Study on ammonia-N, nitrate-N and nitrite-N remedial target values of groundwater of a coastal contaminated site considering marine environmental risks

Contaminated groundwater from seaside contaminated sites may cause sea contamination. This study investigated the remedial target values of a compound fertilizer production enterprise adjacent to the sea. Three methods to determine the remedial target values of groundwater "three nitrogen" (ammonia-N, nitrate-N and nitrite-N pollution) were tested, including groundwater environmental quality standards, risk assessment based on human health, and hydrogeological risk assessment model used to protect the water environment. The scientificity and rationality of the remediation target values were analyzed and discussed. The enterprise was located in the coastal industrial park of a city in the north of China, and the boundary of the enterprise was about 108 m away from the coast. There was no exploitation and utilization of groundwater in this site, and the ammonia nitrogen remedial target value obtained from the human health risk assessment calculations was as high as 57 200 mg/L due to the absence of a human exposure pathway. Even if the groundwater Class Ⅳ water standard was taken as the remedial target, i.e., the remedial target values of ammonia nitrogen,nitrate nitrogen and nitrite nitrogen (all in N) were 1.50, 30.00 and 4.80 mg/L, respectively, the concentrations were much higher than the seawater water quality standard (total inorganic nitrogen was less than 0.50 mg/L), and there may be a risk of contamination of seawater. Therefore, using the hydrogeological risk assessment model to protect the water environment in the United Kingdom, the remedial target value of total inorganic nitrogen in the groundwater at the site was calculated to be 42 mg/L. A comparison of the three sets of remedial target values showed that the remedial target value based on the groundwater quality standard was too stringent. Although it prevented environmental risks, it was difficult to achieve through remediation simulation prediction. The remedial target value based on the protection of human health was too loose. If this target value was adopted, the total inorganic nitrogen concentration of the groundwater from the site when flowing into the ocean was predicted to be 31.91 mg/L, which would cause serious pollution to the marine environment. In contrast, the remedial target value based on protecting the marine environment not only avoided the risk of ocean pollution but also was more achievable.