Design of Land Application Systems for Water Reuse

Water reuse via land application is old technology; but the water balance only design approach and practice has not worked well. There are many benefits of water reuse by irrigating crops; however, there are some risks if not designed properly. When the design approach uses a combined water-nutrient-salt balance, the most effective and sustainable, long-term system is achieved. This approach provides a design based on land area requirements, on-site water storage, and economic return from the irrigated crops. The single, most often overlooked step in the water balance is accounting for the water stored in the soil. When spread over large areas, this quantity of water results in considerably less required surface water storage, which saves capital costs. This design approach has been used successfully on multiple sites for over 30 years without failure

Re-evaluating Surface Application Rates for Texas OSSF Systems

Approximately 25% of the nation’s housing units utilize on-site treatment and disposal systems. Mostly, on-site treatment consists of a septic tank-soil adsorption configuration, though surface disposal systems are used in areas where the soil is not suitable for an adsorption field. One of the concerns with the use of on-site sewage treatment systems is the potential for nitrate pollution of the groundwater resources. Current procedures for designing surface application systems for on-site sewage facilities (OSSFs), with an emphasis on aerobic systems, in Texas have been reviewed. Concerns with the current procedures for designing sprinkler systems include the sizing of the spray field area, the volume of effluent storage required, and the absence of the uniformity of sprinkler distribution patterns. Currently the spray field area is determined by the estimated daily volume of water applied divided irrigation water requirement (evaporation minus precipitation). A proper design needs to be adaptable to the many climates and soils that exist within the state, while maintaining the integrity of the environment. To meet this goal, an alternative, easy to follow, design procedure is proposed. The proposed design method incorporates the concept of water application rate, soil infiltration rate, crop water use, crop nutrient uptake rate, water application efficiency, and irrigation layout design and nozzle selection. With any surface application system for wastewater effluent, control of the nitrogen applied is essential to minimize the impact on regional water resources, whether surface water or ground water. If an OSSF is designed with a typical type of sprinkler and no overlap of the spray pattern is provided, the potential mass of nitrogen that can move below the crops root zone can be substantial. The quantity of nitrogen that could potentially move below the crops root zone ranges from 16 percent of the nitrogen applied in East Texas to 59 percent of the nitrogen applied in West Texas. Poor distribution of the effluent applied on portions of the spray field may cause the nutrients (e.g. nitrate-nitrogen) to be applied at levels exceeding the plants assimilation capacity. If a sprinkler design provides an overlapping spray pattern and the wastewater application rate is limited based on the crops ability to utilize the applied nitrogen, the nitrogen that could potentially move below the crops root zone can be limited to 7 percent of the total nitrogen applied or less. This limited nitrogen movement is realized when the wastewater distribution uniformity coefficient is 80 percent or greater. Another advantage of the proposed design procedure is the smaller land area requirement in some parts of the state. In east Texas for example, the land area reduction is about 27 percent while the land area required in West Texas increases by two times. The additional system requirements under the proposed design procedure are an increase in the number of sprinkler heads and a zone sprinkler controller. This latter device is required to cycle the application of the wastewater effluent to the various quadrants of the spray field. It is recommended that the following changes be made to the current Texas Administrative Code 285 rules in order to provide for the least amount of negative impact our the states environment. All surface application systems designed for an on-site sewage facility should consider both a water balance and a nutrient balance for the final design. The layout of the site for effluent application should be in a block pattern such that the sprinklers can be arranged to have a head-to-head overlap. If this is not available, then the system should be designed such that the proper overlap can be provided in order to achieve a uniformity coefficient of 80 percent or greater. Spray head type of sprinklers should not be used in an OSSF system while the gear head type should be used. All sprinklers are designed to operate at an optimum pressure range to obtain the specified pattern of water distribution and the OSSF design pressure should be in the middle of the specified range. Sprinklers operating at pressures lower or higher than designed will produce unreliable patterns that will result in very low water application efficiencies and low application uniformity. The time used to apply the effluent should not exceed 1 hour and the average design should be 0.5 hours. The base water intake rate of the soil should follow that described by Saxton et al. (1986) provided more precise information on the soil is not available. The base soil infiltration rate should be set equal to the saturated hydraulic conductivity of the top 18 inches of soil. A check-off list of design considerations should be developed and used on all new and renovated designs of OSSF where surface application of the effluent is utilized

Utilizing Compost as an Alternative Method to Standard Seedings [Project Summary Report]

This research investigated whether the establishment of vegetation on highway ROW could be improved by the application of compost as mulch compared to various traditional methods of protection. Conclusions drawn from examination of the evidence indicate that a layer of compost mulch greater than two inches adversely affected emergence and establishment of desired vegetation, whereas soil moisture retention was comparable on sub-plots treated with straw mulch held in place by jute netting

Use of Alternative Water Sources

0-4412Due to rapid growth in population and construction activity, the demand of good quality water continues to increase in many parts of Texas. The use of non-conventional, or \u201calternate,\u201d sources of water as a substitute for quality drinking water in construction applications could potentially reduce the cost of construction while conserving quality water resources. The primary objective of this research project was to identify alternative water sources that may be used in construction applications such as pavement subgrade, base, embankment fill and structure backfill compaction, vegetative watering, soil stabilization, and dust control. The alternate sources of water considered in this study are: wastewater from municipal wastewater treatment plants, brine water from oil wells, surface and groundwater that do not meet the drinking water quality standards, and ocean water. The various issues addressed by this research project are the effect of alternate water on construction materials, legal issues addressing the use of alternate water in Texas, safety and health concerns of workers and the public, and the impact on the environment by the use of low quality alternate sources of water. A decision matrix is presented to facilitate the evaluation of alternative water construction applications combinations

Use of Alternative Water Sources: [Project Summary]

The principal area of contribution by Texas Tech University (TTU) researchers has been the effects of alternate water sources on engineering properties and constructability for transportation activities requiring large quantities of water. This research also focused on legal issues addressing the use of alternate water sources (wastewater from municipal wastewater treatment plants, brine water from oil wells, surface and groundwater that do not meet the drinking water quality standards, and ocean water) in Texas, safety and health concerns of workers and the public, and the impact on the environment by the use of alternate sources of water. Prominent products achieved from the TTU work include: \u2022 A review of the major alternate water sources and a summary of their associated critical water quality parameters \u2022 A review of potential environmental impacts of alternate water sources and their availability \u2022 Determination of construction activities having significant water demands and the associated issue related to performance which might be impacted by the water quality of alternate water sources \u2022 Laboratory testing of various soil types to determine allowable ranges of specific parameters and in some cases development of test methods \u2022 Model development to predict final soil sulfate content and changes in soil resistivity

Utilizing Compost as an Alternative Method to Standard Seedings: Final Report

Project 0-4571The research underlying this report consisted of an investigation designed to determine if the establishment of vegetation on Highway ROW could be improved by the application of compost as mulch compared to various traditional methods of protection. Conclusions drawn from examination of the evidence indicate that a layer of compost mulch greater than 2 inches adversely affected emergence and establishment of desired vegetation, whereas soil moisture retention was comparable on sub-plots treated with by straw mulch held in place by jute netting. Compost manufactured topsoil, or a 4-inch layer of compost mulch