Division of Environmental Health Drinking Water Program

Flood Preparation and Recovery for Drinking Water Systems

Types of Floods

Riverine

Periodic overbank flow of rivers and streams.

Flash

Quickly rising small streams after heavy rain or rapid snowmelt.

Urban

Overflow of storm sewer system usually due to poor drainage following heavy rain or rapid snowmelt.

Coastal

Flooding along coastal areas associated with severe storms, hurricanes or other events.

Many areas of the state are at risk of flooding from heavy rains, spring ice jams, rapid snow melt, tidal storm surges and wave run-up. Floods account for approximately 40% of the state’s disaster emergencies. Most floods are of the Riverine variety, as defined above. The South-central, Western, and Interior Regions of the state are especially prone to spring flooding during breakup of the rivers, and summer and fall rainfall events. Coastal areas of the state, especially the Western Region, are prone to storm driven waves that can flood a community.

Floods can also cause natural and environmental emergencies such as erosion and landslides. Many existing populated areas are known to be located within flood vulnerability zones. Consequences to property and people can include a disruption of vital services such as water, sewer, power, gas, communication, transportation, damage or destruction of roadways, buildings, structures, bridges, port and harbor facilities, airports, and vehicles.

The Alaska Department of Environmental Conservation (DEC) is available to provide technical assistance on environmental issues associated with floods. See the list of DEC Drinking Water Program offices at the back of this information packet.

Flood waters may impact drinking water system infrastructure (wells, intakes, and treatment plants) withcontaminants carried by surface waters or saturated soil. Contaminants may include bacteria, viruses, protozoa, or petroleum products from fuel spills in nearby areas. These forms of contamination may constitute a hazard to public health. Shallow wells near a river or flood area, may be at increased risk even when the wellhead itself has not been flooded. DEC advises that precautionary measures be taken before and after the flood to protect your well and drinking water system.

Before the Flood

Keep Water Out

• Sand bag if possible around structures and at building entrances. Keep in mind that the effectiveness of sandbags is limited when they are frozen.
• Plug floor drains to prevent entrance of water from the drain system. Preferably, inflatable plumbing plugs should be used but if they are not available some utilities have used water plug cement for this purpose. (Note: This would require effort to restore the drain following the flood.)

Secure Water and Chemical Storage Tanks / Safeguard Chemical Supplies

• Chemical supplies (hypochlorites, fluoride, corrosion control additives, etc.) and chemical solution tanks should be removed from areas of imminent flooding and stored in a secure location. However, if chemical solution tanks cannot be removed, raise the tank above the expected level of floodwater and secure the tank to reduce the chance of flotation or overturning.
• Water storage tanks should be completely filled with water to be ballasted against flotation.
• Pressurized chlorine (i.e., chlorine gas) cylinders should be removed from areas of imminent flooding if at all possible. If the containers must remain in a flood warning area, they should be disconnected from any piping, closed, and process piping closed and secured. Any open‐ended joints should be capped or blinded. A one‐ton chlorine container will float if empty or near empty. Securing the chlorine containers against flotation will be needed to resist the buoyant forces of "empty" containers (i.e., empty of adequately pressurized product, although still containing chlorine gas.) The buoyant uplift force on an empty container can be estimated based on the tare weight of the container (between 1300 and 1650 pounds, depending on the manufacturer), and the weight of displaced water (estimated at 1900 pounds, based on a container design capacity of 1800 pounds of water) to be between 250 and 600 pounds (weights per Chlorine Institute, 1997, and Columbiana Boiler, 1995).

Surface Water Intake Preparation

• During a flooding event, debris often increases within associated surface water bodies. surface water intakes are at risk of becoming damaged or blocked. Ensure water storage tanks are filled to capacity and make provisions for temporary intakes in case the intake requires flushing or is completely blocked.
• Intake structures and water treatment plants along rivers may be subject to damage from ice flows. If possible, remove the intake structure before the flood.

Water Well Preparation

• Ensure that the land surrounding the well is sloped away so that surface water does not flow towards the well.
• If re-grading around the well casing is required be sure that the casing terminates at least 12 inches above grade after the re-grading.
• Well casings must extend at least 12 inches above ground; the casing may have to be extended to meet this requirement. Additionally, consider extending the casing above the 100-year flood level or alternatively sealing the top of the casing and extending the vent above the 100-year flood level.
• Consider protecting the area over the water line between the well and the treatment facility with sand bags because a recently constructed or improperly backfilled trench may provide a flow path for the flood water to the well casing.
• Ensure that the integrity of the surface seal outside the casing is maintained and in good shape. Check that there has been no settling of the soil or that no cavity has developed around the outside of the well casing where surface water would be able to flow down to the aquifer. Fine bentonite chips can be used to make an impervious seal around the well casing (some digging may be required to ensure the seal is installed to as deep as possible).
• The well must have a tight fitting waterproof cap. Many wells have unsealed caps or sanitary seals with vent holes. Some wells require vents for proper operation. If the well is not used for the duration of the flood event the vent holes should be plugged. To further reduce risk, carefully wrap the cap and well casing with durable sheet plastic and duct tape to form as tight a seal as possible. Sand bags can be placed around the well to protect the well and plastic from debris. When sealing the well cap and protecting the well, remember that any sealing material will need to be removable in order to allow future servicing of the well.
• For pumps at risk of becoming flooded, shut off the power just prior to impact. Be aware of the potential to contaminate the distribution system due to a loss of pressure if there is not an adequate supply of stored water.Wells along rivers may be subject to damage from ice flows. Consider placing sandbags or bollards along the upstream side of the well for added protection.
• Ensure that any stand-by or abandoned wells in the area are also protected. Standby wells should be sealed to avoid as much impact to the water source as possible. In addition, an abandoned well is an environmental liability and should be permanently decommissioned to ensure it will not act as a source of groundwater pollution now or in the future. Flood waters entering an abandoned well can contaminate an active well and the associated aquifer. If there is not enough time to do this now, it should be a priority after the flood; measures should be taken to temporarily seal the well from flood waters using sheet plastic and duct tape.

Secure Heating Fuel Tanks

• Secure small fuel containers, fuel tanks, and barrels that are used to store fuel so they do not float away. Above ground tanks, including propane tanks, may shift or fall causing fuel lines to kink, weaken or break, and fittings may be loosened or break. If you have a buried fuel tank, water may seep into the tank and contaminate the fuel. Owners should close the valves on the tanks that are not currently in service and on tanks that are being taken out of service in preparation of a flooding event. Vents should be plugged temporarily if possible. If you have any questions on the integrity of your tanks, fuel lines, tank stand, the fuel itself or need help moving or returning the tank to service, please contact your fuel supplier. If the flooding has caused a fuel, oil, or other hazardous substance spill, report it to the DEC immediately. Contact information has been provided in the back of this pamphlet.

Secure Electrical Assets

• Remove generators and motors not in use to a safe location and make preparations for quick removal of those in service. It is recommended that generators and motors be equipped to accommodate quick removal with disconnect fittings rather than conventional pigtails.
• If flood waters are anticipated to inundate areas where electronic controls are housed, shutdown SCADA system components, programmable logic controllers (PLCs), computers, and other field instruments. Shutdown any backup uninterruptible power supply (UPS) systems because the UPS could maintain sufficient current to the equipment to destroy the instrumentation package when inundated by the flood waters. Note: Shutting off these components will mean your system should post a Boil Water Notice since your normal treatment processes may be offline.
• Shutdown all transformers; identify and locate possible temporary and replacement equipment.

Secure Other Assets

• Move mobile equipment (heavy equipment, ATVs, etc) to higher ground to prevent damaged by flood waters or debris.

Sampling and Disinfection Preparations

• Maintain an adequate supply of coliform bottles to support sampling of the varying components of the system for at least a week.
• If the system is routinely disinfected with chlorine, increase the chlorine level to ensure the chlorine residual remains at 0.2mg/L or higher throughout the distribution system.

Customer Notification

• Public Water Systems are often placed on a Boil Water Notice during a flooding event. In order to ensure the public water system is prepared to issue the notice as soon as possible, a Precautionary Boil Water Notice will often be sent to the water system prior to the flood waters reaching the community. The Boil Water Notice and the Precautionary Boil Water Notice will advise consumers that a loss in pressure to less than 20 PSI due to a power loss, line break, or any other situation has the potential to allow pathogenic contamination into the drinking water. It is extremely important that the water system contacts the DEC as soon as possible if the water system is negatively impacted during a flood event. The department will assist the system with site specific guidance and inform them of the requirements for the specific situation.

After the Flood

Once the flooding has subsided, the Public Water System owner or operator must contact the DEC Drinking Water Program immediately. DEC staff will provide information on disinfection of the water system, sampling requirements, as well as any Boil Water Notices that are required.

If you suspect fuel contamination in the water source do not run the system, as the fuel contamination could spread throughout the treatment and distribution system, potentially damaging various components of the water system infrastructure.

Disinfection of Wells and Small Distribution Systems

Information on well disinfection can be found on our webpage outlining Disinfection Procedures for Surface Water and Well Water Sources.

Emergency Disinfection of Your Personal Drinking Water Supply if Potable Water is not Available

Guidance on personal water disinfection can be found on our Emergency Disinfection of Drinking Water webpage.

Cleaning & Disinfection of Water Holding Tanks for both Residential and Public Water Systems

For information on water storage tanks, visit our Cleaning & Disinfection of Water Holding Tanks webpage.

Other Environmental Health Issues Related to Floods that could Impact Drinking Water Quality

Onsite Sewer Systems

If flooding has impacted your property, DEC recommends that precautions be taken to reduce any threats to public health and the environment from impacted onsite sewer systems. Onsite sewer systems and holding tanks may be damaged due to flooding and/or high groundwater levels. Those with onsite sewer systems that have been flooded or are in the vicinity of flood waters should inspect and clean their system as follows:

• Check for any evidence of sewage on the ground. If found, keep people (especially children) and pets away from the contaminated areas. Disinfect the area by following the instructions below for cleaning up spills outdoors.
• Check for any changes in the ground surface that might indicate movement or damage to any part of the system. Raised areas may indicate that the septic/holding tank may have floated upward due to buoyant forces. If this has occurred, damage to the tank and/or piping is likely. Depressed areas may indicate a collapsed tank, or that the upper soils have sunk downward into the drain field. The system should be checked for damage by a qualified system installer or a professional engineer.
• Floodwaters may have raised the groundwater to levels at or near the ground surface in many locations. Onsite sewer systems do not provide proper wastewater treatment under these conditions. Use of systems under these conditions may lead to groundwater contamination, surfacing of sewage, and/or sewage backing up into your home. All of these conditions pose a significant health threat. It may take some time for the surrounding ground to dry up enough for the drain field to recover and resume its normal absorption capability. During the time when the groundwater level is above or near the level of the drain field area of your sewer system, your system will not function properly. During this period, avoid discharging wastewater to your onsite sewer system. When use of your sewer system is resumed, DEC recommends that you closely monitor its performance and limit water use for at least 30 days.
• Once the flood waters and groundwater levels have receded, the septic tank may be pumped, which can give the drain field a resting period before introducing additional wastewater to the drain field from the tank. Prior to pumping a septic or holding tank, the homeowner should verify that their tank is anchored down to prevent floatation when pumped, and that groundwater levels have receded enough to prevent further inflow of groundwater into the tank, and/or damage to the tank and piping when pumped out.
• Cleanout pipes and monitoring tubes should be inspected to assure those joints and connections have not been damaged and that caps are in place.

For more information regarding disinfection procedures and sewer system monitoring to detect damage, contact your local DEC office.

Standard Procedures for Cleaning Up Domestic Wastewater Spills Outdoors

The following are recommended procedures for cleaning up untreated or inadequately treated sewage spilled to the ground surface.

1. In all conditions:
   • If the area where the spill occurred is accessible to the public or domestic pets, the contaminated area must be clearly marked or cordoned off to restrict access.
   • Protective clothing (at a minimum, rubber or latex gloves and rubber boots) should be worn when cleaning up a sewage spill. Dispose of gloves and wash rubber boots when leaving spill site. Keep children and interested bystanders away from cleanup activities.
   • Please note that hydrated lime is a caustic material and can be dangerous to handle and apply. Lime should only be used or applied by people experienced in using this material.
   • Do not mix cleaning or disinfecting products or chemicals. Cleaning products can react with one another to produce toxic vapor or liquid substances.
2. In non-freezing conditions when sewage is a mixture of liquid and solid material the following steps should be taken:
   • If the spilled material cannot be recovered using hand tools, a commercial vacuum/pump truck should be called to remove all visible liquid and solid material.
   • When the area is visibly clean, either a chlorine and water solution (using Clorox or an equal bleach) or hydrated lime should be applied to the spill area to disinfect it. To make a 5% chlorine solution, add 3/4 cup Clorox bleach to one (1) gallon of water. You can verify the chlorine concentration by using test paper available at food supply warehouses or chemical supply companies. Only use bleach that has “sanitizes” or “kills germs” on the label.
   • If the spill occurred in a heavily populated area and odor may be an issue or within 100 feet of surface water, hydrated lime should be applied to the area in place of chlorine bleach. Enough hydrated lime should be applied to raise the pH to at least 12. By raising the pH to 12 for at least 1 hour, the area will be disinfected. You can test the pH by using litmus paper obtained at a chemical supply facility. Lime is a caustic material; access to the area treated with lime must be restricted during the disinfection process.
   • After the spill area has been cleaned and disinfected (24 hours after the chlorine solution or hydrated lime has been applied), the barriers may be removed and access to the area restored.
3. In freezing or frozen conditions.
   • An attempt should be made to clean up the spill before it becomes completely frozen.
   • If possible, the frozen sewage should be removed down to the natural ground surface (or at least one inch below the spilled sewage if on thicker ice) and the recovered material disposed of properly. This could require that approval be obtained from the local government for disposal in a permitted landfill. An acceptable alternative solution is to stock pile the frozen sewage in an approved lined containment area until conditions are more favorable for transport and disposal. Each spill site and situation is different; please contact your local DEC office for recommendations regarding constructing an acceptable containment area. If the material thaws, the liquid must be properly handled and disposed of at a permitted wastewater treatment and disposal facility. Keep in mind that frozen and/or thawed sewage may still contain active, harmful bacteria, cysts and viruses.
   • When the area is visibly clean, either a chlorine and water solution (using Clorox or an equal bleach) or hydrated lime should be spread across the spill area to disinfect. You can verify the chlorine concentration by using test paper available at food supply warehouses or chemical supply companies.
   • If the spill occurred in a heavily populated area and odor may be an issue or within 100 feet of surface water, hydrated lime should be applied to the spill area in place of chlorine bleach. The hydrated lime will raise the pH to 12, which will disinfect the area. By raising the pH to 12 for at least 1 hour, the area will be disinfected. You can test the pH by using litmus paper obtained at a chemical supply facility. Because lime is a caustic material, access to the area treated with lime must be restricted during the disinfection period.
   • When the spill area has been cleaned and disinfected (24 hours after the chlorine solution or hydrate lime has been spread), the barriers can be removed and access to the area restored.

Standard Procedures for Cleaning Up Domestic Wastewater Spills Inside Buildings

• If sewage is on nonabsorbent floor material like tile, vinyl, concrete or other non-absorbent surfaces, cleanup of the visible water and semi-solid materials should be accomplished using a vacuum or mop and by using the proper concentrations of sanitizers to disinfect. Make sure that the sanitizer is of the proper concentration and that all affected areas are thoroughly sanitized.
• If the sewage is on an absorbent floor material, such as carpet, the material that has absorbed the sewage should be vacuumed to remove as much waste as possible.
• Do not mix cleaning/disinfecting products or chemicals. Cleaning products can react with each another to produce toxic vapors or liquid substances.

The following is a list of common sanitizers:

• Chlorine: For chlorine solutions, the chlorine concentration should be in the range of 50 to 1000 parts per million (ppm) or (mg/l) for disinfecting surfaces of appliances and food preparation areas and 200 ppm (mg/l) for walls and floors. You can verify the chlorine concentration by using test paper available at food supply warehouses or chemical supply companies. As a rule of thumb, add 3/4 cup Clorox Bleach to one (1) gallon of water. Only use bleach that has "sanitizes" or "kills germs" on the label.
• Alternative disinfectants: Other disinfectants, which include iodine and quaternary solutions, must be used according to the manufacturer’s specifications/recommendations if used for disinfecting sewage spills.

It is extremely difficult to adequately sanitize carpet, carpet pad, and absorbent flooring materials. DEC recommends that saturated flooring materials be removed and disposed of at a permitted solid waste disposal facility. Contact DEC for more information.

Solid Waste Disposal

Cleanup of flood impacted property can expose you to potential hazards or hazardous materials. Filter masks and protective clothing are highly recommended. Many household items soaked with floodwater, such as clothing, bedding, linens, leather goods, books, papers, appliances, furniture, rugs and carpets, can be salvaged by cleaning and disinfecting. These items, and other solid waste debris, can also be disposed of at the local landfill. Household hazardous materials, such as kitchen and bathroom cleaning products, paints, solvents, batteries, and asbestos containing material, need to be properly handled and disposed of.

For more information on what can be disposed of in the local landfill, contact your local landfill operator or your local DEC office.

Fuel/Oil/Hazardous Substance Spills

If a flood has caused a release of fuel, oil, or other hazardous substance, report the spill to your local Fire Department or Village Public Safety Officer, and call DEC immediately.

Propane Tanks

Propane suppliers recommend customers contact them for an inspection of the tank and fittings prior to reusing the system. The tank may have shifted which can cause fuel lines to kink or weaken or there may be loosened or damaged fittings that may be unsafe. Valves should be turned off and remain closed until the propane supplier inspects the system.

Home Heating Fuel Tanks

Heating oil suppliers recommend customers contact them for an inspection prior to reusing their system. If you have an above ground fuel tank, the tank may have shifted or fallen from the stand causing fuel lines to kink or weaken, or there may be loosened or damaged fittings and filters. If you have a buried fuel tank, water may have seeped into the tank and contaminated the heating oil. You should contact your fuel supplier to have the contents of the tank checked. If you have questions on the integrity of the tank, fuel lines, tank stand, or the fuel, or need assistance in moving the tank or returning it to service, contact your fuel supplier.

If the heating tank spilled and you have soil or water contamination, report the spill to DEC Spill Prevention and Response.

Food

If you have food items that have been in contact with floodwaters, and are not in watertight containers, they should be thrown away. Root vegetables can be used, but they should be thoroughly washed in clean water, peeled and cooked before eating.

Canned foods should be checked carefully for leaks. Any questionable cans should be thrown out. Containers with tight seals should be washed first and then disinfected by soaking for approximately 15 minutes in chlorine water. Adding one tablespoon of household bleach to one gallon of water can make this solution. Chlorine is poisonous, so be careful not to breathe the vapors or swallow any of the chlorine water. After sterilizing the container, be sure to rinse it thoroughly in fresh water.

If you have a freezer, either a chest or upright, which was covered with floodwaters, chances are the food inside has been damaged through seepage. All of this food should be thrown away. If the electricity has been cut off, but no floodwater has seeped into the freezer, the food will last for awhile depending on the amount of food in the box. A fairly full freezer should last two or three days without much loss of quality or flavor. Partially thawed meat should be refrozen at once. If meat has been completely thawed, it should be used at once, or may be cooked and refrozen. Any meat, poultry, fish, or containers of fruit and vegetables that show any sign of spoilage should be thrown away.