Assessing the Risk of Groundwater Contamination from

Worksheet 9

Silage is an important feed for animal-based agriculture. When properly harvested and stored, silage poses little or no pollution threat. Improper handling and inclement weather, however, can lead to a significant flow of silage juices (or leachate) from the silo. Leachate is an organic liquid that results from pressure in the silo, from putting up feed that is too wet, or from extra water entering the silo. It is usually a problem only when silage is fresh or just after it is stored in covered silos. Storage in uncovered silos is not recommended, because exposure to the weather accelerates the decrease of silage quality. Loss of leachate represents a major loss of nutrient value from the silage.

If silage leachate enters a stream, its high organic content feeds bacteria that rob the water of oxygen. The capacity of a contaminant to rob water of oxygen is called biochemical oxygen demand (BOD). The BOD of silage effluent is 150 times greater than that of human sewage. BOD from 1 ton of silage with a moisture content of 23.4% is equal to approximately 4,755 gallons of sewage. Groundwater contaminated with silage juices has a disagreeable odor and shows increased acidity, ammonia, nitrate, and iron.

Silage liquid is often highly acidic and can be corrosive to concrete and steel. In addition to the pollutants found in silage leachate, an even greater potential threat exists. The low pH created by the presence of acids in silage leachate can free up and release naturally occurring metals in the soil and aquifer, which can increase the concentration of metals in groundwater.

Nitrate-nitrogen levels in drinking water greater than federal and state drinking water standards of 10 mg/L* can pose health problems, including the condition known as methemoglobinemia (blue baby syndrome), for infants younger than 6 months of age. Young animals are also susceptible to health problems from high nitrate-nitrogen levels. Levels of 20-40 mg/L in the water supply may prove harmful to young animals, especially in combination with high levels (1,000 ppm) of nitrate-nitrogen from feed sources.

The goal of Home·A·Syst is to help you protect the groundwater that supplies your drinking water.

*means milligrams per liter, equivalent to parts per million for water measure

• It will take you step-by-step through your silage storage practices.
  
  
• It will rank your activities according to how they might affect the groundwater that provides your drinking water supplies.
  
  
• It will provide you with easy-to-understand rankings that will help you analyze the risk level of your silage storage practices.
  
  
• It will help you determine which of your practices are reasonably safe and effective, and which practices might require modification to better protect your drinking water.

Step 1: In the table below summarize your risk scores by checking the appropriate box for each risk category you answered on this worksheet.

Step 2: Look over your rankings for individual activities:

• High risk practices (1's) pose a high risk of polluting groundwater.
  
  
• Moderate-to-high risk practices (2's) are inadequate protection in many circumstances.
  
  
• Low-to-moderate risk practices (3's) provide reasonable groundwater protection.
  
  
• Low risk practices (4's) are ideal; should be your goal despite cost and effort.

Any practices in shaded areas should be carefully reviewed. Some concerns you can take care of right away; others could be major or costly projects, requiring planning and prioritizing before you take action. The long-term goal of the Home·A·Syst program is to improve homestead practices and structures, so that they are classed as low risk. Activities classed as low risk generally reflect best management practices.

Transfer any activities that you ranked in the shaded areas in step 1 to the "High-Risk Activities" table on pages 2-3 of worksheet 12.

Step 3: Read fact sheet 9, Improving Silage Storage, if you haven't already. Consider how you might modify your homestead practices to better protect your drinking water.

The Homestead Assessment System is a cooperative project of Washington State University Cooperative Extension, Washington Department of Ecology, and the U.S. Environmental Protection Agency Region X.

Home·A·Syst team members: Christopher F. Feise and Edward B. Adams, WSU Cooperative Extension Water Quality Coordinators; James D. LaSpina, Homestead Assessment System Project Associate.

Silage Storage Technical Reviewers: Ronald E. Hermanson, WSU Cooperative Extension; Andy Werkhoven, Dairy Farmer; Anne Schwartz, Washington Tilth; John A. Gillies, USDA-Soil Conservation Service; John W. Bernard, WSU Cooperative Extension; Philip A. KauzLoric, Washington Department of Ecology; Steven C. Fransen, WSU Cooperative Extension.

Adapted for Washington from material developed by the Wisconsin, Minnesota, and Kansas Cooperative Extension and Farm·A·Syst Programs. Washington Home·A·Syst development was supported by the National Farmstead Assessment Program.

Information derived from Home·A·Syst worksheets is intended only to provide general information and recommendations to rural dwellers regarding their own homestead practices. It is not the intent of this educational program to keep records of individual results.