The monitoring objectives will determine approximately where sampling must occur relative to the BMP implementation. Site-specific characteristics must be considered, however, to assure that samples are representative and applicable to the project needs. Physical constraints of a site, the time required to reach a sampling location, legal and physical access to a site, and safety issues must be considered when making site selections. Whenever possible, visit all proposed sampling locations before the first monitoring event to evaluate potential problems.
Constraints due to choice of monitoring equipment and instrumentation
When selecting a site, consider how conditions will change with season or during extreme weather. Is access to the site adequate for the monitoring design and equipment to be used? Consider all possible flow conditions and other environmental conditions that might occur. Determine whether the equipment required for the proposed monitoring plan will be adequate under all these possible conditions.
Consider seasonal changes at the site. Can equipment be installed sufficiently above the high water mark to prevent it from being flooded or otherwise damaged by high water? Is there evidence of past standing water in the selected site? During low water conditions, will probes and other equipment be sufficiently submerged? Will measurements be possible if surface or anchor ice forms? Will a bridge be necessary to measure discharge during high flow periods?
If equipment is to be left at the site, determine whether it can be attached sufficiently to assure it will remain in place. Boulders in mountain streams look immovable during low flow but may become mobile during high flow. Trees, shrubs, and fence posts near a stream can be uprooted by high flows.
Power needs at the site should be evaluated when appropriate. Is electricity available from the grid? If not, will batteries be sufficient, or can a solar cell provide for power needs?
Is there road access to the site? If not, what are the challenges to carrying monitoring equipment to the sites?
If data are to be downloaded from remote locations, determine that there is sufficient clearance or adequate repeaters to get a signal from the site. For example, it can be very difficult to transmit a signal through narrow, steep canyons; several repeater stations are often necessary.
Time constraints associated with site selection
Some sites may be ideal in many respects but quite difficult and time consuming to visit. Even “automatic” samplers and probes require regular visits to check power, calibrate equipment, and conduct other QA checks. When multiple sites need to be visited, consider whether the budget and sampling plan can accommodate the time required to get to individual sites. Road or trail conditions are also highly variable throughout a year. Consider whether site choices will require all terrain vehicles or snow machines to access during portions of the year and whether the monitoring budget allows for these provisions.
Many pollutant samples have a maximum holding time between sample collection and analysis or further processing. For example, bacteriological samples may have a holding time of only a few hours. Exceeding the holding time generally results in data that are of limited value, so assure that site choices do not result in holding time violations. Holding times should be documented in the Sample and Analysis Plan (SAP); if not, check with the laboratory that will be analyzing the samples.
Always contact the property owner(s) or land manager(s) responsible for the actual site location and for any land that would need to be crossed to access the site. Be respectful of all private property. Always contact private landowners for permission to cross their land. Always get permission to leave equipment at the site or to attach equipment to bridges, pilings, or other structures.
Assure that all gates are left as you found them. If an unopened gate is found, alert the property owner if possible. Animals in fenced areas may change throughout a season, so always check for dangerous livestock with each visit. Alternatively, assure that your presence in no ways causes harm to crops or livestock.
Carefully assess sites for safety considerations and be aware of how potential hazards and risks may change with the season. Does the access to the site cross hazardous conditions or terrain? Is the water too deep or too fast to safely collect a sample? Are there obstructions, steep banks, submerged wire or debris, poisonous plants or animals, or dangerous holes that may place samplers at risk?