Groundwater quality regulation in Aichi Prefecture operates through a layered structure that sits on top of national law but frequently adds its own requirements, timetables, and thresholds. For facilities that handle designated hazardous substances — solvents, heavy metals, petroleum compounds — those local additions are not minor footnotes. They determine how often your site must sample, which laboratory parameters you are required to run, and what you must submit to the prefectural or municipal authority, and by when. Getting this wrong carries real administrative consequences: orders to expand the monitoring network, mandatory public disclosure, and in serious cases, remediation directives. This overview is written for environmental managers, site compliance officers, and engineers who need a working map of those obligations rather than a restatement of the national Soil Contamination Countermeasures Act. The focus is specifically on Aichi Prefecture and the ordinances and guidance documents that have force within it.

The regulatory foundation: national law and the Aichi layer on top

Japan's Soil Contamination Countermeasures Act (Act No. 53 of 2002, most recently amended in 2017) establishes the baseline for soil and groundwater investigation at sites where specified hazardous substances have been used. Aichi Prefecture supplements this through its own environmental ordinance framework, principally the Aichi Prefecture Environmental Pollution Prevention Ordinance, and through guidance circulars issued by the Aichi Prefectural Environment Bureau. Where a facility sits within a designated city (seirei shitei toshi) such as Nagoya, the city authority carries delegated enforcement power and may publish additional procedural guidance. The practical effect is that a facility in Nagoya's Minato Ward handling trichloroethylene, for instance, receives oversight from both the national Act and from Nagoya City's environmental department acting under delegated prefectural authority. Both channels must be satisfied, and their reporting calendars do not always coincide.

Which sites carry monitoring obligations

The trigger for mandatory groundwater monitoring under the Aichi framework is normally one of three situations. First, a facility has used a Type 1 designated hazardous substance (volatile organic compounds including trichloroethylene, tetrachloroethylene, benzene, and cis-1,2-dichloroethylene) or a Type 2 substance (heavy metals including cadmium, lead, arsenic, and hexavalent chromium) above de minimis quantities. Second, a change of use or closure of a qualifying site activates investigation and, where contamination is found or reasonably suspected, ongoing monitoring. Third, a site has already been designated as a contaminated area under Article 6 of the national Act, in which case monitoring continues under the terms of the designation order. Industrial zones along the Ise Bay coast, including parts of Tokai City, Chita City, and the Kinjo Futo landfill area, have historically seen high designation rates due to the concentration of chemical processing, plating, and petrochemical operations. Facilities in those areas should assume a heightened scrutiny posture.

Sampling frequency: the standard schedule and when it changes

Under standard Aichi practice, groundwater monitoring at a designated or conditionally managed site is conducted once per year (annual sampling) for the majority of parameters. However, where a previous investigation has detected concentrations exceeding the environmental quality standards (kankyo kijun), the authority ordinarily requires quarterly sampling, four times per year, until two consecutive annual rounds return results below the standard. For volatile organic compounds specifically, the prefecture's guidance aligns with Ministry of the Environment notification and requires that each sampling round cover all monitoring wells installed at the site, not a rotating subset. Sites that installed observation wells under an approved investigation plan must sample each well in the same campaign so that results are spatially comparable across rounds. Seasonal timing matters: Aichi's groundwater levels fluctuate with summer rainfall and snowmelt from the Kiso River system, and the authority may specify that at least one sampling round occurs during the high-water-table period, typically June through August, to capture the conditions under which lateral plume movement is most active.

Required parameters and analytical standards

The parameter list for Aichi groundwater monitoring is drawn from the 28 items specified in the national environmental quality standards for groundwater (Ministry of the Environment, updated through 2021), but the authority can and does require additional items based on site history. For a typical metal-plating facility, the standard panel includes hexavalent chromium, total chromium, lead, cadmium, arsenic, fluorine, boron, and cyanide compounds, alongside pH and electrical conductivity as field indicators. For sites with solvent history, the panel extends to trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and vinyl chloride. All analysis must be conducted by a registered environmental measurement agency (kankyo keisoku shi toroku kikan) under the Environmental Measurement Law. The laboratory must apply the analytical methods specified in JIS K 0102 or the Ministry's testing method notifications, and the detection limits achieved must be below the environmental quality standard for each parameter, not merely at or near it. Results reported at the detection limit without confirmation of a true non-detect are typically flagged during review.

Reporting obligations and submission timelines

Monitoring results must be compiled in a prescribed format and submitted to the relevant authority within three months of the completion of the sampling campaign, as a general rule under Aichi practice, though the specific deadline will be stated in the site's designation order or monitoring plan approval document and takes precedence. The submission package typically includes the monitoring well location map (to scale, with coordinates), field measurement logs, chain-of-custody records, the registered laboratory's analytical report with QA/QC data, and a trend analysis comparing results against all prior monitoring rounds. Where any parameter exceeds the environmental quality standard, the operator is required to notify the authority promptly (often within 30 days of receiving laboratory results) and to propose a response plan. Delay in notification is treated seriously: the Aichi framework treats exceedance notification as a protective measure, and failure to report in time has resulted in enhanced oversight conditions being added to designation orders at sites in the Tokai industrial corridor.

Monitoring well installation and maintenance requirements

The physical infrastructure for monitoring must meet specifications set out in the prefecture's investigation guidelines. Wells are generally drilled to a minimum depth that intercepts the uppermost unconfined aquifer, with screen intervals positioned to capture the zone of likely contamination based on site stratigraphy. Aichi's guidance references the Japan Environmental Management Association for Industry (JEMAI) standard methods for well construction, requiring bentonite sealing above the screen interval to prevent vertical cross-contamination between aquifer layers. Wells must be surveyed at installation for ground-level elevation and coordinates, and those records become part of the permanent site file. Periodic well development is required before each sampling event to remove stagnant water and ensure that samples represent formation water rather than well water. Any well that becomes damaged, silted, or otherwise non-functional must be reported to the authority, and a replacement or supplementary well may be required before the next monitoring round. Abandoning a monitoring well without approval is a common compliance error at sites undergoing ownership transfers in Aichi's active industrial land market.

Practical steps for maintaining ongoing compliance

A site-specific monitoring management plan, maintained internally and updated after each sampling round, is the most reliable tool for staying current with Aichi obligations. That plan should record the designation order reference number, the approved monitoring well network, the required parameter list, the sampling schedule with calendar dates, the registered laboratory used, and the name of the person responsible for submission. Aichi's Environment Bureau conducts periodic inspections of designated sites, and inspectors will ask to see this documentation. Coordinating the laboratory contract well in advance of each sampling season is important: registered environmental measurement agencies in the Chubu region operate at capacity during the spring and summer sampling window, when many sites schedule their annual campaigns. A booking lead time of six to eight weeks is realistic. Finally, when a site changes operator or undergoes partial demolition, the new operator should verify with the authority whether the existing monitoring plan remains valid or whether an updated plan must be submitted, since structural changes to a site can alter groundwater flow paths and may require additional wells to maintain adequate coverage.

Aichi's groundwater monitoring framework is more specific in its procedural expectations than many facility managers initially anticipate, particularly around analytical method compliance and exceedance notification timelines. The obligations are manageable when they are mapped clearly at the outset of site occupancy and reviewed each time site conditions or ownership change. Silt Lab Zone works with facilities across the Chubu region on investigation planning, monitoring program design, and submission support under the Aichi ordinance framework.