPH methodology for petroleum-based hydrocarbons and project the spatial distribution of all hydrocarbon and related compound contamination. Because the mobile constituents, mostly aromatic VOCs, such as benzene, toluene, ethylbenzene and xylenes readily partition into vapor phase representative analytical measurements could be made on soil gases, collected by relatively conservative methodologies, at a given site with little or no holding time losses. Moreover, gas phase halogenated VOCs were also frequently identified with respect to sites where only fuel or waste oils were to be expected. In many instances, collateral measurement of fixed and biogenic gases at the same time provided a proxy measure of heavier hydrocarbon distribution. Multi-depth spatial patterns of gases more closely connected site discharge and source area than did sole reliance on soil matrix sampling and the vagaries of holding time losses over as much as a fourteen day period. Investigations weremore » designed to evaluate waste discharge to the vadose zone, assess the lateral and vertical distribution of contamination and to determine if the ground water was being threatened by migration from surface and subsurface discharges. The data and information derived indicate that in order to fully protect groundwater resources, soil gases should be measured together with soil matrix samples at each site under investigation.« less

A groundwater source of nitrate in nearshore marine sediments

Contamination of groundwater is a pervasive and serious problem in many developed coastal areas1–3, but potential interactions of groundwaters with, and their impact on, adjoining coastal waters have generally not been considered. Although submarine ground-water discharge could be an important source of nitrogen to coastal marine environments4, there has been no direct evidence for this. Recently, subsurface discharge has been shown to account for about 10–20% of the freshwater input to Great South Bay, New York5. The upper aquifer is the presumed source of this discharge and, because it is heavily contaminated with nitrate6, we suggest that groundwater is an important source of nitrate to the bay. Our determinations of the interstitial nutrient chemistry of freshly collected cores from nearshore sediments support this hypothesis. Although highly variable in time, cores taken after substantial rainfall showed increasing nitrate concentrations and decreasing salinities with depth. We conclude that submarine groundwater discharge is indeed a source of nitrate which should be considered in estimates of nitrogen influx to coastal marine ecosystems.

Use of Peat for On‐Site Wastewater Treatment: II. Field Studies

AbstractThree full‐size sphagnum (Sphagnum spp.) peat filter fields were monitored to determine the treatment levels after application of septic tank effluent (STE). Systems I and II were designed with a liner and had overboard discharges, whereas system III was constructed with a subsurface discharge. Gravity‐feed, dosed‐feed, and pressure distribution systems all provided excellent organic and 99% fecal coliform removal without additional disinfection.The 5‐day biochemical oxygen demand (BOD5) reduction exceeded 90% and chemical oxygen demand (COD) reduction exceeded 80% in all three systems. Total suspended solids (TSS) measured 16 and 9 mg/L in the effluent from systems I and II, respectively. Systems I and II showed 58 and 62% total P reduction, respectively, while a total P reduction of 96% was obtained in system III. Nitrate‐N in the effluent from all three systems was < 4.5 mg/L, well below the recommended limit of 10 mg/L. The pH of the effluents ranged from 5.3 to 6.5 and color averaged 330 standard units. In Maine, or other areas where the natural waters tend to be both colored and slightly acidic, neither parameter would be problematic when using an overboard discharge. Effluent from the well‐aerated fields contained dissolved O2 averages of 4.6 and 6.7 mg/L for systems I and II.Annual variation in weather conditions, including prolonged cold, with and without snow cover, and extreme short‐term precipitation, had no adverse effects on the performance of the peat filter fields. The use of sphagnum peat for on‐site wastewater treatment seems to be an acceptable alternative for areas where conventional systems cannot be installed.

Bacteriological Quality of Surface and Subsurface Runoff from Manured Sandy Clay Loam Soil

AbstractThe bacterial quality of surface waters determines their acceptability for both drinking and recreational uses. Since livestock activities have been implicated as sources of fecal contamination, information on the bacterial quality of runoff from manured cropland is required. Bacteriological parameters (total coliform [TC], fecal coliform [FC], and fecal streptococcus [FS]) were monitored in spring surface and subsurface discharge from continuously corn‐cropped sandy clay loam that was amended with either liquid dairy manure, chemical N‐P‐K fertilizer at about recommended rates, or no fertilizer. Liquid manure was applied for 6 years at three rates, which averaged 105, 263, and 420 m3 ha−1 year−1, plowed under after harvest, in spring prior to seeding, or split between spring and fall. Liquid manure was also applied directly to snow or frozen ground.With the exception of winter‐applied treatments, neither rate nor time of manure application significantly affected organism contents in spring surface or subsurface discharge. Winter manure applications resulted in significantly higher FC and FS counts in surface runoff and FS counts in subsurface discharge when compared with other application times. Fecal coliform and FS counts did not increase with increased winter application rates. Fecal streptococcus populations of winter‐applied manure changed little during the first 100 days after application, while both TC and FC counts declined in the manure to low levels 24–40 days after spreading.

Wastewaters in the Vadose Zone of Arid Regions: Geochemical Interactionsa

ABSTRACTBecause of increasingly stringent laws governing discharge of fluid wastes to surface waters, the alternative of discharge to the subsurface has become attractive. The physical‐chemical processes that prevail in the subsurface are not well understood, but they are clearly not identical to processes of purification in surface waters. For example, in the subsurface the process of oxidation may be of little value in significantly reducing the concentration of discharged contaminants; in contrast, oxidation plays an important role in purifying surface waters. Eleven physical‐chemical processes can be identified as having potential value for purifying wastes discharged to the subsurface, as follow: dilution, buffering of pH, precipitation by reaction, hydrolysis, oxidation or reduction, filtration, volatilization, biological assimilation, radioactive decay, membrane filtration, and sorption.Discharge to the vadose zone may be a safe means of disposal of wastes in arid regions. But it is necessary to carefully test the suitability of a particular site for a particular waste. Processes of purification in the vadose zone can be incorporated into a workable plan of discharge if adequate studies and safeguards are employed. Regulations governing subsurface discharge should take into account the physical‐chemical processes that may act to purify the waste fluids. In one set of experiments, a soil from Sulfur Springs, New Mexico was capable of removing large quantities of dissolved molybdenum and copper from a synthetic mill water, and the soil was able to quantitatively retain the copper during subsequent leaching by fresh and metal‐free mill waters. Such studies permit rational plans of discharge to be developed.

Nitrogen in Subsurface Discharge from Agricultural Watersheds

AbstractThe nitrogen in subsurface discharge and surface runoff was measured from four agricultural watersheds on Missouri Valley deep loess near Treynor, Iowa, from April 1969 through March 1974.The data showed that, with the agricultural management practices used on the watersheds, the subsurface discharge of water ranged from 62 to 88% of the average annual stream flow. Nitrate in subsurface discharge accounted for 84 to 95% of the total average annual soluble N discharged in stream flow.A terraced watershed continuously cropped to corn (Zea mays L.) had reduced surface runoff, sheet‐rill erosion, and associated nitrate‐nitrogen discharges, but had increased subsurface discharge of water and soluble N as compared with two contoured corn watersheds. Nitrogen fertilizer applied at a high rate (448 kg ha−1 year−1) exceeding crop needs on the terraced and contoured corn watersheds, increased five‐ and threefold the average annual subsurface discharge of NO3‐N, respectively, as compared with a contoured watershed fertilized with N at a normal rate (168 kg ha−1 year−1).To control the watershed discharge of N and subsequent pollution of stream flow from the Iowa and Missouri deep loess hills requires N fertilizer application rates that do not exceed crop needs and using conservation practices that minimize soil erosion and deep percolation.

Effect of Long Term Land Disposal by Spray Irrigation of Food Processing Wastes on Some Chemical Properties of the Soil and Subsurface Water

AbstractFood processing waste waters at two irrigated land disposal sites and subsurface waters (perched and ground waters) were monitored at daily to monthly intervals over one annual cycle of production. Soil profiles were sampled to depths up to 6.6 m in the early fall.Yearly inputs were calculated at 487 kg/ha total N (Kjeldahl plus NO3‐N) and 101 kg/ha soluble PO4‐P (orthophosphate) from cannery wastes at site 1. Estimates for milk wastes at site 2 were 562 kg/ha total N and 522 kg/ha PO4‐P.The range for NO3‐N in subsurface waters was 7 to 16 ppm at site 1 (perched water at 1.5 m) and 2 to 41 ppm at site 2 (ground water at 0.9 m). Maximum concentrations, found in summer, were essentially the same as the average for total N in the input wastes (16 ppm at site 1 and 38 ppm at site 2). Nitrate was stable in the percolation stream below the root zone. Annual additions to subsurface waters were estimated at 76% of input N at site 1 and 65% at site 2.The range of PO4‐P in subsurface waters was 0.5 to 1.5 ppm at site 1 and 0.04 to 1.8 ppm at site 2; average waste water concentrations were 3 and 35 ppm. The highest concentrations in subsurface water were found in spring. Annual subsurface discharge was estimated at 27% of input P at site 1 and 2% at site 2. The extensive removals of PO4 and the similar concentrations encountered in subsurface waters are of theoretical and practical interest since PO4‐P had already accumulated in soil profiles at both sites in quantities which exceed the Langmuir maxima for nonirrigated control soils.During seasons of major irrigation input, NO3 appeared in subsurface waters in concentrations exceeding public health standards; PO4 concentrations exceeded environmental guidelines at all times except where irrigation was discontinued during the winter at site 2.Soil systems appeared poised to discharge at the observed rates because of the large quantities of organic N and fixed P which had accumulated in the profiles over 20 years operation at site 1, and 10 years at site 2. The rate of residual accumulation in soil could have been reduced by harvest, to extend system life materially. The harvest potential of three grass clippings per season removed for silage, was estimated experimentally at 31% of input N at both sites and 80% of input PO4 at site 1; 27% at site 2.

Water Quality and Effluent Standards of Hawaii

The sequential development of water quality standards for the State of Hawaii, commencing with the passage of the federal Water Quality Act of 1965, resulted in the enactment of receiving water standards in January 1968 that were expressed in terms of basic freedoms and through eight specific standards which applied to separate classes (two fresh waters and three coastal waters) of all surface fresh and near and offshore coastal waters in the state. In order to meet the receiving water requirements at the point of discharge the present or potential discharger can apply for a variance or zone of mixing permit within specific boundaries. The enactment of PL 92-500 together with other reasons prompted the state to develop effluent limitation standards (effective August 1973) that apply to fresh and nearshore coastal waters and subsurface discharges which for practical reasons are limited to discharges of less than 1 mgd (3,785 m³/day) that have received tertiary treatment.

The Visibility of Oil-Water Discharges

ABSTRACT Oil Spills: Controlled oil films from 15 through 3000 nanometers (3 microns) thick show reflectance and interference color effects that vary in an orderly way with film thickness, and that agree with the well-known table published by the American Petroleum Institute. This inherent appearance depends only upon local film thickness and is independent of oil type. Visibility of a given film is variable and is affected by ambient factors that include sky conditions, water surface state, and the depth and color of the water. Oil-Water Discharges: Controlled streams of 25 to 100 gpm, containing 5 to 250 ppm of oil, were discharged into Raritan Bay from a 65-foot vessel. Discharge points were above the surface or 2 to 5 feet below the surface, with the vessel an anchor in tidal currents, simulating a fixed source in a low current. Above-surface discharges were also made with the vessel underway at 6 to 15 knots. The visibility and appearance of films resulting from the discharges were recorded from the vessel and from a helicopter. The visibility of above-surface discharges for all combinations of water rate, oil content, and vessel speed, is correlated by a Specific Oil Rate (SOR) parameter: Discharges of SOR = 4 or less were not visible, while those of SOR = 40 or more were visible. Visibility varied for intermediate discharges in the SOR range of 4 to 40. Visibility was infrequent near SOR = 4, and became more frequent as SOR increased. Fifty percent of the SOR = 20 discharges were visible. This correlation is for observations made from an aircraft. Results of discharges reported by the Coast Guard for vessel speeds of 10–17 kt and by the British for 8–16 kt correlate with ours via the SOR parameter. These observations were also from aircraft. Subsurface discharges appeared substantially less visible than corresponding above surface discharges. Replication, however, was insufficient to allow development of a correlation.