Land Treatment of Wastewater
We are a full-service environmental consulting firm, providing technical and regulatory support to projects involving the subsurface or land discharge of wastewater throughout the Mid-Atlantic region. We possess expertise in technical and field evaluations and related regulatory permitting for individual and community on-site sewage disposal systems. Among other specialty services, we perform percolation and infiltrometer testing and related evaluations of soil and its capability to store and/or transmit water.
Our soils and hydrogeological experts have completed site suitability and groundwater discharge evaluations in both bedrock and in Coastal Plain hydrogeologic settings These projects generally involve classifying subsurface materials (i.e. soils), constructing monitoring wells and piezometers, designing and executing soil infiltration tests, assessing baseline water quality and aquifer hydraulics, and estimating groundwater mounding and nutrient loading potential.
Led by Professional Geologists, Licensed Environmental Health Specialists and Registered Sanitarians, with success we have supported wastewater discharge plans for municipalities, county utilities and other large projects throughout the Mid-Atlantic region. We also support schools, churches, shopping centers, camps and campgrounds, and other projects of more intermediate size.
Our groundwater discharge specialists perform rapid, accurate and cost-effective soil suitability evaluations, double-ring infiltrometer tests, percolation tests and other field programs to support groundwater mounding evaluations and related permit application requirements.
Groundwater Discharge Evaluations
Percolation & Infiltrometer Testing
Monitoring Well Design & Installation - Regulatory agencies usually require the installation and development of at least three specially designed groundwater monitoring wells surrounding a proposed disposal area, at locations selected based on the upgradient (one) and downgradient (two) hydrologic gradient. Sometimes it is necessary or desirable to install additional small diameter piezometers for water level monitoring beneath proposed reserve areas and elsewhere across a site. The wells and piezometers usually need to be sampled for certain baseline water quality parameters and gauged to form the basis of water table contour maps. When groundwater is deep, long-term groundwater level monitoring may not be unnecessary. The observation of shallow groundwater levels, and/or unusually low slug test results, could mandate long-term groundwater monitoring as an additional investigative measure.
Water Sampling & Analyses
Nutrient Loading Analyses - Nitrogen often is the most limiting nutrient for wastewater application projects. The extent to which nitrogen is utilized, removed or volatilized from the fields is important when determining the feasibility of a planned wastewater application. For this reason, ALWI uses nitrogen dilution calculations to estimate the degree of pretreatment necessary to achieve project water quality objectives.
Groundwater Mounding - Regulatory agencies such as the MDE Groundwater Discharge Permitting Program usually require a quantitative prediction of the potential for groundwater mounding associated with the proposed discharge. The required calculations frequently are sensitive to variations in horizontal hydraulic conductivity, often requiring careful and repeat slug tests to quantify.
Mounding evaluations are useful in forecasting the degree of unsaturated soil that will continue to remain available for land treatment and percolate filtration. Once horizontal hydraulic conductivity data are developed from slug tests, in projects the height of the resultant groundwater mound under various operational scenarios, as a vertical difference from the baseline represented by the present water table height as recorded in the monitoring wells and piezometers.
Wastewater Discharge Feasibility Evaluations
Innovative Testing in Challenging Terrains
Discharge Method Cost/Benefit Analyses
Soil Permeability Testing - The Firm’s wastewater division specializes in fulfilling technical permit application requirements for large groundwater discharge projects in Maryland and neighboring states. For example, in Maryland wastewater disposal systems over 5,000 gpd in design capacity are subject to MDE discharge permitting requirements. COMAR 26.04.02 and MDE’s “Guidelines for Large Onsite Sewage Disposal Systems” govern the technical content of the submittals supporting an application for groundwater discharge permits. To comply with these Guidelines, usually three interdependent physical properties of the soils require assessment: infiltration capacity, groundwater table mounding potential and nutrient loading potential.
Borings and Soil Characterization
Horizontal Hydraulic Conductivity (Slug) Testing - One of the key input parameters for mounding estimates is called horizontal hydraulic conductivity, and arises from specialized field-testing performed within on-site monitoring wells. Sometimes pre-existing values can be used for estimating this parameter; associated project cost savings can arise.
These tests are termed “slug tests” because the response of the aquifer is observed to the sudden insertion within the monitoring well(s), and later removal of a “slug” of known dimension.
Water level changes in response to slug insertion and removal are a function of the needed horizontal hydraulic conductivity value. Specialized instrumentation and repeat slug testing is needed for accurate and defensible results.
Expert Testimony and Litigation Support