Groundwater Quality Monitoring Plan

The water stored in soil and rock voids (pores, fissures, dissolved fissures) is collectively referred to as groundwater. Groundwater is buried at different depths in the geological strata, and its fluidity and water quality parameters change relatively slowly compared to surface water.

（1） Principles for the layout of monitoring network points

(1) Overall and macroscopically, it should be able to control different hydrogeological units and reflect the environmental quality status of the groundwater system and spatial changes in groundwater quality in the region;

(2) Monitoring focuses on aquifers for water supply purposes;

(3) Monitor key areas of groundwater pollution and potential areas of pollution, monitor the degree and dynamic changes of groundwater pollution caused by pollution sources, to reflect the pollution characteristics of groundwater in the region;

(4) Can reflect the source of groundwater recharge and the hydraulic connection between groundwater and surface water; Monitor the funnel area of groundwater level decline, ground subsidence, and this particular hydrogeological issue;

(5) Consider the impact of industrial construction projects, mining development, water conservancy engineering, petroleum development, and agricultural activities on groundwater;

(6) The principle for the density of monitoring network points is that the main water supply areas are dense, while general areas are sparse; Urban areas are dense, while rural areas are sparse; Groundwater pollution

Severe areas are dense, while non polluted areas are sparse. Obtain sufficient representative environmental information with the minimum number of monitoring points as much as possible; Choose monitoring points from frequently used civilian wells, production wells, and springs as much as possible.

（2） Investigation and data collection

Before setting up a monitoring point network, local hydrological and geological data should be collected, including:

(1) Geological map, profile map, relevant parameters of existing water wells (well location, drilling date, well depth, well completion method, aquifer location, pumping test data, drilling unit, utility value, water quality data, etc.);

(2) The geographical distribution and hydrological characteristics (water level, water depth, flow velocity, flow rate) of rivers, lakes, and seas as local groundwater recharge sources, water conservancy engineering facilities, utilization of surface water, and water quality status;

(3) Distribution of aquifers, direction of groundwater recharge, runoff, and discharge, types of groundwater quality, and development and utilization of groundwater resources; Spring water exposure, formation type, supply source, flow rate, water temperature, water quality, and utilization status;

(4) Regional planning and development, distribution of urban and industrial areas, resource development and land use, application of fertilizers and pesticides, water pollution sources and sewage discharge characteristics.

（3） Setting of sampling points

Due to the complexity and specificity of hydrogeological factors, the setting of groundwater sampling points is relatively complex. The density of national controlled groundwater monitoring points is generally not less than 0.1 wells per 100km2, and each county should have at least 1-2 wells. In plain (including basin) areas, the density is generally 0.2 wells per 100km2. In important water source areas or heavily polluted areas, the density should be appropriately increased. In desert areas, hilly areas, karst mountainous areas, etc., typical representative areas can be selected as needed to set up monitoring points. The density of groundwater monitoring points under provincial and municipal control can be determined according to specific circumstances and relevant regulations.

Monitoring points (monitoring wells) should be set up in areas where groundwater is the main source of water supply, areas with high incidence of drinking water endemic diseases (such as high fluoride disease), and areas that have a significant impact on regional groundwater, such as sewage irrigation areas, garbage disposal sites, groundwater recharge areas, and large mine drainage areas.

In order to understand the types, distribution, and diffusion conditions of pollutants, as well as the stratification and flow direction of groundwater, it is usually necessary to set up background value monitoring wells and pollution control monitoring wells.

1. Layout of background value monitoring wells (points)

According to the regional hydrogeological unit conditions and the main source of groundwater recharge, one or several background value monitoring wells should be set up upstream of the groundwater flow in the periphery of the polluted area. Monitoring wells for background values should be located as far away as possible from urban residential areas, industrial areas, pesticide and fertilizer application areas, agricultural irrigation areas, and transportation arteries.

2. Layout of pollution control monitoring wells (points)

The distribution of pollution sources and the diffusion form of pollutants in groundwater are the primary considerations for setting up pollution control monitoring wells. Various regions can adopt a combination of point and surface methods to set up pollution control monitoring wells based on the local groundwater flow direction, distribution of pollution sources, and the diffusion form of pollutants in groundwater. The monitoring focus is on the protection areas of water supply sources.

① The pollutants in seepage pits, seepage wells, and solid waste disposal areas diffuse in a strip like manner in areas with high permeability of aquifers. Monitoring wells should be arranged along the direction of groundwater flow and controlled by parallel and vertical monitoring lines; The pollutants in seepage pits, seepage wells, and solid waste disposal areas diffuse in a point like manner in areas with low permeability of the aquifer. Monitoring lines can be set up in a cross shape near the pollution source for control;

② When pollutants such as industrial wastewater and domestic sewage are discharged or leaked along rivers and canals, and spread in a belt like manner, monitoring lines perpendicular to the rivers and canals should be set up using a grid layout method based on the state of the rivers and canals, the direction of groundwater flow, and the geological conditions in which they are located; Sewage irrigation areas and residential areas lacking sanitation facilities are prone to causing large-scale vertical block pollution to the surrounding environment, and monitoring points should be set up in parallel and perpendicular to the direction of groundwater flow;

③ The funnel area where the groundwater level drops mainly forms lateral pollution diffusion near the mining funnel. Monitoring points should be set up at the center of the funnel, and if necessary, monitoring lines can be set up outside the funnel center in a cross or radial shape;

④ Strong diffusion areas with good permeability or old pollution sources with a long history may have a larger pollution range, and the monitoring line can be appropriately extended. Conversely, monitoring points can only be set up near the pollution source.

（4） Determination of Sampling Time and Sampling Frequency

(1) Background value monitoring wells and regionally controlled pore pressure water wells are sampled once a year during the dry season;

(2) Pollution control monitoring wells are sampled once a month and six times a year; If a monitoring project falls below one-fifth of the control standard value for two consecutive years and there are no new pollution sources near the monitoring well, and the existing pollution sources have not increased their discharge, the project can be sampled once a year during the dry season. Once the monitoring results exceed one-fifth of the control standard value, or when there are new pollution sources near the monitoring well or an increase in the discharge of existing pollution sources, the normal sampling frequency shall be restored;

(3) As a groundwater monitoring well for centralized supply of drinking water, it is sampled once a month;

(4) The sampling time of monitoring wells in the same hydrogeological unit should be relatively concentrated, and the date span should not be too large;

(5) When encountering special situations or pollution accidents that may affect groundwater quality, the sampling frequency should be increased at any time.